Potential confounders of bisphenol-a analysis in dental materials.

OBJECTIVES: In the published literature, a variety of analytical methods have been used to quantify and report bisphenol A (BPA) release from dental resins. The objective of this study was to compare results obtained for quantification of BPA in dental resin extracts using an LC/UV analytical method and an LC/MS/MS method. METHODS: A cured Bis-GMA-based resin representative of commercial dental products was extracted according to ISO 10993 guidelines for medical devices. d16BPA was included as an internal standard. Sample processing followed expert recommendations for minimizing BPA sample contamination. Extracts were separated using HPLC methods and analyzed for BPA using LC/UV and LC/MS/MS detection methods. RESULTS: The reported BPA concentrations were about 30-fold higher using LC/UV vs. LC/MS/MS. Full scan LC/MS/MS in both positive and negative modes showed that the apparent high BPA values seen with LC/UV were caused by co-elution of a previously unidentified chemical, thought to arise from one of the polymerization initiators. SIGNIFICANCE: These results emphasize the potential difficulties in obtaining accurate analyses of BPA in complex mixtures such as dental resins and their extracts. Both good separation methodology and a detection method with high specificity and sensitivity are important to avoid incorrect identification of extractables, and consequent incorrect quantitative assignments for species of interest. Reliable methods are essential for accurate estimation of patient exposure to BPA and development of meaningful health risk assessments.

Alpha,2-, alpha,3-, and alpha,4-dehydrophenol radical anions: formation, reactivity, and energetics leading to the heats of formation of alpha,2-, alpha,3-, and alpha,4-oxocyclohexadienylidene.

We have regiospecifically generated the alpha,2-, alpha,3-, and alpha,4-dehydrophenoxide anions by collisional activation of o-, m-, and p-nitrobenzoate. The alpha,2 and alpha,4 isomers also were synthesized by reacting o-benzyne radical anion with carbon dioxide and electron ionization of p-diazophenol. All three dehydrophenol radical anions were differentiated from each other and identified by probing their chemical reactivity with several reagents. Each isomer was converted to phenoxide and its corresponding quinone as well. Thermochemical measurements were carried out on all three radical anions and their hydrogen-atom affinities, proton affinities, and electron binding energies are reported. These measured quantities are combined in thermodynamic cycles to derive the heats of formation of each of the radical anions and their corresponding carbenes (i.e., alpha,2-, alpha,3-, and alpha,4-dehydrophenol). These results are compared to MCQDPT2, G3, G2+(MP2), and B3LYP calculations and experimental data for appropriate reference compounds.

Formation of a 1-bicyclo[1.1.1]pentyl anion and an experimental determination of the acidity and C-H bond dissociation energy of 3-tert-butylbicyclo[1.1.1]pentane.

Decarboxylation of 1-bicyclo[1.1.1]pentanecarboxylate anion does not afford 1-bicyclo[1.1.1]pentyl anion as previously assumed. Instead, a ring-opening isomerization which ultimately leads to 1,4-pentadien-2-yl anion takes place. A 1-bicyclo[1.1.1]pentyl anion was prepared nevertheless via the fluoride-induced desilylation of 1-tert-butyl-3-(trimethylsilyl)bicyclo[1.1.1]pentane. The electron affinity of 3-tert-butyl-1-bicyclo[1.1.1]pentyl radical (14.8 plus minus 3.2 kcal/mol) was measured by bracketing, and the acidity of 1-tert-butylbicyclo[1.1.1]pentane (408.5 +/- 0.9) was determined by the DePuy kinetic method. These values are well-reproduced by G2 and G3 calculations and can be combined in a thermodynamic cycle to provide a bridgehead C-H bond dissociation energy (BDE) of 109.7 +/- 3.3 kcal/mol for 1-tert-butylbicyclo[1.1.1]pentane. This bond energy is the strongest tertiary C-H bond to be measured, is much larger than the corresponding bond in isobutane (96.5 +/- 0.4 kcal/mol), and is more typical of an alkene or aromatic compound. The large BDE can be explained in terms of hybridization.