Cyclocondensation of 2,3-butanedione in the presence of amino acids and formation of 4,5-dimethyl-1,2-phenylendiamine

The chemical interaction of 2,3-butanedione with amino acids through Strecker reaction has been studied extensively. However, the formation of previously reported 4,5-dimethyl-1,2-benzoquinone from 2,3-butanedione/amino acid model systems has not been investigated in detail. In this study such model systems containing 2,3-butanedione were investigated under pyrolytic conditions using glycine, sodium glycinate and glycine hydrochloride as amino acids able to modulate acid/base catalytic activity of the reaction medium. The analysis of the data indicated that replacing glycine with its corresponding salts promoted significantly the generation of 2,3,6,7-tetramethylquinoxaline relative to tetramethylpyrazine, the indicator compound for the Strecker reaction. The origin of the 2,3,6,7-tetramethylquinoxaline was traced back to the formation of 4,5-dimethyl-1,2-benzoquinone through isotope labelling studies. Furthermore, these studies have also indicated the ability of glycine not only to catalyse the cyclocondensation of butanedione into 4,5-dimethyl-1,2-benzoquinone but also its conversion into 4,5-dimethyl-1,2-phenylenediamine through Strecker-type transformations. The trapping of 2,3-butanedione by this in situ generated 4,5-dimethyl-1,2-phenylenediamine gave rise to the observed 2,3,6,7-tetramethylquinoxaline.     

Functional and molecular properties of calcium precipitated soy glycinin and the effect of glycation with κ-carrageenan

This study describes an extraction process for the preparation of highly purified calcium precipitated glycinin (11S). Initial extraction of soy proteins using isoelectric precipitation at pH 6.8 followed by cryo-precipitation yielded 4.2% product (11S) recovery with 98% protein purity for the control extracted with NaOH. Addition of calcium chloride (CaCl₂) doubled the extraction yield (9%) compared to the control and when two other salts were used (i.e., sodium (Na₂SO₄) and ammonium (NH₄)₂SO₄ sulfate, average yields of 4.4% and 5.17%, respectively). Thermal and molecular stability under varying conditions (pH, salts, SDS as a protein structure perturbing agent), and effect of glycation on functional and structural properties were investigated. Size exclusion chromatography and electrophoresis confirmed the predominance of a major band with MW of ～342 kDa with 98.4% purity. Differential scanning calorimetry (DSC) yielded one endothermic transition peak at 95.5 °C. Denaturation temperatures were >100 °C for all salt concentrations studied. The pH had a dominant influence on the structural properties of glycinin. In the presence of NaCl and CaCl₂ (0.2–1 M), the protein structure showed very little denaturation and no aggregation bands were observed even on heating to 95 °C. Lower SDS concentrations (0.5–1%) resulted in denaturation and aggregation, while at 2% SDS only denaturation was observed. Glycation did not alter the conformational structure of protein. Improvements in surface properties were observed with moderate degree of glycation (6–24 h).     

Vinylogous Amadori rearrangement: implications in food and biological systems

The 4-hydroxy-alkenals are important lipid peroxidation products and are known to play a major role both in the development of degenerative diseases in biological systems and off-flavors, or rancidity in food systems. The 4-hydroxy-alkenals can also be formed in nonlipid systems from 2-deoxy-sugar moieties such as 2-deoxy-ribose. FTIR spectroscopic evidence was provided for such a transformation catalyzed by amino acids through monitoring the decrease in intensity of the aldehydic band centered at 1716 cm(-1) of the open form of 2-deoxy-ribose and increase in the intensity of the formed conjugated aldehydic band centered at 1672 cm(-1). Furthermore, 4-hydroxy-alkenals can react with nitrogen nucleophiles such as amino acids and proteins to form Schiff base adducts that are able to undergo vinylogous Amadori rearrangement (vARP) and subsequently cyclize to generate a pyrrole moiety. This cyclization is prevented in the case of secondary amino acids such as proline to form a stable vinylogous Amadori rearrangement product (vARP). Monitoring this reaction of proline with 4-hydroxy-2-nonenal (HNE) has indicated that within 15 min at 28 degrees C the 1685 cm(-1) band of HNE completely disappears and that at 50 degrees C, vARP is formed within 5 min, as indicated by the formation of a characteristic band at 1709 cm(-1).     

Thermal degradation of sucralose and its potential in generating chloropropanols in the presence of glycerol

Sucralose, a polychlorinated synthetic high-intensity sweetener is being increasingly used in relatively large amounts in baked products under high temperature environments. This necessitates understanding its thermal decomposition and studying the consequences of hydrogen chloride release from sucralose and its ability to chlorinate various food related ingredients such as glycerol to generate chloropropanols a potentially toxic class of compounds. Studies conducted on the thermal degradation of sucralose under dry heating conditions have indicated that the glycosidic cleavage occurs through the formation of a galactopyranosyl cation contrary to sucrose where fructofuranosyl cation dictates the major breakdown products. Consequently the major product detected was levoglucosenone and its precursor. Subsequent degradation of the two monosaccharide derivatives causes dehydrochlorination and dehydration reactions to produce furan-related products. In addition, pyrolysis of sucralose in the presence of glycerol generated significant amounts of 3-monochloropropanediol and 1,2- and 1,3-dichloropropanols based on the relative intensities of their chromatographic peaks which amounted to 15% of the total chromatographic peak area.     

伊拉克摩苏尔大坝溃坝危机与解决方案

摩苏尔大坝是一座多用途填土坝,长3.4 km,高113 m,库容11.11 km3,死库容2.95 km3。大坝位于伊拉克北部的底格里斯河,距离摩苏尔城西北约60 km。大坝建在熔岩高度岩溶的石膏、泥岩和石灰岩床上。大坝于1986年开始运行,从那时,由于石膏床溶解、存在岩溶作用、以及地下水的影响,渗流问题就开始显现了。为停止渗流,确保大坝的稳定,防渗灌浆的方案一直未停止。2014年,ISIS占领了大坝地区,停止了灌浆作业,情况恶化。对近期状况的评估表明,大坝有随时溃坝风险。一旦溃坝,将有600万人受灾、7 202 km2的土地被淹没。为了阻止这场灾难,灌浆作业应该继续进行,以延长大坝寿命。水库内水位应保持低位,以减少溃坝造成的危害。作为永久解决方案,应在摩苏尔大坝下游建造另一座大坝,以抵挡摩苏尔溃坝的下泄洪水。     

Chromatographic Separation of Synthesized Phenolic Lipids from Krill Oil and Dihydroxyphenyl Acetic Acid

The separation and characterization of novel biomolecules, phenolic lipids, obtained by the enzymatic transesterification in organic solvent-free media of krill oil with 3,4-dihydroxyphenylacetic acid were investigated. The experimental findings showed that by increasing the polarity of the gradient eluent and by decreasing the solvent strength of the mobile phase, from methanol to acetonitrile, a higher resolution was obtained. The use of a shorter column and smaller particle packing size resulted in an enhancement of the efficiency, with decreases in both separation time and solvent consumption. Overall, the evaporative light-scattering detector (ELSD) showed better repeatability of the resolution (R), theoretical plate number (n), plates per meter (N) and the retention time values as compared to that of the UV detection at 210 and 280 nm. In terms of detection and repeatability, ELSD was shown to be a more appropriate tool for the quantitative analysis of the components of krill oil and its esterified phenolic lipids than UV detection. Fourier transform infrared spectroscopy analysis tentatively confirmed the nature of the separated compounds. In addition, the structural analyses of novel biomolecules by HPLC–MS–APCI/ESI suggested the formation of two phenolic monoacylglycerols.     

Formation of the peptide-specific imidazolidin-4-one moiety in alanine containing Maillard reaction mixtures

Due to the facile formation of amide linkages during Maillard reaction and their possible conversion into imidazolidin-4-one moiety through interaction with aldehydes, such structures were sought and identified in simple Maillard model systems such as alanine, glucose/alanine, and glyoxal/alanine to minimise the complexity of the possible imidazolidin-4-one structures and to facilitate the interpretation of label incorporation data. To confirm the formation of imidazolidin-4-ones in these model systems a useful strategy based on Py-GC/MS analysis was developed using isotope labelling technique to identify products incorporating two nitrogen atoms, three C-3′, three C-2′ and one C-1′ atom from alanine. Products simultaneously possessing these atom configurations and having a molecular weight of 142 amu were targeted using specifically labelled precursors such as [¹⁵N]alanine, [¹³C-1]alanine, [¹³C-2]alanine, [¹³C-3]alanine and [U-¹³C₆]glucose. Based on isotope labelling studies, spiking with known precursors and comparison with established mass spectral fragmentation patterns, the formation of isomeric 3-ethyl-2,5-dimethylimidazolidin-4-ones was proposed.     

Chemistry of Amadori rearrangement products: Analysis,synthesis, kinetics,reactions, and spectroscopic properties

The chemistry of the key intermediate in the Maillard reaction, the Amadori rearrangement product, is reviewed covering the areas of synthesis, chromatographic analyses, chemical and spectroscopic methods of characterization, reactions, and kinetics. Synthetic strategies involving free and protected sugars are described in detail with specific synthetic procedures. GC‐ and HPLC‐based separations of Amadori products are discussed in relation to the type of columns employed and methods of detection. Applications of infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy for structural elucidation of Amadori products are also reviewed. In addition, mass spectrometry of free, protected, and protein‐bound Amadori products under different ionization conditions are presented. The mechanism of acid/base catalyzed thermal degradation reactions of Amadori compounds, as well as their kinetics of formation, are critically evaluated.     

Insight into Isomeric Diversity of Glycated Amino Acids in Maillard Reaction Mixtures

Maillard reactions generate a wide array of amino acid- and sugar-derived intermediates; the isomeric mixtures of glycated amino acids are of particular interest. Excluding stereoisomers, regioisomers, and various anomers, most amino acids can form two monoglycated and three N,N-diglycated isomers when reacted with sugars during the Maillard reaction. Using synthetic Schiff bases and Amadori compounds as standards, we have demonstrated that diagnostic ions obtained from MS/MS fragmentations in negative ionization mode can be used effectively for the discrimination between glucose-derived Schiff bases and their corresponding Amadori compounds in both mono- and diglycated forms. The utilization of these diagnostic ions and isotopic labeling in the glycine/glucose model system revealed that milling glucose/glycine mixtures for 30 min/30 Hz at ambient temperature produced monoglycated glycine in equal proportions of Amadori and Schiff base forms, whereas diglycated glycine was a mixture of the three isomers: Schiff-Schiff, Schiff-Amadori, or Amadori-Amadori in approximately equal molar proportions. The above results were further corroborated using a synthetic histidine Amadori product, N,N-difructosyl-β-alanine, dipeptides, and ribose. Using mechanochemistry as a convenient synthetic tool in combination with MS/MS diagnostic ions, the isomeric diversity of the early stages of the Maillard reaction can be revealed.