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High-molecular-weight dinitrosyl iron complexes (DNICs) are formed in living systems and are a stable depot of nitrogen monoxide (NO). In this work, using experimental and theoretical methods, we investigated the interaction of their synthetic analog, a promising cardiotropic complex of the composition [Fe(SC(NH

The effects of the newly synthesized covalent conjugates of water-soluble fullerene derivatives (WSFD) with xanthene dyes: polyanionic WSFD-fluorescein (1), polycationic WSFD-fluorescein (2), polyanionic WSFD-eosin (3), and polyanionic WSFD (4), polycationic WSFD (5), fluorescein (6) and eosin (7), on activity of the membrane-bound Ca2+-ATPase of the sarcoplasmic reticulum (SR Ca2+-ATPase) were studied. Compounds 1, 3, 4, 6, and 7 inhibit the hydrolytic function of the enzyme, the inhibition constants for these compounds are Ki=1.3×10-5 M (1), Ki=4.7×10-6 M (3), Ki=2.5×10-6 M (4), Ki=6.1×10-5 M (6), and Ki=5.8×10-6 M (7). The effects of compounds 3, 6, and 7 on the hydrolytic function of the enzyme is competitive; compounds 1 and 4 are noncompetitive. Polycationic WSFD fluorescein (2) and polycationic WSFD (5) do not affect ATP hydrolysis, but inhibit active Ca2+ transport in a concentration of 0.01 mM by 100±10 and 40±4%, respectively. Conjugates 1 and 3 completely inhibit the hydrolytic and transport functions of the enzyme in a concentration of 0.01 mM, and in a concentration of 0.001 mM inhibit active Ca2+ transport by 60±6 and 55±6% uncoupling the hydrolytic and transport functions of SR Ca2+-ATPases. The obtained results demonstrate a significant effect of the studied compounds on the active transmembrane transfer of Ca2+ and make it possible to predict the presence of antimetastatic and antiaggregatory activities of the studied compounds.

Dinitrosyl iron complexes (DNICs) are a depot and potential source of free NO in organisms. Their synthetic analog, N-ethylthiourea DNIC [Fe(SC(NH

The nitrite-generating activity of 2-ethyl-3-hydroxy-6-methylpyridinium 2-nitroxysuccinate as a promising NO-donor has been investigated in reactions with various reducing agents. Reduction of the NO-donor with cysteine was analyzed using a kinetic modeling method. The calculated rate constants satisfactorily describe the experimental data, thereby confirming the proposed reaction mechanism.

In this work, transformation of DNIC with thiourea ligands, [Fe(SС(NH2)2)2(NO)2]Сl∙H2O (I), in an aqueous buffer solution at neutral pH and in the presence of reduced glutathione (GSH) has been studied. Decomposition of the complex was shown to occur in the buffer solution, with removal of the first thiourea ligand having a higher rate (k=(3.8 ± 1.3)∙10-4 s-1) than the NO group release (k=(0.7 ± 0.2)∙10-4 s-1). This corroborates a quantum-chemical model of I decomposition suggested earlier. Using UV–Vis spectrophotometry and EPR spectrometry, the interaction of I with GSH in solution was shown to yield a new binuclear tetranitrosyl iron complex (TNIC) with two GS−- ligands (II). Using quantum-chemical modeling, the reaction scheme was suggested, which involves replacement of one thiourea ligand by GS−, and then dimerization of the forming complexes accompanied by removal of the second thiourea ligand. Theoretical UV–Vis spectra were calculated and interpreted for the initial I and for the product of the substitution reaction, II.

The ability of the 2-nitroxysuccinate 3-hydroxy-6-methyl-2-ethylpyridine (I) compound to generate nitrite ions (NO2) and nitrogen monoxide (NO) in model systems with cysteine (Cys) and deoxyhemoglobin (Hb) has been studied. It has been established that there is a more efficient release NO2 and NO from compound I than from Nicorandil. The accumulation rate is 1.5 times higher in the system of Cys with I than with Nitroglycerin. It is shown that, unlike Nitroglycerin, compound I is not reduced by Hb.

Using methods of absorption and fluorescence spectroscopy, we show that noncovalent complexes based on a water-soluble fullerene derivative and chlorin e6 dissolved either in water or in ethanol are formed as a result of electrostatic interactions. The formation of these complexes causes a red shift of the absorption spectrum of chlorin e6 and efficient quenching of the intensity of its fluorescence. The Stern–Volmer quenching constants of complexes in water and ethanol are 7.3 × 105 and 2 × 105 M–1, respectively. We show that, in an aqueous solution, the complex consists, on average, of one molecule of the water-soluble fullerene derivative and three dye molecules, whereas this ratio in ethanol is 1 : 1.

The ability of 3-hydroxy-6-methyl-2-ethylpyridine 2-nitroxysuccinate (I) to generate nitrite ions ( $${\text{NO}}_{2}^{ - }$$ ) and nitrogen monoxide (NO) in model systems with cysteine (Cys) and deoxyhemoglobin (Hb) has been studied. Compound I has been found to release $${\text{NO}}_{2}^{ - }$$ and NO more efficiently than Nicorandil. The accumulation rate of $${\text{NO}}_{2}^{ - }$$ in the system of Cys with I is by a factor of 1.5 higher than that with Nitroglycerin. It has been shown that, in contrast to Nitroglycerin, compound I is not reduced by Hb.

The synthesis, photophysical and photodynamic properties of two water-soluble hybrid structures based on the polycationic or polyanionic fullerene [60] derivative covalently linked to fluorescein are described. The significant influence of electrostatic charges on the conformation of the studied fullerene–fluorescein structures in aqueous solution and on their photophysical properties and photochemical activity was demonstrated. A polycationic fullerene derivative–fluorescein conjugate exhibits a pronounced quenching of fluorescence (more than 25 times) due to the energy and/or electron transfer from dye to fullerene. Such activation of fullerene generates reactive oxygen species greater than 15 times more effectively than an individual dye or fullerene does. In contrast, for the polyanionic fullerene derivative–fluorescein conjugate such effects are practically absent. The demonstrated effects open up wide opportunities for a directional design of highly efficient water-soluble photosensitizers by combining the singlet-excited dyes and fullerene [60] for applications in photodynamic therapy.

Interaction and transformation of the mononuclear cationic dinitrosyl iron complex [Fe(SC(NH2)2)2(NO)2]+ (complex 1) upon binding with bovine serum albumin (BSA) have been explored using kinetic measurements, UV-Vis and fluorescence spectroscopy, and computational molecular modeling. BSA was found to bind up to five molecules of complex 1 per one protein molecule; as a result, the rate of NO release by complex 1 into solution decreases by a factor of 10. The binding constant of complex 1 with BSA measured by the quenching of intrinsic fluorescence of BSA is 5 × 105 М-1. Molecular docking calculations at pH = 7 have determined five-six low-energy binding sites for complex 1 at subunits I and II of BSA. The most stable protein-ligand complexes are located at the protein pockets near Cys34. The spectroscopic measurements and docking calculations have shown that the decomposition product of complex 1, the Fe(NO)2+ fragment, can form an adduct Fe(Cys34)(His39)(NO)2 (complex 2) with the coordination bonds of Fe with atoms S of Cys34 and ND of His39. The structure of complex 2 was supported by the density functional calculations of the absorption spectrum. Decomposition of complex 2 leads to nitrosylation of BSA at atom S of Cys34. Complexes 1 (bound with BSA), 2 and the nitrosylated BSA can serve as NO depot in plasma.

Free fluorescence spectra in solution and surface-enhanced Raman scattering (SERS) and surface enhanced fluorescence (SEF) spectra of chlorin e6 and water-soluble covalent fullerene–chlorin dyads have been studied. It has been demonstrated that chlorin e6 and covalent fullerene–chlorin dyads have similar characteristic SERS spectra. The fullerene–chlorin dyads show a pronounced SEF signal, while native chlorin e6 has no fluorescence on surface, which is consistent with the theory predicting an inverse dependence of the SEF intensity on the free fluorescence quantum yield. The concentration dependence of the SEF intensity is linear for the dyads in the range 0.1–2.0 μmol/L. These effects allow one to determine, with high sensitivity, the content of fullerene–chlorin dyads with a low quantum yield of free fluorescence in solutions, which opens wide opportunities for study of biological properties of fullerene–chlorin dyads and their applications in medicine.

Regularities of interaction of water-soluble pentaamino acid derivatives of fullerenes (WPDFs) with the lipid bilayer of phosphatidylcholine liposomes were studied using the fluorescent probe method. The studied WPDFs act as quenchers of fluorescence of the hydrophilic probe 2,7-dibromoproflavine in aqueous solutions and in the membranes of phsophatidylcholine liposomes, as well as of the hydrophobic probe pyrene in the phospholipid membrane. The singlet state of the probes is deactivated due to the formation of the long-lived WPDF—probe complex rather than their dynamic interaction. The WPDFs stud- ied were revealed to penetrate into the bilayer membrane of phosphatidylcholine liposomes. The localization of the pentaamino acid fullerene derivatives in the region of polar heads and fatty acid chains of the membrane phospholipids was established on the basis of estimation of the equilibrium constants in the WPDF—probe complexes.

The effect of iron nitrosyl complexes, NO donors, of a general formula [Fe2(L)2(NO)4] with functional sulfur-containing ligands (L-3-nitro-phenol-2-yl, 4-nitro-phenol-2-yl, or 1-methyl-tetrazol-5-yl) on the activity of sarcoplasmic reticulum Ca2+-ATPase and cyclic guanosine monophosphate phosphodiesterase (cGMP PDE) was studied. The test complexes uncoupled the hydrolytic and transport functions of Ca2+- ATPase, thus disturbing the balance of Ca2+ ions in cells, which may affect the formation of thrombi and adhesion of metastatic cells to the endothelium of capillaries. They also inhibited the activity of cGMP PDE, thereby contributing to the accumulation of the second messenger cGMP. The studied iron nitrosyl complexes can be considered as potential drugs.

Synthesis, spectral properties, and photodynamic activity of water-soluble amino acid fullerene C60 derivatives (AFD) and four original AFD-PPa dyads, obtained by covalent addition of dye pyropheophorbide (PPa) to AFD, were studied. In aqueous solution, these AFD-PPa dyads form nanoassociates as a result of self-assembly. In this case, a significant change in the absorption spectra and strong quenching of the dye fluorescence in the structure of the dyads were observed. A comparison of superoxide or singlet oxygen generation efficiency of the studied compounds in an aqueous solution showed the photodynamic mechanism switching from type II (singlet oxygen generation of the native dye) to I type (superoxide generation of dyads). All dyads have pronounced phototoxicity on cells Hela with IC50 9.2 µM, 9.2 µM, 12.2 µM for dyads Val-C60-PPa, Ala-C60-PPa and Pro-C60-PPa, respectively. Such facilitation of type I photodynamic mechanism could be perspective against hypoxic tumors.

In this work, transformations of two cationic dinitrosyl iron complexes (DNICs), namely, mononuclear with N-ethylthiourea ligands [Fe(SC(NH2)(NHC2H5))2(NO)2]+Cl−∙[Fe(SC(NH2)(NHC2H5))Cl(NO)2]0 (complex 1) and binuclear with penicillamine ligands [Fe2(S(C(CH3)2CH(NH3)COOH))2(NO)4]SO4·5H2O (complex 2) have been investigated in an aqueous solution in the presence of bovine serum albumin (BSA) under anaerobic and aerobic conditions. The spectroscopic measurements have shown that the complexes bind to the protein, which leads to their stabilization. The resulting products are much more stable in the absence of oxygen. The fluorescence measurements indicated that complexes 1 and 2 interact with BSA with equilibrium constants K = 4.9∙105 M−1 and 5.3∙105 M−1, respectively. Complex 1 can bind to the surface due to weak intermolecular interactions, resulting in prolonged generation of NO. Also, the decay product of complex 1, both under anaerobic conditions and in the presence of oxygen, is coordinated with Cys34 and His39 in the hydrophobic pocket of albumin, as evidenced by the appearance of a shoulder at 370–410 nm. As a result of these interactions, a high molecular weight albumin-bound complex is formed, which then slowly decomposes in more than 40 h. Complex 2 and its products are adsorbed on the surface of the protein. However, in the presence of oxygen, protein does not significantly affect the NO release rate.

Chlorin e6 derivative and water-soluble dyad resulting from covalent bonding of polyanionic fullerene С60 derivative to chlorin e6 derivative were synthesized and studied for spectral properties and photochemical activity. A considerable change in the absorption spectra and pronounced fluorescence quenching for the chlorin moiety included in the dyad were identified. The singlet excited state of chlorin is quenched via electron transfer from the excited chlorin to the fullerene core. A comparison of the photochemical activities of the test compounds in aqueous solutions showed a tenfold increase in the photochemical activity of the chlorin–fullerene dyad compared with free chlorin per absorbed light quantum.

We studied the effects of new water-soluble polysubstituted fullerene C60 (PFD) derivatives on activity of Ca2+-Mg2+ ATPase of the sarcoplasmic reticulum and cGMP phosphodiesterase. All examined fullerene derivatives inhibited activity of both enzymes. For instance, PFD-I, PFD-II, PFD-III, PFD-V, PFD-IX, PFD-X, and PFD-XI in a concentration of 5×10—5 M completely inhibited hydrolytic and transport functions of Ca2+-ATPase. These compounds in a concentration of 5×10—6 suppressed active transport of calcium ions by 51±5, 77±8, 52±5, 52±5, 100±10, 80±8, and 100±10%, respectively, and inhibited ATP hydrolysis by 31±3, 78±8, 18±2, 29±3, 78±8, 63±7, and 73±9%, respectively, uncoupling the hydrolytic and transport functions of the enzyme. PFD-I noncompetitive and reversibly reduced activity of Ca2+-ATPase (Ki=2.3×10—6 M). All the studied fullerene derivatives (except for PFD-VII) inhibited cGMP phosphodiesterase by more than 80% in concentration of 10—4 M and higher and by more than 50% in concentration of 10—5 M. PFD-I is a non-competitive reversible inhibitor of cGMP phosphodiesterase (Ki=7×10—6 M). These results allow us to expect antimetastatic, antiaggregatory, antihypertensive and vasodilative activity of the studied compounds.

By the use of absorption spectroscopy, steady-state and time resolved fluorimetry xanthene dyes fluorescein, eosin Y and erythrosin B were shown to form complexes with polycationic fullerene derivative due to electrostatic interactions in aqueous solution and in the structure of the liposomes. It was found that the singlet excited states of dyes are effectively quenched either due to excitation energy transfer or electron transfer from singlet excited state of the dye to the fullerene core. Photodynamic activity of the complex is much higher than the activity of the dye or the fullerene derivative as the individual compounds. Photostability of the dyes increases in the complex structure as well. These effects allow predicting the development of a new generation hybrid photosensitizers. Noteworthy, one can use a dye excited only in a singlet state in combination with fullerene, which greatly enhances the directional design of such hybrid structures.

Two decomposition mechanisms of nitrosyl iron complexes (NICs) [Fe2(μ-SR)(NO)4] in aqueous medium are known. One mechanism (for instance, in the case of complex [Fe2(μ-SC4H3N2)2(NO)4]) involves irreversible and rapid hydrolysis of NIC with the NO release accompanied with the formation of the products of further NO transformations. In the other mechanism (for instance, in the case of complexes [Fe2(μ-S(CH2)2NH3)2(NO)4]SO4• •2.5H2O and [Fe2(μ-SC5H11NO2)2(NO)4]SO4•5H2O), no hydrolysis occurs but NICs reversibly dissociate to release both NO and thiolate ligand into the medium. In the present work, the difference in the mechanisms of the NIC decomposition is explained by the difference in the NIC redox potentials. The experimental evidences of this fact are given.

Decomposition of binuclear neutral iron nitrosyl complex [Fe2(S2C7H4N)2(NO)4]0 (I) of μ-N–C–S structural type in aqueous solution has been studied. Effect of glutathione GSH on the decomposition of complex I has been studied.

The effects of deoxyhemoglobin (Hb) and albumin on the NO-donor activity of the anionic tetranitrosyl iron complex with thiosulfate ligands (1) were studied for the first time. It was shown that Hb significantly stabilizes complex 1; in its presence, NO generation from the complex proceeds at a noticeably slower rate. A similar effect is observed when complex 1 is bound to albumin, in which case complex 1 decomposes 27 times slower than in the absence of albumin in the solution. The observed effects provide a prolonged action of complex 1 as NO-donor, which may enhance its potential pharmacological efficacy.

The effect of N-nitroxymethyl succinimide (1), N-(2-nitroxyethyl) succinimide (2) and N-(3-nitroxypropyl) succinimide (3) on enzymatic activity of cyclic guanosine monophosphate (cGMP) phosphodiesterase was studied and crystal structure of compound (2) was determined. It was shown that all studied N-nitroxy succinimides inhibited cGMP phosphodiesterase in a concentration range of 0.1-0.001 mM. Compound (2) noncompetitively and reversibly inhibited hydrolytic function of enzyme with Ki=1.7×10-5 М. Inhibition constant for the reference compound N-(2-nitroethyl) nicotinamide (nicorandil) was 3×10-5 М.

Using spectrophotometry and stationary and kinetic fluorimetry, we have shown that xanthene dye fluorescein forms complexes with polycationic derivative of fullerene in aqueous solutions mainly due to electrostatic interactions. It is found that efficient quenching of singlet excited states of dye occurs in the structure of these complexes due to the transfer of excitation or electron from dye to fullerene. As a result, the photodynamic activity of the newly formed complex is much higher than that of fluorescein and fullerene derivative. This effect makes it possible to predict the formation of new-generation hybrid photodynamic preparations using dyes excited only into a singlet state; as a result, directed searches for these dyes are significantly facilitated.

The potential of surface enhanced Raman spectroscopy (SERS) for the detection of water-soluble fullerene derivatives and their covalent conjugates with xanthene dyes was investigated in model biological liposome membranes and in the albumin protein structure. It was shown that in liposomes and in albumin, fullerene derivatives and their covalent conjugates with dyes show characteristic SERS spectra, which allows detection of water-soluble fullerene derivatives in phosphatidylcholine liposomes at the lipid/fullerene derivative ratio of 100 as well as fullerene–dye conjugates in liposomes and albumin.

We studied the effects of water-soluble cationic dinitrosyl iron complexes with thiocarbamide and its aliphatic derivatives, new synthetic analogs of natural NO donors, active centers of nitrosyl [1Fe-2S]proteins, on activities of Ca2+-ATPase of sarcoplasmic reticulum and cGMP phosphodiesterase. Nitrosyl iron complexes [Fe(C3N2H8S)Cl(NO)2]0[Fe(NO)2(C3N2H8S)2]+Cl— (I), [Fe(SC(N(CH3)2)2(NO)2]Cl (II), [Fe(SC(NH2)2)2(NO)2Cl×H2O (III), and [Fe(SC(NH2)2)2(NO)2]2SO4×H2O (IV) in a concentration of 10—4 M completely inhibited the transporting and hydrolytic functions of Ca2+-ATPase. In a concentration of 10—5 M, they inhibited active Ca2+ transport by 57±6, 75±8, 80±8, and 85±9% and ATP hydrolysis by 0, 40±4, 48±5, and 38±4%, respectively. Complex II reversibly and noncompetitively inhibited the hydrolytic function of Ca2+-ATPase (Ki=1.7×10—6 M). All the studied iron—sulphur complexes in a concentration of 10—4 M inhibited cGMP phosphodiesterase function. These data suggest that the studied complexes can exhibit antimetastatic, antiaggregation, vasodilatatory, and antihypertensive activities.

The synthesis of water-soluble dyads PFD-Chl(1), PFD-Chl(Zn) and PFD-Chl(2) based on a polyanionic fullerene[60] derivative PFD covalently linked to chlorin e6 was described. Photophysical properties, generation of superoxide and singlet oxygen in water and liposomes, and photodynamic activity on HeLa cancer cells of obtained dyads were analyzed. The significant influence of linker length between fullerene[60] core and dye, presence of metal (Zn) atom in chlorin moiety on photophysical properties, and photodynamic activity of the dyads was demonstrated. All dyads exhibit quenching of chlorin fluorescence by 7–120 times due to the electron transfer from the dye to fullerene and they formed nanoassociates in aqueous solutions with an effective radius in the range of 30–500 nm due to their pronounced amphiphilic properties. Such nanoassociates were able to effectively interact with membranes of liposomes, which led to a sharp increase of fluorescence signal. This effect could be applied for the design of various fullerene-based nanoscale switch-off systems. The dyad PFD-Chl(1) – with the shortest linker and metal-free dye – had the superoxide generation efficiency 5.6 and 3.4 times higher compared to free chlorin Се6 in water and liposomes, respectively, while its singlet oxygen generation was reduced. The phototoxicity of this dyad in HeLa cells was almost equal to that of the native chlorin, despite the reduction of singlet oxygen generation efficiency. Upon the incorporation of zinc atom into a chlorin moiety of this dyad, photodynamic activity and phototoxicity of PFD-Chl(Zn) dyad became negligible. The PFD-Chl(2) dyad – with the longest linker and metal-free chlorin – had about two times lower photodynamic activity and phototoxicity compared to Ce6 due to weak interaction between fullerene core and the dye. A significant increase of the type I pathway efficiency, demonstrated in the PFD-Chl(1) dyad, could be applied for the creation of photosensitizers, highly effective against hypoxic tumors. The demonstrated approach opens up vast opportunities for a directional design of highly efficient fullerene-based water-soluble photosensitizers for photodynamic therapy.

In this work, transformations of the anionic binuclear tetranitrosyl iron complex with thiosulfato ligands (Na2[Fe2(S2O3)2(NO)4]·4H2O) (1) have been studied in aqueous anaerobic and aerobic solutions. Under anaerobic conditions, complex 1 was shown to undergo intramolecular isomerization, in addition to NO generation, due to embedding of the oxygen atom of the thiosulfato ligand in the Fe-S bonds. The complex becomes more stable, so its further transformation, including NO release, is unlikely. The model for the complex decomposition has been suggested, and reaction rate constants have been calculated using the kinetic modeling method. As follows from the experimental data, under aerobic conditions, complex 1 is oxidized and becomes a more effective NO donor. Due to the incorporation of the oxygen atom into the Fe-S bonds, mononuclear nitrosyl intermediates are formed, which have a typical EPR signal (g = 2.03).

The influence of the substitution pattern and chemical nature of the substituents on the pKa values of seven hydro[60]fullerenes in DMSO was explored using quantum mechanical calculations. Two experimentally observed addition topologies with two (RC60H) and six (R5C60H) substituents were considered. In the latter case, five substituents form a regular pentagram around the central pentadienyl fragment. The gas-phase free energies were calculated using DFT B3LYP and the free energies in solvent were calculated using Hartree–Fock PCM. For the substitution topologies studied, C60H6 had greater gas-phase basicity than C60H2. Differing impacts of the gas-phase and solvent free energies on the computed pKas were revealed and analyzed.

In this paper, the kinetics of the interaction of the nitrosyl iron complex with the ligands penicillamine [Fe2(SC5H11NО2)2(NO)4]SO4·5H2O (I) with deoxyhemoglobin (Hb) was studied. The kinetic modeling method defined the number of binding (I) molecules and equilibrium constant of the coupling reaction of (Biomedicine, Iron-Sulfur Cluster, Ligand Binding, Heme, Nitric Oxide ) with Hb (Ks). At equimolar concentrations of (I) and Hb (2 × 10−5 M), the Hb molecule binds only one (I) with Ks equal to 4.3 × 107 M−1. When increasing the (Biomedicine, Iron-Sulfur Cluster, Ligand Binding, Heme, Nitric Oxide ) concentration, the number of binding sites of Hb increases and Ks decreases. These results are analyzed in accordance with the data on the existence of cations binding sites in Hb.

Self-diffusion of water-soluble fullerene derivative (WSFD) C60[S(CH2)3SO3Na]5H in mouse red blood cells (RBC) was characterized by 1H pulsed field gradient NMR technique. It was found that a fraction of fullerene molecules (~13% of the fullerene derivative added in aqueous RBC suspension) shows a self-diffusion coefficient of (5.5 ± 0.8)·10−12 m2/s, which is matching the coefficient of the lateral diffusion of lipids in the erythrocyte membrane (DL = (5.4 ± 0.8)·10−12 m2/s). This experimental finding evidences the absorption of the fullerene derivative by RBC. Fullerene derivative molecules are also absorbed by RBC ghosts and phosphatidylcholine liposomes as manifested in self-diffusion coefficients of (7.9 ± 1.2)·10−12 m2/s and (7.7 ± 1.2)·10−12 m2/s, which are also close to the lateral diffusion coefficients of (6.5 ± 1.0)·10−12 m2/s and (8.5 ± 1.3)·10−12 m2/s, respectively. The obtained results suggest that fullerene derivative molecules are, probably, fixed on the RBC surface. The average residence time of the fullerene derivative molecule on RBC was estimated as 440 ± 70 ms. Thus, the pulsed field gradient NMR was shown to be a versatile technique for investigation of the interactions of the fullerene derivatives with blood cells providing essential information, which can be projected on their behavior in-vivo after intravenous administration while screening as potential drug candidates.

The effects of cognitive-stimulating substance BD-2 of the γ-carboline family and a hybrid compound based on fullerene C60 and attached BD-2 on various aspects of the behavior of animals were studied. The synthesized hybrid fullerene compound (HFC) has no side psychostimulating effect characteristic of BD-2 but fully retains the properties of a cognitive-stimulating agent. The design of hybrid compounds based on fullerene C60 and pharmacologically active groups can be one of the ways for optimizing therapeutically promising compounds.

The membranotropic and relaxation properties of novel water-soluble gadolinium endometallofullerene derivatives (EMFD) were studied. Localization of EMFD in membranes and EMFD-induced changes in the membrane structure were determined by measuring the emission quenching of pyrene as a fluorescent probe. It was demonstrated that EMFD efficiently interact with pyrene molecules in model membranes, thus changing their microviscosity. Pulsed 1H NMR experiments revealed that the hydroxylated endometallofullerene Gd@C82(OH)∼30 has the highest relaxivity (R1 = 7.390 L mol−1 s−1) among the test EMFD and that its efficiency is 3.6 times that of the commercial MRI contrast agent Magnevist. The data obtained suggest that these EMFD are promising for use as low-toxicity contrast agents for magnetic resonance imaging.

The absolute pKa values of the α-COOH, α-NH, and CH groups of the fullerene derivative l-Ala-C60H in water were calculated by quantum chemical methods. The gas phase basicities were calculated by the DFT method B3LYP/6-31G(d)//B3LYP/6-311++G(2d,p). The Gibbs free energies of solvation were calculated at the Hartree-Fock and B3LYP levels in combination with the polarizable continuum model. The stabilities of the l-Ala-C60H isomers and the lowest-energy conformers for neutral and anionic states were determined at the B3LYP/6-31G(d) level. The CH group at fullerene in l-Ala-C60H is less basic in the gas phase than the CH group in C60H2 and than the COOH group in l-Ala-C60H and AcOH. The calculated pKa values of the dissociating groups in water increase in the order: NH2+(COOH-CH(Me)-NH2+-C60H) < COOH (COOH-CH(Me)-NH-C60H) < COOH (AcOH) < CH (COOH-CH(Me)-NH-C60H) < CH (C60H2) < NH3+ (Me-NH3+). The amino group in l-Ala-C60H is electrically neutral, while the carboxy group is negatively charged at physiological pH values. The COOH group in l-Ala-C60H is more acidic (pKa = 4.2) than the CH group at fullerene (pKa = 5.8). The results of the calculations agree with the experimental data on the chemical reactivities of these compounds.

This paper describes the comparative study of the decomposition of two iron nitrosyl complexes (NICs) with a cysteamine thiolate ligand {Fe2[S(CH2)2NH3]2(NO)4}SO4·2.5H2O (I) and a glutathione (GSH)-ligand, [Fe2(SC10H17N3O6)2(NO)4]SO4·2H2O (II), which spontaneously evolve NO in aqueous medium. NO formation was measured by using a spectrophotometric method by the formation of a hemoglobin (Hb)–NO complex. Spectrophotometry and mass-spectrometry methods have firmly shown that the cysteamine ligands are exchanged for 2 GS− during decomposition of 1.5 × 10−4 M (I) in the presence of 10−3 M GSH, with 77% yield at 68 h. As has been established, such behaviour is caused by the resistance of (II) to decomposition due to the higher affinity of iron towards GSH in the complex. The discovered reaction may impede S-glutathionation of the essential enzyme systems the presence of (I) and is important for metabolism of NICs, connected with their anti-tumor activity.

We report the investigation of the molecular mechanisms responsible for the neuroprotective activity of water-soluble [60]fullerene derivatives (WS[60]FDs). It has been shown that WS[60]FDs influence the therapeutically important targets of the Alzheimer disease by inhibiting the catalytic activity of the monoaminooxidase B in vitro, decreasing the level of free radical species and behaving as positive modulators of AMPA receptors of Purkinje neurons in the cerebellum of rats. The cognitive stimulatory effects of WS[60]FDs were revealed in vivo through behavioural experiments in mice.

We studied the effect of iron nitrosyl complexes, NO donors, of various structural types on the activity of Ca2+-ATPase of sarcoplasmic reticulum (SR) and phosphodiesterase (PDE) of cyclic guanosine monophosphate (cGMP). It was established that iron nitrosyl complexes with organic ligands modulate functions of both enzymes. They effectively inhibited the hydrolytic and transport functions of Ca2+-ATPase SR at concentrations 0.1 – 0.01 mM and decoupled ATP hydrolysis and active Ca2+ transport at concentrations 0.01 – 0.0001 mM, thus disrupting the Ca2+ balance in cells. This influenced thrombogenesis and adhesion of metastatic cells to capillary endothelium. The compound [Fe(SC(NH2)2)2(NO)2]2[Fe2(S2O3)2(NO)4] produced non-competitive and reversible inhibition of Ca2+-ATPase SR functioning with K i = 0.70∙10–6 M. All studied iron nitrosyl complexes inhibited the activity of PDE-cGMP, which led to accumulation of cGMP, which is a secondary messenger influencing the in vivo anti-aggregation effect. The obtained results suggested that the studied iron nitrosyl complexes could be considered as potential drugs.

The effects of new fullerene derivatives on the functioning of the hydrolases sarcoplasmic reticulum (SR) Ca2+-ATPase and cyclic guanosine monophosphate phosphodiesterase (cGMP PDE) were studied. Most of the fullerene derivatives studied were found to inhibit the activity of both enzymes. Thus, compounds PSF-1, PSF-II, and PSF-III completely inhibited Ca2+ transport at a concentration of 0.009 mM but inhibited ATP hydrolysis by only 55 ± 6%, 42 ± 8%, and 60 ± 6% respectively, thus uncoupling the hydrolytic and transport functions of the enzyme. This induced changes in the extra- and intracellular Ca2+ ion levels and affected adhesion of metastatic cells to the capillary endothelium. Compound PSF-III had noncompetitive, reversible effects on the hydrolytic function of SR Ca2+-ATPase with K i = 1.6 × 10–6 M. All the fullerene derivatives studied inhibited cGMP PDE function and could induce an antiaggregation effect which resulted from accumulation of the cGMP PDE substrate, i.e., cGMP, which is a second messenger in living organisms. These results can be used to predict the potential therapeutic effects of the fullerene derivatives studied.

229 As known, fullerenes are photoexcited to a triplet state in 100% quantum yield, which then is deacti vated to generate, depending on the polarity of a medium, either singlet oxygen О2 or superoxide radi cal anions and other active radicals [1]. Numerous studies have addressed the photodynamic effect of fullerene and their derivatives: the generation of active radicals upon photoexcitation is responsible for dam age of DNA, proteins, and membranes, as well as for the suppression of the reproduction of tumor cells, viruses, and bacteria [2]. However, the efficiency of the photodynamic action of fullerenes and the pros pects for their application in medicine are essentially limited by the weak absorption by fullerenes of visible light, especially in the range 650–800 nm, which is most suitable for photodynamic therapy. The photodynamic effect of fullerenes can be con siderably enhanced by creating hybrid nanostructures − О2 . (HNSs) via the formation of a fullerene complex with a dye that efficiently absorbs visible light [3]. In such a complex, the dye can efficiently absorb light and transfer excitation energy or electron to the fullerene. Further excitation transfer or electron transfer from the fullerene to molecular oxygen will generate active oxygen species. The creation of such an HNS based on fullerene and a dye can thereby significantly enhance the efficiency of photodynamic therapy.

Deoxyhemoglobin (Hb) stabilizes the cationic nitrosyl iron complex with cysteamine {Fe2[S(CH2)2NH3]2(NO)4}SO4·2.5H2O (CysAm), by slowing down its hydrolysis. In the absence of Hb, the electrochemical detection of NO release in the course of the hydrolysis using a sensor electrode gave the rate constant of (5.2±0.2)·10−5 s−1. The release of NO is a reversible process, and the amount of released NO is 1.4% of the CysAm concentration. In the presence of Hb, NO is released much more slowly, and the reaction is more intense than that in the absence of Hb. The adsorption of CysAm by an Hb molecule results in NO release from the CysAm-Hb complex with a rate constant of 1·10−8 s−1. The analysis of the Hb surface revealed the possible location of the cation-binding sites, which reversibly bind the cationic CysAm complex. The kinetic parameters of NO release from CysAm in the absence and in the presence of Hb were studied by the kinetic modeling.

It has been shown by the use of steady-state and time-resolved fluorimetry and kinetic phosphorescent spectroscopy that a polycationic fullerene derivative forms complexes with eosine Y in solution due to electrostatic interactions. It has been found that singlet excited states of eosine Y are effectively quenched due to either the excitation energy transfer or electron transfer from the dye to the fullerene core. This leads to a substantial increase in the photodynamic activity of the fullerene derivative and the dye in the structure of the complex when it is excited by light in the absorption band of the dye.

The aqueous solutions of C60 fullerene derivatives were studied by means of dynamic light scattering, their effect on the peroxide oxidation of lipids (POL) in aqueous solutions was investigated via chemiluminescence method. It was shown that the colloidal solubility in water, which defines the antioxidant activity of C60 fullerene derivatives during POL, is controlled by the chemical structure of the addend added to C60 fullerene. For the studied derivatives, the direct dependence of the efficiency of POL inhibition on the lipophilicity was established.

Octa[(4′-benzo-15-crown-5)oxy]phthalocyanine was shown to dissolve in the presence of water-soluble fullerene compounds C60Cl(NHCH2CH2NH3 +)5(−OOCCF3)5 or C60Cl(C6H4CH2CH2COONa)5. The solubilization of phthalocyanine was attributed to the possibility of formation of the hydrogen bonds N-H...O(CH2) and coordination of the sodium cations inside the cavities of the crown ether fragments for the cationic and anionic fullerene derivatives, respectively. Solubilization of the crown-containing phthalocyanine with participation of water-soluble fullerene compounds proceeded with the formation of aggregated forms. A monomeric form of nickel tetrasulfonated phthalocyaninate in the presence of an equimolar amount of C60Cl(NHCH2CH2NH3 +)5(−OOCCF3)5 in 50% ethanol is transformed into a dimeric form. The structures of the fullerene-containing compounds and their state in solution facilitate the stacking aggregation of phthalocyanines.

Patterns of the interaction between water-soluble polysubstituted fullerene derivatives (PFDs) and the lipid bilayer of phosphatidylcholine liposomes were investigated by applying triplet and fluorescent probes. Objective quantitative criteria have been proposed for the evaluation of membranotropic action of chemical substances, notably, fullerene derivatives that quench fluorescent probes with different localizations within the membrane. Thus, the defined criteria are the rate constants for the quenching of the fluorescence of triplet probes and the equilibrium constants for PFD-probe complexes, which characterize their stability. The localization of PFDs in the membrane was determined by comparing rate constants for the quenching of eosin phosphorescence and equilibrium constants for PFD-chromophore complexes. In addition, the efficiency of the interaction of PFDs with various sites of the phospholipid membrane has been seen to depend on the charge of addends that are attached to the polysubstituted derivatives.