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Tooth development is under strict genetic control. Oligodontia is defined as the congenital absence of 6 or more permanent teeth, excluding the third molar. The occurrence of non-syndromic oligodontia is poorly understood, but in recent years several cases have been described where a single gene mutation is associated with oligodontia. Several studies have shown that MSX1 and PAX9 play a role in early tooth development. We screened one family with non-syndromic oligodontia for mutations in MSX1 and PAX9. The pedigree showed an autosomal-dominant pattern of inheritance. Direct sequencing and restriction enzyme analysis revealed a novel heterozygous A to G transition mutation in the AUG initiation codon of PAX9 in exon 1 in the affected members of the family. This is the first mutation found in the initiation codon of PAX9, and we suggest that it causes haploinsufficiency.

In this paper, we describe a parallel molecular dynamics simulation scheme in NPT ensemble which can be used for studying molecular systems with bond constraints. As an example of application, we choose to investigate general anesthesia whose molecular mechanism is largely unknown. In doing that, we performed two simulations. One is pure lipid bilayer simulation and the other is lipid bilayer simulation with 50 mol% halothane (which is a well-known inhaled anesthetic). From the simulations, we have found that d-spacing increases and area per molecule decreases in the presence of the halothane molecules. We have also found that the halothane molecules are distributed in the hydrophobic tail region, but near headgroup region

1. The synthetic peptide H10A24 self-assembles in aqueous solution into a 4-helix bundle, which exhibits saturable binding of halothane. 2. Molecular dynamics simulation techniques have been used to study the vacuum structure of this bundle. 3. The simulation, initiated as four ideal parallel α -helices, resulted in a compact bundle, whose secondary structure remains predominantly α -helical. 4. The hydrophobic core has no apparent pocket large enough to accomodate halothane.

A new model e--NH3 pseudopotential parameterized to ab initio quantum chemistry calculations on small lithium ammonia clusters is studied in a variety of environments. Results for Li(NH3)n(n = 1,4) presented in a previous work are reviewed. Large clusters (n = 16, 32, 64, 128) are then studied. The valence electron is found to exist in a surface state far from the lithium ion which is localized at the center of mass of the cluster. Bulk properties of both a single excess electron and the lithium atom in solution are also reported. The solvation energy and spectrum of the excess electron are found to agree well with experiment though the spectrum is somewhat blue shifted. The valence electron of the lithium atom is found to dissociate spontaneously, a property which has not been reproduced in early work. Some preliminary results on the singlet state of two excess electrons in ammonia are presented.

Molecular dynamics calculations are used to investigate the behavior of overlayers of ethylene molecules physisorbed on graphite. The ethylene intermolecular potential, which is taken from the literature, is shown to yield a reasonable structure for the bulk crystal. The well depth of the ethylene/ graphite potential, which is also derived from atom-atom potentials, is fitted to the isosteric heat of adsorption at zero coverage on the assumption that the graphite surface is planar. Solid monolayers are shown to exist in which the ethylene CC axes are either parallel (LD phase) or perpendicular (HD phase) to the graphite basal plane. At low temperatures and under the constraint of zero spreading pressure, both solid phases order into herringbone structures. On heating, these solids transform to rotator phases before melting. Calculated translational and rotational diffusion constants for the disordered phases are compared with experimental values derived from quasielastic neutron scattering data. The density of states for collective translational and librational motions in the solid phases are presented along with the spectrum for motion of the H atoms. The latter is compared with the results of incoherent inelastic neutron scattering experiments. Despite the simplified nature of the molecule-surface interaction potential, the molecular dynamics calculations provide detailed interpretations of the above mentioned experimental results. The research exemplifies how simulation techniques offer a powerful complement to experimental investigations.

We have carried out lattice dynamical calculations at k = 0 for solid α-F2 using atom-atom potentials both with and without the EQQ interaction. Reasonable agreement of the calculated external vibration frequencies with observed Raman and far infrared spectra is obtained for the C2/m structure. On the basis of our calculations, an assignment of each Raman and far infrared band is made which is consistent with the observed Raman intensities. However, a unique assignment is not made for the intramolecular Raman bands. The intermolecular forces operative in α-F2 are discussed, and it is concluded that it would be of great interest to have detailed MO calculations for F2 dimers, especially for configurations that arise in the solid, so that a more fundamental intermolecular force model can be constructed.

A new method is used to measure the self-diffusion coefficient in gaseous argon as a function of temperature. Data obtained from 77.5°K to 121°K and at room temperature (294°K) agree well with earlier data obtained by Winn with a different method. The data are shown to be consistent with both the viscosity and second virial coefficient of argon. They are also used to estimate the effective long-range dispersion interaction- energy between argon atoms. The value thus derived for the interaction-energy agrees well with sum-rule calculations.

We have used the Dagens-Rasolt-Taylor pseudopotential to carry out a molecular dynamics simulation of S(Q, ω) of solid b.c.c. potassium at temperatures corresponding roughly to 0.5 and 0.9 of melting. The calculated temperature broadening of the one-phonon peaks, and the interference of these peaks with the multiphonon background agree well with experimental neutron scattering data.

We have used the classical Molecular Dynamics method to calculate the structure factor S(Q) of liquid Li and we compare this quantity with that measured by neutron scattering. We have employed a system of 1458 Li atoms interacting, via periodic boundary conditions, with a recently derived interionic pair potential. The good agreement between the calculation and experiment is taken to indicate that the explicit many body interionic forces are not important in liquid Li.

Numerical results are presented for the first quantum correction (proportional to ħ 2) to the classical two-dimensional second virial coefficient assuming a Lennard-Jones (12–6) form for the pair interaction. It is pointed out that a previous calculation of this quantity by Sams is in error.

Measurements of the isotopic separation for the physical adsorption of argon atoms on graphitized carbon blacks P33 (2700°C) and Spheron 6 have been obtained in the temperature range 78°K to 100°K at several values of the adsorption pressure. Using the grand partition function we have derived a general expression for the separation factor α in terms of the surface-adatom forces and the adatom-adatom forces. Our experimental results are compared with the theory by introducing specific simple models. Values of lnα extrapolated to p → O obey a 1/T2 law and are used with data from low pressure adsorption isotherms to derive the parameters of an assumed surface-adatom potential. The observed pressure dependence of 1nα appears to be inconsistent with the assumption of a planar and energetically homogeneous surface.

Recent experiments on the temperature dependence of the velocity of sound in solid argon are compared with model calculation using a Mie-Lennard-Jones interatomic potential. At high temperatures theory and experiment are in fair agreement, but at low temperatures, the work of Gsanger et al. is in definite disagreement with theory.

Thermodynamic properties of solid Ne are evaluated using an improved self-consistent phonon theory that explicitly includes odd derivatives of the potential. The T dependence of thermodynamic properties of Ne are in good agreement with experiment (except for the isothermal compressibility near the melting point — a difficult quantity to measure!) and differ substantially from the predictions of the lowest order theory.

The phonon spectrum of hcp o-D2 is calculated using a self consistent phonon theory and a Jastrow function. TO and LO phonons are compared with recent values obtained by neutron inelastic scattering. (Author)

Contrary to a recent letter, we point out that both theory and experiment support the equality of thermal and elastic Debye temperatures for copper at the absolute zero.