Conjugated Polyene Structure Research Articles

Plasticizing Effect of Camellia oleifera Seed-Oil-Based Plasticizer on PVC Material Modification

In this study, as the plasticizer, <i>Camellia oleifera</i> seed-oil-based cyclohexyl ester (COSOCE) was prepared by the reaction of cyclohexene oxide and refined <i>C. oleifera</i> seed oil (RCOSO) obtained by acidification hydrolysis after saponification. In addition, the structure of the target product was confirmed by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and Raman spectroscopy. COSOCE was used as plasticizer-modified polyvinyl chloride (PVC) membranes. The structure of the COSOCE-modified PVC membranes were characterized by Raman spectroscopy and scanning electron microscopy (SEM). The properties of the COSOCE-modified PVC membrane were characterized by contact angle measurements, universal testing machine, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The results revealed that (1) The COSOCE-modified PVC membranes exhibit a good microscopic morphology. Combined with energy-dispersive X-ray spectroscopy (EDS) and contact angle measurement results, the COSOCE-modified PVC membranes are confirmed to be a hydrophilic material. (2) The modified PVC membrane with 60% COSOCE exhibited the best mechanical properties. The tensile strength reached 23.56 ± 2.94 MPa. (3) COSOCE-modified PVC material exhibited better thermal stability, with a loss rate of less than 75% at the end of the first decomposition stage. Compared with that of the dioctyl-phthalate (DOP)-modified PVC membrane, the initial decomposition temperature of PVC was increased by 1.17°C–8.17°C, and the residual rate was increased by 0.67%–5.75%. The carbon–carbon double bond in the COSOCE molecular structure can remove the free radicals generated during the degradation of PVC material and slow down the decomposition rate of PVC. In addition, the double bond can be cross-linked partially with the PVC molecular chain containing the conjugated polyene structure, thereby increasing the movement resistance of the PVC molecular chain segment. Hence, COSOCE can replace DOP as a PVC plasticizer.

Effect of ambient atmosphere on the formation and evolution of conjugated structure of pre-oxidized polyacrylonitrile

The ambient atmosphere has the remarkable effect on the chemical reaction mechanism and the formation of characteristic chemical structures and conjugated structures for pre-oxidized polyacrylonitrile (PAN). In the present paper, fourier transform infrared spectroscopy (FT-IR) and ultraviolet visible spectroscopy (UV–vis) were used to characterize the variations of chemical reaction characteristic structures and conjugate structures of copolymerized PAN in nitrogen and air atmosphere, respectively. Combined with the multivariate reaction model proposed by the predecessors, it can be found that two main conjugated structures (conjugated polyene and conjugated aromatic heterocycle) formed during the pre-oxidation process of copolymerized PAN. In nitrogen atmosphere, the formed main structure units were the conjugated diene and conjugated double ring with 1–2 double bonds. By contrast, the formed main units in air were the conjugated diene and conjugated tricyclic with a double bond. During the whole pre-oxidation process, the maximum unit numbers of conjugated double bonds and conjugated rings were no more than four and six, respectively. Increasing the heat treatment temperature favored to form more conjugate structures than prolonging the heat treatment time. Furthermore, with the increase of heat treatment temperature or time in air, the main conjugate unit numbers had no obvious change, while the maximum unit numbers increased slightly. For the exposure in nitrogen atmosphere, the main conjugated polycyclic structure was transformed into conjugated tricyclic structure after the heat treatment at 250 °C for more than 3 h. In addition, when the heat treatment temperature and time were 280 °C for more than 4 h, the main conjugated polyene structure was transformed into conjugated triene, and the maximum conjugated unit numbers increased slightly.

THE CHEMISTRY AND BIOLOGY OF LYCOPENE : ANTIOXIDANT FOR HUMAN HEALTH

More than 600 carotenoids are known to be naturally occurring. These predominantly colourful molecules, found in plants, fungi and bacteria undergoing photosynthesis, are widespread in vegetables and fruits. Carotenoids are divided into two main groups. Of them, the highly unsaturated hydrocarbons consisting of lycopene, α-, β-, and γ-carotene build the first group, whereas xanthophylls, such as β-cryptoxanthin, lutein and zeaxanthin are considered as the second big carotenoid group. Lycopene, a representative of the hydrocarbon carotenoids with the molecular formula of C40H56, has an acyclic open-chain structure consisting of 13 double-bonds. Two of them are non-conjugated, whereas eleven are conjugated double bonds, thereby building a chromatophore. This distinctive conjugated polyene structure accounts for the ruby colour and the antioxidant properties of lycopene. It has a distinct lipophilic character, which makes it nearly insoluble in ethanol, methanol and water. Due to its acyclic structure and the absence of a β-ionone ring, there is no pro-vitamin A activity to be found in lycopene, which is the reason for its differing biochemistry, as compared to α- and β-carotene. Due to its polyene-structure, providing an electron-rich system, lycopene is an eligible target for electrophilic reagents. Thus, it shows an extreme reactivity towards oxygen and free radicals. Lycopene is known to be the most potent oxygen quenching reagent among carotenoids, and furthermore, it provides the ability to intervene in reactions initiated by free radicals, like OH−· or peroxy radicals. Its excellent anti-oxidant properties are most likely the basis for its preventive role towards cancer and other chronic diseases. However, the lycopene concentration in fresh fruits and vegetables shows a great variability, depending on seasonal environmental conditions, geographic location, climatic situation, species and maturity which may be taken as indices for the best sowing season, place, species/varieties to be planted and date/time of harvest. The vegetables and fruits thus obtained would be rich in lycopene content, which in turn would have a major beneficial impact on human health.

Carbon nanotubes stabilize poly(vinyl chloride) against thermal degradation

In this study, multiwalled carbon nanotubes (CNT), ball-milled CNT (bmCNT), and acid-treated CNT (CNT-COOH) were assessed as thermal stabilizers in poly(vinyl chloride) (PVC). Films of pure PVC, CNT/PVC, bmCNT/PVC, and CNT-COOH/PVC cast from tetrahydrofuran were subjected to thermal aging in N2 in a test tube submerged in an oil bath maintained at 180 °C for a certain time. FTIR and UV-Vis spectra and discoloration of aged PVC composites were investigated on the formation of conjugated polyene structure in PVC. The results found that all three types of CNT of small amounts (0.1 or 0.3 phr) could stabilize PVC against thermal degradation by retarding the rate of formation of a conjugated polyene structure, with the stabilizing efficacy in the order of bmCNT > CNT > CNT-COOH. Moreover, Congo red and dehydrochlorination (pH measurement) tests were investigated on the degradation of PVC to HCl during the thermal aging as a function of time, CNT type and content. Thermal degradations of PVC to HCl were promoted by all three types of CNT in the initial 30 min of aging but were clearly stabilized against degradation over prolonged aging (for instance, 120 min) by bmCNT followed by CNT-COOH, both exhibiting the optimal stabilizing efficacy at 1 phr. The bmCNT was the most effective thermal stabilizer among the three types of nanotubes studied in PVC to resist both its discoloration and degradation of HCl. This newly-developed PVC composite with CNT as an additive provides an efficient route towards the development of highly thermal-stabilized PVC.

UV-Visible Spectrophotometry for the Determination of Conjugated Polyene Structures of Poly(vinyl chloride) in 1,2-Dichloroethane

The article presents an improved UV-visible spectroscopic analysis to determine the types and contents of conjugated polyene structures in poly(vinyl chloride) (PVC) chains based on the derived formulas in 1,2-dichloroethane solution. Due to the restriction of delocalized π electrons by the interaction forces among PVC chains, the effect of concentration was investigated, and the best resolution was achieved when vinyl chloride structure unit concentration (Cvc) was 0.08 mol/L. Compared with the results of the film method, the solution method showed better resolution and lower deviation, especially for low contents of tetraene, pentaene, and hexaene in PVC chains.

Structural elucidation of palytoxin analogs produced by the dinoflagellate Ostreopsis ovata IK2 strain by complementary use of positive and negative ion liquid chromatography/quadrupole time‐of‐flight mass spectrometry

The ovatoxins are palytoxin analogs of a dinoflagellate origin implicated in human intoxication. The structures of ovatoxin-a, ovatoxin-d, and ovatoxin-e produced by the IK2 strain of Ostreopsis ovata collected in Japan were elucidated using liquid chromatography/quadrupole time-of-flight mass spectrometry (LC/QTOFMS). The novel structures and a new insight into the spectral data are presented. The structural elucidations were carried out by complementary use of positive and negative ion LC/QTOFMS. Ostreocin-D (C127H219N3O53), another palytoxin congener previously elucidated by negative fast-atom bombardment collision-induced tandem mass spectrometry (FAB CID MS/MS), was used as a reference. Positive ion spectra allowed deduction of hydroxyl positions based on the conjugated polyene structures produced, while the negative ion spectra allowed assignments of cleavage sites of C-C bonds. The analysis could be performed using a small sample without extensive purification. Ovatoxin-a IK2 (C129H223N3O52), ovatoxin-d IK2 (C129H223N3O53), and ovatoxin-e IK2 (C129H223N3O53) were tentatively assigned to 42-hydroxy-17,44,70-trideoxypalytoxin, 42-hydroxy-17,70-dideoxypalytoxin and 42,82-dihydroxy-17,44,70-trideoxypalytoxin, respectively. The wide applicability of the method was suggested.

Direct Synthesis of Nitriles from Alcohols with Trialkylsilyl Cyanide Using Brønsted Acid Montmorillonite Catalysts

We reported a simple protocol for nitrile synthesis by the direct cyanation of various secondary/tertiary benzylic and allylic alcohols with trialkylsilyl cyanide (TASCN) with moderate to excellent yields as well as high regioselectivities and turnover numbers/frequencies catalyzed by solid Brønsted acids of metal ion-exchanged montmorillonites (M-Mont; M = Sn and Ti). The easily prepared montmorillonites demonstrated a significant catalytic performance for the cyanation of various alcohols that is far superior to those by control catalysts, such as proton ion-exchanged zeolites, homogeneous Lewis acids, and homogeneous Brønsted acids. The water-tolerant character of the montmorillonites led to high catalytic activities, even in a crude solvent. In addition, they were easily recovered from the reaction mixtures by filtration and reused without any loss of activity. The corresponding trimethylsilyl (TMS) ethers of alcohols were also found transformable into the nitriles using TASCN in the presence of the montmorillonite catalysts. However, the conversions of alcohols with TASCN were faster than those of the corresponding TMS ethers with TASCN, indicating that the activity of the TMS ethers was lower than that of alcohols. It was determined that the cyanation of allylic alcohols having a conjugated polyene structure afforded a single isomer among the possible regioisomers. Interestingly, the use of tert-butyldimethylsilyl cyanide is superior in the cyanation of alcohols and their TMS ethers to that of TMSCN.

Analysis of Retinoids and Carotenoids: Problems Resolved and Unsolved

Progress in nutritional biochemistry has always depended on progress in analysis of nutrients. Animal growth assays were fundamentally important in the discovery and initial isolation of the fat-soluble vitamins. Chromatography, initially introduced by Tswett for separation of plant pigments (including carotenoids), quickly became indispensable for separation of carotenoids and vitamin A compounds; the early open-column methods were eventually superseded by more efficient HPLC techniques, and reversed-phase HPLC has become the current method of choice for analysis of retinoids and carotenoids in biological tissues. Detection and quantitation of retinoids and carotenoids most often has depended on their unparalleled spectral properties; the conjugated polyene structures of these compounds give them unique light absorption spectra and high molar absorptivities, and hence outstanding lower limits of detection. Other techniques, such as gas chromatography (GC) and mass spectroscopy (coupled with GC and HPLC), immunoassays, supercritical fluid chromatography, and capillary electrophoresis, have proven useful in certain applications. Analysis of retinoid-binding proteins has been mostly by conventional protein methods, although the fluorescence of the retinol ligand has been useful in some instances to provide a highly specific assay. Current challenges in retinoid and carotenoid analysis include the resolution of stereoisomers, and quantitation of these compounds at ultratrace levels in biological tissues. Possible new approaches include accelerator mass spectroscopy, and use of gene expression assays to assess vitamin A status.

Synthesis of 8,16-Ethanoretinals and Their Interactions with Apoprotein of Phoborhodopsin from Natronobacterium pharaonis

Several 8,16-Ethanoretinals 3 were synthesized from cyclohexanones. From the binding experiments of these analogs with apoprotein of phoborhodopsin, it was found that retinal was incorporated as 6s-trans conformation in the protein and the fine structure in absorption spectra of pigments were dependent on the coplanarity of the conjugated polyene structure in the chromophore. Keywords: ethanoretinal, retinal analog, phoborhodopsin, chromophore, s-trans conformation

Synthesis of a novel highly conjugated conducting polymer

The new conjugated polyacetylene derivative dehydrated poly(4-hydroxy-4-phenyl-1-butyne) [dehydrated poly(HPB)] was synthesized from poly(4-hydroxy-4-phenyl-1-butyne) [poly(HPB)], which was obtained by the polymerization of 4-hydroxy-4-phenyl-1-butyne. The resulting dehydrated poly(HPB) was soluble in common organic solvents. The dehydrated poly(HPB) was found to have extended conjugated polyene structure. The dehydrated poly(HPB) was thermally stable up to 300°C. The electrical conductivity of I 2 -doped dehydrated poly( HPB ) was 10 -2 S cm -1 .

Polymerization of 1-methoxy-1-ethynylcyclohexane by transition metal catalysts

The polymerization of 1-methoxy-1-ethynylcyclohexane (MEC) was carried out by various transition metal catalysts. The catalysts MoCl5, MoCl4, and WCl6 gave a relatively low yield of polymer (≤ 16%). The catalytic activity of Mo-based chloride catalyst was greater than that of W-based chloride catalyst. However, catalyst tungsten carbene complex (I) gave a larger molar mass and higher yield in the presence of a Lewis acid such as AlCl3 than in the absence of a Lewis acid. The activity of the tungsten carbene complex was obviously affected by Lewis acidity. The catalyst PdCl2 was a very effective catalyst for the present polymerization and gave polymers in a high yield. The structure of the resulting poly(MEC) was identified by various instrumental methods as a conjugated polyene structure having an α-methoxycyclohexyl substituent. The poly(MEC)s were mostly light-brown powders and completely soluble in various organic solvents such as tetrahydrofuran (THF), chloroform (CHCl3), ethylacetate, n-butylacetate, dimethylformamide, benzene, xylene, dimethylacetamide, 1,4-dioxane, pyridine, and 1-methyl-2-pyrrolidinone. Thermogravimetric analysis showed that the polymer started to lose mass at 125°C and that maximum decomposition occurred at 418°C. The x-ray diffraction diagram shows that poly(MEC) has an amorphous structure. © 1997 John Wiley & Sons, Inc.

Studies of the structure and thermal degradation of poly(vinyl chloride)—poly ( N-vinyl-2-pyrrolidone) blends by using Raman and FTIR emission spectroscopy

Poly(vinyl chloride) (PVC) is miscible with poly(vinyl pyrrolidone) (PVP) over the whole composition range. In this paper, we describe the specific interactions and degradation features in this blend system investigated by using Raman and Fourier transform infra-red (FTIR) emission spectroscopy. No appreciable hydrogen bonding between the amide groups in PVP and the αhydrogen in PVC is observed, but the presence of dipole-dipole interaction between C-Cl and OC leads to decreased association of PVP chains and good dispersion in PVC. Facile dehydrochlorination of PVC in the blends is promoted by PVP in that increasing the amount of PVP in the blends decreases the dehydrochlorination temperature. At elevated temperatures, there are longer sequences of polyene in the blend which are formed at lower temperatures than in PVC homopolymer. However, in the early stage of degradation, the polyene structures are developed in a more regular trans configuration, yielding significant amounts of poly(acetylene)-like structures before further degradation reactions occur. This seems to suggest that dehydrochlorination of PVC in blend systems might be controlled to give conjugated polyene structures with fewer defects.

Electrical conductivity of thermally degraded poly(vinyl chloride)–polyacrylonitrile blends

AbstractFinely powdered blends of poly(vinyl chloride) (PVC) and polyacrylonitrile (PAN) have been thermally degraded at 275°C for 24 h in an inert atmosphere to effect complete de‐hydrochlorination of PVC to a conjugated polyene structure and simultaneous internal polymerization of nitrile groups in PAN to a conjugated polyimine sequence. The room temperature d.c. conductivity of the degraded blends showed clear synergistic behavior. A maximum conductivity has been observed with a blend of 60 PAN/40 PVC which is about 4 orders of magnitude over the linearly weighted average conductivity of the individual degraded homopolymers. The results have been interpreted in terms of a possible donor‐acceptor interaction between the degraded homopolymers leading to mutual doping and, hence, an enhanced electrical conductivity. © 1995 John Wiley &amp; Sons, Inc.

Polymerization of Hydroxyalkylacetylenes by Transition Metal Catalysts

Abstract The polymerization of hydroxyalkylacetylenes [HC°C(CH2)n-OH, n = 1–4) was carried out with various transition metal catalysts. Mo-based catalysts and PdCl2 were very effective for the polymerization of hydroxyalkylacetylenes. The polymer yields generally decreased as the number of methylene units between the hydroxy and acetylene functional groups increased from 1 to 4. Polymer solubility increased as the number of methylene units increased. The resulting polymers had a conjugated polyene structure with linear hydroxyalkyl substituents. The resulting polymers were black or light-brown powders. The thermal properties were studied by thermogravimetric analysis. X-ray diffraction analysis data indicated that the polymers are mostly amorphous.

Polymerization of 1-Ethynyl-1-Cyclohexanol by Transition Metal Catalysts

Abstract The polymerization of 1-ethynyl-l-cyclohexanol (ECHO) was carried out by various transition metal catalysts. The Mo- and W-based catalysts gave a relatively low yield of polymer (≤32%). The catalytic activity of Mo-based catalysts was greater than that of W-based catalysts. PdCl2 was a very effective catalyst for the present polymerization and gave a high yield of polymer. (Ph3P)2PdCl2 and PtCl2 were also found to be effective catalysts. The structure of the resulting poly(ECHO) was identified by various instrumental methods as a conjugated polyene structure having an α-hydroxycyclohexyl substituent. The poly(ECHO)s were mostly light-brown powders and completely soluble in various organic solvents such as chloroform, chlorobenzene, benzene, DMSO, and THF. Thermal and morphological properties were also studied.

Dehydrochlorination of Poly(vinyl chloride) in Isotactic Systems

The dehydrochlorination of isotactic, low-molecular-weight models of PVC, dimers to pentamers, was studied using the semiempirical MNDO method. The results obtained lead to the conclusion that the thermal dehydrochlorination of PVC can occur through either a radical or an ionic mechanism, depending on the reaction conditions. The arising conjugated polyene structures do not grow by the generally accepted "zip" mechanism, but rather through the "alternating growth" mechanism. A comparison was also made to the reactivity of isotactic and syndiotactic sequences from the point of view of kinetic and thermodynamic factors. It follows from the computations that the splitting off of the first HCl molecule is easier in the isotactic sequence, but that subsequent growth of the polyene chain occurs more readily in syndiotactic systems.

Peroxyl-Radical Reaction of Retinyl Acetate in Solution

Retinyl acetate suppressed the free radical-induced oxidation of methyl linoleate. Retinyl acetate was reacted with an alkylperoxyl radical in two solvent systems, methanol and benzene. The alkylperoxyl radical was generated by the thermal decomposition of a free radical initiator, 2,2′-azobis(2,4-dimethylvaleronitrile), at 37°C. The reaction products were isolated by HPLC and their structures were identified. The main product in methanol was 14-hydroxy-13-methoxyretinyl acetate in addition to some minor products. The reaction in benzene gave some products with low yields. They were 5,6-epoxyretinyl acetate, 11,14-epoxyretinyl acetate, and 5,6,11,14-diepoxyretinyl acetate. The results indicate that retinyl acetate is capable of scavenging peroxyl radicals by its conjugated polyene structure.

Structural study of polyacrylonitrile fibers during oxidative thermal degradation by pyrolysis-gas chromatography, solid-state carbon-13 NMR, and Fourier-transform infrared spectroscopy

The main stabilization mechanism of the PAN fibers to form cyclic ladder structures was confirmed by PyGC, 13 C NMR, and FT-IR. Furthermore, the contribution of dehydrogenation and/or dehydrocyanide reactions to form conjugated polyene structures suggested by the data of PyGC, especially for the PAN fibers stabilized at relatively higher temperatures, was also supported by those of 13 C NMR and FT-IR

Polymerization of 1‐aryl‐2‐trimethylsilylacetylenes by transition metal catalysts(II)

AbstractPolymerization of 1‐aryl‐2‐trimethylsilylacetylene (aryl = thienyl, furyl, and pyridyl) was carried out by transition metal catalysts. The polymer yield was generally low due to the steric hindrance. R4Sn (R = Me, n‐Bu, Ph) exhibits some cocatalytic activities with respect to polymer yield and molecular weight. On the other hand, the polymerization was decelerated when organoaluminum compounds were used as cocatalysts. The polymer yield increased in the following order: phenyl &gt; thienyl &gt; furyl &gt; pyridyl, according to the aryl substituents. The NMR (1H‐ and 13C‐), IR, and UV‐visible spectra indicated that the resulting polymers have a linear conjugated polyene structure each containing the aromatic substituent and trimethylsilyl group. From 1H‐NMR integration, it was found that the resulting polymers are partially desilylated depending on the substituents of monomer and the polymerization conditions. The solubility behavior, stability and fluoride‐ion induced desilylation reaction of the polymers were also studied.

Spectral differences in photodegraded polystyrene in various solvents

During ultra-violet irradiation of polystyrene in solution in cyclohexane, dichloromethane or chloroform, yellowing of the dissolved polymer occurs. Ultra-violet/visible absorption and fluorescence emission spectra show some spectral differences but in general they support the formation of conjugated polyene structures, which are probably formed by the same mechanism independent of type of solvent and/or the presence of oxygen.