@article {4677, title = {Intermolecular potentials in liquid crystals: Comparison between simulations and NMR experiments}, journal = {International Journal of Modern Physics C}, volume = {10}, number = {2-3}, year = {1999}, note = {ISI Document Delivery No.: 222HPTimes Cited: 12Cited Reference Count: 21Meeting on Recent Developments in the Computer Simulations of Liquid CrystalsJUN 18, 1998ERICE, ITALY}, month = {May}, pages = {403-413}, type = {Proceedings Paper}, abstract = {The anisotropic intermolecular forces responsible for the orientational ordering in liquid crystals are probed by comparing Monte Carlo (MC) simulations with experimental nuclear magnetic resonance (NMR) results for solutes in nematic liquid crystals. In a special liquid crystal mixture where all long-range interactions are assumed to be minimized, the models for short-range interactions which best fit NMR experimental solute order parameters also best fit solute order parameters from MC simulations of hard ellipsoids. This is taken as an indication that in this special mixture the intermolecular potential is dominated by short-range forces. However, for liquid crystals where long-range interactions are important, simulations of hard ellipsoids with point quadrupoles cannot reproduce even the gross effects observed with experimental NMR data.}, keywords = {anisotropic intermolecular force, ELECTRIC-DIPOLE INTERACTIONS, interaction, liquid crystal, MOLECULES, Monte Carlo, MONTE-CARLO SIMULATIONS, NEMATIC SOLVENTS, nuclear magnetic resonance experiment, ORDER, ORIENTATIONAL, quadrupole interaction, SHAPE, SHORT-RANGE, SIMULATION, SIZE, SOLUTES}, isbn = {0129-1831}, url = {://000081779000007}, author = {Syvitski, R. T. and Polson, J. M. and Burnell, E. E.} } @article {4245, title = {Applications of collision dynamics in quadrupole mass spectrometry}, journal = {Journal of the American Society for Mass Spectrometry}, volume = {9}, number = {2}, year = {1998}, note = {ISI Document Delivery No.: YT841Times Cited: 50Cited Reference Count: 44}, month = {Feb}, pages = {101-113}, type = {Article}, abstract = {Some applications of collision dynamics in the field of quadrupole mass spectrometry are presented. Previous data on the collision induced dissociation of ions in triple quadrupole mass spectrometers is reviewed. A new method to calculate the internal energy distribution of activated ions directly from the increase in the cross section for dissociation with center of mass energy is presented. This method, although approximate, demonstrates explicitly the high efficiency of transfer of translational to internal energy of organic ions. It is argued that at eV center of mass energies, collisions between protein ions and neutrals such as Ar are expected to be highly inelastic. The discovery and application of collisional cooling in radio frequency quadrupoles is reviewed. Some previously unpresented data on fragment ion energies in triple quadrupole tandem mass spectrometry are shown that demonstrate directly the loss of kinetic energy of fragment ions in the cooling process. The development of the energy loss method to measure collision cross sections of protein ions in triple quadrupole instruments is reviewed along with a new discussion of the effects of inelastic collisions in these experiments and related ion mobility experiments. (C) 1998 American Society for Mass Spectrometry.}, keywords = {ACTIVATION, BOND-ENERGIES, GAS-PHASE, INDUCED DISSOCIATION, ION FRAGMENTATION, IONS, MECHANISM, MOLECULES, POLYATOMIC, SIZE, TRIPLE QUADRUPOLE}, isbn = {1044-0305}, url = {://000071650400001}, author = {Douglas, D. J.} } @article {4210, title = {Inhibition of liposome-induced complement activation by incorporated poly(ethylene glycol) lipids}, journal = {Archives of Biochemistry and Biophysics}, volume = {357}, number = {2}, year = {1998}, note = {ISI Document Delivery No.: 119UCTimes Cited: 65Cited Reference Count: 50}, month = {Sep}, pages = {185-194}, type = {Article}, abstract = {Complement activation causes opsonization of foreign particles leading to particle elimination from the blood. Complement-mediated opsonization of charged and large liposomes presents a fundamental problem in their use to deliver therapeutic agents in vivo. To prolong the circulation half-lives of such liposomes, complement activation must be curtailed. The aim of this study was to assess the ability of poly(ethylene glycol)-lipids (PEG-lipids) to inhibit the in vitro activation of the classical pathway of complement in human serum by anionic liposomes. Incorporation of cholesterol-PEG(600) (CH-PEG(600)), cholesterol-PEG(1000) (CH-PEG(1000)), or phosphatidylethanolamine-PEG(2000) (PE-PEG(2000)) resulted in dose-dependent inhibition of Clq binding and complement activation. The dose of PEG-lipid at which complement activation was blocked was inversely related to the PEG chain length. Complement activation was strongly inhibited when 15 mole\% of CH-PEG(600), 10 mole\% CH-PEG(1000), or 5 mole\% PE-PEG(2000), was incorporated into 100-nm anionic liposomes. PEG-lipid incorporation into larger liposomes (240 nm) was also successful in blocking C1q binding and complement activation. Radiolabeled cholesterol-PEG(similar to 1400) was prepared and used to determine both the percentage of CH-PEG incorporated into the liposomes and the percentage maintained in the liposomes in the presence of 50\% human serum at 37 degrees C for up to 24 h. (C) 1998 Academic Press.}, keywords = {C1q, CHOLESTEROL, CLEARANCE, complement activation, HEPATIC-UPTAKE, INVIVO, LARGE UNILAMELLAR VESICLES, LIPOSOMES, POLY(ETHYLENE GLYCOL), POLYETHYLENE-GLYCOL, PROLONGED CIRCULATION TIME, SERUM, SIZE, SURFACE-CHARGE}, isbn = {0003-9861}, url = {://000075915200002}, author = {Bradley, A. J. and Devine, D. V. and Ansell, S. M. and Janzen, J. and Brooks, D. E.} } @article {3801, title = {Monte Carlo simulations of orientational ordering of solutes in a nematic solvent: Comparison with mean-field models}, journal = {Molecular Physics}, volume = {88}, number = {3}, year = {1996}, note = {ISI Document Delivery No.: UT951Times Cited: 16Cited Reference Count: 23}, month = {Jun}, pages = {767-782}, type = {Article}, abstract = {Monte Carlo simulations were used to study orientational ordering of solutes in a nematic phase. Nematogens were modelled as hard prolate ellipsoids with an axis ratio of 5:1. Solutes were also modelled as hard prolate ellipsoids, with a variety of sizes and shape anisotropies. Solute order parameters and singlet orientational distribution functions were analysed using several mean-field models. The results confirm that these empirical mean-field potentials are closely linked to the anisotropic short-range repulsive forces that are crucial for the formation of the nematic phase.}, keywords = {ANISOTROPIC SYSTEMS, COMPUTER-SIMULATION, ELECTRIC-DIPOLE INTERACTIONS, LIQUID-CRYSTALS, MOLECULES, NEMATOGEN, PHASE, POTENTIALS, SIZE}, isbn = {0026-8976}, url = {://A1996UT95100015}, author = {Polson, J. M. and Burnell, E. E.} } @article {3270, title = {AN ORIENTATIONAL STUDY OF SMALL SOLUTES IN ZERO ELECTRIC-FIELD GRADIENT NEMATIC LIQUID-CRYSTAL MIXTURES}, journal = {Journal of Physical Chemistry}, volume = {99}, number = {18}, year = {1995}, note = {ISI Document Delivery No.: QW705Times Cited: 2Cited Reference Count: 32}, month = {May}, pages = {7054-7059}, type = {Article}, abstract = {The solutes m-dichlorobenzene, o-dichlorobenzene. p-dichlorobenzene, o-dicyanzene, furan, tetrathiofulvalene, and fluorobenzene are studied in the zero electric field gradient mixtures 56.5 wt \% 1132/EBBA and 70 wt \% 5CB/EBBA using proton NMR. The two second-rank-order parameters obtained for each solute from analysis of the NMR spectra indicate that the solutes experience a similar anisotropic potential in both mixtures. The results are interpreted in terms of two models for the short-range anisotropic potential experienced by the solutes.}, keywords = {ALKYL CHAINS, BEHAVIOR, DIPOLE INTERACTIONS, MEAN TORQUE, MOLECULES, PHASE, POTENTIALS, SHAPE, SIZE, SOLVENTS}, isbn = {0022-3654}, url = {://A1995QW70500043}, author = {Chandrakumar, T. and Smith, L. and Burnell, E. E.} } @article {2945, title = {ANISOTROPIC SHORT-RANGE POTENTIALS FOR SOLUTES IN NEMATIC LIQUID-CRYSTALS}, journal = {Molecular Physics}, volume = {78}, number = {3}, year = {1993}, note = {ISI Document Delivery No.: KQ355Times Cited: 35Cited Reference Count: 12}, month = {Feb}, pages = {687-702}, type = {Article}, abstract = {Recently, it has been suggested that the orientational order of solutes dissolved in nematic liquid crystals results from short range forces which depend on the size and shape of the solute molecule and from the interaction between the molecular quadrupole moment and the average electric field gradient experienced by the molecule. In this paper, we model the size and shape-dependent short range potential by assuming that the contribution to the potential from each surface element of a cavity representing the molecule depends on the orientation of the surface element with respect to the director. We have tried a variety of potentials based on this assumption, and we report here the ones which yielded the best agreement between theory and experiment. One of the potentials is obtained by integrating, along the director, the circumference of a slice cut through the molecule perpendicular to the director; better fits are obtained by adding a term which depends on a Hooke{\textquoteright}s law elastic distortion of the liquid crystal solvent. Another potential depends on the surface area of a cavity formed from the projections onto a plane perpendicular to the director and onto walls parallel to it. These models are used to fit the experimental order parameters of a collection of 46 molecules dissolved in a special mixture where the ordering is dominated by the size and shape potential. We attribute the superior quality of the resulting fits to the fact that these potentials depend in a more sensitive manner on the details of the geometry of the molecules than previously used ones.}, keywords = {orientational order, SIZE}, isbn = {0026-8976}, url = {://A1993KQ35500011}, author = {Zimmerman, D. S. and Burnell, E. E.} } @article {2920, title = {THE ORIENTATION OF MOLECULES WITH INTERNAL-ROTATION IN NEMATIC PHASES}, journal = {Molecular Physics}, volume = {80}, number = {1}, year = {1993}, note = {ISI Document Delivery No.: LW723Times Cited: 10Cited Reference Count: 33}, month = {Sep}, pages = {177-189}, type = {Article}, abstract = {The anisotropic couplings obtained from the H-1 nuclear magnetic resonance (NMR) spectra of partially oriented molecules with internal rotation are difficult to analyse because the order parameters for each conformer cannot be deduced without assumptions. The purpose of this paper is to show how a model for the anisotropic short-range potential can be useful in the interpretation of the high-resolution H-1 NMR spectra of the flexible molecules furfural, 2-chlorobenzaldehyde, and 2,2{\textquoteright}-dithiophene dissolved in a 55\% Merck ZLI 1132-45\% N-(p-ethoxybenzylidene)-2,6-dideutero-p{\textquoteright}-n-butylaniline (w/w) mixture. In this nematic mixture there is no contribution to the anisotropic potential from the interaction between the solute molecular quadrupole moment and the average electric field gradient of the liquid crystal solvent; the dominant anisotropic intermolecular potential in this mixture is taken to result solely from short-range interactions. We find good agreement between experiment and the order parameters calculated by the model of short-range interactions. The ratios of order parameters for the s-cis and s-trans conformers predicted by the model are used to calculate the statistical weights of the s-trans conformation for the solutes: at 304 K, p(trans)(furfural) = 0.45 +/- 0.02, p(trans)(2-chlorobenzaldehyde) = 0.901 +/- 0.006 and p(trans)(2,2{\textquoteright}-dithiophene) = 0.6094 +/- 0.0008.}, keywords = {BARRIER, CONFORMATION, LIQUID-CRYSTALS, ORDER, SIZE, SOLUTES}, isbn = {0026-8976}, url = {://A1993LW72300013}, author = {ter Beek, L. C. and Zimmerman, D. S. and Burnell, E. E.} } @article {2860, title = {ORIENTATIONAL ORDER OF PLANAR SOLUTES IN A ZERO AVERAGE ELECTRIC-FIELD GRADIENT NEMATIC ENVIRONMENT}, journal = {Molecular Physics}, volume = {78}, number = {3}, year = {1993}, note = {ISI Document Delivery No.: KQ355Times Cited: 6Cited Reference Count: 31}, month = {Feb}, pages = {673-685}, type = {Article}, abstract = {The order matrices for 19 dihalobenzenes of C(s) and C2v symmetry have been measured using the NMR spectra of these molecules as solutes in the nematic mixture of 55 wt\% Merck ZLI-1132 and 45 wt\% N-(4-ethoxybenzylidene)-2,6-dideutero-4{\textquoteright}-n-butylaniline. In this liquid crystal, the contribution to the orientational potential from the interaction between the molecular quadrupole moment and the mean electric field gradient of the liquid crystal can be neglected. The results are compared with predictions of a model which describes the anisotropic intermolecular potential in terms of (1) an elastic distortion of the liquid crystal and (2) an anisotropic surface interaction between solute and liquid crystal. Not only are the largest (in magnitude) order parameters very well fitted, but also the calculated anisotropies in the order matrices agree with the experimental ones. It is demonstrated that the results cannot be fitted with a bond-additive approach.}, keywords = {HYDROGEN, LIQUID-CRYSTALS, NMR, SIZE}, isbn = {0026-8976}, url = {://A1993KQ35500010}, author = {Li, K. Y. Z. and Zimmerman, D. S. and Burnell, E. E.} } @article {2714, title = {ZERO ELECTRIC-FIELD GRADIENT MIXTURES FOR THE ELUCIDATION OF ORIENTATIONAL MECHANISMS}, journal = {Liquid Crystals}, volume = {13}, number = {3}, year = {1993}, note = {ISI Document Delivery No.: KX191Times Cited: 22Cited Reference Count: 28}, month = {Mar}, pages = {319-343}, type = {Article}, abstract = {A novel zero electric field gradient nematic liquid crystal made up from two nematic liquid crystal components is employed as a solvent for a series of molecules ranging from small molecules to mesogens themselves. Nuclear magnetic resonance is used to determine the degree of order of the solute and solvent molecules. Results are compared to those obtained for two completely different zero electric field gradient nematic mixtures. The comparison strongly indicates that for a variety of molecules largely differing in size, shape and flexibility their degree of order can be described by a single orientation mechanism. This mechanism can be adequately modelled by a simple phenomenological mean field model based on the size and shape anisotropy of the dissolved species. The use of zero electric field gradient mixtures in combination with this mean field model allows the prediction of solute order parameters at approximately the 10 per cent level.}, keywords = {ANISOTROPIC ENVIRONMENTS, METHANES, MOLECULES, NEMATIC LIQUID-CRYSTALS, NMR, ORDER, SIZE, SOLUTES, SOLVENTS}, isbn = {0267-8292}, url = {://A1993KX19100001}, author = {Barnhoorn, J. B. S. and de Lange, C. A. and Burnell, E. E.} } @article {7119, title = {THE CONFORMATION OF 2,2{\textquoteright}-DITHIOPHENE IN NEMATIC SOLVENTS DETERMINED BY H-1-NMR}, journal = {Molecular Physics}, volume = {74}, number = {5}, year = {1991}, note = {ISI Document Delivery No.: GY085Times Cited: 24Cited Reference Count: 26}, month = {Dec}, pages = {1027-1035}, type = {Article}, abstract = {In this paper we report a determination of the structure 2,2{\textquoteright}-dithiophene dissolved in different nematic liquid crystal solvents. The H-1-NMR spectra of this molecule dissolved in a 55\% Merck ZLI 1132/45\% N-(4-ethoxybenzylidene)-4{\textquoteright}-n-butylaniline (w/w) mixture are recorded at 300 and 304 K and are analysed. The dipolar coupling constants obtained are used to show that the solute molecule exists in both the s-cis and the s-trans conformations. The s-trans conformer is planar and the absolute value of the dihedral angle-PHI between the two thiophene ring planes for the s-cis conformer is found to be (24 +/- 1)degrees. Using the same method of analysis we reinterpreted two additional independent sets of published dipolar coupling constants from H-1-NMR spectra of 2,2{\textquoteright}-dithiophene dissolved in Merck Phase IV at room temperature and in 80\% N-(4-ethoxybenzylidene)-4{\textquoteright}-n-butylaniline/20\% O-carbobutoxy-4-oxybenzoic acid ethoxy phenyl ester at 301 K. These additional studies yield the same results for the structure of 2,2{\textquoteright}-dithiophene. We also estimate that in each of the three nematic solvents (61 +/- 3)\% of the solute 2,2{\textquoteright}-dithiophene exists in the s-trans state.}, keywords = {2, 2{\textquoteright}-BITHIENYL, BARRIER, LIQUID-CRYSTALS, MOLECULES, orientational order, PHASE, SIZE, SOLUTES}, isbn = {0026-8976}, url = {://A1991GY08500007}, author = {ter Beek, L. C. and Zimmerman, D. S. and Burnell, E. E.} }