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

Far-infrared intensity studies of complexes of some pyridine bases with iodine monochloride

Infrared spectrum of acetonitrile: Analysis of Coriolis resonance

Contact charge-transfer spectra of iodine in some hydrocarbon solvents

New experimental studies of the infrared spectra of uracil, 1-methyluracil, 3-methyluracil, and 1,3-dimethyluracil all isolated in Ar matrices at 10 K are compared with calculated spectra. The calculations for uracil are ab initio quantum-mechanical calculations of frequencies and intensities reported by us recently, and the CNDO calculations by Harsanyi and Csaszar. Both simulated calculated spectra agree quite well with the experimental infrared spectrum of matrix isolated uracil. Additional calculations have been made for the methyl-substituted uracils by transferring the ab initio calculated force constants and intensity parameters from uracil. A comparison of these calculated infrared spectra for 1-methyl-, 3-methyl-, and 1,3-dimethyluracil with the experimental spectra indicates the quality of the agreement. The potential-energy distributions are given for all the fundamental modes of the deuterated uracil derivatives and for the methyluracil molecules for the three fundamental vibrations of these molecules in the carbonyl region (1600–1800 cm−1). This comparison indicates the effect of methyl and deuterium substitution on the relative contributions of C2O, C4O, and C5C6 stretching motions to each fundamental mode. This result explains the puzzling anomalies in the intensity patterns observed experimentally in this region of the spectra of isolated deutero- and methyl-substituted uracil molecules.

Vibrational spectra of uracils: Experimental infrared matrix studies and ab initio quantum‐mechanical calculations

The complete neglect of differential overlap (CNDO) approximate wavefunctions for formaldehyde have been applied to the calculation of the derivatives of the dipole moment with respect to the symmetry coordinates (∂p/∂Sj). Agreement between the calculated derivatives and the experimental values given by Hisatsune and Eggers for the A1 symmetry species is exceptionally good, permitting an interpretation of the experimental results in terms of electronic distributions in the molecule. The agreement for the B1 and B2 symmetry species is also very good except for the asymmetric in‐plane CH bend. However, the theory successfully predicts that charge reorientation for this motion is quite different from that which occurs in the out‐of‐plane CH bend, so that these motions are represented by CH bond moments of opposite polarity. An analysis is given of the results in terms of derivatives with respect to internal coordinates (∂p/∂rk). Comparison of ∂p/∂rCO values from a series of X2CO molecules (and also with ∂p/∂...

Willis B. Person

Papers

Far-infrared intensity studies of complexes of some pyridine bases with iodine monochloride

Infrared spectrum of acetonitrile: Analysis of Coriolis resonance

Contact charge-transfer spectra of iodine in some hydrocarbon solvents

Vibrational spectra of uracils: Experimental infrared matrix studies and ab initio quantum‐mechanical calculations

CNDO calculation of dipole moment derivatives and infrared intensities of formaldehyde