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M Caffrey

Publications and source records attributed to M Caffrey.

At least 73 records · Page 4Linked to original sources
PubMed1993

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.

Calorimetry↗
PubMed1992

Resonance-enhanced x-rays in thin films: a structure probe for membranes and surface layers.

An x-ray resonance effect in an organic thin film on an x-ray reflecting mirror is reported. The resonance effect is the result of interference between reflected and refracted x-rays at the air-organic thin film interface and occurs at incident angles slightly above the critical angle of the film. In excellent agreement with theory, the primary resonant x-ray electric field that is confined in the organic thin film is approximately 20 times as intense as the electric field of the incident beam when measured at a position close to the center of the film. Resonance-enhanced x-rays can be used to characterize the internal structure of Langmuir-Blodgett thin film membranes. This effect may also find use in x-ray-based thin film devices and in the structural analysis of adlayers and surfaces that have thus far proved difficult, if not impossible, to study because of sensitivity limitations.

Electron Probe Microanalysis↗
PubMed1992

Cytochrome c2 mutants of Rhodobacter capsulatus.

Although structurally related to other members of the class I c-type cytochromes, the cytochromes c2 have little amino acid sequence homology to the eukaryotic cytochromes c. Moreover, the cytochromes c2 exhibit distinct properties such as redox potential and an isoelectric point. In an effort to understand the differences between the cytochromes c2 and the other class I c-type cytochromes, we have developed a genetic system to study Rhodobacter capsulatus cytochrome c2 by site-directed mutagenesis. We describe here overproduction of R. capsulatus wild-type cytochrome c2 in cytochrome c2-minus strains of R. capsulatus and Rhodobacter sphaeroides. We demonstrate that R. capsulatus wild-type cytochrome c2 can transcomplement for photosynthetic growth in R. sphaeroides. Further, we describe the generation, expression, and in vivo functionality properties of nine R. capsulatus site-directed mutants. We show that mutants K12D, K14E, K32E, K14E/K32E, P35A, W67Y, and Y75F are overproduced and functional in vivo. In contrast, mutants Y75C and Y75S are expressed at low levels and exhibit poor functionality in vivo. These findings establish an effective system for the production of R. capsulatus site-directed mutants and demonstrate that interspecies complementation can be used to detect defective cytochrome c2 mutants.

Amino Acid Sequence↗
PubMed1992

LIPIDAT: a database of lipid phase transition temperatures and enthalpy changes. DMPC data subset analysis.

The systematic study of the mesomorphic phase properties of synthetic and biologically derived lipids began some 30 years ago. In the past decade, interest in this area has grown enormously. As a result, there exists a wealth of information on lipid phase behavior, but unfortunately these data have until now been scattered throughout the literature in a variety of books, proceedings and journals. The data have recently been compiled in a centralized database, LIPIDAT, with a view to providing ready access to the data and to the appropriate literature. LIPIDAT consists of a tabulation of all known mesomorphic and polymorphic phase transition temperatures and enthalpy changes for synthetic and biologically-derived lipids in the dry and in the partially and fully hydrated states. Also included is the effect of pH, and of salt and metal ion concentration and other additives such as proteins, drugs, etc., on the thermodynamic values. The methods used in making the measurements and the experimental conditions are reported. Bibliographic information includes comprehensive literature referencing and list of authors, but does not at the present time include article titles. As of this writing, the database is current through June, 1990 and is approaching 10,000 records in length. Each record contains 28 fields. In this paper we report the contents and present an analysis of LIPIDAT as it refers to fully hydrated 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). This database subset represents about 7% of all LIPIDAT records. It includes data collected over a 23-year period from 1967 to 1989 and consists of 702 records obtained from 336 articles in 55 different journals. The number of records per year rises steadily beginning in 1971, reaches a maximum of 89 records/year in 1977 and remains relatively constant at 60-70 records/year in the succeeding period. Journals making the greatest contribution to the DMPC subset include Biochimica et Biophysica Acta, Biochemistry, Chemistry and Physics of Lipids and the Biophysical Journal. These four journals account for 71% of the total records in the database subset. The analysis shows that differential scanning calorimetry, electron spin resonance, fluorescence, nuclear magnetic resonance and Raman spectroscopy are the methods most commonly used for DMPC transition temperature determination. An interesting pattern emerges as to the place in time the different methods assume or loose popularity.(ABSTRACT TRUNCATED AT 400 WORDS)

Calorimetry, Differential Scanning↗
PubMed1992

Direct correlation of structure changes and thermal events in hydrated lipid established by simultaneous calorimetry and time-resolved x-ray diffraction.

In many lipid systems, polymorphic and mesomorphic behavior depends on sample thermal history. To establish unequivocally the structural origin of endothermic and exothermic events in such systems, we have performed simultaneous calorimetry and time-resolved x-ray diffraction (SCALTRD). To this end, aluminum calorimetry crucibles were used to contain the hydrated lipid sample, and the calorimeter was mounted with the base of the crucible oriented perpendicular to a synchrotron-derived focused monochromatic x-ray beam for SCALTRD data collection. Measurements were made with hydrated monoelaidin and 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (DEPE) contained in hermetically sealed crucibles. Time-resolved x-ray diffraction (TRXRD) data were collected using an x-ray image intensifier/video system and a streak camera containing an x-ray sensitive image plate and/or film. SCALTRD analysis of the lamellar gel to lamellar liquid crystalline phase transition in hydrated monoelaidin gives identical progress curves by calorimetry and TRXRD at a scan rate of 1 degree C/min. At faster rates, calorimetry shows a broader phase transition that starts at a lower and ends at a higher temperature than is observed by TRXRD. The disparity arises in part because the x-ray beam used in TRXRD interrogates only a small portion of the sample, whereas the calorimeter responds to the entire sample volume. Because data collection times are relatively long, radiation damage is an important potential problem for SCALTRD measurements. Such an effect was observed with DEPE/water in that TRXRD shows the lamellar gel to lamellar liquid crystalline phase transition occurring at a lower temperature than observed by calorimetry. We speculate that the sample accumulates impurities locally as a result of radiation damage that has the effect of lowering the phase transition temperature at the site of interrogation by the x-ray beam. This "methods-in-combination" SCALTRD approach facilitates the direct correlation of structure rearrangements and thermal events in the same sample under identical conditions of thermal history. The information content of the data so derived far surpasses that available from either method used in isolation.

Calorimetry↗
PubMed1992

Calorimetric and x-ray diffraction studies of rye glucocerebroside mesomorphism.

Glucocerebrosides (GlcCer) isolated from the leaves of winter rye (Secale cereale L. cv Puma) differ from the more commonly investigated natural and synthetic cerebrosides, in that greater than 95% of the fatty acids are saturated and monounsaturated hydroxy fatty acids. Isomers of the trihydroxy long chain base hydroxysphingenine (t1(8:18 cis or trans)) and isomers of sphingadienine (d18:2(4trans, 8 cis or trans)) comprise 77% and 17%, respectively, of the total long chain bases. The phase behavior of fully hydrated and dry rye leaf GlcCer was investigated using differential scanning calorimetry (DSC) and x-ray diffraction. On initial heating, aqueous dispersions of GlcCer exhibit a single endothermic transition at 56 degrees C and have an enthalpy (delta H) of 46 J/g. Cooling to 0 degrees C is accompanied by a small exothermic transition (delta H = -8 J/g) at 8 degrees C. On immediate reheating, a broad exothermic transition (delta H = -39 J/g) is observed between 10 and 20 degrees C in addition to a transition at 56 degrees C. These transitions are not reversible, and the exothermic transition rapidly diminishes when the sample is held at low temperature. Using x-ray diffraction, it was determined that the endotherm at 56 degrees C represents a transition from a highly ordered lamellar crystalline phase (Lc) with a d-spacing of 57 A and a series of wide-angle reflections in the 3-10 A range, to a lamellar liquid crystalline (L alpha) phase having a d-spacing of 55 A and a diffuse wide-angle scattering peak centered at 4.7 A. Cooling leads to the formation of a metastable gel phase (L beta) with a d-spacing of 64.0 A and a single broad reflection at 4.28 A. Subsequent warming to above 15 degrees C restores the original Lc phase. Thus, rye GlcCer in excess water exhibit a series of irreversible transitions and gel phase metastability. Dry GlcCer undergo an initial heating endothermic transition at 130 degrees C, which is ascribed to a transformation into the HII phase from a two phase state characterized by the coexistence of phases with disordered (alpha) and helical (delta) type chain conformations but of unknown lattice identity: An exotherm at 67.5 degrees C observed upon subsequent cooling is of unknown origin. Since an undercooled HII phase persists down to 19 degrees C, the exotherm may derive in part from an alpha-to-delta type chain packing conformational change especially under slow cooling conditions. Upon reheating from low temperatures to 65 degrees C, a phase with a two-dimensional, primitive rectangular lattice and delta-like chain packing (R8 phase) in coexistence with the HI, phase emerges. With continued heating to 90 degrees C these coexisting phases give way to a phase with a two-dimensional, centered rectangular lattice and delta-like chain packing (P8phase) which again coexists with the HI, phase. Above 130 degrees C, the Pb phase disappears and the sample converts completely to the HI, phase as observed upon initial heating. These results indicate that the mesomorphic behavior of rye leaf GIcCer is distinct from that of other cerebrosides.

Biophysical Phenomena↗
PubMed1992

Internal and interfacial structure of membranes studied using X-ray standing waves.

The X-ray standing wave (XSW) method developed in the mid-Sixties was used then to determine the position of heavy atoms in and on crystals of silicon and germanium with sub-Angström resolution. The advent of layered synthetic microstructures, used primarily as wide-bandpass X-ray monochromators, heralded a new era in the use of XSW to study biologically relevant structures with a length scale of the order of tens of Angströms. The original measurements were performed on model membrane Langmuir-Blodgett (LB) films and served to establish the utility of the XSW approach in determining heavy-atom location in such systems with sub-Angström resolution and in tracking the heavy-atom layer as it moves during a thermotropic transition. Recent measurements show that the XSW is well defined at close to 1000 A from the XSW generating surface. Thus, the useful probing distance of XSW is of this length scale also without a compromise in resolution. In addition to the above measurements on well ordered systems the XSW method is being used to profile ion distribution 'directly' at the membrane/aqueous interface. Recent results show that the diffuse double layer can be established reversibly by suitably adjusting the pH of the aqueous phase next to a phospholipid membrane. The advantages and disadvantages of this new surface technique as applied to the study of membrane structure and interfacial phenomena are discussed.

Crystallography, X-Ray↗
PubMed1991

Structural studies of membranes and surface layers up to 1,000 A thick using X-ray standing waves.

The X-ray standing wave (XSW) method, developed in the 1960s, was used originally to determine heavy atom positions in and on silicon and germanium single crystals. An X-ray standing wave generated by the interference of coherent incident and reflected beams excites X-ray fluorescence from the heavy atom, the intensity of which as a function of incident angle provides an indication of the atom's distance from the X-ray reflecting surface. The availability of X-ray mirrors and the ability to prepare layered synthetic microstructures has made possible the study of biologically relevant structures using the XSW technique on length scales of typically tens to hundreds of ångströms, allowing heavy atoms in such structures to be located with ångström or subångström resolution. Many model biological systems (such as Langmuir-Blodgett films, which mimic membranes) require access to still larger scales, but it is not obvious that an XSW will remain coherent over such length scales. Here we report studies of a lipid multilayer system using the XSW method, in which we have been able to locate the metal atoms in a zinc arachidate bilayer with ångström resolution at a distance of almost 1,000 A above the surface of a gold mirror. Our results indicate that the XSW technique should be useful for structural studies of supramolecular aggregates, receptor-ligand interactions and multi-membrane stacks, in which length scales of this order are encountered.

Arachidonic Acids↗
PubMed1991

Kinetics and mechanism of the pressure-induced lamellar order/disorder transition in phosphatidylethanolamine: a time-resolved X-ray diffraction study.

By using synchrotron radiation, a movie was made of the X-ray scattering pattern from a biological liquid crystal undergoing a phase transition induced by a pressure jump. The system studied includes the fully hydrated phospholipid dihexadecylphosphatidylethanolamine in the lamellar gel (L beta') phase at a temperature of 68 degrees C and a pressure of 9.7 MPa (1400 psig). Following the rapid release of pressure to atmospheric the L beta' phase transforms slowly into the lamellar liquid crystal (L alpha) phase. The pressure perturbation is applied with the intention of producing a sudden phase disequilibrium followed by monitoring the system as it relaxes to its new equilibrium condition. Remarkably, the proportion of sample in the L alpha phase grows linearly with time, taking 37 s to totally consume the L beta' phase. The time dependencies of radius, peak intensity, and width of the powder diffraction ring of the low-angle (001) lamellar reflections were obtained from the movie by image processing. The concept of an "effective pressure" is introduced to account for the temperature variations that accompany the phase transition and to establish that the observed large transit time is indeed intrinsic to the sample and not due to heat exchange with the environment. The reverse transformation, L alpha to L beta', induced by a sudden jump from atmospheric pressure to 9.7 MPa, is complete in less than 13 s. These measurements represent a new approach for studying the kinetics of lipid phase transitions and for gaining insights into the mechanism of the lamellar order/disorder transition.

Kinetics↗
PubMed1991

Diacetylenic lipid microstructures: structural characterization by X-ray diffraction and comparison with the saturated phosphatidylcholine analogue.

Thermotropic and lyotropic mesomorphism in the polymerizable lecithin 1,2-ditricosa-10,12-diynoyl-sn-glycero-3-phosphocholine and its saturated analogue, 1,2-ditricosanoyl-sn-glycero-3-phosphocholine, has been investigated by wide- and low-angle X-ray diffraction of both powder and oriented samples and by differential scanning calorimetry. Previous studies have shown that the hydrated diacetylenic lipid forms novel microstructures (tubules and stacked bilayer sheets) in its low-temperature phase. The diffraction results indicate that at low temperatures fully hydrated tubules and sheets have an identical lamellar repeat size (d001 = 66.4 A) and crystalline-like packing of the acyl chains. Chain packing in the lamellar crystalline phase is hydration independent. A model for the polymerizable lecithin with (1) fully extended all-trans methylene segments, (2) a long-axis tilt of 32 degrees, and (3) minimal chain interdigitation seems most reasonable on energetic grounds, is consistent with the diffraction data (to 3.93-A resolution), and is likely to support facile polymerization. Above the chain "melting" transition the lamellar repeat of the polymerizable lipid increases to 74 A. The conformational similarity between tubules, sheets, and the dry powder is corroborated by calorimetry, which reveals a cooling exotherm at the same temperature where tubules form upon cooling hydrated sheets. The data suggest that although a high degree of conformational order is a pertinent feature of tubules, this character alone is not sufficient to account for tubule formation. The conformation of the corresponding saturated phosphatidylcholine appears to be similar to that of other saturated phosphatidylcholines in the lamellar gel phase. Furthermore, above the main transition temperature, the dry, saturated lipid shows evidence of a P delta phase (112 degrees C), whereas the diacetylenic lipid appears to exhibit a centered rectangular phase, R alpha (55 degrees C).

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1991

A database of lipid phase transition temperatures and enthalpy changes.

The systematic study of the mesomorphic phase properties of synthetic and biologically derived lipids began some 30 years ago. In the past decade, interest in this area has grown enormously. As a result, there exists a wealth of information on lipid phase behavior, but unfortunately these data have, until now, been scattered throughout the literature in a variety of books, proceedings and journals. The data have recently been compiled in a centralized database with a view to providing ready access to same and to the appropriate literature. The compilation facilitates review of what has thus far been accomplished and highlights what remains to be done in this active research area. As such, it represents a convenient summary of the existing data which, when evaluated, will enable us to identify where deficits exist in the data, to reveal the fundamental physicochemical principles upon which lipid phase behavior is based and to understand more completely lipid phase relations in biological, reconstituted and formulated systems. The compilation consists of a tabulation of all known mesomorphic and polymorphic phase transition temperatures and enthalpy changes for synthetic and biologically-derived lipids in the dry and in the partially and fully hydrated states. Also included is the effect on these thermodynamic values of pH, and of salt and metal ion concentration and other additives such as proteins, drugs, etc. The methods used in making the measurements and the experimental conditions are reported. Bibliographic information includes complete literature referencing and list of authors. As of this writing, the database is current through June, 1990 and contains in excess of 9500 records. Each record contains 28 fields. Here, we describe how the database originated, its scope and contents, data abstraction procedures, and issues relating to mesophase and lipid nomenclature, data analysis and evaluation, and database maintenance and distribution.

Databases, Factual↗
PubMed1991

Kinetics of the barotropic ripple (P beta')/lamellar liquid crystal (L alpha) phase transition in fully hydrated dimyristoylphosphatidylcholine (DMPC) monitored by time-resolved x-ray diffraction.

We present here the first study of the use of a pressure-jump to induce the ripple (P beta')/lamellar liquid crystal (L alpha) phase transition in fully hydrated 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). The transition was monitored by using time-resolved x-ray diffraction (TRXRD). Applying a pressure-jump from atmospheric to 11.3 MPa (1640 psig, 111.6 atm) in 2.5 s induces the L alpha to P beta' phase transition which takes place in two stages. The lamellar repeat spacing initially increases from a value of 66.0 +/- 0.1 A (n = 4) to a maximum value of 70.3 +/- 0.8 A (n = 4) after 10 s and after a further 100-150 s decreases slightly to 68.5 +/- 0.3 A (n = 4). The reverse transition takes place following a pressure jump in 5.5 s from 11.3 MPa to atmospheric pressure. Again, the transition occurs in two stages with the repeat spacing steadily decreasing from an initial value of 68.5 +/- 0.3 A (n = 3) to a minimum value of 66.6 +/- 0.3 A (n = 3) after 50 s and then increasing by approximately 0.5 A over a period of 100 s. The transition temperature increases linearly with pressure up to 14.1 MPa in accordance with the Clapeyron relation, giving a dT/dP value of 0.285 degrees C/MPa (28.5 degrees C/kbar) and an associated volume change of 40 microliters/g. A dynamic compressibility of 0.13 +/- 0.01 A/MPa has been determined for the L alpha phase. This value is compared with the equilibrium compressibilities of bilayer and nonbilayer phases reported in the literature. The results suggest testable mechanisms for the pressure-induced transition involving changes in periodicity, phase hydration, chain order, and orientation. A more complete understanding of the transition mechanism will require improvement in detector spatial resolution and sensitivity, and data on the pressure sensitivity of phase hydration.

Biophysical Phenomena↗
PubMed1991

A database of lipid phase transition temperatures and enthalpy changes.

The systematic study of the mesomorphic phase properties of synthetic and biologically derived lipids began some 30 years ago. In the past decade, interest in this area has grown enormously. As a result, there exists a wealth of information on lipid phase behavior, but unfortunately, these data have, until now, been scattered throughout the literature in a variety of books, proceedings, and journals. The data have recently been compiled in a centralized database with a view to providing ready access to the same and to the appropriate literature. The compilation facilitates review of what has thus far been accomplished and highlights what remains to be done in this active research area. As such, it represents a convenient summary of the existing data which, when evaluated, will enable us to identify where deficits exist in the data, to reveal the fundamental physicochemical principles upon which lipid phase behavior is based, and to understand more completely lipid phase relations in biological, reconstituted, and formulated systems. The compilation consists of a tabulation of all known mesomorphic and polymorphic phase transition temperatures and enthalpy changes for synthetic and biologically derived lipids in the dry and in the partially and fully hydrated states. Also included is the effect on these thermodynamic values of pH, and of salt and metal ion concentration and other additives such as proteins, drugs, etc. The methods used in making the measurements and the experimental conditions are reported. Bibliographic information includes complete literature referencing and list of authors. As of this writing, the database is current through June 1990 and contains 9500 records. Each record contains 28 fields. Here, we describe how the database originated, its scope and contents, data abstraction procedures, and issues relating to mesophase and lipid nomenclature, data analysis, and evaluation, and database maintenance and distribution.

Databases, Factual↗
PubMed1990

Diffuse-double layer at a membrane-aqueous interface measured with x-ray standing waves.

The ion distribution in an electrolyte solution in contact with a charged polymerized phospholipid membrane was directly measured with long-period x-ray standing waves. The 27-angstrom-thick lipid monolayer was supported on a tungsten/silicon mirror. X-ray standing waves were generated above the mirror surface by total external reflection of a 9.8-kiloelectron volt x-ray beam from a synchrotron undulator. The membrane surface, which contained negatively charged phosphate headgroups, was bathed in a dilute ZnCl2 solution. The concentration of Zn2+ in the condensed layer at the membrane surface and the Zn2+ distribution in the diffuse layer were measured as a function of headgroup charge. The Debye length of the diffuse layer varied between 3 and 58 angstroms. The results qualitatively agree with the Gouy-Chapman-Stern model.

Chemical Phenomena↗
PubMed1990

Kinetics of the lamellar and hexagonal phase transitions in phosphatidylethanolamine. Time-resolved x-ray diffraction study using a microwave-induced temperature jump.

The kinetics of the thermotropic lamellar gel (L beta')/lamellar liquid crystal (L alpha) and L alpha/inverted hexagonal (HII) phase transitions in fully hydrated dihexadecylphosphatidylethanolamine (DHPE) have been studied. Measurements were made by using time-resolved x-ray diffraction (TRXRD) to monitor progress of the transitions. In these studies microwave energy at 2.5 GHz was used to increase the sample temperature rapidly and uniformly through the phase transition regions. The L beta'/L alpha and L alpha/HII transitions of DHPE were examined under active microwave heating and passive cooling. The transitions were found to be repeatable and reversible, and to have an upper bound on the time required to complete the transition of less than 3 s. Regardless of the direction of the transition, both phase transitions appeared to be two-state with no accumulation of intermediates to within the sensitivity limits of the TRXRD method. The rate and amplitude of the temperature jump can be controlled by regulating microwave radiation input power. A temperature jump rate of 29 degrees C/s was obtained at a final microwave power setting of 120 W. Comparisons between previously reported fluid flow (Caffrey, M. 1985. Biochemistry. 24:4826-4844) and microwave heating studies suggest that the determination of limiting transit times will require faster heating.

Kinetics↗
PubMed1990

Kinetics of the premelting (L beta'-P beta') and main transition (P beta'-L alpha) in hydrated dipalmitoylphosphatidylcholine. A time-resolved x-ray diffraction study using microwave-induced temperature-jumps.

The dynamics and mechanism of the premelting (L beta'-P beta') and main transitions (P beta'-L alpha) in fully hydrated dipalmitoylphosphatidylcholine were examined by low-angle time-resolved x-ray diffraction (TRXRD) using microwave radiation to effect uniform, internal sample heating. Equilibrium and dynamic aspects of the transitions were investigated. The dynamic studies involved applying a temperature jump of sufficient amplitude to effect the two transitions sequentially. Our findings are as follows. (a) Microwave radiation has proven useful as a means for implementing rapid and uniform internal heating in temperature-jump studies of lipid-phase transition kinetics. (b) Heating rate can be controlled by adjusting microwave power setting. (c) The thermal expansion coefficient of the three lyotropic phases follows the sequence L beta' not equal to O greater than P beta' much greater than L alpha. (d) Regardless of temperature-jump amplitude and sample heating rate the P beta' phase was always in evidence as an intermediate between the L beta' and L alpha phases. (e) The degree of development of the P beta' phase was inversely proportional to temperature-jump amplitude and heating rate. (f) The shortest transit time recorded for the combined L beta'-P beta', and P beta'-L alpha transitions was less than 1 s. (g) Upon cooling from the L alpha phase the onset of the chain disorder/order transition was apparent as a dramatic change of slope in the scattering angle vs. time plot which is interpreted as arising from sample heating by the latent heat of the transition. (h) Based on the shape of the low-angle diffraction pattern of the P beta' phase the P beta'-L alpha transition appears to be reversible with no evidence of metastability as was observed in the slow scan TRXRD measurements of Tenchov et al. (1989. Biophys. J. 56:757-768).

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1989

A lyotrope gradient method for liquid crystal temperature-composition-mesomorph diagram construction using time-resolved x-ray diffraction.

A new method for rapidly constructing isobaric temperature-composition-mesomorph (T-C) diagrams is described. The method involves establishing a lyotrope concentration gradient in a liquid crystal lengthwise in an x-ray capillary tube. At a fixed temperature such a sample corresponds to an isotherm in the corresponding isobaric T-C diagram. The concentration gradient is conveniently established by bringing the two components into contact in the capillary and allowing limited diffusion of one component into the other. Phase boundaries are located and phases are identified and structurally characterized continuously along the length of the capillary using time-resolved x-ray diffraction. Repeating the measurement on the same sample at a series of temperatures in the range of interest completes that T-C diagram. The method has been used to construct the T-C diagram for detergent/water and lipid/water binary and ternary systems in the 20-120 degrees C range. They agree well with and extend the results obtained by conventional methods.

Crystallization↗