David Pink

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Papers by David Pink

Polarisation domain effects on ultrasonic velocity in antiferromagnetic chromium

Journal of Physics F: Metal Physics, 1978

ABSTRACT Data on ultrasonic velocity have been successfully interpreted on the basis of the therm... more

Computer simulation of DNA interacting electrostatically with phosphatidylcholine and trimethylammoniumpropane interfaces

Physical Chemistry Chemical Physics, 2000

The region of a lipid membrane, with all hydrocarbon chains equal, embedded in an aqueous solutio... more

Resolution of a Discrepancy Concerning the Average Dipole Moment in KH2PO4−Type Ferroelectrics

physica status solidi (b), 1970

Bilayers of Monomeric and Polymeric 4,N-POMECY and Dimyristoylphosphatidylcholine

Macromolecules, 1995

We have modeled mixed bilayers of dimyristoylphosphatidylcholine (DMPC) and the polymerizable amp... more We have modeled mixed bilayers of dimyristoylphosphatidylcholine (DMPC) and the polymerizable amphiphile 4,N-POMECY monomers as well as bilayers of DMPC and 4,16-POMECY polymers (macrolipids). Our intention was to answer three questions: (i) Why, with two C-16 hydrocarbon chains, does pure monomeric 4,16-POMECY exhibit a phase transition at P : = 29 "C? (ii) Why then do the pure (polymerized) 4,16-POMECY macrolipids possess I", RZ 45 "C? (iii) What does the measured phase diagram imply about macrolipid structure. Using analytic methods and computer simulation to obtain phase diagrams, we conclude that the answer to (i) is that the entropy of the relatively long polar group contributes to reducing T , from -41 to -29 "C. When the macrolipids are formed, via polymerization in their polar groups, this entropy is lost and T , is then determined by the interaction between hydrocarbon chains which yields T, 41 "C. We modeled the macrolipids as (a) flexible chains, (b) compact hexagons, or (c) rigid rods of fixed length. We found that none of these models described the experimental data. We simulated the polymerization process in the bilayer and found that the average length of the polymers formed increased with initial monomer concentration. Using these results we constructed a phase diagram using model b and found good agreement with experiment. We deduced that 4,16-POMECY macrolipids formed in a bilayer are probably rigid with compact segments connected, possibly by rigid rods. We make predictions of the transition temperatures of monomeric and polymeric 4s-POMECY for N = 14 and 18.

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A theoretical model for phase transitions in lipid monolayers

The Journal of Chemical Physics, 1982

The statistics of Guggenheim are used in conjunction with a ten-state conformational model (origi... more The statistics of Guggenheim are used in conjunction with a ten-state conformational model (originally formulated for phase transitions in lipid bilayers) to predict gel–fluid and fluid–vapor phase boundaries for lipid monolayers. The theoretical model is a model of interacting dimers on a two-dimensional lattice with each dimer representing a lipid molecule with two acyl chains and one polar head. The acyl chains are assumed to interact via anisotropic van der Waals interactions. The interaction between the polar heads is simulated by an attractive isotropic interaction with coupling constant K0. The analysis of Costas and Sanctuary is then combined with this model so as to obtain self-consistently the fraction of occupied and vacant lattice sites for the monolayer at different pressures. Surface pressure-area isotherms and coexistence curves are obtained for fixed van der Waals interactions and several values of K0. It is shown that a fluid–vapor phase boundary occurs for values o...

Models of protein lateral arrangements in lipid bilayer membranes. Application to electron spin resonance studies of cytochrome c oxidase

Chemistry and Physics of Lipids, 1988

We consider the situation of integral membrane proteins in a lipid bilayer matrix where the size ... more We consider the situation of integral membrane proteins in a lipid bilayer matrix where the size of the polar group of the protein is important in determining the lateral packing of the proteins. We represent the cross-section of the protein hydrophobic core as a hexagon moving on a lattice, and represent the projection of the polar group onto the plane of the bilayer as a shape, parts of which overlap the hexagon. Lattice sites represent lipid molecules. We calculate the fraction of lipid molecules which are adjacent to the hydrophobic core of at least one protein. We use this data to consider the "motion restricted" spectrum observed in electron spin resonance (ESR) probe studies, and compute the dependence of the "'motion restricted" fraction upon protein concentration. The resulting curves can be used to analyse ESR data in order to deduce the size and shape of the proteins" polar segment. We have used the range of models examined to study the dependence upon protein concentration of the particular case of the "'motion restricted" spectrum of a spin-labelled lipid freely diffusing or, alternatively, covalently bound to cytochrome c oxidase. We find that our calculations are in accord with a model where ~ 60 lipid molecules can fit around an isolated such protein in both halves of the bilayer, and where the polar segment is substantially anisotropic and extends laterally beyond the limits of the hydrophobic core. The latter is in accord with what is known about the structure of cytochrome c oxidase. We indicate further measurements that should be performed in order to establish more definitively the dependence of the "motion restricted" component upon protein concentration, giving the lipid protein ratios at which they should be performed, and we make predictions concerning the results. Finally we argue for a particular unified way of plotting experimental data.

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The effect of electrostatic interactions and water polarization on the properties of charged lipid membranes: a theoretical approach

Canadian Journal of Physics, 1985

We describe the physical properties of a planar interface between an electrolyte and a charged li... more We describe the physical properties of a planar interface between an electrolyte and a charged lipid membrane. The model differs from the usual Gouy–Chapman–Debye–Huckel theory for electrolytes in that the dipolar nature of the water molecules is explicitly included. The polarization, dielectric constant, and electric potential of the electrolyte are calculated as functions of distance from the interface. The change in gel – liquid-crystal transition temperature is obtained as a function of pH and salt concentration from the free energy of the system. The results are compared to previous calculations using the Gouy–Chapman–Debye–Huckel theory and to experimental data for dimyristoyl-methylphosphoric acid.

The thermodynamic properties of mixed phospholipid bilayers: a theoretical analysis

Biochemistry and Cell Biology, 1984

A theoretical model is presented with the intention of describing lateral phase separations in bi... more A theoretical model is presented with the intention of describing lateral phase separations in binary lipid mixtures in which the acyl chains of the components differ in their length. The model includes explicitly interactions between the acyl chains and between polar heads of the lipid molecules. Phase diagrams and thermodynamic properties of binary lipid mixtures were calculated using a wide range of interaction parameters. It is shown that the occurrence of immiscibility in the gel phase is related to the interactions between the polar heads of the lipid molecules. The calculated results for binary lipid mixtures are compared with the available experimental data. In particular, the calculated specific heat for dilauroyl phosphatidylcholine – distearoyl phosphatidylcholine is in reasonable agreement with experimental results obtained from differential scanning calorimetry measurements.

Thermodynamics of glycophorin in phospholipid bilayer membranes

Biochemistry, 1987

We have developed a model of glycophorin in a phospholipid bilayer membrane in order to study the... more We have developed a model of glycophorin in a phospholipid bilayer membrane in order to study the thermodynamics of this system and to understand the detailed behavior of recent calorimetric data. We assume that the larger glycophorin polar group can be considered as either adopting a pancakelike conformation at the bilayer interface (D state) or be directed generally away from the interface (U state) [Ruppel,

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Intrinsic proteins and their effect upon lipid hydrocarbon chain order

Biochemistry, 1981

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Intersecting polymers in lipid bilayers: cliques, static order parameters and lateral diffusion

Biochimica et Biophysica Acta (BBA) - Biomembranes, 1993

We have modelled a macrolipid polymer composed of lipid molecules (monomers) embedded in a lipid ... more We have modelled a macrolipid polymer composed of lipid molecules (monomers) embedded in a lipid bilayer or monolayer and polymerized via their polar groups. Because of fluctuations perpendicular to the plane of the bilayer, the polar region occupied by the polymer chain possesses sufficient space so that the polymer might exhibit 'self-intersection' if its conformational state is projected onto the plane of the bilayer/monolayer. We represent the plane of the bilayer/monolayer by a triangular lattice. Each site can be occupied by a monomer or be empty (and thus occupied by one of the unpolymerizable lipids which make up the bilayer/monolayer). A macrolipid is represented by a sequence of N monomers connected by N-1 bonds. Bonds may be either short (connecting nearest neighbour monomers) or long (between second neighbour monomers), in accord with the average properties of the spacers between the polymerized lipids. We have carried out computer simulation of this system using the Carmesin-Kremer bond stretching algorithm. Although no two monomers can occupy the same site, bonds may cross each other. We analyzed the dependence of (R 2) and (R 2) ~ N 2~c and (Nsc) + (Nmc) ~ N 2crc, where N~ and Nmc are the number of bond-crossings in the same macrolipid ('self-crossing') or in two different macrolipids ('mutual-crossing'). For single macrolipids, we confirmed that u c = 3/4 and have found that tr c = 0.52, which we consider supports that tr c = 1/2. For the dense case with monomer concentration, c = 0.72, we found that vc = 1/2 and that tr c ---0.52 supports that ~r~ = 1/2. In the semi-dilute regime (c = 0.2) we found crossover behaviour, although tr~ = 1/2. The total number of bond crossings thus scale like N, independent of concentration. We studied the connectivity of the system by calculating the weight averaged cluster, or 'clique', size. Cliques are defined as being composed of all macrolipids which exhibit at least one crossing bond with one other member of the clique. We found that while the average clique contains about two macrolipids at low concentrations, the clique size approaches the maximum possible value at high concentrations if the macrolipids are sufficiently long. In the latter case a transition appears to occur as the macrolipid length increases. This transition occurs at length = 40 when c = 0.72. These observations should have experimental consequences for the viscoelastic properties of the system. We defined an order parameter, B, and showed that although B depended upon c, it appeared to be independent of N for both crossing and non-crossing macrolipids. We calculated the dependence of the lateral diffusion coefficient upon c for some values of N and compared it to the case of non-crossing macrolipids and single lipid molecules. We suggest how the existence of crossing bonds might be observed.

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Intrinsic Molecules in Fluid Phospholipid Bilayers. Fluorescence Probe Studies

European Journal of Biochemistry, 1981

Fluorescence probe data using 1,6-diphenyl-I ,3,5-hexatriene for various concentrations of intrin... more Fluorescence probe data using 1,6-diphenyl-I ,3,5-hexatriene for various concentrations of intrinsic molecules (cholesterol, gramicidin A and cytochrome oxidase) within fluid lipid bilayers have been examined. The polarization value increases with increasing concentration of intrinsic molecule and then approaches a limiting value. Empirical curve-fitting of the experimental data, change of polarization with concentration, shows that each system can be fitted approximately by an exponential curve. A theory has been constructed based upon the assumption that only one intrinsic molecule need be adjacent to a fluorescent probe molecule to affect its motion drastically. The change in probe motion then depends upon the probability p of all positions next to a lipid chain being free of intrinsic molecules. The value of the probability p

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On the spin wave approximation

Physica, 1966

Abstract Probability distribution functions for systems with a spiral spin arrangement have been ... more Abstract Probability distribution functions for systems with a spiral spin arrangement have been calculated and an application has been made to the particular case of dysprosium. It is found that, for the range of the parameters investigated, the probability of finding no spin deviations at a given site at zero temperature is greater than or equal to 0.97. Some previous results have been rederived very simply by making use of the properties of Stirling numbers.

Surface States of an Induced-Moment System and a Hydrogen-Bonded Ferroelectric

Physical Review B, 1973

On two kinds of induced-moment system

Journal of Physics C: Solid State Physics, 1968

Double-time temperature-dependent Green functions have been used to investigate the excitation sp... more Double-time temperature-dependent Green functions have been used to investigate the excitation spectra and magnetization of two kinds of magnetic system. The first example involves an induced-moment system in which the ions possess a singlet ground state and a singlet excited state, while in the second two limiting cases of a mixed system in which the ions possess a singlet ground state and three excited states are considered. The first example is also similar to a simple model of a hydrogen-bonded ferroelectric with the magnetization becoming the polarization. In both cases an approximation has been used to decouple the hierarchy of equations. Comparisons are made with previous work on this topic and it is found that the systems in which the magnetization is due only to an induced moment display first-order magnetic transitions at the critical point.

Ultrasonic attenuation and the phase diagram of antiferromagnetic chromium

Journal of Physics F: Metal Physics, 1980

ABSTRACT The authors have used the thermal activation model for polarisation domains in antiferro... more

Domain-domain interactions and internal strains in chromium

Journal of Physics F: Metal Physics, 1988

ABSTRACT Experimental results on chromium are reinterpreted in terms of a modification of the the... more ABSTRACT Experimental results on chromium are reinterpreted in terms of a modification of the thermally activated polarisation domain model, to include interactions between domains together with the effects due to internal strains. The authors suggest that various &#39;anomalous&#39; peaks observed in ultrasonic attenuation data can be understood as arising because of domain-domain interactions together with internal stresses, and they point out that the associated critical point might be experimentally observable through the application of a compressive uniaxial stress.

Sheared edible oils studied using dissipative particle dynamics and ultra small angle X-ray scattering: TAGwood orientation aggregation and disaggregation

Food & Function, 2017

The following work examines the aggregation of supramolecular triglyceride crystalline structures... more

Magnetic excitations on atomically rough surfaces

Physica B+C, 1977

ABSTRACT

Intersecting Adsorbing Polymers in Lipid Bilayers - Thermodynamics of Cliques and Static Order Parameters

Thin Solid Films, 1994

... Thin Solid Films, 244 (1994) 827-831 Intersecting adsorbing polymers in lipid bilayers: therm... more

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