Charge separation in Na<Superscript>+</Superscript>Cl<Superscript>-</Superscript>(H<Subscript>2</Subscript>O)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> clusters in water vapors. 2. Free energy

Charge separation in “soft” nanoparticles composed of water molecules, as well as sodium and chlorine ions, is studied by computer simulation. The detailed model of intermolecular interactions that includes, in addition to Coulomb, exchange, and dispersion forces, many-particle polarization and covalent interactions, as well as the effect due to the transfer of excess ion charges and influence of ion field on molecular interactions, is constructed. Model potentials are calibrated using experimental data on the free energy and enthalpy of the addition of vapor molecules to the hydration shells of ions, as well as the data of quantum-chemical calculations for stable cluster configurations and the vibration frequency of interionic bonds. The allowance for many-particle interactions makes it possible to improve the agreement between experimental and quantum-chemical data by more than an order of magnitude. The disregard for many-particle interactions leads to the significant overestimation of cluster stability.     

Charge separation in Na<Superscript>+</Superscript>Cl<Superscript>-</Superscript>(H<Subscript>2</Subscript>O)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> clusters in water vapors. 1. Intermolecular interactions

Charge separation in “soft” nanoparticles composed of water molecules, as well as sodium and chlorine ions, is studied by computer simulation. The detailed model of intermolecular interactions that includes, in addition to Coulomb, exchange, and dispersion forces, many-particle polarization and covalent interactions, as well as the effect due to the transfer of excess ion charges and influence of ion field on molecular interactions, is constructed. Model potentials are calibrated using experimental data on the free energy and enthalpy of the addition of vapor molecules to the hydration shells of ions, as well as the data of quantum-chemical calculations for stable cluster configurations and the vibration frequency of interionic bonds. The allowance for many-particle interactions makes it possible to improve the agreement between experimental and quantum-chemical data by more than an order of magnitude. The disregard for many-particle interactions leads to the significant overestimation of cluster stability.     

Quadrupole coupling constants of deuterons in molecular clusters Ca<Superscript>2+</Superscript>(D<Subscript>2</Subscript>O)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 6, 8, 10, 18)

Characteristic features of the structure of Ca²⁺ hydration shells were considered. The results of quantum chemical calculations were compared with experimental data obtained from the study of nuclear magnetic relaxation of deuterons in aqueous solutions of calcium salts. The influence of the basis set and computational procedure on the calculated ²D quadrupole couling constants (QCC) in isolated water molecule was investigated. The ²D QCC in molecular clusters (D₂O)₅ and Ca²⁺(D₂O) _n (n =6, 8, 10, 18) were calculated using the B3LYP/6-31++G** density functional method.     

The Association Constants of H<Superscript><Emphasis Type="Italic">+</Emphasis></Superscript> and Ca<Superscript><Emphasis Type="Italic">2 +</Emphasis></Superscript> with 2-Keto-D-Gluconate in Aqueous Solutions

2-Keto-D-gluconate (kG) is naturally produced in soils, sediments and rock faces through the microbial oxidation of glucose. Studies have qualitatively shown kG to enhance the dissolution of soil minerals. However, quantitative information, such as the log K values for the formation of metal–kG complexes, are not available. This paper presents the results of potentiometric titration studies that employ H⁺ and Ca²⁺ ion selective electrodes (ISEs) to determine the conditional ion association constants (log Q values) for the protonation and deprotonation of kG and the formation of Ca–kG complexes. The experimentally-determined log Q values were then converted to the corresponding ion association constants (the zero ionic strength condition; log K values) by employing a modified Davies equation for charged species and the Setchenów equation for neutral species. The log K values were determined by potentiometric titrations at constant kG concentration, varied ionic strengths, 25 or 22 ^∘C, and in the absence of CO₂. The computer model GEOCHEM-PC was used to determine the aqueous speciation of ions other than kG and the computer model FITEQL was used to estimate conditional log Q values for reactions in the various chemical models. Based on our evaluations, equilibrium constants for the following reactions were determined: H⁺+ kG^– ⇌ HkG⁰, log K_a1 = (3.00 ± 0.06), kG^–⇌ H_–1kG^2–+ H⁺, log K_a–1 = –(11.97 ± 0.41), and Ca²⁺+ kG^–⇌ CakG⁺, log K₁₀₁ = (1.74 ± 0.04).     

The photoisomerization of <Emphasis Type="Italic">trans</Emphasis>-stilbene in Triton X-100/<Emphasis Type="Italic">n</Emphasis>-C<Subscript>5</Subscript>H<Subscript>11</Subscript>OH/H<Subscript>2</Subscript>O microemulsions

Different from organic solvent, self-assemblies are environment friendly media, and moreover, if they are used as micro-reactor, many meaningful and exciting results may be obtained. In this paper, we investigated the photoisomerization of trans-stilbene in Triton X-100/n-C₅H₁₁OH/H₂O microemulsions (a kind of self-assemblies) with different compositions and structures to establish the relationship between the reaction yields and the compositions and structures of microemulsions. The results show that the yield of cis-stilbene is increased with the increase of water content or with the decrease of Triton X-100 content, and oil in water (O/W) structure is the best structure for this reaction, which makes it possible to decrease the pollution of environment by organic solvent always used in organic reactions.     

Na<Superscript>+</Superscript>-stimulated ATPase of alkaliphilic halotolerant cyanobacterium <Emphasis Type="Italic">Aphanothece halophytica</Emphasis> translocates Na<Superscript>+</Superscript> into proteoliposomes via Na<Superscript>+</Superscript> uniport mechanism

Background  

When cells are exposed to high salinity conditions, they develop a mechanism to extrude excess Na⁺ from cells to maintain the cytoplasmic Na⁺ concentration. Until now, the ATPase involved in Na⁺ transport in cyanobacteria has not been characterized. Here, the characterization of ATPase and its role in Na⁺ transport of alkaliphilic halotolerant Aphanothece halophytica were investigated to understand the survival mechanism of A. halophytica under high salinity conditions.     

Structures and magnetic properties of Ni<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 36-40) clusters from first-principles calculations

A genetic algorithm (GA) coupled with a tight-binding (TB) interatomic potential is used to search for the low-energy structures of medium-sized Ni _n (n = 36-40) clusters. Structural candidates obtained from our GA search are further optimized with first-principles calculations. The medium-sized nickel clusters ranging from 36 to 40 atoms are found to favor the double-icosahedron-based structures with a Ni₇ core (a pentagonal bipyramidal structure) except Ni₃₈ cluster. The lowest-energy structure of Ni₃₈ can be considered to be a magic cluster, which is a typical face-centered cubic structure with large stability and magnetic moment.     

Computer simulation of molecular complexes H<Subscript>3</Subscript>O<Superscript>+</Superscript>(H<Subscript>2</Subscript>O)<Subscript>n</Subscript> under conditions of thermal fluctuations: I. Interactions in the system

The simplest pair model of intermolecular interactions fails to reproduce known experimental free energy and entropy of hydration of H₃O⁺ ions in water vapor. A fit to experiment is attained only when covalent bonds and nonpair interactions, which are of particular importance at contact distances from the ion, are taken into account. An interaction model was constructed, which allows the experimental free energies of cluster formation to be reproduced to fractions of k _B T by the Monte-Carlo method. Numerical values of interaction parameters were obtained by fitting simulated results to refined experimental data.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 9, 2004, pp. 1409–1417.Original Russian Text Copyright © 2004 by Shevkunov.This revised version was published online in April 2005 with a corrected cover date.     

Quantum-chemical study of C<Subscript>n</Subscript>F2<Subscript><Emphasis Type="Italic">n</Emphasis>+2</Subscript> conformers. Structure and IR spectra

Quantum-chemical calculations of the geometrical structure and vibrational spectra of C_nF_2n+2 oligomers (n = 5–8) in the chain and branched conformations are reported. The lengthening of the chain of C_nF_2n+2 does not substantially affect the geometrical parameters of the oligomers. In all cases under study, the most optimal structure of the molecule is a zigzag chain with bond lengths R(C-C) = 1.53 –1.54 and R(C-F) = 1.36 –1.34 ; the chain is rolled into a helix, which makes an angle of 17° with the plane. The IR spectra are sensitive to the structural deficiency of oligomers C_nF_2n+2 associated with the lateral trifluoromethyl groups formed in the chain; the spectra can be used for revealing defects of this type in the structure of polytetrafluoroethylene (PTFE). The possibility of defects associated with the lateral CF₃ groups in the structure of PTFE and its low-temperature modifications is explained based on the calculated total energies of C_nF2 _n+2.Original Russian Text Copyright © 2004 by L. N. Ignatieva, A. Yu. Beloliptsev, S. G. Kozlova, and V. M. BuznikTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 632–643, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Calculated properties of neutral and charged Al<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">m</Emphasis></Subscript> clusters by density functional theory

Density functional calculations are performed to study the structures and electronic properties of Al _n Co _m clusters with n = 1–7 and m = 1–2. Frequency analysis is also performed after structural optimization to make sure that the calculated ground states are real minima. The corresponding total and binding energies, adiabatic electron affinities and ionization potentials are presented and discussed to aid the identification of our calculations. The BSSE correction is also considered in our calculation. Among Al _n Co _m , Al _n Co _m ⁻, and Al _n Co _m ⁼ clusters (n = 1–7 and m = 1–2), Al₄Co⁻, Al₆Co⁻, Al₂Co₂, and Al₆Co₂ are predicted to be more stable. Our results are consistent with the available experimental data.     

Two-quantum photochemistry of the complex <Emphasis Type="Italic">cis</Emphasis>,<Emphasis Type="Italic">trans</Emphasis>-[Pt<Superscript>IV</Superscript>(en)(I)<Subscript>2</Subscript>(CH<Subscript>3</Subscript>COO)<Subscript>2</Subscript>]

The two-quantum photochemistry of aqueous solutions of cis,trans-[Pt^IV(en)(I)₂(CH₃COO)₂] (complex 1) has been studied by laser flash photolysis using an irradiation wavelength of 355 nm. This compound can be considered as a model representative of the mixed-ligand Pt(IV) complexes tested for use in photodynamic therapy. The appearance of transient absorption, presumably due to two consecutively produced Pt(III) complexes, has been revealed. The spectral and kinetic characteristics of the intermediates have been determined. A mechanism of two-quantum photolysis of complex 1 is proposed on the basis of the data obtained.     

Spatial structure and stability of Mo<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>Si<Subscript><Emphasis Type="Italic">m</Emphasis></Subscript> nanoparticles

By means of the ab initio DMol³ method Mo _n Si _m nanoparticles and fragments of Mo₃Si and MoSi₂ crystal lattices are theoretically modeled. For both crystals a few neutral Mo₄Si₆ and Mo₆Si₆ fragments of different shapes and symmetry are considered. In each case, after cluster separation its geometry is optimized, as a result of which the geometric structure noticeably changes and its stability increases. In order to theoretically search for the spatial configurations of Mo₄Si₆ and Mo₆Si₆ nanoparticle, two approaches are used: 1) in the most stable Fe₄C₆ and Fe₆C₆ isomers found previously, iron and carbon atoms are replaced by molybdenum and silicon respectively and then the geometry is optimized to obtain new equilibrium distances and angles; 2) the search for main Mo₄Si₆ and Mo₆Si₆ configurations is performed using the binominal scheme, starting from Mo₂, MoSi, and Si₂ dimers. The nanoparticle structures are found to contain metal atom chains and isolated pairs and triples of silicon atoms. In most cases, the nanoparticle stability proves to be higher than that of the crystal clusters.     

Splitting of the <Emphasis Type="Italic">d</Emphasis><Superscript><Emphasis Type="Italic">N</Emphasis></Superscript> atomic states in icosahedral 3<Emphasis Type="Italic">d</Emphasis> metal endofullerenes M@C<Subscript>60</Subscript>

Group-theoretical and quantum-chemical investigations of the spectrum of low-lying excited states have been performed by the ROHF and FCI-RAS (Full CI in Restricted Active Space) methods for 3d metal endofullerenes (MEFs) M@C₆₀ (M =Mn, Cr, and Fe) in different charged states. The major purpose of this study is quantum-chemical verification of the anomalous (“non-Bethe’s”) character of splitting of the d ^N atomic states in an electrostatic field with icosahedral symmetry, predicted previously within the theory of integral invariants theory. The interrelation between the integral invariants theory and the quantumchemical methods applied in this work is considered in detail. Our calculations suggest that the d ^N atomic states in the icosahedral field generated by fullerene C60 (I _h ) on a metal atom (ion) remain non-split for different charged states of the metal and C₆₀. Reasons for this phenomenon and other possible approaches to verification of the prediction are discussed. It is demonstrated that the d ^N states of the encapsulated metal are split in icosahedral 3d MEFs only under very strong compression of these structures.     

Study of the structure and stability of aqua ions La(H<Subscript>2</Subscript>O)<Stack><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript><Superscript>3+</Superscript></Stack> (<Emphasis Type="Italic">n</Emphasis> = 8, 9) by ab initio methods

The structural and energetic characteristics of aqua ions La(H₂O) ₈ ³⁺ and La(H₂O) ₉ ³⁺ . have been calculated by the ab initio RHF and MP2 methods with the use of different quasi-relativistic effective core potentials for the lanthanum atom.     

4<Emphasis Type="Italic">p</Emphasis><Superscript>2</Superscript> resonances in photoionization from 4<Emphasis Type="Italic">s</Emphasis>4<Emphasis Type="Italic">p</Emphasis> levels in neutral zinc

In neutral zinc the 4p ² configuration lies above the 3d ¹⁰4s ionization limit and its levels become perturbers in the continuum. Lines have been identified in the Zn I spectrum for the multiplet, whereas no lines have been found for transitions to 4p ^{2 1} D or ¹ S. In this paper, cross sections for photoionization from 4s4p levels are reported that reveal the positions and widths of the 4p ² resonances. Calculations were performed using the multiconfiguration Hartree-Fock (MCHF) and B-spline R-matrix (BSR) method. Results from Breit–Pauli calculations that ignore the background continua are also presented. Included in the latter are energies for the levels and transition data (transition energies, line strengths, f-values, and A-rates) for all E1 transitions between these levels. Transition energies and the agreement in the length and velocity values, particularly for allowed transitions, indicate the accuracy of the computational model. Line widths are compared with other estimates. Contribution to the Serafin Fraga Memorial Issue.     

<Emphasis Type="Italic">N</Emphasis>-doped carbon supported Pd catalysts for <Emphasis Type="Italic">N</Emphasis>-formylation of amines with CO<Subscript>2</Subscript>/H<Subscript>2</Subscript>

Using mesoporous N-doped carbons (NCs) derived from glucose and melamine as the supports, a series of Pd/NC catalysts were prepared, in which Pd nanoparticles with average size<2.0 nm were uniformly distributed on the supports. It was indicated that the resultant Pd/NC catalysts were effective for N-formylation of amines with CO₂ and H₂ in ethanol without any additives. Especially, the catalyst Pd/NC-800-6.9% containing quaternary N showed the best performance, affording a series of formylamides in good or even excellent yields. Further investigation reveals that the interaction between the Pd nanoparticles and quaternary nitrogen in the NC support was responsible for the good performance of the catalyst.     

The dynamics of nonadiabatic transitions in collisions between the I<Subscript>2</Subscript>(<Emphasis Type="Italic">E</Emphasis>) and I<Subscript>2</Subscript>(<Emphasis Type="Italic">X</Emphasis>) molecules

The paper presents the results of a theoretical study of the dynamics of nonadiabatic transitions between the ion-pair states E0 _g ⁺ and D0 _u ⁺ of the I₂ molecule induced by collisions with the I₂ molecule in the ground electronic state X0 _g ⁺ . The potential energy surfaces and diabatic coupling matrix elements of electronic states were obtained using a model based on the diatomics-in-molecule approximation. Special perturbation theory for intermolecular interaction was used to show that the large transition dipole moment between the E0 _g ⁺ and D0 _u ⁺ states caused the appearance of additional long-range corrections, an electrostatic dipole-quadrupole correction to the diabatic coupling matrix elements and induction dipole-dipole correction to the potential energy surface. The influence of these corrections on nonadiabatic dynamics was studied at the level of the semiclassical approximation. The electrostatic correction was found to sharply increase the contribution of resonance (accompanied by minimum kinetic energy changes) vibronic transitions at large distances between the colliding molecules. The induction correction had the opposite effect because of the high transition probability at short distances. The results obtained were in qualitative agreement with experimental data. The conclusion was drawn that obtaining quantitative agreement required a more balanced inclusion of interactions at short and long distances.     

Synthesis of epothilones molecule fragment (15<Emphasis Type="Italic">R</Emphasis>)-C<Superscript><Emphasis Type="Italic">13</Emphasis></Superscript>-C<Superscript><Emphasis Type="Italic">21</Emphasis></Superscript> from D-mannitol

Efficient synthesis of an epothilone molecules fragment (15R)-C¹³-C²¹ was carried out from D-mannitol through its conversion into methyl 2,3-O-cyclohexylidene-D-glycerate followed by the cyclopropanation of the ester group with ethylmagnesium bromide in the presence of titanium(IV) isopropoxide and the transformation of the obtained cyclopropanol into the corresponding 2-substituted allyl bromide. The coupling of the latter catalyzed by copper with 2-methylthiazolyl-4-magnesium bromide, the shift of a double carbon-carbon bond in the product obtained into the position, conjugated with the thiazole ring, and the common transformation of the protected 1,2-diol function afforded the target compound in 15% yield.     

The molecular designs and properties of asymmetric heterocycles (HBrBN<Subscript>3</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 1-4)

The structures and properties of asymmetric heterocycles (HBrBN₃) _n (n = 1-4) are systematically studied at the B3LYP/6-31G* level. The molecules (HBrBN₃) _n (n = 2-4) have the core structures of a 2n-membered ring with alternating boron and α-nitrogen atoms. The relationships between geometrical parameters and oligomerization degree n are discussed. The calculated IR spectra have four main characteristic regions. Trends in thermodynamic properties with temperature and oligomerization degree n are discussed. Thermodynamic analysis of the gas-phase oligomerizations shows that formation of the most stable heterocycles (HBrBN₃) _n (n = 2-4) is enthalpy driven in the range of 200-800 K.