Determination of perfluorooctanoic acid (PFOA) extractable from the surface of commercial cookware under simulated cooking conditions by LC/MS/MS

Salts of pentadecafluorooctanoic acid (PFOA) are polymerization aids used in the manufacture of fluoropolymers; one of the applications of fluoropolymers is the coating of metal cookware products. A method was developed to determine if PFOA might be present in and extracted from the surface of commercial frying pans coated with a DuPont fluoropolymer under simulated cooking conditions. Commercial grade cookware was obtained, then extracted with water and ethanol/water mixtures at 100 and 125 degrees C, and the resulting extracts were analyzed by liquid chromatography tandem mass spectrometry (LC/MS/MS). Detection and quantification limits as low as 100 pg cm(-2) were demonstrated. None of the fluoropolymer treated cookware samples analyzed showed detectable levels of PFOA when extracted under simulated cooking conditions.     

Extending the use of certified reference sediments for assessment of accuracy in determinations of trace metals

Straightforward analysis for components in a single certified reference sediment is of limited use for assessing the accuracy of environmental determinations. A systematic approach requires mixing of certified sediments, one with another and with environmental samples, and the preparation of secondary reference material by the laboratory. Use of Youden pairs, reference material embedded in samples and linear models should enable valid accuracy statements to be made based on well known statistical concepts. For assessing accuracy, reference sediments which are matched in particle size, and are end-members for components or sediment types are most useful.     

A new photochemically removable protecting group for amines

A new arylmethylsulfonyl chloride reacts with secondary or primary amines to give sulfonamides which can be photochemically cleaved, making it suitable for use as a photoremovable protecting group.     

General deoxyribozyme-catalyzed synthesis of native 3'-5' RNA linkages

An elusive goal for nucleic acid enzymology has been deoxyribozymes that ligate RNA rapidly, sequence-generally, with formation of native 3'-5' linkages, and in preparatively useful yield. Using in vitro selection, we have identified Mg2+- and Zn2+-dependent deoxyribozymes that simultaneously fulfill all four of these criteria. The new deoxyribozymes operate under practical incubation conditions and have modest RNA substrate sequence requirements, specifically D downward arrowRA for 9DB1 and A downward arrowR for 7DE5 (D = A, G, or U; R = A or G). These requirements are comparable to those of deoxyribozymes such as 10-23 and 8-17, which are already widely used as biochemical tools for RNA cleavage. We anticipate that the 9DB1 and 7DE5 deoxyribozymes will find immediate practical application for RNA ligation.     

DNA-templated three-branched nanostructures for nanoelectronic devices

Three-branched DNA molecules have been designed and assembled from oligonucleotide components. These nucleic acid constructs contain double- and single-stranded regions that control the hybridization behavior of the assembly. Specific localization of a single streptavidin molecule at the center of the DNA complex has been investigated as a model system for the directed placement of nanostructures. Highly selective silver and copper metallization of the DNA template has also been characterized. Specific hybridization of these DNA complexes to oligonucleotide-coupled nanostructures followed by metallization should provide a bottom-up self-assembly route for the fabrication and characterization of discrete three-terminal nanodevices.     

Open-tubular capillary electrochromatography/electrospray ionization-mass spectrometry using polymeric surfactant as a stationary phase coating

We describe the use of the polymeric surfactant poly(sodium undecylenic sulfate) (poly-SUS) as a stationary phase coating in open-tubular capillary electrochromatography (OT-CEC) coupled with electrospray ionization-mass spectrometry (ESI-MS) for the analysis of beta-blocker and benzodiazepine analytes. The production of a polymeric surfactant coating on the capillary inner wall involves (i) adsorption of the cationic polymer poly(diallyldimethylammonium chloride) (PDADMAC) to the inner surface of capillary, and (ii) adsorption of the negatively charged poly-SUS onto the cationic polymer layer via strong physical interaction of the two polymer layers. As compared with micellar electrokinetic chromatography (MEKC) coupled with ESI-MS, the main advantage of this proposed method is minimization of introduction of the monomeric or polymeric surfactant into the mass spectrometer, thus avoiding the interference of the nonvolatile micelle in ESI-MS. The effects of buffer pH and applied voltage on the separation of the analytes are also discussed. Under optimum conditions, four of the five beta-blockers and four benzodiazepines are separated.     

(18)O]-oxygen incorporation reveals novel pathways in spiroacetal biosynthesis by Bactrocera cacuminata and B. cucumis

The origins of the oxygen atoms in 1,7-dioxaspiro[5.5]undecane (1) and hydroxyspiroacetal (2) from Bactrocera cacuminata, and in 2,8-dimethyl-1,7-dioxaspiro[5.5]undecane (3) and hydroxyspiroacetal (4) from B. cucumis, have been investigated by incorporation studies from both [(18)O(2)]-dioxygen and [(18)O]-water. Combined GC-MS examination and high-field NMR analysis have demonstrated that all oxygen atoms in 1 and 2 from B. cacuminata are dioxygen derived, but in contrast, the spiroacetals 3 and 4 from B. cucumis incorporate one ring oxygen from water and one ring oxygen (and the hydroxyl oxygen in 4) from [(18)O(2)]-dioxygen. These results reveal not only the generality of monoxygenase mediation of spiroacetal formation in Bactrocera sp., but also an unexpected complexity in their biosynthesis. A general paradigm accommodating these and other observations is presented.     

Substitution reactions of [Ru(dppe)(CO)(H(2)O)(3)][OTf](2)

The labile nature of the coordinated water ligands in the organometallic aqua complex [Ru(dppe)(CO)(H(2)O)(3)][OTf](2) (1) (dppe = Ph(2)PCH(2)CH(2)PPh(2); OTf = OSO(2)CF(3)) has been investigated through substitution reactions with a range of incoming ligands. Dissolution of 1 in acetonitrile or dimethyl sulfoxide results in the facile displacement of all three waters to give [Ru(dppe)(CO)(CH(3)CN)(3)][OTf](2) (2) and [Ru(dppe)(CO)(DMSO)(3)][OTf](2) (3), respectively. Similarly, 1 reacts with Me(3)CNC to afford [Ru(dppe)(CO)(CNCMe(3))(3)][OTf](2) (4). Addition of 1 equiv of 2,2'-bipyridyl (bpy) or 4,4'-dimethyl-2,2'-bipyridyl (Me(2)bpy) to acetone/water solutions of 1 initially yields [Ru(dppe)(CO)(H(2)O)(bpy)][OTf](2) (5a) and [Ru(dppe)(CO)(H(2)O)(Me(2)bpy)][OTf](2) (6a), in which the coordinated water lies trans to CO. Compounds 5a and 6a rapidly rearrange to isomeric species (5b, 6b) in which the ligated water is trans to dppe. Further reactivity has been demonstrated for 6b, which, upon dissolution in CDCl(3), loses water and coordinates a triflate anion to afford [Ru(dppe)(CO)(OTf)(Me(2)bpy)][OTf] (7). Reaction of 1 with CH(3)CH(2)CH(2)SH gives the dinuclear bridging thiolate complex [[(dppe)Ru(CO)](2)(mu-SCH(2)CH(2)CH(3))(3)][OTf] (8). The reaction of 1 with CO in acetone/water is slow and yields the cationic hydride complex [Ru(dppe)(CO)(3)H][OTf] (9) via a water gas shift reaction. Moreover, the same mechanism can also be used to account for the previously reported synthesis of 1 upon reaction of Ru(dppe)(CO)(2)(OTf)(2) with water (Organometallics 1999, 18, 4068).     

Anatoxins and degradation products, determined using hybrid quadrupole time-of-flight and quadrupole ion-trap mass spectrometry: forensic investigations of cyanobacterial neurotoxin poisoning

The potent neurotoxins from cyanobacteria, anatoxin-a (AN), its methyl analogue, homoanatoxin-a (HMAN), and their degradation products, have been studied using nano-electrospray hybrid quadrupole time-of-flight mass spectrometry (QqTOF-MS). The anatoxin degradation products, which are readily produced in vivo by either reduction or epoxidation, were also examined in this study. The high mass accuracy QqTOF-MS data was used to confirm formula assignments for major product ions and quadrupole ion-trap (QIT)-MS was used to construct fragmentation pathways for anatoxins. Significant differences between these fragmentation pathways were observed. Comparisons between the spectra of compounds that differ in side-chain length (the AN and HMAN series) were used to identify ions that are characteristic of the homologues. The application to forensic samples in which the principal neurotoxin had undergone rapid biodegradation has been demonstrated and used to confirm anatoxin poisoning of dogs.     

Dihydrogen complexes of rhodium: [RhH2(H2)x (PR3)2]+ (R = Cy, iPr; x = 1, 2)

Addition of H2 (4 atm at 298 K) to [Rh(nbd)(PR3)2][BAr(F)4] [R = Cy, iPr] affords Rh(III) dihydride/dihydrogen complexes. For R = Cy, complex 1a results, which has been shown by low-temperature NMR experiments to be the bis-dihydrogen/bis-hydride complex [Rh(H)2(eta2-H2)2(PCy3)2][BAr(F)4]. An X-ray diffraction study on 1a confirmed the {Rh(PCy3)2} core structure, but due to a poor data set, the hydrogen ligands were not located. DFT calculations at the B3LYP/DZVP level support the formulation as a Rh(III) dihydride/dihydrogen complex with cis hydride ligands. For R = iPr, the equivalent species, [Rh(H)2(eta2-H2)2(P iPr3)2][BAr(F)4] 2a, is formed, along with another complex that was spectroscopically identified as the mono-dihydrogen, bis-hydride solvent complex [Rh(H)2(eta2-H2)(CD2Cl2)(P iPr3)2][BAr(F)4] 2b. The analogous complex with PCy3 ligands, [Rh(H)2(eta2-H2)(CD2Cl2)(PCy3)2][BAr(F)4] 1b, can be observed by reducing the H2 pressure to 2 atm (at 298 K). Under vacuum, the dihydrogen ligands are lost in these complexes to form the spectroscopically characterized species, tentatively identified as the bis hydrides [Rh(H)2(L)2(PR3)2][BAr(F)4] (1c R = Cy; 2c R = iPr; L = CD2Cl2 or agostic interaction). Exposure of 1c or 2c to a H2 atmosphere regenerates the dihydrogen/bis-hydride complexes, while adding acetonitrile affords the bis-hydride MeCN adduct complexes [Rh(H)2(NCMe)2(PR3)2][BAr(F)4]. The dihydrogen complexes lose [HPR3][BAr(F)4] at or just above ambient temperature, suggested to be by heterolytic splitting of coordinated H2, to ultimately afford the dicationic cluster compounds of the type [Rh6(PR3)6(mu-H)12][BAr(F)4]2 in moderate yield.