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Carboxylative enzymes are involved in many pathways and their regulation plays a crucial role in many of these pathways. In particular, γ‐glutamylcarboxylase (GGCX) converts glutamate residues (Glu) into γ‐carboxyglutamate (Gla) of the vitamin K‐dependent proteins (VKDPs) activating them. VKDPs include at least 17 proteins involved in processes such as blood coagulation, blood vessels calcification, and bone mineralization. VKDPs are activated by the reduced form of vitamin K, naturally occurring as vitamin K1 (phylloquinone) and K2 (menaquinones, MKs). Among these, MK7 is the most efficient in terms of bioavailability and biological effect. Similarly to other trans isomers, it is produced by natural fermentation or chemically in both trans and cis. However, the efficacy of the biological effect of the different isomers and the impact on humans are unknown. Our study assessed carboxylative efficacy of trans and cis MK7 and compared it with other vitamin K isomers, evaluating both the expression of residues of carboxylated Gla‐protein by western blot analysis and using a cell‐free system to determine the GGCX activity by HPLC. Trans MK7H2 showed a higher ability to carboxylate the 70 KDa GLA‐protein, previously inhibited in vitro by warfarin treatment. However, cis MK7 also induced a carboxylation activity albeit of a small extent. The data were confirmed chromatographically, in which a slight carboxylative activity of cis MK7H2 was demonstrated, comparable with both K1H2 and oxidized trans MK7 but less than trans MK7H2. For the first time, a difference of biological activity between cis and trans configuration of menaquinone‐7 has been reported. [ABSTRACT FROM AUTHOR]

Crystal structures for a series of bis(acetylacetonato)oxovanadium(IV) complexes containing N-donor pyridyl ligands are reported, namely, bis(acetylacetonato-κ2O,O′)oxido(pyridine-κN)vanadium(IV), [V(C5H7O2)2O(C5H5N)], 1, bis(acetylacetonato-κ2O,O′)oxido(pyridine-4-carbonitrile-κN)vanadium(IV), [V(C5H7O2)2O(C6H4N2)], 2, and bis(acetylacetonato-κ2O,O′)(4-methoxypyridine-κN)oxidovanadium(IV), [V(C5H7O2)2O(C6H7NO)], 3, Compounds 1–3 have the formulae VO(C5H7O2)2L, where L = pyridine (1), 4-cyano-pyridine (2), and 4-methoxypyridine (3). Compound 1 was previously reported [Meicheng et al. (1984). Kexue Tongbao, 29, 759–764 and DaSilva, Spiazzi, Bortolotto & Burrow (2007). Acta Crystallogr., E63, m2422] and redetermined here at cryogenic temperatures. Compounds 1 and 2 as pyridine and 4-cyanopyridine adducts, respectively, crystallize as distorted octahedral structures with the oxo and pyridyl ligands trans to one another. A crystallographic twofold axis runs through the O—V—N bonds. Compound 3 containing a 4-methoxypyridine ligand crystallizes as a distorted octahedral structure with the oxo and pyridyl ligands cis to one other, removing the twofold symmetry seen in the other complexes.

We present an approach for the elucidation of C=C bond position and cis/trans isomers, which is achieved by the reaction of ambient water radical cations and double bonds, followed by the fragmentation of epoxide radical cations to generate diagnostic ions in tandem mass spectrometry. Hexenol double bond positional isomers and cis/trans isomers which exhibit different properties and biological functions are characterized as a proof of concept. The merits of the approach include the simplicity of experimental setup, rapid derivatization (within seconds), the obviation of organic solvents, as well as easy spectral interpretation. Image 1 • A novel approach for the elucidation of C=C bond position and cis/trans isomers. • In situ epoxidation reaction of ambient water radical cations and C=C bonds. • No need of special instrumentation and organic solvents. [ABSTRACT FROM AUTHOR]

An aqueous normal-phase high-performance liquid chromatography method was developed to separate cis/trans isomers of 4,5-dihydroxy-imidazolidine-2-thione and 4,5-dimethoxy-imidazolidine-2-thione on a Luna HILIC 200 Å column containing silica surface covered with cross-linked diol with an eluent acetonitrile/water in the ratio of 95:5 v/v. Changing of the analysis parameters leads to selectivity of cross-linked diol towards analyte with a predominance of adsorption mechanism between the phase and compounds. The separation in reversed-phase and normal-phase modes are unsuccessful. Chromatographic peaks of the cis/trans isomers are identified by the HR-LC–MS and the spectral ratios. The results of the determination of the isomer ratio for 4,5-dihydroxy-imidazolidine-2-thione by the HPLC are consistent with the 1H NMR data. The existence of the previously undescribed cis-4,5-dimethoxy-imidazolidine-2-thione is confirmed by the HR-HPLC–MS. This method allows providing simultaneous rapid separation and determination of the ratio of isomers in the samples of 4,5-dihydroxy-imidazolidine-2-thione and 4,5-dimethoxy-imidazolidine-2-thione. [ABSTRACT FROM AUTHOR]

Crystal structures for a series of bis­(acetyl­acetonato)oxovanadium(IV) complexes containing N-donor pyridyl ligands are reported, namely, bis­(acetyl­acetonato-κ²O,O′)oxido(pyridine-κN)vanadium(IV), [V(C5H7O2)2O(C5H5N)], 1, bis­(acetyl­acetonato-κ²O,O′)oxido(pyridine-4-carbo­nitrile-κN)vanadium(IV), [V(C5H7O2)2O(C6H4N2)], 2, and bis­(acetyl­acetonato-κ2O,O′)(4-meth­oxy­pyridine-κN)oxidovanadium(IV), [V(C5H7O2)2O(C6H7NO)], 3, Compounds 1–3 have the formulae VO(C5H7O2)2L, where L = pyridine (1), 4-cyano-pyridine (2), and 4-meth­oxy­pyridine (3). Compound 1 was previously reported [Meicheng et al. (1984). Kexue Tongbao, 29, 759–764 and DaSilva, Spiazzi, Bortolotto & Burrow (2007). Acta Crystallogr., E63, m2422] and redetermined here at cryogenic temperatures. Compounds 1 and 2 as pyridine and 4-cyano­pyridine adducts, respectively, crystallize as distorted octa­hedral structures with the oxo and pyridyl ligands trans to one another. A crystallographic twofold axis runs through the O—V—N bonds. Compound 3 containing a 4-meth­oxy­pyridine ligand crystallizes as a distorted octa­hedral structure with the oxo and pyridyl ligands cis to one other, removing the twofold symmetry seen in the other complexes. [ABSTRACT FROM AUTHOR]

• Four genera of thermophilic bacteria were analyzed. • Using off-line two-dimensional LC-tandem MS menaquinones (MK5) to MK15 were found. • A mixture of menaquinones having cis/trans double bond(s) was separated. Thermophilic bacteria of four genera in contrast to the commonly used production strains such as Bacillus subtilis , produce homologs other than menaquinone (MK) with seven isoprene units. The number of isoprene units and the configuration of double bonds are essential factors for their biological activity. The goal was to obtain a strain of bacteria that produces a wide range of MK homologs and only all- trans geometrical isomers, which was the strain G. kaustophilus. Using off-line two-dimensional LC–tandem MS in columns with the RP18 phase and the COSMOSIL cholester phase (separation according to the geometric configuration of double bonds) it was shown that thermophilic bacteria grown at different temperatures produce only all- trans isomers of menaquinones from MK-5 (menaquinone with five isoprenyl units) to MK-15 (fifteen isoprenyl units). Therefore, G. kaustophilus appears to be a biotechnologically important strain produces only trans isomers and additionally homologs from 5 to 15 isoprene units. [ABSTRACT FROM AUTHOR]

The aim of this paper was to determine the chemical structure of cis/trans isomers of vitamin K 2 MK-7 found in dietary supplements. Vitamin K 2 MK-7 was extracted, along with contamination in the form of cis/trans isomers of menaquinone-7, from dietary supplements through tetrahydrofuran and then subjected to fractionation using the semi-preparative chromatography column with cholesteryl group phase (strong stereoselectivity for hydrophobic compounds). The obtained fractions of cis/trans isomers of menaquinone-7 underwent analysis with the use of multidimensional NMR methods optimized for maximum signal separation. NMR analysis made it possible to identify the first geometric isomer of (E,Z3,E2,ω)-menaquinone-7, which underwent NMR comparative analysis with a known “full trans ” isomer. It was also possible to confirm the presence of other cis/trans isomers in menaquinone-7 in the collected fractions. Due to the fact that the other fractions indicate a mixture of at least two geometric isomers of menaquinone-7, it was not possible to conduct full structural identification. [ABSTRACT FROM AUTHOR]

The optimization of a porous structure to ensure good separation performances is always a significant issue in high-performance liquid chromatography column design. Recently we reported the homogeneous embedment of Ag nanoparticles in periodic mesoporous silica monolith and the application of such Ag nanoparticles embedded silica monolith for the high-performance liquid chromatography separation of polyaromatic hydrocarbons. However, the separation performance remains to be improved and the retention mechanism as compared with the Ag ion high-performance liquid chromatography technique still needs to be clarified. In this research, Ag nanoparticles were introduced into a macro/mesoporous silica monolith with optimized pore parameters for high-performance liquid chromatography separations. Baseline separation of benzene, naphthalene, anthracene, and pyrene was achieved with the theoretical plate number for analyte naphthalene as 36 000 m−1. Its separation function was further extended to cis/trans isomers of aromatic compounds where cis/trans stilbenes were chosen as a benchmark. Good separation of cis/trans-stilbene with separation factor as 7 and theoretical plate number as 76 000 m−1 for cis-stilbene was obtained. The trans isomer, however, is retained more strongly, which contradicts the long- established retention rule of Ag ion chromatography. Such behavior of Ag nanoparticles embedded in a silica column can be attributed to the differences in the molecular geometric configuration of cis/trans stilbenes. [ABSTRACT FROM AUTHOR]

In regard to [(N-heterocyclic carbene)Ru]-based catalysts, it is still a matter of debate if the substrate binding is preferentially cis or trans to the N-heterocyclic carbene ligand. By means of static and molecular dynamic DFT calculations, a simple olefin, like ethylene, is shown to be prone to the trans binding. Bearing in mind the higher reactivity of trans isomers in olefin metathesis, this insight helps to construct small alkene substrates with increased reactivity. [ABSTRACT FROM AUTHOR]

The synthesis of octahedral complexes [SnCl4L2] (L = R2NP(O)(OCH2CF3)(O-p-tolyl): R2N = Me2N (1), Et2N (2), CH2(CH2CH2)2N (3), and O(CH2CH2)2N (4), or L = R2NP(O)(OCH2CF3)(O-p-PhNO2): R2N = Me2N (5), Et2N (6), and O(CH2CH2)2N (7) is described. The new adducts have been characterized by multinuclear (31P,19F,119Sn) NMR, IR spectroscopy, and elemental analyses. The solution NMR data show the presence of a mixture ofcisandtransisomers. The structure of the complexes in solution was further confirmed by119Sn NMR spectra, which display a triplet for each isomer, indicating an octahedrally coordinated tin center. The effects of the nature of R and Ar substituents on the donor ability of the P=O group in the ligands R2NP(O)(OCH2CF3)(OAr) were investigated on the basis of119Sn NMR chemical shifts and used to classify these ligands according to their Lewis basicity. [ABSTRACT FROM PUBLISHER]

Imaging technology based on fluorescent dyes is of great significance in tumor diagnosis. The fluorescent probes with antitumor effect at the same time can further expand the application of the probes in tumor. Inspired by the rigid cyclic structure of heme, the isomers cis/trans-BP with intramolecular eight-membered ring structure were obtained by innovatively combining two groups in unrelated fields, BODIPY and pyrimidine, together through substitution reaction and then by simple column chromatography. cis/trans-BP has stable spectral properties and can generate obvious fluorescence signals in organisms. The transmission electron microscope visually showed the uptake and distribution of the compounds by HeLa, and the subsequent apoptosis. The antitumor mechanisms of the compounds were further studied by flow cytometry. The results showed that trans-BP retained the function of fluorescent probe and simultaneously possessed antitumor activity. [Display omitted] • The target compound has both anticancer activity and fluorescent probe capability. • The compounds with nitrogen-boron rigid eight-membered ring structure in the molecule were synthesized. • Conformational isomers were obtained by column chromatography. • Two different domain groups of pyrimidine and BODIPY are combined on the same compound. [ABSTRACT FROM AUTHOR]

A sensitive and accurate high performance liquid chromatography assay (HPLC) technique was applied for determination of permethrin isomers. Cis-/trans-Permethrin isomers were separated at room temperature in raw material as well as pharmaceutical products such as lotions and creams without extraction. The calibration curve was found to be linear (r ⩾ 0.9975) over the concentration range of 0.80-1.66 μm/ml. The samples were measured at 280 nm detection wavelength as internal standard of quantitaion. Mean percentage (%) recovery ± % relative standard deviation (RSD) ranged from 97.50 ± 1.36 to 100.08 ± 0.39. Within-day and between-day precision were also in acceptable range below 2%. The reported method for the simultaneous estimation of cis-/trans-permethrin isomers provides several advantages e.g simplicity, highly specificity, accuracy and very short runcycle time. [ABSTRACT FROM AUTHOR]

Abstract: The reaction of SnF4 with (R2N) n P(O)(OCH2CF3)3−n (n =0–2) produces a series of new octahedral complexes of SnF4L2 type (L=(R2N)2P(O)OCH2CF3; R=Me (1); Et (2), L=R2NP(O)(OCH2CF3)2; R=Me (3); Et (4) or L=P(O)(OCH2CF3)3 (5)). The adducts have been characterized by multinuclear (19F, 31P and 119Sn) NMR, IR spectroscopy and elemental analyses. The NMR data particularly the 19F NMR spectra show the existence of complexes as mixtures of cis and trans isomers. The variable temperature NMR study in CH2Cl2 solutions in the presence of excess ligand indicated that the ligand exchange at room temperature is slow for 1–4 and fast only for 5. The results were compared with those of SnCl4 analogues and show the formation of higher trans ratios for the studied complexes. [Copyright &y& Elsevier]

Abstract: In a series of desaturation reactions, the trienoic structures of phytoene and diapophytoene are extended to a maximum of 15 or 11 conjugated double bonds, respectively. After the cloning of several genes from bacteria and eukaryotes, the desaturation reactions were first analyzed in a heterologous host by functional genetic complementation. In addition, different desaturases were heterologously expressed and the reactions studied in vitro. This revealed that in archaea, non-photosynthetic prokaryotes and fungi the desaturases differ significantly from convergently evolved desaturases in cyanobacteria, Chlorobaculum (old name Chlorobium) species and eukaryotic photosynthetic organisms including plants. Detailed analysis of the desaturation reactions including the determination of the substrates converted by the enzymes, the intermediates and the products formed in the reactions revealed the bacterial all-trans desaturation pathway catalyzed by a single enzyme and the cyanobacterial/plant type poly-cis desaturation pathway which involves two closely related desaturases. This indicates that in the course of evolution of carotenogenesis from bacteria via cyanobacteria to plants, the simple situation of one enzyme for the entire reaction sequence from phytoene to all-trans lycopene changed to a more complex process. Three individual enzymes, newly acquired phytoene and ζ-carotene desaturases, as well as a carotene isomerase which is phylogenetically related to CrtI are involved. Only the CrtI-type enzymes seem to have the property to catalyze cis to trans conversion of carotenes. [Copyright &y& Elsevier]

Abstract: Research on the biosynthesis of carotenoid pigments, from diverse points of view, has undergone a considerable boost in recent years due to the large body of studies that highlights their beneficial effects in humans. To obtain valuable information from such surveys, it is of paramount importance to reduce the tentativeness with which some carotenoids are still identified, above all, when they are key compounds for the synthesis of other important metabolites. This is the case for neoxanthin (5′,6′-epoxy-6,7-didehydro-5,6,5′,6′-tetrahydro-β,β-carotene-3,5,3′-triol), an epoxycarotenoid which can be found in the light harvesting apparatus of plants and whose cleavage leads to the formation of xanthoxin and then of the plant hormone abscisic acid, among other compounds. Hence, this paper presents pieces of evidence that may put in doubt the presence of such a carotenoid in orange juice, as a consequence of which we propose that the compound formerly tentatively identified as neoxanthin should be referred to as “unidentified” prior to its conclusive characterization and identification. [Copyright &y& Elsevier]

Fifteen title compounds with four fused rings and two varying substituents were used to further specify the scope and limitation of a theoretical approach (the Snyder theory and LSChrom software) for selection of mobile phases avoiding any trial and error experiments. Based on the structure of the compounds, the theoretical treatment predicted values of strength ε of suitable mobile phases for TLC, namely 0.311 for silica and 0.446 for alumina. Sixteen specific mobile phases with such or close values of ε were arbitrarily selected from lists prepared by complex calculations. They were used to perform TLC. The data obtained showed that the retentions in all 256 measurements done were above the origin and below the solvent front. Thus, a good agreement between the theoretical and experimental data was established, thus proving a successful application of the approach. The retentions of all compounds and separation of one cis/trans pair depended on the stationary phase, ε, and the tuning parameters m and P' of the mobile phases. [ABSTRACT FROM AUTHOR]

Avoiding any trial and error experiments, the LSChrom software incorporating the Snyder theory was applied successfully to automatic selection of mobile phases for thin‐layer chromatography (TLC) of substituted isochromanones 1–8 and the spiro analogues 9–12. The procedure takes into account the adsorption properties of the mobile phase (parameter ε and tuning parameters m and P ′), stationary phase and sample structure expressed by relevant groups. The calculations yielded a recommended value of ε and subsequently a list of mobile phases having this value of ε. The approach was applied to TLC on two types of silica and, for the first time, on alumina. Within about 130 measurements using 10 computer selected mobile phases, the retention of any compound fell in a favorable range (0 F [ABSTRACT FROM AUTHOR]

2,5-Diphenyl-1,4-distyrylbenzene (DPDSB) with all-cis (cis-DPDSB) and all-trans double bonds (trans-DPDSB) were synthesized by Wittig reaction and the differences in structural and optical properties between the cis- and trans-isomers are discussed in detail. Both compounds were fully characterized by NMR spectroscopy, FT-IR spectroscopy, x-ray crystallography, differential scanning calorimetry (DSC) and electrochemical methods. X-ray analysis and molecular simulation revealed that the structure of cis-DPDSB obviously deviates from planarity along both the distyrylbenzene and terphenyl directions, and less intermolecular interaction exists in crystal. The cis-isomer shows a large blue shift in the absorption spectrum in comparison with that of the trans-isomer, and cyclic voltammetric measurements give bandgaps of 3.16 and 2.97 eV for cis- and trans-DPDSB, respectively. Both compounds show unusually strong blue fluorescence in the solid state, probably due to the weak intermolecular interaction existing in both isomers owing to the large steric hindrance induced by the substituted phenyl groups. DSC experiments determined that both isomers have excellent thermal stability, which indicates that they can be used as active layers to make stable devices. Quantum chemical calculations for the frontier molecular orbital and the cation and anion properties reveal that the HOMO and LUMO are completely localized in the distyrylbenzene direction and the distyrylbenzene segment has more sensitive electroactivity than the terphenyl segment whether it is cis- or trans-DPDSB. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The thermal decomposition reactions of the complexes cis/trans-[Cu(gly)2] • H2O were studied by TG-DSC methods. The results showed that they have similar decomposition process, which occur in two steps. The first step is the loss of water and the second step is the decomposition of anhydrous complexes. But for cis-[Cu(gly)2]•H2O, the temperature of losing water is higher than that of trans-isomer. Their reaction mechanisms of the two-step decomposition were also proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Some d 6 transition metal [M(DABF) 2 A 2 + complexes should prefer trans geometries. • Preferences for trans geometries trend with increasing ligand atom atomic number. • This conflicts with geometric predictions from the trans influence concept. • Energy decompositions suggest DFT exchange underlies the anomalous preferences. Computational studies of low spin d 6 cis– and trans– [M(DABF) 2 A 2 + complexes (M = Co, Rh, Ir; A = anionic ligand) employing multiple model chemistries find that cis geometries are preferred for complexes where the binding atom in A is high and/or to the left in the Periodic Table, while trans geometries are preferred for complexes where the binding atom is heavy or to the right of the Periodic Table. This holds despite the fact that consideration of the trans influence for the π-acceptor spectator DABF ligand suggest that all such complexes should prefer cis geometries. Energy decomposition analysis ties the phenomenon mostly to the degree of DFT exchange; that this benefits trans geometries more than cis geometries is thought to arise from the greater electronic symmetry of the former. This is supported by predictions for haloborane complexes [M(DABF) 2 (BX 2) 2 +. In contrast, [M(CO) 4 A 2 + complexes, containing better π-accepting CO spectator ligands (presumably higher in the trans influence series), are predicted to prefer cis geometries except for the halogen complexes [M(CO) 4 X 2 + (X = F, Cl, I), where no distinct preferences exist. [ABSTRACT FROM AUTHOR]

In nature tocotrienols (compounds of vitamin E) have only been found in the 2 R,3′ trans,7′ trans ( R, trans- trans) configuration whereas synthetic tocotrienols often represent a mixture of cis and trans side chain isomers. In this study tocotrienols were isolated from samples (egg yolk, palm oil, and ewe's milk) by extraction of the unsaponifiable matter and subsequent semi-preparative high-performance liquid chromatography (HPLC). A recently developed HPLC method [two series-connected columns ET 200/4 NUCLEODEX β-PM (200×4 mm ID, permethylated β-cyclodextrin phase; Macherey-Nagel, Düren, Germany), acetonitrile/water eluent (58 : 42 by vol.), fluorescence detection at an emission wavelength of 330 nm (excitation wavelength = 295 nm)] was used to separate the isolated tocotrienols into the four potential cis/trans side chain isomers. Commercially available, synthetic α-tocotrienol was orally administered to a laying hen. In the egg yolk all four α-tocotrienol geometrical isomers could be determined, thus demonstrating the bioavailability. Furthermore, no cis/trans isomers of γ-tocotrienol from hardened palm oil (melting point 46 °C) could be detected, i.e. the hydrogenation process during oil hardening evidently caused no isomerization of γ-tocotrienol. Finally, it is shown that ewe's milk does not contain a detectable amount of cis/transα-tocotrienol isomers, which might derive from biohydrogenation during microbial metabolism in the rumen. [ABSTRACT FROM AUTHOR]

For the first time, the cis/trans isomer content of menaquinone-7 in food products has been identified and marked. A novel method of marking isomers of vitamin K 2 MK-7 in dietary supplements was developed and validated. Five different isomers of cis/trans vitamin K 2 MK-7 were identified. Identification of cis/trans isomers was performed by HRMS-QTOF, whereas their quantities were determined by using CAD and DAD detectors. In the majority of cases, the content of biologically active all trans vitamin K 2 MK-7 was below its declared content. The content of all trans K 2 MK-7 was in the range between 5.5 and 49 µg in pills. In one of the studied supplements, this vitamin was not found, regardless of the claim on the product label. The content of cis/trans isomers in certain dietary supplements exceeded the content of all trans K 2 MK-7 by up to 3.7 times., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

A new vacuum ultraviolet (VUV) detector for gas chromatography was recently developed and applied to fatty acid methyl ester (FAME) analysis. VUV detection features full spectral acquisition in a wavelength range of 115-240nm, where virtually all chemical species absorb. VUV absorption spectra of 37 FAMEs, including saturated, monounsaturated, and polyunsaturated types were recorded. Unsaturated FAMEs show significantly different gas phase absorption profiles than saturated ones, and these classes can be easily distinguished with the VUV detector. Another advantage includes differentiating cis/trans-isomeric FAMEs (e.g. oleic acid methyl ester and linoleic acid methyl ester isomers) and the ability to use VUV data analysis software for deconvolution of co-eluting signals. As a universal detector, VUV also provides high specificity, sensitivity, and a fast data acquisition rate, making it a powerful tool for fatty acid screening when combined with gas chromatography. The fatty acid profile of several food oil samples (olive, canola, vegetable, corn, sunflower and peanut oils) were analyzed in this study to demonstrate applicability to real world samples., (Copyright © 2015 Elsevier Ltd. All rights reserved.)