Steroid Carboxylic Acids
Ronald Hobkirk in Steroid Biochemistry, 1979
In the above examples of direct epimerization, stereochemical considerations determined the formation of 20β derivatives during rearrangement. That the carboxyl group plays an important role in determining functional group interactions is also shown by NMR analysis. Benn244 had observed that epimeric Δ16-20 hydroxy steroids could be distinguished by the magnitude of the C-18 shift. In the 20α-hydroxy steroid series, the C-18 signal was downfield to that of 20β. This was confirmed by Robinson and Hofer245 for other steroids. For methyl 20-hydroxy-3-oxo-pregn-4-en-21-oic acids, acetylation at C-20α and C-20β caused an upfield shift of C-18 of 0.02 and 0.09 ppm, respectively. The effects of acetylation indicated that, in contrast with other steroids studied, side chain conformation of the 21-oic acid series permitted greater deshielding of C-18 by the β isomer.
The Reaction Mechanism
D. B. Keech, J. C. Wallace in Pyruvate Carboxylase, 2018
Perhaps the most significant feature of this work was that it demonstrated that proton abstraction could occur without concomitant carboxyl group transfer from carboxybiotin to the acceptor substrate. Also, the proposed mechanism postulated the presence of a base in the catalytic subsite of the enzyme. However, in terms of a general mechanism for all biotin-dependent carboxylases (in particular, pyruvate carboxylase), it does not take into account the fact that carboxybiotin (of pyruvate carboxylase) is unstable in the second subsite251 (i.e., carboxybiotin is capable of reacting with water in the second subsite). Nor does it account for the instability of carboxybiotin in propionyl-CoA carboxylase in the presence of β-fluoropropionyl-CoA.
Toxicology Studies of Semiconductor Nanomaterials: Environmental Applications
Suresh C. Pillai, Yvonne Lang in Toxicity of Nanomaterials, 2019
Covalent binding of biomolecules with nanosemiconductors can be made possible by using coupling agents like carbodiimide reagents (Chan et al., 1998). Most biomolecules contain amino and carboxyl groups. The reaction between these groups to form amide linkage can be catalysed by carbodiimide reagents. As an example, InP/ZnS semiconductor QDs were activated with dicyclohexylcarbodiimide (DCC) to yield a carboxylated intermediate which can react with the amino group of folic acid. These folate InS/ZnS conjugates were used for folate receptor-mediated delivery. Similar to carbodiimide conjugation, other strategies that are capable of covalent binding biomolecules to QDs include amine sulfhydryl reaction (Hildebrandt, 2011) and aniline-catalysed hydrazone (Blanco-Canosa et al., 2010) reactions (Figure 4.9).
Evaluation of anionic surfactants effects on the skin barrier function based on skin permeability
Published in Pharmaceutical Development and Technology, 2019
Mana Okasaka, Koji Kubota, Emi Yamasaki, Jianzhong Yang, Sadaki Takata
For amino acid surfactants other than those in the glutamate series (i.e. alaninate series, glycinate series, and taurate series), the Transmission Index values were ∼1 or less. Alanine and glycine are neutral amino acids, unlike glutamic acid. Taurine is not classified as an amino acid in the strictest sense; however, it has similar properties to natural amino acids and is known as an amino sulfonic acid. There is no notable alanine or glycine content in biological proteins relative to glutamic acid. Taurine is a biologically essential component functioning in the digestive and neurotransmitter systems. There is a little distribution of taurine in body surface tissues. Thus, the adsorption of the alaninate, glycinate, and taurate series on the skin is weaker than that of the glutamate series. Therefore, their effects on skin barrier function are very limited. The acidity of glutamic acid is another possible factor. Glutamic acid is an acidic amino acid possessing two carboxyl groups. One carboxyl group functions as the anion to form an ionic pair, whereas the other remains as a free acid. Therefore, glutamate surfactants may be acidic as sulfate-based surfactants.
Design and construction of a magnetic targeting pro-coagulant protein for embolic therapy of solid tumors
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2020
Mingyuan Zou, Peilan Xu, Li Wang, Lanlan Wang, Tingting Li, Cong Liu, Lei Shi, Jun Xie, Wanyun Li, Shengyu Wang, Guoqiu Wu, Fanghong Luo, Ting Wu, Jianghua Yan
The FTIR spectra of Fe3O4(a), OCMC(b)and OCMC/Fe3O4(c) are shown in Figure 4(D). The characteristic peaks of Fe3O4 at 564 cm−1 and 584 cm−1 were found in curve(a) and (c). The absorption centred at 564 cm−1 and 584 cm−1 corresponding to the Fe-O vibration related to the magnetite phase. The characteristic peaks of OCMC at 1408 cm−1 and 1411 cm−1 are found in curves (b) and (c), which were (C-O) of the carboxyl groups. Compared with curve(a) and (c), The band shifts of Fe–O stretching from 564 cm−1 and 584 cm−1and of C–O bending vibration from 1408 to 1411 cm−1 are significant. This phenomenon (blue shifted) indicates that OCMC/Fe3O4 combined by chemical cross linking with the formation of new bonds between the Fe3O4 and OCMC.
Nutraceuticals-based therapeutic approach: recent advances to combat pathogenesis of Alzheimer’s disease
Published in Expert Review of Neurotherapeutics, 2021
Marjan Talebi, Eleni Kakouri, Mohsen Talebi, Petros A. Tarantilis, Tahereh Farkhondeh, Selen İlgün, Ali Mohammad Pourbagher-Shahri, Saeed Samarghandian
Biologically important molecules that have long attracted scientists’ interest are the carotenoids derived from the plant of Crocus sativus L, and specifically from its red stigmas, namely crocins (CRCs) and crocetin [150]. There are five different types of CRCs identified at the stigmas of the plant which differ at the sugar moiety attached at the terminals of the carbohydrate skeleton [151]. Because of their glycosylated ends, CRCs are water-soluble carotenoids. On the other hand, crocetin a dicarboxylic acid, basically the aglycon part of CRCs, is found in minor quantity with respect to CRCs. Each terminal part of the carbohydrate skeleton is occupied by a carboxyl group (-COOH). Both molecules are capable of delaying the progression of neurodegenerative disorders, such as Alzheimer’s disease [152]; as we describe below.