Hydrolytic degradation of α‐substituted polyglycolic acids: A semiempirical computational study

Abstract

The two-step hydrolyses of substituted polyglycolic acids are modeled by the semiempirical MNDO Hamiltonian using small molecule analogs to determine the effect of the alkyl substituents on the reaction and activation enthalpies. Reaction enthalpies remain reasonably constant up to three carbons, before becoming less exothermic for large alkyl substituents. Activation enthalpies show patterns that can be explained by steric effects. 0 1993 by John Wiley & Sons, Inc.

Base-catalysed hydrolysis of ?-lactones: reactivity-structure correlations for 3-(aryl- and alkylmethylene)-(Z)-1(3H)-isobenzofuranones

“…The reasons for this are threefold: (i) small anions are generally poorly described by semi-empricial methods (more specifically, by any method using small basis sets, including ab initio calculations); 18 (ii) the addition of nucleophiles to carbonyl compounds in the gas phase occurs without any barrier and thus experimentally measured activation energies of such reactions in solution almost exclusively reflect the desolvation energies of the reactants 21 and in the calculations, therefore, a reasonable solvation shell would be needed; and (iii) in reaction path calculations involving the hydroxide anion, besides the presumed addition, deprotonation reactions or additions to the nearest positively charged centre may occur. 22 Using water instead of hydroxide anion as nucleophile will have two major drawbacks: (i) the calculated activation energies will be much too high since besides the addition of the nucleophile proton transfer also has to take place; and (ii) the activation energies for the second step in the proposed mechanism of the alkaline hydrolysis, i.e. ring opening to form the enol of 2-acylbenzoic acid 10, shown in Scheme 2, will also be too high since in our experience the stability of the tetrahedral intermediates 9 is overestimated by AM1.…”

The role of superoxide ions in the degradation of synthetic absorbable sutures

“…These factors include the pH of the degradation media, 2,3 the type of electrolytes in the degradation media, 4 the external stress/strain applied, [5][6][7] the temperature of the degradation media, 1,8 ␥-irradiation, 9-12 free radicals, [13][14][15][16] a variety of enzymes, 11,[17][18][19][20] bacteria, [21][22][23][24][25][26] lipids, 27,28 synovial fluid, 29,30 plasma surface modification, 31 and computer modeling of the effects of steric hindrance and electronic induction on hydrolytic degradation. 32 A review of these factors recently was written by Chu et al 1 Among the factors studied, the role of free radicals on the biodegradation of synthetic absorbable sutures is one of the least investigated even though this factor probably is one of the few very important ones in biological systems. It is important because inflammatory cells, particularly leukocytes and macrophages, are able to produce highly reactive oxygen species, such as superoxide (иO 2 − ) and hydrogen peroxide, during inflammatory reactions of foreign materials.…”