Selected Model Compounds Research Articles

Attempts on Fluorinative Transformation of Selected Functionalized Cycloalkene Scaffolds through Aziridination/Aziridine-Opening Protocol

AbstractStudies on the transformations of some functionalized cycloalkene derivatives through their ring olefin-bond aziridination/aziridine opening with fluoride are presented. The selected model compounds submitted to fluorinative functionalization were an amino ester and diesters with a cyclohexene skeleton as well as a cyclopentene-fused β-lactam. Functionalization proceeded across a substrate-directed diastereoselective olefin-bond aziridination, followed by fluoride-mediated aziridine opening or intramolecular lactonization giving some fluorinated amino ester or amino lactone derivatives.

Insights into the selectivity of polar stationary phases based on quantitative retention mechanism assessment in hydrophilic interaction chromatography

Hydrophilic interaction chromatography (HILIC) offers different selectivity than reversed-phase liquid chromatography (RPLC). However, our knowledge of the driving force for selectivity is limited and there is a need for a better understanding of the selectivity in HILIC. Quantitative assessment of retention mechanisms makes it possible to investigate selectivity based on understanding the underlying retention mechanisms. In this study, selected model compounds from the Ikegami selectivity tests were evaluated on different polar stationary phases. The study results revealed significant insights into the selectivity in HILIC. First, hydroxy and methylene selectivity is driven by hydrophilic partitioning; but surface adsorption for 2-deoxyuridine or 5-methyluridine reduces the selectivity factor. Furthermore, the retention of 2-deoxyuridine or 5-methyluridine by surface adsorption in combination with the phase ratio explain the difference in hydroxy or methylene selectivity observed among different stationary phases. Investigations on xanthine positional isomers (1-methylxanthine/3-methylxanthine, theophylline/theobromine) indicate that isomeric selectivity is controlled by surface adsorption; however, hydrophilic partitioning may contribute to resolution by enhancing overall retention. In addition, two pairs of nucleoside isomers (adenosine/vidarabine, 2′-deoxy and 3′-deoxyguanosine) provide an example that isomeric selectivity can also be controlled by hydrophilic partitioning if their partitioning coefficients are significantly different in HILIC. Although more data is needed, the current study provides a mechanistic based understanding of the selectivity in HILIC and potentially a new way to design selectivity tests.

Role of Nb2O5 Crystal Phases on the Photocatalytic Conversion of Lignin Model Molecules and Selectivity for Value-Added Products.

The photocatalytic conversion in aqueous media of phenol and guaiacol as a lignin model compound using Nb2O5 with different crystal phases was studied. Nb2O5 particles were synthesized using hydrothermal methods, where it was observed that changes in the solvent control their morphology and crystal phase. Different photocatalytic behavior of Nb2O5 was observed with the selected model compounds, indicating that its selection directly impacts the resulting conversion and selectivity rates as well as the reaction pathway, highlighting the relevance of model molecule selection. Photocatalytic conversion of phenol showed conversion rate (C%) up to 25 % after 2 h irradiation and high selectivity (S%) to pyrogallol (up to 50 %). Orthorhombic Nb2O5 spheres favored conversion through free hydroxyl radicals while monoclinic rods did not convert phenol. Guaiacol photocatalytic oxidation showed high conversion rate but lower selectivity. Orthorhombic and monoclinic Nb2O5 favored the formation of resorcinol with S % ~0.43 % (C % ~33 %) and ~13 % (C % ~27 %) respectively. The mixture of both phases enhanced the guaiacol conversion rate to ~55 % with ~17 % of selectivity to salicylaldehyde. The use of radical scavengers provided information to elucidate the reaction pathway for these model compounds, showing that different reaction pathways may be obtained for the same photocatalyst if the model compound is changed.

An Ex vivo Investigation on Drug Permeability of Sheep Nasal Epithelial Tissue Membranes from the Respiratory and Olfactory Regions.

Besides systemic drug delivery, the intranasal route of administration has shown potential for direct nose-to-brain drug delivery, which has gained popularity because it bypasses the blood-brain barrier. The region in the nose from which the epithelial tissue membrane is excised to conduct ex vivo permeation studies for nasal drug delivery studies may be of importance, but the permeability of the epithelium from the different nasal regions has not yet been investigated in the sheep model. The permeation of five selected model compounds (i.e., atenolol, caffeine, Rhodamine 123, FITC-dextran, and Lucifer Yellow) was measured across epithelial tissues that were excised from two different areas of the sheep nasal cavity, namely the ventral nasal concha (representing respiratory epithelium) and the ethmoid nasal concha (representing olfactory epithelium). Although the selected compounds' permeation was generally slightly higher across the olfactory epithelial tissues than across the respiratory epithelial tissues, it was not statistically significant except in the case of atenolol. The presence of olfactory nerves and supporting cells and the gaps between them in the olfactory epithelial tissues may have contributed to the higher permeation of atenolol, but this needs to be further investigated to elucidate the precise mechanism.

Development of hydrolytic stability screening methods for early drug discovery with high differentiation and predictive power

In early drug discovery, hydrolytic chemical stability is routinely assessed to ensure future developability of quality compounds and stability in in vitro test environments. When conducting high-throughput hydrolytic stability analyses as part of the compound risk assessment, aggressive conditions are typically applied to allow for faster screening. However, it can be challenging to extrapolate the real stability risk and to rank compounds due to over-estimating risk based on aggressive conditions and the narrow discriminative window. In this study, critical assay parameters including temperature, concentration, and detection technique were systematically assessed using selected model compounds, and the impact and interplay of these parameters on predictive power and prediction quality were evaluated. Improved data quality was achieved using high sample concentration and reduced temperature, combined with ultraviolet (UV) detection, while mass spectrometry (MS) detection was found to be a useful complementary detection technique. Therefore, a highly discriminative stability protocol with optimized assay parameters and experimental data quality is proposed. The optimized assay can provide early guidance on the potential stability risk of a drug molecule as well as enable more confident decision-making in compound design, selection, and development.

Elucidating Biomass-Derived Pyrolytic Lignin Structures from Demethylation Reactions through Density Functional Theory Calculations

Pyrolytic lignin is a fraction of pyrolysis oil that contains a wide range of phenolic compounds that can be used as intermediates to produce fuels and chemicals. However, the characteristics of the raw lignin structure make it difficult to establish a pyrolysis mechanism and determine pyrolytic lignin structures. This study proposes dimer, trimer, and tetramer structures based on their relative thermodynamic stability for a hardwood lignin model in pyrolysis. Different configurations of oligomers were evaluated by varying the positions of the guaiacyl (G) and syringyl (S) units and the bonds βO4 and β5 in the hardwood model lignin through electronic structure calculations. The homolytic cleavage of βO4 bonds is assumed to occur and generate two free radical fragments. These can stabilize by taking hydrogen radicals that may be in solution during the intermediate liquid (pathway 1) formation before the thermal ejection. An alternative pathway (pathway 2) could occur when the radicals use intramolecular hydrogen, turning themselves into stable products. Subsequently, a demethylation reaction can take place, thus generating a methane molecule and new oligomeric lignin-derived molecules. The most probable resulting structures were studied. We used FTIR and NMR spectra of selected model compounds to evaluate our calculation approach. Thermophysical properties were calculated using group contribution methods. The results give insights into the lignin oligomer structures and how these molecules are formed. They also provide helpful information for the design of pyrolysis oil separation and upgrading equipment.

Electrocatalytic conversion of G-type and S-type phenolic compounds from different tree species in a heteropolyacid fluidized system

The electrocatalytic hydrodeoxygenation (ECH) of lignin typical model compounds and lignin-derived oil from different tree species into (alkyl)-cyclohexane and (alkyl)-cyclohexanol in the fluidized electrocatalysis system were investigated in this research. The selected model compounds include two G-type compounds: eugenol (EO) and guaiacol (GO), and two S-type compounds: 4-allyl-2,6-dimethoxyphenol (4-DMP) and 2,6-dimethoxyphenol (2,6-DMP). This ECH system consisted of phosphotungstic acid (PW12) electrolyte, catalyst that suspended in the electrolyte, and NaBH4 reductant in the cathode. The results showed that 4-DMP could be converted using Pt/C as the catalyst at 25 mA/cm2 current density and 80°C for 60 min, with higher faradaic efficiency of 90% and the selectivity of PCH and 4-PCH was 62% and 20%, respectively. For CO bond cleavage, the DFT calculations showed that, for EO, GO, and 4-DMP, the C-OCH3 bond will be firstly broken, while for 2,6-DMP, it is preferred that C-OH bond will be firstly broken. It was found that G-type (EO, GO) was more easily hydrodeoxygenated than S-type (4-DMP, 2,6-DMP) compounds, with the reaction rate in the order of GO > EO > 2,6-DMP > 4-DMP, indicating that the allyl group had a negative effect on the electrocatalytic conversion. Furthermore, it was also found that the complete conversion of lignin-derived oil monomers of pine (mainly G-type) and poplar (mainly S-type) can be achieved, with the yield of target products (PCH and 4-PCH) of 64% and 43%, respectively. Overall, this work innovatively integrates biomass refining and electrocatalytic upgrading, which provides a green and environmentally friendly solution for lignin conversion and utilization.

A DFT Study of the VRFB Positive Electrode: Carbon Active Sites for the VO2 +/VO2+ Reaction

The vanadium redox flow battery (VRFB) is a promising candidate for use in grid-scale battery applications to support a deeper reliance on intermittent renewable energy. However, it suffers from a sluggish redox reaction at the positive electrode. Previous studies indicate that its performance can be improved by oxidizing a graphene-based carbon electrode and thus increasing the concentration of its oxygen-containing surface sites. While such performance enhancement does not appear to be controversial, the underlying mechanisms is far from being clear. Some authors suggest that this procedure increases the number of electrocatalytically active sites; others simply attribute it to improved wettability. In this ongoing study, we use density functional theory (DFT) to examine the role of hydroxyl and carboxyl groups, as well as free edge carbon atoms, in the oxygen transfer process at the positive electrode. Preliminary results using carefully selected model compounds (with appropriate charge C and spin multiplicity M) indicate that oxygen functional groups are unlikely to be active sites in the electrochemical redox process, which in many respects is analogous to the oxidation reduction reaction (ORR). Both the thermodynamics (less favorable adsorption energy of vanadium oxide) and the kinetics (problematic transition states) are less plausible than in analogous mechanistic steps involving carbene-type active sites. The carbene site was probed through two possible reaction mechanisms: V-down and O-down (see graph below). The former adsorption step is essentially a ‘dead-end’ process. The latter is not only thermodynamically and kinetically more feasible; it is consistent with other oxygen-mediated electron transfer processes occurring on the surface of graphene-based materials, be they catalysts or reactants. Furthermore, it has been shown in such processes that the presence of oxygen functional groups can stabilize and enhance the concentration of free carbene-type sites at graphene edges. Figure 1

Effect of activated sludge treatment on the formation of N[sbnd]nitrosamines under different chloramination conditions

Municipal wastewater discharge is considered as one of the main sources of N-nitrosamine precursors which can impact the qualities of downstream source waters and reclaimed wastewaters for potable reuse. NNitrosamine precursors can be removed to various degrees during biological wastewater treatment (e.g., the activated sludge (AS) process). So far, little is known about the impact of the AS process on N-nitrosamine formation under practical disinfection condition (e.g., uniform formation condition (UFC)). In this study, N-nitrosamine UFC from selected model compounds, sewage components (i.e., blackwaters and greywaters) and sewage samples were comprehensively investigated during batch AS treatment tests. NNitrosodimethylamine (NDMA) formation from the tested precursor compounds (i.e., trimethylamine (TMA) and sumatriptan (SMTR)) under UFC chloramination decreased mostly after 6 or 24 hr treatment with different types of AS (i.e., domestic rural AS, domestic urban AS, and textile AS), and the reductions in NDMA UFC were comparable to their NDMA formation potential (FP) reductions. In urine and feces blackwaters, NDMA UFC increased after 6 or 24 hr treatment with the domestic (i.e., rural and urban) AS, while NDMA FP decreased substantially. The increases in NDMA UFC after AS treatment was presumably attributed to the removal of bulk organic matters (e.g., dissolved organic carbon (DOC)) which favored NDMA formation under UFC. On the other hand, in laundry greywaters having relatively abundant DOC, N-nitrosamine UFC was less affected by DOC removal before or after AS treatment, but decreased to similar degrees with N-nitrosamine FP. In sewage samples collected from wastewater treatment plants, N-nitrosamines UFC tended to increase or remain constant during AS treatment, despite the decreases in their FPs. These results suggest that biological wastewater treatment (e.g., the AS process) may not effectively reduce N-nitrosamine formation (e.g., measured under UFC) partially because the concurrent removal of bulk organic matters (e.g., DOC) favored N-nitrosamine formation in s econdary effluents.

Multivariate optimization of a two-way technique for extraction of pharmaceuticals in surface water using a combination of membrane assisted solvent extraction and a molecularly imprinted polymer

This work demonstrates development and evaluation of a two-way technique based on the combination of membrane assisted solvent extraction and a molecularly imprinted polymer (MASE-MIP) for selective and efficient extraction of five selected pharmaceuticals belonging to five different therapeutic classes. The pharmaceuticals were extracted from surface water samples followed by liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-qTOF/MS) determination. A central composite design was applied to optimize the influence of the sample salt content, the stirring rate, the stirring time and the amount of MIP on the extraction of an anticonvulsant (carbamazepine), a cardiac stimulant (etilefrine), a muscle relaxant (methocarbamol), an antiretroviral (nevirapine) and an antidepressant (venlafaxine) from surface water. Optimization of the analytical method was performed by spiking water with a mixture of all five pharmaceuticals at 500 ng mL−1. Optimum extraction conditions for a sample volume of 18 mL were found to be 5 g of salt content, a stirring rate of 400 rpm, an extraction time of 60 min and 50 mg of MIP. The MASE-MIP-LC-qTOF/MS method gave detection and quantification limits ranging from 0.09 to 0.20 ng mL−1 and 0.31–0.69 ng mL−1, respectively. The spiked river water samples yielded recoveries ranging from 38 to 91% for the selected model compounds belonging to the five classes of pharmaceuticals. Upon the application of the developed analytical method in water analysis, all selected pharmaceuticals were detected in South African river water with nevirapine and venlafaxine being more prominent attaining the maximum concentrations of 1.64 and 2.48 ng mL−1, respectively.

Synergistic effect for efficient oxidization of refractory organics with high chroma by an innovative persulfate assisted microbial electrolysis ultraviolet cell

UV based advanced oxidation processes including the newly developed microbial electrolysis ultraviolet cell (MEUC) are easy to operate, but always exhibit an ineffective treatment of wastewater with high chroma due to the low UV transmittance. Herein, an innovative persulfate-assisted MEUC process (MEUPS) was developed to treat such wastewaters. The MEUPS can achieve complete decolorization of the selected model compound (40 mg L−1 of methylene blue, MB) within 140 min and a mineralization degree of 97% within 5 h under optimal operating conditions. The hybrid MEUPS process showed a much better treatment performance than that of the individual process and the synergy factor was quantified as 6.42. •SO4−, •OH, and •O2− were proved to be the major reactive radicals involved in MB degradation, and the degree of contribution was ranked as •SO4−, •OH, and •O2−. Correspondingly, the working mechanism of the MEUPS process was inferred, in which the boosted above listed major reactive radicals can be attributed to the catalytic effect of bioelectrons and UV irradiation, thus the synergistic effect on the efficient treatment of MB-contaminated wastewater. Additionally, the treated effluent exhibited non-toxic by using aquatic plant Lemna minor as an indicator. This research provides a new perspective for the efficient and cost-effective treatment of industrial wastewater with high chroma and refractory organics over a broad pH range together with catalyst-free conditions by using PS-assisted microbial photoelectrochemical technologies.

Inhibitive Action of Selected Model Compounds of Eugenol on Mild Steel Corrosion in Salty Medium

Inhibitive Action of Selected Model Compounds of Eugenol on Mild Steel Corrosion in Salty Medium

Deep Learning Based Optimization of Lennard-Jones Parameters for the Drude General Force Field (DGenFF)

The CHARMM Drude polarizable force field (FF) incorporates induced polarization effects in molecular dynamics (MD) simulations based on the classical Drude oscillator model. Implementation of this model improves simulation of electrostatic interactions in MD simulations. The Drude polarizable FF currently extends to proteins, nucleic acids, lipids, carbohydrates; however, it has a limited set of drug-like (organic) molecules. This study focuses on extending CHARMM Drude polarizable FF to a complete set of small molecules to release Drude General Force Field (DGenFF). Parametrization of DGenFF requires introduction of 49 new atom types for a complete expansion comparable to its additive counterpart - CHARMM General Force Field (CGenFF). Introduction of new atom types involves optimization of Lennard-Jones (LJ) parameters targeting model compounds specifically selected for various atom types. The optimization targets experimental thermodynamic properties, like enthalpy of vaporization (ΔHvap) molecular volume (VMol), dielectric constant, and viscosity, among others. To perform LJ parametrization while accounting for correlation and high dimensionality of parameters we harness the predictive ability of Deep Learning (DL) by combining it with an initial design algorithm, Latin Hypercube Design (LHD). LHD extensively explores the multidimensional LJ parameter space for multiple atom types simultaneously to identify a subset of distributed parameter sets. ΔHvap and VMol are then calculated via MD simulations for the LJ parameter sets for selected model compounds creating training for the DL model. The trained DL model then identifies optimal sets of parameters closer to the target experimental data, which are refined and ranked based on QM interactions with rare gases, water and other experimental observables. The developed DL-based parametrization framework represents a high-throughput method of LJ parameter optimization based on experimental and QM properties, whose application to several new atom types will be presented.

Simultaneous photometric determination of oxidation kinetics and average manganese valence in manganese products in situ formed in the reactions of aqueous permanganate with model organic compounds and natural organic matters

In this study, a colorimetric method using 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS) was adopted to investigate oxidation kinetics by permanganate (Mn(VII)) in trace levels (lower than 1 mg/L or 6 µM) and measure average manganese valence in manganese product bulks in (i) synthetic waters containing selected model compounds with electron-rich moieties, (ii) natural organic matters (NOM) isolate solution, and (iii) real water samples including river water, reservoir water and secondary wastewater effluent. The second-order rate constant for Mn(VII) oxidation of phenol determined using ABTS method was demonstrated to be comparable to that measured by traditional high-performance liquid chromatography (HPLC) method at pH 5–9. This method was applied to measure the rate constants of the reactions between Mn(VII) and model compounds with electron-rich moieties. Average manganese valence in manganese product bulks from Mn(VII) oxidation of selected model compounds was lower than 4 at acidic pH, suggesting that Mn(III) was likely to be generated during Mn(VII) oxidation. Possible mechanisms for Mn(III) formation via one/two-electron process were also proposed. Mn(VII) reaction with NOM isolate sample followed two-phase kinetics with rate constants of 3.47 × 10-5 s−1 (mg C/L)-1 and 6.94 × 10-6 s−1 (mg C/L)-1 in the initial and secondary phases at pH 8. Similarly, two-phase kinetics were also found in the consumption of Mn(VII) in real waters. Mn(VII) consumption rates in different real waters followed the order of their dissolved organic carbon levels. In contrast, chlorine decay rates were mainly based on the order of their dissolved organic nitrogen levels. Moreover, average valence in manganese products in real water samples was determined as around 4, which was mainly ascribed to the one-electron-transfer processes of Mn(VII) with NOM constituents in real water samples such as phenols and amines at ambient weak alkaline pH.

Further insight into some properties of pyrolytic carbon black obtained from scrap truck tires

The virgin CBp produced from scrap truck tires pyrolysis was analyzed both under N2 and under air flow with thermogravimetric analysis coupled with differential thermal analysis (TGA-DTA). Complementary information was derived from the two analysis. The rubber pyrolytic residues present on virgin CBp are better determined quantitatively by TGA-DTA under N2 flow. On the other hand, for the quantification of pure CBp and moreover of the ashes, the TGA-DTA under air flow is a necessary approach. It was also found that the rubber pyrolytic residues coating the virgin CBp surface can be determined quantitatively by a DSC scan under O2 flow up to 450 °C integrating the exothermal peak at about 340 °C and using as reference the thermo-oxidative enthalpy measured on a reference sample of natural rubber or selected model compounds. It is shown that the light pyrolysis process to clean CBp from the rubber pyrolytic deposits is completely satisfactory when conducted in a DSC scan under oxygen flow rather than under nitrogen flow.

Golden seaweed tides from beach inundations as a valuable sustainable fuel resource: Fast pyrolysis characteristics, product distribution and pathway study on Sargassum horneri based on model compounds

This study investigates the pyrolysis characteristics and product distribution in the individual pyrolysis of Sargassum horneri (S. horneri) golden seaweed tide components (cellulose, protein and polysaccharide model compounds) and how the primary components lead to the observed product selectivity to explore their application as feedstocks for bio-oil production. The thermogravimetric analysis (DTG) curve of S. horneri was fitted by single pyrolysis curves of cellulose, protein and polysaccharide, which verified the feasibility of the selected model compounds. A higher heating rate significantly enhances the devolatilization performance of S. horneri and its main pseudocomponents. The fast pyrolysis of protein involves random cleavage of the main chain to form diketopiperazines (DKPs), and the side group will undergo cross-linking, cyclization, dehydroaromatization and other reactions to form amide/amines/nitriles, esters, hydrocarbons and N-heterocyclic compounds in particular. The fast pyrolysis of cellulose involves dehydration and 1,4-glycosidic bond-cleavage reactions as well as further rearrangement of intramolecular structures to form the intermediate product levoglucosan, secondary decomposition of levoglucosan to form aldehydes and ketones and rearrangement of intramolecular structures to form furan and its derivatives. The fast pyrolysis of polysaccharide involves depolymerization, dehydration, decarboxylation, decarbonylation and scission and condensation reactions to form lower molecular weight products, such as furfural, carbon dioxide, ketoesters and hydrocarbons. The results also indicate that the three main model compounds of S. horneri each exert a different influence on the product distribution under high-temperature pyrolysis.

Application of a Dual-Solvent Method in Separating Paraffin from a Shale Oil: A Combined Experimental and DFT Study

An effective dual-solvent (DS) extraction combined with recrystallization was designed for refined paraffin (RP) separation from a shale oil (SO). The content of wax enriched with acetonitrile (AN)/petroleum ether is higher than that with other DSs. The maximum recovery of RP is 22.1 wt % obtained by regulating the DS/SO ratio, extraction time (ET), and extraction times (ETs). The corresponding total relative content of oil obtained by controlling solvent polarity during the recrystallization is 1.9% based on the analysis with a gas chromatograph/mass spectrometer. Long-chain n-alkanes are predominant in RPs, which is consistent with Fourier transform infrared analysis. In addition, the mechanisms for synergic DS extraction were revealed by quantum chemistry calculation with density functional theory, i.e., C–H···π and X–H···Y bonds exist between AN and selected model compounds according to the analyses of electrostatic potential and average local ionization energy. The low boiling point and immiscibility...

Map and model-moving from observation to prediction in toxicogenomics.

BackgroundChemicals induce compound-specific changes in the transcriptome of an organism (toxicogenomic fingerprints). This provides potential insights about the cellular or physiological responses to chemical exposure and adverse effects, which is needed in assessment of chemical-related hazards or environmental health. In this regard, comparison or connection of different experiments becomes important when interpreting toxicogenomic experiments. Owing to lack of capturing response dynamics, comparability is often limited. In this study, we aim to overcome these constraints.ResultsWe developed an experimental design and bioinformatic analysis strategy to infer time- and concentration-resolved toxicogenomic fingerprints. We projected the fingerprints to a universal coordinate system (toxicogenomic universe) based on a self-organizing map of toxicogenomic data retrieved from public databases. Genes clustering together in regions of the map indicate functional relation due to co-expression under chemical exposure. To allow for quantitative description and extrapolation of the gene expression responses we developed a time- and concentration-dependent regression model. We applied the analysis strategy in a microarray case study exposing zebrafish embryos to 3 selected model compounds including 2 cyclooxygenase inhibitors. After identification of key responses in the transcriptome we could compare and characterize their association to developmental, toxicokinetic, and toxicodynamic processes using the parameter estimates for affected gene clusters. Furthermore, we discuss an association of toxicogenomic effects with measured internal concentrations.ConclusionsThe design and analysis pipeline described here could serve as a blueprint for creating comparable toxicogenomic fingerprints of chemicals. It integrates, aggregates, and models time- and concentration-resolved toxicogenomic data.

UV-induced colour generation of pulp and paper mill effluents as a proxy of ligno-cellulosic biorefinery wastewater

UV-induced colour generation of treated (clear) wastewater effluents from a modern bisulphite pulp and paper mill was investigated as a model for aqueous discharges likely to be encountered with emerging biorefinery concepts. Aqueous solutions of selected model compounds, namely lignosulfonic acid (LSA), humic acid and vanillin were exposed to UV light and the colour generation of these solutions compared to the industrial effluent. The colour generation trend of the wastewater was found to be similar to that of LSA. Analysis by HPLC, FTIR, MS and NMR showed that the colour development of the wastewater mimicked the paper yellowing mechanism, with the formation of quinones as a major route. UV-induced dimerization of vanillin solutions showed a dramatic increase in colour. Thus results suggest the UV induced polymerization of lignin compounds play a major role in colour development of lignocellulosic wastewater effluents unless the phenol precursors are removed or degraded.

A green and robust method to measure nanomolar dissolved organic nitrogen (DON) by vacuum ultraviolet

Quantifying trace dissolved organic nitrogen (DON) in water is currently challenging for conventional methods not only because of the presence of dissolved inorganic nitrogen (DIN) species, which usually dominate in total nitrogen (TN), but also because of the high method detection limits (MDLs) of current TN methods, which are ≥100 μg/L. In order to overcome these barriers, an earlier study has applied electrodialysis to eliminate DINs from water, thereby reducing the interference of DIN. However, it remains difficult to analyze DON at nanomolar level. To address this issue, this study proposes to convert DON completely into DIN by vacuum ultraviolet irradiation (VUV) and then to measure DON by the sum of DINs (i.e., ammonia, nitrite, and nitrate). A number of verification tests show that the proposed method had comparable results with conventional methods for selected model compounds and real samples. The average nitrogen recovery for sixteen model DON compounds (each at 2.0 mg-N/L) with varying structures and molecular weights was 89 ± 16%, similar to those obtained by thermal-activated persulfate oxidation (87 ± 18%) and high temperature catalytic oxidation (86 ± 20%) methods. Moreover, this method features an advantage that it reached a MDL of 1.5 μg-N/L, much lower than conventional TN methods. With a prolonged 12-h irradiation, this approach was able to convert ammonia completely into nitrate, thus enabling detection of DON by using ion chromatography only.