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Physical Chemistry Chemical Physics: PCCP

F J Martínez-Casado, M Ramos-Riesco, J A Rodríguez-Cheda, M I Redondo-Yélamos, L Garrido, A Fernández-Martínez, J García-Barriocanal, I da Silva, M Durán-Olivencia, A Poulain
The long-chain members of the lead(ii) alkanoate series or soaps, from octanoate to octadecanoate, have been thoroughly characterized by means of XRD, PDF analysis, DSC, FTIR, ssNMR and other techniques, in all their phases and mesophases. The crystal structures at room temperature of all of the members of the series are now solved, showing the existence of two polymorphic forms in the room temperature crystal phase, different to short and long-chain members. Only nonanoate and decanoate present both forms, and this polymorphism is proven to be monotropic...
June 21, 2017: Physical Chemistry Chemical Physics: PCCP
E Posada, N López-Salas, R J Jiménez Riobóo, M L Ferrer, M C Gutiérrez, F Del Monte
Deep eutectic solvents (DESs) offer a suitable alternative to conventional solvents in terms of both performance and cost-effectiveness. Some DESs also offer certain green features, the greenness of which is notoriously enhanced when combined with water. Aqueous DES dilutions are therefore attracting great attention as a novel green medium for biotechnological processes, with the aqueous dilutions of reline - a DES composed of urea and choline chloride - being one of the most studied systems. Despite their macroscopic homogeneous appearance, both (1)H NMR spectroscopic studies and molecular dynamics simulations have revealed the occurrence of certain dynamic heterogeneity at a microscopic molecular level...
June 21, 2017: Physical Chemistry Chemical Physics: PCCP
V A Gorbunov, S S Akimenko, A V Myshlyavtsev
Using a simple lattice gas model we study the features of self-assembly in adsorption layers where both "molecule-surface" and "molecule-molecule" interactions are anisotropic. Based on the example of adsorption layers of mono-functional organic molecules on the heterogeneous surface with strip-like topography, we have revealed plenty of possible self-assembled structures in this simple system, such as discrete, linear, zigzag, chess board-like, two-dimensional porous and close-packed patterns. However, the phase behavior of the adsorption layer is much richer, if the interactions between functional and non-functional parts of adjacent adsorbed molecules have comparable strength and opposite signs...
June 21, 2017: Physical Chemistry Chemical Physics: PCCP
Vadim V Neklyudov, Nail R Khafizov, Igor A Sedov, Ayrat M Dimiev
One of the main advantages of graphene oxide (GO) over its non-oxidized counterpart is its ability to form stable solutions in water and some organic solvents. At the same time, the nature of GO solutions is not completely understood; the existing data are scarce and controversial. Here, we demonstrate that the solubility of GO, and the stability of the as-formed solutions depend not just on the solute and solvent cohesion parameters, as commonly believed, but mostly on the chemical interactions at the GO/solvent interface...
June 21, 2017: Physical Chemistry Chemical Physics: PCCP
Fernando Murillo, Alba Vargas-Caamal, Sudip Pan, José Luis Cabellos, Miguel J Mora-Fonz, Alvaro Muñoz-Castro, Albeiro Restrepo, Gabriel Merino
The possible existence of H4SO5 in aqueous sulfuric acid is analyzed in detail. For bare H4SO5, the computed free energy barrier for the exergonic transformation of H4SO5 into the H2SO4H2O complex is only 3.8 kcal mol(-1). The presence of water or sulfuric acid catalyzes the dehydration to such an extent that it becomes almost a barrierless process. In the gas phase, dehydration of H4SO5 is an autocatalytic reaction as the water molecule produced by the decomposition of one H4SO5 molecule induces further dissociation...
June 21, 2017: Physical Chemistry Chemical Physics: PCCP
P Jasik, J E Sienkiewicz, J Domsta, N E Henriksen
The adiabatic potential energy curves of the (1)Σ(+) and (1)Π states of the LiH molecule were calculated. They correlate asymptotically to atomic states, such as 2s + 1s, 2p + 1s, 3s + 1s, 3p + 1s, 3d + 1s, 4s + 1s, 4p + 1s and 4d + 1s. A very good agreement was found between our calculated spectroscopic parameters and the experimental ones. The dynamics of the rotational predissociation process of the 1(1)Π state were studied by solving the time-dependent Schrödinger equation. The classical experiment of Velasco [Can...
June 21, 2017: Physical Chemistry Chemical Physics: PCCP
Jiří Černý, Bohdan Schneider, Lada Biedermannová
Water molecules represent an integral part of proteins and a key determinant of protein structure, dynamics and function. WatAA is a newly developed, web-based atlas of amino-acid hydration in proteins. The atlas provides information about the ordered first hydration shell of the most populated amino-acid conformers in proteins. The data presented in the atlas are drawn from two sources: experimental data and ab initio quantum-mechanics calculations. The experimental part is based on a data-mining study of a large set of high-resolution protein crystal structures...
June 21, 2017: Physical Chemistry Chemical Physics: PCCP
Xiaoyan Mu, Justin Kai-Chi Lau, Cheuk-Kuen Lai, K W Michael Siu, Alan C Hopkinson, Ivan K Chu
Four isomers of the radical cation of tripeptide phenylalanylglycyltryptophan, in which the initial location of the radical center is well defined, have been isolated and their collision-induced dissociation (CID) spectra examined. These ions, the π-centered [FGWπ˙](+), α-carbon- [FGα˙W](+), N-centered [FGWN˙](+) and ζ-carbon- [Fζ˙GW](+) radical cations, were generated via collision-induced dissociation (CID) of transition metal-ligand-peptide complexes, side chain fragmentation of a π-centered radical cation, homolytic cleavage of a labile nitrogen-nitrogen single bond, and laser induced dissociation of an iodinated peptide, respectively...
June 20, 2017: Physical Chemistry Chemical Physics: PCCP
Amparo Fernández-Pérez, Verónica Rodríguez-Casado, Teresa Valdés-Solís, Gregorio Marbán
In a previous work by the authors (A. Fernández-Pérez el al., Room temperature sintering of polar ZnO nanosheets: I-evidence, 2017, DOI: 10.1039/C7CP02306E), polar ZnO nanosheets were stored at room temperature under different atmospheres and the evolution of their textural and crystal properties during storage was followed. It was found that the specific surface area of the nanosheets drastically decreased during storage, with a loss of up to 75%. The ZnO crystals increased in size mainly through the partial merging of their polar surfaces at the expense of narrow mesoporosity, in a process triggered by the action of moisture, oxygen and, in their absence, by light...
June 20, 2017: Physical Chemistry Chemical Physics: PCCP
David Ayuso, Alicia Palacios, Piero Decleva, Fernando Martín
The combination of attosecond pump-probe techniques with mass spectrometry methods has recently led to the first experimental demonstration of ultrafast charge dynamics in a biomolecule, the amino acid phenylalanine [Calegari et al., Science, 2014, 346, 336]. Using an extension of the static-exchange density functional theory (DFT) method, the observed dynamics was explained as resulting from the coherent superposition of ionic states produced by the broadband attosecond pulse. Here, we have used the static-exchange DFT method to investigate charge migration induced by attosecond pulses in the glycine molecule...
June 20, 2017: Physical Chemistry Chemical Physics: PCCP
José A Sánchez-Rodríguez, Abed Mohamadzade, Sebastian Mai, Brennan Ashwood, Marvin Pollum, Philipp Marquetand, Leticia González, Carlos E Crespo-Hernández, Susanne Ullrich
Single-atom substitution within a natural nucleobase-such as replacing oxygen by sulfur in uracil-can result in drastic changes in the relaxation dynamics after UV excitation. While the photodynamics of natural nucleobases like uracil are dominated by pathways along singlet excited states, the photodynamics of thiobases like 2-thiouracil populate the triplet manifold with near unity quantum yield. In the present study, a synergistic approach based on time-resolved photoelectron spectroscopy (TRPES), time-resolved absorption spectroscopy (TRAS), and ab initio computations has been particularly successful at unraveling the underlying photophysical principles and describing the dissimilarities between the natural and substituted nucleobases...
June 20, 2017: Physical Chemistry Chemical Physics: PCCP
Sabyasachi Roy Chowdhury, Sabyashachi Mishra
In the search for single molecule magnets, metal ions are considered pivotal towards achieving large magnetic anisotropy barriers. In this context, the influence of ligands with heavy elements, showing large spin-orbit coupling, on magnetic anisotropy barriers was investigated using a series of Mn(ii)-based complexes, in which the metal ion did not have any orbital contribution. The mixing of metal and ligand orbitals was achieved by explicitly correlating the metal and ligand valence electrons with CASSCF calculations...
June 20, 2017: Physical Chemistry Chemical Physics: PCCP
Yuewen Mu, Qiang Chen, Na Chen, Haigang Lu, Si-Dian Li
We propose a novel stable borophene (referred to as H-borophene) by tiling seven-membered rings side by side, which is a novel construction pattern never reported in boron sheets or other sheets. It is able to serve as the common precursor of borospherenes (e.g., B39(-), B40, B41(+), and B42(2+)). Interestingly, a Dirac point appeared at about 0.33 eV below the Fermi level. We found that nanotubes formed by rolling up H-borophene had a great advantage over other boron nanotubes in the case of high curvature, which accounted for the reason why heptagons were preferred in borospherenes...
June 20, 2017: Physical Chemistry Chemical Physics: PCCP
Amparo Fernández-Pérez, Verónica Rodríguez-Casado, Teresa Valdés-Solís, Gregorio Marbán
Polar ZnO nanosheets of a high specific surface area (∼120 m(2) g(-1)) were subjected to storage under different atmospheres at room temperature and analyzed for changes in their textural and crystal properties. During their storage under laboratory conditions (in closed transparent polypropylene vials kept under the light of the laboratory on worktop tables) the nanosheets lost up to 75% of their specific surface area in approximately two months, with most of the loss occurring during the first two weeks...
June 20, 2017: Physical Chemistry Chemical Physics: PCCP
Lucas J Karas, Patrick R Batista, Renan V Viesser, Cláudio F Tormena, Roberto Rittner, Paulo R de Oliveira
Intramolecular hydrogen bonding (IAHB) is one of the most important intramolecular interactions and a critical element in adopted molecular arrangements. Moreover, slight substitution in a molecule can affect its strength to a great extent. It is well established that alkyl groups play a positive role in IAHB strength. However, the effects that drive it are specific to each system. To investigate the influence of IAHB and its strength dependency on different acyclic compounds, the conformational preferences of propane-1,3-diol, 3-methoxypropan-1-ol, 3-ethoxypropan-1-ol, 3-isopropoxypropan-1-ol, 3-(tert-butoxy)propan-1-ol, butane-1,3-diol, 3-methoxybutan-1-ol, 3-methylbutane-1-diol, and 3-methoxy-3-methylbutan-1-ol were evaluated experimentally using infrared spectroscopy theoretically supported by topological and natural bond orbital analyses...
June 19, 2017: Physical Chemistry Chemical Physics: PCCP
Xian Kong, Diannan Lu, Jianzhong Wu, Zheng Liu
Supported lipid bilayers (SLBs) have been widely used in drug delivery, biosensors and biomimetic membranes. The microscopic mechanism of SLB formation and stability depends on a number of factors underlying solvent-mediated lipid-lipid and lipid-substrate interactions. Whereas recent years have witnessed remarkable progress in understanding the kinetics of SLB formation, relatively little is known about the lipid phase behavior controlling the SLB stability under diverse solution conditions. In this work, we examine the structure of SLBs using classical density functional theory (CDFT) in the context of a coarse-grained model that accounts for ion-explicit electrostatic interactions, surface hydrophobicity, as well as the molecular characteristics of the lipid tails...
June 19, 2017: Physical Chemistry Chemical Physics: PCCP
Danilo Loche, Claudia Marras, Daniela Carta, Maria Francesca Casula, Gavin Mountjoy, Anna Corrias
Samples of nickel cobaltite, a mixed oxide occurring in the spinel structure which is currently extensively investigated because of its prospective application as ferromagnetic, electrocatalytic, and cost-effective energy storage material were prepared in the form of nanocrystals stabilized in a highly porous silica aerogel and as unsupported nanoparticles. Nickel cobaltite nanocrystals with average size 4 nm are successfully grown for the first time into the silica aerogel provided that a controlled oxidation of the metal precursor phases is carried out, consisting in a reduction under H2 flow followed by mild oxidation in air...
June 19, 2017: Physical Chemistry Chemical Physics: PCCP
Linda Giacomozzi, Michael Gatchell, Nathalie de Ruette, Michael Wolf, Giovanna D'Angelo, Henning T Schmidt, Henrik Cederquist, Henning Zettergren
We have studied collisions between tetraphenylporphyrin cations and He or Ne at center-of-mass energies in the range 50-110 eV. The experimental results were interpreted in view of density functional theory calculations of dissociation energies and classical molecular dynamics simulations of how the molecules respond to the He/Ne impact. We demonstrate that prompt atom knockout strongly contributes to the total destruction cross sections. Such impulse driven processes typically yield highly reactive fragments and are expected to be important for collisions with any molecular system in this collision energy range, but have earlier been very difficult to isolate for biomolecules...
June 19, 2017: Physical Chemistry Chemical Physics: PCCP
Jan Schaefer, Grazia Gonella, Mischa Bonn, Ellen H G Backus
Surface-specific vibrational sum-frequency generation spectroscopy (V-SFG) is frequently used to obtain information about the molecular structure at charged interfaces. Here, we provide experimental evidence that not only screening of surface charges but also interference limits the extent to which V-SFG probes interfacial water at sub-mM salt concentrations. As a consequence, V-SFG yields information about the ∼single monolayer interfacial region not only at very high ionic strength, where the surface charge is effectively screened, but also for pure water due to the particularly large screening length at this low ionic strength...
June 19, 2017: Physical Chemistry Chemical Physics: PCCP
M H Yang, J H Li, B X Liu
In the present study, atomistic simulation reveals that the microscopic mechanism of the relaxation dynamics in amorphous materials is governed by the activating atoms that jump more than half of the average nearest neighbor distance within a given time. Based on the unsupervised machine-learning algorithm, hierarchical clustering analysis shows that the activating atoms are excited in a cooperative and avalanche-like model to form activating units. Correlation analysis suggests that large free volumes facilitate the formation of activating atoms...
June 19, 2017: Physical Chemistry Chemical Physics: PCCP
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