- Synthesis and solvent-controlled self-assembly of diketopiperazine-based polyamides from aspartame
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An aspartame-based AB-type diketopiperazine monomer, cyclo(l-aspartyl-4-amino-l-phenylalanyl) (ADKP), was synthesized and subsequently utilized in the polycondensation of homo-polyamides with high molecular weights. By using various amino acids, dicarboxylic acids, and diamines, random DKP-based copolymers were also synthesized. The self-assembly properties of ADKP and poly(cyclo(l-aspartyl-4-amino-l-phenylalanyl)) (PA1) were studiedviathe solvent displacement method. Notably, PA1 self-assembled into particles with various morphologies in different solvent systems, such as irregular networks, ellipsoids, and hollow particles. The morphological transformation was also confirmed by dropping acetone and toluene onto the PA1 particles. Furthermore, infrared spectra and Hansen solubility parameters of PA1 and different solvents revealed the particle formation mechanism, which provided more insights into the relationship between the morphology and strength of the hydrogen bonding of each solvent.
- Yin, Hongrong,Takada, Kenji,Kumar, Amit,Hirayama, Thawinda,Kaneko, Tatsuo
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- Investigation of solid-state reactions using variable temperature X-ray powder diffractrometry. I. Aspartame hemihydrate
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Purpose. The object of this study was to demonstrate the applicability of variable temperature X-ray powder diffractometry (XRD) to investigate solid-state reactions using aspartame as a model compound. Methods. Aspartame exists as a hemihydrate (ASH) under ambient conditions and converts to aspartame anhydrate (ASA) at ～130°C. ASA on further heating to ～180°C undergoes decomposition (intramolecular cyclization) to form a diketopiperazine derivative (DKP). The dehydration as well as the decomposition kinetics were studied isothermally at several temperatures. The unique feature of this technique is that it permits simultaneous quantification of the reactant as well as the product. Results. While the dehydration of ASH appeared to follow first-order kinetics, the cyclization of ASA was a nucleation controlled process. The rate constants were obtained at various temperatures, which permitted the calculation of the activation energies of dehydration and cyclization from the Arrhenius plots. The activation energy of dehydration was also calculated according to the method described by Ng (Aust. J. Chem., 28:1169-1178, 1975) and the two values were in good agreement. Conclusions. The study demonstrates that XRD is an excellent complement to thermal analysis and provides direct information about the solid-states of various reaction phases.
- Rastogi,Zakrzewski,Suryanarayanan
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p. 267 - 273
(2007/10/03)
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- Cyclo(dipeptide) as Low-molecular-mass Gelling Agents to Harden Organic Fluids
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Cyclic dipeptides consisting of diverse amino acids can cause physical gelation in a wide variety of organic fluids, including edible oils, glyceryl esters, alcohols and aromatic molecules; the gelation phenomenon is characterized by minimum gel concentration, FTIR spectroscopy, transmission electron microscopy, and X-ray diffraction.
- Hanabusa, Kenji,Matsumoto, Yoshimitsu,Miki, Toru,Koyama, Toshiki,Shirai, Hirofusa
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p. 1401 - 1402
(2007/10/02)
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- Hexafluoroacetone as Protecting Group and Activating Reagent in Amino Acid and Peptide Chemistry, XI. A New Simple Preparative Access to 2,5-Dioxopiperazines and 2,5-Dioxomorpholines
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2,5-Dioxopiperazines with symmetrical as well as unsymmetrical substituent pattern can be obtained via 2,2-bis(trifluoromethyl)-1,3-oxazolidin-5-ones, and 2,5-dioxomorpholines via 2,2-bis(trifluoromethyl)-1,3-dioxolan-4-ones, respectively. Keywords: Hexafluoroacetone; α-Amino acids; α-Hydroxy acids; 2,2-Bis(trifluoromethyl)-1,3-oxazolidin-5-ones; 2,2-Bis(trifluoromethyl)-1,3-dioxolan-4-ones; 2,5-Dioxopiperazines; 2,5-Dioxomorpholines.
- Burger, K.,Rudolph, M.,Windeisen, E.,Worku, A.,Fehn, S.
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p. 453 - 464
(2007/10/02)
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- Stability of aspartame in water:organic solvent mixtures with different dielectric constants
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In order to examine the influence of solvent composition on the stability of aspartame (N-α-L-aspartyl-L-phenylalanine-1-methyl ester) in solution (5 mg/mL), the degradation of aspartame was carried out in water:methanol, water:ethanol, and water:glycerine mixtures with dielectric constant values of 45, 55, and 65, respectively. The rate of disappearance of aspartame was measured by a sensitive HPLC assay. The degradation rate of aspartame increased as the dielectric constant of the solvent mixture decreased in all three solvents systems. For example, at 60 °C, the degradation rate constants were 4.1, 5.9, and 8.4 x 10-3 h-1 at dielectric constant of 65, 55, and 45, respectively. From these results, it can be concluded that the stability of aspartame in aqueous solutions cannot be enhanced by the replacement of water by solvents of lower dielectric constant.
- Sanyude,Locock,Pagliaro
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p. 674 - 676
(2007/10/02)
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