Light-absorbing Compounds Research Articles

Photodynamic activity of curcumin against Candida biofilms on toothbrushes

Oral hygiene is necessary for maintaining human health, and regular brushing is recommended to control oral microbial biofilm. Toothbrushes are manufactured free of microorganisms, but after the first use they become contaminated and can represent a potential source of cross-contamination. Regular replacement or decontamination of toothbrushes is recommended. In this context, antimicrobial photodynamic therapy (aPDT) is a technology based on the production of reactive oxygen species, when light-absorbing compounds (photosensitizers) react with light and oxygen. The products of these reactions have antimicrobial activity and are used in dentistry to control microbial biofilms. Take into account, this study evaluated the activity of curcumin photoactivated with 450nm LED light against Candida krusei Ck7 and Candida albicans ATCC 10231 biofilms adhered to toothbrushes. Curcumin without photoactivation reduced the number of viable cells by 77.5% and 91.73%, respectively. Photoactivated curcumin reduced the biofilm of C. krusei Ck7 by 97.94% and C. albicans by 98.8%. Therefore, photoactivated curcumin provided a powerful reduction in the number of viable yeasts associated with the biofilm and may represent a promising complementary technique to conventional antimicrobial agents.

Effects of Ferrate (VI) Pre-oxidation in the Coagulation Treatment of Drinking Water

Although ferrate (Fe(VI)) is introduced as a feasible replacement for pre-oxidation in the treatment of drinking water, limited research is available on effects of utilizing ferrate for the treatment of drinking water sources to produce potable water. In the present study, an experimental program was conducted on the employment of ferrate in drinking water treatment; this program included batch and continuous flow tests on multiple samples of natural water from different sources. According to the batch test results, the ferrate pre-oxidation led to improved ultraviolet light-absorbing compounds (UV254) removal by subsequent coagulation in a small portion of the samples but showed no enhancement in the majority of samples. In continuous flow tests, ferrate was added to small-scale models of existing treatment plants. Compared to the case with no pre-oxidation, ferrate pre-oxidation generally enhanced UV254 absorption, finished water turbidity, and disinfection by-product formation. Therefore, ferrate can be viably used in the treatment systems of drinking water and provide a superior replacement to available oxidants by allowing for the oxidation and disinfection of inorganic materials without negative effects on downstream processes. More researches are needed to examine a more viable combination of ferrate with other methods and obtain more knowledge about the mechanisms of the known synergistic applications of ferrate.

Analytical Methods for Oxalate Quantification: The Ubiquitous Organic Anion

Oxalate is a divalent organic anion that affects many biological and commercial processes. It is derived from plant sources, such as spinach, rhubarb, tea, cacao, nuts, and beans, and therefore is commonly found in raw or processed food products. Oxalate can also be made endogenously by humans and other mammals as a byproduct of hepatic enzymatic reactions. It is theorized that plants use oxalate to store calcium and protect against herbivory. Clinically, oxalate is best known to be a major component of kidney stones, which commonly contain calcium oxalate crystals. Oxalate can induce an inflammatory response that decreases the immune system's ability to remove renal crystals. When formulated with platinum as oxaliplatin (an anticancer drug), oxalate has been proposed to cause neurotoxicity and nerve pain. There are many sectors of industry that are hampered by oxalate, and others that depend on it. For example, calcium oxalate is troublesome in the pulp industry and the alumina industry as it deposits on machinery. On the other hand, oxalate is a common active component of rust removal and cleaning products. Due to its ubiquity, there is interest in developing efficient methods to quantify oxalate. Over the past four decades, many diverse methods have been reported. These approaches include electrochemical detection, liquid chromatography or gas chromatography coupled with mass spectrometry, enzymatic degradation of oxalate with oxalate oxidase and detection of hydrogen peroxide produced, and indicator displacement-based methods employing fluorescent or UV light-absorbing compounds. Enhancements in sensitivity have been reported for both electrochemical and mass-spectrometry-based methods as recently as this year. Indicator-based methods have realized a surge in interest that continues to date. The diversity of these approaches, in terms of instrumentation, sample preparation, and sensitivity, has made it clear that no single method will work best for every purpose. This review describes the strengths and limitations of each method, and may serve as a reference for investigators to decide which approach is most suitable for their work.

Measurement report: Changes in light absorption and molecular composition of water-soluble humic-like substances during a winter haze bloom-decay process in Guangzhou, China

Abstract. Water-soluble humic-like substances (HULIS) absorb light in near-UV and visible wavelengths and exert significant influence on the atmospheric environment and climate. However, knowledge on HULIS evolution during haze bloom-decay process is limited. Herein, PM2.5 samples were obtained during a winter haze event in Guangzhou, China, and the light absorption and molecular composition of HULIS were investigated by UV–Vis spectrophotometry and ultrahigh-resolution mass spectrometry. Compared with HULIS on clean days, the absorption coefficients (Abs365) of HULIS on haze days were significantly higher but the mass absorption efficiencies (MAE365) were relatively low, suggesting diverse and dynamic absorption properties of HULIS during haze episodes. The CHO and CHON compounds were the most abundant components in HULIS, followed by CHOS, CHONS, and CHN. Haze HULIS presented comparatively high molecular weight; a lower aromaticity index (AImod); and higher O/Cw, O/Nw, and O/Sw ratios, indicating that HULIS fractions undergo relatively high oxidation during haze days compared to clean days. Moreover, CHON and CHO compounds with high AImod were the major potential chromophores in HULIS and significantly contributed to HULIS light absorption. It is worth noting that the proportions of these chromophores decreased during haze events, mainly owing to their higher oxidation during haze episodes. Besides, accumulated contribution of organic compounds emitted from vehicles and formed from reactions of biogenic volatile organic compounds (bio-VOCs) also diluted light-absorbing compounds in haze HULIS. These findings help us to understand HULIS evolution during haze bloom-decay processes in the subtropic region of China.

Co-Sensitization Effects of Indoline and Carbazole Dyes in Solar Cells and Their Neutral-Anion Equilibrium in Solution.

Co-sensitization of two or more light-absorbing compounds on a TiO2 surface has recently become one of the most successful strategies in the development of dye-sensitized solar cells (DSSCs). The specific structure of the dyes for DSSCs implies that they can partly exist in anionic forms in popular solvents used for sensitization. Our study concerns the above two issues being analyzed in detail using the example of the popular carbazole (MK2) and indoline (D205) dyes, studied by stationary absorption and emission, femtosecond transient absorption (in complete cells and in the solutions), current-voltage measurements, DFT and TD-DFT theoretical calculations. After the addition of D205 to DSSC with MK2, the fill factor of the cells was improved, and the electron recombination between TiO2 and the dyes was blocked (observed on sub-nanosecond time scales). Thus, the active co-adsorbent can take the role of the typically used passive additive, like chenodeoxycholic acid. Evidence of the concentration-dependent equilibrium between neutral and anionic forms of dyes with different lifetimes was found in acetonitrile solutions (the best for sensitization), while in ethanol solution the dominant form was the anion (worse for sensitization). Our findings should help in better understanding the operation and optimization of DSSC.

Suitability of Different Methods for Measuring Black Carbon Emissions from Marine Engines

Black carbon (BC) emissions intensify global warming and are linked to adverse health effects. The International Maritime Organization (IMO) considers the impact of BC emissions from international shipping. A prerequisite for the anticipated limits to BC emissions from marine engines is a reliable measurement method. The three candidate methods (photoacoustic spectroscopy (PAS), laser-induced incandescence (LII), and filter smoke number (FSN)) selected by the IMO were evaluated with extensive ship exhaust matrices obtained by different fuels, engines, and emission control devices. A few instruments targeted for atmospheric measurements were included as well. The BC concentrations were close to each other with the smoke meters (AVL 415S and 415SE), PAS (AVL MSS), LII (Artium-300), MAAP 5012, aethalometers (Magee AE-33 and AE-42), and EC (TOA). In most cases, the standard deviation between instruments was in the range of 5–15% at BC concentrations below 30 mg Sm−3. Some differences in the BC concentrations measured with these instruments were potentially related to the ratio of light-absorbing compounds to sulphates or to particle sizes and morphologies. In addition, calibrations, sampling, and correction of thermophoretic loss of BC explained differences in the BC results. However, overall differences in the BC results obtained with three candidate methods selected by the IMO were low despite challenging exhaust compositions from marine diesel engines. Findings will inform decision making on BC emission control from marine engines.

Revisiting the reaction of dicarbonyls in aerosol proxy solutions containing ammonia: the case of butenedial

Abstract. Reactions in aqueous solutions containing dicarbonyls (especially the α-dicarbonyls methylglyoxal, glyoxal, and biacetyl) and reduced nitrogen (NHx) have been studied extensively. It has been proposed that accretion reactions from dicarbonyls and NHx could be a source of particulate matter and brown carbon in the atmosphere and therefore have direct implications for human health and climate. Other dicarbonyls, such as the 1,4-unsaturated dialdehyde butenedial, are also produced from the atmospheric oxidation of volatile organic compounds, especially aromatics and furans, but their aqueous-phase reactions with NHx have not been characterized. In this work, we determine a pH-dependent mechanism of butenedial reactions in aqueous solutions with NHx that is compared to α-dicarbonyls, in particular the dialdehyde glyoxal. Similar to glyoxal, butenedial is strongly hydrated in aqueous solutions. Butenedial reaction with NHx also produces nitrogen-containing rings and leads to accretion reactions that form brown carbon. Despite glyoxal and butenedial both being dialdehydes, butenedial is observed to have three significant differences in its chemical behavior: (1) as previously shown, butenedial does not substantially form acetal oligomers, (2) the butenedial/OH− reaction leads to light-absorbing compounds, and (3) the butenedial/NHx reaction is fast and first order in the dialdehyde. Building off of a complementary study on butenedial gas-particle partitioning, we suggest that the behavior of other reactive dialdehydes and dicarbonyls may not always be adequately predicted by α-dicarbonyls, even though their dominant functionalities are closely related. The carbon skeleton (e.g., its hydrophobicity, length, and bond structure) also governs the fate and climate-relevant properties of dicarbonyls in the atmosphere. If other dicarbonyls behave like butenedial, their reaction with NHx could constitute a regional source of brown carbon to the atmosphere.

Aqueous-phase oxidation of syringic acid emitted from biomass burning: Formation of light-absorbing compounds

Syringic acid is a methoxyphenol model compound derived from biomass burning, and its photooxidation processes have important effects on atmospheric chemistry. However, its aqueous-phase photochemistry remains unclear. In this study, we systematically report the photooxidation of syringic acid induced by OH radicals in the aqueous phase. Employing the relative rate technique, the bimolecular rate constant for syringic acid reaction with OH radicals was acquired to be (1.1 ± 0.3) × 1010 M−1 s−1. Notably, colored products were formed as the reaction progressed. Furthermore, the UV–vis and fluorescence spectra confirmed the formation of light-absorbing organic species, and the results agreed well with previous results on atmospheric and natural humic-like substances (HULIS). The photooxidation products were detected by high performance liquid chromatography mass spectrometry (HPLC/MS), and a possible reaction mechanism was proposed. The aqueous-phase reaction of syringic acid would undergo functionalization process forming a hydroxylation product that enhances the degree of oxidation of aqueous secondary organic aerosol (aqSOA), and goes through dimerization process by C-C or C-O coupling of phenoxy radicals which may conduce to the formation of HULIS. These findings suggest that the photooxidation of syringic acid is an important pathway for highly oxygenated phenolic aqSOA formation, providing a secondary source for HULIS in a liquid phase or in deliquescent particles surrounded by a layer of water.

A new strategy for a combined isolation of EPS and pigments from cyanobacteria

Cyanobacteria obtain their energy through photosynthesis and live embedded in a matrix of extracellular polymeric substances (EPS) containing valuable products, e.g., polysaccharides, lipids, proteins, and antimicrobials. Besides chlorophyll a and carotenoids, they have light-absorbing compounds in the form of light-harvesting complexes, the so-called phycobilisomes, consisting of different phycobiliproteins. Together they close the “green gap” whereby cyanobacteria can use light more effective than higher plants. Cultivation of cyanobacteria on a lab-scale results in small amounts of biomass for their characterization or a comprehensive screening. EPS are, for example, produced as a protection against suboptimal culture conditions. Carotenoids are essential light-harvesting pigments for photosynthesis, play a key role in photoprotective reactions, and are produced for cell wall stabilization. Essentially, the pigment composition of cyanobacteria depends on the available light spectrum, nitrogen content, and temperature. Especially the production of EPS and pigments are indicators for the cell-condition. Therefore, different EPS extraction methods were tested including the determination of inhibitory effects of extracts against Escherichia coli. Based on the best EPS extraction method, a new strategy for downstream processing (DSP) was developed to determine EPS, the pigments chlorophyll a and carotenoids, and phycobiliproteins from only one sample. As cyanobacterial model organisms Trichocoleus sociatus and Nostoc flagelliforme were used, and DSP strategy was successfully transferred to four additional cyanobacteria. The final DSP includes the following steps: (i) EPS extraction, (ii) lyophilization of biomass, (iii) extraction of phycobiliproteins, and a final (iv) chlorophyll a and carotenoid extraction. The new strategy allows a comprehensive characterization of cyanobacterial cells.

Methodologies in Spectral Tuning of DSSC Chromophores through Rational Design and Chemical-Structure Engineering.

The investigation of new photosensitizers for Grätzel-type organic dye-sensitized solar cells (DSSCs) remains a topic of interest for researchers of alternative solar cell materials. Over the past 20 years, considerable and increasing research efforts have been devoted to the design and synthesis of new materials, based on “donor, π-conjugated bridge, acceptor” (D–π–A) organic dye photosensitizers. In this paper, the computational chemistry methods are outlined and the design of organic sensitizers (compounds, dyes) is discussed. With reference to recent literature reports, rational molecular design is demonstrated as an effective process to study structure–property relationships. Examples from established organic dye sensitizer structures, such as TA-St-CA, Carbz-PAHTDDT (S9), and metalloporphyrin (PZn-EDOT), are used as reference structures for an examination of this concept applied to generate systematically modified structural derivatives and hence new photosensitizers (i.e., dyes). Using computer-aided rational design (CARD), the in silico design of new chromophores targeted an improvement in spectral properties via the tuning of electronic structures by substitution of molecular fragments, as evaluated by the calculation of absorption profiles. This mini review provides important rational design strategies for engineering new organic light-absorbing compounds towards improved spectral absorption and related optoelectronic properties of chromophores for photovoltaic applications, including the dye-sensitized solar cell (DSSC).

Wintertime Optical Properties of Primary and Secondary Brown Carbon at a Regional Site in the North China Plain.

The light-absorbing properties of atmospheric brown carbon (BrC) are poorly understood due to its complex chemical composition. Here, a black-carbon-tracer method was coupled with source apportionments of organic aerosol (OA) to explore the light-absorbing properties of primary and secondary BrC from the North China Plain (NCP). Primary emissions of BrC contributed more to OA light absorption than secondary processes, and biomass burning OA accounted for 60% of primary BrC absorption at λ = 370 nm, followed by coal combustion OA (35%) and hydrocarbon-like OA (5%). Secondary BrC absorption was high in the early morning and later decreased due to the bleaching of chromophores. Nighttime aqueous-phase chemistry promoted the formation of secondary light-absorbing compounds and the production of strongly absorbing particles. Source analysis showed that the NCP region was the most important source for primary and secondary BrC subtypes at the study site. The mean direct radiative forcing for BrC was 0.15 W m-2 (0.11 W m-2 and 0.04 W m-2 for the primary and secondary fractions, respectively). This study provides new information on the optical properties of primary and secondary BrC and highlights the importance of atmospheric oxidation on BrC absorption.

Systematic Evaluation of Light-Activatable Biohybrids for Anti-Glioma Photodynamic Therapy.

Photosensitizing biomolecules (PSBM) represent a new generation of light-absorbing compounds with improved optical and physicochemical properties for biomedical applications. Despite numerous advances in lipid-, polymer-, and protein-based PSBMs, their effective use requires a fundamental understanding of how macromolecular structure influences the physicochemical and biological properties of the photosensitizer. Here, we prepared and characterized three well-defined PSBMs based on a clinically used photosensitizer, benzoporphyrin derivative (BPD). The PSBMs include 16:0 lysophosphocholine-BPD (16:0 Lyso PC-BPD), distearoyl-phosphoethanolamine-polyethylene-glycol-BPD (DSPE-PEG-BPD), and anti-EGFR cetuximab-BPD (Cet-BPD). In two glioma cell lines, DSPE-PEG-BPD exhibited the highest singlet oxygen yield but was the least phototoxic due to low cellular uptake. The 16:0 Lyso PC-BPD was most efficient in promoting cellular uptake but redirected BPD’s subcellular localization from mitochondria to lysosomes. At 24 h after incubation, proteolyzed Cet-BPD was localized to mitochondria and effectively disrupted the mitochondrial membrane potential upon light activation. Our results revealed the variable trafficking and end effects of PSBMs, providing valuable insights into methods of PSBM evaluation, as well as strategies to select PSBMs based on subcellular targets and cytotoxic mechanisms. We demonstrated that biologically informed combinations of PSBMs to target lysosomes and mitochondria, concurrently, may lead to enhanced therapeutic effects against gliomas.

Composition and light absorption of N-containing aromatic compounds in organic aerosols from laboratory biomass burning.

This study seeks to understand the compositional details of N-containing aromatic compounds (NACs) emitted during biomass burning (BB) and their contribution to light-absorbing organic carbon (OC), also termed brown carbon (BrC). Three laboratory BB experiments were conducted with two U.S. pine forest understory fuels typical of those consumed during prescribed fires. During the experiments, submicron aerosol particles were collected on filter media and subsequently extracted with methanol and examined for their optical and chemical properties. Significant correlations (p < 0.05) were observed between BrC absorption and elemental carbon (EC)/OC ratios for individual burns data. However, the pooled experimental data indicated that the BB BrC absorption depends on more than the BB fire conditions as represented by the EC/OC ratio. Fourteen NAC formulas were identified in the BB samples, most of which were also observed in simulated secondary organic aerosol (SOA) from photo-oxidation of aromatic VOCs with NOX. However, the molecular structures associated with the identical NAC formula from BB and SOA are different. In this work, the identified NACs from BB are featured by methoxy and cyanate groups, and are predominately generated during the flaming phase. The mass concentrations of identified NACs were quantified using authentic and surrogate standards, and their contributions to bulk light absorption of solvent extractable OC were also calculated. The contributions of identified NACs to organic matter (OM) and BrC absorption were significantly higher in flaming-phase samples than those in smoldering-phase samples, and correlated with EC/OC ratio (p < 0.05) for both individual burns and pooled experimental data, indicating that the formation of NACs from BB largely depends on burn conditions. The average contributions of identified NACs to overall BrC absorption at 365 nm ranged from 0.087 ± 0.024 to 1.22 ± 0.54%, 3 - 10 times higher than their mass contributions to OM (0.023 ± 0.0089 to 0.18 ± 0.067%), so the NACs with light absorption identified in this work from BB are likely strong BrC chromophores. Further studies are warranted to identify more light-absorbing compounds to explain the unknown fraction (> 98%) of BB BrC absorption.

Effect of short-chain alcohols on the bulk-phase reaction between glyoxal and ammonium sulfate

The chemical and physical properties of secondary organic aerosol (SOA) may be influenced by the aqueous environment within which SOA-forming reactions occur. Bulk-phase reactions between glyoxal and ammonium sulfate produce light-absorbing compounds such as imidazole-2-carboxaldehyde (IC) and biimidazole (BI) and model aerosol-phase chemistry. The effect of solvent composition on IC and BI production kinetics were examined for solutions containing a series of short-chain alcohols (methanol, ethanol, 1-propanol, 2-propanol, 2-butanol, tert-butanol, and 3-methyl-2-butanol), as functions of the species and concentration added. The addition of an alcohol likely altered the solvent by inducing the formation of micro-heterogeneities of hydrated alcohol molecules. An increased alcohol concentration in solution resulted in a general increase in the production of IC and BI, with ethanol and the secondary alcohols causing the largest changes. The rate constants for IC and BI production in solutions that do not contain alcohol are found to be (4.03 ± 2.02) x 10−6 s−1 and (3.48 ± 1.75) x 10−6 s−1, respectively. In solutions that do contain an alcohol, rate constant values range from 3.23 × 10−6 s−1 to 6.61 × 10−6 s−1 for IC and 0.985 × 10−6 s−1 to 6.87 × 10−6 s−1 for BI, depending on the alcohol and the concentration. While these prevailing trends of more alcohol in solution leading to amplified production of imidazoles were observed for all seven alcohols, the diversity of responses implies the mode of action depends strongly on the species of alcohol added. Properties that describe a solution in bulk, such as dielectric constant, are not found to be reliable predictors of subsequent system behavior. Solvent composition influences SOA chemistry, and interactions between relevant functional groups within solution drive this influence, which suggests the importance of understanding individual relationships between aerosol-phase chemicals and SOA properties and production.

Cylindrical NIR-Responsive Metallopolymer Containing Möbius Metalla-aromatics.

Metalla-aromatic complexes are very stable and excellent light-absorbing compounds, owing to their highly conjugated frameworks. The metallopolymers containing metalla-aromatic substructures consist of a new type of functional polymer, because they exhibit characteristics of both metalla-aromatic and polymeric units. Herein, we reported a corn-like cylindrical metallopolymer, prepared from the controlled polymerization of N-isopropylacrylamide (NIPAM) by a polyrotaxane-based macroinitiator, followed by postpolymerization modification with a photothermal metalla-aromatic complex. The corn-like shape of this metallopolymer was confirmed by transmission electron microscopy (TEM). Combining the photothermal effect of the metalla-aromatic unit and the thermosensitive property of PNIPAM, the corn-like metallopolymer exhibits a NIR-responsive behavior and represents a new smart material.

Sources, compositions, and optical properties of humic-like substances in Beijing during the 2014 APEC summit: Results from dual carbon isotope and Fourier-transform ion cyclotron resonance mass spectrometry analyses

Humic-like substances (HULIS) are a class of high molecular weight, light-absorbing compounds that are highly related to brown carbon (BrC). In this study, the sources and compositions of HULIS isolated from fine particles collected in Beijing, China during the 2014 Asia-Pacific Economic Cooperation (APEC) summit were characterized based on carbon isotope (13C and 14C) and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses, respectively. HULIS were the main light-absorbing components of water-soluble organic carbon (WSOC), accounting for 80.2 ± 6.1% of the WSOC absorption capacity at 365 nm. The carbon isotope data showed that HULIS had a lower non-fossil contribution (53 ± 4%) and were less enriched with 13C (−24.2 ± 0.6‰) relative to non-HULIS (62 ± 8% and −20.8 ± 0.3‰, respectively). The higher relative intensity fraction of sulfur-containing compounds in HULIS before and after APEC was attributed to higher sulfur dioxide levels emitted from fossil fuel combustion, whereas the higher fraction of nitrogen-containing compounds during APEC may have been due to the relatively greater contribution of non-fossil compounds or the influence of nitrate radical chemistry. The results of investigating the relationships among the sources, elemental compositions, and optical properties of HULIS demonstrated that the light absorption of HULIS appeared to increase with increasing unsaturation degree, but decrease with increasing oxidation level. The unsaturation of HULIS was affected by both sources and aging level.

Characterization of Light-Absorbing Oligomers from Reactions of Phenolic Compounds and Fe(III)

Phenolic compounds are common constituents of atmospheric aerosols. They form by pyrolysis of lignin and by biodegradation of plant material and are commonly found in biomass burning plumes, resuspended soil dust, and in anthropogenic secondary organic aerosols (SOA). In this study, we show that reactions of Fe(III), a major constituent of mineral dust, with several phenolic compounds (guaiacol, catechol, syringol, o- and p-cresol) that are common in atmospheric aerosols, result in the formation of water insoluble light-absorbing compounds and reduced Fe(II). The study was conducted under acidic conditions (pH = 1–2), relevant for areas impacted by biomass burning, anthropogenic emissions, and mineral dust. The reaction products have been characterized using a high-performance liquid chromatography coupled to photodiode array and high-resolution mass spectrometry detectors, UV–visible spectroscopy, X-ray photoelectron spectroscopy, and thermal gravimetric analysis. The major identified chromophores are ol...

Photochemistry of Products of the Aqueous Reaction of Methylglyoxal with Ammonium Sulfate

Aqueous reactions of methylglyoxal (MG) and glyoxal with ammonium sulfate (AS) produce light-absorbing compounds (chromophores) and may serve as a source of atmospheric secondary “brown carbon” (BrC). The molecular composition of these chromophores is ambiguous, and their transformation due to exposure to solar UV radiation is not well understood. We examined the molecular composition, mass absorption coefficients, and fluorescence spectra of BrC samples produced by the evaporation of aqueous MG/AS solutions. Chromatograms of BrC produced by evaporation were different from those of BrC produced by slow MG/AS reaction in water, highlighting the substantial sensitivity of BrC to its formation conditions. The BrC samples were characterized before and after their exposure to broadband (270–390 nm) UV radiation. Irradiation led to rapid photobleaching, a decrease in the characteristic 280 nm absorption band, a complete loss of fluorescence, and a dramatic change in molecular composition. By comparing the compo...

Contributions of nitrated aromatic compounds to the light absorption of water-soluble and particulate brown carbon in different atmospheric environments in Germany and China

Abstract. The relative contributions of eight nitrated aromatic compounds (NACs: nitrophenols and nitrated salicylic acids) to the light absorption of aqueous particle extracts and particulate brown carbon were determined from aerosol particle samples collected in Germany and China.High-volume filter samples were collected during six campaigns, performed at five locations in two seasons: (I) two campaigns with strong influence of biomass-burning (BB) aerosol at the TROPOS institute (winter, 2014, urban background, Leipzig, Germany) and the Melpitz research site (winter, 2014, rural background); (II) two campaigns with strong influence from biogenic emissions at Melpitz (summer, 2014) and the forest site Waldstein (summer, 2014, Fichtelgebirge, Germany); and (III) two CAREBeijing-NCP campaigns at Xianghe (summer, 2013, anthropogenic polluted background) and Wangdu (summer, 2014, anthropogenic polluted background with a distinct BB episode), both in the North China Plain. The filter samples were analyzed for NAC concentrations and the light absorption of aqueous filter extracts was determined. Light absorption properties of particulate brown carbon were derived from a seven-wavelength aethalometer during the campaigns at TROPOS (winter) and Waldstein (summer). The light absorption of the aqueous filter extracts was found to be pH dependent, with larger values at higher pH. In general, the aqueous light absorption coefficient (Abs370) ranged from 0.21 to 21.8 Mm−1 under acidic conditions and 0.63 to 27.2 Mm−1 under alkaline conditions, over all campaigns. The observed mass absorption efficiency (MAE370) was in a range of 0.10–1.79 m2 g−1 and 0.24–2.57 m2 g−1 for acidic and alkaline conditions, respectively. For MAE370 and Abs370, the observed values were higher in winter than in summer, in agreement with other studies. The lowest MAE was observed for the Waldstein (summer) campaign (average of 0.17 ± 0.03 m2 g−1), indicating that freshly emitted biogenic aerosols are only weakly absorbing. In contrast, a strong relationship was found between the light absorption properties and the concentrations of levoglucosan, corroborating findings from other studies. Regarding the particulate light absorption at 370 nm, a mean particulate light absorption coefficient babs, 370 of 54 Mm−1 and 6.0 Mm−1 was determined for the TROPOS (winter) and Waldstein (summer) campaigns, respectively, with average contributions of particulate brown carbon to babs, 370 of 46 % at TROPOS (winter) and 15 % at Waldstein (summer). Thus, the aethalometer measurements support the findings from aqueous filter extracts of only weakly absorbing biogenic aerosols in comparison to the more polluted and BB influenced aerosol at TROPOS (winter). The mean contribution of NACs to the aqueous extract light absorption over all campaigns ranged from 0.10 to 1.25 % under acidic conditions and 0.13 to 3.71 % under alkaline conditions. The high variability among the measurement sites showed that the emission strengths of light-absorbing compounds and the composition of brown carbon were very different for each site. The mean contribution of NACs to the particulate brown carbon light absorption was 0.10 ± 0.06 % (acidic conditions) and 0.13 ± 0.09 % (alkaline conditions) during the Waldstein (summer) campaign and 0.25 ± 0.21 % (acidic conditions) and 1.13 ± 1.03 % (alkaline conditions) during the TROPOS (winter) campaign. The average contribution of NACs to the aqueous extract light absorption over all campaigns was found to be 5 times higher than their mass contribution to water-soluble organic carbon indicating that even small amounts of light-absorbing compounds can have a disproportionately high impact on the light absorption properties of particles.

Strategies to Document Adulteration of Food Supplement Based on Sea Buckthorn Oil: a Case Study

In this case study, a food supplement with declared content of sea buckthorn oil was investigated since it was suspected to be adulterated by sunflower oil. Polar and non-polar fractions extracted from oil supplement were analyzed and compared with authentic sea buckthorn and sunflower oils examined in the same way. Three different analytical platforms were used in order to characterize these samples: (i) ambient mass spectrometry consisting of direct analysis in real time (DART) ion source coupled to quadrupole time-of-flight mass spectrometry (Q-TOF MS); (ii) ultra performance liquid chromatography (UHPLC) coupled to quadrupole time-of-flight mass spectrometry, and (iii) high-performance liquid chromatography coupled to diode array detector (HPLC-DAD). The fingerprints of polar and non-polar extracts, regardless they were obtained by DART-HRMS and/or UHPLC-HRMS, were almost identical with those of sunflower “reference” oil. The last of employed techniques, HPLC-DAD, provided complementary information on the occurrence of various visible light-absorbing compounds. While a rich carotenoid profile was shown in sea buckthorn oil, dominated by β-carotene, lutein, and lycopene, the color of the suspected sample was caused only by high concentration of β-carotene. In principle, these techniques proved to be suitable and complementary tools for oil authentication and allowed an oil supplement to be rapidly verified.