Collisional activation study of cyclic polysulfides

Sulfur organic compounds in bottom sediments of the eastern Gulf of Finland

BACKGROUND, AIMS AND SCOPE

Despite the large number of studies on the forms of sulfur in marine deposits, investigations on sulfur organic compounds are still rare. It is known that the processes leading to formation of intermediate and final sulfur compounds (including organic ones) in modern deposits are the results of microbiological transformation of sulfur containing proteins, as well as the microbiological reduction of sulfate ions. The latter are finally reduced by anaerobic sulfate-reducing bacteria to H2S, HS- and S2-; the total sum of these is referred to as 'hydrogen sulfide' in chemical oceanography. Further, the formation of reduced sulfur organic derivatives (sulfides and polysulfides) is the result of interaction of the organic substance destruction products with the sulfide ions. In such cases, the main source of organic substances, as well as sulfates for the sulfur reducing processes, is the pore water in the sediments. The choice of the target of our study is based on the fact that the eastern part of the Gulf of Finland water area receives the bulk of the anthropogenic load of the St. Petersburg region. Low vertical intermixing of the water thickness is observed there (thus creating a deficiency of oxygen near the bottom), and the bottom sea current transfers the polluted salty water of the Baltic Sea into the Neva Bay. The whole of the above are the preconditions for the formation of sulfur-bearing organic compounds. A great number of bottom sediment samples for analytical surveys were collected in the Eastern Gulf of Finland during research expeditions in the years of 1997 and 2001. These were screened for structures of sulfur organic microcontaminants, including organic forms of sulfur, using advanced instrumentation and experienced personnel in our two, cooperating laboratories. This work is a part of the research being carried out on organic micro-admixtures present in bottom sediments, and is the summary of our findings on previously unstudied sulfur organic substances there.

MATERIALS AND METHODS

A number of sulfur organic compounds present in nineteen bottom sediment samples from the Eastern Gulf of Finland (EGF) were characterized by high performance gas chromatography connected to low and high resolution mass spectrometers (GC/LRMS and GC/HRMS). The structure screening was carried out as compared with literature and library mass spectra, and taking the GC retention times into account. In the cases of an absence of mass spectra not in the literature, interpretation of the most probable structures was performed with the help of high resolution mass-spectrometric data, fragmentation rules for sulfur-bearing organic substances and ICLU simulation of spectra. These data were registered to form a conclusive 'fingerprint' for identification and confirmation of the structure of each novel compound found, e.g. by later syntheses of authentic model compounds. The relative contents of sulfur organic compounds were determined from MS response ratios of each compound to 2-fluorine naphthalene (internal standard).

RESULTS

This paper is a completion of work, which has been published in part as three papers in the European Journal of Mass Spectrometry. As the total study result, 43 sulfur-bearing compounds were characterized. The mass spectra of 20 of them were found in the literature. The most probable structures for the 23 compounds whose mass-spectra were not available in the literature data were proposed. All of those 23 compounds were detected in bottom sediments for the first time, and 5 of them were described as originating from plants or being generated by chemical synthesis products, while the remaining 18 substances were previously unknown. The structures of these were deduced to be most probably the following (in order of their GC retention): dichloromethyl thiylsulfenylchloride, chloromethyl dichloromethyl disulfide, 3,4-dithiacyclohexene, 1,2,4-trithiacycloheptane, 1,2,3-trithiacyclohexane, tetrathiacyclopentane, 3,4,5-trithiacyclohexene, 1,2,4-trithiacyclohexane, cyclopropylhydrotrisulfide, 1,2-dithiane-3-thiol, 1,3-dithiane-2-thiol, bis(trichloromethyl)-tri-sulfide, 1,2,4,5-tetrathiacyclohexane, 1,2,3,4-tetrathiacycloheptane, 1,2,3,4-tetrathiacycloheptane, 1,2,3,4-tetrathia-cyclo-hexane, pentathiacyclohexane, and 1,2,4,6-tetrathiacyclooctane. The highest amounts of sulfur organic compounds were found in the deepest, bottom areas in the open part of the sea, where the salinity was highest, and oxygen deficiency occurred as well. Also, some coastal places with a high solid matter deposition rate had elevated contents of sulfur organic compounds.

DISCUSSION

From the 43 sulfur organic compounds found, the HRMS data provided the atomic composition of the molecular ions for 16 compounds with a high confidence (see Table 3). The LRMS spectra could be identified with catalogue or literature spectra in 29 cases. The MS information obtained was insufficient in two cases: 1) The obvious molecular ion (at m/z 110) of compound 1 was not visible in LRMS. 2) For compound 43, the HRMS measurement, due to the low intensity (2%) of the molecular ion (m/z 210), could not exclude the presence of 2 oxygen atoms (instead of one sulfur atom) in the molecule. Major fragments, however, of our 43, certainly contained no oxygen atoms according to HRMS. The limited LRMS data in the literature, for an isomer of 43, had m/z values of all fragments different from those of the compound found by us. The retention times (RT) formed one more evidence for identity between compounds in different samples. The use of different non-polar columns in GC and similar, but not identical, temperature programs produced eluted peaks of novel and known compounds in each sample (mixture) in GC/HRMS and GC/LRMS. These gave sets of RTs which were in a very significant linear correlation (measured example R = 0.999866, p = 1.85E-06, N = 5). Therefore, the RTs in the HRMS analysis systems could be converted to values comparable with those from the LRMS device. The RT values, HRMS m/z values, LRMS spectra, and ICLU simulation results for each organic sulfur compound form an identification 'fingerprint'. The interpretation of these experimental data, with supporting use of fragmentation rules, allow the giving of a provisional name and structure to the 'suspect'. In this study and in environmental surveys of micropollutants in general, the compounds suspected of anthropogenic or natural origin occur at low levels in complex mixtures. Therefore, no bulk amount of an authentic, pure model substance for the suspect is available quite often. The most probable name and structure from the fingerprint data are very useful in guiding the preparation of the model substance for a conclusive identification. Similarly, the unknown criminal can be identified in advance by forensic science and his fingerprint, DNA, etc. as registered before the arrest. The analogy can be found in the literature and CAS register of organic polysulfides, which in great part consists of the results of sensitive mixture analysis methods.

CONCLUSIONS

Sediment of the Eastern Gulf of Finland is over large areas anaerobic, as indicated by the existence of novel, non-oxygenated sulfur organic microcontaminants. These substances were most abundant in anoxic and saline, deep bottom regions, and, in addition, in one coastal area near industrial discharges. This occurrence, and also the limited information about sulfur organic compounds in scientific literature, is considered evidence for the dominantly natural processes in their formation.

RECOMMENDATIONS AND PERSPECTIVES

The importance and necessity of investigating the sulfur organic compounds in the bottom sediments, result from the fact that their presence can be an indicator of stable anaerobic processes. Similarly, the oxygen disappearance (anoxia) in the marine water, due to a high concentration of the sulfate ions and relatively high content of organic matter, is practically always connected with the appearance of hydrogen sulfide and sulfides. The generation of sulfur organic compounds precedes the formation of the new, or expansion of the existing anaerobic ('hydrogen sulfide') zones, which lead to such environmental disasters as mass destruction of hydrobionts. Many organic compounds of sulfur, including sulfides and polysulfides, are toxic to the aquatic organisms. Therefore, in addition to the danger of mass wholesale deaths of marine fauna in the bottom sediments region, there exists a probability of secondary pollution of the water thickness as well, due to the entry of those substances from bottom sediments in the water when the environmental conditions are changed (stormy weather, floods, geological activity of the earth's crust, etc.).

Identification, Synthesis, and Conformation of Tri- and Tetrathiacycloalkanes from Marine Bacteria

Seven new cyclic natural polysulfides 1-7 were identified in extracts of two bacterial Cytophaga strains (CFB-phylum) isolated from biofilms from the North Sea. Their structures are based on mono- and dimeric-cyclization products of 2-methylpropane-1,2-dithiol 8, which was also present in the extract in trace amounts. The structures were deduced by analysis of their mass spectra and confirmed by synthesis. The 1H NMR spectra of some these compounds suggested a high flexibility of the trithiepane and tetrathiocane systems. Therefore, their conformation was further analyzed by DFT calculations and dynamic NMR spectroscopy. While thiepane 4 possesses a twist-chair lowest energy conformation, its isomers 2 and 3 adopt a chairlike conformation, as does the tetrathiocane 5. In contrast, tetrathiocane 6 favors again a twisted chair conformation.

POPs and organic polysufides in sediments of Lake Ladoga

The study included one station close to a pollution source (depth 59 m) and another far from polluted areas (depth 40 m). Samples were analysed for organic chlorine, bromine and sulfur compounds. Samples taken with a corer were sliced to the layers of 0-1, 1-4, 4-7 cm etc. down to the depth of 34 cm. The dating was made with two independent methods, the 210Po method and with the soot particle counting method. The analyses were made with a multiresidue method. Gas chromatography was connected to low resolution mass spectrometry (LRMS) or to high resolution mass spectrometry (HRMS). A different extraction was applied to screen the possible occurrence of polysulfides. Typical chlorophenol and chlorohydrocarbon traces from chlorobleaching of pulp were non-detectable. Also PCDDs, PCDFs, PCBs and various organochloride pesticides, fire retardant residues PBDEs, PBDDs and PBDFs and polychlorinated phenyl salicylates were not detected. Instead, methylated dibenzothiophenes Me-DBTs and Di-Me-DBTs, typical traces of oil based defoamers used in e.g. paper mills were found in the surface layers of the polluted site. Polysulfides were analyzed from layers representing years 1955-1970 from the polluted site. The structures of five congeners were according to GC/MS dimethyl trisulfide, 1,2,3,4-tetrathiepane, pentathiane, 1,2,3,4-tetrathiane and 1,2,4,5-tetrathiepane. Many of the analyzed pollutants have not been reported earlier from Lake Ladoga. The only positive observations were from oil-based defoamers used in paper mills, and from polysulfides, which are either of natural origin or indicate a discharge in the 1950s and 1960s. Owing to the large spreadout and dilution, the concentrations are low even at moderate distances from the pollution centers.

Mass spectrometric identification of cyclic polysulfides in sediment of the Eastern Gulf of Finland. II

Nine polysulfides, previously unknown as environmental organic pollutants, were analyzed from a sediment sample from the Eastern Gulf of Finland. The determinations were done by gas chromatography connected to low- and high-resolution mass spectrometers. The structure of the polysulfides was elucidated by determination of isotopic composition of abundant molecular and fragment ions by high-resolution mass spectrometry (HRMS), the interpretation of ion structures in low-resolution mass spectra (LMRS) using the thermochemical approach, the application of fragmentation rules and performing the ICLU simulation of abundance of ions in isotope clusters. Seven compounds were known in literature, but mass spectra were reported for only two of them, both recorded from mixture. Struture evaluation was successful for other substances, but not for the substance(s) in first eluting GC peak, where HRMS date were not obtained. Suggested structures of the cyclic compounds were (in the order of GC retention) 3,4-dithiacyclohexene, 1,2,3-trithiacyclohexane, 3,4,5- trithiacyclohexene, 1,2,4-trithiacyclohexane, cyclopropyl hydrodisulfide, 1,2-dithiole-3-thione and 1,2,3,4,5-penta- thiacyclo-octane. One acyclic congener identified was dimethyl tetrasulfide.

Mass spectrometric identification of cyclic polysulfides in sediment of the Eastern Gulf of Finland. I

Structures of six cyclic polysulfides, previously unknown as organic environmental pollutants, were analyzed from a sediment sample from the Eastern Gulf of Finland. The determinations were done by gas chromatography connected to mass spectrometry. High resolution (HRMS) measurements of the isotopic composition of four compounds could be done to confirm their molecular formulae. Total low resolution (LRMS) spectra were used to elucidate structures of all six compounds by thermochemical approach, application of fragmentation rules and by ICLU simulation of the spectra. The compounds were deduced to be (in the order of GC- retention) 1,2,4-trithiacycloheptane, tetrathiacyclopentane, 1,2,4,5-tetrathia-cyclohexane, 1,2,3,4- tetrathiacycloheptane, 1,2,3,4-tetrathiacyclohexane and 1,2,4,6-tetrathiacyclooctane.