Photochemical Probes Research Articles

Constructing the facet junction on solid solution BiOBr1-xClx for efficient photocatalytic CO2 reduction with H2O

Photocatalytic conversion of CO2 to renewable clean fuels was a promising way to alleviate the energy crisis and solve environmental issues. However, it remained significantly challenging for designing highly efficient photocatalysts. Herein, the solid solution BiOBr1-xClx (0 ≤ x ≤ 1, BOBC-n, n represented the amount of molten salt) with (001)/(102) facet junction was constructed through a molten salt method. In situ photochemical probing demonstrated that distinct exposed facets allowed photogenerated holes and electrons to migrate to the dominantly exposed and co-exposed facets and thus exhibited different reactivity. Benefiting from facet junction, the optimized BOBC-0.5 exhibited the superior performance of photocatalytic CO2 to CH3OH (5.52 μmol·g−1·h−1) to that of BiOBr with (001)/(110) facet junction (1.78 μmol·g−1·h−1). The density functional theory (DFT) calculations further confirmed the separation path of photogenerated carriers between distinct facets, which realized the effective spatial separation of electrons and holes. Moreover, the (102) facet revealed superior adsorption energy of CO2 molecules to that of (110) facet. This work highlighted a molten-salt strategy to build facet junction for boosting photocatalytic CO2 performance.

Unraveling the Role of Interface in Photogenerated Charge Separation at the Anatase/Rutile Heterophase Junction

Heterophase junctions have emerged as an effective strategy for spatial charge separation in photocatalysis. However, the photogenerated charge separation pathway at the junction region remains in doubt, and how the interfacial structure affects charge separation is unclear. Herein, we fabricate well-defined TiO2 heterophase junctions between rutile and anatase and employ in situ photochemical probing reactions to track the interfacial charges distribution by means of spherical aberration correction transmission electron microscope (CS aberration TEM). The photoreduction deposition of platinum (Pt) nanoclusters and photo-oxidation deposition of metal oxide nanoparticles demonstrate that the photogenerated electrons smoothly migrate across the interfacial phase junction from rutile to anatase phases and the photogenerated holes move in an opposite direction, which provides direct evidence on the spatial charge separation at the heterophase junction. Moreover, the atomic interfacial structure of anatase/rutile TiO2 heterophase junction formed is conducive for photogenerated charges moving from one phase to the other. This study revises the photogenerated charge separation at the anatase/rutile heterophase junction and demonstrates the important role of the interfacial structure on spatial charge separation.

RhB-Embedded Zirconium-Biquinoline-Based MOF Composite for Highly Sensitive Probing Cr(VI) and Photochemical Removal of CrO42-, Cr2O72-, and MO.

How to accurately detect and efficiently sweep Cr(VI) from contaminated water has come into focus. Zirconium-based metal-organic frameworks (MOFs) play vital roles in water environmental chemistry due to excellent hydrolysis-resistant stability. However, as photochemical probes and photocatalysts, poor performances in detection sensitivity, selectivity, and photosensitiveness limit sole Zr-MOFs' applications. So, it is urgent to quest valid strategies to break through the dilemmas. Embedding luminous dyes into MOFs has been considered one of the most feasible avenues. Herein, a dual-emissive RhB@Zr-MOF with orange-yellow fluorescence has been assembled by in situ-encapsulating rhodamine B (RhB) into a zirconium-biquinoline-based MOF. Actually, within RhB@Zr-MOF, the aggregation fluorescence quenching (ACQ) effect of RhB molecules was effectively avoided. Notably, RhB@Zr-MOF exhibits a rapid fluorescence quenching response toward Cr(VI) ions with high selectivity, sensitivity, and anti-interference abilities. More interestingly, unlike the most widely reported fluorescence resonance energy transfer (FRET) between MOFs and encapsulated guest modules, photoinduced electron transfer from RhB to Zr-MOF has been confirmed by modeling the ground state and excited states of RhB@Zr-MOF using density functional theory (DFT) and time-dependent DFT (TD-DFT). The effective electron transfer makes RhB@Zr-MOF more sensitive in probing Cr2O72- and CrO42- ions with ultralow detection limit (DL) values of 6.27 and 5.26 ppb, respectively. Prominently, the detection sensitivity based on DL values has been increased about 6 and 9 times, respectively, compared with pristine Zr-MOF. Moreover, rather negative CB and positive VB potentials make RhB@Zr-MOF have excellent photochemical scavenging ability toward Cr(VI) and MO.

Photochemical Probe Identification of a Small-Molecule Inhibitor Binding Site in Hedgehog Acyltransferase (HHAT)*.

The mammalian membrane‐bound O‐acyltransferase (MBOAT) superfamily is involved in biological processes including growth, development and appetite sensing. MBOATs are attractive drug targets in cancer and obesity; however, information on the binding site and molecular mechanisms underlying small‐molecule inhibition is elusive. This study reports rational development of a photochemical probe to interrogate a novel small‐molecule inhibitor binding site in the human MBOAT Hedgehog acyltransferase (HHAT). Structure‐activity relationship investigation identified single enantiomer IMP‐1575, the most potent HHAT inhibitor reported to‐date, and guided design of photocrosslinking probes that maintained HHAT‐inhibitory potency. Photocrosslinking and proteomic sequencing of HHAT delivered identification of the first small‐molecule binding site in a mammalian MBOAT. Topology and homology data suggested a potential mechanism for HHAT inhibition which was confirmed by kinetic analysis. Our results provide an optimal HHAT tool inhibitor IMP‐1575 (K i=38 nM) and a strategy for mapping small molecule interaction sites in MBOATs.

Photochemical Probe Identification of a Small-Molecule Inhibitor Binding Site in Hedgehog Acyltransferase (HHAT).

The mammalian membrane-bound O-acyltransferase (MBOAT) superfamily is involved in biological processes including growth, development and appetite sensing. MBOATs are attractive drug targets in cancer and obesity; however, information on the binding site and molecular mechanisms underlying small-molecule inhibition is elusive. This study reports rational development of a photochemical probe to interrogate a novel small-molecule inhibitor binding site in the human MBOAT Hedgehog acyltransferase (HHAT). Structure-activity relationship investigation identified single enantiomer IMP-1575, the most potent HHAT inhibitor reported to-date, and guided design of photocrosslinking probes that maintained HHAT-inhibitory potency. Photocrosslinking and proteomic sequencing of HHAT delivered identification of the first small-molecule binding site in a mammalian MBOAT. Topology and homology data suggested a potential mechanism for HHAT inhibition which was confirmed by kinetic analysis. Our results provide an optimal HHAT tool inhibitor IMP-1575 (K i=38 nM) and a strategy for mapping small molecule interaction sites in MBOATs.

Intrinsic Facet‐Dependent Reactivity of Well‐Defined BiOBr Nanosheets on Photocatalytic Water Splitting

AbstractSurface atomic arrangement and coordination of photocatalysts highly exposed to different crystal facets significantly affect the photoreactivity. However, controversies on the true photoreactivity of a specific facet in heterogeneous photocatalysis still exits. Herein, we exemplified well‐defined BiOBr nanosheets dominating with respective facets, (001) and (010), to track the reactivity of crystal facets for photocatalytic water splitting. The real photoreactivity of BiOBr‐(001) were evidenced to be significantly higher than BiOBr‐(010) for both hydrogen production and oxygen evolution reactions. Further in situ photochemical probing studies verified the distinct reactivity is not only owing to the highly exposed facets, but dominated by the co‐exposing facets, leading to an efficient spatial separation of photogenerated charges and further making the oxidation and reduction reactions separately occur with different reaction rates, which ordains the fate of the true photoreactivity.

Meso-Substituted Carbocyanines as Effective Spectral-Fluorescent and Photochemical Probes for Structurally Organized Systems Based on Macromolecules

Studies of the photonics of dyes in structurally organized systems are of great fundamental and applied importance. In this regard, the search for simple and convenient methods for analyzing the composition and studying structurally organized systems based on biomolecules (proteins, nucleic acids, etc.) using dye probes is highly relevant. meso-substituted polymethine (carbocyanine) dyes can serve as such probes, as such dyes have a unique set of spectral-fluorescent and photochemical properties that are sensitive to the molecular environment. In structurally organized systems, the photonics of these dyes changes drastically, which allows them to be used in studies of such systems. One peculiarity of these dyes is the mobile equilibrium between the trans- and cis-isomers, which differently interact with biomolecules. The interaction of the dyes with components of structurally organized systems leads to an increase in fluorescence and intersystem crossing to the triplet state. We have developed and put into practice spectral-fluorescent and photochemical probes based on meso-substituted carbocyanines. In particular, we widely used one of the anionic carbocyanines as a probe in biological systems containing serum albumin and collagens. This review is devoted to the works of the authors on the interaction of meso-substituted carbocyanine dyes with biomolecules and the photonics of meso-substituted carbocyanines in complexes with biomolecules. The works on the use of these dyes as probes in biological systems are also considered.

Monitoring Microalgal Biofilm Growth and Phenol Degradation with Fiber-Optic Sensors.

Simple D-type plastic optical fiber (POF) probes (i.e., sensor, reference, and photochemical probes) were created to accurately monitor the progression and phenol degradation of a Chlorella vulgaris biofilm. The sensor and reference probes were used to monitor the biofilm growth (thickness). The sensor probe, which consisted of a D-shaped POF and Canada balsam doped with GeO2 (CBG) coating, was developed to monitor the biofilm growth and change in the liquid-phase composition and its concentration inside the biofilm. The reference probe, which comprised a D-shaped POF, CBG coating, and glass fiber membrane (to separate the liquids from Chlorella vulgaris), was used to measure the response to changes in the liquid phase. A model was developed to demonstrate the accurate measurement of the biofilm thickness. The photochemical POF probe was coupled with a high-permselectivity phenol polymer membrane to monitor the phenol concentration and analyze the degradation time of 50 mg/L phenol with microalgal biofilms. A fixed relationship was obtained between the biofilm sensor output information and biofilm thickness for a biofilm thickness range of 0-290 μm with a periodic supply of 50 mg/L phenol solution. The highest phenol degradation rate occurred at a biofilm thickness of 191-222 μm. The proposed system can be used to investigate microalgal biomass and can provide a promising avenue for research on renewable resources and pollutant degradation.

Probing of G-Quadruplex Structures via Ligand-Sensitized Photochemical Reactions in BrU-Substituted DNA

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.

Development of Anionically Decorated Caged Neurotransmitters: In Vitro Comparison of 7-Nitroindolinyl- and 2-(p-Phenyl-o-nitrophenyl)propyl-Based Photochemical Probes.

Neurotransmitter uncaging, especially that of glutamate, has been used to study synaptic function for over 30 years. One limitation of caged glutamate probes is the blockade of γ-aminobutyric acid (GABA)-A receptor function. This problem comes to the fore when the probes are applied at the high concentrations required for effective two-photon photolysis. To mitigate such problems one could improve the photochemical properties of caging chromophores and/or remove receptor blockade. We show that addition of a dicarboxylate unit to the widely used 4-methoxy-7-nitroindolinyl-Glu (MNI-Glu) system reduced the off-target effects by about 50-70 %. When the same strategy was applied to an electron-rich 2-(p-Phenyl-o-nitrophenyl)propyl (PNPP) caging group, the pharmacological improvements were not as significant as in the MNI case. Finally, we used very extensive biological testing of the PNPP-caged Glu (more than 250 uncaging currents at single dendritic spines) to show that nitro-biphenyl caging chromophores have two-photon uncaging efficacies similar to that of MNI-Glu.

Graphene as a Quencher of Electronic Excited States of Photochemical Probes

Graphene sheets quench the singlet and triplet excited states of a series of six photochemical probes including pyrene, acridine orange, tris(2,2́-bipyridyl)ruthenium(II) dichloride, methylene blue, meso-tetrakis(phenylsulphonate)porphyrin, and 5,10,15,20-tetraphenyl-21H,28H-porphine zinc. It was found that Stern-Volmer fluorescence quenching can fit to one or two different quenching regimes depending on the probe. In addition, the quenching can be either static or dynamic depending on the fluorophore. The occurrence of several quenching regimes has been interpreted considering that quenching arises from the crowding of the fluorophore on both graphene faces, or site isolation on the graphene sheets. Laser flash photolysis has shown that the triplet lifetime of the probes generally decreases due to graphene quenching and that no new transients appear except in the case of methylene blue, where a new absorption spectrum characterized by a continuous absorption band is observed and attributed to graphene radical ion. This spectroscopic evidence suggests that the most general quenching mechanism is energy transfer from the singlet or triplet excited state of the dye to graphene. This raises the issue of determining the energy of the electronic excited states of graphene.

Designing and Synthesis of New Fluorine Substituted Pyrimidine-Thion-5-Carbonitriles and the Related Derivatives as Photochemical Probe Agents for Inhibition of Vitiligo Disease

A new biocidal agents fluorine substituted-3-thioxopyrimidine-5-carbonitriles (2-9) and/or the related fluorine substi- tuted pyrimido (4,5-d) pyrimidines (10-14) were synthesized by the cycloaddition of fluorinated β- arylidine malo- nonitriles (1a-c) followed by a nucleophilic attack against α,β-bifunctional reagents in different conditions. Structures of the fluorine targets were characterized by their elemental analysis and spectral data (UV, IR, 1H NMR, 13C NMR and mass measurements) and further evaluated as photochemical probe for inhibition of Vitiligo, it was found that compounds 5, 9, 11 and 12 exhibited high potency over the investigated compounds.

A DNA minor groove electronegative potential genome map based on photo-chemical probing

The double-stranded DNA of the genome contains both sequence information directly relating to the protein and RNA coding as well as functional and structural information relating to protein recognition. Only recently is the importance of DNA shape in this recognition process being fully appreciated, and it also appears that minor groove electronegative potential may contribute significantly in guiding proteins to their cognate binding sites in the genome. Based on the photo-chemical probing results, we have derived an algorithm that predicts the minor groove electronegative potential in a DNA helix of any given sequence. We have validated this model on a series of protein–DNA binding sites known to involve minor groove electrostatic recognition as well as on stable nucleosome core complexes. The algorithm allows for the first time a full minor groove electrostatic description at the nucleotide resolution of any genome, and it is illustrated how such detailed studies of this sequence dependent, inherent property of the DNA may reflect on genome organization, gene expression and chromosomal condensation.

Synthesis, Physiochemical Properties, Photochemical Probe, and Antimicrobial Effects of Novel Norfloxacin Analogues

The emerging resistance to antimicrobial drugs demands the synthesis of new remedies for microbial infections. Attempts have been made to prepare new compounds by modifications in the quinolone structure. An important method for the synthesis of new quinolone is using Vilsmeier approach but has its own limitations. The present work aimed to synthesize novel norfloxacin analogues using modified Vilsmeier approach and conduct preliminary investigations for the evaluation of their physicochemical properties, photochemical probe, and antimicrobial effects. In an effort to synthesize norfloxacin analogues, only 7-bromo-6-N-benzyl piperazinyl-4-oxoquinoline-3-carboxylic acid was isolated using Vilsmeier approach at high temperature, where N, N′-bis-(4-fluoro-3-nitrophenyl)-oxalamide and N, N′-bis-(3-chloro-4-fluorophenyl)-malonamide were obtained at low temperature. Correlation results showed that lipophilicity, molecular mass, and electronic factors might influence the activity. The synthesized compounds were evaluated for their antimicrobial effects against important pathogens, for their potential use in the inhibition of vitiligo.

A laser photolysis study of the decay kinetics of the triplet states and radicals of flavins in the bovine eye lens

The decay kinetics of the triplet states and radicals of riboflavin and flavin mononucleotide, which were introduced into the bovine eye lens as kinetic photochemical probes, was studied by nanosecond laser photolysis, as a function of dilution of the lens with water. Correlations were found between the kinetic parameters and the degree of ordering of crystallins in the aqueous solution of the lens.

Synthesis of Some More Fluorine Heterocyclic Nitrogen Systems Derived From Sulfa Drugs as Photochemical Probe Agents for Inhibition of Vitiligo Disease‐Part I

Some more new bioactive fluorine heterocyclic systems containing sulfur and nitrogen as five‐membered rings: pyrazoline, imidazole, imidazolopyrimidine, thiazolidinone and 1,2,4‐triazole derivatives (3‐13) have been synthetically derived from the interaction of sulfa drugs with fluorine aromatic aldehyde and/or hexa fluoroacetic anhydride followed by heterocyclization reactions. Former structures of the targets have been deduced upon the help of elemental and spectral data.. Compounds 7a‐f, 10c and 13 could be used as photochemical probe agents for inhibition of Vitiligo diseases, in compare with Nystatin and Nalidixic acid.

Synthesis of Polyfunctional Organic Systems Containing 1-Acyl/Aroyl-anilido-butadienes and their uses as Photochemical Probes and Chelating Agents for Removal of Bismuth (III) from Industrial Wastewater

The present article reports the synthesis of a series of some new 1-acyl/ benzoyl -1-anilido-4-methyl /aryl-1, 3-butadiene derivatives (II - IV) by warming primary heteroamines and/ or sulfa drugs with pre heated ethyl acetoacetate and / or ethyl benzoylacetate in dry conditions followed by condensation with unsaturated aromatic aldehydes in boiling ethanol-piperidine. The chemical structures of the compounds were characterized via their elemental analysis and spectroscopic measurements (UV Vis., IR, 1 HNMR). Some of the compounds (IIId, e, f, IV d, e,f) were tested as antimicrobial and photochemical probe agents. Compound IVa was physically loaded onto polyurethane solid sorbent and successfully used for the removal and / or pre concentration of bismuth (III) from industrial wastewater. The voltammetric behavior of the two compounds IIa and IVa in N, N-dimethylformamide was investigated.

Synthesis of Fluorine Heterocyclic Nitrogen Systems Derived From Sulfa Drugs as PhotochemicalProbe Agents for Inhibition of Vitiligo Disease‐Part II

Some more new bioactive fluorine heterocyclic systems containing sulfur and nitrogen as six‐membered rings such as; N,Nʼ‐disubstituted‐thiobarbituric acid, 3‐thioxo‐1,2,4‐triazino[5,6‐b]indole, 3‐sulfanilamido‐1,2,4‐triazino[5,6‐b]indole and 2‐trifluoromethyl‐4‐imino‐6‐(sulfamido)1,3,5‐triazino [3,2‐a]indole derivatives (2‐13) have been synthetically derived from the interaction of sulfa drugs with fluorine organic compounds (aldehydes, ketones, anhydride) followed by ring closure reactions. Structures of the targets have been established from their elemental and spectral data. Compounds 3, 6, 10 and 13 could be used as photochemical probe agents in compared with nystatin and nalidixic acid for inhibition of vitiligo diseases.

Electrochemical and photochemical characterization of novel ferrocenyl–azobenzene labeled PNA monomers for DNA detection

Ferrocenyl–azobenzene carboxylic acid was synthesized and used as electrochemically and spectroscopically active marker that was conjugated to thymine PNA monomer. Ferrocenyl–azobenzene labeled PNA monomer of thymine (Fc–Azo–T) shows highly electrochemical and photochemical activity. The detection limit of Fc–Azo–T can reach 10−6M by using differential pulsed voltammogram (DPV), and the UV–vis limit is in the order 10−7M in ethanol. Fc–Azo–T can undergo facile isomerization by photoirradiation. The results give great motivity for synthesizing ferrocenyl–azobenzene labeled PNA oligomers used as an effective electrochemical and photochemical probes.

Photochemical probing of the B–A conformational transition in a linearized pUC19 DNA and its polylinker region

We induced the B-to-A conformational transition by ethanol in a linearized pUC19 DNA. A primer extension method was used in combination with UV light irradiation to follow the transition, based on pausing of DNA synthesis due to the presence of damaged bases in the template. Primer extension data highly correlated with the results of another method monitoring the B–A transition, i.e. inhibition of restriction endonuclease cleavage of UV light-irradiated DNA. Primer extension enabled us to locate damaged nucleotides within the region of interest. Most damaged nucleotides were located in B-form trimers, exclusively containing both pyrimidine bases (TTC, TCT, CTC, and CTT), and in a cytosine tetramer. The amount of damaged bases decreased in the course of B–A transition. Some of the damage even disappeared in the A-form, which mainly concerns the C 4 and C 3 blocks. The cleavage was nearly restored in the A-form within this region ( Eco88I). On the contrary the decrease of damage was less significant with thymine dimers, only dropping to 50–60% of the B-form level. Consequently, the cleavage with EcoRI and HindIII remained mostly as before the transition (75% and 60% of uncleaved DNA preserved). We found significant differences in the B- and A-form pattern of UV light-damaged bases within the same region (polylinker) of DNA embedded within long (plasmid) or short (127 bp fragment) DNA molecules. The B–A transition of the fragment was found less cooperative than with linearized plasmid, which was confirmed by both CD spectroscopy and restriction cleavage inhibition.