Structure of adducts in solution

This section reviews a selection of the more quantitative uses of LSR for substrate structure determinations. The substrates are grouped according to their donor properties. 

Oxygen donor substrates continue to be extensively studied. Conformations of esters, (427) aldehydes and ketones, (428, 429) ketones, (430, 431) cyclohexanones, (432, 433) carboxylates, (434) benzene-1,2-dioxydiacetate, (435) borneols, (436) troponeiron tricarbonyl, (437) and nitrosopiperidines (438) have been deduced. It is 

A theoretical calculation has been made (443) of the structures of mono-adducts of tris-(/i-diketonato) LSR of the type [Ln(bidentate)3 (unidentate)]. Three favoured structures having similar potential energies are suggested. These are a capped octahedron (C3 ), an irregular polyhedron (CJ, and a structure intermediate between a pentagonal bipyramid and a capped trigonal prism. The first two structures have been observed experimentally when the unidentate ligand is water or a carbonyl function. 

Nitrogen-donor substrates that have been studied in some detail include pyridines and piperidines, (444, 446) pyrroles, (447) quinoline and isoquinoline, (448) naphthylamine, (449) and nitriles. (450) The study of 1- and 2-naphthylamine (449) involved the use of the paramagnetic reagents Gdfdpmjj, Ni(acac)2, and Pr(fod)3 which induced predominant relaxation, contact shift, and pseudocontact shift 

The application of LSR to amino-acids has received some attention. (451-456, 498) Such studies are an essential preliminary to the use of LSR for amino-acid sequence determination in simple peptides and proteins. The latter are discussed more comprehensively in Section G. A detailed study has been made (453) of the interaction of Eu(iii), Pr(iii), Gd(iii), and La(iii) with iV-acetyl-L-3-nitrotyrosine in order to characterize the nitrotyrosine residue as a potential specific lanthanide binding site in proteins. The parameters of the dipolar interaction indicate a significant contribution from non axially symmetric terms. The conformations of the nucleotides cyclic j8-adenosine 3, 5 -phosphate (3, 5 -AMP) (457, 458) and adenosine triphosphate (ATP) (459) have been deduced using LSR. In the former case the conformation of the ribose and phosphate groups is consistent with the solid state structure. A combination of lanthanide shift and relaxation reagents was used to deduce the most favoured family of conformations for ATP in aqueous solution. One of these conformations corresponds closely to one of the crystal structure forms. 

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