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 conformation of the dilithioacetylene molecule has been investigated up to the CCSD+T(CCSD) level with the 6-311G*(*) basis. The geometry of the molecule has been fully optimized on the SCF and MBPT(2) levels with a variety of basis sets. It has been found that the equilibrium geometry is rather sensitive to the choice of the basis. Calculations on the CCSD+T(CCSD) level have shown that, although the second-order MBPT energy term destabilized the planar structure, the sum of the higher order corrections slightly stabilized this form. The planar doubly bridged (D2h) structure is predicted to be the most stable one.

Study of the conformation of the dilithioacetylene molecule

Zweidimensionaler anharmonischer oscillator, anwendung auf 2,5-dihydrofuran

A study of the vibrational fundamentals of N{sub 2}H{sub 4} and all nine f its deuterated derivatives has been conducted using a combination of ab inito calculations with FT-IR matrix-isolation (N{sub 2}, Ar) methods. The ab inito calculations, made using the 3-21G and 6-31G** bases with the Gaussian 82 program, were instrumental in establishing the experimental assignments. The concentration dependences of N{sub 2}H{sub 4}/Ar and N{sub 2}H{sub 4}/N{sub 2} spectra assisted in resolving much of the uncertainty in previous matrix and vapor-phase vibrational assignments for N{sub 2}H{sub 4}. The ratio of natural abundances of N{sub 2}H{sub 3}D{sub 0} to N{sub 2}H{sub 3}D{sub i} (i.e., the ratio of outer to inner deuterium-substituted species) has been found to be approximately 19:10.

Willis B. Person

Papers

Study of the conformation of the dilithioacetylene molecule

Zweidimensionaler anharmonischer oscillator, anwendung auf 2,5-dihydrofuran

Experimental and Theoretical Studies of the Infrared Spectra of Hydrazines: N2H4, N2H3D, N2H2D2, N2HD3, and N2D4.

Thiouracils. Part 2. Tautomerism and IR Spectra of Thiouracils (I)-(V). Matrix Isolation and ab initio Studies.

Absolute ir-intensitaeten der fundamentalabsorptionsbanden der festen halogencyane xcn (x=cl, br, j)