CHAPTER 4. Cleavable Dimethacrylate-end-linked Amphiphilic Polymer Co-networks Prepared Using Degradable, Hemiacetal Ester Group-containing Bifunctional Initiators

2020 ◽  
pp. 77-94
Author(s):  
Costas S. Patrickios ◽  
Maria Rikkou-Kalourkoti
Keyword(s):  
Ester Group ◽  
Amphiphilic Polymer ◽  
Bifunctional Initiators

Participation of 19-ester groups in the cleavage of 2α,3α- and 5α,6α-steroid epoxides. A case of competition between participation and external nucleophile attack

1979 ◽  
Vol 44 (5) ◽  
pp. 1496-1509 ◽  
Author(s):  
Pavel Kočovský ◽  
Václav Černý
Keyword(s):  
Perchloric Acid ◽  
Hydrobromic Acid ◽  
Ester Group ◽  
Carbonyl Oxygen ◽  
Cyclic Carbonate ◽  
Cyclic Ether ◽  
Normal Reaction ◽  
Neighboring Group ◽  
Ether Oxygen ◽  
The Difference

Acid cleavage of the acetoxy epoxide IIIa with aqueous perchloric acid or hydrobromic acid gave two types of products, i.e. the diol Va or the bromohydrin VIa, and the cyclic ether VIII. The latter compound arises by participation of ether oxygen of the ester group. On reaction with perchloric acid the epoxide IVa gave the diol XIIIa as a product of a normal reaction and the isomeric diol Xa as a product arising by intramolecular participation of the carbonyl oxygen of the 19-acetoxy group. Participation of the 19-ester group is confirmed by the formation of the cyclic carbonate XI when the 19-carbonate IVb is treated analogously. On reaction with hydrobromic acid, the epoxide IVa gave solely the bromohydrin XIVa as a product of the normal reaction course. Discussed is the similarity of these reactions with electrophilic additions to the related 19-acetoxy olefins I and II, the mechanism, the difference in behavior of both epoxides III and IV, the dependence of the product ratio on the nucleophility of the attacking species, and the competition between participation of an ambident neighboring group and an external nucleophile attack.

scholarly journals Asymmetric Hydrogenation of β-Aryl Alkylidene Malonate Esters: Installing an Ester Group Significantly Increases the Efficiency

2021 ◽  
Vol 23 (5) ◽  
pp. 1675-1680 ◽  
Author(s):  
Qian-Kun Zhao ◽  
Xiong Wu ◽  
Lin-Ping Li ◽  
Fan Yang ◽  
Jian-Hua Xie ◽  
...  
Keyword(s):  
Asymmetric Hydrogenation ◽  
Ester Group

scholarly journals Adjustment of Hydrophobic Properties of Cellulose Materials

Polymers ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1241
Author(s):  
Michael Ioelovich
Keyword(s):  
Ester Group ◽  
Hydroxyl Groups ◽  
Chemical Methods ◽  
Hydrophobic Properties ◽  
Cellulose Esters ◽  
Cellulose Modification ◽  
Polar Groups ◽  
Polar Substituents ◽  
Hydrolysis Of ◽  
Cellulose Materials

In this study, physicochemical and chemical methods of cellulose modification were used to increase the hydrophobicity of this natural semicrystalline biopolymer. It has been shown that acid hydrolysis of the initial cellulose increases its crystallinity, which improves hydrophobicity, but only to a small extent. A more significant hydrophobization effect was observed after chemical modification by esterification, when polar hydroxyl groups of cellulose were replaced by non-polar substituents. The esterification process was accompanied by the disruption of the crystalline structure of cellulose and its transformation into the mesomorphous structure of cellulose esters. It was found that the replacement of cellulose hydroxyls with ester groups leads to a significant increase in the hydrophobicity of the resulting polymer. Moreover, the increase of the number of non-polar groups in the ester substituent contributes to rise in hydrophobicity of cellulose derivative. Depending on the type of ester group, the hydrophobicity increased in the following order: acetate < propionate < butyrate. Therefore, tributyrate cellulose (TBC) demonstrated the most hydrophobicity among all studied samples. In addition, the mixed ester, triacetobutyrate cellulose (TAB), also showed a sufficiently high hydrophobicity. The promising performance properties of hydrophobic cellulose esters, TBC and TAB, were also demonstrated.

Study on the Aging Rules of Rigid Polyurethane Foams at Indoor Storage and Different Hygrothermal Conditions

2005 ◽  
Vol 24 (4) ◽  
pp. 197-208 ◽  
Author(s):  
Yuan-Jun Liu ◽  
Wen Zhai ◽  
Chuan-Lan He ◽  
Jian-Guo Deng ◽  
Ke-Jian Ji ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Aging Time ◽  
Fire Retardant ◽  
Ester Group ◽  
Polyurethane Foams ◽  
Compressive Modulus ◽  
Glass Beads ◽  
Hygrothermal Aging ◽  
Aging Properties ◽  
Mass Dimension

The aging rules of rigid polyurethane foam (PUR) at indoor storage and different hygrothermal conditions have been studied. Four parameters, which are mass, dimension, compressive strength and compressive modulus were tested. At indoor storage, mass, dimension and compressive strength vary slowly with an increase in aging time, while compressive modulus decreases quickly. PUR is sensitive to relative humidity (RH) verified by accelerated hygrothermal aging, and hydrolysis of ester group is the main reason resulting in the decrease of compressive properties. The filling with fire retardant and glass beads had some effect on hygrothermal aging properties of PUR. The addition of fire retardant increased compressive strength with aging time in the total trend, but it made dimension stability worse. The addition of glass beads slightly improved hygrothermal aging properties.

Selective acid hydrolysis of 2,4,6-trimethylbenzyl esters and its application in peptide synthesis

1966 ◽  
Vol 19 (8) ◽  
pp. 1511 ◽  
Author(s):  
FHC Stewart
Keyword(s):  
Acid Hydrolysis ◽  
Peptide Synthesis ◽  
Trifluoroacetic Acid ◽  
Ester Group ◽  
Protecting Groups ◽  
Alkaline Conditions ◽  
Hydrolysis Of

Experiments with various N-acylamino acid 2,4,6-trimethylbenzyl esters have shown that the ester group is cleaved selectively by cold trifluoroacetic acid without affecting benzyloxycarbonyl, formyl, or phthaloyl amino-protecting groups present. The possible value of this selective behaviour in peptide syntheses where the use of alkaline conditions would be detrimental is illustrated by the synthesis of certain dipeptide derivatives.

Cocaine: Pharmacokinetics and biotransformation in man

1989 ◽  
Vol 67 (9) ◽  
pp. 1154-1157 ◽  
Author(s):  
T. Inaba
Keyword(s):  
Methyl Ester ◽  
Ester Group ◽  
Oral Route ◽  
Plasma Cholinesterase ◽  
Pharmacokinetic Studies ◽  
Hydrolytic Cleavage ◽  
Bicyclic Structure ◽  
Anesthetic Action ◽  
Pharmacologically Active ◽  
Cytochrome P 450

Pharmacokinetic studies of cocaine have been carried out only in the last decade, although its local anesthetic action and addictive properties have been known for almost 100 years. Elimination half-lives of cocaine in man estimated from serial plasma concentration are relatively short and range from 0.5 to 1.1 h after i.v. and 0.9–1.5 h after administration by the nasal or oral route. The bioavailability after nasal inhalation is about 60%. The bicyclic structure of cocaine is characterized by functional groups including N-methyl, carboxyl methyl ester, and benzoyl ester, which are susceptible to biotransformation. Hydrolysis of the benzoyl group to ecgonine methyl ester is catalyzed by plasma cholinesterase and is thus under monogenic control. The hydrolytic cleavage of the other ester group, methyl ester, to benzoyl ecgonine occurs spontaneously at body temperature. In contrast, N-demethylation of cocaine mediated by microsomal cytochrome P-450 produces norcocaine and this metabolite was shown to be pharmacologically active, the action being similar to cocaine.Key words: cocaine, hydrolysis, plasma cholinesterase, cytochrome P-450.

scholarly journals Amphiphilic-Polymer-Guided Plasmonic Assemblies and Their Biomedical Applications

2016 ◽  
Vol 28 (1) ◽  
pp. 105-114 ◽  
Author(s):  
Jibin Song ◽  
Gang Niu ◽  
Xiaoyuan Chen
Keyword(s):  
Biomedical Applications ◽  
Amphiphilic Polymer
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