HPLC-MS of anthraquinoids, flavonoids, and their degradation products in analysis of natural dyes in archeological objects

LC with MS detection was optimized for sensitive and selective analysis of main classes of natural dyes used in ancient times for dyeing textiles -- red anthraquinoids, yellow flavonoids, and known degradation products of flavonols -- hydroxybenzoic acids. Fragmentation patterns of both negative and positive molecular ions for the above mentioned compounds were investigated. Three acquisition modes of MS analysis: scanning, SIM, and multiple reaction monitoring (MRM) in both positive and negative ion modes were optimized and compared with each other and with the UV-Vis diode-array detection. Even though in the applied chromatographic system formic acid was used in the mobile phase, SIM in the negative ion mode was the most selective and sensitive detection for all the investigated compounds when both mixtures of standards and analysis of extracts from archeological samples were concerned, with one exception -- alizarin, for which MS detection in positive ion mode was more sensitive. Detection limits obtained with MS detection for all investigated compounds except quinizarin were lower than the ones obtained with the diode-array UV-Vis detection, making MS detection the most suitable tool for the analysis of natural dyes and their degradation products in extracts from archeological samples.     

Investigation of crimson-dyed fibres for a new approach on the characterization of cochineal and kermes dyes in historical textiles

The colorant behaviour of cochineal and kermes insect dyes in 141 experimentally-dyed and 28 artificially-aged samples of silk and wool was investigated using ultra-high performance liquid chromatography coupled to photodiode array detector (UHPLC-PDA), liquid chromatography electrospray ionisation mass spectrometry (LC-ESI-MS) and image scanning electron microscopy – energy dispersive X-ray spectroscopy (SEM-EDX). Partial-least squares discriminant analysis (PLS-DA) was then used to model the acquired UHPLC-PDA data and assess the possibility of discriminating cochineal insect species, as well as their correspondent dyed and aged reference fibres. The resulting models helped to characterize a set of 117 red samples from 95 historical textiles, in which UHPLC-PDA analyses have reported the presence of cochineal and kermes insect dyes.     

Investigation of natural dyes occurring in historical Coptic textiles by high-performance liquid chromatography with UV-Vis and mass spectrometric detection

Liquid chromatography (LC) combined with ultraviolet-visible (UV-Vis) and mass spectrometric (MS) detection was utilized to study the chemical components present in extracts of natural dyes originating from fiber samples obtained from Coptic textiles from Early Christian Art Collection of National Museum in Warsaw. Chromatographic retention, ionization, UV-Vis and mass spectra of twenty selected dye compounds of flavanoid-, anthraquinone- and indigo-types were studied. Most of the investigated compounds could be ionized by positive and negative ion electrospray ionization. Difficulties with the ionization by electrospray were experienced for indigotin and brominated indigotins, but these were ionized by atmospheric pressure chemical ionization. Mass spectrometric detection, utilizing different scanning modes of a triple quadrupole mass spectrometer, combined with the UV-Vis detection was demonstrated to be a powerful approach to detection and identification of dyes in the extracts of archeological textiles. Using this approach the following compounds were identified in the extracts of Coptic textiles: luteolin, apigenin, rhamnetin, kaempferol, alizarin, purpurin, xanthopurpurin, monochloroalizarin, indirubin, and so the type of dye that was utilized to dye the textiles could be identified. Detection capabilities for several dye-type analytes were compared for the UV-Vis and mass spectrometric detection. The signal-to-noise ratios obtained for luteolin, apigenin, and rhamnetin were higher for the MS detection for most of the examined sample extracts. Purpurin, alizarin, and indirubin showed similar signal-to-noise ratios for UV-Vis and mass spectrometric detection.     

Fe2O3掺杂对WO3光催化降解有机染料X3B的影响

发展高效的可见光催化剂是太阳能化学利用的一个挑战. 本文采用简单的混合方法, 制备了WO₃和Fe₂O₃的混合物, 研究了该复合氧化物在H₂O₂存在下光催化降解有机染料X3B的活性. 实验表明, 催化剂的光催化活性与其煅烧温度和Fe₂O₃含量有关. 最佳煅烧温度和Fe₂O₃含量分别等于400 °C 和1.0% (w). 根据自由基捕获电子顺磁共振(EPR)波谱分析, 复合氧化物产生羟基自由基的量远高于Fe₂O₃和WO₃. 我们推测, 这种协同效应来源于WO₃和Fe₂O₃之间的电荷转移, 从而加快半导体光生载流子的分离和X3B的光催化降解.     

A theoretical study on the ground and excited state behaviors of TTBC related carbocyanine dyes

The effects of functional groups on the benzimidazole rings, length of the conjugated chain and alkyl groups bonded to the nitrogen atoms on the ground and excited state behaviors of the 1,1′,3,3′-tetraethyl-5,5′,6,6′-tetrachlorobenzimidazolocarbocyanine (TTBC or JC-1) have been analyzed via quantum chemical methods. DFT and TDDFT with B3LYP/6-31G(d,p) level of theory were used for the ground and excited state calculations, respectively. It has been found that TTBC has a very rigid geometry; no significant effect of functional groups has been predicted either as donor or acceptor on its optimum structure. However, the length of alkyl groups changes the structure of the molecule. It is possible to increase λ_max of TTBC based carbocyanine dye with NH₂, butyl/propyl and increasing polymethine chain length.     

Thermal analysis applied to the characterization of degradation in soil of polylactide: II. On the thermal stability and thermal decomposition kinetics

The disposal stage of polylactide (PLA) was assessed by burying it in active soil following an international standard. Degradation in soil promotes physical and chemical changes in the polylactide properties. The characterization of the extent of degradation underwent by PLA was carried out by using Thermal Analysis techniques. In this paper, studies on the thermal stability and the thermal decomposition kinetics were performed in order to assess the degradation process of a commercial PLA submitted to an accelerated soil burial test by means of multi-linear-non-isothermal thermogravimetric analyses. Results have been correlated to changes in molecular weight, showing the same evolution as that described by the parameters of thermal stability temperatures and apparent activation energies. The decomposition reactions can be described by two competitive different mechanisms: Nucleation model (A2) and Reaction Contracting Volume model (R3). The changes in the kinetic parameters and kinetic models are in agreement with the calorimetric and dynamic-mechanical-thermal results, presented in the Part I of the study [1].     

A detailed study of sorption equilibria and kinetics of a model disperse dye in cellulose acetate

A detailed investigation of the sorption of 4-aminoazobenzene by cellulose acetate films from aqueous solution is reported. Sorption isotherms at 75 and 60°C were linear up to saturation, in agreement with previous findings that have led to the conclusion that cellulose acetate-disperse dye systems are thermodynamically ideal. Thermodynamic analysis of these data also gave results consistent with such previous findings. The isotherms for 45 and 25°C, on the other hand, exhibited increasing curvature, in line with similar recent findings for a variety of hydrophobic polymer-disperse dye systems, and consistent with the presence of some strong absorption sites. However, the situation appears to be more complex than envisaged by simple dual-mode sorption theory. Early time desorption kinetic data were found to be consistent with Fick's law, with no indication of any significant dependence of the diffusion coefficient D on concentration (in the medium- to high-concentration range) or on film thickness. On the other hand, D was affected significantly by the history of film formation, the method of introducing the dye or heat treatment of the film. The origin of these effects was traced by DSC to definite microstructural differences. Late time kinetic data deviated significantly from the theoretical predictions based on the corresponding early time data, indicating a progressive slowdown of the desorption process. The deviations in question were generally more marked at higher temperature or film thickness, or when dyeing had been effected from the vapor phase, and were attributed to slow release of strongly adsorbed dye molecules. © 1994 John Wiley & Sons, Inc.     

Dielectric and thermal effects on the optical properties of natural dyes: a case study on solvated cyanin

The optical properties of the flavylium state of the cyanin dye are simulated numerically by combining Car-Parrinello molecular dynamics and linear-response time-dependent density functional theory calculations. The spectrum of the dye calculated in the gas phase is characterized by two peaks in the yellow and in the blue (green and violet), using a GGA-PBE (hybrid-B3LYP) DFT functional, which would bring about a greenish (bright orange) color incompatible with the dark purple hue observed in nature. Describing the effect of the water solvent through a polarizable continuum model does not modify qualitatively the resulting picture. An explicit simulation of both solvent and thermal effects using ab initio molecular dynamics results instead in a spectrum that is compatible with the observed coloration. This result is analyzed in terms of the spectroscopic effects of the molecular distortions induced by thermal fluctuations.     

A comparative study of the effects of decomposition rate control and mechanical grinding on the thermal decomposition of aluminum hydroxide

Summary Two different processes of the thermal decomposition of synthetic bayerite, i.e., the non-isothermal decomposition of mechanically ground sample in flowing N₂ and the controlled rate thermal decomposition of crystalline bayerite under vacuum, were investigated comparatively. In comparison with the conventional non-isothermal decomposition of crystalline bayerite in flowing N₂, the reaction temperature of the thermal decomposition was lowered by the individual effects of mechanical grinding of the sample and the reaction rate control. These decomposition processes indicated similar behavior characterized by the restricted changes of the specific surface area during the course of decomposition reaction and the formation of an amorphous alumina as the decomposition product. Different thermal behaviors were observed for those amorphous Al₂O₃ produced by the respective decomposition processes.     

Complexes of polyelectrolyte hydrogels with organic dyes: Effect of charge density on the complex stability and intragel dye aggregation

The swelling behavior of polyelectrolyte gels based on poly(diallyldimethylammonium chloride) (copolymers of diallyldimethylammonium chloride and acrylamide with the variable composition) and poly(methacrylic acid, sodium salt) in the presence of organic water soluble dyes (alizarin, naphthol blue black, rhodamine) was studied. The collapse of the polyelectrolyte gels in the presence of oppositely charged dyes together with the effective absorption of dyes was observed. The shrinking degree and the dye absorption by the gel depend on the charges of the polymer network and the dye, and also on the dye concentration. Stability of the gel–dye complexes in a salt solution of NaCl and Al₂(SO₄)₃ was studied. It was shown that the complex stability in the salt solution depends on the charge density of the polymer chains forming the gel. The increase of charge density of polymer generally leads to the enhancement of the complex stability. For the systems with the fraction of charged poly(diallyldimethylammonium chloride) monomer units above 0.5 the release of alizarin to the external solution of Al₂(SO₄)₃ reservoir is practically completely suppressed. The obtained results show that oppositely charged dyes are generally from stable complexes with polyelectrolyte gels. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1209–1217, 1999     

Reaction mechanism of methanol decomposition on Pt‐based model catalysts: A theoretical study

The decomposition mechanisms of methanol on five different Pt surfaces, the flat surface of Pt(111), Pt‐defect, Pt‐step, Pt(110)(1 × 1), and Pt(110)(2 × 1), have been studied with the DFT‐GGA method using the repeated slab model. The adsorption energies under the most stable configuration of the possible species and the activation energy barriers of the possible elementary reactions involved are obtained in this work. Through systematic calculations for the reaction mechanism of methanol decomposition on these surfaces, we found that such a reaction shows the same reaction mechanism on these Pt‐based model catalysts, that is, the final products are all H (H_ads) and CO (CO_ads) via O? H bond breaking in methanol and C? H bond scission in methoxy. These results are in general agreement with the previous experimental observations. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010.     

A theoretical study on the decomposition mechanism of artemisinin

A theoretical study on the artemisinin decomposition mechanism is reported. The suggested pathways have been reproduced and the appearance of the final products can be explained in a satisfactory way. In addition, several intermediates and radicals have been found as relatively stable species, thus giving support to the current hypothesis that some of these species can be responsible for the antimalarial action of artemisinin and its derivatives.     

Molecular imprinting of natural flavonoid antioxidants: application in solid-phase extraction for the sample pretreatment of natural products prior to HPLC analysis

As shown in the past years, SPE based on molecularly imprinted polymers (MIPs) may provide significant enhancement of selectivity in sample preparation and analyte preconcentration. The objective of this work was the fabrication of MIPs for the specific adsorption of rutin and quercetin. The two flavonoids were used as the template molecules for the preparation of MIP phases in a self-assembly (noncovalent) approach. The produced MIPs were validated with regard to the imprinting efficiency as media for LC and SPE. The retention behavior of several flavonoid compounds was studied using as stationary phases imprinted, control nonimprinted polymers, and commercial silica-based materials. MIPs were applied as materials for the selective SPE and preconcentration of the flavonoids from white and red wine, orange juice, and tea. The collected fractions were analyzed by high-pressure LC. MIP-SPE facilitated specific analyte isolation and effective sample clean-up. The results show that molecularly imprinted SPE can be a useful tool for the simple, selective, and cost-effective pretreatment of samples containing natural antioxidants.     

Synthesis of the DE-ring of goniodomin A and prediction of its natural relative stereochemistry

Goniodomin A (1) was first isolated from Alexandrium hiranoi as a stereochemically unidentified antifungal agent in 1987 by Murakami. In this study, two stereoisomeric series of non-macrocyclic and macrocyclic DE-ring model compounds of 1 were synthesized, and the natural relative stereochemistry of the DE-ring was predicted by NMR comparison of 1 with these model compounds.     

酸洗预处理对纤维素热裂解的影响研究

为获得液体产量的最大化和提高产物中糖类的质量分数,采用盐酸（3%、5%、7%）、磷酸（7%）和硫酸（7%）对纤维素进行酸洗预处理。不同酸洗预处理下纤维素的微观结构和聚合度变化表明,酸处理损坏了纤维素的物理结构,并使聚合度大幅度降低。在“┣”形石英玻璃反应器的快速热裂解试验装置上进行了不同酸处理前后的纤维素热裂解试验,发现酸浸泡处理后,生物油产率下降,相应的气体和焦炭产率提高,并且随着酸浓度的提高,该趋势逐渐增强。与盐酸和磷酸相比,硫酸对生物油的生成具有更强的抑制作用,这表明,酸对纤维素交联和脱水反应的催化效果。通过GC-MS色质联机分析技术对生物油成分进行分析,发现酸的存在并没有改变生物油成分的种类,但使化合物之间的相对质量分数发生了变化。左旋葡聚糖的质量分数随稀酸溶液浓度的增加呈下降趋势,原因是残留在物料中的微量酸以催化脱水和交联反应的方式,对其生成起抑制作用。     

Thermal decomposition of natural and synthetic plumbojarosites: Importance in ‘archeochemistry’

Plumbojarosite and argentoplumbojarosite were sources of lead and silver in ancient and medieval times. The understanding of the chemistry of the thermal decomposition of these minerals is of vital importance in ‘archeochemistry’. The thermal decomposition of plumbojarosite was studied using a combination of thermogravimetric analysis coupled to a mass spectrometer. Three mass loss steps are observed at 376, 420 and 502 °C. These are attributed to dehydroxylation, loss of sulphate occurs at 599 °C, and loss of oxygen and formation of lead occurs at 844 and 953 °C. The temperatures of the thermal decomposition of the natural jarosite were found to be less than that for the synthetic jarosite. This is attributed to a depression of freezing point effect induced by impurities in the natural jarosite. Raman spectroscopy was used to study the structure of plumbojarosite. Plumbojarosites are characterised by stretching bands at 1176, 1108, 1019 and 1003 cm⁻¹ and bending modes at 623 and 582 cm⁻¹. Changes in the molecular structure during thermal decomposition were followed by infrared emission spectroscopy. The technique shows the loss of intensity in the hydroxyl stretching region attributed to dehydroxylation. Loss of sulphate only occurs after dehydroxylation. Lead is formed at higher temperatures through oxygen evolution.     

Reaction Mechanism on the Synergistic Photodegradation of Dye X3B and Photoreduction of Dichromate in the Presence of Polyoxometalate

Photodegradation of a textile dye X3B and photoreduction of dichromate (Cr(VI)) in an acidic aqueous solution were studied under 320 nm cut-off UV light irradiation in the presence of two polyoxometalates (POM), H₃PW₁₂O₄₀ (PW), and H₄SiW₁₂O₄₀ (SiW). The reactions in POM-X3B-Cr(VI) system were faster than those in POM-X3B, POM-Cr(VI), and X3B-Cr(VI) systems. For all reactions, PW was more photoactive than SiW. The reaction rates were proportional to the initial concentration of each component. The effects of N₂, O₂, and air were small but regular, indicating Cr(VI) photoreduction by a reduced POM. Quenching experiments with H₂O₂ and ethanol revealed that X3B photodegradation mainly occurred through hydroxyl radical (OH). It was proposed that the production of OH and a reduced POM⁻ by the reaction between H₂O and excited POM^* was the rate determining step, with which all evidence could be well interpreted. Different effects of POM concentration in a two- or three-component system on the reaction rates suggested that the reaction between H₂O and excited POM^* was reversible.     

杂多酸存在下X3B染料光降解和Cr(VI)光还原的协同反应机理

以H3PW12O40(PW)和H4SiW12O40(SiW)杂多酸(POM)为催化剂, 波长大于320 nm的高压氙灯为光源, 研究了混合水溶液中活性艳红染料X3B的光致降解和重铬酸根(Cr(VI))的光致还原. 结果表明, POM-X3B-Cr(VI)三元体系的反应效率高于POM-X3B、POM-Cr(VI)和X3B-Cr(VI)二元体系的反应效率, PW的光活性高于SiW, 且X3B光降解和Cr(VI)光还原之间存在明显的协同作用. 通过考察各组分起始浓度以及N2、O2、H2O2和乙醇的影响, 实验发现, 激发态POM*与H2O反应产生POM-和·OH是反应的决速步骤. X3B光降解和Cr(VI)光还原分别主要通过·OH 和POM-进行, 而X3B和Cr(VI)之间光化学反应的贡献较小. 在二元和三元体系中POM浓度对反应速率表现出不同的影响, 表明激发态POM*与H2O之间的反应具有可逆性.