文献汇报课件.pptVIP

文献汇报;什么是文献汇报;为什么要进行文献汇报;怎样进行文献汇报;文献汇报的结构;如何选择文献;如何查找文献;如何查找文献;如何阅读文献;文献结构;选择文献;文献简介;文献背景(大背景和小背景);小背景（同行研究水平）：Nevertheless, methods have emerged for bioconjugation with natural and unnatural amino acids in protein molecules6,7.Cysteine is a key residue for the chemical modification of proteins owing to the unique reactivity of the thiol functional group and the low abundance of cysteine residues in naturally occurring proteins8,9. Michael addition to maleimides and SN2 reaction with alkyl halides are commonly used for cysteine modification. The resulting conjugates tend to decompose in the presence of external bases or thiol nucleophiles10, which prompted the recent development of advanced cysteine bioconjugations for the improved stability of conjugates. The ability to achieve high levels of chemo- and regioselectivity through the judicious choice of metal and ligand design suggest that metal-mediated processes could be very attractive for the development of new bioconjugations. Existing metal-based transformations often rely on the use of functional handles12 or unnatural amino acids, such as 4-iodophenylalanine and aldehyde- or alkyne-containing amino acids3,4,13, and require high concentrations (mM) of derivatizing agents, which can cause off-target reactivity or purification problems. ;We considered that palladium complexes resulting from the oxidative addition of aryl halides or trifluoromethanesulfonates14 could be used for the transfer of aryl groups to cysteine residues in proteins (Fig. 1a). (For existing transition-metal-catalysed C–S bond-forming reactions, see ref. 15.) The efficiency and selectivity of the proposed reaction with the highly active palladium species may be hampered by the presence of a variety of functional groups within complex biomolecules. Furthermore, the presence of free thiols has been previously shown to inhibit palladium-catalysed cross-coupling reactions on peptides16, while Pd(II)-complexes have also been shown to exhibit prot