ABSTRACT
Methods for the efficient solid-phase synthesis of glycopeptides have developed rapidly over the past two decades. Incorporation of both O- and N-linked glycosides, as well as branched carbohydrates, into peptides is readily achieved. Synthetic glycoproteins of modest size have also been constructed. As glycopeptide synthesis protocols have progressed, so has the recognition of distinct categories of synthetic difficulties. Such categories include (a) unstable glycosidic linkages, (b) multifunctional amino acids not easily glycosylated and incorporated into peptides, and (c) glycosylated peptide sequences that are subject to side reactions. In the present overview,we describe specific examples for each category of problematic glycopeptide syntheses, as well as solutions to these problems.
ABSTRACT
Interference effects of NaCl on the ET-AAS determination of Ge have been studied. The use of several matrix modifiers to alleviate this problem such as Ni and Zn perchlorates and nitrates, nitric acid, ammonium nitrate are reported. The stabilizing effect of Zn and Ni perchlorates allows the use of high pretreatment temperatures. NaCl is thus thermally volatilized from the atomizer by employing pretreatment temperatures higher than 1500 degrees C resulting in an improved sensitivity. Germanium levels in zinc plant slag samples, have been determined and compared to those obtained for the same samples spiked with NaCl with platform and wall atomization using nickel perchlorate as a matrix modifier. The results were compared with those from a hydride generation system equipped with a liquid nitrogen trap. The recoveries for germanium have been almost complete and amount to 99% for the original slag samples and 80% for 15% (w/w) NaCl containing spiked samples.
