David Gosser

The electrochemical (EC) reduction mechanism of methylcobalamin (Me-Cbl) in a mixed DMF/MeOH solvent in 0.2 M tetrabutylammonium fluoroborate electrolyte was studied as a function of temperature and solvent ratio vs a nonaqueous Ag/AgCl/Cl(-) reference electrode. Double-potential-step chronoamperometry allowed the rate constant of the subsequent homogeneous reaction to be measured over the temperature range from 0 to -80 degrees C in 40:60 and 50:50 DMF:MeOH ratios. Activation enthalpies are 5.8 +/- 0.5 and 7.6 +/- 0.3 kcal/mol in the 40:60 and 50:50 mixtures of DMF/MeOH, respectively. Digital simulation and curve-fitting for an EC mechanism using a predetermined homogeneous rate constant of 5.5 x 10(3) s(-1) give E degrees' = -1.466 V, k degrees = 0.016 cm/s, and alpha = 0.77 at 20 degrees C for a quasi-reversible electrode process. Digital simulation of the results of Lexa and Savéant (J. Am. Chem. Soc. 1978, 100, 3220-3222) shows that the mechanism is a series of stepwise homogeneous equilibrium processes with an irreversible step following the initial electron transfer (ET) and allows estimation of the equilibrium and rate constants of these reactions. An electron coupling matrix element of H(kA) = (4.7 +/- 1.1) x 10(-4) eV ( approximately 46 J/mol) is calculated for the nonadiabatic ET step for reduction to the radical anion. A reversible bond dissociation enthalpy for homolytic cleavage of Me-Cbl is calculated as 31 +/- 2 kcal/mol. The voltammetry of the ethyl-, n-propyl-, n-butyl-, isobutyl-, and adenosyl-substituted cobalamin was studied, and estimated reversible redox potentials were correlated with Co-C bond distances as determined by DFT (B3LYP/ LANL2DZ) calculations.

Cardiolipin (CL) is found in inner mitochondrial membranes and the plasma membrane of aerobic prokaryotes. CL is tightly bound to those transmembrane enzymes associated with oxidative phosphorylation. CL has earlier been reported to have a single pK at low pH. We have titrated CL in aqueous suspension (bilayers) and in solution in methanol/water (1∶1, vol/vol) and found it to display two different pK values, pK1 at 2.8 and pK2 initially at 7.5 but shifting upwards to 9.5 as the titration proceeds. The unusually high pK2 might be explained by the formation of a unique hydrogen bond in which the free hydroxyl on the central glycerol forms a cyclic intramolecular hydrogen-bonded structure with one protonated phosphate (P-OH group). We have therefore chemically synthesized the 2′-deoxycardiolipin analogue, which lacks the central free hydroxyl group, and measured its pH-dissociation behavior by potentiometric titration, under the same conditions as those for CL. The absence of the hydroxyl group changes the titration dramatically so that the deoxy analogue displays two closely spaced low pK values (pK1=1.8; pK2=4.0). The anomalous titration behavior of the second dissociation constant of CL may be attributed to the participation of the central glycerol OH group in stabilizing the formation of a cyclic hydrogen-bonded monoprotonated form of CL, which may function as a reservoir of protons at relatively high pH. This function may have an important bearing on proton pumping in biological membranes.

... Vicki Roth Learning Assistance Services, University of Rochester, Rochester, NY 14618 NSF Highlights Projects Supported by the NSF Division of Undergraduate Education ... Ed. 1996, 1(1). 2. Woodward, A; Gosser, D.; Weiner, M. J. Chem. Educ. 1993, 70, 651. ...

... Jerry L. Sarquis, Linda J. Dixon, David K. Gosser, JA Kampmeier, Vicki Roth, Victor S. Strozak, and Pratibha Varma-Nelson ... City College of New York, CUNY (Woodward, Gosser & Weiner, 1993); the development of the model involved New York City Technical College, St. ...

Prevailing modes of instruction, often passive in nature, do not address crucial issues for student success in science: the need for students to become part of an intellectual community, the differences in the ways students learn, and the powerful role that mentoring can play in involving students in science. Furthermore, students who spend most of their instructional time listening to lectures seldom learn to communicate scientific ideas and to become part of a problem-solving team, skills that industry tells us are crucial to success in the workplace. Workshop Chemistry is a peer-led team-learning model of instruction that provides an active learning experience for students, creates new leadership roles for those who have done well, and involves faculty in the process of reform. A modest reduction in lecture or recitation time is replaced by a two-hour student-directed small group roblem-solving and model-building workshop. The Workshop Chemistry Project is a coalition of faculty, learning specialists, and students from a variety of institutions organized around the theme of developing the workship model as an integral part of the course structure. Several brief descriptions of the workshop courses offered in the Fall of 1995 are provided, along with some sample workshop problems. Surveys, focus groups, student logs, faculty interviews, and actual course results provide insight into the enhanced learning in the workshop and the progress of the project towards its goals.

A pilot program to restructure the conventional two semester general chemistry lecture course for science and engineering majors with two main goals: 1) improve student performance in the course and 2) increase student interest in chemistry.