Stephen E. Schullery

Are Heterogeneous or Homogeneous Groups More Beneficial to Students

This study investigated the relative benefits to the student of working in homogeneous versus heterogeneous classroom groups. Correlation analysis of 18 desirable outcomes versus 8 personality-based heterogeneity variables reveals that heterogeneity associates with advantages as well as disadvantages. Ways in which group composition might be customized to benefit students with particular needs or to emphasize particular goals are described, along with their potential downsides.

Relationship of Argumentativeness to Age and Higher Education

Communication traits comprise an important part of communication theory, yet, little is known about either their longitudinal stability over the life course or their cross‐sectional uniformity in the adult population. We report a cross‐sectional study (N = 639) of trait argumentativeness as a function of age and higher education, and test hypotheses based on physiological, cultural, and developmental perspectives. Argumentativeness associates negatively with age and positively with level of higher education. Optimal scaling shows that the age‐related argumentativeness decrease among men is greatest through the twenties and levels off around age forty‐five. By contrast, the decrease among women begins slowly around age thirty and accelerates through the fifties. The education effect is stronger among men than women, and neither the age nor education effects are significant in a high‐argumentative subsample (median split).

Phospholipid vesicle fusion and drug loading: temperature, solute and cholesterol effects, and, a rapid preparation for solute-loaded vesicles

Abstract The fusion of sonicated dipalmitoylphosphatidylcholine (DPPC) vesicles was studied by gel-exclusion chromatography as a function of temperature, permeable and impermeable solute concentration, and cholesterol content of the bilayer membrane. Fusion is faster at lower temperatures: there is no fusion at or above 35.5°C (0.10 M DPPC/0.1 M K 2 SO 4 /0.01 M Hepes buffer (pH 7.4)/0.02% NaN 3 ). There is about 10% fusion after 1 week at 30°C, and about 60% fusion after 2 days at 13–25°C. Between 13 and 8°C, the fusion product changes from 700-A-diameter vesicles to the 950-A vesicles previously reported by Wong et al. (Wong, M., Anthony, F.W., Tillack, T.W. and Thompson, T.E. (1982) Biochemistry 21, 4126–4132). At 1°C, fusion is about 90% complete after 1 day. Membrane-impermeable solutes (NaCl, trehalose and glucose) inhibit fusion in a manner reflecting the total particle concentration. There is no detectable fusion after 3 days (22°C) in either 1.0 M NaCl or 2.0 M sugar, the highest concentrations studied. A suggested explanation is that impermeable solutes osmotically inhibit the influx of solution that accompanies the fusion of vesicles to form a larger vesicle, and, could conceivably thereby inhibit the fusion reaction. By contrast, membrane-permeable solutes (glycerol, ethylene glycol, propylene glycol and ethanol) dramatically increase the fusion rate. 1.0 M ethanol causes 100% fusion in 15–30 min at 22°C. The simultaneous presence of 0.15 M NaCl entirely negates the fusion-promoting effect of 1.0 M ethanol. 1 mol% cholesterol completely inhibits fusion in 0.1 M KCl (20°C), and greatly slows it down either in 1.0 M ethanol at 20°C or in 0.1 M KCl at 4°C. A suggested mechanism is that cholesterol might concentrate in and stabilize bilayer lattice defect sites that are critical for the fusion reaction. The trapping efficiency of vesicles formed by the fast ethanol fusion conditions in the presence of the water-soluble markers, chromate and arsenazo III, ranged from 9.0 to 12.7% of the marker captured in the vesicles, corresponding to trapped volumes of 1.8 to 2.5 1/mol DPPC. Bromophenol blue gave anomalously high values of 67% and 13 1/mol DPPC, which presumably reflect binding, in addition to encapsulation.

Dipalmitoylphoshatidylcholine-palmitic acid phase diagram studied by 13C nuclear magnetic resonance

The phase diagram of dipalmitoylphosphatidylcholine (DPPC) and palmitic acid mixtures in excess D2O was studied by 13C-NMR. Phase boundaries were determined from plots of apparent spin-spin relaxation time T2 (for both choline methyl and fatty acid chain carbons) versus temperature. A peritectic transition in the 1-10 mol% region, whose existence has been theoretically inferred from the Gibbs phase rule but which was undetectable by differential thermal analysis (DTA) (S.E. Schullery et al. Biochemistry, 20 (1981) 6818-6824), was located by NMR at 41.6 degrees C. A second, nearby peritectic line at 44 degrees C, which had been shown by DTA to extend from about 3-25 mol% palmitic acid, was seen by NMR only above 10 mol%. The palmitic acid/DPPC complex (2:1), with a sharp melting point at 64 degrees C, reported in earlier studies, was also seen by NMR. A phase diagram including both NMR and DTA results is presented. Important general conclusions from this study are: (i) NMR and scanning thermal analysis are complementary techniques for phase studies; each can see transitions that are invisible to the other. (ii) The case for the applicability of the Gibbs phase rule to lipid bilayer systems has been strengthened by the observance of two predicted, close-spaced boundaries. (iii) Low concentrations of fatty acids and related molecules can not be assumed to disperse as simple ideal solutes in the bilayer matrix.

Studies on phosphatidylcholine model membranes. I. Size-heterogeneity effect on permeability measurements

Abstract The osmotic shrinking rate of unsonicated egg phosphatidylcholine (PC) liposomes in hypertonic NaCl was studied by determining the initial time rate of change of the reciprocal of the optical density, d(OD) −1 d t , in a stopped-flow kinetics apparatus, d(OD) −1 dt was found to be a linear function of reciprocal OD and reciprocal PC concentration, where the linear parameters were quite different depending on the size distribution of liposomes in the dispersion. An approximate theoretical calculation of relative shrinking rates suggests that the larger liposomes mask the osmotic activity of smaller liposomes in the same dispersion. It is concluded that this method should only be used for comparing osmotic permeabilities of liposomes dispersions when both the OD and liposome size distribution of the dispersions are the same.

Binding to δ and μ opioid receptors by deltorphin I/II analogues modified at the Phe3 and Asp4/Glu4 side chains: a report of 32 new analogues and a QSAR study

The synthesis and binding affinities of 32 X3Gly4 dual-substitution analogues of the natural opioid heptapeptides deltorphin I and II are reported. A multiple regression QSAR analysis was performed using those results along with literature data for the X3Asp4 and Phe3X4 side chain analogues. Fitting to a three-term potential well model with hydrophobic and van der Waals attraction terms and a steric repulsion term indicates that the delta and mu receptor sites for binding the residue three side chain are similar, and that the binding interaction is primarily van der Waals and secondarily hydrophobic. Further analysis indicates that both sites are more constrained with respect to side chain length than width or thickness, and the mu site appears to be somewhat larger. A binding model consistent with these findings pictures the native third residues Phe ring laying on a step notched out of the receptor surface, pointing toward the back (riser) of the step, and sandwiched between the receptor and ligand. However, the binding sites for the residue four side chains are quite different on delta and mu receptors. Binding to the delta site appears to involve both electrostatic attraction (probably to a partial positive charge) and van der Waals attraction, but not necessarily hydrogen bonding, and more constraint with respect to side chain length than width or thickness. In contrast, there is no evidence for any kind of binding attraction between the side chain of residue four and the mu site, which acts more as steric repulsion site, as though the space that is a pocket on the delta receptor is filled in on the mu receptor. A regression model based only on steric repulsion by van der Waals bulk and/or the effective bulk of a hydration layer accounts for over 80% of the residue four related variation in mu affinity.

Amine and phenol solvation by Lewis bases: calculated binding constants and stoichiometries presented as evidence of bifurcated and trifurcated hydrogen bonds

Abstract Evidence is presented for multiple solvation of individual polar hydrogens by aprotic Lewis bases, forming bifurcated, trifurcated and possibly tetrafurcated hydrogen bonds. In addition to this primary furcation, secondary bifurcation or trifurcation to multiple atoms within one Lewis base molecule occurs when the orbital geometry is appropriate. For example, a single hydrogen appears to be solvated by all six oxygens of two trioxanes. We propose that such multiple bonding is characteristic of solvation by hydrogen bonding and is to be expected whenever it is sterically possible and one of the participants is in sufficient excess to qualify as “solvent”. These conclusions are based on non-linear least squares fitting of a two-site solvation model to equilibrium data for the proton-transfer complex of 2,4-dinitrophenol and diethylamine in benzene/Lewis base mixed solvents. Solvation binding constants and stoichiometries for both the amine in the proton-transfer complex and the free dinitrophenol are reported for 21 different Lewis bases. The most common stoichiometry is two solvent molecules per hydrogen, corresponding to primary bi furcation. The solvation binding constants range from 10 to 200 (molarity scale) for the complexed amine, and from 2 to 100 for the free dinitrophenol. Unexpectedly large solvation constants for a cyclic triether and certain cyclic diethers are attributed to secondary trifurcation and bifurcation, respectively, involving all of the oxygen atoms in the ring.

Gel filtration of egg phosphatidylcholine vesicles

The abilities of Sepharose 2B (Pharmacia), Controlled Pore Glass (Electro-Nucleonics) and Bio-Gel A150m (Bio-Rad) to purify small unilamellar vesicles prepared by sonication and the ethanol-injection methods were compared. The Bio-Gel causes complete aggregation of the sonicated vesicles and partial aggregation of the ethanol-injection vesicles. Both Sepharose and Controlled Pore Glass are acceptable for purifying vesicles from multilamellar liposomes; however, neither will separate the vesicles from sonication by-products which might be formed.

Short range solvation of proton transfer complexes by 2,2-dimethyl-1,3-dioxane and trioxane☆

Abstract Bifurcated hydrogen bonds are involved in the short range solvation of amines by electron donating solvents. Further, six-membered ring cyclic diethers involve interaction of both oxygens of the diether with the amine proton. We report the expansion of these results to include 2,2-dimethyl-1,3-dioxane and trioxane. The results suggest that the latter is involved in a trifurcated hydrogen bond.

Studies on phosphatidylcholine model membranes. I. Iodide permeability measurement by specific ion electrode

An iodide specific ion electrode was used to measure iodide released from egg phosphatidylcholine liposomes after passage through an ion exchange column. The permeation process was shown to be a sum of two separate first order processes. The method permits linear initial rates of iodide release to be determined for the first 5 min of permeation. Iodide permeability in the absence of Tris buffer was found to be a decreasing function of pH. In the presence of Tris, iodide permeability went through a minimum ofrom ph 7.3-8.5. the permeability was found to decrease when cholesterol was incorporated into the liposomes.