Proper Hydrogen Bonds Research Articles

A structural role for tryptophan in proteins, and the ubiquitous Trp Cδ1-H...O=C (backbone) hydrogen bond.

Tryptophan is the most prominent amino acid found in proteins, with multiple functional roles. Its side chain is made up of the hydrophobic indole moiety, with two groups that act as donors in hydrogen bonds: the Nϵ-H group, which is a potent donor in canonical hydrogen bonds, and a polarized Cδ1-H group, which is capable of forming weaker, noncanonical hydrogen bonds. Due to adjacent electron-withdrawing moieties, C-H...O hydrogen bonds are ubiquitous in macromolecules, albeit contingent on the polarization of the donor C-H group. Consequently, Cα-H groups (adjacent to the carbonyl and amino groups of flanking peptide bonds), as well as the Cϵ1-H and Cδ2-H groups of histidines (adjacent to imidazole N atoms), are known to serve as donors in hydrogen bonds, for example stabilizing parallel and antiparallel β-sheets. However, the nature and the functional role of interactions involving the Cδ1-H group of the indole ring of tryptophan are not well characterized. Here, data mining of high-resolution (r ≤ 1.5 Å) crystal structures from the Protein Data Bank was performed and ubiquitous close contacts between the Cδ1-H groups of tryptophan and a range of electronegative acceptors were identified, specifically main-chain carbonyl O atoms immediately upstream and downstream in the polypeptide chain. The stereochemical analysis shows that most of the interactions bear all of the hallmarks of proper hydrogen bonds. At the same time, their cohesive nature is confirmed by quantum-chemical calculations, which reveal interaction energies of 1.5-3.0 kcal mol-1, depending on the specific stereochemistry.

Targeting EGFR Tyrosine Kinase: Design, Synthesis and Biological Evaluation of Novel Quinazolinone Derivatives.

Impaired cell cycle regulation and disturbance in signal transduction pathway are two major causes of a condition defined as cancer, one of the significant reasons for mortality worldwide. Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) have been commonly used as anticancer agents, and the majority of this medications possess quinazoline moiety as a heteroaromatic core. In this study, two novel series of EGFR-TKIs containing quinazolinone core were designed and synthesized. Most compounds showed reasonable inhibitory activity against EGFR-TK compared to that of erlotinib, a reversible inhibitor of this enzyme. Compound 8b, 2-((2-chlorobenzyl)amino)-6-phenoxyquinazolin-4(1H)-one, with an IC50 value of 1.37 nM exhibited the highest potency. Molecular docking study of compound 8b showed that it had the same direction of erlotinib and formed proper hydrogen bonds and hydrophobic interactions with the important amino acid residues of the active site. Based on in-silico calculations of ADME properties, our novel compounds have the potential to be orally active agents.

Insight into the physicochemical properties of deep eutectic solvents by systematically investigating the components

Deep eutectic solvents (DESs) have been recognized as environmentally friendly alternatives to the conventional fossil solvents, which are in consistent with the concept of green chemistry. In order to offer theoretical guidance for designing DESs with specific physicochemical properties, the structure–function relationships between the molecular structures of DESs components and their physicochemical properties were systematically analyzed. The investigation of the functional groups, carbon chain length and type of halogen ions in DESs components provided a deeper understanding of the formation and properties of DESs. Density, viscosity, solvatochromic parameters (ENR value、π* value、α value and β value) were selected as the analyzable physicochemical properties. Except for the conclusion about the proper hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs) for DESs with specific physicochemical properties, an effective neural network model system was also provided for the prediction of DESs properties. The molecular structural parameters of DESs used as input layers were calculated from the initial and constant molecular structural parameters of HBAs and HBDs. Not only considerable time was saved without complex calculation of the interactions energy between components, it was also helpful in constructing comprehensive database of the molecular information of the DESs components to provide convenience for future research.

The importance of hydrophobic interactions in the structure of transcription systems.

Hydrophobic forces play a crucial role in both the stability of B DNA and its interactions with proteins. In the present study, we postulate that the hydrophobic effect is an essential component in establishing specificity in the interaction transcription factor proteins with their consensus DNA sequence partners. The PDB coordinates of more than 50 transcription systems have been used to analyze the hydrophobic attraction of proteins towards their DNA consensus. This analysis includes computing the hydrophobic energy of the interacting molecules by means of their hydrophobic moments. Hydrophobic moments have successfully been used in previous studies involving self-assembly protein systems. In the present case, in spite of some variability, we found specificity in transcription factors when interacting with their respective consensus DNA sequences. By applying our model of biological membrane pattern for hydrophobic interactions, we postulate that hydrophobic forces constitute the necessary intermediate interaction between the unspecific electrostatic attraction for DNA phosphate groups and the very short-range interaction promoting hydrogen bonds. We conclude that hydrophobic interactions serve as the intermediate force guiding transcriptions factors towards the proper hydrogen bonds to their DNAs.

Anti-melanogenic activity of Myristica fragrans extract against Aspergillus fumigatus using phenotypic based screening

BackgroundAspergillus fumigatus, an opportunistic fungal pathogen is associated with a wide array of diseases. It produces 1, 8-dihydroxy naphthalene (DHN) melanin that imparts greenish grey color to conidia and is an important virulence factor. It masks various molecular patterns associated with A. fumigatus and protects the fungus from host immune system. Myristica fragrans, enriched with secondary metabolites has been traditionally used for the treatment of infectious and inflammatory diseases. The present study was aimed to explore the anti-melanogenic effect of M. fragrans extracts on A. fumigatus.MethodsM. fragrans extracts (hexane, chloroform, methanol and ethanol) were prepared through polarity guided extraction. Phytochemical analysis was performed to detect the chemical constituents of the extracts. The minimum effective concentration (MEC) of the extracts against A. fumigatus melanin was determined by broth micro-dilution assay. Various virulence factors were assayed by spectrophotometric methods. Electron microscopic studies were performed to evaluate the effect of the hexane extract of M. fragrans on A. fumigatus cell surface morphology. The major active compounds of the extract were detected by gas chromatography-mass spectrometry (GC-MS). Docking was performed to study the interaction between the major identified compounds and the ketosynthase domain of polyketide synthase protein.ResultsThe results indicated that the hexane extract of M. fragrans inhibited melanin production (76.09%), reduced ergosterol content (83.63%) and hydrophobicity of the cell (72.2%) at the MEC of 0.078 mg/mL. Altered conidial surface, disappearance of protrusions and absence of melanin layer on outer cell surface was observed in electron microscopy. Forty-two compounds were identified by GC-MS. The main constituents were identified as sabinene (12.2%), linoleic acid (11.7%), hexadecanoic acid (10.5%), safrole (8.1%) and elemicin (7.8%). Docking studies revealed that hexadecanoic acid, its derivative compound cis-9-hexadecenal and isoeugenol have lower binding energy forming proper hydrogen bond with ketosynthase domain of polyketide synthase protein.ConclusionThe study concludes that the extract of M. fragrans has potential antifungal properties that can be explored in combination with available antifungals. This combination approach may be helpful for large number of patients suffering with A. fumigatus infections.

Theoretical Investigations of Hydrogen Bonding Interactions of (E)-1-(1H-Benzo[d]imidazol-2-yl)-3-Phenylprop-2-en-1-one Momoners and Dimers: NBO, QTAIM and NCI Study

Hydrogen bonding is an essential interaction in nature and plays a crucial role in many formations of materials and biological processes, requiring a deeper understanding of its formation. Benzimidazole is an important structural unit found in a large number of natural and pharmacologically active molecules. In the present work, the electronic structures and properties and relatives stabilities of a series of (E)-1-(1H-benzo[d]imidazol-2-yl)-3-phenylprop-2-en-1-one monomers and dimers have been studied by density functional theory using B3LYP 6-31+G (d, p) calculation level. the strengths of the noncovalent interactions have been analyzed in terms of the QTAIM analysis, NCI analysis and natural bond orbital approaches. It was found that the dimers are formed by double N-H⋯O hydrogen bond. QTAIM analysis proved the presence of intramolecular hydrogen bond in monomers and coexistence of intramolecular and intermolecular hydrogen bond in dimers. Frequency analysis show that intermolecular N-H⋯O interactions are proper hydrogen bond while intramolecular C-H⋯N, C-H⋯O, C-H⋯H-C interactions are improper hydrogen bond. NBO and NCI analyses confirm the existence of hydrogen bonds in the studied monomers and dimers. The presence of weakly electron acceptor group on benzene ring favor the total interaction energy of dimerization.

Theoretical investigation on hydrogen bond interaction of diketo/keto-enol form uracil and thymine tautomers with intercalators.

The interaction of diketo and keto-enol form of thymine and uracil tautomers with acridine (Acr), phenazine (Phen), benzo[c]cinnoline (Ben), 1,10-phenanthroline (1,10-Phe), and 4,7-phenenthroline (4,7-Phe) intercalating drug molecules was studied using density functional theory at B3LYP/6-311++G** and M05-2×/6-311++G** levels of theory. From the interaction energy, it is found that keto-enol form tautomers have stronger interaction with intercalators than diketone form tautomers. On complex formation of thymine and uracil tautomers with benzo[c]cinnoline the drug molecules have high interaction energy values of -20.14 (BenT3) and -20.55 (BenU3) kcal mol-1, while phenazine has the least interaction energy values of -6.52 (PhenT2) and -6.67 (PhenU2) kcal mol-1. The closed shell intermolecular type interaction between the molecules with minimum elliptical value of 0.018 and 0.019 a.u at both levels of theory has been found from topological analysis. The benzo[c]cinnoline drug molecule with thymine and uracil tautomers has short range intermolecular N-H…N, C-H…O, and O-H...N hydrogen bonds (H-bonds) resulting in higher stability than other drug molecules. The proper hydrogen bonds N-H..N and O-H..N have the frequency shifted toward the lower side (red shifted) with the elongation in their bond length while the improper hydrogen bond C-H...O has the frequency shifted toward the higher side (blue shifted) of the spectral region with the contraction in their bond length. Further, the charge transfer between proton acceptor and donor along with stability of the bond is studied using natural bond orbital (NBO) analysis. Graphical abstract Hydrogen bond interaction of diketo/keto-enol form uracil and thymine tautomers with intercalators.

Proper and improper hydrogen bonds in liquid water

The total lifetime distributions for hydrogen bonds in snapshots of molecular dynamics simulations of water serve as a basis to identify a class of proper hydrogen bonds. Proper bonds emerge and break up when restructuring the surrounding area of the hydrogen bond networkwhich weakly depend on the properties of this individual bond, i.e., almost randomly. Therefore, the distribution of the bond lifetimes is described by an exponential function similar to the distribution of the mean free path time in gas. It is shown that proper hydrogen bonds are strong, long-lived, and tetrahedrally oriented bonds. They account for about 80% of the bonds in each snapshot. Thus, these bonds form the basis or framework of the hydrogen bond network of water. The other, improper bonds have a substantially shorter lifetime; these are weak, bifurcated, and quickly switching bonds.

Mannose-recognition mutant of the galactose/N-acetylgalactosamine-specific C-type lectin CEL-I engineered by site-directed mutagenesis

BackgroundCEL-I is a galactose/N-acetylgalactosamine-specific C-type lectin isolated from the sea cucumber Cucumaria echinata. Its carbohydrate-binding site contains a QPD (Gln-Pro-Asp) motif, which is generally recognized as the galactose specificity-determining motif in the C-type lectins. In our previous study, replacement of the QPD motif by an EPN (Glu-Pro-Asn) motif led to a weak binding affinity for mannose. Therefore, we examined the effects of an additional mutation in the carbohydrate-binding site on the specificity of the lectin. MethodsTrp105 of EPN-CEL-I was replaced by a histidine residue using site-directed mutagenesis, and the binding affinity of the resulting mutant, EPNH-CEL-I, was examined by sugar-polyamidoamine dendrimer assay, isothermal titration calorimetry, and glycoconjugate microarray analysis. Tertiary structure of the EPNH-CEL-I/mannose complex was determined by X-ray crystallographic analysis. ResultsSugar-polyamidoamine dendrimer assay and glycoconjugate microarray analysis revealed a drastic change in the specificity of EPNH-CEL-I from galactose/N-acetylgalactosamine to mannose. The association constant of EPNH-CEL-I for mannose was determined to be 3.17×103M−1 at 25°C. Mannose specificity of EPNH-CEL-I was achieved by stabilization of the binding of mannose in a correct orientation, in which the EPN motif can form proper hydrogen bonds with 3- and 4-hydroxy groups of the bound mannose. ConclusionsSpecificity of CEL-I can be engineered by mutating a limited number of amino acid residues in addition to the QPD/EPN motifs. General significanceVersatility of the C-type carbohydrate-recognition domain structure in the recognition of various carbohydrate chains could become a promising platform to develop novel molecular recognition proteins.

Experimental and computational studies on the tautomerism of N-substituted 3-amino-5-oxo-4-phenyl-1H-pyrazolo-1-carboxamides with antibacterial activity

The tautomerism of N-substituted 3-amino-5-oxo-4-phenyl-1H-pyrazolo-1-carboxamides with antibacterial activity is studied with X-ray crystallography, IR, 1H and 13C NMR (including NOESY spectra) and quantum chemical calculations. It is found that the form with the keto group at position 5 is the preferred one in the crystalline state and in DMSO, although some fraction with the corresponding hydroxy group also occurs in both states. This finding was related to the antibacterial activity of the studied compounds as the energetic stabilization of the keto group may determine their proper hydrogen bond interactions with the bacterial enzyme.

Promiscuous esterase activities of the C–C hydrolases from Dyella ginsengisoli

A C-C hydrolase gene (bphD(LA-4)) from strain Dyella ginsengisoli LA-4 was cloned and expressed in Escherichia coli BL21 (DE3). BphD(LA-4) together with another hydrolase MfphA(LA-4), which derived from the same strain, possessed esterase activities. p-Nitrophenyl butyrate was the best substrate for both enzymes. BphD(LA-4) had high catalytic efficiency to p-nitrophenyl benzoate, whereas MfphA(LA-4) had no activity. Homology modeling and docking studies demonstrated that the proper hydrogen bond interaction was important for the reactivity of specific substrate.

Computational study of proper and improper hydrogen bonding in methanol complexes

The bulk properties of alcohols, like those of aqueous solutions, are governed mostly by hydrogen bonding; however, in contrast with water molecules, the chemical structure of a simple alcohol such as methanol offers an opportunity to explore the effects of both proper and improper hydrogen bonding on a single hydrogen donor. The presence of the hydroxyl group generally gives rise to a strong proper hydrogen bond, while the methyl group of methanol is likely involved in the weaker improper hydrogen bond, among other weak non-covalent interactions. The effects of the two types of hydrogen bonds on the stability, geometric parameters, and properties of electron density of methanol complexes are examined while considering different geometrical arrangements of the methanol dimer and the binary complexes of methanol with water, acetonitrile, and chloromethane. Subsequently, potential conclusions about the nature of improper hydrogen bonding and the origin of the C–H bond contraction that results upon complex formation are discussed. Quantum theory of atoms in molecules and natural bond orbital methods were used in the analysis; all calculations were performed at the MP2(full)/6-311++G(d,p) level of theory.

Study of proper and improper hydrogen bonding using Bader's atoms in molecules (AIM) theory and NBO analysis

Theoretical methods have been used to study the proper and improper hydrogen bonds, considering the hydrogen bond length, interaction energy, and charge transfer, for some hydrogen-bonded complexes. Topological analysis has been performed for the complex molecules, employing Bader's Atoms in Molecules theory. The topological properties, correlate well with the structural parameters and the interaction energies. Natural Bond Orbital analysis has been performed to study the effects of charge transfer and the behaviour of X–H bonds of the proton donor on interaction of the molecules. In the proper hydrogen bond, charge transfer takes place from lone pair electrons of the proton acceptor atom to the antibonding orbital of the X–H bond, which results in elongation. In the improper hydrogen bond, contraction of X–H bonds takes place due to the charge transfer to the remote parts of the donor molecule and as well as the competitive effect between intermolecular and intramolecular charge transfer.

Use of molecular analogs for the bases in DNA: Stability of molecular pairs in gas phase and aqueous media and possible role of hydrogen bonding

In a recent experimental study, it was reported that replacement of thymine in the adenine–thymine base pair of DNA by its molecular analogs which cannot form proper hydrogen bonds with adenine (A) does not cause disruption of DNA structure and synthesis. AM1 and ab initio molecular orbital calculations and electric field mapping were carried out in order to examine the possibility of pairing of A with each one of two analogs of thymine in the gas phase. Self-consistent reaction field calculations were also carried out on the individual molecules and their pairs using the polarized continuum model in order to examine their stability in aqueous media. Our results are broadly in agreement with the conclusions drawn in the above-mentioned experimental work. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 351–355, 1998