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Analytische chemie

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Chemistry --- chemie

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Speci?c binding of a ligand to a receptor is a key step in a variety of biol- ical processes, such as immune reactions, enzyme cascades, or intracellular transport processes. The ligand-receptor terminology implies that the rec- tor molecule is signi?cantly larger than the ligand, and the term bioactive conformation  usually characterizes the conformation of a ligand when it is bound to a receptor. In a more general sense, bioactive conformation applies toanymoleculeinabiologicallyrelevantboundstateregardlessofsizecons- erations. Mostofthecontributions tothisbookaddressligandsthat aremuch smaller than their receptors. X-ray crystallography and high resolution NMR spectroscopy are the two main experimental techniques used to study bioactive conformations. The- fore,the twovolumes ofthisbookcover approachesthat use either ofthetwo techniques, or a combination thereof. The combination of X-ray crystallog- phy and NMR spectroscopy is particularly useful when a crystal structure of areceptorprotein,butnotofthereceptorprotein-ligandcomplex,isavailable. Anumberofexperimentaltechniquestoanalyzethebioactiveconformationof aligandwithNMRarebasedontheobservationoftheresonancesignalsofthe free ligand that is in exchange with the bound ligand. Several chapters focus onsuchapproachesthat rangefromclassical transferredNOEexperiments, totransferreddipolarcouplings,toSTD(SaturationTransferDifference)NMR techniques. Incaseswhere tightbinding inthesub-nanomolar rangeprevents the analysis of the bioactive conformation via free ligand signals, the ligand- protein complex has to be analyzed with protein NMR-based techniques or by crystallography. Since this area has been the subject of many reviews and monographs it will not be covered here in particular detail. As a unifying theme, all contributions target the question of how molecular recognition of biologically active molecules is achieved on the atomic scale.

Organic chemistry --- organische chemie

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In the last 50 years molecular biology was dominated by the exploration of proteins and nucleic acids. Beside their role in energy metabolism, oligos- charides,which represent thethirdclass ofbiomacromolecules, have received less attention. Today it is well established that oligosaccharides are involved in many important biologicalregulation and recognition processes fromp- tein folding to cell-cell communication. Glycosylation of proteins is the most complexformofco-andposttranslationalmodi?cation. Thedeterminationof structure-function relationships, however, remains dif?cult due to the mic- heterogeneity of glycoproteins that exist in many different glycoforms. Thus chemical synthesis of glycoproteins and glycopeptides with de?ned glycan structures plays a pivotal role for the detailed determination of the role of protein glycosylation. This topic is covered by the ?rst two chapters of this bookdealingwiththechemicaland enzymatic synthesis ofglycopeptides and glycoproteins. The third chapter describes the construction of glycopeptide andglycoproteinmimetics containingnon-naturalstructuralelements. These so-calledneoglycopeptidesandneoglycoproteins,respectively,canprovide- sight on the importance of distinct structural elements on biological activity andmayhaveimproved propertiessuchasanincreased stability. Theappli- tion of synthetic glycopeptides, in many cases at the clinical level, as vaccines forbothcancerandHIVisthesubjectofthefourthchapter. Glycopeptide antibiotics are glycosylated secondary metabolites of bacteria and fungi that are synthesized by non-ribosomal peptide synthetases. Some of them serve as antibiotics of last resort in the treatment of nosocomial infections with enterococci and methicillin-resistant Staphylococcus aureus (MRSA) strains. Their structure, biosynthesis, and mode of action are summarized in the ?fth chapter. The last chapter covers current methods for the determination of high-resolution structures of glycopeptides and glycoproteins mainly based onNMRspectroscopy, X-raycrystallography,and molecular modeling.

Organic chemistry --- organische chemie

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Solid-state systems are frequently classi?ed according to their physical, str- tural or chemical properties. Such schemes are extremely helpful since pr- erties related to any such classi?cation are typically known and facilitate id- tifying solids with special material classes. The best-known examples of these schemes are conductivity or resistivity measurements by means of which m- als are easily distinguishable from insulators. However, frequently clear-cut decisions between material classes are not possible, since anisotropy, chemical composition, binding forces and local effects wash out distinct properties and lead to competition or coexistence. Such unresolved situations are especially typical for transition metal oxides that exhibit a variety of ground-state properties in a fascinating way. Here chemical substitution, doping, pressure or temperature effects easily in?uence the physical properties and may, for instance, induce metal/insulator, antif- romagnet/ferromagnet, insulator/superconductor transitions. This situation is analogous to perovskite ferroelectrics and hydrogen-bonded ferroelectrics, where ferroelectric/antiferroelectric transitions occur with chemical substi- tions of one of the constituent sublattices. In addition, glass-like states (dipolar glasses) are observed and relaxor ferroelectricity with a large potential for - plication frequently occurs.

Inorganic chemistry --- anorganische chemie