Novel Dechlorane Analogues and Possible Sources in Peregrine Falcon Eggs and Shark Livers from the Western North Atlantic Regions.

During the investigation of dechlorane-related chemicals in North American wildlife, two unknown polychlorinated compounds (referred to as U1 and U2) were discovered. After extensive sample cleanup, structural information on U1 and U2 was characterized by gas chromatography (GC) coupled with single quadrupole mass spectrometer (MS) or GC-quadrupole time-of-flight (QToF) MS. Mass spectral evidence suggests that both U1 and U2 are structurally related to Dechlorane 603 (Dec603; C17H8Cl12), an analogue of the chlorinated flame retardant Dechlorane Plus. From the results we suspect U1 (C17H9Cl11) to be a monohydro analogue of Dec603 (i.e., one chlorine atom in Dec603 is replaced by a hydrogen atom). U1 may be formed via the degradation of Dec603's stereoisomers or present as an impurity in commercial Dec603 products. Mass spectral characterization of U2 (C17H7OCl11) suggests it is a carbonylic derivative of Dec603, likely formed via metabolic transformation of Dec603 or its photoisomer. Semiquantitative measurement revealed that U1 and U2 were present at estimated median concentrations of 49 ng/g lipid weight (lw) and 59 ng/g lw in peregrine falcon ( Falco peregrinus) eggs, from the mid-Atlantic region of the United States, and 4.6 and 3.0 ng/g lw in shortfin mako shark ( Isurus oxyrinchus) livers from the western North Atlantic Ocean, respectively. Our results demonstrate the occurrence of these two novel Dec603-related chemicals in both terrestrial and aquatic ecosystems.

Characterization of Nine Isomers in Commercial Samples of Perfluoroethylcyclohexanesulfonate and of Some Minor Components Including PFOS Isomers.

Electrochemical fluorination of 4-ethylbenzenesulfonyl halides produces a mixture of compounds that has found extensive use as an erosion inhibitor in aircraft hydraulic fluids. This paper reports a study of the composition of commercial samples of this material from two industrial scale manufacturers in terms of the structures and relative concentrations of their components, the major of which is perfluoroethylcyclohexanesulfonate (PFECHS). Fractionation of one of these mixtures by column chromatography produced fractions in which all significant components were of sufficient purity to allow assignment of their structures by 19F NMR spectroscopy. Assessment of the relevant signals in the 19F NMR spectra of the commercial mixtures by integration revealed the presence of 14 constituents at levels ≥0.5% in terms of molar contributions. Ten of these involve five pairs of geometric isomers, including cis- and trans-PFECHS which accounted for between 55% and 60% of the components present. Three constituents were determined to be isomers of perfluorooctanesulfonate (PFOS), two branched and the other linear PFOS itself. The availability of samples of the various components also allowed us to identify the compounds responsible for the peaks observed when the commercial samples were analyzed by LC/MS using either C18 or perfluorophenyl stationary phases.

Dechlorinated Analogues of Dechlorane Plus.

Degradation products of the chlorinated additive flame retardant Dechlorane Plus (DP) have been discovered globally. However, the identity of many of these species remains unknown due to a lack of available analytical standards, hindering the ability to quantitatively measure the amounts of these compounds in the environment. In the present study, synthetic routes to possible dechlorinated DP derivatives were investigated in an effort to identify the environmentally significant degradation products. The methano-bridge chlorines of anti- and syn-DP were selectively replaced by hydrogen atoms to give six new hydrodechlorinated DP analogues. The identity and absolute configuration of all of these compounds were confirmed by GC-MS, NMR spectroscopy, and X-ray diffraction studies. These compounds were observed in sediment samples from streams and rivers in relatively rural areas of Ontario and are thus environmentally relevant.

Enantioselective Analytical- and Preparative-Scale Separation of Hexabromocyclododecane Stereoisomers Using Packed Column Supercritical Fluid Chromatography.

Hexabromocyclododecane (HBCDD) is an additive brominated flame retardant which has been listed in Annex A of the Stockholm Convention for elimination of production and use. It has been reported to persist in the environment and has the potential for enantiomer-specific degradation, accumulation, or both, making enantioselective analyses increasingly important. The six main stereoisomers of technical HBCDD (i.e., the (+) and (-) enantiomers of α-, ß-, and γ-HBCDD) were separated and isolated for the first time using enantioselective packed column supercritical fluid chromatography (pSFC) separation methods on a preparative scale. Characterization was completed using published chiral liquid chromatography (LC) methods and elution profiles, as well as X-ray crystallography, and the isolated fractions were definitively identified. Additionally, the resolution of the enantiomers, along with two minor components of the technical product (δ- and ε-HBCDD), was investigated on an analytical scale using both LC and pSFC separation techniques, and changes in elution order were highlighted. Baseline separation of all HBCDD enantiomers was achieved by pSFC on an analytical scale using a cellulose-based column. The described method emphasizes the potential associated with pSFC as a green method of isolating and analyzing environmental contaminants of concern.

Evidence for Anaerobic Dechlorination of Dechlorane Plus in Sewage Sludge.

The environmental occurrence of dechlorination moieties from the high production volume flame retardant, Dechlorane Plus (DP), has largely been documented; however, the sources have yet to be well understood. In addition, few laboratory-based studies exist which identify the cause for the occurrence of these chemicals in the environment or humans. Anaerobic dechlorination of the two DP isomers was investigated using a laboratory-simulated wastewater treatment plant (WWTP) environment where anaerobic digestion is used as part of the treatment regime. Known amounts of each isomer were added separately to sewage sludge which provided the electron-donating substrate and at prescribed time points in the incubation, a portion of the media was removed and analyzed for DP and any dechlorination metabolites. After 7 days, monohydrodechlorinated products were observed for both the syn- and anti-DP which were continued throughout the duration of our study (49 days) in an increasing manner giving a calculated formation rate of 0.48 ± 0.09 and 0.79 ± 0.12 pmols/day for syn- and anti-DP, respectively. Furthermore, we observed a second monohydrodechlorinated product only in the anti-DP isomer incubation medium. This strongly suggests that anti-DP is more susceptible to anaerobic degradation than the syn isomer. We also provide compelling evidence to the location of chlorine loss in the dechlorination DP analogues. Finally, the dechlorination DP moieties formed in our study matched the retention times and identification of those observed in surficial sediment located downstream of the WWTP.

Synthesis, reactivity, and computational analysis of halophosphines supported by dianionic guanidinate ligands.

The reported chemistry and reactivity of guanidinate supported group 15 elements in the +3 oxidation state, particularly phosphorus, is limited when compared to their ubiquity in supporting metallic elements across the periodic table. We have synthesized a series of chlorophosphines utilizing homo- and heteroleptic (dianionic)guanidinates and have completed a comprehensive study of their reactivity. Most notable is the reluctancy of these four-membered rings to form the corresponding N-heterocyclic phosphenium cations, the tendency to chemically and thermally eliminate carbodiimide, and the scarcely observed ring expansion by insertion of a chloro(imino)phosphine into a P-N bond of the P-N-C-N framework. Computational analysis has provided corroborating evidence for the unwillingness of the halide abstraction reaction by demonstrating the exceptional electron acceptor properties of the target phosphenium cations and the underscoring strength of the P-X bond.

Electrogenerated chemiluminescence of triazole-modified deoxycytidine analogues in N,N-dimethylformamide.

Triazole-modified deoxycytidines have been prepared for incorporation into single-stranded deoxyribonucleic acid (ssDNA). Electrochemical responses and electrogenerated chemiluminescence (ECL) of these deoxycytidine (dC) analogues, 1-4, were investigated as the monomers. Cyclic voltammetry and differential pulse voltammetry techniques were used to determine the oxidation and reduction potentials of 1-4, along with the reversibility of their electrochemical reactions. The dC analogues, in N,N-dimethylformamide containing 0.1 M tetra-n-butylammonium perchlorate as electrolyte, exhibited weak relative ECL efficiencies following the annihilation mechanism, while these efficiencies were enhanced with the use of benzoyl peroxide following the coreactant mechanism. It was shown that these nucleosides could generate excited monomers, and excimers as seen by the red-shifted ECL maxima relative to their corresponding photoluminescence peak wavelengths.

Blue fluorescent deoxycytidine analogues: convergent synthesis, solid-state and electronic structure, and solvatochromism.

We report the synthesis and photospectroscopic characterisation of intrinsically fluorescent triazole-appended cytidines. Fluorescence was found to be highly dependent on solvent conditions. X-Ray crystallographic data show the proton of the exocyclic amine of the nucleobase and the triazole N(3) engaged in a H-bond.

Chiral, hemilabile palladium(II) complexes of tridentate oxazolidines, including C2-symmetric "pincers".

Two classes of diastereomerically enriched chiral tridentate ligands incorporating either two oxazolidine and one pyridine ( 1) or two pyridine and one oxazolidine ( 2a-c) donor groups have been made in a high-yielding modular fashion from readily available enantiopure amino alcohols and aldehydes. Both ligand classes readily formed metal complexes via 1:1 reactions with trans-PdCl 2(PhCN) 2. The compounds Pd( 1)Cl 2 and Pd( 2a-c)Cl 2 were formed as mixtures of 3 and 2 diastereomers, respectively, owing to indeterminate absolute configuration at the C (2) position of their constituent oxazolidine rings. Within each diastereomeric manifold, the metal complexes existed as equilibrium mixtures of bi- and tridentate isomers in solution, the interconversion between which was very rapid even at -50 degrees C. The fluxional nature of the compounds was inferred from a combination of (1)H and (15)N NMR spectroscopic and solution conductivity data. Substitution of one chloride ligand for hexafluorophosphate gave as mixtures of diastereomers the salts [Pd( 1-kappa N,kappa (2) N')Cl]PF 6 ( 8) and [Pd( 2a-c-kappa N,kappa N',kappa N'')Cl]PF 6 ( 12a-c) in which the ligands were coordinated through all three N-donors. A single recrystallization of 8 gave in optically pure form the major diastereomer 8 ( maj ), which was characterized crystallographically. Complexes of 2a-c differed substantially from those of the bis(pyridylmethyl)amine (bpma) ligand family with which they shared direct atom-for-atom connectivity in the coordinating groups. The amines are known to form exclusively the static tridentate complexes [PdCl(bpma-kappa N,kappa (2) N')]Cl; the difference was attributed to torsional strain associated with the rigid oxazolidine ring in tricoordinated 2a-c.

Anion Sensing with a Blue Fluorescent Triarylboron-Functionalized Bisbenzimidazole and Its Bisbenzimidazolium Salt.

A blue fluorescent p-dimesitylboryl-phenyl-functionalized 1,3-bisbenzimidazolyl benzene molecule (1) has been synthesized in high yield by Stille coupling of bisbenzimidazolyl bromobenzene with p-BMes2-SnBu3-benzene. Methylation of 1 led to the formation of the bisbenzimidazolium salt (2). The utility of both 1 and 2 in sensing CN- and halide (F-, Cl-, Br-, and I-) was examined, and it was found that only the small fluoride and cyanide anions were able to bind to the boron atom with binding constants in the range of 2.9 × 104 to 5 × 105 M-1. Computational studies provided insight into the photophysical properties of the molecules and verified that a charge-transfer process is quenched in these "turn-off" molecular sensors.

Chemistry of the heavy group 15 elements with the pyridyl tethered 1,2-bis(imino)acenaphthene "clamshell" ligand.

Cobaltocene has been used as a one-electron reductant in a facile route to generate pnictogen(I) (P, As) synthons. These subsequently undergo a formal 4 + 2 cycloaddition with a pyridyl tethered 1,2-bis(imino)acenaphthene "clamshell" ligand to yield N-heterocyclic chlorophosphines and -arsines, which are precursors to the corresponding N-heterocyclic pnictenium cations. In the absence of a reductant the "clamshell" ligand can be used in forming hypervalent donor-acceptor complexes with heavy main group elements (Sn, Sb and Bi).

A base-stabilised arsenic(III) dication.

A bulky guanidinate ligand has been utilized in supporting a dichloroarsine, which is an excellent precursor to an arsenium cation and a 2,2'-bipyridine base stabilised arsetidinium dication.

A new approach to internal Lewis pairs featuring a phosphenium acid and a pyridine base.

A bis(imino)acenaphthene (BIAN) ligand containing a pendant Lewis base has been used as a new framework to support a N-heterocyclic phosphenium cation (NHP). Reactivity studies demonstrate the ability of the ligand to act as a Lewis base, while the phosphorus centre provides a Lewis acidic site, giving new opportunities in NHP chemistry.

Theoretical and experimental investigations of ligand exchange in guanidinate ligand systems for group 13 metals.

The ligand exchange of guanidinate ligands between metal centres can play an important role in guanidinate chemistry, and ligand exchange between aluminium centres will form a dimeric intermediate. The synthesis and characterization of the dimer [Me(2)NC(N(i)Pr)(2)](2)Al(2)Cl(4) is reported here: compound crystallizes with a twisted boat conformation of its dimer ring. This compound decomposes to monomers at room temperature over four days, or within 18 hours at 90 degrees C. We undertook a detailed computational characterization of the reaction pathway, which supported the dimer structure and subsequent monomer formation. The ligand exchange route was also exploited for the synthesis of [MeC(N(i)Pr)(2)](2)AlCl, [EtC(N(i)Pr)(2)](2)AlCl, [MeC(N(i)Pr)(2)](2)GaCl, and [Me(2)NC(N(i)Pr)(2)](2)GaCl.

Synthesis and thermolysis of aluminum amidinates: a ligand-exchange route for new mixed-ligand systems.

A novel ligand-exchange route for the synthesis of amidinate-containing compounds of aluminum is explored. Syntheses of three new compounds, MeC(NiPr)2AlEt2 (4), EtC(NiPr)2AlMe2 (5), and (Me2NC(NiPr)2)2AlH (6), are presented. These mixed-ligand compounds are difficult to make in high yields by the more traditional routes of carbodiimide insertion or salt metathesis. The thermal reactivities of these compounds and their parent homoleptic compounds [MeC(NiPr)2]3Al (1), [Me2NC(NiPr)2](3)Al (2), and [EtC(NiPr)2]3Al (3) are explored in detail and analyzed with respect to their utility as potential atomic-layer-deposition precursors for aluminum-containing films. The major mechanism of thermal decomposition is found to be carbodiimide deinsertion to form aluminum alkyls or amides. Because of their thermal characteristics, both compounds 3 and 5 hold promise for use as precursors.