Spectroscopic insights into BSA-mediated deaggregation of m-THPC.

Meta-tetra(hydroxyphenyl)chlorin (m-THPC) is among the most potent photosensitizers, known for its high singlet oxygen generation efficiency. However, its clinical effectiveness in photodynamic therapy (PDT) is compromised by its propensity to aggregate in aqueous solutions, adversely affecting its photophysical properties and therapeutic potential. A series of spectroscopic techniques, including UV-Vis absorption, fluorescence spectroscopy, and laser flash photolysis, revealed that m-THPC exhibits significant aggregation, particularly in MeOH-PBS mixtures with MeOH content below 30%.

The structure of model and peptide disulfides markedly affects their reactivity and products formed with singlet oxygen.

Disulfide bonds are critical structural elements in proteins and stabilize folded structures. Modification of these linkages is associated with a loss of structure and function. Previous studies have reported large variations in the rate of disulfide oxidation by hypohalous acids, due to stabilization of reaction intermediates.

Tetramethylalloxazines as efficient singlet oxygen photosensitizers and potential redox-sensitive agents.

Tetramethylalloxazines (TMeAll) have been found to have a high quantum yield of singlet oxygen generation when used as photosensitizers. Their electronic structure and transition energies (S → S, S → T, T → T) were calculated using DFT and TD-DFT methods and compared to experimental absorption spectra. Generally, TMeAll display an energy diagram similar to other derivatives belonging to the alloxazine class of compounds, namely π,π* transitions are accompanied by closely located n,π* transitions.

Novel Short PEG Chain-Substituted Porphyrins: Synthesis, Photochemistry, and In Vitro Photodynamic Activity against Cancer Cells.

This work presents the synthesis and characterization of metal-free, zinc (II), and cobalt (II) porphyrins substituted with short PEG chains. The synthesized compounds were characterized by UV-Vis, H and C NMR spectroscopy, and MALDI-TOF mass spectrometry. The origin of the absorption bands for tested compounds in the UV-Vis range was determined using a computational model based on the electron density functional theory (DFT) and its time-dependent variant (TD-DFT).

Sensitized photoreduction of selected benzophenones. Mass spectrometry studies of radical cross-coupling reactions.

The hydrogen atom transfer reaction (HAT) between selected benzophenones (benzophenone BP, 3-carboxybenzophenone 3CB, and 4-carboxybenzophenone 4CB) and 2-propanol was reinvestigated focusing on stable product analysis. As expected, the primary species of these HAT's are the respective diphenyl and dimethyl ketyl radicals that eventually undergo several radical coupling reactions leading to stable photoproducts. However, the mechanisms of these free radical reactions remain unclear and open to question.

Understanding structure-properties relationships of porphyrin linked to graphene oxide through π-π-stacking or covalent amide bonds.

Two graphene oxide nanoassemblies using 5-(4-(aminophenyl)-10,15,20-triphenylporphyrin (TPPNH) were fabricated by two synthetic methods: covalent (GO-CONHTPP) and noncovalent bonding. GO-CONHTPP was achieved through amide formation at the periphery of GO sheets and the hybrid material was fully characterized by FTIR, XPS, Raman spectroscopy, and SEM. Spectroscopic measurements together with theoretical calculations demonstrated that assembling TPPNH on the GO surface in DMF-HO (1:2, v/v) via non-covalent interactions causes changes in the absorption spectra of porphyrin, as well as efficient quenching of its emission.

Reductive Modification of Carbon Nitride Structure by Metals-The Influence on Structure and Photocatalytic Hydrogen Evolution.

Pt, Ru, and Ir were introduced onto the surface of graphitic carbon nitride (g-CN) using the wet impregnation method. A reduction of these photocatalysts with hydrogen causes several changes, such as a significant increase in the specific surface area, a C/N atomic ratio, a number of defects in the crystalline structure of g-CN, and the contribution of nitrogen bound to the amino and imino groups. According to the X-ray photoelectron spectroscopy results, a transition layer is formed at the g-CN/metal nanoparticle interphase, which contains metal at a positive degree of oxidation bonded to nitrogen.

In-Depth Studies of Ground- and Excited-State Properties of Re(I) Carbonyl Complexes Bearing 2,2':6',2″-Terpyridine and 2,6-Bis(pyrazin-2-yl)pyridine Coupled with π-Conjugated Aryl Chromophores.

In the current work, comprehensive photophysical and electrochemical studies were performed for eight rhenium(I) complexes incorporating 2,2':6',2″-terpyridine (terpy) and 2,6-bis(pyrazin-2-yl)pyridine (dppy) with appended 1-naphthyl-, 2-naphthyl-, 9-phenanthrenyl, and 1-pyrenyl groups. Naphthyl and phenanthrenyl substituents marginally affected the energy of the MLCT absorption and emission bands, signaling a weak electronic coupling of the appended aryl group with the Re(I) center. The triplet MLCT state in these complexes is so low lying relative to the triplet IL that the thermal population of the triplet excited state delocalized on the organic chromophore is ineffective.

Radiation- and Photo-Induced Oxidation Pathways of Methionine in Model Peptide Backbone under Anoxic Conditions.

Within the reactive oxygen species (ROS) generated by cellular metabolisms, hydroxyl radicals (HO) play an important role, being the most aggressive towards biomolecules. The reactions of HO with methionine residues (Met) in peptides and proteins have been intensively studied, but some fundamental aspects remain unsolved. In the present study we examined the biomimetic model made of Ac-Met-OMe, as the simplest model peptide backbone, and of HO generated by ionizing radiation in aqueous solutions under anoxic conditions.

Carbazole effect on ground- and excited-state properties of rhenium(i) carbonyl complexes with extended terpy-like ligands.

The ground- and excited-state properties of three novel complexes [ReCl(CO)(L-κN)] bearing 2,2':6',2''-terpyridine, 2,6-di(thiazol-2-yl)pyridine and 2,6-di(pyrazin-2-yl)pyridine functionalized with 9-carbazole attached to the central pyridine ring of the triimine core via phenylene linkage were investigated by spectroscopic and electrochemical methods and were simulated using density functional theory (DFT) and time-dependent DFT. To get a deeper and broader understanding of structure-property relationships, the designed Re(i) carbonyl complexes were compared with previously reported analogous systems - without any groups attached to the phenyl ring and bearing pyrrolidine instead of 9-carbazole. The results indicated that attachment of the N-carbazolyl substituent to the triimine core has less influence on the nature of the triplet excited state of [ReCl(CO)(L-κN)] than the pyrrolidine group.

Photoinduced Skeletal Rearrangement of -Substituted Colchicine Derivatives.

Colchicine is an active pharmaceutical ingredient widely used for treating gout, pericarditis, and familial Mediterranean fever with high antimitotic activity. The photoisomerization of colchicine deactivates its anti-inflammatory and antimitotic properties. However, despite numerous reports on colchicine derivatives, their photostability has not been investigated in detail.

Towards better understanding of the photophysics of platinum(II) coordination compounds with anthracene- and pyrene-substituted 2,6-bis(thiazol-2-yl)pyridines.

The photophysical properties of platinum(ii) compounds with 4-(9-anthryl)-2,6-bis(thiazol-2-yl)pyridine (1) and 4-(1-pyrenyl)-2,6-bis(thiazol-2-yl)pyridine (2) were widely investigated. In DMSO and MeCN, the triplet emission of (1) and (2) most probably experiences the solvent-induced exciplex quenching and both complexes exhibit ligand-based fluorescence with maxima in the range of 468-570 nm. In non-coordinating dichloromethane, the emission of (1) and (2) shifts to longer wavelengths, and the lifetimes in microseconds are indicative of phosphorescence.

Early Events of Photosensitized Oxidation of Sulfur-Containing Amino Acids Studied by Laser Flash Photolysis and Mass Spectrometry.

The mechanism of photooxidation of methionine (N-Ac-Met-NH-CH, ) and methyl-cysteine (N-Ac-MeCys-NH-CH, ) analogues by 3-carboxybenzophenone triplet (3CB*) in neutral aqueous solution was studied using techniques of nanosecond laser flash photolysis and steady-state photolysis. The short-lived transients derived from 3CB and sulfur-containing amino acids were identified, and their quantum yields and kinetics of formation and decay were determined. The stable photoproducts were analyzed using liquid chromatography coupled with high-resolution mass spectrometry.

Hydrogen Bond-Mediated Conjugates Involving Lanthanide Diphthalocyanines and Trifluoroacetic Acid (Lnpc@TFA): Structure, Photoactivity, and Stability.

The interaction between lanthanide diphthalocyanine complexes, LnPc (Ln = Nd, Sm, Eu, Gd, Yb, Lu; Pc = CHN, phthalocyanine ligand) and trifluoroacetic acid (TFA) was investigated in benzene, and the stability of the resulting molecular system was assessed based on spectral (UV-Vis) and kinetic measurements. Structural Density Functional Theory (DFT) calculations provided interesting data regarding the nature of the bonding and allowed estimating the interaction energy between the LnPc and TFA species. Conjugates are created between the LnPc and TFA molecules via hydrogen bonds of moderate strength (>N∙∙H··) at the - -bridges of the Pc moieties, which renders the sandwich system to flatten.

Unexpected light emission from tyrosyl radicals as a probe for tyrosine oxidation.

Tyrosine residues (Tyr) on proteins are a favoured site of one-electron oxidation due to their low one-electron reduction potentials. In this work, light-induced oxidation of Tyr residues was investigated using direct ionisation (via 266 nm light excitation) and sensitized photo-oxidation (by 3-carboxybenzophenone as sensitizer and 355 nm). Light emission (fluorescence) was observed at 410-440 nm as a result of Tyr oxidation.

Unexpected Reaction Pathway of the Alpha-Aminoalkyl Radical Derived from One-Electron Oxidation of -Alkylglutathiones.

Laser flash photolysis and high-resolution mass spectrometry were used to investigate the mechanism of one-electron oxidation of two -alkylglutathiones using 3-carboxybenzophenone (3CB) as a photosensitizer. This report indicates an unexpected reaction pathway of the α-aminoalkyl radical cation (αN) derived from the oxidation of -alkylglutathiones. Instead of a common hydrolysis reaction of αN reported earlier for methionine and other sulfur-containing aminoacids and peptides, an intramolecular ring-closure reaction was found for -alkylglutathiones.

Near-Infrared Photoactive Aza-BODIPY: Thermally Robust and Photostable Photosensitizer and Efficient Electron Donor.

We report herein the synthesis of aza-BODIPY substituted with strongly electron-donating p-(diphenylamino)phenyl substituents (p-Ph N-) at 3,5-positions. The presence of p-Ph N- groups lowers the energy of the singlet excited state (E ) to 1.48 eV and induces NIR absorption with λ at 789 nm in THF.

Fluorescent 2-(Pyridin-2-yl)vinyl Pyridine Dyes and Their Thermocontrolled Release.

The generation of unique thermosensitive fluorescent dyes via heteroaromatic Heck cross-coupling and -pyridin-2-yl nucleophilic substitution was described. To demonstrate thermosensitive properties, the precursor was converted into carbonates or phosphates and heated at various temperatures and for various time periods. Significant changes in the fluorescence intensity and emission wavelengths, between carbonates and the cyclic product, were observed, and it was proved that the dyes may serve as removable fluorescent labels with large Stokes shifts (>80 nm).

Synthesis, Photophysics and Redox Properties of Aza-BODIPY Dyes with Electron-Donating Groups.

A series of novel aza-BODIPY dyes substituted with p-(dimethylamino)phenyl groups were synthesized and their spectral and electrochemical properties were compared. In particular, the impact of p-(Me N)Ph- groups on these characteristics was of consideration. For two aza-BODIPYs studied, a near-IR absorption band was observed at circa λ =796 nm.

Facile Synthesis, Triplet-State Properties, and Electrochemistry of Hexaiodo-Subphthalocyanine.

In view of the ever-growing demand for efficient triplet photosensitizers and photoactive components of various optoelectronic devices, we herein report the synthesis and properties of hexaiodo-subphthalocyanines (I SubPcs). The improved five-step route to 4,5-diiodophthalonitrile, which serves as precursor for the synthesis of the I SubPcs, is reported. The improved synthesis merely required one chromatographic separation to afford the high-purity target product.

Identification of a biliverdin geometric isomer by means of HPLC/ESI-MS and NMR spectroscopy. Differentiation of the isomers by using fragmentation "in-source".

Abstract: A commercially available biliverdin sample was analyzed by means of HPLC/ESI-MS and NMR spectroscopy. It was been found that beside the main IXα 5,10,15 isomer, the sample contains also the geometric isomer IXα 5,10,15 It was also found the isomers behave differentially upon "in-source" fragmentation in negative ion mode (in contrast to the their behavior upon "in-source" fragmentation in positive ion mode and to their behavior upon MS/MS fragmentation in both modes): the relative abundances of deprotonated molecules and fragment ions are significantly different for both isomers, which can be used as an analytical tool to differentiate between the isomers.

Visible-Light Photoactive, Highly Efficient Triplet Sensitizers Based on Iodinated Aza-BODIPYs: Synthesis, Photophysics and Redox Properties.

A series of novel iodinated NO -substituted aza-BODIPYs have been synthesized and characterized. Highly desirable photophysical and photochemical properties were induced in NO -substituted aza-BODIPYs by iodination of the pyrrole rings. In particular, high values of singlet oxygen quantum yields (Φ ) ranging from 0.

Experimental and theoretical studies on fluvastatin primary photoproduct formation.

Fluvastatin (FLV) belongs to the group of compounds referred to as statins, also known as 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors. Statins act as cholesterol-lowering agents and are among the most frequently prescribed drugs. They upregulate low-density lipoprotein receptors in the liver by binding to the active site of HMG-CoA reductase, which is the key enzyme in cholesterol biosynthesis.

Structural Aspects of the Antiparallel and Parallel Duplexes Formed by DNA, 2'-O-Methyl RNA and RNA Oligonucleotides.

This study investigated the influence of the nature of oligonucleotides on the abilities to form antiparallel and parallel duplexes. Base pairing of homopurine DNA, 2'-O-MeRNA and RNA oligonucleotides with respective homopyrimidine DNA, 2'-O-MeRNA and RNA as well as chimeric oligonucleotides containing LNA resulted in the formation of 18 various duplexes. UV melting, circular dichroism and fluorescence studies revealed the influence of nucleotide composition on duplex structure and thermal stability depending on the buffer pH value.