Visible Spectral Changes Research Articles

Preparation of ultra-sensitive and selective hydrogen peroxide-based colorimetric sensor using highly exfoliated g-C3N4 nanosheets with peroxidase-like activity.

Ahighly sensitive, portable, rapid, and accurate colorimetricsensing method is presented.It isbased upon exfoliated g-C3N4 nanosheets (E-g-C3N4 NSs), having peroxidase nanozyme-like properties. The as-prepared catalyst (E-g-C3N4 NSs) tends to oxidize the colorless tetramethyl-benzidine (TMB) into oxidized-TMB in the presence of hydrogen peroxide (H2O2) generating adark blue color and corresponding ultraviolet visible-spectral changes following aMichaelis-Menten kinetic. The prepared colorimetric sensor exhibited response within the range 0.001-0.450μM having R2 value of 0.999 and adetective limit (LOD) of 0.15 ± 0.04nM. Furthermore, the sensor also displayed outstanding selectivity, ample stability (10weeks), and excellent practicability in real sample applications. All these outstanding properties were highly attributed to the large surface area with exposed actives sites, high surface energy, and large conductive structure of E-g-C3N4 NSs. For comparison of thecatalytic study, we have also explored the sensing mechanism of B-g-C3N4, using thesame optimized experimental conditions. Resultantly, we concluded that the proposed sensor (E-g-C3N4 NSs) will gain considerable attention for on-site environmental and health monitoring in future endeavor.

An azine‐based halochromic molecular chameleon

Halochromism has a plethora of uses in the textile industry, including wound treatments and protective apparel. Reactive dye’s fastness and a wide variety of hues, from bright to dull, make it ideal for coloring cotton and other regenerated cellulose fibers. It is also fundamentally paramount importance to determine the freshness of packaging foods. In this study, a halochromic probe, 4,4′-((1E,1′E,3E,3′E)-hydrazine-1,2-diylidenebis(prop-1-en-1-yl-3-ylidene))bis(N, N-dimethylaniline), HDBD, has been introduced utilizing a simple condensation reaction. Through the protonation and deprotonation process with the addition of acid and base in the non-aqueous medium, HDBD shows visual colorimetric as well as ratiometric UV–visible absorption spectral change. A colorimetric paper strip-based experiment has been demonstrated to detect trace amounts of acid and its reversibility with bases in non-aqueous solvents. Further, a dip-stick experiment was also carried out for the detection of acid-base vapor in a wide range of concentrations. Furthermore, the overlapping indicator method is explored to estimate acid dissociation constants in the non-aqueous medium. Moreover, we have constructed the INHIBIT (INH) and IMPLICATION (IMP) molecular logic gates exploring the reversibility of HDBD due to the cascade introduction of acid-base as chemical encoded inputs. Utilizing a reversible and reproducible detecting method, we have constructed a molecular-scale additional memory device that demonstrates binary logic “Writing-Reading-Erasing-Reading” and “Multi-write” functions. This finding provides a new way for designing acid-base indicators, which could estimate the acid dissociation constants of various acids in the non-aqueous environment which is fundamentally important in the field of acid-catalyzed organic synthesis.

A highly sensitive colorimetric and fluorometric sensor for the detection of cyanide

Certain anions play a vital role in metabolic reactions in our body, but the cyanide ion is highly toxic and poisonous to humans, animals, and the environment even at extremely low concentrations. To detect CN−ions, a highly sensitive electron donor-π-acceptor molecular system (IC) was designed based on the carbazole electron donor and 1,3-indanedione electron acceptor. The IC molecular probe was synthesized through simple organic transformations with good yields and characterized by all spectroscopic methods, including single-crystal X-ray diffraction. The IC probe molecule absorbs in the UV–visible region (200–550 nm), and fluorescence emission encompasses 400–750 nm with LE and CT emission bands. A systematic study suggests that the addition of cyanide ions caused both longer wavelength absorption bands and CT fluorescence emission intensity to decrease. Cyanide ion detection can be visualized with the naked eye, where the yellow color of the IC probe solution changes to colorless upon adding cyanide ion solution. Both UV–visible and fluorescence emission spectral changes with the addition of cyanide ions are attributed to the nucleophilic addition of cyanide at the vinylic carbon, which is confirmed by the 1H NMR, HRMS and fluorescence lifetime studies. The cyanide ion detection limit of the IC has been estimated to be 0.43 µM, far below the WHO permissible limit for cyanide ion concentration in potable water, thus broadening the utility of the IC probe in detecting cyanide in Tapioca. A prototype TLC testing strip has been fabricated for the qualitative determination of cyanide in THF/water medium.

Development of a novel sensory material for rapid detection of mercury ions in various water sources: Solution and solid-state analysis

A xanthene propane nitrile-based sensor material was successfully prepared, and an attempt towards the preparation of polymer bead form was made for the sensitive or selective detection of mercury ions (Hg2+) in water. The sensor material in solution as well as in polymeric form showed amazing selectivity over other added metal ions with a naked eye color change, UV visible spectral and fluorescence spectral change, and a rapid and excellent color change from colorless to purple. The 1H NMR study exposed the probable binding site of the probe with the added mercury ion. In this study, the imine nitrogen and the C = O interact with the mercury ion, resulting in the ring opening of lactam with a vivid color change. The EDTA test was done to verify the reversible behavior of the probe and confirmed its reversibility by UV–visible and fluorescence spectral studies. The polymer bead made using this probe can be used as a tool for monitoring mercury ions in real time in different sources of water samples. The sensor molecule itself senses the mercury ion in its solid state by simple grinding and changes its color from pale yellow to deep purple. The sensor color change response is very rapid towards mercury detection, which is confirmed by the prepared test strip.

Discovery of a strong rotation of the X-ray polarization angle in the galactic burster GX 13+1

Weakly magnetized neutron stars in X-ray binaries show a complex phenomenology with several spectral components that can be associated with the accretion disk, the boundary, and/or a spreading layer, a corona, and a wind. Spectroscopic information alone, however, is not enough to distinguish these components. The analysis of the timing data revealed that most of the variability, and in particular, kilohertz quasi-period oscillations, are associated with the high-energy component that corresponds to the boundary and/or spreading layer. Additional information about the nature of the spectral components, and in particular, about the geometry of the emission region, can be provided by X-ray polarimetry. One of the objects of the class, a bright, persistent, and rather peculiar galactic Type I X-ray burster was observed with the Imaging X-ray Polarimetry Explorer (IXPE) and the X-ray Multi-Mirror Mission Newton ( Using the data, we obtained the best-fit values for the continuum spectral parameters and detected strong absorption lines associated with the accretion disk wind. IXPE data showed the source to be significantly polarized in the 2--8 keV energy band, with an overall polarization degree (PD) of $1.4<!PCT!> at a polarization angle (PA) of $-2 (errors at the 68<!PCT!> confidence level). During the two-day long observation, we detected rotation of the PA by about 70 with the corresponding changes in the PD from 2<!PCT!> to nondetectable and then up to 5<!PCT!>. These variations in polarization properties are not accompanied by visible spectral state changes of the source. The energy-resolved polarimetric analysis showed a significant change in polarization, from being strongly dependent on energy at the beginning of the observation to being almost constant with energy in the later parts of the observation. As a possible interpretation, we suggest a constant polarization component, strong wind scattering, or a different polarization of the two main spectral components with an individually peculiar behavior. The rotation of the PA suggests a misalignment of the neutron star spin from the orbital axis.

Synthesis, characterization, solvatochromic, computational and antibacterial studies of a series of new 4-imino-3-(2-heteroarylhydrazono)chroman-2-one dyes

Herein, 4-aminocoumarin was synthesized and reacted with some diazonium salts derived from substituted 2-aminothiazoles to produce corresponding new azo dyes. These newly synthesized compounds were fully characterized by FT-IR and NMR spectroscopies and mass spectral analysis. The results testified that the obtained products exclusively exist in the hydrazone tautomeric form both in solid and solution states, and no spectral evidence of an azo structure was detected. The visible absorption spectral changes of the dyes were also studied in acetic acid, ethanol, chloroform, acetonitrile, dimethyl formamide, and dimethyl sulfoxide in the region of 300–600 nm, and the results were discussed according to possible electronic transitions in the compounds. The visible spectral behavior of ethanol-water solutions (50:50, v: v) of the dyes was also examined at different pH values at ambient temperature. Furthermore, the geometries of the proposed azo and hydrazone tautomeric forms of the dyes were optimized at B3LYP/6-311++G (d, p) level of theory. DFT calculations have been performed to evaluate the stability of the proposed azo and hydrazone tautomeric forms of the prepared dyes both in the gas phase and in solution, and the outcomes were compared with spectroscopic findings. Besides, antibacterial activities of the dyes dissolved in DMSO were evaluated using the well diffusion method against Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922) bacterial strains.

A selective chromo-fluorogenic chemosensor for visual detection of solution and vapor phase of sarin, tabun mimics diethyl chlorophosphate, diethyl cyanophosphonate

The abuse of nerve agents has become a severe threat to peaceful modern civilization. Hence, it is of paramount importance to the scientific communities to detect and degrade them for a modern society. In the present contribution, we have introduced a selective chromo-fluorogenic probe (AMP) based on neutral red dye for visual detection of the solution and vapor phase of sarin & tabun mimics, namely diethyl chlorophosphate (DCP) and diethyl cyanophosphonate (DCNP), respectively. A ratiometric UV–visible absorption spectral change with colorimetric visualization from yellow to bright pink is observed in the presence of both mimics. A “turn-off” photoluminescence from yellow color to non-fluorescence is observed in the presence of both mimics. The spectral and chromo-fluorgenic behavior is reversed in the presence of triethylamine (TEA). The sensitivity of AMP towards the detection of targeted analytes is recorded in the μM range. Additionally, filter paper-based strips are fabricated for the actual applicability of the current probe to identify trace amounts of both analytes in the presence of various types of analogous target analytes. The vapor phase sensing and two types of soil analysis are also employed to check the sensor's potential in real-life applications. The present report has revealed prompt, sensitive, selective, in-situ, accurate sample detectors of sarin & tabun gas in actual threatening situations.

UV–visible spectral changes of gamma irradiated olive leaves extract

Olive leaves benefits are less well known, despite having potential health benefits that could make them a valuable addition to a daily diet, compared to olive oil, which is well known for the many benefits it provides. The antioxidant capacity of olive leaves extract (OLE) is higher than that of the most known powerful antioxidants, such as vitamins C and E or pure hydroxytyrosol. The aim of this study was first to maximize the bioactive compounds in extra virgin olive oil (EVOO) by enriching it with olive leaves; the EVOO acts as an extraction solvent, and a study of the macerating period was carried out to select the best macerating period to improve the stabilization of the bioactive compounds in the olive oil matrix. Once the best macerating period was selected (7 days), OLE was gamma-irradiated with a dose of 25 kGy to assess its oxidative stability. To this end, UV–visible spectroscopy was used to perform stability and quality analysis of the OLE during a macerating period of 21 days and after irradiation. The results of this study show an extremely significant (p < 0.0001) improvement in the quality parameters (K232, K270, and ΔK) and in total carotenoids and chlorophylls, assessed by K470 and K670, among all the macerating periods of OLE compared to the control group. Regarding the irradiated OLE compared to the irradiated EVOO, there was an extremely significant (p < 0.0001) difference in ΔK. In addition, there was a significant decrease in total carotenoids and chlorophylls in the irradiated EVOO compared to the irradiated OLE. In conclusion, olive leaves extract in olive oil could be used as a free radical scavenger in food irradiation and tissue sterilization to alleviate the detrimental effects of ionizing radiation.

Rational design and construction of S-scheme CeO2/AgCl heterojunction with enhanced photocatalytic performance for tetracycline degradation

Semiconductor-based photocatalysis has attracted extensive attentions in waste water treatment and environment remediation. However, a single semiconductor photocatalyst inevitably encounters a dilemma between light absorption and redox ability of photoinduced holes and electrons. In this work, an S-scheme CeO2/AgCl heterojunction photocatalyst was designed, prepared and characterized by various techniques. The as-prepared CeO2/AgCl composite photocatalyst exhibited enhanced photocatalytic activity compared with single CeO2 and AgCl as revealed by the photodegradation of tetracycline (TC), a widely used antibiotic. According to UV–Vis spectral changes and degradation mass spectra of TC, the CeO2/AgCl composite photocatalyst not only can destroy the B, C, D rings, but also the A ring of TC, which cannot be destroyed by most of previously reported photocatalysts. The enhanced photocatalytic ability of CeO2/AgCl composite was due to the formation of an S-scheme heterojunction structure between CeO2 and AgCl, which simultaneously retained the maximum redox ability of photoinduced holes and electrons in the valence band of AgCl and in the conduction band of CeO2, respectively, resulting in the production of highly efficient O2−, OH and h+. This work provided insight into the rational design and construction of S-scheme heterojunction composites and new possibility of photocatalytic degradation of antibiotic wastewater.

Chromogenic, specific cascade detection of fluoride and alkaline earth metal ions

A salen-based colorimetric chemosensor (MM) has been designed and synthesized to selectively recognize F− and alkaline earth metal ions in solution and solid phase, respectively. A ratiometric UV–visible absorption spectral change with a colorimetric visualization from yellow to pink is observed in the presence of F− ions. The detection of F− ions is fully reversible in alkaline earth metal ions. The limit of detection (LOD) of F− ions by our as-prepared MM could be possible down to the μM range. A paper strips-based test kit has been fabricated to detect F− ions selectively by the naked eye. A smartphone-based assay analysis is also successfully performed to identify F− ions in the non-aqueous media. Such a dual ions sensing system with excellent reversibility and repeatability prompted us to consider probe MM a viable choice for fabricating molecular logic circuits and set-reset memorized molecular devices.

Combined calorimetric, spectroscopic and microscopic investigation on the inclusion complex from cyclocurcumin and sulfobutylether-β-cyclodextrin in aqueous solution and Kinetics of thermal cis-trans isomerization

The complexation reaction between cyclocurcumin (CyCur), a natural curcuminoid with bioactive effects, and sulfobutylether-β-cyclodextrin (SBE-βCD), one of the more versatile and tolerate β-cyclodextrin derivates, was investigated in aqueous solution at 298 K. The UV–vis spectral changes of CyCur in the presence of SBE-βCD indicate the formation of the host-guest inclusion complex according to a 1:1 stoichiometry. The binding constant (Kb) determined by applying the Benesi-Hildebrand model was comparable to the value obtained by Isothermal Titration Calorimetry (ITC) measurements. Moreover, the thermodynamic parameters of the SBE-βCD/CyCur interactions demonstrate that the complexation process is enthalpically driven. Interestingly, microscopy analysis highlights the tendency of cyclocurcumin to aggregate into spherical fluorescent structures able to change their aspect and morphology in the presence of SBE-βCD. Finally, the thermal cis-trans isomerization rates of CyCur in the temperature range 294–314 K and the energetic parameters calculated by Arrhenius and Eyring plots were spectroscopically determined in SBE-βCD aqueous solution.

Colorimetric detection of phosphate-based on iron complexing catechol-displacement assay in eutrophicated water bodies

A simple, sensitive, and inexpensive colorimetric indicator-displacement assay based on Fe3+-catechol complex has been developed to determine PO43-. The Fe3+ and catechol formed a greenish color complex, upon the addition of PO43- to the complex, it exhibited a visual color change immediately from greenish to colorless along with UV–vis spectral change. This change was mainly attributed to the high binding affinity of PO43- with Fe3+ by displacing catechol from the Fe3+-catechol complex. The developed sensor showed good sensitivity for the determination of PO43- in a wide linear range from 2 − 1000 µM with a limit of detection (LOD) of 0.5 µM which was found to be lower than the permissible limit. The sensor presented good selectivity towards the detection of PO43- in the existence of other potential interfering anions. Furthermore, the method was successfully applied to determine PO43- in eutrophicated water bodies (river and lake water) with good recoveries and without showing any significant matrix effect.

Photochemical Nitric Oxide Release from S‐Nitrosothiol‐Functionalized Chitosan

AbstractS‐nitrosothiols (RSNOs) are nitric oxide (NO) donor molecules with potential biomedical applications since they mimic NO biological functions, such as vasodilation and inflammatory process regulation. In this work, chitosan (CS), a natural biopolymer widely used as a biomaterial, is functionalized with thioglycolic acid (TGA) or mercaptosuccinic acid (MSA) in reactions mediated by a carbodiimide, yielding CS with thiol contents of 88 µmol g–1 (CS‐TGA) and 126 µmol g–1 (CS‐MSA). The subsequent S‐nitrosation of CS‐TGA and CS‐MSA generates the corresponding S‐nitroso derivatives, CS‐TGA(SNO) and CS‐MSA(SNO). The UV–Vis spectral changes associated with the S‐NO bond cleavage of CS‐TGA(SNO) and CS‐MSA(SNO), monitored in solution over 18 days of storage in a common refrigerator, reveal that these S‐nitroso CS derivatives display enhanced thermal stability in the dark, with half‐life values of 36.1 for CS‐TGA(SNO) and 16.1 days for CS‐MSA(SNO). Conversely, CS‐TGA(SNO) and CS‐MSA(SNO) can release NO photochemically on‐demand under visible light irradiation in a first‐order process triggered by photon absorption that leads to a half‐life of 33 min for both S‐nitroso CS. These results show that CS‐TGA(SNO) and CS‐MSA(SNO) may emerge as new CS‐based biomaterials for providing light‐triggered local NO release in biomedical applications.

A Coumarin151 derived ratiomteric and turn on chemosensor for rapid detection of sarin surrogate

A coumarin151-derived electron donor–acceptor-based dyad (DATC) has been designed and developed for the selective detection of sarin surrogate diethylchlorophosphate (DCP) in solution and gas phases, respectively. A ratiometric UV–visible absorption spectral change with a colorimetric visualization from yellow to colorless is observed in the presence of DCP. Turn-on fluorescence at 480 nm is found due to the disrupted excited state intramolecular proton transfer process (ESIPT) within the DATC. Also, the photoinduced electron transfer (PET) process from electron-rich N, N-diethylamino (-NEt2), and imine (–CH = N) functional groups to coumarin moiety is inhibited due to the phosphorylation process. A visual cyan color could be seen under 365 nm UV light irradiation, which is also well supported by the color chromaticity diagram. The sensitivity of DATC toward the detection of DCP can be possible down to the nanomolar (nM) range from aqueous to a non-aqueous medium. Further, a paper strips-based test kit has been fabricated for the practical utility of the present DATC probe to identify a trace amount of DCP in the stockpiles of related analytes. Also, a dip-stick experiment has been demonstrated for the selective detection of DCP vapor. The performance of DATC toward the DCP proved that it could be exploited as a signal tool for real sample analysis.

Multispectroscopic and computational evaluation of the binding of flavonoids with bovine serum albumin in the presence of Cu2+

Bovine serum albumin (BSA) has the potential application of establishing a delivery system for flavonoids. However, the effect of copper on the binding of flavonoids with BSA is unclear. Therefore, the binding of six flavonoids with BSA containing Cu2+ was investigated using UV–vis, fluorescence, and molecular docking. The UV–vis spectral changes demonstrated the formation of flavonoid-Cu2+ complexes. The fluorescence quenching results suggested that the chelation of Cu2+ increased the binding affinity of galangin and baicalin to the BSA but decreased the binding capacity of chrysin, baicalein, luteolin, and vitexin. Synchronous fluorescence data revealed that Cu2+ could influence the secondary structure conformation of BSA binding with flavonoids, which was further confirmed by ANS-binding fluorescence, circular dichroism, and molecular docking. These findings demonstrate that the complexation of Cu2+ significantly affects the binding of flavonoids with BSA, which provides the theoretical basis for the development of natural product-metal complex functional foods.

Colorimetric “off–on” fluorescent probe for selective detection of toxic Hg2+ based on rhodamine and its application for in-vivo bioimaging

A novel “turn on” fluorimetric sensor 1-benzyl-N-(3',6'-bis(ethylamino)-2',7'-dimethyl-3-oxospiro[isoindoline-1,9'-xanthen]-2-yl)-7-hydroxy-5-oxo-1,2,3,5-tetrahydroimidazo[1,2-a]pyridine-8-carboxamide (RhB) based on rhodamine moiety has been designed and synthesized. The cation sensing ability of RhB was examined and validated using UV–visible, fluorescence, and NMR spectral studies. The probe RhB exhibits selective and sensitive sensing towards Hg2+ over the other competitive metal cations like Ag+, Al3+, Ba2+, Cu2+, Cd2+, Fe3+, Fe2+, K+, Li+, Mg2+, Mn2+, Pb2+, Ni2+, Na+, Zn2+ in EtOH:HEPES buffer solution (1:1, v/v) medium and a rapid 1:1 stoichiometric irreversible reaction were obtained between RhB and Hg2+. The UV–vis and fluorescence spectral changes suggest the effectiveness of the probe and the rapid response of RhB towards Hg2+ could be due to the formation of the coordinate bond between the ligand and metal. The spirolactam ring opening followed by the formation of suitable coordinate geometry in the RhB is the reason for the selective sensing of Hg2+ ion. NMR titration experiments further confirmed this. The binding constant was calculated by the B-H plot and found to be 4.0 × 109 M−1. The LOD for UV–vis and fluorescencebased detection was found to be 2.57 µM (0.516 mg L−1). Likewise, an economically feasible, easy-to-use test strips of RhB was developed for the naked-eye detection of Hg2+ in 100% aqueous solution. However, it was found to be much less sensitive than the spectrophotometric method. Further, in vivo experiments were performed using Drosophila melanogaster that led to demonstrate its efficacy at identifying mercury toxicity within an organism.

Triazine and Porphyrin-Based Cross-Linked Conjugated Polymers: Protonation-Assisted Dissolution and Thermoelectric Properties

As two pivotal functional segments, triazine and porphyrin can be coupled to form a highly cross-linked conjugated polymer. Although the obtained conjugated polymers are almost insoluble in most so...

Secondary organic aerosol formation from 3C⁎-initiated oxidation of 4-ethylguaiacol in atmospheric aqueous-phase

In this study, we investigated aqueous-phase triplet excited states (3C⁎)-induced photo-degradation of 4-ethylguaiacol (EG) under both simulated sunlight and ultraviolet (UV) light irradiations. Through quencher experiments, the relative contributions of reactive oxygen species (ROS, such as 1O2/O2−/·OH) and 3C⁎ were calculated and results showed three reactive species, e.g., 3C⁎, 1O2 and O2−, all seemed to play important roles in the photo-degradation of EG, but contribution from ·OH was relatively minor. High steady-state 1O2 concentration after 1 h irradiation further revealed the major contribution of 1O2 to photo-degradation under Xe light irradiation. The degradation experiment under three saturated gases (air, O2 and N2) showed that the degradation rate in air-saturated condition was the largest owing to synergistic effect of 1O2 and 3C⁎. Oxidative capacity of aqueous secondary organic aerosol (aqSOA) increased with reaction time by monitoring oxygen-to‑carbon (O/C) ratio and carbon oxidation state (OSc) via an aerodyne soot particle aerosol mass spectrometer (SP-AMS). Moreover, aqSOA mass yields were calculated via SP-AMS data. The UV–vis spectral change suggested formation of light-absorbing organics at first stage under simulated sunlight irradiation. Based on the identified products and the reactive intermediates, we postulated that 3C⁎-induced oxidation might be attributed to direct reactions by 3C⁎ and 1O2, chemical reaction by ROS, as well as oligomerization via H-abstraction. To the best of our knowledge, this is the first time to explore systematically reaction pathways of 4-ethylguaiacol under 3C∗ radical on the basis of thorough analysis of products and reactive species. Our findings highlight the impacts of aqSOA from biomass burning emissions on air quality and climate change.

Tuning of renewable biomass lignin into high value-added product: Development of light resistant azo-lignin colorant for coating application

The valorization of lignin by virtue of functionalization of its aromatic backbone with different moieties through diazo coupling reaction and its utilization as a leather chemical has been attempted. The 4-aminoazobenzene functionalized lignin based azo polymer (4-AAB-IL) was characterized using Nuclear Magnetic Resonance Spectroscopy (NMR), Heteronuclear Single Quantum Correlation (HSQC), Fourier - Transform Infrared Spectroscopy (FT-IR), UV–visible absorption, and dynamic light scattering techniques. The CHNS analysis reveals the increase in the percentage of nitrogen after diazotization which could have originated from the diazo functional groups. UV–visible absorption spectra of azo-modified lignin exhibit the characteristic features of azobenzene. The photoisomerization of lignin bearing azobenzene from trans→cis isomer was understood from the characteristic UV–visible spectral changes monitored during the course of the reaction. Notably the photostationary state (PSS), an indicator for the extent of trans isomer converted into cis isomer, PSStrans/cis is found to be 92:8 for 4-AAB-IL whereas that of the parent compound 4-aminoazobenzene (4-AAB) is 32:68. This indicates the higher photostability of 4-AAB-IL which would have originated from the restrictions in the structural motions around the diazo moiety imposed by the lignin skeleton, which is essential for the isomerization reaction. Since the azo compounds are evolved as dyes in leather industries, the applicability of synthesized 4-AAB-IL on leather was tested and the results showed excellent light fastening properties even after prolonged irradiation. In addition, the 4-AAB-IL provides darker shade to the crust leather when compared to the 4-AAB, thus these results suggest that functionalization of lignin could pave the way to alter the color of the lignin in a desired way by employing suitable substituents. This functional lignin based colorant would find a new green and sustainable pathway for cleaner application of lignin in coating.

Aqueous-phase oxidation of three phenolic compounds by hydroxyl radical: Insight into secondary organic aerosol formation yields, mechanisms, products and optical properties

This work performed a systematic investigation on the aqueous hydroxyl radical (OH) - induced photochemical oxidation of three modestly-soluble precursors from biomass combustion including 4-methylsyringol (DMP), eugenol (Eug), and 2,4,6-trimethylphenol (TRMP) under both simulated sunlight and ultraviolet (UV) light irradiations. An Aerodyne soot particle aerosol mass spectrometer (SP-AMS) was used to monitor the bulk chemical and elemental compositions of aqueous secondary organic aerosol (aqSOA) formed. AqSOA mass yields varied in ranges of 80–190% and 0–200% under sunlight and UV light conditions, respectively. AqSOA oxygen-to-carbon (O/C) ratio and carbon oxidation state increased steadily under sunlight + OH condition, but increased then decreased under UV + OH condition. Organic acids including malic acid, glycolic acid, formic acid and oxalic acid were formed, and their total accounted for ~12% of SOA mass. The UV–vis spectral change suggested formation of light-absorbing organics. Reaction pathways were proposed by combining gas chromatography-mass spectrometry (GC-MS) and SP-AMS results. Under sunlight + OH condition, oligomerization, functionalization, and fragmentation processes all involved in aqSOA evolution, with more contribution from functionalization via hydroxylation and oxygenation reactions. Reaction mechanism of UV + OH oxidation was initially dominated by functionalization then by fragmentation, indicating by the decrease of total organic carbon (TOC) contents, formation of small organic acids and low-molecular-weight products. Our work highlights that combination of SP-AMS with GC-MS is a powerful method for laboratory investigation of aqueous-phase reactions.