Three-dimensional spectroscopy

Three-dimensional spectroscopy of vibrational energy relaxation in liquids. 

The use of three-dimensional spectroscopy involving chemical shift/ H- N dipolar coupling/ N chemical shift correlation has been shown to improve spectral resolution in studies of membrane proteins with helices aligned parallel to the membrane surface. Such a measurement on the antibiotic peptide magainin enabled the three-dimensional orientation of this helical peptide to be determined in the lipid bilayer. The orientation of the insect antiobiotic peptide cecropin A in the phospholipid bilayer membrane has been determined using solid-state NMR spectroscopy and the result discussed in relation to the mechanism of action of the peptide. ... 

Three-dimensional spectroscopy of vibrational energy relaxation in liquids Z. Wang, A. Pakoulev, Y. Pang and D.-D. Dlott... 

Oschkinat H, Muller T and Dieckmann T 1994 Protein structure determination with three- and four-dimensional spectroscopy Angew. Chem. Int. Ed. Engl. 33 277-93... 

The physical, chemical cind biological properties of a molecule often depend critically upo the three-dimensional structures, or conformations, that it can adopt. Conformational analysi is the study of the conformations of a molecule and their influence on its properties. Th development of modem conformational analysis is often attributed to D H R Bcirton, wh showed in 1950 that the reactivity of substituted cyclohexanes wcis influenced by th equatoricil or axial nature of the substituents [Beirton 1950]. An equcilly important reaso for the development of conformatiorml analysis at that time Wcis the introduction c analytic il techniques such as infreired spectroscopy, NMR and X-ray crystaillograph] which actucilly enabled the conformation to be determined. 

Present day techniques for structure determination in carbohydrate chemistry are sub stantially the same as those for any other type of compound The full range of modern instrumental methods including mass spectrometry and infrared and nuclear magnetic resonance spectroscopy is brought to bear on the problem If the unknown substance is crystalline X ray diffraction can provide precise structural information that m the best cases IS equivalent to taking a three dimensional photograph of the molecule... 

Clore, G.M., Gronenborn, A.M. Determination of three-dimensional structures of proteins and nucleic acids in solution by nuclear magetic resonance spectroscopy. CRC Crit. Rev. Biochem. 24 479-564, 1989. 

STM and SFM are most commonly used for topographic imaging, three-dimensional profilometry and spectroscopy (STM only). 

Spectroscopic properties of 5 were studied (OOMIll). Spectral characteristics of 5 of 0.1 N NaOH solution were investigated by UV spectroscopy (97MI17). Three dimensional fluorescent spectral characteristics of fluoroquinolones, including 5, were studied in varying media (00SA(A)1787). The structure of 8 was confirmed by UV and IR studies (98MI89). 

If two different three-dimensional arrangements in space of the atoms in a molecule are interconvertible merely by free rotation about bonds, they are called conformationsIf they are not interconvertible, they are called configurations Configurations represent isomers that can be separated, as previously discussed in this chapter. Conformations represent conformers, which are rapidly interconvertible and are thus nonseparable. The terms conformational isomer and rotamer are sometimes used instead of conformer . A number of methods have been used to determine conformations. These include X-ray and electron diffraction, IR, Raman, UV, NMR, and microwave spectra, photoelectron spectroscopy, supersonic molecular jet spectroscopy, and optical rotatory dispersion (ORD) and CD measurements. Some of these methods are useful only for solids. It must be kept in mind that the conformation of a molecule in the solid state is not necessarily the same as in solution. Conformations can be calculated by a method called molecular mechanics (p. 178). 

THREE-DIMENSIONAL STRUCTURE IS DETERMINED BY X-RAY CRYSTALLOGRAPHY OR BY NMR SPECTROSCOPY... 

Partial Least Squares (PLS) regression (Section 35.7) is one of the more recent advances in QSAR which has led to the now widely accepted method of Comparative Molecular Field Analysis (CoMFA). This method makes use of local physicochemical properties such as charge, potential and steric fields that can be determined on a three-dimensional grid that is laid over the chemical stmctures. The determination of steric conformation, by means of X-ray crystallography or NMR spectroscopy, and the quantum mechanical calculation of charge and potential fields are now performed routinely on medium-sized molecules [10]. Modem optimization and prediction techniques such as neural networks (Chapter 44) also have found their way into QSAR. 

The determination of the three-dimensional conformation of molecules is an important aspect of QSAR, which can be obtained from x-ray crystallography [66], NMR spectroscopy or, in the case of small molecular fragments by quantum-mechanical calculations [67,68]. 

Ammalahti, E. Brunow, G. Bardet, M. Robert, D. Kilpelainen, I. Identification of side-chain structures in a poplar lignin using three-dimensional HMQC-HOHAHA NMR spectroscopy. J. Agric. Food Chem. 1998, 46, 5113-5117. 

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