Separation of large DNA molecules by pulsed-field gel electrophoresis A review of the basic phenomenology

Pulsed-field gel electrophoresis is a method of separating large DNA molecules. The distinctive feature of this method is that the direction of the electric field is changed periodically. During the five years since Schwartz and Cantor introduced this technique, there has been dramatic progress in pulsed-field instrumentation and in associated electrophoretic methods. Progress has been driven by practical experience with little guidance from theory. In this review, the basic phenomenology of pulsed-field gel electrophoresis is summarized and some speculations are advanced about possible molecular mechanisms.     

Heterocyclic studies—XXIV: Mass spectra of some pteridin-4(3H)-ones and 3-methoxypteridin-4(3H)-ones

Mass spectra of pteridin-4(3H)-one and all its mono-, di- and tri-C-methyl derivatives are recorded. Spectra of 3-methoxypteridin-4(3H)-one and four of its mono- and dimethyl derivatives are also recorded. Pteridin-4(3H)-one fragments mainly by loss of CO and HCN in either order. Methyl substitution in the pyrazine ring leads to that ring fragmenting in preference to the oxygen bearing pyrimidine ring. Elucidation of fragmentation pathways was facilitated by changes in peak positions with changing methyl substitution patterns. 3-Methoxypteridin-4(3H)-ones fragment mainly through initial loss of CH₂O, but the ions so produced break down differently from isomeric molecular ions of pteridin-4(3H)-ones. Several fragmentation pathways are discussed.