Quantitative analysis of aggregation in dilute solutions of effectively rigid biomacromolecules via the combination of oscillatory flow birefringence and viscoelasticity measurements: example study of aggregation of bovine fibrinogen in aqueous glycerol, and detection of a large aggregate formed on addition of guanidine hydrochloride.

Oscillatory flow birefringence (OFB) properties have been measured for dilute solutions of bovine fibrinogen in 65-68% aqueous glycerol with the Miller-Schrag Thin Fluid Layer (TFL) apparatus employing either titanium or stainless steel surfaces in contact with the solutions. The shearing frequency range was 1 to 2500 Hz, the concentrations ranged from 4 to 8 mg/ml, and measurement temperatures were 9.9, 10.0, and 15.8 degrees C. The data showed evidence of significant amounts of aggregation that apparently is caused by the presence of glycerol; contributions from the various aggregates were readily detected since the staggered half-overlap aggregation in this system results in substantial differences in the rotational relaxation times of the various effectively rigid aggregates. The combination of oscillatory flow birefringence and viscoelasticity (VE) data provided sensitive and precise characterization of aggregation in these example systems; all aggregates exhibited the expected positive optical anisotropy. The length of unaggregated fibrinogen in solution was found to be that obtained via electron microscopy. Addition of guanidine hydrochloride to hopefully reduce aggregation did so but also resulted in formation of a very large (2800 to 3500 A), apparently nearly monodisperse, negatively birefringent aggregate, suggesting that this new species might be formed by lateral aggregation.

Enhancing the prediction of self-handicapping.

Levels of test anxiety, Type A and Type B coronary-prone behavior, fear of failure, and covert self-esteem were studied as predictors of self-handicapping performance attributions for college women who were placed in either a high- (N = 49) or low- (N = 49) evaluative test or task situation. We hypothesized that test anxiety. Type A or Type B level, and their interaction would account for reliable variance in the prediction of self-handicapping. However, we also theorized that underlying high fear of failure and low covert self-esteem would explain the self-handicapping claims of test-anxious and Type A subjects. The results indicated that only high levels of test anxiety and high levels of covert self-esteem were related to women's self-handicapping attributions.

Viscoelastic properties of very dilute paramyosin solutions.

The storage and loss shear moduli, G' and G'', have been measured for dilute solutions of paramyosin from the clam Mercenaria mercenaria in water and glycerol--water mixtures containing potassium chloride and phosphate buffer. The Birnboim--Schrag multiple-lumped resonator was used in the frequency range from 150 to 8100 Hz; the concentration range was 0.7 to 2 X 10(-3) g/mL and the temperature range was 0.0 to 6.0 degrees C. The intrinsic moduli were obtained by extrapolation to infinite dilution. When compared with predictions of Yamakawa for a rigid cylindrical molecule, they agreed at low frequencies but diverged at high frequencies. Excellent agreement was obtained with calculations for a hybrid model whose relaxation times are attributed to rigid-body end-over-end rotation together with some internal modes of motion, probably flexural. The rotational relaxation time agreed rather well with that determined by DeLaney and Krause from electrical birefringence measurements. From the ratio of the rotational to the longest flexural relaxation time, the flexural rigidity and Young's modulus of the paramyosin molecule were estimated by relations derived by Wada and collaborators; the modulus was 1.2 X 10(10) dyn/cm2.