Physical Sciences and Mathematics Commons^™

Cosmological Constant As Confining U(1) Charge In Two-Dimensional Dilaton Gravity, Daniel Grumiller, Robert Mcnees, Jakob Salzer

Robert A McNees IV

The cosmological constant is treated as a thermodynamical parameter in the framework of two-dimensional dilaton gravity. We find that the cosmological constant behaves as a U(1) charge with a confining potential, and that such potentials require a novel Born-Infeld boundary term in the action. The free energy and other thermodynamical quantities of interest are derived, from first principles, in a way that is essentially model independent. We discover that there is always a Schottky anomaly in the specific heat and explain its physical origin. Finally, we apply these results to specific examples, like anti-de Sitter–Schwarzschild–Tangherlini black holes, Bañados-Teitelboim-Zanelli black holes …

Nanomolar Binding Of Peptides Containing Noncanonical Amino Acids By A Synthetic Receptor, Leigh Logsdon, Christopher Schardon, Vijayakumar Ramalingam, Sharon Kwee, Adam Urbach

Adam R Urbach

This paper describes the molecular recognition of phenylalanine derivatives and their peptides by the synthetic receptor cucurbit[7]uril (Q7). The 4-tert-butyl and 4-aminomethyl derivatives of phenylalanine (tBuPhe and AMPhe) were identified from a screen to have 20–30-fold higher affinity than phenylalanine for Q7. Placement of these residues at the N-terminus of model tripeptides (X-Gly-Gly), resulted in no change in affinity for tBuPhe-Gly-Gly, but a remarkable 500-fold increase in affinity for AMPhe-Gly-Gly, which bound to Q7 with an equilibrium dissociation constant (Kd) value of 0.95 nM in neutral phosphate buffer. Structure–activity studies revealed that three functional groups work in a positively cooperative …

Nature Of PtN/Tio2 (110) Interface Under Water-Gas Shift Reaction Conditions: A Constrained Ab Initio Thermodynamics Study, Salai Ammal, Andreas Heyden

Salai C. Ammal

No abstract provided.

The Aminopeptidase From Aeromonas Proteolytica Can Function As An Esterase, David Bienvenue, Rebecca Matthew, Dagmar Ringe, Richard Holz

Richard C. Holz

The aminopeptidase from Aeromonas proteolytica (AAP) can catalyze the hydrolysis of L-leucine ethyl ester (L-Leu-OEt) with a rate of 96±5 s–1 and a K m of 700 µM. The observed turnover number for L-Leu-OEt hydrolysis by AAP is similar to that observed for peptide hydrolysis, which is 67±5 s–1. The k cat values for the hydrolysis of L-Leu-OEt and L-leucine-p-nitroanilide (L-pNA) catalyzed by AAP were determined at different pH values under saturating substrate concentrations. Construction of an Arrhenius plot from the temperature dependence of AAP-catalyzed ester hydrolysis indicates that the rate-limiting step does not change as a function of temperature …

Benchmark Structures And Binding Energies Of Small Water Clusters With Anharmonicity Corrections, Berhane Temelso, Kaye A. Archer, George C. Shields

Berhane Temelso

For (H2O)n where n = 1–10, we used a scheme combining molecular dynamics sampling with high level ab initio calculations to locate the global and many low lying local minima for each cluster. For each isomer, we extrapolated the RI-MP2 energies to their complete basis set limit, included a CCSD(T) correction using a smaller basis set and added finite temperature corrections within the rigid-rotor-harmonic-oscillator (RRHO) model using scaled and unscaled harmonic vibrational frequencies. The vibrational scaling factors were determined specifically for water clusters by comparing harmonic frequencies with VPT2 fundamental frequencies. We find the CCSD(T) correction to the RI-MP2 binding …

Computational Study Of The Hydration Of Sulfuric Acid Dimers: Implications For Acid Dissociation And Aerosol Formation, Berhane Temelso, Thuong Ngoc Phan, George C. Shields

Berhane Temelso

We have investigated the thermodynamics of sulfuric acid dimer hydration using ab initio quantum mechanical methods. For (H2SO4)2(H2O)n where n = 0−6, we employed high-level ab initio calculations to locate the most stable minima for each cluster size. The results presented herein yield a detailed understanding of the first deprotonation of sulfuric acid as a function of temperature for a system consisting of two sulfuric acid molecules and up to six waters. At 0 K, a cluster of two sulfuric acid molecules and one water remains undissociated. Addition of a second water begins the deprotonation of the first sulfuric acid …

The Role Of Anharmonicity In Hydrogen-Bonded Systems: The Case Of Water Clusters, Berhane Temelso, George Shields

Berhane Temelso

The nature of vibrational anharmonicity has been examined for the case of small water clusters using second-order vibrational perturbation theory (VPT2) applied on second-order Møller–Plesset perturbation theory (MP2) potential energy surfaces. Using a training set of 16 water clusters (H2O)n=2–6,8,9 with a total of 723 vibrational modes, we determined scaling factors that map the harmonic frequencies onto anharmonic ones. The intermolecular modes were found to be substantially more anharmonic than intramolecular bending and stretching modes. Due to the varying levels of anharmonicity of the intermolecular and intramolecular modes, different frequency scaling factors for each region were necessary to achieve the …

Thermodynamic And Structural Characterization Of Amino Acid-Linked Dialkyl Lipids., Stephanie Tristram-Nagle, Ruthven Lewis, Joseph Blickenstaff, Michael Diprima, Bruno Marques, Ronald Mcelhaney, John Nagle, James Schneider

Prof. Stephanie Tristram-Nagle Ph.D.

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 …

Hiv Fusion Peptide Penetrates, Disorders, And Softens T-Cell Membrane Mimics., Stephanie Tristram-Nagle, Rob Chan, Edgar Kooijman, Pradeep Uppamoochikkal, Wei Qiang, David Weliky, Pradeep Uppamoochikkal

Prof. Stephanie Tristram-Nagle Ph.D.

This work investigates the interaction of N-terminal gp41 fusion peptide (FP) of human immunodeficiency virus type 1 (HIV-1) with model membranes in order to elucidate how FP leads to fusion of HIV and T-cell membranes. FP constructs were (i) wild-type FP23 (23 N-terminal amino acids of gp41), (ii) water-soluble monomeric FP that adds six lysines on the C-terminus of FP23 (FPwsm), and (iii) the C-terminus covalently linked trimeric version (FPtri) of FPwsm. Model membranes were (i) LM3 (a T-cell mimic), (ii) 1,2-dioleoyl-sn-glycero-3-phosphocholine, (iii) 1,2-dioleoyl-sn-glycero-3-phosphocholine/30 mol% cholesterol, (iv) 1,2-dierucoyl-sn-glycero-3-phosphocholine, and (v) 1,2-dierucoyl-sn-glycero-3-phosphocholine/30 mol% cholesterol. Diffuse synchrotron low-angle x-ray scattering from fully …

Lipid Bilayers: Thermodynamics, Structure, Fluctuations, And Interactions., Stephanie Tristram-Nagle, John Nagle

Prof. Stephanie Tristram-Nagle Ph.D.

This article, adapted from our acceptance speech of the Avanti Award in Lipids at the 47th Biophysical Society meeting in San Antonio, 2003, summarizes over 30 years of research in the area of lipid bilayers. Beginning with a theoretical model of the phase transition (J.F.N.), we have proceeded experimentally using dilatometry and density centrifugation to study volume, differential scanning calorimetry to study heat capacity, and X-ray scattering techniques to study structure of lipid bilayers as a function of temperature. Electron density profiles of the gel and ripple phases have been obtained as well as profiles from several fluid phase lipids, …

Polymorphism In Myristoylpalmitoylphosphatidylcholine., Stephanie Tristram-Nagle, Yisrael Isaacson, Yulia Lyatskaya, Yufeng Liu, Kay Brummond, John Katsaras, John Nagle

Prof. Stephanie Tristram-Nagle Ph.D.

This study focuses on the mixed-chain lipid myristoylpalmitoylphosphatidylcholine (MPPC) near full hydration. The lipid, synthesized according to the procedure of (Mason et al., 1981a, has a low degree of acyl chain migration. When MPPC is temperature-jumped (T-jumped) from the L alpha phase (T = 38 degrees C) to T = 20 degrees C or below, a subgel phase forms; this formation takes less than 1 h at a temperature below T = 12 degrees C. The subgel remains stable up to T = 29 degrees C. When MPPC is T-jumped from the L alpha phase to T = 24 degrees …

Polyunsaturated Docosahexaenoic Vs Docosapentaenoic Acid-Differences In Lipid Matrix Properties From The Loss Of One Double Bond., Nadukkudy Eldho, Scott Feller, Stephanie Tristram-Nagle, Ivan Polozov, Klaus Gawrisch

Prof. Stephanie Tristram-Nagle Ph.D.

Insufficient supply to the developing brain of docosahexaenoic acid (22:6n3, DHA), or its omega-3 fatty acid precursors, results in replacement of DHA with docosapentaenoic acid (22:5n6, DPA), an omega-6 fatty acid that is lacking a double bond near the chain's methyl end. We investigated membranes of 1-stearoyl(d(35))-2-docosahexaenoyl-sn-glycero-3-phosphocholine and 1-stearoyl(d(35))-2-docosapentaenoyl-sn-glycero-3-phosphocholine by solid-state NMR, X-ray diffraction, and molecular dynamics simulations to determine if the loss of this double bond alters membrane physical properties. The low order parameters of polyunsaturated chains and the NMR relaxation data indicate that both DHA and DPA undergo rapid conformational transitions with correlation times of the order of …

Physicochemical Study Of Spiropyran-Terthiophene Derivatives: Photochemistry And Thermodynamics, Michele Zanoni, Simon Coleman, Kevin J. Fraser, Robert P. Byrne, Klaudia K. Wagner, Sanjeev Gambhir, David L. Officer, Gordon G. Wallace, D Diamond

Gordon Wallace

The photochemistry and thermodynamics of two terthiophene (TTh) derivatives bearing benzospiropyran (BSP) moieties, 1-(3,3''-dimethylindoline-6'-nitrobenzospiropyranyl)-2-ethyl 4,4''-didecyloxy-2,2':5',2''-terthiophene-30-acetate (BSP-2) and 1-(3,3''-dimethylindoline-6'- nitrobenzospiropyranyl)-2-ethyl 4,4''-didecyloxy-2,2':5',2''-terthiophene-30-carboxylate (BSP-3), differing only by a single methylene spacer unit, have been studied. The kinetics of photogeneration of the equivalent merocyanine (MC) isomers (MC-2 and MC-3, respectively), the isomerisation properties of MC-2 and MC-3, and the thermodynamic parameters have been studied in acetonitrile, and compared to the parent, non-TTh-functionalised, benzospiropyran derivative, BSP-1. Despite the close structural similarity of BSP-2 and BSP-3, their physicochemical properties were found to differ significantly; examples include activation energies (Ea(MC-2) = 75.05 kJ mol-1, Ea(MC-3) = 100.39 …

Thermodynamics Of A Free Q Fermion Gas, Asim Gangopadhyaya

Asim Gangopadhyaya