Ethylene Bridge Research Articles

A ratiometric emission NIR-fluorescent probe for sensing and imaging pH changes in live cells

A novel ratiometric emission NIR-fluorescence probe N,N-dimethyl-4-((1E, 3E)-4-(3,3-dimethyl-3H-indol-2-yl)buta-1,3-dienyl)benzenamine, namely, DIDBA, is facilely synthesized on the basis of ethylene bridging of indole derivatives and 4-(dimethylamino) cinnamaldehyde. The probe exhibits a remarkable NIR ratiometric fluorescence emission (F618nm/F697nm) characteristic with pKa 4.5, and the linear response over the pH range of 3.5–5.2. DIDBA also displays favorable features include large Stokes shift of 200 nm under acidic conditions, high sensitivity, good selectivity, fine photostability and reversibility. The probe has low cytotoxicity and excellent cell membrane permeability, and is applied successfully to visualize intracellular pH fluctuations in live cells without influence of autofluorescence and native cellular species in biological systems.

Trends in bond dissociation energies of brominated flame retardants from density functional theory

Bond dissociation enthalpies (BDEs) are computed using the Density Functional Theory (DFT) for a selected set of C–Br, C–O, and C–Br bonds susceptible to homolysis in the thermal degradation of four brominated flame retardants (BFRs): decabromo-diphenyl, decabromo-diphenylethane, 1,2-bis(2,4,6-tribromophenoxy)-ethane, and 3,4,5,6-tetrabromo-1,2-diethyl-phtalate. Based on BDEs computed at M06/cc-pVTZ level, choice based on a previous benchmark, we find debromination as the dominant decomposition pathway of brominated diphenyls and brominated phtalates, whereas scission to form brominated phenoxyls and benzyl radicals is preferred in aromatic BFRs containing ether and alkyl bridges, respectively. Trends in computed BDEs are rationalized in terms of (de)localization of spin density in the electronic structure of the resulting radicals.

Hybrid Disila-Crown Ethers as Hosts for Ammonium Cations: The O–Si–Si–O Linkage as an Acceptor for Hydrogen Bonding

Host-guest chemistry was performed with disilane-bearing crown ethers and the ammonium cation. Equimolar reactions of 1,2-disila[18]crown-6 (1) or 1,2-disila-benzo[18]crown-6 (2) and NH4PF6 in dichloromethane yielded the respective compounds [NH4(1,2-disila[18]crown-6)]PF6 (3) and [NH4(1,2-disila-benzo[18]crown-6)]PF6 (4). According to X-ray crystallographic, NMR, and IR experiments, the uncommon hydrogen bonding motif O(Si)∙∙∙H could be observed and the use of cooperative effects of ethylene and disilane bridges as an effective way to incorporate guest molecules was illustrated.

Oral delivery system enhanced the bioavailability of stilbenes: Resveratrol and pterostilbene.

Stilbenes are a large group of compounds with the C6 C2 C6 skeleton, in which two aromatic rings are connected by an ethylene bridge. Resveratrol and its structural analog, pterostilbene, are by far the two most widely researched stilbenes in terms of their beneficial bioactivities. However, the bioefficacy of these compounds is greatly reduced when consumed orally due to their poor aqueous solubility, which leads to poor bioavailability. To overcome the limitation, strategies improving their solubility, absorption, and systemic concentration were applied when designing a suitable edible delivery system. This review will summarize the findings from the studies evaluating the oral bioavailability of stilbenes with emphasize on the resveratrol and pterostilbene. It will also include the edible delivery systems currently available and their effect on the oral bioavailability. © 2018 BioFactors, 44(1):5-15, 2018.

A benzimidazole-based highly selective colorimetric and far-red fluorometric pH sensor for intracellular imaging

A turn-on fluorescent probe (E)-4-(2-(1H-benzo[d]imidazol-2-yl)vinyl)-N,N-diphenylaniline (BVD) was facilely synthesized via the ethylene bridging of triphenylamine and benzimidazole.

3-{(E)-[4-(4-Hy-droxy-3-meth-oxy-phen-yl)butan-2-yl-idene]amino}-1-phenyl-urea: crystal structure and Hirshfeld surface analysis.

Two independent mol-ecules (A and B) comprise the asymmetric unit of the title compound, C18H21N3O3. The urea moiety is disubstituted with one amine being linked to a phenyl ring, which is twisted out of the plane of the CN2O urea core [dihedral angles = 25.57 (11) (A) and 29.13 (10)° (B)]. The second amine is connected to an imine (E conformation), which is linked in turn to an ethane bridge that links a disubstituted benzene ring. Intra-molecular amine-N-H⋯N(imine) and hydroxyl-O-H⋯O(meth-oxy) hydrogen bonds close S(5) loops in each case. The mol-ecules have twisted conformations with the dihedral angles between the outer rings being 38.64 (81) (A) and 48.55 (7)° (B). In the crystal, amide-N-H⋯O(amide) hydrogen bonds link the mol-ecules A and B via an eight-membered {⋯HNCO}2 synthon. Further associations between mol-ecules, leading to supra-molecular layers in the ac plane, are hydrogen bonds of the type hydroxyl-O-H⋯N(imine) and phenyl-amine-N-H⋯O(meth-oxy). Connections between layers, leading to a three-dimensional architecture, comprise benzene-C-H⋯O(hy-droxy) inter-actions. A detailed analysis of the calculated Hirshfeld surfaces shows mol-ecules A and B participate in very similar inter-molecular inter-actions and that any variations relate to conformational differences between the mol-ecules.

Chiral ethylene-bridged flavinium salts: the stereoselectivity of flavin-10a-hydroperoxide formation and the effect of substitution on the photochemical properties

A series of chiral non-racemic N1,N10-ethylene bridged flavinium salts 4 was prepared using enantiomerically pure 2-substituted 2-aminoethanols (R = isopropyl, phenyl, benzyl, 4-methoxybenzyl, 4-benzyloxybenzyl) derived from amino acids as the sole source of chirality. The flavinium salts were shown to form 10a-hydroperoxy- and 10a-methoxy-adducts with moderate to high diastereoselectivity depending on the ethylene bridge substituent originating from the starting amino acid. High diastereoselectivities (dr values from 80:20 to >95:5) were observed for flavinium salts bearing benzyl substituents attached to the ethylene bridge. The benzyl group preferred the face-to-face (syn) orientation relative to the flavinium unit; thereby effectively preventing nucleophilic attack from one side. This conformation was found to be the most stable according to the DFT calculations. Consequently, the presence of benzyl groups causes intermolecular fluorescence quenching resulting in a significant decrease in the fluorescence quantum yield from 11% for 4a bearing an isopropyl substituent to 0.3% for 4c containing a benzyl group and to a value lower than 0.1% for the benzyloxybenzyl derivative 4e.

Micropore structure stabilization in organosilica membranes by gaseous catalyst post-treatment

A post-treatment involving repeated exposure to gaseous HCl alternated with heating is demonstrated to strongly accelerate the recently reported structural evolution in organically bridged silica networks. Films, powders and membranes derived from 1,2-bis(triethoxysilyl)ethane were exposed to in-situ synthesized HCl gas, alternated with heat treatments at 150–300°C in air or N2. The film thickness, network condensation, chemical integrity and micropore structure were monitored with X-ray reflectivity, 29Si direct-excitation magic-angle spinning nuclear magnetic resonance, Fourier-transform infrared spectroscopy and gas permeation. Treatment with HCl was found to predominantly catalyze hydrolysis, enabling network optimization via iterative bond breakage and reformation. Network shrinkage, widening or opening of the smallest pores and densification of the overall pore structure were accelerated while the ethylene bridges remained intact. The achieved acceleration of material evolution makes iterative hydrolysis and condensation a promising approach for increasing the long-term micropore stability of molecular sieving membranes.

Immunomodulatory Polyketides from a Phoma-like Fungus Isolated from a Soft Coral.

Fourteen new polyketides with a trans-fused decalin ring system, libertalides A-N (3-16), together with two known analogues, aspermytin A and its acetate (1, 2), were isolated from the fermentation extract of a coral-derived Libertasomyces sp. fungus. Their relative configurations were elucidated on the basis of detailed spectroscopic analysis, and the absolute configurations were determined by TDDFT-ECD and optical rotation (OR) calculations. The OR of 1 and 2 were found to have opposite signs in CH3CN and CHCl3, which was in agreement with the OR calculations producing alternating signs for the optical rotation depending on the applied conditions. Because the signs of the OR for 1 and 2 showed high solvent dependence, they may not be used alone to correlate the absolute configurations. Compound 16 displayed structural novelty characterized by an α-enol ether bridge conjugated with an aldehyde group. In in vitro immunomodulatory screening, compounds 1, 4, and 10 significantly induced the proliferation of CD3+ T cells, while compounds 2, 7, 11, and 14 significantly increased the CD4+/CD8+ ratio at 3 μM. A preliminary structure-activity analysis revealed a crucial role of Δ7 and a terminal OH group in the regulation of CD3+ T cell proliferation. This is the first report of immunoregulatory activity for metabolites of this kind.

Triaryl-Boron Functionalized Dinuclear Platinum Complexes Linked by Photoisomerizable Bpe Ligand: Luminescence and Isomerism.

We report herein a series of triarylboron-functionalized Pt(II) dinuclear complexes using a photoactive bis(4-pyridyl)ethylene (bpe) bridging unit. The new Pt(II) complexes display phosphorescence at both room temperature and 77 K. Depending on the conditions under which crystals of the complexes were grown, either the cis- or trans-isomers could be obtained. The trans and cis isomers were found to undergo light-induced isomerization in solution with the trans isomer being the dominant species.

Evaluation of the aqueous phototransformation routes of phenyl ethyl azolic fungicides by liquid chromatography accurate mass spectrometry

Similarities and differences among the phototransformation routes of four azolic fungicides (diniconazole, DIN, imazalil, IMA; penconazole, PEN; and propiconazole, PRO) in surface water aliquots are investigated. Selected compounds share a common chemical structure consisting on dichlorophenyl and azolic rings connected through an ethylene bridge, which is substituted with different functionalities. Liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) was employed as analytical technique to follow the time-course of precursor fungicides and to detect and to identify their photo-transformation products (TPs). Under solar light, the substituents linked to the ethylene chain controlled the stability of the fungicides. Whilst PEN and PRO remained stable, DIN and IMA showed moderate reactivities, with half-lives (t1/2) of 5.1 and 33.5h, respectively. When exposed to UV (254nm) radiation, all compounds were effectively degraded with t1/2 in the range from seconds to a few minutes. Dechlorination followed by intramolecular cyclization, between phenyl and azolic rings, was identified as a common phototransformation route under UV irradiation. Depending on the length and the kind of the functionalities attached to the ethylene bridge, additional cyclization reactions are also possible. In-silico toxicity predictions pointed out to dechlorinated tricyclic TPs as the most concerning ones, with predicted lethal concentrations (LC50) in the same range as the precursor fungicides.

Bromination/debromination-induced thermal crosslinking of 6FDA-Durene for aggressive gas separations

A new method for enhancing condensable gas-induced plasticization resistance of aromatic polyimides (PIs) as well as increasing the flux of gas penetrants with negligible selectivity loss was demonstrated via a so-called bromination/debromination-induced thermal crosslinking. Our newly developed crosslinking approach essentially loosened the polymeric chain packing of 6FDA-Durene PIs by forming ethylene crosslinking bonds, while retaining its rigid PI backbone. As the degree of crosslinking increased, the permeability increased with trivial selectivity loss. Notably, the 75% bromination/debromination-induced crosslinked PI membranes drastically improved CO2 and C3H6 permeabilities by as much as 157% and 172%, respectively, compared to those of the pristine-PI analogs due to the debromination-induced free volume enhancement, while maintaining good selectivity due to the crosslinked ethylene bridges. As a result, outstanding separation performances for CO2/N2, CO2/CH4 and C3H6/C3H8 gas pairs have been obtained, and most importantly, a high tolerance to CO2- or C3H6-induced plasticization was observed up to CO2 or C3H6 pressure of 24 and 10atm, respectively. Our current crosslinking approach can be extended to industrially attractive hollow fiber forms of various aromatic PIs for high plasticization resistance as well as high flux.

Two new algal bromophenols from Odonthalia corymbifera

Two new algal bromophenols, odonthalol and odonthadione, were isolated from the alga Odonthalia corymbifera. Odonthalol was determined as a trimer of brominated hydroxylated benzyl (BHB) units. Three units were connected via ether and methylene bridges. Odonthadione was identified as a hybrid compound of the BHB unit and a unique cyclopentenedione. The cyclopentenedione unit has not been reported from natural origin.

Proton-conducting phosphotungstic acid/sulfonated fluorinated block copolymer composite membrane for polymer electrolyte fuel cells with reduced hydrogen permeability

A sulfonated fluorinated block copolymer (SFBC) consisting of sulfone and ether bridges was synthesized via nucleophilic substitution polymerization, and then incorporated with 10, 20 or 30 wt% of phosphotungstic acid (PWA) using facile solution casting approach to fabricate composite membranes. The monomer sulfonation was carried out for SFBC to avoid the random sulfonation that can degrade the mechanical strength of polymer chains. A higher local concentration of acidic moieties within molecular frameworks of PWA and good mechanical properties allow for an unprecedented approach to tailor the proton conductivity as well as mechanical strength of composite membrane, as evidenced by alternating current (AC) impedance and dynamic mechanical (DMA) analyses. The surface morphological properties and roughness of membranes were investigated by field emission scanning electron microscope (FE-SEM) and atomic force microscope (AFM); the composite membranes exhibited even and denser dispersion of PWA in polymer matrix. Compared to pristine SFBC-50, the water uptake, hydrophilicity and ion exchange capacity of SFBC-50/PWA-X membranes were significantly improved. The peak proton conductivity of SFBC-50/PWA-30 membrane at 90 °C under 100% relative humidity (RH) is 105.22 mS/cm, which is 2.55 folds higher than that of pristine SFBC-50 (41.11 mS/cm) and 1.2 folds lower than that of Nafion-117 membrane (127.12 mS/cm). The peak power density delivered by the PEFC containing SFBC-50/PWA-30 membrane is 377.83 mW/cm2 at a load current of 864.29 mA/cm2 while operating the cell at 60 °C under 100% RH. In contrast, under identical condition, the pristine SFBC-50 membrane delivered the peak power density of 147.37 mW/cm2 at a load current of 353.52 mA/cm2, a 2.56-fold lower performance compared to composite membrane. Furthermore, composite membrane exhibited much lower H2 permeability compared to that of SFBC-50 and Nafion-117 membrane.

Hydrogen-Atom Transfer Oxidation with H2O2 Catalyzed by [FeII(1,2-bis(2,2'-bipyridyl-6-yl)ethane(H2O)2]2+: Likely Involvement of a (μ-Hydroxo)(μ-1,2-peroxo)diiron(III) Intermediate.

The iron(II) triflate complex (1) of 1,2-bis(2,2'-bipyridyl-6-yl)ethane, with two bipyridine moieties connected by an ethane bridge, was prepared. Addition of aqueous 30% H2O2 to an acetonitrile solution of 1 yielded 2, a green compound with λmax=710 nm. Moessbauer measurements on 2 showed a doublet with an isomer shift (δ) of 0.35 mm/s and a quadrupole splitting (ΔEQ) of 0.86 mm/s, indicative of an antiferromagnetically coupled diferric complex. Resonance Raman spectra showed peaks at 883, 556 and 451 cm-1 that downshifted to 832, 540 and 441 cm-1 when 1 was treated with H218O2. All the spectroscopic data support the initial formation of a (μ-hydroxo)(μ-1,2-peroxo)diiron(III) complex that oxidizes carbon-hydrogen bonds. At 0°C 2 reacted with cyclohexene to yield allylic oxidation products but not epoxide. Weak benzylic C-H bonds of alkylarenes were also oxidized. A plot of the logarithms of the second order rate constants versus the bond dissociation energies of the cleaved C-H bond showed an excellent linear correlation. Along with the observation that oxidation of the probe substrate 2,2-dimethyl-1-phenylpropan-1-ol yielded the corresponding ketone but no benzaldehyde, and the kinetic isotope effect, kH/kD , of 2.8 found for the oxidation of xanthene, the results support the hypothesis for a metal-based H-atom abstraction mechanism. Complex 2 is a rare example of a (μ-hydroxo)(μ-1,2-peroxo)diiron(III) complex that can elicit the oxidation of carbon-hydrogen bonds.

A Formal Total Synthesis of (+)‐Frondosin A

AbstractAn enantio‐ and stereoselective formal total synthesis of (+)‐frondosin A was accomplished through an oxidopyrylium‐ion‐mediated [5+2] cycloaddition reaction. The cycloaddition reaction provided not only an efficient way of constructing the frondosin skeleton but also facial discrimination through an ether bridge for complete control of relative stereochemistry of the substituents in frondosin A.

Aerobic Dimerization of Ethyl 4-Thienyl-3-ketobutanoate toward a Modifiable Photochromic Diarylethene Precursor.

A unique chemical transformation, the base-induced aerobic dimerization of ethyl 4-(2,5-dimethylthiophen-3-yl)-3-ketobutanoate leading to photochromic diarylethene with a 4-hydroxy-4-methylcyclopent-2-ene-1-one as an ethene bridge, is described. This compound is easily subjected to various chemical modifications and can be used as a new diarylethene precursor to produce photoactive compounds with desired properties and functions.

Electrode grafting by oxidation of an amine catalyzed by a ferrocenyl “antenna” through intramolecular electron transfer

Two aminoferrocene complexes were studied by electrochemical techniques. Molecules retain the redox properties of both ferrocene and amine groups, but fundamentally different behaviours were observed depending on whether the linker between the two redox end groups was saturated (ethyl bridge) or not (ethynyl bridge). The possibility of an intramolecular electron transfer from the amine to the ferricenium moiety through the π-conjugated linker was demonstrated and the ethynyl bridge is expected to have a dual effect by facilitating both the oxidation of the amine into the cation radical and the production of aminyl radical, due to its strong electron withdrawing effect. Because of this synergy of properties, grafting of the conjugated aminoferrocene complex can occur just by oxidizing the ferrocene group without the presence of a base in solution.

Chemical-structural properties of the coke produced by low temperature oxidation reactions during crude oil in-situ combustion

Chemical-structural properties of the coke produced by crude oil low temperature oxidation (LTO) reactions during in-situ combustion are still highly lacking due to the difficulty in coked sand characterization. This study proposed an experimental methodology to prepare the useful LTO coke with the chemical-structural properties studied using a combination of Energy-dispersive X-ray spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) techniques. The XRD and the HRTEM analyses showed the LTO coke mainly consisted of highly disorder amorphous structures with limited amount of poorly order ‘onion-like’ structures. The LTO coke was found to contain numerous oxygen functionalities and highly-substituted aromatic rings. The concentration of the carbonyl showed no significant decline with the LTO temperature increasing to 310°C. Nevertheless, the carbon structure with sp3-rich characteristics was found to selectively consumed by O2 to reduce the amount of coke deposition, and enriched the aromatic layer systems as inferred by Raman and FTIR analyses. There was a good agreement between the amount of the ‘onion-like’ structures viewed from HRTEM and the changes in the ether bridging groups. Additionally, the changes in the coke chemical-structural properties agreed with the measured coke reactivity by Thermogravimetric analyses.

Synthesis and cytotoxicity evaluation of A-ring derivatives of cycloartanone

Sixteen derivatives, eight of which are new compounds, were prepared from cycloartenone (1) and cycloartanone (2), and the cytotoxic activity of 14 of these compounds, together with 1 and 2, was evaluated against a panel of four cell lines. Compound 1 was obtained from the epiphyte plant Tillandsia tenuifolia collected at Salta, Argentina. Due to chemoselectivity and regioselectivity problems observed in the reactions of compound 1, this substance was hydrogenated to compound 2. The attempted transformations were focused on ring A of the cited triterpenes with the aim to verify previous structure-activity relationships obtained from related compounds. The cytotoxicity results of the derivatives showed that only the diosphenol 13 displayed significant activity against all the tested cell lines. These results show that an oxidized side chain, for example an ether bridge between the side chain and ring D, is necessary for the cytotoxic activity of cycloartane derivatives.