Intramolecular Hydrogen Bonding Involving Organic Fluorine: NMR Investigations Corroborated by DFT-Based Theoretical Calculations

Identification and Characterization of a Blood-Brain Barrier Penetrant Inositol Hexakisphosphate Kinase (IP6K) Inhibitor

Inositol hexakisphosphate kinases (IP6Ks) have been studied for their role in glucose homeostasis, metabolic disease, fatty liver disease, chronic kidney disease, neurological development, and psychiatric disease. IP6Ks phosphorylate inositol hexakisphosphate (IP6) to the pyrophosphate, 5-diphosphoinositol-1,2,3,4,6-pentakisphosphate (5-IP7). Most of the currently known potent IP6K inhibitors contain a critical carboxylic acid which limits blood-brain barrier (BBB) penetration. In this work, the synthesis and testing of a variety of carboxylic acid isosteres resulted in several new compounds with improved BBB penetration. The most promising compound has an IP6K1 IC50 of 16 nM with an improved brain/plasma ratio and a favorable pharmacokinetic profile. This series of brain penetrant compounds may be used to investigate the role of IP6Ks in CNS disorders.

Understanding the Cis-Trans Amide Bond Isomerization of N,N'-Diacylhydrazines to Develop Guidelines for A Priori Prediction of Their Most Stable Solution Conformers

N,N'-diacylhydrazines (R1CO-NR3-NR4-COR2) are a class of small molecules with a wide range of applications in chemistry and biology. They are structurally unique in the sense that their two amide groups are connected via a N-N single bond, and as a result, these molecules can exist in eight different isomeric forms. Four of these are amide isomers [trans-trans (t-t), trans-cis (t-c), cis-trans (c-t), and cis-cis (c-c)] arising from C-N bond restricted rotation. In addition, each of these amide isomers can exist in two different isomeric forms due to N-N bond restricted rotation, especially when R3 and R4 groups are relatively bigger. Herein, we have systematically investigated the conformations of 55 N,N'-diacylhydrazines using a combination of solution NMR spectroscopy, X-ray crystallography, and density functional theory calculations. Our data suggest that when the substituents R3 and R4 on the nitrogen atoms are both hydrogens. These molecules prefer twisted trans-trans (t-t) (>90%) geometries (H-N-C═O ∼ 180°), whereas the N-alkylated and N,N'-dialkylated molecules prefer twisted trans-cis (t-c) geometries. Herein, we have analyzed the stabilization of the various isomers of these molecules in light of steric and stereoelectronic effects. We provide a guideline to a priori predict the most stable conformers of the N,N'-diacylhydrazines just by examining their substituents (R1-R4).

Quantification of Hydrogen-Bond-Donating Ability of Biologically Relevant Compounds

Hydrogen bonding is a key factor in the design of ligands for biological binding, including drug targets. Our group previously developed a method for experimentally assessing the hydrogen-bond-donating ability of an analyte using UV-vis titrations with a colorimetric sensor. Using this method, 79 new titrations were performed on weak hydrogen-bond donors, with a focus on heterocycles and pharmaceutically relevant motifs. The hydrogen-bond donating abilities of drug compounds and the substructures of drug compounds were also measured. These titrations will be used to build a database of hydrogen-bond donors.

Monofluoromethylation of N-Heterocyclic Compounds

The review focuses on recent advances in the methodologies for the formation or introduction of the CH2F moiety in N-heterocyclic substrates over the past 5 years. The monofluoromethyl group is one of the most versatile fluorinated groups used to modify the properties of molecules in synthetic medical chemistry. The review summarizes two strategies for the monofluoromethylation of N-containing heterocycles: direct monofluoromethylation with simple XCH2F sources (for example, ICH2F) and the assembly of N-heterocyclic structures from CH2F-containing substrates. The review describes the monofluoromethylation of pharmaceutically important three-, five- and six-membered N-heterocycles: pyrrolidines, pyrroles, indoles, imidazoles, triazoles, benzothiazoles, carbazoles, indazoles, pyrazoles, oxazoles, piperidines, morpholines, pyridines, quinolines and pyridazines. Assembling of 6-fluoromethylphenanthridine, 5-fluoromethyl-2-oxazolines, C5-monofluorinated isoxazoline N-oxides, and α-fluoromethyl-α-trifluoromethylaziridines is also shown. Fluoriodo-, fluorchloro- and fluorbromomethane, FCH2SO2Cl, monofluoromethyl(aryl)sulfoniummethylides, monofluoromethyl sulfides, (fluoromethyl)triphenylphosphonium iodide and 2-fluoroacetic acid are the main fluoromethylating reagents in recent works. The replacement of atoms and entire functional groups with a fluorine atom(s) leads to a change and often improvement in activity, chemical or biostability, and pharmacokinetic properties. The monofluoromethyl group is a bioisoster of -CH3, -CH2OH, -CH2NH2, -CH2CH3, -CH2NO2 and -CH2SH moieties. Bioisosteric replacement with the CH2F group is both an interesting task for organic synthesis and a pathway to modify drugs, agrochemicals and useful intermediates.

Crystalline Nanoparticles of Water-Soluble Covalent Basket Cages (CBCs) for Encapsulation of Anticancer Drugs

We herein describe the preparation, assembly, recognition characteristics, and biocompatibility of novel covalent basket cage CBC-11, composed of four molecular baskets linked to four trivalent aromatic amines through amide groups. The cage is tetrahedral in shape and similar in size to small proteins (Mw =8637 g/mol) with a spacious nonpolar interior for accommodating multiple guests. While 24 carboxylates at the outer surface of CBC-11 render it soluble in aqueous phosphate buffer (PBS) at pH=7.0, the amphiphilic nature prompts its assembly into nanoparticles (d=250 nm, DLS). Cryo-TEM examination of nanoparticles revealed their crystalline nature with wafer-like shapes and hexagonally arranged cages. Nanoparticulate CBC-11 traps anticancer drugs irinotecan and doxorubicin, with each cage binding up to four drug molecules in a non-cooperative manner. The inclusion complexation resulted in nanoparticles growing in size and precipitating. In media containing mammalian cells (HCT 116, human colon carcinoma), the IC50 value of CBC-11 was above 100 μM. While this work presents the first example of a large covalent organic cage operating in water at the physiological pH and forming crystalline nanoparticles, it also demonstrates its biocompatibility and potential to act as a polyvalent binder of drugs for their sequestration or delivery.

i-Motif folding intermediates with zero-nucleotide loops are trapped by 2'-fluoroarabinocytidine via F···H and O···H hydrogen bonds

G-quadruplex and i-motif nucleic acid structures are believed to fold through kinetic partitioning mechanisms. Such mechanisms explain the structural heterogeneity of G-quadruplex metastable intermediates which have been extensively reported. On the other hand, i-motif folding is regarded as predictable, and research on alternative i-motif folds is limited. While TC₅ normally folds into a stable tetrameric i-motif in solution, we report that 2'-deoxy-2'-fluoroarabinocytidine (araF-C) substitutions can prompt TC₅ to form an off-pathway and kinetically-trapped dimeric i-motif, thereby expanding the scope of i-motif folding landscapes. This i-motif is formed by two strands, associated head-to-head, and featuring zero-nucleotide loops which have not been previously observed. Through spectroscopic and computational analyses, we also establish that the dimeric i-motif is stabilized by fluorine and non-fluorine hydrogen bonds, thereby explaining the superlative stability of araF-C modified i-motifs. Comparative experimental findings suggest that the strength of these interactions depends on the flexible sugar pucker adopted by the araF-C residue. Overall, the findings reported here provide a new role for i-motifs in nanotechnology and also pose the question of whether unprecedented i-motif folds may exist in vivo.

Intramolecular N-H⋅⋅⋅F Hydrogen Bonding Interaction in a Series of 4-Anilino-5-Fluoroquinazolines: Experimental and Theoretical Characterization of Electronic and Conformational Effects

The 4-anilino-6,7-ethylenedioxy-5-fluoroquinazoline scaffold is presented as a novel model system for the characterization of the weak NH⋅⋅⋅F hydrogen bonding (HB) interaction. In this scaffold, the aniline NH proton is forced into close proximity with the nearby fluorine (dH,F ∼2.0 Å, ∠∼138°), and a through-space interaction is observed by NMR spectroscopy with couplings (1h JNH,F ) of 19±1 Hz. A combination of experimental (NMR spectroscopy and X-ray crystallography) and theoretical methods (DFT calculations) were used for the characterization of this weak interaction. In particular, the effects of conformational rigidity and steric compression on coupling were investigated. This scaffold was used for the direct comparison of fluoride with methoxy as HB acceptors, and the susceptibility of the NH⋅⋅⋅F interaction to changes in electron distribution and resonance was probed by preparing a series of molecules with different electron-donating or -withdrawing groups in the positions para to the NH and F. The results support the idea that fluorine can act as a weak HB acceptor, and the HB strength can be modulated through additive and linear electronic substituent effects.

2-Trifluoromethyl-6-mercurianiline Nucleotide, a Sensitive 19F NMR Probe for Hg(II)-mediated Base Pairing

A 2-trifluoromethylaniline C-nucleoside was synthesized, incorporated in the middle of an oligonucleotide, and mercurated. The affinity of the mercurated oligonucleotide toward complementary strands placing each of the canonical nucleobases opposite to the organomercury nucleobase analogue was examined by ultraviolet (UV), circular dichroism (CD), and 19F NMR spectroscopy analyses. According to the UV melting profile analysis, the organomercury nucleobase analogue showed increased affinities in the order T > G > C > A. The CD profiles indicated the typical B-type helix in each case. The 19F resonance signal proved sensitive for the local environmental changes, showing clearly distinct signals for the duplexes with different opposing nucleobases. Furthermore, valuable information on the mercurated oligonucleotide and its binding to complementary strands at varying temperature could be obtained by 19F NMR spectroscopy.

Conformational Analysis of Fluoro-, Chloro-, and Proteo-Alkene Gly-Pro and Pro-Pro Isosteres to Mimic Collagen

Collagen is the most abundant human protein, with the canonical sequence (Gly-Pro-Hyp)_n in its triple helix region. Cis-trans isomerization of the Xaa-Pro amide has made two of these amide bonds the target of alkene replacement: the Gly-Pro and the Pro-Hyp positions. The conformations of Gly-Pro and Pro-Pro (as a Pro-Hyp model) fluoro-, chloro-, and proteo-alkene mimic models were investigated computationally to determine whether these alkenes can stabilize the polyproline type II (PPII) conformation of collagen. Second-order Møller-Plesset (MP2) calculations with various basis sets were used to perform the conformational analyses and locate stationary points. The calculation results predict that fluoro- and chloro-alkene mimics of Gly-Pro and Pro-Pro can participate in n→π* donation to stabilize PPII conformations, yet they are poor n→π* acceptors, shifting the global minima away from PPII conformations. For the proteo-alkene mimics, the lack of significant n→π* interactions and unstable PPII-like geometries explains their known destabilization of the triple helix in collagen-like peptides.

Pseudocyclic Form of 4-Hydroxypyrrolidine-2-carboxanilide Podands with Trioxyethylene Chain: Modeling, Conformational Search, and NMR Analysis

The 4-hydroxypyrrolidine-2-carboxanilide podand salt demonstrates catalytic activity in asymmetric Biginelli reaction. The systematic search for prevalent conformational state of the cation was carried out by computer simulations in combination with one- and two-dimensional NMR experiments. For that purpose, we proposed a novel algorithm for the generation and selection of conformers based on molecular dynamics and clustering in the space of principal components. The search had found an important trend of the podand to form a pseudocyclic structure with a horseshoe-shaped conformation of the oligooxyethylene fragment. This conformation is stabilized by different types of intramolecular hydrogen bonds between the acidic and basic centers of the two 4-hydroxypyrrolidine-2-carboxanilide residuals (branches). The proposed approach had made it possible to identify the major structural factors, providing a correlation between the calculated and experimental chemical shifts of hydrogen atoms in the ¹H NMR spectra of the protonated podand.

Consequences of Amide Connectivity in the Supramolecular Polymerization of Porphyrins: Spectroscopic Observations Rationalized by Theoretical Modelling

The correlation between molecular structure and mechanism of supramolecular polymerizations is a topic of great interest, with a special focus on the pathway complexity of porphyrin assemblies. Their cooperative polymerization typically yields highly ordered, long 1D polymers and is driven by a combination of π-stacking due to solvophobic effects and hydrogen bonding interactions. Subtle changes in molecular structure, however, have significant influence on the cooperativity factor and yield different aggregate types (J- versus H-aggregates) of different lengths. In this study, the influence of amide connectivity on the self-assembly behavior of porphyrin-based supramolecular monomers was investigated. While in nonpolar solvents, C=O centered monomers readily assemble into helical supramolecular polymers via a cooperative mechanism, their NH centered counterparts form short, non-helical J-type aggregates via an isodesmic pathway. A combination of spectroscopy and density functional theory modelling sheds light on the molecular origins causing this stunning difference in assembly properties and demonstrates the importance of molecular connectivity in the design of supramolecular systems. Finally, their mutual interference in copolymerization experiments is presented.

Competing HB acceptors: an extensive NMR investigations corroborated by single crystal XRD and DFT calculations

A series of N-benzoylanthranilamide derivatives have been synthesized with the substitution of competitive HB acceptors and investigated by NMR spectroscopy and single crystal XRD. The interesting rivalry for HB acceptance between [double bond splayed left]C[double bond, length as m-dash]O and X (F or OMe) is observed in the investigated molecules which leads to an unusual increase in the electron density at the site of one of the NH protons, reflecting in the high field resonance in the 1H NMR spectrum. The NMR experimental findings and single crystal XRD are further reinforced by the DFT studies.

Targeted modifications in ionic liquids - from understanding to design

Ionic liquids are extremely versatile and continue to find new applications in academia as well as industry. This versatility is rooted in the manifold of possible ion types, ion combinations, and ion variations. However, to fully exploit this versatility, it is imperative to understand how the properties of ionic liquids arise from their constituents. In this work, we discuss targeted modifications as a powerful tool to provide understanding and to enable design. A 'targeted modification' is a deliberate change in the structure of an ionic liquid. This includes chemical changes in an experiment as well as changes to the parameterisation in a computer simulation. In any case, such a change must be purposeful to isolate what is of interest, studying, as far as is possible, only one concept at a time. The concepts can then be used as design elements. However, it is often found that several design elements interact with each other - sometimes synergistically, and other times antagonistically. Targeted modifications are a systematic way of navigating these overlaps. We hope this paper shows that understanding ionic liquids requires experimentalists and theoreticians to join forces and provides a tool to tackle the difficult transition from understanding to design.

HDAC7 Inhibition by Phenacetyl and Phenylbenzoyl Hydroxamates

The zinc-containing histone deacetylase enzyme HDAC7 is emerging as an important regulator of immunometabolism and cancer. Here, we exploit a cavity in HDAC7, filled by Tyr303 in HDAC1, to derive new inhibitors. Phenacetyl hydroxamates and 2-phenylbenzoyl hydroxamates bind to Zn²⁺ and are 50-2700-fold more selective inhibitors of HDAC7 than HDAC1. Phenylbenzoyl hydroxamates are 30-70-fold more potent HDAC7 inhibitors than phenacetyl hydroxamates, which is attributed to the benzoyl aromatic group interacting with Phe679 and Phe738. Phthalimide capping groups, including a saccharin analogue, decrease rotational freedom and provide hydrogen bond acceptor carbonyl/sulfonamide oxygens that increase inhibitor potency, liver microsome stability, solubility, and cell activity. Despite being the most potent HDAC7 inhibitors to date, they are not selective among class IIa enzymes. These strategies may help to produce tools for interrogating HDAC7 biology related to its catalytic site.

Role of hydrogen bonding interactions within of the conformational preferences of calix[n = 4,6,8]arene: DFT and QTAIM analysis

Understanding the interactions of the cage molecules with a variety of invited molecules is getting very important. But, the hydrogen bonds can also play a crucial role in the interaction phenomenon. In this work, natural population analysis (NPA), chemical shifts, and atom in molecules (AIM) analysis have been used to identify the role of hydrogen bonds in the stability of CX[n] molecules. According to our calculation, the ¹³C NMR spectra are also sensitive to the nature of hydrogen bonds. We note that the DFT calculations have reproduced with a very good agreement, the experimentally observed chemical shifts of CX[4].

Quantum chemical determination of molecular geometries and spectral investigation of 4-ethoxy-2, 3-difluoro benzamide

The present work reports the application of density functional theory (DFT) at B3LYP with various basis sets which provide the relationship between the structural and spectral properties of 4-ethoxy-2, 3-difluoro benzamide (4EDFB). A Complete vibrational analysis has been performed at the density functional theory (DFT) method with various basis sets in the ground state. The results of vibrational wave numbers are in good agreement with the experimental spectra (Infrared and Raman). Energy gap of the molecule is evaluated using frontier molecular orbital energies (HOMO-LUMO). The frontier energy gap value reveals the chemical reactivity and intermolecular charge transfer occur within the molecule. Global chemical descriptors provide the local and global softness and local reactivity parameters used to identify the nucleophilic and electrophilic behavior of a specific site within the compound. The dimer structure is performed to evaluate the intermolecular hydrogen bond (O-H-O). The title molecule is capable of receiving second harmonic generation (SHG) is due to high value of hyperpolarizability indicates the NLO activity of the molecule. Apart from NLO entities, aromaticity and the molecular electrostatic potential surface (MEP) explain the hydrogen bonding and provide the reactive behavior of the molecule. The Mulliken population analysis leads to redistribution of electron density in the ring.

Intramolecular Hydrogen Bonds in Selected Aromatic Compounds: Recent Developments

A review of intramolecular hydrogen bonding in ortho-hydroxyaryl Schiff bases, ortho-hydroxyaryl Mannich bases, dipyrrins, ortho-hydroxyaryl ketones, ortho-hydroxyaryl amides, and 4-Bora-3a,4a-diaza-s-indacene (BODIPY) dyes with tautomeric sensors as substituents is presented in this paper. Ortho-hydroxy Schiff and Mannich base derivatives are known as model molecules for analysing the properties of intramolecular hydrogen bonding. The compounds under discussion possess physicochemical features modulated by the presence of strong intramolecular hydrogen bonds. The equilibrium between intra- and inter-molecular hydrogen bonds in BODIPY is discussed. Therefore, the summary can serve as a knowledge compendium of the influence of the hydrogen bond on the molecular properties of aromatic compounds.

Theoretical insights into the hydrogen bonding interaction in the complexation of epinephrine with uracil

The present study is aimed at probing the hydrogen bonding interaction between epinephrine and uracil by means of density functional theory calculations concerning their complexation's geometries, interaction energies, and vibrational frequencies. Geometry optimization was carried out giving 19 stable geometries of epinephrine-uracil complex with interaction energies in a range of - 21.51 to - 62.37 kJ mol^-1 using the basis set superposition error (BSSE) correction. The analysis of structure and vibration shows that the hydrogen bonding elongates the length of corresponding bond O(N)-H and decreases the symmetric stretching vibrational frequency, which indicates red-shifted H-bonding interactions in all the geometries. Additionally, the analysis with theories of natural bond orbital (NBO), atoms in molecules (AIM), and the reduced density gradient (RDG) of hydrogen bonding properties and characteristics of the 19 geometries suggests that the hydrogen bonding in all the optimized structures of epinephrine-uracil complex is kind of a closed-shell interaction and mainly electrostatic dominant.

Correction: Mishra, S.K. and Suryaprakash, N. Intramolecular Hydrogen Bonding Involving Organic Fluorine: NMR Investigations Corroborated by DFT-Based Theoretical Calculations: Molecules 2017, 22, 423

The authors wish to make the following corrections to their paper [...].

Acetyl Coenzyme A Analogues as Rationally Designed Inhibitors of Citrate Synthase

In this study, we probed the inhibition of pig heart citrate synthase (E.C. 4.1.3.7) by synthesising seven analogues either designed to mimic the proposed enolate intermediate in this enzyme reaction or developed from historical inhibitors. The most potent inhibitor was fluorovinyl thioether 9 (K_i =4.3 μm), in which a fluorine replaces the oxygen atom of the enolate. A comparison of the potency of 9 with that of its non-fluorinated vinyl thioether analogue 10 (K_i =68.3 μm) revealed a clear "fluorine effect" favouring 9 by an order of magnitude. The dethia analogues of 9 and 10 proved to be poor inhibitors. A methyl sulfoxide analogue was a moderate inhibitor (K_i =11.1 μm), thus suggesting hydrogen bonding interactions in the enolate site. Finally, E and Z propenoate thioether isomers were explored as conformationally constrained carboxylates, but these were not inhibitors. All compounds were prepared by the synthesis of the appropriate pantetheinyl diol and then assembly of the coenzyme A structure according to a three-enzyme biotransformation protocol. A quantum mechanical study, modelling both inhibitors 9 and 10 into the active site indicated short CF⋅⋅⋅H contacts of ≈2.0 Å, consistent with fluorine making two stabilising hydrogen bonds, and mimicking an enolate rather than an enol intermediate. Computation also indicated that binding of 9 to citrate synthase increases the basicity of a key aspartic acid carboxylate, which becomes protonated.

Polysulfonate Cappings on Upconversion Nanoparticles Prevent Their Disintegration in Water and Provide Superior Stability in a Highly Acidic Medium

The stability of organic cappings on hexagonal NaYF4:Ln3+ upconversion nanoparticles (UCNPs) is crucial for their luminescence efficiency in aqueous solutions. The capping removal quickens as the acidity of the medium increases. We demonstrate here that polysulfonates, namely poly(2-acrylamido-2-methyl-1-propanesulfonate) (PAMPS) and poly(sodium 4-styrene sulfonate) (PSS), remain anchored to the surface of NaYF4:Yb3+,Er3+/Tm3 UCNPs even at a pH as low as 2 due to strong acidity of the sulfonate anchoring groups (pK a of ca. -3). Bare UCNPs progressively disintegrate into their compositional F-, Na+, Y3+, and Ln3+ ions. Their disintegration is particularly worrying in highly diluted dispersions of nanoparticles because both the lanthanide ions and/or the bare UCNPs can cause undesirable interference in a chemical or biological environment. Remarkably, the UC@PSS nanohybrid is particularly chemically stable, exhibiting an amazingly low release of Y3+ and Ln3+ ions for up to 96 h in highly diluted water dispersions (10 μg/mL). Additional advantages of the use of PSS as capping layer are its biocompatibility and its high dispersibility in water, together with easy further functionalization of the UCNP@PSS nanohybrids.

Intramolecular hydrogen bond directed distribution of conformational populations in the derivatives of N′-benzylidenebenzohydrazide

The extensive NMR investigations reveal the presence of E-isomers in the derivative of N′-benzylidenebenzohydrazide. The different conformer populations are controlled by the strength of intramolecular hydrogen bonds.

Retention of strong intramolecular hydrogen bonds in high polarity solvents in binaphthalene–benzamide derivatives: extensive NMR studies

Advanced multidimensional NMR techniques have been employed to investigate the intramolecular hydrogen bonds (HBs) in a series of N,N′-([1,1′-binaphthalene]-2,2′-diyl)bis(benzamide) derivatives, with the site-specific substitution of different functional groups. The existence of intramolecular HBs and the elimination of any molecular aggregation and possible intermolecular HBs are ascertained by various experimental NMR techniques, including solvent polarity dependent modifications of HB strengths. In the fluorine substituted derivative, direct evidence for the engagement of organic fluorine in HB is obtained by the detection of heteronuclear through-space correlation and the coupling between two NMR active nuclei where the transmission of spin polarization is mediated through HBs (^1hJ_FH). The extent of reduction in the strength of ^1hJ_FH on dilution with high polarity solvents directly provided the qualitative measure of HB strength. The HB, although becoming weakened, does not get nullified even in pure high polarity solvent, which is attributed to the structural constraints. The rate of exchange of a labile hydrogen atom with the deuterium of the solvent permitted the measurement of their half-lives, that are correlated to the relative strengths of HBs. The experimental NMR findings are further validated by XRD and DFT-based theoretical computations, such as, NCI and QTAIM.

NMR studies reveal very strong hydrogen bond unbreakable even in high polarity solvents.

Intramolecular hydrogen bond directed stable conformations of benzoyl phenyl oxalamides: unambiguous evidence from extensive NMR studies and DFT-based computations

A number of benzoyl phenyl oxalamide derivatives have been synthesized and characterized by the extensive utility of one- and two-dimensional NMR experimental techniques. The manifestation of intramolecular hydrogen bonds in all of the synthesized molecules, convincingly established using NMR studies, governs the stable conformations of the molecules. In the fluorine substituted molecules, the coupling between two NMR active nuclei mediated through hydrogen bonds has been detected. The measured chemical shift difference of an NH proton has been employed to calculate the energy of the HBs. NMR analysis revealed the electrostatic nature of the hydrogen bonds in all of the molecules. The NMR experimental findings have been validated using Density Functional Theory (DFT)-based Non Covalent Interactions (NCIs) and Quantum Theory of Atoms In Molecules (QTAIM) computations.

Rotational spectra and theoretical study of tetramers and trimers of 2-fluoroethanol: dramatic intermolecular compensation for intramolecular instability

Cooperativity and chirality dominate in stabilizing the 2-fluoroethanol tetramer, thanks to a fully bifurcated C–H⋯F H-bond network.

Dendrimers, Carotenoids, and Monoclonal Antibodies

Dendrimers are unimolecular architectural nano- or microparticle entities that can accommodate various nutraceuticals and pharmaceuticals between their branches (dendrons) and provide targeted delivery of biomimetics into different tissues upon addition of functionalized groups to the dendrimer's surface. Covalent binding, hydrogen bonds, and electrostatic interactions between dendrimer-composing molecules are known to form and stabilize dendrimer structure. Carotenoids have recently been shown to form dendrimer-like structures and promote targeted delivery of "cargo" molecules into organs characterized by high-carotenoid uptake (adrenal glands, prostate, liver, and brain). The use of carotenoid dendrimers, in particular lycosome particles loaded with various xenobiotics (resveratrol, cocoa flavanols, and HMG-CoA reductase inhibitors), reportedly has a beneficial effect in diabetic foot syndrome, prehypertension, and cardiovascular disease. New applications for carotenoid dendrimers may arise from the use of complexes formed by carotenoid dendrimers and monoclonal antibodies (mAbs). The internalization of carotenoid dendrimer-mAb complexes through receptor-mediated mechanisms may prevent interactions of dendrimer-incorporated xenobiotics with membrane-associated P-glycoprotein, a major factor of drug resistance in tumor cells. The incorporation of mAb fragments with higher binding capacity to the membrane receptors and higher affinity to the target molecule may further increase the bioavailability of "cargo" molecules transported by the carotenoid dendrimer-mAb complexes and open new doors in nanodelivery technologies.