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Papers by David Pink

Langmuir, Dec 9, 2009

Nanoscale materials can have cytotoxic effects. Here we present the first combined empirical and ... more Nanoscale materials can have cytotoxic effects. Here we present the first combined empirical and theoretical investigation of the influence of electrostatic attraction on nanoparticle cytotoxicity. Modeling electrostatic interactions between cells and 13 nm spheres of zinc oxide nanoparticles provided insight into empirically determined variations of the minimum inhibitory concentrations between four differently charged isogenic strains of Pseudomonas aeruginosa PAO1. We conclude that controlling the electrostatic attraction between nanoparticles and their cellular targets may permit the modulation of nanoparticle cytotoxicity.

Physics of Fluids, 2019

We have used Ultra Small Angle X-ray Scattering (USAXS) and mathematical models to study seemingl... more We have used Ultra Small Angle X-ray Scattering (USAXS) and mathematical models to study seemingly-spontaneous aggregation structures in two pasteurized bovine milks. Although extensive studies of casein micelles and their aggregation have been carried out, few have been done to numerically characterize submicron structures to micron-scale structures. We measured the USAXS intensity, I(q), as a function of the scattering vector magnitude, q, for commercial pasteurized skim milk and nonhomogenized whole milk at two temperatures, 7 °C and 45 °C. We observed broad peaks, reported previously to be related to casein micelles, centered at q ≈ 2 × 10−2 Å−1 and at q ≈ 9 × 10−2 Å−1. At lower q values, log I(q) displayed a behavior characteristic of aggregation manifested for a slope in the region 3–7 × 10−4 Å−1 < q < 4 × 10−3 Å−1. This behavior appeared in the absence of (a) chymosin, (b) any change in pH or CaCl2 concentration, and (c) temperature changes. We introduced a model of mil...

Chemistry Letters, 2017

First insights into the mechanical properties of a single fat spherulite were obtained by the ind... more First insights into the mechanical properties of a single fat spherulite were obtained by the indentation with microcolloidal probes. We found that the single spherulite of triacylglycerol acts like an elastic body after pushing several times with a microcolloidal probe. The calculated elastic modulus for the single spherulite was comparable with that of condensed triacylglycerol samples, measured using a bulk rheometer, despite an apparent difference in morphology and volume fraction.

Corkery et al. have proposed that the high-temperature state of the triglyceride trilaurin (TL) i... more Corkery et al. have proposed that the high-temperature state of the triglyceride trilaurin (TL) is a Y-conformer, in which the three hydrocarbon chains are dynamically twisted with an average angle of ˜120 between them. Using computer simulations, we first show that the high-temperature state is indeed the Y conformation. We then develop a theory of the liquid-solid transition of this

Journal de physique. Colloque, Feb 1, 1971

Rkume.-Nous avons ktudik la dkcroissance de la tempkrature magnktique critique quand des substanc... more Rkume.-Nous avons ktudik la dkcroissance de la tempkrature magnktique critique quand des substances, ayant une interaction de superkchange dominante au moyen d'une liaison hydrogkne, sont deuterkes. On propose que, si la liaison est suffisamment courte, l'effet tunnel du proton dans un puits de potentiel minimum double pourrait 6tre important. Le cas de HCr02 est considkrk et des approximations reproduisent la dkcroissance de la tempkature critique dkja observke.

RSC Advances, 2015

Blending and interesterification of high oleic algal oil with medium chain triglycerides decrease... more Blending and interesterification of high oleic algal oil with medium chain triglycerides decreased viscosity and inhibited crystallization of triacylglycerol oils used as sustainable lubricant feedstocks.

Current Opinion in Colloid & Interface Science, 2014

Triacylglycerols (TAGs) are the majority molecules present in edible fats and oils. Many of the f... more Triacylglycerols (TAGs) are the majority molecules present in edible fats and oils. Many of the functional characteristics of fat products depend on the colloidal fat crystal network present. Identifying the hierarchies of these colloidal networks and how they spontaneously self-assemble is important to understand their functionality and the oil binding capacity, and new insights into the nano-to meso-scale structure in these colloidal fat networks have been reported in recent years. Ultra small angle X-ray scattering (USAXS) is a technique new to the study of edible oil structures and, when combined with modelling and computer simulation, has enabled significant advances to be made in understanding the nano-to micro-scale crystalline structures of edible oils. In the four years since crystalline nanoplatelets (CNPs) were characterized, models have been made of these highly anisotropic nanoscale structures in which they were treated as the primary unit. In those models, CNPs were represented as close-packed rigid layers of spheres, so chosen because the van der Waals sphere-sphere interaction is known. The intent of the models was to predict the hierarchy of colloidal fat networks that would self-assemble from the components in edible oils. Initially, CNP aggregation was modeled under the assumption that all CNPs are present before aggregation begins and that their solubility in the liquid oil is very low. The models successfully predicted the fractal dimensions subsequently measured using USAXS. This brief review reports on some of the latest models and simulations together with the results of USAXS experiments carried out on binary lipid systems, such as SSS in OOO, as well as certain complex systems that contain many different TAG molecules. The excellent agreement between the two approaches has established that USAXS is a powerful tool in the elucidation of the nano-to meso-length scales in fats and oils. 1-INTRODUCTION Edible fats are a class of colloidal gels in which an oleogel crystal network is formed as the triacylglyceride (TAG) molecules crystallize from the melt. Crystalline nano-platelets (CNPs) [1-6] have been found to be the basic components of the complex macro-colloidal structure of these edible fats. These CNPs aggregate to form

Food Funct., 2014

Polycrystalline particles composed of triacylglycerol (TAG) molecules, and their networks, in anh... more Polycrystalline particles composed of triacylglycerol (TAG) molecules, and their networks, in anhydrous TAG oils find extensive use as edible oils in the food industry.

We present a calculation of the physical properties of solid triglyceride particles dispersed in ... more We present a calculation of the physical properties of solid triglyceride particles dispersed in an oil phase, using atomic- scale molecular dynamics. Significant equilibrium density oscillations in the oil appear when the interparticle distance, d, becomes sufficiently small, with a global minimum in the free energy found at d 1.4 nm. We compare the simulation values of the Hamaker coefficient

Journal of Physics: Condensed Matter, 2014

Triacylglycerols (TAGs) are biologically important molecules which form crystalline nanoplatelets... more Triacylglycerols (TAGs) are biologically important molecules which form crystalline nanoplatelets (CNPs) and, ultimately, fat crystal networks in edible oils. Characterizing the self-assembled hierarchies of these networks is important to understanding their functionality and oil binding capacity. We have modelled CNPs in multicomponent oils and studied their aggregation. The oil comprises (a) a liquid component, and (b) components which phase separately on a nano-scale (nano-phase separation) to coat the surfaces of the CNPs impenetrably, either isotropically or anisotropically, with either liquid-like coatings or crystallites, forming a coating of thickness ?. We modelled three cases: (i) liquid?liquid nano-phase separation, (ii) solid?liquid nano-phase separation, with CNPs coated isotropically, and (iii) CNPs coated anisotropically. The models were applied to mixes of tristearin and triolein with fully hydrogenated canola oil, shea butter with high oleic sunflower oil, and cotton seed oil. We performed Monte Carlo simulations, computed structure functions and concluded: (1) three regimes arose: (a) thin coating regime, Δ &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.0701 u (b) transition regime, 0.0701 u ≤ Δ ≤ 0.0916 u and (c) thick coating regime, Δ &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; 0.0916 u. (arbitrary units, u) (2) The thin coating regime exhibits 1D TAGwoods, which aggregate, via DLCA/RLCA, into fractal structures which are uniformly distributed in space. (3) In the thick coating regime, for an isotropic coating, TAGwoods are not formed and coated CNPs will not aggregate but will be uniformly distributed in space. For anisotropic coating, TAGwoods can be formed and might form 1D strings but will not form DLCA/RLCA clusters. (4) The regimes are, approximately: thin coating, 0 &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; Δ &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 7.0 nm transition regime, 7.0 &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; Δ &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 9.2 nm and thick coating, Δ &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; 9.2 nm (5) The minimum minority TAG concentration required to undergo nano-phase separation is, approximately, 0.29% (thin coatings) and 0.94% (thick coatings). Minority components can have substantial effects upon aggregation for concentrations less than 1%.

Proceedings of the National Academy of Sciences, 1979

A lattice model has been developed to study the effects of intrinsic membrane proteins upon the t... more A lattice model has been developed to study the effects of intrinsic membrane proteins upon the thermodynamic properties of a lipid bilayer membrane. We assume that only nearest-neighbor van der Waals and steric interactions are important and that the polar group interactions can be represented by effective pressure—area terms. Phase diagrams, the temperature T 0 , which locates the gel—fluid melting, the transition enthalpy, and correlations were calculated by mean field and cluster approximations. Average lipid chain areas and chain areas when the lipid is in a given protein environment were obtained. Proteins that have a “smooth” homogeneous surface (“cholesterol-like”) and those that have inhomogeneous surfaces or that bind lipids specifically were considered. We find that T 0 can vary depending upon the interactions and that another peak can appear upon the shoulder of the main peak which reflects the melting of a eutectic mixture. The transition enthalpy decreases generally, a...

Physical Review Letters, 1974

Note that less divergent contributions which are of the type no h2g P~g-n (2l-r)n 7 n= & give ris... more Note that less divergent contributions which are of the type no h2g P~g-n (2l-r)n 7 n= & give rise to terms like Ih I'+".~T here is no apparent way to obtain a closed expression for A(t) in Eq. (8).

Journal of the American Oil Chemists' Society, 2002

The feasibility of using UV spectrophotometry to develop multivariate models for prediction of to... more The feasibility of using UV spectrophotometry to develop multivariate models for prediction of total phenolic acids content in crude polyphenol extracts from defatted canola and rapeseed meals was investigated. The polyphenols were extracted from the meals with methanol/acetone/water (7∶7∶6, by vol). Partial least squares regression was used to correlate the spectral data of the crude polyphenols in methanol between 320 and 355 nm with the total phenolic acid content in canola and rapeseed meals. The Folin‐Denis assay was used to provide reference data for creating the model. The predictive ability of the model is good, as indicated by the RPD value (the ratio of the SD of data to the standard error of calibration) of 3.84.

Canadian Journal of Physics, 1997

We introduce a novel interpretation of the sequence of commensurate lock-ins of the spiral wave v... more We introduce a novel interpretation of the sequence of commensurate lock-ins of the spiral wave vector, τ , observed in the helimagnetic phase of holmium in the presence of c-axis magnetic fields. This is the first successful model for the prediction of these lock-ins. We show that a model which combines a spin-slip model with an assumption concerning the spin structure along the c-axis in finite size "domains", yields excellent predictions when the energetics of this system with an applied c-axis magnetic field are considered.

The Journal of Chemical Physics, 2010

We investigated theoretically two competing published scenarios for the melting transition of the... more We investigated theoretically two competing published scenarios for the melting transition of the triglyceride trilaurin (TL): those of (1) Corkery et al. [Langmuir 23, 7241 (2007)], in which the average state of each TL molecule in the liquid phase is a discotic “Y” conformer whose three chains are dynamically twisted, with an average angle of ∼120° between them, and those of (2) Cebula et al. [J. Am. Oil Chem. Soc. 69, 130 (1992)], in which the liquid-state conformation of the TL molecule in the liquid phase is a nematic h∗-conformer whose three chains are in a modified “chair” conformation. We developed two competing models for the two scenarios, in which TL molecules are in a nematic compact-chair (or “h”) conformation, with extended, possibly all-trans, chains at low-temperatures, and in either a Y conformation or an h∗ conformation in the liquid state at temperatures higher than the phase-transition temperature, T∗=319 K. We defined an h-Y model as a realization of the proposa...

Molecules, 2020

It is proposed that “crystal memory”, observed in a discontinuous solid-liquid phase transition o... more It is proposed that “crystal memory”, observed in a discontinuous solid-liquid phase transition of saturated triacylglycerol (TAG) molecules, is due to the coexistence of solid TAG crystalline phases and a liquid TAG phase, in a superheated metastable regime. Such a coexistence has been detected. Solid crystals can act as heterogeneous nuclei onto which molecules can condense as the temperature is lowered. We outlined a mathematical model, with a single phase transition, that shows how the time-temperature observations can be explained, makes predictions, and relates them to recent experimental data. A modified Vogel-Fulcher-Tammann (VFT) equation is used to predict time-temperature relations for the observation of “crystal memory” and to show boundaries beyond which “crystal memory” is not observed. A plot of the lifetime of a metastable state versus temperature, using the modified VFT equation, agrees with recent time-temperature data. The model can be falsified through its predic...

Journal of Bacteriology, 1999

Atomic force microscopy was used to measure the thickness of air-dried, collapsed murein sacculi ... more Atomic force microscopy was used to measure the thickness of air-dried, collapsed murein sacculi from Escherichia coli K-12 and Pseudomonas aeruginosa PAO1. Air-dried sacculi from E. coli had a thickness of 3.0 nm, whereas those from P. aeruginosa were 1.5 nm thick. When rehydrated, the sacculi of both bacteria swelled to double their anhydrous thickness. Computer simulation of a section of a model single-layer peptidoglycan network in an aqueous solution with a Debye shielding length of 0.3 nm gave a mass distribution full width at half height of 2.4 nm, in essential agreement with these results. When E. coli sacculi were suspended over a narrow groove that had been etched into a silicon surface and the tip of the atomic force microscope used to depress and stretch the peptidoglycan, an elastic modulus of 2.5 × 10 7 N/m 2 was determined for hydrated sacculi; they were perfectly elastic, springing back to their original position when the tip was removed. Dried sacculi were more rigi...

European Biophysics Journal, 2015

All cell membranes are packed with proteins. The ability to investigate the regulatory mechanisms... more All cell membranes are packed with proteins. The ability to investigate the regulatory mechanisms of protein channels in experimental conditions mimicking their congested native environment is crucial for understanding the environmental physicochemical cues that may fundamentally contribute to their functionality in natural membranes. Here we report on investigations of the voltage-induced gating of lysenin channels in congested conditions experimentally achieved by increasing the number of channels inserted into planar lipid membranes. Typical electrophysiology measurements reveal congestion-induced changes to the voltage-induced gating, manifested as a significant reduction of the response to external voltage stimuli. Furthermore, we demonstrate a similar diminished voltage sensitivity for smaller populations of channels by reducing the amount of sphingomyelin in the membrane. Given lysenin's preference for targeting lipid rafts, this result indicates the potential role of the heterogeneous organization of the membrane in modulating channel functionality. Our work indicates that local congestion within membranes may alter the energy landscape and the kinetics of conformational changes of lysenin channels in response to voltage stimuli. This level of understanding may be extended to better characterize the role of the specific membrane environment in modulating the biological functionality of protein channels in health and disease.

Proceedings of the National Academy of Sciences, 2010

A model of the outer membrane of Gram-negative bacteria was created by the deposition of a monola... more A model of the outer membrane of Gram-negative bacteria was created by the deposition of a monolayer of purified rough mutant lipopolysaccharides at an air/water interface. The density profiles of monovalent (K + ) and divalent (Ca 2+ ) cations normal to the lipopolysaccharides (LPS) monolayers were investigated using grazing-incidence X-ray fluorescence. In the absence of Ca 2+ , a K + concentration peak was found in the negatively charged LPS headgroup region. With the addition of CaCl 2 , Ca 2+ ions almost completely displaced K + ions from the headgroup region. By integrating the experimentally reconstructed excess ion density profiles, we obtained an accurate measurement of the effective charge density of LPS monolayers. The experimental findings were compared to the results of Monte Carlo simulations based on a coarse-grained minimal model of LPS molecules and showed excellent agreement.