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

The analysis of infrared intensity data to obtain atomic ``polar tensors,'' introduced first by Biarge, Herranz, and Morcillo (1961), is reviewed and slightly reformulated to make it more consistent with nomenclature currently in use for normal coordinate calculations. Some properties of these polar tensors are examined, including their relation to the ``effective charges'' introduced by King, Mast, and Blanchette (1972). The procedure is illustrated for formaldehyde and for ethylene to obtain the polar tensors and effective charges for the H, C, and O atoms. A revised set of normal coordinates is used for the latter molecule. The results are compared and discussed.

Dipole moment derivatives and infrared intensities. I. Polar tensors

Author Institution: Youngatown State University, Youngatown, Ohio 44555; University of Florida, Gainesville, Florida 32611

Properties of Hydrogen-Bonded Complexes Obtained from the B3LYP Functional with 6-31G(d,p) and 6-31+G(d,p) Basis Sets: Comparison with MP2/6-31+G(d,p) Results and Experimental Data

Matrix isolation infrared studies of nucleic acid constituents. 5. Experimental matrix-isolation and theoretical ab initio SCF molecular orbital studies of the infrared spectra of cytosine monomers

A Criterion for Reliability of Formation Constants of Weak Complexes

The infrared absorption spectra of carbon monoxide in argon matrices have been studied over a wide range of CO concentrations. The absolute infrared intensities of pure crystalline CO and of CO in argon matrices have been measured. The technique of using the second moment to determine the baseline of the absorption band has been tested and found to improve the data. The absolute integrated molar absorption coefficient of pure solid CO was found to be A=58.1±5.50 km mol−1 (1 km/mole=100 cm/mmole) and that for CO in the argon matrices is 66.5±2.4 km mol−1. The two values are believed to be the same within experimental error. Studies were also made of CO trapped in different matrices, including SF6, C6H6, and CCl4. The absolute intensity of CO increases from the gas phase (A=58.0 km mole−1) to the pure solid phase (A=58.1) or to the solid matrices (66.5−114 km mol−1, depending on the matrix) apparently due for the most part to the electric field effect. The band shapes have been analyzed to obtain the second and fourth moments and hence the intermolecular torques and dipole time−correlation functions. The large values for the torques and slow decay of the correlation function with time from one system to another suggest that the CO molecules have either greatly hindered rotation or no rotation at all in the pure solid and in the solid matrices.

Willis B. Person

Papers

Dipole moment derivatives and infrared intensities. I. Polar tensors

Properties of Hydrogen-Bonded Complexes Obtained from the B3LYP Functional with 6-31G(d,p) and 6-31+G(d,p) Basis Sets: Comparison with MP2/6-31+G(d,p) Results and Experimental Data

Matrix isolation infrared studies of nucleic acid constituents. 5. Experimental matrix-isolation and theoretical ab initio SCF molecular orbital studies of the infrared spectra of cytosine monomers

A Criterion for Reliability of Formation Constants of Weak Complexes

Absolute infrared intensities and band shapes in pure solid CO and CO in some solid matrices