Search results for "calor"
showing 10 items of 866 documents
The structure, phase transition and molecular dynamics of [C(NH2)3]3[Sb2Br9]
2005
The crystal structures of [C(NH2)3]3[Sb2Br9] (Gu3Sb2Br9) at 300 K and of [C(NH2)3]3[Sb2Cl9] (Gu3Sb2Cl9) at 90 and 300 K are determined. The compounds crystallize in the monoclinic space group: C 2/c. The structure is composed of Sb2X93− (X = Cl, Br) ions, which form two-dimensional layers through the crystal, and guanidinium cations. In Gu3Sb2Br9 the structural phase transformation of the first-order type is detected at 435/450 K (on cooling/heating) by the DSC and dilatometric techniques. The dielectric relaxation process in the frequency range between 75 kHz and 5 MHz over the low temperature phase indicates reorientations of weakly distorted guanidinium cations. The proton 1H NMR second-…
Crystal structure, phase transition and ferroelectric properties of the [(CH3)3NH]3[Sb2Cl9(1 x)Br9x] (TMACBA) mixed crystals
2003
The paraelectric–ferroelectric phase transition in the [(CH3)3NH]3[Sb2Cl9(1−x) Br9x] (TMACBA) mixed crystals is investigated by the differential scanning calorimetry, dilatometric and dielectric methods. The phase transition is found at 363.5, 362.7, 360.5 and 350.9 K (on cooling) for TMACBA crystals with x = 0, 0.02, 0.17 and 0.42, respectively. The crystal structures of the pure bromine analogue (x = 1), TMABA, and the mixed crystal TMACBA (x = 0.55) are determined at 297 K. TMABA crystallizes in the trigonal space group Rc: a = 15.098(2) A, c = 21.906(4) A, Z = 3, R1 = 0.0393, wR2 = 0.0746. Its structure is built up of discrete Sb2Br93− bioctahedra and disordered trimethylammonium cation…
Structure, phase transitions and molecular motions in ferroelastic (C4H8NH2)SbCl6·(C4H8NH2)Cl
2002
The crystal structure at 293 K of the new pyrrolidinium chloroantimonate (V) analogue, (C4H8NH2)SbCl6(C4H8NH2)Cl, has been determined by x-ray diffraction as monoclinic, space group P21/c, Z = 8. The crystal is built up of isolated SbCl6- anions, two types of inequivalent pyrrolidinium cation and isolated Cl- ions. It undergoes five solid-solid phase transitions: at 351/374 K of first-order type (cooling/heating, respectively), at 356 and 152 K second order and at 135/141 and 105/134 K first order, detected by differential scanning calorimetry, dilatometric and dielectric measurements. The ferroelastic domain structure appears between 152 and 135 K. The proton nuclear magnetic resonance sec…
Structure and phase transitions in the ferroelastic [C(NH2)3]3Bi2Br9crystal
1999
Differential scanning calorimetry, dilatometric, dielectric and linear birefringence measurements have been used to study the ferroelastic [C(NH2)3]3Bi2Br9 crystal. The x-ray studies showed that it crystallizes at room temperature in the monoclinic symmetry, space group P21/m. The crystal undergoes a complex sequence of phase transitions: at 311 K, 333.5 K, 350 K, 415 K and 425 K. All phase transitions were found to be of first order type. The ferroelastic domain structure is maintained from room temperature up to 425 K. The temperature measurements of the linear birefringence and optical observations suggest the tetragonal symmetry of the parent paraelastic phase above 425 K.
Protective Effects of L- and D-Carnosine on R-Crystallin Amyloid Fibril Formation: Implications for Cataract Disease
2009
Mildly denaturing conditions induce bovine ?-crystallin, the major structural lens protein, to self-assemble into fibrillar structures in vitro. The natural dipeptide L-carnosine has been shown to have potential protective and therapeutic significance in many diseases. Carnosine derivatives have been proposed as potent agents for ophthalmic therapies of senile cataracts and diabetic ocular complications. Here we report the inhibitory effect induced by the peptide (L- and D-enantiomeric form) on ?-crystallin fibrillation and the almost complete restoration of the chaperone activity lost after denaturant and/or heat stress. Scanning force microscopy (SFM), thioflavin T, and a turbidimetry ass…
Indication of an order-order-transition by a partial disordering in ABC-triblock copolymers
1996
Poly(ethylene-alt-propylene)-block-polyethylethylene-block-polystyrene (PEP-b-PEE-b-PS) triblock copolymers were synthesized by anionic polymerization and subsequent hydrogenation of poly-1,4-isoprene-block-poly-1,2-butadiene-block-polystyrene triblock copolymers (1,4PI-b-1,2PB-b-PS). Differential scanning calorimetry and dynamic mechanical spectroscopy reveal an order-order transition which is induced by the mixing of PEP and PEE above their respective order-disorder transition (ODT).
Synthesis of Areno-Condensed [24]Annulenes
2001
[24]Annulenes condensed with three phenanthrene units (11a−d) or with three chrysene ring systems (22) were prepared by multi-step syntheses. The cyclic condensation reaction in the final step led to highly symmetrical compounds. Long flexible alkoxy groups attached to the periphery enhance the solubility and give rise to a strong aggregation of the molecules which was observed in solution by NMR and fluorescence excitation spectroscopy, and in the pure state by the detection of liquid crystalline phases in differential scanning calorimetry and polarization microscopy.
Yeast cultures with UCP1 uncoupling activity as a heating device
2009
7 páginas, 5 figuras, 3 tablas -- PAGS nros. 300-306
Iron(II) metallomesogens based on symmetrical tripod ligands
2012
Abstract Novel mononuclear tripodand-based iron(II) complexes showing liquid crystal properties have been synthesized and characterized. These are based on ligands tris[3-aza-4-((5-Cn)(6-R-2-pyridyl))but-3-enyl]amine, where R = hydrogen or methyl, 1,3,5-cis,cis-tris[1-aza-2-((5-alkyloxy)(2-pyridyl))vinyl]cyclohexane and 2,2,2-tris(2-aza-3-((5-alkyloxy)(2-pyridyl))prop-2-enyl)ethane. The physical characterization has been carried out by means of single-crystal X-ray diffraction measurements, magnetic susceptibility, differential scanning calorimetry, X-ray powder diffraction and Mossbauer spectroscopy.
(DIS)Assembly and Structural Stability of mtHsp60 and its Precursor NaÏve Form
2015
Heat shock protein 60kDa is a molecular chaperone (GroEL human homolog) that assists protein folding in mitochondria (mtHsp60). It is synthesized in the cell cytoplasm as a higher molecular weight precursor form (p-mtHsp60) containing a N-terminal targeting sequence, that is cleaved after import into the mitochondrial matrix [1, 2].It has been established, and demonstrated by various techniques, Hsp60 can accumulate in the cytosol, in various pathological conditions (i.e., cancer and chronic inflammatory diseases). The cytosolical Hsp60 accumulation mechanism may occur with or without mitochondrial release concomitantly, so that in the cytosol the two types of 60 kDa chaperonin proteins, (m…