Fragmentation studies of pentacoordinated bisaminoacylspirophosphoranes by negative electrospray ionization mass spectrometry.
Fragmentation pathways of a series of pentacoordinated bisaminoacylspirophosphoranes were elucidated by electrospray ionization multistage mass spectrometry (ESI-MS(n)) in negative mode. The deprotonated ions of pentacoordinated bisaminoacylspirophosphoranes tend to eliminate a corresponding amino acid to form base peak. The hydrogen/deuterium exchange experiment, the high-resolution mass spectrometry, (13)C stable isotope labeling experiment and theoretical calculations were used to rationalize the proposed fragmentation pathways and to verify the differences between the fragmentation pathways. The results indicate that the negative molecular ions of pentacoordinated bisaminoacylspirophosphoranes dissociate through its open-chain tricoordinated tautomers. The relative Gibbs free energies (ΔG) of the product ions and proposed fragmentation pathways were estimated using the B3LYP/6-31 + + G(d, p) model. The results have some potential applications in the identification structures of similar spirophosphorane compounds by ESI-MS(n).
Configuration Determination of Bimolecular L-Valine Hydridophosphorane
Bimolecular L-valine hydridophosphorane was synthesized by the reaction between L-valine and phosphorus trichloride in tetrahydrofuran (THF). Complete assignment of the 1H and 13C NMR chemical shifts of the compound was obtained by 2D NMR techniques, including 1H-1H COSY, DEPT and HSQC. Based on the results of NMR characterization, the structure of L-valine hydridophosphorane was elucidated. The 31P NMR spectrum of the compound showed two separated peaks at δ -64.66 and δ -67.81, suggesting that it is comprised of a pair of diastereomers. The configuration of one of the diastereomers was determined by NOESY, and further confirmed by X-ray crystallography.
THE IRON-ACETOCARMINE METHOD OF FIXING AND STAINING CHROMOSOMES
A short description of this procedure was given in Vol. 55 of the American Naturalist, pp. 573â€”574. The method has now been used almost daily for five years, and certain improvements have suggested themselves. The solution can be prepared by mixing about equal volumes of glacial acetic acid and water. To this is added powdered carmine in excess. The liquid is then â€ ? just brought to boil, cooled, and decanted. To the red solution there are then added a few drops of a solution of ferric hydrate in 50 per cent. acetic acid, to act as a mordant. The amount of iron varies with different objects. Too much produces a precipitate in a short time. The more