Types Of Hydrogen Bonds Research Articles

Chemical bonds and hair behaviour-A review.

When undertaking any review of the structure of the hair and its mechanical properties it becomes apparent that the overall behaviour of keratin fibres is commonly attributed to the presence of hydrogen, disulfide and ionic bonds. The action of physico-chemical agents used during various cosmetic treatments is viewed as the result of an interaction with these bonds. Thus, the breaking of bonds by chemical agents, or via mechanical or thermal stresses, affects the relative balance of disulfide and hydrogen bonds and the contribution of hydrophobic interactions, which are all important factors that may alter hair behaviour. Generally, these chemical bonds are considered as responding homogeneously to the environmental and cosmetic factors. This unitary image is challenged, however, by evaluating the results of chemical, nanomechanical, tensile and thermal measurements, which suggest that disulfide bonds may be grouped into several types, according to their location within the fibre and the way they respond to various agents. A compensatory effect of newly formed hydrogen bonds for broken disulfide bonds may also be seen, and additionally involves different types of hydrogen bonds. As a result, the picture of chemical bonding in hair appears to be far from a homogeneous one. In addition, it is apparent that further investigation is required for clarifying the action of ionic bonds and hydrophobic interactions within the hair fibre. The present review aims, thus, at offering a deeper background for understanding how the hair behaves under various conditions.

Green and Efficient Extraction of Phenolic Components from Plants with Supramolecular Solvents: Experimental and Theoretical Studies.

The supramolecular solvent (SUPRAS) has garnered significant attention as an innovative, efficient, and environmentally friendly solvent for the effective extraction and separation of bioactive compounds from natural resources. However, research on the use of a SUPRAS for the extraction of phenolic compounds from plants, which are highly valued in food products due to their exceptional antioxidant properties, remains scarce. The present study developed a green, ultra-sound-assisted SUPRAS method for the simultaneous determination of three phenolic acids in Prunella vulgaris using high-performance liquid chromatography (HPLC). The experimental parameters were meticulously optimized. The efficiency and antioxidant properties of the phenolic compounds obtained using different extraction methods were also compared. Under optimal conditions, the extraction efficiency of the SUPRAS, prepared with octanoic acid reverse micelles dispersed in ethanol-water, significantly exceeded that of conventional organic solvents. Moreover, the SUPRAS method demonstrated greater antioxidant capacity. Confocal laser scanning microscopy (CLSM) images revealed the spherical droplet structure of the SUPRAS, characterized by a well-defined circular fluorescence position, which coincided with the position of the phenolic acids. The phenolic acids were encapsulated within the SUPRAS droplets, indicating their efficient extraction capacity. Furthermore, molecular dynamics simulations combined with CLSM supported the proposed method's mechanism and theoretically demonstrated the superior extraction performance of the SUPRAS. In contrast to conventional methods, the higher extraction efficiency of the SUPRAS can be attributed to the larger solvent contact surface area, the formation of more types of hydrogen bonds between the extractants and the supramolecular solvents, and stronger, more stable interaction forces. The results of the theoretical studies corroborate the experimental outcomes.

Intermolecular Forces Regulating the Phase-Transition Temperatures in Organic-Inorganic Hybrid Materials.

Organic-inorganic hybrid phase-transition materials have attracted widespread attention in energy storage and sensor applications due to their structural adaptability and facile synthesis. However, increasing the phase-transition temperature (Tc) effectively remains a formidable challenge. In this study, we employed a strategy to regulate intermolecular interactions (different types of hydrogen bonds and other weak interactions), utilizing bismuth chloride as an inorganic framework and azetidine, 3,3-difluoro azetidine, and 3-carboxyl azetidine as organic components to synthesize three compounds with different Tc values: [C3H8N]2BiCl5 (1, 234 K), [C3H6NF2]3BiCl6 (2, 256 K), and [C4H8O2N]3BiCl6 (3, 350 K). 1 is a one-dimensional chain structure and 2 and 3 are zero-dimensional structures. Analysis of the crystal structure and the Hirshfeld surface and 2D fingerprints further suggests that the intermolecular forces are efficiently modulated. These findings emphasize the efficacy of our strategy in enhancing Tc and may facilitate further research in this area.

A Study on How Conformation Entropy of Attached Macromolecules Drives Polymeric Collapse and Protein Folding

AbstractThe conformation of macromolecules attached to a surface is influenced by both their excluded volume and steric forces. Here, self‐avoiding random walk simulations are used to evaluate the occurrence of various conformations as a function of the number of monomeric units to estimate the effect of conformational entropy of a tethered chain. Then, a more realistic scenario is assessed, which can more accurately reproduce the shape of a tethered macromolecule. The simulations presented here confirm that it is more likely for a polymer to undergo a collapse conformation rather than a stretched one, as a collapse conformation can be realized in more different ways. Also, they confirm the “mushroom” shape of polymers close to a surface. From this simple approach, the conformation entropy of a model 100‐unit polymer close to a surface is estimated to contribute with over 129 toward its collapse. This conformation entropy is higher than that of typical hydrogen bonds and even barriers that keep proteins folded. As such, entropic collapse of macromolecules plays an important role in realizing the mushroom shape of attached polymers and can be the driving force in protein folding, while the polypeptide chain emerges from the ribosome.

Theoretical investigation of the nature of hydrogen bonds and cooperativity effect in methanol-water and ethanol-water clusters

ABSTRACT This study aims to cast light on the nature of hydrogen bonds and their cooperativity that exists in alcohol-water ( ROH ( H 2 O ) n ) ( R = − C H 3 ( − Me ) , − C H 2 C H 3 ( − Et ) ) (n = 1–10) clusters using atoms in molecules (AIM) theory and symmetry-adapted perturbation theory (SAPT). The investigation of optimum structures suggests that alcohol ( ROH ) forms two hydrogen bonds, one primary hydrogen bond ( O − H ⋅ ⋅ ⋅ O ) , and one secondary hydrogen bond ( C − H ⋅ ⋅ ⋅ O ) Two types of hydrogen bonds are addressed in these studies, where alcohol works as the hydrogen bond donor ( ROH ⋅ ⋅ ⋅ O H 2 ) and hydrogen bond acceptor ( RHO ⋅ ⋅ ⋅ HOH ) . The AIM results reveal that RHO ⋅ ⋅ ⋅ HOH and ROH ⋅ ⋅ ⋅ O H 2 hydrogen bonds are partially covalent. The SAPT study demonstrates that in all the clusters studied herein, the electrostatic interaction between alcohol and water is the main attractive force, and its contribution may be two times larger than the separate corresponding contributions from the dispersion and the induction terms. The electron density (ρ) at the bond critical point (BCP) is a suitable parameter to assess the strength of the interaction. The current study shows the strength and nature of ROH ⋅ ⋅ ⋅ O H 2 and RHO ⋅ ⋅ ⋅ HOH hydrogen bond, and cooperative effect in ( ROH ( H 2 O ) n ) ( R = − C H 3 ( − Me ) , − C H 2 C H 3 ( − Et ) .) (n = 1–10).

Electrodeposition of Magnesium in Deep Eutectic Solvents Based on Magnesium Chloride Hexahydrate and Choline Chloride with Urea Added

Magnesium (Mg) alloy has small density, large elastic modulus, good heat dissipation and corrosion resistance to organic matter and alkali. At present, magnesium alloy is more and more used in automotive industry, medical devices and aerospace industry. However, the traditional preparation method of Mg has the disadvantages of high investment, high labor intensity and great environmental pollution. Therefore, it is of great significance to develop simple, environment-friendly methods of the magnesium. In this study, urea was added to adjust the electrochemical property of the deep eutectic solvent (DES) mixed by choline chloride (ChCl) and magnesium chloride hexahydrate (MgCl2·6H2O). Cyclic Voltammetry (CV) curves reveals that the addition of urea made the reduction potential of Mg shifted from -0.9 V to -1.3 V. Among the CV curves, one was proposed as the “dividing line”, which shows that the electroactive species in the two DESs, ChCl-MgCl2·6H2O and urea-MgCl2·6H2O, are different due to the changes of the component of the DESs. Fourier transform infrared (FTIR) data shows the type of hydrogen bond had been changed with the increase of urea content. Furthermore, the Raman spectra indicates that Mg2+ was coordinated with urea chains, which did not exist in ChCl-MgCl2·6H2O. Moreover, it was found that urea changed the electrochemical performance of the ChCl-Urea-MgCl2·6H2O by changing the hydrogen bond in the system and coordination form of the electroactive species, rather than adsorbing onto the electrode surface. Combined with geometry calculations at the B3LYP/6-311++G (d, p), the most probable mechanism of electrodeposition process was deduced.

Machine-learning accelerated structure search for ligand-protected clusters.

Finding low-energy structures of ligand-protected clusters is challenging due to the enormous conformational space and the high computational cost of accurate quantum chemical methods for determining the structures and energies of conformers. Here, we adopted and utilized a kernel rigid regression based machine learning method to accelerate the search for low-energy structures of ligand-protected clusters. We chose the Au25(Cys)18 (Cys: cysteine) cluster as a model system to test and demonstrate our method. We found that the low-energy structures of the cluster are characterized by a specific hydrogen bond type in the cysteine. The different configurations of the ligand layer influence the structural and electronic properties of clusters.

Modification of faba bean protein isolate by high-intensity ultrasound treatment: screening of physicochemical, thermal, and structural properties

This study aimed to investigate the impacts of high-intensity ultrasound treatments on the physicochemical, thermal, and structural properties of faba bean protein isolates (FPI). Aqueous FPI suspensions were sonicated at 20 kHz for 1, 3, 5, and 10 min. Ultrasound treatment increased the solubility of FPI at all sonicated times, with maximum solubility (89.11%) observed at the 3-min treatment. Particle size (from 370.47 to 187.87 nm) and zeta potential (from − 40.83 to − 37.17 mV) reduction (in magnitude) by sonication were observed at all studied times. The usage of ultrasound has been found to have a more pronounced antibrowning impact compared to unsonication (higher L* and b*, lower a*, C*, H*, BI, and ΔE). With the increase in sonication treatment from 0 to 3 min, the Td decreased from 103.07 to 99.58 °C and ΔHd from 2.21 to 1.12 J/g, which were related to the changes in the secondary structure of proteins. Sonication changed the secondary structure of FPI, decreasing the α-helix, β-turn, and random coil content, and increasing the β-sheet for samples treated up to 3 min. Prolonged sonication increased the α-helices due to the extension of certain types of hydrogen bonds in the structure. The microstructural changes of FPI caused by ultrasound were further validated through observations made using a scanning electron microscope, which revealed the presence of smaller fragments. The present study indicates that the use of ultrasound has the potential to improve the functionality of FPI, hence potentially enhancing the efficacy of FPI-based food products.Graphical abstract

Substitution reactions in the acenaphthene analog of quino[7,8-h]quinoline and an unusual synthesis of the corresponding acenaphthylenes by tele-elimination.

The possibility of functionalization of dipyrido[3,2-e:2',3'-h]acenaphthene containing a quino[7,8-h]quinoline fragment and being a highly basic diazine analog of 1,8-bis(dimethylamino)naphthalene ("proton sponge") has been studied for the first time. In addition to the pronounced tendency of the title compound to form associates with an intramolecular hydrogen bond of the NHN type (new examples with the participation of pyridine rings, including self-associates are shown) and its inertness to amination reactions of the pyridine rings, the naphthalene core at positions 5(8) and the CH2CH2 bridge (dehydrogenation) undergo chemical modifications under mild conditions, giving the corresponding acenaphthylenes. The latter can also be obtained in an unusual way by tele-elimination from 5,8-dibromodipyridoacenaphthene by reaction with neutral or anionic bases.

Mechanofluorochromic Properties of 1,4-Diphenylanthracene Derivatives with Hypsochromic Shift.

Several types of 1,4-diphenylanthracene derivatives 1-4 were prepared, and their photophysical properties were observed in the solid and solution states. Interestingly, the CN-group-substituted 1,4-diphenylanthracene derivative 2 was found to exhibit a higher fluorescence quantum yield (ϕf = 0.71) in the solid state than in the solution state, probably due to the formation of an intermolecular Ar-CN⋯H-Ar hydrogen bond and antiparallel type locked packing structure in the solid state. Furthermore, for some derivatives, an increase in the fluorescence quantum yield was observed in the PMMA film (1 wt%) over both the solid state and the solution state. More interestingly, some of the 1,4-diphenylanthracene derivatives exhibited unusual mechanofluorochromic properties with a "hypsochromic shift" in luminous color depending on the substituents of the phenyl group, and with the derivatives having CF3, OMe, CN, and two F substituents (1d-1f, 2-4) showing a significant luminous color change with a "hypsochromic shift" after grinding. However, no change in the luminous color was observed for the derivatives having H, Me, and one F substituent (1a-1c), and especially for some of the CN-substituted derivatives, a reversible luminous color change with a "hypsochromic shift" was observed, probably due to the formation of an antiparallel type packing structure. These "hypsochromic" anthracene derivatives could probably be utilized as new mechanofluorochromic materials.

Structural and Dynamical Basis of VP35-RBD Inhibition by Marine Fungi Compounds to Combat Marburg Virus Infection.

The Marburg virus (MBV), a deadly pathogen, poses a serious threat to world health due to the lack of effective treatments, calling for an immediate search for targeted and efficient treatments. In this study, we focused on compounds originating from marine fungi in order to identify possible inhibitory compounds against the Marburg virus (MBV) VP35-RNA binding domain (VP35-RBD) using a computational approach. We started with a virtual screening procedure using the Lipinski filter as a guide. Based on their docking scores, 42 potential candidates were found. Four of these compounds-CMNPD17596, CMNPD22144, CMNPD25994, and CMNPD17598-as well as myricetin, the control compound, were chosen for re-docking analysis. Re-docking revealed that these particular compounds had a higher affinity for MBV VP35-RBD in comparison to the control. Analyzing the chemical interactions revealed unique binding properties for every compound, identified by a range of Pi-cation interactions and hydrogen bond types. We were able to learn more about the dynamic behaviors and stability of the protein-ligand complexes through a 200-nanosecond molecular dynamics simulation, as demonstrated by the compounds' consistent RMSD and RMSF values. The multidimensional nature of the data was clarified by the application of principal component analysis, which suggested stable conformations in the complexes with little modification. Further insight into the energy profiles and stability states of these complexes was also obtained by an examination of the free energy landscape. Our findings underscore the effectiveness of computational strategies in identifying and analyzing potential inhibitors for MBV VP35-RBD, offering promising paths for further experimental investigations and possible therapeutic development against the MBV.

Hydrogen bonding regulation on phase change in stimuli responsive copolymer aqueous solution

Hydrogen bonding (HB) is vital for the phase transition and physical properties of stimuli responsive copolymers. However, the governing mechanism remains unclear. Herein, we investigated the HB dynamics in a representative thermo-responsive copolymer (PNIPAM-AM) aqueous solution. Three types of HB were identified: polymer-polymer chain (CO:H–N), polymer chain-water molecule (CO:H–O) and water-water molecules (H–O:H–O) by vibrational spectroscopy. Increasing polymer concentration, the H–O:H–O softened and CO:H–O stiffened, leading to the destruction of HB network in water-water clusters. Upon increasing solution temperature, CO:H–O softened while CO:H–N stiffened, resolving the dehydration and cross-linking of polymer chains. Confinement of water molecules in the “cages” (∼ tens to hundreds of micrometers) after sol-gel phase transition was visualized, disclosing the mechanism of water holding capacity of PNIPAM-AM. The correlation of molecule vibration and copolymer microscopic structure was established, contributing to the fundamental understanding of phase behavior and physical properties regulations in stimuli responsive copolymer aqueous solution.

Decoding the enigma of RNA-protein recognition: quantum chemical insights into arginine fork motifs.

Arginine (Arg) forks are noncovalent recognition motifs wherein an Arg interacts with the phosphates and guanine nucleobases of RNA, providing extraordinary specific RNA:protein recognition. In this work, we carried out an in-depth DFT based quantum mechanical investigation on all known classes of Arg forks to estimate their intrinsic structural stabilities and interaction energies. The optimized structures closely mimic the structural characteristics of Arg forks and this close match between experimental and optimized geometries suggests that Arg forks are intrinsically stable and do not require additional support from other RNA or protein components. Both hydrogen-bonding and cation-π interactions are important for the intrinsic stability of Arg forks, providing an average interaction energy of -36.7 kcal mol-1. Furthermore, we found a direct correlation between Arg forks' interaction energies and the number of phosphates involved, which is more delicately modulated by other factors, like the types of hydrogen bonds and cation-π interactions that constitute the Arg fork. Additionally, we observed a positive correlation between the average interaction energies of Arg forks and the frequency of their occurrence in available crystal structures. At the broader level, this work establishes the groundwork for more precise modeling and understanding of RNA-protein interfaces, which could have potential implications in advancing the knowledge of biomolecular recognition patterns.

Investigation of the Molecular Structure and DFT Insights into (4-(4-Nitrophenyl)-9-(phenylsulfonyl)-9H-carbazole-2,3-diyl)bis(p-tolylmethanone)

Carboxylate molecules have been distinguished as the potential compound in the largely emergent chemical world of heterocyclic compounds shows likely pharmacological characteristics. The knowledge of a mixture of synthetic pathways and the different physicochemical parameters of such compounds describe the especial interest of medicinal chemists to produce combinatorial collection and carry out in-depth efforts in the search of lead molecules. Among the various group of compounds studied, carboxylate moieties stand out to be unique in features due to their biological, pharmacological and medicinal properties. Synthesis, crystal structure, conformation and density functional theory of (4-(4-Nitrophenyl)-9-(phenylsulfonyl)-9H-carbazole-2,3-diyl)bis(p-tolylmethanone) derivative have been investigated in detail. Carboxylate moiety is in planar conformation, C-H…O type of hydrogen bonds and van der Waals forces. Density functional theory was utilised to investigate the carboxylate derivative. Similar to co-crystal ligands, carboxylate compounds exhibited potent interactions with the target protein. The supramolecular properties were measured and validated using Hirshfeld surface studies.

Intrinsic dynamic and static natures of APn--X+--BPn σ(3c-4e) type interactions (APn = BPn = N, P, As and Sb; X = H, F, Cl, Br and I) in bicyclo[3.3.3] and bicyclo[4.4.4] systems and their behaviour, elucidated with QTAIM dual functional analysis.

The intrinsic dynamic and static natures of APn--X+--BPn (APn = BPn: N, P, As and Sb; X = H, F, Cl, Br and I) in 1a+-8c+ were elucidated with the quantum theory of atoms-in-molecules dual functional analysis (QTAIM-DFA). Species 1a+-8c+ were formed by incorporating X+ between APn and BPn of APn(CH2CH2CH2)3BPn (1-4) and APn(CH2CH2CH2CH2)3BPn (5-8). The relative stabilities between the symmetric and nonsymmetric structures along with their transition states were investigated. Various natures from typical hydrogen bonds (t-HB) to classical covalent bonds were predicted for the APn-X/BPn-X interactions in APn--X+--BPn with QTAIM-DFA. The secondary interactions of H-H and X-C were also detected. The vdW to molecular complexes through charge transfer natures were predicted for them. Natural bond orbital analysis clarified that the CT terms were caused by not only n(APn)→ σ*(X-BPn) but also σ(APn-C)→σ*(X-BPn), σ(APn-C/BPn-C)→np(X+) and n(X)→ns(Pn+). The direction and magnitude of the p-character of n(APn) were the factors that determined the types of donor-acceptor interactions. Estimating the order of the interaction strengths was attempted. The σ(3c-4e) characters of APn--X+--BPn were also examined by analysing the charge distributions on APn--X+--BPn. These results would provide fundamentally important insight into designing molecules with high functionality containing X+ in symmetric and nonsymmetric structures.

Profound importance of the conventional O-H⋯O hydrogen bond versus a considerable blue shift of the Csp2-H bond in complexes of substituted carbonyls and carboxyls.

Using quantum chemical approaches, we investigated the conventional O-H⋯O and nonconventional Csp2-H⋯O hydrogen bonds between carboxylic acids and aldehydes in 21 stable complexes. The strength of complexes is determined by the conventional O-H⋯O bond together with the nonconventional Csp2-H⋯O hydrogen bond, in which the former one is 4-5 times as strong as the latter one. Proportional linear correlations of the interaction energy with both individual energies of the O-H⋯O and Csp2-H⋯O hydrogen bonds are proposed. Different impacts of electron-donating and electron-withdrawing groups in substituted formaldehyde and formic acid on characteristics of conventional and nonconventional hydrogen bonds, as well as the strength of both hydrogen bond types and complexes, are also evaluated. Following complexation, it is noteworthy that the largest blue shift of the Csp2-H stretching frequency in the Csp2-H⋯O bond up to 105.3 cm-1 in CH3CHO⋯FCOOH is due to a decisive role of the O-H⋯O hydrogen bond, which has been rarely reported in the literature. The obtained results show that the conventional O-H⋯O hydrogen bond plays a pivotal role in the significant blue shift of the Csp2-H stretching frequency in the nonconventional Csp2-H⋯O hydrogen bond. Remarkably, the considerable blue shift of the Csp2-H stretching frequency is found to be one H of C-H in formic acid substituted by the electron-withdrawing group and one H in formaldehyde substituted by the electron-donating group. In addition, the change in the Csp2-H stretching frequency following complexation is proportional to both changes of electron density in σ*(Csp2-H) and σ*(O-H) orbitals, in which a dominant role of σ*(O-H) versus σ*(Csp2-H) is observed.

Hydrogen bond types which do not fit accepted definitions.

There are various interactions that either partially fit or do not fit the currently accepted definitions of the hydrogen bond. However, they possess characteristics of this interaction. It seems that it is partly connected to the fact that these definitions are not precise. The typical 3c-4e (three centres - four electrons) A-H⋯B hydrogen bond is characterized by the single-atom A and B centres that are highly electronegative. On the other hand, non-typical interactions that do not fit the hydrogen bond definitions well are characterised by uncommon proton donors and/or proton acceptors. The cases of multi-centre proton acceptors, π-electron or σ-electron systems are well known - such interactions are designated as A-H⋯π and A-H⋯σ hydrogen bonds, respectively. However, the cases of interactions with the multi-centre proton donors and proton acceptors do not fit the majority of definitions of hydrogen bond. The π⋯H+⋯π system in the proton-bound homodimer of acetylene is an example. This system can be classified as a hydrogen bond according to the two-sites hydrogen bond, 2sHB, definition. There are various types of interactions discussed in this review; among them, those that are undoubtedly unclassified as hydrogen bonds, i.e., hydride bonds, and charge inverted hydrogen bonds, CIHBs. Special emphasis is also put here on the proton sponges and other systems such as the [FHF]- anion or [NgHNg]+ cation (Ng is the noble gas centre).

IR spectrum of SiH3OH2+SiH4: cationic OH⋯HSi dihydrogen bond versus charge-inverted SiH⋯Si hydrogen bond.

The low electronegativity of Si gives rise to a variety of nonconventional intermolecular interactions in clusters of silanes and their derivatives, which have not been well characterized yet. Herein, we characterize the structures of various isomers of bare and Ar-tagged SiH3OH2+SiH4 dimers composed of protonated silanol and silane by infrared photodissociation (IRPD) of mass-selected ions and dispersion-corrected density functional calculations (B3LYP-D3/aug-cc-pVTZ). The analysis of the IRPD spectra recorded in the OH stretch range reveals the competition between two types of nonconventional hydrogen bonds (H-bonds). The first one represents a OH⋯HSi ionic dihydrogen bond (DHB), in which SiH4 interacts with the H2O moiety of SiH3OH2+. The second one represents a charge-inverted SiH⋯Si ionic H-bond (CIHB), in which the SiH4 ligand interacts with the SiH3 moiety of SiH3OH2+. The latter may also be considered as a weak three-centre two-electron (3c-2e) bond. Although both types of H-bonds are computed to have comparable interaction strengths for SiH3OH2+SiH4 (D0 ≈ 35-40 kJ mol-1), DHB isomers dominate the population in the supersonic plasma expansion, while the abundance of CIHB isomers is roughly one order of magnitude lower, probably as a result of entropic factors.

Synthesis, Characterization and X-Ray Crystal Structures of Oxidovanadium(V) Complexes Derived from N'-(2-Hydroxy-5-methylbenzylidene)-4-methylbenzohydrazide with Antibacterial Activity.

A dinuclear oxidovanadium(V) complex [V2O2L2(OMe)2] (1) was synthesized from N'-(2-hydroxy-5-methylbenzylidene)-4-methylbenzohydrazide (H2L) and VO(acac)2 in MeOH. Reaction of complex 1 with 3-hydroxy-2-methyl-4-pyrone (HL') afforded a mononuclear oxidovanadium(V) complex [VOLL'] (2). The hydrazone and both complexes were characterized by IR, UV and 1H NMR spectroscopy, as well as X-ray single crystal determination. X-ray powder diffraction of the complexes was performed. The V atoms in the two complexes are in octahedral coordination. The molecules of complex 2 are linked through non-classical hydrogen bonds of type C-H∙∙∙O to form one-dimensional chains running along the a axis. The biological assay indicates that the complexes have good antimicrobial activities on the bacteria strains P. aeroginosa, S. aureus, B. subtilis and E. coli.

Ab initio Modeling of Hydrogen Bonding of Remdesivir and Adenosine with Uridine.

Remdesivir (RDV) emerged as an effective drug against the SARS-CoV-2 virus pandemic. One of the crucial steps in the mechanism of action of RDV is its incorporation into the growing RNA strand. RDV, an adenosine analogue, forms Watson-Crick (WC) type hydrogen bonds with uridine in the complementary strand and the strength of this interaction will control efficacy of RDV. While there is a plethora of structural and energetic information available about WC H-bonds in natural base pairs, the interaction of RDV with uridine has not been studied yet at the atomic level. In this article, we aim to bridge this gap, to understand RDV and its hydrogen bonding interactions, by employing density functional theory (DFT) at the M06-2X/cc-pVDZ level. The interaction energy, QTAIM analysis, NBO and SAPT2 are performed for RDV, adenosine, and their complex with uridine to gain insights into the nature of hydrogen bonding. The computations show that RDV has similar geometry, energetic, molecular orbitals, and aromaticity as adenosine, suggesting that RDV is an effective adenosine analogue. The important geometrical parameters, such as bond distances and red-shift in the stretching vibrational modes of adenosine, RDV and uridine identify two WC-type H-bonds. The relative strength of these two H-bonds is computed using QTAIM parameters and the computed hydrogen bond energy. Finally, the SAPT2 study is performed at the minima and at non-equilibrium base pair distances to understand the dominant intermolecular physical force. This study, based on a thorough analysis of a variety of computations, suggests that both adenosine and RDV have similar structure, energetic, and hydrogen bonding behaviour.