Representations of molecular force fields. IV. Vibrational stress, isotope effects, and structure of ethane

The transformation of molecular force fields from natural curvilinear coordinates S to rectilinear coordinates S (yielding simpler equations of motion) is discussed. Rectilinear cubic constants include mass dependent terms arising from the nonlinear coordinate transformation as well as contributions from the cubic constants for the S displacements. These contributors to anharmonicity lead to intramolecular ’’vibrational stresses’’ resolvable into components FC, FT, and FF which induce rectilinear molecular strain components 〈S〉C, 〈S〉T, and 〈S〉F, each of which has its own physical interpretation. More significant than the rectilinear quantities are the curvilinear stresses and strains which, it is shown, are readily expressed in terms of the above components. Each of the foregoing quantities is easily decomposed into contributions from the various types of vibration. Magnitudes are illustrated by computations of cubic force constants and selected stress and strain components in C2H6 and C2D6.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70860/2/JCPSA6-67-9-4168-1.pd

Representations of molecular force fields. I. Ethane: Ab initio and model, harmonic and anharmonic

The quadratic and selected cubic force constants for ethane have been computed, using single determinant molecular orbital wavefunctions at the 4‐31G level, with a view to testing and extending model consistent force fields (CFF) for ’’molecular mechanics’’ calculations. Results agree semiquantitatively with experiment, but experimental force constants of sufficient reliability to provide a definitive comparison are not yet available. In a comparison with the most rational general CFF available, that of Ermer and Lifson, the most significant discrepancies found to occur are those for certain stretch–bend couplings assumed to be zero in the CFF but shown to be appreciable by quantum calculation. It is observed that these couplings, but not the stretch–stretch couplings, are well accounted for by a steric interaction model. The ab initio cubic constants examined display the same pattern of conformity with a steric model. Bend–bend–bend and bend–bend–stretch but not all stretch–stretch–stretch interactions agree with those of the steric model. The partial success of the steric model shows that it is possible to represent a large number of interaction constants, quadratic and higher order, by a small number of parameters in molecular mechanics. The failure of the steric model to account for predominantly stretching interactions confirms that ’’classical’’ nonbonded interactions as embodied in conventional Urey–Bradley fields are not the only major contributors to off‐diagonal force constants. An alternative model, the anharmonic model of Warshel, as modified by Kirtman et al., was found to account well for pure stretches but not for bends or stretch–bend interactions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70643/2/JCPSA6-63-11-4750-1.pd

Leisure, refuge and solidarity:messages in visitors’ books as microforms of travel writing

Visitors’ books not only trace developments in modern tourism, but they also reveal changes in the socio-cultural and language attitudes of travellers from all walks of life over prolonged periods of time. This article investigates messages in visitors’ books from Wales from the mid-nineteenth century up to the present and argues for their recognition as microforms of travel writing. Despite their brevity, entries in visitors’ books are a highly complex form of travel writing particularly in the inscribers’ self-fashioning of identity for future readers. The article examines how writerly choices are not only directly rooted in the discourse of travel, but also in socio-political circumstances in the individual travellers’ countries of origin and their travel destinations

Aptamer-based multiplexed proteomic technology for biomarker discovery

Interrogation of the human proteome in a highly multiplexed and efficient manner remains a coveted and challenging goal in biology. We present a new aptamer-based proteomic technology for biomarker discovery capable of simultaneously measuring thousands of proteins from small sample volumes (15 [mu]L of serum or plasma). Our current assay allows us to measure ~800 proteins with very low limits of detection (1 pM average), 7 logs of overall dynamic range, and 5% average coefficient of variation. This technology is enabled by a new generation of aptamers that contain chemically modified nucleotides, which greatly expand the physicochemical diversity of the large randomized nucleic acid libraries from which the aptamers are selected. Proteins in complex matrices such as plasma are measured with a process that transforms a signature of protein concentrations into a corresponding DNA aptamer concentration signature, which is then quantified with a DNA microarray. In essence, our assay takes advantage of the dual nature of aptamers as both folded binding entities with defined shapes and unique sequences recognizable by specific hybridization probes. To demonstrate the utility of our proteomics biomarker discovery technology, we applied it to a clinical study of chronic kidney disease (CKD). We identified two well known CKD biomarkers as well as an additional 58 potential CKD biomarkers. These results demonstrate the potential utility of our technology to discover unique protein signatures characteristic of various disease states. More generally, we describe a versatile and powerful tool that allows large-scale comparison of proteome profiles among discrete populations. This unbiased and highly multiplexed search engine will enable the discovery of novel biomarkers in a manner that is unencumbered by our incomplete knowledge of biology, thereby helping to advance the next generation of evidence-based medicine

Formulation And Study Of Ab Initio Ethane And Modified Urey-bradley Hydrocarbon Force Fields; Molecular Structures Of N-butane And N-hexadecane By Electron Diffraction.

PhDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/189236/2/7619131.pd

Molecular structure of n-butane: calculation of vibrational shrinkages and an electron diffraction re-investigation

A normal coordinate analysis was carried out based on the force field of Schachtschneider and Snyder in order to calculate all amplitudes of vibration and shrinkage corrections for n-butane. The results are tabulated to aid diffraction analyses of related substances. A vapor-phase electron diffraction reinvestigation of n-butane led to experimental measurements of the principal amplitudes of vibration and to the following molecular parameters (+/- 3[sigma] ): rg(C-C) = 1.531(2)A, rg(C-H)= 1.117(5)A, [angle]CCC (trans. gauche average) = 113.8(4)[deg], [angle]CCH (ave) = 111.0(5)[deg] , gauche CCCC dihedral angle 65(6)[deg], % trans CONFORMER = 54 +/- 9%, and [Delta]G[deg] (gauche-- trans) = 497 +/- 220 cal mol-1.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22926/1/0000492.pd

Ab initio study of secondary isotope effects on molecular structure

An ab initio calculation of a secondary isotope effect on a bond length has been carried out for the first time. Single determinant molecular orbital computations indicate that the mean C–C bond length at 0 °K is longer in C2H6 than in C2D6 by 0.0015 Å. A comparison with model calculations supports a steric interpretation in which H atoms act as if they are bulkier than D atoms owing to their larger bending amplitudes of vibration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69391/2/JCPSA6-63-7-3042-1.pd

The Reaction Of Organometallic Reagents With Unsymmetrically Substituted Vinamidinium And Chloropropeniminium Salts

A variety of organometallic reagents have been found to undergo regioselective reaction with 1-aryl-vinamidinium salts and 3-aryl-3-chloropropeniminium salts. The products of such reactions were found to be α,β-unsaturated ketones and chlorovinyl amines, respectively