Degree Of Isomerization Research Articles

Intensified bacterial productivity during the Paleocene–Eocene thermal maximum: Molecular evidence in the Tarim Basin in the eastern Tethyan realm

The investigation of bulk and molecular compositions in organic matter at the Bashibulake Section in the SW Tarim Basin, West China, across the Paleocene–Eocene boundary reveals a complex mixture of marine and terrigenous origins during the Paleocene–Eocene Thermal Maximum (PETM) in the eastern Tethys. Source-related biomarkers, such as n-alkanes, isoprenoid alkanes, steranes, hopanes and methylhopanes, exhibit diverse compositions influenced by both marine and terrigenous sources. Sterane and hopane isomer distributions, indicative of immature OM, are primarily controlled by biological configurations. Changes in compound class abundance and isomer ratios reflect variations in source inputs and depositional conditions. Elevated concentrations of n-alkanes from higher plants, along with ratios of C29-C32 moretanes/hopanes and C31/C32 homohopanes, suggest increased terrigenous OM supply during the PETM. However, the significant differences in concentration between n-alkanes from higher land plants and bacterial hopanes, coupled with the presence of 2α-methylhopanes, prevalence of C27 compounds in regular steranes, and absence of oleanane suggest a dominant aquatic bacterial contribution. The study highlights the role of enhanced continental flux and warming in stimulating microbial activity, enriching OM, a factor often overlooked by other analytical methods. The absence of carbonate carbon and low trisnorhopane isomerization provide supportive evidence of ocean acidification and carbonate dissolution during the PETM. Reduced pregnanes and tricyclic terpanes, along with low degree of hopane and sterane isomerization, indicate rising sea levels and low salinity. The findings emphasize the significance of the biomarker approach in identifying OM origin and characterizing the depositional environment in PETM-related sequences, suggesting a more substantial role of bacterial contributions than previously recognized.

Platinum(II) complexes containing pyridyl-substituted thiourea dianion and monoanion ligands: Synthesis, structural chemistry, and theoretical investigations

Reactions of cis-[PtCl2(PPh3)2] with the 2-pyridyl-substituted thioureas py(CH2)nNHC(S)NHC6H4R (R = H, OMe or NO2; n = 0, 1 or 2) in methanol with Et3N base, followed by precipitation with water gave good yields of the complexes [Pt{SC(NC6H4R)(N(CH2)npy)}(PPh3)2]. The compounds were characterised 1H NMR, 31P{1H} NMR, FTIR and single crystal X-ray crystallography. The initial NMR investigation indicated the possibility of isomerism in the complexes. 31P{1H} NMR investigations revealed the presence of an initial distal isomer for the dianion complexes, which underwent solution phase isomerization into the proximal isomeric forms of the complexes and/or a mixture of the proximal and distal isomers. The opposite trend was recorded for the monoanionic complex with the formation of an initial proximal isomer and subsequent isomerisation into 1:3 mixture of the distal and proximal isomeric forms of the complex. The degree of isomerization was observed to be related to the difference in energy between the two isomeric forms of the complex and the nature and size of the R substituents in the complex. The molecular geometries of a number of the compounds showed a distorted square-planar geometry defined by a NP2S donor set. The thiourea ligand acts as (N,S)-chelating dianionic ligand so that each donor atom is opposite a phosphane-P atom; a trans-influence is evident on the Pt-P bonds. In each complex, the pyridyl-substituted nitrogen is coordinated to platinum. The cationic complex [Pt{SC(NPh)(NHCH2py)}(PPh3)2]+ was also isolated as its BF4- salt by addition of excess NaBF4 to the reaction mixture. In this complex, the thiourea monoanion coordinates in a distal manner, with the NHCH2py group remote from the platinum centre. Charge-assisted ammonium-NH…N(pyridyl) bonding leads to dimeric aggregates. These, along with the neutral molecules [Pt{SC(Np-C6H4R2)(N(CH2)npy)}(PPh3)2] are assembled into the three-dimensional crystal via weak non-covalent interactions. Characterisation by 31P{1H} NMR spectroscopy showed the presence of several isomeric species in solution.

Effects of time and temperature of storage on chemical and nutritional characteristics of raw milk for Provolone Valpadana PDO cheesemaking: a multivariate approach.

We evaluated the possibility of increasing the storage temperature of raw milk for Provolone Valpadana cheesemaking, to identify the most suitable conditions of time and temperature for a pre-maturation process. We used Principal Component Analysis (PCA) to analyze the overall effects of different storage conditions on chemical, nutritional and technological characteristics of the raw milk. Four different thermal storage cycles, two at fixed temperature/time (6 and 12°C for 60 h) and two with two-phase thermal cycle (10 and 12°C for 15 h, followed by refrigeration at 4°C for 45 h) were studied. Although a moderate heterogeneity among raw milks from the 11 producers of Provolone Valpadana cheese was observed, PCA revealed the critical aspects of the extreme storage conditions (60 h of refrigeration). Some samples resulted in anomalous behaviors, probably related to unexpected fermentation phenomena occurring with increasing storage temperature. The acidification and the increase in the contents of lactic acid, soluble calcium, and degree of retinol isomerization observed in the anomalous samples can compromise the technological functionality of milk. Conversely, the storage with a two-phase thermal cycle did not lead to variations in any measured characteristic, suggesting that mild refrigeration conditions (10 or 12°C for 15 h followed by 4°C for 45 h) could be a good compromise in favoring milk pre-maturation without altering its quality characteristics.

In-situ FTIR investigation of isomerisation of cis-butadiene rubber during the vulcanization

The physical properties of cis-butadiene rubber (BR) have been shown to be critically dependent on its stereoregularity. In this work, the evolution process and influencing factors of cis-trans isomerisation of BR based on the conventional formulation system during its vulcanization process are systematically investigated using in-situ Fourier transform infrared spectroscopy (FTIR) technology. The results show that the isomerisation occurs in the BR compound with sulphur vulcanization system in both non-isothermal and isothermal vulcanization processes because of the polysulfide bonds formed by sulphur in the system, and it is more obvious than that with dicumyl peroxide (DCP) vulcanization system. The degree of isomerisation shows a positive correlation with the sulphur dosage and can reach 10% with 3 phr sulphur. Experiments also prove that zinc oxide (ZnO) and antioxidants have a significant inhibitory effect on the isomerisation during the vulcanization. The isomerisation degree of BR/ZnO-4 is reduced by half compared to that of BR/ZnO-0. The effect of antioxidant poly (1,2-dihydro-2,2,4-trimethyl-quinoline) (RD) is greater than that of N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine (6PPD) due to its higher activity. The isomerisation of BR compound in the vulcanization is not affected significantly by the accelerator types. Besides, the isomerisation degree of Nd-BR with higher chain regularity is lower than that of Ni-BR with the same vulcanization system. The investigation above provides new perspectives and inspirations for the optimization of formula and scientific analysis on the structure-property relationship of BR composite.

The guest CH3CN molecule triggers solid-state photochromism in a Cu2I2-based MOF for advanced time-dependent encryption and inkless erasable printing

It remains a big challenge to develop solid-state stimuli-responsive materials for time-dependent information encryption and inkless erasable printing with long retention times. Herein, a 2D Cu2I2-based MOF with photoresponsive spiropyran (SP) groups orderly installed on its skeleton is developed. The structural isomerization from SP to colored merocyanine (MC) form can be triggered by removing the CH3CN guests. Besides, the degree of structural isomerization and the retention time can be adjusted by controlling the amount of CH3CN guests, exhibiting dynamic photochromic behavior with multicolor states and tunable retention time. Based on these advantages, time-dependent information encryption is successfully achieved. Furthermore, the long retention time (>72 h) of the MC form under daylight conditions in the CH3CN-removed Cu2I2-based MOF and good repeatability make it promising in various applications, such as temporary calendars, price-cards, billboards, and reusable identity cards. This work provides a novel design strategy to fabricate multi-functional MOF-based smart materials for challenging applications of time-dependent information encryption and inkless erasable printing.

Assessing tolerability and physiological responses to 17α-estradiol administration in male rhesus macaques.

17α-estradiol has recently been shown to extend healthspan and lifespan in male mice through multiple mechanisms. These benefits occur in the absence of significant feminization or deleterious effects on reproductive function, which makes 17α-estradiol a candidate for translation into humans. However, human dosing paradigms for the treatment of aging and chronic disease are yet to be established. Therefore, the goals of the current studies were to assess tolerability of 17α-estradiol treatment, in addition to evaluating metabolic and endocrine responses in male rhesus macaque monkeys during a relatively short treatment period. We found that our dosing regimens (0.30 and 0.20mg/kg/day) were tolerable as evidenced by a lack of GI distress, changes in blood chemistry or complete blood counts, and unaffected vital signs. We also found that the higher dose did elicit mild benefits on metabolic parameters including body mass, adiposity, and glycosylated hemoglobin. However, both of our 17α-estradiol trial doses elicited significant feminization to include testicular atrophy, increased circulating estrogens, and suppressed circulating androgens and gonadotropins. We suspect that the observed level of feminization results from a saturation of the endogenous conjugation enzymes, thereby promoting a greater concentration of unconjugated 17α-estradiol in serum, which has more biological activity. We also surmise that the elevated level of unconjugated 17α-estradiol was subjected to a greater degree of isomerization to 17β-estradiol, which is aligned with the sevenfold increase in serum 17β-estradiol in 17α-estradiol treated animals in our first trial. Future studies in monkeys, and certainly humans, would likely benefit from the development and implementation of 17α-estradiol transdermal patches, which are commonly prescribed in humans and would circumvent potential issues with bolus dosing effects.

Applications of low molecular weight polycyclic aromatic hydrocarbons (PAHs) and diamondoids ratios/indices on the maturity assessment of coal-bearing source rock: Insight from mature to overmature Longtan Shale

Gas chromatography-mass spectroscopy (GC–MS) and highly selective and sensitive gas chromatography–triple quadrupole mass spectrometry (GC–MS–MS) detections were applied to investigate low molecular weight polycyclic aromatic hydrocarbons (PAHs; alkylnaphthalenes, alkylphenanthrenes, and alkyldibenzothiophenes) variations and quantify diamondoids (adamantanes and diamantanes) on a set of coal-bearing Longtan Shale samples within the thermal maturity range of 1.53–3.38%VRr (random vitrinite reflectance). Under consideration of pyrolytic results of kerogen (type I, II, and III), source rock extracts, and oil, the following conclusions were drawn: 1) Poor correlation was observed between PAH isomerization ratios and vitrinite reflectance, which suggests that they are not primarily dependent on thermal maturity. 2) The yield peaks of both adamantanes and diamantanes occur at the maturity of 1.74%VRr; the adamantanes concentration increases and sharply exhausts thereafter, whereas the amount of diamantanes reduces gradually with increasing maturity after the yield peak. 3) Diamondoids concentration and isomerization indices show a significant dependency depend on thermal maturity; adamantanes-related maturity indices show positive correlations with increasing thermal maturity up to 3.0%VRr and reverse correlations after that, whereas diamantanes indices show the reverses later than 3.0%VRr. 4) The distributions of aromatic isomers are affected by organic matter types, while the isomerization indices of diamondoids seem independent of organic matter origin. 5) Clay minerals can catalyze the degree of isomerization of alkylphenanthrenes and adamantanes, and enhance the yield of diamondoids at maturities <1.80%VRr; while mineral compositions have minor effects at maturities higher than 2.53%VRr. 6) The total sulfur content has little effect on the variation of aromatics maturity indices and diamondoids yields. Sulfur-derived dealkylation, however, should be considered in the evaluation of methyl adamantanes and ethyl adamantanes. Consequently, diamondoids concentration and isomerization indices may serve as stronger maturity indicators than low PAHs isomerization ratios at the mature to overmature stage.

Molecular Motion in the Interconverting σ-H2, Di-, and Tri-hydride Regimes: .

The transition-metal complex is known to exist in three possible isomeric forms, including a nonclassical, σ-bound dihydrogen complex and two classical dihydride isomers. As such, it has served as a model complex for the energies of conversion between these limiting structural regimes. In the present study, ab initio molecular dynamics computer simulations, combined with enhanced sampling techniques, were utilized to directly assess the degree of motion and isomerization of the dihydrogen/dihydride moieties in this complex. Ligand rotations (for both the H2 unit and the phosphine units) were found to be dominant in the low-temperature (298 K) regime, and the classical thermodynamic distribution showed no probability of thermally accessing dihydride forms, although unrestrained molecular dynamics trajectories showed fleeting configurations outside of the σ-H2 configuration. Simulations at higher temperatures surprisingly revealed new tri-hydride isomers that are energetically competitive with the σ-H2 and cis-/trans-dihydride isomers. Low-energy pathways to hydrogen/hydride transfer and phosphine dissociation were readily accessible, which considerably expands the known isomeric flexibility of this complex.

From cis-Lobeline to trans-Lobeline: Study on the Pharmacodynamics and Isomerization Factors.

Lobeline is an alkaloid derived from the leaves of an Indian tobacco plant (Lobelia inflata), which has been prepared by chemical synthesis. It is classified as a partial nicotinic agonist and has a long history of therapeutic usage ranging from emetic and respiratory stimulant to tobacco smoking cessation agent. The presence of both cis and trans isomers in lobeline is well known, and many studies on the relationship between the structure and pharmacological activity of lobeline and its analogs have been reported. However, it is a remarkable fact that no studies have reported the differences in pharmacological activities between the two isomers. In this article, we found that different degrees of isomerization of lobeline injection have significant differences in respiratory excitatory effects in pentobarbital sodium anesthetized rats. Compared with cis-lobeline injections, the respiratory excitatory effect was significantly reduced by 50.2% after administration of injections which contained 36.9% trans-lobeline. The study on the influencing factors of isomerization between two isomers shown that this isomerization was a one-way isomerism and only converted from cis to trans, where temperature was the catalytic factor and pH was the key factor. This study reports a new discovery. Despite the widespread use of ventilators, first-aid medicines such as nikethamide and lobeline has retired to second line, but as a nonselective antagonist with high affinity for a4b2 and a3b2 nicotinic acetylcholine receptors (nAChRs). In recent years, lobeline has shown great promise as a therapeutic drug for mental addiction and nervous system disorders, such as depression, Alzheimer disease and Parkinson disease. Therefore, we suggest that the differences between two isomers should be concerned in subsequent research papers and applications.

Liquid and Photoliquefiable Azobenzene Derivatives for Solvent-free Molecular Solar Thermal Fuels.

A series of liquid and photoliquefiable azobenzene (Azo) derivatives (Azo-Cn-Br) have been synthesized for molecular solar thermal fuels. Each of the liquid and photoliquefiable azo derivatives shows a high degree of isomerization, a fast isomerization rate, a long half-life, an appropriate energy storage density, and a solvent-free "charging" and "discharging" process. The photoliquefied azo derivatives can isomerize upon UV light irradiation at low temperatures to give the "UV-charged" azo ones. Therefore, the phase transition enthalpy is stored simultaneously along with the isomerization enthalpy. The "UV-charged" azo derivatives are capable of releasing heat under the manipulation of blue light.

Cis-trans retinol isomerisation: Influence of microorganisms during the production of pasta filata cheeses

The isomerisation index, or degree of retinol isomerisation (DRI), i.e. the percentage ratio between 13-cis and all-trans retinol, could be used as process and product index in dairy products. To better investigate microbial influence on retinol isomerisation, retinol isomerisation and microbial levels have been monitored during the technological process and the storage of different “pasta filata” cheeses. In the investigated cheeses, after a saponification procedure and HPLC analysis, 13-cis retinol, all-trans retinol and other cis retinols were detected. During production, an increase of 13-cis retinol and of the DRI was found. As to their initial values, an increment in almost all microorganisms, most remarkable for lactic acid bacteria, was detected. The isomerisation index was found to be significantly correlated to the growth of thermophilic lactic acid bacteria during the production process.

INVESTIGATION OF THE ISOMERIZATION REACTION OF BUTENE-1 TO BUTENES-2 ON BINARY TUNGSTEN-CONTAINING CATALYSTS

The activity of tungsten-containing catalysts in the reaction of isomerization of butene-1 to butenes-2 was studied in the work. The results obtained showed that the ^ introduction of the second element into the composition of the tungsten oxide catalyst had a different effect on its activity in the butene-1 isomerization reaction. It was established that an increase in the amount of molybdenum in the composition of a binary tungsten-containing catalyst at low temperatures leads to a decrease in the degree of butene-1 isomerization while at high temperatures it leads to an increase in the rate of butene-1 isomerization. It found that the addition of titanium to the composition of the tungsten oxide catalyst leads to an increase in the butene-1 isomerization rate. When copper is added to the composition of the tungsten oxide catalyst, the total yield of butene-2 passes through a maximum, and on samples rich in copper, the isomerization of butene-1 practically does not occur. It revealed that the activity of binary tungsten oxide catalysts in the isomerization reaction of butene-1 to butenes-2 changes in the following order: Ti-W-O &gt; Mo-W-O &gt; Cu-WO.

Investigation on chlorogenic acid stability in aqueous solution after microwave treatment

Recently, several health benefits associated with the consumption of foods rich in chlorogenic acid (5-CQA) have been reported. However, an important issue is its low stability during extraction and food processing, resulting in isomerization to neochlorogenic and cryptochlorogenic acids and the formation of further degradation products. This work describes the evaluation of 5-CQA reactivity in commercial waters after microwave treatment. An optimized HPLC-UV method was used to monitor 5-CQA conversion to its main isomers, while LC-HRMS/MS was performed for the elucidation of transformation products. Results revealed different degrees of isomerization in 5-CQA depending on the water sample, and the formation of oxidation derivatives of CQA isomers. This study highlights the importance of analytical monitoring of food compounds, during microwave treatment for example. In the case of 5-CQA, understanding of the degradation process would allow better preservation of bioactive constituent in foods and beverages and health promoting effects.

Studies of the content of optical isomers of amino acids in food

Food products undergo a wide range of chemical changes during their processing and storage. As a result of such reactions, both new chemical compounds and optical isomerization of compounds already present in the composition can be formed. The second case concerns the formation of D-enantiomers of amino acids from their L-forms. D-forms of amino acids not only have no biological value for the body, but also often have a negative effect on the human body due to the impossibility of metabolizing them and, as a consequence, their accumulation in the body. The aim of the work was to study the quantitative content of D-isomers of amino acids in milk that passed the ultra-pasteurization process and dairy products based on bacterial starter culture. The research results showed that in both cases of the considered technological methods, amino acid isomerization occurs. The highest degree of isomerization was observed in kefir samples relative to other samples. However, from the results obtained, it is not possible to estimate which amino acid is most susceptible to the racemization process, since different samples contained different D-isomers of amino acids. The smallest amount of D-isomers is found in milk that has not undergone any industrial processing. Studies have shown that technological processing of milk inevitably leads to the formation of D-isomers of amino acids, and this, in turn, at least reduces the nutritional and biological value of the product, which makes it necessary to conduct deeper studies in this direction to establish the most important factors in the process of racemization of amino acids in food products.

Stabilization of magnetic fluid with polydimethylsiloxane kills three birds with one stone

ABSTRACT The stability of a stabilized with polydimethylsiloxane (PDMS) magnetic fluid to alcohols of a saturated homologous series was investigated. We used alcohols with a linear molecular structure and their possible isomers. It was found that the solubility of the PDMS stabilized particles strongly depends on the molecular weight of the coagulant and, quite unexpectedly, on the degree of isomerization. The first tested coagulants, ethanol and acetone, did not mix with PDMS stabilized magnetic fluid. The next member of the homologous series, linear propanol, is the most effective coagulant that causes a sharp precipitation of particles. Meanwhile, with isopropanol, coagulation occurs very smoothly. The butanol isomers differ even more. Normal butanol causes the liquid to coagulate at a higher concentration than propanol, whereas tret-butanol mixes with PDMS stabilized magnetic fluid in any proportion. The last linear alcohol in the homologous series that can serve as a coagulant is hexanol-1. The next members of the homologous series do not mix with the PDMS stabilized magnetic fluid. This is typical only for linear molecules. For example, 2-ethylhexanol (isooctanol) perfectly dissolves PDMS stabilized particles. This property can be used to separate mixtures of isomers and linear molecules.

Model Studies on the Reaction Products Formed at Roasting Temperatures from either Catechin or Tea Powder in the Presence of Glucose.

During tea processing, roasting significantly affects the transformation pathway of catechins. When (-)-epigallocatechin gallate (EGCG) and glucose were roasted at different pH values, the degree of degradation and isomerization of EGCG was the lowest at pH 7 and the highest at pH 8. Thirty-five products were found in the model reaction of EGCG and glucose under high temperatures, of which four EGCG-glucose adducts were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and nuclear magnetic resonance (NMR). In addition, catechins, gallic acid, and theanine in tea with added glucose were significantly reduced during roasting. The contents of four EGCG-glucose adducts were increased significantly at 150 °C after 30 min and dropped gradually after 60 min. Therefore, based on the present study, EGCG could form crosslinks with glucose under high temperatures in a short time, which provides insight for tea processing and synthesis of catechin-sugar adducts.

Wax Hydrocracking over Pt/SiO2–Al2O3 at 2 MPa: Product Characterization and Its Implications for Catalysis

Hydrocracking of Fischer–Tropsch wax can be used to produce kerosene-range products that can be blended in jet fuel. Performing the hydrocracking at pressures near that of Fischer–Tropsch synthesis could be beneficial for some refinery scenarios, as unconverted H₂ from Fischer–Tropsch synthesis can be used for hydrocracking without further compression. At lower pressure, the equilibrium alkene content during hydrocracking is increased and this could affect the product distribution. In particular, the degree of isomerization of the kerosene-range products affects the properties of hydrocracked kerosene to be used for jet fuel. The purpose of this study was to gain a better understanding of the isomer distribution obtained by wax hydrocracking. Hydrocracking of paraffin wax was carried out over a 0.5 wt % Pt/SiO₂–Al₂O₃ catalyst at a pressure of 2 MPa. Detailed chromatographic analysis of narrow distillation cuts of the obtained kerosene-range product was used to obtain isomer distributions for the C₈, C₉, and C₁₁ alkanes formed during hydrocracking. While the observed carbon number and isomer distributions were generally what would be expected from the hydrocracking and hydroisomerization mechanism, there were two observations that could not be explained in this way. (i) The isomer distributions were not equilibrated and were dominated by 2- and 3-methylalkanes. (ii) There were also percentage levels of cyclic compounds. An increased contribution of Pt catalysis under the chosen low-pressure conditions contributed to the observed deviations. The formation of cyclic compounds could be attributed to the increased contribution of Pt catalysis at 2 MPa. Although some speculation was offered about what could have affected the isomer distribution, the prevalence of 2- and 3-methylalkanes in the product remained unexplained.

OXIDATION OF ETHANOL OVER BINARY COPPER-TUNGSTEN OXIDE CATALYSTS

The oxidation reaction of ethanol on binary copper-tungsten oxide catalysts has been studied. It was shown that at temperatures up to 300°C, acetaldehyde is practically the only product of the ethanol oxidation reaction on copper-tungsten oxide catalysts. At higher temperatures, in addition to acetaldehyde, acetone, carbon dioxide and ethylene are also formed. It is found that the isomerization of butene-1 on the Cu-W-O catalysts begins from a temperature of 200°C and with an increase in temperature, the yield of butenes-2 increases and at 350°C reaches its maximum. It was shown that the dependence of the yields of butenes-2 on the atomic ratio of copper to tungsten has the form of a curve with a maximum on the sample Ti-W=3-7. On this sample, the maximum yield of butenes-2 reaches 57%. It is found that with an increase in the degree of isomerization, the yields of acetaldehyde and ethylene increase, and the yield of the product of deep oxidation decreases, which is due to formation of carbon dioxide at sites of basic nature. Keywords: Ethanol oxidation, isomerization, binary catalysts, tungsten oxide, copper oxide, acetaldehyde.

Diffusion-dependent upgrading of hydrocarbons synthesized by Co/zeolite bifunctional Fischer–Tropsch catalysts

The design of efficient zeolite-supported Co catalysts is essential for the further development of the one-step production of liquid fuels via the low-temperature Fischer–Tropsch synthesis (FTS). Herein, Co/zeolite catalysts were prepared from zeolites SSZ-13, ZSM-22, ZSM-11, ZSM-5, Mordenite, and Y. Their textural and acidic properties, Co dispersion, and internal diffusion behaviors were comprehensively analyzed, along with their FTS product mixtures. Counterintuitively, the degree of isomerization and hydrocarbon decomposition did not correlate with the acidic properties of the zeolite support. Instead, catalysts with high characteristic diffusivity delivered product mixtures with high degree of isomerization and decomposition, suggesting that the access of paraffinic hydrocarbons to the internal acid sites of the zeolite determines the upgrading performance of the bifunctional Co/zeolite catalyst in the low-temperature FTS reaction. Hence, the present findings support upcoming efforts on the design of new and effective FTS catalysts.

Study on the Δ3 - Δ2 Isomerization During Preparation of Cefuroxime Double Ester Prodrugs

Δ3->Δ2 Isomerization during preparation of cephalosporin ester prodrugs has been frequently reported. Methods to eliminate the isomerization must be established. In the course of preparing cefuroxime double ester prodrugs, quarternary ammonium salts with different counter ions were used as catalysts for alkylations and their effects on the isomerization were compared. The structures ofΔ3 andΔ2 isomeric esters 1a and 1b were identified with 1H-1H COSY 2D NMR and DEPT 135 NMR.The degree of isomerization during alkylation was monitored with HPLC. It was demonstrated that tetrabutyl ammonium hydrogen sulfate (TBA+HS04-) was a better catalyst than TBA+I-in regard to preventing any isomerization. The desired cefuroxime double ester 1a was obtained as a sole product in this reaction when the molar ratio of TBA+ HSO4- to cefuroxime sodium was beyond 0.35. We have successfully eliminated theΔ3->Δ2 isomerization commonly reported for preparation of cephalosporin esters.