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This paper describes two methods to estimate the effective charge of a protein in solution by capillary electrophoresis and demonstrates these methods by using representative proteins. In one method, a "charge ladder"-a series of derivatives of a protein differing by known increments of charge but differing only minimally in hydrodynamic drag-is generated by covalent modification of the e-amino groups of lysines with 4-sulfophenyl isothiocyanate or acetic anhydride. In the second method, the equivalent of a charge ladder is produced by noncovalent association of a protein with differently charged ligands. (1) is straightforward and can be used to estimate the net charge of a protein over a range of values of pH. This method, however, requires substantial quantities (2-10 mg) of pure protein, and the measurement may be influenced by association of the protein with ions in solution. Winzor and Ojteg (2, 3) have estimated net charges of proteins based on Donnan potential measurements. These methods permit the charge ofa protein to be determined over a range ofionic composition and values ofpH but also require significant quantities (1-10 mg) of a protein.Here we report two related procedures for estimating the effective charge of a protein in solution at arbitrary values of pH by using capillary electrophoresis (CE) (4-8). The two procedures are complementary, but both rely on the same strategy: to generate and compare the electrophoretic mobilities of a protein with a series of derivatives of the protein that differ in effective charge by simple multiples of a unit charge but that differ only minimally in hydrodynamic drag.

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Pyrimidine synthesis starting from acrylonitrile has been known since the 1960s. The new Lewis acid-catalyzed condensation reaction allows the synthesis of 4-aminopyrimidines starting from the easily accessible chemical acrylonitrile without the need for carcinogenic chemicals and costly derivatization in up to 90% yield. The method is versatile and applicable for industrial-scale synthesis of biologically relevant substances such as vitamin B1 and trimethoprim.

Starting from the enantiomerically pure or racemic nucleophile 1-phenylethylamine (L) chiral cobalt complexes with the general formula [Co(Hdmg) 2 XL] (Hdmg dimethylglyoximate, X CN, NO 2 ) were obtained as homochiral or heterochiral crystalline solids, respectively. The crystal structures of the resulting cyano and nitro complexes were determined by single crystal X-ray diffraction. The homochiral solids crystallize in space group P2 1 with two molecules per asymmetric unit, the racemates in P2 1 /c with only one independent molecule. From a solution containing equimolar amounts of enantiomerically pure S-L cyano and R-L nitro complexes a stable and well-ordered binary solid could be crystallized and structurally characterized. The molecular constituents of opposite chirality are arranged in pairs in the vicinity of pseudo inversion centers forming a quasi-racemate in space group P2 1 . The driving force for the formation of this cocrystal is discussed in terms of intermolecular geometry and energy: The crystal structures of all five complexes are similar with respect to lattice parameters and intermolecular arrangement, but comparisons based on space filling and lattice energy confirm higher packing efficiency for the racemates and the quasi-racemate than for the enantiopure compounds.