Virginia D. Hogan

Bio: Virginia D. Hogan is an academic researcher from Picatinny Arsenal. The author has contributed to research in topics: Potassium perchlorate & Ignition system. The author has an hindex of 5, co-authored 9 publications receiving 64 citations.

Liquid scintillation counting of aqueous samples

Abstract: A sample preparation method which permits liquid scintillation counting of aqueous suspensions or dry powders is described The addition of 4% by weight of Cab-O-Sil (finely divided silicon dioxide) to the liquid scintillation gel produces a transparent and colorless gel which is stable for 1 to 2 weeks. Counting efficiency of 65 and 14% is reported for C/sup 14/- and H/sup 3/-labeled compounds, respectively, which are soluble or suspended in milk. (C.J.G.)

Precision Measurements of Binary and Multicomponent Diffusion Coefficients in Protein Solutions Relevant to Crystal Growth: Lysozyme Chloride in Water and Aqueous NaCl at pH 4.5 and 25 °C ┴

Abstract: Accurate models of protein diffusion are important in a number of applications, including liquid−liquid phase separation and growth of protein crystals for X-ray diffraction studies. In concentrated multicomponent protein systems, significant deviations from pseudobinary behavior can be expected. Rayleigh interferometry is used to measure the four elements (Dij)v of the ternary diffusion coefficient matrix for the extensively investigated protein, hen egg-white lysozyme (component 1) in aqueous NaCl (component 2) at pH 4.5 and 25 °C. These are the first multicomponent diffusion coefficients measured for any protein system at concentrations high enough to be relevant to modeling and prediction of crystal growth or other phase transitions, and the first for a system involving lysozyme at any concentration. The four ternary diffusion coefficients for the system lysozyme chloride/NaCl/water are reported for lysozyme chloride at 0.60 mM (8.6 mg/mL) and NaCl at concentrations of 0.25, 0.50, 0.65, 0.90, and 1.30...

Extraction of Thermodynamic Data from Ternary Diffusion Coefficients. Use of Precision Diffusion Measurements for Aqueous Lysozyme Chloride-NaCl at 25 °C To Determine the Change of Lysozyme Chloride Chemical Potential with Increasing NaCl Concentration Well into the Supersaturated Region †

Abstract: For ternary systems, we present a method for using measured values of the four ternary diffusion coefficients and the Onsager reciprocal relations to extract derivatives of solute chemical potentials with respect to solute molar concentrations. The method is applicable to systems in which the molar concentration of one solute is very small compared to that of the other, and also small enough that an inverse concentration dependence dominates certain activity coefficient derivatives. These conditions apply to a large number of aqueous systems involving macromolecules of biological interest. Unlike other techniques, the present method can be used to study undersaturated and supersaturated solutions. The approach is illustrated for the lysozyme chloride - NaCl-H2O system at 25 °C, using data reported here for pH 6.0 at 0.60 mM (8.6 mg/mL) lysozyme chloride and 0.25, 0.50, 0.65, 0.90, and 1.30 M (1.4, 2.8, 3.7, 5.1, and 7.2 wt %) NaCl concentrations, and our earlier data for pH 4.5 at the same concentrations. We use these solute chemical potential derivatives to compute the protein cation charge approximately, and to construct a function approximating the derivative of the lysozyme chloride chemical potential with respect to NaCl concentration, which we integrate over a range of NaCl concentrations. This provides the change of the lysozyme chloride chemical potential with NaCl concentration well into the supersaturated region, and hence provides the driving force for nucleation and crystal growth of lysozyme chloride as a function of the extent of supersaturation. We also compute the diffusion Onsager coefficients (Lij)0 for each composition at pH 4.5 and 6.0. Binary diffusion coefficients of aqueous lysozyme chloride at 0.89 mM (12.7 mg/mL) for pH values from 4.0 to 6.0, and at pH 6.0 for concentrations from 0.25 to 1.95 mM (3.6-27.9 mg/mL) are also reported.

Mechanism of Protein−Poly(ethylene glycol) Interaction from a Diffusive Point of View

Abstract: The first multicomponent diffusion data ever determined in protein−polymer systems are presented for the system lysozyme(1)−PEG 400(2)−water. Although there are no specific interactions between protein and polymer, the cross-term diffusion coefficient D21, that links the PEG flow to the protein concentration gradient, is up to 35 times the main-term diffusion coefficient of the protein. This observation can only be due to a “crowding effect” and not to specific interactions, such as electrostatic ones. The exclusion effect is also qualitatively confirmed by the measured counter-flow associated with the protein motion. On the base of a hard core potential, our recent predictive equations are used to predict diffusion coefficients in this ternary system, and a good agreement with the experimental D21 is obtained. The PEG concentration dependence of the main-term diffusion coefficient of the protein cannot be interpreted exclusively by the excluded volume effect. Some dielectric effect or aggregation phenome...

Investigation on thermal analysis of binary zirconium/oxidant pyrotechnic systems

Abstract: Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) have been used to examine the thermal behavior of powdered zirconium with some pyrotechnic oxidants, in relation to the behavior of the individual constituents. The results showed that decomposition temperature for pure compounds (potassium nitrate, potassium chlorate, potassium perchlorate, barium nitrate and barium peroxide) are 540, 472, 592, 745 and 600°C, respectively. Pure zirconium powder ignited in air at about 600°C. On the other hand, TG/DTA of Zr/KClO3 indicates that this mixture decomposes at 375°C. Also, when KClO3 is replaced by KClO4 as oxidizer of the fuel, zirconium, the sensitivity of the mixture to thermal ignition will decrease. Zr/KNO3 pyrotechnic mixture has ignition temperature around 427°C. Zr/Ba(NO3)2 pyrotechnic system has a fusion temperature around 625°C and decomposes at 663°C. However, when Ba(NO3)2 is replaced by BaO2 as oxidizer in pyrotechnic mixture containing zirconium, the ignition temperature decr...