Polyene Structure Research Articles

Behavioral features of photostimulated processes in the heterogeneous composition of polymer–semiconductor–salt of a metal

In the current study experimental data about changes in the photosensitive composition consisting of polyvinyl alcohol, zinc oxide and bismuth chloride (PVA–ZnO–BiCl 3) under UV-irradiation are presented. There are both organic (PVA) and inorganic compounds of the named composition whose changes are determined. The main products of the photostimulated reactions are metal bismuth, bismuth oxide and polyene structures of various lengths in the form of a polyvinyl alcohol. In this research a heuristic scheme of photostimulated reactions in the photosensitive composition of PVA–ZnO–BiCl 3 and in similar compositions was suggested.

Thermal stability of the copolymers of silicon-containing arylacetylene resin and acetylene-functional benzoxazine

Acetylene-functional benzoxazine resin (AFBEN) was used to modify silicon-containing aryacetylene resin (SCAAR). The thermal stability, degradation and ablation mechanisms were investigated. Based on the results of Py/GC/MS methods, we concluded that the cross-linking reactions of poly(dimethylsilyleneethynylene–phenyleneethynylene)(DMSEPE, a class of SCAAR) were due to (1) the Diels–Alder reaction between Ph–C C and C C, (2) the ring trimerization of C C and (3) radical polymerization of C C to form polyene structure. During the curing of AFBEN, polyene was the main product of the polymerization of ethynyl in AFBEN and the activation of the para positions of the aniline ring increased due to the introduction of ethynyl. XRD and XPS results showed that SiO 2 and SiC formed on the surface of the composites in the process of ablation.

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.

Characterization of the poly(vinyl alcohol)/cellulose whisker gel spun fibers

The current work reports the preparation and characterization of the nanocomposites reinforced with highly oriented cellulose whiskers (CWs) in a polymer matrix. The nanocomposites were prepared using polyvinyl alcohol (PVA) and a stable suspension of CWs prepared from cotton. The macroscopically homogeneous PVA–CW suspensions were gel spun. The produced fibers exhibited a high orientation of CWs in a direction parallel to the fiber axis. A DSC study of the PVA–CW fibers showed no crystallization exotherm during cooling after PVA melting due to the transformation of PVA to a polyene structure caused by the surface sulfate groups of the CWs. Storage modulus (E′) of the composite fibers showed outstanding enhancement with increasing CW content, even with a small amount of CWs (5wt.% of solid PVA). This is attributed to the favorable interaction between PVA and the CWs through hydrogen bonding and effective stress transfer from PVA to the CWs.

Study of the influence of UV-irradiation on the photodegradation of plasticized poly(para-tert-butylstyrene) films

Abstract The photodegradation of thin films of poly(para-tert-butylstyrene) with 265 nm radiation in the presence of oxygen, and as a function of irradiation time, has been studied using fluorescence, Fourier transform-infrared spectroscopy, and ultraviolet-visible spectroscopy. The influence of phthalate and terephthalate plasticizers on photo-oxidative degradation was also investigated. Blending with phthalate plasticizers was found to cause a higher efficiency of degradation than that obtained for doping with terephthalate plasticizers. The intensity of absorption was also found to increase with time of irradiation and in the intensity of a new absorption band at longer wavelength, thus indicating a possibility of photodegradation of polymer films. The analysis of the Fourier transform-infrared spectra of the irradiated and non-irradiated samples showed an increase in the intensities of the carbonyl and hydroxyl regions of the Fourier transform-infrared spectra providing evidence for the photodegradation as well as the photo-oxidation of polymeric chains. The increase in the analyzed ranges is attributed to the formation of alcohols, aliphatic ketones and to the increase in the number of polyene structures that resulted from hydrogen abstraction during photodegradation reactions.

Polymerization of 1,2,4,5-tetramethylbenzene (durene) in direct-current discharge

Polymer films possessing dielectric properties were prepared from 1,2,4,5-tetramethylbenzene (durene) at the cathode in a dc discharge. The chemical structure of the films was studied by IR and UV spectroscopy. It was shown that the polymer synthesized from durene in a dc discharge contains basically polyene structures produced via the opening of aromatic rings.

Conjugated Molecules Described by a One-Dimensional Dirac Equation.

Starting from the Hückel Hamiltonian of conjugated hydrocarbon chains (ethylene, allyl radical, butadiene, pentadienyl radical, hexatriene, etc.), we perform a simple unitary transformation and obtain a Dirac matrix Hamiltonian. Thus already small molecules are described exactly in terms of a discrete Dirac equation, the continuum limit of which yields a one-dimensional Dirac Hamiltonian. Augmenting this Hamiltonian with specially adapted boundary conditions, we find that all the orbitals of the unsaturated hydrocarbon chains are reproduced by the continuous Dirac equation. However, only orbital energies close to the highest occupied molecular orbital/lowest unoccupied molecular orbital energy are accurately predicted by the Dirac equation. Since it is known that a continuous Dirac equation describes the electronic structure of graphene around the Fermi energy, our findings answer the question to what extent this peculiar electronic structure is already developed in small molecules containing a delocalized π-electron system. We illustrate how the electronic structure of small polyenes carries over to a certain class of rectangular graphene sheets and eventually to graphene itself. Thus the peculiar electronic structure of graphene extends to a large degree to the smallest unsaturated molecule (ethylene).

10.1007/s11449-008-1008-y

The behavior of the positions and shapes of the fluorescence bands of di-, tetra-, and hexamethine merocyanine dyes with 3H-indolyliden (dyes 1–3) and benzoimidazolyliden (dyes 4–6) as electron-donating substituents and malononitrile as an electron-accepting substituent is studied by the method of moments in solvents of different polarity. The solvatofluorochromic shifts have been found to be smaller than the solvatochromic shifts not only for negatively solvatochromic merocyanines 4–6, but also for dyes 1–3 whose solvatochromism is positive. For dyes 4–6, cases of a change of the sign of solvatofluorochromism with respect to the sign of solvatochromism are revealed. These nontrivial effects are accounted for by transitions between the polyene and polymethine electronic structures of merocyanines in the fluorescence state S 1 that occur with increasing medium polarity. In contrast to the absorption spectra of merocyanines 1–3, an increase in the chain length results in an increase in the vinylene shifts in the fluorescence spectra of these dyes, as well as in a decrease in the deviations and in the narrowing of the bands. This is explained by the fact that the electronic structure of these merocyanines in the S 1 state is closer to that of the ideal polymethine (the cyanine limit) than in the S 0 state. The fluorescence bands of merocyanines 4–6 are observed to be broader compared to the absorption bands. This broadening is caused by a change in the relation between intermolecular and vibronic interactions during absorption and emission of light. The interactions of these types have a decisive effect on the behavior of the Stokes shifts and fluorescence quantum yields of merocyanines 1–6.

Luminescence and color of radiation-modified polytetrafluoroethylene in blocks

Spectral-luminescent analysis has shown that γ-irradiation of bulky PTFE samples (blocks) in the range 330–340°C initiates generation of the same optical centers as in thin films. The irradiated samples become fluorescent and acquire a color ranging from light yellow to yellow. The spectral composition of fluorescence and the color of the samples depend on the absorbed dose and the irradiation temperature. The spectrum of fluorescence excited at a wavelength of 313 nm lies within 350–600 nm, and it is determined by various optical emitting centers. The fluorescence and color centers are distributed over the bulk of the samples in different ways. The concentration of optical centers in the near-surface layers of the samples (to a depth of 0.3–1.0 mm, depending on the sample) is higher than that in layers remote from the surface. In the latter layers, the spectral composition of fluorescence is primarily determined by shorter wavelength fluorescence centers. Almost no fluorescence is emitted from the central zone of the sample, and this zone is colorless. It is inferred that the nonuniform distribution of optical centers is related to the concentration gradient of molecular oxygen in the bulk of the samples appearing in the course of their radiation treatment (the inner layers are depleted of oxygen, while the surface layers are enriched in oxygen). New evidence is derived that polyene structures responsible for the fluorescent behavior and color of the modified PTFE are formed in main chains. The structure of these moieties is described by the structural formula ...CF2-(CF=CF)n-CF2, where ...n = 4–7.

Radiation-Induced Polymerization of Vinylidene Chloride in Bulk and Included in Thiourea Crystals

Vinylidene chloride (VDC) or 1,1-dichloroethylene was polymerized with γ radiation in bulk or as inclusion complex in thiourea crystals (inclusion polymerization). The resulting poly(vinylidenechloride) (PVDC) samples obtained from the two different polymerization techniques were characterized by FT-IR and electronic absorption spectroscopies, by ozonolysis and by thermal analysis (TGA, DTG and DTA). It was found that two selective secondary reactions occur in the two PVDC samples, respectively obtained from bulk polymerization or from inclusion polymerization. In the former case, the main reaction is only a crosslinking reaction, while in the latter case, with the PVDC included into the thiourea channels, the crosslinking reaction is fully inhibited and instead a dehydrohalogenation reaction takes place producing the polyene structures. The presence of polyene structures in the PVDC synthesized by the inclusion polymerization was demonstrated by electronic absorption spectroscopy and by ozonolysis experiments. The presence of polyene segments in the PVDC causes a reduction in the thermal stability of the polymer, lowers its melting point and reduces its crystallinity.

Synthesis and optical properties of water-soluble poly(vinylpyrrolidone) - modified fullerene C60

The effect of fullerene on the radical polymerization of N-vinylpyrrolidone with lauroyl peroxide in toluene was investigated kinetically. C60 was found to act both as inhibitor and as retarder because the polymerization rate and the molecular weight of resulting poly(vinylpyrrolidone) is decreasing with the increase of the fullerene concentration (0-6.94 x 10-4 mol l-1). The water-soluble poly(vinylpyrrolidone)-modified fullerene C60 compound was characterized by differential scanning calorimetric, Infrared and Raman spectroscopy, UV absorption and photoluminescence. Based on the results obtained by optical measurements, it is argued that by the covalent attachment of the polymeric radicals to fullerene cage the extended electronic conjugation system of the C60 is broken leading to the appearance of a polyene structure.

Electronic structure and fluorescent properties of malononitrile-based merocyanines with positive and negative solvatochromism

The behavior of the positions and shapes of the fluorescence bands of di-, tetra-, and hexamethine merocyanine dyes with 3H-indolyliden (dyes 1–3) and benzoimidazolyliden (dyes 4–6) as electron-donating substituents and malononitrile as an electron-accepting substituent is studied by the method of moments in solvents of different polarity. The solvatofluorochromic shifts have been found to be smaller than the solvatochromic shifts not only for negatively solvatochromic merocyanines 4–6, but also for dyes 1–3 whose solvatochromism is positive. For dyes 4–6, cases of a change of the sign of solvatofluorochromism with respect to the sign of solvatochromism are revealed. These nontrivial effects are accounted for by transitions between the polyene and polymethine electronic structures of merocyanines in the fluorescence state S1 that occur with increasing medium polarity. In contrast to the absorption spectra of merocyanines 1–3, an increase in the chain length results in an increase in the vinylene shifts in the fluorescence spectra of these dyes, as well as in a decrease in the deviations and in the narrowing of the bands. This is explained by the fact that the electronic structure of these merocyanines in the S1 state is closer to that of the ideal polymethine (the cyanine limit) than in the S0 state. The fluorescence bands of merocyanines 4–6 are observed to be broader compared to the absorption bands. This broadening is caused by a change in the relation between intermolecular and vibronic interactions during absorption and emission of light. The interactions of these types have a decisive effect on the behavior of the Stokes shifts and fluorescence quantum yields of merocyanines 1–6.

Amylosin from Bacillus amyloliquefaciens, a K + and Na + channel-forming toxic peptide containing a polyene structure

Bacillus amyloliquefaciens strains isolated from the indoor environment of moisture-damaged buildings produce a 1197 Da toxin, named amylosin. Nuclear magnetic resonance (NMR) data showed that amylosin contains a chromophoric polyene structure and the amino acids leucine/isoleucine, proline, aspartic acid/asparagine, glutamic acid/glutamine and tyrosine. A quantitation method for amylosin was developed using commercially available amphotericin B as a reference compound and a known concentration of amylosin determined by NMR with the electronic reference to access in vivo concentration (ERETIC) method. Purified amylosin inhibited motility of boar sperm cells at an exposure concentration of 135 nM and hyperpolarized their cell membrane and depolarized their mitochondria at exposure to concentration of 33–67 nM for 10 min. In a 3-d exposure time only 27 nM of amylosin was needed to provoke the same toxicity functions. Amylosin was cytotoxic to feline lung cells at concentrations of < 170 nM . Purified amylosin provoked adenosine 5′-triphosphate (ATP)-independent cation influx into isolated rat liver mitochondria (RLM), inducing swelling of the mitochondria at concentrations of 200 nM K + or >250 nM Na + medium. In the K + - or Na + -containing medium, amylosin uncoupled RLM, causing oxidation of pyridine nucleotides (PN), loss of the mitochondrial membrane potential, and suppressed ATP synthesis. Purified amylosin produced cation channels in black-lipid membranes (BLMs) with a selectivity K +>Na + at a concentration of 26 nM, i.e. the same concentration at which amylosin was toxic to boar sperm cells. The amylosin cation channels were cholesterol- and ATP-independent and more effective with K + than with Na +. We propose that the toxicity of amylosin may be due its ionophoric properties, representing the first K +/Na + channel-forming substance reported from B. amyloliquefaciens.

Crystallographic Analysis of Primary Visual Photochemistry

A curved retinal: Difference electron-density data between the photoreceptor protein rhodopsin and its primary photoreaction intermediate bathorhodopsin have provided a crystallographic model for the cis–trans isomerization of the chromophore retinal therein during the primary process in dim-light vision (see picture; the curved polyene structure of retinal in bathorhodopsin is shown in red, while that in rhodopsin is colored green).

The curing reactions of ethynyl-functional benzoxazine

The model compounds 3-(3-ethynyl-phenyl)-6-methyl-3,4-dihydro-2H-benzoxazine (EPMB) and 6-methyl-3-phenyl-3,4-dihydro-2H-benzoxazine (PMB) were synthesized and the influence of ethynyl group on the thermal cure reaction of benzoxazine compound was investigated. The bond parameters of benzoxazine ring calculated at the level of B3LYP/6-31G(d) showed that the variations of benzoxazine structures due to the introduction of ethynyl were negligible. The cure reaction of EPMB and PMB was studied by DSC and kinetic parameters were determined by an autocatalytic model. The results revealed that the apparent activation energy for cure reaction of EPMB was 103.90 kJ/mol which was lower than that of PMB (124.14 kJ/mol). The kinetic parameters of cure reactions of PMB and EPMB obtained by the Kissinger and Ozawa methods agreed well with the results by the autocatalytic model. The structures of the cured EPMB were characterized by 1H NMR and solid-state 13C NMR. The results showed there are polyene structures and hydrogen bonds in the cured EPMB.

DSC and FTIR study of the gamma radiation effect on cis-1,4-polyisoprene

The effect of γ-radiation on the cis-1,4-polyisoprene in the presence of oxygen is investigated by ATR-FTIR technique and non-isothermal DSC measurements. FTIR measurements have shown that the formation of hydroperoxides, ketones, alcohols and/or ethers is apparent already at lower, 20–50 kGy, doses of γ-radiation and it increases significantly with the exposure time. Besides, lactones, anhydrides, peresters, carboxylic acids, and esters are formed, too. Spectral changes in the region of C=C conjugated double bonds indicate a formation of shorter polyene structures and aromatic rings. Kinetic parameters describing the temperature dependence of the induction period have been obtained from DSC measurements using the isoconversional method. Residual stabilities have been calculated in order to characterize the gamma radiation effect on polyisoprene thermooxidative stability. Both methods proved that doses lower than 50 kGy do not cause severe changes in polymer properties.

Thermal analysis of 1,4‐di[n′‐(quinolyl)]buta‐1,3‐diynes, structure, and topo‐oligomerization: Polymerization of 3‐ethynylquinoline with the triethyl aluminum/vanadium 2,4‐pentanedionate catalyst system

AbstractConjugated 1,4‐bis(n′‐quinolyl)‐1,3‐butadiynes were obtained through the oxidative dimerization of the corresponding n′‐ethynylquinolines catalyzed by cuprous chloride. Differential scanning calorimetry analysis of the 1,4‐bis[n′‐(quinolyl)]buta‐1,3‐diyne molecules produced evidence of a syn–anti rotational equilibrium around the 1,3‐diyne axis and an irreversible transformation into a thermopolymer. The topo‐oligomerization of 1,4‐bis[3′‐(quinolyl)]buta‐1,3‐diyne, which took place by irradiation with sunlight, was investigated with matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. Accurate X‐ray molecular structure and refinement analysis of 1,4‐bis[3′‐(quinolyl)]buta‐1,3‐diyne was conducted. The molecular crystalline packing consisted of parallel arrays of two groups of centrosymmetric molecules (antirotamer) in a herringbone assemblage in the solid state. The polymerization of 3‐ethynylquinoline was carried out with the AlEt3/V(acac)3 system to produce a mixture of 1,2,4‐ and 1,3,5‐tris(3′‐quinolyl)benzene cyclotrimers and a trans–cisoid polyene structure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6031–6040, 2004

Change in Electronic Structure of Polyenes Due to Interaction with Polyacenes and with Graphitic Strips

Hartree−Fock calculations are first presented when a polyene is brought down parallel to the plane of some polyacenes and also, for one case, in a perpendicular orientation. Attention is given to the variation of (a) bond lengths and (b) the HOMO−LUMO energy gap. Following these numerical investigations on finite systems, some tight-binding models (Hückel-like) are worked out to illustrate the effects of different environments on the π-electron assembly in polyenes. Again the focal points are whether bond alternation is enhanced, or suppressed, and the consequences for the HOMO−LUMO energy gap. Some analytic progress proves possible for an infinite polyene chain interacting with (a) an infinite polyacene and (b) an infinite polyphenacene, when a “hopping” energy is used to couple the polyene with its “environment”. In the former model (a), with no HOMO−LUMO gap in the isolated infinite polyacene, a π−electron polyene gap is opened up. In model (b), a similar variation of the energy gap is found. For future studies, reference is finally made to experiments on the (polyene) chromophore in the retinal protein bacteriorhodopsin. The observed red shift needs mechanisms additional to those considered in the present study, and some suggestions are made here.

Synthesis of thermally crosslinkable fluorine‐containing poly(arylene ether ketone)s—II. Propargyl ether terminated poly(arylene ether ketone)s

AbstractNovel thermally crosslinkable fluorine‐containing poly(arylene ether ketone)s comprised of 2,3,5, 6‐tetrafluoro‐1,4‐phenylene moiety were synthesized by the termination of polymer chain ends with propargyl ether groups in order to improve solvent resistance. Crosslinking reaction occurred over 250°C through the formation of both chromen ring and polyene structure. This structure change brought about not only the outstanding solvent resistance but also the increase in glass transition temperature (Tg). The cured films also exhibited excellent thermal stability, transparency and hydrophobicity derived from fluorine atoms. Copyright © 2004 John Wiley &amp; Sons, Ltd.

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.