Additional Isomers Research Articles

Synthesis, NMR and ultraviolet spectroscopy of [10] (N6,9)-6-aminopurinophane; calculation of the chemical shifts in the [n](N6,9)-6-aminopurinophane series

[10](N6,9)-6-Aminopurinophane was prepared via a Mitsunobu reaction involving 6-chloropurine and 10-azido-1-decanol. Reduction of the azido moiety to an amine allowed for subsequent cyclization to the cyclophane. N6-Nonyladenine, 9-nonyladenine, and N6,9-dinonyladenine were also prepared using the established chemistry. Heating the [10](N6,9)-6-aminopurinophane to 90 °C allowed for a complete assignment of the proton and carbon spectra, while cooling the sample to −77 °C revealed additional isomers likely due to the anti–syn isomerization about the N6—C6 bond. A variable temperature proton NMR study revealed a ΔGc≠ of 59.4 ± 5.5 kJ mol−1 associated with the interchange between the two major conformers. The ultraviolet spectra of the [n](N6,9)-6-aminopurinophane series show a bathochromic shift and a hypochromic effect in the transitions as the methylene chain length decreases (i.e., n = 10 to 9 to 8). The aminopurinophanes are used to assess the relative merits of a semi-empirical model that allows for the calculation of the chemical shifts of the methylene bridge protons. Keywords: synthesis of heterocyclophanes, variable temperature NMR, cyclophane conformational analysis, ultraviolet spectroscopy, calculation of chemical shift.

Quantification of glyceollins in non-elicited seedlings of Glycine max by gas chromatography-mass spectrometry

A sensitive gas chromatography-mass spectrometry method is described for detection and quantification of small amounts of phytoalexins, especially glyceollins. This method allowed identification of canescacarpin (glyceollin V) besides appreciable amounts of glyceollin isomers I–III and glyceofuran in unchallenged parts of soybean seedlings. Based on this quantification method the glyceollin content of soybean roots, either untreated, wounded or incubated with a glucan elicitor from Phytophthora sojae, was compared. The proportions of glyceollin isomers in the mixture of compounds were determined in different soybean tissues. Single-ion monitoring revealed the presence of four additional glyceollin isomers with benzofuranoid structure.

DDT, A Potential Source of Environmental Tris(4-chlorophenyl)methane and Tris(4-chlorophenyl)methanol

Tris(4-chlorophenyl)methane (4,4',4-TCPM) and its presumed metabolite tris(4-chlorophenyl)methanol (4,4',4-TCPM-OH) are among the most recently identified organochlorine contaminants in environmental biological samples. The compounds are present on a global scale and found in samples from practically all continents. Initially discovered in various aquatic species, they have now also been detected in human milk. However, despite of their widespread occurrence, the source and the origin of these compounds are so far unknown. In this study, we report the first evidence of a link between environmental TCPM and DDT. 4,4',4-TCPM and two additional isomers, 2,2',4- and 2,4',4-TCPM, were formed in small amounts from the reaction of chloral, chlorobenzene, and fumic sulfuric acid under conditions such as those used in the technical synthesis of DDT. The same TCPM isomers were also detected in two samples of technical DDT, one more than 40 years old. In environmental biological samples, particularly at highertrophic levels, generally just a single isomer of TCPM and TCPM-OH is present ; the latter was previously identified as the 4,4',4-isomer, and the same isomerism is now confirmed for the former. Preferred degradation of the isomers with 2-chloro rings in metabolic actions presumably is the reason for the absence of other isomers in biological samples. All 10 possible TCPM isomers were formed in a novel reaction of DDT with chlorobenzene in the presence of AlCl 3 . They were completely resolved by high-resolution gas chromatography and assigned from retention and mass spectrometric data.

Absorption spectroscopy and photodissociation dynamics of small helium cluster ions

The optical absorption of size-selected helium cluster ions was studied via photofragmentation spectroscopy. Absorption cross sections were measured for He+n (n=3, 4, 10, 21, and 30). A broad absorption peak was found, which for He+3 is centered at ≊5.3 eV, and which with increasing cluster size shifts slightly to the red. In addition, the kinetic energy release to the ionized and neutral photofragments was measured by a time-of-flight technique for cluster sizes between n=3 and 10. From the energy balance the total binding energy of the He+3 trimer ion was determined to be 2.6±0.15 eV. The results further indicate that a charged linear trimer acts as a core molecule for the sizes n=4–7. For n≳7, an additional isomer with a tetramer core is identified. The results are compared with recent ab initio calculations.

Theoretical and photophysical study of photoisomerism of cyanine dyes: bisphenylaminopentamethine cyanine (BPPC)

The trans-cis photoisomerism of BPPC was investigated as part of a comprehensive, both theoretical and experimental, study on the photophysical and photochemical properties of cyanines having pentamethine cyanine as a common chromophore. In this work the determination of the trans → cis photoisomerization and thermal back isomerizatkm kinetics in alcohols was combined with CS INDO CI calculations of S 0 and S 1 potential energy curves for the paths leading to mono-cis isomers, where the dielectric solvent effects were taken into account by the simple virtual charge model. In agreement with the indications of a previous steady-state spectroscopy study, it was concluded that irradiation of BPPC into the visible absorption region gives rise to formation of the C(3)–C(4) cis planar isomer, already observed with the parent chromophore (BMPC), and an additional isomer, N(1)-C(2) cis, peculiar to BPPC. The role of the solute-solvent interactions is discussed with reference to the purely intramolecular model previously proposed for the cyanine photoisomerization.

Substituent control of intramolecular hydrogen bonding in formyl-protonated o-anisaldehydes: a stable ion and semiempirical MO investigation

o-Anisaldehyde and its 5-Br, 5-F, 5-CF 3 , 5-CN, 5-NO 2 , and 5-COMe derivatives are protonated at the formyl group in 1:1 SbF 5 -FSO 3 H/SO 2 (or SO 2 ClF) to give persistent carboxonium ions as mixtures of Z and G geometrical isomers. The cyano, nitro, and acetyl substituents are also protonated, leading to dications and additional geometrical isomers in the nitro and acetyl cases. The carboxonium ions are predominantly in the Z,syn configuration, but with increased amounts of the E,anti configuration with increased electron withdrawal by the substituents

Phosphorus derivatives of anthracene and their dimers

AbstractThe syntheses of the (9‐anthracenyl)phosphanes 2 to 7 and of the metal carbonyl complexes 8 and 9 are described. Both 1 and 4 undergo [4 + 4] cycloaddition when irradiated, forming the dimers 10 and 11. Only one of the six possible rotamers for 10 is formed. For 11 one additional rotational isomer is observed. The relationship between the [4 + 4] dimerization and steric effects of the PR2 group is discussed. The compounds 6, 8 and 11 were characterized by X‐ray diffraction. The structure of 6 was rendered imprecise by the presence of disordered toluene, but the influence of the bulky anthracenyl groups was clear, with wide CPC angles of 110.4°. The molecule displays imposed threefold symmetry. The two independent molecules of complex 8, which crystallizes as a dichloromethane hemisolvate, are closely similar to each other; the WP bond lengths are 254.3 and 253.4 pm. The WC bonds trans to phosphorus are 4 pm shorter than those cis. The phosphane dimer 11 crystallizes with imposed centrosymmetry. The H atom positions, which could be tentatively identified from difference syntheses, indicate a different rotamer than was formed for the analogous fluorophosphane dimer 10.

Conformation of cyclic analogs of substance P: NMR and molecular dynamics in dimethyl sulfoxide

The conformational analysis of two cyclic analogues of substance P has been carried out using NMR spectroscopy and restrained molecular dynamics calculations. The cyclic analogues, cyclo[-(CH 2 ) m -NH-CO-(CH 2 ) n -CO-Arg-Phe-Phe-N-]-CH 2 -CO-Leu-Met-NH 2 (with m, n=3, 2 and 3, 3), show a large percentage of cis configurational isomers (18 and 22%) about the substitutcd amide. The additional isomers lead to severe spectral overlap of the proton resonances

Super-deformation and shape isomerism: Mapping the isthmus

An isthmus of shape isomerism is mapped in the region of recently discovered super-deformation by computing well depths and excitation energies for 148 nuclei in fully microscopic, HF-BCS calculations. In all instances in which super deformed isomers have been experimentally observed, our calculations have predicted well deformed second minima with excitation energies and rigid body moments of inertia consistent with the data. Predictions for additional isomers are inferred from the present work.

Structure of phosphorus clusters using simulated annealing. II. P9, P1, P11, anions P2−4, P2−10, P3−11, and cations P+n to n=11

Previous calculations on the structures of isomers of phosphorus clusters P2 to P8 [density functional calculations with simulated annealing (SA), J. Chem. Phys. 92, 6710 (1990)] have been extended to P9, P10, and P11. The tendency of phosphorus to form tubular structures is already evident in clusters of this size. We have also performed calculations on additional isomers of the hexamer P6, positive ions up to P+11, and the P2−4, P2−10, and P3−11 anions. Ionization energies agree well with available measurements [P1 to P4] and show trends that can be correlated with the structures and the measured relative abundances of the ions. The calculated structure of P3−11 agrees very well with x-ray diffraction data, and we observe isomerization in P9 resulting from charge transfer. A simplified SA scheme using a linear combination of atomic orbitals (LCAO) has been used to aid the analysis of the results.

High-performance liquid chromatography determination of phenolic acids in potato tubers (Solanum tuberosum) during wound healing

The content of phenolic acids formed during wound healing of γ-irradiated and nonirradiated potato tubers was determined. Chlorogenic acid, caffeic acid, p-coumaric acid, and ferulic acid were detected in small quantities in resting whole tubers of irradiated and nonirradiated potatoes. During wound healing their content increased many fold, and in addition, the neo and crypto isomers of chlorogenic acid accumulated in the wound healing tissue. The increased formation of phenolics was accompanied by a parallel rise in phenylalanine ammonia-lyase activity

Studies in fluorinated 1,3-diketones and related compounds. Part XVI: Mixed ligand complexes of ruthenium with fluorinated 1,3-diketones

Spectral data of some new ruthenium(II) complexes with 1,5-cyclooctadiene (COD) and fluorinated 1,3-diketones reveal marked effects on the geometry of these complexes on incorporation of fluorine in the 1,3-diketone skeleton. As the degree of fluorination in these diketonates increases, the presence of an additional isomer is observed.

Agonist-induced Regulation of Inositol Tetrakisphosphate Isomers and Inositol Pentakisphosphate in Adrenal Glomerulosa Cells

In adrenal glomerulosa cells, angiotensin II (AII) rapidly stimulates the formation of inositol 1,4,5-trisphosphate (Ins-1,4,5-P3) and causes marked long-term changes in the levels of highly phosphorylated inositols. Glomerulosa cells prelabeled with [3H]inositol for 48 h and exposed to AII for 10 min showed prominent increases in inositol 1,3,4,5-tetrakisphosphate (Ins-1,3,4,5-P4) and smaller increases in two additional tetrakisphosphates, Ins-1,3,4,6-P4 and another (Ins-3,4,5,6-P4) eluting in the position of Ins-3,4,5,6-P4 and its stereoisomer, Ins-1,4,5,6-P4, on anion exchange liquid chromatography. A concomitant decrease in InsP5 indicates that an increase in Ins-1,4,5,6-P4, the breakdown product of InsP5, is probably responsible for the initial rise in Ins-3,4,5,6-P4 during 10 min stimulation by AII. During prolonged stimulation by AII, Ins-1,3,4,5-P4 began to decline from its high, stimulated level after the first hour but the level of Ins-1,3,4,6-P4 remained elevated for several hours. There were also progressive increases in the levels of Ins-3,4,5,6-P4 and InsP5 during stimulation for up to 16 h with AII. Treatment of adrenal cells for 16 h with the cyclic AMP-mediated secretagogue, adrenocorticotropic hormone (ACTH), slightly increased basal levels of Ins-1,3,4,6-P4, Ins-3,4,5,6-P4, and InsP5, and enhanced the subsequent AII-stimulated increases in the two additional tetrakisphosphate isomers but not of inositol trisphosphates or Ins-1,3,4,5-P4. This change in the pattern of the higher inositol phosphate response to AII was manifested within 2 h after exposure to ACTH, and was mimicked by treatment with 8-bromo cyclic AMP or forskolin. Treatment with 50 microM cycloheximide abolished the ACTH-induced increases in inositol polyphosphate responses during AII stimulation, but had no effect on the responses of untreated cells to AII. The conversion of [3H]Ins-1,3,4-P3 to [3H]Ins-1,3,4,6-P4, a reaction linking the receptor-mediated InsP3 response to higher inositol phosphates, was enhanced in permeabilized cells that were pretreated for 16 h with either ACTH or AII. These results demonstrate that the reactions by which Ins-1,3,4,6-P4 and Ins-3,4,5,6-P4 are formed and converted to InsP5 are influenced by agonist-stimulated regulatory processes that include both calcium-dependent and cyclic AMP-dependent mechanisms of target cell activation. They also reveal changes consistent with agonist-induced conversion of InsP5 to its dephosphorylated metabolite, Ins-1,4,5,6-P4, during short-term stimulation by AII.

The Multimodal Cyclodextrin Bonded Stationary Phases for High Performance Liquid Chromatography

Abstract The use of α-, β-, and γ-cyclodextrin bonded stationary phases as multimodal support in HPLC is discussed. These supports are being used as reversedphase and normal phase for the separation of widely different groups of compounds. Also, they are used as for the separation of optical, geometrical, positional and structural isomers in addition to ions and organo-metallic compounds. A brief discussion of separation mechanisms and application and their use with other stationary phases to improve selectivity are also presented.

Purification of D-myo-inositol 1,4,5-trisphosphate 3-kinase from rat brain.

The ATP-dependent, calmodulin-sensitive 3-kinase responsible for the conversion of D-myo-inositol 1,4,5-trisphosphate to D-myo-inositol 1,3,4,5-tetrakisphosphate has been purified 2,700-fold from rat brain to a specific activity of 2.3 mumol/min/mg protein. A method of purification is described involving chromatography on phosphocellulose, Orange A dye ligand, calmodulin agarose, and hydroxylapatite columns. Neither the highly purified enzyme nor enzyme eluting from the phosphocellulose column were activated by Ca2+. However, enzyme in the 100,000 x g supernatant from rat brain was activated by Ca2+ over the range from 10(-7) to 10(-6) M and Ca2+ sensitivity of the purified enzyme was restored by the addition of calmodulin. The enzyme has a catalytic subunit Mr of 53,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Size exclusion chromatography of the purified enzyme on a Superose 12 column gave a Mr value of 70,000, indicating that the purified enzyme was present as a monomer. In contrast, the 100,000 x g supernatant and the purified enzyme after addition of calmodulin and 10(-6) M Ca2+ chromatographed on size exclusion chromatography with a Mr of 150,000-160,000. These results imply that the native enzyme is a dimeric structure of two catalytic subunits plus calmodulin. The purified enzyme showed a Km of 0.21 +/- 0.08 microM for D-myo-inositol 1,4,5-trisphosphate and had a pH optimum of 8.5. Addition of calmodulin increased both the Km and the Vmax of the purified enzyme about 2-fold. The high affinity of the 3-kinase for D-myo-inositol 1,4,5-trisphosphate together with its activation by Ca2+/calmodulin suggests that this enzyme may exert an important regulatory role in inositol phosphate signaling by promoting the formation of additional inositol polyphosphate isomers.

Photochromism of spirooxazines II. CARS‐investigation of solvent effects on the isomeric distribution

AbstractThe isomeric distribution of metastable “photomerocyanines” produced by UV‐photolysis of spiroindolinonaphthoxazine derivatives is examined by resonance‐enhanced CARS spectroscopy. — In unpolar and polar aprotic solvents CARS spectra prove the existence of two pairwise similar isomeric species. They differ, however, in Franck‐Condon factors for excitation S0 → S1. In the protic solvent methanol an additional isomer is found for certain derivatives.

Cyclic fatty esters: hydroperoxides from autoxidation of methyl 9-(6-propyl-3-cyclohexenyl)-(Z)8-nonenoate.

Autoxidation of the cyclic fatty acid ester, methyl 9-(6-propyl-3-cyclohexenyl)-(Z)8-nonenoate (I) was investigated to characterize the hydroperoxide isomers formed and to provide basic information on their chemistry, detection and effect on the quality of polyunsaturated cooking oils. Oxidation at 60 C with 1% hydroperoxide initiator produced a monohydroperoxide fraction containing five positional isomers (7-, 11-, 12-, 13- and 14-OOH), resolved by high performance liquid chromatography, as their allylic hydroxy esters. Their structures were established by 1H- and 13C-NMR spectroscopy and by capillary gas chromatography-mass spectrometry (GC-MS) as trimethylsilyl ether derivatives. Two additional isomers (8- and 9-OOH) were detected by GC-MS in only trace (less than 1%) quantities. Capillary GC resolved some geometric and stereoisomers, as well as positional isomers. Compared to photosensitized oxidation, two additional positional isomers (11- and 14-OOH) were produced by autoxidation. More stereoisomers were formed, and oxidation of the ring double bond was favored 8:1 over that of the side chain. This selectivity may be attributed to greater steric hindrance for oxygen attack at the side-chain double bond. A free radical mechanism is proposed to explain the greater isomeric complexity of the hydroperoxide products compared to photosensitized oxidation.

Heat-Stress Proteins of Rat Lung Endothelial and Mammary Adenocarcinoma Cells

A rat mammary adenocarcinoma cell clone, MTC, and a rat lung endothelial cell clone, RLE cl.4, both syngeneic to the Fisher 344 rat, were compared for proteins synthesized at 37 degrees C and after a 1-h, 42 degrees C heat dose. The heat stress-induced or -enhanced synthesis of a series of molecular mass groups and isoelectric point species (isomers) was observed in both equilibrium and nonequilibrium two-dimensional gel electrophoresis. Tumor and endothelial cell heat-stress proteins (hsp) were strikingly similar with most hsp in 11 or 13 molecular mass groups having from 1 to 12 major isomers. In comparing the two cell types, 6 of about 23 major hsp isomers appeared different in equilibrium pH gels, with tumor cells seemingly exhibiting less synthesis of these 6 isomers. Four additional endothelial cell hsp isomers were apparent in nonequilibrium pH gels. Since two of these later hsp can be found at higher heat doses in tumor cells, some of these apparent differences between tumor and endothelial cells may be attributable to different dose ranges for induction of hsp. Fluorograms and silver-stained gels showed that several hsp were being synthesized at appreciable levels in unheated cells. However, there were hsp whose synthesis appeared to be de novo rather than representing enhanced synthesis of existing proteins. These last two observations were made in both tumor and normal cells. The constitutive levels of hsp synthesis appeared to be generally similar in unheated tumor and normal cells in vitro with few exceptions. These results indicate the presence of few unique hsp in syngeneic tumor and normal cells in vitro. However, focusing subsequent studies on the few differences may lead to insights concerning hyperthermic biology of tumor and normal cells, phenotypic differences between these cells, and roles of some hsp.

Liquid chromatographic assay for constituent disaccharides of hyaluronic acid and chondroitin sulphate isomers

An improved high-performance liquid chromatographic (HPLC) method for unsaturated disaccharides prepared from hyaluronic acid and various chondroitin sulphate and dermatan sulphate isomers was developed, which involves an ion-exchange resin prepared from a sulphonated styrene-divinylbenzene copolymer. The retention times of the individual unsaturated disaccharides were unique and reproducible, the disaccharides appearing in the following order: unsaturated non-sulphated disaccharide derived from hyaluronic acid, then unsaturated 6-sulphated, non-sulphated and 4-sulphated disaccharides from chondroitin sulphate isomers. Unsaturated disulphated siaccharide G had a much shorter retention time than the unsaturated non-sulphated disaccharide derived from hyaluronic acid. The contents of these individual unsaturated disaccharides could be determined with similar sensitivities on the basis of their ultraviolet absorbance. Selective and unique retention times and good resolutions were found for various unsaturated disulphated and trisulphated disaccharides. The proposed method can be used to determine various chondroitin sulphate and dermatan sulphate isomers in addition to hyaluronic acid in amounts as small as 100 ng to 8 μg. The practicality of this method was verified by its application to the separation and determination of the different types of chrondroitin sulphate and dermatan sulphate isomers derived from human arteries in the presence of appreciable amounts of hyaluronic acid.

Identification of 27-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24 xi, 25 xi,26-hexol and partial characterization of the bile alcohol profile in urine.

The nature of the bile alcohols present in urine of an infant with neonatal cholestasis has been investigated. Urine was extracted with Sep-Pak C18 cartridges and a glucuronide fraction was isolated by ion exchange chromatography on Lipidex-DEAP. Following enzymatic hydrolysis and purification on Lipidex-DEAP, the bile alcohols were isolated by high performance liquid chromatography. Fourteen compounds were studied by a combination of microchemical reactions and capillary column gas-liquid chromatography-mass spectrometry. Both C26 and C27 bile alcohols were present. Among the former, three additional isomers of the previously identified 27-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24 xi,25 xi-pentol were detected. A new C26 bile alcohol, 27-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24 xi,25 xi,26 -hexol, was identified, and a 27-norcholestane-pentolone with hydroxyl groups at C-24 and C-25 and a keto group in the ring system was partially characterized. The C27 bile alcohols consisted of cholestanepentols, -tetrolones, and -pentolones. 5 beta-Cholestane-3 alpha,7 alpha,12 alpha,25,26-pentol (5 beta-bufol), one of its isomers and an isomer of cholestane-3,7,12,24,26-pentol were present. Two cholestanetetrolones and two cholestanepentolones having the keto group in the ring system were partially characterized. The hydroxyl groups in the side chain of the tetrolones were at C-24,26 and C-25,26, respectively, whereas the pentolones had hydroxyl groups at C-24,25 and C-25,26, respectively. The excretion of glucuronidated bile alcohols in urine is suggested to reflect an alternative metabolism of intermediates in the normal biosynthesis of bile acids.