Cis And Trans Research Articles

Identification, Quantitation, and Sensory Evaluation of Thiols in Bordeaux Red Wine with Characteristic Aging Bouquet.

Great Bordeaux red wines are known for their distinctive aging bouquet. However, the nature of volatile chemicals underpinning this sensory expression is not fully understood. This work investigated the empyreumatic aging bouquet of a collection of premium Bordeaux red wines using silver-ion (Ag+) solid-phase extraction, cryogenic heart-cutting multidimensional gas chromatography mass spectrometry/olfactometry, and comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry. In doing so, a substantial number of "meaty" odors were revealed. Three detected "meaty" notes were tentatively or unequivocally attributed to furan thiols. Among them, 2-methyltetrahydrofuran-3-thiol (1) with a pleasant "meaty" aroma was reported in wine for the first time. Its trans isomer (trans-1a) was resolved from its racemate by chemical modification, which confirmed its presence in wine. The odor detection threshold of trans-1a in the model wine was determined at 55 ng/L. Moreover, an additive effect between 1 and literature-known 2-methyl-3-furanthiol was observed. By a new ultra high-performance liquid chromatography quadrupole Orbitrap high-resolution mass spectrometry method, the concentration of trans-1a, in addition to those of 2-methyl-3-furanthiol and 2-furfuryl thiol, was measured in the wines at ng/L levels.

Amide isomerization pathways: Electronic and structural background of protonation- and deprotonation-mediated cis-trans interconversions.

The cis-trans isomerization of amide bonds leads to wide range of structural and functional changes in proteins and can easily be the rate-limiting step in folding. The trans isomer is thermodynamically more stable than the cis, nevertheless the cis form can play a role in biopolymers' function. The molecular system of N-methylacetamide · 2H2O is complex enough to reveal energetics of the cis-trans isomerization at coupled cluster single-double and coupled cluster single-double and perturbative triple [CCSD(T)] levels of theory. The cis-trans isomerization cannot be oversimplified by a rotation along ω, since this rotation is coupled with the N-atom pyramidal inversion, requesting the introduction of a second dihedral angle "α." Full f(ω,α) potential energy surfaces of the different amide protonation states, critical points and isomerization reaction paths were determined, and the barriers of the neutral, O-protonated and N-deprotonated amides were found too high to allow cis-trans interconversion at room temperature: ∼85, ∼140, and ∼110 kJ mol-1, respectively. For the N-protonated amide bond, the cis form (ω = 0°) is a maximum rather than a minimum, and each ω state is accessible for less than ∼10 kJ mol-1. Here we outline a cis-trans isomerization pathway with a previously undescribed low energy transition state, which suggests that the proton is transferred from the more favorable O- to the N-protonation site with the aid of nearby water molecules, allowing the trans → cis transition to occur at an energy cost of ≤11.6 kJ mol-1. Our results help to explain why isomerase enzymes operate via protonated amide bonds and how N-protonation of the peptide bond occurs via O-protonation.

Halogen addition to NHC-gold(I) chloride complexes in the framework of the Inverted Ligand Field

The conversion of LAuX to LAuX3, where L is a neutral ligand such as a phosphane or a carbene and X = Cl, Br or I, can be performed by halogen addition reactions in mild conditions. The formation of complexes with mixed halides, such as LAuY2X, also evoking the possibility of geometrical isomerization, is less investigated. In this work the iodine and bromine addition reactions, under mild conditions, to a symmetrically disubstituted carbene 1,3-dimethyl-imidazolyl-2-yl-gold(I)chloride were considered. The molecular structures highlight the formation of the trans LAuI2Cl in the case of iodine addition and a mixture of the geometrical isomers for bromine. DFT analysis points out a stepwise addition of halogen atom to the linear gold(I) complex without a net change in metal electronic population, suggesting the occurrence of the Inverted Ligand Field.

First Stereoselective Synthesis of Diethyl cis- and trans-(4-Hydroxy-1,2,3,4-tetrahydroquinolin-2-yl)phosphonates and Ethyl Phenylphosphinates from Quinolin-4(1H)-one

AbstractWe report a practical method for the first stereoselective synthesis of diethyl cis- and trans-(4-hydroxy-1,2,3,4-tetrahydroquinolin-2-yl)phosphonates, as well as ethyl cis- and trans-(4-hydroxy-1,2,3,4-tetrahydroquinolin-2-yl)phenylphosphinates. The main feature of this method is the regioselective 1,4-phosponylation to N-Cbz quinolin-4(1H)-one using diethyl phosphite or ethyl phenylphosphinate followed by a highly diastereoselective reduction to give the cis stereoisomers as favored products, which were converted into trans stereoisomers through the Mitsunobu reaction. Cleavage of the N-Cbz bond under hydrogenolysis gave the target heterocyclic α-aminophosphonates and α-aminophosphinates.

ERCC8 related Cockayne syndrome type-1: A rare entity diagnosed in a Turkish boy

Cockayne syndrome (CS, OMIM #216400 and OMIM #133540) is a rare, progressive, multisystemic disorder that results in premature aging and cachectic dwarfism. It is an autosomal recessive disorder with a prevalence of 2-2.5 per million. Pathogenic variants detected in the ERCC excision repair 6 (ERCC6) and ERCC excision repair 8 (ERCC8) genes are responsible for molecular pathogenesis. In this case report, an 11-year-old boy with severe microcephaly, growth retardation, loss of subcutaneous fat tissue, neuromotor developmental delay, bilateral cataracts, and facial dysmorphism but without dermal photosensitivity, who had a novel missense variant in trans configuration with a nonsense variant is presented.

Antioxidant Capacity of Carotenoid Extracts from the Haloarchaeon Halorhabdus utahensis.

Herein, we report on the production, characterization, and antioxidant power assessment of carotenoids from the haloarchaeon Halorhabdus utahensis. It was grown at 37 °C and 180 rpm agitation in halobacteria medium supplemented with glucose, fructose, and xylose, each at concentrations of 0.2%, 1%, and 2%, and the carotenoid yield and composition were investigated. The microorganism produced the carotenoids under all the conditions tested, and their amount followed the order glucose < xylose < fructose. The highest yield was achieved in 2% fructose growth medium with 550.60 ± 7.91 μg/g dry cell and 2428.15 ± 49.33 μg/L. Separation and identification of the carotenoids were performed by RP-HPLC and HPLC/APCI-ITMSn. Bacterioruberin was the main carotenoid detected and accounted for 60.6%, 56.4%, and 58.9% in 2% glucose, 1% xylose, and 2% fructose extracts, respectively. Several geometric isomers of bacterioruberin were distinguished, and representatives of monoanhydrobacterioruberin, and bisanhydrobacterioruberin were also detected. The assignment to cis-isomers was attempted through analysis of the UV/Vis spectra, intensity of cis peaks, and spectral fine structures. The extracts exhibited superoxide scavenging activity higher than butylhydroxytoluene, ascorbic acid, and Trolox, selected as antioxidant references. The anti-hyaluronidase capacity was investigated, and the 2% fructose extract showed the highest activity reaching 90% enzyme inhibition with 1.5 μg. The overall data confirm that Hrd. utahensis can be regarded as an interesting source of antioxidants that can find applications in the food and cosmetic sectors.

Cebranopadol: An Assessment for Its Biased Activation Potential at the Mu Opioid Receptor by DFT, Molecular Docking and Molecular Dynamic Simulation Studies

AbstractCocaine use disorder is a psychiatric condition affecting millions of people worldwide. Up till now, there are no FDA approved medications reported against this disorder. Previous pharmacological studies suggested that, simultaneously targeting all types of opioid receptors, some agonistically while others antagonistically have been proven a much useful strategy for the treatment of cocaine addiction. Recent evidence indicated that a novel agonist cebranopadol has a high binding affinity towards Nociceptin opioid receptor (NOP) and Mu opioid receptor (MOP), and partial affinity with Kappa opioid receptor (KOP) and Delta opioid receptor (DOP). Interestingly, in vivo studies revealed that cebranopadol blocked the cocaine seeking in animal models. In the present study, quantum chemical calculations were performed to calculate various thermodynamic parameters of cebranopadol using density functional theory. Flexible docking was performed to rationalize the molecular basis of cis and trans isomers of cebranopadol. Further, the atomistic description of activation mechanism of MOP receptor by cebranopadol investigated by sub‐microsecond timescale molecular dynamic (MD) simulation. Our results revealed that the operating mode of the activation switch composed of Trp2936.48 and Asn3287.45 residues, was accountable for down‐ and up‐regulation, respectively, of the β‐arrestin signaling. This particular conformational change in turn affected the G‐protein‐biased activation of MOP receptor. Cebranopadol stabilized the Asn3287.45 by mediating halogen bond formation. According to best of our knowledge, this is the first mechanistic study of cebranopadol with MOP receptor using the quantum mechanical calculations and MD simulations to explain the inhibition of cocaine addiction.

Amphotropic liquid crystal polyacetylene derivative bearing pyrimidine type mesogen

An amphotropic liquid crystal polyacetylene derivative with pyrimidine–type two-ringed mesogenic core, exhibiting both thermotropic and lyotropic liquid crystallinity, was synthesized in this study. The polyacetylene derivative showed a lyotropic liquid crystal in d-limonene. The cis configuration of the main chain was confirmed via 1H NMR. Heat treatment induced cis–trans isomerization of the as-prepared polymer. Gas-phase iodine doping of the polymer initiated a chemical interaction between the polyene and iodine, acting as an electron acceptor, generating charge carriers (radical cations, solitons) detected with the electron spin resonance spectroscopy. Moreover, gas phase doping of the polymer induced cis–trans isomerization.

Photoisomerisation of Exo-Imine Complexes and the Role of MECP in the Reverse Thermal Equilibrium: An Experimental and DFT Computational Investigation.

Complexes [MCl2Cp*]2 (M= Ir, Rh), [RuCl2(p-cymene)]2 and [Ir(C^N)2Cl]2 (HC^N = a, phenylpyridine ; b, phenylpyrazole,) react with imine ligands derived from o-aminophenol to yield complexes with an exocyclic C=N bond which has a cis or trans configuration. The trans isomer is favoured except for sterically crowded complexes Cp*M (M = Ir, Rh) when the imine has a mesityl substituent, for which the cis isomer is favoured. The complexes undergo photoisomerization in visible light but revert back to the original isomer over time or when heated. The rate of the thermal reverse isomerisation depends on the imine substituent and the metal fragment. DFT calculations correctly reproduce the favoured isomer and suggest that the reverse isomerisation occurs by a rehybridisation at the N atom as found in organic imines. In addition, a triplet state, thermally accessible by a Minimum Energy Crossing Point (MECP) provides a low energy pathway for reverse isomerisation in the case of the half-sandwich complexes.

Correlations between Quantum Calculations and the Contribution of Factors Affecting the Structural Stability and Electronic Properties of Vinyl Azide and Vinyl Isocyanate

Abstract: The conformational features of vinyl isocyanate (1) and vinyl azide (2) have been analyzed using G4MP2, CCSD(T)/6-311+G**, B3LYP/6-311+G** and LC-ωPBE/6-311+G** theory levels. Published experimental data indicate that the stability of the cis-isomer of vinyl azide (2) is more than the trans-isomer. This is consistent with the findings attained using G4MP2 and LC-ωPBE/6- 311+G** levels, whereas B3LYP/6-311+G** and CCSD (T)/6-311+G** levels provide false energetic outcomes. Natural Bond Orbital (NBO) interpretation is used to interpret the reason for the stability of the cis stereoisomer of compound 2 and the structural features of compound 1. Dipole-dipole interactions, steric effects, and resonance energies on the structural behaviors of compounds 1 and 2 are also investigated using NBO analysis. The results showed that the stability of the cis conformer of compound 2 compared to its trans conformer could be explained using the steric effect (Pauli Exchange Type Repulsion or PETR). Dipole moments of the cis conformer of compound 2 are evaluated experimentally (from Rotational Spectroscopy) and theoretically. The experimental (from Rotational Spectroscopy) and theoretically evaluated dipole moments of trans-conformation of compound 2 are slightly greater than that in cis-conformation, which is in favor of the cis-conformation, while dipoledipole interactions are in favor of the cis-conformation of compound 1. Accordingly, the electrostatic interactions associated with dipole-dipole interactions do not explain the conformational behaviors of compound 1. The stabilization energies related to the delocalization of electrons are in favor of the cis-conformation of compound 1, whereas it has no considerable effect on compound 2’s conformational behavior.

Intrinsic disorder and conformational coexistence in auxin coreceptors

AUXIN/INDOLE 3-ACETIC ACID (Aux/IAA) transcriptional repressor proteins and the TRANSPORT INHIBITOR RESISTANT 1/AUXIN SIGNALING F-BOX (TIR1/AFB) proteins to which they bind act as auxin coreceptors. While the structure of TIR1 has been solved, structural characterization of the regions of the Aux/IAA protein responsible for auxin perception has been complicated by their predicted disorder. Here, we use NMR, CD and molecular dynamics simulation to investigate the N-terminal domains of the Aux/IAA protein IAA17/AXR3. We show that despite the conformational flexibility of the region, a critical W-P bond in the core of the Aux/IAA degron motif occurs at a strikingly high (1:1) ratio of cis to trans isomers, consistent with the requirement of the cis conformer for the formation of the fully-docked receptor complex. We show that the N-terminal half of AXR3 is a mixture of multiple transiently structured conformations with a propensity for two predominant and distinct conformational subpopulations within the overall ensemble. These two states were modeled together with the C-terminal PB1 domain to provide the first complete simulation of an Aux/IAA. Using MD to recreate the assembly of each complex in the presence of auxin, both structural arrangements were shown to engage with the TIR1 receptor, and contact maps from the simulations match closely observations of NMR signal-decreases. Together, our results and approach provide a platform for exploring the functional significance of variation in the Aux/IAA coreceptor family and for understanding the role of intrinsic disorder in auxin signal transduction and other signaling systems.

DFO-Km: A Modular Chelator as a New Chemical Tool for the Construction of Zirconium-89-Based Radiopharmaceuticals.

Zirconium-89-labeled monoclonal antibodies and other large macromolecules such as nanoparticles hold great promise as positron emission tomography imaging agents. In general, zirconium-89 is an ideal radionuclide for long-circulating vectors such as antibodies or nanoparticles. It is also a promising radionuclide for theranostic radiopharmaceuticals due to its suitable match in half-life with actinium-225, thorium-227, lutetium-177, and others. As such, demand for new and optimized bifunctional chelators for zirconium-89 continues to grow. Herein, we present the modular chelator DFO-Km, which is octadentate and features lysine as a modular amino acid linker. The modular amino acid linker can be changed to other natural or unnatural amino acids to access different bioconjugation chemistries, while the chelating portion is unchanged thus retaining identical metal ion coordination properties to DFO-Km. The epsilon-amine in the DFO-Km linker (lysine) was used to complete synthesis of a bifunctional derivative bearing a p-SCN-Ph moiety. The chelator DFO-Km includes a redesigned hydroxamic acid, which provides more flexibility for metal ion coordination relative to the monomer used in the previously published DFO-Em. Moreover, a set of comprehensive DFT calculations were performed to model and evaluate 16 geometric isomers of Zr-(DFO-Km), which suggested the complex would form the optimum cic-cis-trans-trans octadentate Zr(IV) coordination geometry with no aqua or hydroxide ligands present. The bifunctional derivative p-SCN-Ph-DFO-Km was compared directly with the commercially available p-SCN-Ph-DFO, and both underwent efficient conjugation to a nonspecific human serum antibody (IgG) to yield two model immunoconjugates. The behavior of [89Zr]Zr-DFO-Km-IgG was studied in healthy mice for 2 weeks and compared to an equivalent cohort injected with [89Zr]Zr-DFO-IgG as a clinical "gold standard" control. PET-CT and biodistribution results revealed higher stability of [89Zr]Zr-(DFO-Km)-IgG in vivo over [89Zr]Zr-DFO-IgG, as demonstrated by the significant reduction of zirconium-89 in the whole skeleton as visualized and quantified by PET-CT at 1, 3, 7, and 14 days post-injection. Using CT-gated regions of interest over these PET-CT images, the whole skeleton was selected and uptake values were measured at 14 days post-injection of 3.6 ± 0.9 (DFO) vs 1.9 ± 0.1 (DFO-Km) %ID/g (n = 4, * p = 0.02), which represents a ∼48% reduction in bone uptake with DFO-Km relative to DFO. Biodistribution experiments performed on these same mice following the 14 day imaging time point revealed bone (both tibia) uptake values of 3.7 ± 1.3 (DFO) vs 2.0 ± 0.6 (DFO-Km) %ID/g (n = 6, * p < 0.05), with the tibia uptake values in close agreement with whole-skeleton ROI PET-CT data. These results indicate that DFO-Km is an improved chelator for [89Zr]Zr4+ applications relative to DFO. The bifunctional chelator p-SCN-Ph-DFO-Km shows potential as a new chemical tool for creating bioconjugates using targeting vectors such as antibodies, peptides, and nanoparticles.

Theoretical studies on the photo protective mechanism of curcuminoids

In this work, the deactivation pathways of curcuminoids after photoexcitation was studied by employing density functional theory to explore their UVA radiation screening capacity. A comprehensive computational characterization of the excited-state processes of curcumin, demethoxycurcumin, and bis-demethoxycurcumin was done. The molecules exist in diketo and enol forms which are in equilibrium and interconvertible through keto-enol tautomerism. The enolic forms of each of the studied molecules have eight geometric cis–trans isomers as a result of torsion rotation about three different carbon–carbon double bonds across the aliphatic chain. For each geometric isomer, sixteen possible rotamers are found to exist due to rotation about five different carbon–carbon single bond rotations, also across the skeleton of the aliphatic chain. Upon photoexcitation, the studied molecules follow three main pathways of radiationless decay: (a) rotamerism and interconversion between rotamers of comparable energies which are in equilibrium, (b) interconversion between the cis–trans geometrical isomers where an efficient vibrational relaxation path is formed at ∼90° during torsion rotation about carbon–carbon double bond, and (c) excited state intramolecular proton transfer in a single O–H stretching vibration through a cyclic intramolecular hydrogen bonded ring formed at the centre of the molecule giving back the original structure. The absorption and emission spectra of the molecules were also simulated where the theoretically obtained absorption and emission maxima are close to the reported experimental values.

Geometrical Isomers of Dantrolene and Their Interactions with Calcium and Magnesium Cations

Geometrical isomers of dantrolene are considered within the constraints of density functional theory at the level of B3LYP/6-31++G(d,p). Dantrolene is a skeletal muscle relaxant which interferes with the release of calcium ion from the sarcoplasmic reticulum. On the other hand, some evidence exists that dantrolene is Mg2+-dependent at least in certain species. Therefore, the present study not only considers the geometrical isomers of dantrolene but also focused on the interaction of isomers of dantrolene with Ca+2 and Mg+2 ions at the molecular level. All the systems of present interest have exothermic heat of formation values and favorable Gibbs free energy of formation values. They are electronically stable. In the case of composite from the anti isomer, Ca+2 or Mg+2 ion locates itself in the cavity/fjord formed in the composite of dantrolene whereas in the syn composite, Mg+2 prefers a location outside the cavity/fjord of the composite molecule. Various quantum chemical data have been collected and discussed including UV-VIS spectra.

Identification, Antioxidant Capacity, and Matrix Metallopeptidase 9 (MMP-9) In Silico Inhibition of Haloarchaeal Carotenoids from Natronococcus sp. and Halorubrum tebenquichense.

Natural pigments from haloarchaea are of great interest; bacterioruberin is the major pigment, it shows higher antioxidant power when compared with β-carotene. However, characterization of bacterioruberin and its isomers along with its antioxidant and the matrix metallopeptidase 9 (MMP-9) inhibition activities in extracts from Natronoccoccus sp. TC6 and Halorubrum tebenquichense SU10 was not previously described, being the aim of this work. The carotenoids profile was performed by UV-Vis spectrophotometry, thin-layer chromatography, nuclear magnetic resonance spectroscopy, and high-resolution mass spectrometry (UPLC-ESI-MS/MS). Antioxidant capacity was determined for DPPH, ABTS, and FRAP. In addition, MMP-9 inhibition was studied using docking simulations. The carotenoid profile of studied strains was composed of bacterioruberin, some derivatives like mono, bis, and tris anhydrobacterioruberin, and also some bacterioruberin cis isomers. The carotenoid pools showed antioxidant capacity for DPPH > ABTS > FRAP; Natronococcus sp. TC6 carotenoid pool was better for ABTS and DPPH, while Halorubrum tebenquichense SU10 carotenoid pool was better for FRAP. Additionally, docking and molecular dynamics suggest that bacterioruberin inhibits MMP-9 through hydrophobic interactions near the catalytic site. Bacterioruberin shows the higher binding energy of -8.3 (kcal/mol). The carotenoids profile of both strains was elucidated, their antioxidant activity and singular participation of each carotenoid on MMP-9 in silico inhibition were evaluated.

QUANTUM CHEMICAL STUDY OF HYDROGENATION OF SUNFLOWER OIL OVER NICKEL CATALYSTS

Vegetable oil hydrogenation is vital in edible margarine production, preventing rapid deterioration caused by double bond oxidation. Hydrogenation preserves vegetable oils by countering double bond oxidation, ensuring product quality. During this process, geometric isomers, notably trans isomers, form, driven by thermodynamic stability. Nickel catalysts are crucial in the oil and ghee industry for efficient hydrogenation. Purpose. Our study investigates the hydrogenation of sunflower oil with nickel catalysts, aiming to uncover molecular dynamics and interactions shaping this process. We reveal essential insights into linoleic acid-nickel interactions, elucidating hydrogenation mechanisms and implications for glycerol production. Methodology. Quantum chemical calculations and HyperChem software were employed to study the linoleic acid-nickel interaction during hydrogenation. This study delves into the hydrogenation of sunflower oil using nickel catalysts, employing quantum chemical calculations and HyperChem software. Results. Our research elucidates robust linoleic acid-nickel interactions through optimized structures, molecular electrostatic maps, molecular orbitals, bond lengths, and energies. These findings enhance our understanding of hydrogenation mechanisms. Additionally, we found that nickel-metal interactions primarily drive glycerol production from biofuels, promising efficiency gains. Conclusion. Our study yields insights into vegetable oil hydrogenation with nickel catalysts, optimizing processes in the oil and ghee industry. Furthermore, it has implications for glycerol production from biofuels, offering potential advancements in this area.

Double Bond Geometric Isomers of Pentaketide Ansamycins from Streptomyces sp. S008.

Six new pentaketide ansamycins, namely, shengliangmycins A-F (1-6, respectively), were obtained from the fermentation products of Streptomyces sp. S008OEslmR2 that was derived by constitutive expression of LAL regulator gene slmR2. The structures of 1-6 were determined through comprehensive spectroscopic analysis and single-crystal X-ray diffraction. Compound 1 has a cis-C6═C7 bond, which is different from that of compounds 2-5. Compounds 3-6 feature a morpholinone structural moiety, whereas 5 is characterized by a pyrazoline ring, which is rare in natural products.

High-power ultrasound bleaching technique for canola oil (Brassica napus L.): Pigments removal and quality parameters

Canola seeds (Brassica napus L.) are among the most commonly used seeds in Mexico for vegetable oil production. This is based on the high yield and content of polyunsaturated and monounsaturated fatty acids. During oil bleaching, it is important to maintain fatty acids in their cis configuration because of the health concerns associated with trans-fatty acid consumption. In this sense, the industrial processing parameters employed for this purpose present some limitations, such as high temperatures and long times, which may change the cis configuration to trans. In addition, the amount of bleaching clay employed for this process could be a source of contamination because it is disposed of after treatment. Therefore, the aim of this study was to develop a bleaching process for canola oil using high-power ultrasound (US). US processing was applied to nine treatments with different processing times (60, 75, and 90 min), clay percentages (1, 2, and 3%), and temperatures (60 and 80 °C) to determine the concentrations of chlorophyll a and b (µg chlo/100 g oil), carotenes (µg β-carotene/100 g oil), color (L*, a*, b*, C*, and h°), iodine value (g I2/100 g oil), and finally carrying out a spectroscopic analysis (ATR-FTIR and Raman). A conventional bleaching treatment (100 °C for 180 min, 3% bleaching clay) was used as a control. The results revealed that US treatments with 2% clay at 60 °C for 60 and 90 min eliminated most of the chlorophyll compounds (98%). However, in terms of carotenes reduction, these identical treatments exhibited a similar tendency to that of the control (approximately 30% decrease). These findings also affected the sample color, in which US treatments revealed chromatic coordinates that indicated yellow tones with chroma values that were more intense than those in the control samples. In terms of the iodine value, such treatments fulfilled the international standards for vegetable oils (90–100 g I2/100 g oil). Finally, the spectroscopic study revealed no trans configurations or the presence of different chemical compounds after US treatment, because neither of them presented typical peaks for those molecular configurations. In this regard, US can be a useful methodology for bleaching vegetable oils, helping to reduce time, and bleaching clay with similar pigment reduction results.

A Dinuclear Re Complex as a Multi Talent – Photocatalysis and Electrocatalysis combined with Spectroscopy

AbstractMononuclear rhenium complexes have been widely studied as photo‐ and electrocatalysts. However, dinuclear systems with cooperative properties have rarely been investigated. On the basis of two homobimetallic rhenium complexes, we report the synthesis and characterization of two isomers and their photo‐ and electrochemical properties. By combining the respective isomer with the photosensitizer [Ir(dFppy)3] (Ir, dFppy=2‐(4,6‐difluorophenyl) pyridine)) enhanced CO2 to CO transformation could be observed and by further spectroscopic investigations the reaction mechanism could be fathomed. The observed enhanced catalytic activity compared to monometallic systems derives from the cooperative Re−Re interaction through two electron reduction on the complex (and thereby formation of an intermediate species with a Re−Re bond). Using LSV measurements the cooperative CO2 activation was also observed for one of the isomers, cisL1‐Re2Cl2, in electrocatalytic measurements. The two isomers have a somewhat lower catalytic activity than earlier prepared geometric isomers, but show better catalytic properties than their mononuclear counterpart.

Changes in the cis-trans isomer selectivity of a reversed-phase liquid chromatography column during use with acidic mobile phase conditions

Reversed-phase liquid chromatography (RPLC) is the analytical tool of choice for monitoring process-related organic impurities and degradants in pharmaceutical materials. Its popularity is due to its general ease-of-use, high performance, and reproducibility in most cases, all of which have improved as the technique has matured over the past few decades. Nevertheless, in our work we still occasionally observe situations where RPLC methods are not as robust as we would like them to be in practice due to variations in stationary phase chemistry between manufactured batches (i.e., lot-to-lot variability), and changes in stationary phase chemistry over time. Over the last three decades several models of RPLC selectivity have been developed and used to quantify and rationalize the effects of numerous parameters (e.g., effect of bonded phase density) on separation selectivity. The Hydrophobic Subtraction Model (HSM) of RPLC selectivity has been used extensively for these purposes; currently the publicly available database of column parameters contains data for 750 columns. In this work we explored the possibility that the HSM could be used to better understand the chemical basis of observed differences in stationary phase selectivity when they occur – for example, lot-to-lot variations or changes in selectivity during column use. We focused our attention on differences and changes in the observed selectivity for a pair of cis-trans isomers of a pharmaceutical intermediate. Although this is admittedly a challenging case, we find that the observed changes in selectivity are not strongly correlated with HSM column parameters, suggesting that there is a gap in the information provided by the HSM with respect to cis-trans isomer selectivity specifically. Further work with additional probe molecules showed that larger changes in cis-trans isomer selectivity were observed for pairs of molecules with greater molecular complexity, compared to the selectivity changes observed for simpler molecules. These results do not provide definitive answers to questions about the chemical basis of changes in stationary phase chemistry that lead to observed differences in cis-trans isomer selectivity. However, the results do provide important insights about the critical importance of molecular complexity when choosing probe compounds and indicate opportunities to develop improved selectivity models with increased sensitivity for cis-trans isomer selectivity.