Deviation from van't Hoff dependence in RP-LC induced by tautomeric interconversion observed for four compounds

Effect of Milk Protein-Polyphenol Conjugate on the Regulation of GLP-1 Hormone

Modern functional foods are designed to provide health benefits beyond basic nutrition. They are enriched with bioactive ingredients like probiotics, vitamins, minerals, and antioxidants. These foods support overall health, enhance immune function, and help prevent chronic diseases. Milk proteins and tea are known to influence satiety and regulate body weight. Studies have shown that green tea polyphenols, namely, (-)-epigallocatechin gallate (EGCG), and whey proteins, predominantly lactoferrin (LF) from milk, play a role in regulating satiety. This study aims to investigate the effect of conjugating EGCG with apo-lactoferrin (Apo-LF) and assessing these effects on satiety through monitoring glucagon-like peptide-1 (GLP-1) regulation in a human colon (NCI-H716) cell line. Apo-LF-EGCG conjugates were synthesized and characterized in terms of structural and functional properties. The effect on GLP-1 regulation was assessed by real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA) to monitor gene and protein expressions, respectively. The results revealed that the protein-polyphenol interaction occurs through the complex formation of hydrogen bonds at the O-H and carbonyl groups of EGCG. The conjugates also showed a significant up-regulation of gene and protein expression levels of GLP-1 while also preventing EGCG from degradation, thereby preserving its antioxidant properties. The Apo-LF-EGCG conjugates increase satiety via increasing GLP-1 secretion in human colon cells while simultaneously retaining the antioxidant properties of EGCG. Therefore, these conjugates show potential for use as dietary supplements to enhance satiety.

Exploring the Solubility Limits of Edaravone in Neat Solvents and Binary Mixtures: Experimental and Machine Learning Study

This study explores the edaravone solubility space encompassing both neat and binary dissolution media. Efforts were made to reveal the inherent concentration limits of common pure and mixed solvents. For this purpose, the published solubility data of the title drug were scrupulously inspected and cured, which made the dataset consistent and coherent. However, the lack of some important types of solvents in the collection called for an extension of the available pool of edaravone solubility data. Hence, new measurements were performed to collect edaravone solubility values in polar non-protic and diprotic media. Such an extended set of data was used in the machine learning process for tuning the parameters of regressor models and formulating the ensemble for predicting new data. In both phases, namely the model training and ensemble formulation, close attention was paid not only to minimizing the deviation of computed values from the experimental ones but also to ensuring high predictive power and accurate solubility computations for new systems. Furthermore, the environmental friendliness characteristics determined based on the common green solvent selection criteria, were included in the analysis. Our applied protocol led to the conclusion that the solubility space defined by ordinary solvents is limited, and it is unlikely to find solvents that are better suited for edaravone dissolution than those described in this manuscript. The theoretical framework presented in this study provides a precise guideline for conducting experiments, as well as saving time and resources in the pursuit of new findings.

Intermolecular Interactions as a Measure of Dapsone Solubility in Neat Solvents and Binary Solvent Mixtures

Dapsone is an effective antibacterial drug used to treat a variety of conditions. However, the aqueous solubility of this drug is limited, as is its permeability. This study expands the available solubility data pool for dapsone by measuring its solubility in several pure organic solvents: N-methyl-2-pyrrolidone (CAS: 872-50-4), dimethyl sulfoxide (CAS: 67-68-5), 4-formylmorpholine (CAS: 4394-85-8), tetraethylene pentamine (CAS: 112-57-2), and diethylene glycol bis(3-aminopropyl) ether (CAS: 4246-51-9). Furthermore, the study proposes the use of intermolecular interactions as molecular descriptors to predict the solubility of dapsone in neat solvents and binary mixtures using machine learning models. An ensemble of regressors was used, including support vector machines, random forests, gradient boosting, and neural networks. Affinities of dapsone to solvent molecules were calculated using COSMO-RS and used as input for model training. Due to the polymorphic nature of dapsone, fusion data are not available, which prohibits the direct use of COSMO-RS for solubility calculations. Therefore, a consonance solvent approach was tested, which allows an indirect estimation of the fusion properties. Unfortunately, the resulting accuracy is unsatisfactory. In contrast, the developed regressors showed high predictive potential. This work documents that intermolecular interactions characterized by solute-solvent contacts can be considered valuable molecular descriptors for solubility modeling and that the wealth of encoded information is sufficient for solubility predictions for new systems, including those for which experimental measurements of thermodynamic properties are unavailable.

Environmental chemistry response of beryllium to diverse soil-solution conditions at a waste disposal site

This study evaluated how the variation in different sorption conditions of beryllium (Be) in soil-water systems (electrolytes; ionic strengths; competing, counter, and co-existing ions; concentrations of Be and soil; and temperature) affected Be's environmental behaviour. For this reason, potentially contaminated soil was collected from a legacy waste site near Sydney, Australia. The sorption-desorption plateau for Be was found at >12.5 g L^-1 (soil/solution), considering higher sorption and limited desorption. Variable surface charges developed by different added ions (competing ions, counter ions, and co-existence of all ions) were not always correlated with Be sorption. However, effects of added ions in Be sorption (increased by counter ions and decreased by competing ions) primarily occurred at low pH, with no noticeable changes at pH > 6 due to the hydration and precipitation behaviour of Be at higher pH. Both laboratory data and modelling indicated the substantial effect of counter ions on increased sorption of Be. Relatively higher amounts of sorption under the co-existence of all added ions were suggested from synergistic actions. Sorption was favourable (K_L > 0, and 0 < R_L < 1) across all concentrations and temperatures at pH 5.5, and high retention (84-97%) occurred after four desorption cycles indicated specific sorption. The sorption process was exothermic (ΔH > -43 kJ mole^-1), while desorption was endothermic (ΔH > +78.4 kJ mole^-1). All sorption-desorption reactions were spontaneous (ΔG = -Ve), and executed without any structural deformation (ΔS = nearly zero) of soil particles. However, the effect of temperature on desorption was influenced by the concentrations of Be. Higher retention and different sorption-desorption parameters (K_d-desorption > K_d-sorption; K_f-desorption > K_f-sorption; n_desorption/n_sorption < 1) indicate limited mobility of Be and the presence of desorption hysteresis in the studied soil under the experimental conditions.

Simultaneous effect of different chromatographic conditions on the chromatographic retention of pentapeptide derivatives (HGRFG and NPNPT)

Introduction: Oligopeptides exhibit great prospects for clinical application and its separation is of great importance in new drug development. Methods: To accurately predict the retention of pentapeptides with analogous structures in chromatography, the retention times of 57 pentapeptide derivatives in seven buffers at three temperatures and four mobile phase compositions were measured via reversed-phase high-performance liquid chromatography. The parameters ( k H A , k A , and p K a ) of the acid-base equilibrium were obtained by fitting the data corresponding to a sigmoidal function. We then studied the dependence of these parameters on the temperature (T), organic modifier composition (φ, methanol volume fraction), and polarity ( P m N parameter). Finally, we proposed two six-parameter models with (1) pH and T and (2) pH and φ or P m N as the independent variables. These models were validated for their prediction capacities by linearly fitting the predicted retention factor k-value and the experimental k-value. Results: The results showed that log k H A and log k A exhibited linear relationships with 1 / T , φ or P m N for all pentapeptides, especially for the acid pentapeptides. In the model of pH and T, the correlation coefficient (R²) of the acid pentapeptides was 0.8603, suggesting a certain prediction capability of chromatographic retention. Moreover, in the model of pH and φ or P m N , the R² values of the acid and neutral pentapeptides were greater than 0.93, and the average root mean squared error was approximately 0.3, indicating that the k-values could be effectively predicted. Discussion: In summary, the two six-parameter models were appropriate to characterize the chromatographic retention of amphoteric compounds, especially the acid or neutral pentapeptides, and could predict the chromatographic retention of pentapeptide compounds.

One-Step Preparation of Activated Carbon for Coal Bed Methane Separation/Storage and Its Methane Adsorption Characteristics

Different coals were used as raw material for the preparation of carbonization precursors and coal-based activated carbons. The physicochemical structure and adsorption performance of the samples were tested. Results show that the carbonization and activation process greatly changed the molecular structure of raw coal, and a large number of organic functional groups disappeared. The carbonization process has enriched the pore structure of coal by thermal ablation, and it has a pore expansion effect on all the pores in coal, while the activation process is more conducive to micropore generation. The calculated mean isosteric heat of adsorption showed that the activated carbon needs to release more heat in the adsorption process as the same equilibrium pressure increased due to the adsorption capacity of the prepared activated carbon being far more than that of the raw coal. Adsorption processes of activated carbons are more sensitive to temperature changes, providing a certain guiding significance for the temperature swing adsorption and pressure swing adsorption.

Variable-Temperature NMR Analysis of the Thermodynamics of Polymer Partitioning between Aqueous and Drug-Rich Phases and Its Significance for Amorphous Formulations

We previously reported that the polymers used in amorphous solid dispersion (ASD) formulations, such as polyvinylpyrrolidone (PVP), polyvinylpyrrolidone/vinyl acetate (PVP-VA), and hypromellose (HPMC), distribute into the drug-rich phase of ibuprofen (IBP) formed by liquid-liquid phase separation, resulting in a reduction in the maximum drug supersaturation in the aqueous phase. Herein, the mechanism underlying the partitioning of the polymer into the drug-rich phase was investigated from a thermodynamic perspective. The dissolved IBP concentration in the aqueous phase and the amount of polymer distributed into the IBP-rich phase were quantitatively analyzed in IBP-supersaturated solutions containing different polymers using variable-temperature solution-state nuclear magnetic resonance (NMR) spectroscopy. The polymer weight ratio in the IBP-rich phase increased at higher temperatures, leading to a more notable reduction of IBP amorphous solubility. Among the polymers, the amorphous solubility reduction was the greatest for the PVP-VA solution at lower temperatures, while HPMC reduced the amorphous solubility to the greatest extent at higher temperatures. The change in the order of polymer impact on the amorphous solubility resulted from the differences in the temperature dependency of polymer partitioning. The van't Hoff plot of the polymer partition coefficient revealed that both enthalpy and entropy changes for polymer transfer into the IBP-rich phase from the aqueous phase (ΔH_{aqueous→IBP-rich} and ΔS_{aqueous→IBP-rich}) gave positive values for most of the measured temperature range, indicating that polymer partitioning into the IBP-rich phase was an endothermic but entropically favorable process. The polymer transfer into the IBP-rich phase was more endothermic for HPMC than for PVP and PVP-VA. The solid-state NMR analysis of the IBP/polymer ASD implied that the newly formed IBP/polymer interactions in the IBP-rich phase upon polymer incorporation were weaker for HPMC, providing a rationale for the larger positive transfer enthalpy for HPMC. The change in Gibbs free energy for polymer transfer (ΔG_{aqueous→IBP-rich}) showed negative values across the experimental temperature range, decreasing with an increase in temperature, indicating that the distribution of the polymer into the IBP-rich phase is favored at higher temperatures. Moreover, ΔG_{aqueous→IBP-rich} for HPMC showed the greatest decrease with the temperature, likely reflecting the temperature-induced dehydration of HPMC in the aqueous phase. This study contributes fundamental insights into the phenomenon of polymer partitioning into drug-rich phases, furthering the understanding of achievable supersaturation levels and ultimately providing information on polymer selection for ASD formulations.

Temperature dependence of the gas-particle partitioning of selected VOCs

The gas-particle partitioning coefficients for volatile organic compounds (VOCs) are difficult to acquire because discriminating the small mass fraction of the VOCs in the aerosol particle relative to that in the gas phase is challenging. In this paper, we report the temperature dependence of the gas-particle partitioning coefficient (Kp) for n-butanol (n-BuOH) and trichloroethylene (TCE). Using the bench-scale system that we developed, we measured the Kp of surrogate VOCs, n-BuOH, and TCE onto inorganic (ammonium sulfate, Am Sulf) and organic (succinic acid, SA) aerosol particles at a fixed relative humidity (RH) of 35%. At this RH level and temperature range of 278.15-308.15 K, the ln Kp for TCE and n-BuOH partitioning on SA aerosol particles were -27.0 ± 0.70 to -27.9 ± 0.01 and -13.9 ± 0.03 to -17.4 ± 0.17. In contrast, the ln Kp for TCE and n-BuOH partitioning on Am Sulf aerosol particles ranged from -26.4 ± 0.70 to -27.4 ± 0.71 and -14.1 ± 0.03 to -17.1 ± 0.17, respectively. Results showed that TCE fitted well with the classic van't Hoff relationship. The enthalpy of desorption (ΔHdes) for TCE was constant over the temperature range of 278.15 K to 308.15 K, behaving similarly to 1,2-dichlorobenzene. At a similar temperature range, n-BuOH partitioning into both aerosol particles exhibited nonlinear temperature dependence. The minimum ratio of ΔHdes (Am Sulf:SA) for n-BuOH partitioning on each aerosol type was at ∼278.15 K. The magnitude of the entropy ΔSdes for all VOCs was <1 kJ mol-1.

A thermodynamic study of capillary electrochromatographic retention of aromatic hydrocarbons on a lauryl acrylate porous polymer monolithic column with measured phase ratio

The phase ratio of a chromatographic system is an important measurement that has long been estimated or calculated, but rarely directly measured. This study utilized a nanoflow liquid chromatography instrument to more accurately measure the phase ratio for a lauryl acrylate porous polymer monolith. Direct measurement of the phase ratio, and its dependence on temperature, allows for a better understanding of the thermodynamics of retention of small analytes. This study investigates the retention of an alkyl benzene series, toluene to octylbenzene, via capillary electrochromatography. The phase ratio was determined to be 0.202 at 303 K and 0.213 at 333 K. Using the directly measured phase ratio, entropic contributions to retention can also be obtained. Therefore, the Gibbs free energy calculations from these measurements and methods can give insight to modes of retention. The free energy of retention for toluene is -3.97 kJ/mol at 303 K and -3.78 kJ/mol at 333 K. The trends for enthalpy, entropy, and Gibbs free energy of transfer show that retention is enthalpically driven in this capillary electrochromatography (CEC) porous polymer monolith system.

Structure of the Lennard-Jones liquid estimated from a single simulation

Combining the recent Piskulich-Thompson approach [Z. A. Piskulich and W. H. Thompson, J. Chem. Phys. 152, 011102 (2020)JCPSA60021-960610.1063/1.5135932] with isomorph theory, from a single simulation the structure of a single-component Lennard-Jones (LJ) system is obtained at an arbitrary state point in almost the whole liquid region of the temperature-density phase diagram. The LJ system exhibits two temperature ranges where the van't Hoff assumption that energetic and entropic forces are temperature independent is valid to a good approximation. A method to evaluate the structure at an arbitrary state point along an isochore from the knowledge of structures at two temperatures on the isochore is also discussed. We argue that, in general, the structure of any hidden scale-invariant system obeying the van't Hoff assumption in the whole range of temperatures can be determined in the whole liquid region of the phase diagram from a single simulation.

Unravelling the nature of a toluene-fumaronitrile complex

In this research, the occurrence and anomalous increase of an additional absorption band observed in the spectrum of fumaronitrile dissolved in toluene are explained and characterized. The formation of a stable ground-state complex between these two molecules is evidenced by both experimental and theoretical studies. TD-DFT calculations show that the presence of an unexpected signal in the absorption spectra originates from the photoinduced intermolecular charge-transfer process occurring within this system. The mechanism and the efficiency of the adduct formation were investigated using both spectral measurements (UV-Vis, IR) and quantum-mechanical calculations (DFT). The influence of the solvent polarity on the complex stability was also evaluated. Since the forces responsible for the adduct formation turn out to be of a rather weak, dispersive character, the related equilibrium stability constant is relatively low and becomes even lower with the increase in solvent polarity. Finally, the system was analyzed for the expected fluorescence emission of the resulting complex, but none was observed.

Fast and sensitive detection of acrolein in environmental water samples without derivatization using liquid chromatography tandem mass spectrometry

A fast and sensitive SPE-LC-MS/MS method for the determination of acrolein in environmental water samples using activated charcoal as SPE adsorbent was developed. The novelty of this study consists in acrolein extraction, separation and detection without the need of a derivatization process. Physicochemical properties of acrolein, such as low molecular weight and high polarity represent real challenges for extraction, separation, and detection of this pollutant using SPE-LC-MS/MS. These were addressed by choosing a suitable chromatographic column which ensures a good peak symmetry and retention for the analyte, as well as the choice of SPE adsorbent suitable for retaining very polar compounds like acrolein from the aqueous matrix. The chromatographic column was a Synergi Fusion RP (150 × 2.0 mm, 4.0 μm) with a C18 stationary phase modified with polar embedded amide groups. Activated charcoal adsorbent used as SPE extraction media was able to extract efficiently highly polar molecules such as acrolein and ¹³C₃-acrylamide (internal standard) from water samples. Using this method, the obtained extraction recovery for acrolein was 88% at a 50 ng/L concentration level. Overall method quantitation limit (LOQ) for acrolein in water was established at 3.8 ng/L. The newly developed SPE-LC-MS/MS method was successfully applied to detect acrolein occurrence in wastewater and drinking water samples. Acrolein level in these samples ranged from LOQ to 122 ng/L.

Sources of Nonlinear van't Hoff Temperature Dependence in High-Performance Liquid Chromatography

In HPLC, the nonlinear behavior of the retention factor k' with temperature (dependence of ln k' on 1/T) can be attributed to the multiple interactions of a unique analyte in the separation process and/or to the existence in solution of multiple forms of the analyte (also leading to different free enthalpies of interaction). In this study, several examples of nonlinear retention-temperature dependence are evaluated for both reversed-phase (RP) and hydrophilic interaction chromatography (HILIC) separations. The potential explanation for nonlinear retention-temperature behavior is evaluated for each example, some caused by multiple interactions in the separation system of a unique analyte and others by multiple forms of the analyte. In cases where the analyte does not have more forms and the separation is based predominantly on one type of interaction (e.g., hydrophobic interaction in RP-HPLC), the dependence is linear, as expected. By studying the changes in the chemical structure of a compound as a function of pH it is possible to decide, in many cases, if a unique form or multiple forms of a compound are present in the solution. The use of this information allows us to determine when the lack of linearity (when present) is caused by multiple interactions in the separation system (for one form of the compound) and when more forms are causing the lack of linearity. The approximation with a quadratic form for the nonlinear dependence has been verified in most cases to be good, and only minor improvements were obtained when using higher polynomial dependencies.

Evaluation of three temperature- and mobile phase-dependent retention models for reversed-phase liquid chromatographic retention and apparent retention enthalpy

Predicting retention and enthalpy allows for the simulation and optimization of advanced chromatographic techniques including gradient separations, temperature-assisted solute focusing, multidimensional liquid chromatography, and solvent focusing. In this paper we explore the fits of three expressions for retention as a function of mobile phase composition and temperature to retention data of 101 small molecules in reversed phase liquid chromatography. The three retention equations investigated are those by Neue and Kuss (NK) and two different equations by Pappa-Louisi et al., one based on a partition model (PL-P) and one based on an adsorption model (PL-A). More than 25 000 retention factors were determined for 101 small molecules under various mobile phase and temperature conditions. The pure experimental uncertainty is very small, approximately 0.22% uncertainty in retention factors measured on the same day (2.1% when performed on different days). Each of the three equations for ln(k) was fit to the experimental data based on a least-squares approach and the results were analyzed using lack-of-fit residuals. The PL-A model, while complex, gives the best overall fits. In addition to examining the equations' adequacy for retention, we also examined their use for apparent retention enthalpy. This enthalpy can be predicted by taking the derivative of these expressions with respect to the inverse of absolute temperature. The numerical values of the fitted parameters based on retention data can then be used to predict retention enthalpy. These enthalpy predictions were compared to those obtained from a modified van 't Hoff equation that included a quadratic term in inverse temperature. Based on analysis of 1 211 van 't Hoff plots (solute-mobile phase-day combinations), ninety-eight percent showed a significantly better fit when using the modified van 't Hoff expression, justifying its use to provide apparent enthalpies as a function of mobile phase composition and temperature. The foregoing apparent enthalpies were compared to the apparent enthalpies predicted by the three models. The PL-A model, which contains a temperature dependent enthalpy, provided the best enthalpy prediction. However, there is virtually no correlation between the overall lack of fit to experimental ln(k) for each model and the corresponding lack of fit of the linear (in 1/T) van 't Hoff expression. Thus, the temperature-dependent enthalpy is apparently not the cause of a model's ability to fit ln(k) as a function of mobile phase composition and temperature. The value in these expressions is their ability to predict chromatograms, allowing for optimization of an advanced chromatographic technique. The two simpler models NK and PL-P, which do not contain a temperature dependent enthalpy, have their merits in modelling retention (NK being the better of the two) and enthalpy (PL-P being the better of the two) if a simpler expression is required for a given application.

Effect of temperature on the retention of Janus kinase 3 inhibitor in different mobile phase compositions using reversed-phase liquid chromatography

In this study, the thermodynamic dissociation constant (pK_a) values of tofacitinib in acetonitrile-water binary mixtures with of 25%, 30%, 35% and 45% (v/v) have been determined at 25-45 °C range of temperatures with reversed-phase liquid chromatography (RPLC). The chromatographic determination was achieved on a Kinetex Core-Shell EVO C18-Phenomenex (150 mm x 4.6 mm, 5 μm) analytical column. For each case pK_a values and retention factors of tofacitinib by taking into account the effect of the activity coefficients in hydro-organic water-acetonitrile binary mixtures have been evaluated and which obtain by SOLVER algorithm of spreadsheet program Excel to fit experimental data to the nonlinear expression derived. From these values, the thermodynamic aqueous pK_a value of the drug was calculated by different approaches. Thermodynamic parameters standard Gibbs free energy (ΔG°), standard enthalpy (ΔH°) and standard entropy (ΔS°) derived from dissociation constant measurements at six different temperatures were calculated by from linearity plots of IogK_a against 1/T (van't Hoff plot).

Mechanistic Modeling of Reversed-Phase Chromatography of Insulins within the Temperature Range 10-40 °C

In the many published theories on the retention in reversed-phase chromatography (RPC), the focus is generally on the effect of the concentration of the mobile phase modulator(s), although temperature is known to have a significant influence both on the retention and on the selectivity between the adsorbates. The aim of this study was to investigate and model the combined effects of the temperature and the modulator concentrations on RPC of three insulin variants. KCl and ethanol were used as mobile phase modulators, and the experiments were performed on two different adsorbents, with C₁₈ and C₄ ligands. The temperature dependence was investigated for the interval 10-40 °C and at two different concentrations of each modulator. The model is derived from the expression for the adsorption equilibrium, which assumes that ethanol is adsorbed to the ligands and displaced by the insulin molecules, similar to the displacement of counterions in the steric mass-action model for ion-exchange chromatography. A good model fit to the new linear-range retention data was achieved by only adding and calibrating three parameters for the temperature dependence of the equilibrium. We found that a lower temperature results in a longer retention time for all adsorbates, adsorbents, and modulator concentrations used in this study, indicating that the adsorption process is enthalpy-driven. A comparison of the different contributions to the temperature dependence revealed that the large contribution from the equilibrium constant is dampened by the significant contributions of the opposite sign from the changes in activity coefficients of insulins and ethanol. Neglect of these effects when comparing different adsorbents and modulators might yield incorrect conclusions because the equilibrium constant varies with both, whereas the activity coefficients should be independent of the adsorbent. As expected, the conditions that promote higher retention also give a higher selectivity between the adsorbates. Nonetheless, in relation to its effect on the retention, the influence of the KCl concentration on the selectivity was significantly stronger than that of the temperature or that of the ethanol concentration.

Phytochemicals as Dynamic Surface Ligands To Control Nanoparticle-Protein Interactions

The rapid formation of the protein corona on to the nanoparticle (NP) surface is the key that confers biological identity to NPs and subsequently dictates their fate both in vitro and in vivo. Despite significant efforts, the inability to control the spontaneous interaction of serum proteins with the administered NPs remains a major constraint in clinical translation of nanomedicines. The ligands present on the NP surface offer promise in controlling their biological interactions; however, their influence on the NP-protein interaction is not well-understood. The current study investigates the potential of phytochemical-capped silver nanoparticles (AgNPs) toward allowing a control over NP interactions with the human serum albumin (HSA), the most abundant protein in the biological fluids. Specifically, we demonstrate the ability of curcumin (Cur) and epigallocatechin-3-gallate (EGCG) to independently act as reducing agents to produce phytochemical-capped AgNPs that show biologically desirable interactions with HSA. The key finding of our study is that the phytochemical-capped AgNPs initially interact with HSA more strongly compared to the citrate-stabilized AgNPs; however, the resultant NP-HSA complexes are less stable in the case of the former, which causes a lesser degree of changes in the protein conformation during interactions. Further, the choice of the phytochemical allows control over NP-HSA interactions, such that Cur- and EGCG-capped AgNPs interacted with HSA in a static versus dynamic manner, respectively. The diversity of the functional groups present in natural phytochemicals and their potential as in situ capping ligands during synthesis offer new opportunities in controlling the interactions of NPs with complex biological fluids, with implications in nanodiagnostics and nanomedicine.

Chromatographic retention behaviour, modelling and optimization of a UHPLC-UV separation of the regioisomers of the Novel Psychoactive Substance (NPS) methoxphenidine (MXP)

A detailed investigation into the chromatographic retention behaviour and separation of the three regioisomers of the Novel Psychoactive Substance (NPS) methoxphenidine (i.e. 2-, 3- and 4-MXP isomers) has revealed the ionization state of the analyte and stationary phase, to be the controlling factor in dictating which retention mechanism is in operation. At low pH, poor separation and retention was observed. In contrast, at intermediate pH, enhanced retention and separation of the three MXP isomers was obtained; it appeared that there was a synergistic effect between the electrostatic and hydrophobic mechanisms. At high pH, the MXP isomers were retained by hydrophobic retention. Accurate retention time predictions (<0.5%) were achievable using non-linear retention models (3 × 3). This allowed the optimization of the gradient separation of the MXP isomers using a two-dimensional gradient and temperature design space. Prediction errors for peak width and resolution were, in most cases, lower than 5%. The use of linear models (2 × 2) still afforded retention time and resolution accuracies of <2.3 and 11% respectively. A rapid and highly sensitive LC-MS friendly method (i.e. R_smin > 5 within 4 min) was predicted and verified. The developed methodology should be highly suitable for the rapid, specific and sensitive detection and control of MXP regioisomers.

Probing the Nanoscopic Thermodynamic Fingerprint of Paramagnetic Ligands Interacting with Amphiphilic Macromolecules

Self-assembly of macromolecules with ligands is an intricate dynamic process that depends on a wide variety of parameters and forms the basis of many essential biological processes. We elucidate the underlying energetic processes of self-assembly in a model system consisting of amphiphilic core-shell polymers interacting with paramagnetic, amphiphilic ligand molecules from temperature-dependent continuous wave electron paramagnetic resonance (CW EPR) spectroscopy subsequent to spectral simulation. The involved processes as observed from the ligands’ point of view are either based on temperature-dependent association constants (K_A,j,k) or dynamic rotational regime interconversion (IC) constants (K_IC,j,k). The interconversion process describes a transition from Brownian (b₁) towards free (b₂) diffusion of ligand. Both processes exhibit non-linear van’t Hoff (lnK vs. T⁻¹) plots in the temperature range of liquid water and we retrieve decisive dynamic information of the system from the energetic fingerprints of ligands on the nanoscale, especially from the temperature-dependent interconversion heat capacity (∆C°_P,IC).

Calcium d-Saccharate: Aqueous Solubility, Complex Formation, and Stabilization of Supersaturation

Molar conductivity of saturated aqueous solutions of calcium d-saccharate, used as a stabilizer of beverages fortified with calcium d-gluconate, increases strongly upon dilution, indicating complex formation between calcium and d-saccharate ions, for which, at 25 °C, Kassoc = 1032 ± 80, ΔHassoc° = −34 ± 6 kJ mol–1, and ΔSassoc° = −55 ± 9 J mol–1 K–1, were determined electrochemically. Calcium d-saccharate is sparingly soluble, with a solubility product, Ksp, of (6.17 ± 0.32) × 10–7 at 25 °C, only moderately increasing with the temperature: ΔHsol° = 48 ± 2 kJ mol–1, and ΔSassoc° = 42 ± 7 J mol–1 K–1. Equilibria in supersaturated solutions of calcium d-saccharate seem only to adjust slowly, as seen from calcium activity measurements in calcium d-saccharate solutions made supersaturated by cooling. Solutions formed by isothermal dissolution of calcium d-gluconate in aqueous potassium d-saccharate becomes spontaneously supersaturated with both d-gluconate and d-saccharate calcium salts, from which only calcium d-saccharate slowly precipitates. Calcium d-saccharate is suggested to act as a stabilizer of supersaturated solutions of other calcium hydroxycarboxylates with endothermic complex formation through a heat-induced shift in calcium complex distribution with slow equilibration upon cooling.

Explicit analytic equations for multimolecular thermal melting curves

The analysis of thermal melting curves requires the knowledge of equations for the temperature dependence of the relative fraction of folded and unfolded components. To implement these equations as standard tools for curve fitting, they should be as explicit as possible. From the van't Hoff formalism it is known that the equilibrium constant and hence the folded fraction is a function of the absolute temperature, the van't Hoff transition enthalpy, and the melting temperature. The work presented here is devoted to the mathematically self-contained derivation and the listing of explicit equations for the folded fraction as a function of the thermodynamic parameters in the case of arbitrary molecularities. Part of the results are known, others are new. It is in particular shown for the first time that the folded fraction is the composition of a universal function which depends solely on the molecularity and a dimensionless function which is governed by the concrete thermodynamic regime but is independent of the molecularity. The results will prove useful for extracting the thermodynamic parameters from experimental data on the basis of regression analysis. As supporting information, open-source Matlab scripts for the computer implementation of the equations are provided.