CC Double Bond Research Articles

A study on the severe crazing phenomenon of the PMMA canopy under prolonged exposure to tropical climates

The severe crazing occurred in the poly(methyl methacrylate), PMMA canopy of the light aircraft operated in the tropics for more than seven years. The crazing phenomenon was investigated to identify the root cause and the mechanism for the formation of the crazing. The crazing was characterized using optical microscopy, ultraviolet–visible spectroscopy (UV–VIS), attenuated total reflectance-fourier transform infrared (ATR-FTIR) technique, pyrolysis-gas chromatography mass spectrometry (Py-GCMS) together with thermo-gravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). In microscopic observation, most crazes were distributed horizontally rather than vertically from the front of the light aircraft. The horizontally crazed sizes in micrometers are much longer and wider than the vertically crazed sizes. The crazed width at the center region is much larger than that at both tips, showing the close relation with the crazing growth process. In the chemical analysis, the results showed that in the crazed regions ester pendant groups (COOCH3) and partial or continuous monomers [CH = C(CH3)COOCH3] from the main chain could be cleaved by chain scissions via photolysis. Thus, polymers with several types of CC double bonds, volatile monomers, and small amount of tertiary alcohols were produced. From these results, we suggested numerous voids (defects) by chain scissions in nanometers probably functioned as the initial points of crazing and crazes continued to grow symmetrically from the starting points to both tips in micrometers under the repeated action of thermal expansion and compression before rupture. These crazes proceeded in the same two aligned directions as the internal tension stress formed during the canopy manufacturing process. This study explains that the combined and synergistic interaction of crazing and environmental stress iteratively occurred on the outer surface of the PMMA canopy through prolonged exposure to tropical climates, finally resulting in the severe crazing.

Chemical analysis and identification the fluorophores of photoluminescent carbon dots beyond infrared and X-ray photoelectron energy spectra

Carbon dots or Carbon quantum dots (herein after abbreviated as CDs) with bight luminescence, derived from carbohydrates such as citric acid, glucose or sucrose, have been widely reported in recent publications. However, as to which functional groups and structures in CDs are responsible for luminescence, most explanations in current references are normally based on assumptions, instead of being convinced by the accurate information resting on experimental facts. Herein, we conducted an experimental study targeting at finding the fluorophores of CDs prepared from citric acid and glycine by fluorescent quenching. The experimental results revealed that the essence of fluorescence was manipulated by fluorophores of conjugated CC double bonds and aldehyde groups. The destruction of aldehyde groups or CC double bonds in the CDs led to a complete decay of luminescence. In addition, the results of this experiment were similar to those of CDs prepared from the sole citric acid, glucose or sucrose, which predicted the analogy of the CDs in chemical structures. Such information about fluorophore of CDs was valuable for further exploring more extensive application of CDs in sense technologies.

Hypochlorous acid initiated lipid chlorination at air-water interface

There has been a surge of interest in interfacial hypochlorous acid (HOCl) chemistry for indoor air quality and public health. Here we combined nanoelectrospray mass spectrometry (nESI-MS) and acoustic levitation (AL) techniques to study the chlorination chemistry of three model lipids (DPPE, POPG, DOPG) mediated by HOCl at the air-water interface of levitated water droplet. For DPPE with no CC double bonds, HOCl was insensitive to the alkane chains, and showed considerable delay directing to head amino groups compared to that in aqueous environment. Chlorination chemistry, for POPG and DOPG with CC double bonds, preferentially reacted with double bonds of one chain. The mechanism was discussed in light of these observations, and it is concluded that the increased hydrophilicity of the chlorinated chain disturbed the lipid packing and attracted it toward the water phase. In addition, the reaction rate constant and reactive uptake coefficient suggested that the chlorination of lipids exposed to HOCl at the air-water interface is likely to occur rapidly. These results gain the knowledge of HOCl mediated lipid interface reaction at the molecule level, and would better understand the adverse health effects associated with elevated indoor pollutants.

Visible-light promoted allylation of N-substituted tetrahydroisoquinoline using riboflavin tetra-acetate as photocatalyst

Riboflavin (RF) and relative derivatives are important coenzyme of some redox enzymes controlling the growing development of plants by harvesting light. The unique isoalloxazine structure unit with special photoredox capacity makes it applicable to induce single electron transfer (SET) oxidation of organic molecules. We report here that riboflavin tetra-acetate (RFTA) catalyzed the oxidation of N-phenyl tetrahydroisoquinoline to α-amino C-radical which subsequently undergoes radical type Michael addition to CC double bond of allylsulfone to access 1-allylated N-phenyl tetrahydroisoquinoline.

Selective ability of rat 7-Dehydrocholesterol reductase (DHCR7) to act on some 7-Dehydrocholesterol metabolites but not on lumisterol metabolites

7-Dehydrocholesterol reductase (DHCR7) catalyses the final step of cholesterol biosynthesis in the Kandutsch-Russel pathway, the reduction of 7-dehydrocholesterol (7DHC) to cholesterol. 7DHC can be acted on by a range of other enzymes including CYP27A1 and CYP11A1, as well as by UVB radiation, producing a number of derivatives including hydroxy-metabolites, some of which retain the C7-C8 double bond and are biologically active. These metabolites include lumisterol (L3) which is a stereoisomer of 7DHC produced in the skin by UVB radiation of 7DHC, as well as vitamin D3. The aim of this study was to test whether these metabolites could act as substrates or inhibitors of DHCR7 in rat liver microsomes. To initially screen the ability of these metabolites to interact with the active site of DHCR7, their ability to inhibit the conversion of ergosterol to brassicasterol was measured. Sterols that significantly inhibited this reaction included 7DHC (as expected), 20S(OH)7DHC, 27(OH)DHC, 8DHC, 20S(OH)L3 and 22(OH)L3 but not 7-dehydropregnenolone (7DHP), 25(OH)7DHC, L3 or vitamin D3 and its hydroxyderivatives. Sterols that inhibited ergosterol reduction were directly tested as substrates for DHCR7. 20S(OH)7DHC, 27(OH)DHC and 7-dehydrodesmosterol were confirmed to be substrates, giving the expected product with the C7-C8 double bond removed. No products were observed from 8DHC or 20S(OH)L3 indicating that these sterols are inhibitors and not substrates of DHCR7. The resistance of lumisterol and 7DHP to reduction by DHCR7 in cells will permit other enzymes to metabolise these sterols to their active forms retaining the C7-C8 double bond, conferring specificity to their biological actions.

Spirocyclizative Remote Arylcarboxylation of Nonactivated Arenes with CO 2 via Visible-Light-Induced Reductive Dearomatization

Spirocyclizative Remote Arylcarboxylation of Nonactivated Arenes with CO ₂ via Visible-Light-Induced Reductive Dearomatization

Piperlongumine Analogs Promote A549 Cell Apoptosis through Enhancing ROS Generation.

Chemotherapeutic agents, which contain the Michael acceptor, are potent anticancer molecules by promoting intracellular reactive oxygen species (ROS) generation. In this study, we synthesized a panel of PL (piperlongumine) analogs with chlorine attaching at C2 and an electron-withdrawing/electron-donating group attaching to the aromatic ring. The results displayed that the strong electrophilicity group at the C2–C3 double bond of PL analogs plays an important role in the cytotoxicity whereas the electric effect of substituents, which attached to the aromatic ring, partly contributed to the anticancer activity. Moreover, the protein containing sulfydryl or seleno, such as TrxR, could be irreversibly inhibited by the C2–C3 double bond of PL analogs, and boost intracellular ROS generation. Then, the ROS accumulation could disrupt the redox balance, induce lipid peroxidation, lead to the loss of MMP (Mitochondrial Membrane Potential), and ultimately result in cell cycle arrest and A549 cell line death. In conclusion, PL analogs could induce in vitro cancer apoptosis through the inhibition of TrxR and ROS accumulation.

Electrochemical sensor studies of dopamine using multiwalled carbon nanotubes by CVD technique

The synthesized Multiwall carbon nanotubes (MWCNTs) structural conformation studies were carried out using the powder X-ray diffraction. Plane 002 shows the crystallinity of graphite hexagonal carbon structure. The Fourier transform spectroscopy shows the presence of CC double bond which reveals the presence of MWCNTs. Morphology and Elemental analysis were studied by SEM-EDX analysis. HR-TEM and SAED pattern shows that the formation of MWCNTs and the same is matched with XRD pattern. In addition to that, the thermal stability of the MWCNTs was carried out using differential scanning calorimetry and thermo-gravimetric analysis. The UV–visible spectroscopy shows the strong absorption band at 357 nm and the corresponding energy band gap was found to be 3.34ev. In the present study the synthesized MWCNTs used as bare carbon paste electrode (BCPE) and modified carbon paste electrode (MCPE) to study the electrochemical biosensor behavior of dopamine (DA) using the cyclic voltammetric technique. DA represents the oxidation peak is 0.1009 V and 0.1049 V and also the reduction peak is 0.1470 V and 0.1522 V at the BCPE and MWCNT/MCPE. Hence the oxidation and reduction peak range of DA at the modified MWCNTs were significantly higher. The electron transfer reaction of DA is shown by the effect of scan rate and the concentration of dopamine. The modified electrode's stability was investigated with the outcomes indicating it is relatively stable. The developed sensor had a high level of sensitivity, stability, and reproducibility.

Discovering the role of substrate in aldehyde hydrogenation

In this manuscript, we investigated in detail one of the critical parameters that govern the reactivity of the carbonylic group toward hydrogenation and hydrodeoxygenation: the effect of the side chains of aldehydes. We observed that the presence of a π-electron conjugation on the side chains strongly affects the conversion of aldehydes to alcohols and hydrocarbons under the reaction conditions studied. In particular, the presence of a strong π-electron conjugation, such as the aromatic ring, enables the hydrogenation and further hydrodeoxygenation of the carbonylic group, while, on the other hand, molecules with no or weak π-electron conjugation (such as alkyl chains or single conjugated CC double bonds) remained inactive. These results were supported by adsorption analyses as well as theoretical models, which showed that differences in adsorption mode and strength between two model substrates (benzaldehyde and octanal) were not the decisive factors in the conversion of the carbonyl group.

Developing quantitative synthesis-structure-function relations for framework aluminum arrangement effects in zeolite acid catalysis

In this manuscript, we investigated in detail one of the critical parameters that govern the reactivity of the carbonylic group toward hydrogenation and hydrodeoxygenation: the effect of the side chains of aldehydes. We observed that the presence of a π-electron conjugation on the side chains strongly affects the conversion of aldehydes to alcohols and hydrocarbons under the reaction conditions studied. In particular, the presence of a strong π-electron conjugation, such as the aromatic ring, enables the hydrogenation and further hydrodeoxygenation of the carbonylic group, while, on the other hand, molecules with no or weak π-electron conjugation (such as alkyl chains or single conjugated CC double bonds) remained inactive. These results were supported by adsorption analyses as well as theoretical models, which showed that differences in adsorption mode and strength between two model substrates (benzaldehyde and octanal) were not the decisive factors in the conversion of the carbonyl group.

Metal-free C(sp2)-H perfluoroalkylsulfonylation and configuration inversion: Stereoselective synthesis of α-perfluoroalkylsulfonyl E-enaminones

The perfluoroalkylsulfonylation (CF3SO2, C2F5SO2 and CHF2SO2) in the enaminone CH bonds has been developed simply via the promotion of molecular iodine by using stable and cheap sodium perfluoroalkyl sulfinates as coupling partners. The stereoselective synthesis of E-configurated α-perfluoroalkylsulfonyl enaminones has been realized via unprecedented CH bond elaboration and CC double bond configuration inversion by free radical process.

Naturally-occurring spinosyn A and its derivatives function as argininosuccinate synthase activator and tumor inhibitor

Argininosuccinate synthase (ASS1) is a ubiquitous enzyme in mammals that catalyzes the formation of argininosuccinate from citrulline and aspartate. ASS1 genetic deficiency in patients leads to an autosomal recessive urea cycle disorder citrullinemia, while its somatic silence or down-regulation is very common in various human cancers. Here, we show that ASS1 functions as a tumor suppressor in breast cancer, and the pesticide spinosyn A (SPA) and its derivative LM-2I suppress breast tumor cell proliferation and growth by binding to and activating ASS1. The C13-C14 double bond in SPA and LM-2I while the Cys97 (C97) site in ASS1 are critical for the interaction between ASS1 and SPA or LM-2I. SPA and LM-2I treatment results in significant enhancement of ASS1 enzymatic activity in breast cancer cells, particularly in those cancer cells with low ASS1 expression, leading to reduced pyrimidine synthesis and consequently the inhibition of cancer cell proliferation. Thus, our results establish spinosyn A and its derivative LM-2I as potent ASS1 enzymatic activator and tumor inhibitor, which provides a therapeutic avenue for tumors with low ASS1 expression and for those non-tumor diseases caused by down-regulation of ASS1.

Pd catalysts supported on different hydrophilic or hydrophobic carbonaceous substrate for furfural and 5-(hydroxymethyl)-furfural hydrogenation in water

We hydrogenated furfural and 5-(hydroxymethyl)furfural (HMF) in water in a reaction catalyzed by Pd nanoparticles on carbonaceous materials with different morphology and hydrophobic degree. The different Pd catalysts were prepared by dipping the carbonaceous material into a Pd0 micro-emulsion. The catalyst support affected the catalytic hydrogenation of furfural and HMF. By using micrometric active carbon (AC) combined with cup-stacked carbon nanotubes (CSCNTs) and Pd0/2+ nanoparticles (Pd), we obtained a micro/nanostructured material designated Pd/CSCNT-AC, which performed better than the other carbonaceous materials containing similar Pd nanoparticle loading. Pd/CSCNT-AC produced tetrahydrofurfuryl alcohol from furfural with excellent selectivity (>99 %). Unlike Pd on hybrophobic spheroid graphite or hydrophilic AC, Pd/CSCNT-AC hydrogenated both the CO and CC double bonds of furfural and catalyzed HMF hydrogenation at the CO double bond more selectively: between 85 % and 99 % selectivity toward 2,5-dihydroxymethylfuran. We also investigated how temperature, hydrogen pressure, and reaction time affected HMF hydrogenation in water. Finally, Pd/CSCNT-AC was recycled several times without significant catalytic activity loss.

Asymmetric Total Synthesis of Phomarol

Asymmetric Total Synthesis of Phomarol

Kinetic stability and NBO analysis of the C20-nAln nanocages (n = 1–5) using DFT investigation

Following our quest for novel heterofullerenes, we have compared and contrasted substitution effects on C20-nAln structures with n = 1–5, from kinetically view point at density functional theory (DFT). Structures with the odd numbered heteroatom (C19Al1, C17Al3 and C15Al5) appear open shell singlet ground state while the even ones (C18Al2-a, C18Al2-b, C16Al4-a and C16Al4-b) show closed shell singlet ground state. The high NBO charge distribution on the surface of C15Al5 nanocage provokes the more investigation for hydrogen storage. The overall trend for kinetic stability based on their band gap (ΔEHOMO-LUMO) in eV is C15Al5 (3.36) > C20 (2.31) > C18Al2-a (2.25) > C17Al3 (1.96) ≥ C19Al1 (1.95) > C16Al4-b (1.86) > C16Al4-a (1.56) > C18Al2-b (1.03). Evidently, the C15Al5 heterofullerene is as the most kinetic stable species against electronic excitation from the occupied HOMO orbital to the corresponding unoccupied LUMO orbital and contains five aluminum atom alternatively in equatorial. Furthermore, C15Al5 displays the highest energy of HOMO (EHOMO = -0.23321 a.u.), the lowest energy of LUMO (ELUMO = -0.10981 a.u.), the lowest nucleophilicity (N = 3.11 eV), the lowest electrophilicity (ω = 3.24 eV), the highest hardness (η = 3.36 eV) and the lowest softness (S = 0.15 eV) among the scrutinized species. Isolation of the two Al substitutions from each other by means of strong CC double bonds, increases N (4.48 eV), ω (9.69 eV) making C18Al2-b as the most nucleophilic and electrophilic species.

Blue-light emitting aminated pectin for detecting Cu2+ ion

This research studied the chemo-sensing of low-cost aminated pectin (PE) obtained by a facile calcination under ammonia gas at temperature no higher than 175 °C without excessive use of alkaline, acid or solvents. The ammonia gas was found to replace the hydroxyl and methoxyl group, enhancing the crystallinity and solubility of the resultant pectin than those calcined in air or in 5% H2. Though the increase of light absorption could be attributed mainly to the dehydration during calcination which caused the formation of CC double bond or aromatic ring, the N incorporation could be important to the photoluminescence (PL) emission. The PL quenching of the blue fluorescent aminated pectin showed a good linearity with the concentration of Cu2+, Fe3+ and the highest sensitivity toward Cu2+ among the investigated metal ions. In order to further increase the PL quenching toward Cu2+ and decrease the interference of Fe3+, a method involving H2O2 and ultraviolet illumination was developed to catalyze the oxidation of fluorophores on the polymer. This work provides new horizon on the modification and application of pectin in chemosensing.

Discovery of an ene-reductase for initiating flavone and flavonol catabolism in gut bacteria

Gut microbial transformations of flavonoids, an enormous class of polyphenolic compounds abundant in plant-based diets, are closely associated with human health. However, the enzymes that initiate the gut microbial metabolism of flavones and flavonols, the two most abundant groups of flavonoids, as well as their underlying molecular mechanisms of action remain unclear. Here, we discovered a flavone reductase (FLR) from the gut bacterium, Flavonifractor plautii ATCC 49531 (originally assigned as Clostridium orbiscindens DSM 6740), which specifically catalyses the hydrogenation of the C2–C3 double bond of flavones/flavonols and initiates their metabolism as a key step. Crystal structure analysis revealed the molecular basis for the distinct catalytic property of FLR. Notably, FLR and its widespread homologues represent a class of ene-reductases that has not been previously identified. Genetic and biochemical analyses further indicated the importance of FLR in gut microbial consumption of dietary and medicinal flavonoids, providing broader insight into gut microbial xenobiotic transformations and possible guidance for personalized nutrition and medicine.

Effect of flavonoid structure and pH on iron-mediated pectin interaction

Flavonoids are polyphenolic natural compounds with suggested health-promoting properties and impact on sensory aspects. Processing, as well as mastication of plant-based food, can allow interactions between flavonoids and plant cell wall material (CWM). Pectin is a cell wall polysaccharide, present in all plant-based products, and used in a wide range of foods. Recently, a novel iron-mediated mechanism for pectin-flavonoid interactions was suggested. The current work aimed to study the impact of flavonoid structure and pH on the iron-mediated interaction by using 7 aglycones (belonging to the flavonol, flavanonol, and flavone sub-groups) differing by specific small structural moieties resulting in different binding sites. By using commercial water-soluble pectin from apple pomace and an identical (except a higher content of iron) iron enriched pectin, we have qualitatively and quantitatively presented the importance of the C2–C3 double bond for such interactions. Without such a bond the aglycones do not bind to the pectin, likely due to the loss of molecular planarity. This was studied using UV-VIS spectroscopy and membrane centrifugation. Also, the binding dissociation constants (Kd) of the flavonoids presenting a specific wavelength for the ternary complexes were determined using UV-VIS spectroscopy, showing that the lack of a hydroxyl group on C3 only slightly reduces the affinity (Kd increased from 13.4 × 10−6 M for quercetin to 29.2 × 10−6 M for luteolin), while a covalently bound disaccharide at this position practically nullifies the binding. pH 2.5 significantly reduced such binding while the difference between 4.5 and 6.5 was small and structure dependent.

Binuclear ethylenedithiolate iron carbonyls: A density functional theory study

The structures and energetics of the binuclear ethylenedithiolate iron carbonyls H2C2S2Fe2(CO)n (n = 8, 7, 6, 5, 4) have been studied using density functional theory. The experimental H2C2S2Fe2(CO)6 structure with the ethylenedithiolate ligand bridging the central Fe–Fe bond through both of its sulfur atoms but with an uncomplexed CC double bond is predicted to be the lowest energy structure by a margin of ∼10 kcal/mol. The lowest energy singlet pentacarbonyl H2C2S2Fe2(CO)5 structure can be derived from this hexacarbonyl structure by displacement of one of its CO groups through coordination of the ethylenedithiolate CC double bond. For the tetracarbonyl H2C2S2Fe2(CO)4 the lowest energy singlet structure has a central distorted bicapped tetrahedral Fe2C2S2 unit shown to be aromatic by a highly negative diatropic nucleus independent chemical shift (NICS) value. Low-energy triplet and quintet structures are also found for the pentacarbonyl and the tetracarbonyl, respectively. The calculated ΔE and ΔG values for CO dissociation of the carbonyl richer octacarbonyl and heptacarbonyl H2C2S2Fe2(CO)n (n = 8, 7) indicate them to be disfavored relative to formation of the hexacarbonyl H2C2S2Fe2(CO)6 by CO loss.

Reaction of enamines with semicarbazone-based amidoalkylating reagents: A straightforward synthesis of annulated 1-aminopyrimidin-2-one derivatives

An efficient synthesis of 1-arylideneamino-substituted hexahydro-1H-cyclopenta[d]pyrimidin-2-ones and octahydroquinazolin-2-ones has been developed. The synthesis involves a stereo- and regioselective cascade reaction of the corresponding 4-(tosylmethyl)semicarbazones with 1-morpholinocyclopentene or 1-morpholinocyclohexene to give predominantly bicyclic pyrimidines with an exocyclic CC double bond (80–97%). The later undergo rapid isomerization when heated in THF in the presence of TsOH to form bicyclic pyrimidines with a significant predominance of those with an endocyclic CC double bond (90–97%).