Polysaccharides Fourier transforms

Intracellular and Extracellular Polysaccharides.—Fourier transform infrared... 

Structural study of polysaccharides and other carbohydrates in solution or in the amorphous state has been significantly enhanced through the application of Fourier-transform, infrared spectroscopy. Among the advantages of this method may be mentioned the high quality of the spectra, and the in-house ability to interact with the computer, so that the digitized spectra may be stored and manipulated in such a way that additional information is obtained. The application of F.t.-i.r. spectroscopy in the field of carbohydrate chemistry and biochemistry is still in its infancy,182 but... 

New techniques for data analysis and improvements in instrumentation have now made it possible to carry out stmctural and conformational studies of biopolymers including proteins, polysaccharides, and nucleic acids. NMR, which may be done on noncrystalline materials in solution, provides a technique complementary to X-ray diffraction, which requires crystals for analysis. One-dimensional NMR, as described to this point, can offer structural data for smaller molecules. But proteins and other biopolymers with large numbers of protons will yield a very crowded spectrum with many overlapping lines. In multidimensional NMR (2-D, 3-D, 4-D), peaks are spread out through two or more axes to improve resolution. The techniques of correlation spectroscopy (COSY), nuclear Overhausser effect spectroscopy (NOESY), and transverse relaxation-optimized spectroscopy (TROSY) depend on the observation that nonequivalent protons interact with each other. By using multiple-pulse techniques, it is possible to perturb one nucleus and observe the effect on the spin states of other nuclei. The availability of powerful computers and Fourier transform (FT) calculations makes it possible to elucidate structures of proteins up to 40,000 daltons in molecular mass and there is future promise for studies on proteins over 100,000... 

Professor Tadakoro s recent book(l ) illustrates the considerable advantages and benefits to be gained by coupling infra-red spectroscopy with fibre x-ray diffraction. The increasing availability of Fourier transform infra-red spectrometers allows the same thick samples, suitable for x-ray work, to be used in the spectrometer thus ensuring that both sets of information emanate from the same structure. The delightful selected area electron diffraction patterns obtained from polysaccharides by Dr. Chanzy (2), which exhibit such remarkable resolution and definition, indicate the importance and value of the modern application of electron micro-... 

Infrared-spectrometry (IR) was used for the investigation of substituent acetyl groups in the molecules of the polysaccharides. A Fourier transform IR Perkin-Elmer spectrometer, Model 1720-X, was used. The... 

Coates, M. L., and Wilkins, C. L. (1987). Laser-desorption Fourier transform mass spectra of polysaccharides. Anal. Chem. 59 197-200. 

Fourier-transform instruments, the two techniques are sufficiently different to be valuable complements to each other. In many cases, in particular when dealing with complex molecules, such as polysaccharides, the amount of information obtainable from H-n.m.r. spectra is limited, compared to that revealed3 by 13C-n.m.r. spectra. Monosaccharides may also yield H-n.m.r. spectra that are poorly resolved, even at high field, and that contain little information. On the other hand, proton-decoupled,, 3C-n.m.r. spectra are well resolved and, even if the signals are not assigned, a spectrum will provide an almost unambiguous identification of a compound. 

Carbon-13, spin-lattice relaxation-rates may be readily measured with pulsed, Fourier-transform instruments, and they primarily provide information about the molecular motion in solution.3,4,22 75,76,123 Carbon-13 relaxation-rates have mosdy been used to obtain structural information on polysaccharides.3... 

Fig. 1.—Fourier-transformed, C-N.m.r. Spectrum of the Native Polysaccharide Antigen of Group A Neisseria meningitidis. [Upper, containing (a) O-acetylated and (b) unacetylated residues, and lower, its fully O-deacetylated form.]...

After their isolation by chromatographic techniques (anion-exchange chromatography, size exclusion, etc.), different analytical methodologies have been used to identify and quantify the polysaccharides in wine the most commonly used being the traditional methylation analysis followed by GC-MS (Doco and Bril-louet 1993). Polysaccharides have also been determined after solvolysis with anhydrous methanol containing HCl by GC-MS of their per-G-trimethylsilylated methyl glycosides (Vidal et al. 2003). Other techniques such as Fourier transform infrared spectroscopy (FTIR) have been more recently proposed (Coimbra et al. 2002,2005 Boulet et al. 2007). 

Boulet, J.C., Williams, P., Doco, T. (2001). A Fourier transform infrared spectroscopy study of wine polysaccharide. Carbohydr. Polym., 69, 79-85. 

The enormous complexity of spectra of large biomolecules such as proteins, polynucleotides, and polysaccharides has led to the development of three- and four-dimensional experiments. Two independently incremented evolution periods (t and t2), in conjunction with three separate Fourier transformations of them and of the acquisition period, result in a cube of data with three frequency coordinates. 

It is at this time difficult to envisage that any of these techniques, alone, would simplify p.m.r. studies to the point where detailed assignments for polysaccharides could be made without a determined effort. Yet, the great biochemical importance of many polysaccharides provides a compelling reason to persevere, and the author personally considers that the recent progress resulting from the development of Fourier-transform spectroscopy is encouraging indeed. 

Figure 3. Repealing unit of the native Type HI streptococcal polysaccharide antigen and its fourier-transformed C-13 NMR spectrum (25.2 MHz) taken with an aquisition time of 0.3 s and a spectral width of 5 kHz. The number of induction...

I.r. Spectroscopy, — Structures of polysaccharides have been investigated using Fourier-transform i.r. difference spectra. The i.r. absorbance difference spectra of dextrans have been correlated to the type and degree of branching of the polysaccharide which have previously been established by permethylation analysis. 

Chemically defined, highly branched dextrans have been studied by a spin-lattice relaxation method. Correlations were made to the positions of carbon atoms associated with branching residues, permitting the values of O-substitution to be established for D-glucopyranosyl residues. Fourier-transform-i.r. difference spectra of dextrans have been correlated to the type and degree of branching, which had been established previously by permethylation for these polysaccharides. A combination of n.m.r.- and Fourier-transform-i.r.-spectroscopy has been used to give complementary information on the structure of dextrans. 

A recent publication [41] related to this process describes that 1° O—H bond are cleaved to generate the free radical sites. Fourier-transform infrared spectroscopy (FTIR) confirmed that free radicals are formed on polysaccharide backbone by cleavage of 1°—OH bond, indicating that free radicals are generated by means of microwave effect and not due to thermal decomposition. 

A Fourier-transform method has been used to measure the spin-lattice relaxation times (Ti-values) of the anomeric protons of a selection of di-, oligo-, and polysaccharide derivatives ie.g. cellobiose, maltose, gentiobiose, maltotriose, and a- and j8-Schardinger dextrins). Differences in the Ti-values of the anomeric protons were found for each of the disaccharides examined, the anomeric proton of the non-reducing residue having a smaller 71-value in each case - for cellobiose,... 

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