Carrie L. Hogue

Topological Principles of Borosilicate Glass Chemistry

Borosilicate glasses display a rich complexity of chemical behavior depending on the details of their composition and thermal history. Noted for their high chemical durability and thermal shock resistance, borosilicate glasses have found a variety of important uses from common household and laboratory glassware to high-tech applications such as liquid crystal displays. In this paper, we investigate the topological principles of borosilicate glass chemistry covering the extremes from pure borate to pure silicate end members. Based on NMR measurements, we present a two-state statistical mechanical model of boron speciation in which addition of network modifiers leads to a competition between the formation of nonbridging oxygen and the conversion of boron from trigonal to tetrahedral configuration. Using this model, we derive a detailed topological representation of alkali-alkaline earth-borosilicate glasses that enables the accurate prediction of properties such as glass transition temperature, liquid fragility, and hardness. The modeling approach enables an understanding of the microscopic mechanisms governing macroscopic properties. The implications of the glass topology are discussed in terms of both the temperature and thermal history dependence of the atomic bond constraints and the influence on relaxation behavior. We also observe a nonlinear evolution of the jump in isobaric heat capacity at the glass transition when substituting SiO(2) for B(2)O(3), which can be accurately predicted using a combined topological and thermodynamic modeling approach.

Crystallization of Silicon Pyrophosphate From Silicophosphate Glasses as Monitored by Multi-Nuclear NMR

Binary silicophosphate glasses containing between 7 and 35 mol% P 2 O 5 were made by conventional melt quenching techniques and characterized by 29 Si and 31 P NMR spectroscopy. 31 P and 29 Si NMR data show that, as the P 2 O 5 content is raised in these glasses, the network connectivity is decreased by a dilution of the silicate network with less polymerized Q 3 phosphate groups. In addition to such changes in the network structure, 29 Si NMR spectra for the most P 2 O 5 -rich glasses reveal the presence of silicon atoms with 5- and 6-fold coordination. These species increase in concentration with increasing P 2 O 5 above approximately 30 mol% P 2 O 5 . Self-nucleating SiP 2 O 7 glass-ceramics can be formed from the binary silicophosphate glasses with >25mol% P 2 O 5 . 29 Si and 31 P NMR results were used to monitor the crystallization of SiP 2 O 7 by providing details on amount of crystallinity, relative grain sizes and even composition of the residual glassy matrix. Stabilization of octahedral Si as well as the onset of phase separation correlates with propensity for crystallization of SiP 2 O 7 during subsequent heat treatment.

Chemical identity and mechanism of action and formation of a cell growth inhibitory compound from polycarbonate flasks

This paper reports the chemical identity and mechanism of action and formation of a cell growth inhibitory compound leached from some single-use Erlenmeyer polycarbonate shaker flasks under routine cell culture conditions. Single-use cell culture vessels have been increasingly used for the production of biopharmaceuticals; however, they often suffer from issues associated with leachables that may interfere with cell growth and protein stability. Here, high-performance liquid-chromatography preparations and cell proliferation assays led to identification of a compound from the water extracts of some polycarbonate flasks, which exhibited subline- and seeding density-dependent growth inhibition of CHO cells in suspension culture. Mass spectroscopy, nuclear magnetic resonance spectroscopy, and chemical synthesis confirmed that this compound is 3,5-dinitro-bisphenol A. Cell cycle analysis suggests that 3,5-dinitro-bisphenol A arrests CHO-S cells at the G1/Go phase. Dynamic mass redistribution assays showed that 3,5-dinitro-bisphenol A is a weak GPR35 agonist. Analysis of the flask manufacturing process suggests that 3,5-dinitro-bisphenol A is formed via the combination of molding process with γ-sterilization. This is the first report of a cell culture/assay interfering leachable compound that is formed through γ-irradiation-mediated nitric oxide free radical reaction.