Conformation of complexes

Higher eukaryotic expression systems are usually used for production of small amounts of protein for example, for analytical purposes or if a native conformation of complex enzymes has to be obtained. They can further be used to modify enzymes which were produced by lower... 

Molecular Mechanics NMR Pseudoenergy Protocol To Determine Solution Conformation of Complex Oligosaccharides... 

S S CONTENTS Preface, C. Allen Bush. Methods in Macromo-lecular Crystallography, Andrew J. Howard and Thomas L. Poulos. Circular Dichroism and Conformation of Unordered Polypeptides, Robert W. Woody. Luminescence Studies with Horse Liver Dehydrogenase Information on the Structure, Dynamics, Transitions and Interactions of this Enzyme, Maurice R. Eftink. Surface-Enhanced Resonance Raman Scattering (SERRS) Spectroscopy A Probe of Biomolecular Structure and Bonding at Surfaces, Therese M. Cotton, Jae-Ho Kim and Randall E. Holt. Three-Dimensional Conformations of Complex Carbohydrates, C. Allen Bush and Perse-veranda Cagas. Index. 

The conformation of complex side groups that consist of more than one atom is more difficult to assess from X-ray liber diagrams, and much work remains to be done to obtain detailed structural data for such polyphosphazenes. 

Stereoselectivity ond In addition to the dissymmetry generated by the tris(chclaie) structure of octahedral he Conformation of complexes, it is possible to have dissymmetry in the ligand as well. For example. Ihe Chelate Rings gauche confiwmalion of ethylenediamine is dissymetric (Fig. 12.27) and could be... 

The optically active ligands, RR-ptn and SS-ptn, adopt skew boat conformations in which both methyls are equatorial (76). Thus RR-ptn adopts the X conformation, and SS-ptn forms the 8 conformation of the skew boat. The meso form of the ligand, RS-ptn, however, must adopt a chair conformation if both methyls are to be equatorially oriented. Tris complexes composed solely of RR- (or SS-) ptn are therefore restricted to the lela and 083 isomers. Molecular mechanics calculations have predicted that the lel conformation of complexes with the racemic ligands (e.g., A XXX) is significantly (4-7 kJ mol ) more stable than the 083 (A XXX) (77, 78). The tris chair form of RS-ptn was estimated to be very similar in strain energy to the RR-ptn leh complex (78). 

Molecular modeling is an effective tool to elucidate the conformations of complex molecules. They are used in the structural elucidation of compounds 399, 400 and 804 [179], hopeaphenol A (718),... 

Ring scission of cyclic p-halogeno ethers to olefinic alcohols mediated by Sml2 has been studied. Scission in the tetrahydrofuran series could be accelerated by addition of HMPA or DMPU with only a small deterioration in diastereo-selectivity, but in the tetrahydropyran series there was a drastic change in the stereochemistry of the product when DMPU was used. Obviously, DMPU has a substantial effect on the formation and conformation of complexes in solution [88,89]. 

In the last few years, Tabushi et al. (27), Koga and co-workers (24, 28), Jarvi and Whitlock (29), Breslow and co-workers (30), Diederich and coworkers (31, 32), and Vogtle and co-workers (33, 34) as well as our group (35) have shown that azacyclophanes in the form of their ammonium salts can very effectively complex lipophilic substrates. Even hydrocarbons bind with association constants of 1000 or more in aqueous solutions. Our own studies of such host-guest systems were initiated by the desire to use complexations of alkanes for the selective functionalization of paraffins (23, 36) [in addition to our interest (37, 38) in conformations of complex ring systems and their study by NMR methods as well as by force field model calculations]. 

The model systems devised to examine the binding strength of the interactions where the aromatic and amine motifs are not interconnected are shown in Schemes 18.2 and 18.3. The main questions addressed here were regarding the relative preference of Li" " and Mg + to bind to an aromatic ring in a n fashion and of amines to bind in a a fashion, the differences in conformations of complexes involving metal compared with those of protonated ones and the extent of strucmral reorganization required to achieve bidentate confirmations. 

Bush CA, Martin-Pastor M, and Imberty A (1999) Structure and conformation of complex carbohydrates of glycoproteins, glycohpids, and bacterial polysaccharides. Annual Review of Biophysics and Biomolecular Structure 28 269-293. 

Case Bulkiness Configurational relationship Conformation of complex VI... 

The effects on the conformations of complexes of Sb(III) and Bi(III) of the rigid maleonitrile units present in four related mixed thia-oxa macrocycles and of the ligands themselves has been investigated by variable temperature solution and C H NMR studies together with molecular modeling. The Sb and Bi complexes were thought to show a preference for coordination via the ether-O atoms. " ... 

Copper. Variable temperature H NMR spectroscopy and Ti measurements have been used to study the interconversion of conformers of complexes such as [Cu(L-phenylalanine)(phen)(OH2)]. A complex equilibrium involving copper complexes such as [Cu(saccharinate)(PPh3)2] has been studied by NMR spectroscopy. Variable temperature P NMR spectra of [Cu2(p-dppm)3(02CR)2] have revealed at least three dimeric species in equihbrium. ... 

Similar investigations have been carried out on H2XP PCX complexes (X = F, Cl, OH, NC, CN, CCH, CH3, and H, Fig. 4b), in search of complexes stabilized by P-P pnicogen bonds. Three conformations of complexes were considered. Depending on the conformation and X substituent, computed t(/(P)P) coupling constants wiried from ca. 7 to 210 Hz. The authors have found a correlation between 7(P,P) and P-P distances. 

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