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acid compounds such as l -argininium dinitrate [ 6 ], l -arginine hydrochloride [ 7 ], l -alanine acetate [ 8 ], and glycine sodium nitrate [ 9 ] have been reported. The amino acid l -alanine forms a number of complexes in coordination with

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series, namely: glycine, l -alanine, and l -proline. However, the solubility of proline in water is much higher than even glycine and its enthalpy of solution in water is exothermic unlike other amino acids. It was shown that in terms of heat capacity

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In recent TLC and polarimetric studies we showed, for the first time, the tendency of profen drugs to undergo spontaneous oscillatory chiral inversion in vitro. Because profen drugs are chiral propionic acid derivatives, we sought other chiral compounds with similar chemical structures and hence a similar tendency to spontaneously change their steric configuration. We have previously demonstrated that l -α-phenylalanine and l -tyrosine also undergo oscillatory in-vitro chiral inversion. We also demonstrated the effect of temperature and mixing on the process, and proposed a detailed model of the oscillator, providing the basis for mechanistic understanding of the oscillatory chiral inversion of these compounds. In this study we focused our attention on l -alanine, another amino acid with a chemical structure formally derived from propionic acid, and, again, by use of TLC and polarimetry, investigated the tendency of l -alanine to undergo oscillatory in-vitro chiral inversion when dissolved in neutral, acidic, and basic solvents. We also studied the effect of temperature and sample mixing. It was confirmed that l -alanine also undergoes chiral inversion. The dynamics of the process are specific to each compound.

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Enthalpies and entropies of sublimation for N-acetylglycine amide (NAGA), N-acetyl-L-alanine amide (L-NAAA), and N-acetyl-D-leucine amide (D-NALA) were determined from the dependence of their vapour pressures on temperature, as measured by the torsion-effusion method.

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. Experimental Materials Biochemical reagent grade glycine, L-alanine, L-valine, L-serine, L-threonine, and L-proline were used after recrystallization from a water–methanol mixture and dried in vacuum desiccators until their weights

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Journal of Thermal Analysis and Calorimetry
Authors: T. Tanaka, J. Magoshi, Y. Magoshi, B. Lotz, S.-I. Inoue, M. Kobayashi, H. Tsuda, M. Becker, Zh. Han, and Sh. Nakamura

Abstract  

The crystal structure, thermal properties and growth rates of spherulites of the Tussah silk fibroin, produced upon drying of the silk taken directly from the lumen which is essentially a poly(L-alanine)polypeptide, are investigated. Depending on casting conditions, spherulites with either αhelical chain conformation or β parallel sheet structure are produced. The growth rates display a strong positive temperature coefficient, with an apparent transition, which however cannot be related with the formation of two different crystal structures at this stage.

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Abstract  

In this paper a review of recent results concerning thermodynamic properties of solid uncharged derivatives of some amino acids and small peptides is reported. The experimental data obtained by different calorimetric methods are: sublimation enthalpies, heat capacities, enthalpies and temperatures of fusion and, in few cases, enthalpies and temperatures of solid-to-solid transitions. The standard molar and specific enthalpies and entropies of sublimation at 298.15 K have been calculated integrating the heat capacities of solids and vapours as function of temperature or directly measuring by calorimetry the heating enthalpies. The first ones have been obtained by interpolation of the values calculated according to the group additivity method of Benson. The sublimation thermodynamic properties have regarded N-acetylamides of glycine (NAGA), L-alanine (L-NAAA), L-valine (L-NAVA), D- and L-leucine (D-NALA and L-NALA, respectively) and L-isoleucine (L-NAIA) as well as the cyclic dipeptides glycyl-glycine (c-Gly-Gly), glycyl-L-alanine (c-Gly-L-Ala), L-alanyl-L-alanine (c-L-Ala-L-Ala) and sarcosyl-sarcosine (c-Sar-Sar). Heat capacities of the solid phases have been included also for N-acetylamide of L-proline (L-NAPA), N-methyl derivatives of the N-acetylamides previously cited and other amino acids, such as phenylalanine (F), isobutyric acid (isoBu), norvaline (norV) and norleucine (norL). In the text these substances are indicated as NAFAMe, etc. The heat capacities of their racemes are also reported. The fusion properties have concerned only two raceme mixtures (D,L-NAAA and D,L-NALA) and N-acetylamides of the cited amino acids, sarcosine (NASarA) and the following di-or tripeptides: glycyl-L-alanine (NAGAA), L-alanyl-L-alanine (NAA2A), glycyl-L-proline (NAGPA), L-prolyl-glycine (NAPGA), L-leucyl-L-proline (NALPA) and L-prolyl-L-leucyl-glycine (NAPLGA). Finally, solid-to-solid transitions have been found and characterized for L-NALA and NAGPA. All thermodynamic properties are discussed in the light of the crystal packing parameters determined during parallel crystallographic studies. It allows a comprehensive rationale of the behaviour of the solid state and its transitions for this interesting family of substances.

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Journal of Thermal Analysis and Calorimetry
Authors: G. Barone, C. Giancola, T. H. Lilley, C. A. Mattia, and R. Puliti

Enthalpies and temperatures of fusion or transition for four substituted dipeptides (Nacetylamides of glycyl-L-alanine (NAGAA),L-alanyl-L-alanine (NAA2A),L-prolyl-glycine (NAPGA) andL-leucyl-L-proline monohydrate (NALPA·H2O)) were determined by differential scanning calorimetry and the entropies of fusion derived. The results obtained have been compared with those of the corresponding substituted aminoacids and some of their racemic crystalline mixtures. The enthalpies and entropies of fusion of some substituted aminoacids have been redetermined. The results are discussed in comparison with crystal structural data, which has been reported in the literature or determined recently by some of the authors. Rationalization of the fusion parameters was attempted mainly on the basis of the number of intramolecular hydrogen bonds and the packing densities in the crystals.

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Abstract  

The alanine dosimeter made for evaluation by diffuse light reflection spectrophotometry (ALA/DRS) does not show the effect of orientation of crystals. Supposed deviation from random orientation has been investigated by EPR spectroscopy. EPR investigation shows that in spite of the very fine size of L-alanine crystals, they are oriented in thin layers of the polyethylene matrix. Specially prepared films with deliberately well oriented crystals have confirmed this observation. Our ALA/DRS dosimeter can be evaluated by the EPR method for the concentration of free radicals, providing that the dominating crystal orientation in the dosimetric film is indicated on it as an arrow, and the sample is inserted into the magnetic cavity always in the same orientation as has been done during the calibration operation.

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