Advances in identification of plant gums in cultural heritage by thermally assisted hydrolysis and methylation

Plant gums are present in works of art as binding media for watercolours and adhesives for cellulosic substrates. Thermally assisted hydrolysis and methylation (THM) in combination with analytical pyrolysis coupled to GC/MS has been applied to the characterisation of plant gums typically used in artworks. THM products from standard samples of arabic gum, tragacanth gum and cherry gum were characterised. The main products identified are permethylated and partially methylated aldonic acids, characteristic of specific epimeric sugars. Aldonic acids were formed by alkaline hydrolysis of free reducing sugars and of reducing polysaccharide terminal groups, while methylation occurs during pyrolysis. The presence of these characteristic markers allows gum identification. A systematic analysis of all the parameters that can affect the marker yields was performed. In particular, the influence of pyrolysis temperature, reagent concentration and contact time between tetramethylammonium hydroxide and sample were studied, and different kinds of sample preparation procedures were tested. Some analyses on real watercolours were performed, and gum binders were classified using the peak area ratio of the main monosaccharide markers.     

Complementary analysis of lipids in whole bacteria cells by thermally assisted hydrolysis and methylation-GC and MALDI-MS combined with on-probe sample pretreatment

The molecular structure of lipids in whole bacteria cells was characterized in detail by using two different and complementarily direct analyses; thermally assisted hydrolysis and methylation-gas chromatography (THM-GC) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) combined with on-probe sample pretreatment. First, THM-GC in the presence of tetramethylammonium hydroxide (TMAH) was applied to compositional analysis of the fatty acid components of lipids in whole bacterial cells. On the resulting chromatograms, a series of fatty acid components in bacterial lipids were clearly observed as resolved peaks of their methyl esters. The fatty acid compositions determined on the basis of the peak intensities were in good agreement with those obtained by the conventional technique involving solvent extraction of the lipids in the samples. Furthermore, MALDI-MS combined with the on-probe sample treatment, using 2,5-dihydroxybenzoic acid (DHB) and sodium iodide (NaI) as matrix and cationization reagents, respectively, was used to detect intact phospholipids directly from whole bacterial cells. The MALDI spectra thus obtained showed an array of ions generated from bacterial phospholipids, such as phosphatidylethanolamines (PEs) and phosphatidylglycerols (PGs). Finally, the bacterial lipids were comprehensively characterized in terms of the acyl groups and the molecular structures by taking both of the results obtained by THM-GC and MALDI-MS into consideration.     

Simultaneous analysis of tannin and lignin signatures in soils by thermally assisted hydrolysis and methylation using 13C-labeled TMAH

Tannin, condensed and hydrolysable, and lignin are two of the most abundant natural biopolymers in the environment. Yet it is still not possible using one analytical technique to simultaneously track each of their dynamics in litter and soils. Thermally assisted hydrolysis and methylation (THM) using tetramethylammonium hydroxide (TMAH) has been employed to investigate the cycling of tannin and lignin forms in one analysis, but sometimes with equivocal results as many of the products released may originate from both biopolymers. In this study we applied ¹³C-labeled TMAH in the analysis of soil organic matter in a soil profile under Corsican pine, an input lacking in hydrolysable tannins, to show the potential of this tool in tracking complex phenol chemistry. This method successfully allowed for a qualitative distinction among tannin and lignin input as well as permitting the inference of ring specific decay of condensed tannins.     

Characterization of thermally assisted hydrolysis and methylation products of polyphenols from modern and archaeological vine derivatives using gas chromatography-mass spectrometry

If some ceramics, such as vinary amphorae attest the consumption and trade of wine in the Roman world, the first wine productions in Occident often stay undocumented. Chemical analysis of organic materials preserved in archaeological vessels is the only way to bring new lights about the elaboration and the consumption of this fermented beverage. To determine the preservation state of wine and other grape derivatives residues, we proceeded to in situ tetramethylammonium hydroxide (TMAH) treatment followed by thermally assisted hydrolysis and methylation—gas chromatography—mass spectrometry (THM-GC-MS). The objectives of the study were (i) the understanding of the pyrolytic mechanisms of proanthocyanidins and (ii) the assessment of the usefulness of thermochemolysis for the identification of phenolic markers from polymeric solid deposit in modern wine bottle and Roman amphorae. THM-GC-MS was revealed to be an efficient method for the characterization of fruit derivatives even if mixed with another organic material, such as pitch used to ensure the watertightness of the ceramic container. The preservation of tannins during millennia in archaeological context is here enlightened for the first time by using analytical pyrolysis. The proposed identification of vinary residues is now based on the detection of the association of more than 30 pyrolytic markers derived from di- and trimethoxylated benzenoid compounds. THM-GC-MS represents a new method for the rapid detection of wine traces in ancient ceramics, adapted to tiny samples (<0.1 mg), allowing to precise the role and function of pottery during antiquity.     

Analysis of catechins and condensed tannins by thermally assisted hydrolysis/methylation-GC/MS and by a novel two step methylation

The objective of this study is to observe high molecular weight markers of catechins and condensed tannins by thermally assisted hydrolysis/methylation (THM)-GC/MS. Techniques for formation of intact methylated flavanols of catechins using THM in the presence of trimethylsulfonium hydroxide (TMSH), and, of a dimer marker of condensed tannins using a novel two step methylation technique, are presented. The two step methylation procedure involves pre-methylation of the sample with trimethylsilyl diazomethane (TMS-diazomethane) followed by THM. The dimer marker, a methylated product containing the C–C linkage between adjacent flavanol units, has a molecular weight of 540. Intact methylated flavanols of catechins were also successfully observed as high molecular weight compounds including partially methylated catechin and epicatechin (3-flavanol, 3′,4′,5,7-tetramethoxy, cis/trans; m/z = 346), epigallocatechin and gallocatechin (3-flavanol, 3′,4′,5,5′,7-pentamethoxy, cis/trans; m/z = 376). These techniques were successfully applied to the analysis of series of condensed tannins isolated from plants, and catechins and other phenolics present in (hot water) extracts of tea leaves. In green tea the major catechins were identified as epicatechin and epigallocatechin along with flavonols and tannin dimers.     

Determination of the carbon isotopic composition of whole/intact biological specimens using at-line direct thermal desorption to effect thermally assisted hydrolysis/methylation

In this paper, we discuss the use of a direct thermal desorption (DTD) interface as an alternative to Curie-point flash pyrolysis system as an inlet technique in gas chromatography-combustion isotope-ratio mass spectrometry (GC/C-IRMS) analysis of whole/intact phytoplankton and zooplankton specimens. The DTD in combination with a combipal auto-injector is programmed to perform the injection, evaporation of solvents, transport of capped programmed-temperature vaporizer (PTV) liners to the PTV injector and chemical derivatisation (thermally assisted hydrolysis/methylation; THM) such that a profile of a cellular fatty acids is obtained. Flow-cytometric sorted microalgae and handpicked zooplankton are used as samples with trimethylsulfonium hydroxide (TMSH) as methylating reagent. A major advantage of this novel approach over the Curie-point technique is the automation of the total procedure, which allows unattended analysis of large sample series. The profiles and delta(13)C carbon isotopic signatures of the fatty acid methyl esters (FAMEs) produced are very similar to those obtained using the Curie-point flash pyrolysis method. It is shown that algal samples must be kept no longer than 48 h in the DTD sample tray prior to the THM-analysis in order to maintain the integrity of their FAME profile.     

Rapid molecular assessment of the bioturbation extent in sandy soil horizons under pine using ester-bound lipids by on-line thermally assisted hydrolysis and methylation-gas chromatography/mass spectrometry

Each plant species has a unique chemical composition, and also within a given plant the various tissues differ from one another in their chemistry. These different compositions can be traced back after decay of the plant parts when they are transformed into soil organic matter (SOM). As a result, the composition of SOM reflects not only the plant origin, but also the various tissues, and the composition consequently provides an estimate of the contribution of above-ground vs. below-ground litter. From the latter distribution the extent of bioturbation (mixing of above-ground litter with the mineral soil) can be assessed.Application of thermally assisted hydrolysis and methylation (THM) using tetramethylammonium hydroxide (TMAH) and subsequent analysis by gas chromatography/mass spectrometry (GC/MS) releases all typical cutin- and suberin-derived aliphatic monomers (mono-, di- and trihydroxyalkanoic acids, alpha,omega-alkanedioic acids) as their methyl esters and/or ethers in a rapid manner. Using the distribution of omega-hydroxyalkanoic acids that are present in pine needle cutin (C(12) and C(14)) and not in root suberin, and those that are present in roots but not in needles (C(20) and C(22)), the extent of bioturbation (mixing of above-ground plant litter with the mineral soil) can be assessed. Similarly, the (9,16-dihydroxyhexadecanoic acid+9,10,18-trihydroxyoctadecanoic acid)/(C(20) + C(22) alpha,omega-alkanedioic acids) ratio reflects the degree of bioturbation. Three mineral soil profiles under Corsican pine with an A horizon that exhibited extensive bioturbation phenomena, and underlying C horizons with hardly any or no bioturbation, were investigated in order to examine the applicability of such an approach. It appeared that the A horizons contained all four mentioned omega-hydroxyalkanoic acids, while the C horizons contained virtually only the C(20) and C(22) members. The results not only suggest that bioturbation occurs in the A horizons, but also that possible illuviation or other transport mechanisms of omega-hydroxyalkanoic acids seem hardly ever or never to occur, which is a prerequisite for applying this biomarker approach in assessing degrees of bioturbation.     

Evaluation of comprehensive on-line liquid chromatography thermally assisted hydrolysis and methylation-gas chromatography-mass spectrometry for characterization of sulfonated lignins

Sulfonated lignins, used as dispersants in agrochemical formulations, have been characterized by hyphenation of ion-pair RPLC and thermally assisted hydrolysis and methylation-GC-MC (THM-GC-MS). The chemical structure of a series of selected lignins was evaluated, both in terms of overall composition and in terms of composition as a function of molecular size. Some sulfonated lignins give rise to unstable formulations. In the compositional analysis, these samples were found to yield additional fragments. A newly developed comprehensive method made it possible to monitor the occurrence of these fragments as a function of molecular size. In addition to differences in the molecular size between "good" and "bad" batches, clear differences in chemical composition were established.     

The effect of afforestation on the soil organic carbon (SOC) of a peaty gley soil using on-line thermally assisted hydrolysis and methylation (THM) in the presence of 13C-labelled tetramethylammonium hydroxide (TMAH)

In Britain substantial areas of both deep and shallow peatland have been afforested with conifers since the 1950s. However, information about the effects of afforestation on the properties of soil organic carbon (SOC) is lacking. Investigating the geochemical changes that take place when lignin- and tannin-derived phenols are degraded and incorporated into SOC will provide us with an insight into soil carbon dynamics at the molecular level. Here we compare the phenolic distributions in two different peaty gley soil profiles using on-line thermally assisted hydrolysis and methylation (THM) in the presence of both unlabelled and ¹³C-labelled tetramethylammonium hydroxide (TMAH). The two soil profiles were beneath respectively an unforested moorland (ML) and a second rotation Sitka spruce (Picea sitchensis) afforested moorland (SS), from Harwood (Northumberland, northeast England, UK). THM of these soils in the presence of ¹³C-labelled TMAH enabled us to assess the relative contributions of lignin, demethylated lignin, and non-lignin phenolics. The lignin phenolic distributions differed in both soil profiles reflecting changing source and decay dynamics within and between the sites. A progressive degradation of syringyl (S) and guaiacyl (G) phenolics was observed in the ML soil, compared with an increase of such components in the organic/mineral horizons of the SS soil. A significant tannin input was observed, particularly in the upper horizons of the SS soil. The S/G ratio gradually decreased with increasing burial in the ML soil, whilst a change in vegetation input and land preparation was recorded by this ratio in the SS soil. Overall, this suggests that afforestation influences the phenolic compositional profiles in these peaty gley soils as a result of one or more of the following processes: changing vegetation input, horizon inversion prior to planting, root input or leaching. This highlights the potential of using lignin and tannins as molecular indicators to assess the effects of afforestation on SOC.     

Compositional analysis of copoly (DL-lactic/glycolic acid) (PLGA) by pyrolysis-gas chromatography/mass spectrometry combined with one-step thermally assisted hydrolysis and methylation in the presence of tetramethylammonium hydroxide

Rapid and precise compositional analysis of copoly (DL-lactic/glycolic acid) (PLGA) was performed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) combined with one-step hydrolysis and methylation in the presence of tetramethylammonium hydroxide (TMAH). Pyrolysis of PLGA with TMAH gave two characteristic products, derivatives of DL-lactic acid and glycolic acid, which directly reflect the average molar composition of PLGA. The analytical results for PLGA samples with various compositional ratios were in good agreement with those obtained by 1H-NMR spectrometry, and the precision was satisfactory.     

Precise compositional analysis of liquid crystalline aromatic polyesters containing aromatic amide linkages by thermally assisted hydrolysis and methylation-gas chromatography

Multi-component liquid crystalline aromatic polyesters (LCPs) containing 4-aminophenol (PAP) units to form amide linkages were characterized by thermally assisted hydrolysis and methylation-gas chromatography (THM-GC). Under the given THM conditions (300 °C; in the presence of 25 wt% tetramethylammonium hydroxide in methanol), the aromatic amide linkages in the LCP chains were only methylated but hardly cleaved, whereas the ester bonds almost quantitatively decomposed into methyl esters and methyl ethers. Thus dimeric and trimeric products consisting of PAP and another monomer unit linked through methylated amide linkage(s) were observed in the THM chromatograms along with dimethyl derivatives of the monomer units other than PAP. The compositions of the LCP samples containing PAP units were then determined from the relative peak intensities observed in the THM chromatograms, and showed quite good agreement with the original monomer compositions in feed with superior reproducibility; less than 1% relative standard deviation.     

Spectrophotometric determination of paracetamol with microwave assisted alkaline hydrolysis

A novel and rapid spectrophotometric method for the determination of paracetamol is proposed in this paper. The proposed method is based on the microwave assisted alkaline hydrolysis of paracetamol to p-aminophenol that reacts with S2- in the presence of Fe3+ as oxidant to produce a methylene blue-like dye having an absorptivity maximum at 540 nm. The experiment showed that paracetamol could be hydrolysed quantitatively to p-aminophenol in only 1.5 min under radiation power 640 W using a microwave in NaOH medium. The system obeys Beer's law in the range of 0-3.0 x 10(-4) mol l(-1) paracetamol. The molar absorptivity and Sandell's sensitivity were found to be 3.2 x 10(-3) l mol(-1) cm(-1) and 0.047 microg cm(-2), respectively. The relative standard deviation (n=11) was 1.7% for 8.0 x 10(-5) mol l(-1) paracetamol. The method has been applied successfully to analysis of paracetamol in pharmaceutical preparation.     

Carbazolylgold(iii) complexes with thermally activated delayed fluorescence switched on by ligand manipulation as high efficiency organic light-emitting devices with small efficiency roll-offs

A series of carbazolyl ligands has been designed and synthesized through the integration of various electron-donating and electron-accepting motifs, including electron-donating 4-(diphenylamino)aryl and electron-accepting cyano and diphenylphosphine oxide moieties, for the development of a new class of gold(iii) complexes, where the energies of their triplet intraligand and ligand-to-ligand charge transfer excited states can be manipulated for the activation of thermally activated delayed fluorescence (TADF). Upon excitation, these complexes show high photoluminescence quantum yields of up to 80% in solid-state thin films, with short excited state lifetimes down to 1 μs. Vacuum-deposited and solution-processed organic light-emitting devices based on these complexes demonstrate promising electroluminescence (EL) performance with maximum external quantum efficiencies of 15.0% and 11.7%, respectively, and notably small efficiency roll-off values of less than 1% at the practical luminance brightness level of 1000 cd m⁻². These distinct EL performances are believed to be due to the occurrence of multichannel radiative decay pathways via both phosphorescence and TADF that significantly shorten the emission lifetimes and hence reduce the occurrence of the detrimental triplet–triplet annihilation in the gold(iii) complexes.

Switch on of TADF can be achieved by tuning the excited state energy levels via ligand manipulation of the carbazolylgold(iii) C^C^N complexes. The resulting OLEDs show maximum EQEs of over 11% and efficiency roll-offs of down to less than 1%.     

Influence of various additives on base hydrolysis of chlorine-containing organic impurities in naphtha fractions

Degree of dechlorination of chlorine-containing naphtha fractions in the course of their base hydrolysis in the presence of phase-transfer catalyst and other compounds was studied. The optimal type of the phase-transfer catalyst was determined.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 11, 2004, pp. 1920–1921.Original Russian Text Copyright © 2004 by Gogotov, Silinskaya, Kolotov, Tomin.     

Reaction of sulfur with organic compounds

Catalytic reaction of sulfur with the appropriate ethers and esters of p-isopropylphenol has given several previously unknown 4-p-alkoxyphenyl-, 4-p-aryloxyphenyl-, and 4-p-aroyl-oxyphenyl-1,2-dithiole-3-thiones.For part XVIII, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 5, pp. 592–594, May, 1970.     

Reaction of sulfur with organic compounds

The effect of the number and position of phenyl groups in a four-carbon chain on the yields of di- and triphenylthiophenes in the reaction of sulfur with phenylbutanes was investigated. New, simple methods were developed for the synthesis of 2,3-diphenylthiophene (from 1,2-diphenylbutane), 3,4-diphenylthiophene (from 2,3-diphenylbutane), 2,5-diphenylthiophene (from 1,4-diphenylbutane), and 2,3,5-triphenylthiophene (from 1,3,4-triphenyl-1-butanone). Di-, tri-, and tetrasubstituted butanes, butenes, and butadienes that contain two aromatic substituents attached to the same carbon atom do not react with sulfur under the investigated conditions.See [1] for communication XXI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 755–758, June, 1971.     

Reaction of a diphosphene with various halogens

Bis(2,4,6-tri-$\text{tert}$-butylphenyl) diphosphene reacts with various halogens to give the corresponding phosphoric dihalides, haloarene, and arene depending upon the halogen and solvent used.