Trans Ratio Research Articles

Synthesis of the cis‐ and trans‐3‐Fluoro Analogues of Febrifugine and Halofuginone

AbstractThe novel synthesis of racemic cis‐ and trans‐3‐fluorofebrifugine and halofuginone is described. This straight‐forward seven‐step process relies on an electrophilic fluorination‐allylation sequence that generates a mixture of N‐Cbz protected, diastereomeric 2‐allyl‐3‐fluoropiperidines. On separation, a Wacker oxidation‐methyl functionalisation sequence enabled introduction of the required quinazolinone portion. Finally, removal of the N‐Cbz protecting group lead to isolation of the 3‐fluorofebrifugine dihydrobromide analogues that are of potentially pharmacological use. Analysis of the NMR spectra for each stereoisomer provides information concerning the preferred conformers of the different diastereomers. Evidence indicates that the cis‐diastereomer favours a conformation where the F‐atom occupies an axial orientation. In contrast, for its trans‐stereoisomeric counterpart, the 2‐substituent overrides any F‐atom effect and it preferentially occupies a conformer where both substituents occupy equatorial positions. Finally, interconversion between the cis‐ and trans‐diastereomers was studied. In DMSO‐d6 and as their free‐bases, isomerisation of each diastereomer gave a common 65 : 35 ratio of trans‐ to cis‐3‐fluorofebrifugine. Determination of the reaction rate constants for the isomerisation process at different temperatures enabled calculation of the activation energy barriers, for each process, using an Arrhenius plot. The activation energy barrier for the isomerisation of the trans‐isomer was 94.3±4.9 kJ mol−1, whereas for the cis‐isomer it was 84.5±3.9 kJ mol−1.

Copper Complexes with Protein-Based N-Donor Ligands as cis-Selective Nascent Cyclopropanases.

In this study, we aimed to develop protein-based metal ligands to catalyze cis-selective cyclopropanation using the TM1459 cupin protein superfamily. Copper complexes with TM1459 mutants containing the 3-His metal-binding site exhibited excellent diastereoselectivity in cyclopropanation reactions with styrene and ethyl diazoacetate. Further mutations in the secondary coordination sphere increased the cis-preference with t-butyl diazoacetate as the substrate with up to 80 : 20 (cis:trans ratio) and high enantioselectivity (90 % ee).

Calorimetric and Raman spectroscopic studies of zwitterionic and anionic membrane interactions of phenolic compound coumarin

It is well known that polyphenols possess potent antioxidant qualities. However, the precise antioxidant action mechanism of phenolic compounds is still not well defined. It is evident that understanding the molecular mechanisms behind polyphenol-lipid interactions is necessary to comprehend this impact. The objective of this work is to examine the effect of phenolic compound coumarin on the physicochemical properties of cell membrane models. To accomplish this goal, model membranes made up of zwitterionic dimyristoylphosphatidylcholine (DMPC) and anionic dimyristoylphosphatidylglycerol (DMPG) lipids were used. These lipid species are the main component of the mammalian and gram-positive bacteria membranes, respectively. Differential scanning calorimetry (DSC) and Raman spectroscopy were applied for studying the interaction of coumarin with DMPC and DMPG. From the DSC results, it was found that pretransition was abolished for both lipid systems at 20 mol% coumarin. Main phase transition shifted to lower temperatures and broadened, but there was not a complete disappearance of main transition and coumarin was not fully miscible. A sharp peak at a higher temperature and a broad shoulder at a lower temperature of the main transition of DMPC were detected when compared to coumarin/DMPG binary system. A reduction in calorimetric enthalpy and entropy values of coumarin/DMPC system at 20 mol% was observed whereas an increase in these calorimetric parameters for coumarin/DMPG system occurred. Thus, the disorder was caused when 20 mol% coumarin interacts with DMPC lipid bilayers. The increase in enthalpy could be a result of the 20 mol% coumarin interactions with DMPG lipid bilayers or a possible generated partial interdigitation. From the Raman results, the peak height Raman intensity ratio I1090/I1130 showed that coumarin induces disorder in the DMPG bilayers in the gel phase due to the increasing gauche:trans ratio. According to the results obtained by DSC and Raman spectroscopy, it was found that coumarin has a varied effect on membranes made from lipids with choline and glycerol head groups. Thus, it is obvious that the polyphenol/membrane interactions can be significantly impacted by the lipids’ structural variations.

Infrared spectroscopy for evaluating the effect of electron beam sterilization on polyethylene terephthalate medical tubes

The paper studies the effect of electron beam sterilization on the polyethylene terephthalate parts of blood sampling systems. The structural state and crystallinity degree of polyethylene terephthalate are estimated from the analysis of infrared spectra. Relative intensities are calculated by the reference band (overall intensity level) at 1410 cm−1. The Gaussian intensities of the absorption bands for trans and gauche conformations with respect to reference band at 1505 cm–1 are calculated. The spectral coefficients D973/D795, D848/D795, D1042/D795, D895/D795, D1098/D1370, and D1255/D1370 are determined. The dose of up to 25 kGy has no significant effect on either the ratio of integral intensities or the ratio of trans and gauche conformations.

Effect of Halides on MPS Orientation and Cu Deposition Rates at Cu Surfaces

Surface enhanced Raman spectroscopy (SERS), electrochemical measurements, and contact angles were used to evaluate the effect of halides on Cu electrodeposition rates in the presence of 3-mercapto-1-propanesulfonate (MPS). The Cu(II) reduction rate was shown to decrease in the order Cl− > Br− > I−. In-situ SERS and contact angle measurements showed that adsorbed MPS will exhibit decreased gauche to trans (g:t) ratio and decreased hydrophobicity in the same order as the Cu(II) reduction rate. The amount of MPS in the gauche form, due to the hydrophobicity of the halide decorated surface, is a key factor in the Cu(II) reduction rate in acid sulfate baths containing the accelerator.

Rubber Oxygenase Degradation Assay by UV-Labeling and Gel Permeation Chromatography.

A versatile and robust end-group derivatization approach using oximes has been developed for the detection of oxidative degradation of synthetic polyisoprenes and polybutadiene. This method demonstrates broad applicability, effectively monitoring degradation across a wide molecular weight range through ultraviolet (UV)-detection coupled to gel permeation chromatography. Importantly, it enables the effective monitoring of degradation via derivatization-induced UV-maximum shifts, even in the presence of an excess of undegraded polyene, overcoming limitations previously reported with refractive index detectors. Notably, this oxime-based derivatization methodology is used in enzymatic degradation experiments of synthetic polyisoprenes characterized by a cis: trans ratio with the rubber oxygenase LcpK30. It reveals substantial UV absorption in derivatized enzymatic degradation products of polyisoprene with molecular weights exceeding 1000g mol-1 - an unprecedented revelation for this enzyme's activity on such synthetic polyisoprenes. This innovative approach holds promise as a valuable tool for advancing research into the degradation of synthetic polyisoprenes and polybutadiene, particularly under conditions of low organocatalytic or enzymatic degradation activity. With its broad applicability and capacity to reveal previously hidden degradation processes, it represents a noteworthy contribution to sustainable polymer chemistry.

Experimental validation of quadratic-boost-zeta converter based on coat circuit

<p>This work proposed a high step-up DC-DC converter with a voltage gain of 12 at a duty cycle of 48.25% with a single active switch. The new design combines the quadratic-boost converter and an isolated zeta converter with a single-stage coat circuit by a transformer with a trans ratio of 2.3. This can result in low voltage stress on switch and diodes with low conduction losses without using an additional clamp circuit, which in turn causes an increase in total efficiency. It has continuous and low ripples in the input and output currents. The voltage conversion ratio and the component voltage stresses are calculated in continuous conduction mode (CCM). The prototype was constructed and tested practically while considering an input voltage of 30 V, an input power of 240 W, an output voltage of 360 V, and a switching frequency of 100 kHz to validate the theoretical evaluations. The maximum efficiency at maximum output power is 94.5%.</p>

Potential and kinetic interaction of two internal tops in molecules belonging to C2v(M) molecular symmetry group

Fourier analysis of the kinetic and potential interactions of non-coaxial internal tops in the molecules C6H4(OH)2, HO(CH2)OH, HOOOH, HOSOH, HSSSH, and HSOSH was carried out. It was found that for the all six molecules, in which both tops are characterized by a period 2 π, the harmonics with a period of π are dominate, with its contribution to the Fourier representation of potential surfaces increasing in the sequence mentioned above. Contributions of internal tops interactions to the kinetic and potential energies were determined for analyzed molecules. The influence of potential and kinetic interactions of internal tops on 1) the features of tunneling splitting of the ground and excited torsional states of molecules, 2) the landscape of 2D potential energy surfaces, 3) frequencies of fundamental torsional vibrations of hydroxyl and thiol groups, 4) the ratio of trans - and cis - conformer energies is also analyzed.

BUTEN-1-in BUTEN-2-yə İZOMERLƏŞMƏSİ REAKSİYASINDA BİNAR KOBALT TƏRKİBLİ KATALİZATORLARIN AKTİVLİYİ

Hydrogen is considered the main source of chemical energy that can be converted directly into electricity and with the help of fuel cells into zero emissions of harmful waste, such as volatile organic compounds, nitrogen oxides and carbon. The production of hydrogen in accordance with the generation of energy using a fuel cell is considered a promising alternative to stationary and portable power generation plants in the future. Various methods are used to produce hydrogen: water electrolysis, gasification, partial oxidation of heavy oil and steam corrugation of organic compounds. Currently, in industry, about 90% of hydrogen is produced by the reaction of high-temperature steam reforming of light fractions of natural gas or oil. An attractive alternative to hydrogen production is the reaction of ethanol steam reforming. The activity of binary iron-cobalt, zinc-cobalt and magnesium-cobalt oxide catalysts in the reaction of isomerization of butene-1 to butenes-2 was studied. Iron-cobalt, zinc-cobalt and magnesium-cobalt oxide catalysts were prepared by co-precipitation from aqueous solutions of iron, zinc, magnesium and cobalt nitrate salts. The resulting mixture was evaporated at 95-100°C, then the resulting precipitate was dried at 100-120°C and then decomposed at 250°C until the nitrogen oxides were completely separated. The resulting solid was calcined at 700°C for 10 hours. Thus, 27 catalysts were prepared satisfying the following conditions: mA/NB, where A is Mo, Ti, Cu; cis, m,n=1-9, m+n=10. The isomerization reaction of butene-1 to butene-2 was carried out at a rate of 1200 h-1 volume of feedstock in the temperature range of 150-400°C. The reactor was filled with 5 mL of 1-2 mm thick catalyst and fed with a reaction mixture consisting of butene-1 and nitrogen. The ratio of butene-1 to nitrogen is 1:9. It is shown that with increasing cobalt content in the Fe-Co-o catalyst composition, its activity in the isomerization reaction reaches a maximum on catalysts with equivalent ratio of initial elements. The ratio of trans- and cis-butenes-2 practically does not change and is equal to 1.2. It is found that both Lewis acid centers and Bransted acid centers are present on the surface of this catalyst in approximately equal amounts. It was found that with increasing zinc content in the catalyst composition, the degree of butene-1 isomerization decreases and the ratio of trans-butene-2 to cis-butene-2 increases from 0 to 2.1, indicating the presence of Lewis and Bronsted acid centers on the surface of Zn-Co-O catalysts. It is found that for the Mg-Co-O catalytic system the ratio of trans and cis butenes-2 yields varies in the range 0.8-1.5. It is shown that, in the whole temperature range studied, the atomic ratio of cobalt and magnesium has a strong influence on their activity in the reaction of Butene-1 isomerization into Butene-2. It is found that the number of Lewis and Bronsted acid centers is practically independent of the composition of the Mg-Co-O catalytic system. Based on the study of the reaction of butene-1 to butene-2 isomerization on binary cobalt-containing catalysts, it was found that the samples with equimolar ratios of primary elements in Fe-Co-O catalysts, as well as samples with one of the predominant elements in the catalytic systems Zn-Co-O and Mg-Co-O are active. Keywords: Isomerization, butene-1, butenes-2, binary catalysts Cobalt oxide.

Diastereofacial selectivity of α-aminonitrile formation from substituted cyclohexanones

The formation of α-aminonitriles from substituted cyclohexanones exhibits diastereofacial selectivity resulting in unequal amounts of the two possible geometric isomers. The degree of selectivity increases with the nature of the substitution on the cyclohexyl ring indicating that this likely results from the degree to which the substitution can ‘lock’ the conformation of the cyclohexyl ring into the most stable conformation. The ratio of trans:cis isomers seen for the reaction of 4-substituted cyclohexanones with dimethylamine hydrochloride and potassium cyanide in water were 92:8 for 4-phenyl, 81:19 for 4-t-butyl, and 62:38 for 2-methyl. Varying the size of the amino group substituents did not have a dramatic effect on the selectivity that was observed.

Cardo polyimides with high Tg and transparency derived from bisphenol fluorenes and 1,4-bis(4-fluorophthalimide)cyclohexanes via aromatic nucleophilic substitution

Two series of transparent cardo polyimides (PIs) derived from bisphenol fluorenes and 1,4-bis(4-fluorophthalimide)cyclohexanes (BFCH) with different ratios of trans- and cis-1,4-diaminocyclohexane were prepared via aromatic nucleophilic substitution. These PIs exhibited high glass transition temperatures (Tgs) of 271–352 °C, 5% weight loss temperatures (Td5%) of 400–433 °C in nitrogen, mechanical properties of tensile strengths of 62–107 MPa, tensile moduli of 3.0–4.4 GPa and elongations at break of 1.7–4.5% and great solubility in a variety of organic solvents. These PI films appeared excellent optical transparency, which displayed the cut-off wavelengths from 323 to 355 nm and high transmittance at 450 nm with more than 85 %. The steric effects of different substituent groups on bisphenol fluorene and different ratios of trans/cis configuration were also investigated.

Stereocontrolled acyclic diene metathesis polymerization.

The cis/trans geometry of olefins is known to dramatically influence the thermal and mechanical properties of polyalkenamers. Yet, polymerization methods that efficiently control this parameter are scarce. Here we report the development of a stereoretentive acyclic diene metathesis polymerization that uses the reactivity of dithiolate Ru carbenes combined with cis monomers. These Ru catalysts exhibit exquisite retention of the cis geometry and tolerate many polar functional groups, enabling the synthesis of all-cis polyesters, polycarbonates, polyethers and polysulfites. The stereoretentive acyclic diene metathesis polymerization is also characterized by low catalyst loadings and tolerance towards trans impurities in the monomer batch, which should facilitate large-scale implementation. Modulation of the reaction temperature and time leads to an erosion of stereoretention, permitting a stereocontrolled synthesis of polyalkenamers with predictable cis:trans ratios. The impact of the stereochemistry of the repeating alkenes on the thermal properties is clearly demonstrated through differential scanning calorimetry and thermogravimetric analysis.

Hybrid-Lipid Bilayers Induce n-Alkyl-Chain Order in Reversed-Phase Chromatographic Surfaces, Impacting their Shape Selectivity for Aromatic Hydrocarbon Partitioning.

Shape selectivity is important in reversed-phase liquid chromatographic separations, where stationary phases are capable of separating geometric isomers, thereby resolving solutes based on their three-dimensional structure or shape rather than other chemical differences. Numerous chromatographic studies have been carried out using n-alkyl-chain-modified columns to understand how molecular shape affects retention. For polycyclic aromatic hydrocarbons (PAHs), it was found that planar compounds were selectively retained over nonplanar structures of comparable molecular weight on surfaces with longer n-alkyl chains, higher chain-density, or at lower temperatures, where selectivity likely arises with greater ordering of the n-alkyl chains. A limitation of these studies, however, is the small range of chain ordering that can be achieved and lack of a direct measure of the n-alkyl-chain order of the stationary phases. In this work, we employ a C18 stationary phase modified with a monolayer of phospholipid as a means of significantly varying the n-alkyl chain order. These hybrid-supported lipid bilayers, which have previously been employed as membrane-like stationary phases for measuring lipophilicity, provide a unique approach to control n-alkyl chain ordering by varying the acyl chain length and degree of unsaturation of the phospholipid modifier. The degree of alkyl-chain order of the resulting modified surfaces is determined from the ratio of trans- versus gauche-conformers, measured in situ within individual porous particles by confocal Raman microscopy. This methodology was also used to assess the affinity of these surfaces for planar versus nonplanar PAH molecules. The retention selectivity for the planar versus nonplanar compounds, thus determined, was found to vary significantly and systematically with the degree of order of the acyl/alkyl chains in the hybrid-supported lipid bilayers. The investigation also demonstrates the utility of confocal Raman microscopy for interrogating the impact of solute partitioning on stationary-phase structure within porous chromatographic particles.

Rapid tannin profiling of tree fodders using untargeted mid-infrared spectroscopy and partial least squares regression

BackgroundThe presence of condensed tannins (CT) in tree fodders entails a series of productive, health and ecological benefits for ruminant nutrition. Current wet analytical methods employed for full CT characterisation are time and resource-consuming, thus limiting its applicability for silvopastoral systems. The development of quick, safe and robust analytical techniques to monitor CT’s full profile is crucial to suitably understand CT variability and biological activity, which would help to develop efficient evidence-based decision-making to maximise CT-derived benefits. The present study investigates the suitability of Fourier-transformed mid-infrared spectroscopy (MIR: 4000–550 cm−1) combined with multivariate analysis to determine CT concentration and structure (mean degree of polymerization—mDP, procyanidins:prodelphidins ratio—PC:PD and cis:trans ratio) in oak, field maple and goat willow foliage, using HCl:Butanol:Acetone:Iron (HBAI) and thiolysis-HPLC as reference methods.ResultsThe MIR spectra obtained were explored firstly using Principal Component Analysis, whereas multivariate calibration models were developed based on partial least-squares regression. MIR showed an excellent prediction capacity for the determination of PC:PD [coefficient of determination for prediction (R2P) = 0.96; ratio of prediction to deviation (RPD) = 5.26, range error ratio (RER) = 14.1] and cis:trans ratio (R2P = 0.95; RPD = 4.24; RER = 13.3); modest for CT quantification (HBAI: R2P = 0.92; RPD = 3.71; RER = 13.1; Thiolysis: R2P = 0.88; RPD = 2.80; RER = 11.5); and weak for mDP (R2P = 0.66; RPD = 1.86; RER = 7.16).ConclusionsMIR combined with chemometrics allowed to characterize the full CT profile of tree foliage rapidly, which would help to assess better plant ecology variability and to improve the nutritional management of ruminant livestock.

Hydrogenation of Cyclic 1,3-Diones to Their 1,3-Diols Using Heterogeneous Catalysts: Toward a Facile, Robust, Scalable, and Potentially Bio-Based Route.

Cyclopentane-1,3-diol (4b) has gained renewed attention as a potential building block for polymers and fuels because its synthesis from hemicellulose-derived 4-hydroxycyclopent-2-enone (3) was recently disclosed. However, cyclopentane-1,3-dione (4), which is a constitutional isomer of 3, possesses a higher chemical stability and can therefore afford higher carbon mass balances and higher yields of 4b in the hydrogenation reaction under more concentrated conditions. In this work, the hydrogenation of 4 into 4b over a commercial Ru/C catalyst was systematically investigated on a bench scale through kinetic studies and variation of reaction conditions. Herein, the temperature, H2-pressure, and the solvent choice were found to have significant effects on the reaction rate and suppression of undesired dehydration of 4. The cis–trans ratio of 4b is naturally generated as 7:3 in these reactions. However, at elevated reaction temperatures, 4b epimerizes, yielding more trans products. This effect was also studied and rationalized from a thermodynamic perspective using DFT. The combined optimized reaction conditions provided 78% yield for 4b, and successful applications to 8-fold scaled up reactions (40 g) and a substrate scope of several 1,3-diones demonstrate the general applicability of this catalytic approach.

Enzymatic degradation of synthetic polyisoprenes via surfactant-free polymer emulsification

A bioinspired emulsification strategy resulted in substantially increased enzymatic activities in the degradation of synthetic polyisoprene with the latex clearing protein LcpK30, even with cis : trans ratios of 56 : 27.

Associations Between Nicotine Metabolite Ratio and Gender With Transitions in Cigarette Smoking Status and E-Cigarette Use: Findings Across Waves 1 and 2 of the Population Assessment of Tobacco and Health (PATH) Study.

Nicotine metabolite ratio (NMR), the ratio of trans 3'-hydroxycotinine to cotinine, is a biomarker of nicotine metabolism. Discrepant findings among clinical trials and population-based studies warrant replication on whether higher NMR, or faster nicotine metabolism, is associated with quitting cigarette smoking. Associations of NMR and e-cigarette use are largely unknown, as well as the relationship between NMR and gender on quitting cigarette smoking or e-cigarette use. The Population Assessment of Tobacco and Health (PATH) Study is a nationally representative, longitudinal cohort study assessing tobacco use in the US population. In the current study, the PATH (waves 1 and 2; adult interviews) was used to evaluate longitudinal predictions in relationships among NMR and gender and their association with transitions (quit vs. current stable) in cigarette smoking status and e-cigarette use status across waves 1 and 2 of the PATH study. NMR and gender were not significantly associated with quit behavior for combustible cigarettes. Regarding e-cigarettes, a significant two-way interaction demonstrated that women with higher NMR were less likely to quit e-cigarette use compared to women with lower NMR (odds ratio [OR] = 0.10, 95% confidence interval [CI] = 0.02-0.57; p = .01). Findings identify that women with faster nicotine metabolism were 10 times less likely to quit e-cigarettes compared to women with slower nicotine metabolism across waves 1 and 2 of the PATH study. Results suggest that NMR may be used as a biomarker for transitions in e-cigarette quit behavior for women. Findings identify that women with faster nicotine metabolism were 10 times less likely to quit e-cigarettes compared to women with slower nicotine metabolism. Results suggest that NMR may be used as a biomarker for transitions in e-cigarette quit behavior for women. Establishing parameters for NMR collection and for the use of NMR as a biomarker for cigarette smoking behavior and e-cigarette use is an important next step, and may have implications for early intervention and treatment for cessation.

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Atrorosins: a new subgroup of Monascus pigments from Talaromyces atroroseus

A new series of azaphilone pigments named atrorosins have been isolated from the filamentous fungus Talaromyces atroroseus. Atrorosins have a similar azaphilone scaffold as the orange Monascus pigment PP-O, with a carboxylic acid group at C-1, but are unique by their incorporation of amino acids into the isochromene system. Despite that the atrorosin precursor PP-O, during fermentation, was initially produced as two isomers (3:2, cis:trans ratio), the atrorosins were surprisingly almost exclusively (99.5%) produced as the cis-form, possibly due to steric interactions with the incorporated amino acid. When grown on complex media, a whole range of atrorosins is produced, whereas individual atrorosins can be produced selectively during fermentation by supplementing with the desired primary amine-containing compound.

Hyperpolarization of Pyridyl Fentalogues by Signal Amplification By Reversible Exchange (SABRE).

Fentanyl, also known as ‘jackpot’, is a synthetic opiate that is 50–100 times more potent than morphine. Clandestine laboratories produce analogues of fentanyl, known as fentalogues to circumvent legislation regarding its production. Three pyridyl fentalogues were synthesized and then hyperpolarized by signal amplification by reversible exchange (SABRE) to appraise the forensic potential of the technique. A maximum enhancement of ‐168‐fold at 1.4 T was recorded for the ortho pyridyl 1H nuclei. Studies of the activation parameters for the three fentalogues revealed that the ratio of ligand loss trans to hydride and hydride loss in the complex [Ir(IMes)(L)3(H)2]+ (IMes=1,3‐bis(2,4,6‐trimethylphenyl)imidazole‐2‐ylidene) ranged from 0.52 to 1.83. The fentalogue possessing the ratio closest to unity produced the largest enhancement subsequent to performing SABRE at earth's magnetic field. It was possible to hyperpolarize a pyridyl fentalogue selectively from a matrix that consisted largely of heroin (97 : 3 heroin:fentalogue) to validate the use of SABRE as a forensic tool.