Summary: Methods have been developed for the preparation of suspensions of washed platelets from humans. Heparin is used in the washing fluids to prevent: thrombin generation and apyrase is used to prevent adenine nucleotide accumulation. Platelets suspended in Eagle's tissue culture medium containing albumin were more responsive to ADP than platelets in Tyrode's‐albumin solution. Addition of fibrinogen is required for maximum sensitivity to ADP‐induced aggregation. These platelets can be stored for 4 hr or more at 37°C in the presence of apyrase and maintain their ability to aggregate upon the addition of low concentrations of ADP. Without apyrase the platelets gradually become insensitive to ADP upon storage at 37°C; this is presumably caused by the accumulation of ADP in the suspending fluid because sensitivity can be partially restored by the addition of apyrase and further incubation.

The torsional tunneling splittings of the asymmetric C-H stretches ( 2 and 9 ) in methanol are inverted with the E level lower in energy than the A level, whereas the symmetric C-H stretch ( 3 ) is normal with A below E. An internal coordinate model, which treats the torsion and the three C-H stretches simultaneously, accounts for the observed tunneling splittings. The model parameters are the local stretching frequency ϭ2934.0 cm Ϫ1 , the direct local-local coupling ϭϪ42.2 cm Ϫ1 , and a single stretch-torsion coupling parameter ϭ12.9 cm Ϫ1 . The torsion-vibration coupling is nonadiabatic in the sense that it is not consistent with a Born-Oppenheimer separation of the torsion from the other vibrations. The fact that the model is based largely on the G 6 molecular symmetry suggests that tunneling inversion may be common in torsional molecules. The torsionally mediated couplings among the C-H stretches do not conserve symmetry in the C s point group and are strong enough to contribute to rapid intramolecular vibrational redistribution ͑IVR͒.

Can. J. Chem. 72, 652 (1994). Evidence is presented to show that intramolecular vibrational relaxation (IVR) is faster in flexible molecules when the initially prepared vibration is close to the bond about which the large-amplitude motion occurs. In each of I-pentyne, ethanol, and propargyl alcohol, IVR lifetimes are known for two different hydride stretches and in each molecule internal rotation connects gauche and trans conformers. In each case the vibration that is closer to the center of flexibility shows faster relaxation. This trend is supported by the available IVR lifetimes for other flexible molecules (hydrogen peroxide, I-butene, n-butane, methyl formate, and propargyl amine) and for some "rigid" molecules (I-butyne, isobutane, propyne, trans-2-butene, and tert-butylacetylene). The lifetimes for the halogenated molecules, 2-fluoroethanol, 1,2-difluoroethane, trans-lchloro-2-fluoroethane, and trifluoropropyne are all in the range expected for rigid molecules. An algorithm is presented for the consistent calculation of IVR lifetimes from discrete frequency-resolved spectra, which range from the sparse through intermediate coupling cases. Wherever possible, the reported lifetimes have been calculated (or recalculated) from the original line positions and intensities. The lifetimes may be compared directly to those deduced from homogeneously broadened spectral features with a Lorentzian contour. On prksente des donnkes pour dkmontrer que la relaxation vibrationnelle intramolkculaire (RVI) est plus rapide dans les molCcules flexibles lorsque la vibration prCparCe initialement est proche de la liaison autour de laquelle le mouvement de grande amplitude se produit. Dans le pent-I-yne, l'kthanol et l'alcool propargylique, les temps de vie des RVI des deux modes diffkrents d'Clongation de l'hydrure sont connus et, pour chaque molkcule, la rotation interne permet de joindre les conformkres gauche et trans. Dans chaque cas, la vibration la plus proche du centre de flexibilitk prksente la relaxation la plus rapide. Cette tendance est supportke par les temps de vie RVI disponibles pour d'autres molCcules flexibles (peroxyde d'hydrogkne, but-I-kne, n-butane, formate de methyle et amine propargylique) et pour quelques molCcules << rigides D (but-I-yne, isobutane, propyne, trans-but-2-kne et tert-butylacktylkne). Les temps de vies des molCcules halogknkes, 2-fluoroCthanol, 1,2-difluorokthane, trans-I-chloro-2-fluoroethane et trifluoropropyne sont tous de l'ordre de grandeur attendu pour des molkcules rigides. On prksente un algorithme qui permet de calculer d'une facon cohkrente les temps de vie RVI ?I partir de spectres discrets rksolus en frkquence qui couvrent les cas des couplages faibles ?I intermkdiaires. Dans tous les cas possibles, les temps de vie rapportis ont Ct C calculks (ou recalculks) B partir des positions et des intensitks originales des bandes. On peut comparer les temps de vie directement B ceux dkduits ?I partir de caractkristiques spectrales Clargies d'une facon homogkne avec un contour lorentzie...

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10Chirped-Pulse millimetre-Wave (CPmmW) rotational spectroscopy provides a new class of information about photolysis transition state(s). Measured intensities in rotational spectra determine species-isomervibrational populations, provided that rotational populations can be thermalized. The formation and detection of S 0 vinylidene is discussed in the limits of low and high initial rotational excitation. CPmmW 15 spectra of 193 nm photolysis of Vinyl Cyanide (Acrylonitrile) contain J=0-1 transitions in more than 20 vibrational levels of HCN, HNC, but no transitions in vinylidene or highly excited local-bender vibrational levels of acetylene. Reasons for the non-observation of the vinylidene co-product of HCN are discussed. A. Introduction 20Chirped-Pulse millimetre-Wave (CPmmW) spectroscopy 1-3 is capable of determining the relative species-conformervibrational level populations of all polar products of a photolysis reaction. These experimentally determined populations encode the structures of the transition states 25 that are most important at each photolysis wavelength or combination of wavelengths. 4 The isomer-conformervibrational level population information obtained from a CPmmW spectrum is more complete than what is obtainable by mass spectrometry 5 and free of the need for 30 the transition strength and quantum yield determinations that are required for most laser-based population measurements. However, difficulties exist in the use of populations determined by CPmmW spectroscopy to characterize transition states. B. Chirped Pulse SpectroscopyChirped Pulse Fourier Transform Microwave Spectroscopy 55 is a revolutionary technique developed in the research group of Brooks Pate at the University of Virginia. 2,3 In its initial implementation, the frequency of a microwave pulse is chirped linearly in time over several GHz. This microwave pulse is broadcast into a gas phase molecular 60 sample, polarizing all two-level systems with frequencies within the spectral interval of the chirped pulse. These polarizations relax by Free Induction Decay (FID), which is a voltage vs. time signal that is collected, downconverted by mixing with a local oscillator (heterodyne where  is the electric dipole moment,  0 is the peak microwave electric field, N 1,2 is the population density 75 difference between levels 1 and 2,  is the chirp rate, A is

An ab initio-based improved force field is reported for poly(3-hexylthiophene) (P3HT) in the solid state, deriving torsional parameters and partial atomic charges from ab initio molecular structure calculations with explicit treatment of the hexyl side chains. The force field is validated by molecular dynamics (MD) simulations of solid P3HT with different molecular weights including calculation of structural parameters, mass density, melting temperature, glass transition temperature, and surface tension. At 300 K, the P3HT crystalline structure features planar backbones with non-interdigitated all-trans hexyl side chains twisted ~90° from the plane of the backbone. For crystalline P3HT with infinitely long chains, the calculated 300 K mass density (1.05 g cm(-3)), the melting temperature (490 K), and the 300 K surface tension (32 mN/m) are all in agreement with reported experimental values, as is the glass transition temperature (300 K) for amorphous 20-mers.

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An antithrombin III mutation database was collated and published in L99L by a group of investigators working on the molecular basis of antithrombin III deficiency (1). Soon after, under the auspices of the ISTH SSC, an Antithrombin III Working Party was formed of those involved in the preparation of the database, with the instruction to report to the "Thrombin and its Inhibitors" SSC on the developments in this and related areas. This document is one outcome of the work of the Antithrombin III Working Party and is a partial report of the deliberations of the "Thrombin and its Inhibitors" SSC Meeting held in Munich, July 1992. Other items discussed at this meeting included the nomenclature of the plasma coagulation inhibitors. Three alternative names were considered for this inhibitor, antithrombin III, antithrombin and thrombin inhibitor I. No unanimous view emerged regarding the name, other than the rejection of the term thrombin inhibitor I. For this report, the historical name antithrombin III will be used, despite the preference for anti. thrombin by the majority of the authors of this database. This is in deference to the journal, Thrombosis and Haemostasis, pending any final decision of the SSC regarding nomenclature. The intention behind the production and updating of the antithrombin III database has been to provide a readily accessible and up-to-date source of known mutations of antithrombin III. The complex effects of some mutations on structure/function relationships of the protein can only be indicated. For more information on this and on possible mechanisms involved in gene mutation (see below for brief consideration of mutations involving CpG dinucleotides), the reader is referred to the original papers and to several reviews in this area (2-6).