Małgorzata Czerwicka

Application of Spectroscopic Methods for Structural Analysis of Chitin and Chitosan

Chitin, the second most important natural polymer in the world, and its N-deacetylated derivative chitosan, have been identified as versatile biopolymers for a broad range of applications in medicine, agriculture and the food industry. Two of the main reasons for this are firstly the unique chemical, physicochemical and biological properties of chitin and chitosan, and secondly the unlimited supply of raw materials for their production. These polymers exhibit widely differing physicochemical properties depending on the chitin source and the conditions of chitosan production. The presence of reactive functional groups as well as the polysaccharide nature of these biopolymers enables them to undergo diverse chemical modifications. A complete chemical and physicochemical characterization of chitin, chitosan and their derivatives is not possible without using spectroscopic techniques. This review focuses on the application of spectroscopic methods for the structural analysis of these compounds.

Identification of ionic liquid breakdown products in an advanced oxidation system

Commonly used alkylimidazolium ionic liquids are poorly to negligibly biodegradable, and some are toxic, with the potential to poison typical biological test systems. Therefore, when ionic liquids are present in technological wastewaters they could break through classical wastewater treatment systems into natural waters and become potentially persistent pollutants. A recent study investigating different advanced oxidation processes found that the H(2)O(2)/UV system degraded dissolved imidazolium ionic liquids with the greatest efficiency. In the present study, high performance liquid chromatography was coupled with electrospray mass spectrometry to separate, analyse and identify degradation products following the treatment of ionic liquid solutions with H(2)O(2) in the presence of UV irradiation. It was found that hydroxylation in short-chain entities occurred mainly within the ring moiety, whereas in the case of longer alkylated cations, oxidation of the alkyl chain yielded several products. The potential transformation products were identified structurally by MS/MS analysis and are discussed in the light of their putative toxicity and biodegradability.

Structure of the O-polysaccharide isolated from Cronobacter sakazakii 767

The Cronobacter spp., previously known as Enterobacter sakazakii, are Gram-negative enterobacterial pathogens that can cause necrotizing enterocolitis, meningitis, and septicemia with a high mortality rate in neonates. The O-specific polysaccharide (O-PS) was isolated from Cronobacter sakazakii strain 767 and structurally characterized using (1)H and (13)C NMR spectroscopy, including two-dimensional DQF-COSY, TOCSY, ROESY, HSQC, and HMBC experiments. Further compositional determination was undertaken using classical chemical methods followed by GLC, and GLC-MS analysis. The repeating unit of O-PS isolated from C. sakazakii 767 was a branched heptasaccharide composed of l-Rha, d-Glc, d-GlcNAc, and d-GalA, and had the structure shown below. One of the Rha residues was partially O-acetylated at C-4. C. sakazakii 767 was originally isolated from a fatal neonatal meningitic case, and the structure of its O-PS significantly differs from the O-PS structures previously described for Cronobacter spp.

Ionic Liquids: Methods of Degradation and Recovery

In recent years ionic liquids (ILs) have attracted considerable attention owing to their potential use in a diversified range of applications. It is believed that ILs can successfully replace volatile organic media in a wide range of chemical processes. They have been studied and applied in organometallic catalysis, organocatalysis and biocatalysis, where they provide unique reaction media offering better selectivity, faster rates and greater catalyst or enzyme stability in comparison to conventional solvents (Buszewski & Studzinska, 2008; Dupont et al., 2002; Liu et al., 2010; Mathews et al., 2000; Minami, 2009; Welton, 1999). The applications of ILs also include areas such as electrochemical transformation, fuel cells, solar cells, sensors and nanochemistry. They are emerging as lubricants, modifiers of mobile and stationary phases in the separation sciences, and are candidates for the dissolution of cellulose, starch and wood (Wassersheid & Welton, 2003). ILs are characterized by properties such as negligible vapour pressure and non-flammability under ambient conditions, high thermal conductivity, a wide electrochemical window and high polarity. They also have the ability to dissolve a wide diversity of materials, including salts, fats, proteins, amino acids, surfactants, sugars, polysaccharides and organic solvents. However, the most important attribute of ILs is the possibility of designing their properties to order. Thanks to the enormous number of cation and anion combinations, ILs can possess a wide spectrum of physical and chemical properties (solubility, polarity, viscosity or solvent miscibility), and they are already recognized by the chemical industry as new, target-oriented reaction media. The properties of ILs can be used for developing new processes that are technologically, environmentally and economically advantageous. Listed benefits include the possibilities of reusing and relatively easily recovering ILs, which effectively reduces the amount of waste generated during technological operations. It is, however, important to remember that ILs are still quite expensive media, and their recycling after regeneration or recovery makes such a technology economically all the more justified. Among available technologies, conventional processes such as distillation, membrane separation and extraction can be

Influence of the Chemical Structure and Physicochemical Properties of Chitin- and Chitosan-Based Materials on Their Biomedical Activity

Chitin and chitosan are an important family of linear polysaccharides consisting of varying amounts of ┚-(1→4)-linked 2-acetamido-2-deoxy-┚-D-glucopyranose (GlcNAc) and 2amino-2-deoxy-┚-D-glucopyranose (GlcN) units (Muzzarelli, 1973; Roberts, 1992). Chitin samples contain a high content of GlcNAc units; hence, they are insoluble in water and common organic solvents. On the other hand, they dissolve only in solvents such as N,Ndimethylacetamide, hexafluoroacetone or hexafluoro-2-propanol (Pillai et al., 2009; Austin, 1988; Kurita, 2001). When the degree of N-acetylation (defined as the average number of N-acetyl-D-glucosamine units per 100 monomers expressed as a percentage) is less than 50%, chitin becomes soluble in aqueous acidic solutions (pH < 6.0) and is called chitosan (Pillai et al., 2009). This means that the term “chitosan” represents a group of fully and partially deacetylated chitins, but a rigid nomenclature with respect to the degree of Ndeacetylation between chitin and chitosan has not been established (Ravi Kumar, 2000). Some authors consider that chitosan is a polysaccharide containing at least 60% GlcN residues (Aiba, 1992). According to the nomenclature proposed by the European Chitin Society (EUCHIS) (Roberts, 2007), chitin and chitosan should be classified on the basis of their insolubility and solubility in 0.1 M acetic acid; the insoluble material is called chitin, whereas the soluble one is chitosan. The structures of “ideal” chitin and “ideal” chitosan, and the “real“ structures of these compounds are presented in Figure 1. Chitin is the second most abundant polysaccharide (next to cellulose) synthesized by a great number of living organisms, serving in many functions where reinforcement and strength are required (Muzzarelli et al., 1986). In nature, chitin is found as structural components in the exoskeleton of arthropods or in the cell walls of fungi and yeast. It is also produced by a number of other living organisms in the lower plant and animal kingdoms. It has been

Chemometric optimization of derivatization reactions prior to gas chromatography–mass spectrometry analysis

Derivatization is a methodological technique that can be used to make an organic compound more suitable for qualitative and/or quantitative analysis (e.g. pharmaceuticals). However, many analysts try to avoid this analytical procedure as it is time-consuming and labour-intensive. On the other hand, an inter-laboratory study demonstrated that with regard to sensitivity and measurement uncertainty, gas chromatography coupled to mass-spectrometry was superior to liquid chromatography coupled to mass spectrometry for the trace analysis of organic compounds in matrices of greater complexity. In our previous paper (Kumirska et al., J. Chemometr. 25 (2011) 636-643) we suggested using principal component analysis (PCA) to optimize the derivatization of six compounds (5 oestrogenic steroids and diethylstilbestrol) prior to GC-MS analysis. In the present work we applied a highly sophisticated model - 24 pharmaceuticals derived from six classes of drugs. The efficiency of different derivatization reactions was evaluated by PCA and compared with that obtained from cluster analysis (CA), the latter method being applied in this context for the first time. Derivatization using N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and 1% trimethylchlorosilane (TMCS) in pyridine and ethyl acetate (2:1:1, v/v/v) for 30min at 60°C was found to be optimal. The SPE-GC-MS method was also validated and successfully applied to the analysis of selected pharmaceuticals in wastewater and surface waters in Poland.

Detection of Denatonium Benzoate (Bitrex) Remnants in Noncommercial Alcoholic Beverages by Raman Spectroscopy

Illegal alcoholic beverages are often introduced into market using cheap technical alcohol, which is contaminated by denatonium benzoate (Bitrex) of very small concentration. Bitrex is the most bitter chemical compound and has to be removed before alcohol consumption. The home‐made methods utilize sodium hypochlorite to disintegrate particles of denatonium benzoate in alcohol and to remove bitter taste before trading. In this experimental studies, we propose a novel method that detects in a fast way the remnants of denatonium benzoate in dubious alcohol samples by Raman spectroscopy. This method applies a portable Raman spectrometer of excitation wavelength 785 nm and utilizes the effect of surface‐enhanced Raman spectroscopy (SERS) to recognize the suspected alcoholic beverages. High effectiveness (over 98%) of YES/NO classification of the investigated samples was observed when the nonlinear algorithm support vector machine (SVM) was exploited at carefully adjusted detection parameters. The method can identify illicit alcohol within minutes.

A new silylation reagent dimethyl(3,3,3-trifluoropropyl)silyldiethylamine for the analysis of estrogenic compounds by gas chromatography-mass spectrometry.

In this study we applied DIMETRIS (dimethyl(3,3,3-trifluoropropyl)silyldiethylamine), a new silylating reagent, to derivative natural estrogens such as estrone (E1), 17β-estradiol (E2) and estriol (E3), as well as the synthetic 17α-ethinylestradiol (EE2) and the non-steroid diethylstilbestrol (DES). Its derivatizing properties were compared with those of the commonly used mixture of BSTFA (N,O-bis(trimethylsilyl)trifluoroacetamide)+1% trimethylchlorosilane (TMCS) and with MTBSTFA (N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide). The use of DIMETRIS for the silylation all of them is reported for the first time. The nucleophilic properties of DIMETRIS were found to be superior to those of MTBSTFA, but slightly inferior to those of BSTFA. It was used to derivatize steroid (E1, E2, E3 and EE2) and non-steroid (DES) estrogens at 30°C prior to GC/MS analysis. These DMTFPS-derivatives exhibited good separation (low retention times despite the high molecular masses) and ionization properties in GC/MS analyses (the highest relative response factors for DMTFPS-derivatives among those tested). However, DIMETRIS and MTBSTFA (which produce mono-O-silyl derivatives of EE2) should not be used for the simultaneous analysis of EE2 and E1. Only a mixture of BSTFA+1% TMCS in pyridine, which generates the fully derivatized EE2 product (stable in GC injector), permits the determination of these two estrogenic compounds during one GC-MS run. On the other hand, because DIMETRIS requires a lower derivatization temperature than BSTFA, it could be very useful for the derivatization of thermally unstable estrogenic compounds. In the next step of this study, the SPE-GC-MS method based on DIMETRIS derivatization for the analysis of DES, E2 and E3 in aqueous samples was evaluated and validated. The MQL values: 1.4, 1.6 and 1.5ngL(-1) for DES, E2 and E3, respectively, proved its suitability to determine target compounds in environmental samples. Finally, the proposed method was successfully applied to the analysis of selected estrogenic compounds in real seawater and wastewater samples in Poland.

Chemical structure of wall teichoic acid isolated from Enterococcus faecium strain U0317.

Wall teichoic acid (WTA) was isolated from Enterococcus faecium strain U0317 and structurally characterized using (1)H, (13)C, and (31)P NMR spectroscopy, including two-dimensional COSY, TOCSY, ROESY, HMQC, and HMBC experiments. Further compositional determination was undertaken using classical chemical methods and HF treatment followed by GLC and GLC-MS analyses. The repeating unit of WTA consisted of two residues of 2-acetamido-2-deoxy-D-galactose, glycerol (Gro), and phosphate, and has the structure shown below: [See formula in text].

Chemical structure of the O-polysaccharides isolated from Cronobacter turicensis sequence type 5 strains 57, 564, and 566

The Cronobacter spp. are Gram-negative bacterial pathogens that can cause infections in all age groups, and have a high mortality rate in neonates due to necrotizing enterocolitis and meningitis. Recent genotyping studies have revealed a strong clonal lineage in the genus, but this has not been compared with physiological traits. The O-polysaccharides (OPS) were isolated from three C. turicensis sequence type 5 strains (57, 564, and 566) and structurally characterized using (1)H and (13)C NMR spectroscopy, including two-dimensional DQF-COSY, TOCSY, ROESY, and HSQC analysis. Further compositional determination was undertaken using classical chemical methods followed by GLC, and GLC-MS analysis. The repeating unit of the isolated O-polysaccharides consists of GlcNAc, Rha, Glc, and had the structure shown below and therefore complemented the sequence type. [structure: see text].