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Probing of G-Quadruplex Structures via Ligand-Sensitized Photochemical Reactions in BrU-Substituted DNA
摘要： We studied photochemical reactions of BrU-substituted G-quadruplex (G4) DNA substrates with two pyrene-substituted polyazamacrocyclic ligands, M-1PY and M-2PY. Both ligands bind to and stabilize G4-DNA structures without altering their folding topology, as demonstrated by FRET-melting experiments, fluorimetric titrations and CD spectroscopy. Notably, the bis-pyrene derivative (M-2PY) behaves as a significantly more affine and selective G4 ligand, compared with its mono-pyrene counterpart (M-1PY) and control compounds. Upon short UVA irradiation (365 nm) both ligands, in particular M-2PY, efficiently sensitize photoreactions at BrU residues incorporated in G4 structures and give rise to two kinds of photoproducts, namely DNA strand cleavage and covalent ligand–DNA photoadducts. Remarkably, the photoinduced strand cleavage is observed exclusively with G4 structures presenting BrU residues in lateral or diagonal loops, but not with parallel G4-DNA structures presenting only propeller loops. In contrast, the formation of fluorescent photoadducts is observed with all BrU-substituted G4-DNA substrates, with M-2PY giving significantly higher yields (up to 27%) than M-1PY. Both ligand-sensitized photoreactions are specific to BrU-modified G4-DNA structures with respect to double-stranded or stem-loop substrates. Thus, ligand-sensitized photoreactions with BrU-substituted G4-DNA may be exploited (i) as a photochemical probe, allowing “photofootprinting” of G4 folding topologies in vitro and (ii) for covalent trapping of G4 structures as photoadducts with pyrene-substituted ligands.
关键词： covalent photoadducts,pyrene-substituted ligands,photochemical reactions,G-quadruplex,BrU-substituted DNA,DNA strand cleavage
更新于2025-09-09 09:28:46
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Pitfalls in the ABTS Peroxidase Activity Test: Interference of Photochemical Processes
摘要： ABTS (2,2′-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid) oxidation to form its radical cation in the presence of H2O2 is frequently used as a test for determining the peroxidase activity of enzyme mimics. Detailed studies using salen-type Mn(III) complexes show that photochemical processes involving H2O2, ABTS, and the complex itself can lead to erroneous results. The capability of the complexes to act as ?OH scavengers can be also relevant when the mechanism of their biological activity is considered.
关键词： photochemical processes,ABTS,peroxidase activity,?OH scavengers,Mn(III) complexes
更新于2025-09-09 09:28:46
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Development of a photochemical source for the production and calibration of acyl peroxynitrate compounds
摘要： A dynamic system for the calibration of acyl peroxynitrate compounds (APNs) has been developed in the laboratory to reduce the difficulty, required time, and instability of laboratory-produced standards for difficult-to-synthesize APN species. In this work we present a photochemical source for the generation of APN standards: acetyl peroxynitrate (PAN), propionyl peroxynitrate (PPN), acryloyl peroxynitrate (APAN), methacryloyl peroxynitrate (MPAN), and crotonyl peroxynitrate (CPAN). APNs are generated via photolysis of a mixture of acyl chloride (RC(O)Cl) and ketone (RC(=O)R) precursor compounds in the presence of O2 and NO2. Subsequent separation by a prep-scale gas chromatograph and detection with a total NOy instrument serve to quantify the output of the APN source. Validation of the APN products was performed using iodide ion chemical ionization mass spectroscopy (I? CIMS). This method of standard production is an efficient and accurate technique for the calibration of instrumentation used to measure PAN, PPN, APAN, MPAN, and CPAN.
关键词： PPN,calibration,PAN,APAN,acyl peroxynitrate compounds,photochemical source,CPAN,MPAN
更新于2025-09-09 09:28:46
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Numerical Demonstration of In-Tube Liquid-Column Migration Driven by Photoisomerization
摘要： Droplet manipulation by light-induced isomerization was numerically demonstrated and investigated regarding the driving mechanism. Such a non-invasive manipulation of a droplet in a microchannel can be realized, for example, by the use of watery solution of photoresponsive surfactant that exhibits the isomerization. Due to variable fluid properties between the cis and trans isomers, one-side light irradiation on a liquid column in a tube would lead to some kind of imbalance between the two ends of the liquid column and then drive droplet migration. The present numerical simulations of air–liquid two-phase flow and its scalar transport of the isomer, considering the variable static contact angle, agreed quantitatively with the experimental results in terms of the migration speed. This fact supports the contention that the droplet migration is more likely to be driven by an imbalance in the wettability, or the contact angle. The migration speed was found to be less dependent on the liquid-column length, but proportional to the tube diameter.
关键词： photochemical reaction,non-invasive control,wettability,surface tension,microfluidics,computational fluid dynamics,lab-on-a-chip,droplet manipulation,two-phase flow,photoresponsible surfactant
更新于2025-09-09 09:28:46
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Technical note: Evaluation of the simultaneous measurements of mesospheric OH, HO<sub>2</sub>, and O<sub>3</sub> under a photochemical equilibrium assumption – a statistical approach
摘要： This Technical Note presents a statistical approach to evaluating simultaneous measurements of several atmospheric components under the assumption of photochemical equilibrium. We consider simultaneous measurements of OH, HO2, and O3 at the altitudes of the mesosphere as a specific example and their daytime photochemical equilibrium as an evaluating relationship. A simplified algebraic equation relating local concentrations of these components in the 50–100 km altitude range has been derived. The parameters of the equation are temperature, neutral density, local zenith angle, and the rates of eight reactions. We have performed a one-year simulation of the mesosphere and lower thermosphere using a 3-D chemical-transport model. The simulation shows that the discrepancy between the calculated evolution of the components and the equilibrium value given by the equation does not exceed 3–4 % in the full range of altitudes independent of season or latitude. We have developed a statistical Bayesian evaluation technique for simultaneous measurements of OH, HO2, and O3 based on the equilibrium equation taking into account the measurement error. The first results of the application of the technique to MLS/Aura data (Microwave Limb Sounder) are presented in this Technical Note. It has been found that the satellite data of the HO2 distribution regularly demonstrate lower altitudes of this component’s mesospheric maximum. This has also been confirmed by model HO2 distributions and comparison with offline retrieval of HO2 from the daily zonal means MLS radiance.
关键词： photochemical equilibrium,mesosphere,MLS/Aura,O3,OH,statistical evaluation,HO2
更新于2025-09-09 09:28:46
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Fundamental investigation on interaction between hexafluoroisopropylalcohol-containing styrene and photochemical acid generator for rationale design of photoresist system
摘要： This article presents the effect of some ionic photochemical acid generators (PAGs) to inhibit the dissolution of hexafluoroisopropylalcohol (HFA)-containing polystyrene to an aqueous alkaline developer, which is a highly important effect in photoresist application to enhance resolution of patterning. The dissolution inhibiting factors and mechanisms were investigated by evaluating the solubility and the 1H-NMR analysis of OH proton in HFA moiety. The dissolution inhibition effect was enhanced when the structures of PAGs fulfill some requirements: (a) their anions should have higher basicity and smaller van der Waals volume; (b) their cations should be stabilized by conjugation with electron-rich aromatics. In the dissolution inhibition, the HFA moiety interacts with the anionic part of PAGs liberated from the electrostatic interaction with the counter cation. These interactions were predicted and quantified by DFT calculations using Gaussian 09, leading to the rational designs of PAGs with higher dissolution inhibiting effect in photoresist systems.
关键词： fluoropolymers,photochemical acid generator,calculations,dissolution inhibition effect,photoresists
更新于2025-09-09 09:28:46
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Low-Energy Chlorophylls in Fucoxanthin Chlorophyll <i>a/c</i> -Binding Protein Conduct Excitation Energy Transfer to Photosystem I in Diatoms
摘要： Photosynthetic organisms handle solar energy precisely to achieve efficient photochemical reactions. Since there are a wide variety of light-harvesting antennas in oxyphototrophs, the excitation-energy-transfer mechanisms are thought to differ significantly. In this study, we compared excitation-energy dynamics between photosystem I (PSI) cores and a complex between PSI and fucoxanthin chlorophyll a/c-binding protein (PSI-FCPI) isolated from a diatom, Chaetoceros gracilis, by means of picosecond time-resolved fluorescence analyses. Time-resolved spectra measured at 77 K clearly show that low-energy Chls in the FCPI transfers not only most of the excitation energy to the reaction-center Chls in the PSI cores but also the remaining energy to carotenoids for quenching. Under room-temperature conditions, the energy in the low-energy Chls is rapidly equilibrated on Chls in the PSI cores by uphill energy transfer within a few tens of ps. These findings provide solid evidence that the low-energy Chls in the FCPI contribute to the photochemical reactions in PSI.
关键词： light-harvesting antennas,low-energy Chls,Photosynthetic organisms,PSI-FCPI,excitation-energy-transfer mechanisms,photochemical reactions
更新于2025-09-09 09:28:46
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A Pentacene-based Nanotube Displaying Enriched Electro/Photochemical Activities
摘要： This article reports the synthesis and characterization of a pentacene-based nanotube that exhibits enriched electrochemical and photochemical activities. The nanotube is constructed from a pentacene chromophore and features a tubular conformation with a triangular cross-section, enabling unique electronic and photophysical properties. The study demonstrates the nanotube's ability to facilitate efficient intramolecular charge transfer and triplet-state generation, highlighting its potential for applications in optoelectronic devices and photocatalysis.
关键词： nanotube,electrochemical,pentacene,triplet-state,charge transfer,photochemical
更新于2025-09-04 15:30:14
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Photochemical resolution of a thermally inert cyclometalated Ru(phbpy)(N-N)(sulfoxide)+ complex
摘要： In this work a photosubstitution strategy is presented that can be used for the isolation of chiral organometallic complexes. A series of five cyclometalated complexes [Ru(phbpy)(N-N)(DMSO-κS)]+ ([1]PF6-[5]PF6) were synthesized and characterized, where Hphbpy = 6’-phenyl-2,2’-bipyridyl, and N-N = bpy (2,2’-bipyridine), phen (1,10-phenanthroline), dpq (pyrazino[2,3-f][1,10]phenanthroline), dppz (dipyrido[3,2-a:2',3'-c]phenazine, or dppn (benzo[i]dipyrido[3,2-a:2',3'-c]phenazine), respectively. Due to the asymmetry of the cyclometalated phbpy? ligand, the corresponding [Ru(phbpy)(N-N)(DMSO-κS)]+complexes are chiral. The exceptional thermal inertness of the Ru-S bond made chiral resolution of these complexes by thermal ligand exchange unrealistic. However, photosubstitution by visible light irradiation in acetonitrile was possible for three of the five complexes ([1]PF6-[3]PF6). Further thermal coordination of the chiral sulfoxide (R)-methyl p-tolylsulfoxide to the photoproduct [Ru(phbpy)(phen)(NCMe)]PF6, followed by reverse phase HPLC, led to the separation and characterization of the two diastereoisomers of [Ru(phbpy)(phen)(MeSO(C7H7))]PF6, thus providing a new photochemical approach towards the synthesis of chiral cyclometalated ruthenium(II) complexes. Full photochemical, electrochemical, and frontier orbital characterization of the cyclometallated complexes [1]PF6-[5]PF6 was performed to explain why [4]PF6 and [5]PF6 are photochemically inert, while [1]PF6-[3]PF6 perform selective photosubstitution.
关键词： photochemical resolution,chiral organometallic complexes,thermal inertness,cyclometalated Ru complex,photosubstitution
更新于2025-09-04 15:30:14
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Catalytic deracemization of chiral allenes by sensitized excitation with visible light
摘要： Chiral compounds exist as enantiomers that are non-superimposable mirror images of each other. Owing to the importance of enantiomerically pure chiral compounds—for example, as active pharmaceutical ingredients—separation of racemates (1:1 mixtures of enantiomers) is extensively performed. Frequently, however, only a single enantiomeric form of a chiral compound is required, which raises the question of how a racemate can be selectively converted into a single enantiomer. Such a deracemization process is entropically disfavoured and cannot be performed by a conventional catalyst in solution. Here we show that it is possible to photochemically deracemize chiral compounds with high enantioselectivity using irradiation with visible light (wavelength of 420 nanometres) in the presence of catalytic quantities (2.5 mole per cent) of a chiral sensitizer. We converted an array of 17 chiral racemic allenes into the respective single enantiomers with 89 to 97 per cent enantiomeric excess. The sensitizer is postulated to operate by triplet energy transfer to the allene, with different energy-transfer efficiencies for the two enantiomers. It thus serves as a unidirectional catalyst that converts one enantiomer but not the other, and the decrease in entropy is compensated by light energy. Photochemical deracemization enables the direct formation of enantiopure materials from a racemic mixture of the same compound, providing a novel approach to the challenge of creating asymmetry.
关键词： chiral sensitizer,triplet energy transfer,deracemization,chiral compounds,visible light,enantiomers,photochemical
更新于2025-09-04 15:30:14