Molecular wheel to monocyclic ring transition in boron-carbon mixed clusters C2B6⁻ and C3B5⁻

In this joint experimental and theoretical work we present a novel type of structural transition occurring in the series of C(x)B(8-x)(-) (x=1-8) mixed clusters upon increase of the carbon content from x=2 to x=3. The wheel to ring transition is surprising because it is rather planar-to-linear type of transition to be expected in the series since B(8), B(8)(-), B(8)(2-) and CB(7)(-) are known to possess wheel-type global minimum structures while C(8) is linear.     

Study of the reaction 2-(p-nitrophenyl)ethyl bromide + OH⁻ in dimeric micellar solutions

The dehydrobromination reaction 2-(p-nitrophenyl)ethyl bromide + OH? was investigated in several alkanediyl-α-ω-bis(dodecyldimethylammonium) bromide, 12-s-12,2Br? (with s = 2, 3, 4, 5, 6, 8, 10, 12) micellar solutions, in the presence of NaOH 5 × 10?3 M. The kinetic data were quantitatively rationalized within the whole surfactant concentration range by using an equation based on the pseudophase ion-exchange model and taking the variations in the micellar ionization degree caused by the morphological transitions into account. The agreement between the theoretical and the experimental data was good in all the dimeric micellar media studied, except for the 12-2-12,2Br? micellar solutions. In this case, the strong tendency to micellar growth shown by the 12-2-12,2Br? micelles could be responsible for the lack of accordance. Results showed that the dimeric micelles accelerate the reaction more than two orders of magnitude as compared to water.     

Predicting properties of new ionic liquids: density functional theory and experimental studies of tetra-alkylammonium salts of (thio)carboxylate anions, RCO2⁻, RCOS⁻ and RCS2⁻

Density functional theory calculations of alkyl-carboxylate anions and their sulfur substituted variants are presented here as an aid for the development of new ionic liquids. Electron transfer both within the anion, and between the anion and cation of an ion pair, are described using natural bond order analysis, using tetraethylammonium as a common cation. The overall stabilising effect of this electron transfer is quantified for the series of anions, and is found to correlate with clear trends in ion-pair binding energy. These and other electronic properties determine which compounds are synthesised, and experimental results validate the computational results. In combination with tetraethylammonium, a carboxylate with an unsaturated alkyl chain produces an ionic liquid at room temperature. However, computations suggest that sulfur substituted anions will produce a lower melting point and perhaps more fluid ionic liquid, but one which would be less stable against oxidation.     

Thermodynamics of oxygen in CaMnO3 − δ

The experimental data for equilibrium oxygen content were used in order to extract increments of partial molar thermodynamic functions of oxygen with changes of oxygen stoichiometry in calcium manganite CaMnO_3???δ . It is shown that along with the oxygen exchange reaction, thermal excitation of Mn⁴⁺ cations plays an important role in equilibration of charged manganese species that appear in response to the loss of oxygen at heating. The interrelation of partial molar enthalpy and entropy of oxygen with electron and ion defect formation parameters is obtained in approximation of the point defect model. The nearly linear changes of oxygen partial molar enthalpy are shown to directly reflect thermally driven changes in concentration of Mn³⁺ cations.     

Photosensitization of trans-Vitamin D3 to cis-Vitamin D3 in Heterogeneous System

Two modes of heterogeneous photoisomerization of trans-vitamin D3 to cis-vitamin D3 are described. The occurrence of isomerization on the substrate bounded to the polymeric support gives us the possibility in succession synthesis of 1α-hydroxyvitamin D3. The polymer-bound anthracene can sensitize isomerization of trans-vitamin D3 to cis-vitamin D3 efficiently and ease the separation process.     

Increase of Calcium Levels at Interphase in NIH 3T3 Cells

The fluorescent calcium ion indicator dye Fluo-3 and DNA-binding dye Hoechst 33342 were employed to determine, in a quantitative microspectrofluorometric study, the intracellular calcium ion concentration ([Ca~(2+)]_i) and the DNA content of individual living NIH3T3 cells. The well-separated excitation and emission properties of these dyes allowed us to establish for each cell both the phase of the cell cycle using DNA content and [Ca~(2+)]_i. We found that the transition from G_1, through S, to the G_2 phase is accompanied by a two-fold increase in [Ca~(2+)]_i. The [Ca~(2+)]_i was inhomologous in each phase of the interphase (G_1, S and G_2) although [Ca~(2+)]_i in the S and G_2 phases was never lower than certain threshold values in the G_1 and S phases respectively. [Ca~(2+)]_i in G_0 cells was lower than that in G_2 cells. These changes in [Ca~(2+)]_i suggest that [Ca~(2+)]_i may be an import regulator of cell cycle progression.     

The role of 3d orbitals in the bonding of phosphorus compounds

Ab initio LCAO-MO-SCF calculations for several typical molecules containing phosphorushave been undertaken to study the role of phosphorus 3d orbitals in the bonding.It is emphasizedthat the discussion about the 3d orbital participation in bonding should be based on a reasonable choiceof basis sets and it seems suitable to choose the atomic orbitals in proper molecular environment asthe basis set.As an approximation,the optimized minimal STO-NG basis sets have been adoptedin the present paper.The results obtained well exhibit the model of 3d orbital participation in bonding.It is shown that under the influence of highly electronegative ligands the phosphorus 3d orbitals con-tract greatly,their energy levels drop considerably,and thus they can effectively participate in bond-ing.The presence of highly electronegative ligands seems necessary.The contribution of 3d orbitalsto bonding is achieved mainly through the concertedformation of σ bonds and p-d backbonds,thoughthe contribution to σ bonding is minor.The three-center,four-electron bond modelis only approxi-mately correct.The results of the present paper demonstrate that the model of 3d orbital participationin bonding favoured by experimental chemists is reasonable and possesses sound ground.     

One electron oxidation of triferrocenylmethanol: synthesis, metal atom dynamics, electron delocalization, and the crystal structure of [Fc3COH](+) PF6⁻

The title compound 2 was prepared and its crystal structure was determined at 100 K. The neat solid was examined by temperature dependent (57)Fe M?ssbauer effect (ME) spectroscopy over the interval 92 < T < 318 K, and evidences two diamagnetic Fe(II) sites and one paramagnetic Fe(III) site. The latter shows spin-lattice relaxation, but there is no evidence of electron delocalization among the three iron sites in the above temperature interval. The mean-square-amplitude-of-vibration of the diamagnetic iron site has been determined from the recoil-free fraction ME resonance, and compared to the neutral Fc(3)COH homologue (1). The ME dynamical data are in good agreement with the U(i,j) value at 100 K extracted from the crystallographic results. The ME parameters at 5 K have also been determined with the sample compound embedded in a paraffin wax matrix as well as pelletized with BN.     

Synthesis of 2-aryl-3H-indol-3-ones via trapping reaction in singlet oxygenation of 2-arylindoles

2-Aryl-3H-indol-3-ones (3a-o) have been synthesized via methanol trapping reaction in singlet oxygenation of 2-arylindoles (1a-o), followed by thermal decomposition of the resultant 2-aryl-2-methoxy-3-oxo-2,3-dihydroindoles (2a-o) in good yields.     

Stereochemistry of electrophilic attack at 34e⁻ dimetallic complexes: the case of diiron dithiolato carbonyls + MeS⁺

Experimental and computational experiments show that the electrophile MeS(+) attacks a single Fe center in Fe(2)(propanedithiolate)(CO)(4)(PMe(3))(2) followed by isomerization of this terminal thiolato complex to the corresponding μ-SMe derivative.     

Preparation of nanometer FeCuP alloy and its application in decomposition of PH3

A new ternary Fe-based alloy catalyst FeCuP applied to decompose PH_3 was prepared with low-cost material by chemical reduction deposition method.The properties of it were characterized by XRD,ICP and SEM.Its catalytic activity on the decomposition of PH_3 and the decomposition conditions were studied.FeCuP alloy exhibits high thermal stabilities and high catalytic activity.Using it as catalyst,the decomposition temperature of phosphine decreases from over 800℃to 400-500℃.The decomposition rate of phosphine achieved 100%.     

Sequence-based analysis of 5′UTR and coding regions of CASP3 in terms of miRSNPs and SNPs in targetting miRNAs

Apoptosis is described as a mechanism of cell death occurring after adequate cellular harm. Deregulation of apoptosis occurs in many human conditions such as autoimmune disorders, ischemic damage, neurodegenerative diseases and different cancer types. Information relating miRNAs to cancer is increasing. miRNAs can affect development of cancer via many different pathways, including apoptosis. Polymorphisms in miRNA genes or miRNA target sites (miRSNPs) can change miRNA activity. Although polymorphisms in miRNA genes are very uncommon, SNPs in miRNA-binding sites of target genes are quite common. Many researches have revealed that SNPs in miRNA target sites improve or decrease the efficacy of the interaction between miRNAs and their target genes. Our aim was to specify miRSNPs on CASP3 gene (caspase-3) and SNPs in miRNA genes targeting 5′UTR and coding exons of CASP3, and evaluate the effect of these miRSNPs and SNPs of miRNA genes with respect to apoptosis. We detected 141 different miRNA binding sites (126 different miRNAs) and 7 different SNPs in binding sites of miRNA in 5′UTR and CDS of CASP3 gene. Intriguingly, miR-339-3p’s binding site on CASP3 has a SNP (rs35372903, G/A) on CASP3 5′UTR and its genomic sequence has a SNP (rs565188493, G/A) at the same nucleotide with rs35372903. Also, miR-339-3p has two other SNPs (rs373011663, C/T rs72631820, A/G) of which the first is positioned at the binding site. Here, miRSNP (rs35372903) at CASP3 5′UTR and SNP (rs565188493) at miR-339-3p genomic sequence cross-matches at the same site of binding region. Besides, miR-339-3p targets many apoptosis related genes (ZNF346, TAOK2, PIM2, HIP1, BBC3, TNFRSF25, CLCF1, IHPK2, NOL3) although it had no apoptosis related interaction proven before. This means that miR-339-3p may also have a critical effect on apoptosis via different pathways other than caspase-3. Hence, we can deduce that this is the first study demonstrating a powerful association between miR-339-3p and apoptosis upon computational analysis.     

Dissociation energies of O–H bonds in 3-pyridinols

The O?H bond dissociation energy (D _O?H) has been estimated for 20 substituted 3-pyridinols and a substituted 3-pyrimidinol from experimental kinetic data by the intersecting parabolas method using α-tocopherol and 4-methoxyphenol as reference compounds. The following D _O?H values (kJ/mol) have been obtained: 363.7 for 3-pyridinol, 365.3 for 2-alkyl-3-pyridinols (five compounds), 358.8 for 2-alkyl-6-methyl-3-pyridinols (six compounds), 378.1 for 5-benzyl-3-pyridinol, 353.2 for 2,4,6-trimethyl-3-pyridinol, 340.9 for 2-benzyl-6-methoxy-3-pyridinol, 345.8 for 2,6-dimethoxy-5-benzyl-3-pyridinol, 381.7 for 2-ethyl-4-nitro-6-methyl-3-pyridinol, 376.8 for 2-isopropyl-4-nitro-6-methyl-3-pyridinol, 318.3 for 2,4-dimethyl-6-dimethylamino-3-pyridinol, 357.3 for mexidol, and 322.2 for 2,4-dimethyl-6-dimethylamino-3-pyrimidinol. The substituent effect on the O?H bond dissociation energy in 3-pyridinols is considered. The stabilization energies of pyridinoxyl and phenoxyl radicals are compared. The activation energies and rate constants have been calculated for a series of reactions of various radicals with 3-pyridinols.     

Chemiluminescence activated by Β- diketonate complexes of Eu3+ in the thermolysis of diphenyldiazomethane in the presence of oxygen

Chemiluminescence activated by the chelates Eu(tta)₃phen and Eu(dbm)₃phen in the thermal decomposition of diphenyldiazomethane in benzene in the presence of oxygen was examined at 333 K. The following photophysical characteristics of the luminescence emitter, excited triplet benzophenone (BP), were found: the phosphorescence quantum yield ϕ _BP ⁰ = 1.0 × 10⁻⁵, the true lifetime τ _BP ⁰ = 7 × 10⁻⁸ s, and the rate constant of radiative deactivationk _{r, BP} = ϕ _BP ⁰ τ _BP ^{0 −1} = 160 s⁻¹.     

Quantum chemical modeling of the cis-trans isomerization of the allyl ligand in Ni(η3-C3H5)2 in the presence of norbornadiene

Quantum chemical (DFT/PBE) modeling of the cis-trans isomerization of the allyl ligand in bis(η³-allyl)nickel in the presence of norbornadiene revealed that the type of coordination of the norbornadiene ligand affects the energy parameters of its isomerization. The Gibbs energies of activation of the rate-limiting step for different isomerization pathways range from 23.7 to 27.8 kcal mol^?1.     

Application of Et3NHCl-AlCl3 Ionic Liquid as an Initiator in Cationic Copolymerization of 1, 3-Pentadiene with Styrene

Room temperature ionic liquids (RTILs) as advanced, technological solvents can be designed to fit a particular application. They used as green “media and/or catalysts” for chemical synthesis have been extensively reviewed recently. RTILs1 not only show …     

Modes of coordination and stereochemistry of the NO3 − anions in inorganic nitrates

Stereochemical features of 950 nitrate groups in the structures of 365 inorganic nitrates were analyzed using TOPOS software. The types of coordination of nitrate groups are systematized by means of Voronoi-Dirichlet polyhedra and the method of intersecting spheres. Terminal coordination (53% of the total number of nitrate groups), most of all terminal bidentate coordination (47%) was found to prevail. Bridging nitrate groups occur less frequently (20%). A considerable number of nitrate groups are not incorporated in the coordination sphere of the complexing atom but form H-bonds or bonds of mainly ionic nature (27%). A number of metal cations show clear-cut tendency for a certain mode of coordination of the NO₃ group. Criteria for classification of nitrate groups into four types (slightly distorted groups and groups with monodentate, bidentate and asymmetric type distortion) are proposed. Structural features of nitrate groups depending on the mode of coordination are considered. The geometry of mono- or bidentate nitrate groups can differ appreciably from the typical one because of participation of terminal oxygen atoms in ionic or hydrogen bonds. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 429–440, March, 2008.