Lignin Chemistry: Biosynthetic Study and Structural Characterisation of Coniferyl Alcohol Oligomers Formed In Vitro in a Micellar Environment

Model coniferyl alcohol lignin (the so‐called dehydrogenative polymerisate, DHP) was produced in water under homogeneous conditions guaranteed by the presence of a micellised cationic surfactant. A complete study of the activity of the enzymatic system peroxidase/H₂O₂ under our reaction conditions was reported and all the reaction products up to the pentamer were characterised by ¹H NMR spectroscopy and ESI mass spectrometry. Our system, and the molecules that have been generated in it, represent a closer mimicry of the natural microenvironment since an enzyme, under micellar conditions, reproduces the cell system better than in buffer alone. On the basis of the oligomers structures a new biosynthetic perspective was proposed that focused attention on a coniferyl alcohol dimeric quinone methide as the key intermediate of the reaction. A formal, strictly alternate sequence of a radical and an ionic step underlines the reaction, thus generating ordered oligolignols structures. Alternatively to other model lignins, our olignols present a lower degree of radical coupling between oligomeric units. This offers a closer biosynthetic situation to the observation of a low rate of radical generation in the cell wall.     

Photochemical isomers of tropolone alkaloids

This review, which covers the literature up to 1989, generalizes advances in the field of the study of the photochemical isomers of colchicine and tropolone alkaloids related to it. Information is given on their natural sources, methods of isolation, structure, and configuration, and photochemical and thermal interconversions. Characteristics distinguishing them from the topolone alkaloids in their UV, IR, mass, and²H and¹³C NMR spectra of the photochemical isomers are pointed out.Deceased.Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 147–165, March–April, 1990.     

Photocrosslinking of poly(methyl acrylate)s containing the 1,3-dioxolane structure as a pendant group

(2-Ethyl-2-methyl-1,3-dioxolan-4-yl)methyl- and (2-methyl-2-phenyl-1,3-dioxolan-4-yl) methyl acrylates were synthesized and polymerized. The photochemical behavior of the resulting polymers was investigated to determine whether the polymers pending on the 1,3-dioxolane structure were readily crosslinked with ultraviolet (UV) irradiation. The degree of crosslinking was estimated by the weight-loss method by immersion in acetone, with the result that the polymer with an aromatic substituent was more photocrosslinkable than the polymer that bore the aliphatic substituent. The catalytic effect on photocrosslinking of polymers was also studied by using benzoin and cobalt naphthenate. The infrared (IR) spectra of polymers irradiated in air that showed the new band at 3450 cm^?1 were attributed to a hydroxyl group; however, the spectra of polymers irradiated in vacuum displayed little absorption at 3450 cm^?1. To explain the mechanism of crosslinking model compounds were prepared and irradiated with UV light. It was concluded that crosslinking proceeds mainly from the fission of the 1,3-dioxolane ring and the coupling of the yielding radicals, together with autooxidation by atmospheric oxygen.     

Reaction of poly(vinyl alcohol) with superoxide anion

Reaction of pol(vinyl alcohol) (PVA) with superoxide anion was carried out in a dimethyl sulfoxide solution at 40°C under nitrogen and changes in the yield of recovered polymer, molecular weight, and chemical structure were examined. Appreciable decreases in the yield of recovered polymer and molecular weight were observed during the reaction, which indicated that a main chain scission of the polymer had occurred. Residual acetyl groups identified by the absorption peaks at ca. 1720 and 1250 cm^?1 in infrared (IR) spectra were removed rapidly and β-diketone groups identified by the peaks at ca. 1640 and 1560 cm^?1 in IR spectra and at ca. 255 nm in ultraviolet (UV) spectra were formed during the reaction. Formation of carboxylate groups was also assumed. The reaction mechanism was discussed on the basis of the results obtained.     

Enzymatic Preparation of Coniferaldehyde from Coniferyl Benzoate ex. Siam Benzoin

Siam benzoin is a natural resin that contains up to 65% of coniferyl benzoate. Treatment of this material with an esterase followed by an alcohol dehydrogenase in a one-pot procedure gave 1.5 g/L coniferaldehyde in 36% molar yield. Several lipases and esterases were tested, but only pig liver esterase gave significant results. Various alcohol oxidases and alcohol dehydrogenases were screened for their ability to oxidize coniferyl alcohol to coniferaldehyde. Horse liver alcohol dehydrogenase coupled with a cofactor regeneration system was the most efficient of the enzymes tested.     

Photochemical and photophysical properties of three carbon-bridged fullerene dimers: C121 (I, II, III)

The photochemical and photophysical properties of the three C121 isomers (I, II, III) were investigated with MADLI-TOF-MS, UV-vis spectra, fluorescence spectra, absorption spectra of their DMA complexes, and theoretical calculations. The three isomers of C121 (I, II, III) have different stabilities under laser irradiation, but isomer I and isomer II show good stability against the heat-induced conversion between different isomers: No conversion between the isomers was found after heating the mixture of isomer I and isomer II at 353 K for 12 h in Ar atmosphere. The results of UV-vis absorption and fluorescence spectra indicate that interactions between two C60 moieties of C60=C=C60 in the ground and singlet states are not significant, C121 (I, II, III) behaves as an electron-acceptor similar to C60. These indicate that the formation of the fullerene chain structure (e.g., C60=C=C60) does not disturb the photochemical and photophysical properties of the C60 monomer itself, even that the properties were enhanced by the formation of the polymer. This is significant for the C60 polymer in photochemical or photoelectronic applications in which C60=C=C60 can be an excellent basic unit of polymers.     

Vibrational spectra and noncovalent interactions of carbohydrates molecules

The differences between the vibrational spectra of carbohydrates of the same chemical structure caused by the noncovalent intra- and intermolecular interactions have been systematized. In the general case, these differences show up as the following specific features of changes in the bond intensities: change in the intensity ratio of closely spaced bands (IR and Raman spectra); selective change (increase, decrease) in intensities of individual bands (IR and Raman spectra); change (increase, decrease) in intensities of practically all bands (IR and Raman spectra); appearance of strong bands in the region of low frequencies from 50 to 200 cm⁻¹ (Raman spectra); appearance of strong diffuse bands in the low-frequency range with a simultaneous great reduction in the other bands (practical disappearance of the majority of bands) (Raman Spectra). The causes of such a kind of changes in the band intensities in the vibrational spectra of carbohydrates are discussed.     

Laser Raman spectroscopy of polyacrylamide

The Raman spectra of polyacrylamide and its covalently crosslinked gel (with N,N′-methylenebis-acrylamide as the crosslinking agent) in the region of 200–3600 cm^?1 are discussed. The vibrational band assignments for polyacrylamide are made on the basis of a comparison with the spectra of acrylamide, acrylic acid, polyacrylic acid, poly(vinyl alcohol), and other vinyl polymers. The Raman spectra of polyacrylamide in the solid phase and in aqueous solution have similar spectral features. The Raman spectra of gels with low crosslink content and of polyacrylamide in aqueous solution are comparable except that one new band, predominantly due to the residual monomer, appears in the gel phase. An analysis based on polarized Raman, infrared and NMR spectra, model building, and group theoretical calculations suggests a structure dominated by isotactic species.     

Studies of reactions with polymers. V. The reaction mechanism and resultant structure of PVA with PAN in DMSO without any catalyst

The reaction of polyacrylonitrile with poly(vinyl alcohol) in dimethyl sulfoxide without any catalyst was studied, and it showed that the adjacent nitrile groups on polyacrylonitrile could be linked up to form conjugated carbon-nitrogen sequence by the presence of poly(vinyl alcohol). However, no such reaction occurred when poly(vinyl alcohol) was replaced by i-propanol or poly(vinyl alcohol) graft copolymers. The structure of the resulting polymers were proposed by means of IR, UV, ¹H, and ¹³C-NMR spectroscopies. On the basis of the results, the effect of polymer feed and polymerization condition on this reaction were discussed. The compositions were determined by elemental analysis. The viscosity and thermal analysis of the products were also determined. At feed weight ratios of poly(vinyl alcohol) to polyacrylonitrile above one-half, gels were obtained.     

Photochemical construction of nanoporous polymer microspheres in Cu/Cu2O nanoparticle suspensions

Taking the poly(styrene-co-acrylamide) (P(St-AM)) as a model material, a novel two-step photochemical method was introduced to construct nanoporous polymer microspheres at room temperature. Under ultraviolet light irradiation, suspensions composed of Cu/Cu₂O nanoparticles were first prepared in an alcohol solution of acetylacetonate and benzophenone. Subsequently, the monomers were photopolymerized around the nanoparticles in the suspension-added precursor solution to form polymer–nanoparticle composite microspheres. Nanoporous polymer microspheres could then be obtained by removing the particles with acid. The products had been investigated by XRD, SEM, TEM, IR, DSC, and BET. Results showed the typical microspheres had diameters of 200~300?nm, and the specific areas and pore volume regularly varied with the quantity of the suspensions. By the optimum control, porous P(St-AM) microspheres with average pore size of 5.7?nm, pore volume of 0.18?cm³/g, and specific surface area of 123.54?m²/g could be obtained. The method represents a new, easily manipulated, cost-effective, and safe route for preparation of porous polymer microspheres using inorganic porogens.     

Synthesis of poly-α,α-diphenylglycine. I. Thermal polymerization of 4,4-diphenyl-Δ2-1,2,3-triazolin-5-one

The thermal decomposition of 4,4-diphenyl-Δ²-1,2,3-triazolin-5-one (I) was reinvestigated and shown to yield poly-α,α-diphenylglycine (III) instead of the previously reported 3,3,6,6-tetraphenylpiperazine-2,5-dione (II). Differentiation between the two structures was made by molecular weight determinations and spectroscopic analyses. The infrared spectra were studied in detail and compared with model compounds. They showed that the absorption peak at 1470 cm^?1 must be attributed to the trans-amide II absorption of the polymer. Furthermore, the polymers were found to contain terminal CONH₂ as well as triazolinone or ether functions (from alcohol). Fractionation was performed in three solvents based on solubility differences: dichloroethane (or chloroform), methanol, and n-hexane. All the fractions were characterized by physical methods. A mechanistic investigation revealed that the polymerization process cannot be rationalized by a radical or cationic mechanism, but is compatible with a molecular mechanism involving triazolinone functions at the growing chain ends.     

The question of the chemical structure of amber

Summary 1. The identity of the IR spectra of the main types of amber (transparent, semitransparent, opaque and bone ambers) in the 700–2000 cm^–1 region has been confirmed. At the same time, differences between them have been shown by elemental analysis.2. In order to isolate the fraction of amber soluble in alcohol, extraction with boiling alcohol instead of by prolonged extraction at room temperature has been proposed.3. The amber fraction soluble in alcohol and petroleum ether can be separated into acid and ester (lactone) fractions by successive treatment of its ethereal solution with 1% and 15% aqueous alkalis.4. The acid fraction isolated from the alcohol-soluble and the petroleum ether-insoluble fractions of amber have similar IR spectra but differ in elemental composition.5. Succinin contains lactone (or ester) groupings whose hydrolysis forms hydroxyacids.Khimiya Prirodnykh Soedinenii, Vol. 2, No. 6, pp. 429–436, 1966     

Polymerization of oriented monomers. V. Radiation-induced polymerization of 3n-dodecyl-1-vinylimidazolium iodide in micellar aggregates

In the present study radiation-induced polymerization of 3n-dodecyl-1-vinylimidazolium iodide (I) in micellar aggregates was investigated. For comparison, the corresponding isotropic polymerization of I was also studied. Micellization was obtained in concentrated aqueous solutions; that is, above the monomer's critical micelle concentration (CMC) polymers obtained by both modes of polymerization were treated similarly and subsequently subjected to physical characterization. The main purpose of this study was to investigate whether the degree of organization of the monomer in micelles would affect polymer properties. Attempts to determine tacticity by ¹³C-NMR spectrometry failed because of the particular structure of the polymer. Crystallization of these polymers from ethyl alcohol or acetone was not possible as indicated by x-ray powder diffraction patterns that were characteristic of amorphous polymers. On the other hand, viscosity data of polymers do not depend on the mode of polymerization. It is therefore concluded that micellar aggregates are not sufficiently organized to affect polymer properties.     

Rotational isomerism in 1,4-disilabutane

Raman spectra of 1,4-disilabutane (DSB) are recorded in both liquid and solid states. IR spectra in the gas and solid phases are also recorded. Two rotational isomers, trans and gauche, are present in the gas and pure liquid phases. An assignment of the main features of the IR and Raman spectra is made, with the aid of normal coordinate calculations for the two isomers. The temperature dependence of the Raman spectrum of DSB is studied in the range 77–300 K. The enthalpy difference between the two isomers is 5.01 ± 0.31 kJ mol^?1. This value is expected to be higher for gaseous DSB.     

Raman spectral changes during the solid-state polymerization of diacetylenes

Raman spectral changes resulting from the solid-state 1,4-addition polymerization of conjugated diacetylenes are reported. The monomers show an intense C?C stretching frequency near 2260 cm^?1, where as the polymers showed two strong bands, a C?C vibration near 2100 cm^?1 and a C?C vibration near 1500 cm^?1. The presence of both double and triple bonds in the polymers suggests the backbone structure (?C? C?C? C?)_n. The alternate mesomeric structure (? C?C?C?C? )_n can be eliminated as a possibility by the presence of the strong C?C vibration in the polymer. Sequential Raman spectra obtained during radiation-induced polymerization revealed intermediate spectral states between the initial monomer and final polymer. Intermediate-state vibrations first increase and then decrease in intensity as polymerization proceeds. However, the observed vibtrational frequencies of intermediate states were not dependent upon the extent of polymerization. Whether polymerization occurred thermally or as a result of radiation did not appear to influence the spectrum of the final polymer, but the observed number of intermediate states differed. Polymerization mechanisms, required molecular motions, and resulting structural changes are discussed.     

Photochemical production of electroluminescent image

A polymer containing donorN-epoxypropylcarbazolyl groups and the acceptor tris(8-quinolinolato) aluminum (Alq₃) was shown to form a light-sensitive, acid-producing polymeric composition. The acid in the presence of 8-quinolinol (8-hydroxyquinoline) ensured photochemical dissolution of aluminum in the polyeric layer, yielding additionally organic aluminum complexes, such as Alq₃, Alq²⁺, and Alq ₂ ⁺ , and Alq₃-con-taining polymers. This led to a emergence of electroluminescence (EL) upon application of a potential difference to a sandwich diode representing transparent anode/exposed polymer layer/aluminum cathode. Electroluminescence did not appear at an Alq₃ concentration of 6 wt % and less in the composition, and only partial dissolution of the aluminum film after its deposition on the exposed polymeric layer provided the emergence of EL whose intensity increased with increasing the dose absorbed by the polymer. The addition of the chemical sensitizer dimethylaminobenzaldehyde to the composition triggered the conventional process of chemical amplification which consists in thermal buildup of the acid in exposed area. This provided a significant increase in concentration of organoaluminum complexes and enhancement of EL intensity.     

Conjugated polymers containing phenothiazine moieties in the main chain

Several conjugated polymers containing phenothiazine moieties in the main chain were synthesized by Knovenagel or Wittig condensations. The polymers were identified and characterized by ¹H‐NMR, IR, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), UV‐vis and fluorescent (FL) spectra. Results indicated that the m‐polymer, which was prepared from the polycondensation of N‐octyl‐3,7‐diformylphenothiazine with m‐phenylene diacetonitrile, is the most thermally stable one in all the polymers synthesized. While, the p‐polymer, which was prepared from the polycondensation of N‐octyl‐3,7‐diformylphenothiazine with p‐phenylene diacetonitrile, is the most thermally instable one. The introduction of a cyano group made the absorption and emissive maxima red‐shift from 429 and 537 nm for the Ph‐polymer to 465 and 597 nm for the p‐polymer respectively. The quinoid structure formation allows the p‐polymer to have a lower band gap than any other polymers. Emissive spectra of all these polymers in tetrahydrofuran (THF) solution have a narrow half‐peak width. Copyright © 2006 John Wiley & Sons, Ltd.     

Furfuryl alcohol polymerisation by iodine in methylene chloride

Furfuryl alcohol (FA) was polymerised by iodine in methylene chloride to give a coloured, amorphous and branched polymer. Structure of FA polymers obtained with iodine have no significant differences according to the IR and NMR spectra respect to those obtained by using Brönsted or Lewis acids as initiators. Changes on the experimental conditions, such as the presence of air, iodine concentration or reaction temperature, did not lead to an increase in the linear structure of the polymer. On the contrary, an increase in the iodine concentration or in the temperature produces a highly crosslinked polymer. DSC of the polymer indicates that remaining groups are able to undergo further exothermic reactions and crosslinking. A mechanism of polymerisation was proposed to explain all the above features.     

Isotopic shifts due to heavy and very heavy atom substitution: a new sum rule and on the sensitivity of force constants to very small frequency shifts

IR and Raman spectra of dihydro-9,10 anthracene and dihydroanthracene-D₄(9,10) have been investigated in the 3100 to 100 cm^?1 region; an assignment is given. Spectra are interpreted in terms of a molecule composed of two ortho disubstituted benzene rings very similar to that of o-xylene. The symmetry of the dihydro-9,10 anthracene molecule in solution is discussed. The differences with respect to anthracene spectra are correlated with the electronic structure of the latter compound.     

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

Polymerization 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 > thienyl > furyl > 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.