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High-resolution (600 MHz) 1H and 13C chemical shift and 2D HETCOR NMR spectra of [60]PCBM were recorded. Resonances from every carbon atom of the ester, phenyl and cyclo-fullerenyl groups, were fully accounted. Assignments of the fullerene cyclopropa-ring, and all phenyl and ester carbons to their respective resonances were based on a HETCOR 2D NMR spectrum. Remaining fullerene assignments were made to a high level of confidence with the aid of an ωB97X hybrid HF/DFT simulation of the 13C NMR spectrum employing a triple zeta Dunning-type basis set. The best result was obtained with the range-separation parameter ω set effectively to zero. This indicates that the fraction of HF in the HF/DFT hybrid at very short range is the dominant factor in achieving good NMR results, that ωB97X with its 15.77% HF fraction at rij = 0 seems very well suited, and that allowing the HF fraction to increase with range is not particularly beneficial. The resulting spectrum had a remarkable qualitative agreement with experiment with a very low mean absolute error for fullerene carbons of 0.09 ppm, which was considerably lower than the 0.28 ppm of the more commonly used B3LYP/6-31G(d,p) method.

This work builds on our recently published anisotropic potential for polycyclic aromatic hydrocarbons (PAH) [T.S. Totton, A.J. Misquitta, M. Kraft, J. Chem. Theory Comput. 6 (2010) 683] by developing a new transferable electrostatic model for PAH molecules. Using this model, the atomic charge parameters used in the PAH anisotropic potential may be rapidly calculated from a set of predefined parameters rather than from molecule-specific ab initio calculations. The importance of the out-of-the-plane quadrupolar moments is highlighted and they are used as the basis for an accurate and transferable electrostatic model for PAHs. This model exhibits an r.m.s. deviation of 1.7 kJ mol - 1 - an order of magnitude less than previous models.

In this paper we present studies of clusters assembled from polycyclic aromatic hydrocarbon (PAH) molecules similar in size to small soot particles. The clusters studied were comprised of coronene (C 24 H 12 ) or pyrene (C 16 H 10 ) molecules and represent the types of soot precursor molecule typically found in flame environments. A stochastic ‘basin-hopping’ global optimisation scheme was used to locate low-lying local minima on the potential energy surface of the molecular clusters. TEM-style projections of the resulting geometries show similarities with those observed experimentally in TEM images of soot particles. The mass densities of these clusters have also been calculated and are lower than bulk values of the pure crystalline PAH structures. They are also significantly lower than the standard value of 1.8 g/cm 3 used in our soot models. Consequently we have varied the mass density between 1.0 g/cm 3 and 1.8 g/cm 3 to examine the effects of varying soot density on our soot model and observed how the shape of the particle size distribution changes. Based on similarities between nascent soot particles and PAH clusters a more accurate soot density is likely to be significantly lower than 1.8 g/cm 3 . As such, for modelling purposes, we recommend that the density of nascent soot should be taken to be the value obtained for our coronene cluster of 1.12 g/cm 3 .

In Symmetry-Adapted Perturbation Theory the charge-transfer energy is normally absorbed into the induction energy, but it can be treated separately. There are two contributions: the long-range or polarization term, which ignores effects due to exchange of electrons between the interacting molecules, and an exchange term. The sum of the two is much smaller than the polarization term, by up to an order of magnitude. The net contribution to hydrogen bond energies is a few kJ mol −1 at equilibrium, and is approximately proportional to the exchange-repulsion energy at other geometries and no more than 10% of it in magnitude.

We have constructed an intermolecular potential for the 1,3-dibromo-2-chloro-5-fluorobenzene molecule from first principles using SAPT(DFT) interaction energy calculations and the Williams–Stone–Misquitta method for obtaining molecular properties in distributed form. This molecule was included in the fourth Blind Test of crystal structure prediction organised by the Cambridge Crystallographic Data Centre. Using our potential, we have predicted the crystal structure of C 6 Br 2 ClFH 2 and found the lowest energy solution to be in excellent agreement with the experimentally observed crystal when it was subsequently revealed.

Symmetry-adapted perturbation theory based on Kohn–Sham determinants, SAPT(KS), was shown before to perform poorly for the electrostatic energy which is potentially exact in this approach. We demonstrate that some deficiencies of SAPT(KS) result from wrong asymptotics of exchange-correlation potentials. On applying an asymptotic correction, we were not only able to recover the electrostatics, but also the first-order exchange and second-order induction and exchange-induction energies fairly accurate. Dispersion is still reproduced poorly but can be computed reasonably accurately from the damped asymptotic expansion.

At-home bleaching with 10 percent carbamide peroxide in a custom-fitted tray has been reported to change the color of dentin. The purpose of this study was to validate the color change of dentin and to determine whether the color change was uniform or occurred from the outside (the dentinoenamel junction) to the inside (the pulpal wall).The authors sectioned 10 extracted human teeth incisogingivally through the midfacial long axis, and sealed their cut surface against glass microscope slides. Identifying marks were placed on the glass over the tooth sections to serve as a color control and in the dentinal areas closest to the dentinoenamel junction and the pulpal wall. Teeth were bleached for 10 days with 10 percent carbamide peroxide. Photographs were taken from the glass-covered side of the teeth, digitized and converted to gray-scale levels (consisting of 256 shades of gray ranging from black to white). Marked areas were measured with a National Institutes of Health Image software program and analyzed statistically for changes in lightness between the control marks and the inner and outer dentinal marks over time.Paired t-tests and analysis of variance indicated a significant increase in lightness (P = .01) for the inner and outer dentinal areas during bleaching compared with the control areas. No significant differences were found in the rate of change for the inner and outer dentinal areas (P = .89).The increase in lightness confirms that a significant color change occurred in the dentin during bleaching with 10 percent carbamide peroxide. This change occurred throughout the dentin at a uniform rate, rather than from the outside inward.The results of this study show that at-home bleaching with 10 percent carbamide peroxide can change the color of dentin, which is important to treat intrinsic stains from tetracycline treatment, trauma and aging or inherited discolorations. The bleaching material easily penetrates the tooth to change the dentin color at the same rate throughout, indicating that the type of stain may be the important factor in determining bleaching success.

Cerebral-evoked responses from 128 uncategorized, impotent men were compared with responses from 17 healthy age-height matched controls, after stimulation of two penile sites, and one tibial nerve at the ankle. Our goal has been to establish a simple screening test to identify neurogenic impotence in patients with normal superficial sensation. High frequency stimulation at 5.7 c/s and minimal repetitions (300) per trial, allowed thirty to forty minute sessions in alert subjects. With these methods, the amplitudes of cerebral responses at N2 were most informative. All volunteers had measurable amplitude while 11.9 percent of patients did not. An additional 4.5 percent of patients had amplitude suppression of 2 SD compared with the control mean, suggesting that as many as 16.4 percent of such patients may have neural damage. Prolonged latencies alone were rare and not included in this total. Ninety-two of these 128 patients had Doppler flow studies, and only 2 showed both Doppler and electrical abnormalities. This suggests that neurogenic problems may often be independent of vascular disease. This evoked-response screen of the entire genitocerebral neuraxis offers a safe method of identifying a portion of those patients with neurogenic impotence.

1. 1. Everted sacs of rat jejunum, ileum, and colon were used to investigate the possibility of active F − transport. Fluoride was placed in equal concentration in both compartments at the initial levels of 0.083, 0.167, and 1.670 mM. A secretion of F − against its electrochemical gradient was observed across ileum at 0.167 mM F − and either 1.9 or 1.0 mM Ca 2+ , and across jejunum and ileum at 0.167 and 1.670 mM F − in the presence of 0.5 mM Ca 2+ . 2. 2. When 0.167 mM F − was placed initially on either the mucosal or the serosal| side, at 1.9 mM Ca 2+ , fluoride crossed each section of the intestine freely in both the absorptive and secretory directions. The translocation of F − , however, was greater in the direction of secretion with jejunal and ileal sacs. 3. 3. With equal initial concentration of F − in both compartments, alteration of| the exogenous Ca 2+ concentration and also the addition of 2,4-dinitrophenol affected only the net movement of F − in the mucosal compartment. Since the loss of F − from the serosal compartment was not influenced, it appeared that this effect was localized at the mucosal surface. 4. 4. The net movement of F − against its electrochemical gradient was inhibited| by the addition of 1 mM dinitrophenol at 0° confirming the existence of active F − transport in jejunum and ileum. A less active F − pump also appeared to exist in the colon.