Conformations of monoacyl and 1,3-diacylbenzimidazoline-2-thiones and dihydrobenzimidazoles

The endo confrontation of monoacyl and 1,3-diacylbenzimidazoline-2-thiones is predominant at ambient temperatures. Nmr temperature-dependent studies suggest that this is also true over a wide range of temperatures. In agreement with previous results (6) the exo-endo conformation in 1,3-diacyl-1,2-dihydrobenzimidazoles is generally the predominant one.     

Reaction of acetylenic ketones with hydrazine derivatives. Synthesis of hydroxypyrazoles

Aroylphenylacetylenes Ia-c react with (-butyl hydrazinecarboxylate (IIa) and 2-furylhydrazide (IIb) to give the corresponding hydroxydihydropyrazole derivatives IVa-f. This cyclic structure is supported by chemical transformations. Thus, when compounds IVa-c are heated with acetic anhydride, they yield the corresponding 5-aryl-1-(t-butoxycarbonyl)-3-phenylpyrazoles Va-c which, upon hydrolysis with methanolic potassium hydroxide, produce the corresponding 5(3)aryl-3(5)phenylpyrazoles VI. Spectroscopic data also confirm the suggested cyclic structure IV.     

Well-Known Distinctive Signatures of Quantum Phase Transition in Shape Coexistence Configuration of Nuclei

It is interesting that a change of nuclear shape may be described in terms of a phase transition. This paper studies the quantum phase transition of the U(5) to SO(6) in the interacting boson model (IBM) on the finite number N of bosons. This paper explores the well-known distinctive signatures of transition from spherical vibrational to γ-soft shape phase in the IBM with the variation of a control parameter. Quantum phase transitions occur as a result of properties of ground and excited states levels. We apply an affine \(\widehat {SU(1,1)}\) approach to numerically solve non-linear Bethe Ansatz equation and point out what observables are particularly sensitive to the transition. The main aim of this work is to describe the most prominent observables of QPT by using IBM in shape coexistence configuration. We calculate energies of excited states and signatures of QPT as energy surface, energy ratio, energy differences, quadrupole electric transition rates and expectation values of boson number operators and show their behavior in QPT. These observables are calculated and examined for ^{98 ? 102}Mo isotopes.     

Exploration of the reactivity of N2O5 with two Si(OH)4 monomers using electronic structure methods

The heterogeneous uptake of N₂O₅ on mineral dust particles may play an important role in the removal of nitrogen oxides from the atmosphere. However, the reaction of N₂O₅ with the mineral particles is not well understood. The reaction of N₂O₅ with two Si(OH)₄ monomers is explored using theoretical methods. This study represents a first step towards understanding the interaction of N₂O₅ with the hydroxyl groups of silica particles. Energies are calculated using MP2 single point calculations on the B3LYP optimized geometries and including B3LYP thermodynamic corrections. Four mechanisms are considered for the formation of two HNO₃ and one H₆Si₂O₇. The rate limiting activation barrier of the most favorable path is found to be 12.5 kcal mol^?1. This reaction appears to be more favorable than the hydrolysis of N₂O₅ with one water molecule. These results are in agreement with experimental observations, which show that N₂O₅ reacts with OH groups of Saharan dust to form nitrate. © 2012 Wiley Periodicals, Inc.     

Structure and stability of VO2+ in aqueous solution: a Car-Parrinello and static ab initio study

Quantum chemical calculations have been carried out to get some insight concerning the effects of temperature and solvent acidity on the structure and stability of solvated VO2+ as the elementary chemical unit involved in the nucleation of vanadophosphates. First, because some recent theoretical studies have suggested a tendency of density functional theory (DFT) to favor lower coordination numbers for such systems, static calculations have been performed on [VO2(H2O)(4-n)]+.nH2O (n=0-2) conformers at the MP2 and DFT level of theory, using two different combinations of basis sets. The results of two pure-GGA (BP86 and PBEPBE), two hybrid-GGA (PBE1PBE and mPWPW91), and two hybrid-meta-GGA (mPW1B95 and B1B95) functionals were analyzed on these systems. The comparison of the results indicates that the stability differences between the two methodologies are resolved when hydration energy is taken into account, provided that some amount of HF exchange is introduced in the DFT calculations. In a second step, Car-Parrinello simulations have been carried out starting from VO2(H2O)4+ surrounded by water molecules. The calculations at 300 K show the natural tendency of VO2(H2O)4+ to decompose to VO2(OH)2- and the requirements to work with an already acidified medium to be able to investigate the coordination sphere of VO2+ for an extended period of time. Under such conditions, we have obtained a clear preference for a five-coordinated vanadium. The molecular dynamics simulations performed at 500 K starting from hydrated VO2+ in a protonated medium found VO(OH)3 to be the most stable structure, whereas this ideal candidate for oxolation reactions is expected to be a very minor species at room temperature.     

Cálculo eficiente de las energías de formación de escalones dobles en materiales BCC

Motion of screw dislocations in BCC materials at low temperature is believed to be related to the formation of mobile kinks on the dislocation line. Therefore, the accurate prediction of kink nucleation energies is required to fully describe mobility of screw dislocations in these materials. Studies of fundamental dislocation processes at atomic length scale are numerically and computationally intensive problems. This work studies the calculation of zero-stress formation energies of kink-pair configurations for BCC crystals. Our model for stored energy associated to a dislocation line configuration is based on the theory of discrete dislocations of Ariza and Ortiz. Its value is computed efficiently using an algorithm developed on the NVIDIA Compute Unified Device Architecture (CUDA). Results confirm those obtained using atomistic potentials and first principles calculations, and those based on the continuum theory of dislocations.     

Seafood Paramyosins as Sources of Anti-Angiotensin-Converting-Enzyme and Anti-Dipeptidyl-Peptidase Peptides after Gastrointestinal Digestion: A Cheminformatic Investigation

Paramyosins, muscle proteins occurring exclusively in invertebrates, are abundant in seafoods. The potential of seafood paramyosins (SP) as sources of anti-angiotensin-converting-enzyme (ACE) and anti-dipeptidyl-peptidase (DPP-IV) peptides is underexplored. This in silico study investigated the release of anti-ACE and anti-DPP-IV peptides from SP after gastrointestinal (GI) digestion. We focused on SP of the common octopus, Humboldt squid, Japanese abalone, Japanese scallop, Mediterranean mussel, Pacific oyster, sea cucumber, and Whiteleg shrimp. SP protein sequences were digested on BIOPEP-UWM, followed by identification of known anti-ACE and anti-DPP-IV peptides liberated. Upon screening for high-GI-absorption, non-allergenicity, and non-toxicity, shortlisted peptides were analyzed via molecular docking and dynamic to elucidate mechanisms of interactions with ACE and DPP-IV. Potential novel anti-ACE and anti-DPP-IV peptides were predicted by SwissTargetPrediction. Physicochemical and pharmacokinetics of peptides were predicted with SwissADME. GI digestion liberated 2853 fragments from SP. This comprised 26 known anti-ACE and 53 anti-DPP-IV peptides exhibiting high-GI-absorption, non-allergenicity, and non-toxicity. SwissTargetPrediction predicted three putative anti-ACE (GIL, DL, AK) and one putative anti-DPP-IV (IAL) peptides. Molecular docking found most of the anti-ACE peptides may be non-competitive inhibitors, whereas all anti-DPP-IV peptides likely competitive inhibitors. Twenty-five nanoseconds molecular dynamics simulation suggests the stability of these screened peptides, including the three predicted anti-ACE and one predicted anti-DPP-IV peptides. Seven dipeptides resembling approved oral-bioavailable peptide drugs in physicochemical and pharmacokinetic properties were revealed: AY, CF, EF, TF, TY, VF, and VY. In conclusion, our study presented in silico evidence for SP being a promising source of bioavailable and safe anti-ACE and anti-DPP-IV peptides following GI digestions.     

Induced-charge electrophoresis near a wall

Induced-charge electrophoresis (ICEP) has mostly been analyzed for asymmetric particles in an infinite fluid, but channel walls in real systems further break symmetry andlead to dielectrophoresis (DEP) in local ?eld gradients. Zhao and Bau (Langmuir 2007, 23,4053) predicted that a metal (ideally polarizable) cylinder is repelled from an insulating wall in a DC field. We revisit this problem with an AC field and show that attraction to the wall sets in at high frequency and leads to an equilibrium distance, where DEP balances ICEP, although, in three dimensions, a metal sphere is repelled from the wall at all frequencies. This conclusion, however, does not apply to asymmetric particles. Consistent with the experiments of Gangwal et al. (Phys. Rev. Lett. 2008, 100, 058302), we show that a metal/insulator Janus particle is always attracted to the wall in an AC field. The Janus particle tends to move toward its insulating end, perpendicular to the field, but ICEP torque rotates this end toward the wall. Under some conditions, the theory predicts steady translation along the wall, perpendicular to the field, at an equilibrium tilt angle around 451, consistent with the experiments, although improved models are needed for a complete understanding of this phenomenon.     

Heterocycles from nitrile oxides. I. 5-imino-Δ2 -1,4,2-oxathiazolines

The reaction of some arylnitrile oxides with potassium thiocyanate in acetone at ambient temperature, has been investigated. Those having para- or meta-halo (or nitro)substituents give 3-aryl-5-imino-Δ²-1,4,2-oxathiazolines as stable cycloadducts. ortho-Substitutionn, on the other hand, led directly to the corresponding 5- (carbamido) imino analogues. The structures of these new heterocycles are supported by elemental analyses and spectral data.