Network Of Intermolecular Hydrogen Bonds Research Articles

Cavitand-Based Polyphenols as Highly Reactive Organocatalysts for the Coupling of Carbon Dioxide and Oxiranes.

A variety of cavitand-based polyphenols was prepared from cheap and accessible aldehyde and resorcinol/pyrogallol reagents to give the respective resorcin[4]- or pyrogallol[4]arenes. The preorganization of the phenolic units allows intra- and intermolecular hydrogen bond (HB) networks that affect both the reactivity and stability of these HB-donor catalysts. Unexpectedly, we found that the resorcin[4]arenes show cooperative catalysis behavior compared to the parent resorcinol in the catalytic coupling of epoxides and CO2 with a significantly higher turnover. At elevated reaction temperatures, the resorcin[4]arene-based catalyst 3 d displays the best catalytic performance with very high turnover numbers and frequencies, combining increased reactivity and stability compared to pyrogallol, and an ample substrate scope. This type of polyphenol structure thus illustrates the importance of a new, highly competitive organocatalyst design to devise sustainable CO2 conversion processes.

The Temperature-Dependent Thermal Expansion of 2,6-Diamino-3,5-dinitropyrazine-1-oxide Effected by Hydrogen Bond Network Relaxation

The temperature-dependent thermal expansion of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) was investigated by using powder X-ray diffraction (PXRD) together with Rietveld refinement to estimate the dimension at a crystal lattice level. In the temperature range of 30–200°C, the coefficient of thermal expansion (CTE) of LLM-105 is temperature dependent, which is different from other explosives, such as hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 2,2′,4,4′,6,6′-hexanitrostilbene (HNS) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), with constant CTEs. The results of temperature-dependent infrared (IR) spectra indicated that the intermolecular hydrogen bond network relaxes with increasing temperature, which results in temperature-dependent thermal expansion. In this work, more accurate CTEs for LLM-105 crystals are obtained and the effects of the hydrogen bond network on the thermal expansion are further clarified. These results are beneficial to the design of materials with structural peculiarities and as-expected thermal expansion to satisfy different application requirements.

Synthesis and structures of a chiral phosphine–phosphoric acid ligand and its rhodium(I) complexes

The synthesis and characterization of a novel chiral phosphine–phosphoric acid ligand, (R)-3-diphenylphosphino-1,1′-binaphthyl-2,2′-diyl hydrogenphosphate (2) and its rhodium(I) complexes are described. The single-crystal X-ray diffraction analysis of 2 showed the intermolecular hydrogen-bonding network of the phosphoric acid moiety. The reactions of 2 with [RhCl(cod)]2 in the presence of KOtBu or with [Rh(acac)(CO)2] (acac=acetylacetonate) gave P,O-chelating rhodium(I) complexes [Rh(2–H+)(cod)] 3 or [Rh(2–H+)(CO)]24, respectively. Their molecular structures were determined by single-crystal X-ray diffraction.

The slow molecular mobility in amorphous captopril and captopril disulfide: A DSC and TSDC study

The slow molecular mobility in the amorphous pharmaceutical drug captopril is studied by differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). The general kinetic features of the secondary relaxations and of the main relaxation were determined by TSDC. The dynamic fragility of captopril is obtained by DSC and TSDC, and the values compared with that obtained by dielectric relaxation spectroscopy (DRS). The local motional modes of the fast secondary relaxation were found to be slightly aging sensitive, even at temperatures lower than 100° below Tg, which was ascribed to the intermolecular hydrogen bond network that is reported to exist in the amorphous solid state of captopril. Captopril disulfide, a metabolite product of captopril, was synthetized and characterized by DSC and TSDC. Compared to captopril, it behaves as a stronger glass forming liquid.

Docking studies and the crystal structure of two tetrazole derivatives: 5-(4-chlorophenyl)-1-{4-(methylsulfonyl)phenyl}-1H-tetrazole and 4-{5-(4-methoxyphenyl)-1H-tetrazol-1-yl}benzenesulfonamide

The structures of 5-(4-chlorophenyl)-1-{4-(methylsulfonyl)phenyl}-1H-tetrazole (3) and 4-{5-(4-methoxyphenyl)-1H-tetrazol-1-yl}benzenesulfonamide (5) have been determined by X-ray crystallography. Tetrazoles 3 and 5 crystallize in the monoclinic space groups Ia and P21/c, respectively. The cell dimensions of azole 3 are a = 11.0413 (5) Å, b = 11.8428 (5) Å, c = 12.2483 (5) Å3, β = 111.7129 (4)°, V = 1487.95 (11) Å3, and Z = 4. Its structure was refined to R1 = 0.0254 (for 3429 observed reflections [I ≥ 2σ(I)]) and wR2 = 0.0651 (for all 3300 unique reflections). The cell dimensions of azole 5 are a = 17.112 (3) Å, b = 6.5904 (10) Å, c = 12.935 (2) Å3, β = 93.1981 (19)°, V = 1456.5 (4) Å3, and Z = 4. Its structure was refined to R1 = 0.0336 (for 3010 observed reflections [I ≥ 2σ(I)]) and wR2 = 0.0875 (for all 2463 unique reflections). The tetrazole rings are essentially planar, while the aryl rings at the 1- and 5-positions of each compound show no conjugation to the tetrazole groups. Compound 5 exhibits a network of intermolecular hydrogen bonds generated by interactions between adjacent sulfonamide groups. The molecular docking studies were carried out to understand the orientation and the interaction of each molecule inside the active site of the cyclooxygenase-2 enzyme, followed by comparison with the bioassay studies as COX-2 inhibitors.

Orientation and Order of the Amide Group of Sphingomyelin in Bilayers Determined by Solid-State NMR

Sphingomyelin (SM) and cholesterol (Chol) are considered essential for the formation of lipid rafts; however, the types of molecular interactions involved in this process, such as intermolecular hydrogen bonding, are not well understood. Since, unlike other phospholipids, SM is characterized by the presence of an amide group, it is essential to determine the orientation of the amide and its order in the lipid bilayers to understand the nature of the hydrogen bonds in lipid rafts. For this study, 1′-13C-2-15N-labeled and 2′-13C-2-15N-labeled SMs were prepared, and the rotational-axis direction and order parameters of the SM amide in bilayers were determined based on 13C and 15N chemical-shift anisotropies and intramolecular 13C-15N dipole coupling constants. Results revealed that the amide orientation was minimally affected by Chol, whereas the order was enhanced significantly in its presence. Thus, Chol likely promotes the formation of an intermolecular hydrogen-bond network involving the SM amide without significantly changing its orientation, providing a higher order to the SM amide. To our knowledge, this study offers new insight into the significance of the SM amide orientation with regard to molecular recognition in lipid rafts, and therefore provides a deeper understanding of the mechanism of their formation.

Assignment of terahertz vibrational modes of L-glutamine using density functional theory within generalized-gradient approximation**Project supported by the National Natural Science Foundation of China (Grant Nos. 61302007 and 60977065), the Fundamental Research Funds for the Central Universities of China (Grant No. FRF-SD-12-016A), and the Engineering Research Center of Industrial Spectrum Imaging of Beijing, China.

The crystal structure of L-glutamine is stabilized by a three-dimensional network of intermolecular hydrogen bonds. We utilize plane-wave density functional theory lattice-dynamics calculations within the generalized-gradient approximation (GGA), Perdew–Burke–Ernzerhof (PBE), PBE for solids (PBEsol), PBE with Wu–Cohen exchange (WC), and dispersion-corrected PBE, to investigate the effect of these intermolecular contacts on the absorption spectra of glutamine in the terahertz frequency range. Among these calculations, the solid-state simulated results obtained using the WC method exhibit a good agreement with the measured absorption spectra, and the absorption features are assigned with the help of WC. This indicates that the vibrational modes of glutamine were related to the combination of intramolecular and intermolecular motions, the intramolecular modes were dominated by rocking or torsion involving functional groups; the intermolecular modes mainly result from the translational motions of individual molecules, and the rocking of the hydrogen-bonded functional groups.

Formation of Hydrogen-Bonded Supramolecular Assemblies Based on Functionalized Saddle-Distorted Porphyrins

Supramolecular assemblies consisting of porphyrins have been intensively investigated in the light of promising photo-functionality including photoinduced electron transfer, photo-conducting materials, dye-sensitized solar cells, and guest inclusion toward the emergence of novel functions on the basis of unique spatial host-guest arrangements and interactions. Along this line, we have developed a series of supramolecular assemblies using the diprotonated form of saddle-distorted dodecaphenylporphyrin (H2DPP) through intermolecular π-π interaction, such as Porphyrin Nanochannels, which include electron-donating guest molecules.1 In this presentation, we present formation and characterization of supramolecular assemblies based on H2DPP derivatives having hydrogen-bonding functional groups and their metal complexes. Introduction of carboxyl groups or hydroxyl groups to the meso-phenyl groups of H2DPP as hydrogen-bonding sites allows us to construct robust and well-organized supramolecular assemblies. A diprotonated tetracarboxyl-DPP derivative (1, Fig. 1a), for example, formed two-dimensional hydrogen-bonding networks (Fig. 1b) to form a porphyrin nanochannel structure, which were reminiscent of that formed by [H4DPP2+]Cl2 and was persistent up to 150°C, in contrast to that of [H4DPP2+]Cl2.2 To expand the size of the nanochannels, we also introduced 4-carboxylphenyl groups at the 4-positions of the meso-phenyl groups of H4DPP2+. A Zn(II) complex of H2DPP derivatives having hydroxyl groups at the 4-positions of the meso-phenyl groups (2) was prepared to form a dimer bridged by 4,4’-bypyridine.3 The dimer was revealed to form intermolecular hydrogen-bonding network among the hydroxyl groups in the crystal. In addition to the crystal structures, we will also mention adsorption of gaseous molecules such as N2 and CO2 with porous supramolecular assemblies of functionalized H2DPP derivatives in the solid state. References (a) R. Harada et al., Chem. Commun. 2005, 716. (b) T. Kojima et al., Chem.–Eur. J. 2007, 13, 8714. (c) T. Nakanishi et al., Chem. Mater. 2008, 21, 7492. (d) S. Fukuzumi et al., Coord. Chem. Rev. 2012, 256, 2488.T. Ishizuka et al. Chem. Commun. 2012, 48, 6481.T. Ishizuka et al. Dalton Trans. 2013, 42, 16073. Figure 1

Rigid urea and self-healing thiourea ethanolamine monolayers.

A series of long-tail alkyl ethanolamine analogs containing amide-, urea-, and thiourea moieties was synthesized and the behavior of the corresponding monolayers was assessed on the Langmuir-Pockels trough combined with grazing incidence X-ray diffraction experiments and complemented by computer simulations. All compounds form stable monolayers at the soft air/water interface. The phase behavior is dominated by strong intermolecular headgroup hydrogen bond networks. While the amide analog forms well-defined monolayer structures, the stronger hydrogen bonds in the urea analogs lead to the formation of small three-dimensional crystallites already during spreading due to concentration fluctuations. The hydrogen bonds in the thiourea case form a two-dimensional network, which ruptures temporarily during compression and is recovered in a self-healing process, while in the urea clusters the hydrogen bonds form a more planar framework with gliding planes keeping the structure intact during compression. Because the thiourea analogs are able to self-heal after rupture, such compounds could have interesting properties as tight, ordered, and self-healing monolayers.

Synthesis, crystal structure and local anti-inflammatory activity of the L-phenylalanine methyl ester derivative of dexamethasone-derived cortienic acid

L-phenylalanine methyl ester derivative of dexamethasone - derived cortienic acid (DF) was synthesized and its crystal structure was characterized by X-ray diffraction method. The crystal system is orthorhombic with space group P212121 and cell constants a = 8.2969 (3) ?, b = 18.9358 (8) ?, c = 20.0904 (6) ?, V = 3156.4 (2) ?3 and Z = 4. Ring A of the steroid nucleus and phenyl ring in the 17?-side chain are almost planar. Rings B and C have a slightly distorted chair conformation, whereas ring D has an envelope conformation. The packing of DF is characterized by a network of intermolecular hydrogen bonds involving the O4 atom from one side of the steroid nucleus and O1 and F1 atoms from the other side as hydrogen bond acceptors. Apart from the intermolecular hydrogen bonds in the crystal packing, there are also numerous intramolecular hydrogen bonds of the N-H...O, C-H...O and C-H...F type. Local anti-inflammatory activity of DF was evaluated by use of croton oil-induced ear edema test. This derivative achieved maximal inhibition of ear edema at significantly lower concentration in comparison with dexamethasone.

Organic photovoltaics without p-n junctions: a computational study of ferroelectric columnar molecular clusters.

Structural and electronic properties of ferroelectric columnar clusters constructed from benzene-1,3,5-tricarboxylic acid, (B3CA)N, were investigated at the Hartree-Fock level. It is shown that B3CA stacks form helix-shaped molecular tubes which are stabilized by intermolecular hydrogen bonds. It is furthermore shown that the strong electric field generated by the uniaxial alignment of the carboxyl groups can split an optically prepared exciton into an electron-hole pair and can drive the charge carriers to the opposite ends of the tube. Some consequences of the phenomenon for photovoltaic applications are discussed.

Crystal Structure and Molecular Mechanics Modelling of 2-(4-Amino-3-benzyl-2-thioxo-2,3-dihydrothiazol-5-yl)benzoxazole

The crystal structure of the title compound, 2-(4-amino-3-benzyl-2-thioxo-2,3-dihydrothiazol-5-yl)benzoxazole, was determined. The crystal has P1 space group and triclinic system with unit cell parameters a = 5.174(3) Å, b = 6.411(6) Å, c = 12.369(10) Å, α = 86.021(4)°, β = 84.384(5)°, and γ = 77.191(5)°. The structure consists of benzoxazole group connected with benzyl via thiazole (attached with amino and thione). Benzoxazole and thiazole rings are almost planar (maximum deviation at C1, −0.013(3) Å, and C10, 0.0041(3) Å, resp.). The phenyl ring is nearly perpendicular to both thiazole and benzoxazole rings. A network of intermolecular hydrogen bonds and intermolecular interactions stabilizes the structure, forming parallel layers. The molecular geometry obtained using single crystal analysis is discussed along with results of the molecular mechanics modeling (MM), and the results showed the same cis conformation between benzoxazole nitrogen atom and the amino group.

Hydrogen bonding in polyamino-polyalcohols: a monohydrated cocrystal of 1,3-diamino-5-azaniumyl-1,3,5-trideoxy-cis-inositol iodide and 1,3,5-triamino-1,3,5-trideoxy-cis-inositol

In the title monohydrated cocrystal, namely 1,3-diamino-5-azaniumyl-1,3,5-trideoxy-cis-inositol iodide-1,3,5-triamino-1,3,5-trideoxy-cis-inositol-water (1/1/1), C6H16N3O3(+)·I(-)·C6H15N3O3·H2O, the neutral 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (taci) molecule and the monoprotonated 1,3-diamino-5-azaniumyl-1,3,5-trideoxy-cis-inositol cation (Htaci(+)) both adopt a chair conformation, with the three O atoms in axial and the three N atoms in equatorial positions. The cation, but not the neutral taci unit, exhibits intramolecular O-H···O hydrogen bonding. The entire structure is stabilized by a complex three-dimensional network of intermolecular hydrogen bonds. The neutral taci entities and the Htaci(+) cations are each aligned into chains along [001]. In these chains, two O-H···N interactions generate a ten-membered ring as the predominant structural motif. The rings consist of vicinal 2-amino-1-hydroxyethylene units of neighbouring molecules, which are paired via centres of inversion. The chains are interconnected into undulating layers parallel to the ac plane, and the layers are further held together by O-H···N hydrogen bonds and additional interactions with the iodide counter-anions and solvent water molecules.

Effects of hydrogen bonds on solid state TATB, RDX, and DATB under high pressures

To probe the behavior of hydrogen bonds in solid energetic materials, we conduct ReaxFF and SCC–DFTB molecular dynamics simulations of crystalline TATB, RDX, and DATB. By comparing the intra- and inter-molecular hydrogen bonding rates, we find that the crystal structures are stabilized by inter-molecular hydrogen bond networks. Under high-pressure, the inter- and intra-molecular hydrogen bonds in solid TATB and DATB are nearly equivalent. The hydrogen bonds in solid TATB and DATB are much shorter than in solid RDX, which suggests strong hydrogen bond interactions existing in these energetic materials. Stretching of the C–H bond is observed in solid RDX, which may lead to further decomposition and even detonation.

Cholesterol stabilizes fluid phosphoinositide domains

Local accumulation of phosphoinositides (PIPs) is an important factor for a broad range of cellular events including membrane trafficking and cell signaling. The negatively charged phosphoinositide headgroups can interact with cations or cationic proteins and this electrostatic interaction has been identified as the main phosphoinositide clustering mechanism. However, an increasing number of reports show that phosphoinositide-mediated signaling events are at least in some cases cholesterol dependent, suggesting other possible contributors to the segregation of phosphoinositides. Using fluorescence microscopy on giant unilamellar vesicles and monolayers at the air/water interface, we present data showing that cholesterol stabilizes fluid phosphoinositide-enriched phases. The interaction with cholesterol is observed for all investigated phosphoinositides (PI(4)P, PI(3,4)P2, PI(3,5)P2, PI(4,5)P2 and PI(3,4,5)P3) as well as phosphatidylinositol. We find that cholesterol is present in the phosphoinositide-enriched phase and that the resulting phase is fluid. Cholesterol derivatives modified at the hydroxyl group (cholestenone, cholesteryl ethyl ether) do not promote formation of phosphoinositide domains, suggesting an instrumental role of the cholesterol hydroxyl group in the observed cholesterol/phosphoinositide interaction. This leads to the hypothesis that cholesterol participates in an intermolecular hydrogen bond network formed among the phosphoinositide lipids. We had previously reported that the intra- and intermolecular hydrogen bond network between the phosphoinositide lipids leads to a reduction of the charge density at the phosphoinositide phosphomonoester groups (Kooijman et al., 2009). We believe that cholesterol acts as a spacer between the phosphoinositide lipids, thereby reducing the electrostatic repulsion, while participating in the hydrogen bond network, leading to its further stabilization. To illustrate the effect of phosphoinositide segregation on protein binding, we show that binding of the tumor suppressor protein PTEN to PI(5)P and PI(4,5)P2 is enhanced in the presence of cholesterol. These results provide new insights into how phosphoinositides mediate important cellular events.

The macular degeneration-linked C1QTNF5 (S163) mutation causes higher-order structural rearrangements

The C1q-tumor necrosis factor 5 (C1QTNF5) protein plays a significant role in retinal pigmented epithelium (RPE) cellular adhesion. The C1QTNF5 gene is co-transcribed with the frizzled-related protein (MFRP) gene. A Ser-to-Arg mutation at site 163 (S163R) in C1QTNF5 is known to cause late-onset retinal macular degeneration (L-ORMD). Here we also found that C1QTNF5 monomers can multimerize into a bouquet-like octadecamer. We found that a novel intermolecular hydrogen-bond network of S163 that glues adjacent globular heads of C1QTNF5 together was weakened or abolished by the R163 pathogenic mutation. These findings could underlie the structural basis of this protein's adhesive function and relate to the pathogenesis of its S163R mutation. Additionally, the fact that C1QTNF5 immobilized to a resin selectively enriched detergent extracted membrane-bound MFRP, further confirmed their interaction, implying functions other than cellular adhesion for C1QTNF5.

Enantiomeric Selective Adsorption of Amino Acid by Polysaccharide Composite Materials

A composite containing cellulose (CEL) and chitosan (CS) synthesized by a simple and recyclable method by using butylmethylimmidazolium chloride, an ionic liquid, was found to exhibit remarkable enantiomeric selectivity toward the adsorption of amino acids. The highest adsorption capacity and enantiomeric selectivity are exhibited by 100% CS. A racemic amino acid can be enantiomerically resolved by 100% CS in about 96-120 h. Interestingly, adsorption by 50:50 CEL/CS is more similar to that by 100% CS than to 100% CEL. Specifically, whereas 100% CEL has the lowest adsorption capacity and enantiomeric selectivity, 50:50 CEL/CS has sufficient enantiomeric selectivity to enable it to be used for chiral resolution. This is significant because in spite of its high enantiomeric selectivity 100% CS cannot practically be used because it has relatively poor mechanical properties and undergoes extensive swelling. Adding 50% CEL to CS substantially improves the mechanical properties and reduces its swelling while it retains sufficient enantiomeric selectivity to enable it to be used for routine chiral separations. The kinetic results indicate that the enantiomerically selective adsorption is due not to the initial surface adsorption but rather to the subsequent stage in which the adsorbate molecules diffuse into the pores within the particles of the composites and consequently are adsorbed by the interior of each particle. The strong intermolecular and intramolecular hydrogen bond network in CEL enables it to adopt a very dense structure that makes it difficult for adsorbate molecules to diffuse into its interior, thereby leading to low enantiomeric selectivity. Compared to hydroxy groups, amino groups cannot form strong hydrogen bonds. The hydrogen bond network in CS is not as extensive as in CEL, and its inner structure is relatively less dense than that of CEL. Adsorbate molecules can, therefore, diffuse from the outer surface to its inner structure relatively more easily than in CEL, thereby leading to higher enantiomeric selectivity for 100% CS.

Preparation and Characterization of Cellulose Regenerated from Phosphoric Acid

Native cellulose has a highly crystalline structure stabilized by a strong intra- and intermolecular hydrogen-bond network. It is usually not considered as a good gelling material and emulsion stabilizer due to its insolubility in water. Chemical modification is generally necessary to obtain cellulose derivatives for these applications. In this study, we have shown that, by simply disrupting the hydrogen-bond network of cellulose with phosphoric acid treatment, the regenerated cellulose can be a good gelling material and emulsion stabilizer. Microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analysis have confirmed that the regenerated cellulose is primarily amorphous with low crystallinity in the structure of cellulose II. Stable aqueous suspensions and opaque gels that resist flowing can be obtained with the regenerated cellulose at concentrations higher than 0.6% and 1.6%, respectively. Moreover, it can effectively stabilize oil-in-water emulsions at concentrations less than 1% by a mechanism that combines network and Pickering stabilization.

Phosphatidylinositol-4,5-bisphosphate ionization in the presence of cholesterol, calcium or magnesium ions

Phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) is an important signaling lipid and plays a crucial role in a wide variety of cellular processes by interacting with protein targets and localizing proteins at the plasma membrane. These interactions are strongly influenced by the lateral distribution of PI(4,5)P2 as well as its ionization state. The characterization of the PI(4,5)P2 ionization state provides important information about how PI(4,5)P2 interacts with other membrane resident or associated chemical species. In this study we have used solid-state MAS 31P NMR to investigate the interactions of PI(4,5)P2 with potential cluster promoting agents, divalent cations and cholesterol. Both Ca2+ and cholesterol were found previously to promote formation of local PI(4,5)P2 clusters in vitro. The NMR approach allows us to probe independently the ionization state of PI(4,5)P2 two phosphomonoester groups. We investigated mixed phosphatidylcholine (PC)/PI(4,5)P2 multilamellar vesicles in the presence of micro and millimolar concentrations of Ca2+ and Mg2+. We found that both cations lead to an increased downfield chemical shift of the PI(4,5)P2 phosphomonoester peaks, indicating an increased ionization in the presence of the divalent cations. Ca2+ has a much larger effect on PI(4,5)P2 as compared to Mg2+ at similar concentrations. Physiological concentrations of Ca2+ are significantly lower than those found for Mg2+ and the comparison of the PI(4,5)P2 ionization in the presence of Ca2+ and Mg2+ at physiological concentrations resulted in similar charges of the phosphomonoester groups for both cations. PI(4,5)P2 was also examined with vesicles containing cholesterol since cholesterol has been shown to promote PI(4,5)P2 clustering. In the presence of 40mol% cholesterol, the PI(4,5)P2 phosphomonoester 31P NMR peaks shifted slightly downfield, indicating a small increase in charge. Previously published data suggest that PI(4,5)P2 is capable of forming an intra- and intermolecular hydrogen bond network, which leads to a reduction of the charge at the phosphomonoester groups through dissipation of the charge across the bilayer/water interface. We hypothesize that cholesterol participates in this intermolecular hydrogen bond network, resulting in a stabilization of PI(4,5)P2 enriched domains due an increased spacing between the PI(4,5)P2 headgroup. We also examined the cumulative effects of cholesterol combined with the divalent cations, phosphatidylethanolamine (PE), and phosphatidylinositol (PI), separately. The combination of cholesterol and divalent cations results in an additive effect on PI(4,5)P2 ionization, while the effect of cholesterol on PI(4,5)P2 ionization is reduced in the presence of PE or PI.

Theoretical study on excited-state intermolecular proton transfer reactions of 1H-pyrrolo[3,2-h]quinoline with water and methanol

The dynamics of the ultrafast excited-state multiple intermolecular proton transfer (PT) reactions in gas-phase complexes of 1H-pyrrolo[3,2-h]quinoline with water and methanol (PQ(H2O) n and PQ(MeOH) n , where n = 1, 2) is modeled using quantum-chemical simulations. The minimum energy ground-state structures of the complexes are determined. Molecular dynamics simulations in the first excited state are employed to determine reaction mechanisms and the time evolution of the PT processes. Excited-state dynamics results for all complexes reveal synchronous excited-state multiple proton transfer via solvent-assisted mechanisms along an intermolecular hydrogen-bonded network. In particular, excited-state double proton transfer is the most effective, occurring with the highest probability in the PQ(MeOH) cluster. The PT character of the reactions is suggested by nonexistence of crossings between ππ* and πσ* states.