A. I. Kotelnikov

Membranotropic properties of the water soluble amino acid and peptide derivatives of fullerene C60.

The modifying effects of the products of the equimolar addition of dl‐alanine and dl‐alanyl‐dl‐alanine to fullerene C60 on the structure and permeability of the lipid bilayer of phosphatidylcholine liposomes has been studied using the luminescence probe technique. It is shown that these water soluble amino acid and dipeptide derivatives of fullerene (C60‐AD) are quenchers of pyrene fluorescence and erythrosine phosphorescence of in both a water solution and liposomes. To study the permeability of the lipid bilayer a procedure based on the triplet probe technique has been developed. It has been found that the C60‐AD derivatives under study are able to localize inside the artificial membrane, to penetrate into the liposomes through the lipid bilayer and to perform activated transmembrane transport of bivalent metal ions.

Quantum chemical calculations of the dissociation constants pK a for l-Ala-C60H (an amino acid derivative of fullerene) in water

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.

Influence of water-soluble derivatives of [60]fullerene on therapeutically important targets related to neurodegenerative diseases

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.

Coupling of Electron Transfer and Protein Dynamics

Electron transfer (ET) reaction with participation of special proteins is the key process of functioning of biological systems. Till recently the high effectiveness and specific features of ET in proteins have been described solely by allowing for a protein’s static structure but their molecular dynamics has not been taken into account. However, according to the Marcus theory [1] the dynamic properties of medium constitute one of the most important parameters that govern the effectiveness of electron transfer in condensed media. The dynamic properties of proteins differ appreciably from the analogous parameters of liquids and solids. The local structural adjustment of the active center or the conformational transition of the entire protein globule during the catalytic act is a unique property of enzymes enabling them to optimize and control the chemical process. The aim of this paper is to critically analyze the existing models of long-range ET reactions in proteins. To correct the revealed discrepancies we propose a model, taking into account the molecular dynamics of proteins with a broad distribution of the relaxation times.

Photodynamic Activity of Hybrid Nanostructure on the Basis of Polycationic Fullerene Derivative and Xanthene Dye Eosine Y

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.

Membranotropic and relaxation properties of water-soluble gadolinium endometallofullerene derivatives

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.

Application of SERS and SEF Spectroscopy for Detection of Water-Soluble Fullerene–Chlorin Dyads and Chlorin e6

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.

Self-diffusion of water-soluble fullerene derivatives in mouse erythrocytes

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.

Enzyme-like effect of metmyoglobin on the thermal cis-trans isomerization of stilbazolium betaine.

A photochromic compound, stilbazolium betaine M, when associated with metmyoglobin undergoes an accelerated thermal cis→trans isomerization. A study of the pH and ionic strength dependence of the isomerization reaction rate of the photochrome associated with metmyoglobin was perfomed. A comparative investigation of the reaction carried out in the presence of three proteins, metmyoglobin, apomyoglobin, and human albumin, indicates a specific influence of the heme pocket environment on the reaction. Possible mechanisms of the reaction acceleration are considered.