C—O ester bonds

In 2-trimethylsilylethyl 4-phenylbenzoate 44, the C—Si and C—O ester bonds are in an antiperiplanar conformation, and the C—O ester bond is significantly longer than expected for an alkyl ester bond at a primary centre. This is consistent with a oq si T c o interaction in the ground state. In /raw.v-2-(di methyl phenyl si ly I )cyclohexyl-3,5-dinitrobcnzoate 45, the dihedral angle between the C—Si and C—O ester bonds is found to be just over 60°, and there appears to be little lengthening of the C—O bond. 

The proton donated from the OH group of Ser 195 to His 57 is then donated to the N atom of the scissile bond, cleaving the C-N peptide bond (or the C-O ester bond) to produce the amine and the acyl-enzyme intermediate. The amine is that part of the substrate which follows the scissile bond in the sequence the acyl-enzyme intermediate is the remaining fragment covalently bound to Ser 195. 

Fig. 3 shows ATR-FTIR spectra for pure PVDF film (a), G-PMMA master (b), 80 20 (c), 70 30 (d), 70 30 NoG (e), 60 40 (f) which were annealed at 50°C from 550-2000 crtri. When MG was incorporated in PMMA matrix (G-PMMA master), the absorption originating from MG particles alone were hardly visible. G-PMMA master spectrum clearly shows several characteristic peaks at 1723,1449 and 1142 cm-i which are related to the ptresence of PMMA chains, assigned to ester carbonyl (C=0), O-CHsand C-O (ester bond) stretching. 

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See also in sourсe #XX -- [ ]

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