Conversion Of Isomers Research Articles

Kinetics of Non-Radiative Rotational Isomer Butane Transitions

A theoretical model for calculation of equilibrium concentrations of isomeric butane molecule forms, and also the forms of hydrocarbons of the alkene series, is proposed. We considered the changes of internal rotational potential energy in respect of reaction coordinate, of rapid conversion of butane isomers from one form to another at room temperature. This is very important for better understanding of the nature of chemical reactions in butane, because the changes of internal rotational potential energy re∞ect conformational transitions of butane and changes of its chemical and physical properties. The presented model is based on Gribov’s system of kinetic equations for isomer{isomer transitions. The canonical ensemble is used to calculate the room temperature probabilities of the rotoisomer conformational states as functions of dihedrial angle, and the obtained results are in good agreement with available ones. Also, in a sense of calculated lifetime of unstable rotoisomers (< 10 i10 s), our results are comparable with coupled cluster and density functional calculations on alkene derivatives.

Interconversion between (3,1) and (4,0) Isomers of Ru2(L)4X Complexes where L is 2-Anilinopyridinate or 2-(2,4,6-Trifluoroanilino)pyridinate Anion and X = Cl− or C≡CC5H4N−

A reaction between the (4,0) isomer of Ru 2(ap) 4Cl and LiC[triple bond]CC5H4N leads to a (3,1) isomer of Ru 2(ap) 4(C[triple bond]CC5H4N) 2 1 (ap = anilinopyridinate anion), whereas a reaction involving the (3,1) isomer of Ru 2(F 3ap) 4Cl and TBACl.H 2O leads to (4,0) Ru 2(F 3ap) 4Cl 2 (F 3ap = 2-(2,4,6-trifluoroanilino)pyridinate anion). To our knowledge, these are the first documented examples for isomeric conversion involving diruthenium compounds with tetracarboxylate-type structures. The structural, electrochemical, and spectroscopic properties of 1 and 2 were examined. The reversible Ru 2 (5+/6+) process of (3,1) [Ru 2(F 3ap) 4Cl] (+) is located at 0.62 V in CH 2Cl 2, 0.1 M TBAP but shifts to 0.29 V upon formation of (3,1) Ru 2(F 3ap) 4Cl 2 in CH 2Cl 2 containing chloride from added TBACl.H 2O and shifts even further to E 1/2 = 0.10 V after generation of (4,0) Ru 2(F 3ap) 4Cl 2 in solution. The 190 mV potential difference between the Ru 2 (6+/5+) redox couples of (3,1) Ru 2(F 3ap) 4Cl 2 and (4,0) Ru 2(F 3ap) 4Cl 2 in chloride-containing media can be compared to a smaller potential difference of only 60 mV between the Ru 2 (6+/5+) redox couples of (3,1) Ru 2(F 3ap) 4Cl and (4,0) Ru 2(F 3ap) 4Cl in CH 2Cl 2 containing 0.1 M tetrabutylammonium perchlorate (TBAP) as supporting electrolyte. The larger Delta E 1/2 in the case of the bis-chloride complexes in solutions containing 0.1 M TBACl.H 2O can be accounted for in large part by structural differences that manifest themselves in different strengths of axial coordination to the Ru 2 (5+) form of the compounds.

Development and verification of a model to describe an immobilized glucose isomerase packed bed bioreactor

In this paper, the performance of immobilized packed bed glucose isomerase enzyme was mathematically modeled. A modified Michaelis–Menten type relation was used to describe the enzyme kinetics. Mass transfer inside the biocatalyst particle and through the bed column was analyzed simultaneously. Using measured data, physicochemical properties including diffusivity, viscosity and density of sugar solutions were correlated with its concentrations and were used to provide precision in solving the set of model equations. Model equations were solved using the Runge–Kutta and Gauss–Seidel algorithms and finite difference numerical method in MATLAB environment. Model output was used to demonstrate the effect of parameters such as velocity and bulk substrate concentration on the concentration profile within the biocatalyst particle, effectiveness factor and bulk substrate concentration along the bed. Model predictions were further validated against experimental data collected from a lab scale isomerization bioreactor. Measurements of the overall bioreactor conversion at various substrate concentrations were shown to lie within 5% of the values as put forth by the model. Using experimental data, a criteria was proposed to maximize the isomerization conversion from the immobilized bioreactor.

A new device for combined Coulomb excitation and isomeric conversion electron spectroscopy with fast fragmentation beams

A new setup has been designed to perform Coulomb excitation experiments with fragmentation beams at intermediate energy and to measure at the same time conversion electrons from isomeric states populated in the fragmentation reaction. The newly designed setup is described and experimental results from a first experiment are shown. Radioactive even–even nuclei in the mass region A ≃ 70 close to the N = Z line were Coulomb excited after fragmentation of an intense primary 78Kr beam and selection in flight with the LISE3 spectrometer at GANIL. The γ rays emitted after Coulomb excitation were detected in an array of four large segmented HPGe clover detectors in a very close geometry. The scattered ions were identified in a stack of highly segmented annular silicon detectors combined with a time-of-flight measurement using beam tracking detectors. Conversion electrons from isomeric 0 2 + states decaying via electric monopole transitions were detected in an array of segmented cooled silicon detectors surrounding a telescope of plastic scintillators. Reduced transitions probabilities B ( E 2 ; 0 1 + → 2 1 + ) were deduced for several stable and radioactive nuclei.

Transformations of β-alkylcyclohexane hydrocarbons on modified pentasils with participation of methanol and oxidants

The reactions of dehydroalkylation of methylcyclohexane, ethylcyclohexane, and methylcyclohexene isomers and toluene alkylation with methanol on platinum-and gallium-modified pentasil in the presence of an O2-CO2 mixture was studied. Optimum conditions were found for the one-step dehydroalkylation of methylcyclohexane on the ring. Under these conditions, the degree of conversion of methylcyclohexane and methylcyclohexene isomers into xylene isomers is above that of toluene alkylation to afford xylene. According to the discussed reaction mechanism, the dehydroalkylation of cyclohexane hydrocarbons on Pt, Ga-pentasil involves both the steps of formation of unsaturated intermediates and toluene in status nascendi.

Controlled Conversion of Isomers in a Hybrid Biphotochromic System

[reaction: see text] The photochromic performance of a hybrid system connecting naphthopyran and dithienylethene was investigated, and the photochemistry of eight different isomers was explored by choosing an appropriate wavelength of light.

Zeolite beta catalysts for n-C7 hydroisomerization

Zeolite β with Si/2Al ratios of 60, 100, and 200 were synthesized using tetraethlammonium hydroxide (TEAOH) as the structure-directing agent (SDA) in the absence of alkali metal cations. Pt, Pd and Pt-Pd catalysts supported on the zeolite β samples were studied in n-heptane (n-C7) hydroisomerization. The Pt/β catalysts showed a higher catalytic activity than the Pd/β catalysts. For the Pt/β with a Si/2Al ratio of 100, its n-C7 conversion and selectivity of C7 isomers were observed to be 87.06% and 75.48% respectively at 250∘C. The activity of n-C7 conversion was stable for at least 82 h. However, the selectivity of C7 isomers was gradually decreased with the reaction time. Experimental data also showed that the addition of Pd to catalyst Pt/β enhanced the n-C7 conversion, but lowered the selectivity of C7 isomers. Pd catalyst was also observed to minimize the formation of aromatics in comparison with Pt catalyst.

Tautomerism of peroxyacetic acid derivatives: a quantum chemical study

The electronic and molecular structures and the relative stabilities of organic peracids X=C(R)-COOH and their cyclic tautomers, dioxiranes Open image in new window , with R = Me, CF3; X = O, NH, were studied using the ab initio Hartree-Fock method and the density functional theory (B3LYP version) as well as at the MP2-MP4 Moller-Plesset levels of perturbation theory. Geometry optimization was performed by the UHF and B3LYP methods with the 6-31G** basis set and at the MP2/cc-pvtz level of theory. The acyclic form of the peracid is more stable than the cyclic dioxirane form irrespective of the nature of the substituent. The energy difference between these tautomers increases as the CF3 and NH groups are replaced by Me and O, respectively. Parameters of the activation barrier to tautomeric conversion increase in parallel with enhancement of the electron-accepting properties of both substituents. The transition state of tautomeric interconversion, which is topologically similar to the acyclic structure of the carbonyl oxide derivative R(HX)C=O+-O−, was found and characterized taking peroxyacetic acid as an example. The characteristic features of the transition state are an intramolecular “multicenter” H-bond and the charge distribution that is inconsistent with the canonical structure mentioned above. An appropriate reaction coordinate for the transformation of the quasi-tetrahedral dioxirane structure into a planar peroxyacetic acid structure is provided by the dihedral angle. Deprotonated anionic systems are characterized by much smaller differences between the relative stabilities of the open and closed forms of isomers and by much lower activation barriers to isomeric conversions.

Pharmacokinetics of the diastereomers of arteether, a potent antimalarial drug, in rats

The pharmacokinetics of alpha- and beta- diastereomers of arteether, a potent erythrocytic schizontocidal agent, and their active metabolite dihydroartemisinin were studied in male Sprague-Dawley rats after oral, intramuscular and intravenous administrations. Oral and intramuscular studies were carried out at three dose levels at 9, 17.5 and 30 mg kg(-1). The ratio of alpha- and beta-isomers was maintained at 30:70% w/w in the formulations used for the study. The average oral bioavailabilities of alpha-and beta-isomers, relative to intramuscular administration, were 9.6% and 3.8%, respectively, and the average in vivo alpha- to beta- ratio was 2.5. Following intravenous and intramuscular administrations the in vivo alpha- to beta- ratios were 0.7 and 0.9, respectively. The beta-isomer of arteether was characterized by a longer elimination half-life and a relatively larger volume of distribution than the alpha-isomer, suggesting that beta-arteether may be responsible for the prolonged in vivo schizontocidal activity. The alpha-isomer was absorbed rapidly after oral and intramuscular administrations and showed higher peak plasma concentrations but possessed a relatively shorter half-life. There was an apparent lack of linearity observed in terms of dose and AUCs for both alpha- and beta-arteether after oral and intramuscular administrations, suggesting nonlinear dose dependent pharmacokinetics at the dose levels studied. The rate and extent of conversion of arteether isomers to dihydroartemisinin was highest with oral and intravenous administration and least with intramuscular indicating that the intramuscular route of administration of the isomeric mixture may be more beneficial for malarial chemotherapy.

Alumina-promoted mesoporous sulfated zirconia: A catalyst for n-butane isomerization

Mesoporous sulfated zirconia (MP-ZrO 2) were synthesized hydrothermally using Zr(O- nPr) 4 as zirconium precursor, ammonium sulfate as sulfur source and CTABr as template. Then the as-synthesized mesoporous materials were directly impregnated with aluminum sulfate to give the acidic Al-promoted mesoporous sulfated zirconia. (AS/MP-ZrO 2). The AS/MP-ZrO 2 catalyst was characterized by nitrogen physisorption (BET) for texture properties, by X-ray diffraction (XRD) for confirming the phase and by TEM for particle sizes. The catalytic conversion of n-butane isomerization was measured in a flow reactor. With the addition of a proper amount of aluminum as a promoter, the catalytic behavior for n-butane isomerization at low temperature in flow system was strongly promoted. The increase of activity was determined primarily by the amount of alumina addition and by the temperature of calcination. The highest catalytic performance is for the catalyst prepared at an optimum 3 mol.% Al loading and calcination at 650 °C. The nature of the acidic sites was determined by X-ray photoelectron spectroscopy (XPS) measurements of N 1 s of the adsorbed pyridine. Three kinds of acid sites were identified on the catalyst: a Lewis site, a weak Brønsted site and a strong Brønsted site. The catalytic activities are correlated with the amount of weak Brønsted acid sites. The remarkable activity and stability of the Al-promoted catalysts are due to a balanced distribution of acid sites strength with an enhanced amount of weak Brønsted acid sites.

Al- and Ga-promoted WO 3/ZrO 2 strong solid acid catalysts and their catalytic activities in n-butane isomerization

A series of Al- and Ga-promoted tungstated zirconia strong solid acid catalysts were prepared. The effect of Al 2O 3 and Ga 2O 3 on the structural, acidic and redox features of WO 3/ZrO 2 (WZ) has been characterized by means of X-ray powder diffraction (XRD), N 2 adsorption (BET), UV–visible diffuse reflectance spectra (UV–vis), infrared spectra (IR), NH 3 temperature-programmed desorption (NH 3-TPD) and H 2 temperature-programmed reduction (H 2-TPR). With respect to tungstated zirconia, the promoted catalysts stabilized the zirconia tetragonal phase, prevented crystalline WO 3 growth. Al or Ga addition to WZ had less effect on the strength of the acid sites, but effected reduction temperature of WZ. The isomerization of n-butane was investigated at 300 °C over tungstated zirconia and promoted catalysts. The promoted catalysts improved the isomerization conversion and stability in the presence of hydrogen. The best Al and Ga loading in these catalysts is around 0.5 and 1.0%, respectively, and the optimal calcination temperature is ∼850 °C. The experiment results showed that Ga was a more efficient promoter than Al. Pt addition to promoted catalysts showed great improvement on the performance of selectivity and stability.

Prostaglandin J2 family and the cardiovascular system.

Prostaglandins (PGs) of the J2 family including PGJ2, delta12-PGJ2, and 15-deoxy-delta12,14-PGJ2 (15d-PGJ2) are naturally occurring metabolites of PGD2. Among them, 15d-PGJ2 is a powerful ligand for the peroxisome proliferator-activated receptor-gamma (PPARgamma). 15d-PGJ2 and synthetic PPARgamma ligands have been reported to exert several effects on vascular cells, such as anti-proliferative, differentiation-inducing, anti-apoptotic, and anti-inflammatory effects, most of which seem to be atheroprotective, although PPARgamma-independent mechanisms may be involved. Vascular endothelial cells, intimal smooth muscle cells, and cardiomyocytes express lipocalin-type PGD synthase (L-PGDS) in vivo, which catalyzes the isomeric conversion of PGH2 to PGD2. L-PGDS expression in endothelial cells is stimulated by laminar fluid shear stress. PGD2 and 15d-PGJ2 are detected in the culture medium of endothelial cells exposed to shear stress. Serum and urinary levels of L-PGDS increase in diseases with vascular injuries, such as hypertension and diabetes. Based on these findings, we hypothesize that PGs of the J2 series are physiological substances produced in the vascular wall to protect vascular cells from injurious stimuli and to repress inflammatory reactions. If this hypothesis is correct, PGJ2 family members or other similar substances may provide novel preventive and therapeutic strategies for the treatment of vascular diseases.

Synthesis, characterization, and biological evaluation of neutral nitrido technetium(V) mixed ligand complexes containing dithiolates and aminodiphosphines. A novel system for linking technetium to biomolecules.

A new biomolecule labeling method that utilizes the [(99m)Tc(N)(PNP)](2+) metal fragment is presented. Thus, a series of nitrido mixed-ligand M(V) complexes (M = (99m)Tc, (99g)Tc, Re), [M(N)(Ln)(PNP)], where Ln is the dianionic form of a dithiolate or substituted-dithiolate ligand and PNP is an aminodiphosphine, is described. (99m)Tc complexes can be prepared using either a two-step or a three-step procedure starting from generator-eluted pertechnetate through a prereduced mixture of [(99m)Tc(N)]-containing species, followed by sequential or contemporary addition of the relevant dithiolate and aminodiphosphine. The reactions of 2,3-dimercaptopropionic acid (H(2)L1) with [Tc(N)(PNP)](2+) were investigated in detail. It was found that this bidentate ligand coordinated the metal fragment through the [S(-),S(-)] donor atom pair, to yield neutral mixed-ligand complexes [(99m)Tc(N)(L1)(PNP)] in high specific activity. The additional carboxylic functional group was not involved in metal coordination, thus remaining available for conjugation to target-specific molecules. Dithiolates incorporating pendant functional group(s) gave rise to a 1:1 diastereoisomeric mixture of syn-[M(N)(Ln)(PNP)] and anti-[M(N)(Ln)(PNP)] derivatives, depending on the relative orientation of the dithiolate substituent(s) with respect to the terminal nitrido group, and no isomeric conversion was detected. (99m)Tc species had been proven to be identical with the (99g)Tc complexes prepared at the macroscopic level by comparison of the corresponding radiometric and UV/vis HPLC profiles. Challenge experiments with cysteine or glutathione indicated that these physiological agents had no effect on the stability of this class of mixed-ligand (99m)Tc-complexes. Biodistribution studies in rats of selected (99m)Tc-complexes showed a rapid clearance from the blood and tissues after 60 min pi.

Thermodynamic Rearrangement Synthesis and NMR Structures of C1, C3 and T Isomers of C60H36.

The structures of three C60H36 isomers, produced by high-temperature transfer hydrogenation of C(60) in a 9,10-dihydroanthracene melt, was accomplished by 2D (1)H-detected NMR experiments, recorded at 800 MHz. The unsymmetrical C(1) isomer is found to be the most abundant one (60-70%), followed by the C(3) isomer (25-30%) and the least abundant T isomer (2-5%). All three isomers are closely related in structure and have three vicinal hydrogens located on each of the 12 pentagons. Facile hydrogen migration on the fullerene surface during annealing at elevated temperatures is believed to be responsible for the preferential formation of these thermodynamically most stable C60H36 isomers. This hypothesis was further supported by thermal conversion of C60H36 isomers to a single C(3v) isomer of C60H18.

Production of electronically excited CH via the vacuum ultraviolet photodissociation of ethylene and the possible role of the ethylidene isomer

The visible fluorescence of CH fragments (A 2Δ→X 2Π and B 2Σ−→X 2Π transitions) formed in the vacuum ultraviolet photodissociation of ethylene in the 11.7–21.4 eV energy region, was recorded. Two formation thresholds for each excited fragment, CH* (A) or CH* (B), were identified and associated with two dissociation channels namely CH*+CH3 and CH*+CH+H2. Unlike previous studies of the dissociation dynamics on the ground-state potential energy surface, neither of these channels exhibit an energy barrier within the experimental uncertainty, even in the latter case of molecular H2 elimination. It is proposed that both channels pass via an ethylidene intermediate (H3CCH:), an isomer never previously experimentally detected and whose existence has been debated in theoretical publications. The observed behavior, at the excitation energies used in the present work, also suggests that fast isomerization and internal conversion to excited states of ethylene precede fragmentation. Above 18.5 eV, that is around the ionization limit C2H4+ (D 2B1u), dissociative ionization starts to compete with neutral dissociation into excited CH fragments giving rise to a substantial decrease in the neutral fragment signal.

Thermodynamic rearrangement synthesis and NMR structures of C1, C3, and T isomers of C60H36.

The structures of three C60H36 isomers, produced by high-temperature transfer hydrogenation of C(60) in a 9,10-dihydroanthracene melt, was accomplished by 2D (1)H-detected NMR experiments, recorded at 800 MHz. The unsymmetrical C(1) isomer is found to be the most abundant one (60-70%), followed by the C(3) isomer (25-30%) and the least abundant T isomer (2-5%). All three isomers are closely related in structure and have three vicinal hydrogens located on each of the 12 pentagons. Facile hydrogen migration on the fullerene surface during annealing at elevated temperatures is believed to be responsible for the preferential formation of these thermodynamically most stable C60H36 isomers. This hypothesis was further supported by thermal conversion of C60H36 isomers to a single C(3v) isomer of C60H18.

Electron Transfer-Induced cis−trans Isomerization of [Mn(CN)(CO)2{P(OPh)3}(Ph2PCH2PPh2)]: Solution and Solid State Voltammetric Studies

Fast scan rate cyclic voltammetry has been used to elucidate the heterogeneous and homogeneous aspects of the redox chemistry of cis- and trans-[Mn(CN)(CO)2{P(OPh)3}(Ph2PCH2PPh2)]. The cis species, on oxidation, isomerizes to the trans conformation, and the various processes can be understood as components of a square reaction scheme. In solution phase, the homogeneous rate constant for isomeric conversion is found to be independent of solvent and concentration, with a value of 38 s-1 obtained by comparison with digitally simulated responses. The heterogeneous rate constants for the cis0/cis+ and trans0/trans+ couples in acetonitrile have values of 0.06 and 0.065 cm s-1 respectively. The cis or trans complex was readily immobilized on an electrode surface, either by mechanical attachment or by precipitation from solution. However, electrolysis in the solid state was strongly dependent on the identity of the supporting electrolyte anion. This dependence is similar to the Hofmeister series of anions with la...

Isopropylation of Xylenes Catalyzed by Ultrastable Zeolite Y (USY) and Some Other Solid Acid Catalysts

The isopropylation of all three xylene isomers was carried out over ultrastable zeolite Y (USY) catalyst to give corresponding dimethyl (1-methylethyl) benzenes, or in other words dimethyl cumenes (DMCs), using isopropanol as alkylating agent. The effect of reaction temperature, space velocity, substrate-to-alkylating-agent molar ratio, and time-on-stream on conversion of xylene isomers and selectivity to dimethyl cumene was studied. Isopropylation of xylenes over USY gives quite high (80 to 95%) DMC selectivity among the dimethyl cumenes, along with a 70–90% yield of DMCs in total products with respect to limiting reagents, i.e., isopropylating agents at relatively low reaction temperatures (423±10 K) and at quite high xylene conversions (85–97% of theoretical maximum value). The solid acid catalysts zeolites H–Y, H-beta, H–mordenite, as well as silica–alumina and sulfated zirconia, were included for comparative studies in the isopropylation of m-xylene.

Effect of dietary conjugated linoleic acid (CLA) on metabolism of isotope-labeled oleic, linoleic, and CLA isomers in women.

The purpose of this study was to investigate the effect of dietary CLA on accretion of 9c-18:1, 9c,12c-18:2, 10t,12c-18:2, and 9c,11t-18:2 and conversion of these FA to their desaturated, elongated, and chain-shortened metabolites. The subjects were six healthy adult women who had consumed normal diets supplemented with 6 g/d of sunflower oil or 3.9 g/d of CLA for 63 d. A mixture of 10t,2c-18:2-d4, 9c,11t-18:2-d6, 9c-18:1-d8, and 9c,12c-18:2-d2, as their ethyl esters, was fed to each subject, and nine blood samples were drawn over a 48-h period. The results show that dietary CLA supplementation had no effect on the metabolism of the deuterium-labeled FA. These metabolic results were consistent with the general lack of a CLA diet effect on a variety of physiological responses previously reported for these women. The 2H-CLA isomers were metabolically different. The relative percent differences between the accumulation of 9c,11t-18:2-d6 and 10t,12c-18:2-d4 in plasma lipid classes ranged from 9 to 73%. The largest differences were a fourfold higher incorporation of 10t,12c-18:2-d4 than 9c,11t-18:2-d6 in 1-acyl PC and a two- to threefold higher incorporation of 9c,11t-18:2-d6 than 10t,12c-18:2-d4 in cholesterol esters. Compared to 9c-18:1-d8 and 9c,12c-18:2-d2, the 10t,12c-18:2-d4 and 9c,11t-18:2-d6 isomers were 20-25% less well absorbed. Relative to 9c-18:1, incorporation of the CLA isomers into 2-acyl PC and cholesterol ester was 39-84% lower and incorporation of 10t,12c-18:2 was 50% higher in 1-acyl PC. This pattern of selective incorporation and discrimination is similar to the pattern generally observed for trans and cis 18:1 positional isomers. Elongated and desaturated CLA metabolites were detected. The concentration of 6c,10t,12c-18:3-d4 in plasma TG was equal to 6.8% of the 10t,12c-18:2-d4 present, and TG was the only lipid fraction that contained a CLA metabolite present at concentrations sufficient for reliable quantification. In conclusion, no effect of dietary CLA was observed, absorption of CLA was less than that of 9c-18:1, CLA positional isomers were metabolically different, and conversion of CLA isomers to desaturated and elongated metabolites was low.

Mycosporines: Detection Methodologies and Assessment

AbstractMycosporine‐like amino acids (MAAs) are found in a variety of prokaryotic and eucaryotic algae, as well as higher plants, fungi, and animals. These compounds function as a photoprotective sunscreen to prevent ultra‐violet light damage. MAAs may thus be one of the competitive advantages that facilitated development of ozone (by oxytrophs), and thereby may be a competitive advantage for the proliferation of cyanobacteria and other harmful algal species. Numerous difficulties exist with assessment of MAAs, including identification of the compounds, conversion of isomers during HPLC preparation as a result of pH shifts, as well as the ecological implications of the presence, concentration, and forms of these compounds (see J Phycology 1999; 35, for relevant papers). This symposium will provide opportunities for intercalibration of laboratories involved in MAA analyses, suggestions regarding standardization of extraction protocols, as well as results from field‐ and laboratory‐based studies.