Role Of Hydrogen Bonding Interactions Research Articles

Chiral Oxazaborolidinium Ion (COBI)-Catalyzed Reaction of Aldimine with Tributyltin Cyanide: Mechanism and Origin of Stereoselectivity.

By conducting density functional theory (DFT) calculations, the detailed reaction mechanisms of aldimines with tributyltin cyanide under the catalytic influence of chiral oxazaborolidinium ion (COBI) have been uncovered. Three potential reaction pathways were examined, and two stereoselective routes were determined for the most energetically favorable mechanism. In the primary route, a proton is transferred from the COBI catalyst to the aldimine substrate, which is then followed by the C-C bond formation to produce the final product. Subsequently, NBO analyses of the stereoselectivity-determining transition states were conducted to identify the crucial role of hydrogen bond interactions in controlling stereoselectivity. These computed findings should prove invaluable in comprehending the detailed mechanisms and underlying origins of stereoselectivity for COBI-mediated reactions of this type.

Design, synthesis and apoptosis inducing activity of nonsteroidal flavone-methanesulfonate derivatives on MCF-7 cell line as potential sulfatase inhibitor

In recent years, focusing on new potent anticancer agents with selective activity is one of the greatest challenges in cancer therapy. Breast cancer is the most common cancer and the main cause of cancer deaths in women. The sulfatase enzyme plays an important role in converting the sulfated steroids into non-sulfate steroid hormones, which increases the growth and development of many hormone-dependent cancers, such as breast cancer. In this regard, structure-based optimization was conducted to design novel flavone-sulfonates pharmacophore as a new steroid sulfatase inhibitor. In the present work, the conventional methods for the synthesis of 4-oxo-2-phenyl-4H-chromen-7-yl methanesulfonate derivatives were reported. Their cytotoxicity was evaluated with MTT assay against a breast cancer cell line (MCF-7). The apoptosis inducing activity of the most cytotoxic compound 3c with an IC50 value of 0.615 µM was evaluated in comparison to docetaxel in the presence of estradiol which is a crucial growth factor to survive the cancerous cells. The results of double staining Annexin V-FITC/PI analysis suggested that the cytotoxic activity of this compound 3c in MCF-7 cells occurs via apoptosis. Molecular docking studies were conducted to clarify the inhibition mode of the most promising compound (3c) over the sulfatase (1P49) binding site. The analysis revealed the role of hydrogen bond interaction with Gly181 and hydrophobic interactions through the 1P49 active site in the ligand-receptor complex as significant descriptors to rationalize the potential inhibition activity.

Acidity enhancement of α‐carbon of beta diketones via hydroxyl substituents: A density functional theory study

AbstractDensity functional theory method and B3LYP/6‐311++G(d,p) level of theory were used to determine the acidity of α‐carbon in the hydroxyl derivatives of beta diketones in the gas phase. An investigation of acidity strength in the gas phase indicates that α‐carbon of hydroxyl derivatives of beta diketones become stronger acids than the α‐carbon of beta diketone itself as their conjugate bases gain more stability via both enolate and hydrogen bond formation. Natural bond orbital and quantum theory of atoms in molecules analyses also confirm the role of hydrogen bond interactions on increasing the acidity of α‐carbon of hydroxyl derivatives of beta diketones.

QSPR models for predicting the adsorption capacity for microplastics of polyethylene, polypropylene and polystyrene

Microplastics have become an emerging concerned global environmental pollution problem. Their strong adsorption towards the coexisting organic pollutants can cause additional environmental risks. Therefore, the adsorption capacity and mechanisms are necessary information for the comprehensive environmental assessments of both microplastics and organic pollutants. To overcome the lack of adsorption information, five quantitative structure–property relationship (QSPR) models were developed for predicting the microplastic/water partition coefficients (log Kd) of organics between polyethylene/seawater, polyethylene/freshwater, polyethylene/pure water, polypropylene/seawater, and polystyrene/seawater. All the QSPR models show good fitting ability (R2 = 0.811–0.939), predictive ability (Q2ext = 0.835–0.910, RMSEext = 0.369–0.752), and robustness (Qcv2 = 0.882–0.957). They can be used to predict the Kd values of organic pollutants (such as polychlorinated biphenyls, chlorobenzene, polycyclic aromatic hydrocarbons, antibiotics perfluorinated compounds, etc.) under different pH conditions. The hydrophobic interaction has been indicated as an important mechanism for the adsorption of organic pollutants to microplastics. In sea waters, the role of hydrogen bond interaction in adsorption is considerable. For polystyrene, π–π interaction contributes to the partitioning. The developed models can be used to quickly estimate the adsorption capacity of organic pollutants on microplastics in different types of water, providing necessary information for ecological risk studies of microplastics.

Insights into the effect of molecular crowding on the structure, interactions and functions of siRNA–PAZ complex through molecular dynamics studies

siRNA molecules are well known to be involved in the post-transcriptional regulation of gene expression and play a key role in understanding the intricacies of eukaryotic gene regulation. While it is widely known that 3′ end of siRNA binds to the PAZ domain of Argonaute proteins, it remains unclear whether the molecular crowding facilitates or hinders the overall siRNA-protein interactions during RNA interference. The biological interaction networks controlling the cellular functions of any biological cell may behave very differently in crowded environment as compared to the dilute conditions. Therefore, it is of interest to study the siRNA–protein interactions under more physiologically relevant conditions. In our previous work, we studied the role of hydrogen bond interactions and water network interactions towards the structural integrity of siRNA–PAZ complex. We also described the motions relevant for the functioning of the complex and analyzed the biphasic interaction of the 3′ end of siRNA within the PAZ domain under aqueous condition. In the present work, we studied the dynamics of siRNA–PAZ complex in the presence of water-soluble crowding agent. We observed significant changes in interactions and dynamics of siRNA–PAZ complex in the presence of crowder. The conserved H-bond interactions were destabilized by ≈12%, while interfacial water networks were stabilized in the presence of crowder. The analysis of siRNA–PAZ dynamics revealed the stabilizing role of ARG52, ARG172, LYS53 and LYS173 in siRNA–PAZ complex. Interestingly, despite increase in flexibility as measured by RMSD, crowding stabilized top modes.Communicated by Ramaswamy H. Sarma

Role of hydrogen bond interactions in water–polyol medium in the thickening behavior of cornstarch suspensions

Rheological properties of suspensions are influenced by changes in the particle’s or suspending medium’s traits. Due to the ability of water and cornstarch to develop strong hydrogen bonds with each other and with hydroxyl groups of other liquids, it is promising to modify the suspending media with polyols to analyze the change in the Newtonian behavior of the suspensions. Cornstarch–water suspensions were prepared by adding different polyols viz.., glycerine, ethylene glycol (EG), and polyethylene glycol (PEG) to the suspending liquid (water) at various concentrations. The presence of possible chemical interaction due to the hydroxyl groups within the water–polyol systems was confirmed by Fourier transfer infrared spectroscopy (FTIR). The rheological parameters of pure cornstarch–water suspension were compared with that of water–polyol-based shear thickening fluids (STFs). The thickening behavior enhanced by three orders of magnitude with increasing glycerine and EG content for a constant particle concentration. However, the presence of PEG in the suspension resulted in a shear thinning phenomenon with a high yield stress unlike the other polyols. Thus, the presence of O–H interactions in the suspending liquid was presumed to control the flow phenomenon of these suspensions. A possible mechanism based on interactions has been proposed for the non-Newtonian flow in each suspension. The current work is one of a kind in demonstrating the role of hydrogen interactions within suspending medium on the thickening behavior of the cornstarch–water suspensions.

The role of hydrogen bond interaction on molecular orientation of alkanolamines through temperature and pressure variation: A mixed molecular dynamics and quantum mechanics study

The role of hydrogen bond interaction on the structural orientation of pure alkanolamines, monoethanolamine (MEA), diethanolamine (DEA), and methyl diethanolamine (MDEA), was under consideration by computer simulation, molecular dynamics simulation as well as density functional theory. Molecular dynamics simulations were carried out at different pressures and temperatures to discover structural stability. A comprehensive force field validation was performed to obtain accurate density. It was also observed that independent of pressure and temperature, MEA molecules prefer head-tail parallel orientation, DEA molecules show both vertical and parallel orientation, and MDEA molecules favor parallel arrangement in liquid state. The probability of hydrogen bond as a substantial intermolecular interaction was also investigated and substantial sites were evaluated. Intermolecular and intramolecular energy, hydrogen bond strength, and transport properties, as well as cluster formation, were investigated to offer an irrefutable proof on structural orientation. Ab initio computation by analyzing frequency, stabilization energy, and electron location function confirmed similar orientation, proposed by molecular dynamics simulation.

The emerging role of hydrogen bond interactions in polyglutamine structure, stability and association

Polyglutamine regions in proteins have been associated with protein aggregation and the development of serious neurodegenerative diseases. Using a bottom-up approach, the molecular properties of glutamine and single polyglutamine chains can be understood, providing a promising route to uncover the mechanisms of polyglutamine-related protein aggregation. In this article we highlight recent advances in the study of both glutamine and polyglutamine using novel biophysical tools. A recurring theme in these studies is the importance of hydrogen bonding in driving glutamine association.

Unexpected Configuration in Stereoselectively Synthesis of Some Novel (1Z)-1-(morpholin-1-yl)-N2-Arylamidrazones

The nucleophilic substitution reaction of hydrazono-N-(aryl)-propanehydrazonyl chlorides 7 with piperidine or morpholine, under the same reaction conditions, resulted in the formation of 1-(piperdin-1-yl / morpholine-1-yl)-N2- arylamidrazones 8a-k, respectively. The X-ray diffraction of piperidin-1-yl-N2-arylamidrazone (8b) confirmed its 1Econfiguration in agreement with the previously reported, whereas X-ray showed the unexpected 1Z-configuration of their analogs, morpholin-1-yl-N2-arylamidrazone (8j). This study established the role of hydrogen bond interaction in the stereochemistry of this class of amidrazones. Keywords: Amidrazones, hydrogen bond interaction, stereoselectively, x-ray diffraction analyses, nucleoside, hydrolase, cholinesterase, glycosidase, molecules, stereochemistry

Plasticizing while toughening and reinforcing poly(propylene carbonate) using low molecular weight urethane: Role of hydrogen-bonding interaction

Poly(propylene carbonate) (PPC), a biodegradable plastic produced by alternating copolymerization of carbon dioxide and propylene oxide, is amorphous at glass-transition temperature of ∼35 °C; therefore, it becomes brittle at temperatures <20 °C. This article reports on the synthesis of low molecular weight urethanes, such as 1,6-bis(hydroxyethyl urethane)hexane (BEU), 1,6-bis(hydroxyisopropyl urethane)hexane (BPU), and 1,6-bis(methyl urethane)hexane (HDU) bearing rich NH and CO bonds, by a non-isocyannate method and their use as plasticizers for PPC. The hydrogen-bonding interaction between BPU and PPC was found to be significantly more effective as compared with BEU and HDU, and the highest hydrogen-bonding interaction fraction reached 5.2% in a PPC/BPU blend with 15 wt% BPU loading. Solubility parameters calculated from Hoy’s method, in combination with differential scanning calorimetric analysis, indicated that HDU and BPU were miscible with PPC at a molecular scale, while BEU was immiscible with PPC. Usually, plasticizing is generally accompanied by sacrificing of tensile strength; however, it was encouraging to observe that the elongation at break for PPC/HDU blend with 10 wt% of HDU loading reached 727% – an increase 53 times that of pure PPC – while the tensile strength was maintained at 30 MPa, which was comparable with that of linear low-density polyethylene. The hydrogen-bonding interaction generated a remarkable improvement in the mechanical performance of PPC; it not only confined the migration of the plasticizer to the surface and thus ensured stability of the blending material over time, but it also maintained the mechanical strength of the plasticized PPC.

The role of hydrogen-bonding interaction in poly(vinyl alcohol)/poly(acrylic acid) blending solutions and their films

The aim of this work is to investigate the hydrogen-bonding interaction in poly(vinyl alcohol) (PVA)/poly(acrylic acid) (PAA) blending system and its influence on rheological properties in solution and the physical properties in solid state. Introducing PAA into PVA solutions resulted in a thickening behavior of blend solutions. The viscosity of the solutions increased with PAA content increasing, and a maximum viscosity could be obtained when the ratio of PVA/PAA was 70/30. The intermolecular hydrogen-bonding and miscibility between PVA and PAA in solid state were investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and mechanical measurements. The results displayed the great influence of introducing PAA on the properties of blending films. The tensile strength increased from 89.31 MPa to 119.8 MPa and Young’s modulus improved by over 300% with increasing PAA concentration compared with those of pure PVA films. By systematically studying the rheological behaviors of solutions and the physical properties of films, the influence of hydrogen-bonding in solutions and solid states were discussed.

The role of hydrogen-bonding interactions in acidic sugar reaction pathways

Previously, theoretical multiple sugar (β- d-xylose and β- d-glucose) reaction pathways were discovered that depended on the initial protonation site on the sugar molecules using Car–Parrinello-based molecular dynamics (CPMD) simulations [Qian, X. H.; Nimlos, M. R.; Davis, M.; Johnson, D. K.; Himmel, M. E. Carbohydr. Res. 2005, 340, 2319–2327]. In addition, simulation results showed that water molecules could participate in the sugar reactions, thus altering the reaction pathways. In the present study, the temperature and water density effects on the sugar degradation pathways were investigated with CPMD. We found that changes in both temperature and water density could profoundly affect the mechanisms and pathways. We attributed these effects to both the strength of hydrogen bonding and proton affinity of water.

The Richest Collection of Tautomeric Polymorphs: The Case of 2‐Thiobarbituric Acid

Five new polymorphs and one hydrated form of 2-thiobarbituric acid have been isolated and characterised by solid-state methods. In both the crystalline form II and in the hydrate form, the 2-thiobarbituric molecules are present in the enol form, whereas only the keto isomer is present in crystalline forms I (reported in 1967 by Calas and Martinex), III, V and VI. In form IV, on the other hand, a 50:50 ordered mixture of enol/keto molecules is present. All new forms have been characterised by single-crystal X-ray diffraction, 1D and 2D ((1)H, (13)C, and (15)N) solid-state NMR spectroscopy, Raman spectroscopy and X-ray powder diffraction at variable temperature. It has been possible to induce keto-enol conversion between the forms by mechanical methods. The role of hydrogen-bond interactions in determining the relative stability of the polymorphs and as a driving force in the conversions has been ascertained. To the best of the authors' knowledge, the 2-thiobarbituric family of crystal forms represents the richest collection of examples of tautomeric polymorphism so far reported in the literature.

Influence of hydrogen bonding upon the TiO 2 photooxidation of isopropanol and acetone in aqueous solution

This study investigates the aqueous photocatalytic degradation of small polar organic compounds (SPOCs) that bear hydrogen-bonding capabilities but do not readily adsorb to the TiO 2 catalyst. The effect of pH on the TiO 2 surface hydroxyl speciation and surface acid/base equilibria was used to elucidate the possible role of hydrogen-bonding interactions in the degradation of acetone and isopropanol in aqueous TiO 2 photocatalytic systems. The kinetic parameters describing the decomposition of these two model compounds were obtained by gas chromatographic analysis of their photoreaction systems and interpreted on the grounds of the Brönsted acid/base properties of the TiO 2 surface speciation and solute hydrogen-bonding numerical scales. The results showed that the fastest initial degradation rates of acetone and isopropanol occurred in a pH range where the optimal conditions for adsorption through hydrogen bonding to the TiO 2 surface and optimum concentration of hydroxyl radicals (OH ) coincide. The fastest degradation constants were observed at pH 6.04 and 8.61 for acetone and isopropanol, respectively. The hypothesis of hydrogen bonding to surface hydroxyl groups presented in this study challenges the common assumption that these model compounds do not adsorb to surface sites, and that their oxidative pathways of degradation only occur via homogeneous-phase reaction with free OH radicals.

Direct, Facile Aldehyde and Ketone α-Selenenylation Reactions Promoted byl-Prolinamide and Pyrrolidine Sulfonamide Organocatalysts

[reaction: see text] A new catalytic method for direct alpha-selenenylation reactions of aldehydes and ketones has been developed. The results of exploratory studies have demonstrated that L-prolinamide is an effective catalyst for alpha-selenenylation reactions of aldehydes, whereas pyrrolidine trifluoromethanesulfonamide efficiently promotes reactions of ketones. Under optimized reaction conditions, using N-(phenylseleno)phthalimide as the selenenylation reagent in CH2Cl2 in the presence of L-prolinamide (2 mol %) or pyrrolidine trifluoromethanesulfonamide (10 mol %), a variety of aldehydes and ketones undergo this process to generate alpha-selenenylation products in high yields. Mechanistic insight into the L-proline and L-prolinamide catalyzed alpha-selenenylation reactions of aldehydes with N-(phenylseleno)phthalimide has come from theoretical studies employing ab initio methods and density functional theory. The results reveal that (1) the rate-limiting step of the process involves attack of the enamine intermediate at selenium in N-(phenylseleno)phthalimide and (2) the energy of the transition state for the reaction catalyzed by prolinamide is lower than that promoted by proline. This result is consistent with experimental observations. The role of hydrogen bond interactions in stabilizing the transition states for this process is also discussed.

Supramolecular hydrogen-bonded liquid crystals

The role of hydrogen-bonding interactions in the formation and/or stabilization of liquid crystalline phases has been recognized in recent years and significant work has been conducted. Following the first and well-established examples of liquid crystal formation through the dimerization of aromatic carboxylic acids, several classes of compounds have been prepared by the interaction of complementary molecules, the liquid crystalline behaviour of which is crucially dependent on the structure of the resulting supramolecular systems. In this review the main classes of liquid crystals prepared through hydrogen-bonding interactions are presented, with the aim of establishing, in the first place, the diversity of organic compounds that can be used as building elements in the process of liquid crystal formation. Rigid-rod anisotropic or amphiphilic-type molecules, appropriately functionalized with recognizable moieties, interact in the melt or in solution and lead to the formation of supramolecular complexes that may exhibit thermotropic liquid crystalline character. Depending on the nature, number and position of the groups able to form hydrogen bonds, a diversity of supramolecular structures, both dimeric and polymeric, have been obtained, affording in turn various liquid crystalline phases. The structure and stability of these hydrogen-bonded supramolecular complexes and their relation to the observed liquid crystalline phases are the main topics of this review.

The role of hydrogen-bonding interactions in stabilising trigonal planar copper(I) in Cu(BF4)–pyridazine–nitrile systems †

Regardless of conditions, reaction of [Cu(NCMe)4][BF4] with pyridazine (pydz) or 3-methylpyridazine (Mepydz) in MeCN or with pydz in PhCN invariably gave tris-bridged dinuclear cations, [{Cu(NCR)}2(µ-diimine)3]2+. Structural analysis, by single crystal X-ray diffraction, of complexes containing [{Cu(NCMe)}2(µ-pydz)3]2+, [{Cu(NCMe)}2(µ-Mepydz)3]2+ and [{Cu(NCPh)}2(µ-pydz)3]2+ confirmed the presence of two tetrahedral copper(I) centres bridged by three pyridazine molecules and terminally co-ordinated by nitriles. This chemistry contrasts with that for 2-cyanoguanidine (cnge), a planar nitrile with considerable hydrogen-bonding potential, which leads to both bis- and tris-bridged dinuclear cations, [{Cu(cnge)}2(µ-pydz)2]2+ and [{Cu(cnge)}2(µ-pydz)3]2+. Whereas the tris-bridged cation is based on four-co-ordinate tetrahedral copper(I), the bis-bridged cation contains three-co-ordinate trigonal planar copper(I). The unique ability of cnge to stabilise co-ordinatively unsaturated copper(I) in the solid state with pydz bridged dications is attributed to the formation of an extended 2-D sheet architecture based on hydrogen-bonding intermolecular interactions. This type of molecular construction, which is common to all copper(I)–cnge three-co-ordinate structures, suggests that the three-co-ordinate geometry is not an intrinsic property of copper(I) systems but a result of the efficient packing of parallel two-dimensional sheets. Treatment of [{Cu(NCMe)}2(µ-diimine)3]2+ with CO led to [{Cu(CO)}2(µ-diimine)3]2+; reaction of [{Cu(cnge)}2(µ-diimine)2]2+ with CO or PPh3 gave [{Cu(cnge)(L)}2(µ-diimine)2]2+ (L = CO or PPh3). Recrystallisation of [{Cu(cnge)(PPh3)}2(µ-diimine)2]2+ yielded a variety of crystalline products including [Cu(pydz)2(PPh3)2][BF4] and [{Cu(PPh3)}2(µ-pydz)3][PF6]2. Structural studies confirmed the former to be a mononuclear cation with four monodentate (two pydz and two Ph3P) ligands and the latter to be a tris(µ-pydz) dinuclear cation with terminal Ph3P molecules. The copper(I) co-ordination geometries in both complexes are tetrahedral, the three-co-ordinate copper(I) geometry of [{Cu(cnge)}2(µ-diimine)2]2+ being lost on treatment with Ph3P. In the absence of structural data, [{Cu(CO)}2(µ-diimine)3]2+ and [{Cu(cnge)(CO)}2(µ-diimine)2]2+ are considered to comprise tris- and bis-(µ-diimine) dinuclear cations based on tetrahedral copper(I) with terminal CO.

Miscibility and interactions in a mixture of poly(ethylene oxide) and an aromatic poly(ether amide)

Results concerning a mixture of an experimental aromatic poly(ether amide) and poly(ethylene oxide) are reported. The presence of other groups in both polymers, and the possibility of a great number of intermolecular hydrogen bonds, give rise to polymer-polymer interactions that result in partial miscibility, as it has been demonstrated by FT-i.r., differential scanning calorimetry and optical microscopy. These results are qualitatively consistent with theoretical phase diagrams calculated from an association model which emphasizes the role of hydrogen bond interactions in this type of blend.

Thermodynamics of Inter- and Intramolecular Hydrogen Bonding in (Diphosphine)platinum(II) Diolate Complexes and Its Role in Carbohydrate Complexation Regioselectivity.

Thermodynamic data are reported for intermolecular hydrogen-bonding association of 1 and 2 equiv of phenol with [1,3-bis(diphenylphosphino)propane](phenylethane-1,2-diolato)platinum(II) ((dppp)Pt(Ped)) in dichloromethane solution: = -7.0 +/- 0.1 kcal/mol, = -7.7 +/- 0.4 kcal/mol, = -11.3 +/- 0.4 eu, and = -17.8 +/- 1.2 eu. For comparison, the thermodynamics for hydrogen bonding of phenol to triphenylphosphine oxide in dichloromethane were also determined: DeltaH degrees = -5.1 +/- 0.3 kcal/mol; DeltaS degrees = -8.8 +/- 1.0 eu. Competitive coordination exchange reactions have been used to determine the apparent intramolecular hydrogen bond strengths in (dppp)Pt(1,2-O,O'-glycerolate) and (dppp)Pt(1,2-O,O'-butane-1,2,4-triolate) in both dichloromethane (DeltaG(313) = -2.05 +/- 0.05 and -2.52 +/- 0.06 kcal/mol, respectively) and pyridine (DeltaG(313) = -0.62 +/- 0.03 and -0.82 +/- 0.03 kcal/mol, respectively). Based on these findings, the role of hydrogen-bonding interactions in determining the regioselectivities of complexation of carbohydrates to diphosphine Pt(II) is discussed.

Picosecond laser photolysis studies of hydrogen-atom transfer reaction via heteroexcimer state in pyrene-primary and pyrene-secondary aromatic amine systems: role of hydrogen-bonding interaction between amino group of donor and π electrons of acceptor in the heteroexcimer

Picosecond laser photolysis studies of hydrogen-atom transfer reaction via heteroexcimer state in pyrene-primary and pyrene-secondary aromatic amine systems: role of hydrogen-bonding interaction between amino group of donor and π electrons of acceptor in the heteroexcimer