- Melting of saturated fatty acid zinc soaps
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The melting of alkyl chains in the saturated fatty acid zinc soaps of different chain lengths, Zn(CnH2n-1COO)2; n = 11, 13, 15, and 17, have been investigated by powder X-ray diffraction, differential scanning calorimetry, and vibrational spectroscopy. These compounds have a layer structure with the alkyl chains arranged as tilted bilayers and with all methylene chains adopting a planar, all-trans conformation at room temperature. The saturated fatty acid zinc soaps exhibit a single reversible melting transition with the associated enthalpy change varying linearly with alkyl chain length, but surprisingly, the melting temperature remaining constant. Melting is associated with changes in the conformation of the alkyl chains and in the nature of coordination of the fatty acid to zinc. By monitoring features in the infrared spectra that are characteristic of the global conformation of the alkyl chains, a quantitative relation between conformational disorder and melting is established. It is found that, irrespective of the alkyl chain length, melting occurs when 30% of the chains in the soap are disordered. These results highlight the universal nature of the melting of saturated fatty acid zinc soaps and provide a simple explanation for the observed phenomena.
- Barman,Vasudevan
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- Ternary synthesis of colloidal Zn3P2 quantum dots
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The synthesis and characterization of crystalline colloidal zinc phosphide quantum dots with observable excitonic transitions ranging between 424-535 nm (2.3-2.9 eV) are reported. A ternary combination of ZnEt2, Zn(O2CR)2, and P(SiMe3)3, forms a pentanuclear zinc cluster on mixing followed by conversion to (Et2Zn)P(ZnO2CR)2(SiMe3) in a rate-determining step prior to quantum dot formation. This journal is
- Glassy, Benjamin A.,Cossairt, Brandi M.
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supporting information
p. 5283 - 5286
(2015/03/30)
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- Room temperature molecular and lattice structures of a homologous series of anhydrous zinc(II) n-alkanoate
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The room temperature structures and lattice arrangements of a homologous series of zinc(II) n-alkanoates from chain length, nC = 4-20, inclusive, have been studied using infrared spectroscopy, X-ray diffraction and polarizing light microscopy. Lattice parameters from single crystal and powder diffraction data, for zinc(II) hexanoate, are compared to validate the use of the powder method. Since they are in excellent agreement, the powder data are analyzed by a software programme to determine lattice parameters for all the homologues. These are used, in conjunction with infrared, X-ray, density and molecular model calculations to determine molecular and lattice structures. The compounds are isostructural, in that, each zinc atom is tetrahedrally coordinated to oxygen atoms from four different carboxylate groups and each ligand forms a Z,E-type bidentate bridge with two tetrahedral zinc atoms resulting in a syn-anti arrangement. The hydrocarbon chains are in the fully extended all-trans configuration and are tilted at an average angle of 60° to the zinc basal plane. For the short chain length compounds with nC ≤ 8, a double bilayer in-plane-perpendicular-perpendicular-in-plane arrangement of hydrocarbon chains, with two molecules per unit cell, is indicated. For the others, an interdigitating in-plane-in-plane bilayer with head-to-tail interactions, with one molecule per unit cell, is proposed. A geometric model is presented to account for odd-even chain effects and to explain the differences in melting points and densities between these adducts. All the compounds crystallize in the monoclinic space group with P symmetry and are arranged in a two-dimensional network along the ac plane within the unit cell.
- Taylor, Richard A.,Ellis, Henry A.
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- Coated pigment and cosmetic materials comprising the same
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Pigments coated with metallic soap and containing water easily disperse in the water and yet demonstrate water-repellency. The present pigments will thus obtain cosmetic which will give the user a refreshment and longer lasting and water-repellent make-up.
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