Showing papers on "Hydrogen bond published in 2016"
TL;DR: A hydrogen bond assisted azine-linked covalent organic framework, COF-JLU3, was synthesized under solvothermal conditions, and can be the first COF as a fluorescent sensor for toxic metal ions, exhibiting high sensitivity and selectivity to Cu(2+).
283 citations
TL;DR: The pairwise interactions of the constituent components of the choline chloride-urea DES are examined and it is found that the covalency of doubly ionic H-bonds can be greater than, or comparable with, neutral and ionic examples.
Abstract: Deep eutectic solvents (DESs) are exemplars of systems with the ability to form neutral, ionic and doubly ionic H-bonds. Herein, the pairwise interactions of the constituent components of the choline chloride-urea DES are examined. Evidence is found for a tripodal CHCl doubly ionic H-bond motif. Moreover it is found that the covalency of doubly ionic H-bonds can be greater than, or comparable with, neutral and ionic examples. In contrast to many traditional solvents, an "alphabet soup" of many different types of H-bond (OHO[double bond, length as m-dash]C, NHO[double bond, length as m-dash]C, OHCl, NHCl, OHNH, CHCl, CHO[double bond, length as m-dash]C, NHOH and NHNH) can form. These H-bonds exhibit substantial flexibility in terms of number and strength. It is anticipated that H-bonding will have a significant impact on the entropy of the system and thus could play an important role in the formation of the eutectic. The 2 : 1 urea : choline-chloride eutectic point of this DES is often associated with the formation of a [Cl(urea)2](-) complexed anion. However, urea is found to form a H-bonded urea[choline](+) complexed cation that is energetically competitive with [Cl(urea)2](-). The negative charge on [Cl(urea)2](-) is found to remain localised on the chloride, moreover, the urea[choline](+) complexed cation forms the strongest H-bond studied here. Thus, there is potential to consider a urea[choline](+)·urea[Cl](-) interaction.
253 citations
TL;DR: Measurements of splitting patterns in rotational transitions of the water hexamer prism are reported, and quantum simulations are used to show that they result from geared and antigeared rotations of a pair of water molecules.
Abstract: The nature of the intermolecular forces between water molecules is the same in small hydrogen-bonded clusters as in the bulk. The rotational spectra of the clusters therefore give insight into the intermolecular forces present in liquid water and ice. The water hexamer is the smallest water cluster to support low-energy structures with branched three-dimensional hydrogen-bond networks, rather than cyclic two-dimensional topologies. Here we report measurements of splitting patterns in rotational transitions of the water hexamer prism, and we used quantum simulations to show that they result from geared and antigeared rotations of a pair of water molecules. Unlike previously reported tunneling motions in water clusters, the geared motion involves the concerted breaking of two hydrogen bonds. Similar types of motion may be feasible in interfacial and confined water.
245 citations
TL;DR: It is shown that an analogous quantum symmetrization occurs in the recently discovered sulfur hydride superconductor with a superconducting transition temperature Tc of 203 kelvin at 155 gigapascals—the highest Tc reported for any super Conductor so far.
Abstract: The quantum nature of the proton can crucially affect the structural and physical properties of hydrogen compounds. For example, in the high-pressure phases of H2O, quantum proton fluctuations lead to symmetrization of the hydrogen bond and reduce the boundary between asymmetric and symmetric structures in the phase diagram by 30 gigapascals (ref. 3). Here we show that an analogous quantum symmetrization occurs in the recently discovered sulfur hydride superconductor with a superconducting transition temperature Tc of 203 kelvin at 155 gigapascals--the highest Tc reported for any superconductor so far. Superconductivity occurs via the formation of a compound with chemical formula H3S (sulfur trihydride) with sulfur atoms arranged on a body-centred cubic lattice. If the hydrogen atoms are treated as classical particles, then for pressures greater than about 175 gigapascals they are predicted to sit exactly halfway between two sulfur atoms in a structure with Im3m symmetry. At lower pressures, the hydrogen atoms move to an off-centre position, forming a short H-S covalent bond and a longer H···S hydrogen bond in a structure with R3m symmetry. X-ray diffraction experiments confirm the H3S stoichiometry and the sulfur lattice sites, but were unable to discriminate between the two phases. Ab initio density-functional-theory calculations show that quantum nuclear motion lowers the symmetrization pressure by 72 gigapascals for H3S and by 60 gigapascals for D3S. Consequently, we predict that the Im3m phase dominates the pressure range within which the high Tc was measured. The observed pressure dependence of Tc is accurately reproduced in our calculations for the phase, but not for the R3m phase. Therefore, the quantum nature of the proton fundamentally changes the superconducting phase diagram of H3S.
217 citations
TL;DR: The results point to the existence of a structure-specific fluorophore that does not require the presence of aromatic residues or multiple bond conjugation that characterize conventional fluorescent systems and may have a wide range of implications in biological systems and in the design of self-assembled functional materials.
Abstract: Protein structures which form fibrils have recently been shown to absorb light at energies in the near UV range and to exhibit a structure-specific fluorescence in the visible range even in the absence of aromatic amino acids. However, the molecular origin of this phenomenon has so far remained elusive. Here, we combine ab initio molecular dynamics simulations and fluorescence spectroscopy to demonstrate that these intrinsically fluorescent protein fibrils are permissive to proton transfer across hydrogen bonds which can lower electron excitation energies and thereby decrease the likelihood of energy dissipation associated with conventional hydrogen bonds. The importance of proton transfer on the intrinsic fluorescence observed in protein fibrils is signified by large reductions in the fluorescence intensity upon either fully protonating, or deprotonating, the fibrils at pH = 0 or 14, respectively. Thus, our results point to the existence of a structure-specific fluorophore that does not require the presence of aromatic residues or multiple bond conjugation that characterize conventional fluorescent systems. The phenomenon may have a wide range of implications in biological systems and in the design of self-assembled functional materials.
172 citations
TL;DR: A general approach to the catalytic activation of C–C bonds in simple cyclopentanones and some cyclohexanones that can substantially enhance the efficiency of the enantioselective synthesis of some natural products of terpenoids.
Abstract: In the chemical industry, molecules of interest are based primarily on carbon skeletons. When synthesizing such molecules, the activation of carbon-carbon single bonds (C-C bonds) in simple substrates is strategically important: it offers a way of disconnecting such inert bonds, forming more active linkages (for example, between carbon and a transition metal) and eventually producing more versatile scaffolds. The challenge in achieving such activation is the kinetic inertness of C-C bonds and the relative weakness of newly formed carbon-metal bonds. The most common tactic starts with a three- or four-membered carbon-ring system, in which strain release provides a crucial thermodynamic driving force. However, broadly useful methods that are based on catalytic activation of unstrained C-C bonds have proven elusive, because the cleavage process is much less energetically favourable. Here we report a general approach to the catalytic activation of C-C bonds in simple cyclopentanones and some cyclohexanones. The key to our success is the combination of a rhodium pre-catalyst, an N-heterocyclic carbene ligand and an amino-pyridine co-catalyst. When an aryl group is present in the C3 position of cyclopentanone, the less strained C-C bond can be activated; this is followed by activation of a carbon-hydrogen bond in the aryl group, leading to efficient synthesis of functionalized α-tetralones-a common structural motif and versatile building block in organic synthesis. Furthermore, this method can substantially enhance the efficiency of the enantioselective synthesis of some natural products of terpenoids. Density functional theory calculations reveal a mechanism involving an intriguing rhodium-bridged bicyclic intermediate.
171 citations
TL;DR: Up-to-date experimental and computational studies of the structural, energetic, and spectroscopic parameters and natures of dihydrogen-bonded complexes of the form M-H···H-X are collated, as such species are now known for a wide variety of hydrido compounds.
Abstract: The dihydrogen bond—an interaction between a transition-metal or main-group hydride (M—H) and a protic hydrogen moiety (H—X)—is arguably the most intriguing type of hydrogen bond. It was discovered in the mid-1990s and has been intensively explored since then. Herein, we collate up-to-date experimental and computational studies of the structural, energetic, and spectroscopic parameters and natures of dihydrogen-bonded complexes of the form M—H···H—X, as such species are now known for a wide variety of hydrido compounds. Being a weak interaction, dihydrogen bonding entails the lengthening of the participating bonds as well as their polarization (repolarization) as a result of electron density redistribution. Thus, the formation of a dihydrogen bond allows for the activation of both the MH and XH bonds in one step, facilitating proton transfer and preparing these bonds for further transformations. The implications of dihydrogen bonding in different stoichiometric and catalytic reactions, such as hydrogen ex...
166 citations
TL;DR: In this paper, a combination of experimental and computational studies allows further understanding of active organocatalytic system with Boronic acids together with onium salts for the conversion of CO2 with epoxides into various cyclic carbonates in H2O under mild conditions.
Abstract: Boronic acids together with onium salts provide highly efficient organocatalysts for the conversion of CO2 with epoxides into various cyclic carbonates in H2O under mild conditions. The combination of experimental and computational studies allows further understanding of this active organocatalytic system.
144 citations
TL;DR: In this article, the interactions between a Cu-based metal-organic framework (MOF), Cu-BTC, and an ionic liquid (IL), 1-ethyl-3methylimidazolium ethyl sulfate, were studied by employing density functional theory (DFT) calculations and vibrational spectroscopy.
Abstract: The interactions between a Cu-based metal–organic framework (MOF), Cu-BTC, and an ionic liquid (IL), 1-ethyl-3-methylimidazolium ethyl sulfate, were studied by employing density functional theory (DFT) calculations and vibrational spectroscopy. The Fourier transform infrared (FTIR) and Raman spectra show that the confinement of the IL in the MOF has significant impact on the structure of the MOF as well as on the IL. Raman spectra and DFT calculations reveal a perturbation of the symmetry of the MOF structure due to the interaction of the IL anion with the Cu ions. FTIR and Raman spectra show that the molecular interactions in turn influence the structure of the ion pair. Inside the MOF, two different types of structure of IL ion pairs are formed. One ion-pair structure exhibits enhanced interionic interactions by strengthening the hydrogen bonding between cation and anion, whereas the other structure corresponds to weaker interactions between the IL cation and anion. Moreover, it is shown that the IL imi...
142 citations
TL;DR: 1 is one of the most active catalysts for CO2 hydrogenations under additive‐free conditions reported to date, and the thermodynamic stabilization of the reaction product by the reaction medium, through hydrogen bonds between formic acid and clusters of solvent or water, were rationalized by DFT calculations.
Abstract: The novel [Ru(Acriphos)(PPh3)(Cl)(PhCO2)] [1; Acriphos=4,5-bis(diphenylphosphino)acridine] is an excellent precatalyst for the hydrogenation of CO2 to give formic acid in dimethyl sulfoxide (DMSO) and DMSO/H2O without the need for amine bases as co-reagents. Turnover numbers (TONs) of up to 4200 and turnover frequencies (TOFs) of up to 260 h−1 were achieved, thus rendering 1 one of the most active catalysts for CO2 hydrogenations under additive-free conditions reported to date. The thermodynamic stabilization of the reaction product by the reaction medium, through hydrogen bonds between formic acid and clusters of solvent or water, were rationalized by DFT calculations. The relatively low final concentration of formic acid obtained experimentally under catalytic conditions (0.33 mol L−1) was shown to be limited by product-dependent catalyst inhibition rather than thermodynamic limits, and could be overcome by addition of small amounts of acetate buffer, thus leading to a maximum concentration of free formic acid of 1.27 mol L−1, which corresponds to optimized values of TON=16×103 and TOFavg≈103 h−1.
139 citations
TL;DR: The quantitative assessment of nuclear quantum effects on the strength of a single hydrogen bond formed at a water-salt interface is reported, using tip-enhanced inelastic electron tunneling spectroscopy based on a scanning tunneling microscope.
Abstract: We report the quantitative assessment of nuclear quantum effects on the strength of a single hydrogen bond formed at a water-salt interface, using tip-enhanced inelastic electron tunneling spectroscopy based on a scanning tunneling microscope. The inelastic scattering cross section was resonantly enhanced by "gating" the frontier orbitals of water via a chlorine-terminated tip, so the hydrogen-bonding strength can be determined with high accuracy from the red shift in the oxygen-hydrogen stretching frequency of water. Isotopic substitution experiments combined with quantum simulations reveal that the anharmonic quantum fluctuations of hydrogen nuclei weaken the weak hydrogen bonds and strengthen the relatively strong ones. However, this trend can be completely reversed when a hydrogen bond is strongly coupled to the polar atomic sites of the surface.
TL;DR: It is shown that there exist two distinct types of the hydrogen-bonding interaction, naming α- and β-modes, in the tetragonal MAPbI3 on the basis of symmetry argument and density-functional theory calculations.
Abstract: In spite of the key role of hydrogen bonding in the structural stabilization of the prototypic hybrid halide perovskite, CH3NH3PbI3 (MAPbI3), little progress has been made in our in-depth understanding of the hydrogen-bonding interaction between the MA+-ion and the iodide ions in the PbI6-octahedron network. Herein, we show that there exist two distinct types of the hydrogen-bonding interaction, naming α- and β-modes, in the tetragonal MAPbI3 on the basis of symmetry argument and density-functional theory calculations. The computed Kohn-Sham (K-S) energy difference between these two interaction modes is 45.14 meV per MA-site with the α-interaction mode being responsible for the stable hydrogen-bonding network. The computed bandgap (Eg) is also affected by the hydrogen-bonding mode, with Eg of the α-interaction mode (1.73 eV) being significantly narrower than that of the β-interaction mode (2.03 eV). We have further estimated the individual bonding strength for the ten relevant hydrogen bonds having a bond critical point.
TL;DR: The first infrared study of water uptake at controlled vapor pressure in single walled carbon nanotubes with diameters ranging from 0.7 to 2.1 nm is reported, revealing a predominant contribution of loose H bonds even for fully hydrated states, irrespective of the nanotube size.
Abstract: A groundbreaking discovery in nanofluidics was the observation of the tremendously enhanced water permeability of carbon nanotubes, those iconic objects of nanosciences. The origin of this phenomenon is still a subject of controversy. One of the proposed explanations involves dramatic modifications of the H-bond network of nanoconfined water with respect to that of bulk water. Infrared spectroscopy is an ideal technique to follow modifications of this network through the inter- and intramolecular bonds of water molecules. Here we report the first infrared study of water uptake at controlled vapor pressure in single walled carbon nanotubes with diameters ranging from 0.7 to 2.1 nm. It reveals a predominant contribution of loose H bonds even for fully hydrated states, irrespective of the nanotube size. Our results show that, while the dominating loosely bond signature is attributed to a one-dimensional chain structure for small diameter nanotubes, this feature also results from a water layer with “free” OH ...
TL;DR: It is found that two molecular tubes with inwardly directed hydrogen-bond donors recognize highly hydrophilic solvent molecules in water with high selectivity.
Abstract: Selective recognition of neutral hydrophilic molecules in water is a challenge for supramolecular chemistry but commonplace in nature. By mimicking the binding pocket of natural receptors, endo-functionalized molecular tubes are proposed to meet this challenge. We found that two molecular tubes with inwardly directed hydrogen-bond donors recognize highly hydrophilic solvent molecules in water with high selectivity. In the complexes, hydrogen bonding occurs in the deep and hydrophobic cavity. The cooperative action between hydrogen bonding and hydrophobic effects accounts for the high affinity and selectivity. The molecular receptor is fluorescent and can detect concentrations of 1,4-dioxane—a known carcinogen and persistent environmental contaminant—in water at a limit of 119 ppb. The method simplifies the analytic procedure for this highly hydrophilic molecule.
TL;DR: In this article, the authors presented stimuli-responsive long aqueous cylindrical vesicles (nanotubes) synthesized directly using hydrogen bonding-driven polymerization-induced self-assembly (PISA) under visible-light-mediated RAFT aqueOUS dispersion polymerization at 25 °C.
Abstract: Analogous to cellulose, polymers whose monomer units possess both hydrogen donators and acceptors are generally insoluble in ambient water because of hydrogen bonding (HB). Herein we present stimuli-responsive long aqueous cylindrical vesicles (nanotubes) synthesized directly using HB-driven polymerization-induced self-assembly (PISA) under visible-light-mediated RAFT aqueous dispersion polymerization at 25 °C. The PISA undergoes an unprecedented film/silk-to-ribbon-to-vesicle transition and films/silks/ribbons formed at low DPs (∼25–85) of core-forming block in free-flowing aqueous solution. Pore-switchable nanotubes are synthesized by electrostatic repulsive perturbation of the HB association in anisotropic vesicular membranes via inserting minor ionized monomer units into the core-forming block. These nanotubes are synthesized at >35% solids, and tubular membranes are more sensitive than spherical counterparts in response to aqueous surroundings. This facile, robust, and general strategy paves a new av...
TL;DR: Direct spectroscopic evidence for hydrogen‐bonded clusters of like‐charged ions is reported for ionic liquids and DFT‐D3 calculations of the pure multiply charged clusters suggest that the attractive hydrogen bonds can compete with repulsive Coulomb forces.
Abstract: Direct spectroscopic evidence for hydrogen-bonded clusters of like-charged ions is reported for ionic liquids. The measured infrared O-H vibrational bands of the hydroxyethyl groups in the cations can be assigned to the dispersion-corrected DFT calculated frequencies of linear and cyclic clusters. Compensating the like-charge Coulomb repulsion, these cationic clusters can range up to cyclic tetramers resembling molecular clusters of water and alcohols. These ionic clusters are mainly present at low temperature and show strong cooperative effects in hydrogen bonding. DFT-D3 calculations of the pure multiply charged clusters suggest that the attractive hydrogen bonds can compete with repulsive Coulomb forces.
TL;DR: It is shown that two bisulfate anions can form such dimers, which stabilize each other with self-complementary hydrogen bonds, by encapsulation inside a pair of cyanostar macrocycles.
Abstract: Contrary to the simple expectations from Coulomb's law, Weinhold proposed that anions can stabilize each other as metastable dimers, yet experimental evidence for these species and their mutual stabilization is missing. We show that two bisulfate anions can form such dimers, which stabilize each other with self-complementary hydrogen bonds, by encapsulation inside a pair of cyanostar macrocycles. The resulting 2:2 complex of the bisulfate homodimer persists across all states of matter, including in solution. The bisulfate dimer's OH⋅⋅⋅O hydrogen bonding is seen in a 1H NMR peak at 13.75 ppm, which is consistent with borderline-strong hydrogen bonds.
TL;DR: New linear relationships were found between the calculated ρBCP and V parameters and the hydrogen bond energies obtained from empirical 1H NMR data that allow the comparison of the energies of different types of hydrogen bonds for various molecules and biological ensembles.
Abstract: The values of the downfield chemical shift of the bridge hydrogen atom were estimated for a series of compounds containing an intramolecular hydrogen bond O–H⋯O, O–H⋯N, O–H⋯Hal, N–H⋯O, N–H⋯N, C–H⋯O, C–H⋯N and C–H⋯Hal. Based on these values, the empirical estimation of the hydrogen bond energy was obtained by using known relationships. For the compounds containing an intramolecular hydrogen bond, the DFT B3LYP/6-311++G(d,p) method was used both for geometry optimization and for QTAIM calculations of the topological parameters (electron density ρBCP and the density of potential energy V in the critical point of the hydrogen bond). The calculated geometric and topological parameters of hydrogen bonds were also used to evaluate the energy of the hydrogen bond based on the equations from the literature. Comparison of calibrating energies from the 1H NMR data with the energies predicted by calculations showed that the most reliable are the linear dependence on the topological ρBCP and V parameters. However, the correct prediction of the hydrogen bond energy is determined by proper fitting of the linear regression coefficients. To obtain them, new linear relationships were found between the calculated ρBCP and V parameters and the hydrogen bond energies obtained from empirical 1H NMR data. These relationships allow the comparison of the energies of different types of hydrogen bonds for various molecules and biological ensembles.
TL;DR: The HB non-additivity in intramolecular and intermolecular interactions is examined by examining different structures of the water hexamer by relying on the interacting quantum atoms (IQA) topological energy partition, an approach that has been successfully used to study similar effects in smaller water clusters.
Abstract: The hydrogen bond (HB), arguably the most important non-covalent interaction in chemistry, is getting renewed attention particularly in materials engineering. We address herein HB non-additive features by examining different structures of the water hexamer (cage, prism, book, bag and ring). To that end, we rely on the interacting quantum atoms (IQA) topological energy partition, an approach that has been successfully used to study similar effects in smaller water clusters (see Chem. – Eur. J., 19, 14304). Our IQA interaction energies, , are used to classify the strength of HBs in terms of the single/double character of the donor and acceptor H2O molecules involved in the interaction. The strongest hydrogen bonds on this new scale entail double donors and acceptors that show larger values of than those observed in homodromic cycles, paradigms of cooperative effects. Importantly, this means that besides the traditional HB anticooperativity ascribed to double acceptors and donors, the occurrence of these species is also related to HB strengthening. Overall, we hope that the results of this research will lead to a further understanding of the HB non-additivity in intramolecular and intermolecular interactions.
TL;DR: In this article, complex χ(2) spectra of buried silica/isotopically diluted water (HOD-D2O) interfaces were measured using multiplex heterodyne-detected vibrational sum frequency generation spectroscopy to elucidate the hydrogen bond structure and up/down orientation of water at the SILICA/water interface at different pHs.
Abstract: Complex χ(2) spectra of buried silica/isotopically diluted water (HOD-D2O) interfaces were measured using multiplex heterodyne-detected vibrational sum frequency generation spectroscopy to elucidate the hydrogen bond structure and up/down orientation of water at the silica/water interface at different pHs. The data show that vibrational coupling (inter- and/or intramolecular coupling) plays a significant role in determining the χ(2) spectral feature of silica/H2O interfaces and indicate that the doublet feature in the H2O spectra does not represent two distinct water structures (i.e., the ice- and liquid-like structures) at the silica/water interface. The observed pH dependence of the imaginary χ(2) spectra is explained by (1) H-up oriented water donating a hydrogen bond to the oxygen atom of silanolate, which is accompanied by H-up water oriented by the electric field created by the negative charge of silanolate, (2) H-up oriented water which donates a hydrogen bond to the neutral silanol oxygen, and (3)...
TL;DR: A synthetic strategy that leads to the successful encapsulation of one or two water molecules inside fullerene C70 offers the opportunity to study the intrinsic properties of a single water molecule without any hydrogen bonding, as well as an isolated water dimer with a single hydrogen bond between the two molecules.
Abstract: Endohedral C70 fullerenes containing either one or two water molecules have now been prepared using a molecular-surgery approach. The structure of H2O@C70 was determined by single-crystal X-ray analysis, revealing the encapsulated water molecule to be in an off-centre position. In (H2O)2@C70, the two water molecules form a discrete dimer held together with a single hydrogen bond.
19 Mar 2016
TL;DR: In this paper, the authors performed spectroscopic analysis associated with the Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR- FTIR), Raman and 1HNMR spectroscopies to evaluate the effect of Near-Infrared (NIR) or IR-A, Short-Wavelength Infrared (SWIR), IR-B, Midwavelength IR (MWIR), Intermediate Infrared(IIR), IR -C, Long-WIR (LWIR), LongWIR, IR-C and Far-
Abstract: Human tissues are connective tissues which are surrounded the surface of the kidney. They consist of Osteoid (Collagen containing component of bone) fibers (67% Osteoid Type (I) and 33% Osteoid Type (III)), Lysyl Oxidase and LOXL1, LOXL2, LOXL3, LOXL4 fibers in Collagen formation, Hydrolyzed Collagen (a common form in which Collagen is sold as a supplement) fibers, Collagenase (the enzyme involved in Collagen breakdown and re–modelling) fibers and Sponge (cell types) fibers among elastic fibers (Figures 1–6). These tissues are used as graft, since Collagenous tissues begin to be denatured after excision; chemical physics methods like Infrared (IR) light are used to improve chemical physics properties. In the current editorial, the spectroscopic analysis was performed associated with the Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR– FTIR), Raman and 1HNMR spectroscopies to evaluate the effect of Near–Infrared (NIR) or IR–A, Short–Wavelength Infrared (SWIR) or IR–B, Mid–Wavelength Infrared (MWIR) or IR–C, Intermediate Infrared (IIR) or IR–C, Long–Wavelength Infrared (LWIR) or IR–C and Far–Infrared (FIR) lights on the tissues, respectively [1–9].
TL;DR: The role of the hydrogen bond in thermal transport across interfaces between hard and soft materials with different surface functionalizations around room temperature is studied using molecular dynamics simulations to provide important insight into the design of hard/soft materials or structures for a wide range of applications.
Abstract: The nature of the bond is a dominant factor in determining the thermal transport across interfaces. In this paper, we study the role of the hydrogen bond in thermal transport across interfaces between hard and soft materials with different surface functionalizations around room temperature using molecular dynamics simulations. Gold (Au) is studied as the hard material, and four different types of organic liquids with different polarizations, including hexane (C5H11CH3), hexanamine (C6H13NH2), hexanol (C6H13OH), and hexanoic acid (C5H11COOH), are used to represent the soft materials. To study the hydrogen bonds at the Au/organic liquid interface, three types of thiol-terminated self-assembled monolayer (SAM) molecules, including 1-hexanethiol [HS(CH2)5CH3], 6-mercapto-1-hexanol [HS(CH2)6OH], and 6-mercaptohexanoic acid [HS(CH2)5COOH], are used to functionalize the Au surface. These SAM molecules form hydrogen bonds with the studied organic liquids with varying strengths, which are found to significantly im...
TL;DR: This study attempted to sample the complete conformational space of CsA in chloroform and in water by molecular dynamics simulations in order to better understand its conformational behavior in these two environments and to rationalize the good membrane permeability ofCsA observed experimentally.
Abstract: The membrane permeability of cyclic peptides and peptidomimetics, which are generally larger and more complex than typical drug molecules, is likely strongly influenced by the conformational behavior of these compounds in polar and apolar environments. The size and complexity of peptides often limit their bioavailability, but there are known examples of peptide natural products such as cyclosporin A (CsA) that can cross cell membranes by passive diffusion. CsA is an undecapeptide with seven methylated backbone amides. Its crystal structure shows a “closed” twisted β-pleated sheet conformation with four intramolecular hydrogen bonds that is also observed in NMR measurements of CsA in chloroform. When binding to its target cyclophilin, on the other hand, CsA adopts an “open” conformation without intramolecular hydrogen bonds. In this study, we attempted to sample the complete conformational space of CsA in chloroform and in water by molecular dynamics simulations in order to better understand its conformati...
TL;DR: In this article, the authors investigated the effect of strong alkali on the texture of ovalbumin molecules and found that the secondary and tertiary structures of the gelatinous protein changed after treatment with strong acidity.
TL;DR: This study has clearly clarified the viewpoint that two kinds of tautomeric forms (K1, K2)originated from ESIPT process resemble the first electronic excited state (S1) and hydrogen bonding interaction strengthening has been proved by comparing the changes of infrared vibrational spectra and bond parameters of the hydrogen bonding groups in the ground state with that in the first excited state.
Abstract: The investigation of excited-state intramolecular proton transfer (ESIPT) has been carried out via the density functional theory (DFT) and the time-dependent density functional theory (TDDFT) method for natural product quercetin in dichloromethane (DCM) solvent. For distinguishing different types of intramolecular interaction, the reduced density gradient (RDG) function also has been used. In this study, we have clearly clarified the viewpoint that two kinds of tautomeric forms (K1, K2)originated from ESIPT processconsist inthe first electronic excited state (S1). The phenomenon of hydrogen bonding interaction strengtheninghas been proved by comparing the changes of infrared (IR) vibrational spectra and bond parameters of the hydrogen bonding groups in the ground state with that in the first excited state. The frontier molecular orbitals (MOs)provided visual electron density redistribution have further verified the hydrogen bond strengthening mechanism. It should be noted that the ESIPT process of the K2 form is easier to occur than that of the K1 form via observing the potential energy profiles. Furthermore, the RDG isosurfaces has indicated that hydrogen bonding interaction of the K2 form is stronger than that of the K1 formin the S1 state, which is also the reason why the ESIPT process of the K2 form is easier to occur.
TL;DR: In this paper, the performance of a series of deep eutectic solvents was evaluated for their selective extraction of toluene from n-heptane mixtures.
TL;DR: In this article, the interaction between β-lactoglobulin (β-lg) and water-soluble fraction of Persian gum (WPG) was studied under the effects of extrinsic parameters including pH, protein to polysaccharide mixing ratio (MR 8:1-1:4), total biopolymer concentration (TC 0.1-0.6% (w/w)), ion type (Na+ and Ca2+), ionic strength (0-100mM) and temperature (25, 40 and 55 ǫ).
TL;DR: In this paper, the adsorption energies and geometries as well as electronic properties of a single water molecule on external surfaces of sodium-montmorillonite (Na-MMT) including (001) basal and (010) edge surface were theoretically investigated based on periodic density functional theory (DFT) method.
TL;DR: Crystal structure analysis revealed the interplay between the hydrogen and halogen bonding motifs, also shedding light on the variables affecting their formation.
Abstract: A carefully designed strategy is presented for the construction of ternary cocrystals, based on the orthogonality of two supramolecular interaction modes: hydrogen bonding between crown ethers and thioureas and the halogen bonding between thioureas and perfluorohalocarbons. Tested on a set comprising two crown ethers, two thioureas and five halogen bond donors, the strategy resulted in a high, 75% success rate, with 15/20 component combinations yielding at least one cocrystal. Crystal structure analysis revealed the interplay between the hydrogen and halogen bonding motifs, also shedding light on the variables affecting their formation.