E Vinski | PubMed Health

PubMed1995

Optimization of a modified electrode for the sensitive and selective detection of alpha-dipeptides.

Sensitive and selective detection of dipeptides is important in neurochemistry. We have developed a flexible detection scheme for dipeptides based on a modified carbon electrode. The modification arises from the anodic treatment of the carbon electrode in alkaline solution. The flexibility of the detection scheme arises from the different conditions used in both the modification and the detection. It is shown that the modification step requires the presence of cupric ion, while the detection step does not. On the other hand, it is shown that the presence of copper in the detection eluent, as well as the pH of the environment, can be used in controlling the selectivity of the modified electrode. For example, the modified electrode is more selective for alpha-dipeptides over beta- and gamma-dipeptides as well as amino acids at pH 9.8, whereas it is selective for all dipeptides over amino acids at pH 8.0. Detection limits of dipeptides on the order of 10 nM were achieved at pH 8.0 by flow-injection analysis with a knotted Teflon tubing connecting the injector and the detector that gave a typical peak volume of about 0.50 ml at 1.0 ml/min. From surface analysis it is shown that the oxygenation of the glassy carbon electrode gives rise to the selectivity. The oxidation of dipeptides at the modified electrode is completely inhibited by 10 mM Mg2+ in the eluent.

Chromatography, Liquid↗

PubMed1991

Generating makes words memorable, but so does effective reading.

In many experiments, memorial benefits have been found when subjects generate items from fragments rather than read items in their complete forms. Does generation cause this difference, or are subjects disposed to adopt different strategies when generating as opposed to reading? If generating causes the difference, items processed in the same way apart from a generative stage should therefore benefit from that generative stage. Our experiments did result in benefits for generating as opposed to reading, but only when the readers processed the words poorly--by pronouncing them. When the readers processed the items well, by imagining them, generating was no better than reading. A new generation effect was found in metamemory. Subjects thought they would remember more generated items than read items; however, the act of making the prediction entailed meaningful processing, and the generated items were not actually remembered better than the read ones.

Adult↗