Cynthia L. Sevilla

An esr study of radical intermediates formed by γ - radiolysis of tripalmitin and dipalmitoyl phosphatidylethanolamine

Radicals resulting from the 7-radiolysis at 77 K of neat tripalmitin and neat dipalmitoyl phosphatidylethanolamine were investigated by electron spin resonance spectroscopy (ESR). Analyses of the spectra of these complex lipids were aided by ESR studies of their components phosphorylethanolamine, palmitic acid and hexa-decane. Concentrations of various radicals were followed as a func-tion of temperature after γ-irradiation at 77 K. Both tripalmitin and dipalmitoyl phosphatidylethanolamine show anion radicals formed by electron addition to the ester groups and aliphatic side-chain radicals (-CH2-CH-CH2-) which are thought to be the result of deprotonation of the original positive hole. Computer analyses of the spectra as the temperature increases show loss of the anion radicals with an increase in a new radical produced by the abstrac-tion of a hydrogen atom from the α carbon on an acyl side chain. In the case of dipalmitoyl phosphatidylethanolamine, a radical of the phosphorylethanolamine portion of the molecule is detected as an intermediate. Mechanisms for the formation and decay of the free radical intermediates are discussed.

Plasminogen activator-anti-human fibrinogen conjugate

A covalent conjugate between the plasminogen activator urokinase and polyclonal rabbit anti-human fibrinogen has been formed using the heterobifunctional coupling reagent N-succinimidyl 3-(2-pyridyldithio) propionate. The resultant urokinase-anti-human fibrinogen conjugate was separated from unreacted material by gel filtration. The conjugate exhibited amidase activity against the small chromogenic substrate pyroglutamyl-glycyl-arginine-p-nitroanilide as well as plasminogen activator activity in an assay employing plasminogen and the plasmin substrate D-valyl-leucyl-lysine-p-nitroanilide. Retention of antibody specificity for fibrinogen was demonstrated using an enzyme linked immunoassay procedure. The conjugate was found to have greater stability in human plasma than unconjugated urokinase.

An electron spin resonance investigation of ester cation radicals at low temperatures. Proton transfer and rearrangement reactions

The cation radicals of a series of esters have been produced by γ-irradiation of CFCl3 matrices containing the ester at 77 K. In previous work cations of methyl and ethyl esters were investigated. In this work we report results for larger esters. The cations of these esters are found to undergo immediate internal proton-transfer reactions involving specific sites on one of the alkyl substituents. For example, deuteration studies show that proton transfer occurs from the terminal methyl group in propyl formate to produce —OCH2CH2CH·2, whereas in propyl acetate —OCH2ĊHCH3 is produced. The proton lost from these groups is assumed to add to an oxygen on the ester functional group. In the case of propyl acetate and esters with branched side chains we find that fragmentation reactions follow the proton transfer. In the cases of t-butyl acetate and isobutyl formate the fragmentation process occurs at 77 K and results in the isobutylene cation. Neopentyl formate gives evidence for the cation radical, an RCH·2 radical and the fragmentation radical cation as the sample is annealed. These results show that ester cation radicals are highly reactive even at low temperatures where proton-transfer and fragmentation reactions are found.

Hydrogen abstraction reactions by amide electron adducts: A comparison to acid, ester, aldehyde and ketone electron adducts

Abstract Electron reactions with a number of peptide model compounds (amides and N-acetylamino acids) in aqueous glasses at low temperature have been investigated using ESR spectroscopy. The radicals produced by electron attachment to amides, RC(OD)NDR′, are found to act as hydrogen abstracting agents. For example, the propionamide electron adduct is found to abstract from its parent propionamide. Electron adducts of other amides investigated show similar behavior except for acetamide electron adduct which does not abstract from its parent compound, but does abstract from other amides. The tendency toward abstraction for amide electron adducts are compared to electron adducts of several carboxylic acids, ketones, aldehydes and esters. The comparison suggests the hydrogen abstraction tendency of the various deuterated electron adducts (DEAs) to be in the following order: aldehyde DEA > acid DEA ≅ ester DEA > ketone DEA > amide DEA. In basic glasses the hydrogen abstraction ability of the amide electron adducts is maintained until the concentration of base is increased sufficiently to convert the DEA to its anionic form, RC(O−)ND2. In this form the hydrogen abstracting ability of the radical is greatly diminished. Similar results were found for the ester and carboxyclic acid DEAs tested. A reinvestigation of previous work found for acetylamino acid DEA also shows evidence for hydrogen abstraction by the DEA from the parent compound. This mechanism is proposed as a likely competing reaction to the well established mechanism involving secondary deamination of the electron adduct.