Search

Tungsten trioxide has been found to be a convenient precursor for the synthesis of metal cluster compounds with new types of cluster cores. The reaction between WO3 and KCN led to the formation of the cluster complex [{W6(μ4-O)2(μ3-CCN)4}(CN)16]10−. Unexpectedly, it includes the fully deprotonated form of acetonitrile, the CCN3− anion, as a μ3-bridging ligand coordinated to the trigonal faces of the bitetrahedral W6 metallocluster. A similar complex [{W6(μ4-O)2(μ3-As)4}(CN)16]10− containing μ3-As3− ligands instead of μ3-CCN3− ones has been synthesized by the reaction between WO3, As and KCN.

Cerium ammonium nitrate (NH4)2CeIV(NO3)6 (CAN) is widely used as a photolytic source of NO3 radicals in acetonitrile. In spite of that, the mechanistic aspects of CAN photochemistry were poorly discussed in the literature. In this work CAN photochemistry in CH3CN was studied using the combination of stationary methods and laser flash photolysis. In accordance with the literature, the inner-sphere electron transfer was found to be the primary photochemical process. The (NH4)2CeIII(NO3)5(CH3CN) complex was found to be the only reaction product formed with the rather high quantum yield (0.6 and 0.4 upon 308 and 355 nm excitation correspondingly). The NO3 radicals decay is mainly caused by the second-order reactions; their rate constants are determined. In addition to the direct release of the NO3 radicals, a part of the light-excited CAN molecules were found to form the radical complex [(NH4)2CeIII(NO3)5…NO3 ], which lifetime is ca. 2 μs.

This article reports the synthesis, crystal structure of new molybdenum hexaazide cluster complex ( n Bu 4 N) 2 [{Mo 6 I 8 }(N 3 ) 6 ] ( 3 ) and comparison of its photophysical and electrochemical properties to those of earlier reported analogues ( n Bu 4 N) 2 [{Mo 6 X 8 }(N 3 ) 6 ] (X = Cl, Br). Additionally, the dimerisation of 3 as a result of hydrolysis was revealed by mass spectrometry and single crystal X-Ray diffraction. Indeed, the structurally characterised compound ( n Bu 4 N) 4 [({Mo 6 I 8 }(N 3 ) 5 ) 2 O] represents the first example of oxo-bridged dimer of octahedral molybdenum clusters complexes.

In this work we have demonstrated that the ruthenium nitrosyl complex [RuNO(β-Pic)2(NO2)2OH] is suitable for investigation of the inactivation of DNA repair enzymes in vitro. Photoinduced inhibition of DNA glycosylases such as E. coli Endo III, plant NtROS1, mammalian mNEIL1 and hNEIL2 occurs to an extent of ≥90% after irradiation with the ruthenium complex. The photophysical and photochemical processes of [RuNO(β-Pic)2(NO2)2OH] were investigated using stationary and time-resolved spectroscopy, and mass spectrometry. A possible mechanism of the photo-processes was proposed from the combined spectroscopic study and DTF calculations, which reveal that the photolysis is multistage. The primary and secondary photolysis stages are the photo-induced cleavage of the Ru-NO bond with the formation of a free nitric oxide and RuIII complex followed by ligand exchange with solvent. For E. coli Endo III, covalent interaction with the photolysis product was confirmed by UV-vis and mass spectrometric methods.

Influence of the metal core composition and geometry on the structure, spectroscopic properties and redox potentials was investigated for the first time for heterometallic (Re/Mo)

Tungsten trioxide has been found to be a convenient precursor for the synthesis of metal cluster compounds with new types of cluster cores. The reaction between WO3 and KCN led to the formation of the cluster complex [{W6(μ4-O)2(μ3-CCN)4}(CN)16]10-. Unexpectedly, it includes the fully deprotonated form of acetonitrile, the CCN3- anion, as a μ3-bridging ligand coordinated to the trigonal faces of the bitetrahedral W6 metallocluster. A similar complex [{W6(μ4-O)2(μ3-As)4}(CN)16]10- containing μ3-As3- ligands instead of μ3-CCN3- ones has been synthesized by the reaction between WO3, As and KCN.

The synthesis of the natural molecular UV filters − kynurenines (KN) − covalently bound to nitroxides has recently been proposed as an alternative for traditional combination of antioxidants and UV-filters in sunscreen formulations. Due to the spin-exchange interaction between KN and nitroxide moieties, the triplet lifetimes in such conjugates are much shorter than in KN molecule, but the triplet quantum yields are significantly higher. The reaction of intramolecular electron transfer between photoexcited KN and nitroxide moieties is the main factor determining the quantum yield of KN-RNO conjugates photodecomposition. Searching for a method to suppress this side process we synthesized analogues of previously prepared conjugates with the enlarged spacer between the nitroxide and kynurenine parts and with the sterically hindered access to the nitroxide group. The new spin-labeled kynurenines showed at least three-fold higher photostability compared to the previously synthesized compounds of this type.

Spatial distribution of 34 metabolites along the optical and equatorial axes of the human lens has been determined. For the majority of metabolites, the homogeneous distribution has been observed. That suggests that the rate of the metabolite transformation in the lens is low due to the general metabolic passivity of the lens fiber cells. However, the redox processes are active in the lens; as a result, some metabolites, including antioxidants, demonstrate the "nucleus-depleted" type of distribution, whereas secondary UV filters show the "nucleus-enriched" type. The metabolite concentrations at the lens poles and equator are similar for all metabolites under study. The concentric pattern of the "nucleus-depleted" and "nucleus-enriched" distributions testifies that the metabolite distribution inside the lens is mostly governed by a passive diffusion, relatively free along the fiber cells and retarded in the radial direction across the cells. No significant difference in the metabolite distribution between the normal and cataractous human lenses was found.

The reactions of photoexcited kynurenic acid (KNA) with bovine α-crystallins under anaerobic conditions proceed via the electron transfer from tryptophan (Trp) and tyrosine (Tyr) residues to the triplet KNA molecules. The subsequent radical reactions lead to the protein aggregation and insolubilization. The absorption of the photolyzed proteins at 335 nm as well as their total fluorescence significantly increases, while the tryptophan-related fluorescence decreases. It has been established that the alterations of the protein optical properties are related to the modifications of Trp residues. Intrinsic lens antioxidants ascorbate (Asc) and glutathione (GSH) that are present in the human lens at the millimolar level effectively block the formation of the observed light-induced protein modifications. The protective effect of Asc was attributed to its ability to quench highly reactive triplet states, while the role of GSH, most likely, corresponds to the reduction of photochemically formed radicals into a diamagnetic state. The results obtained disclose the possible mechanism of UVA-induced modifications of the lens crystallins, leading to the formation of cataract, and the role of major lens antioxidants Asc and GSH in the protection of the lens proteins.

Photodegradation of thin films of organic semiconducting electron-donor materials P3HT, PCDTBT, DRCN5T and BTR upon illumination with visible light in air was studied. The changes of UV–vis absorption, photoluminescence and EPR spectra were monitored as functions of illumination time. Stable radicals were generated at concentrations that exceed the values of charge carrier density of organic solar cells in the operating conditions. Increase of the radical concentration was observed for P3HT, PCDTBT, DRCN5T. On the contrary, for BTR the radical concentration drops to zero after initial increase. This indicates different photodegradation processes in studied materials.

Octahedral rhenium cluster complexes with organic apical ligands have a high potential to be used in different fields due to their intrinsic luminescence and X-ray contrast properties. A series of new compounds based on cations [{Re6Q8}(3-Me-pzH)6]2+, where Q is S or Se and 3-Me-pzH is 3-methylpyrazole, were obtained and characterized in the solid state (FTIR, elemental and single crystal diffraction analysis) and in solution (1H NMR and ESI-MS). The compounds possess luminescence properties that mainly depend on inner Q ligands indicating the {Re6Q8}2+ core-centered nature of emission.

Reaction of (NH4)[NbO(C2O4)2(H2O)2]·3H2O with K12[H2P2W12O48]∙24H2O in aqueous solution at pH 1.7 leads to the formation of mixed Nb/W species based on [(P2M18O60)2(µ-O)2]n− (M is a Nb/W mixture, when Nb ratio ranges from 6 to 8 and charge differs from 14- to 16- correspondingly) archetype. Direct crystallization from the reaction media results in colorless crystals with the composition formulated as K9(NH4)5[cis-(P2W15Nb3O61)2]·48H2O (1). Crystallization in the presence of (NMe2H2)Cl yields two phases (2a and 2b), containing the same [trans-(P2W14.7Nb3.3O61)2]14.6− anions but different cation/H2O compositions. Both phases are present in a mixture with bulk composition corresponding to (NMe2H2)14.6[P2W14.7Nb3.3O61]2·28H2O (2). The solution behavior of 1 and 2 was studied with HR-ESI-MS and HPLC-ICP-AES. During XRPD study of 2 we found blue coloration of the thin film of the complex. This effect has only surface nature and was studied by diffuse reflectance spectra.

Metabolites are essential for the proper functioning of the eye lens, they either enter the lens from the aqueous humor (AH), or are synthesized in the lens epithelium. Antioxidants, osmolytes and UV filters are especially important for the lens protection, and their lack may cause the development of ophthalmic diseases. Comparison of the metabolomic compositions of lenses and AH taken from cataract patients with that taken from human cadavers without cataract can shed light onto molecular mechanisms underlying onset of age-related nuclear cataract. Combined use of 1H nuclear magnetic resonance and high performance liquid chromatography with optical and high-resolution mass spectrometric detection for the identification and quantification of metabolites in the lens and AH extracts. The concentrations of 86 metabolites were determined for four groups of samples, including lenses and AH from cataract patients and from human cadavers. In cataractous lens the most abundant metabolites are (in descending order): myo-inositol, lactate, acetate, glutamate, glutathione; in AH—lactate, glucose, glutamine, alanine, valine. The concentrations of the majority of metabolites in normal post-mortem samples of both lens and AH are higher than that in samples from the cataract patients. Comparison of metabolite concentrations in lens and corresponding AH reveal that the most important for the lens protection metabolites are synthesized in the lens epithelial cells. The reduced levels of antioxidants, UV filters, and osmolytes were found in the cataractous lenses what cannot be explained by post-mortem changes in normal lens; that indicates that the age-related nuclear cataract development may originate from the dysfunction of the lens epithelial cells.

This work represents the first comprehensive report on quantitative metabolomic composition of tissues of pike-perch (Sander lucioperca) and Siberian roach (Rutilus rutilus lacustris). The total of 68 most abundant metabolites are identified and quantified in the fish lenses and gills by the combination of LC-MS and NMR. It is shown that the concentrations of some compounds in the lens are much higher than that in the gills, that indicates the importance of these metabolites for the adaptation to the specific living conditions and maintaining the homeostasis of the fish lens. The lens metabolome undergoes significant seasonal changes due to the variations of dissolved oxygen level and fish feeding activity. The most season-affected metabolites are osmolytes and antioxidants, and the most affected metabolic pathway is the histidine pathway. In late autumn, the major lens osmolytes are N-acetyl-histidine and threonine phosphoethanolamine (Thr-PETA), while in winter the highest concentrations were observed for serine phosphoethanolamine (Ser-PETA) and myo-inositol. The presence of Thr-PETA and Ser-PETA in fish tissues and their role in cell osmotic protection are reported for the first time. The obtained concentrations can be used as baseline levels for studying the influence of environmental factors on fish health.

Cluster compounds based on a new {Re

Cornea is the outermost part of the eye supplied mostly by aqueous humor (AH). Therefore, the comparison of the metabolomic compositions of AH and cornea may help to determine which compounds are produced inside the cornea, and which penetrate into cornea from AH for intra-corneal consumption. Keratoconus (KC) is the most common form of the cornea dystrophy, and the analysis of KC corneas can unravel the metabolomic changes occurring in AH and cornea of KC patients. The work is aimed at the determination of concentrations of a wide range of metabolites in the human cornea and AH, the comparison of the metabolomic profiles of cornea and AH, and the comparison of the metabolomic compositions of samples taken from KC patients and normal donors (post-mortem). The quantitative metabolomic profiling was carried out with the use of two independent methods—high-frequency 1H NMR spectroscopy and HPLC with high-resolution ESI-MS detection. The concentrations of 71 most abundant metabolites in cornea and AH from keratoconus patients and from human cadavers have been measured. It is found that the concentrations of purines and organic acids in cornea are significantly higher than in AH. The KC corneas are characterized by the enhanced levels of acetate and citrate, and also by low values of GSH/GSSG ratios. A significant difference in the metabolomic compositions of the human AH and cornea has been revealed. The concentrations of glucose and some amino acids in cornea are significantly lower than in AH, indicating their fast consumption inside the cornea. The high levels of organic acids, purines and GSH in cornea should be attributed to their production in the cornea. The enhanced levels of acetate and citrate as well as the low values of GSH/GSSG ratios in KC corneas are the indicators of the oxidative stress.

The ability of SkQ1 eye drops to slow down the cataract development is demonstrated on the senescence-accelerated OXYS rats: the SkQ1 treatment leads to the considerable improvement of the lens condition as compared to the control group. The comparison of the chaperone activities of α-crystallins isolated from the rat lenses did not reveal significant difference between SkQ1-treated and control rats. The contents of major metabolites (23 compounds) in lenses of SkQ1-treated and untreated rats are also very similar, though the concentration of reduced glutathione (GSH) in lenses of SkQ1-treated rats is 12% lower. This difference may be attributed to the reduction of the oxidative stress under action of SkQ1 eye drops, and to the decreased requirement to produce high amounts of this antioxidant.

Quantitative metabolomic profiles of normal and cataractous human lenses were obtained with the combined use of high-frequency nuclear magnetic resonance (NMR) and high-performance liquid chromatography with high-resolution mass-spectrometric detection (LC-MS) methods. The concentration of more than fifty metabolites in the lens cortex and nucleus has been determined. For the majority of metabolites, their concentrations in the lens cortex and nucleus are similar, which confirms low metabolic activity in the lens core. The difference between the metabolite levels in the cortex and nucleus of the normal lens is observed for antioxidants and UV filters, which demonstrates the activity of redox processes in the lens. A huge difference is found between the metabolomic compositions of normal and age-matched cataractous lenses: the concentrations of almost all metabolites in the normal lens are higher than in the cataractous one. The most pronounced difference is observed for compounds playing a key role in the lens cell protection and metabolic activity, including antioxidants, UV filters, and osmolytes. The results obtained imply that the development of the age-related cataracts might originate from the metabolic dysfunction of the lens epithelial cells.

The first example of dodecanuclear chalcohalide rhenium cluster complex, (Et4N)4(Me2NH2)2[Re12CS17Br6] (1), has been synthesized by reaction of polymeric cluster solid Re12CS17 with excess of Et4NBr in boiling DMF. The compound was characterized by a set of methods, including IR and UV–Vis spectroscopy, elemental analysis, EDS, mass-spectrometry, single-crystal X-ray diffraction analysis, and quantum-chemical calculations. The crystal structure presents an interesting case of 1D supramolecular architecture based on notably short Br⋯Br interactions of 3.432 A between the terminal bromide trans-ligands of adjacent [Re12CS17Br6]6− cluster anions. The DFT calculations performed for the [Re12CS17Br6]6− anion showed good agreement between calculated and experimental data.

Nanosecond laser flash photolysis and time-resolved fluorescence were used to study photochemistry of 4,4-Bis(4-hydroxyphenyl)valeric acid (diphenolic acid, DPA) and complex of DPA with β-cyclodextrin (DPA-βCD) in aqueous solutions. For both systems the primary photochemical process was found to be photoionization with the formation of a hydrated electron–phenoxyl radical pair. Inclusion of DPA in cyclodextrin cavity leads to the great increase of photoionization and fluorescence quantum yield (from 0.01 to 0.14) as well as fluorescence lifetime (from 0.17 to 2.9 ns) due to decreasing of the quenching rate of the singlet excited state of complexed DPA by solvent molecules.

The influence of irradiation wavelength and intensity on photochemistry of acetaminophen (APAP) in aqueous solution was investigated by combination of steady-state and laser flash photolysis as well as HPLC and LC–MS. Steady-state irradiation at 254 nm leads to APAP disappearance with the quantum yield 0.0014 and to formation of 1-(2-amino-5-hydroxyphenyl)ethanone ( P1 ) as a main primary photo-Fries product. In opposite the laser excitation at 266 nm leads predominantly to two-photon ionization of APAP with the quantum yield 0.013 ( I = 70 mJ/cm 2 ) and to the formation of one main product of phenoxyl radical reactions – N-(3,4-dihydroxyphenyl)acetamide ( P5 ). Steady-state excitation at 282 nm leads to both P1 and P5 products formation indicating competition of photo-Fries and photoionization processes. The wavelength-dependent mechanism of APAP photolysis is proposed and discussed.

The optical elements of the eye—cornea, lens, and vitreous humor—are avascular tissues, and their nutrition and waste removal are provided by aqueous humor (AH). The AH production occurs through the active secretion and the passive diffusion/ultrafiltration of blood plasma. The comparison of the metabolomic profiles of AH and plasma is important for understanding of the mechanisms of biochemical processes and metabolite transport taking place in vivo in ocular tissues. The work is aimed at the determination of concentrations of a wide range of most abundant metabolites in the human AH, the comparison of the metabolomic profiles of AH and serum, and the analysis of the post-mortem metabolomic changes in these two biological fluids. The quantitative metabolomic profiling was carried out with the use of two independent methods—high-frequency 1H NMR spectroscopy and HPLC with high-resolution ESI-MS detection. The concentrations of 71 most abundant metabolites in blood serum and AH from living patients and human cadavers have been measured. It has been found that the level of ascorbate in AH is by two orders of magnitude higher than that in serum; the levels of other metabolites are either similar to that in serum, or differ from that by a factor of 2–5. The post-mortem metabolomic composition of both serum and AH undergoes rapid and strong changes. The differences between the metabolomic profiles of AH and serum for majority of metabolites can be attributed to the metabolic activity of the ocular tissues leading to the lack or excess of some metabolites, while the high concentration of ascorbate in AH demonstrates the activity of ascorbate-specific pumps at the blood-aqueous border. The post-mortem metabolomic changes are caused by the disruption of the major biochemical cycles and cell lysis. These changes should be taken into account in the analysis of disease-induced changes in post-mortem samples of the ocular tissues.

Correction for ‘Niobium uptake by a [P8W48O184]40−macrocyclic polyanion’ by Alexandra A. Shmakovaet al.,New J. Chem., 2019,43, 9943–9952.

The analysis of post-mortem metabolomic changes in biological fluids opens the way to develop new methods for the estimation of post-mortem interval (PMI). It may also help in the analysis of disease-induced metabolomic changes in human tissues when the postoperational samples are compared to the post-mortem samples from healthy donors. The goals of this study are to observe and classify the post-mortem changes occurring in the rabbit blood, aqueous and vitreous humors (AH and VH), to identify the potential PMI markers among a wide range of metabolites, and also to determine which biological fluid—blood, AH or VH—is more suitable for the PMI estimation. The quantitative metabolomic profiling of samples of the rabbit serum, AH and VH taken at different PMIs has been performed with the combined use of high-frequency NMR and high-resolution LC–MS methods. The quantitative levels of 61 metabolites in the rabbit serum, AH and VH at different PMIs have been measured. It has been found that the post-mortem metabolomic changes in AH and VH proceed slower than in blood, and the data scattering is lower. Among the metabolites whose concentrations increase with time, the most significant and linear growth is found for hypoxanthine, choline and glycerol. The obtained results suggest that the ocular fluids AH and VH may have some advantages over blood serum for the search of potential biochemical markers for the PMI estimation. Among the compounds studied in the present work, hypoxanthine, choline and glycerol give the biggest promise as the potential PMI biomarkers.

Due to ability of stable nitroxides to interact with free radicals, they are used as antioxidants for therapeutic and research goals in biology and medicine. A modern trend in medical chemistry is the design of multifunctional molecules such as UV absorbers covalently bound to nitroxides, which provides both UV protection and antioxidant properties combined in the same molecule. In the present work, we report the synthesis of conjugates of a natural UV filter kynurenine (KN) with nitroxides (KN-RNO(•) conjugates) and the study of their photochemical properties in aqueous and methanol solutions. Due to the spin-exchange interaction between KN and nitroxide moieties, the triplet lifetimes in conjugates are much shorter than in KN molecule, but the triplet quantum yields are significantly higher. The reaction of intramolecular electron transfer between photoexcited KN and nitroxide moieties is the main factor determining the quantum yield of KN-RNO(•) conjugates photodecomposition. Consequently, KN-RNO(•) conjugates in aqueous solution are photochemically less stable than the parent KN molecule. Nevertheless, the photostability of KN-RNO(•) conjugates is much higher than that of cinnamates which are widely used as UV absorbers in modern sunscreen formulations. Thus, the combination of the endogenous chromophore KN with nitroxides is very promising for medical applications.

The reactions of triplet kynurenine and 4-(2-aminophenyl)-4-oxocrotonic acid, formed upon the thermal decomposition of kynurenine, with nitroxyl radicals and cyclic N-hydroxylamines were studied. Nitroxyl radicals were found to quench efficiently the triplet state of kynurenine (rate constant 3–6·.108 L mol-1 s-1). The quenching proceeds via the spin-exchange mechanism and affords no new products. Neither nitroxyl radicals, nor hydroxyl-lamines react with 4-(2-aminophenyl)-4-oxocrotonic acid under conditions similar to physiological.

This work is the first comprehensive report on the quantitative metabolomic composition of the rat lens. Quantitative metabolomic profiles of lenses were acquired with the combined use of high-frequency nuclear magnetic resonance (NMR) and high-performance liquid chromatography with high-resolution mass-spectrometric detection (LC-MS) methods. More than forty low molecular weight compounds found in the lens have been reliably identified and quantified. The most abundant metabolites in the 3-month-old Wistar rat lens are taurine, hypotaurine, lactate, phosphocholine and reduced glutathione. The analysis of age-related changes in the lens metabolomic composition shows a gradual decrease of the content of most metabolites. This decrease is the most pronounced between 1 and 3 months, which probably corresponds to the completion of the lens maturation in one-month-old rats and to the high rate of the young lens growth. The enhanced levels of tryptophan, tyrosine, carnitine, glycerophosphate, GSH and GSSG were found in lenses of senescence-accelerated OXYS rats; for some metabolites, this effect may probably be attributed to the compensatory response to oxidative stress.

The photophysics and photochemistry of kynurenine (KN) covalently bound to the amino acids lysine, cysteine, and histidine, the antioxidant glutathione, and the protein lysozyme have been studied by optical spectroscopy with femto- and nanosecond time resolution. The fluorescence quantum yield of the adducts of KN to amino acids is approximately 2 times higher than that of the free KN in solution; KN attached to protein exhibits a 7-fold increase in the fluorescence quantum yield. The S(1) state dynamics of KN-modified lysozyme reveals a multiphasic decay with a broad dispersion of time constants from 1 ps to 2 ns. An increase of the triplet yield of KN bound to lysozyme is also observed; the triplet state undergoes fast intramolecular decay. The obtained results reveal an increase of the photochemical activity of KN after its covalent attachment to amino acids and proteins, which may contribute to the development of oxidative stress in the human lenses-the main causative factor for the cataract onset.

The properties of xanthurenic acid (XAN) in ground and photoexcited states have been studied using steady-state and time-resolved optical methods as well as quantum chemistry calculations. In neutral aqueous solution and in alcohols, XAN is present in a single tautomeric form (keto form), whereas in aprotic solvents and probably in basic aqueous solutions, more than one tautomeric form is present. UV irradiation of aqueous and alcoholic solutions of XAN results in a very rapid solvent-assisted tautomerization to the enol form, the later undergoes solvent-assisted transformation back to the keto form. The photolysis of XAN in aprotic solvents gives rise to the formation of numerous intermediate forms of XAN in both triplet and ground states. Under intense laser irradiation, XAN undergoes biphotonic ionization, the precursor for ionization being the excited singlet state.