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The Use of Complexation Induced Proton NMR Chemical Shifts for Structural Analysis of Host–Guest Complexes in Solution
Author(s) -
Rüdiger Volker,
Schneider HansJörg
Publication year - 2000
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20001016)6:20<3771::aid-chem3771>3.0.co;2-4
Subject(s) - intramolecular force , intermolecular force , chemistry , supramolecular chemistry , proton , anisotropy , chemical shift , chemical physics , cyclophane , computational chemistry , ring (chemistry) , crystallography , force field (fiction) , electrostatics , molecule , stereochemistry , crystal structure , physics , quantum mechanics , organic chemistry
Proton shielding variations in supramolecular complexes contain a wealth of information on complex geometries in solution that has been until now mostly neglected. We describe herein ways for such analyses with five cyclophane and two cyclodextrin complexes in water, by using a program SHIFT which is based on and parametrized with the analyses of over 300 intra molecular proton shift variations in well defined molecular frameworks such as steroids or cyclophanes. The inter molecular shift changes in the host–guest complexes at 100 % complexation (CIS values) are calculated as sum of anisotropy effects Δ χ from aromatic ring currents and linear electric field effects LEF, based on force field generated geometries. The conformations with the best agreement between calculated and observed CIS values are at least for non‐charged guest compounds close to those obtained from molecular mechanics and/or MD calculations and intermolecular NOEs (where available), noticeably without adjusting the complex geometries to the experimental CIS. Through‐space electrostatic field effects LEF, which have been until now often neglected, can be sizeable also for non‐charged systems; best agreement between experiment and calculation is observed with Gasteiger atomic charges.