Annual Reports on NMR Spectroscopy

1. Auflage 2015
ISBN: 978-0-12-803379-1
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, Band Volume 85, 260 Seiten

Reihe: Annual Reports on NMR Spectroscopy

Nuclear magnetic resonance (NMR) is an analytical tool used by chemists and physicists to study the structure and dynamics of molecules. In recent years, no other technique has gained such significance as NMR spectroscopy. It is used in all branches of science in which precise structural determination is required and in which the nature of interactions and reactions in solution is being studied. Annual Reports on NMR Spectroscopy has established itself as a premier means for the specialist and non-specialist alike to become familiar with new techniques and applications of NMR spectroscopy. - This volume of Annual Reports on NMR Spectroscopy focuses on the analytical tools used by chemists and physicists, taken together with other volumes of this series, an excellent account of progress in NMR and its many applications is provided and anyone using NMR will find interest in this Serial

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Chapter Two 31P NMR Studies of Phospholipids
Andrei V. Filippov*,†,1; Aidar M. Khakimov†; Bulat V. Munavirov†    * Chemistry of Interfaces, Lulea University of Technology, Lulea, Sweden
† Institute of Physics, Kazan Federal University, Kazan, Russian Federation
1 Corresponding author: email address: [e-mail] Abstract
31P nuclear magnetic resonance (NMR) can provide information on the composition of phospholipid (PL) membranes, lipid headgroup orientation relative to the bilayers normal, and the phase state of PL systems. Interaction of the membrane with ions, drugs, other small molecules and peptides may lead to lipid phase change and lamellar phase disturbances, which can also be revealed in 31P NMR spectra. Traditional 31P NMR spectroscopy has been used for years, mainly to study lipid phase state. In the last few years, however, its utility has been extended by a number of solid-state methods in field-cycling spectroscopy. Membrane mimicking systems have been complemented with bicelles, which are more convenient for studying peptide structure in lipid–peptide interactions. Another challenge is the study of ordered membrane domains (rafts) induced in the presence of cholesterol or certain proteins. As a result, recent work has refined the structure of PL headgroups and elucidated membrane responses to interactions with peptides and other molecules. Selected examples of such fascinating investigations are presented here. Keywords 31P NMR Cholesterol Lipid rafts Lipid bilayers Lipid mesophases Lipid/peptide systems Phospholipids Abbreviations CHOL cholesterol CSA chemical shift anisotropy DHDMAB dihexadecyldimethylammonium bromide DHPC diheptanoylphosphatidylcholine DHSM dihydrosphingomyelin DLPC dilauroylphosphatidylcholine DLPE dilaurylphosphatidylethanolamine DMPC dimyristoylphosphatidylcholine DMPE dimyristoylphosphatidylethanolamine DOPA dioleoylphosphatidic acid DOPC dioleoylphosphatidylcholine DOPMe dioleoylphosphatidylmethanol DOPS dioleoylphosphatidylserine DPPC dipalmitoylphosphatidylcholine DPPE dipalmitoylphosphatidylethanolamine DSC differential scanning calorimetry ESM egg sphingomyelin ESR electron spin resonance FWHM full-width at half-maximum H|| inverted hexagonal phase HETCOR heteronuclear correlation LUVs large unilamellar vesicles La liquid-crystalline lamellar phase MLVs multilamellar vesicles NMR nuclear magnetic resonance NOE nuclear Overhauser effect PA phosphatidic acid PC phosphatidylcholine PE phosphatidylethanolamine PG phosphatidylglycerol PL phospholipid POPC palmitoyloleoylphosphatidylcholine POPE palmitoyloleoylphosphatidylethanolamine POPG palmitoyloleoylphosphatidylglycerine PS phosphatidylserine SM sphingomyelin so solid-ordered phase SOPC stearoyloleoylphosphatidylcholine Tm gel-to-liquid-crystal phase-transition temperature ULVs unilamellar vesicles 1 Introduction
Biological membranes of living cells are formed by lipids, which are predominantly phospholipids (PLs) that contain one phosphorus nucleus per molecule. Because of the amphipathic nature of lipids, they are present in the anisotropic smectic liquid-crystalline phase in biomembranes. Phosphorus nuclear magnetic resonance (NMR) is a convenient technique for studying biomembranes, for reasons that are well known. (i) The 31P isotope of phosphorus has 100% natural abundance, and 31P NMR is less sensitive than 1H but more sensitive than 13C NMR. (ii) 31P nuclei, which are not present in proteins and peptides, provide selectivity for the lipid signal in lipid/protein systems. (iii) Chemical shift anisotropy (CSA) of the 31P nucleus is high, allowing study of lipid structures and variations of lipid headgroups in biomembranes. Application of 31P NMR to lipid biomembrane research has a long history, which began in the early 1970s with the majority of the basic work being done from 1970 to 1980. Nevertheless, interest in the application of this technique to lipid systems and biomembranes studies has not diminished in subsequent years. Figure 1 shows the number of journals published on this topic in the last decade. Figure 1 Number of papers containing 31P NMR data during 2004–2013 according to Scopus®. 31P NMR spectroscopy of PL molecules can be used for two general applications [1]: (1) analysis of PL structures and phases based on anisotropic line shapes and (2) differentiation of individual PL species in mixtures based on their isotropic chemical shift. A number of review papers analyzed results that are directly and indirectly related to 31P NMR spectroscopy of PL systems and biomembranes. The review by Joachim Seelig [2] presents theoretical aspects of 31P NMR and a number of experimental results obtained up until 1977. A modern, more specific 31P NMR review of PLs was published by Schiller and coworkers in 2007 [1], describing many applications of phosphorus NMR in the study of micelles, bicelles, and cells. The reviews by Schiller and Arnold [3] and Lee and coworkers [4] also deal with 31P NMR indirectly associated with biomembranes. Because of the numerous and diverse results generated by using 31P NMR in lipid systems and biomembranes, we did not aim to present a comprehensive evaluation of all techniques, approaches, and outcomes. Instead, we intended to provide an author's view of this research field that would be of basic and practical interest to those characterizing the chemical–physical properties of lipids in model systems. In particular, the effects of cholesterol (CHOL) near and above the gel–liquid phase-transition temperature are the areas of interest that continue to be explored. Another relatively new subject is liquid–liquid phase separation in two- or multicomponent lipid membranes induced by CHOL or certain peptides, which may result in formation of ordered domains or so-called “rafts” [5,6]. 2 Basics of 31P NMR
Phosphorus has 23 known isotopes from 24P to 46P. Nevertheless, only one among them is stable—31P; thus, it is considered a monoisotopic element [7]. 31P has a nuclear spin I = 1/2, which makes it possible to be observed by NMR. The gyromagnetic ratio for 31P is approximately 2.5 times smaller than that of 1H [8]. As a result, in the same magnetic field, 31P is observed at frequencies 2.5 times smaller than that of 1H. For example, when 1H is observed at 400 MHz, 31P is observed at approximately 161 MHz. The nuclear spin I = 1/2 gives 31P a dipolar nucleus. Dipolar nuclei appear spherical, with a uniform charge distribution over the entire surface [8]. Since the nucleus appears spherical, it disturbs a probing electromagnetic field independent of direction. The result is a strong, sharp NMR signal. Quadrupolar nuclei (whose spin I > 1/2) have a nonspherical charge distribution, and thus give rise to nonspherical electric and magnetic fields. As a result, they present much more complicated spectral shapes—broadened lines, shallow peaks, and difficulties with phasing and integration. It is fortunate that 31P has a dipolar nucleus; however, it is frequently bound to quadrupolar nuclei, which may result in additional complications in the shape of the spectra [8,9]. The magnitude of complications depends on various factors such as the natural abundance of the isotope, the quadrupole moment, and the relative receptivity [8]. Moreover, 31P couples to any other nucleus with a nuclear spin I > 0. Apart from 1H and 13C, 31P nuclei couple to themselves (P–P coupling), fluorine (19F), boron (10B and 11B), and a variety of metals [8]. Coupling to 1H—the most common case for biological systems—can be deactivated using proton...