Hybrid Complexes of Photosensitizers with Luminescent Nanoparticles: Design of the Structure.

Increasing the efficiency of the photodynamic action of the dyes used in photodynamic therapy is crucial in the field of modern biomedicine. There are two main approaches used to increase the efficiency of photosensitizers. The first one is targeted delivery to the object of photodynamic action, while the second one is increasing the absorption capacity of the molecule. Both approaches can be implemented by producing dye-nanoparticle conjugates. In this review, we focus on the features of the latter approach, when nanoparticles act as a light-harvesting agent and nonradiatively transfer the electronic excitation energy to a photosensitizer molecule. We will consider the hybrid photosensitizer-quantum dot complexes with energy transfer occurring according to the inductive-resonance mechanism as an example. The principle consisting in optimizing the design of hybrid complexes is proposed after an analysis of the published data; the parameters affecting the efficiency of energy transfer and the generation of reactive oxygen species in such systems are described.

Temperature Dependence of Tryptophan Fluorescence Lifetime as an Indicator of Its Microenvironment Dynamics.

The spectral-kinetic characteristics of the fluorescence of the tryptophan molecule in an aqueous solution and in the composition of a protein (albumin) were studied in the temperature range from -170 to 25°C. To explain the observed changes in the spectra and the tryptophan fluorescence lifetime with temperature, a model of transitions between the excited and ground states involving a charge-transfer state was used, which takes into account the nonlinear nature of the dynamics of these transitions. In these processes, an important role is played by the interaction of tryptophan molecules with its microenvironment, as well as rearrangements in the system of hydrogen bonds of the water-protein matrix surrounding the tryptophan molecule.

Photophysical Properties of Upconverting Nanoparticle-Phthalocyanine Complexes.

Interaction between upconverting nanoparticles and aluminum octacarboxyphthalocyanine was studied. The efficiency of non-radiative energy transfer from the nanoparticles to phthalocyanine increased with the number of phthalocyanine molecules adsorbed on the nanoparticle, but only up to a certain limit. Further increase in the phthalocyanine concentration resulted in a decrease of its sensitized fluorescence due to the dimerization of dye molecules on the nanoparticle surface. When subjected to infrared irradiation, phthalocyanine molecules in the hybrid complex generated singlet oxygen. The observed effects are of interest in regard to the targeted search for new components of efficient third-generation hybrid photosensitizers.

[Use of the standard theory of electronic transitions in the description of oscillations in the kinetics of electron transfer in reaction centers of purple bacteria].

The standard theory of the electron transfer between donor and acceptor molecules was used to describe oscillations in the reduction kinetics of the intermediate electron acceptor BA and the primary electron acceptor HA. The kinetics of the reduction of BA and HA were simulated on the basis of the model in which one and two accepting modes were used. A principal experiment is offered for the selection of the suitable theory for adequate description of oscillations in the kinetics of electron transfer in the reaction centers of purple bacteria.

[A method for determining the individual optical characteristics of posttranslational fluorescent forms of fluorescent proteins with the use of nonlinear laser fluorimetry].

A method for determining the individual optical characteristics (fluorescence quantum yield, the rate constant and quantum yield of singlet-triplet conversion, excitation of fluorescence cross-section, extinction coefficient) and concentration correlations between the fluorescent forms of fluorescent proteins arising in the reaction of posttranslational chromophore formation has been developed, which is based on combined application of absorption spectroscopy and classical and nonlinear laser fluorimretry. The method allows one to determine the share of fluorescent forms in the mixture of chromoproteins. The individual optical characteristics of the red form of the fluorescent protein mRFP1 has been determined: the fluorescence quantum yield eta = 0.24 +/- 0.03; the extinction coefficient in the maximum of absorbance band (584 nm) epsilon = 213 +/- 40 mM(-1) cm(-1) (the cross-section of absorbance sigma = (8.2 +/- 1.5).10(-16) cm2); the constant of singlet-triplet conversion rate K32 = (0 +/- 0.6)-10970 s(-1). The part of the red form in the mixture of chromoproteins is 26 +/- 6%.

[Fluorescence characteristics and photophysical parameters of aggregates of light-harvesting chlorophyll a/b complexes].

Changes in the fluorescence characteristics and molecular photophysical parameters induced by disaggregation of light-harvesting chlorophyll a/b complexes isolated from pea were studied. Disaggregation was achieved by increasing the concentration of the detergent triton X-100 (concentration range 0-230 microM, chlorophyll concentration 2.45 microg/ml). Laser fluorimetry methods were used to measure the molecular photophysical parameters. It was shown that the decrease in aggregate size is accompanied by a decrease in fluorescence at 700 nm at 77 K, a fall of the singlet-singlet annihilation rate (by more than two orders), and the growth of fluorescence life time (from 160 ps to 3.2 ns).

[The application of PS II model for the analysis of fluorescence yield transients induced by actinic single turnover flash in the time range from 100 ns to 10 s].

Changes in flash-induced fluorescence yield in preparations of thermophilic Chlorella pyrenoidosa Chick cells (native and in the presence of DCMU) were investigated in the time range from 100 ns to 10 s using a new measuring system. The results were analyzed by mathematical modeling of processes in photosystem II. It was shown that the detailed description of recombination (including nonradiative) processes in photosystem II is important to simulate the fluorescence yield transients induced by an actinic single turnover flash. The model photosystem II parameters were modified to describe the light-induced effects in the presence of DCMU. By comparing the theoretical fluorescence curves with experimental ones, we obtained the values of relative fluorescence yield and the FM/F0 ratio, which is typical for experimental data. As a result of simulation, the values of the model parameters (rate constants of electron transfers at the donor and acceptor sites of photosystem II, pH in stroma, initial redox state of the plastoquinone pool, the rate of plastoquinol oxidation, and the rate constants of nonradiative recombination processes) were determined.

Role of viscosity and permeability of the erythrocyte plasma membrane in changes in oxygen-binding properties of hemoglobin during diabetes mellitus.

Changes in viscosity and permeability of the plasma membrane and conformation of erythrocyte hemoglobin hematoporphyrin were found in patients with diabetes mellitus. The decrease in oxygen binding and increase in deoxyhemoglobin concentration during diabetes mellitus were accompanied by changes in viscosity and permeability of the membrane for Na+, H+, Ca2+, and K+. Our results suggest that oxygen-binding properties of hemoglobin depend on viscosity and permeability of the erythrocyte plasma membrane.

[A network of hydrogen bonds in the reaction centers of Rhodobacter sphaeroides serves as a regulatory factor of the temperature dependence of the recombination rate constant of photooxidized bacteriochlorophyll and primary quinone acceptors]. / Sistema vodorodnykh sviazei reaktsionnykh tsentrov Rhodobacter sphaeroides kak reguliatornyi faktor temperaturnoi zavisimosti skorosti rekombinatsii fotookislennogo bakteriokhlorofilla i pervichnogo khinonnogo aktseptora.

The dark recombination rate constant for the photooxidized bacteriochlorophyll (P) and reduced primary quinone acceptor (QA) in the photosynthetic reaction centers (RC) from purple bacterium Rhodobacter sphaeroides depends nonmonotonically on temperature. The time of this reaction is approximately 100 ms at 270-300 K and decreases as the temperature both increases and decreases beyond this temperature range. It is known that the dome-shaped dependence of the thermodynamic stability on temperature is an intrinsic feature of many proteins in solution. The experimental results on the nonmonotonous temperature dependence of P+ and QA- recombination rate constant are discussed in terms of general thermodynamic approaches. The dynamic properties of the network of hydrogen bonds that are involved in the relaxation processes accompanying the electron transport are considered as a regulatory factor of the efficiency of electron transfer.

[Possible effect of structural phase transition in the reactive center of Rhodobacter sphaeroides on the rate of dark adaptation of photooxidized bacteriochlorophyll from primary quinone]. / Vozmozhnoe vliianie strukturnogo fazovogo perekhoda v reaktsionnykh tsentrakh Rhodobacter sphaeroides na skorost' temnovogo vosstanovleniia fotookislennogo bakteriokhlorofilla ot pervichnogo khinona.

The dependence of the rate of dark recombination between the photooxidized primary donor--dimer bacteriochlorophyll molecule (P) and reduced primary quinone acceptor (QA), P+QA(-)-->PQA was studied in photosynthetic reaction centers (RC) from Rhodobacter sphaeroides in the temperature range of 100-320 K. Control RC preparations, RC species with the removed H-subunit as well as RC samples with the hydrogen bonds network modified by isotopic D2O-H2O substitution were investigated. An anomalous temperature dependence of the recombination time (tau rec) of dark reaction P+QA(-)-->PQA was found for all RC samples. It was found that upon heating from 120 to 290 K tau rec increased 2.5 fold. However, upon further heating to 320 K, tau rec decreased again. The temperature dependences of the P+QA(-)-->PQA recombination time were compared with those of the thermodepolarization current of RC preparations in the same temperature range. The temperature curve of the thermodepolarization current was also nonmonotonous. The theoretical interpretation of the temperature dependence of tau rec as well as of the thermodepolarization current was made in the framework of the theory of structural phase transitions within the hydrogen bond network in the water-protein surrounding of the redox centers participating in the electron transfer reactions.

[Effects of relaxation processes on the temperature dependence of oxidation rate of photooxidized bacteriochlorophyll on the primary quinone in reaction centers of Rhodobacter sphaeroides]. / Vliianie relaksatsionnykh protsessov na temperaturnuiu zavisimost' skorosti vosstanovleniia fotookislennogo bakteriofilla ot pervichnogo khinona v reaktsionnykh tsentrakh Rhodobacter sphaeroides.

The temperature dependence of the time of dark recombination of charges between photooxidized bacteriochlorophyll and reduced primary quinone acceptor (tau e) in Rhodobacter sphaeroides photosynthetic reaction centers was studied in the temperature range 140-320 K. It was found that the function tau e = tau e(T) is nonmonotonous: in the temperature range from 140 to 290 K, tau e is increased from 40 to 100 ms; however, under further heating to 320 K, tau e decreased to 80 ms. The replacement of H2O by D2O in these preparations caused an acceleration of the recombination process in the range of physiological temperatures, but the nonmonotonous character of the function tau e(T) remained. The theoretical interpretation of the results was made in the framework of the theory of electron-phonon interactions with allowance for the relaxation processes.

[Relation between structural-dynamic organization of reaction centers in Rhodobacter sphaeroides and picosecond steps of photosynthesis]. / Sviaz' strukturno-dinamicheskoi organizatsii reaktsionnykh tsentrov purpurnoi bakterii Rhodobacter sphaeroides s pikosekundnymi stadiiami fotosinteza.

The effect of deuteration, and the addition of glycerol and dimethylsulfoxide on the redox midpoint potential Em of bacteriochlorophyll of the special pair ¿PMPL¿, the rate of energy migration from bacteriopheophytin HM to ¿PMPL¿, and electron transfer from ¿PMPL¿ to HL and from HL to quinone QA in reaction centers of Rhodobacter sphaeroides was studied. It was shown that H2O-->D2O substitution did not change Em of the special pair, while the addition of 70% glycerol and 35% dimethylsulfoxide (v/v) increased the Em value by 30 and 45 mV, correspondingly. The rate constants of energy migration [formula: see text], charge separation [formula: see text], electron transfer to QA kQ remained unchanged upon the addition of glycerol. The isotopic substitution of water and addition of dimethylsulfoxide led to a 2-3-fold increase in km, ke and kQ values. The dependence of the potential of redox center on the dielectric constant epsilon was analyzed. It was shown that replacement of H2O by dimethylsulfoxide can increase Em by tens of millivolt. There was no correlation between changes in Em and the values of km, ke and kQ upon deuteration and addition of cryoprotectors. It was concluded that the processes of energy migration, charge separation, and electron transfer to the quinone acceptor are preceded by the solvation of states H*M, ¿P+MP-L¿* and [formula: see text].

Investigation of the electron transfer reactions and redox characteristics of photoactive bacteriochlorophyll in Rhodobacter sphaeroides reaction centers modified by D2O and cryoprotectants.

The effects of D2O, glycerol and dimethyl sulfoxide (DMSO) on redox potential Em of bacteriochlorophyll of a special P2 or [P(M)P(L)] pair, the rate of energy migration from bacteriopheophytin H(M) to [P(M)P(L)], electron transfer from [P(M)P(L)] to bacteriopheophytin H(L) and then to quinone Q(A) in reaction centers (RC) of Rhodobacter sphaeroides were studied. The H2O --> D2O substitution did not change Em of the special pair, whereas addition of 70% glycerol or 35% DMSO (v/v) increased the values of Em by 30 and 45 mV, respectively. Rate constants of energy migration km(H(M)* (km)--> P2), charge separation ke([P(M)P(L)] *H(L) (ke)--> [P(M)P(L)] +H(L)-), electron transfer to quinone kQ did not change after the glycerol addition, whereas isotopic substitution and addition of DMSO caused a 2-3-fold increase in km, ke, and kQ values. Theoretical analysis of the redox center potential dependence on dielectric permeability epsilon, swelling of the protein globule in a solvent, and on changes in the charge distribution (charge shifts) in the protein interior near the redox center was carried out. It has been shown that the H2O replacement with DMSO can result in the Em increase by tens of mV. No correlation was found between the Em values and the rate of charge separation upon isotopic substitution and addition of cryoprotectants. The effect of epsilon of the medium on the rate of electron transport due to changes of energy of intermolecular interaction between the donor and acceptor molecules was estimated.