[Quenching of chlorophyll and pheophytin fluorescence with fucoxanthin]. / Tushenie fluorestsentsii khlorofilla i feofitina fukoksantinom.

Quenching of chlorophyll a and pheophytin a fluorescence with fucoxanthin in acetone and n-hexanole at room temperature was investigated. The relationship between fluorescence yield and concentration of the quencher is subject to Stern--Folmer relation. The velocity constants were calculated and the efficiency of fluorescence quenching was determined. The energetic estimation has shown that the fluorescence quenching mechanism when the excited chlorophyll a molecule collides with fucoxanthin molecule may involve electron transfer from chlorophyll to fucoxanthin. In case of pheophytin a transfer of the electron from fucoxanthin to pheophytin is likely to take place.

[Photophysics of complex formations between chlorophyll a and its analogs with pi acceptors]. / Fotofizika protsessov v kompleksakh khlorofilla a i ego analogov s lambda-aktseptorami.

Efficient quenching of fluorescence was shown to proceed in the complexes of chlorophyll a and its analogs with tetracyanochinodimethane (TCD), 1,3,5-trinitrobenzene (TNB), m-dinitrobenzene (DNB) and n-benzoquinone. In chlorophyll a--TCD and--DNB complexes quenching is characterized by the rate constant approximately greater than 5 x 10(10) s-1, and in chlorophyll a--n-benzoquinone greater approximately than 5 x 10(9) s-1. Possible ways of desactivation of singlet-excited state of chlorophyll a in the complexes with TCD and TNB were analysed. No triplet states of chlorophyll a complexes with TCD and TNB and no cation-radicals were recorded. It is suggested that efficient desactivation of the pigment singlet-excited state may be explained by a reversible phototransfer of the electron.

[Mobility of photo-generated vacuoles in layers of chlorophyll a]. / Podvizhnost' fotogenerirovannykh dyrok v sloiakh khlorofilla a.

The method of crystalline counter was used for investigating the movement of photogenerated holes in chlorophyll a layers. It has been shown that kinetics of the increase of tension impulses U(t, V) contains two phases: the initial phase of fast increment of impulses for the time (2 divided by 10) x 10(-7) s and the phase of successive slowed down accumulation of the charge. The value of the signal in the initial phase increases almost linearly with t increase. The time of increment of the initial phase ti linearly depends on 1/V, where V--tension applied to the sample. It is concluded from the analysis of these data that the initial phase of the curves U(t, V) is conditioned by the transit of some photogenerated holes up to the rear electrode without their seizure with deep traps within the layer. From the changes of ti mobility of holes is calculated: mu = (1.8--5.0) x 10(-6) M2 . b-1 . s-1. The phase of slow charge accumulation is explained by the seizure of the holes by surface traps and their release after the time t approximately greater than ti. Mean time of holes presence in small traps in the layer volume t congruent to (1--2) x 10(-7) s. is evaluated.

[Role of singlet-excited and triplet states in chlorophyll photooxidation]. / O roli singletno-vozbuzhdennogo i tripletnogo sostoianii pri fotookislenii khlorofilla.

Effect of p-benzoquinone concentration [Q] on the yield of ion-radicals during photooxidation of chlorophyll a with p-benzoquinone was studied by the method of impulse photoconductivity. It has been shown that in the studied range [Q] = 10(-6)--10(-1) M the relationship delta n ([Q]) has a bell-like shape with the maximum at [Q] approximately 10(-3) M. From the relationship obtained the ratio beta = delta ns/delta nt of the contributions of singlet--excited (Chl) and triplet (Chl) states of the pigment into the total yield of ion-radicals is evaluated: for [Q] less than or equal to 10(-1) M beta less than or approximately 10(-3). Primary contribution of the triplet state to the formation of ion-radical is explained, first, by a larger, as compared to the singlet-excited state, life time of the state Chl in solution and second, by the fact that the ion-radical pair 3(Chl+Q-) in the triplet state regenerates less effectively to Chl+Q, than the pair (Chl+Q-).

[Impulse photoconductance of solutions of chlorophyll and its analogs. IV. Absolute quantum yield of ion radical formation during photooxidation of chlorophyll a by n-benzoquinone]. / Impul'snaia fotoprovodimost' rastvorov khlorofilla i ego analogov. IV. Ob absoliutnom kvantovom vykhode obrazovaniia ion-radikalov pri fotookislenii khlorofilla a n-benzokhinonom.

The values of absolute quantum yield phi of the formation of free ion-radicals during the illumination of alkohol solutions of chlorophyll alpha (Chl) and rho-benzoquinone (Q) at room temperature were obtained by the method of impulse photoconductance. With an increase of the dielectric constant epsilon of the solvent from approximately 6 to approximately 25 phi increases by two orders ( approximately 10(-3)--approximately 10(-1). That obtained relationship phi (epsilon) is explained by epsilon effect on the efficiency of dissociation of "solvent-shared" ion-radical pair Chls+. Os-. The comparison of experimental data and theoretically expected ones allowed the estimation of some parameters to be obtained which characterize the ion-radical pair: interionic distance (10 A), the dissociation velocity constant ( approximately 10(5)--10(8) s-1), the velocity constant of reverse electron transfer (10(8) s-1), the life time approximately 10(-8) s).

[Photochenical and photoelectronic properties of components of the photosynthetic apparatus. II. Stationary photoconductivity in chlorophyll-acceptor and chlorophyll+protein-acceptor lamellar systems]. / Fotokhimicheskie i fotoélektronnye svoistva komponentov fotosinteticheskogo apparata. II. Statsionarnaia fotoprovodimost' v lamelliarnykh sistemakh khlorofill-aktseptor i khlorofill+belok-aktseptor.

It has been shown that the treatment of chlorophyll a amorphous layer surface with the electron acceptor n-chloranyl leads to an increase of photocurrent by 10(1)--10(3) times. The photoinduced polarization in the lamellar system chlorophyll a--n-chloranyll is studied. It has been shown that under the effect of the red light the n-chloranyl layer is negatively charged in relation to the pigment layer. Photoconductivity was discovered in the rigid layers of chlorophyll a+human serum albumin. When a thin film of n-chloranyl is sprayed on the surface of the chlorophyll-protein layer, the photocurrent increases approximately 6--7 times. The experimental results are discussed within the scheme according to which the formation of free radical carriers in chlorophyll layers is carried out by the destruction of excited states, possibly excitons on the electron-acceptor centres of dissociation.

[Impulse photoconductivity of solutions of ohlorophyll and its analogs. III. Photoconductivity of hexanol solutions of chlorophyll a in the presence of n-benzoquinone. Kinetic and temperature measurements]. / Impul'snaia fotoprovodimost' rastvorov khlorofilla i ego analogov. III. Fotoprovodimost' geksanolovykh rastvorov khlorofilla a v prisutstvii n-benzokhinona. Kineticheskie i temperaturnye izmereniia

It is shown that an increase deltasigma of electroconductivity of chlorophyll "a" (Chlalpha) solution in hexanole in the presence of n-benzoquinone (Q) under impulse illumination of solution is proportional to flash intensity: deltasigma=1(0,99+/-0,07). Dependence deltasigma on solution temperature is of an exponential character with the activation energy Esigma=0,30+/-0,01 ev. In the temperature range studied (248--298 degrees K) the ratio between the recombination velocity constant and the mobility of ion-radicals Chlalpha+ and Q-(Kp/mu) is shown to be equal (8+/-1)X 10(-8) cm-v. The activation energy for the dissociation of coulomb pair (Chlalpha+Q-) into free ion-radicals Epiapproximately0,1 ev is evaluated. The value of total mobility of negative and positive ion-radicals is calculated from the date obtained and literature ones: mu=(1,0+/-0,2)X10(-5) cm2/v-sec.

[Impulse photoconductivity of solutions of chlorophyll and its analogs. II. Effect of medium polarity on the yield of ion-radicals during the photoxidation of chlorophyll a ]. / Impul'snaia fotoprovodimost' rastvorov khlorofilla i ego analogv. II. Uliianie poliarnosti sredy na vykhod ion-radikalov pri fotookislenii khlorofilla a

The effect of the dielectric constant epsilon of the solvent on the yield delta n of ion-radicals during photooxidation of chlorophy-l a with n-benzoquinone was studied by the method of impulse photoconductivity. It was shown that in the studied range of dielectric constant valve (epsilon congruent to 5-25) delta n monotonously increased with an increase of epsilon the relationship delta n (epsilon) being of clearly pronounced S-like character with a bend in the region of epsilon congruent to 10. A half-quantitative explanation of the data obtained is presented.