Three competitive dissociation pathways of glyoxalate

Three possible lower barrier dissociation pathways of the deportonated glyoxylic acid in aqueous solution are predicated by means of B3LYP and CCSD（T） （single-point） methods. The calculated results suggest that the formation of formate ion is the energetically most favorable process, and that the decomposition reaction is occurring through nucleophilic attack of negatively charged carboxylic oxygen on the α-carbon. This is in good agreement with the proposed mechanisms of the mass spectrometry experiment.

Overview of the Synthesis, Characterization, and Application of Tannin-Glyoxal Adhesive for Wood-Based Composites

More than a century after its initial synthesis,urea-formaldehyde(UF)resins still have dominant applications as adhesives,paints,and coatings.However,formaldehyde in this industry produces formaldehyde emissions that are dangerous to health.Scientists have spent the last decade replacing formaldehyde and phenol with environmentally friendly substances such as glyoxal and tannin to create bio-based adhesives.This review covers recent advances in synthesizing glyoxal tannin-based resins,especially those made from sustainable raw material substitutes and changes made to synthetic processes to improve mechanical properties.The efficacy of using tannin-glyoxal adhesives in producing wood-based composites has been proven.The glyoxylate reaction forms cross-linked bridges between the aromatic sites of the tannin and glyoxal molecular structures.Glyoxal tannin adhesive with a greater percentage of glyoxal than tannin will produce an adhesive with better characteristics.The gel time reduces as the hardener concentration rises from 7.5%to 15%when glyoxal is used in adhesives.However,excessive amounts of glyoxal will result in a decrease in viscosity values.Glyoxal exhibits faster delivery degradation when it reaches a maximum temperature of approximately 130°C,although it initiates the curing process slightly slower at 110°C.Adding glyoxal to tannin-based adhesives can improve the mechanical properties of composite boards.The wet shear strength of the resulting plywood is increased by 105.4%with the addition of 5-weight percent tannin-based resin with glyoxal as a cross-linker in Soy Protein Adhesive.With glyoxal as a hardener,the panels produced showed good internal bond strengths(>0.35 MPa)and met the international standard specifications for interior-grade panels.

Crosslinking Mechanism of Soy Protein-based Adhesives based on Glyoxal and a Compound of Protein Model

The crosslinking mechanism of glyoxal and asparagine was analyzed,and the relationship between the mechanism and practical performances of soy protein-based adhesives was also discussed.It is shown that when pH=1 and 3,glyoxal reacted with asparagine in the form of major cyclic ether compounds.When pH=5,glyoxal reacted with asparagine in two structural forms of sodium glycollate and cyclic ether compounds.However,amidogens of asparagine were easy to develop protonation under acid conditions.Supplemented by the instability of cyclic ether compounds,the reaction activity and reaction degree between glyoxal and asparagine were relatively small.Under alkaline conditions,glyoxal mainly reacted with asparagine in the form of sodium glycollate.With the increase of pH,the polycondensation was more sufficient and the produced polycondensation products were more stable.The reaction mechanism between glyoxal and asparagine had strong correspondence to the practical performances of the adhesives.Glyoxal solution could develop crosslinking reactions with soy protein under both acid and alkaline conditions.Bonding strength and water resistance of the prepared soy protein-based adhesives were increased significantly.When pH>7,glyoxal had relatively high reaction activity and reaction intensity with soy protein,and the prepared adhesives had high crosslinking density and cohesion strength,showing relatively high bonding strength,water resistance and thermal stability.

Theoretical Studies on Mechanism and Rate Constant of Gas Phase Hydrolysis of Glyoxal Catalyzed by Sulfuric Acid

The gas phase hydration of glyoxal （HCOCHO） in the presence of sulfuric acid （H2SO4） were studied by the high-level quantum chemical calculations with M06-2X and CCSD（T） theoretical methods and the conventional transition state theory （CTST）. The mechanism and rate constant of the five different reaction paths are consid- ered corresponding to HCOCHO＋H2O, HCOCHO＋H2O… H2O, HCOCHO… H2O＋H2O, HCOCHO＋H2O… H2SO4 and HCOCHO… H2O＋H2SOa. Results show that H2SO4 has a strong catalytic ability, which can significantly reduce the energy barrier for the hydration reaction of glyoxal. The energy barrier of hydrolysis of glyoxal in gas phase is lowered to 7.08 kcal/mol from 37.15 kcal/mol relative to pre-reactive complexes at the CCSD（T）/6- 311＋＋G（3df, 3pd）//M06-2X/6-311＋＋G（3df, 3pd） level of theory. The rate constant of the H2SO4 catalyzed hydrolysis of glyoxal is 1.34×10-11 cm3/（molecule.s）, about 1013 higher than that involving catalysis by an equal number of water molecules, and is greater than the reaction rate of glyoxal reaction with OH radicals of 1.10×10-11 cm3/（molecule·s） at the room temperature, indicating that the gas phase hydrolysis of glyoxal of H2SO4 catalyst is feasible and could compete with the reaction glyoxal＋OH under certain atmospheric condi- tions. This study may provide useful information on understanding the mechanistic features of inorganic acid-catalyzed hydration of glyoxal for the formation of oligomer.

Oxidation of glyoxal to glyoxylic acid by oxygen over V_2O_5/C catalyst

A novel vanadium oxide catalyst supported on active carbon was prepared by an incipient wetness impregnation method, and the precursor was obtained from oxalic acid aqueous solutions of NH4VO3. The catalyst was applied liquid phase oxidation of glyoxal to glyoxylic acid. It was found that V2O5/C catalyst exhibited obvious activity for glyoxal oxidation. Glyoxylic acid could be obtained without pH regulation during the reaction. By using this catalyst, the conversion of glyoxal and the yield of glyoxalic acid were 29.2% and 13.6%, respectively at 313 K and oxygen flow 0.1 L/rain after reaction for 10 h.

Study on the Soy Protein-Based Adhesive Cross-Linked by Glyoxal

Based on the ESI-MS and ^(13)C-NMR analysis of the forms of glyoxal in acidic and alkaline solutions,the soy-based adhesive cross-linked by glyoxal was prepared in this work.The results showed that glyoxal existed in water in different forms at different pH levels.Under alkaline conditions,glyoxal transformed to glycolate through the intramolecular disproportionation reaction.Under acidic conditions,although some of glyoxal transformed to glycolate as what happened under alkaline conditions,most of glyoxal molecules existed in the form of fiveor six-membered cyclic ether structure.No ethylene tetraol or free aldehyde group was actually detected under these conditions.Although glyoxal reacted with soy protein under both acidic and alkaline conditions,alkaline conditions were more favorable for the improvement of mechanical performance and water resistance of soybased adhesives than acid conditions.

Ultrasonicwave-assisted tandem-reaction for synthesis of symmetrical vicinal diamines

A practical synthesis of symmetrical vicinal diamines with broad chemistry scope is described. The key step is the ultrasonicwave promoted tandem-reaction, two-step reaction sequence combining Mannich double condensations with benzo- triazole, glyoxal and primary or secondary amines and reduction of the bis（benzotriazole）-adducts with sodium borohydride proceeded smoothly in tetrahydrofuran in high yield at room temperature.

AN EXPERIMENTAL STUDY ON THE SOL/GEL PHASE TRANSITION OF LINEAR POLYMER IN THE PRESENCE OF CROSSLINKERS

The sol/gel phase diagrams were studied for two systems: polyacrylamide/Cr (III) and polyacrylamide/glyoxal. Sol or gel phase could be distinguished according to the concentrations of polymer and crosslinker. The boundary polymer concentration did not depend on the types of gelation and decreased with increasing polymer dimension (molecular weight and conformation). The gelation, which is basically interchain bonding, requires the occurrence of entanglement. The overlap concentration is thus considered as the minimum polymer concentration required for gelation.

Formaldehyde Free Renewable Thermosetting Foam Based on Biomass Tannin with a Lignin Additive

This study presents easily prepared free formaldehyde bio-based foam based on a prepared thermosetting resin comprising tannin–lignin–furfuryl alcohol-glyoxal(TLFG)via mechanical stirring in presence of ether as a foaming agent.The foam was developed through a co-polycondensation reaction of glyoxal and furfuryl alcohol with condensed tannin and lignin,which is a forest-derived product.Investigation using scanning electron microscopy(SEM)showed more closed-cell structure without cracks and collapse in the TLFG foam,with a higher apparent density with respect to tannin–furanic–formaldehyde(TFF)foam.Differential scanning calorimetry(DSC),dynamic thermomechanical analysis(DTMA),and thermogravimetric analysis(TGA)investigations revealed that the curing process of TLFG foam proceeds easily even at a lower temperature.Additionally,it acquired higher heat resistance than TFF foam.Moreover,TLFG has a more robust chemical network structure,which contributes efficiently to the mechanical strength and a lower pulverization degree compared with TFF-derived foam.Fourier transform infrared spectrometry(FTIR)and electrospray ionization mass spectrometry(ESI-MS)proved that the cross-inking reactions between tannin,lignin,furfuryl alcohol,and glyoxal have been proceeded efficiently.

Crosslinking as an Efficient Tool for Decreasing Moisture Sensitivity of Biobased Nanocomposite Films

Chitosan-nanoclay bio-hybrid films were successfully crosslinked with glutaraldehyde, genipin and glyoxal. Moisture sensitivity of films decreased as a result of crosslinking which led to improved barrier properties against water vapor and oxygen. Films containing chitosan (6.6 g/m2) with genipin (3.3 g/m2) and nanoclay (6.6 g/m2) had water vapor transmission rate of 72 g × 100 μm/(m2 × 24 h) which was 34% lower as compared to pure chitosan and 30% lower as compared to chitosan/nanoclay without crosslinkers. Glyoxal induced crosslinking resulted in 92% reduction in oxygen transmission rate at 80% relative humidity as compared to pure chitosan films. Oxygen transmission through glyoxal (3.3 g/m2) treated chitosan/nanoclay film was 2.8 cm3 × 100 μm/(m2 × 24 h) which was 53% lower as compared to chitosan/nanoclay without crosslinkers. In addition, nanoclay and especially glyoxal crosslinking prevented the water vapor sorption of chitosan considerably. Crosslinking may be used as an efficient tool for enhancing the exploitability of naturally hydrophilic biopolymers towards new high-value applications, such as food packaging.

Study on Various Compositions of Polyvinyl Alcohol and Starch Blends by Cross-Linking with Glyoxal

The aim of this study is to analyze the various compositions of polyvinyl alcohol (PVA) and starch blends. The blends have been cross-linked with glyoxal to enhance its properties. The hydroxyl groups of PVA and starch react with glyoxal via formation of acetal bonds;hence crosslinking could take place. The cross-linking of glyoxal is observed in various analytical methods such as DSC and FTIR. The cross-linked blends showed better thermal and mechanical properties. Viscosity, tensile shear strength, pencil hardness and ultimate stress were evaluated to estimate the changes due to cross-linking. It was observed that the cross-linking is directly proportional to starch, since the starch hydroxyl groups are easily accessible for reacting. The cross-linked blend showed better cohesion between its chains, thereby increasing glass transition temperature. It was reflected in the subsequent increase in tensile strength properties.

Chlorine-radical Induced Oxidation of Glyoxal and Glyoxal-S(IV) Adducts in the Aqueous Phase

A laser flash photolysis study of the reactivity of Cl˙with glyoxal, glyoxal mono- and dibisulfite adducts, 1-hydroxy-2, 2-diol-ethanesulfonate and 1, 2-dihydroxy-1, 2-ethanedi sulfonate in the aqueous phase was carried out. The obtained rate constants can be used for atmospheric modeling.

Glyoxal induced advanced glycation end products formation in chicken meat emulsion instead of oxidation

Advanced glycation end products(AGE) are potential harmful substances formed in the advanced Maillard reaction and increasingly investigated in muscle foods. However, the contribution of oxidation to the AGE formation is controversial. Moreover, reports on glyoxal(GO) induced AGE formation in chicken meat emulsion(CME) are limited. Thus, the effects of GO on emulsifying properties, rheological behavior and AGE formation in CME were investigated. Our findings exhibited that levels of Nε-carboxymethyllysine(CML) and Nε-carboxyethyllysine(CEL) were associated with lipid oxidation but not significantly(P > 0.05). Levels of AGE peaked when GO concentration ranged from 5 mmol/L(CML) to 10 mmol/L(CEL). The droplets’ aggregation associated with the disulfide bond when the concentration of GO was at 0.5–30 mmol/L while non-disulfide bond association occurred at 30–50 mmol/L GO concentration. In conclusion, compared to the effect of oxidation, GO exhibited the main role in the AGE formation of CME. This study will provide theoretical significance for further understanding and controlling the formation of AGE in CME.

Study of the Crosslinking of PVA with Glyoxal in LbL Nanocomposites

Crosslinking is a common practice to improve the barrier properties of polymers. In this study, Montmorillonite (MMT) was used with Polyvinyl alcohol (PVA) to deposit nanocomposite coatings which were crosslinked with glyoxal (Gly) by Layer by Layer (LbL) on a PET substrate. Two crosslinking conditions were studied, under mild condition and with an acidic environment. Mild condition was useful to identify the reversibility steps and the optimum crosslinking times while the acidic environment was essential to investigate the crosslinking mechanism, by determining the permeability for different crosslinking times. PVA and PVA-MMT coatings showed a strong correlation between the permeability coefficients for different crosslinking times and the FTIR results.

Rapid Determination of Calcium in Milk and Water Samples by Reflectance Spectroscopy

Reflectance spectroscopy (RS) can be used as a rapid and sensitive method for the quantitative determination of low amounts of calcium. In this analytical technique, the analyte in complex samples is extracted onto a solid sorbent matrix loaded with glyoxal bis (2-hydroxyanil (GBHA) and then quantified directly on the sorbent surface. The measurements were carried out at a wavelength of 566.1 nm yielding the largest divergence of reflectance spectra before and after reaction with the analyte element. The optimum response was obtained in 0.2 mol●L–1 NaOH solution, and the response time of the sensor was about 5 min, depending on the concentration of Ca(II). The calibration curve of Ca(II) was found to be linear on semi-logarithmic scale within the concentration range of 0.3 - 40 mg●L–1, with a LOD of 0.15 mg●L–1 in the low concentration range. The sensor response from different sensors (n = 5) gave an R.S.D. of 1.4% at 10 mg●L–1 Ca(II). The response characteristics of the sensor including dynamic range, reversibility, reproducibility, response time and lifetime are discussed in detail. The main advantages of this prototype device are sensitivity and higher selectivity over Mg(II). The proposed method has been successfully applied to the determination of Ca(II) in milk and drinking water samples.

Reactive carbonyl compounds(RCCs) cause aggregation and dysfunction of fibrinogen

Fibrinogen is a key protein involved in coagulation and its deposition on blood vessel walls plays an important role in the pathology of atherosclerosis.Although the causes of fibrinogen(fibrin)deposition have been studied in depth,little is known about the relationship between fibrinogen deposition and reactive carbonyl compounds(RCCs),compounds which are produced and released into the blood and react with plasma protein especially under conditions of oxidative stress and inflammation.Here,we investigated the effect of glycolaldehyde on the activity and deposition of fibrinogen compared with the common RCCs acrolein,methylglyoxal,glyoxal and malondialdehyde.At the same concentration(1 mmol/L),glycolaldehyde and acrolein had a stronger suppressive effect on fibrinogen activation than the other three RCCs.Fibrinogen aggregated when it was respectively incubated with glycolaldehyde and the other RCCs,as demonstrated by SDS-PAGE,electron microscopy and intrinsic fluorescence intensity measurements.Staining with Congo Red showed that glycolaldehyde-and acrolein-fibrinogen distinctly formed amyloid-like aggregations.Furthermore,the five RCCs,particularly glycolaldehyde and acrolein,delayed human plasma coagulation.Only glycolaldehyde showed a markedly suppressive effect on fibrinogenesis,none did the other four RCCs when their physiological blood concentrations were employyed,respectively.Taken together,it is glycolaldehyde that suppresses fibrinogenesis and induces protein aggregation most effectively,suggesting a putative pathological process for fibrinogen(fibrin)deposition in the blood.

Investigating the impact of Glyoxal retrieval from MAX-DOAS observations during haze and non-haze conditions in Beijing

This study presents the Multi Axis Differential Optical Absorption Spectroscopy(MAXDOAS) measurements for Glyoxal(CHOCHO) in Beijing, China(39.95°N, 116.32°E). CHOCHO is the smallest compound of di-carbonyl group. As a primary sink of CHOCHO, its photolysis with NOx(oxides of nitrogen) results in the production of tropospheric ozone. Therefore,the focus of CHOCHO DOAS measurements is increasing in trend. We did the measurements from 09 May 2017 to 09 September 2017. The study was conducted to compare different retrieval settings in order to reveal best DOAS fit settings for CHOCHO;furthermore, effect of haze and non-haze days on CHOCHO concentration was examined.The root mean square of residual and Differential Slant Column density(dSCD) error was reduced when measurements were done with lower wavelength limit around 432–438 nm and upper intervals around 455–460 nm. Thus, lower wavelength intervals around432–438 nm and upper intervals around 457–460 nm were best for the retrieval of dSCDs for CHOCHO. Meteorological conditions like haze or non-haze days did not have significant effect on DOAS fit parameters. The CHOCHO vertical column densities range from 1.33 E +14 to 9.77 E + 14 molecules/cm2 during the study period with average of 6.16 E +14 molecules/cm2. The results indicated that during haze days CHOCHO concentration was higher because of lower rate of photolysis and atmospheric oxidation potential. Our results did not show any significant weekend effect on CHOCHO atmospheric concentration.

Vertical distribution and temporal evolution of formaldehyde and glyoxal derived from MAX-DOAS observations:The indicative role of VOC sources

Formaldehyde(HCHO)and glyoxal(CHOCHO)are important oxidization intermediates of most volatile organic compounds(VOCs),but their vertical evolution in urban areas is not well understood.Vertical profiles of HCHO,CHOCHO,and nitrogen dioxide(NO_(2))were retrieved from ground-based Multi-Axis Differential Optical Absorption Spectroscopy(MAXDOAS)observations in Hefei,China.HCHO and CHOCHO vertical profiles prefer to occur at higher altitudes compared to NO_(2),which might be caused by the photochemistry-oxidation of longer-lived VOCs at higher altitudes.Monthly means of HCHO concentrations were higher in summer,while enhanced amounts of NO_(2)were mainly observed in winter.CHOCHO exhibited a hump-like seasonal variation,with higher monthly-averaged values not only occurred in warm months(July-August)but also in cold months(November-December).Peak values mainly occurred during noon for HCHO but emerged in the morning for CHOCHO and NO_(2),suggesting that HCHO is stronger link to photochemistry than CHOCHO.We further use the glyoxal to formaldehyde ratio(GFR)to investigate the VOC sources at different altitudes.The lowest GFR value is almost found in the altitude from 0.2 to 0.4 km,and then rises rapidly as the altitude increases.The GFR results indicate that the largest contributor of the precursor VOC is biogenic VOCs at lower altitudes,while at higher altitudes is anthropogenic VOCs.Our findings provide a lot more insight into VOC sources at vertical direction,but more verification is recommended to be done in the future.

Investigating missing sources of glyoxal over China using a regional air quality model (RAMS-CMAQ)

Currently, modeling studies tend to significantly underestimate observed space-based glyoxal （CHOCHO） vertical column densities （VCDs）, implying the existence of missing sources of giyoxal. Several recent studies suggest that the emissions of aromatic compounds and molar yields of glyoxal in the chemical mechanisms may both be underestimated, which can affect the simulated glyoxal concentrations. In this study, the influences of these two factors on glyoxal amounts over China were investigated using the RAMS-CMAQ modeling system for January and July 2014. Four sensitivity simulations were performed, and the results were compared to satellite observations. These results demonstrated significant impacts on glyoxal concentrations from these two factors. In case 1, where the emissions of aromatic compounds were increased three-fold, improvements to glyoxal VCDs were seen in high anthropogenic emissions regions. In case 2, where molar yields of glyoxal from isoprene were increased five-fold, the resulted concentrations in July were B-B-fold higher, achieving closer agreement between the modeled and measured glyoxal VCDs. The combined changes from both cases 1 and 2 were applied in case B, and the model succeeded in further reducing the underestimations of glyoxal VCDs. However, the results over most of the regions with pronounced anthropogenic emissions were still underestimated. So the molar yields of giyoxal from anthropogenic precursors were considered in case 4. With these additional mole yield changes （a two-fold increase）, the improved concentrations agreed better with the measurements in regions of the lower reaches of the Yangtze River and Yellow River in January but not in July.

V_2O_5/C catalyst for liquid phase oxidation of glyoxal to glyoxylic acid

A study of the catalytic activity of V2O5/C catalyst for the oxygen oxidation of glyoxal has been made, showing that glyoxylic acid can be formed without control of pH value and there is little oxalic acid from the excessive oxidation of glyoxylic acid. The studies of XRD and TEM have shown that V2O5 diffraction peaks gradually strengthen with the increase of the content of V2O5. With the content of 3% V2O5 and the calcination temperature of 573 K, V2O5/C catalyst displayed the best activity and selectivity. The conversion of glyoxal and the selectivity of glyoxylic acid reached 18.76% and 77.70% after 5 h, respectively. Moreover, V2O5/C catalyst showed small deactivation after recycling three times, which indicates that V2O5/C has a higher stability than noble metal catalysts in the reaction medium.