Thermodynamics Research Today is a free monthly online journal that collates and summarizes the latest research about Thermodynamics, including details on enthalpy, entropy, energy transitions. | ||||||
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Contact Mechanics of Nanometer-Scale Molecular Contacts: Correlation between Adhesion, Friction, and Hydrogen Bond Thermodynamics.Busuttil K, Geoghegan M, Hunter CA, Leggett GJ Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, U.K. Using a scanning force microscope, adhesion forces have been measured between carboxylic acid terminated self-assembled monolayers in different nonpolar solvents or in two-component liquid mixtures consisting of a polar solvent (ethyl acetate or acetone) in heptane. The adhesion forces measured in pure acetone and ethyl acetate were small (0.24 nN) but increased logarithmically as the concentration of the polar solvent decreased to reach a maximum value (2.77 nN), equal to that measured in pure heptane, and for lower concentrations of polar solvent, the adhesion force remained constant. This behavior is identical to that observed for association constants measured for the formation of 1:1 H-bonded complexes between dilute solutes in solvent mixtures. The transition between the solvent-dependent and -independent regimes occurs at a polar solvent concentration corresponding to 1/K(S), where K(S) is the equilibrium constant for solvation of a carboxylic acid by the polar solvent in heptane. A simple model, in which the solvation of the carboxylic acid groups may be estimated by considering the concentration and polarity of functional groups in the liquid, accurately predicts values of K(S) that were found to correlate very well with the observed solvent-dependence of the adhesion force. Friction-load relationships were measured using friction-force microscopy. In pure acetone and ethyl acetate, a linear friction-load relationship was observed, in agreement with Amontons' law. However, as the concentration of polar solvent was reduced, a nonlinear relationship was observed and the friction-load relationship was found to fit the Derjaguin-Müller-Toporov (DMT) model for single asperity contacts. For pure heptane and a range of other nonpolar liquids with identical dielectric constants, the friction-load relationship was described by DMT mechanics. Exceptionally, for perfluorodecalin, Johnson-Kendall-Roberts mechanics was observed. These observations may be rationalized by treating the friction force as the sum of load-dependent and shear contributions. Under conditions of low adhesion, where the carboxylic acid surface is solvated by polar solvent molecules, the shear term is negligible and the sliding interaction is dominated by load-dependent friction. As the degree of solvation of the carboxylic acid groups decreases and the adhesion force increases, the shear friction contribution increases, dominating the interaction for media in which the adhesion force is greater than ca. 0.6 nN. Published 12 May 2011 in J Am Chem Soc. Articles on Thermodynamics published 12 May 2011: Thermodynamic Analysis for the Controllability of Elements in the Recycling Process of Metals. Environ Sci Technol. This study presents the results of chemical thermodynamic analysis on the distribution of elements in the smelting process of metallic materials to examine the controllability of impurities in the pyrometallurgical technique. The results of the present work can give an answer against the frequently given question; "Which impurity element can be removable in metallurgical process?" or "How far can the impurity level be controlled?". The proposed method was applied to estimate ... [Abstract] [Full-text] Guanylate cyclase activating protein-2 (GCAP-2) is a Ca(2+) -binding protein of the neuronal calcium sensor (NCS) family. Ca(2+) -free GCAP-2 activates the retinal rod outer segment guanylate cyclases ROS-GC1 and 2. Native GCAP-2 is N-terminally myristoylated. Detailed structural information on the Ca(2+) -dependent conformational switch of GCAP-2 is missing so far, as no atomic resolution structures of the Ca(2+) -free state have been determined. The role of the myristoyl moiety remains poorly ... [Abstract] [Full-text] Effect of Dipole Functionalization on the Thermodynamics and Dynamics of Discotic Liquid Crystals. J Phys Chem B, 115(19): 5807-5814. The effect of dipole substitution on the self-assembly, thermodynamics, and dynamics has been studied in a series of hexa-peri-hexabenzocoronenes (HBCs). The HBCs bear the same number and type of aliphatic chains, but different dipoles directly attached to the cores ranging from ∼0 to ∼3.4 D. Dipole substitution alters the energetics and reduces the transition temperature favoring the columnar hexagonal liquid crystalline phase at the expense of the crystalline phase. The equation of state ... [Abstract] [Full-text] Hydration thermodynamics using the reference interaction site model: speed or accuracy? J Phys Chem B, 115(19): 6011-22. We report a method to dramatically improve the accuracy of hydration free energies (HFE) calculated by the 1D and 3D reference interaction site models (RISM) of molecular integral equation theory. It is shown that the errors in HFEs calculated by RISM approaches using the Gaussian fluctuations (GF) free energy functional are not random, but can be decomposed into linear combination of contributions from different structural elements of molecules (number of double bonds, number of OH groups, ... [Abstract] [Full-text] Articles on Thermodynamics published 11 May 2011: Ezrin mRNA target site selection for DNAzymes using secondary structure and hybridization thermodynamics. Tumour Biol. Ezrin, a membrane organizer and linker between plasma membrane and cytoskeleton, is well documented to play an important role in the metastatic capacity of cancer cells especially for osteosarcoma cells. It has provided an ideal target for cancer gene therapy. RNA-cleaving 10-23 DNAzymes, consisting of a 15-nucleotide catalytical domain flanked by two target-specific complementary arms, can cleave the target mRNA at purine-pyrimidine dinucleotide effectively. In the present study, we designed ... [Abstract] [Full-text] Thermodynamics of membrane protein folding measured by fluorescence spectroscopy. J Vis Exp. Membrane protein folding is an emerging topic with both fundamental and health-related significance. The abundance of membrane proteins in cells underlies the need for comprehensive study of the folding of this ubiquitous family of proteins. Additionally, advances in our ability to characterize diseases associated with misfolded proteins have motivated significant experimental and theoretical efforts in the field of protein folding. Rapid progress in this important field is unfortunately ... [Abstract] [Full-text] Thermodynamic Stabilization of Hydrous Ferric Oxide by Adsorption of Phosphate and Arsenate. Environ Sci Technol. Hydrous ferric oxide (HFO) is an X-ray amorphous compound with a high affinity for anions under strongly or mildly acidic conditions. Because of the usually small particle size of HFO, the adsorption capacity is high and adsorption may significantly impact the thermodynamic properties of such materials. Here we show that adsorption of phosphate and arsenate stabilizes HFO by experimental determination of enthalpies of formation (by acid-solution calorimetry) and estimates of standard entropies ... [Abstract] [Full-text] Articles on Thermodynamics published 10 May 2011: DNA Interstrand Cross-Links of an Antitumor Trinuclear Platinum(II) Complex: Thermodynamic Analysis and Chemical Probing. Chem Asian J. The trinuclear platinum compound [{trans-PtCl(NH(3) )(2) }(2) (μ-trans-Pt(NH(3) )(2) {NH(2) (CH(2) )(6) NH(2) }(2) )](4+) (BBR3464) belongs to the polynuclear class of platinum-based anticancer agents. These agents form in DNA long-range (Pt,Pt) interstrand cross-links, whose role in the antitumor effects of BBR3464 predominates. Our results show for the first time that the interstrand cross-links formed by BBR3464 between two guanine bases in opposite strands separated by two base pairs ... [Abstract] [Full-text] © 2005-2011 Thermodynamics Research Today. All Rights Reserved. |
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