Peptide synthesis by means of immobilized enzymes

-Chymotrypsin covalently bound to silica, enzacryl AA, and enzacryl AH catalyzes peptide bond formation between N-protected dipeptide methyl esters and H-Leu-NH₂ with results similar to those with the free enzyme. The influence of water-miscible and water-immiscible cosolvents, of the supports, and of the structure of the substrates is shown to be of importance for the ease of the chymotrypsin-medicated coupling reactions. The best yields were obtained using biphasic aqueous-organic solvent mixtures, silica-bound chymotrypsin, and substrates with leucine in the P₂-position. The yields of the syntheses are discussed in terms of the reactivity of substrates with similar structure in enzymatic hydrolyses. All the immobilized chymotrypsin preparations could be re-utilized successfully for further couplings. Abbreviations: IUPAC/IUB rules for peptides are followed, see Eur. J. Biochem.27, 201 (1972); Glt=4-carboxybutyrul (glutaryl),-Nan=4-nitroanilide. All amino acids except glycine are of L-configuration.     

Resonant Bhabha scattering at MeV energies

We discuss, on a phenomenological level, the possible appearance of resonances ine ⁺+e ^? scattering at energies in the MeV region. The expected resonance cross section and angular distribution are examined. The observability depends crucially on the attainable energy resolution which is limit by the momentum distribution of the electrons contained in the target.     

Towards J/mol Accuracy for the Cohesive Energy of Solid Argon

The cohesive energies of argon in its cubic and hexagonal closed packed structures are computed with an unprecedented accuracy of about 5 J mol^?1 (corresponding to 0.05 % of the total cohesive energy). The same relative accuracy with respect to experimental data is also found for the face‐centered cubic lattice constant deviating by ca. 0.003 Å. This level of accuracy was enabled by using high‐level theoretical, wave‐function‐based methods within a many‐body decomposition of the interaction energy. Static contributions of two‐, three‐, and four‐body fragments of the crystal are all individually converged to sub‐J mol^?1 accuracy and complemented by harmonic and anharmonic vibrational corrections. Computational chemistry is thus achieving or even surpassing experimental accuracy for the solid‐state rare gases.     

Analysis of pure copper – a comparison of analytical methods

The reliability and performance of various analytical methods for the determination of 22 trace elements in pure copper is compared and discussed. The work was performed in the framework of an interlaboratory comparison for the preparation of four pure copper reference materials with graded element mass fractions of Ag, Al, As, Bi, Cd, Co, Cr, Fe, Mg, Mn, Ni, P, Pb, S, Sb, Se, Si, Sn, Te, Ti, Zn, and Zr. Special analytical results (ET-AAS, ICP-MS) obtained by the authors were described in more detail and were compared to the certified values. Special regard was paid to the influence of the copper matrix on performance and sensitivity of each analytical method and to the dissolution procedure of copper matrix and interferences from insoluble residues. For a generalized evaluation of the figures of merit for each applied elemental analytical method results from several independent laboratories were included in the discussion. Correspondence: Britta Lange, Department of Analytical Chemistry, Reference Materials, Federal Institute for Materials Research and Testing (BAM), Richard-Willstaetter-Str. 11, D-12489 Berlin, Germany