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

Ab initio theoretical and matrix isolation experimental studies of hydrogen bonding: evidence of a dramatic effect of the matrix on the structure and vibrational spectrum of HBr:3,5-dichloropyridine

A review is presented of experimental studies of infrared and Raman spectra of thymine isolated in an argon matrix at about 12 K. The experimental techniques for study of the vibrational spectra of matrix-isolated pyrimidines are described, and the reasons for such studies are illustrated by comparison of the infrared and Raman spectra of matrix-isolated thymine with spectra in the solid phase. Comparison of the infrared spectrum of p-quinone isolated in an argon matrix with that for the molecule in the gas phase establishes that the spectra of matrix-isolated molecules are expected to be very similar to those for the gas phase, except for the lack of rotational structure in the matrix spectra. On the other hand, hydrogen bonding in the solid phase has a profound effect on the infrared spectrum, with much smaller effect on the Raman spectrum. Ab initio quantum-mechanical calculations at the HF/6–3 lG(d) level made for the isolated molecules are compared with the experimental spectra and their application to the interpretation of the latter is illustrated.

Experimental and Ab Initio Quantum Mechanical Studies of the Vibrational Spectra of Isolated Pyrimidine Bases

Configuration-dependent raman bands of phospholipid surfaces. 1. carbonyl stretching modes at the bilayer interface

Measurement of absolute vibrational band intensities has always been an exceedingly difficult problem. The measurements in the gas phase have long been notorious for errors of as much as a factor of ten; even now one is not surprised too much to find that one’s new measurements differ by a factor of two from previous results in the literature. Nevertheless, the situation is improving rapidly and it is now possible for two carefully conducted measurements by different research groups to agree within 1 or 2% [1]. The use of computers with Fourier transform interferometers, and also in conventional dispersion spectrometers, makes what was once a very long and tedious measurement to obtain an intensity now completely routine. We can now predict with confidence that accurate infrared intensities will be routinely available from almost any experiment performed in gas or solution phases. Measurements in matrices have some unique problems, described below, but have the potential for providing unique and extremely useful results. We shall give here a general survey, outlining some of the problems and some preliminary results, in the hope of interesting others in the possibilities of studying vibrational band intensities in matrices.

Willis B. Person

Papers

Ab initio theoretical and matrix isolation experimental studies of hydrogen bonding: evidence of a dramatic effect of the matrix on the structure and vibrational spectrum of HBr:3,5-dichloropyridine

Experimental and Ab Initio Quantum Mechanical Studies of the Vibrational Spectra of Isolated Pyrimidine Bases

Configuration-dependent raman bands of phospholipid surfaces. 1. carbonyl stretching modes at the bilayer interface

Vibrational Band Intensities In Matrices

Matrix isolation studies of nucleic acid constituents. 2. quantitative ab initio prediction of the infrared spectrum of in-plane modes of uracil