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J S Lindsey

Publications and source records attributed to J S Lindsey.

3 recordsLinked to original sources
PubMed1995

Flexible protocols improve parallel experimentation throughput.

Advanced chemical workstations offer the potential to substantially improve the productivity of experimental research. To fully exploit such technologies, effective scheduling of experiments is crucial. Chemists tend to define experimental protocols with rigid time constraints, although often the scientific objectives can be achieved without adhering to such constraints. Investigation of a scheduling algorithm that allows flexible time constraints shows that improvements in workstation throughput as great as 50% can be reached by modest flexibility in the timing of operations in the experiments. Several heuristics that might be used with the scheduling algorithm were tested; a heuristic that schedules long experiments while first keeping the workstation busy was shown to be a good general choice.

Algorithms↗
PubMed1992

252Cf plasma desorption mass spectrometry in the synthesis of porphyrin model systems.

252Cf plasma desorption mass spectrometry has been used in the characterization of more than 100 synthetic porphyrins ranging in mass from 614 u for tetraphenylporphyrin to over 2000 u for some porphyrin model systems. In virtually every case, 252Cf plasma desorption mass spectrometry yielded an intense ionized molecule ion [M.+ and/or (M+H)+], irrespective of the groups appended to the porphyrin. The appended groups include carboxylic acids, amides, imides, chloroacetamides, Fmoc-protected amino acids, aromatic amines, nitriles, alkynes, alkenes, esters, active esters, benzyl ethers, acetals, dithioacetals, ketones, imines, phenols, quinone, hydroquinone, ferrocene, cyanine dyes, trimethylsilyl protecting groups, nitro groups, and combinations of these functionalities. Metalloporphyrins and porphyrin-porphyrin dimers are also analyzed with ease. Resolved isotopic peaks were observed for porphyrins with molecular weights below 1000, and unresolved isotopic peaks yielding average masses were observed for porphyrin compounds with higher molecular weights. The limited resolution in the higher molecular weight range does not lessen the utility of the method because the observation of the molecule ions [M.+ and/or (M+H)+] provides unambiguous evidence concerning the success of the synthesis. The 252Cf plasma desorption mass spectra of porphyrins are not complicated by chemical transformations. This method is ideally suited for rapid analysis of synthetic porphyrins and provides a powerful tool for chemists engaged in the synthesis of complex organic molecules.

Californium↗