Synthesis and crystal structure of a polymeric erbium(III)-sodium(I) coordination complex of picolinic acid N-oxide

A new Er(III)-Na(I) coordination polymer of stoichiometry [NaEr2L5(H2O)(6)(NO3)](NO3). 3.5H(2)O (HL = picolinic acid N-oxide) has been synthesized and characterized by single-crystal X-ray analysis. Crystals are triclinic, P (1) over bar with a = 9.823(2), b = 12.453(2), c = 20.643(4) Angstrom; alpha = 98.49(3), beta = 101.40(3), gamma = 108.69(3)degrees; V = 2284(1) Angstrom(3); Z = 2. Of the two independent eight-coordinate erbium(III) ions in this complex, one is surrounded by four bidentate chelating L ligands, and the other by one bidentate chelating L ligand, four aqua ligands and two anti-carboxylate oxygen atoms from two neighboring [ErL4] units. The sodium(I) ion is in a distorted octahedral environment, being coordinated by a unidentate nitrate anion, three aqua ligands and two anti-carboxylate oxygen atoms from two adjacent [ErL4] units. The complex is built from zigzag chains of syn-anti carboxylate-bridged erbium(III) moieties directed in the a direction, which are cross-linked pairwise by aqua-bridged dimeric sodium(I) units. The resulting composite polymeric chains are further connected by hydrogen bonds to form a three-dimensional network.

Studies on beta-cyclodextrin amino acids inclusion complexes by electrospray ionization mass spectrometry

The positive- and negative-ion electrospray ionization mass spectra of beta-cyclodextrin-amino acids complexes in NH4Ac buffer have been reported in this paper. Compared with positive-ion ESI mass spectra of beta-cyclodextrin-amino acids complexes under the same condition, negative-ion mass spectra obtained for inclusion complexes of beta-cyclodextrin (CD) with tyrosine, phenylalanine and tryptophan, respectively, were completely dominated by deprotonated complex ions and [CD-H](-) ion which is the only daughter ion in collision-induced dissociation (CID) experiment of deprotonated complexes, The results indicated that the charged position for protonated and deprotonated complexes is different from each other. In addition, two complex ions for the same complex have similarly relative dissociation energies, which are higher than that of [CD+NH4](+), indicating that complexes observed in gasphase are not electrostatic adducts at all but complexes formed by hydrogen bonds.

Characterization of the structural and functional changes of hemoglobin in dimethyl sulfoxide by spectroscopic techniques

Circular dichroism (CD), fourier transform infrared (FTIR), and fluorescence spectroscopy were used to explore the effect of dimethyl sulfoxide (DMSO) on the structure and function of hemoglobin (Hb). The native tertiary structure was disrupted completely when the concentration of DMSO reached 50% (v/v), which was determined by loss of the characteristic Soret CD spectrum. Loss of the native tertiary structure could be mainly caused by breaking the hydrogen bonds, between the heme propionate groups and nearby surface amino acid residues, and by disorganizing the hydrophobic interior of this protein. Upon exposure of Hb to 52% DMSO for ca. 12 h in a D2O medium no significant change in 1652 cm(-1) band of the FTIR spectrum was produced, which demonstrated that alpha-helical structure predominated. When the concentration of DMSO increased to 57%: (1) the band at 1652 cm(-1) disappeared with the appearance of two new bands located at 1661 and 1648 cm(-1); (2) another new band at 1623 cm(-1) was attributed to the formation of intermolecular beta-sheet or aggregation, which was the direct consequence of breaking of the polypeptide chain by the competition of S=O groups in DMSO with C=O groups in amide bonds. Further increasing the DMSO concentration to 80%, the intensity at 1623 cm(-1) increased, and the bands at 1684, 1661 and 1648 cm(-1) shifted to 1688, 1664 and 1644 cm(-1), respectively. These changes showed that the native secondary structure of Hb was last and led to further aggregation and increase of the content of 'free' amide C=O groups. In pure DMSO solvent, the major band at 1664 cm(-1) indicated that almost all of both the intermolecular beta-sheet and any residual secondary structure were completely disrupted. The red shift of the fluorescence emission maxima showed that the tryptophan residues were exposed to a greater hydrophilic environment as the DMSO content increased. GO-binding experiment suggested that the biological function of Hb was disrupted seriously even if the content of DMSO was 20%. (C) 1998 Elsevier Science B.V. All rights reserved.

The miscibility of homopolymer random copolymer blends .3. Blends of SAA with polymethacrylates and polyesters

The miscibility of blends of poly(styrene-co-allyl alcohol) (SAA) with poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), poly(n-butyl methacrylate) (PnBMA), poly-epsilon-caprolactone (PCL) or polycarbonate (PC) has been studied by means of NMR, FT-IR and DSC techniques. It was found that SAA and PMMA, PEMA or PCL form miscible blends and SAA is only partially miscible with PC or PnBMA. Both phenyl groups and hydroxyl groups in SAA are involved in the intermolecular interactions between SAA and PMMA, PEMA or PCL. Also the hydroxyl-carbonyl hydrogen bonds existing in all the miscible blends studied are formed partially at the expense of the disruption of self-association of hydroxyl groups in pure SAA. (C) 1997 Elsevier Science Ltd. All rights reserved.

Novel poly(aryl ether ketone)s containing various pendant groups .2. Gas-transport properties

The gas transport of hydrogen, oxygen, nitrogen, carbon dioxide, and methane gases in a series of poly(aryl ether ketone)s was examined. These polymer membranes have a wide range of permeability coefficients and permselectivity coefficients, showing excellent gas-transport properties. The enhanced interchain interaction in the polymers due to intermolecular hydrogen bonds and ionic bonds results in a considerable increase in permselectivity but a decrease in permeability. On the contrary, the polymers with bulky arkyl substituents show significantly increased permeability. The causes of this trend are interpreted in terms of the free volume, interchain distance, and glass transition temperature together with the respective contribution of gas solubility and diffusivity to the overall permeability. Of interest is the observation that the ionomer IMPEK-K+, which simultaneously contains bulky isopropyl substituents and pendant carboxylate groups, exhibits over twice higher CO2 permeability and 15% higher CO2/CH4 permselectivity than those of bisphenol-A p'olysulfone (PSF). The possibility of using the new synthesized poly(aryl ether ketone)s in gas separation membrane application is also discussed. (C) 1997 John Wiley & Sons, Inc.

Study of the miscibility and thermodynamics of cellulose diacetate-poly(vinyl pyrrolidone) blends

The miscibility of blends of cellulose diacetate (CDA) and poly(vinyl pyrrolidone) (PVP) was extensively studied by means of differential thermal analysis and dynamic mechanical thermal analysis, tensile test, measuring viscosity of diluted and concentrated solutions of blends in acetone-ethanol mixture and morphological observations. A single glass transition temperature is observed, which is intermediate between the glass transition temperatures associated with each component and depends on composition. A synergism in mechanical properties of blends was found. The absolute viscosity and the intrinsic viscosity of solutions of blends are much higher than the weight average values of solutions of CDA and PVP. Optically clear and thermodynamically stable films were formed in the composition range of CDA/PVP = 100/0 to 50/50w/w. Fourier transform infrared was used to investigate the nature of CDA-PVP interaction. Hydrogen bonds were formed between hydroxyl groups of CDA and carbonyl groups of PVP. Heats of solutions of CDA/PVP blends and their mechanical mixtures were measured by using a calorimeter. Mixing enthalpy obtained with Hess's law approach was used to quantify interaction parameters of this blending system. It was found that mixing enthalpies and interaction parameters were negative and composition dependent. (C) 1997 Elsevier Science Ltd.

The crystal structure and supramolecular chain of [La(NO3)(3)(OH2)(2)(phen)]center dot 15-crown-5

[La(NO3)(3)(OH2)(2)(phen)]. 15-crown-5 is hexagonal, P6(5), with a = 10.955(2), c = 43.769(9) Angstrom, and D-calc = 1.668 g cm(-3) for Z = 6. In the complex, two nitrogen atoms (from phen) and eight oxygen atoms (six from three bidentate nitrate anions and two from water molecules) are coordinated to the central La(III) ion, forming a coordination polyhedron which is approximately a bicapped square antiprism. The coordinated water molecules donate hydrogen bonds to the oxygen atoms of the crown ether, forming polymeric hydrogen bonded chains which wrap helically along the unit cell direction c.

A NMR-STUDY OF THE INTERACTION OF SILICA WITH DIPALMITOYLPHOSPHATIDYLCHOLINE LIPOSOMES

The interaction of silica with dipalmitoylphosphatidylcholine (DPPC) liposomes has been studied by detecting H-1 and 2D NOESY NMR spectra and measuring proton spin-lattice relaxation time (T-1). The antagonistic effect of aluminium citrate on silica has also been studied by measuring the proton T-1 values, The results show that silica particles mainly bind to the phosphate moiety of the polar headgroup of DPPC bilayers through hydrogen bonds between Si-OH and O-P groups, but they have no significant effect on the conformation of the choline group of the polar headgroup, The addition of silica particles decreases the mobilities of the hydrocarbon chains slightly, Proton T-1 data also indicate that aluminium citrate reduces the effect of silica, A possible mechanism for the toxicity of silica and the antagonistic effect of aluminium titrate on silica is suggested. (C) 1995 Academic Press Inc.

HOST-GUEST INTERACTIONS OF THIAMINE WITH ANIONS - CRYSTAL-STRUCTURE OF THIAMINE IODIDE SESQUIHYDRATE

The crystal structure of thiamine iodide sesquihydrate has been determined by X-ray diffraction methods as a host-guest model for coenzyme-substrate interactions. The asymmetric unit contains two chemical units. Both the thiamine molecules A and B, which are crystallographically independent, assume the usual F conformation and have a disordered hydroxyethyl side chain. An iodide anion (or a water molecule) bridges the pyrimidine and thiazolium rings of molecule A (or B) by forming a hydrogen bond with the amino group and an electrostatic contact with the thiazolium ring to stabilize the molecular conformation. In the crystal the thiamine molecules self-associate to form a pipe-like polymeric structure, in which four thiamine hosts surround an iodide guest and hold it through C(2)-H...I hydrogen bonds and thiazolium...I electrostatic interactions. Crystal data: C12H17N4OS+.I- . 1.5 H2O, monoclinic, P2(1)/c, a = 12.585(2), b = 25.303(5), c = 12.030(2) angstrom, beta = 115.15(1)degrees, V = 3468(1) angtrom3, Z = 8, D(c) = 1.606 g cm-3, R = 0.045 for 3328 observed reflections.

STRUCTURE OF AN ERBIUM COMPLEX WITH L-PROLINE

In the structure of catena-poly[{triaqua(L-pro-line-O)erbium(III)}-bis-mu-(L-proline-O:O')-{triaqua-(L-proline-O)erbium(III)}-bis-mu-(L-proline-O:O') hexaperchlorate], each Er3+ ion is coordinated by five carboxyl O atoms from the L-proline molecules and three water molecules. Four of the SiX L-proline molecules act as bidentate bridging ligands to link the Er3+ ions through the carboxyl groups, thus producing a one-dimensional chain structure. The other two ligands coordinate unidentately to the rare-earth ions. Hydrogen bonds formed between the coordinated water molecules and between the water and unidentate proline ligand stabilize the polymeric chain.

A HIGH-RESOLUTION SOLID-STATE NMR AND DSC STUDY OF MISCIBILITY AND CRYSTALLIZATION BEHAVIOR OF POLY(VINYL ALCOHOL)/POLY(N-VINYL-2-PYRROLIDONE) BLENDS

Blends of crystallizable poly(vinyl alcohol) (PVA) with poly(N-vinyl-2-pyrrolidone) (PVPy) were studied by C-13 cross-polarization/magic angle spinning (CP/MAS) n.m.r. and d.s.c. The C-13 CP/MAS spectra show that the blends were miscible on a molecular level over the whole composition range studied, and that the intramolecular hydrogen bonds of PVA were broken and intermolecular hydrogen bonds between PVA and PVPy formed when the two polymers were mixed. The results of a spin-lattice relaxation study indicate that blending of the two polymers reduced the average intermolecular distance and molecular motion of each component, even in the miscible amorphous phase, and that addition of PVPy into PVA has a definite effect on the crystallinity of PVA in the blends over the whole composition range, yet there is still detectable crystallinity even when the PVPy content is as high as 80 wt%. These results are consistent with those obtained from d.s.c. studies.

AN INFRARED SPECTROSCOPIC STUDY ON THE STRUCTURAL PHASE-TRANSITIONS OF LAURYLAMMONIUM CHLORIDE

Infrared spectroscopy was used to study the structural phase, transitions of laurylammonium chloride in the temperature range from 290 to 365K. It was shown that there is a solid-solid phase transition at 339 K with a pre-transition at 327 K. The infrared spectra indicated that virgin crystals at room temperature form a well-ordered phase with all-trans hydrocarbon chains, and the lengths of N-H...Cl hydrogen bonds are different. The spectra suggested that the gauche conformers begin to appear at temperature above 327 K. The spectra at high temperature over 339 K demonstrated that the interaction between the chains decreases, the partial ''melting'' of the chains is obvious, and the hydrogen bonds (N-H...Cl) have the same lengths. The main transition and pre-transition are mainly assigned to the intramolecular and intermolecular order-disorder changes, respectively.

AN INFRARED SPECTROSCOPIC STUDY OF THE STRUCTURAL PHASE-TRANSITION IN THE PEROVSKITE-TYPE LAYER COMPOUND [N-C16H33NH3]2COCL4

The solid-solid phase transitions in the perovskite-type layer compound [n- C16H33NH3]2CoCl4 have been studied by infrared spectroscopy. A new phase transition at 340 K was found by comparison with differential scanning calorimetry results. A temperature dependence study of the infrared spectra provides evidence of the occurrence of structural phase transitions related to the dynamics of the alkylammonium ions and hydrogen bonds. The main transition at 374 K corresponds to the conformational order-disorder change in the chain, which probably couples with reorientational motions of the NH3 polar heads. GTG or GTG' defects appear in the high temperature disordered phase.

STRUCTURE OF THIAMINE BROMIDE SESQUIHYDRATE

3-[(4-Amino-2-methyl-5-pyrimidinyl)-methyl]-5-hydroxyethyl-4-methylthiazolium bromide sesquihydrate, C12H17N4OS+.Br-.1.5H2O, M(r) = 372.28, monoclinic, P2(1)/a, a = 11.676 (2), b = 24.819(7), c = 12.344 (3) angstrom, beta = 113.74(2)-degrees, V= 3274 (1) angstrom3 , Z = 8, D(x) = 1.51 g cm-3 (Mo Kalpha) = 0.71069 angstrom, mu = 26.2 cm-1, F(000) = 1528, T 293 K, R = 0.062 for 2720 observed reflections. Both the independent thiamine molecules A and B in the asymmetric unit adopt the common F conformation. A bromide anion is held by four neighbouring thiamine molecules through C(2)-H...Br hydrogen bonds and Br ... thiazolium-ring electrostatic interactions. Another bromide anion (or a water molecule) bridges the pyrimidine and thiazolium moieties of molecule A (or B) through a hydrogen bond with the amino group and an electrostatic interaction with the thiazolium ring.

STRUCTURE OF CIS-DIAQUABIS(1,10-PHENANTHROLINE)ZINC SULFATE HEXAHYDRATE

[Zn(C12H8N2)2(H2O)2]SO4.6H2O, M(r) = 665.98, triclinic, P1BAR, a = 10.070 (4), b = 12.280 (3), c = 13.358 (2) angstrom, alpha = 109.12 (2), beta = 92.58 (2), gamma = 110.85 (2)-degrees, V = 1433.9 (7) angstrom 3, Z = 2, D(x) = 1.54 g cm-3, lambda(Mo K-alpha) = 0.71069 angstrom, mu = 10.1 cm-1, F(000) = 692, T = 293 K, R = 0.044 for 3985 observed reflections. The Zn atom is coordinated in a distorted octahedral geometry by four N atoms from two 1,10-phenanthroline (phen) ligands and two water molecules. The intermolecular ring-stacking interactions between the phen ligands occur in two forms: infinite chains and discrete dimers. Hydrogen bonds further stabilize the structure.