Photochemical Reaction Products Research Articles

Maskless, Reusable Visible-Light Direct-Write Stamp for Microscale Surface Patterning.

We report a straightforward method for creating large-area, microscale resolution patterns of functional amines on self-assembled monolayers by the photoinduced local acidification of a flat elastomeric stamp enriched with photoacid. The limited diffusivity of the photoactivated merocyanine acid in poly(dimethylsiloxane) (PDMS) enabled to confine efficient deprotection of N-tert-butyloxycarbonyl amino group (N-Boc) to line widths below 10 μm. The experimental setup is very simple and is built around the conventional HD-DVD optical pickup. The method allows cost-efficient, maskless, large-area chemical patterning while avoiding potentially cytotoxic photochemical reaction products. The activation of the embedded photoacid occurs within the stamp upon illumination with the laser beam and the process is fully reversible. Preliminary positive results highlight the possibility of repeatable use of the same stamp for the creation of different patterns.

The unexpected effect of ferrocenyl substituents on the photochemistry of dianthryl sulfoxides.

Photoexcitation of ferrocenyl substituted dianthryl sulfoxide results in photochemical reaction products that differ from all known compounds of this class. This is enabled by energy transfer to a low-lying state, even in the case of the oxidized ferrocenium-containing compound.

LED-based solar simulator to study photochemistry over a wide temperature range in the large simulation chamber AIDA

Abstract. A light source has been built at the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) simulation chamber at the Karlsruhe Institute of Technology, simulating solar radiation at ground level. Instead of full spectra light sources, it uses a combination of LEDs with a narrow emission spectrum, resulting in a combined spectrum similar to the solar spectrum between 300 and 530 nm. The use of LEDs leads to an energy-efficient, robust and versatile illumination concept. The light source can be used over a wide temperature range down to −90 ∘C and is adjustable in intensity and spectral width as well as easily adjustable to new technological developments or scientific needs. Characterization of the illumination conditions shows a vertical intensity gradient in the chamber. The integral intensity corresponds to a NO2 photolysis frequency j(NO2) of (1.58±0.21(1σ))×10-3 s−1 for temperatures between 213 and 295 K. At constant temperature, the light intensity is stable within ±1 %. While the emissions of the different LEDs change with temperature, they can be adjusted, and thus it is possible to adapt the spectrum for different temperatures. Although the illumination of the simulation chamber leads to an increase of 0.7 K h−1 of the mean gas temperature, it is possible to perform experiments with aqueous droplets at relative humidities up to ≤95 % and also above water or ice saturation with corresponding clouds. Additionally, temperature- and wavelength-dependent photolysis experiments with 2,3-pentanedione have been conducted. The photolysis of 2,3-pentanedione occurs mainly between 400 and 460 nm, resulting in a mean photolysis frequency of (1.03±0.15)×10-4 s−1 independent of temperature in the range 213–298 K with a quantum yield of 0.36±0.04. In contrast, the yield of the two main photolysis products, acetaldehyde and formaldehyde, decreases with temperature. Furthermore, the light source was applied to study the photochemistry of aerosol particles. For the atmospheric brown carbon proxy compound 3,5-diacetyl-2,4,6-trimethyl-1,4-dihydropyridine, photochemical reaction products were identified. In aerosol particles containing iron oxalate as a photosensitizer, the photosensitized degradation of organic acids (pinic and pinonic acid) was studied. Although the light source only generates about one-third of the maximum solar irradiation at ground level at Karlsruhe (49.007∘ N, 8.404∘ E; 12:00 UTC+2) on a clear summer day with a substantial intensity gradient throughout the simulation chamber, it could be shown that this type of light source allows reproducible experiments over a wide range of simulated atmospheric conditions and with a large flexibility and control of the irradiation spectrum.

Effects of Meteorological Factors on the Vertical Distribution of Peroxyacetyl Nitrate in Autumn in Tianjin

With the decrease of PM2.5 concentration, atmospheric photochemical pollution in North China Plain has attracted more and more attention. Peroxyacetyl nitrate (PAN) is an important product and reliable indicator of atmospheric photochemical reaction. In this study, the measured concentrations of PAN near the surface and at 220 m were obtained from the Tianjin Meteorological Tower in October 2018. The results showed that the average concentrations of PAN at ground and 220m platform were 1.65 ± 1.34 ppb and 1.76 ± 1.41 ppb respectively during the day, and the mixture was relatively uniform. The average concentrations of PAN were 0.99 ± 0.94 ppb and 1.42 ± 1.28 ppb during the nighttime, respectively, indicating that the vertical difference was significantly increased. The standard deviation of PAN concentration was close to the average value, indicating that the concentration fluctuated greatly. The correlation coefficient between PAN and PM2.5 was higher than that of O3, indicating that stable weather was an important factor affecting PAN concentration. Based on the analysis of the vertical wind speed by the wind profile radar and ozone concentration vertical distribution data, we believe that there is a downdraft in the upper atmosphere of the boundary layer. The higher concentration of PAN at 220 m at night came from the high-altitude pollution air mass. The analysis of 40 m and 200 m turbulence data showed that the weak turbulence hindered the vertical exchange between the surface and the upper atmosphere, resulting in the high concentration of PAN unable to reach the surface. The boundary layer structure is one of the important reasons for the vertical difference of PAN concentration at night in autumn in NCP.

Four- and Five-Carbon Dicarboxylic Acids Present in Secondary Organic Aerosol Produced from Anthropogenic and Biogenic Volatile Organic Compounds

To better understand precursors of dicarboxylic acids in ambient secondary organic aerosol (SOA), we studied C4–C9 dicarboxylic acids present in SOA formed from the oxidation of toluene, naphthalene, α-pinene, and isoprene. C4–C9 dicarboxylic acids present in SOA were analyzed by offline derivatization gas chromatography–mass spectrometry. We revealed that C4 dicarboxylic acids including succinic acid, maleic acid, fumaric acid, malic acid, DL-tartaric acid, and meso-tartaric acid are produced by the photooxidation of toluene. Since meso-tartaric acid barely occurs in nature, it is a potential aerosol tracer of photochemical reaction products. In SOA particles from toluene, we also detected a compound and its isomer with similar mass spectra to methyltartaric acid standard; the compound and the isomer are tentatively identified as 2,3-dihydroxypentanedioic acid isomers. The ratio of detected C4–C5 dicarboxylic acids to total toluene SOA mass had no significant dependence on the initial VOC/NOx condition. Trace levels of maleic acid and fumaric acid were detected during the photooxidation of naphthalene. Malic acid was produced from the oxidation of α-pinene and isoprene. A trace amount of succinic acid was detected in the SOA produced from the oxidation of isoprene.

Oxime Ether Synthesis through O-H Functionalization of Oximes with Diazo Esters under Blue LED Irradiation.

A green and sustainable oxime ether formation method via the visible-light-promoted O-H functionalization of oximes with diazo esters is described. The reaction occurs under very mild conditions (catalyst- and additive-free) with a high yield and a high functional group tolerance. When the reaction was performed with a cyclic ether as the solvent (e.g., THF, 1,4-dioxane, tetrahydropyran, ect.), an interesting photochemical three-component reaction product was obtained in good yields.

Assessing volatile organic compound sources in a boreal forest using positive matrix factorization (PMF)

Ambient volatile organic compound (VOC) concentrations including individual monoterpenoids, sesquiterpenes (SQTs), isoprene, 2-methyl-3-buten-1-ol (MBO), methacrolein (MACR), C5–C10 aldehydes, benzene and toluene were measured in a coniferous forest in Hyytiälä, southern Finland, in April–November 2016 with 1–2 h time resolution. Positive matrix factorization (PMF) was used to resolve the major sources which were responsible for the observed ambient VOC concentrations. The most reliable results were obtained with a 10 factor solution including four anthropogenic and six biogenic sources. Three of the biogenic factors were induced by light. They were either light dependent emissions or products of photochemical reactions. Three factors appeared to be temperature dependent emissions. Biogenic emissions were clearly the most important source of the measured VOCs, but the contribution from a local sawmill was also significant. About half of the monoterpenes (MTs) could be appointed to Scots pine emissions, but the influence from the activities at a near-by sawmill and Norway spruce emissions were also found. In the case of some individual MTs (e.g. limonene), spruce emissions dominated. Spruce emissions were also mainly responsible for ambient SQTs, aldehydes, and isoprene. For anthropogenic compounds, benzene and toluene, background, and local activities were the main sources. PMF was useful in resolving the sources of ambient VOCs.

Сравнительный анализ методов исследования отложений копоти на местах пожаров

Introduction. Smokes are aerosols that contain sublimating substances and condensing vapors, as well as products of chemical and photochemical reactions. In addition to solid and liquid particles, they contain gaseous products of both complete and incomplete decomposition during combustion process, as well as nitrogen and the remains of unreacted oxygen during combustion. The aerosol substance of smoke that has settled on any surface is called soot, which often acts as an object of fire-technical expertise, and the aggregate of soot particles that form zones of various configurations is called smokiness. Goals and objectives. The aim of the work is to study soot and its components for the development of a comprehensive methodology for the study of fires in determining both the focus and the cause of the fire, as well as the pathways of the spread of hazardous factors of fire at different stages of fire development. The main task of the work is to determine the dependence of the qualitative and quantitative indicators of soot and its component composition on the temperature conditions of combustion of various materials in order to establish the conditions for the course of a fire. Research methods. Field and laboratory methods for the study of soot are considered. Field methods include visual analysis of soot deposits (identifying the configuration of soot, color and intensity of the soot layer) and measuring the electrical resistance of the soot layer using a field contact probe. Laboratory methods include the method of microscopic morphological analysis, the method of thermal analysis, molecular spectroscopy and gas chromatography, which are indirect and direct methods for studying extracted organic components of soot. Results and its discussion. The modern methods of research of soot are analyzed. A scheme of laboratory methods is proposed. It allows carry out full morphological analysis, to evaluate the behavior of soot components during heating and composition of extracted components for solving the problems of studying fires. Regression dependences of the content of bituminous components on the logarithm of the electrical resistance of the soot layer were obtained, which showed that, regardless of the type of combustible material, a transition zone is observed on them, in which, with a relatively small change in electrical resistance, a significant increase in the content of bituminous components is observed. Conclusion. The paper considers an comprehensive approach to the study of extractable components of soot. The obtained dependences of the qualitative and quantitative indicators of soot and its component composition on the temperature conditions of combustion of various materials will improve the quality and level of reliability of information in the study of fires in order to determine the focus and cause of a fire, as well as the ways of spreading hazardous factors of a fire at different stages of its development. Key words: smoke, soot, extractable organic compounds, bitumen components, soot layer electrical resistance, molecular spectroscopy, Boltzmann function, fire investigation.

Long-term observations of oxygenated volatile organic compounds (OVOCs) in an urban atmosphere in southern China, 2014-2019.

Oxygenated volatile organic compounds (OVOCs) are important precursors and intermediate products of atmospheric photochemical reactions, which can promote the formation of secondary pollutants such as ozone (O3) and secondary organic aerosol (SOA). However, there have been few studies on the sources of and long-term variation in ambient OVOCs. This study combined sensitive, near real-time measurements of VOCs by proton transfer reaction-mass spectrometry (PTR-MS) with an improved photochemical age parameterization method to quantify daytime sources of OVOCs in an urban atmosphere in China from 2014 to 2019, permitting the observation of the impacts of emission control strategies that were implemented during this period. Temporal variation in six key OVOCs (methanol, acetaldehyde, acetone, methyl ethyl ketone (MEK), formic acid, and acetic acid) were observed. The sum of concentrations of OVOCs was averagely 13% higher during the dry season (November to April), when winds transported polluted air masses to Shenzhen from the continent, than during the wet season, and peak diurnal levels occurred during the daytime year-round due to photochemical production and higher daytime anthropogenic emissions. The average dry season concentration of OVOCs declined from a peak of 30.3ppb in 2015 to 18.7ppb in 2019. The results of source apportionment showed that primary anthropogenic sources contributed the most to methanol, MEK, and acetic acid (32-51%); the dominant sources of acetaldehyde and formic acid were both primary and secondary anthropogenic sources; and biomass burning contributed a small fraction (5-11%) to the six OVOCs. From 2014 to 2019, contributions from primary anthropogenic sources of OVOCs decreased significantly by 50-60% due to intensive pollution control measures in Shenzhen, whereas pollution control measures had no observable impact on secondary OVOCs, indicating their formation was not limited by availability of their primary VOC precursors.

Measurement of gaseous and particulate formaldehyde in the Yangtze River Delta, China

Formaldehyde (HCHO) is one of the most important intermediate products of atmospheric photochemical reactions and is also a radical source that promotes ozone formation. Given its high solubility, HCHO is likely to exist in particulate form. In this work, gaseous HCHO (HCHOg) and particulate HCHO (HCHOp) were separated and collected by a rotating wet annular denude (RWAD) and an aerosol growth chamber–coil aerosol cooler (AC). The collected HCHO from the RWAD and AC are measured by two online Hantzsch method-based formaldehyde analyzers. The comprehensive campaign was held in the Yangtze River Delta of China from 15 May to 18 June 2018, which is during the harvest season. Several biomass burning events were identified by using acetonitrile as a tracer. During the period influenced by biomass burning, the mixing ratios of HCHOg and HCHOp were respectively 122% and 231% higher than those during other time periods. The enhancement ratio of HCHOg to acetonitrile obtained from this work generally agrees with those from the existing literature. Biomass burning contributed 14.8% to HCHOg, but the abundant freshly discharged precursors it emitted greatly promoted the secondary production of HCHOg. We suggest that the high concentration of HCHOp during the biomass burning period was from uptake of HCHOg by aerosols during their transportation; the liquid state particles are conducive to HCHOg uptake. High relative humidity, a low particle rebound fraction f, as well as low temperatures may result in higher uptake coefficient values.

INTERNATIONAL AND NATIONAL LEGISLATION TO CONTROL MICTOXINS IN FOOD: REVIEW

Today, the problem of monitoring mycotoxins has become global in connection with climate change, a violation of the ecological balance for the use of intensive technologies for processing crops, through air pollution and the accumulation of products of photochemical reactions (photooxidants), which leads to a decrease in plant resistance to phytopathogens. Every year, the problem of mycotoxicosis is exacerbated, as toxic fungi adapt quickly to new technologies and modern plant protection products. The increase in mycotoxins in foods also relates to the widespread use of nitrogen fertilizers and pesticides. Natural toxins create risks for the health of humans and animals, affect food security and nutrition, reducing people's access to healthy food. The World Health Organization is constantly appealing to national authorities to monitor and ensure that the levels of the most relevant natural toxins in foods are as low as possible and consistent with both national and international requirements. Ukraine's membership in the WTO, an association with the European Union, and the expansion of international trade require solutions to the issues of free movement of goods, safe and healthy food, and, accordingly, an adequate level of protection of life and health of people. One of the most important ways to solve them is to improve and harmonize national food legislation in line with international standards, including on the control of mycotoxins. The purpose of our work was to conduct an analysis of literary sources, international and national legislative acts on the control of mycotoxins in food products throughout the food chain. To prepare the publication, we have used literary sources on the subject of publication, as well as we have conducted a comparative analysis of national and international legislative acts regulating procedures and methods for controlling the residues of mycotoxins in food. An analysis of numerous sources has shown that the issue of monitoring mycotoxins in foods, improving laboratory control and risk-based approach to preventing foodborne mycotoxicosis worries scientists from different countries, including Ukrainian. The analysis of national legislation shows that national standards on maximum levels of pollutants have been revised in Ukraine and a number of standards have been harmonized for methods of monitoring the residues of mycotoxins in feed for productive animals, food products of animal and vegetable origin. Key words: mycotoxins, food chain, food, international law, national legislation, control, safety, risks.

Reactivity control of a photocatalytic system by changing the light intensity

We report a novel light-intensity dependent reactivity approach allowing us to selectively switch between triplet energy transfer and electron transfer reactions, or to regulate the redox potential available for challenging reductions. Simply by adjusting the light power density with an inexpensive lens while keeping all other parameters constant, we achieved control over one- and two-photon mechanisms, and successfully exploited our approach for lab-scale photoreactions using three substrate classes with excellent selectivities and good product yields. Specifically, our proof-of-concept study demonstrates that the irradiation intensity can be used to control (i) the available photoredox reactivity for reductive dehalogenations to selectively target either bromo- or chloro-substituted arenes, (ii) the photochemical cis-trans isomerization of olefins versus their photoreduction, and (iii) the competition between hydrogen atom abstraction and radical dimerization processes.

Aliphatic Azides as Selective Cysteine Labeling Reagents for Integral Membrane Proteins.

Upon ultraviolet activation, cannabinergic aliphatic azido (N3) ligands covalently label cannabinoid receptors, prominent G-protein-coupled receptor (GPCR) drug targets. We report here the mechanism of covalent attachment to selected substrates of the high-affinity CBR inverse agonist AM1335 and its deuterated analog AM1335(d10), arylpyrazole compounds with an azide moiety at their n-pentyl side chain. To model the receptor interaction, we utilized the human cannabinoid 2 receptor (hCB2R) transmembrane helix 6 (TMH6) peptide and an N-acyl-protected cysteine (NAC). The photochemical reaction products of model substrates with AM1335 and AM1335(d10) were analyzed with tandem electrospray ionization mass spectrometry fragmentation and deuterium exchange mass spectrometry. The nitrene initially formed after photoreaction undergoes rearrangement to an imine which then interacts with the cysteine sulfhydryl group, resulting in ligand attachment. Our results demonstrate that covalent probes carrying aliphatic azides behave more selectively than originally thought and can be used to label protein cysteine residues preferentially.

Modeling C1–C4 Alkyl Nitrate Photochemistry and Their Impacts on O3 Production in Urban and Suburban Environments of Hong Kong

AbstractAs intermediate products of photochemical reactions, alkyl nitrates (RONO2) regulate ozone (O3) formation. In this study, a photochemical box model incorporating master chemical mechanism well reproduced the observed RONO2 at an urban and a mountainous site, with index of agreement in the range of 0.66–0.73. The value 0.0003 was identified to be the most appropriate branching ratio for C1 RONO2, with the error less than 50%. Although levels of the parent hydrocarbons and nitric oxide (NO) were significantly higher at the urban site than the mountainous site, the production of C2–C3 RONO2 was comparable to or even lower than at the mountainous site, due to the lower concentrations of oxidative radicals in the urban environment. Based on the profiles of air pollutants at the mountainous site, the formation of C2–C4 RONO2 was limited by NOx (volatile organic compounds (VOCs)) when total volatile organic compounds (TVOCs)/NOx was higher (lower) than 10.0 ± 0.4 parts per billion by volume (ppbv)/ppbv. This dividing ratio decreased (p < 0.05) to 8.7 ± 0.4 ppbv/ppbv at the urban site, mainly due to the different air pollutant profiles at the two sites. For the formation of C1 RONO2, the NOx‐limited regime extended the ratio of TVOCs/NOx to as low as 2.4 ± 0.2 and 3.1 ± 0.1 ppbv/ppbv at the mountainous and urban site, respectively. RONO2 formation led to a decrease of simulated O3, with reduction efficiencies (O3 reduction/RONO2 production) of 4–5 parts per trillion by volume (pptv)/pptv at the mountainous site and 3–4 pptv/pptv at the urban site. On the other hand, the variations of simulated O3 induced by RONO2 degradation depended upon the regimes controlling O3 formation and the relative abundances of TVOCs and NOx.

The Participation of Apoplast Invertase in the Regulation of Photosynthesis by Stomatal Mechanism

A multi-year research on the influence of donor-acceptor relations between photosynthetic and assimilate-consuming organs on regulation of plant photosynthesis has been summarized. Cause and effect relationships between chloroplast photochemical reactions, CO2 assimilation and oxygen photosynthetic metabolism, transport of sugars in the phloem, apoplastic invertase and leaf stomata activity have been established. A concept, according to which the regulation of photosynthesis at the level of an assimilate donor leaf with the change of illumination or export of products of photosynthesis is effectuated as follows, has been introduced. In case of deficiency of products of chloroplast photochemical reactions there occurs incomplete regeneration of resulting primary CO2 fixation products and rapid accumulation of oxygenated substances in cells, vacuoles and the apoplast of the leaf. Apoplastic fluid pH decrease activates the invertase and intensifies the sucrose splitting in the apoplast, which increases the osmolality of extracellular environment that is increased approaching the guard cells, where the main evaporation of water takes place. The osmolality of extracellular environment decreases the turgor of the guard cells and increases the resistance of СО2 diffusion into the leaf, which leads to photosynthesis decrease. Increased illumination or assimilate consumption activity leads to the opposite outcome. Thus, the intensity of light and dark reactions in photosynthesis is coordinated and chloroplasts are protected against photodamage.

Luminescence and photochemical properties of hydrazones of aromatic aldehydes

Luminescence and photochemical properties found by us earlier for several hydrazones of aromatic aldehydes have been shown to be characteristic also of other compounds of this class. The structure of the product of reversible photochemical reaction of hydrazones of aromatic aldehydes is explained by specific interactions between the lone electron pairs of the two vicinal nitrogen atoms in the molecule of hydrazine. Compounds possessing photochromic properties have been suggested and prerequisites of application of luminescent hydrazones as luminophors have been formulated.

Time-Domain Simulations of Transient Species in Experimentally Relevant Environments.

Simulating the spectroscopic properties of short-lived thermal and photochemical reaction intermediates and products is a challenging task, as these species often feature atypical molecular and electronic structures. The complex environments in which such species typically reside in practice add further complexity to the problem. Herein, we tackle this problem in silico using ab initio molecular dynamics (AIMD) simulations, employing iso-CHBr3, namely H(Br)C-Br-Br, as a prototypical system. This species was chosen because it features both a nonconventional C-Br-Br bonding pattern, as well as a strong dependence of its spectral features on the local environment in which it resides, as illustrated in recent experimental reports. We simulate the UV-vis and IR spectra of iso-CHBr3 in the gas phase, as well as in a Ne cluster (64 atoms) and in a methylcyclohexane cage (14 solvent molecules) representative of the previously characterized matrix isolated and solvated iso-CHBr3 species. We exclusively perform fully quantum mechanical static and dynamic simulations. By comparing our condensed phase simulations to their experimental analogues, we stress the importance of (i) conformational sampling, even at cryogenic temperatures, and (ii) using a fully quantum mechanical description of both solute and bath to properly account for the experimental observables.

A new suprasterol by photochemical reaction of 1α,25-dihydroxy-9-methylene-19-norvitamin D3.

The UV-induced photochemical reaction of 1α,25-dihydroxy-9-methylene-19-norvitamin D3 has been investigated. The pentacyclic structure of the isolated product has been unequivocally established by X-ray crystallographic analysis. The possible reaction paths of the examined photochemical transformation are discussed. Biological in vivo and in vitro tests proved that the photoproduct is devoid of calcemic activity.

Investigation of photochemical reaction products of glucose formed during direct UV detection in CE.

In CE, saccharides are accessible to direct UV detection due to a photochemical reaction in the detection window of the separation capillary resulting in the formation of UV absorbing substances. Employing a CE method that allows long in-capillary irradiation with subsequent UV and MS detection, the present study could identify several reaction products of glucose. Among these were UV absorbing substances so far unknown to be formed during direct UV detection with the chemical formulas C4 H6 O2 , C5 H6 O4 , C5 H8 O3, and C6 H8 O5 . Investigations of the impact of the irradiation time revealed differences between these reaction products suggesting differing reaction mechanisms especially for the smallest products. More detailed information could be obtained by experiments with isotope-labeled substrates performed to determine the parts of glucose that are converted to the particular reaction products. In addition, structural formulas for the reaction products were suggested based on HPLC-MS/MS measurements of off-line irradiated glucose solutions which revealed the existence of functional groups such as carboxylic acid or aldehyde groups.

Current Topics on Vitamin D. Evolution of animals and vitamin D

Vitamin D3 is already found in the early evolution of life, but essentially as inactive products of the photochemical reaction of 7-dehydrocholesterol. The full vitamin D endocrine system characterized by the specific vitamin D transport protein (DBP) , specific vitamin D-metabolizing CYP P450 enzymes, active vitamin D metabolites, 1α,25 (OH) 2D3, specific vitamin D nuclear receptor (VDR), and fibroblast growth factor 23 (FGF23) became essential for maintaining calcium and bone homeostasis in terrestrial animals cope with the challenging of higher gravity and calcium-poor environment. The present review describes the story about the evolution of animals and vitamin D.