Eco-friendly hybrid pigments made of cellulose and iron oxides.

The controlled hydrolysis of FeC2O4 in the presence of vegetable cellulose fibres was investigated to produce a pallet of cellulose/iron oxide hybrid colored materials. Distinct iron oxide phases have been deposited at the cellulose fibres surfaces by varying the relative amount of FeC2O4 and NaOH, here used as starting materials, by performing the synthesis in hydrothermal conditions. This is a new chemical strategy for the production of a number of hybrid materials whose coloristic properties have been evaluated aiming their potential use as novel pigments for polymer based products.

Langmuir monolayers of fractions of cork suberin extract.

The wide variability in composition and molecular weight of natural polymers has hampered understanding of their physicochemical properties and ultimately their use in noble applications, especially in the cases where surface properties need to be probed at the molecular level. A useful approach to analyse data from surface monolayers of complex mixtures is to try distinguishing the effects from the distinct fractions in such mixtures. The cork suberin extract investigated here is known to contain aliphatic monomers with terminal carboxylic acid and methyl ester groups as well as long esterified aliphatic chains dispersed in a polymeric aliphatic matrix. The role of such terminal groups was studied and the results showed that depending on the nature of the terminal groups the monolayers present distinct isotherms due to the different interactions with the water subphase. Fractionation strategies based on different solubilities of the cork suberin components in chloroform were also employed to probe their effect on the monolayer characteristics. From the two sets of experiments it is clear that the presence of monomers with terminal carboxylic acids in the suberin extract affects considerably the monolayer-forming ability. This approach may be used as a complementary, relatively simple route to assess suberin genetic engineering strategies towards resistance to environmental stress.

Lignanamides and other phenolic constituents from the bark of kenaf (Hibiscus cannabinus).

Two new acyclic phenylpropane lignanamides, grossamide K and erythro-canabisine H, and the naphthol glucoside 2,5-dimethyl-3-O-beta-D-glucopyranosylnaphthol, along with six known compounds were isolated from the acetone extract of bark of Hibiscus cannabinus. All structures were established by spectroscopic methods including 2D NMR techniques, which allowed the correction of certain previously reported 13C NMR assignments of grossamide.

Variability of cork from Portuguese Quercus suber studied by solid-state (13)C-NMR and FTIR spectroscopies.

A new approach is presented for the study of the variability of Portuguese reproduction cork using solid-state (13)C-NMR spectroscopy and photoacoustic (PAS) FTIR (FTIR-PAS) spectroscopy combined with chemometrics. Cork samples were collected from 12 different geographical sites, and their (13)C-cross-polarization with magic angle spinning (CP/MAS) and FTIR spectra were registered. A large spectral variability among the cork samples was detected by principal component analysis and found to relate to the suberin and carbohydrate contents. This variability was independent of the sample geographical origin but significantly dependent on the cork quality, thus enabling the distinction of cork samples according to the latter property. The suberin content of the cork samples was predicted using multivariate regression models based on the (13)C-NMR and FTIR spectra of the samples as reported previously. Finally, the relationship between the variability of the (13)C-CP/MAS spectra with that of the FTIR-PAS spectra was studied by outer product analysis. This type of multivariate analysis enabled a clear correlation to be established between the peaks assigned to suberin and carbohydrate in the FTIR spectrum and those appearing in the (13)C-CP/MAS spectra.

Phenolic constituents from the core of kenaf (Hibiscus cannabinus).

Four lignans, boehmenan H [2-(4-hydroxy-3-methoxyphenyl)-5-[3-(4-hydroxy-3-methoxycinnamoyloxy)propyl]-3-hydroxymethyl-7-methoxybenzodihydrofuran], boehmenan K [2-(4-hydroxy-3-methoxyphenyl)-5-[3-(4-hydroxycinnamoyloxy)-1-propenyl]-3-(4-hydroxy-3-methoxycinnamoyloxymethyl)-7-methoxybenzodihydrofuran], threo-carolignan H [threo-1-(4-hydroxy-3-methoxyphenyl)-2-[4-[3-(4-hydroxy-3-methoxycinnamoyloxy)propyl]-2-methoxyphenoxy]-1,3-propanodiol], and threo-carolignan K [threo-1-(4-hydroxy-3-methoxyphenyl)-3-(4-hydroxy-3-methoxycinnamoyloxy)-2-[4-[3-(4-hydroxycinnamoyloxy)-1-propenyl]-2-methoxyphenoxy]-1-propanol] as well as several other lignans, aldehydes and a tyramine derivative were isolated from the acetone extract of core of kenaf (Hibiscus cannabinus). All the structures were established by spectroscopic methods. The hitherto unreported 13C NMR spectra of some compounds are also presented and discussed. 2D NMR techniques have allowed the revision of certain previously reported 13C NMR assignments of some scarce naturally occurring compounds.

(2-O-alpha-D-galactopyranosyl-4-O-methyl-alpha-D-glucurono)-D-xylan from Eucalyptus globulus Labill.

An unusual heteroxylan composed of galactosyl, 4-O-methyl-glucuronosyl and xylosyl residues with molar ratio 1:3:30 was isolated from the wood of Eucalyptus globulus Labill. The results of linkage analysis, supported by data of 1H, 2D 1H-1H COSY and 13C NMR spectroscopy, revealed that the polysaccharide is a (2-O-alpha-D-galactopyranosyl-4-O-methyl-alpha-D- glucurono)-D-xylan with a (1-->4)-linked beta-D-xylopyranosyl backbone branched at O-2 by short side chains composed of terminal 4-O-methyl-alpha-D-glucuronic acid and of 4-O-methyl-alpha-D-glucuronic acid substituted at O-2 with alpha-D-galactose.

Cork suberin as a new source of chemicals. 1. Isolation and chemical characterization of its composition.

Extractive-free cork from Quercus suber L. was submitted to a solvolysis treatment with methanolic NaOH which yielded 37% (o.d. cork) of suberin. This mixture of compounds was thoroughly characterized by FTIR, 1H- and 13C-NMR, gas chromatography coupled with mass spectrometric (GC-MS) analysis, vapour pressure osmometry (VPO), mass spectrography (MS) and gel permeation chromatography (GPC). After derivatization, the main components of the volatile fraction, representing less than half of the total, were found to be omega-hydroxymonocarboxylates, alpha, omega-dicarboxylates, simple alkanoates and 1-alkanols, all with chain lengths ranging from C16 to C24. A second fraction, with an average molecular weight about three times higher, was detected by VPO, MS and GPC. The presence of this important fraction in cork suberin had not been recognized in earlier studies. Both fractions constitute interesting precursors for the elaboration of new materials.

A 13C solid state nuclear magnetic resonance spectroscopic study of cork cell wall structure: the effect of suberin removal.

Solid state 13C NMR measurements of cork, before and after suberin removal, showed that aliphatic suberin is spatially separated from carbohydrate and lignin and experiences higher motional freedom. Two types of chain methylenes, differing in chemical shift and in dynamic properties, were identified in aliphatic suberin. Experimental evidence indicated that the more motionally hindered methylenes are those situated nearer the linkages of aliphatic suberin to the cell wall. These linkages were shown to involve -CH2O- groups, probably engaged in ester linkages to phenylpropane units and carbohydrate C6 carbons. Spectral intensity changes indicated that, during the first steps of alkaline desuberization, these linkages are broken and the shorter aliphatic suberin chains removed. Longer chains require hydrolysis of the ester linkages within the chains and are removed upon stronger alkaline treatment. T1(C), T1 rho (H) and T1 rho (C) relaxation times have shown that the removal of suberin from cork leads to a motionally restricted and more compact environment, on the megahertz and mid-kilohertz timescales. The properties of cork suberin showed that suberin organization in cork is distinct from that in potato tissue.

13C solid-state nuclear magnetic resonance and Fourier transform infrared studies of the thermal decomposition of cork.

The thermal decomposition of cork has been studied by Fourier transform infrared (FTIR) spectroscopy and 13C solid-state nuclear magnetic resonance (NMR) spectroscopy with cross-polarization and magic-angle spinning (CP-MAS), high-power 1H decoupling (HPDEC) and cross-polarization depolarization-polarization (CPDP). Waxes and other soluble components of cork begin to decompose at ca. 150 degrees C. This is accompanied by partial decomposition of suberin, probably initiated at the points of attachment to the cell wall. The carbohydrates begin to decompose at ca. 200 degrees C. The decomposition of lignin begins at 250-300 degrees C, while suberin undergoes further degradation. Significant amounts of coke are formed in the process. At 400 degrees C cork has been transformed into coke with traces of partially decomposed suberin. The thermal decomposition of cork is dependent on the calcination time, particularly in the 200-350 degrees C range.