Major Primary Products Research Articles

Pathways of phenol and benzene photooxidation using TiO 2 supported on a zeolite

The use of photocatalysts supported on adsorbents is gaining substantial attention. Photooxidation of phenol and benzene initiated by light absorption by TiO 2 supported on ZSM-5 zeolite is reported to learn in what ways loading TiO 2 on an adsorbent high silica zeolite modifies the reactions pathways. At equal TiO 2 loading, rates of phenol loss were similar to reactions on P25. In acid media, the major primary products were the result of expected o-, p-hydroxylation. Catechol and hydroquinone were formed and consumed at comparable rate so that a near steady state persisted for about 400 min. In contrast, secondary reactions were faster on P25 and catechol and hydroquinone concentrations decline systematically from 60 min onward. Beyond trihydroxy species, ring opening became important. The open chain oxygenated species built up little and appear to undergo further oxidation rapidly. The zeolite supported photocatalyst had a maximum efficiency at pH=3.4 and lost reactivity at higher pH. In basic media, hydroquinone becomes the dominant primary product. Catechol yields decline, but phloroglucinol, undetected in acid, is found. There is evidence of some polymerization with TiO 2 on the adsorbent zeolite support in base that interferes with mineralization. Reactions of benzene may not be simply limited to initial formation of phenol. The are some differences in the pathway for benzene that suggest other initial steps. It is reasonable to infer that there are differences between phenol and benzene adsorption on the catalyst and that benzene can react with species other than an adsorbed OH radical in an alternate the initial step.

Endosomal Proteolysis of Internalized Insulin at the C-terminal Region of the B Chain by Cathepsin D

The endosomal compartment of hepatic parenchymal cells contains an acidic endopeptidase, endosomal acidic insulinase, which hydrolyzes internalized insulin and generates the major primary end product A(1--21)-B(1--24) insulin resulting from a major cleavage at residues Phe(B24)-Phe(B25). This study addresses the nature of the relevant endopeptidase activity in rat liver that is responsible for most receptor-mediated insulin degradation in vivo. The endosomal activity was shown to be aspartic acid protease cathepsin D (CD), based on biochemical similarities to purified CD in 1) the rate and site of substrate cleavage, 2) pH optimum, 3) sensitivity to pepstatin A, and 4) binding to pepstatin A-agarose. The identity of the protease was immunologically confirmed by removal of greater than 90% of the insulin-degrading activity associated with an endosomal lysate using polyclonal antibodies to CD. Moreover, the elution profile of the endosomal acidic insulinase activity on a gel-filtration TSK-GEL G3000 SW(XL) high performance liquid chromatography column corresponded exactly with the elution profile of the immunoreactive 45-kDa mature form of endosomal CD. Using nondenaturating immunoprecipitation and immunoblotting procedures, other endosomal aspartic acid proteases such as cathepsin E and beta-site amyloid precursor protein-cleaving enzyme (BACE) were ruled out as candidate enzymes for the endosomal degradation of internalized insulin. Immunofluorescence studies showed a largely vesicular staining pattern for internalized insulin in rat hepatocytes that colocalized partially with CD. In vivo pepstatin A treatment was without any observable effect on the insulin receptor content of endosomes but augmented the phosphotyrosine content of the endosomal insulin receptor after insulin injection. These results suggest that CD is the endosomal acidic insulinase activity which catalyzes the rate-limiting step of the in vivo cleavage at the Phe(B24)-Phe(B25) bond, generating the inactive A(1--21)-B(1--24) insulin intermediate.

A Study of the Photolysis and OH-initiated Oxidation of Acrolein and trans-Crotonaldehyde

Experiments have been conducted in the laboratory and in the outdoor smog chamber (EUPHORE) to study the photolysis and the OH-initiated oxidation of (1) acrolein (CH2CHCHO) and (2) trans-crotonaldehyde (CH3CHCHCHO). In addition, the UV−visible absorption spectra for these two unsaturated aldehydes have been determined at (298 ± 2) K, and the rate constants for OH reactions have been measured using PLP-LIF technique as function of pressure (20−300) Torr in the temperature range (243−372) K. The obtained rate constant values are k1 = (6.55 ± 1.22) · 10-12 exp[(333 ± 54)/T] and k2 = (5.77 ± 1.14) · 10-12 exp[(533 ± 58)/T] cm3 molecule-1 s-1. From both midday photolysis rates J1 ≤ 2 · 10-6 s-1 for acrolein and J2 ≤ 1.2 · 10-5 s-1 for trans-crotonaldehyde, measured at EUPHORE during summer, and UV−visible absorption cross sections, very low effective quantum yields were derived: Φeff ≤ 0.005 for acrolein, and Φeff ≤ (0.030 ± 0.006) for trans-crotonaldehyde. The major primary products of the OH-initiated oxid...

Kinetics and mechanism associated with the reactions of hydroxyl radicals and of chlorine atoms with 1‐propanol under near‐tropospheric conditions between 273 and 343 K

AbstractRate constants for the reactions of OH radicals and Cl atoms with 1‐propanol (1‐C3H7OH) have been determined over the temperature range 273–343 K by the use of a relative rate technique. The value of k(Cl + 1‐C3H7OH) = (1.69 ± 0.19) × 10−12 cm3 molecule−1 s−1 at 298 K and shows a small increase of 10% between 273 and 342 K. The value of k(OH + 1‐C3H7OH) increases by 14% between 273 and 343 K with a value of (5.50 ± 0.55) × 10−12 cm3 molecule−1 s−1 at 298 K, and further when combined with a single independent experimentally determined value at 753 K gives k(OH + 1‐C3H7OH) = 4.69 × 10−17T1.8 exp(422/T) cm3 molecule−1 s−1, which fits each data point to better than 2%. Two well‐established structure–activity relationships for H abstraction by OH radicals give accurate predictions of the rate constant for OH + 1‐C3H7OH, provided the β‐CH2 group is given an increased reactivity of a factor of about 2 over that for the structurally equivalent CH2 group in alkanes at 298 K.A quantitative product analysis was carried out at 298 K for the Cl‐initiated photooxidation of 1‐C3H7OH, using both FTIR and gas chromatography. HCHO, CH3CHO, and C2H5CHO were the only major organic primary products observed, although HCOOH was found in much smaller amounts as a secondary product. A key characteristic of the analysis was that the initial values of the product ratio [CH3CHO]/[C2H5CHO] were effectively constant for NO pressures between 0.15 and 0.3 Torr, but fell by about 35% as the pressure fell to 0.0375 Torr. From a detailed consideration of the mechanism for the oxidation, it is suggested that C2H5CHO, CH3CHO (+HCHO), and 3 molecules of HCHO are formed uniquely from CH3CH2CHOH, CH3CHCH2OH, and CH2CH2CH2OH radicals, respectively. On this basis, use of the product yields gives the branching ratios of 56, 30, and 14% for Cl atom reaction at the α‐, β‐, and γ‐CH positions in 1‐C3H7OH at 298 K. Given the very low temperature coefficients involved, little change will occur over tropospheric temperature ranges. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 110–121, 2002

Infrared laser-powered homogeneous decomposition of (chloromethyl)trimethylsilane: 1,2-Cl shift and methene expulsion yielding chlorotrimethylsilane

The infrared laser-induced sulfur hexafluoride-photosensitized decomposition of (chloromethyl)trimethylsilane affords chlorotrimethylsilane and ethene as major primary products, showing this reaction occurring via 1,2-Cl shift and methene expulsion. At conditions of higher effective temperature, decomposition of chlorotrimethylsilane and reactions between sulfur hexafluoride and Si-containing compounds become important.

Competing isomeric product channels in the 193 nm photodissociation of 2-chloropropene and in the unimolecular dissociation of the 2-propenyl radical

This paper presents product translational energy spectroscopy measurements of the primary photofragmentation channels of 2-chloropropene excited at 193 nm and of the unimolecular dissociation of the 2-propenyl radical. Tunable vacuum ultraviolet (VUV) photoionization of the products allows us to distinguish between the various product isomers formed in these processes. The data show evidence for three significant primary reaction channels in the dissociation of 2-chloropropene: An excited-state C–Cl fission channel producing fast Cl atoms, a C–Cl fission channel producing slow Cl atoms, and HCl elimination. A minor C–CH3 fission channel contributes as well. The measured branching of the major primary product channels is: [fast C–Cl]:[slow C–Cl]:[HCl elimination]=62%:23%:15%. The experiments also allow us to resolve selectively the product branching between the unimolecular dissociation channels of the 2-propenyl radical, a high energy C3H5 isomer; we measure how the branching ratio between the two competing C–H fission channels changes as a function of the radical’s internal energy. The data resolve the competition between the unimolecular H+allene and H+propyne product channels from the radical with internal energies from 0 to 18 kcal/mol above the H+propyne barrier. We find that the barrier to H+allene formation from this high-energy C3H5 radical is higher than the barrier to H+propyne formation, in agreement with recent theoretical calculations but in sharp contrast to that predicted for the most stable C3H5 isomer, the allyl radical. The experiments demonstrate a general technique for selectively forming a particular CnHm isomer dispersed by internal energy due to the primary photolysis, thus allowing us to determine the branching between unimolecular dissociation channels as a function of the selected radical isomer’s internal energy.

Major ions, nutrients and primary productivity in volcanic neotropical streams draining rainforest and pasture catchments at Los Tuxtlas, Veracruz, Mexico

Six streams in the Los Tuxtlas region, a volcanic area in southeastern Mexico, were characterized chemically and biologically. Temperature, pH, conductivity, ions (Ca2+, Mg2+, Na+, K+, CaCO− 3 and SO2- 4), nutrients (NO− 3, NH+ 4, total P and PO−3 4), and chlorophyll a from epilithon were measured every other month from September 1996 to July 1997. The streams studied had a consistent pattern of cation dominance (Na+>Ca2+>Mg2+>K+), and ionic concentrations varied little during the year of study; nutrients, however, showed strong temporal variability. The ion chemistry of the streams was influenced by bedrock weathering according to the Gibbs Model. The streams are chiefly mesotrophic, but their primary production may be limited by nitrogen based on the N:P ratio. Streams differed in chlorophyll a concentrations and their productivity changed temporally. They were among the most mineral-rich tropical streams, and both their ion concentration levels and cationic patterns coincided with other neotropical volcanic streams. Although there was a pattern in which ion concentrations of the streams were negatively related to the proportion of conserved vegetation and positively related to the proportion of pastures and croplands, the relationships were not statistically significant. We concluded that differences in the major ions of the streams studied were caused by the great heterogeneity in geology and soil types, as well as by geothermal activity in the area. Temporal changes in nutrients were related to biological processes in the streams that influenced primary productivity. Moreover, the influence of land use might be hidden by the strong effect of this heterogeneity on the streams studied.

Mechanisms of CO and COS Formation in the Claus Furnace

The aim of this study was to determine the major pathways leading to COS and CO formation and consumption during the processing of H2S and CO2 in the partially oxidizing conditions of the Claus furnace. Both species were found to be produced by a multitude of pathways, which include the direct reaction of H2S with CO2 to form COS and H2O and the reaction of CO2 with S2, one of the major primary products in a Claus furnace. This last reaction produced SO2 and CO as the major products, with COS being formed in lesser quantities. The dissociation of H2S to H2 and S2 at high temperatures (>1000 °C) was shown to promote a further cascade of reactions stemming from the reduction of COS and CO2, both of which lead to CO. Because of the known formation of CS2 from hydrocarbon carry-over into the furnace, the reactions of CS2 with CO2, H2O, and SO2 were also studied as potential CO- and COS-forming reactions. Reaction with CO2 was slow at <1200 °C, but reaction with either H2O or SO2 was fast above 900 °C. Convers...

NADPH Supply and Mannitol Biosynthesis. Characterization, Cloning, and Regulation of the Non-Reversible Glyceraldehyde-3-Phosphate Dehydrogenase in Celery Leaves

Mannitol, a sugar alcohol, is a major primary photosynthetic product in celery (Apium graveolens L. cv Giant Pascal). We report here on purification, characterization, and cDNA cloning of cytosolic non-reversible glyceraldehyde-3-P dehydrogenase (nr-G3PDH, EC 1.2.1. 9), the apparent key contributor of the NADPH required for mannitol biosynthesis in celery leaves. As determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, purified nr-G3PDH showed a molecular mass of 53 kD. A 1,734-bp full-length cDNA clone (accession no. AF196292) encoding nr-G3PDH was identified using polymerase chain reaction and rapid amplification of cDNA ends techniques. The cDNA clone has an open reading frame of 1,491 bp encoding 496 amino acid residues with a calculated molecular weight of 53,172. K(m) values for the celery nr-G3PDH were low (6.8 microM for NADP(+) and 29 microM for D-glyceraldehyde-3-P). NADPH, 3-phosphoglycerate, and ATP were competitive inhibitors, and cytosolic levels of these three metabolites (as determined by nonaqueous fractionation) were all above the concentrations necessary to inhibit activity in vitro, suggesting that nr-G3PDH may be regulated through feedback inhibition by one or more metabolites. We also determined a tight association between activities of nr-G3PDH and mannose-6-P reductase and mRNA expression levels in response to both leaf development and salt treatment. Collectively, our data clearly show metabolic, developmental, and environmental regulation of nr-G3PDH, and also suggest that the supply of NADPH necessary for mannitol biosynthesis is under tight metabolic control.

Fate of lipid hydroperoxides in blood plasma

Cholesteryl ester hydroperoxide (CE-OOH) and phosphatidylcholine hydroperoxide (PC-OOH) are the major primary oxidation products of lipoproteins. CE-OOH is present in human and rat plasmas while PC-OOH is undetectable. This is likely due to the enzymatic (plasma glutathione peroxidase) and the nonenzymatic (apolipoproteins A and B-100) reducing activities of PC-OOH in plasma, and to the enzymatic conversion of PC-OOH to CE-OOH by lecithin:cholesterol acyltransferase in high density lipoproteins. The regioisomeric distribution of CE-O(O)H in human plasma indicates that free radical-mediated chain oxidation is an ongoing process, even in healthy young individuals.

Photoinduced reactions of chloranil with 1,1-diarylethenes and product photochemistry-intramolecular

Photoinduced reactions of chloranil (CA) with 1,1-diarylethenes 1 [(p-X-Ph)(2)C=CH(2), X = F, Cl, H, Me] in benzene afforded products 4-14, respectively, with the bicyclo[4.2.0]oct-3-ene-2,5-diones 4, the 6-diarylethenylcyclohexa-2,5-diene-1,4-diones 5, and 2,3,5, 6-tetrachlorohydroquinone 13 as the major primary products. The cyclobutane products 4 are formed via a triplet diradical intermediate without involvement of single electron transfer (SET) between the two reactants, while 5 is derived from a reaction sequence with initial SET interaction between (3)CA and the alkene. The 9-arylphenanthrene-1,4-diones 6 and its 10-hydroxy-derivatives 7 are secondary photochemical products derived from 5. The isomeric cage products 9-11 are formed from 4 via intramolecular benzene-alkene [2 + 2] (ortho-)photocycloadditions induced by the triplet excited enedione moiety. The relative amount of the two groups of products (4 and its secondary products 9-11 via non-SET route vs 5 and its secondary products 6, 7, 8, 12, and 14 via SET route) shows a rather regular change, with the ratio of non-SET route products gradually increasing with the increase in oxidation potential of the alkenes and in the positive free energy change for electron transfer (DeltaG(ET)) between (3)CA and the alkene, at the expense of the ratio of the products from the SET route. The competition between the SET and non-SET routes was also found to be drastically influenced by solvent polarity, with the SET pathways more favored in polar solvent. Photo-CIDNP investigations suggest the intermediacy of exciplexes or contact ion radical pairs in these reactions in benzene, while in acetonitrile, SET process led to the formation of CA(*)(-) and cation radical of the alkene in the form of solvent separated ion radical pairs and free ions.

Reproduction in the Red Sea soft coral Heteroxenia fuscescens : seasonality and long-term record (1991 to 1997)

Heteroxenia fuscescens is a common zooxanthellate soft coral on the shallow reefs in the Gulf of Eilat, northern Red Sea. In the Red Sea, during its prolonged planulation, H. fuscescens is subjected to a seasonal environmental regime that alternates between stratified warm summer waters and upwelling of low-temperature winter waters. To examine the possible relationship between these seasonal fluctuations and the reproductive characteristics of H. fuscescens, we monitored its breeding activity for a 6-year period, including the percentage of colonies releasing planulae, number of planulae released per colony per night (fecundity), planula size and percentage of released deformed planulae. During summer and fall the combined average percentage of planulating colonies of H. fuscescens was significantly higher than in winter and spring. In addition, fecundity was greater during the summer than the rest of the year. Planulae released during summer were longer, with almost zero percent deformation. During the rest of the year they were shorter, with a higher percentage of deformation. The current study indicates that although H. fuscescens reproduces all year round, the quantity and quality of its reproductive features are subject to seasonal variability. In the Gulf of Eilat seasonal changes in the abiotic features of the water may have an impact on its reproduction. During summer, primary productivity reaches a distinctive maximum up to a depth of about 40 m. The winter upwelling waters introduce nutrients from the depths into the upper 200 m, and especially into the major primary productivity zone, thereby triggering the annual phytoplankton bloom. Because colonies of H. fuscescens gain nutritional benefit from uptake of organic material dissolved in the water and by carbon fixation by zooxanthellae, we␣suggest that the seasonal fluctuations in the species' reproductive traits are related to these fluctuations in nutrient and light levels.

Lipid hydroperoxides inhibit nitric oxide production in RAW264.7 macrophages

The effects of oxidatively modified low density lipoprotein (oxLDL) on atherogenesis may be partly mediated by alterations in the production of nitric oxide (NO) by vascular cells. Lipid hydroperoxides (LOOH) and lysophosphatidylcholine (lysoPC) are the major primary products of LDL oxidation. The purpose of this study was to characterize the effects of oxLDL, LOOH and lysoPC on NO production and the expression of inducible nitric oxide synthase (iNOS) gene in lipopolysaccharide (LPS) stimulated macrophages. LDL was oxidized using an azo-initiator 2,2′-azobis (2-amidinopropane) HCl (ABAP) and octadecadienoic acid was oxidized by lipoxygenase to generate 13-hydroperoxyl octadecadienoic acid (13-HPODE). Our study showed that oxLDL markedly decreased the production of NO, the levels of iNOS protein and iNOS mRNA in LPS stimulated macrophages. The inhibition potential of oxLDL on NO production and iNOS gene expression depended on the levels of LOOH formed in oxLDL and was not due to oxLDL cytotoxicity. Furthermore, 13-HPODE markedly reduced NO production and iNOS protein levels, whereas lysoPC showed only slight reduction. The effects of 13-HPODE and lysoPC did not require an acetylated LDL carrier. Our results suggest that 13-HPODE is a much more potent inhibitor of NO production and iNOS gene expression than lysoPC in LPS stimulated RAW264.7 macrophages.

Primary Product Distributions from the Reaction of OH with m-, p-Xylene, 1,2,4- and 1,3,5-Trimethylbenzene

A study was conducted to examine the OH-initiated degradation products of the four title compounds in the presence of sub-part-per-million levels of NOx. The oxidation was conducted in a dynamic reactor to minimize the conversion of the aromatic compounds. The experiments were designed to represent reaction pathways that occur in the atmosphere at ambient NO2 concentrations. A wide range of ring-retaining and ring-cleavage products having widely varying yields were measured during the study. For m-xylene, the major primary products observed (with molar yields) were methyl glyoxal (0.40), 4-oxo-2-pentenal (0.12), glyoxal (0.079), and m-tolualdehyde (0.049). For p-xylene, the major primary products were p-tolualdehyde (0.103), 2,5-dimethylphenol (0.13), cis-3-hexene-2,5-dione (0.176), trans-3-hexene-2,5-dione (0.045), 2-methyl-butenedial (0.071), glyoxal (0.394), and methylglyoxal (0.217). Several other reaction products were measured at yields less than 3%. The primary products for OH + 1,2,4-trimethylbenzene were found as follows: methylglyoxal (0.44), glyoxal (0.066), cis-3-hexene-2,5-dione (0.13), trans-3-hexene-2,5-dione (0.031), biacetyl (0.114), 3-methyl-3-hexene-2,5-dione (0.079), and 2-methyl-butenedial (0.045). Six other (ring retaining) products were measured at yields less than 3%. The primary products for OH + 1,3,5-trimethylbenzene were methylglyoxal (0.90), 3-methyl-5-methylidene-5(2H)-furanone (0.1), 3,5-dimethyl-3(2H)-2-furanone (0.1), 3,5-dimethyl-5(2H)-2-furanone biacetyl (0.08), and 2-methyl-4-oxo-2- pentenal (0.05). Three other products were detected at molar yields less than 5%. In some cases, the yields for the ring fragmentation products could only be based on calibrations from surrogate compounds. Yields for several of the unsaturated dicarbonyl compounds have not been reported previously while yields for methylglyoxal, glyoxal, and biacetyl are largely consistent with previous reports. Some of the primary furanone products are the identical to those reported as secondary products in aromatic systems.

Ion/molecule reactions of protonated diglycine: an electrospray ionization flow tube reactor experiment

Reactions of protonated diglycine, GLY 2H +, with methanol, ammonia, and a series of methylamines were studied under thermal conditions with a combination of an electrospray ion source and a flow tube reactor. The major primary reaction product in all of the systems studied is the complex formed between the ionic and neutral reagents in a ternary association reaction involving the helium carrier gas and oxygen or nitrogen molecules as collisionally stabilizing species. Effective binary rate constants were determined experimentally and compared with calculated ion dipole collision rate constants. Proton transfer was observed from GLY 2H + to trimethylamine but not to any of the other reagents studied. Secondary products observed include formation of protonated mixed trimers of GLY 2 with two amine molecules. In the case of methanol, a secondary product is the protonated mixed dimer of GLY 2 and dimethylether. The results will be discussed in the light of the mechanisms of hydrogen-deuterium (H-D) exchange of GLY 2H + with deuterated isotopomers of methanol and ammonia studied previously by various groups.

Taihu Lake:Past, Present and Future

The presence of roads, farm house foundations, wells and Liangzhu period cultural relics in the bottom of Lake Taihu attest to the fact that this shallow depression was probably dry between 4 and 5 thousand years ago. This interpretation is corroborated by the sudden disappearance of algal pigments at sediment depths carbon-14 dated at 4-5 thousand years before present.<br>In winter, the stronger winds are predominantly from the northeast. These winds result in a powerful counterclockwise current that transports lake sediments and has altered the very shape of the lake over the last 300 years. Winds produce a complex mixing pattern in Lake Taihu with storm induced sediment deposition occurring near the lake's center.<br>During approximately 240 days of the year, the wind blows across Lake Taihu with sufficient force to mix it to its bottom. As a result, this polymictic lake rarely becomes anoxic and dissolved oxygen at the mud water interface is maintained at or above 4 mg·l^-1. The consequences of this high dissolved oxygen are quite impressive as high organic loading to the lake would otherwise render its bottom waters anaerobic killing many of its natural inhabitants.<br>Because suspended solids reduce (attenuate) light penetration, the major primary production takes place in the top metre of the lake (mean Secchi Transparency-0.25 m). Suspended clays are slow to settle and wind mixing keeps fine-grained suspended solids in suspension in all but the most quiet backwaters of the lake.<br>In the recent past about 23 000 metric tonnes of phytoplankton were produced in Lake Taihu. This large production represents only about 5% of the total influx of organic material entering the lake. In summer and fall, cyanobacteria such as Microcystis spp. and Anabaena spp. dominate most of the lake. Recently, however, mixotrophic flagellates displaced cyanobacteria as the dominant algae in parts of Lake Taihu with high bacteria and high suspended solids (e.g. Wuli and Meiliang Bay). In the future, facultative heterotrophs may come to dominate an ever larger portion of the lake waterc column.;The presence of roads, farm house foundations, wells and Liangzhu period cultural relics in the bottom of Lake Taihu attest to the fact that this shallow depression was probably dry between 4 and 5 thousand years ago. This interpretation is corroborated by the sudden disappearance of algal pigments at sediment depths carbon-14 dated at 4-5 thousand years before present.<br>In winter, the stronger winds are predominantly from the northeast. These winds result in a powerful counterclockwise current that transports lake sediments and has altered the very shape of the lake over the last 300 years. Winds produce a complex mixing pattern in Lake Taihu with storm induced sediment deposition occurring near the lake's center.<br>During approximately 240 days of the year, the wind blows across Lake Taihu with sufficient force to mix it to its bottom. As a result, this polymictic lake rarely becomes anoxic and dissolved oxygen at the mud water interface is maintained at or above 4 mg·l^-1. The consequences of this high dissolved oxygen are quite impressive as high organic loading to the lake would otherwise render its bottom waters anaerobic killing many of its natural inhabitants.<br>Because suspended solids reduce (attenuate) light penetration, the major primary production takes place in the top metre of the lake (mean Secchi Transparency-0.25 m). Suspended clays are slow to settle and wind mixing keeps fine-grained suspended solids in suspension in all but the most quiet backwaters of the lake.<br>In the recent past about 23 000 metric tonnes of phytoplankton were produced in Lake Taihu. This large production represents only about 5% of the total influx of organic material entering the lake. In summer and fall, cyanobacteria such as Microcystis spp. and Anabaena spp. dominate most of the lake. Recently, however, mixotrophic flagellates displaced cyanobacteria as the dominant algae in parts of Lake Taihu with high bacteria and high suspended solids (e.g. Wuli and Meiliang Bay). In the future, facultative heterotrophs may come to dominate an ever larger portion of the lake waterc column.

Practical Methods for Lipid Peroxides Determination

Lipid oxidation is a major problem in quality control of oil and fat, oil-containing products, and even in lipid metabolism. Unsaturated lipids form hydroperoxides as the major primary products in their early autoxidation process, followed by producing many kinds of decomposed and polymerized products as the secondary products. Therefore, many determination methods, such as peroxide value method for hydroperoxides, carbonyl value method for carbonyl compounds, acid value for free fatty acid, and various instrumental analyses such as HPLC, GC, some spectrometries etc., have been proposed to evaluate the oxidation degree of lipids. In the determination of lipid peroxides, it is an essential to understand the characteristics of the individual method and then to select the suitable method in accordance with the purpose of measurement and the properties of lipid sample.In the present paper, we will describe some practical determination methods for lipid peroxides, especially in focusing on peroxide value methods including a novel potentiometric titration method for the lipid hydroperoxides determination, which has excellent precision and reproducibility.

Inhibition of oxidation of low density lipoprotein by troglitazone

The effect of a new oral hypoglycemic agent troglitazone, (±)-5-[4-(6-hydroxy-2,5,7,8-tetramethylchroman-2-yl-methoxy)benzyl]-2,4-thiazolidinedione as an antioxidant against the free radical-mediated oxidation of low density lipoprotein (LDL) was studied. The oxidation of LDL gives cholesteryl ester hydroperoxide and phosphatidylcholine hydroperoxide as major primary products. Troglitazone incorporated exogenously into LDL inhibited the oxidations of LDL induced by either aqueous or lipophilic peroxyl radicals and suppressed the formation of lipid hydroperoxides efficiently. Ascorbic acid added into the aqueous phase spared both endogenous α-tocopherol and troglitazone in LDL. It was also found by absorption spectroscopic and electron spin resonance (ESR) studies that troglitazone reacted rapidly with a galvinoxyl radical to give a chromanoxyl radical which gives the same ESR spectrum as α-tocopherol. This ESR spectrum disappeared rapidly when ascorbic acid was added into the system. These results show that troglitazone acts as a potent antioxidant and protects LDL from oxidative modification.

13C MAS NMR mechanistic study of benzene alkylation with propane over Ga-modified H-ZSM-5 catalyst

13C MAS NMR has been performed in situ to investigate the mechanism of benzene alkylation with propane over Ga H-ZSM-5 catalyst. Propane 2- 13C was used as a labelled reactant. In order to clarify the main reaction pathways, conversions of the individual starting materials and some of the reaction intermediates such as cumene and n-propylbenzene were also studied under similar conditions. Benzene alkylation with propane begins at 573 K, toluene and ethylbenzene being the major primary products. The reaction is preceded by the induction period caused by stronger adsorption of benzene that prevents propane activation. The main reaction pathway includes bifunctional propane activation on Brønsted and Ga sites which leads to protonated pseudocyclopropane (PPCP) intermediate, which in turn decomposes preferentially to CH 4 and C 2H + 5, or C 2H 6 and CH + 3. The reaction of C 2H + 5 or CH + 3 carbenium ions with benzene leads to toluene or ethylbenzene, respectively. The less favourable reaction routes give propenium and cycloproponium ions upon PPCP decomposition, and result in observation of the traces of cumene and n-propylbenzene. These routes are reversible, the equilibrium being shifted towards reactants at 573 K.

Mass spectra of 2,4-dinitroimidazole and its isotopomers using simultaneous thermogravimetric modulated beam mass spectrometry

The EI mass spectrum of 2,4-dinitroimidazole (2,4-DNI) was studied at 20 and 70 eV ionizing energy using simultaneous thermogravimetric modulated beam mass spectrometry. Product ion formulas and their origin from within the 2,4-DNI molecule were identified from the evaluation of perdeuterated and various 15 N-labeled 2,4-DNI mass spectra. The molecular ion (M +. ; m/z 158) is present in all the spectra and the NO + ion (m/z 30) is the major primary product ion. The base peak is formed by the M .+ ion at 20 eV and by the NO + ion at 70 eV. Other primary product ions are NO 2 + (m/z 46), CH 2 N + (m/z 28) and CHN 2 O 2 + (m/z 73). Fragmentation pathways are postulated based on the identity and relative abundance of the product ions, and on the change in relative abundance of the ions as a function of ionizing energy. Comparisons of the 70 eV mass spectra of 2,4-DNI, 4,5-dinitroimidazole (4,5-DNI) and 1,4-dinitroimidazole (1,4-DNI) show that the fragment product ions have the same m/z values in the three spectra but differ in their relative abundance and in the ion that forms the base peak. The base peak for 2,4-DNI and 4,5-DNI is formed by the ion at m/z 30 (NO + ) and for 1,4-DNI, the ion at m/z 46 (NO 2 + ). This difference is probably due to the nitramine functionality of 1,4-DNI