Structure and thermotropic properties of 1-stearoyl-2-acetyl-phosphatidylcholine bilayer membranes.

The structural and thermotropic properties of 1-stearoyl-2-acetyl-phosphatidylcholine (C(18):C(2)-PC) were studied as a function of hydration. A combination of differential scanning calorimetry and x-ray diffraction techniques have been used to investigate the phase behavior of C(18):C(2)-PC. At low hydration (e.g., 20% H2O), the differential scanning calorimetry heating curve shows a single reversible endothermic transition at 44.6 degrees C with transition enthalpy delta H = 6.4 kcal/mol. The x-ray diffraction pattern at -8 degrees C shows a lamellar structure with a small bilayer periodicity d = 46.3 A and two wide angle reflections at 4.3 and 3.95 A, characteristic of a tilted chain, L beta' bilayer gel structure. Above the main transition temperature, a liquid crystalline L alpha phase is observed with d = 53.3 A. Electron density profiles at 20% hydration suggest that C(18):C(2)-PC forms a fully interdigitated bilayer at -8 degrees C and a noninterdigitated, liquid crystalline phase above its transition temperature (T > Tm). Between 30 and 50% hydration, on heating C(18):C(2)-PC converts from a highly ordered, fully interdigitated gel phase (L beta') to a less ordered, interdigitated gel phase (L beta), which on further heating converts to a noninterdigitated liquid crystalline L alpha phase. However, the fully hydrated (> 60% H2O) C(18):C(2)-PC, after incubation at 0 degrees C, displays three endothermic transitions at 8.9 degrees C (transition I, delta H = 1.6 kcal/mol), 18.0 degrees C (transition II), and 20.1 degrees C (transition III, delta HII+III = 4.8 kcal/mol). X-ray diffraction at -8 degrees C again showed a lamellar gel phase (L beta') with a small periodicity d = 52.3 A. At 14 degrees C a less ordered, lamellar gel phase (L beta) is observed with d = 60.5 A. However, above the transition III, a broad, diffuse reflection is observed at approximately 39 A, consistent with the presence of a micellar phase. The following scheme is proposed for structural changes of fully hydrated C(18):C(2)-PC, occurring with temperature: L beta' (interdigitated)-->L beta (interdigitated)-->L alpha(noninterdigitated)-->Micelles. Thus, at low temperature C(18):C(2)-PC forms a bilayer gel phase (L beta') at all hydrations, whereas above the main transition temperature it forms a bilayer liquid crystalline phase L alpha at low hydrations and a micellar phase at high hydrations (> 60 wt% water).     

Structural polymorphism of hydrated ether-linked dimyristyl maltoside and melibioside

The structural polymorphism of two selected disaccharide glycolipids with a maltose (DMMA) and a melibiose (DMME) carbohydrate headgroup linked to dimyristyl alkyl chains were investigated by FTIR-spectroscopy, differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS) and film-balance measurements. The compounds displayed thermotropic multilamellar phases. In the gel phase, DMMA formed also a crystalline phase of orthorhombic symmetry, and DMME an interdigitated phase. The gel to liquid crystalline phase transition temperature T(c) of DMMA depended on the storage and hydration conditions, a precooled sample having a T(c) around 45 degrees C, and a freshly prepared sample around 33 degrees C. In contrast, the phase transition temperature for the gel to liquid crystalline phase of DMME was always found at 24 degrees C. Surface pressure isotherms of the lipids on water and buffer showed that DMMA covers only a small surface area (approximately 35A(2)) whereas DMME requires 50 A(2) of space on the surface. Films of DMMA can be compressed up to a maximum compressibility Pi(max) of 54 mN m(-1) whereas the tilted DMME forms less stable films with Pi(max) of 34 mN m(-1). These different structural characteristics reflect the different conformations of the disaccharide head groups. The presence of the alpha1-->4 linked maltose head group in DMMA and an alpha1-->6 linked melibiose head group in DMME induces geometrical structures ranging from a slightly wedge-shaped towards a more tilted structure, and as a consequence of Israelachvilis packing model, to the formation of different phases. In addition, the structural constraints of DMME allow the formation of a phase with interdigitated hydrocarbon chains.     

Thermodynamic, thermomechanical, and structural properties of a hydrated asymmetric phosphatidylcholine.

1-Behenyl-2-lauryl-sn-glycero-3-phosphocholine (22/12 PC) belongs to a unique group of phospholipids in which the molecule has one acyl chain almost twice as long as the other. The temperature-composition phase diagram for this lipid in the range of 25-65 degrees C, and 0 to 84.3% (w/w) water has been constructed by using the isoplethal method in the heating direction and x-ray diffraction for phase identification and structure characterization. At water contents between 10.3 and 34% (w/w) and at temperatures below 43 degrees C, a single mixed interdigitated lamellar gel phase (Lm beta, [symbol: see text]) of the type described by Hui et al. (1984. Biochemistry. 23:5570-5577) and McIntosh et al. (1984. Biochemistry. 23:4038-4044) was found. A second phase consisting of bulk aqueous solution coexists with the Lm beta phase at hydration levels above 34% (w/w) water in the temperature range between 25 and 43 degrees C. Above 43 degrees C, a partially interdigitated lamellar liquid crystalline (Lp alpha) phase ([symbol: see text]) is seen in the water concentration range extending from 0 to 84.3% (w/w). The pure Lp alpha phase is found below 43% (w/w) water, while coexistence of the Lp alpha phase and the bulk aqueous solution is observed above this water concentration which marks the hydration boundary. Interestingly, the latter boundary for both Lm beta and Lp alpha phases is nearly vertical in the temperature range studied. Furthermore, the lamellar chain-melting transition temperature appears to be relatively insensitive to hydration in the range 0-85% (w/w) water. We have confirmed the identify of the Lm beta phase by constructing a 5.7-A resolution electron density profile on oriented samples by the swelling method. Temperature-induced chain melting effects an increase in lipid bilayer thickness suggesting that the Lp alpha phase has chains packed in the partially as opposed to the mixed interdigitated configuration. Unlike the symmetric phosphatidylcholines a ripple (P beta') phase was not found as an intermediate between the low and high temperature lamellar phases of 22/12 PC. The specific volume of 22/12 PC is 940 (+/- 1) microliter/g and 946 (+/- 1) microliter/g in the hydrated lamellar gel state at 28 (+/- 2) and 40 (+/- 2) degrees C, respectively, from neutral buoyancy experiments. Based on measurements of the temperature dependence of the various lattice parameters of the different phases encountered in this study the corresponding lattice thermal expansion coefficients have been measured. These are discussed and their dependence on lipid hydration is reported.     

Dependence of lipid chain and head group packing of the inverted hexagonal phase on hydration

A model which positions the hydrophobic/hydrophilic boundary in phosphatidylethanolamine lipids at the first CH₂ group in the acyl or alkyl chain is used to calculate the surface area per lipid, the mean chain and head-group dimensions and diameters of the hydrophilic tubes of the inverted hexagonal phase of didodecylphosphatidylethanolamine. The calculated surface areas compare favorably with areas obtained for the lamellar liquid crystal phase of the same lipid using the same boundary. Placement of the boundary within the lipid structure permits a determination of the maximum headgroup packing at hydration levels down to complete dehydration. The headgroup dimensions are consistent with a 5 Å diam void at the center of a hydrophilic tube at zero hydration. The calculated mean fluid chain length is ~2 Å smaller than the mean chain length of the lamellar phase at comparable levels of hydration. Comparison of the calculated mean fluid chain length and distances between hydrophobic boundaries shows that the fluid chains are interdigitated between adjacent tubes, and not interdigitated in the central space between three tubes. At low hydration the chains interdigitate in both spaces. The number of lipids packed around a tube at low hydration is only a function of the headgroup geometry, whereas at high hydration, it is a function of the number of carbon atoms in the chains.     

Polymorphism, mesomorphism, and metastability of monoelaidin in excess water.

The polymorphic and metastable phase behavior of monoelaidin dry and in excess water was studied by using high-sensitivity differential scanning calorimetry and time-resolved x-ray diffraction in the temperature range of 4 degrees C to 60 degrees C. To overcome problems associated with a pronounced thermal history-dependent phase behavior, simultaneous calorimetry and time-resolved x-ray diffraction measurements were performed on individual samples. Monoelaidin/water samples were prepared at room temperature and stored at 4 degrees C for up to 1 week before measurement. The initial heating scan from 4 degrees C to 60 degrees C showed complex phase behavior with the sample in the lamellar crystalline (Lc0) and cubic (Im3m, Q229) phases at low and high temperatures, respectively. The Lc0 phase transforms to the lamellar liquid crystalline (L alpha) phase at 38 degrees C. At 45 degrees C, multiple unresolved lines appeared that coexisted with those from the L alpha phase in the low-angle region of the diffraction pattern that have been assigned previously to the so-called X phase (Caffrey, 1987, 1989). With further heating the X phase converts to the Im3m cubic phase. Regardless of previous thermal history, cooling calorimetric scans revealed a single exotherm at 22 degrees C, which was assigned to an L alpha+cubic (Im3m, Q229)-to-lamellar gel (L beta) phase transition. The response of the sample to a cooling followed by a reheating or isothermal protocol depended on the length of time the sample was incubated at 4 degrees C. A model is proposed that reconciles the complex polymorphic, mesomorphic, and metastability interrelationships observed with this lipid/water system. Dry monoelaidin exists in the lamellar crystalline (beta) phase in the 4 degrees C to 45 degrees C range. The beta phase transforms to a second lamellar crystalline polymorph identified as beta* at 45 degrees C that subsequently melts at 57 degrees C. The beta phase observed with dry monoelaidin is identical to the LcO phase formed by monoelaidin that was dispersed in excess water and that had not been previously heated.     

Thermodynamic and structural characterization of amino acid-linked dialkyl lipids

Using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), we determined some thermodynamic and structural parameters for a series of amino acid-linked dialkyl lipids containing a glutamic acid-succinate headgroup and di-alkyl chains: C12, C14, C16 and C18 in CHES buffer, pH 10. Upon heating, DSC shows that the C12, C14 and annealed C16 lipids undergo a single transition which XRD shows is from a lamellar, chain ordered subgel phase to a fluid phase. This single transition splits into two transitions for C18, and FTIR shows that the upper main transition is predominantly the melting of the hydrocarbon chains whereas the lower transition involves changes in the headgroup ordering as well as changes in the lateral packing of the chains. For short incubation times at low temperature, the C16 lipid appears to behave like the C18 lipid, but appropriate annealing at low temperatures indicates that its true equilibrium behavior is like the shorter chain lipids. XRD shows that the C12 lipid readily converts into a highly ordered subgel phase upon cooling and suggests a model with untilted, interdigitated chains and an area of 77.2A(2)/4 chains, with a distorted orthorhombic unit subcell, a=9.0A, b=4.3A and beta=92.7 degrees . As the chain length n increases, subgel formation is slowed, but untilted, interdigitated chains prevail.     

X-ray structure study of thermotropic phases in isoacylphosphatidylcholine multibilayers.

Structures of lamellar phases in aqueous dispersions of diisoacylphosphatidylcholines (17iPC and 20iPC) were determined by x-ray diffraction methods. In agreement with previous DSC studies, subgel, gel, and liquid crystal phases were observed in each homolog. The subgel Lc(c') phases of both homologs show significant two-dimensional long range order and can be described by rectangular lattices. The dimensions of the two rectangular unit cells differ in that the side chains are canted (approximately 33 degrees) in the 20iPC homolog, while in 17iPC the side chains are normal to the bilayer plane. The gel L beta phases of 17iPC (Tgg = 17-19.5 degrees C) and 20iPC (Tgg = 44 degrees C) are similar but not identical and are consistent with a distorted, pseudohexagonal lattice for the rotationally disordered side chains. The liquid crystal phases of 17iPC (Tgl = 28 degrees C) and 20iPC (Tgl = 52 degrees C) are structurally similar and are typical of lipids with fluid side chains. Significant but different changes occur in the long spacings at Tgg and Tgl for the two homologs. This implies that interfacial states (particularly in the subgel phases) differ in the two homologs below the liquid crystal phase transition temperature.     

Polymorphic phase behavior of platelet-activating factor.

Vibrational Raman and 31P NMR spectroscopic experiments have been performed as a function of temperature on aqueous dispersions of 1-0-octadecyl-2-acetoyl-sn-glycero-3-phosphocholine, a chemically synthesized platelet-activating factor. In the temperature range of -7 to 30 degrees C, the C(18)/PAF-H2O system is shown, upon heating, to undergo two thermal phase transitions centered at 9.2 degrees and 18.4 degrees C. The low temperature transition, attributed to the interdigitated lamellar gel (II)----gel (I) phase transition, is characterized by the breakdown of large lamellar organizations into small, but aggregated, bilayer vesicles. The high-temperature transition corresponds to the interdigitated lamellar gel (I)----micellar transition. The molecular ordering and packing structure of C(18)/PAF in the two lamellar phases and phase transition regions are described. It appears that the interdigitated lamellar gel (I) phase is unique for C(18)/PAF dispersions when compared with the behavior of other chemically closely related phospholipids in excess water.     

An ESR Spin label study of structural and dynamical properties of oriented lecithin-cholesterol multibilayers.

Oriented dipalmitoyllecithin-cholesterol multibilayers with 11% water have been studied with the cholestane spin label. From the ESR spectra the order parameters and the mobility of the spin label about its long axis have been calculated. The results on pure lecithin multibilayers indicate a transition from gel to liquid crystalline phase at 52 plus or minus 2 degrees C. In the gel phase the lecithin alkyl chains are highly ordered, but tilted with respect to the normal to the bilayers by about 25 degrees. Above 52 degrees C the tilt disappears and the mobility of the cholestane spin label increases, indicating an increase of mobility of the lecithin alkyl chains. When cholesterol is added, below about 52 degrees C a decrease of order is found. Furthermore, already small cholesterol contents (smaller than or equal to 10 mole %) remove the tilt. Above about 52 degrees C cholesterol improves the order by decreasing the amplitude of the librational motions. Cholesterol lowers the transition temperature of the system and reduces the mobility of the lecithin alkyl chains in the liquid crystalline phase. However an increase in mobility is found at cholesterol contents up to 10 mole %. A very broad phase transition is observed at 50 mole % cholesterol. In all systems an increase in temperature results in a reduction of order through an increase of the amplitude of the librational motions of the molecules. The librational motions are to some extent cooperative. The asymmetry of the order matrix is found to be a measure for the lateral ordering. Cholesterol increases the lateral ordering, indicating that the flat cholesterol molecules orient parallel to each other.     

Physical state of cholesteryl esters deposited in cultured macrophages

J774 macrophages load with cholesteryl ester (CE) when incubated with acetylated low-density lipoprotein and cholesterol-rich liposomes; the CE accumulates as cytoplasmic inclusions 1-2 micron in diameter. The CE core of the droplet comprises about 90% of its mass; the predominant CE species present are cholesteryl palmitate (CP, 41%) and cholesteryl oleate (CO, 37%). The thermotropic properties of the inclusions, both in intact cells and after isolation, have been characterized by differential scanning calorimetry. On heating, the inclusions exhibit two endothermic transitions at about 41 and 53 degrees C with a total enthalpy of 7.7 +/- 1.2 cal/g of CE. Very similar thermal behavior is exhibited by a binary mixture containing equal weights of CO and CP; this indicates that these two species dominate the phase behavior of CE in J774 inclusions. A phase diagram for the CO/CP system has been generated, and this reflects simple eutectic behavior. The eutectic is 83% w/w CO, and it melts at 49-50 degrees C. Below this temperature, CO and CP form two immiscible crystalline phases due to the very limited ability of the unsaturated oleate and saturated palmitate acyl chains to mix in the crystal phase. On heating a 1/1 w/w CO/CP mixture, an isotropic liquid of eutectic composition forms at 49 degrees C, and the remaining crystalline cholesteryl palmitate melts over the temperature range 50-69 degrees C. The phase diagram indicates that bulk mixtures of CE molecules in J774 inclusions should be crystalline at 37 degrees C, the growth temperature of the cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

The kinetics of formation and structure of the low-temperature phase of 1-stearoyl-lysophosphatidylcholine

A combination of differential scanning calorimetry (DSC) and X-ray diffraction have been used to study the kinetics of formation and the structure of the low-temperature phase of 1-stearoyl-lysophosphatidylcholine (18:0-lysoPC). For water contents greater than 40 weight %, DSC shows a sharp endothermic transition at 27 degrees C (delta H = 6.75 kcal/mol) corresponding to a low-temperature phase----micelle transition. This sharp transition is not reversible, but is regenerated in a time and temperature-dependent manner. For example, with incubation at 0 degrees C the maximum transition enthalpy (delta H = 6.75 kcal/mol) is generated in about 45 min after an initial slow nucleation process of approx. 20 min. The kinetics of formation of the low-temperature phase is accelerated at lower temperatures and may be related to the disruption of 18:0-lysoPC micelles by ice crystal formation. X-ray diffraction patterns of 18:0-lysoPC recorded at 10 degrees C over the hydration range 20-80% are characteristic of a lamellar gel phase with tilted hydrocarbon chains with the bilayer repeat distance increasing from 47.6 A at 20% hydration to a maximum of 59.4 A at 39% hydration. At this maximum hydration, approx. 19 molecules of water are bound per molecule of 18:0-lysoPC. Electron density profiles show a phosphate-phosphate distance of 30 A, indicating an interdigitated lamellar gel phase for 18:0-lysoPC at all hydration values. The angle of chain tilt is calculated to be between 20 and 30 degrees. For water contents greater than 40%, this interdigitated lamellar phase converts to the micellar phase at 27 degrees C in a kinetically fast process, while the reverse (micelle----interdigitated bilayer) transition is a kinetically slower process (see also Wu, W. and Huang, C. (1983) Biochemistry 22, 5068-5073).     

Temperature and compositional dependence of the structure of hydrated dimyristoyl lecithin.

Differential scanning calorimetry and x-ray diffraction techniques have been used to investigate the structure and phase behavior of hydrated dimyristoyl lecithin (DML) in the hydration range 7.5 to 60 weight % water and the temperature range -10 to +60 degrees C. Four different calorimetric transitions have been observed: T1, a low enthalpy transition (deltaH approximately equal to 1 kcal/mol of DML) at 0 degrees C between lamellar phases (L leads to Lbeta); T2, the low enthalpy "pretransition" at water contents greater than 20 weight % corresponding to the transition Lbeta leads to Pbeta; T3, the hydrocarbon chain order-disorder transition (deltaH = 6 to 7 kcal/mol of DML) representing the transition of the more ordered low temperature phases (Lbeta, Pbeta, or crystal C, depending on the water content) to the lamellar Lalpha phase; T4, a transition occurring at 25--27 degrees C at low water contents representing the transition from the lamellar Lbeta phase to a hydrated crystalline phase C. The structures of the Lbeta, Pbeta, C, and Lalpha phases have been examined as a function of temperature and water content. The Lbeta structure has a lamellar bilayer organization with the hydrocarbon chains fully extended and tilted with respect to the normal to the bilayer plane, but packed in a distorted quasihexagonal lattice. The Pbeta structure consists of lipid bilayer lamellae distorted by a periodic "ripple" in the plane of the lamellae; the hydrocarbon chains are tilted but appear to be packed in a regular hexagonal lattice. The diffraction pattern from the crystalline phase C indexes according to an orthorhombic cell with a = 53.8 A, b = 9.33 A, c = 8.82 A. In the lamellae bilayer Lalpha strucure, the hydrocarbon chains adopt a liquid-like conformation. Analysis of the hydration characteristics and bilayer parameters (lipid thickness, surface area/molecule) of synthetic lecithins permits an evaluation of the generalized hydration and structural behavior of this class of lipids.     

Phosphorylation of skeletal muscle myosin light chain kinase by the catalytic subunit of cAMP-dependent protein kinase

Phosphatidylethanolamine (PE) was isolated from membranes of Bacillus megaterium. The organism was grown at 20°C and 55°C. The phase equilibria in PE/water systems were studied by ²H and ³¹P nuclear magnetic resonance, and by polarized light microscopy. PE isolated from B. megaterium grown at 20°C forms a lamellar liquid crystalline phase at the growth temperature, and at low water contents a cubic liquid crystalline phase at 58°C. The ratio iso/ante-iso acyl chains was 0.3 in this lipid. PE isolated from this organism grown at 55°C forms only a lamellar liquid crystalline phase up to at least 65°C. In this lipid the ratio iso/ante-iso acyl chains was 3.2.     

Formation of a lamellar compound by reaction of acrylic acid crystallosolvated in highly crystalline beta-chitin

A lamellar compound resulted from reaction of acrylic acid inside crystalline beta-chitin and the structure was investigated. Beta-chitin acts like a layered crystal, having stacked molecular sheets composed of parallel chains bound in one direction by intermolecular amide hydrogen bonding. Small guest molecules can be inserted between the molecular sheets, and a crystallosolvate can be formed. By immersion of beta-chitin in acrylic acid, a crystallosolvate was formed, which was then changed into the more stable lamellar compound by heat treatment at 105 degrees C. NMR measurement and IR spectroscopy showed that during the heat treatment there was a reaction between acrylic acid and the beta-chitin molecular sheet, but the sheet structure was maintained. By IR with deuteration, it was shown that the accessibility of solvents to this lamellar compound was greater than that for the initial beta-chitin. The lamellar compound is considered a kind of "pillared" structure related to the lamellar crystal.     

Temperature dependence of the repulsive pressure between phosphatidylcholine bilayers.

Bilayer structure and interbilayer repulsive pressure were measured from 5 to 50 degrees C by the osmotic stress/x-ray diffraction method for both gel and liquid crystalline phase lipid bilayers. For gel phase dibehenoylphosphatidylcholine (DBPC) the bilayer thickness and pressure-distance relations were nearly temperature-independent, and at full hydration the equilibrium fluid spacing increased approximately 1 A, from 10 A at 5 degrees C to 11 A at 50 degrees C. In contrast, for liquid crystalline phase egg phosphatidylcholine (EPC), the bilayer thickness, equilibrium fluid spacing, and pressure-distance relation were all markedly temperature-dependent. As the temperature was increased from 5 to 50 degrees C the EPC bilayer thickness decreased approximately 4 A, and the equilibrium fluid spacing increased from 14 to 21 A. Over this temperature range there was little change in the pressure-distance relation for fluid spacings less than approximately 10 A, but a substantial increase in the total pressure for fluid spacings greater than 10 A. These data show that for both gel and liquid crystalline bilayers there is a short-range repulsive pressure that is nearly temperature-independent, whereas for liquid crystalline bilayers there is also a longer-range pressure that increases with temperature. From analysis of the energetics of dehydration we argue that the temperature-independent short-range pressure is consistent with a hydration pressure due to polarization or electrostriction of water molecules by the phosphorylcholine moiety. For the liquid crystalline phase, the 7 A increase in equilibrium fluid spacing with increasing temperature can be predicted by an increase in the undulation pressure as a consequence of a temperature-dependent decrease in bilayer bending modulus.     

Inhibition of heat-induced aggregation of beta- and gamma-crystallin by alpha-crystallin evaluated by gel permeation HPLC

The capability of alpha-crystallin (alpha-C), a known molecular chaperon, of protecting beta-C and gamma-C against heat-induced aggregation was studied by gel permeation high performance liquid chromatography. The activity was calculated using a formula based on the changes in the areas under the chromatographic peaks of these proteins, which appeared well separated. When heat-induced aggregation was studied in the range 22-90 degrees C, beta-C appeared more stable than gamma-C. The activity of alpha-C in stabilizing gamma-C but not beta-C was already relevant at 60 degrees C, but the maximum activity was higher (about 35%) for beta-C than for gamma-C. This method could be useful for studying the effect of drugs with potential anti-cataract activity on heat-induced aggregation of individual lens proteins.     

Crystal structure of methyl 3-amino-2,3-dideoxy-beta-D-arabino-hexopyranoside. Stabilization of the crystal lattice by a double network of N-H...O, O-H...N and O-H...O interactions

The structure, conformation and configuration of methyl 3-amino-2,3-dideoxy-beta-D-arabino-hexopyranoside were investigated by (1)H NMR, (13)C NMR and IR spectroscopy, as well as by optical rotation. The crystal structure was confirmed by single-crystal X-ray crystallographic analysis at 293 K and R = 0.0434 based on 910 independent reflections. The crystal belongs to the monoclinic system, space group of P2(1) with cell dimensions a = 6.050(1) Angstroms, b = 7.284(1) Angstroms, c = 10.289(2) Angstroms, beta = 104.69(3) degrees, D(c) = 1.341 Mg cm(-3) and V = 438.9(1) Angstroms(3) for Z = 2. Furthermore, the molecule has a typical (4)C(1) chair conformation. Hydrogen bonds between sugar molecules are responsible for stabilizing the crystal lattice.     

Deuterium magnetic resonance study of the gel and liquid crystalline phases of dipalmitoyl phosphatidylcholine.

Deuterium magnetic resonance is applied to the study of the liquid crystalline and gel phases, and of the phase transition, of a multilamellar dispersion of chain perdeuterated (d62)-dipalmitoyl phosphatidylcholine/H2O. Analysis of the deuterium spectra in terms of the moments of the spectra allows one to make quantitative statements concerning the distribution of quadrupolar splittings even in complicated situations, e.g., when using perdeuterated sampled or when there are mixed phases. This analysis indicates that d62-dipalmitoyl phosphatidylcholine in excess H2O undergoes a sharp phase transition (with a width of less than 1 degree C) at approximately 37 degrees C and that there appears to be hysteresis in the phase transition of approximately 1 degree C. In the lamellar liquid crystalline phase above 37 degrees C the spectra show a number of well-resolved features whose quadrupolar splittings can be followed as the temperature is varied. The gel phase near 20 degrees C possesses a very broad, almost featureless spectrum that does not seem to support a model of the gel phase wherein the hydrocarbon chains are fully extended in the all-trans conformation. At temperatures near 0 degrees C the spectra clearly indicate that a large fraction of the lipid molecules cease the rotation about their long axes, giving a spectrum more characteristic of a rigid or solid sample. These results give a picture of the gel phase as a phase characterized by considerable hydrocarbon chain disorder near 20 degrees C and becoming a more solid-like phase near 0 degrees C. The spin-lattice relaxation time, T1, has been measured at 20 degrees C in the gel phase, and at 37 and 45 degrees C in the liquid crystalline phase. The values of T1 obtained for each of the resolvable peaks in the spectrum at 37 degrees C are compared to the values (for each peak) of T2e, the decay time of the quadrupolar echo, obtained at the same temperature. These results are discussed in terms of a simple two-motion model.     

The lateral order of dipalmitoylphosphatidylcholine model membranes in the presence of N-alkyl-N,N,N-trimethylammonium ions as studied by Raman spectroscopy

Effects of N-alkyl-N,N,N-trimethylammonium ions with different alkyl substituents (hexyl, nonyl, dodecyl, and octadecyl) on the lateral packing of lipids in dipalmitoylphosphatidylcholine (DPPC) dispersions in H2O was investigated by Raman spectroscopy in a spectral region of 2800--3100 cm-1 at temperatures between 22--70 degrees C. The lateral order parameter Slat calculated by empirical equation reveals that the addition of the ions decreases the lateral ordering of lipid hydrocarbon chains in the gel phase, while in the liquid crystalline state the lateral ordering is increased. In addition, this observation is supported by decomposition of the spectra into component bands using a computer fitting program. This enabled to follow changes in individual band parameters (position, amplitude, and height) in dependence on temperature and/or additives. The results suggest that N-alkyl-N,N,N-trimethylammonium ions have a condensing effect on DPPC bilayer in the liquid crystalline state, the effect increasing with the increasing length of the alkyl substituent.     

Molecular structures and hydrogen-bond networks in crystals of synthetic 1-D-galactosamide bolaamphiphiles

The crystal structures of synthetic 1-galactosamide bolaamphiphiles, N,N'-bis(beta-D-galactopyranosyl)decane-1,10-dicarboxamide (1) and N,N'-bis(beta-D-galactopyranosyl)dodecane-1,12-dicarboxamide (2), were determined by single-crystal X-ray analysis. The space groups are P21, Z = 2 with cell dimensions: a = 13.624(2), b = 4.832(3), c = 21.178(3) Angstroms, beta = 98.57(1) degrees for 1; a = 13.521(2), b = 4.838(1), c = 23.706(2) Angstroms, beta = 104.945(10) degrees for 2. The galactopyranosyl rings of 1 and 2 are in a 4C1 chair conformation. The bolaamphiphile molecules are arranged in a layered structure for 1 and 2, with the alkylene chains packed parallel all over the layers. The hydroxyl groups of the galactopyranosyl rings in 1 and 2 form identical three-dimensional hydrogen-bond networks. The connecting decamethylene spacer of 1 has a kink conformation, while the dodecamethylene chain of 2 an all-trans zigzag conformation.