Synthesis and characterization of [Zn(2,2′-bipy)]2(H2PO3)4: A neutral zinc phosphite cluster containing ZnO3N2 and H2PO3 units

The hydrothermal synthesis, crystal structure and some properties of a zinc phosphite with a neutral cluster, [Zn(2,2′-bipy)]₂(H₂PO₃)₄, are reported. This compound crystallizes in the triclinic system of space group P-1 (No. 2), a=8.3067(5) Å, b=8.9545(4) Å, c=10.0893(6) Å, α=95.448(2)°, β=99.7530(10)°, γ=103.461(2)°, V=712.23(7) ų, Z=1. The cluster consists of 4-membered rings formed by alternating ZnO₃N₂ square pyramids and H₂PO₃ pseudo pyramids, with two “hanging” H₂PO₃ groups attached to each of the Zn centers. The clusters are linked together by extensive multipoint hydrogen bonding involving the phosphite units to form a sheet-like structure. This compound represents the first example of zinc phosphite with P---OH bonds. An intense photoluminescence was observed from this compound upon photoexcitation at 388 nm.     

[{(NiOH)2Mo10O36(PO4)Ti2}n]: a novel chainlike trimetal heteropolyanion based on pseudo-keggin fragments

A new mixed Mo/Ni/Ti heteropoly compound [C₅H₅NH]₅ [(NiOH)₂Mo₁₀O₃₆(PO₄)Ti₂] has been hydrothermally synthesized and structurally determined by the single-crystal X-ray diffraction. Black prismatic crystals crystallize in the monoclinic system, space group P2(1)/n, a=11.2075(2), b=37.8328(5) c=13.0888(1) Å, β=101.4580(10)°, M=2276.13, V=5439.19(13) ų, Z=4. Data were collected on a Siemens SMART CCD diffractometer at 293(2) K in the range of 1.68<θ<25.09° using the ω-scan technique (λ=0.71073 Å R(F)=0.0872 for 9621 reflections). The title compound contains a trimetal heteropolyanion polymer and “trans-titanium”-bridging pseudo-Keggin fragments linked to a chain.     

Measurement of inter- and intramolecular charge transfer in the complex N2ICl from analysis of halogen nuclear quadrupole hyperfine structure in the rotational spectrum

The ground-state rotational spectra of two isotopomers ¹⁵N₂I³⁵Cl and ¹⁵N₂I³⁷Cl of a complex formed between dinitrogen and iodine monochloride were observed by pulsed-jet, Fourier-transform microwave spectroscopy. The spectra were interpreted on the basis of a linear equilibrium geometry with the weak bond formed between N and I. The spectroscopic constants B₀, D_J, χ_aa(I), χ_aa(Cl) and M_bb(I) were determined for each isotopomer and various models for the complex were employed to yield the distance r(NI)=3.180(2)Å, the intermolecular stretching force constant k_σ=5.37(3) Nm⁻¹, and the inter- and intramolecular electronic transfers δ_i=0.004(3) and δ_p(Cl)=0.018(2).     

Unusual Disordering of Potassium Ions in the Structures of Cluster Rhenium Thiohalides K3[Re6S7Br7] and K4[Re6S8Cl6]

New cluster compounds — rhenium and potassium thiohalides K₃Re₆S₇Br₇ (I) and K₄Re₆S₈Cl₆ (II) — have been synthesized. Their crystal structures have been determined by single crystal X-ray diffraction. The compounds are monoclinic; (I): space group P2₁/c, a = 9.32(1) Å, b = 13.528 Å, c = 12.413 Å, β = 110.21°, Z = 2, R = 0.038; (II): space group C2/m, a = 10.614 Å, b = 17.268 Å, c = 10.448 Å, β = 110.755°, Z = 2, R = 0.042. In both structures, the potassium ions are considerably distorted. The occupancies of the potassium sites are 0.17-0.34 (I) and 0. 01-0.26 (II), correlating well with the coordination numbers (c.n. 7-10 and 2-7 for I and II, respectively). In I, adjacent positions of potassium atoms are aggregated into discrete tetrahedral and angular clusters; in II, the individual (four-and six-membered) cyclic clusters of potassium sites are present along with bent chains of vertex-and edge-sharing tetrahedral “potassium clusters.” The shortest K-K distances in these “clusters” vary from 1.31 Å to 1.54 Å (I) and from 0.66 Å to 1.65 Å (II). The “instability” of the potassium site suggests that I and II are ion conductors.Original Russian Text Copyright © 2004 by S. F. Solodovnikov, S. S. Yarovoi, Yu. V. Mironov, A. V. Virovets, and V. E. Fedorov__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 909–917, September–October, 2004.     

Bis(diphenylphosphino)methane trimethylphosphine alkyl and η-cyclopentadienyl compounds of rhodium(I); P{H} two dimensional δ/J resolved and Overhauser effect nuclear magnetic resonance spectroscopy

Neutral mononuclear tertiary phosphine rhodium(I) complexes of the formula RhX(PMe₃)(dppm), X = Cl, CH₂SiMe₃, CH₂CMe₃, CH₂CMe₂Ph, η⁵-C₅H₅, DPPM = bis(diphenylphosphino)methane, RhCl(PPh₃)(dppm), RhX(dppm)₂, X = Cl, Me and Rh(η⁵-C₅H₅(dppm) have been synthesised. In Rh(η⁵-C₅H₅)(PMe₃)(dppm), the dppm ligand is unidentate according to ³¹P{¹H} NMR and X-ray data.The ³¹P{¹H} NMR spectral parameters of RhX(PR₃)(dppm) have been determined by a combination of two dimensional δ/J resolved spectroscopy and heteronuclear nuclear Overhauser effect difference spectroscopy (NOEDS) in conjunction with iterative analysis of the one dimensional spectra.     

Solid–liquid metastable equilibria in the quaternary system (NaCl–KCl–CaCl2–H2O) at 288.15 K

The solubilities and the physicochemical properties (densities, viscosities, refractive indices, conductivities, and pH) in the liquid–solid metastable system (NaCl–KCl–CaCl₂–H₂O) at 288.15 K have been studied using the isothermal evaporation method. Based on the experimental data, the dry-salt phase diagram, water-phase diagram and the diagram of physicochemical properties vs. composition in the system were plotted. The dry-salt phase diagram of the system includes one three-salt co-saturated point, three metastable solubility isotherm curves, and three crystallization regions corresponding to sodium chloride, potassium chloride and calcium chloride hexahydrate. Neither solid solution nor double salts were found. Based on the extended Harvie–Weare (HW) model and its temperature-dependent equation, the values of the Pitzer parameters β⁽⁰⁾, β⁽¹⁾, C for NaCl, KCl and CaCl₂, the mixed ion-interaction parameters θ_Na,K, θ_Na,Ca, θ_K,Ca, Ψ_Na,K,Cl, Ψ_Na,Ca,Cl, Ψ_K,Ca,Cl, the Debye–Hückel parameter A and the standard chemical potentials of the minerals in the quaternary system at 288.15 K were obtained. In addition, the average equilibrium constants of metastable equilibrium solids at the same temperature were obtained using a method derived from the activity product constant for the metastable system. Using the standard chemical potentials of the minerals and the average equilibrium constants of solids at equilibrium, the solubility predictions for the quaternary system are presented. A comparison between the calculated and experimental results shows that the predicted solubilities obtained with the extended HW model using the average equilibrium constants agree well with experimental data.     

Polyatomic ions in inductively coupled plasma–mass spectrometry: Part II: Origins of N2H and HxCO ions using experimental measurements combined with calculated energies and structures

Several polyatomic ions in inductively coupled plasma–mass spectrometry are studied experimentally and by computational methods. Novel calculations based on spin-restricted open shell second order perturbation theory (ZAPT2) and coupled cluster (CCSD(T)) theory are performed to determine the energies, structures and partition functions of the ions. These values are combined with experimental data to evaluate a dissociation constant and gas kinetic temperature (T_gas) value. In our opinion, the resulting T_gas value can sometimes be interpreted to deduce the location where the polyatomic ion of interest is generated. The dissociation of N₂H⁺ to N₂⁺ leads to a calculated T_gas of 4550 to 4900 K, depending on the computational data used. The COH⁺ to CO⁺ system yields a similar temperature, which is not surprising considering the similar energies and structures of COH⁺ and N₂H⁺. The dissociation of H₂CO⁺ to HCO⁺ leads to a much lower T_gas (< 1000 to 2000 K). Finally, the dissociation of H₂COH⁺ to HCOH⁺ generates a T_gas value between those from the other H_xCO⁺ ions studied here. All of these measured T_gas values correspond to formation of extra polyatomic ion in the interface or extraction region. The computations reveal the existence of isomers such as HCO⁺ and COH⁺, and H₂CO⁺ and HCOH⁺, which have virtually the same m/z values and need to be considered in the interpretation of results.     

Five-coordinate pentafluorobenzothiolate osmium(IV) complexes [Os(SC6F5)4(P(C6H4X-4)3)] (X = OCH3, CH3, F, Cl or CF3): Solid and solution structural characterization

The reactions of OsO₄ with excess of HSC₆F₅ and P(C₆H₄X-4)₃ in ethanol afford the five-coordinate compounds [Os(SC₆F₅)₄(P(C₆H₄X-4)₃)] where X = OCH₃ 1a and 1b, CH₃ 2a and 2b, F 3a and 3b, Cl 4a and 4b or CF₃ 5a and 5b. Single crystal X-ray diffraction studies of 1 to 5 exhibit a common pattern with an osmium center in a trigonal-bipyramidal coordination arrangement. The axial positions are occupied by mutually trans thiolate and phosphane ligands, while the remaining three equatorial positions are occupied by three thiolate ligands. The three pentafluorophenyl rings of the equatorial ligands are directed upwards, away from the axial phosphane ligand in the arrangement “3-up” (isomers a). On the other hand, ³¹P{¹H} and ¹⁹F NMR studies at room temperature reveal the presence of two isomers in solution: The “3-up” isomer (a) with the three C₆F₅-rings of the equatorial ligands directed towards the axial thiolate ligand, and the “2-up, 1-down” isomer (b) with two C₆F₅-rings of the equatorial ligands directed towards the axial thiolate and the C₆F₅-ring of the third equatorial ligand directed towards the axial phosphane. Bidimensional ¹⁹F–¹⁹F NMR studies encompass the two sub-spectra for the isomers a (“3-up”) and b (“2-up, 1-down”). Variable temperature ¹⁹F NMR experiments showed that these isomers are fluxional. Thus, the ¹⁹F NMR sub-spectra for the “2-up, 1-down” isomers (b) at room temperature indicate that the two S-C₆F₅ ligands in the 2-up equatorial positions have restricted rotation about their C–S bonds, but this rotation becomes free as the temperature increases. Room temperature ¹⁹F NMR spectra of 3 and 5 also indicate restricted rotation around the Os–P bonds in the “2-up, 1-down” isomers (b). In addition, as the temperature increases, the ¹⁹F NMR spectra tend to be consistent with an increased rate of the isomeric exchange. Variable temperature ³¹P{¹H} NMR studies also confirm that, as the temperature is increased, the a and b isomeric exchange becomes fast on the NMR time scale.     

Mixed Monolayers of Amphiphilic Cyclodextrins and Phospholipids: II. Surface Potential–Area Behavior of Per-(6-amino-2,3-di-O-hexyl) β-CD Hydrochloride Salt and 1,2 Dipalmitoyl, 3-sn-Phosphatidic Acid Mixed Monolayers

The dielectric properties of mixed monolayers of per-(6-amino-2,3-di-O-hexyl) β-CD hydrochloride (NH₃-β-CD-OC6) and 1,2 dipalmitoyl, 3-sn-phosphatidic acid (DPPA) have been assessed using surface potential measurements at constant area. From the comparison of these surface potential (ΔV) versus surface density (δ) relationships with those of surface pressure (π) against surface density (δ) it was apparent that the increase in the NH₃-β-CD-OC6 content in mixed films gave rise to a gradual increase in the saturation value of the surface potential (ΔV_max). This potential for pure DPPA was found to be equal to 396 mV and for pure CD 554 mV. The ΔV_maxvalues reflect the onset of reorientation effects that arrive at molar areas before the collapse of these films. Independently of reorientation effects, the obtained results strongly indicate that the dipolar term contributing to the overall ΔVvalue was for NH₃-β-CD-OC6 due to the hydration of its NH⁺₃group. For both DPPA and NH₃-β-CD-OC6 molecules the contribution of the electric double layer (Ψ) was calculated and was found for DPPA and NH₃-β-CD-OC6 to be equal to −249 and +252 mV, respectively. These calculated Ψ values made possible the evaluation of dipole moments for NH₃-β-CD-OC6 and DPPA monolayers which revealed a marked difference in dipolar properties between these two film forming components. In contrast to DPPA which exhibited a decrease in the surface dipole moment (μ) with the decrease inA, NH₃-β-CD-OC6 displayed an increase in μwith the decrease inAforAvalues above 580 Ų. Below this value μdecreases with decreasing molecular area and this variation arises from a change in the polarity of the electric double layer arising from interactions with the complementary anion. The differences in dielectric properties between the two film forming molecules have been attributed to modification, during compression, in the structure of the interfacial water bound to the cyclodextrin.     

Vibrational spectral studies of ion-ion and ion-solvent interactions. II. Zinc nitrate in water/dioxane mixtures

Raman and infrared spectral data have been collected forp-dioxane and solvated and bound nitrate ions for Zn(NO₃)₂/p-dioxane/water systems. It is concluded that Zn²⁺ is preferentially solvated by water and that this aquation is also responsible for a lower concentration of ion pairs than is found for methanol/Zn(NO₃)₂ solutions for which the dielectric constant of the bulk solvent is similar. Values of K₁ (M^–1), the association constant for Zn(NO₃)⁺, are 0.22±0.02 (2/1 solvent,D=12.6) and 0.071±0.01 (4/1 solvent,D=33.0). The log K₁ against 1/D plot is not linear.     

Theoretical study of homogeneous electron self-exchange in polar aromatic molecules: the role of the reactant structure

The solvent reorganization energies λ₀ of the electron self-exchange reaction between neutral molecules (nitrobenzene, its five para-substituted derivatives and benzonitrile) and the corresponding radical anions are discussed in terms of the Kirkwood approach combined with a semi-empirical calculation of the reactant structure (AM1 and intermediate neglect of differential overlap (INDO) methods). The theoretical values of λ₀ are compared with the experimental reorganization energies λ calculated from the Marcus equation and the homogeneous rate constants k_ex. It is found that the values of λ₀ obtained using the INDO method are approximately equal to the experimental λ, whereas the AM1 method gives poor results for para-substituted nitrobenzenes. The linear correlation of log k_ex with a_N² where a_N is a nitrogen coupling constant, established for para-substituted nitrobenzenes is interpreted. A simple criterion for slow electron transfer of an arbitrary flat polar arene is formulated in terms of the reactant structure and the model of the “specifying group” suggested earlier by some of the authors.     

Antiferromagnetic complexes involving metal---metal bonds IV. Synthesis, molecular structure and magnetic properties of the heterotrinuclear cluster, (C5H5Cr)2(μ-SCMe3)(μ-S)2Fe(CO)3, with direct and indirect exchange between Cr and Fe centers

The photochemical reaction between the antiferromagnetic complex (C₅H₅-CrSCMe₃)₂S (I) (containing a Cr---Cr bond 2.689 Å long) and Fe(CO)₅ results in the elimination of two carbonyl groups and one tert-butyl radical to give (C₅H₅Cr)₂(μ²-SCMe₃)(μ³-S)₂ · Fe(CO)₃ (III). As determined by X-ray diffraction, III contains a Cr---Cr bond of almost the same length as in I (2.707 Å), together with one thiolate and two sulphide bridges. The latter are also linked with the Fe atom of the Fe(CO)₃ moiety (average Fe---S bond length 2.300 Å). Fe also forms a direct bond, 2.726 Å long, with one of the Cr atoms, whereas its distance from the other Cr atom (3.110 Å) is characteristic for non-bonded interactions. Complex III is antiferromagnetic, the exchange parameter, −2J, values for Cr---Cr, Cr(1)---Fe and Cr(2)…Fe are 380, 2600 and 170 cm⁻¹, respectively. The magnetic properties of III are discussed in terms of the “exchange channel model”. The contributions from indirect interactions through bridging ligands are shown to be insignificant compared with direct exchange involving metal---metal bonds. The effects of steric factors and of the nature of the M(CO)_n fragments on the chemical transformations of (C₅H₅CrSCMe₃)₂S · M(CO)_n are discussed.     

Crystal structure and IR spectrum of 1-O-α- -glucopyranosyl- -mannitol–ethanol (2/1)

1-O-α- -Glucopyranosyl- -mannitol–ethanol (2/1), (C₁₂H₂₄O₁₁)₂–C₂H₅OH, crystallizes in the monoclinic space group P2₁ with unit cell dimensions a=11.4230(8) Å, b=9.525(4) Å, c=15.854(2) Å, β=102.751(7)° and V=1682.4(7) ų, Z=2, D_x=1.45 Mg m⁻³, λ (Mo-K_α)=0.71069 Å, μ=0.128 mm⁻¹, F(000)=788 and T=293(2) K. The structure was solved by direct methods and refined by least-squares calculations on F² to R₁=0.0371[I>2σ(I)], and 0.0930 (all data, 3542 independent reflections, R_int=0.021). There are two molecules of glucopyranosylmannitol (GPM) and one ethanol molecule in the asymmetric unit, and the glucopyranosyl ring adopts a chair conformation in both GPM molecules. Bond lengths and angles accord well with the mean values of related structures. The conformation along the mannitol side chain for one of the GPM molecules was the same as for the known polymorphs of -mannitol, while the conformation of the other molecule was different, indicating different conformational arrangements in the terminal carbon atoms of the mannitol side chains of the two GPM molecules. The structure in 1-O-α- -glucopyranosyl- -mannitol–ethanol (2/1) is held together by a very complex hydrogen bonding system, which consists of an infinte chain propagating along the b-axis and a discontinuous chain, which binds the ethanol molecule to the structure. The FTIR spectra for anhydrous GPM, GPM dihydrate and GPM–ethanol (2/1) were recorded. Both IR and X-ray results indicate the extensive hydrogen bonding in crystalline state.     

Effect of magnetostrictive phase on structural, dielectric and electrical properties of NiFe2O4 + Pb0.93La0.07(Zr0.60Ti0.40)O3 composites

Particulate composites of NiFe₂O₄ (NFO) and Pb_0.93La_0.07 (Zr_0.60Ti_0.40) O₃ (PLZT) were synthesized by solid-state reaction technique. Structure and surface morphological studies were carried out using X-ray diffraction and scanning electron microscopy techniques, respectively. Frequency dependent variation of dielectric constant (), loss tangent (tan δ) and ac resistivity for (x) NFO + (1−x) PLZT composites in the range 100 Hz–5 MHz at room temperature were studied. The temperature dependence of dielectric constant (′), loss tangent (tan δ) was studied in wide temperature range of measurement at fixed frequencies. Also DC resistivity measurements were carried out in the temperature range of 300 K–923 K. Structural, dielectric and electrical properties show notable change due to presence of magnetostrictive NFO phase along with PLZT.     

Synthesis, crystal structures, phase transition characterization and thermal decomposition of a new dabcodiium hexaaquairon(II) bis(sulfate): (C6H14N2)[Fe(H2O)6](SO4)2

The crystal structures of 1,4-diazabicyclo[2.2.2]octane (dabco)-templated iron sulfate, (C₆H₁₄N₂)[Fe(H₂O)₆](SO₄)₂, were determined at room temperature and at −173 °C from single-crystal X-ray diffraction. At 20 °C, it crystallises in the monoclinic symmetry, centrosymmetric space group P2₁/n, Z=2, a=7.964(5), b=9.100(5), c=12.065(5) Å, β=95.426(5)° and V=870.5(8) ų. The structure consists of [Fe(H₂O)₆]²⁺ and disordered (C₆H₁₄N₂)²⁺ cations and (SO₄)²⁻ anions connected together by an extensive three-dimensional H-bond network. The title compound undergoes a reversible phase transition of the first-order at −2.3 °C, characterized by DSC, dielectric measurement and optical observations, that suggests a relaxor–ferroelectric behavior. Below the transition temperature, the compound crystallizes in the monoclinic system, non-centrosymmetric space group Cc, with eight times the volume of the ambient phase: a=15.883(3), b=36.409(7), c=13.747(3) Å, β=120.2304(8)°, Z=16 and V=6868.7(2) ų. The organic moiety is then fully ordered within a supramolecular structure. Thermodiffractometry and thermogravimetric analyses indicate that its decomposition proceeds through three stages giving rise to the iron oxide.     

On the relationship between the nonlinear dielectric properties and respiratory activity of the obligately aerobic bacterium Micrococcus luteus

We have recently described the construction of a dual-cell, nonlinear dielectric spectrometer, and its application to the study of cell suspensions of S. cerevisiae (A.M. Woodward and D.B. Kell, Bioelectrochem. Bioenerg., 24 (1990) 83). Substantial, odd harmonics were generated by these cells when stimulated by very modest sinusoidal electrical fields, within fairly sharp voltage- and frequency windows (ca. 0.8–2.5 V cm⁻¹, 1–50 Hz). Resting cells were found to generate only odd-numbered harmonics. In the present work, we have simultaneously applied two sinusoidal frequencies which were individually of unsuitable frequency and/or amplitude for the generation of harmonics when applied to suspensions of S. cerevisiae. Strong “sidebands” or “beat frequencies” were observed which were the (odd-numbered) sums and differences of the exciting frequencies (viz. ƒ₁±2ƒ₂, ƒ₂±2ƒ₁). The generation of these beat frequencies was strongly inhibited by low concentrations of sodium metavanadate, suggesting that they may be ascribed largely to the H⁺-ATPase present in the plasma membranes of these cells. We show that the ability of dc fields to inhibit the manifestation of nonlinear dielectric behaviour by these cells is explicable in terms of their ability to act as a field of zero Hz, forcing the excitation out of the amplitude window. When the cells were allowed to glycolyse, beat frequencies of even order (ƒ₁±ƒ₂, ƒ₁±3ƒ₂) were observed. The present approach provides a novel and powerful approach to the registration of nonlinear dielectric spectra, which, due to the greater precision inherent in the discrimination of frequencies rather than voltages may be expected to provide a more sensitive means of detecting nonlinear dielectric properties in biological systems. If the transduction of exogenous electrical field energy recorded by this method is representative of the natural turnover of the H⁺-ATPase in vivo, it may be calculated that the efficiency of the capture of electric field energy by this enzyme is some 3%.     

Spectroscopic investigations on AsH(XΣ) radical using CCSD(T) theory in combination with correlation-consistent quintuple basis set

The equilibrium internuclear separations, harmonic frequencies and potential energy curves of the AsH(X³Σ⁻) radical have been calculated using the coupled-cluster singles–doubles–approximate-triples [CCSD(T)] theory in combination with the series of correlation-consistent basis sets in the valence range. The potential energy curves are all fitted to the Murrell–Sorbie function, which are used to reproduce the spectroscopic parameters such as D_e, ω_eχ_e, α_e, B_e and D₀. The present D₀, D_e, R_e, ω_e, ω_eχ_e, α_e and B_e obtained at the cc-pV5Z basis set are of 2.8004 eV, 2.9351 eV, 0.15137 nm, 2194.341 cm⁻¹, 43.1235 cm⁻¹, 0.2031 cm⁻¹ and 7.3980 cm⁻¹, respectively, which almost perfectly conform to the measurements. With the potential obtained at the UCCSD(T)/cc-pV5Z level of theory, a total of 18 vibrational states is predicted when the rotational quantum number J is set to equal zero (J = 0) by numerically solving the radial Schrödinger equation of nuclear motion. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are determined when J = 0 for the first time, which are in excellent agreement with the experiments.     

Conformational dependence of the intrinsic acidity of the aspartic acid residue sidechain in N-acetyl- -aspartic acid-N′-methylamide

The sidechain conformational potential energy hypersurfaces (PEHS) for the γ_L, β_L, α_L, and α_D backbone conformations of N-acetyl- -aspartate-N′-methylamide were generated. Of the 81 possible conformers initially expected for the aspartate residue, only seven were found after geometric optimizations at the B3LYP/6-31G(d) level of theory. No stable conformers could be located in the δ_L, _L, γ_D, δ_D, and _D backbone conformations. The ‘adiabatic’ deprotonation energies for the endo and exo forms of N-acetyl- -aspartic acid-N′-methylamide were calculated by comparing their optimized relative energies against those found for the seven stable conformers of N-acetyl- -aspartate-N′-methylamide. Sidechain conformational PEHSs were also generated for the estimation of ‘vertical’ deprotonation energies for both endo and exo forms of N-acetyl- -aspartic acid-N′-methylamide. All backbone–sidechain (N–H⁻O–C) and backbone–backbone (N–HO=C) hydrogen bond interactions were analyzed. A total of two backbone–backbone and four backbone–sidechain interactions were found for N-acetyl- -aspartate-N′-methylamide. The deprotonated sidechain of N-acetyl- -aspartate-N′-methylamide may allow the aspartyl residue to form strong hydrogen bond interactions (since it is negatively charged) which may be significant in such processes as protein–ligand recognition and ligand binding. As a primary example, the molecular geometry of the aspartyl residue may be important in peptide folding, such as that in the RGD tripeptide.     

Thermal and dielectric studies of 2,2’-dihydroxybenzophenone

Thermal and dielectric properties of 2,2’-dihydroxybenzophenone were studied in relation with the potential progress of crystal nucleation and growth below the ordinary glass transition temperature, T_gα. Differential scanning calorimetry was carried out in a range 100-350 K. The α glass transition was found to occur at T_gα=239 K. Crystallization and fusion were observed to take place when the sample was cooled down to 103 K, but not observed when cooled to 203 K. Crystal nucleation was interpreted as having happened during annealing for a short time at 103 K which is much below the T_gα. Heat capacities were measured in a range 7-350 K by an intermittent heating method with an adiabatic calorimeter. The temperature, enthalpy and entropy of fusion were determined to be 334.46 K, 20.07 kJ mol^-1 and 60.01 J K^-1mol^-1, respectively. Crystal growth was found to proceed even at 220 K below the T_gα, but no glass transition was detected below 220 K. Dielectric losses were measured in a temperature range of 100-250 K and a frequency range of 30Hz-10 kHz. β-Relaxation process was found dielectrically with the activation energy of 22.6 kJ mol^-1, and the corresponding glass transition was expected to occur at 76.9 K. It is discussed, based on the “structurally ordered clusters aggregation” model for supercooled liquids and glasses, that the β process is potentially attributed to the crystal nucleation progressing at 103 K.     

Accurate analytic potential energy function and spectroscopic study for CH(XΠ) radical using coupled-cluster theory in combination with the correlation-consistent quintuple basis set

The coupled-cluster singles-doubles-approximate-triples [CCSD(T)] theory in combination with the correlation-consistent quintuple basis set (aug-cc-pV5Z) is used to investigate the spectroscopic properties of the CH(X²Π) radical. The accurate adiabatic potential energy curve is calculated over the internuclear separation ranging from 0.07 to 2.45 nm and is fitted to the analytic Murrell–Sorbie function, which is employed to determine the spectroscopic parameters, ω_eχ_e, α_e and B_e. The present D_e, R_e, ω_e, ω_eχ_e, α_e and B_e values are of 3.6261 eV, 0.11199 nm, 2856.312 cm⁻¹, 64.9321 cm⁻¹, 0.5452 cm⁻¹ and 14.457 cm⁻¹, respectively. Excellent agreement is obtained when they are compared with the available measurements. With the potential obtained at the CCSD(T)/aug-cc-pV5Z level of theory, a total of 18 vibrational states is predicted when J = 0 by numerically solving the radial Schrödinger equation of nuclear motion. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are reproduced for the CH(X²Π) radical when J = 0 for the first time, which are in good agreement with the available RKR data.