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Autocatalysis has been recognized to be involved in the emergence of life and intrinsic to biomolecular replication. Recently, an efficient template autocatalysis driven by solvent‐free crystallization has been reported. Herein, we unveil the role of intermolecular hydrogen bonds formed by amides in crystallization‐driven template autocatalysis (CDTA), which involves the autocatalytic activity, template selectivity, and thermal responsiveness. We found that the thermal‐induced cis‐trans isomerization of amides possibly affects the H‐bonding‐mediated template ability of products for autocatalytic transformation. As a result, CDTA can be reversibly inhibited and activated by tuning the reaction temperatures. Our work sheds light on the significance of noncovalent H‐bonding interactions in artificial self‐replicators. [ABSTRACT FROM AUTHOR]

Flexible and highly ultraviolet (UV) sensitive materials garner considerable attention in wearable devices, adaptive sensors, and light‐driven actuators. Herein, a type of nanofilms with unprecedented fully reversible UV responsiveness are successfully constructed. Building upon this discovery, a new system for ultra‐fast, sensitive, and reliable UV detection is developed. The system operates by monitoring the displacement of photoinduced macroscopic motions of the nanofilms based composite membranes. The system exhibits exceptional responsiveness to UV light at 375 nm, achieving remarkable response and recovery times of < 0.3 s. Furthermore, it boasts a wide detection range from 2.85 µW cm−2 to 8.30 mW cm−2, along with robust durability. Qualitative UV sensing is accomplished by observing the shape changes of the composite membranes. Moreover, the composite membrane can serve as sunlight‐responsive actuators for artificial flowers and smart switches in practical scenarios. The photo‐induced motion is ascribed to the cis–trans isomerization of the acylhydrazone bonds, and the rapid and fully reversible shape transformation is supposed to be a synergistic result of the instability of the cis‐isomers acylhydrazone bonds and the rebounding property of the networked nanofilms. These findings present a novel strategy for both quantitative and qualitative UV detection. [ABSTRACT FROM AUTHOR]

Geometrical mono-trans isomers of arachidonic acid (mtAA) are endogenous products of free radical-induced cis-trans double bond isomerization occurring to natural fatty acids during cell metabolism, including lipid peroxidation (LPO). Very little is known about the functional roles of mtAA and in general on the effects of mono-trans isomers of polyunsaturated fatty acids (mtPUFA) in various types of programmed cell death, including ferroptosis. Using HT1080 and MEF cell cultures, supplemented with 20 μM PUFA (i.e., AA, EPA or DHA) and their mtPUFA congeners, ferroptosis occurred in the presence of RSL3 (a direct inhibitor of glutathione peroxidase 4) only with the PUFA in their natural cis configuration, whereas mtPUFA showed an anti-ferroptotic effect. By performing the fatty acid-based membrane lipidome analyses, substantial differences emerged in the membrane fatty acid remodeling of the two different cell fates. In particular, during ferroptosis mtPUFA formation and their incorporation, together with the enrichment of SFA, occurred. This opens new perspectives in the role of the membrane composition for a ferroptotic outcome. While pre-treatment with AA promoted cell death for treatment with H 2 O 2 and RSL3, mtAA did not. Cell death by AA supplementation was suppressed also in the presence of either ferroptosis inhibitors, such as the lipophilic antioxidant ferrostatin-1, or NADPH oxidase (NOX) inhibitors, including diphenyleneiodonium chloride and apocynin. Our results confirm a more complex scenario for ferroptosis than actually believed. While LPO processes are active, the importance of environmental lipid levels, balance among SFA, MUFA and PUFA in lipid pools and formation of mtPUFA influence the membrane phospholipid turnover, with crucial effects in the occurrence of cell death by ferroptosis. [Display omitted] • mtPUFA induce different membrane lipid remodeling with SFA enrichment than PUFA. • mtPUFA do not have pro-ferroptotic activity as PUFA do. • Mono-trans isomers of arachidonic acid (mtAA) were formed upon lipid peroxidation. • Isomerization of AA to mtAA works as a negative feedback mechanism for ferroptosis. [ABSTRACT FROM AUTHOR]

Cis‐trans isomerization of amide bonds impedes de novo design of folded peptoids (poly‐N‐substituted glycines) with precise secondary structures and affects peptoid‐biomolecule binding affinity. Herein, from X‐ray, NMR and DFT studies of azapeptoids, we have discovered a tetrel bonding interaction that stabilizes trans‐peptoids. We show that peptoids having α‐heteroatoms and N‐aryl groups in the sidechain adopt trans‐amide geometries due to the presence of a nX/πAr→σ*Cα−N tetrel bonding interaction between the sidechain α‐heteroatom lone pair (nX) or π‐electrons (πAr) and the σ* orbital of the backbone Cα−N bond. Further, CD spectroscopic studies of oligo‐proline host–guest model peptides showed that azapeptoid residues stabilize polyproline II helical conformation. These data indicate that the sidechain‐backbone tetrel bonding could be leveraged to design peptoids with precise secondary structures for a wide range of biological and material applications. [ABSTRACT FROM AUTHOR]

Photoresponsive molecular devices can be a valuable tool to promote chemical changes in response to multiple signals, such as photons and pH, to deliver drugs or to detect physiological conditions in vivo. For example, trans-chalcones (Ct) from 4′-hydroxyflavylium (F1) and 7-hydroxyflavylium (F2) can undergo cis-trans isomerization by photoreaction into many different structures. The isomerization takes place at a slow rate in response to pH change; however, it can be done in seconds by photoreaction. In the investigation, as confirming the previous reports, 3-(2-hydroxy-phenyl)-1-(4-hydroxy-phenyl)-propenone, the trans-chalcone (CtF1) from F1, produces flavylium ions in pH = 1–4.5. Then, we further discovered that the flavylium quickly releases protons to yield the corresponding quinoidal base (A) in a solution of pH = 5.2 during irradiation with 350 nm. Meanwhile, the photolysis of 3-(2,4-dihydroxy-phenyl)-1-phenyl-propenone, the trans-chalcone (CtF2) from F2 at pH = 5.6, induces photoacid behavior by losing a proton from the trans-chalcone to generate Ct2−. The different outcomes of these nearly colorless chalcones under similar pH conditions and with the same photochemical conditions can be useful when yielding colored AH+, A, or Ct2− in a mildly acidic pH environment with temporal and spatial control using photochemical means. [ABSTRACT FROM AUTHOR]

Mycro 3 is a synthetic pyrazolo[1,5‐a]pyrimidine amide with interesting bioactivity having exhibited promising results in in vivo studies against pancreatic cancer. Even though it is a known compound, no data concerning its conformations have been reported before. The aim of this work is to investigate the formation of its trans‐ and cis‐ isomers, the photophysical processes of the isomerization, and the solvent effect via a DFT study. We found that this isomerization is a thermodynamically favourable reaction, having a small barrier of 10.3 kcal/mol in DMSO. Additionally, the calculated 1H and 13C NMR spectra of the two isomers revealed measurable differences. Furthermore, the S0→S1 excitation was found in vis area at 413 nm (trans‐isomer), while the S2→S0 and S1→S0 excitations are charge transfer (CT) and partially CT state in near‐infrared and vis spectra, showing that mycro 3 also has the potential to be used as a photosensitizer. Finally, its synthesis and its NMR analysis revealed a good agreement with the proposed trans conformation. [ABSTRACT FROM AUTHOR]

Photolabile protecting groups offer synthetic routes with facile deprotection by photolysis, providing higher yields with less workup. Protecting groups producing only gaseous byproducts upon removal are particularly desirable as sustainable reagents. Cheletropic reactions provide just this combination of photocleavable groups with gaseous byproducts. However, only few protecting groups for cheletropic reactions have been described and little is known about their photochemistry and associated stereochemistry. Here we show that the sulfolene protecting group, used for diene protection and functionalization, can be photochemically removed. First, using TD‐DFT, we conclude that the photochemical ring‐opening occurs conrotatorily in a concerted process, consistent with the Woodward‐Hoffmann rules. Experimentally, we demonstrate that this process can be photoinitiated by radiation between 180 and 300 nm and confirm the proposed stereochemistry in solution. Using time‐resolved photoelectron spectroscopy, we determine that the first steps in the photochemical ring‐opening of sulfolene occur on ultrafast timescales (≤84 fs), consistent with a fully concerted process. Our findings expand applications of the sulfolene protecting group and promise an easy strategy for control of cis‐trans isomerization. [ABSTRACT FROM AUTHOR]

[Display omitted] • Seven undescribed compounds were identified from Aglaia odorata. • The cis – trans isomerization equilibrium of tertiary amides was conducted. • Compounds 2–6, 8, 10, and 12 inhibited NO production at the nanomolar concentration. • The anti-neuroinflammatory effects of rocaglaol (12) were investigated in vivo. Fifty compounds including seven undescribed (1 , 13 , 18 – 20 , 30 , 31) and forty-three known (2 – 12 , 14 – 17 , 21 – 29 , 32 – 50) ones were isolated from the extract of the twigs and leaves of Aglaia odorata with anti-neuroinflammatory activities. Their structures were determined by a combination of spectral analysis and calculated spectra (ECD and NMR). Among them, compounds 13 – 25 were found to possess tertiary amide bonds, with compounds 16 , 17 , and 19 – 21 existing detectable cis / trans mixtures in 1H NMR spectrum measured in CDCl 3. Specifically, the analysis of the cis – trans isomerization equilibrium of tertiary amides in compounds 19 – 24 was conducted using NMR spectroscopy and quantum chemical calculations. Bioactivity evaluation showed that the cyclopenta[ b ]benzofuran derivatives (2 – 6 , 8 , 10 , 12) could inhibit nitric oxide production at the nanomolar concentration (IC 50 values ranging from 2 to 100 nM) in lipopolysaccharide-induced BV-2 cells, which were 413–20670 times greater than that of the positive drug (minocycline, IC 50 = 41.34 μM). The cyclopenta[ bc ]benzopyran derivatives (13 – 16), diterpenoids (30 – 35), lignan (40), and flavonoids (45 , 47 , 49 , 50) also demonstrated significant inhibitory activities with IC 50 values ranging from 1.74 to 38.44 μM. Furthermore, the in vivo anti-neuroinflammatory effect of rocaglaol (12) was evaluated via immunofluorescence, qRT-PCR, and western blot assays in the LPS-treated mice model. The results showed that rocaglaol (12) attenuated the activation of microglia and decreased the mRNA expression of iNOS, TNF- α , IL-1 β , and IL-6 in the cortex and hippocampus of mice. The mechanistic study suggested that rocaglaol might inhibit the activation of the NF-κB signaling pathway to relieve the neuroinflammatory response. [ABSTRACT FROM AUTHOR]

The cis-trans isomerization of a metal-centred molecular gear was investigated by density functional theory (DFT). The gear uses Pt(II) as stator, the azaphospha-triptycene as rotor, and the ligand introduces chlorine atoms. Under the conditions driven by light and heat, the gear can undergo switchable motion through the meshing and disengaging of two rotators. To be specific, the geometry optimization of cis-[PtCl2(Tp)2] and trans-[PtCl2(Tp)2] isomers were performed via the M06-2X functional in conjunction with def2-SVP basis set. Through rotating around the Pt-P single bond, the potential energy surface was scanned to explore the different rotational modes of the cis- and trans- isomers. In addition, time-dependent density functional theory (TD-DFT) was used to calculate molecular excitation energy and ultraviolet absorption properties. The reaction transition state of cis→trans isomerization was calculated to study the isomerization process and the motion correlation between the two rotors during rotation. [ABSTRACT FROM AUTHOR]

Phosphorylation-dependent peptidyl-prolyl cis-trans isomerization plays key roles in cell cycle progression, the pathogenesis of cancer, and age-related neurodegeneration. Most of our knowledge about the role of phosphorylation-dependent peptidyl-prolyl cis-trans isomerization and the enzyme catalyzing this reaction, the peptidyl-prolyl isomerase (Pin1), is largely limited to proteins not present in neurons. Only a handful of examples have shown that phosphorylation-dependent peptidyl-prolyl cis-trans isomerization, Pin1 binding, or Pin1-mediated peptidyl-prolyl cis-trans isomerization regulate proteins present at excitatory synapses. In this work, I confirm previous findings showing that Pin1 binds postsynaptic density protein-95 (PSD-95) and identify an alternative binding site in the phosphorylated N-terminus of the PSD-95. Pin1 associates via its WW domain with phosphorylated threonine (T19) and serine (S25) in the N-terminus domain of PSD-95 and this association alters the local conformation of PSD-95. Most importantly, I show that proline-directed phosphorylation of the N-terminus domain of PSD-95 alters the local conformation of this region. Therefore, proline-directed phosphorylation of the N-terminus of PSD-95, Pin1 association, and peptidyl-prolyl cis-trans isomerization may all play a role in excitatory synaptic function and synapse development. [ABSTRACT FROM AUTHOR]

A series of ruthenium hydride compounds containing substituted bidentate pyrrole‐imine ligands were synthesized and characterized. Reacting RuHCl(CO)(PPh3)3 with one equivalent of [C4H3NH(2‐CH=NR)] in ethanol in the presence of KOH gave compounds {RuH(CO)(PPh3)2[C4H3N(2‐CH=NR)]} where trans‐Py‐Ru‐H 1, R = CH2CH2C6H9; cis‐Py‐Ru‐H 2, R = Ph‐2‐Me; and cis‐Py‐Ru‐H 3, R = C6H11. Heating trans‐Py‐Ru‐H 1 in toluene at 70°C for 12 hr resulted a thermal conversion of the trans‐Py‐Ru‐H 1 into its cis form, {RuH(CO)(PPh3)2[C4H3N(2‐CH=NCH2CH2C6H9)]} (cis‐Py‐Ru‐H 1) in very high yield. The 1H NMR spectra of trans‐Py‐Ru‐H 1, cis‐Py‐Ru‐H 2, cis‐Py‐Ru‐H 3, and cis‐Py‐Ru‐H 1 all show a typical triplet at ca. δ–11 for the hydride. The trans and cis form indicate the relative positions of pyrrole ring and hydride. The geometries of trans‐Py‐Ru‐H 1, cis‐Py‐Ru‐H 1, and cis‐Py‐Ru‐H 3 are relatively similar showing typical octahedral geometries with two PPh3 fragments arranged in trans positions. [ABSTRACT FROM AUTHOR]

Abstract Biodiesel is a renewable fuel source comprising of fatty acid methyl esters (FAMEs). However, biodiesel (FAMEs) is susceptible to autoxidation. Therefore, structural modification of FAMEs through decreasing the number of double bonds (e.g., hydrogenation) or trans isomerization of original double bonds in the cis configuration, could improve the oxidative stability of FAMEs. In this work, the trans isomerization of carbon-carbon double bonds in unsaturated FAMEs obtained from edible oils has been successfully achieved using simple and safe p -toluenesulfinic acid as catalyst. And the effects of reaction time, temperature, catalyst loading, amount of water and antioxidants on the trans isomerization were investigated systematically. The results indicated that the amount of water (0–20 wt%) and antioxidants (<200 ppm) had no significant effect on the trans isomerization of unsaturated FAMEs. And the final product (trans FAMEs) was characterized by both GC and FT-IR. The conversion of trans double bonds of the isomerized lard FAMEs could reach 79.9% after heating at 100 °C for only 30 min without changing both the double bonds location and unsaturation degree. In addition, this convenient method was successfully applied in a variety of FAMEs prepared from different vegetable oils (e.g., safflower seed oil, camellia seed oil, high oleic sunflower oil and soybean oil) and approximately 80.0% selectivity of trans isomerization for all FAMEs were obtained. The present study showed a promising method to provide trans -FAMEs products for producing biodiesels with better oxidative stability (for high oleic FAMEs) and without adding of antioxidants. [ABSTRACT FROM AUTHOR]

The energy barrier for cis-to-trans isomerization is among the key parameters for photoswitchable molecules such as azobenzene. Recently, we introduced a well-defined model system based on thin films of crystalline, nanoporous metal-organic frameworks, MOFs. The system enables the precise investigation of the thermal cis-to-trans relaxation of virtually isolated azobenzene pendant groups by means of infrared spectroscopy in vacuum. Here, this approach is extended by using localized surface plasmon resonance spectroscopy. This simple and relatively inexpensive setup enables the investigation of the thermal cis-to-trans isomerization in different environments, here in argon gas or in liquid butanediol. The energy barrier for the cis-to-trans-relaxation in argon, 1.17±0.20eV, is identical to the barrier in vacuum, while the energy barrier in liquid butanediol is slightly larger, 1.26±0.15eV. [ABSTRACT FROM AUTHOR]

Cyclosporin is an 11-amino acid cyclic peptide with pharmacologically valuable properties which has a variety of actual and potential applications. Its activity relies on the cell membrane permeability which, in turn, depends on the structure of cyclosporin and its ability to change the conformation. In this work, conformational exchange processes occurring in cyclosporin C were studied using one- and two-dimensional nuclear magnetic resonance spectroscopy. The free energy barrier separating two major conformers observed in polar solution (acetonitrile) was found to be 77 ± 2 kJ/mol. Less populated conformation states are also present in the solution, which agrees with the ease of formation of multiple forms revealed by MD simulations of cyclosporin C. • Cyclosporin variant C in a polar solvent (acetonitrile) was studied by NMR. • Two distinct conformers were found to prevail in the solution. • Parameters of the chemical exchange between two main conformers were obtained. [ABSTRACT FROM AUTHOR]

Trans fats, unsaturated fatty acids with at least one double bond in the trans configuration, have received a great amount of attention in the field of oleo chemistry and safety. In this work, the cis-trans isomerization of unsaturated fatty acids in edible oils has been successfully developed using simple and cheap p-toluenesulfinic acid as catalyst. The effects of reaction time, temperature, catalyst loading, and the amounts of water and antioxidants on the cis-trans isomerization have been systematically investigated. The results indicate that the amount of water (0-20 wt %) and antioxidants (0-200 mg/kg) had no significant effect on this cis-trans isomerization of unsaturated fatty acids in edible oils. The final products (trans fats) from the cis-trans isomerization reaction were characterized by both GC and React IR. The yield of trans double bonds from the isomerized fat can reach 79.6% after heating at 100 oC for 90 min without changing either the location of the double bonds or the degree of unsaturation. In addition, this convenient method has been applied to various vegetable oils (e.g., olive oil, camellia seed oil, corn oil, sesame oil, sunflower oil and soybean oil) and nearly 80.0% yields of TFA were generated, which shows a promising method to provide trans-fat products for research related to oleo and food chemistry. [ABSTRACT FROM AUTHOR]

[Display omitted] • Redox non-innocence of metalated azoheteroarenes. • Varying strategies for the sequential azo reductions including its scission. • Catalytic activity by virtue of reversible electron storage feature of the azo core. • Light induced E - Z isomerism and application potential towards molecular materials. • A brief overview of synthetic methodologies and bio-relevance of azoaromatics. Reversible electron reservoir feature of redox non-innocent ligand is an important event from the broader perspectives of metal–ligand cooperativity in catalysis as well as in introducing the molecular bistability. In this context, facile reductions of the metal bound azo core ([-N N-]0 → [-NN-] −→[-N N-]2−) of azoheteroarenes such as 2,2′-azobis(pyridine), 2,2′-azobis(benzazole), azo-pincers as well as four-electron reduction mediated cleavage of the azo bond ([-N N-]0 + 4e−→2[=N-]2−) to form metal-imido fragment have been highlighted. Structural authentication of the redox states of azo core under selective coordination situations and their application towards aerobic alcohol oxidation and cycloaddition reactions have been reviewed. It also elaborates strategies towards multi-electron reductions and scission of azoaromatics via (i) metal-to-ligand charge transfer (MLCT) induced inner-sphere electron transfer, (ii) metathesis reaction pathway, where metal–metal bond breaking delivers electrons to the empty π*, σ* orbitals of the azo function, and (iii) synergism of metal with other reducing agent. An account for the synthetic methodologies of azoaromatics and its light triggered cis – trans isomerization including application potential to molecular materials and biological processes have been addressed. [ABSTRACT FROM AUTHOR]

The regularity of cis - trans isomerization of unsaturated fatty acids in camellia oil under heating was revealed adopting fatty acid profile evolution coupled with reaction kinetics. The temperatures of generating mono-trans linoleic acids (C18:2-9c12t and C18:2-9t12c) and linolelaidic acid (C18:2-9t12t) were at 220 °C and 280 °C respectively, both of which were significantly higher than that of elaidic acid (180 °C). And the total trans fatty acids (TFAs) content was increased with the elevating of heating temperature. Furthermore, the reaction rate constants (k) of cis - trans isomerization were observed according to the rate equations. In accordance with the k , the activation energy (Ea) of the cis - trans isomerization was calculated referring to the Arrhenius equation, the Ea of generating elaidic, mono-trans linoleic and linolelaidic acids reactions were 97.22 kJ/mol, 127.4 kJ/mol and 112.6 kJ/mol, respectively. These results indicated that oleic acid is more prone to be converted into trans isomer than linoleic acid, the mono-trans linoleic acids are the precursors of linolelaidic acid in heat-induced camellia oil. This study provides a reference for the potential inhibition of TFAs formation during camellia oil processing. [Display omitted] • The kinetic technique was adopted to reveal the cis -trans isomerization of unsaturated fatty acids. • The oleic acid is more prone to be converted into trans isomer than linoleic acid. • Mono-trans linoleic acids are the precursors of linolelaidic acid. [ABSTRACT FROM AUTHOR]

The synthesis of a covalently bonded new photoresponsive molecular capsule formed from two resorcin[4]arene cavitands by fourfold ether linkages using azobenzene subunits is reported. The new molecular capsule undergoes trans to cis isomerization upon irradiation with 365 nm light and can be reversed back from cis to trans form by means of exposure to visible light (530 nm) in benzene solution. The photo-switchable behaviour was also investigated by 1 H NMR spectroscopy which further substantiated the UV–vis experiment. The quantum chemical calculations both at PM6 as well as at the DFT (B97-D) level of approximation for various stereoisomers starting from all- trans to all- cis indicated an increasing flexibility of these molecular capsules. [ABSTRACT FROM AUTHOR]

The mechanism associated with the cis- to trans-photoisomerization of Ru(II)(2,2’-bipyridine)2(H2O)2 ([Ru(bpy)2(H2O)2]2+) complex in water has been examined using photoacoustic calorimetry (PAC) and density functional theory (DFT). Photolysis of the cis-[Ru(bpy)2(H2O)2]2+ complex results in a ΔH of -27 ±5 kcal mol–1 and ΔV of 0.1±2 mL mol–1. The DFT calculations give a ΔEcis-trans of +12 kcal mol–1, indicating that the observed ΔH contains significant contributions from changes in solvation. The DFT analysis of putative intermediates [Ru(bpy)2(H2O)]2+ and [Ru(bpy)2(H2O)3]2+ suggests the possibility of an associative mechanism for the isomerization process. [ABSTRACT FROM AUTHOR]

Lowering the activation energy of a chemical reaction is an essential part in controlling chemical reactions. By attaching a single electron, a barrierless path for the cis- trans isomerization of maleonitrile on the anionic surface is formed. The anionic activation can be applied in both reaction directions, yielding the desired isomer. We identify the microscopic mechanism that leads to the formation of the barrierless route for the electron-induced isomerization. The generalization to other chemical reactions is discussed. [ABSTRACT FROM AUTHOR]

The distribution and use of nanoparticles increased rapidly during the last years, while the knowledge about mode of action, ecological tolerance and biodegradability of these chemicals is still insufficient. The effect of silver nanoparticles (Ag NP) and free silver ions (Ag+, Ag NO3) on Pseudomonas putida mt-2 as one of the best described bacterial strains for stress response were investigated. The effective concentration ( EC50) causing 50% growth inhibition for Ag NP was about 250 mg L−1, whereas this was only 0.175 mg L−1 for Ag NO3. However, when calculating the amount of free silver ions released from Ag NP both tested compounds showed very similar results. Therefore, the antibacterial activity of Ag NP can be explained and reduced, respectively, to the amount of silver ions released from the nanoparticles. Both tested compounds showed a strong activation of the unique membrane adaptive response of Pseudomonas strains, the cis-trans isomerization of unsaturated fatty acids, whereas another important adaptive response of these bacteria, changes in cell surface hydrophobicity, measured as water contact angle, was not activated. These results are important informations for the estimation of environmental tolerance of newly developed, active ingredients like silver nanoparticles. [ABSTRACT FROM AUTHOR]

Highlights: [•] Synthesis of new photochromic pyrrolidene imines. [•] Photoisomerization of the C N double bond. [•] Thermal cis–trans re-isomerization in few seconds at room temperature [Copyright &y& Elsevier]

The ungerade vibrational levels of the 1Au (S1-trans) state of C2H2 lying in the region 45,800–46,550 cm−1 have been assigned from IR–UV double resonance spectra. The aim has been to classify the complete manifold of S1-trans levels in this region, so as to facilitate the assignment of the bands of S1-cis C2H2. The rotational structure is complicated because of the overlapping of vibrational polyads with different Coriolis and Darling–Dennison parameters, but assignments have been possible with the help of predictions based on the properties of polyads at lower energy. An important result is that the analysis of the (1141, 1161) polyad determines the anharmonicity constants x 14 and x 16, which will be needed to proceed to higher energies. Some regions of impressive complexity occur. Among these is the band given by the 3361, K = 1 state at 45,945 cm−1, where a three-level interaction within the S1 state is confused by triplet perturbations. Several probable S1-cis states have been observed, including cis-62, K = 1; this vibrational level appears to show a K-staggering, of the type that arises when quantum mechanical tunnelling through the barrier to cis-trans isomerization is possible. The total number of identified cis vibrational states is now 6 out of an expected 10 up to the energies discussed in this paper. [ABSTRACT FROM AUTHOR]

We review our comprehensive investigation of light self-localization phenomena in planarly configured azobenzene liquid crystals. Cis-trans isomerization of azobenzene molecules and related changes in the order parameter of the liquid crystals support a high nonlinear response and the formation of optical spatial solitons at microwatt excitations. We describe bright soliton angular steering, deflection, interleaving and merging, as well as dark solitons. [ABSTRACT FROM AUTHOR]

Abstract: DFT at B3LYP/6-31G(d,p) and B3LYP/6-311+G(d,p) levels calculations for the pyridine- and 4,4′-bipyridine-catalyzed isomerization of maleic acid demonstrated that the mechanism involves four steps: (1) a proton transfer from one of maleic acid carboxyl groups onto the amine nitrogen (pyridine or 4,4′-bipyridine) to yield an ion pair INT1. (2) Proton transfer from INT1 to the C–C double bond to give INT2. (3) Rotation about the central C–C single bond followed by proton abstraction by an amine molecule to yield INT3, and (4) proton transfer from the ammonium cation into the carboxylate anion of the fumarate thus formed to furnish the trans isomer, fumaric acid. Moreover, the calculations revealed that an abstraction of a proton from INT2 (step 3) was found to be the rate limiting step. However, the activation energy difference between steps 2 and 3 was not significant. Furthermore, it was found that the solvent dielectric constant has a profound impact on both the isomerization activation energy and the free energy difference between the cis and trans isomers (maleic and fumaric acids). While, polar solvents such as DMSO tend to lower the isomerization activation energy and to increase the free energy difference between the two isomers, apolar solvents such as chloroform behave in an opposite manner. In addition, linear correlation was found between the activation energy and the solvent dielectric constant. [ABSTRACT FROM AUTHOR]

Abstract: The cis to trans isomerizations during the syntheses of trans-[Ru(NO)(OH)(cyclam)](PF6)2, from cis-[RuCl2(cyclam)]Cl, and [Ru(NO)Cl(cyclam)] (PF6)2, from cis-[RuCl2(dmso)4], are reported. The novel trans-[Ru(NO)(OH)(cyclam)](PF6)2 complex was characterized by X-ray crystallography and vibrational infrared and nuclear magnetic resonance spectroscopies. The Ru–N–O bond angle (176.75º) and ν(NO) (1835cm−1) suggest a nitrosonium character for this hydroxo complex. The crystal and molecular structure of trans-[Ru(NO)Cl(cyclam)](ClO4)2·2 H2O is also reported. Results presented here support the cis–trans isomerization observed for the first time with ruthenium cyclam complexes. [Copyright &y& Elsevier]

Abstract: Photoswitchable hydrotropic solubilization has been investigated by cis–trans isomerization about the olefinic bond of sodium cinnamate (Na-CIN) for various solutes such as cinnamic acid, aspartic acid, curcumin, thymol, and benzocaine. The extent and rate of isomerization depend on the concentration of Na-CIN and temperature. The cis–trans isomerization of Na-CIN by UV irradiation allows recovery of the solute from aqueous Na-CIN solutions, without dilution by water. Extraction of forskolin and curcumin from coleus forskholii and curcuma longa, was also studied for recovery under UV irradiation. [Copyright &y& Elsevier]

Abstract: The main objective of this study was to investigate the amine-catalyzed isomerization of dimethyl maleate into dimethyl fumarate in order to utilize the former as a prodrug for the latter. Mechanistic study of this reaction using DFT at B3LYP/6-31G(d,p) level revealed that the reaction is first order in dimethyl maleate, second order in the amine, and overall third order. Moreover, the calculations revealed the existence of a linear correlation between the basicity of the amine catalyst and the isomerization rate. [Copyright &y& Elsevier]

Abstract: We propose a new scheme of the photoactivation and the photobleaching for Dronpa with molecular dynamics method and density functional theory. These processes can be explained by considering cis-trans isomerization in neutral state of chromophore. The proton transfer from anionic to neutral chromophore makes cis-trans isomerization possible via hula-twist rotation process, since the space for cis-trans isomerization is opened at around the region near chromophore by moving out of the imidazole ring on H193 from the position below the phenol ring on chromophore. Then the cis-trans isomerization can occur through the hula-twist process. The contributions from the protein environment around CRO, especially S142 and H193, are indispensable for photoconversion of Dronpa. [Copyright &y& Elsevier]

Abstract: The structure, energies, electronic spectra and thermal trans–cis isomerization of azobenzene (AB) attached non-covalently to the sidewall of CNT(8,8) were calculated using the ONIOM(B3LYP/6–31 + G*:UFF) level of theory. We found that some subtle differences existed between the structures of the attached AB and the isolated one. The combination of AB and CNT(8,8) favored in energy because of their negative interaction energies. The attached trans-AB (TAB) was more stable than the physisorbed cis-AB (CAB). The electronic spectrum calculations showed that the absorption wavelengths of the attached CAB were red-shifted for the lowest three singlet states. The trans–cis isomerization process of the AB attached non-covalently to the CNT(8,8) involved mainly the bending of CNN angle. The π–π interaction between AB and CNT(8,8) was found to restrain the trans-to-cis isomerization of AB, but had little influence on the cis-to-trans backward reaction. [ABSTRACT FROM AUTHOR]

Abstract: The development of a rapid and selective capillary electrophoresis method for the quantitation of ramipril and its eight main impurities in pharmaceutical dosage form is described. Ramipril and three of its impurities contain a proline-similar moiety which causes in solution the presence of interconverting cis–trans isomers with respect to the amide bond. The interplay between electrophoretic migration and isomerization may yield the presence of an undesired interconversion zone between the two isomer peaks in the electropherogram, depending on the experimental conditions. Different capillary electrophoresis operative modes and pseudostationary phases were evaluated, both in normal and reverse polarity, in order to find the essential analytical parameters which could make it possible to overcome this issue and thus accurately quantify the analytes. The best results were obtained by using microemulsion electrokinetic chromatography in reverse polarity, where all the compounds which undergo cis–trans interconversion migrate as a single narrow peak. Experimental design led to identification of the following optimised conditions: background electrolyte, microemulsion made by 88.95% of 90mM phosphate pH 2.5, 1.05% of n-heptane and 10.00% of SDS/n-butanol in 1:2 ratio; voltage, −26kV; temperature, 17°C. Applying these conditions, the baseline separation of the analytes was obtained in about 10min. Validation of the method following ICH guidelines was carried out and the procedure was applied to a real sample of ramipril tablets. [Copyright &y& Elsevier]

Abstract: The electronic ground state potential surface of acetylene (Hh name="tbnd" />Cminimum at the linear conformation, but the excited electronic states may have potential minima at a variety of nonlinear equilibrium shapes. This work is concerned with the group theoretical ideas necessary to treat simultaneously the symmetry properties of rovibronic states associated with three different planar acetylene equilibrium configurations, namely trans bent acetylene, cis bent acetylene, and vinylidene (H2Cke use of three different kinds of groups: (i) point groups, (ii) permutation-inversion (PI) groups, and (iii) extended PI groups. The PI group is G4 or G 8, depending on whether Ceaking is impossible (no bent acetylene↔vinylidene interconversion) or possible. The extended PI groups are and , respectively, when the only large amplitude motions are the CCH bends at each end of the molecule, and and , respectively, when internal rotation is added as a third large amplitude motion. Applied to acetylene, the results indicate that there will be no splittings of the rovibronic levels unless CH bond breaking occurs. Even without bond breaking, however, states of the cis and trans isomers just below their interconversion barrier will show “staggerings” in their K-structures, i.e., a given vibrational level will have three tunneling components at slightly different energies: one component will have levels with K =4n only (where n is an integer), a second component will have levels with K =4n +2 only, and the third will have only odd-K levels. New experimental results for the S1–cis electronic state of acetylene are reviewed, and are found to be consistent with the group theory in so far as comparison is possible. [Copyright &y& Elsevier]

Abstract: Well-defined platinum-based catalysts were prepared using fourth-generation hydroxyl-terminated poly(amidoamine) (PAMAM) dendrimers as templates. Nanoparticles with an average of 40 Pt atoms and an average diameter of 1.5nm were produced this way, and dispersed on a homemade sol–gel silica support. Different treatments were tested for the activation of the resulting catalyst, including heating in vacuum or in oxygen or hydrogen atmospheres. A combination of electron microscopy, infrared absorption spectroscopy, X-ray photoelectron spectroscopy, and catalytic kinetic measurements were used to investigate the effect of those treatments on the decomposition and elimination of the material associated with the dendrimer and on the activity and selectivity of the resulting catalysts. Neither heating in vacuum nor burning with oxygen was deemed acceptable, because much graphitic material is deposited with the former treatment and metal oxidation is induced by the latter. Hydrogen pretreatments, on the other hand, lead to fairly active catalysts with high selectivity for the conversion of trans olefins to their cis counterparts. [ABSTRACT FROM AUTHOR]

Abstract: The pH influence on the cis–trans isomerization of the Valine-Proline dipeptide was investigated by means of NMR spectral techniques and quantum chemical calculations at different computational levels. It was found that the process of isomerization is strongly pH dependent. The trans-isomer of Val-Pro is the more abundant isomer when the amino group is protonated, while an approximately equal distribution between the cis and trans-isomers for the neutral and anion forms of the dipeptide was confirmed. [Copyright &y& Elsevier]

Abstract: The selective isomerization of cis-1,2-diphenylsulfonyl ethylene to trans-1,2-diphenylsulfonyl ethylene proceeded in supercritical carbon dioxide above 393K without an addition of catalyst. The product yield increased with increasing temperature and was almost constant against carbon dioxide density. The 73% of product yield was obtained at 493K and 10MPa of carbon dioxide pressure for 60min. The product yield obtained in supercritical carbon dioxide was larger than those obtained in organic solvents. The supercritical carbon dioxide was a dilute solvent compared with organic solvent, which probably reduced the suppression of the reaction by dense solvent. Further, only cis-sulfonyl ethylenes isomerized among several cis-ethylene derivatives. The sulfonyl group played an important role for the isomerization. [Copyright &y& Elsevier]

With the ultraviolet-visible spectrophotometry and electronic structure calculations, we have investigated the effects of photo-irradiation on the optical properties and electronic structures of an azo-containing banana-shaped liquid crystal. The synthesized compound exhibits two optical absorptions at about 275 and 360 nm, respectively. Our electronic structure calculations reveal that the two absorptions can be attributed to the π→σ* and π→π* transitions in the azo-chromophores of the banana-shaped liquid crystal. Our results have demonstrated that photo-dissociation takes place predominantly when dilute tetrahydrofuran solution of the azo-containing liquid crystal is exposed to the 365 nm irradiation despite tran-to-cis photochemical isomerization is observed. [ABSTRACT FROM AUTHOR]

Abstract: The isomerization of methyl cis-9-octadecenoate (cis isomer) to methyl trans-9-octadecenoate (trans isomer) was studied in the presence of CoSn/ZnO catalysts under hydrogen pressure. The cis–trans isomerization of methyl cis-9-octadecenoate over a CoSn/ZnO catalysts prepared by co-impregnation, was strongly influenced by the nature of the catalytic sites. The support ZnO did not favour this reaction but the hydrogen played an important role since it influenced the relative amount of different cobalt species. In fact cobalt-containing sites (zerovalent species as well as cobalt oxides) predominated over these reactions. The tin species, which acted as a cobalt modifier for the preferential adsorption of the carbonyl group, inhibited the isomerization of the olefinic bond. Such changes could have also been due to a significant diminution of the cobalt content at the catalyst surface especially for a bulk Sn/Co>1. Consequently, the active sites for the cis–trans isomerization reaction should be cobalt species. [Copyright &y& Elsevier]

It has long been understood that the proline residue has lower configurational entropy than any other amino acid residue due to pyrrolidine ring hindrance. The peptide bond between proline and its preceding amino acid (Xaa-Pro) typically exists as a mixture of cis- and trans-isomers in the unfolded protein. Cis–trans isomerization of Xaa-Pro peptide bonds are infrequent, but still occur in folded proteins. Therefore, the effects of the cis–trans isomerization equilibrium in both unfolded and folded states should be taken into account when estimating the stability contribution of a specific proline residue. In order to study the stability contribution of the four proline residues to the hyperthermophilic protein Ssh10b, in this work, we expressed and purified a series of Pro→Ala mutants of Ssh10b, and performed correlative unfolding experiments in detail. We proposed a new unfolding model including proline isomerization. The model predicts that the contribution of a proline residue to protein stability is associated with the thermodynamic equilibrium between cis- and trans-isomers both in the unfolded and folded states, agreeing well with the experimental results. [ABSTRACT FROM AUTHOR]

The conformational study on N-methoxycarbonyl-L-proline-N′-methylamide (Moc-Pro-NHMe, prolylcarbamate) is carried out using ab initio HF and density functional B3LYP methods with the self-consistent reaction field method in the gas phase and in solution (chloroform, acetonitrile, and water). The replacement of the N-acetyl group by the N-methoxycarbonyl group results in the changes in conformational preferences, populations for backbone and prolyl puckering, and barriers to cis-trans isomerization of the prolyl residue in the gas phase and in solution, although there are small changes in the geometry of the prolyl peptide bond and the torsion angles of backbone and prolyl ring. The cis population increases with the increase of solvent polarity, as found for Ac-Pro-NHMe (prolylamide), but it is amplified by 9% in the gas phase and about 17% in solution for prolylcarbamate compared with those for prolylamide. It is found that the cis-trans isomerization for prolylcarbamate proceeds through the clockwise rotation with ω′ ≈ +120° about the prolyl peptide bond in the gas phase and in solution, as found for prolylamide. However, the rotational barriers to the cis-trans isomerization for prolylcarbamate are calculated to be 3.7–4.7 kcal/mol lower than those of prolylamide in the gas phase and in solution, and are found to be less sensitive to the solvent polarity. The calculated rotational barriers for prolylcarbamate in chloroform and water are in good agreement with the observed values. The shorter hydrogen-bond distance between the prolyl nitrogen and the amide H (HNHMe) of the NHMe group, the decrease in electron overlap of the prolyl C&bond;N bond, and the favorable electrostatic interaction between the ester oxygen and the amide HNHMe for the transition state seem to play a role in lowering the rotational barrier of prolylcarbamate. The smaller molecular dipole moments of the ground- and transition-state structures for prolylcarbamate in the gas phase and in solution seem to be one of factors to make the rotational barrier less sensitive to the solvent polarity. As the solvent polarity increases (i.e., from the gas phase to chloroform to acetonitrile), the value of ΔH‡tc decreases and the magnitude of ΔS‡tc increases for prolylcarbamate, which results in a nearly constant value of the rotational barrier. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 [ABSTRACT FROM AUTHOR]

Abstract: Kinetic peculiarities of cis methyl oleate hydrogenation over Pd/C, Ru/C, Rh/C, Pt/C and Ir/C were studied. Liquid phase hydrogenation was carried out at temperature 298≤ T ≤373K and under hydrogen pressure within 1–10bar using n-octane as a solvent. GLC and FTIR techniques were employed to characterize the reaction products. The effects of the catalyst amount, cis methyl oleate concentration, reaction temperature, and hydrogen pressure on the rates of methyl oleate hydrogenation and cis-trans isomerization were investigated. A simple reaction scheme involving cis methyl oleate hydrogenation and cis-trans isomerization was proposed for kinetic modeling. A good agreement was obtained between the calculated kinetic curves and the experimental data for the isomerization and hydrogenation of methyl oleate. It was shown that the second-row metals (Ru, Rh, Pd) display high activity in isomerization whereas the third-row metals (Ir, Pt) exhibit minor activity. [Copyright &y& Elsevier]

Doping two alkali-metal atoms (Li and Na) into the saddle-shaped saddle[4]pyrrole forms four new two-alkali-metal-doped compounds with alkalide or electride characteristic. They are cis-LiNa(saddle[4]pyrrole) isomers 1(singlet) and 2(triplet), and trans-Li(saddle[4]pyrrole)Na isomers 3(singlet) and 4(triplet). The four structures with all-real frequencies are obtained at the density functional theory (DFT) B3LYP/6-311+G(d) level. All calculations of electric properties have been carried out at the second order Møller–Plesset perturbation theory (MP2) level. The order of the β0 values is 3.54 × 103 for trans- 4(triplet) <1.51 × 104 for cis- 1(singlet) <3.57 × 104 for cis- 2(triplet) <2.34 × 105 a.u. for trans- 3(singlet). The static first hyperpolarizability ( β0) depends on the cis– trans isomerization and spin multiplicity. The result demonstrates that the cis– trans isomerization and spin multiplicity controls of the second-order NLO response are possible. [ABSTRACT FROM AUTHOR]

Abstract: Silver modified Mg-Ni/diatomite materials with ratios of SiO2/Ni=1.07 and Mg/Ni=0.1, differing in Ag content (Ag/Ni=0.025 and 0.1) were prepared by the precipitation–deposition method. The effects of silver presence and content on the structure, morphology, texture and H2-adsorption capacity of the obtained precursors were studied by X-ray diffraction, scanning electron microscopy, Hg-porosimetry and H2-chemisorption techniques. The catalytic performance of the corresponding catalysts in the soybean oil hydrogenation was investigated. The increase of the silver loading resulted in the development of macroporosity and increase in the total sample porosity. The decrease of both H2-adsorption capacity and hydrogenation activity are related to the metallic silver covering and blocking effects on the Ni2+ species, thus hampering the access of hydrogen. The decrease of hydrogenation activity and favorable limiting of cis–trans isomerization on the silver modified catalyst are explained by Horiuti–Polanyi mechanism based on the assumption that hydrogenation and isomerization proceed at the same active metallic nickel sites via half-hydrogenated intermediates. It was shown that the adjustment of the catalyst composition by changing the content of silver modifier offers the possibility to control the total amount of solid fat content, stearic acid and detrimental trans fatty acids in the hydrogenated derivatives. The catalyst with higher silver content is proposed as a promising candidate for selective edible oil hydrogenation catalyst. [Copyright &y& Elsevier]

Abstract: Reaction of cis-4-cyclohexene-1,2-dicarboxylic acid with Ca(OH)2 and with BaCO3, under hydrothermal conditions, afforded two new metal dicarboxylates: (cis-4-cyclohexene-1,2-dicarboxylato)calcium(II), [CaC8H8O4] (1) and diaquabis(trans-cyclohex-4-ene-1-carboxylic-2-carboxylato)barium(II), [Ba(C8H9O4)2(OH2)2] (2). Compound (1) is monoclinic, P2 1 /c, with unit cell parameters a =12.6670(14), b =6.7548(7), c =9.5943(10)Å, β =104.108(3)°, V =796.16(15)Å3, Z =4. Compound (2) is orthorhombic, Cmc2 1 , a =28.633(8), b =9.036(3), c =7.438(2), V =1924.4(10)Å3, Z =4. It should be noted that a cis–trans isomerization occurred in the reaction with BaCO3, suggesting an influence of the metal atom in the reaction. [Copyright &y& Elsevier]

Abstract: Two members of the green fluorescent protein family, the purple asFP595 and yellow zFP538 proteins, are perspective fluorescent markers for use in multicolor imaging and resonance energy-transfer applications. We report the results of quantum based calculations of the solution pK a values for selected protonation sites of the denatured asFP595 and zFP538 chromophores in the trans- and cis-conformations in order to add in the interpretation of photo-physical properties of these proteins. The pK a values were determined from the theromodynamic cycle based on B3LYP/6-311++G(2df,2p) calculations of the gas phase free energies of the molecules and the B3LYP/6-311++G(d,p) calculations of solvation energies. The results show that the pK a’s of the protonation sites of the chromophore from asFP595 noticeably depend on the isomer conformation (cis- or trans-), while those of zFP538 are much less sensitive to isomerization. [Copyright &y& Elsevier]

Abstract: MoS2 prepared by thermal decomposition of ammonium tetrathiomolybdate in inert gas at temperatures up to 773 K was activated by treatments involving thermoevacuation at 723 K and/or reduction at 573 K. The effect of different activations on the activity in ethylene hydrogenation, cis–trans isomerization of 2-butene, and H2/D2 isotope exchange (all measured at temperatures around 473 K) was compared, taking into account the extent of Mo exposition as measured by oxygen chemisorption. It was found that activation had a widely varying impact on the test reactions, indicating that these proceed on sites with different numbers of vacancies. Hydrogenation activity was boosted by two orders of magnitude when reduction of the catalyst at 573 K was followed by thermoevacuation at 723 K, whereas this change was moderate with H2/D2 exchange and negative with cis–trans isomerization. For the latter reaction, mere thermoevacuation was a suitable activation, and the impact of subsequent catalyst reduction was negative, whereas appreciable activity in the former reactions was obtained only when thermoevacuation was combined with a subsequent reduction. The data suggest that all three reactions proceeded on different sites, probably 3 vacancies per Mo for olefin hydrogenation, 2 vacancies per Mo for H2/D2 exchange, and 1 vacancy per Mo for cis–trans isomerization, with the latter two reactions involving adjacent . Sites with greater Mo exposure than stated may be suitable for H2/D2 exchange but not for cis–trans isomerization. With increasing severity of the activation treatments, sites with a small number of vacancies appeared to combine and migrate toward the rims or to escape into the bulk. Therefore, very high hydrogenation activity may be seen on surfaces with an oxygen chemisorption capacity far from the maximum value occurring after less drastic treatments. Our findings imply that a combination of chemisorption studies with test reactions may be a valuable tool for surface characterization of sulfide catalysts. [Copyright &y& Elsevier]

Abstract: [Ru(HL)(PPh3)2Cl]Cl complexes have been obtained in which HL= N(4)-ortho (complex 1), N(4)-meta (complex 2) and N(4)-para-tolyl 2-acetylpyridine thiosemicarbazone (complex 3). NMR and electrochemical studies indicate that both cis and trans isomers exist in solution, and that the cis isomers are converted into the trans isomers with time. Crystal structure determination of (1) reveals that the trans isomer is formed in the solid state. [Copyright &y& Elsevier]

Abstract: Non-catalytic biodiesel production technologies from oils/fats in plants and animals have been developed in our laboratory employing supercritical methanol. Due to conditions in high temperature and high pressure of the supercritical fluid, thermal stability of fatty acid methyl esters and actual biodiesel prepared from various plant oils was studied in supercritical methanol over a range of its condition between 270°C/17MPa and 380°C/56MPa. In addition, the effect of thermal degradation on cold flow properties was studied. As a result, it was found that all fatty acid methyl esters including poly-unsaturated ones were stable at 270°C/17MPa, but at 350°C/43MPa, they were partly decomposed to reduce the yield with isomerization from cis-type to trans-type. These behaviors were also observed for actual biodiesel prepared from linseed oil, safflower oil, which are high in poly-unsaturated fatty acids. Cold flow properties of actual biodiesel, however, remained almost unchanged after supercritical methanol exposure at 270°C/17MPa and 350°C/43MPa. For the latter condition, however, poly-unsaturated fatty acids were sacrificed to be decomposed and reduced in yield. From these results, it was clarified that reaction temperature in supercritical methanol process should be lower than 300°C, preferably 270°C with a supercritical pressure higher than 8.09MPa, in terms of thermal stabilization for high-quality biodiesel production. [Copyright &y& Elsevier]