Biomedical subjects

William H Green

Publications and source records attributed to William H Green.

6 recordsLinked to original sources

PubMed2006

Accurate and efficient method for predicting thermochemistry of furans and ortho-arynes: expansion of the bond-centered group additivity method.

The bond-centered group additivity method (BCGA) method for the estimation of the thermochemical properties of polycyclic aromatic molecules is expanded to aromatic molecules containing furan ring(s) and ortho-arynes. The method is based on enthalpies of formation (deltaH(o)f), entropies (S(o)298), and heat capacities (C(o)p) obtained from B3LYP/6-31G(d) calculations. The enthalpies of formation were obtained using a set of homodesmic reactions that include only aromatic molecules as the reference. Two new atom-centered groups are defined for the description of furan ring(s) and ortho-arynes, leading to the addition of 17 new bond-centered groups to the BCGA method. The deltaH(o)f, S(o)298, and C(o)p contributions of these bond-centered groups is derived.

Journal Article↗

PubMed2006

Global dynamic optimization for parameter estimation in chemical kinetics.

We present the first method guaranteed to find the best possible least-squares (chi2) fit of experimental data by a nonlinear kinetic model. Several important advantages of knowing with certainty the best possible fit rather than a locally optimum fit are discussed and demonstrated using data from the recent literature. This is particularly important when the model and the data appear to be inconsistent. With the new method, one can rigorously demonstrate that a nonlinear kinetic model with several adjustable rate parameters is inconsistent with measured experimental data. The numerical method presented is a valuable tool in evaluating the validity of a complex kinetics model.

Journal Article↗

PubMed2006

Forecasting veterinary school admission probabilities for undergraduate student profiles.

Increased competition for veterinary school admission has created a need to determine whether individual students are likely to be successful candidates for veterinary school admission early in their undergraduate careers. Students invest considerable time and money in pre-veterinary courses of study, hoping for acceptance into professional veterinary school. A forecasting model was developed to predict the likelihood of students with particular characteristics gaining acceptance. Characteristics such as gender, age, size of high school, and ACT, are known upon entrance into college and can be used to determine the likelihood of an individual's being accepted. Data were gathered from the Louisiana State University College of Veterinary Medicine (LSU-CVM) admissions for all students applying to veterinary school for the classes of 2006 through 2008 from the top two agricultural programs in the state in terms of quantity of applicants to veterinary school: Louisiana State University and Louisiana Tech University. A one-way ANOVA was used to examine whether there were any statistical differences between known demographic and performance variables and acceptance into veterinary school. A logit forecasting model was then estimated to predict the likelihood of gaining acceptance into veterinary school based only on variables known early in the student's undergraduate career. Age, gender, and ACT scores were determined to be important variables in determining the likelihood of gaining admission. Overall, the forecasting model is of use in assigning probabilities of acceptance into veterinary school for specific student profiles, which can assist in one-on-one assistance from advisor to student.

Analysis of Variance↗

PubMed2005

The electrostatic origin of Abraham's solute polarity parameter.

A computational method was developed which relates the empirical linear solvation energy relationship (LSER) solute polarity parameter, S (formerly denoted ), to two more fundamental quantities: a polarizability term and a computed solvent-accessible-surface electrostatic term. Electrostatics computations were conducted explicitly or with dielectric field polarizable continuum models (PCM, SCIPCM, IPCM), employing a density functional theory (B3LYP/6-311G(2df,2p)) or efficient Hartree-Fock (HF/MIDI!) method for 90 polar and nonpolar organic solutes. Electrostatic parameters calculated at electron isodensity solute surfaces were found to produce significantly better correlations with empirical S values than the same electrostatic parameters deduced from a fixed Bondi atomic radii based surface. The best-fit expression was found employing SCIPCM/IPCM at the 0.0004 e(-)/bohr(3) solvent-accessible-surface: S(fit)() = 0.46E - 0.091SigmaV(s)()(2), with squared correlation coefficient = 0.96 and standard deviation = 0.10, where E is a measured solute excess polarizability scale and SigmaV(s)()(2) is a quantum-calculated solute electrostatic descriptor in kcal A/mol. The resulting model is more accurate than previously developed estimation approaches and relies on only two fitted coefficients; it has the potential advantage of applicability to any solute composed of C, H, N, O, S, F, Cl, and Br. Finally, this investigation offers quantitative insight into the relative contributions of solute polarity and solute polarizability to the empirical LSER polarity parameter, S.

Journal Article↗

PubMed2004

Accurate and efficient method for predicting thermochemistry of polycyclic aromatic hydrocarbons - bond-centered group additivity.

A self-consistent estimation method for the thermochemical properties of polycyclic aromatic hydrocarbons (PAH) is presented. This method is based on enthalpies of formation (DeltaHf(degrees), entropies (S(degrees)298, and heat capacities (C(degrees)p obtained from B3LYP/6-31G(d) calculations of the total energies and frequencies for 139 PAHs, including C(60) and C(70) fullerenes. The enthalpies of formation were calculated using an optimized set of homodesmic reactions given the available experimental DeltaHf(degrees) of PAHs. The theoretical entropies were compared with the existing experimental entropies, and some inconsistencies in the experimental data were identified. The estimation method presented here is a systematic extension of the widely employed atom-centered group additivity method originally proposed by Benson. This new method is based on bond-centered groups that define bonds linking two atom-centered groups and specify the size of the rings to which they belong. In addition, a term to describe the resonance energy is included. The thermochemical properties of PAHs up to C(70) fullerene are estimated with a mean average deviation of 2.8 kcal mol(-1) in DeltaHf(degrees), 0.7 cal K(-1) mol(-1) in S(degrees)298, and about 0.5 cal K(-1) mol(-1) in the C(degrees)p. This bond-centered group additivity method for the thermochemical properties of PAHs significantly expands both the range of systems that can be estimated and the accuracy of the estimations. The results of this work also allow us to assess the quality of available experimental data. For example, there are strong indications that the literature DeltaHf(degrees)of benzo[k]fluoranthene is about 10 kcal mol(-1) too low.

Journal Article↗

PubMed2004

Structure of polymer-stabilized magnetic fluids: small-angle neutron scattering and mean-field lattice modeling.

Small-angle neutron scattering and mean-field lattice modeling were used to characterize a class of water-based magnetic fluids tailored specifically to extract soluble organic compounds from water. The fluids consist of a suspension of approximately 7 nm magnetite (Fe3O4) nanoparticles coated with a bifunctional polymer layer comprised of an outer hydrophilic poly(ethylene oxide) (PEO) region for colloidal stability and an inner hydrophobic poly(propylene oxide) (PPO) region for solubilization of organic compounds. The inner region of the polymer shell is increasingly depleted of water as the fraction of PPO side chains increases. The incorporation of PPO side chains also leads to a small increase in interparticle attraction. The lattice model predicted a shell structure similar to that of a PEO-PPO-PEO triblock copolymer (Pluronic) micelle, with equivalent levels of hydration but with more PEO present in the PPO-rich regions, as the side chains grafted to the surface are less able to segregate than when in free micellar systems.

Journal Article↗