Stereochemical and structural aspects of the variations in the C-terminal residue of L-aspartyl-L-phenylalanine methyl ester have been investigated. Novel configurational analogues such as L-aspartyl-D-alanine benzyl ester and L-aspartyl-D-alpha-aminobutyric acid benzyl ester were found to be sweet. In addition, chiral and achiral alpha, alpha-dialkylglycine and alpha-aminocycloalkanecarboxylic acids were incorporated into the dipeptides. The L-aspartic acid based dipeptide derivatives of alpha-aminoisobutyric acid methyl ester, alpha-aminocyclopropanecarboxylic acid methyl ester, alpha-aminocyclobutanecarboxylic acid methyl ester, and alpha-aminocyclopentanecarboxylic acid methyl ester are sweet. Dipeptides with alpha-aminocyclohexanecarboxylic acid methyl ester and alpha-aminocycloheptanecarboxylic acid methyl ester are bitter, whereas the analogues with alpha-aminocyclooctanecarboxylic acid methyl ester, alpha, alpha-diethylglycine methyl ester, and alpha-aminoisobutyric acid benzyl ester are tasteless. Aspects on chirality and effective volume of the C-terminal residue are discussed and correlated with taste.
Ortho-substitution with hydrophobic aliphatic groups has shown reduced moisture uptake in a variety of thermoset networks. In this study, the number and size of ortho-substituents were systematically varied on the epoxy monomers and aniline curing agents to determine network structure−property relationships. Networks were formed from combinations of four epoxies cured with seven aniline curing agents. The cured epoxy−amine networks were exposed to boiling water for 96 h to determine network moisture uptake, as well as wet thermomechanical properties. Ortho-substitution on both the epoxy and aniline monomers showed a reduced moisture uptake of up to 62% over an unsubstituted network. Also, the substituted networks had smaller wet T G knockdowns compared to the unsubstituted network, and networks derived from 2,2′-(((butane-1,1-diylbis(2-(tert-butyl)-5-methyl-4,1-phenylene))bis(oxy)bis(methylene))bis(oxirane) (t-Bu Bisepoxy) had the smallest wet T G knockdowns of only 5 °C or less. These results show the unique advantages of ortho-substituents on epoxy−amine networks in terms of network hydrophobicity and wet thermomechanical behavior. Applications of the ortho-substituted monomers and networks include use in marine environments as composite materials, hydrophobic coatings, or adhesives.
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