Thermochemical study of three dimethylpyrazine derivatives

The standard (p ⁰=0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T-298.15 K, for 2,5-dimethylpyrazine (2,5-DMePz) and for the two dimethylpyrazine-N,N′-dioxide derivatives, 2,3-dimethylpyrazine-1,4-dioxide (2,3-DMePzDO) and 2,5-dimethylpyrazine-1,4-dioxide (2,5-DMePzDO), were derived from the measurements of standard massic energies of combustion, using a static bomb calorimeter, and from the standard molar enthalpies of vaporization or sublimation, measured by Calvet microcalorimetry. The mean values for the molar dissociation enthalpy of the nitrogen-oxygen bonds, 〈DH _m⁰〉(N-O), were derived for both N,N′-dioxide compounds. These values are discussed in terms of the molecular structure of the two N,N′-dioxide derivatives and compared with 〈DH _m⁰〉(N-O) values previously obtained for other N-oxide derivatives.     

Novel approach to relaxation data analysis in polyhydric alcohols

In this paper the experimental data on dielectric permittivity of 1,3-, 1,4- and 2,3-butanediols within the frequency range from 1 MHz to 36 GHz and the temperature range from 283 to 423 K were analyzed. The correlation between relaxation parameters of the Davidson-Cole equation and molecular structure of the investigated butanediols was established. Values of average dipole moments of molecular clusters, 〈μ_c〉, were calculated according to the Dissado-Hill cluster theory. The dependence of 〈μ_c〉 on energy characteristics of the working model was revealed and discussed in details.     

Correlation between the equilibrium and relaxation dielectric properties of 1,2-ethanediol

The data on the dispersion of the permittivity ?*(ω) of 1,2-ethanediol over the temperature range 161–453 K and the frequency range 0.1 Hz–150 GHz were analyzed using the Dissado-Hill cluster model. The relaxation frequency ω_p = τ _DH ^?1 and intra-(n _DH) and intercluster (m _DH) correlation parameters were calculated. The energy barrier to the libration of molecular axes in clusters was found to be B _DH = 2.96 kJ/mol. The apparent enthalpy of activation was determined; it increased from ΔH _{DH exp} ^# = 22.18 kJ/mol to ΔH _{DH exp} ^# = 129.19 kJ/mol close to the glass transition temperature. The mean dipole moments $ \bar \mu _c The data on the dispersion of the permittivity ɛ*(ω) of 1,2-ethanediol over the temperature range 161–453 K and the frequency range 0.1 Hz–150 GHz were analyzed using the Dissado-Hill cluster model. The relaxation frequency ω_p = τ_DH⁻¹ and intra-(n _DH) and intercluster (m _DH) correlation parameters were calculated. The energy barrier to the libration of molecular axes in clusters was found to be B _DH = 2.96 kJ/mol. The apparent enthalpy of activation was determined; it increased from ΔH _{DH exp}^# = 22.18 kJ/mol to ΔH _{DH exp}^# = 129.19 kJ/mol close to the glass transition temperature. The mean dipole moments of 1,2-ethanediol clusters were calculated; they decreased from 162920 to 18.08 D as the temperature increased from 161 to 453 K. According to approximate estimates, the number of 1,2-ethanediol molecules in a cluster /μ_v decreased from 72405 at 161 K to 8.04 at 453 K (μ_v is the dipole moment of the molecule in the vacuum), which substantiated the suggestion of the existence of a spatial structure close to the boiling point. Original Russian Text ? N.V. Lifanova, T.M. Usacheva, V.I. Zhuravlev, V.K. Matveev, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 10, pp. 1973–1981.     

A dielectric study of the structure of propylene glycol

The dielectric spectra of propylene glycol over the frequency and temperature ranges 10 mHz–75 GHz and 175–423 K, respectively, were analyzed using the Dissado-Hill cluster model. A correlation between relaxation processes of breaking and formation of intermolecular H-bonds in clusters was obtained. A correlation of fluctuation processes of synchronous exchange of molecules between neighboring clusters corresponded to the redistribution of H-bonds between them. The Dissado-Hill theory was used to determine the integral relaxation times, n _DH and m _DH parameters and calculate the mean dipole moments of propylene glycol clusters and the energy characteristics of processes of their rearrangement. The mean dipole moments of clusters (23617–18.65 D) were compared with those of molecules in the liquid phase (3.67–3.03 D). The apparent activation enthalpy of processes of cluster rearrangements decreased from 141.8 to 25.2 kJ/mol, the activation energy decreased from 46.03 to 18.47 kJ/mol, and the energy of orientation dipole-dipole interactions, from 3.78 to 3.45 kJ/mol as the temperature increased.     

Synthesis and properties of <Emphasis Type="Italic">O,O</Emphasis>-dialkyl [1-hydroxy-3-(dialkylamino)-2,2-dimethylpropyl]phosphonates

O,O-Dialkyl [1-hydroxy-3-(dialkylamino)-2,2-dimethylpropyl]phosphonates were prepared for the first time. By means of NMR ¹H, IR spectroscopy and quantum-chemical calculations the presence in them of various H-bonds was established. In the crystalline state P=O…HO intermolecular hydrogen bonds favor the formation of cyclic dimer associates D _P=O. In the liquid state and concentrated solutions P=O…HO and N…HO intermolecular hydrogen bonds cause the formation of cyclic dimer associates D _P=O and D_N, and intramolecular hydrogen bonds provide the existence of different conformations of the monomer form MN, the most stable among them with the non-strained six-membered …NCCCOH… ring.     

Geometric interpretation of density displacements and charge sensitivities

The “geometric” interpretation of the electronic density displacements in the Hilbert space is given and the associated projection-operator partitioning of the hardness and softness operators (kernels) is developed. The eigenvectors |?〉= |α〉 of the hardness operator define the complete (identity) projector P =Σ_α| α〉〈α | = 1 for general density displacements, including thecharge-transfer (CT) component, while the eigenvectors |i〉= |i〉 of the linear response operator determine thepolarizational P-projector, P_p = Σ_i |i〉〈i| . Their difference thus defines the complementary CT-projector: P_CT = 1-P_P. The complete vector space for density displacements can be also spanned by supplementing the P-modes with the homogeneous CT-mode. These subspaces separate the integral (normalization) and local aspects of density shifts in molecular systems.     

A local spin evaluation into the active site models of [2Fe2S] ferrodoxin [Fe<Subscript>2</Subscript>S<Subscript>2</Subscript>(SR)<Subscript>4</Subscript>]<Superscript>2−</Superscript> (R=—H, —CH<Subscript>3</Subscript>)

To test the feasibility of local spin theory of Davidson and Clark for ferrodoxin clusters, the models [Fe₂S₂(SR)₄]²⁻ (R=—H, —CH₃) are chosen for evaluation. This purpose is realized by calculating the local spin expectation values 〈S _A·S _B〉, 〈S _A ² 〉, and m _A and discussing the connection between these expected values and the Heisenberg spin model (HSM) and the Noodleman broken-symmetry approach. In practical calculation, the spin-unrestricted Hartree-Fock (UHF) and spin-polarized density functional theory (DFT) are used and the calculational qualities of these two methods are also discussed. In addition, the theoretical magnetic coupling constants J _AB of these models are calculated by various computational schemes for comparison with both theoretical and experimental results previously reported. Supported by the Doctorial Initial Foundations of Hainan Normal University (Grant No. 13140252)     

Über die Molekulargewichtsverteilung von Desoxyribonucleinsäure in der Ultrazentrifuge

Zusammenfassung Das Molekulargewicht der aus der Forellenmilch gewonnenen Desoxyribonucleins?ure wurde mit Hilfe der Ultrazentrifuge untersucht. Wegen der hohen Viskosit?t mu?te man eine sehr verdünnte L?sung von 0,002% DNS inMcIlvaine- Puffer (p_H 4,97) anwenden. Die experimentellen Konzentrationskurven wurden mit UV-Absorptionsoptik aufgenommen, und danach lie?en sich auch die theoretischen Gradientenkurven ableiten. Es hat sich gezeigt, da? DNS mehrere polydisperse Fraktionen enth?lt, die erne mehrgipfelige charakteristische Verteilung darstellen mit einer mittleren Sedimentationskonstante von 19,35 sved. Auf Grund dieser Konstante sowie auch aus den Viskosit?tsmessungen, die die „intrinsic viscosity“ 〈[π]Φ=0〉=6541 liefern, wurde der Mittelwert für das Achsenverh?ltnis 〈p〉= 380 und für das Molekulargewicht 〈M〉=6100000 festgestellt. Die mittlere Dicke der DNS-Moleküle ist 25 ? und die L?nge 1,178μ. Die Bestimmung der Molekulargewichtsverteilung kann nach dieser Methode sowie auch nach der neuen Momentenmethode bzw. nach der „Dreipunktmethode“ unmittelbar aus der experimentellen Gradientenkurve abgeleitet werden. Mit Unterstützung der Deutschen Forschungsgemeinschaft. Frl. Dr.L. Hübner aus dem Paul-Ehrlich-Institut, Frankfurt a. M., und HerrnG. Zwarg aus dem Beckman-Werk in München danken wir für die Hilfe und die Mitarbeit bei der Durchführung der Sedimentationsversuche.     

A steered molecular dynamics simulation on the elastic behavior of adsorbed star polymer chains

<正>Elastic behavior of 4-branched star polymer chain with different chain length N adsorbed on attractive surface is investigated using steered molecular dynamics(SMD) simulation method based on the united-atom(UA) model for branched alkanes.The simulation is realized by pulling up the chain via a linear spring with a constant velocity v = 0.005 nm/ps.At the beginning,the chain lies extensionally on adsorbed surface and suffers continuous deformations during the tensile process.Statistical parameters as mean-square radii of gyration S~2_(xy),S~2_z,shape factor δ,describing the conformational changes,sectional density den which gives the states of the chain,and average surface attractive energy U_a,average total energy U,average force f probed by the spring,which characterize the thermodynamic properties, are calculated in the stimulant process.Remarkably,distinguishing from the case in linear chains that there only exists one long plateau in the curve of f,the force plateau in our study for star chains is multiple,denoting different steps of desorption,and this agrees well with the experimental results in essence.We find during the tensile process,there are three characteristic distances Z_c,Z_t and Z_0 from the attractive surface,and these values vary with N.When Z=Z_c,the chain is stripped from the surface,but due to the form of wall-monomer interaction,the surface retains weak influence on the chain till Z = Z_c.From Z=Z_t,parameters U_a,U and f respectively reach a stable value,while the shape and the size of the chain still need adjustments after Z_t till Z_0 to reach their equilibrium states.Specifically,for short chain of N= 41,Z_t and Z_0 are incorporated.These results may help us to deepen the knowledge about the elastic behavior of adsorbed star polymer chains.     

Syntheses,spectroscopic study and crystal structures of some new <Emphasis Type="Italic">N</Emphasis>-benzoylphosphoric triamides

The reaction of N-benzoylphosphoramidic dichloride with amines afforded some new N-benzoylphos-phoric triamides with formula C₆H₅C(O)NHP(O)(X)₂, X=NH–CH(CH₃)₂ (1), NH–CH₂–CH(CH₃)₂ (2), NH–CH₂–CH(OCH₃)₂ (3), N(CH₃)[CH₂CH(OCH₃)₂] (4) and N(CH₃)(C₆H₁₁) (5) that were characterized by ¹H,¹³C,³¹P NMR, IR spectroscopy and elemental analysis. The structures have been determined for compounds 4 and 5 by X-ray crystallography. These compounds contain one amidic hydrogen atom and form centrosymmetric dimmers via intermolecular –P–O⋯H–N–hydrogen bonds besides weak C–H⋯O hydrogen bonds that lead to three-dimensional polymeric clusters in the crystalline lattice.     

Synthesis and structure of the mixed-ligand cobalt(III) complex [Co(DH)(Hthsc)2][SiF6] · 2.3H2O

The compound [Co(DH)(Hthsc)₂][SiF₆] · 2.3H₂O, where DH^? is a dimethylglyoxime residue and Hthsc is a thiosemicarbazide molecule, was synthesized and studied by X-ray diffraction. The coordination polyhedron of the central metal ion (distorted octahedron) is formed by two sulfur atoms, two nitrogen atoms of two Hthsc molecules coordinated in the bidentate mode, and two nitrogen atoms of the DH^? ligand. The positions of three metal rings are fixed by two intramolecular hydrogen bonds (N-H…O). A bifurcated system of intermolecular hydrogen bonds forms a framework structure in the crystal.     

Supramolecular structure organization and the biological properties of [Co(DH)<Subscript>2</Subscript>(PP)<Subscript>2</Subscript>][BF<Subscript>4</Subscript>]

The coordination compound [Co(DH)₂(PP)₂][BF₄]₂ · 2H₂O (DH⁻ is the dimethylglyoxime residue, PP is nicotinamide) was synthesized and studied by X-ray diffraction. The equatorial plane of the octahedral Co(III) complex contains two DH⁻ residues combined by intramolecular hydrogen bonds O-H…O, while the apical positions are occupied by two PP molecules. A method for the optimal use of the complex for enhancement of the biosynthesis of standard and acid-stable amylases of the micromycete Aspergillus niger 33–19 CNMN FD 02A and lipases of the micromycete Rhizopus arrhizus Fischer CNMN FD 03L was depeloped. The introduction of the complex in a concentration of 1–5 mg/l into the culture medium of Aspergillus niger 33-19 CNMN FD 02A reduces the process cycle by 24 h. The stimulating effect of the introduction of the complex (5 mg/l) into the culture medium of the Rhizopus arrhizus Fischer CNMN FD 03L strain is 55.5%.     

2,2,2‐Trinitroethanol

2,2,2‐Trinitroethanol, C₂H₃N₃O₇, at 100 (2) K has Z′ = 2 in the space group P2₁/c. The structure displays intramolecular O—H...O hydrogen bonds, as well as intermolecular O—H...O and C—H...O hydrogen bonding; the O—H...O hydrogen bonds, forming R₄⁴(8) rings, and dipolar nitro–nitro interactions account for the high density of 1.839 Mg m⁻³.     

Di‐μ‐chlorido‐bis[chlorido(4′‐p‐tolyl‐2,2′:6′,2′′‐terpyridine‐κ3N,N′,N′′)nickel(II)]: a supramolecular system constructed by C—H...Cl interactions

The title complex, [Ni₂Cl₄(C₂₂H₁₇N₃)₂], was synthesized solvothermally. The molecule is a centrosymmetric dimer with the unique Ni^II centre in a distorted octahedral N₃Cl₃ coordination environment. The chloride bridges are highly asymmetric. In the 4′‐p‐tolyl‐2,2′:6′,2′′‐terpyridine ligand, the p‐tolyl group is perfectly coplanar with the attached pyridine ring, and this differs from the situation found in previously reported compounds; however, there are no π–π interactions between the ligands. The terminal Cl atom forms four intermolecular C—H...Cl hydrogen bonds with one methyl and three methine groups. The methyl group also forms intermolecular C—H...π interactions with a pyridine ring. These nonclassical hydrogen bonds extend the molecule into a three‐dimensional network.     

Trinuclear Metal Cluster Complexes Containing Fischer-Type Carbene Group from Oxidative Addition Reactions of Tris( N , N -diethyldithiocarbamato)cobalt with Co2(CO)8 and Ru3(CO)12

Two new Fischer-type carbene-containing trinuclear transition-metal clusters: (μ ₃-S)Co₃(CO)₇[μ, η ²-SCNEt₂] 1 and CoRu₂(CO)₉[μ ₃, η ²-SCNEt₂] 2 were obtained by the reaction of tris(N,N-diethyldithiocarbamato)cobalt with Co₂(CO)₈ and Ru₃(CO)₁₂. These clusters contain thiocarboxamido ligand in different coordination modes. The thiocarboxamido ligand served as monometalated or dimetalated sulfur(diethy1amino) carbene ligand in these clusters. Clusters 1 and 2 were characterized by IR, ¹H NMR, and single-crystal X-ray diffraction.     

Synthesis,crystal structures,and fluorescence properties of two dinuclear cadmium(II) complexes derived from <Emphasis Type="Italic">N</Emphasis>-isopropyl-<Emphasis Type="Italic">N</Emphasis>′-(1-pyridin-2-ylethylidene)ethane-1,2-diamine

A new tridentate pyridyl Schiff base, N-isopropyl-N′-(1-pyridin-2-ylethylidene)ethane-1,2-diamine (L), was used to synthesize two dinuclear cadmium(II) complexes, [Cd₂L₂(μ _1,1-N₃)₂(N₃)₂] (1) and [Cd₂L₂(μ _1,3-NCS)₂(NCS)₂] (2). X-ray single crystal structure determination reveals that in both centrosymmetric complexes, the Cd atom is in a distorted octahedral coordination. In the crystal structures of 1 and 2, the dinuclear cadmium(II) complex molecules are linked, respectively, through intermolecular N–H···N and N–H···S hydrogen bonds to form infinite 1D chains. The preliminary fluorescence properties of the complexes were investigated.     

Excited state wave functions

Wave functions and energies were calculated for the 2s, 3p ₀, and 4d ₀ states of the hydrogen atom using the Messmer and Rayleigh-Ritz variational methods with minimization of the second eigenvalue. The wave functions were linear expansions of Gaussian functions and both linear and exponential parameters were varied. Except for the two term expansions, calculated values of the energies and expectation values, r ^–1, r and r ² were within two percent of the true values for both methods.     

Hydrogen bonding interactions between <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylformamide and cysteine: DFT studies of structures,properties, and topologies

The hydrogen bonding interactions between cysteine and N,N-dimethylformamide (DMF) were studied at the extended hybrid functional DFT-X3LYP/6-311++G(d,p) level regarding their geometries, energies, vibrational frequencies, and topological features of the electron density. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses were employed to elucidate the interaction characteristics in the complexes. The results show that two intermolecular hydrogen bonds (H-bonds) are formed in one complex except few complexes with one intermolecular H-bond. The H-bonds involving O atom of DMF as H-bond acceptor usually are red-shifting H-bonds, while the blue-shifting H-bond usually involve methyl of DMF or methenyl of cysteine moiety as H-bond donors. Both hydrogen bonding interaction and structural deformation play important roles in the relative stabilities of the complexes. Due to the π-bond cooperativity, the strongest H-bond is formed between hydroxyl of cysteine moiety and O atom of DMF, however, the serious deformation counteract the hydrogen bonding interaction to a great extent. The complex involves a stronger hydrogen bonding interaction as well as the smaller deformation is the most stable one. The electron density (ρ_b) as well as its Laplacian (∇²ρ_b) at the H-bond critical point predicted by QTAIM is strongly correlated with the H-bond structural parameter (δR _H···Y) and the second-perturbation energies E(2) in the NBO scheme.     

Problems of unusual hydrogen bonds between proton donors and transition metal hydrides and borohydrides

The results of experimental and theoretical studies of intermolecular MH...HX and BH...HX hydrogen bonds with the hydride hydrogen atom acting as a proton accepting site are analyzed. Spectral (IR and NMR) criteria for their formation are presented. The spectral, structural, and thermodynamic characteristics of these unusual hydrogen bonds obey the regularities found for classical hydrogen bonds. It was shown that the MH...HX bonds participate in the proton transfer with the formation of nonclassical cationic hydrides and the |M(η²-H₂|⁺ hydrogen bonds are formed in low-polarity media. Problems arising in this new line of investigations are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 846–851, May, 1998.     

Synthesis,crystal structures and xanthine oxidase inhibitory activities of two copper(II) complexes with Schiff bases

Two azido-coordinated Schiff base Cu(II) complexes with the formulae [Cu(L1)(N₃)]·MeOH and [Cu(L2)(μ_1,1-N₃)] _n , where L1 is the deprotonated form of 2-chloro-2-[(2-ethylaminoethylimino)methyl]phenol, and L2 is the deprotonated form of 2,4-dibromo-6-[(2-dimethylaminoethylimino)methyl]phenol, have been synthesized and characterized by physico-chemical and spectroscopic methods. The X-ray crystal structures of both complexes have been determined. The Cu atom in [Cu(L1)(N₃)]·MeOH is four-coordinate in a square planar geometry, while [Cu(L2)(μ_1,1-N₃)] _n is five-coordinate with a square pyramidal geometry. The molecules in [Cu(L1)(N₃)]·MeOH are linked by intermolecular O–H···O and N–H···O hydrogen bonds, forming dimers. The molecules in [Cu(L2)(μ_1,1-N₃)] _n are linked through end-on azido bridges, forming one-dimensional chains. The xanthine oxidase inhibitory activities of both complexes were evaluated.