Lipid spectroscopic analysis

These semisynthetic proteins have served as useful tools to investigate and study the role of Ras proteins in the cell, for instance, new insights in the so-called Ras acylation cycle could be obtained as well as solid-state nuclear magnetic resonance (NMR) spectroscopic analysis of the lipidated membrane anchor and proteins became possible. ... 

Curacins (345-348) are a small family of bioactive compounds with a unique thiazoline-containing lipid bearing a cyclopropane unit. From the cyanobacterium Lingbya majuscula, Gerwick reported the isolation of curacin A (345) in 1994 [265], curacins B (346) and C (347) one year later [266] and, finally, curacin D (348) in 1998 [267]. The structures of these compounds were determined by detailed spectroscopic analysis. The previous absolute configuration proposed for 345 by chemical degradation [268] was confirmed by several total syntheses [269, 270]. The absolute configuration of 346 was deduced by its thermally induced interconversion with 345 [266]. 

Quantitative infrared spectroscopic analysis can be carried out on blood serum to determine the relative amounts of lipid that are present. Triglycerides, phospholipids and cholesteryl esters are the classes of lipid which occur in blood serum. These compounds occur naturally in concentrations which make infrared analysis attractive, and the necessary preliminary separation is simple. These classes of compounds can be characterised using infrared spectroscopy by their carbonyl bands. The peak maxima are as follows ... 

Some of the cuticular lipids are also suitable for spectroscopic analysis. )3-Diketones absorb at 273 nm so that ultraviolet spectroscopy can be used (Tulloch, 1976). The functional groups of various fractions obtained by TLC can be confirmed by infrared analysis. Aldehydes and )8-diketones give useful shifts when examined by nuclear magnetic resonance and this technique can be made considerably more sensitive by the application of C-NMR for some wax components (Tulloch, 1976). 

Spectroscopic analysis of the lipids and sterols yielding vitamin D activity under the influence of ultraviolet irradiation provided useful clues for detecting the active sterols. A preparation acquiring vitamin D activity manifests characteristic absorption spectra not observed in sterols (such as pure cholesterol) that can-... 

The interaction between bacterial lipopolysaccharides (EPS) and phospholipid cell membranes was studied by various physical methods of deep rough mutant EPS (ReEPS) of Escherichia coH incorporated in phospholipid bilayers as simple models of cell membranes. SS P-NMR spectroscopic analysis suggested that a substantial part of ReEPS is incorporated into l,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid bilayers when mixed multilamellar vesicles were prepared. Furthermore the lipid lateral diffusion coefficients measurements at various molar ratios of ReEPS/egg-PC/POPG indicated that the incorporated ReEPS reduces the diffusion coefficients of the phospholipids in the membrane. EUV formed by the ReEPS from Salmonella enterica, eventually in mixture with dilauroyl phosphatidylcholine (DEPC), have been prepared and characterized by DES, SANS and EPR. PFGSE NMR measurements have shown that water permeability through the lipid bilayer is low at room temperature. However, above a transition temperature centered at 30-35 °C, the water permeability increases. ... 

The conditions for accurate quantification of lipid species by ESI-MS or ESI-MS/MS are discussed in Chapter 14. It is recognized that quantification of lipid species by MS is different from that of spectroscopic analysis in which the Beer-Lambert law can be followed. As discussed in Chapter 14, two essential parameters need to be considered in quantification of lipids by MS, i.e., the baseline of a mass spectrum used for the purpose and the response factor of an individual lipid species in comparison to that of the selected internal standard. The contribution of the baseline to the intensity of an ion should be minimal or a correction for the baseline has to be conducted as previously described [1], Regarding the response factor of a lipid species of interest, the essential condition is that it has to be comparable to that of the selected internal standard or a correction factor has to be predetermined. 

FRET is an extremely useful phenomenon when it comes to the analysis of molecular conformations and interactions. F or the analysis of interactions, in which two separate molecules are labeled with an appropriate pair of fluorophores, an interaction can be shown by observing FRET. Further, FRET can be used as a type of spectroscopic ruler to measure the closeness of interactions. Proteins, lipids, enzymes, DNA, and RNA can all be labeled and interactions documented. This general method can be applied not only to questions of cellular function like kinase dynamics [3] but also to disease pathways, for example, the APP-PS1 interaction that is important in Alzheimer s disease (AD) [4], Alternatively, two parts of a molecule of interest can be labeled with a donor and acceptor fluorophore. Using this technique, changes in protein conformation and differences between isoforms of proteins can be measured, as well as protein cleavage. 

HPLC has a number of advantages over other chromatographic techniques for lipids namely, (a) it can be quantitated more easily than TLC, (b) lipids that cannot be separated by GC because they would be decomposed by the high temperatures required or by the catalytic activity of the column may be analyzed using HPLC, and (c) the separated components can be collected and subjected to further analysis, e.g., by spectroscopic techniques. Examination of the literature reveals a number of points of agreement on the difficulties and present limitations of the method. 

Many of the same chromatographic and spectroscopic techniques were applied to the isolation and identification of natural products such as carbohydrates and glyco-lipids. The discovery, isolation, computational analysis, synthesis, and structure-activity relationship studies of antibiotics such as the aminoglycosides kanamycin and neamine are of particular note (Fig. 1.14) [157, 158],... 

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