Andrzej Karocki

Synthesis, photophysical studies and anticancer activity of a new halogenated water-soluble porphyrin

A water‐soluble halogenated porphyrin, namely 5,10,15,20‐tetrakis(2‐chloro‐3‐sulfophenyl)porphyrin (TCPPSO3H), was prepared and evaluated as sensitizer for photodynamic therapy (PDT). Photophysical properties of TCPPSO3H, such as high photostability, long triplet lifetime and high singlet oxygen quantum yield suggest high effectiveness of this class of halogenated porphyrins in PDT. TCPPSO3H is non‐toxic in the dark and causes a significant photodynamic effect examined against MCF7 (human breast carcinoma), SKMEL 188 (human melanoma) and S91(mouse melanoma) cell lines upon red light irradiation (cutoff < 600 nm) at low light doses. Time‐dependent cellular uptake of TCPPSO3H reached plateau at 120 min and was the highest for S91, 20% lower for MCF7 and 70% lower for SKMEL 188. Our results show that this halogenated water‐soluble porphyrin is an efficient photosensitizer and reveal the potential of this class of compounds as PDT agents.

Mechanism of photochemical reduction of chromium(VI) by alcohols and its environmental aspects

Abstract The idea of photochemical abatement of the Cr(VI) pollution has been verified by investigating the photoreduction mediated by aliphatic alcohols under conditions mimicking the environmental ones. Effects of the alcohol nature, pH and presence of oxygen are analysed. The time-resolved spectra are used to follow the generation of the transient chromium Cr(V), Cr(IV) and Cr(II) species and the R 1 R 2 CHOH + radicals. A direct interaction between chromate(VI) and an electron donor is a precondition of the photoreduction via the photoinduced electron transfer (PET). Two pathways of the PET are identified: one-electron transfer for intermolecular and two-electron transfer for the intramolecular systems. In the case of the alcohol mediators the option is pH-controlled.

Photochemistry of the [Fe(CN)5N(O)SR]3- complex : A mechanistic study

Photochemical behaviour of the title complex (RS − = mercaptosuccinate) was defined as photodissociation and photooxidation–

Photochemistry of [(η5-C5H5)Ru(CO)2]2 in polar and non-polar solvents

Abstract The photochemistry of bridged and non-bridged isomers of the title complex was studied in various solvents by flash photolysis and continuous irradiation at different wavelength regions. Reactive decay of the excited non-bridged isomer produced either a polymer (in neat non-polar solvents) or monomeric [CpRu(CO)2Cl] complex (in non-polar solvents containing CCl4) via homolytic cleavage of the RuRu bond. Polymerization was preceded by generation of a transient species (IP1) with λ max ≈470 nm and τ 1 2 ≈4 ms , which was tentatively formulated as a trimer [CpRu(CO)2]3. Photolysis of the bridged isomer generated another transient species, IP2, characterized by the solvent-dependent absorption at 315–330 nm, assigned to the mono-bridged dimer with coordinated solvent L, [Cp(CO)2Ru(μ-CO)Ru(CO)LCp]. The IP2 properties and reactivity led to conclusion that photocleavage of the CO-bridge is the mode for the bridged isomer.

Investigations of the heavy atom effect occurring in bianthryl and 10,10′-dibromobianthryl. Fluorescence, cyclovoltamperometric and actinometric studies

A preliminary study of photophysical and photochemical properties of 9,9′-bianthryl (BA) and 10,10′-dibromo,9,9′-bianthryl (DBrBA) is presented. Dual fluorescence occurring in bianthryl (BA) has been investigated in solvents containing heavy atoms, such as chlorine, bromine and iodine. The presence of heavy atoms reduces strongly the fluorescence lifetimes and the fluorescence quantum yields of BA, the effect is strongest in ethyl iodide, i.e. in the solvent containing the heaviest atom, iodine. On the other hand, it has been found that introduction of two heavy atoms (bromine) into the bianthryl molecule modifies noticeably its fluorescence properties, which indicates existance of an internal heavy atom effect. Again, a reduction of the fluorescence lifetime and the fluorescence quantum yield, compared to the parent molecule, has been observed. On the basis of these observations the mechanism of 1CT ⇒ 3LE intersystem crossing has been discussed. In BA the rate determining process is a reversible spin inversion within the radical pair. In DBrBA where the spin flip is accelerated by the presence of heavy atoms (bromines) the spin-allowed electron transfer 3CT ⇒ 3LE becomes important in the overall intersystem crossing process. It has been found that DBrBA undergoes a photoreduction in the presence of aromatic donors, such as amines, leading finally to BA. Similar reaction seems to be observed in electrochemical measurement. The reduction of DBrBA originates from the primary electron transfer process either photoinduced or electrochemical leading to the free anion radicals of DBrBA.

Thermodynamics and kinetics of RuIII(edta) as an efficient scavenger for nitric oxide in aqueous solution

The edta complex of RuIII reacts very rapidly with NO in aqueous solution at pH = 5 to form a stable nitrosyl complex. The results from FT-IR (ATR) and 15N-NMR studies clearly support the NO+ character of coordinated NO, such that the nitrosyl product can be formulated as [RuII(edta)NO]+. A combination of UV-Vis spectroscopy and electrochemical detection of NO was used to determine the overall equilibrium constant KNO as (9.1 ± 1.2) × 107 M−1 at 25 °C and pH = 5.0. Stopped-flow kinetic studies on the reaction of acetate-buffered solutions of [RuIII(edta)H2O]− with NO gave kon values two orders of magnitude lower than that reported in the literature as a result of buffer effects. The values of kon determined at low and high pH, viz. 3.8 × 104 and 1.2 × 105 M−1 s−1, respectively, are significantly smaller than that found at pH = 5.0, and in agreement with that observed for the substitution reactions of RuIII(edta) with other entering nucleophiles. Attempts to determine kon for the binding of NO to [RuIII(edta)H2O]− using laser flash photolysis failed due to the occurrence of side reactions. Under specific conditions (NO in excess and NO2− as impurity), the formation of the disubstituted [RuII(edta)(NO+)(NO2−)]2− species was detected using 15N-NMR spectroscopy. Laser flash photolysis of this complex leads to multiple chemical reaction steps as a result of the formation of two primary photoproducts, which decay with different rate constants to the starting complex. Possible mechanisms for these photoinduced reactions are proposed and compared to related systems reported in the literature.