Layered structures constructed by second-sphere coordination via N–H ··· Cl and C–H ··· Cl hydrogen bonding: synthesis and crystal structures of tribenzylamine and [MCl6] (M = Sn,Re, and Te)

A series of second-sphere coordination complexes of tribenzylamine (L ¹ ) and [MCl₆] (M = Sn, Re, Te) have been synthesized and characterized by spectroscopic techniques (IR, NMR) and single-crystal X-ray diffraction. The main driving force for the encapsulation of [MCl₆] and recognition with L ¹ is the second-sphere coordination of metal halides by the amide protons of the ligand via hydrogen bonding (N–H ··· Cl–M and C–H ··· Cl–M); new layered structures are described. Thermal stability and irreversible behavior of second-sphere coordination complexes [L ² ] · 0.5[TeCl₆]^2? · HCl · (H₃O)⁺ · 0.5H₂O (L ² = N,N,N′,N′-tetrabenzyl-ethylenediamine) in contact with water vapor are also described.     

Atomistic understanding of the C·T mismatched DNA base pair tautomerization via the DPT: QM and QTAIM computational approaches

It was established that the cytosine·thymine (C·T) mismatched DNA base pair with cis‐oriented N1H glycosidic bonds has propeller‐like structure (|N3C4C4N3| = 38.4°), which is stabilized by three specific intermolecular interactions–two antiparallel N4H…O4 (5.19 kcal mol^?1) and N3H…N3 (6.33 kcal mol^?1) H‐bonds and a van der Waals (vdW) contact O2…O2 (0.32 kcal mol^?1). The C·T base mispair is thermodynamically stable structure (ΔG_int = ?1.54 kcal mol^?1) and even slightly more stable than the A·T Watson–Crick DNA base pair (ΔG_int = ?1.43 kcal mol^?1) at the room temperature. It was shown that the C·T ? C*·T* tautomerization via the double proton transfer (DPT) is assisted by the O2…O2 vdW contact along the entire range of the intrinsic reaction coordinate (IRC). The positive value of the Grunenberg's compliance constants (31.186, 30.265, and 22.166 Å/mdyn for the C·T, C*·T*, and TS_{C·T ? C*·T*}, respectively) proves that the O2…O2 vdW contact is a stabilizing interaction. Based on the sweeps of the H‐bond energies, it was found that the N4H…O4/O4H…N4, and N3H…N3 H‐bonds in the C·T and C*·T* base pairs are anticooperative and weaken each other, whereas the middle N3H…N3 H‐bond and the O2…O2 vdW contact are cooperative and mutually reinforce each other. It was found that the tautomerization of the C·T base mispair through the DPT is concerted and asynchronous reaction that proceeds via the TS_{C·T ? C*·T*} stabilized by the loosened N4? H? O4 covalent bridge, N3H…N3 H‐bond (9.67 kcal mol^?1) and O2…O2 vdW contact (0.41 kcal mol^?1). The nine key points, describing the evolution of the C·T ? C*·T* tautomerization via the DPT, were detected and completely investigated along the IRC. The C*·T* mispair was revealed to be the dynamically unstable structure with a lifetime 2.13·× 10^?13 s. In this case, as for the A·T Watson–Crick DNA base pair, activates the mechanism of the quantum protection of the C·T DNA base mispair from its spontaneous mutagenic tautomerization through the DPT. © 2013 Wiley Periodicals, Inc.     

Structure and Barrier to Internal Rotation of Trichloroacetyl Chloride Molecules,According to ab initio Calculations

The optimal geometry of the CCl₃COCl molecule and the barrier to intramolecular rotation of the CCl₃ group (11.8 kJ mol^{- 1}) were determined by RHF/6-31G* calculations. The results were compared to the experimental data.     

Is the DPT tautomerization of the long A·G Watson–Crick DNA base mispair a source of the adenine and guanine mutagenic tautomers? A QM and QTAIM response to the biologically important question

Herein, we first address the question posed in the title by establishing the tautomerization trajectory via the double proton transfer of the adenine·guanine (A·G) DNA base mispair formed by the canonical tautomers of the A and G bases into the A*·G* DNA base mispair, involving mutagenic tautomers, with the use of the quantum‐mechanical calculations and quantum theory of atoms in molecules (QTAIM). It was detected that the A·G ? A*·G* tautomerization proceeds through the asynchronous concerted mechanism. It was revealed that the A·G base mispair is stabilized by the N6H···O6 (5.68) and N1H···N1 (6.51) hydrogen bonds (H‐bonds) and the N2H···HC2 dihydrogen bond (DH‐bond) (0.68 kcal·mol^?1), whereas the A*·G* base mispair—by the O6H···N6 (10.88), N1H···N1 (7.01) and C2H···N2 H‐bonds (0.42 kcal·mol^?1). The N2H···HC2 DH‐bond smoothly and without bifurcation transforms into the C2H···N2 H‐bond at the IRC = ?10.07 Bohr in the course of the A·G ? A*·G* tautomerization. Using the sweeps of the energies of the intermolecular H‐bonds, it was observed that the N6H···O6 H‐bond is anticooperative to the two others—N1H···N1 and N2H···HC2 in the A·G base mispair, while the latters are significantly cooperative, mutually strengthening each other. In opposite, all three O6H···N6, N1H···N1, and C2H···N2 H‐bonds are cooperative in the A*·G* base mispair. All in all, we established the dynamical instability of the А*·G* base mispair with a short lifetime (4.83·10^?14 s), enabling it not to be deemed feasible source of the A* and G* mutagenic tautomers of the DNA bases. The small lifetime of the А*·G* base mispair is predetermined by the negative value of the Gibbs free energy for the A*·G* → A·G transition. Moreover, all of the six low‐frequency intermolecular vibrations cannot develop during this lifetime that additionally confirms the aforementioned results. Thus, the A*·G* base mispair cannot be considered as a source of the mutagenic tautomers of the DNA bases, as the A·G base mispair dissociates during DNA replication exceptionally into the A and G monomers in the canonical tautomeric form. © 2013 Wiley Periodicals, Inc.     

Ab initio calculations of group IVA tetrachloride complexes: IX. Special features of the energy characteristics of the complexes

Quantum-chemical calculations of systems Cl₄M L and Cl₄M 2L (M = Si, Ge) with full geometry optimization and with a fixed M L distance, as well as calculations of the individual components of the complexes are performed by the RHF/6-31G(d) and B3LYP/6-311+G(2d,p) methods. It is shown that in the crystal state the molecular form may differ from that most favored by energy. The total energy of trans-octahedral complexes of GeCl₄ with organic ligands is lower than the sum of the energies of their constituent components, while that of analogous SiCl₄ complexes may be either lower or higher than the sum of the energies of their constituent components. Even though trigonal-bipyramidal complexes of MCl₄ with organic ligands are commonly energetically unfavorable, they still can form. The formation of MCl₄ complexes is affected substantially by intermolecular interactions in crystal.     

Synthese und XPS-Analyse von nano-skaligen Metall/Metalloxid-Kompositen mit Germanium,Zinn und Blei als metallische Komponente

Synthesis and XPS Analysis of nano-scaled Metal/Metaloxid Composites with Germanium, Tin, and Lead as Metallic Component tert-Butanolates of Germanium(II), tin(II), and lead(II) of the formula {M[O-C(CH₃)₃]₂}_n (M ? Ge, n = 2; M ? Sn, n = 2; M ? Pb, n = 3) as well as the corresponding heterometalalkoxides M′M₂[O? C(CH₃)₃]₆ (M ? Ge, M′ ? Sr, Ba; M ? Sn, M′ ? Ca, Sr, Ba; M ? Pb, M′ ? Ca, Ba) have been subject to a single precursor chemical vapour deposition (CVD) process. In this process the volatile precursor has been pyrolized under reduced pressure (0,1 Torr) on a graphit or metal substrate which has been heated by induction in a microwave field to about 300–500°C. The gases originating from this pyrolisis have been analyzed by means of a quadrupole mass spectrometer whereas the solid coating which contained the micro composite was characterized by X-ray diffraction, electron microscopy, EDX-analysis and XPS-spectra. In all cases the solid material contained two phases, in which the element M ((Ge), Sn, Pb) either had oxidation state 0 or +4 (in the surface of the solids made of germanium containing precursors only Ge^II along with Ge⁰ has been detected by XPS spectroscopy). The group 14-element in the starting material had thus undergone a disproportionation from the +2 oxidation state into a lower and a higher one by two units. The elemental phase and the phase containing the formal +4 cation which is amorphous in most cases and which approaches the formula MO₂ or M′MO³ (M ? (Ge), Sn, Pb; M′ ? Ca, Sr, Ba) are uniformally distributed. The composites consist of ball shaped particles on which other smaller particles are placed in a fractal manner ressembling a black berry. In the case of the composite Sn · BaSnO³ the center of the ball shaped particles has been analyzed as pure elemental tin. The organic substituents of the precursors as well as the dynamic vacuum in the decomposition process seem to be responsible for the ball shaped nature of the solid material. In a test experiment gallium tri-tert-but-oxide has been used as precursor: again ball shaped particles are obtained which have the chemical composition Ga₂O₃ but which contain no elemental gallium.     

Syntheses,structures and properties of four second-sphere coordination complexes via metal halide anion and naphthalene-based ligand

Second-sphere coordination refers to any intermolecular interactions with the ligands directly bound to the primary coordination sphere of a metal ion. Four supramolecular complexes, 0.5[L·2H]²⁺·0.5[MCl₄]^2?·[CH₃OH]·0.5[CH₂Cl₂] (M = Co, crystal 1; M = Mn, crystal 2), 0.5[L·2H]²⁺·0.5[ZnBr₄]^2?·[CH₃OH]·0.5[CH₂Cl₂] (crystal 3), and 0.5[L·2H]²⁺·0.5[Cu₂Br₄]^2?·H₂O (crystal 4), based on naphthalene-based ligand N,N,N′,N′-tetra-p-methylnaphthyl-ethanediamine (L), have been synthesized. X-ray analysis reveals that 1–3 are isostructural, in which the methanol molecules are bridges, connecting the protonated L and metal chloride anions via N–H?O and O–H?Cl (Br) interactions to construct the host framework, and forming X-shaped cavity accessible for the inclusion of weakly polar guest molecules of dichloromethane. Dichloromethane is connected with the host framework through van der Waals forces. In 4, a dinuclear anion [Cu₂Br₄]^2? is connected with the ligand through N–H?Br interactions, in which the water molecules are accommodated between chains formed by the ligand and [Cu₂Br₄]^2?. Structure stability, thermal analysis, and photoluminescent properties were studied for 1–4.     

Synthese und Kristallstrukturen der heteronuklearen Nitrido‐Komplexe [(Me2PhP)3(MeCN)ClRe≡N–MCl5] mit M = Sn und Zr

Synthesis and Structures of the Dinuclear Nitrido Complexes [(Me₂PhP)₃(MeCN)ClRe≡N–MCl₅] with M = Sn and Zr The water sensitive complexes [(Me₂PhP)₃(MeCN)ClRe≡N–MCl₅] (M = Sn ( 1 ) und Zr ( 2 )) are obtained in dichloromethane from [ReNCl₂(PMe₂Ph)₃] and the acetonitrile adducts of SnCl₄ or ZrCl₄. The compounds crystallize as dichloromethane solvate isotypically with [(Me₂PhP)₃(MeCN)ClRe≡N–TiCl₅] · CH₂Cl₂ in the space group P2₁/n. From toluene crystallize monoclinic crystals of 1 · MeCN · C₇H₈. In the diamagnetic complexes 1 and 2 an anion [MCl₅]^– coordinates to the nitrido ligand of the cationic complex [ReNCl(MeCN)(PMe₂Ph)₃]⁺. The resulting nitrido bridges Re≡N–M are almost linear and asymmetric with Re–N = 169.5 pm, Sn–N = 230.1 pm and Re–N–Sn = 164.5° for 1 and Re–N = 168.4 pm, Zr–N = 237.2 pm and Re–N–Zr = 165.6° for 2 . The phosphine ligands at the Re atom are in a meridional arrangement.     

Theoretical studies of structure,stability, and chemical bonding in oxohydride OM4H6 complexes

The results of ab initio RHF/3-21G, RHF/6-31G*, and MP2/6-31G** / / HF/6-31G* calculations for 10 possible configurations of OM₄H₆ molecules (MO · 3MH₂, M = Be, Mg) are reported. Five isomers of OBe₄H₆ and three isomers of OMg₄H₆ have been found within an energy range of ã 15 kcal mol⁻¹. The “lanternlike” C_3v structure is the most favorable one for both complexes. Both molecules OM₄H₆ are stable to decomposition through all of the studied pathways. Chemical bonding in the OM_k polyhedra containing two-, three-and four-coordinated oxygen atoms is discussed. © 1996 John Wiley & Sons, Inc.     

Structure and stability of B+13 clusters

The structures and energies of B⁺₁₃, observed experimentally to be an unusually abundant species among cationic boron clusters, have been studied systematically with B3LYP/6–31G* density functional theory. The most thermodynamically stable B⁺₁₂ and B⁺₁₃ clusters are confirmed to have planar or quasiplanar rather than globular structures. However, the computed dissociation energies of the 3-dimensional B⁺₁₃ clusters are much closer to the experimental values than those of the planar or quasiplanar structures. Hence, planar and 3-dimensional B⁺₁₃ may both exist. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 203–214, 1998     

Dibutyltin(IV) complexes of the 5-[(E)-2-(Aryl)-1-diazenyl]-2-hydroxybenzoic acid ligand: an investigation of structures by X-ray diffraction, solution and solid state tin NMR, electrospray ionisation MS and assessment of in vitro cytotoxicity

A series of dibutylbis{5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoato}tin(IV) complexes, Bu₂Sn(LH)₂, have been prepared and characterized by ¹H, ¹³C, ¹¹⁹Sn NMR and ESI mass spectrometry in solution. The structures of the complexes Bu₂Sn(L¹H)₂ (1), Bu₂Sn(L³H)₂ (3), Bu₂Sn(L⁴H)₂ (4), and Bu₂Sn(L⁶H)₂ (6) (L = 5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoate: aryl = phenyl (L¹H), 3-methylphenyl (L³H), 4-methylphenyl (L⁴H) and 4-bromophenyl (L⁶H)) were determined by X-ray crystallography and ¹¹⁷Sn CP-MAS NMR spectroscopy in the solid state. In general, the complexes were found to adopt a skew-trapezoidal bipyramidal arrangement around the tin atom. In addition, there are weak bridging intermolecular Sn?O contacts in complexes 1 and 3, but not in 4 and 6, where one of the hydroxy oxygen atoms from a neighboring molecule coordinates weakly with the Sn atom, thereby completing a seventh coordination site in the extended Sn coordination sphere. The Sn?O distance is 3.080(2) and 3.439(2) Å in 1 and 3, respectively, which are significantly shorter than the sum of the van der Waals radii of the Sn and O atoms (∼3.8 Å). In 1, this Sn?O interaction links the molecules into polymeric chains. In 3, these interactions link pairs of molecules into head-to-head dimeric units. The in vitro cytotoxicity of compound 2 indicates better results than cisplatin and etoposide against seven well characterized human tumor cell lines.     

Synthese und Strukturuntersuchungen von Ba2H[α-FeO4W12O36] · 26 H2O

Synthesis and Structure Studies of Ba₂H[α-FeO₄W₁₂O₃₆] · 26 H₂O The heteropolyanion compound Ba₂H[α-FeO₄W₁₂O₃₆] · 26 H₂O (I) crystallizes in the tetragonal space group P4 n2 with the lattice parameters a = 12.398(6), c = 18.721(6) Å; Z = 2; D_x = 4.128 g · cm^?3. The structure was solved on a twinned crystal from 1029 observed reflections and refined to an index R of 7.6%. The calculations were done by means of a modified ORFLS-programme by Eitel and Bärnighausen. The heteropolyanion [α-FeO₄W₁₂O₃₆]^5? has the well known α-Keggin structure. The average distance of the four central oxygen atoms to the Fe^III position (0, 0, 0) is 1.84 Å. The angles ? O? Fe? O are 112.3° (4X) and 103.9 (2X), respectively, which leads to an disphenoidal distortion of the FeO₄ tetrahedron. The powder and single crystal ESR spectra of I show the anisotropy of the Fe^III fine structure transition 1/2 ? ?1/2. The Mößbauer spectra confirm the tetragonal distortion of the central FeO₄ tetrahedron (quadrupole splitting Δ ≈ 0.50 mm · s^?1).     

Fluorines in tetrafluoromethane as halogen bond donors: Revisiting address the nature of the fluorine's σhole

It has been demonstrated in several instances that the 0.001 a.u. (electrons per bohr³) isodensity mapped electrostatic surface potentials on the fluorines along the outermost extensions of the C? F covalent bonds in tetrafluoromethane (CF₄) are entirely negative, they are thereby unable to engage in σ_hole bonding interactions with the negative sites on another molecules. In this study, we have attempted at resolving this controversy by performing various high‐level electronic structure calculations with Quadratic Configuration Integrals of Singles and Doubles QCISD(full), second‐order Møller–Plesset MP2(full), and 12 other Density Functional Theory (DFT) based functionals with and without dispersion corrections, all in conjunction with the 6–311++G(2d,2p) basis set. The results achieved with all the levels of theory utilized suggest that the fluorine's σ_holes in CF₄ are positive regardless of the 0.001‐, 0.0015‐, and 0.002‐a.u. isodensity mapped electrostatic surfaces examined. Because of this specific quality, the fluorines in CF₄ have displayed their capacities to form not only 1:1 clusters with the Lewis bases such as water (H₂O), ammonia (NH₃), formaldehyde (H₂C?O), hydrogen fluoride (HF), and hydrogen cyanide (HCN), but also 1:2, 1:3, and 1:4 clusters with the latter three randomly chosen Lewis bases. Various topological and nontopological features obtained from applications of atoms in molecules, noncovalent interaction reduced‐density‐gradient and natural bond orbital analytical tools reveal that the N···F, O···F, and F···F long‐ranged interactions developed between the interacting monomers in H₃N···FCF₃, H₂O···FCF₃, and (Y? D)_n=1–4···F₄C (Y? D = H₂C?O, HCN, and HF) are reminiscent of halogen bonding. The nonadditive cooperative and anticooperative energetic effects emerged on cluster formations are discussed in detail. © 2015 Wiley Periodicals, Inc.     

Liquid density,viscosity and spectroscopic studies of binary mixture of tetraethylene glycol + 1,2-ethanediamine for CO2 capture

Thermophysical properties for binary mixture of tetraethylene glycol (T₄EG) (1) + 1,2-ethanediamine (EDA) (2), a potential scrubbing solution for the absorption of CO₂, are very important as well as lacking in the literatures. This work reports densities and viscosities over the entire concentration range for the binary mixture at T = (293.15-318.15) K under atmospheric pressure. According to the experimental density and viscosity values, the mixtures’ excess molar volume (V_m^E), absolute viscosity deviation (?η), excess free energies of activation (?G*^E), apparent molar volumes, partial molar volumes and isobaric thermal expansion coefficient were calculated, respectively. Meanwhile, the V_m^E, ?η and ?G*^E values were fitted by a Redlich–Kister equation to obtain coefficients. To further study, the Fourier transform infrared, UV-Vis and fluorescence spectra of T₄EG + EDA mixtures with various concentrations were measured, and the intermolecular interaction of T₄EG with EDA was also discussed as the formation of –OCH₂CH₂O–H···N(H₂)CH₂CH₂(H₂)N···.     

Metall-Koordinationsverbindungen aus Essigsäure. I Chlorometallate(III) des Eisens,Chroms und Vanadiums

Metal Coordination Compounds Prepared in Acetic Acid. I. Chlorometalates(III) of Iron, Chromium, and Vanadium Ternary chloride-hydrates A₂MCl₅ · H₂O (A = Cs, Rb, (K)) can be precipitated with HCl from solutions of MCl₃ · 6 H₂O, (M = Fe, Cr, V) and alkali metal acetates in acetic acid. Under special conditions also compounds of the composition Cs₃MCl₆ · H₂O can be obtained. After dehydration of the solutions with acetyl chloride, anhydrous compounds are formed: Cs₃Fe₂Cl₉; A₃CrCl₆ and A₃Cr₂Cl₉ with A = Cs, Rb; Cs₃VCl₆ and Cs₃V₂Cl₉. V^III is partially oxidized to V^IV by an excess of acetyl chloride. Compounds A₂VCl₆ with A = Cs, Rb can be obtained more conveniently by the reaction of VOCl₂ · H₂O in acetic acid with acetyl chloride. The lattice parameters of some compounds were determined from powder patterns in analogy to known structure families.     

Self-assembly of ionic triorganotin(IV) complexes of tetrafluorophthalic acid with a tetranuclear macrocyclic or polymeric structure: syntheses,characterization and crystal structures

Four triorganotin(IV) complexes constructed from tetrafluorophthalic acid (H₂tfp) with a 1?:?1?:?1 molar ratio of H₂tfp: Et₃N: R₃SnCl gave two of type {[R₃Sn (tfp)].Et₃NH}₄ (R?=?Me 1, R?=?n-Bu 2), and two of type [R₃Sn (tfp).Et₃NH] _n (R?=?PhCH₂ 3, Ph 4). All the complexes are characterized by elemental, IR, ¹H, ¹³C and ¹¹⁹Sn NMR analyses. Complexes 1 and 4 were also confirmed by X-ray crystallography. Complex 1 is tetranuclear with a 28-membered C₁₆O₈Sn₄ macrocyclic ring system with a cavity. The supramolecular structure of 1 has been found to consist of a three-dimensional network built up by intermolecular N–H?···?O, C–H?···?O hydrogen bonds and C–F?···?F weak interactions. Complex 4 is an infinite polymeric structure. The salient feature of the supramolecular structure of 4 is that of a two-dimensional plane, in which intermolecular N–H?···?O and C–H?···?π hydrogen bonds are important.     

A theoretical investigation of the interaction between substituted carbonyl derivatives and water: Open or cyclic complexes?

The structures and binding energies of complexes between substituted carbonyl bases and water are the B3LYP/6‐311++G(d,p) computational level. The calculations also include the proton affinity (PA) of the O of the C?O group, the deprotonation enthalpies (DPE) of the CH bonds along a natural bond orbital analysis. The calculations reveal that stable open C?O···H_wO_w as well as cyclic CH···O_wH_w···O?C complexes are formed. The binding energies for the open complexes are linearly related to the PAs, whereas the binding energies for the cyclic complexes depend on both the PA and DPE. Different indicators of hydrogen bonds strength such as electron charge density, intramolecular and intermolecular hyperconjugation energy, occupation of orbitals, and charge transfer show significant differences between open and cyclic complexes. The contraction of the CH bond of the formyl group and the corresponding blue shift of the ν(CH) vibration are explained by the classical trans lone pair effect. In contrast, the elongation or contraction of the CH₃ group involved in the interaction with water results from the variation of the orbital interaction energies from the σ(CH) bonding orbital to the σ* and π* antibonding orbitals of the C?O group. The resulting blue or red shifts of the ν(CH₃) vibrations are calculated in the partially deuterated isotopomers. © 2012 Wiley Periodicals, Inc.     

Stereochemical applications of mass spectrometry. 3—Energy dependence of the fragmentation of stereoisomeric methylcyclohexanols

Breakdown graphs have been constructed from charge exchange data for the epimeric 2-methyl-, 3-methyl- and 4-methyl-cyclohexanols. Although the breakdown graphs for epimeric pairs are essentially identical above ～12 eV recombination energy, significant differences are observed for the epimeric 2-methyl- and 4-methyl-cyclohexanols at low internal energies. For the 2-methylcyclohexanols the ratio ([M? H₂O]^+·/[M]^+·)_cis/([M? H₂O]^+·/[M]^+·)_trans is 3.2 in the [C₆F₆]^+· charge exchange mass spectra. This is attributed to both energetic and conformational effects which favour the stereospecific cis-1,4-H₂O elimination for the cis epimer. The breakdown graph for trans-4-methylcyclohexanol shows a sharp peak in the abundance of the [M? H₂O]^+· ion at ～10 eV recombination energy which is absent from the breakdown graph for the cis epimer. This peak is attributed to the stereospecific cis-1,4-elimination of water from the molecular ion of the trans isomer; the reaction appears to have a low critical energy but a very unfavourable frequency factor, and alternative modes of water loss common to both epimers are observed at higher energies. As a result, in the [C₆F₆]^+· charge exchange mass spectra the ([M? H₂O]^+·/[M]^+·)_trans/([M? H₂O]^+·/[M]^+·)_cis ratio is ～24, compared to the value of 13 observed in the 70 eV EI mass spectra. No differences are observed in either the metastable ion abundances or the associated kinetic energy releases for epimeric molecules.     

Cooperative enhancement of water binding to antiparallel β‐sheet models: Analysis by ab initio calculations

The cooperative enhancement of water binding to the antiparallel β‐sheet models has been studied by quantum chemical calculations at the MP2/6‐311++G**//MP2/6‐31G* level. The binding energies of the two antiparallel β‐sheet models consisting of two strands of diglypeptide are calculated by supermolecular approach. Then water molecules are gradually bonded to the diglypeptide by N? H···OH₂ and C?O···HOH hydrogen bonds. Our calculation results indicated that the hydrogen bond length and the atom charge distribution are affected by the addition of H₂O molecules. The binding energy of antiparallel diglypeptide β‐sheet models has a great improvement by the increasing of the hydrogen bond cooperativity and the more H₂O molecules added the more cooperativity enhancement can be found. The orbital interactions are calculated by natural bond orbital analysis, and the results indicate that the cooperative enhancement is closely related to the orbital interaction. © 2012 Wiley Periodicals, Inc.     

Improving the visible-light photocatalytic activity of SnO<Subscript>x</Subscript>·SiO<Subscript>2</Subscript> glass systems by introducing SnO<Subscript>x</Subscript> nanoparticles

Tin silicate glass without SnO_x nanoparticles (SiO₂·SnO_x), a silica glass containing only SnO_x nanoparticles (SiO₂·SnO_xNP) and the improved product, which combines the tin silicate glass with SnO_x nanoparticles (SiO₂·SnO_x·SnO_xNP) was prepared. For the structural analysis ¹¹⁹Sn Mössbauer spectroscopy and X-ray diffraction were applied. The ¹¹⁹Sn Mössbauer spectra showed that the SiO₂·SnO_x·SnO_xNP sample had the largest Sn^II content (12.0%). It also had an outstanding methylene blue degradation with the first-order rate value with (18?±?2) × 10^?3 min^?1 with visible light irradiation.