Unsaturated Aliphatic Compounds Research Articles

Characterization of the transformation of natural organic matter and disinfection byproducts after chlorination, ultraviolet irradiation and ultraviolet irradiation/chlorination treatment

The ultraviolet (UV)/chlorination process provides an emerging strategy to disinfect and remove trace organic contaminants in drinking water and wastewater treatment plants. Different strategies for UV irradiation, chlorination, and UV/chlorination affect the characteristics of natural organic matter (NOM) and the formation of disinfection by-products (DBPs). The underlying effect remains poorly understood. In this work, Orbitrap-high resolution mass spectrometry, with a high accuracy for mass identification and a low cost, was used to investigate NOM transformation and DBP formation with UV irradiation, chlorination, and UV/chlorination. Of the untreated and treated (UV irradiation, chlorination, and UV/chlorination) NOM sample, most identified compounds were phenolic and highly unsaturated aliphatic compounds. Compared with UV irradiation, chlorination, and UV/chlorination had a stronger effect on the transformation of NOM molecular composition and resulted in more oxidized groups. A comparison of UV/chlorination with chlorination showed that UV/chlorination formed less nitrogen-containing Cl-containing DBPs, and more oxidized and saturated Cl-containing DBPs. After chlorination and UV/chlorination, more than 60% of the identified DBPs could track their precursors on the basis of electrophilic substitution and addition reactions. The UV/chlorination precursors were more saturated than for chlorination. This systematic investigation is expected to guide the future advanced development of water treatment strategies and provide a method to auto-analysis of mass spectra data and visualize the DBP character.

Identification of processes mobilizing organic molecules and arsenic in geothermal confined groundwater from Pliocene aquifers

Organic matter (OM) has been accepted as an important trigger fueling Fe(III) oxide reduction and arsenic release in the late Pleistocene-Holocene anoxic aquifers, whereas its fates and roles on arsenic mobility in the Pliocene aquifer are unclear. To fill this gap, groundwaters from a confined Pliocene aquifer (CG) and an unconfined Holocene aquifer (UG) were sampled in the Guide Basin, China, to monitor evolutions of groundwater geochemistry and OM molecular signatures along the groundwater flow path. The outcomes showed that groundwater pH, temperature, and arsenic concentrations in the CG samples generally increased along the groundwater flow path, which were much higher than those in the UG samples. The numbers and intensities of recalcitrant molecules (polycyclic aromatics and polyphenols) in the CG samples remarkably increased along the path, but relatively labile molecules (highly unsaturated and phenolic compounds and aliphatic compounds) showed the opposite trends. The arsenic-poor (<10 μg/L) UG samples contained more labile molecules than the arsenic-rich CG samples. High groundwater pH, temperature, and sediment age in the confined aquifers may be responsible for the selective mobilization of the unique polycyclic aromatics and polyphenols. The mobilized recalcitrant organic molecules may enhance arsenic release via electron shuttling, complexation, and competition. Furthermore, high temperature and pH may also facilitate arsenic desorption. The study provides molecular-scale evidences that the mobilization of recalcitrant organic molecules and arsenic were concurrent in the geothermal confined groundwater.

Organic compounds in Weiyuan shale gas produced water: Identification, detection and rejection by ultrafiltration-reverse osmosis processes

Quantification of organic pollutants in flowback and produced water is essential to design appropriate treatment strategy and predict the potential environmental toxicity associated with unconventional energy production. Herein, we firstly characterized the important range chemicals of produced water (PW) collected from Weiyuan shale gas play, China. Ultra-high resolution (>10 M) electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry was used to gain insights into molecular compositions of mass range 170–1,000 Da. Oxygen-containing organic compounds (CHO) was the dominant type of compounds in the PW, and classes of O8 and O9 had the highest relative abundance. Highly unsaturated phenolic and aliphatic compounds were identified as the main compounds. Three low molecular weight (LMW, <170 Da) compounds, dimethylbenzylamine (DMBA), indoline, and 6-methyl-quinoline, were firstly revealed in the PW, with their concentrations of 137.11 μg/L, 5.48 μg/L, and 0.9 μg/L, respectively, as determined by liquid chromatography coupled to tandem mass spectrometry. An integrated process of ultrafiltration coupled with reverse osmosis was employed to treat the PW and achieved 78.3%, 96.3%, and 100% removal for these three chemicals. The concentration of DMBA in the effluent is 29.75 μg/L, which potentially cause environmental risks even after advanced membrane treatment, suggesting that LMW chemicals such as DMBA in PW deserves special attention.

Unraveling roles of dissolved organic matter in high arsenic groundwater based on molecular and optical signatures

Dissolved organic matter (DOM) is a crucial controlling factor in mobilizing arsenic. However, direct delineations of DOM regarding both optical properties and molecular signatures were rarely conducted in high-arsenic groundwater. Here, both groundwater and surface water were taken from the Hetao Basin, China, to decipher DOM properties with both optical spectrophotometer and Fourier transform ion cyclotron resonance mass spectrometry. The tryptophan-like component (C4) was averagely less than 30% in groundwater DOM, being positively associated with high H/C-ratio molecules (H/C > 1.2) and mainly grouped as highly unsaturated and phenolic compounds and aliphatic compounds. Other three humic-like components (C1, C2, C3) had positive associations with low H/C-ratio molecules (H/C < 1.2), which mainly consisted of highly unsaturated and phenolic compounds, polyphenols, and polycyclic aromatics. Groundwater arsenic concentrations were positively correlated with humic-like, low H/C-ratio, and recalcitrant organic compounds, which may be the consequence of labile organic matter degradation. The degradation caused Fe(III) oxide reduction and mobilized the solid arsenic. In addition, high abundances of these recalcitrant organic compounds in high-arsenic groundwater may contribute to arsenic enrichment via electron shuttling, competition for surface sites, and complexation process. It suggested that groundwater proxies would be either the result or the cause of biogeochemical processes in aquifers.

Phyllosilicate‐derived Nickel‐cobalt Bimetallic Nanoparticles for the Catalytic Hydrogenation of Imines, Oximes and N‐heteroarenes

AbstractThe development of cost‐effective, noble metal‐free catalytic systems for the hydrogenation of unsaturated aliphatic, aromatic, and heterocyclic compounds is fundamental for future valorization of general feedstock. With this aim, we report here the preparation of highly dispersed bimetallic Ni/Co nanoparticles (NPs), by a one‐pot deposition‐precipitation of Ni and Co phases onto mesoporous SBA‐15 silica. By adjusting the chemical composition in the starting mixture, three supported catalysts with different Ni to Co weight ratios were obtained, which were further subjected to treatments under reducing conditions at high temperatures. Characterization of the resulting solids evidenced a homogenous distribution of Ni and Co elements forming the NPs, the best results being obtained for Ni/Co‐2 : 2 samples, for which 50 wt.% Ni–50 wt.% Co NPs are found located on the surface of the residual phyllosilicate. Ni/Co‐2 : 2, presenting the best performances for the hydrogenation of 2‐methyl‐quinoline, was further evaluated in the catalytic hydrogenation of selected imines, oximes and N‐heteroarenes. Due to the high dispersion of bimetallic Ni−Co NPs, excellent properties (activity and selectivity) in the conversion of the selected substrates are reported.

Alkanes and aliphatic carbonyl compounds in wintertime PM2.5 in Beijing, China

Organic aerosol is one of the dominant components of PM2.5 in megacities. In order to understand the sources and formation processes of aliphatic carbonyl compounds, the concentrations of saturated and unsaturated aliphatic hydrocarbons and carbonyl compounds were determined in the PM2.5 from an urban area of Beijing sampled in November–December 2016 and analysed using two dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC x GC-TOFMS). The data were separated into non-haze and haze days (PM2.5 ≥ 75 μg m−3). n-Alkanes (C10-C36) and n-alkenes (C12-C26) were abundant in the samples during the sampling campaign regardless of non-haze and haze conditions, and the middle chain length n–alkanes (C25–C34) were the most abundant. Aliphatic carbonyls, specifically n-alkanals (C8-C29), n-alkan-2-ones (C8-C31) and n-alkan-3-ones (C8-C30) were also detected in the PM2.5 at concentrations much lower than n-alkanes. The n-alkanals were the most abundant compounds amongst the aliphatic carbonyls, accounting for 65.4% on average of the total mass of aliphatic carbonyls. For the non-haze days, it seems likely that the OH oxidation of n-alkanes was a source of carbonyl compounds, whereas vehicle exhaust makes a significant contribution to the n-alkanes and n-alkanals, but makes a much smaller contribution to the n-alkan-2-ones and n-alkan-3-ones. It appears that primary sources are likely to be a major contributor to concentrations of the high molecular weight carbonyl compounds during the haze episodes, probably deriving from coal combustion. In addition, furanones (γ-lactones) and phytone (6, 10, 14-trimethylpentadecan-2-one) were also detected in our samples and are oxidation products of hydrocarbons and a marker of biogenic input, respectively. Cooking emissions also appear to be a likely contributor to the furanones. This study provides new information on the profiles of PM2.5-associated aliphatic hydrocarbons and carbonyl compounds, and gives insights into their sources. Differences in the concentrations and ratios of carbonyl compounds between Beijing and London are discussed.

Molecular Characterization of Organics Removed by a Covalently Bound Inorganic-Organic Hybrid Coagulant for Advanced Treatment of Municipal Sewage.

Coagulation is an important process to remove organics from water. The molecular composition and structure of organic matter influence water quality in many ways, and the lack of information regarding the organics removed by different coagulants makes it challenging to optimize coagulation processes and ensure reclaimed water safety. In this paper, we investigated coagulation of secondary biological effluent from a municipal sewage treatment plant with different coagulants. We emphasized investigation of organics removal characteristics at the molecular level using Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with electrospray ionization (ESI). We found that conventional coagulants can only partially remove condensed polycyclic aromatics and polyphenols with low H/C (H/C < 0.7) and highly unsaturated and phenolic compounds and aliphatic compounds with high O/C (O/C > 0.6). A new coagulant, CBHyC, had better removal efficiencies for all organics with different element compositions and molecular structures, especially organics that are resistant to conventional coagulants such as highly unsaturated and phenolic compounds and aliphatic compounds located in 0.3 < O/C < 0.8 and 1.0 < H/C < 2.0 regions and sulfur-containing compounds with higher O/C (e.g., anionic surfactants and their metabolites or coproducts). This study provides molecular insights into the organics removed by different coagulants and provides data supporting the possible optimization of advanced wastewater treatment processes.

Molecular composition of dissolved organic matter in the Mediterranean Sea

AbstractThe molecular composition of marine dissolved organic matter (DOM) is still poorly understood, particularly in the Mediterranean Sea. In this work, DOM from the open Mediterranean Sea and the adjacent Northeast Atlantic Ocean was isolated by solid‐phase extraction (SPE‐DOM) and molecularly characterized using Fourier‐transform ion cyclotron resonance mass spectrometry. We assessed the gradual reworking of the SPE‐DOM transported by the shallow overturning circulation of the Mediterranean Sea by following the increase in molecular weight (+20 Da), oxygenation (+5%), degradation index (Ideg +22%), and the proportional decrease of unsaturated aliphatic compounds (+34%) along the Levantine Intermediate Water. This reworked SPE‐DOM that leaves the Mediterranean Sea through the Strait of Gibraltar strongly contrasts with the fresh material transported by the inflow of Atlantic water (Ideg −25%). In the deep eastern and western overturning cells, the molecular composition of the deep waters varied according to their area and/or time of formation. SPE‐DOM of the waters formed in the Aegean Sea during the Eastern Mediterranean Transient (EMT) was more processed than the DOM in pre‐EMT waters formed in the Adriatic Sea (molecular weight and the proportion of unsaturated aliphatic compounds were increased by 5 Da and 9%, respectively). Furthermore, pre‐EMT waters contain more reworked SPE‐DOM (Ideg +7%) than post‐EMT waters formed also in the Adriatic Sea. In summary, our study shows that the Mediterranean Sea constitutes a laboratory basin where degradation processes and diagenetic transformations of DOM can be observed on close spatial and temporal scales.

Linking optical and molecular signatures of dissolved organic matter in the Mediterranean Sea

Dissolved organic matter (DOM) plays a key role in global biogeochemical cycles and experiences changes in molecular composition as it undergoes processing. In the semi-closed basins of the oligotrophic Mediterranean Sea, these gradual molecular modifications can be observed in close proximity. In order to extend the spatial resolution of information on DOM molecular composition available from ultrahigh resolution mass spectrometry in this area, we relate this data to optical (fluorescence and absorption spectroscopy) measurements. Covariance between molecular formulae signal intensities and carbon-specific fluorescence intensities was examined by means of Spearman’s rank correlations. Fifty two per cent of the assigned molecular formulae were associated with at least one optical parameter, accounting for 70% of the total mass spectrum signal intensity. Furthermore, we obtained significant multiple linear regressions between optical and intensity-weighted molecular indices. The resulting regression equations were used to estimate molecular parameters such as the double bond equivalent, degradation state and occurrence of unsaturated aliphatic compounds from optical measurements. The statistical linkages between DOM molecular and optical properties illustrate that the simple, rapid and cost-efficient optical spectroscopic measurements provide valuable proxy information on the molecular composition of open ocean marine DOM.

Probing and Comparing the Photobromination and Photoiodination of Dissolved Organic Matter by Using Ultra-High-Resolution Mass Spectrometry.

Photochemical halogenation of dissolved organic matter (DOM) may represent an important abiotic process for the formation of natural organobromine compounds (OBCs) and natural organoiodine compounds (OICs) within surface waters. Here we report the enhanced formation of OBCs and OICs by photohalogenating DOM in freshwater and seawater, as well as the noticeable difference in the distribution and composition pattern of newly formed OBCs and OICs. By using negative ion electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry, various OBCs and OICs were identified during the photohalogenation processes in sunlit waters. The respective number of OBCs and OICs formed in artificial seawater (ASW) under light radiation was higher than that in artificial freshwater (AFW), suggesting a possible role of the mixed reactive halogen species. OBCs were formed mainly via substitution reactions and addition reactions accompanied by other reactions and distributed into three classes: unsaturated hydrocarbons with relatively low oxygen content, unsaturated aliphatic compounds, and saturated fatty acids and carbohydrates with relatively high hydrogen content. Unlike the OBCs, OICs were located primarily in the region of carboxylic-rich alicyclic molecules composed of esterified phenolic, carboxylated, and fused alicyclic structures and were generated mainly through electrophilic substitution of the aromatic proton. Our findings call for further investigation on the exact structure and toxicity of the OBCs and OICs generated in the natural environment.

Dissolved organic matter composition and photochemical transformations in the northern North Pacific Ocean

AbstractThe composition and photochemical transformations of dissolved organic matter (DOM) in the northern North Pacific Ocean were investigated at the molecular level using ultrahigh resolution mass spectrometry and geochemical tracers. Analyses included vertical profiles and experiments in which deep sea DOM was exposed to sunlight and incubated in the dark. The composition of the deep sea DOM was found to be approximately uniform and enriched with highly unsaturated compounds, with highly aromatic compounds, and with polycyclic aromatics. Surface DOM had a significantly different composition, being enriched with both highly unsaturated and with unsaturated aliphatic compounds potentially due to the addition of photodegradation products and phytoplankton inputs. Deep sea DOM composition is transformed by photoreactions, becoming more similar to surface DOM. The influence of photochemistry extends beyond the photic zone, presumably because of vertical export of DOM previously modified at the surface.

Ru-Based Complexes with Quaternary Ammonium Tags Immobilized on Mesoporous Silica as Olefin Metathesis Catalysts

Ruthenium olefin metathesis catalysts bearing a polar quaternary ammonium group in N-heterocyclic ligand were immobilized on silica and siliceous mesoporous molecular sieves with different pore sizes (SBA-15 and MCM-41). The activity of the heterogeneous catalysts was found to increase with an increase in pore size of the support used, with the best results observed for SBA-15-supported catalyst. The influence of reaction conditions (temperature, solvent, catalyst, and substrate concentration) on the efficiency of new heterogeneous catalysts was established. A significant influence of the counterion present in the ruthenium complex on the activity of immobilized catalysts was also found: those derived from chloride containing ion exhibited the highest activity. High activity in ring-closing metathesis of substrates as citronellene, 1,7-octadiene, and diallyl compounds as well as in cross-metathesis of unsaturated aliphatic compounds with methyl acrylate was observed under optimized conditions. In some cas...

Time Resolved Infrared Spectroscopy of Formation and Processing of Secondary Organic Aerosol

Abstract An aerosol flow reactor was coupled to an infrared absorption cell to study aerosol formation processes with high temporal resolution. The recorded infrared spectra were referenced using aerosol smog chamber experiments. Evaluation was done by studying the formation of secondary organic aerosol from α-pinene and catechol as precursors and ozone as oxidant. Three main infrared absorptions: ν(O-H), ν(C-H) and ν(C=O) were considered, and humic like properties of the secondary organic aerosol are mainly interpreted according to the formation and variations of carbonyl bands in the region between 1850 and 1600 cm−1, especially the ν(C=O) of aryl carbonyls from catechol oxidation products below 1700 cm−1. The relative intensities of two major ν(C=O) stretching vibrations at 1690 cm−1 and 1755 cm−1 were observed to depend strongly on the available ozone concentration. At high precursor/ozone ratios (2:1 or 1:1) the vibration at 1690 cm−1 predominates, indicating aryl carbonyl vibrations. With increasing ozone concentrations this vibration is replaced by the higher carbonyl vibration at 1755 cm−1 indicating unsaturated carbonyl-containing compounds. This is a strong hint at ring opening processes leading to unsaturated aliphatic compounds in the resulting particle. Aryl carbonyls and aromatic or olefinic ν(C=C) at 1620 cm−1 in aged particles remain visible, as aerosol smog chamber studies exhibit – thus a strong hint at humic like properties of the SOA from the spectroscopic point of view.

Block correlated coupled cluster method with the complete active-space self-consistent-field reference function: Applications for low-lying electronic excited states

Block correlated coupled cluster (BCCC) method with the complete active-space (CAS) self-consistent-field reference function (CAS-BCCC) has been applied to investigate the vertical excitation energies of low-lying valence excited states in a number of medium-sized organic molecules, including unsaturated aliphatic hydrocarbons (ethene, E-butadiene, cyclopropene, and cyclopentadiene), aromatic heterocycles (furan and pyrrole), and carbonyl compounds (formaldehyde, acetone, and formamide). An approximate CAS-BCCC with the cluster operator truncated up to the four-block correlation level, CAS-BCCC4, is employed in the calculations. The results are compared with those from the multireference configuration interaction with singles and doubles (MR-CISD and its corrected version, MR-CISD+Q), the complete active space with second-order perturbation theory (CASPT2), and CC3. Our results show that the overall performance of CAS-BCCC4 is competitive with that of the multistate CASPT2 (slightly inferior to MR-CISD+Q), better than that of the single-state CASPT2 and MR-CISD approaches. For triplet excited states, various methods tend to give relatively consistent predictions. However, for singlet excited states, various methods lead to quite different excitation energies in some cases.

Effects of the Zeolite Framework on the Adsorptions and Hydrogen-Exchange Reactions of Unsaturated Aliphatic, Aromatic, and Heterocyclic Compounds in ZSM-5 Zeolite: A Combination of Perturbation Theory (MP2) and a Newly Developed Density Functional Theory (M06-2X) in ONIOM Scheme

The confinement effect on the adsorption and reaction mechanism of unsaturated aliphatic, aromatic and heterocyclic compounds on H-ZSM-5 zeolite has been investigated by the four ONIOM methods (MP2:M06-2X), (MP2:B3LYP), (MP2:HF), and (MP2:UFF). The H-ZSM-5 'nanoreactor' porous intersection, where chemical reactions take place, is represented by a quantum cluster of 34 tetrahedral units. Ethene, benzene, ethylbenzene, and pyridine are chosen to represent reactions of various adsorbates of aliphatic, aromatic and heterocyclic compounds. Among the four combined methods, (MP2:M06-2X) outperforms the others. The results confirm that the method that takes weak interactions, especially the van der Waals interaction, into account is essential for describing the confinement effect from the zeolite framework. The effects of the infinite zeolitic framework on the cluster model are also included by a set of point charges generated by the embedded ONIOM model. The energies for the adsorption of ethene, benzene, ethylbenzene, and pyridine on H-ZSM-5 from an embedded ONIOM(MP2:M06-2X) calculation are predicted to be -14.0, -19.8, -24.7, and -48.4 kcal/mol, respectively, which are very close to available experimental observations. The adsorption energy of pyridine agrees well with the experiment data of -47.6 kcal/mol. We also applied the same computational methodology on the systematic investigation of the H/H exchange reaction of benzene and ethylbenzene with the acidic H-ZSM-5 zeolite. The H/H exchange reaction was found to take place in a single concerted step. The calculated apparent activation energies for benzene and ethylbenzene are 12.6 and 4.9 kcal/mol, which can be compared to the experimental estimates of 11.0 and 6.9 kcal/mol, respectively. The confinement effect of the extended zeolite framework has been clearly demonstrated not only to stabilize the adsorption complexes but also to improve their corresponding activation energies to approach the experimental benchmark.

Benchmarks for electronically excited states: CASPT2, CC2, CCSD, and CC3

A benchmark set of 28 medium-sized organic molecules is assembled that covers the most important classes of chromophores including polyenes and other unsaturated aliphatic compounds, aromatic hydrocarbons, heterocycles, carbonyl compounds, and nucleobases. Vertical excitation energies and one-electron properties are computed for the valence excited states of these molecules using both multiconfigurational second-order perturbation theory, CASPT2, and a hierarchy of coupled cluster methods, CC2, CCSD, and CC3. The calculations are done at identical geometries (MP26-31G*) and with the same basis set (TZVP). In most cases, the CC3 results are very close to the CASPT2 results, whereas there are larger deviations with CC2 and CCSD, especially in singlet excited states that are not dominated by single excitations. Statistical evaluations of the calculated vertical excitation energies for 223 states are presented and discussed in order to assess the relative merits of the applied methods. CC2 reproduces the CC3 reference data for the singlets better than CCSD. On the basis of the current computational results and an extensive survey of the literature, we propose best estimates for the energies of 104 singlet and 63 triplet excited states.

Bacterial hydrolytic dehalogenases and related enzymes: Occurrences, reaction mechanisms, and applications

Dehalogenases catalyze the cleavage of the carbon-halogen bond of organohalogen compounds. They have been attracting a great deal of attention partly because of their potential applications in the chemical industry and bioremediation. In this personal account, we describe occurrences, reaction mechanisms, and applications of bacterial hydrolytic dehalogenases and related enzymes, particularly L-2-haloacid dehalogenase, DL-2-haloacid dehalogenase, fluoroacetate dehalogenase, and 2-haloacrylate reductase. L-2-Haloacid dehalogenase is a representative enzyme of the haloacid dehalogenase (HAD) superfamily, which includes the P-type ATPases and other hydrolases. Structural and mechanistic analyses of this enzyme have yielded important insights into the mode of action of the HAD superfamily proteins. Fluoroacetate dehalogenase is unique in that it catalyzes the cleavage of the highly stable C--F bond of a fluorinated aliphatic compound. In the reactions of L-2-haloacid dehalogenase and fluoroacetate dehalogenase, the carboxylate group of Asp performs a nucleophilic attack on the alpha-carbon atom of the substrate, displacing the halogen atom. This mechanism is common to haloalkane dehalogenase and 4-chlorobenzoyl-CoA dehalogenase. DL-2-Haloacid dehalogenase is unique in that a water molecule directly attacks the substrate, displacing the halogen atom. The occurrence of 2-haloacrylate reductase was recently reported, revealing a new pathway for the degradation of unsaturated aliphatic organohalogen compounds.

Identification of the compounds in the aqueous phases from liquefaction of lignocellulosics

In this study, the compounds in the liquid phases produced from the liquefaction of the lignocellulosic material have been investigated. For this purpose, liquid phases obtained from liquefaction of cotton stalk and cellulose and paper plant solid waste treated with aqueous acetic acid (HAc) or sodium hydroxide (NaOH) (15% by mass) at high initial inert gas pressure and high temperature were selected for the analyses. Phenolic compounds, cyclic compounds, unsaturated aliphatic hydrocarbons and other compounds (benzoquinone, aliphatic alcohols) and furans were identified by TLC, GC and GC/MS equipped with capillary column. It was concluded that lignocellulosic substances were converted into various water-soluble compounds in the liquefaction processes. Furans and cyclic ketones may be cyclization products of dicarbonyl intermediates formed by aldol condensation reaction of low-molecular mass compounds formed from degradation products of the initial stages of liquefaction.

Chlorine stable isotope measurements of chlorinated aliphatic hydrocarbons by thermal ionization mass spectrometry

An improved method for chlorine isotopic analysis using thermal ionization mass spectrometry (TIMS) of Cs 2Cl + has been investigated. The δ 37 Cl values (parts per mil deviations from the standard seawater 37 Cl/ 35 Cl ratio) for 10 commercial chlorinated aliphatic hydrocarbons (CAHs), provided by six suppliers are presented. The CAHs were treated with a sodiumbiphenyl reagent. The liberated chloride ions were converted to CsCl and their isotopic compositions were determined by TIMS. Replicate analysis of the CAHs gave an external precision of 0.1–0.4‰ (1 σ S.D.). As each compound and each supplier has a distinctive δ 37 Cl value ( δ 37 Cl values: −5.0 to +2.9‰), Cl isotope data can be used to trace a specific source of pollutants in the subsurface environment. Trichloroethene (TCE) and tetrachloroethene (PCE) were extracted from aqueous solutions with toluene and their chlorine isotope compositions were analyzed. The solvent extraction method presented here may be applicable to the analysis of actual contaminated water samples. Chlorine atoms were recovered as inorganic chloride from unsaturated chlorinated aliphatic compounds (TCE and PCE) by KMnO 4 oxidation. However, the saturated compounds were resistant to KMnO 4 oxidation. The isotopic compositions of the recovered chloride ion were then determined by TIMS. It is suggested that such compound-specific isotopic analyses may give information about the past record of each contaminant.

Hybrid organic–inorganic multilayer materials: influence of π electrons as magnetic media in a series of bridged-layer compounds M 2(OH) 4− xA x/2 (M=Cu(II) or Co(II), A=dicarboxylate anion)

We report the preparation, structure and magnetic properties of a series of multilayer copper(II) hydroxy-dicarboxylates. These are prepared by anion-exchange, starting from copper(II) hydroxy-acetate Cu 2(OH) 3(OAc)·H 2O. The acetate ion is substituted for n-methylene dicarboxylates O 2CXCO 2 2−, with X=(CH 2) n and n=1 to 8. Similar exchange reactions are carried out with unsaturated dicarboxylate anions (X=(CH) n , with n=2, 4 and X=C 4H 6). The compounds, of general formulation Cu 2(OH) 4− x (XC 2O 4) x/2 .· zH 2O, exhibit a layered structure with a step-like variation of the basal spacing, according to n parity. IR spectroscopy indicates that the carboxylate functions are linked to the metal ions, each aliphatic chain bridging adjacent hydroxide layers. Only compounds with n=2, 4 and 8 show a net magnetic moment within copper(II) layers. For the short chain anions, an antiferromagnetic order occurs at low temperature, with a metamagnetic transition in low field, except for the unsaturated dicarboxylate Cu 2(OH) 1.92(C 4H 6C 2O 4) 1.04·0.22H 2O which exhibits a long-range ferromagnetic order at T C=13 K. For the long-chain anion, X=C 8H 16, a ferrimagnetic 3d order is stabilized below T C=17 K. On the basis of structural and magnetic findings, a comparison is made between the saturated and unsaturated aliphatic chain compounds. This study provides new insight on the influence of π electrons on the ordering between magnetic layers. Finally, preliminary results for the cobalt(II) trans-hexenedioate analog indicate that a 3d ferromagnet is obtained below T C=56.5 K, thus emphasizing the key role of the in-plane spin–spin correlations on the ordering temperature.