Self-propelled object that generates a boundary with amphiphiles at an air/aqueous interface

A benzoic acid (BA) disk was investigated as a novel self-propelled object whose driving force was the difference in surface tension. 4-Stearoyl amidobenzoic acid (SABA) was synthesized as an amphiphile to control the nature of motion based on intermolecular interactions between BA and SABA. The BA disk exhibited characteristic motion depending on the surface density of the SABA on the aqueous phase, that is, reciprocating motion as a one-dimensional motion and restricted and unrestricted motion as a two-dimensional motion. The trajectory of the reciprocating motion was determined by the initial direction of motion, and the boundary between an aqueous surface and the BA-SABA condensed molecular layer was used as the field's boundary. The presented results indicate that the characteristic nature of motion can be designed at the molecular level based on the intermolecular interactions between an energy-source molecule and an amphiphile.

Inclusion complexes of β-cyclodextrin with isomeric ester aroma compounds: Preparation, characterization, mechanism study, and controlled release

Cyclodextrins (CDs) have been discovered to provide an efficient solution to the limited application of ester aroma molecules used in food, tobacco, and medication due to their strong smell and unstable storage. This work combined molecular modeling and experimental to analyze the conformation and controlled release of isomeric ester aroma compounds/β-CD inclusion complexes (ICs). The investigation revealed that ester aroma compounds could be effectively encapsulated within the β-CD cavity, forming ICs with low binding affinity. Furthermore, the key driving forces in ICs were identified as hydrogen bonds and van der Waals interactions through theoretical simulation. Results from the Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR) and Isothermal titration calorimetry (ITC) experiments confirmed the intermolecular interaction predicted by the molecular model. Notably, the release rate of aroma compounds from L-menthyl acetate/β-CD (LMA/β-CD) IC exceeded that of terpinyl acetate/β-CD (TA/β-CD) IC. This difference is attributed to the length of the chain of aroma molecules and the variation in the position of functional groups, influencing the stable formation of ICs with β-CD. These findings hold potential implications for refining the application of ICs across diverse industries.

Myofibrillar proteins' intermolecular interaction weakening and degradation: Are they mainly responsible for the tenderization of meat containing l-arginine, l-lysine, or/and NaCl?

This study explored the effects of l-arginine, l-lysine, and NaCl alone and in combination on the tenderness of porcine meat. Arg, Lys, and NaCl alone improved the tenderness, decreased the cooking loss, and increased the myofibrillar fragmentation index (MFI) of porcine meat; Both Arg and Lys cooperated with NaCl to better achieve this effect. Furthermore, Arg/Lys collaborated with NaCl to increase muscle fiber swelling and moisture content of the meat and promoted the extraction of main myofibrillar proteins. FT-IR revealed that Arg, Lys, or NaCl alone or in combination caused changes in protein-water interactions. Western blotting revealed varying degrees of meat protein degradation in all cases, but the results did not well coincide with those of shear force and the MFI. Therefore, the weakening of intermolecular forces between myofibrillar proteins was considered the main reason for meat tenderization under the present study conditions.

Ionic liquids as the effective technology for enhancing transdermal drug delivery: Design principles, roles, mechanisms, and future challenges

Ionic liquids (ILs) have been proven to be an effective technology for enhancing drug transdermal absorption. However, due to the unique structural components of ILs, the design of efficient ILs and elucidation of action mechanisms remain to be explored. In this review, basic design principles of ideal ILs for transdermal drug delivery system (TDDS) are discussed considering melting point, skin permeability, and toxicity, which depend on the molar ratios, types, functional groups of ions and inter-ionic interactions. Secondly, the contributions of ILs to the development of TDDS through different roles are described: as novel skin penetration enhancers for enhancing transdermal absorption of drugs; as novel solvents for improving the solubility of drugs in carriers; as novel active pharmaceutical ingredients (API-ILs) for regulating skin permeability, solubility, release, and pharmacokinetic behaviors of drugs; and as novel polymers for the development of smart medical materials. Moreover, diverse action mechanisms, mainly including the interactions among ILs, drugs, polymers, and skin components, are summarized. Finally, future challenges related to ILs are discussed, including underlying quantitative structure-activity relationships, complex interaction forces between anions, drugs, polymers and skin microenvironment, long-term stability, and in vivo safety issues. In summary, this article will promote the development of TDDS based on ILs.

Influence on the volatilization of ethyl esters: Nonnegligible role of long-chain fatty acids on Baijiu flavor via intermolecular interaction

Long-chain fatty acids (LCFAs) are commonly presented in Baijiu, but their influence on flavor is ambiguous. The interaction between LCFAs and volatiles was systematically investigated in terms of chemometrics, sensory, and chemical-physical perceptions. The static-headspace-gas-chromatography-mass-spectrometry results demonstrated LCFAs suppressed the volatilizations of most volatiles. According to Phase-ratio-variation analysis, partition coefficients of ethyl acetate (EA) and ethyl hexanoate (EH) decreased 4%-31% and 27%-74%, while those of ethyl butyrate (EB) increased. Calculated by molecular dynamic simulation, the attractive intermolecular forces related to EA/EH increased with oleic acid (OA) addition, while those related to EB decreased. Sensory evaluation confirmed the olfactory threshold of EA and EH increased by 2.4 and 2.7 times respectively, but the threshold of EB decreased from 0.36 to 0.05 mg/L in the presence of OA. Overall, LCFAs altered the intermolecular interaction forces related to esters and ethanol, subsequently affecting the volatile profile and modifying Baijiu flavor's sensory perception.

Theoretical models of staurosporine and analogs uncover detailed structural information in biological solution

Staurosporine and its analogs (STA-analogs) are indolocarbazoles (ICZs) compounds able to inhibit kinase proteins in a non-specific way, while present antimicrobial and cytostatic properties. The knowledge of molecular features associated to the complexation, including the ligand shape in solution and thermodynamics of complexation, is substantial to the development of new bioactive ICZs with improved therapeutic properties. In this context, the empirical approach of GROMOS force field is able to accurately reproduce condensed phase physicochemical properties of molecular systems after parameterization. Hence, through parameterization under GROMOS force field and molecular simulations, we assessed STA-analogs dynamics in aqueous solution, as well as its interaction with water to probe conformational and structural features involved in complexation to therapeutic targets. The coexistence of multiple conformers observed in simulations, and confirmed by metadynamics calculations, expanding the conformational space knowledge of these ligands with potential implications in understanding the ligand conformational selection during complexation. Also, changes in availability to H-bonding concerning the different substituents and water can reflect on effects at complexation free energy due to variation at the desolvation energetic costs. Based on these results, we expect the obtained structural data provide systemic framework for rational chemical modification of STA-analogs.

Theoretical investigation of asphaltene molecules in crude oil viscoelasticity enhancement

Understanding the mechanisms of viscosity enhancement in crude oil phases is crucial for optimizing extraction and transportation processes. The enhanced viscosity mechanism of crude oil phase can be attributed to the intricate intermolecular interactions between asphaltene molecules. However, the molecular mechanism of the viscosification of asphaltene molecules in crude oil is not yet to be fully understood. In this work, molecular dynamics simulations were employed to investigate the dynamic behavior and viscosification mechanism of asphaltene molecules in complex oil phases. Research suggests that the neutral surface of asphaltenes features abundant positive and negative electrostatic potential regions, facilitating complementary pairing between these areas. This significantly augments electrostatic interactions among asphaltene molecules. Besides, the expansive nonpolar expanse on the normal asphaltene surface facilitates interactions between asphaltenes and crude oil molecules. This leads the crude oil viscosity of the system containing normal asphaltene is higher than that of the system containing acidic asphaltene under the same mass fraction (382 μ Pa·s for AAsp and 416 μ Pa·s for NAsp). This work provides insight into the viscosity enhancement mechanisms in crude oil phases and is helpful in improving the efficiency of crude oil extraction and transportation.

Polymer-inducing chemical degradation of amorphous solid dispersions driven by drug-polymer interactions for physical stabilization

Intermolecular interactions between active pharmaceutical ingredients (APIs) and carrier polymers are important for the long-term physical stability of amorphous solid dispersions (ASDs). However, the negative impact of intermolecular interactions on chemical stability has rarely been reported. In this study, the relationship between intermolecular interactions and physical and chemical stability was investigated using two ASDs composed of API and hydroxypropyl methylcellulose acetate succinate (HPMCAS) with different stabilities: ASD1 was physically stable but chemically unstable, whereas ASD2 was physically unstable but chemically stable. Ionic-bonding between the pyridine nitrogen in the API and succinyl group in HPMCAS was found in both ASDs. The additional interaction between the succinyl group in HPMCAS and the hydroxyl group in the API was suggested only in ASD1. It was concluded that the additional interaction contributed to the physical stability of ASD1; however, it accelerated the chemical reaction between the succinyl and hydroxyl groups to generate succinyl ester owing to its close proximity. This study shows that the intermolecular interaction between the API and carrier polymer is not always beneficial for chemical stability. Understanding the molecular states of APIs and polymers in ASDs is important for their successful development.

Heat- and Pressure-driven Room-temperature Polymorphic Transition Accompanied with Switchable SHG Signal in a New Chiral Hexagonal Perovskite

Endowing room-temperature polymorphs with both long-term stability and easy interconvertibility is a big challenge due to the complexity of intermolecular interactions. Herein, we present a chiral hexagonal perovskite (R-3-hydroxy-1-methylpiperidinium)[CdCl3 ] having two room-temperature crystalline forms featuring obviously distinct second-harmonic-generation (SHG) signals with a high switching contrast of ~18 times. The two room-temperature forms could be long-term stable yet easily interconvertible through an irreversible thermal-induced phase transition and a pressure-driven backward transition, by switching hydrogen bonds via collective reorientation of ordered homochiral cations. Based on the essential role of homochiral organic cations in inducing switchable hydrogen bond linkages, this present instance provides good evidence that relatively irregular organic cations could induce more obvious inorganic chain deformations, thus endowing polymorphs with significantly different SHG signals at room temperature.

Differentiation of free d-amino acids and amino acid isomers in solution using tandem mass spectrometry of hydrogen-bonded clusters

Free d-amino acids and amino acid isomers were differentiated using tandem mass spectrometry without chromatographic separation. Ultraviolet photodissociation and water adsorption of leucine (Leu) and isoleucine (Ile) enantiomers hydrogen-bonded with tryptophan (Trp) were investigated at 8 K in the gas phase. The enantiomer-selective Cα-Cβ bond cleavage of Trp was observed in the product ion spectra obtained by 285 nm photoexcitation, where the abundance of NH2CHCOOH-eliminated ion of heterochiral H+(d-Trp)(l-Leu) was higher than that of homochiral H+(l-Trp)(l-Leu). When comparing water adsorption on the surfaces of the heterochiral and homochiral clusters in a cold ion trap, the number of water molecules adsorbed on the heterochiral cluster was greater than that adsorbed on the homochiral cluster. These results indicate that the stronger intermolecular interactions within the homochiral H+(l-Trp)(l-Leu) compared to the heterochiral cluster inhibit enantiomer-selective photodissociation. Leu and Ile were differentiated by the isomer-selective Cα-Cβ bond cleavage of Trp in the clusters. Calibration curves for the differentiation of isomeric amino acids and their enantiomers were developed using monitoring isomer- and enantiomer-selective photodissociation, indicating that the molar fractions in solution could be determined from a single product ion spectrum.

More simple, efficient and accurate food research promoted by intermolecular interaction approaches: A review

The investigation of intermolecular interactions has become increasingly important in many studies, mainly by combining different analytical approaches to reveal the molecular mechanisms behind specific experimental phenomena. From spectroscopic analysis to sophisticated molecular simulation techniques like molecular docking, molecular dynamics (MD) simulation, and quantum chemical calculations (QCC), the mechanisms of intermolecular interactions are gradually being characterized more clearly and accurately, leading to revolutionary advances. This article aims to review the progression in the main techniques involving intermolecular interactions in food research and the corresponding experimental results. Finally, we discuss the significant impact that cutting-edge molecular simulation technologies may have on the future of conducting deeper exploration. Applications of molecular simulation technology may revolutionize the food research, making it possible to design new future foods with precise nutrition and desired properties.

Inert Filler Selection Strategies in Li-Ion Gel Polymer Electrolytes

The main role of inert fillers in polymer electrolytes is to enhance ionic conductivity. However, lithium ions in gel polymer electrolytes (GPEs) conduct in liquid solvent rather than along the polymer chains. So far, the main role of inert fillers in improving the electrochemical performance of GPEs is still unclear. Here, various low-cost and common inert fillers (Al₂O₃, SiO₂, TiO₂, ZrO₂) are introduced into GPEs to study their effects on Li-ion polymer batteries. It is found that the addition of inert fillers has different effects on ionic conductivity, mechanical strength, thermal stability, and, dominantly, interfacial properties. Compared with other gel electrolytes containing SiO₂, TiO₂, or ZrO₂ fillers, those with Al₂O₃ fillers exhibit the most favorable performance. The high performance is ascribed to the interaction between the surface functional groups of Al₂O₃ and LiNi_0.8Co_0.1Mn_0.1O₂, which alleviates the decomposition of the organic solvent by the cathode, resulting in the formation of a high-quality Li⁺ conductor interfacial layer. This study provides an important reference for the selection of fillers in GPEs, surface modification of separators, and cathode surface coating.

Recalibrating polyparameter linear free energy relationships and reanalyzing mechanisms for partition of nonionic organic compounds to low-density polyethylene passive sampler

Equilibrium passive sampling techniques based on the low-density polyethylene (LDPE) film are increasingly used for determining the concentration of contaminants in water and air. Reliable models capable of predicting LDPE-water and LDPE-air partition coefficients (K_iLDPEw and K_iLDPEa) would be very useful. In previous studies, polyparameter linear free energy relationships (PP-LFERs) based on Abraham's solute descriptors were calibrated for LDPE-water and LDPE-air systems. Unfortunately, a portion of unreliable partition coefficients and solute descriptors were included in the calibration sets of these previous studies, leading to unexpected system parameters and predictive performance in the regression results. In this study, more reliable PP-LFERs were recalibrated for LDPE-water and LDPE-air systems (20‒25 °C) using carefully collected reliable partition coefficients and solute descriptors of various polar and nonpolar compounds (over one hundred and with low redundancy) from the literature, as well as the robust regression method. The PP-LFERs performed well with root-mean-square errors of 0.15-0.25 log units and successfully predicted K_iLDPEw and K_iLDPEa values spanning over 10 orders of magnitude for compounds with reliable descriptors. The partitioning mechanisms of compounds to LDPE were also reanalyzed and compared in detail with n-alkanes (C₆-C₁₆). Generally, LDPE is more prone to form dispersion interactions with solutes than n-alkanes, while it is more difficult to form cavities in LDPE. In addition, the crystallinity of LDPE is not the sole reason for the distinct constant terms presenting in PP-LFERs for LDPE-water and n-hexadecane-water systems.

QM/MM study of N501 involved intermolecular interaction between SARS-CoV-2 receptor binding domain and antibody of human origin

Intermolecular interaction between key residue N501 of the epitope on SARS-CoV-2 RBD and screening antibody B38 was studied using the QM/MM and QM approach. The QM/MM optimized geometry shows that angle X-H---Y is 165° for O-H---O between mAb light chain S30 and RBD N501. High level MP2 calculations indicated the interaction between RBD N501 and S30 of B38 Fab light chain provide a relatively strong attractive force of - 3.32 kcal/mol, whereas the hydrogen bond between RBD Q498 and S30 was quantified as 0.10 kcal/mol. The decrease in ESP partial charge on hydrogen atom of hydroxyl group on S30 drops from 0.38 a.u. to 0.31 a.u., exhibiting the sharing of 0.07 a.u. from the lone pair electron oxygen of N501 due to hydrogen bond formation. The NBO occupancy of hydrogen atom also decreases from 25.79 % to 22.93 % in the hydroxyl H-O NBO bond of S30. However, the minor change of NBO hybridization of hydroxyl oxygen of S30 from sp3.00 to sp3.05 implies the rigidity of hydrogen bond tetrahedral geometry in the relative dynamic protein complex. The O-H---O angle is 165° which is close but not exactly linear. The structural requirement for sp3 hybridization of oxygen for hydroxyl group on S30 and dimension of protein likely prevent O-H---O from adopting linear geometry. The hydrogen bond strengths were also calculated using a variety of DFT methods, and the result of - 3.33 kcal/mol from the M06L method is the closest to that of the MP2 calculation. Results of this work may aid in the COVID-19 vaccine and drug screening.

Hydrogen bonding network dynamics of 1,2-propanediol-water binary solutions by Raman spectroscopy and stimulated Raman scattering

Raman spectroscopy and stimulated Raman scattering (SRS) were used to investigate the hydrogen bonding (HB) network in 1,2-propanediol (1,2-PD)-water binary solutions. Abnormal changes in hydrogen bonds (HBs) were detected when V_1,2-PD (volume fraction of the1,2-PD) was 0.4. In the case of Raman spectroscopy, the HB strength of water is weakened and then strengthened with the increase of 1,2-PD volume fraction. In the case of SRS, two new peaks at 3283 cm^-1 and 3319 cm^-1 were appeared, which demonstrated the appearance of ice-like structures near the methyl group and the weakening of HBs. Based on these phenomena, the HB structure of this binary system underwent a transition from H₂O-H₂O to H₂O-1,2-PD when the V_1,2-PD was 0.4 as V_1,2-PD increased. This work serves as a reference value for the study of HB networks in alcohol-water binary solutions.

The polarized Raman spectra of N-methylpyrrolidone-an effective method for determination of intermolecular interaction and H-bond formation

The isotropic and anisotropic component Raman spectra and H NMR of N-methylpyrrolidone (NMP)/carbon tetrachloride and NMP/methanol binary mixture at different volume fractions have been collected. The polarization Raman frequencies and frequency differences of CO stretching vibration for NMP/methanol mixture show unique concentration-dependence and abrupt jump feature. It is found that the H-bond between solute and solvent does not destroy the noncoincidence (NCE) phenomenon, but has a significant synergistic effect on the NCE. Two distinctive clusters constrained by H-bond and intermolecular interactions were easily determined by means of linear extension method from abrupt jump curve. The experimental phenomena can be well explained by aggregation-induced splitting theory with the proposed dimer structure and H-bond cluster model. Applying the same methodology the conformation of NMP in water has been determined successfully. The establishment of this method will play an important role in the determination of biomolecule aggregation behavior and supramolecular self-assembly structure.

High-performance carboxymethyl cellulose-based hydrogel film for food packaging and preservation system

Most traditional food packaging and preservation films suffer from limited stretchability and relatively simple functionality, which severely restricts their practical application. In this study, a highly stretchable and versatile sodium carboxymethyl cellulose (CMC)/polyvinyl alcohol (PVA)/poly(ethylene imine) (PEI)/tannic acid (TA) hydrogel film was elaborately designed and demonstrated as an efficient food packaging and preservation system. The dynamic reversible non-covalent within three-dimensional (3D) network structures served as sacrificial bonds to dissipate the loaded energy and endowed the hydrogel film with excellent elongation ~400 %, which is much larger than that of conventional food packaging films (<50 %). Furthermore, the optimized CMC/PVA/PEI/TA₃ hydrogel film delivers versatile performances, including self-healing, whole UV-blocking (<400 nm), strong adhesive strength (234.08 KPa), antioxidation virtues, oxygen barrier (32.64 cm³*μm/(m²*d*KPa)) and water vapor barrier (642.92 g/(m²*24 h)). Notably, the shelf life of fresh strawberries, mangoes, and cherries was prolonged by at least one week under ambient conditions when the packaging box was covered by the fabricated CMC/PVA/PEI/TA₃ film. Thus, our work not only provides a highly stretchable and versatile hydrogel film but also boosts the in-depth comprehension and rational design of robust food packaging and preservation films.

Aggregation induced spectral splitting and Fermi resonance of Ethylene Carbonate in binary mixture

The vibration band of the ring stretching (ν₁₄), the fundamental ring breathing (ν₁₇) and the Fermi resonance band of carbonyl stretching mixing with the overtone of the ring breathing (ν_{5 +} 2ν₁₇) have been investigated in solid ethylene carbonate (EC) and EC/CH₃CN and EC/CHCl₃ binary mixture. Dimer structure with aggregation-induced spectral splitting model (AIS) was applied to calculate the vibration spectra using the B3LYP-D3/6-311+G (d,p) procedure. The noncoincidence effect (NCE) and concentration induced frequency shifts of the ν₁₄ and ν₅ could be well explained by AIS model based on the dimer structure. Four bands were observed with two in the isotropic and two in the anisotropic Raman spectra and their NCE value decreased with the decrease of EC volume fraction in the binary mixture, and finally disappeared. NCE value and the Fermi resonance constants of EC at different concentrations were calculated from the experimental data.

The Importance of Electrostatics and Polarization for Noncovalent Interactions: Ionic Hydrogen Bonds vs Ionic Halogen Bonds

A series of 26 hydrogen-bonded complexes between Br⁻ and halogen, oxygen and sulfur hydrogen-bond (HB) donors is investigated at the M06-2X/6–311 + G(2df,2p) level of theory. Analysis using a model in which Br⁻ is replaced by a point charge shows that the interaction energy (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\Delta E}_{Int}$$\end{document}ΔEInt) of the complexes is accurately reproduced by the scaled interaction energy with the point charge (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\Delta E}_{Int}^{PC}$$\end{document}ΔEIntPC).This is demonstrated by \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\Delta E}_{Int}=0.86{\Delta E}_{Int}^{PC}$$\end{document}ΔEInt=0.86ΔEIntPC with a correlation coefficient, R² =0.999. The only outlier is (Br-H-Br)⁻, which generally is classified as a strong charge-transfer complex with covalent character rather than a HB complex. \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\Delta E}_{Int}^{PC}$$\end{document}ΔEIntPC can be divided rigorously into an electrostatic contribution (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\Delta E}_{ES}^{PC}$$\end{document}ΔEESPC) and a polarization contribution (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\Delta E}_{Pol}^{PC}$$\end{document}ΔEPolPC).Within the set of HB complexes investigated, the former varies between -7.2 and -32.7 kcal mol⁻¹, whereas the latter varies between -1.6 and -11.5 kcal mol⁻¹. Compared to our previous study of halogen-bonded (XB) complexes between Br⁻ and C–Br XB donors, the electrostatic contribution is generally stronger and the polarization contribution is generally weaker in the HB complexes. However, for both types of bonding, the variation in interaction strength can be reproduced accurately without invoking a charge-transfer term. For the Br⁻···HF complex, the importance of charge penetration on the variation of the interaction energy with intermolecular distance is investigated. It is shown that the repulsive character of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\Delta E}_{Int}$$\end{document}ΔEInt at short distances in this complex to a large extent can be attributed to charge penetration.

Intermolecular interactions between cyclo[18]carbon and XCN (X = H, F, Cl, Br, I): a theoretical study

In this article, the intermolecular interactions of cyclo[18]carbon with XCN (X = H, F, Cl, Br, I) were investigated in detail by quantum chemistry calculations and wavefunction analyses. The electrostatic potential and van der Waals potential of cyclo[18]carbon were examined, then the structures of the complexes, the interaction energies of the intermolecular interactions were studied. Quantum theory of atoms in molecules analysis was performed to help understand the specific interactions. The XCN molecules can insert into the cyclo[18]carbon ring, and ClCN, BrCN, and ICN could also bind with cyclo[18]carbon from outside. Charge transfer in the inner complex is more prominent than that of the outer complex. Plots of electron density difference revealed that electron density shift was significantly different when the X atom changed. The main driving force for molecular binding is dispersion attraction, which is disclosed by interaction region indicator analysis and energy decomposition calculations.

Intermolecular interaction of diamine-diol binary system: A mini-review

The highly selective chemical reaction of carbon dioxide with organic amines is considered to a mature technology and a feasible initial path for carbon capture. In order to solve the disadvantages of high volatility, equipment corrosion and high energy consumption of traditional organic amines, amine alcohol "mixture based" solution has been developed and showed excellent carbon dioxide absorption capacity, which is due to the positive effect of intermolecular interaction in amine alcohol "mixture based" solution system on thermodynamic properties. However, the influencing factors of the intermolecular force in multicomponent solution system are complex, including the chemical, physical, structural effects. Therefore, it is necessary to comprehensively use a variety of characterization methods to systematically understand the form of intermolecular interaction in multicomponent solution system. This review systematically discusses the determination of intermolecular interactions in diamine-diol multicomponent solutions by three mainstream research methods, theoretical calculation method, spectral method, and thermodynamic method, aiming to provide a theoretical reference for the industrial production, the supplement to experimental data, and construction and understanding of theoretical models of multicomponent solution system.

Impact of cocrystal solution-state stability on cocrystal dissociation and polymorphic drug recrystallization during dissolution

The present study aimed to investigate how cocrystal solution-state stability may affect the polymorphic drug formation and transition during dissolution. In this work, curcumin-resorcinol (CUR-RES), curcumin-hydroquinone (CUR-HYQ) and curcumin-phloroglucinol (CUR-PHL) cocrystals were employed for dissolution studies in three buffer systems to study the effects of solvent and cocrystal thermodynamic stability. The undissolved solids were collected at designed time points and characterized by powder X-ray diffraction, differential scanning calorimetry and scanning electron microscopy. In pH 1.2 buffer, three cocrystals generated > 94% of metastable CUR form III with trace amount of stable CUR form I, while the phase purity of CUR form III recrystallized from buffers containing ethanol (EtOH) were decreased dramatically. For the same cocrystal, the cocrystal form maintained longer in the pH 1.2 buffer when compared with buffers containing EtOH. The phase purity of recrystallized CUR form III in the metastable cocrystal systems followed a linear relationship against CUR solubility, while the thermodynamically stable cocrystal resulted in a non-linear relationship. Due to different intermolecular interactions analyzed by ¹H NMR, the stable cocrystal required a higher supersaturation level to precipitate pure CUR form III, in comparison to two metastable cocrystals. Our study offers important insights into mitigating the risk of recrystallization of drug polymorphs during cocrystal dissolution and demonstrates the potential use of cocrystals for drug polymorph preparation, both of which are crucial to the pharmaceutical cocrystal development and reformulation of existing drugs.

Application of terahertz spectroscopy combined with density functional theory to analysis of intermolecular weak interactions for coumarin and 6-methylcoumarin

The terahertz (THz) absorption spectra of coumarin and 6-methylcoumarin have been investigated by terahertz time-domain spectroscopy (THz-TDS) system in the frequency range from 0.4 to 2.8 THz. Density functional theory (DFT) calculations, both with and without London force dispersion corrections, have been used for the assignment of the experimental THz spectra. To thoroughly interpret the spectrum information, we used potential energy distribution (PED) method to assign the vibrational modes of the absorption peaks, and identify the origin of the absorption peaks by electrostatic potential (ESP) and van der Waals (vdW) potential distribution analysis method. The results show that absorption peaks both for coumarin and 6-methylcoumarin are caused by electrostatic interaction in the lower frequency range, while vdW interaction in the higher frequency. Moreover, the potential energy distribution of electrostatic and vdW between them is basically the same, and it led to the similarity of THz spectra between coumarin and 6-MC. This work has demonstrated that using THz spectroscopy combined with DFT calculations is an effective way to analysis of intermolecular weak interactions and biomolecules with similar structures.

A hybrid strategy combining solution NMR spectroscopy and isothermal titration calorimetry to characterize protein-nanodisc interaction

NMR is a powerful tool for characterizing intermolecular interactions at atomic resolution. However, the nature of the complex interactions of membrane-binding proteins makes it difficult to elucidate the interaction mechanisms. Here, we demonstrated that structural and thermodynamic analyses using solution NMR spectroscopy and isothermal titration calorimetry (ITC) can clearly detect a specific interaction between the pleckstrin homology (PH) domain of ceramide transport protein (CERT) and phosphatidylinositol 4-monophosphate (PI4P) embedded in the lipid nanodisc, and distinguish the specific interaction from nonspecific interactions with the bulk surface of the lipid nanodisc. This NMR-ITC hybrid strategy provides detailed characterization of protein-lipid membrane interactions.

Role of polymers in the physical and chemical stability of amorphous solid dispersion: A case study of carbamazepine

Incorporating the amorphous drug in polymeric components has been demonstrated as a feasible approach to enhance the bioavailability of poorly water-soluble drugs. The objective of this study was to investigate the role of polymers in the stability of amorphous solid dispersion (ASD) by evaluating the drug-polymer interaction, microenvironmental pH, and stability of ASD. Carbamazepine (CBZ), a Biopharmaceutics Classification System Class II compound, was utilized as a model drug. Polyvinylpyrrolidone (PVP), poly(1-vinylpyrrolidone-co-vinyl acetate) (PVPVA), polyacrylic acid (PAA), and hydroxypropyl methylcellulose (HPMCAS) were selected as model polymers. CBZ ASDs were characterized by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and dissolution studies. Molecular modeling was conducted to understand the strength of interaction between CBZ and each polymer. FTIR spectroscopy and molecular modeling results show that the interaction between CBZ and PAA is the strongest among all the ASDs, as PAA is an acidic polymer with the potential to form strong hydrogen bonding with CBZ. Besides, hydrophobic interaction is detected between CBZ and HPMCAS. CBZ-PAA and CBZ-HPMCAS ASDs reveal better physical stability than CBZ-PVP and CBZ-PVPVA ASDs under 40 °C/75% RH for 8 weeks. However, CBZ-PAA ASD shows chemical degradation after stability testing due to its acidic microenvironmental pH. This paper shows that strong intermolecular interactions between CBZ and polymers contribute to the physical stability of the ASDs. Additionally, acidic polymers yield an acidic microenvironment pH of the ASDs that causes chemical degradation during storage. Hence, a balance between the ability of a given polymer to promote physical stability and chemical stability may need to be considered.

Moment equations for partial filling capillary electrophoresis

Moment equations were developed for partial filling CE systems, in which solute dissolution phenomena by spherical molecular assemblies or intermolecular interactions take place. Because experimental conditions of partial filling CE are divided into five categories on the basis of the magnitude relationship between the migration velocity of solute molecules and that of molecular assemblies or ligand molecules, the moment equations were systematically developed for each case by using the Einstein equation for diffusion and the random walk model. In order to demonstrate the effectiveness of the moment equations, they were applied to the analysis of partial filling CE behavior, which is correlated with dissolution phenomena of small solute molecules into spherical molecular assemblies as specific examples. Simulation results only in the case that the migration velocity of solute molecules is faster than that of molecular assemblies were represented in this paper. Detailed explanations about the derivation procedure of the moment equations and the simulation results in other cases can be found in the Supporting Information. The moment equations are theoretical bases for applying partial filling CE to the study on solute permeation kinetics at the interface of spherical molecular assemblies and on reaction kinetics of intermolecular interactions.

Computational investigation on the chiral differentiation of D- and L-penicillamine by β-cyclodextrin

The identification of chiral penicillamine (Pen) is of great significance for clinical medication safety. The host-guest systems formed by enantiomers and macromolecule can be applied to differentiate the chiral drugs and enable the drug delayed release. We hereby performed the dispersion corrected density functional theory (DFT-D) calculation on the complex formed by β-cyclodextrin(β-CD) and D/L-penicillamine (D/L-Pen). The diverse encapsulation configurations with different interaction energy show that both D-Pen and L-Pen tend to longitudinally embedded into the narrow aperture of β-CD with the front part of the sulfur group and the methyl group, and the interaction energy between L-Pen and β-CD is 5.47 kJ/mol(M062XD3) lower than that between D-Pen and β-CD. Based on the computed vibration frequency of host, guest, and the most stable complex, it is found that the featured peaks attributed to the vibration of the carboxyl group of guest and the skeleton vibration of complex are the most significant spectral standard to distinguish the β-CD-D/L-Pen and β-CD. Moreover, the peaks resulted from the skeleton vibration in terahertz spectra can be also used to distinguish the complex of β-CD with chiral Pen. Through the topological analysis and the Independent Gradient Model (IGM) analysis, the O-H^…O hydrogen bond in β-CD-D-Pen is stronger than that in β-CD-L-Pen, and the van der Waals interactions such as C-H…O,C-H…N,C-H…S, O…S and C-H…C-H have the most contributions to the intermolecular interaction in β-CD-D/L-Pen. It is also noted that the H(-OH) in D-Pen and S in L-Pen contribute the most to the intermolecular interaction with β-CD in comparison with other atoms in Pen.

Effect of sodium tripolyphosphate on the interaction and aggregation behavior of ovalbumin-lysozyme complex

The mechanism by which sodium tripolyphosphate affected the aggregation behavior of ovalbumin-lysozyme complexes was investigated in this work. The highest stability coefficients were detected for natural ovalbumin and lysozyme at pH 9.0 and pH 5.0, with values of 0.981 and 0.931, respectively. The turbidity of the phosphorylated ovalbumin-lysozyme complexes was 1.71-fold to the natural complexes at pH 7.0. This result was related to the fact that the phosphorylated sample had a lower isoelectric point. Besides, both intermolecular forces and SDS-PAGE analysis indicated that the disulfide bond was the most important interaction in the complex. Circular dichroism analysis showed that phosphorylation weakened the unfolding and stretching of the structure caused by heat treatment. Moreover, transmission electron microscopy pictures confirmed that the network structure of phosphorylated ovalbumin-lysozyme complex was broader than natural protein. This study provides information for further understanding the effect of phosphorylation on protein aggregation behavior.

Efficient and stable inverted perovskite solar cells enabled by inhibition of self-aggregation of fullerene electron-transporting compounds

Fullerene-based electron-transporting layers (ETLs) significantly influence the defect passivation and device performance of inverted perovskite solar cells (PSCs). However, the π-cage structures of fullerenes lead to a strong tendency to self-aggregate, which affects the long-term stability of the corresponding PSCs. Experimental results revealed that [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM)-based ETLs exhibit a certain degree of self-aggregation that affects the stability of the device, particularly under continuous irradiation stress. To modulate the aggregation behavior, we replaced a methyl hydrogen of PCBM with a phenyl group to yield [6,6]-phenyl-C₆₁-butyric acid benzyl ester (PCBB). As verified through X-ray crystallography, this minor structural modification results in more non-covalent intermolecular interactions, which effectively enhanced the electron-transporting ability of the PCBB-based ETL and led to an efficiency approaching 20%. Notably, the enhanced intermolecular forces of PCBB suppressed its self-aggregation, and the corresponding device showed significantly improved stability, retaining approximately 90% of its initial efficiency after 600 h under one-sun irradiation with maximum power point tracking. These findings provide a viable approach for the design of new fullerene derivatives to tune their intermolecular interactions to suppress self-aggregation within the ETL for high-performance PSCs.

Title: insoluble proteins catch heterologous soluble proteins into inclusion bodies by intermolecular interaction of aggregating peptides

Background

Protein aggregation is a biological event observed in expression systems in which the recombinant protein is produced under stressful conditions surpassing the homeostasis of the protein quality control system. In addition, protein aggregation is also related to conformational diseases in animals as transmissible prion diseases or non-transmissible neurodegenerative diseases including Alzheimer, Parkinson’s disease, amyloidosis and multiple system atrophy among others. At the molecular level, the presence of aggregation-prone domains in protein molecules act as seeding igniters to induce the accumulation of protein molecules in protease-resistant clusters by intermolecular interactions.

Results

In this work we have studied the aggregating-prone performance of a small peptide (L6K2) with additional antimicrobial activity and we have elucidated the relevance of the accompanying scaffold protein to enhance the aggregating profile of the fusion protein. Furthermore, we demonstrated that the fusion of L6K2 to highly soluble recombinant proteins directs the protein to inclusion bodies (IBs) in E. coli through stereospecific interactions in the presence of an insoluble protein displaying the same aggregating-prone peptide (APP).

Conclusions

These data suggest that the molecular bases of protein aggregation are related to the net balance of protein aggregation potential and not only to the presence of APPs. This is then presented as a generic platform to generate hybrid protein aggregates in microbial cell factories for biopharmaceutical and biotechnological applications.

A theoretical investigation into the cooperativity effect on the TNT melting point under external electric field

External electric field has been regarded as an effective tool to induce the variation of melting points of molecular crystals. The melting point of 2,4,6-trinitrotoluene (TNT) was calculated by molecular dynamics simulations under external electric field, and the electric field effects on the cooperativity effects of the ternary (TNT)₃ were investigated at the M06-2X/6-311+G(d) and ωB97X-D/6-311++G(2d,p) levels. The results show that the melting points are decreased while the intermolecular interactions are strengthened under the external electric fields, suggesting that the intermolecular interactions cannot be used to explain the decreased melting points. A deduction based on the cooperativity effect is put forward: the enhanced cooperativity effects create the more serious defects in the melting process of the molecular crystal under the external electric fields, and simultaneously the local order parameters are decreased, leading to the decreased melting point. Thus, the cooperativity effect stemmed from the intermolecular C-H∙∙∙O H-bonding interactions controls the change of TNT melting point under the external electric field. Employing the information-theoretic approach (ITA), the origin of the cooperativity effects on the melting points of molecular crystal is revealed. This study opens a new way to challenge the problems involving the melting points for the molecular crystal under the external electric fields. However, note that above deduction needs to be improved; after all, the simple (TNT)₃ model cannot replace the crystal structure.

Effect of high intensity ultrasound on gelation properties of silver carp surimi with different salt contents

Surimi from silver carp with different salt contents (0-5%) was obtained treated by high intensity ultrasound (HIU, 100 kHz 91 W·cm-2). The gelation properties of samples were evaluated by puncture properties, microstructures, water-holding capacity, dynamic rheological properties and intermolecular interactions. As the salt content increased from 0 to 5%, gel properties of surimi without HIU significantly improved. For samples with low-salt (0-2% NaCl) content, HIU induced obvious enhancement in breaking force and deformation. HIU promoted the protein aggregation linked by SS bonds, hydrophobic interactions and non-disulfide covalent bonds in surimi gels with low-salt content. Moreover, microstructures of HIU surimi gels with low-salt content were more compact than those of the corresponding control samples. HIU also improved the gelation properties of surimi with 3% NaCl to an extent. However, for high-salt (4-5% NaCl) samples, HIU decreased the breaking force and deformation of surimi gels due to the degradation of proteins suggested by increased TCA-soluble peptides. In conclusion, HIU effectively improved the gelation properties of surimi with low-salt content (0-2% NaCl), but was harmful for high-salt (4-5% NaCl) surimi. This might provide the theoretical basis for the production of low-salt surimi gels.

Selective stabilization of multiple promoter G-quadruplex DNA by using 2-phenyl-1H-imidazole-based tanshinone IIA derivatives and their potential suppressing function in the metastatic breast cancer

The G-quadruplex (G4) DNA, which has been developed as a potential anticancer target in drug screening and design, plays a crucial role in the oncogene transcription and translation. Tanshinone IIA derivatives with a planar heterocycle structure may function as G4 stabilizers. We present an innovative case of imidazole-based tanshinone IIA derivatives (1-8) especially compound 4 that improve the selectivity and the binding affinity with G4 DNA and enhance the target tumor inhibition. Cellular and in vivo experiments indicate that the tanshinone IIA derivative 4 inhibits the growth, metastasis, and angiogenesis of triple-negative breast cancer cells possibly through the stabilization of multiple G4 DNAs (e.g., c-myc, K-ras, and VEGF) to induce DNA damage. Further investigation of the intermolecular interaction and the molecular docking indicates that tanshinone IIA derivatives have better selective binding capability to various G4 DNAs than to double-stranded DNA. These findings provide guidance in modifying the molecular structures of tanshinone IIA derivatives and reveal their potential to function as specific G4 stabilizers.

van der Waals potential: an important complement to molecular electrostatic potential in studying intermolecular interactions

Electrostatics and van der Waals (vdW) interactions are two major components of intermolecular weak interactions. Electrostatic potential has been a very popular function in revealing electrostatic interaction between the system under study and other species, while the role of vdW potential was less recognized and has long been ignored. In this paper, we explicitly present definition of vdW potential, describe its implementation details, and demonstrate its important practical values by several examples. We hope this work can arouse researchers' attention to the vdW potential and promote its application in the studies of weak interactions. Calculation, visualization, and quantitative analysis of the vdW potential have been supported by our freely available code Multiwfn ( http://sobereva.com/multiwfn ).

Theoretical studies on oxadiazole-based layer stacking nitrogen-rich high-performance insensitive energetic materials

A series of energetic compounds derived from substituted oxadiazole molecules which were theoretically proved to have π-π stacking crystal structure using NIC method and QTAIM theory were designed and investigated theoretically as novel high-performance insensitive energetic materials. The heats of formation (HOFs) and detonation parameters were predicted based on Kamlet-Jacobs equations and Born-Haber cycle. All energetic compounds and derivatives were calculated at DFT-B3PW91/6-31G++(d,p) level and exhibited ideal oxygen balance (OB%) (- 19.50~15.68), positive heats of formation (424.0~957.4 kJ/mol), and pleasant crystal density (1.707~1.901 g/cm³). The predicted results revealed that detonation performances of some designed molecules are equal to traditional energetic materials while they are more stable and insensitive that can be considered to have potential synthesis and application value. Graphical abstract BRIEFS Three energetic molecules that proved may have a π-π stacking crystal structure and its derivatives were designed and investigated theoretical as novel high-performance insensitive energetic materials. The most of compounds exhibited positive solid phase heat of formation, idea oxygen balance and structural stability.

Computational study of the intermolecular interactions and their effect on the UV-visible spectra of the ternary liquid mixture of benzene, ethanol and propylene glycol

Quantum chemical calculations are well-equipped to provide answers to the questions regarding the different aspects of intermolecular interactions. We investigate the benzene, ethanol and 1,2 propanediol ternary mixture with theoretical as well as experimental UV-Vis spectroscopy. An extensive theoretical study on the molecular structure and UV-Vis spectral analysis was undertaken using density functional theory (DFT) method. Structural parameter analysis and the HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) energy gap help to describe the possible interaction between molecules in dimer and in combination. Interaction energy has been calculated from topological study. Time-dependent density functional theory (TDDFT) calculations on dimer/cluster in gas phase help to understand the effect of the molecular interaction on the overall spectral shift and related intensity variation. Our results show that in the ternary mixture, the interaction energies of the interactions are π-π interaction: 0.52-2.57 kcal/mol, Hp-π interaction: 1.15 kcal/mol and H-bonding: 2.49 to 4.46 kcal/mol. The π-π interaction and H-bonding cause red shift in absorption spectra while Hp-π interaction causes blue shift. In the ternary mixture, the strength of different kinds of interaction depends on the concentration, and as each interaction has its own effect on spectral shift, the overall experimental spectra get broader and distorted from the Gaussian shape.

Hansen solubility parameters obtained via molecular dynamics simulations as a route to predict siloxane surfactant adsorption

HYPOTHESIS

The Hansen Solubility Parameters (HSP) derived from Molecular Dynamics (MD) simulations can be used as a fast approach to predict surfactants adsorption on a solid surface. Experiments and simulations: We focused on the specific case of siloxane-based surfactants adsorption on silicon oxide surface (SiO₂), encountered in inkjet printing processes. A simplified atomistic model of the SiO₂ surface was designed to enable the computation of its solubility parameter using MD, and to subsequently determine the interactions of the SiO₂ surface with the siloxane-based surfactant and the various solvents employed. Surfactant adsorption was characterized experimentally using contact angle goniometry, ellipsometry, XPS and AFM.

FINDINGS

Comparison of the numerical results with experiments showed that the HSP theory allows to identify the range of solvents that are likely to prevent surfactant adsorption on the SiO₂ surface. The proposed approach indicates that polar solvents, such as acetone and triacetin, which are strongly attracted to the silicon oxide surface might form a shield that prevents siloxane-based surfactants adsorption. This simple approach, can guide the selection of adequate solvents for surfaces and surfactants with specific chemical structures, providing opportunities for controlling interfacial adsorption.

Recent advances in bioimaging with high-speed atomic force microscopy

Among various microscopic techniques for characterizing protein structures and functions, high-speed atomic force microscopy (HS-AFM) is a unique technique in that it allows direct visualization of structural changes and molecular interactions of proteins without any labeling in a liquid environment. Since the development of the HS-AFM was first reported in 2001, it has been applied to analyze the dynamics of various types of proteins, including motor proteins, membrane proteins, DNA-binding proteins, amyloid proteins, and artificial proteins. This method has now become a versatile tool indispensable for biophysical research. This short review summarizes some bioimaging applications of HS-AFM reported in the last few years and novel applications of HS-AFM utilizing the unique ability of AFM to gain mechanical properties of samples in addition to structural information.

Mitigation of isoquercitrin on β-lactoglobulin glycation: Insight into the mechanisms by mass spectrometry and interaction analysis

Formation of advanced glycation end products (AGEs) on foods imposes threats to human health after intaking. This research firstly evaluated the inhibition of isoquercitrin on β-lactoglobulin (β-Lg) glycation, the mechanisms were elucidated by fluorescence spectroscopy, Orbitrap MSⁿ and molecular docking. Fluorescence spectra indicated that isoquercitrin effectively alleviated the formation of AGEs, it could stabilize the conformation structure of glycated β-Lg (G-β-Lg), change the micro-environment in the vicinity of chromophores. SDS-PAGE analysis revealed the suppressed cross-linking of G-β-Lg induced by isoquercitrin. The number of glycation site detected on G-β-Lg was reduced from ten to eight after the addition of isoquercitrin, and the relative glycation degree of substitution of per site (RGDSP) of most glycation sites were also greatly decreased. As indicated by intermolecular interaction, isoquercitrin quenched the fluorescence of β-Lg via a static mechanism, and their combination is an endothermic processing mainly derived by hydrophobic interaction, hydrogen bonds, and van der Waals forces. Isoquercitrin interacted with β-Lg to form an equimolar complex, and one hydrogen bond was formed between isoquercitrin and Lys69 (4.96 Å). Above results proved that isoquercitrin can be a promising anti-glycation agent used in food system to prevent the formation of harmful glycation products.

Exploring calcium ion-dependent effect on the intermolecular interaction between human secreted phospholipase A2 and its peptide inhibitors in coronary artery disease

Human secreted phospholipase A₂ (hsPLA₂) is a small calcium ion (Ca²⁺)-regulatory protein secreting from platelets, eosinophils and T-lymphocytes, which has been established as an important biomarker and potential target for the diagnosis and therapy of coronary artery disease. Short peptide inhibitors are used to competitively suppress the enzymatic activity of hsPLA₂. Here, Ca²⁺ effect on the intermolecular recognition and interaction between hsPLA₂ and its peptide inhibitors is investigated systematically by using molecular modeling and bioinformatics analysis. Dynamics simulations reveal that the hsPLA₂ structure bound with Ca²⁺ is rather stable and has low thermal motion; removal of Ca²⁺ considerably increases structural flexibility and intrinsic disorder of the protein. Energetics calculations suggest that presence of Ca²⁺ can effectively promote the interaction of hsPLA₂ with peptide inhibitors. In particular, the local substructures of hsPLA₂ such as helix H1, loop L2 and double-stranded β-sheet DS that participate in peptide recognition are involved in or nearby Ca²⁺-coordinating site and can be directly stabilized by the Ca²⁺. In addition, a significant concentration-dependent effect of Ca²⁺ on peptide-hsPLA₂ binding is observed in vitro, that is, a little of Ca²⁺ can largely improve peptide binding affinity, but high Ca²⁺ concentration does not increase the affinity substantially. The correlation between calculated free energy and experimental binding affinity over different peptide inhibitors is improved considerably by adding Ca²⁺ to hsPLA₂. Specifically, the FLSYK peptide can generally bind to Ca²⁺-bound hsPLA₂ with a moderate or high affinity (K_d ranges between 56 and 210 μM), but have only a modest affinity or even nonbinding to Ca²⁺-free hsPLA₂ (K_d > 400 μM or = n.d.).

Preparation of calcium alginate/polyethylene glycol acrylate double network fiber with excellent properties by dynamic molding method

In order to greatly reduce the viscosity of sodium alginate (SA) gel solution and improve the properties of calcium alginate (CA) fiber, SA/polyethylene glycol acrylate (PEGDA) gel spinning solution with interpenetrating network structure was prepared by using one-pot method firstly. Then the solution was extruded continuously into the coagulation bath. CA/PEGDA composite fiber with double network was prepared by ionic crosslinking SA macromolecules with Ca²⁺ during the dynamic molding process of solidification, stretch and curl. Rheological results indicated that the spinning solution's apparent viscosity was 92.8% smaller than that of the pure SA solution at PEGDA content of 20 wt%. As the PEGDA content increased, the storage modulus G' and the loss modulus G" both decreased. FTIR results showed that PEGDA content had an obvious influence on hydrogen bond in CA/PEGDA system. The tensile strength of composite fiber reached maximum of 2.91cN/dtex at PEGDA of 10%.

New insight into transdermal drug delivery with supersaturated formulation based on co-amorphous system

The objective of this study was to prepare a supersaturated formulation based on formation of a co-amorphous system of a drug and a coformer in order to enhance skin permeation. Atenolol (ATE) and urea (URE) were used as the model drug and the coformer, respectively. Thermal analysis of physical mixtures of ATE and URE showed decreases in the melting points and the formation of a co-amorphous system which was in a supercooled liquid state because of a low glass transition temperature. Supersaturated solutions of ATE and URE at different molar ratios in polyethylene glycol 400 (PEG400) were prepared. The precipitations were observed under storage at 25 °C for all formulations except for ATE-URE at 1:8 molar ratio which remained in the supersaturated state for 2 months. ¹H NMR analysis confirmed the interactions between ATE and URE in PEG400. The ATE-URE supersaturated formulation showed higher permeability for mice skin than that of ATE saturated formulation, which was superior to the expected permeability from the degree of supersaturation. We concluded that co-amorphous based supersaturated formulation offers much promise for transdermal drug delivery.

Development of an engineered carbamoyl phosphate synthetase with released sensitivity to feedback inhibition by site-directed mutation and casting error-prone PCR

Carbamoyl phosphate synthetase (CPS) is a key enzyme in both pyrimidine and arginine biosynthesis. However, it is inhibited strongly by uridine monophosphate (UMP), which is an intermediate of the de-novo synthesis of pyrimidine nucleoside. In this study, the native carbamoyl phosphate synthetase, from Escherichia coli, was evolved by site-directed mutation and casting error-prone PCR. Compared with the wild-type, the variant N1015 F had released sensitivity to UMP and exhibited 100% of the initial activity in the presence of UMP. Variant K1006A exhibited 0.14-fold improvement in initial activity and kept above 65% of relative activity under the saturated concentration of inhibitor. Structure analysis of variants demonstrated that the reduced sensitivity to inhibitor was largely attributed to the decreased hydrogen bonds, which could reduce the binding affinity with UMP. Also, Phe with large side chain could narrow the binding pocket and generate more steric hindrance. Based on the results in this study, N1015F was an ideal alternative catalyst for the wild-type CPS for pyrimidine biosynthesis.

Intermolecular interactions of polysaccharides in membrane fouling during microfiltration

Membrane technology has been widely employed for seawater desalination, water and wastewater reclamation, while membrane fouling still remains as a major challenge. The polysaccharides in extracellular polymeric substances (EPS) have been recognized as an important foulant that causes serious membrane fouling, while the detailed structure of polysaccharides and the intermolecular interactions between them have not been adequately disclosed. In this study, two different polysaccharides and their mixtures were used to study the intermolecular cross-linking of polysaccharides as well as its effects on membrane fouling. Results demonstrated that the fouling propensities of distinct polysaccharides were completely different, which was attributed to the different intermolecular interactions lying in polysaccharides. The cross-linking among molecules of polysaccharide, regardless of the homogeneity, was found to form complex networks and determine the effective dimension of polysaccharides. Depending on the effective dimension of foulants, pore blocking and cake layer occurred subsequently during filtration processes. In light of this, it potentially gives new insights into the fouling behaviours by combining the structure-function knowledge of polysaccharides with their fouling propensity. In addition, transparent exopolymeric particles (TEP) measurement was found to provide an intuitionistic evaluation of the complex networks formed from polysaccharides, so that may act as a good indicator of fouling during membrane filtration.

Investigation of supramolecular interaction in 4, 4'-bipyridine crystal by hydrostatic pressure spectroscopies

The luminescence and structural changes of 4, 4'-bipyridine in the crystal and powder forms under the effect of high pressure applied by a diamond anvil cell has been investigated through the fluorescence and Raman spectroscopies. In its single crystal structure, the 4, 4'-bipyridine molecules are paralleled arranged with the identifiable CH⋯N and π⋯π interactions among molecules. However, in the powder form, these intermolecular interactions nearly diminish. The 4, 4'-bipyridine crystal shows the obvious bathochromic-shifting of the emission band, which is different from the powder sample that displays a fixed luminescent band during compression. Additionally, the Raman bands of them both show shifts to higher wavenumbers as different degrees. The detailed peak assignments are performed based on the theoretical calculation through B3LYP method. Comparisons in spectral behaviors between the crystal and powder under compression show the crystal form exhibits a superior mechanochromic performance relative to the powder one, because the intermolecular interactions in the crystal form play dominating roles and they can be easily tuned along with pressure in such a highly ordered structure compared to the powder form. The relation investigation between property and supramolecular interactions not only makes deeper understanding in the mechanochromic mechanisms of 4, 4'-bipyridine, but also gives a helpful reference for the molecular designs of coordination polymers and co-crystals with 4, 4'-bipyridine involved.

Moment analysis for reaction kinetics of intermolecular interactions

Moment equations were developed on the basis of the principle of relativity for analyzing elution peak profiles measured by ACE to analytically determine the association (k_a ) and dissociation (k_d ) rate constants of intermolecular interactions. Basic equations representing the mass balance, mass transfer rate, and reaction kinetics in ACE system in a Galilean coordinate system S were transformed to those in another coordinate system S', which imaginarily moved with respect to S. Moment equations for ACE peaks in S' in the time domain were derived from the analytical solution of the modified basic equations in the Laplace domain. Moment equations for ACE peaks in S were derived from those in S' by the inverse Galilean transformation. The moment equations were used for analyzing some ACE data previously published to determine k_a and k_d values. It was demonstrated that the moment equations were effective for extracting the information about affinity kinetics of intermolecular interactions from the elution peak profiles measured by ACE. The moment equations were also used to discuss the influence of mass transfer and reaction kinetics on ACE peak profiles. Some results of the numerical calculations are also indicated in Supporting Information.

Intermolecular interactions between glycomodules of plant cell wall arabinogalactan-proteins and extensins

Hydroxyproline-rich glycoproteins (HRGPs) are a unique component of plant cell walls, undergoing extensive posttranslational modification such as proline hydroxylation and hydroxyproline-O-glycosylation. Arabinogalactan proteins (AGPs) and extensins are major members of the HRGP superfamily. AGPs have repetitive AlaHyp, SerHyp, and ThrHyp peptides, the Hyp residues being glycosylated with large type II arabinogalactan polysaccharides, while extensins contain characteristic SerHyp4 and SerHyp2 motifs with arabinosylated (1-4 residues) Hyp. Although they are less than ten percent in all wall materials, AGPs and extensins play important roles in all aspects of plant growth and development. The detailed mechanisms of their functions are still under investigation. However, many of the functions may be attributed to their adhesive properties. Here, we used a forced unbinding technique to measure relative adhesive potential of the well characterized (AlaHyp)51 and (SerHyp4)18 glycomodules representing AGPs and extensins, respectively. In the presence of different wall ions such as protons, Ca2+, and boron, the glycomodules exhibited different adhesive patterns, suggesting that the wall ion-regulated intermolecular interactions/adhesions between AGPs and/or extensins may be involved in maintaining wall-plasma membrane integrity during wall loosening processes such as wall elongation or expansion. This research applies a biophysical approach to understand the biological function of plant cell wall glycoproteins.

Surface Effect on Oil Transportation in Nanochannel: a Molecular Dynamics Study

In this work, we investigate the dynamics mechanism of oil transportation in nanochannel using molecular dynamics simulations. It is demonstrated that the interaction between oil molecules and nanochannel has a great effect on the transportation properties of oil in nanochannel. Because of different interactions between oil molecules and channel, the center of mass (COM) displacement of oil in a 6-nm channel is over 30 times larger than that in a 2-nm channel, and the diffusion coefficient of oil molecules at the center of a 6-nm channel is almost two times more than that near the channel surface. Besides, it is found that polarity of oil molecules has the effect on impeding oil transportation, because the electrostatic interaction between polar oil molecules and channel is far larger than that between nonpolar oil molecules and channel. In addition, channel component is found to play an important role in oil transportation in nanochannel, for example, the COM displacement of oil in gold channel is very few due to great interaction between oil and gold substrate. It is also found that nano-sized roughness of channel surface greatly influences the speed and flow pattern of oil. Our findings would contribute to revealing the mechanism of oil transportation in nanochannels and therefore are very important for design of oil extraction in nanochannels.

Theoretical investigation of the effects of the molar ratio and solvent on the formation of the pyrazole-nitroamine cocrystal explosive 3,4-dinitropyrazole (DNP)/2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20)

The effects of the molar ratio, temperature, and solvent on the formation of the cocrystal explosive DNP/CL-20 were investigated using molecular dynamics (MD) simulation. The cocrystal structure was predicted through Monte Carlo (MC) simulation and using first-principles methods. The results showed that the DNP/CL-20 cocrystal might be more stable in the molar ratio 1:1 near to 318 K, and the most probable cocrystal crystallizes in the triclinic crystal system with the space group P[Formula: see text]. Cocrystallization was more likely to occur in methanol and ethanol at 308 K as a result of solvent effects. The optimized structure and the reduced density gradient (RDG) of the DNP/CL-20 complex confirmed that the main driving forces for cocrystallization were a series of hydrogen bonds and van der Waals forces. Analyses of the trigger bonds, the charges on the nitro groups, the electrostatic surface potential (ESP), and the free space per molecule in the cocrystal lattice were carried out to further explore their influences on the sensitivity of CL-20. The results indicated that the DNP/CL-20 complex tended to be more stable and insensitive than pure CL-20. Moreover, an investigation of the detonation performance of the DNP/CL-20 cocrystal indicated that it possesses high power. Graphical abstract DNP/CL-20 cocrystal models with different molar ratios were investigated at different temperatures using molecular dynamics (MD) simulation methods. Binding energies and mechanical properties were probed to determine the stability and performance of each cocrystal model. Solvated DNP/CL-20 models were established by adding solvent molecules to the cocrystal surface. The binding energies of the models in various solvents were calculated in order to identify the most suitable solvent and temperature for preparing the cocrystal explosive DNP/CL-20.

Protein 19F-labeling using transglutaminase for the NMR study of intermolecular interactions

The preparation of stable isotope-labeled proteins is important for NMR studies, however, it is often hampered in the case of eukaryotic proteins which are not readily expressed in Escherichia coli. Such proteins are often conveniently investigated following post-expression chemical isotope tagging. Enzymatic ¹⁵N-labeling of glutamine side chains using transglutaminase (TGase) has been applied to several proteins for NMR studies. ¹⁹F-labeling is useful for interaction studies due to its high NMR sensitivity and susceptibility. Here, ¹⁹F-labeling of glutamine side chains using TGase and 2,2,2-trifluoroethylamine hydrochloride was established for use in an NMR study. This enzymatic ¹⁹F-labeling readily provided NMR detection of protein-drug and protein-protein interactions with complexes of about 100 kDa since the surface residues provided a good substrate for TGase. The ¹⁹F-labeling method was 3.5-fold more sensitive than ¹⁵N-labeling, and could be combined with other chemical modification techniques such as lysine ¹³C-methylation. ¹³C-dimethylated-¹⁹F-labeled FKBP12 provided more accurate information concerning the FK506 binding site.