Ceramics used for the repair and reconstruction of diseased or damaged parts of the musculo-skeletal system, termed bioceramics, may be bioinert (alumina, zirconia), resorbable (tricalcium phosphate), bioactive (hydroxyapatite, bioactive glasses, and glass-ceramics), or porous for tissue ingrowth (hydroxyapatite-coated metals, alumina). Applications include replacements for hips, knees, teeth, tendons, and ligaments and repair for periodontal disease, maxillofacial reconstruction, augmentation and stabilization of the jaw bone, spinal fusion, and bone fillers after tumor surgery. Carbon coatings are thromboresistant and are used for prosthetic heart valves. The mechanisms of tissue bonding to bioactive ceramics are beginning to be understood, which can result in the molecular design of bioceramics for interfacial bonding with hard and soft tissues. Composites are being developed with high toughness and elastic modulus match with bone. Therapeutic treatment of cancer has been achieved by localized delivery of radioactive isotopes via glass beads. Development of standard test methods for prediction of long-term (20-year) mechanical reliability under load is still needed.

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Bioceramics: From Concept to Clinic

Bioceramics : from concept to clinic

In this study, we present conformational energies for a molecular mechanical model (Parm99) developed for organic and biological molecules using the restrained electrostatic potential (RESP) approach to derive the partial charges. This approach uses the simple "generic" force field model (Parm94), and attempts to add a minimal number of extra Fourier components to the torsional energies, but doing so only when there is a physical justification. The results are quite encouraging, not only for the 34-molecule set that has been studied by both the highest level ab initio model (GVB/LMP2) and experiment, but also for the 55-molecule set for which high-quality experimental data are available. Considering the 55 molecules studied by all the force field models for which there are experimental data, the average absolute errors (AAEs) are 0.28 (this model), 0.52 (MM3), 0.57 (CHARMm (MSI)), and 0.43 kcal/mol (MMFF). For the 34-molecule set, the AAEs of this model versus experiment and ab initio are 0.28 and 0.27 kcal/mol, respectively. This is a lower error than found with MM3 and CHARMm, and is comparable to that found with MMFF (0.31 and 0.22 kcal/mol). We also present two examples of how well the torsional parameters are transferred from the training set to the test set. The absolute errors of molecules in the test set are only slightly larger than in the training set (differences of <0.1 kcal/mol). Therefore, it can be concluded that a simple "generic" force field with a limited number of specific torsional parameters can describe intra- and intermolecular interactions, although all comparison molecules were selected from our 82-compound training set. We also show how this effective two-body

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How Well Does a Restrained Electrostatic Potential (RESP) Model Perform in Calculating Conformational Energies of Organic and Biological Molecules

We present an all atom potential energy function for the simulation of proteins and nucleic acids. This work is an extension of the CH united atom function recently presented by S.J. Weiner et al. J. Amer. Chem. Soc., 106, 765 (1984). The parameters of our function are based on calculations on ethane, propane, n−butane, dimethyl ether, methyl ethyl ether, tetrahydrofuran, imidazole, indole, deoxyadenosine, base paired dinucleoside phosphates, adenine, guanine, uracil, cytosine, thymine, insulin, and myoglobin. We have also used these parameters to carry out the first general vibrational analysis of all five nucleic acid bases with a molecular mechanics potential approach.

An all atom force field for simulations of proteins and nucleic acids.

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

Spectroscopic study of some tetrabromomethane complexes

Absolute Infrared Intensities in Crystalline Benzene

The computed MP2/6-31+G(d,p) structure of the HBr:pyridine complex and the computed harmonic and experimental spectra of this complex agree that HBr:pyridine is stabilized by a proton-shared hydrogen bond. However, differences are evident between the computed and experimental spectral patterns with respect to the frequencies and intensities of strong bands. Solution of a one-dimensional nuclear vibrational equation along the normal coordinate mode allows for an estimation of an anharmonicity of the proton-stretching motion. When an anharmonic stretching force constant is used to recompute the spectrum, excellent agreement is found between theory and experiment.

Resolving Discrepancies between Theory and Experiment: IR Spectrum of the Proton-Shared HBr:Pyridine Complex

Calculated dipole moment derivatives from CNDO/2 wavefunctions for the first row diatomic hydride (XH) molecules are compared with the derivatives calculated by Cade and Huo from a near Hartree‐Fock calculation. In making this comparison, a remarkably simple straight‐line relationship is found to exist between these dipole moment derivatives and the atomic members (Zx) of the X atoms. In the CNDO framework, this linear relationship is due to a nearly linear relationship between q1 (the equilibrium charge on each atom in XH) and Zx. Finally, the results from the CNDO/2 and Hartree‐Fock calculations of ∂p/∂R are compared with the values from INDO and CNDO/2D calculations.

Willis B. Person

Papers

Spectroscopic study of some tetrabromomethane complexes

Absolute Infrared Intensities in Crystalline Benzene

Resolving Discrepancies between Theory and Experiment: IR Spectrum of the Proton-Shared HBr:Pyridine Complex

Regularities in calculated dipole moment derivatives of first row diatomic hydrides

Absolute Infrared Intensities in Mixed Hydrogen Halide Crystals