Isolation and analysis of tetraheme-bound-cytochrome from photosynthetic reaction centers of Rhodopseudomonas viridis

A tetraheme cytochrome (BCytc) was isolated from the photosynthetic reaction centers (RC) of Rhodopseudomonas viridis while maintaining the redox activity. BCytc was removed from the H-subunit-detached RC by polyacrylamide electrophoresis using an alkyl ether sulfate mixed with sodium dodecyl sulfate. Redox titration of BCytc showed a simple one-step redox titration curve and a lowered midpoint potential than that of one in RC. Direct electron transfer between BCytc and electrode surfaces, such as indium tin oxide, was successfully performed, indicating a potential for molecular electronic material.     

A theoretical study of electronic excited states of photosynthetic reaction center in Rhodopseudomonas viridis

As well known,photosynthesis is the most impor-tant biochemical process on the earth.With a few mi-nor exceptions,photosynthesis is the only mechanism by which an external source of energy is harnessed by the living world.As a crucial composition of photo…     

Fluorescence properties of tetraphenylporphyrin-polypeptide complexes as model photosynthetic systems

The steady-state and time-resolved fluorescence spectra of complexes formed from α,β,γ,δ-tetrakis(4-carboxyphenyl) porphin and the synthetic sequential polytripeptides poly(L-lysyl-L-leucyl-L-alanine)_n (I) (MW 7900) and poly(L-lysyl-L-alanyl-L-alanine) _n (II) (MW 6900) are studied in phosphate buffer (pH=7.2). The peptide matrices were found to bond 4-5 pigment molecules per one polypeptide. The complexed pigment fluorescent decay kinetics is two-exponential with components τ₁ =240 ps and τ₂=2400 (I) and 3500 ps (II). The relative contributions of τ₁ correlate with the degree of α-helicity of the polypeptide matrix.     

Fluorescence studies on solvent-induced intramolecular charge separation in symmetric biaryls

Fluorescence studies on 5,5′-bi-benz[a]-pyrenyl reveal that the emitting state in polar solvents possesses a high dipole moment. Even in non-polar solvents such as n-hexane, dual fluorescence is emitted, with a structured twisted intramolecular charge transfer band. This puts an upper limit to the dipolar solvent fluctuations necessary to induce symmetry reduction and charge separation in the excited state. Theoretical guidelines to predict further cases of biaryls that exhibit charge separation in the excited state are derived.     

Fluorescence studies of selected 2-alkylaminopyrimidines

The reactions of 2-chloropyrimidine with methylamine, ethylamine and piperidine gave the corresponding 2-N-methylamino-, 2-N-ethylamino- and 2N- piperidinopyrimidines, respectively. The fluorescence properties of these alkylamino derivatives in chloroform, ethyl acetate, carbon tetrachloride, acetone, ether, ethanol and methanol were studied. All the alkylamino derivatives showed the highest fluorescence intensity in polar protic solvents; thus 2-N-methylaminopyrimidine (highest fluorescence intensity at 377 nm when excited at 282 nm) and 2-N-ethylaminopyrimidine (highest fluorescence intensity at 375 nm, when excited at 286 nm) showed the highest fluorescence in methanol. In ethanol, 2-N-piperidinopyrimidine showed a fluorescence peak at 403 nm when excited at 360 nm and in chloroform it fluoresced at 392 nm when excited at 356 nm.     

Fluorescence studies of carbocyanines using AOTF

Over the past few years acceptance of acousto-optic devices which can control optical radiation has increased. In this paper the use an acousto-optic tunable filter (AOTF) within an existing spectrofluorometer as a replacement for the excitation monochromator is reported. Long wavelength absorbing carbocyanine dyes that have strong absorption and high quantum yield are used as standards. The major advantage of using an AOTF filter is the wavelength purity and that it can act as a wavelength selector in place of a monochromator. The use of AOTF in place of bandpass filters for removing laser diode side bands is also discussed.     

Fluorescence studies of protein thermostability in ionic liquids

Using the single tryptophan residue in the sweet protein monellin as a spectroscopic handle, we show the extreme thermodynamic stabilization offered by an ionic liquid; T(un) approximately 105 degrees C in [C4mpy][Tf2N] compared to 40 degrees C in bulk water.     

Alterations in morphological parameters and photosynthetic pigment responses of Catharanthus roseus under soil water deficits

An experiment was conducted in two varieties, rosea and alba, of Catharanthus roseus plants with two watering treatments viz., 100 and 60% of field capacity, to understand the effects of water deficit on early growth, biomass allocation and photosynthetic pigment responses. We found that there were significant differences in early growth, dry matter accumulation and pigment variations between the two varieties. The root length, shoot length, total leaf area, fresh and dry weights were significantly reduced under water stress treatments. There was a significant reduction in the photosynthetic pigment contents in both the varieties. The rosea variety was more affected due to water deficit when compared to alba variety.     

Spectroscopic evidence for triplet excitation energy transfer among carotenoids in the LH2 complex from photosynthetic bacterium Rhodopseudomonas palustris

The LH2 complex from Rhodopsudomonas (Rps.) palustris is unique in the heterogeneous carotenoid compositions. The dynamics of triplet excited state Carotenoids (3Car*) has been investigated by means of sub-microsecond time-resolved absorption spectroscopy both at physiological temperature (295 K) and at cryogenic temperature (77 K). Broad and asymmetric Tn←T-1 transient absorption was observed at room temperature following the photo-excitation of Car at 532 nm, which suggests the contribution from various carotenoid compositions having different numbers of conjugated C=C double bonds (Nc=c). The triplet absorption bands of different carotenoids, which superimposed at room temperature, could be clearly distinguished upon decreasing the temperature down to 77 K. At room temperature the shorter-wavelength side of the main Tn←T1 absorption band decayed rapidly to reach a spectral equilibration with a characteristic time constant of-1 μs, the same spectral dynamics, however, was not observed at 77 K. The     

Fluorescence.detected X-band epr spectroscopy of the photosynthetic bacterial triplet state

The X-band FDMR spectrum of the bacterial triplet in reduced Rhodopseudomonas sphaeroides at 5 K has been obtained. Pure S-T₀ mixing is sufficient and k_z <k_x,k_y necessary to explain the polarization pattern and intensity ratios. The kinetic fluorescence response is sigmoidal due to the second-order kinetics of antenna-reaction center energy transfer.     

Fluorescence polarization studies of B-phycoerythrin oriented in polymer film

Polarized steady-state fluorescence and fluorescence excitation spectra as well as time-resolved fluorescence for B-phycoerythrin (B-PE) from red algae, Porphyridium cruentum, embedded in polyvinyl stretched films were measured. The lifetimes of polarized fluorescence were analyzed using exponential components and fractal models. The interactions between various chromophores of the pigment-protein complexes investigated were discussed. The anisotropy of fluorescence excitation spectra differs from the anisotropy of absorption spectra and depends on the wavelength of observation. This shows that differently oriented chromophores take part in various paths of excitation energy transfer (ET) or change their excitation into heat with various efficiencies (or both). Also, analysis of time-resolved fluorescence measured in various spectral regions gives different polarized components of emission. Fractal analysis of lifetimes, done under supposition of the Foerster resonance ET mechanism, suggests different arrangements of energy donors and acceptors for molecules absorbing in different spectral regions. It shows that several fractions of differently oriented "forms" of chromophores exhibiting different spectral properties occur in B-PE complexes. Small changes in the orientation of the chromophores can be followed by modification of the path of excitation energy migration. Based on the results obtained a new reorientational mechanism of the State 1 --> State 2 transition was proposed: Even small conformational modifications of biliproteins, which could be caused in vivo by the change in the conditions of preillumination of bacteria, are able to modify the path of excitation ET. Such a reorientation may be responsible for the change in the partition of biliprotein excitation energy between photosystem II (PSII) and PSI (State 1 --> State 2 transition). The proposed mechanism needs further verification by the investigation of whole bacteria cells.     

Fluorescence studies of the kinetics of processes in polymers

Using a stopped-flow apparatus with fluorescence detection we followed the expansion of poly(methacrylic acid) after a pH jump, the enhancement of fluorescence of Auramine O after association with poly(methacrylic acid), the counterion exchange in ionomer solutions and the dependence of the rate of inter-polymer reactions on the polymer chainlength. Fluorescence was also used to follow the unfolding of collapsed chains in bulk polymers and counterion diffusion in bulk ionomers.     

Expeditious implementation of two new methods for analysing the pigment composition of photosynthetic specimens

Two new methods for analysing the pigment composition of photosynthetic samples have been developed during the last few years. One, called the spectral reconstruction method, uses linear least-squares fitting, while the other, named the Gauss-peak spectra method, entails non-linear optimisation; each has some advantages over the other, but both use a large number of data points and surpass the traditional method which uses absorbance at a few wavelengths. In order to make the new methods transparent to experimentalists who are not well versed in statistical analysis, curve fitting and interpolation, simple procedures are described for implementing the methods with the aid of a spreadsheet. The problem of analysing a sample containing chlorophyll c, which is difficult to isolate in a form sufficiently pure to serve as an analytical standard, is also briefly addressed.     

Spectroscopic and photochemical studies of model visual pigment chromophores

The primary step in the bleaching sequence of visual pigments has been shown to occur in picoseconds, while the isomerization of model visual pigment chromophores, protonated 11-cis retinylidene Schiff bases, takes place on a time scale several orders of magnitude slower. Thus, the well-accepted notion that the primary step in visual transduction involves a simple isomerization deserves closer examination. Studies of visual pigments and compounds which mimic visual pigment chromophores are discussed in terms of several alternatives for the nature of the primary step. In addition to discussion of photochemical studies, spectroscopic experiments are discussed. To fundamentally understand the nature of the primary processes in visual transduction it is important to understand the photochemistry, and therefore the electronic structure, of pigment chromophores. Spectroscopic studies aimed at elucidating the electronic structure of polyenic systems are thus discussed.     

Fluorescence quenching and time-resolved fluorescence studies on Trichosanthes dioica seed lectin

Fluorescence quenching and time-resolved fluorescence studies have been carried out on the Trichosanthes dioica seed lectin (TDSL). The emission lambdamax of native TDSL, seen at 328nm, shifts to 343nm upon denaturation with 6M guanidinium chloride. Quenching titrations were performed with neutral (acrylamide and succinimide) and ionic (I(-) and Cs(+)) quenchers in order to probe the exposure and accessibility of tryptophan residues of the protein. Maximum quenching was observed with acrylamide, followed by succinimide, iodide and Cs(+). Dramatic increase in the extent of quenching and other quenching parameters by all the quenchers were observed upon denaturation of TDSL, suggesting that all the tryptophan residues in native TDSL are buried in the hydrophobic core of the protein. Increase in the extent of quenching upon denaturation of TDSL was maximum with I(-) and minimum with Cs(+), suggesting the presence of positively charged residue(s), near at least one tryptophan residue. Addition of saccharide ligands such as methyl-beta-d-galactopyranoside and lactose led to a small, but reproducible decrease in the fluorescence intensity of the lectin. The presence of lactose provided a partial protection against quenching by I(-), Cs(+) and succinimide, but not acrylamide. In time-resolved fluorescence measurements the fluorescence decay curves could be best fitted to biexponential patterns with lifetimes of 4.09 and 1.53ns for native lectin, 3.40 and 1.65ns for the lectin in presence of 0.1M lactose and 3.50 and 1.40ns for denatured lectin.     

Fluorescence studies on phenylene moieties embedded in a framework of periodic mesoporous organosilica

The excited state characteristics of phenylene (Ph)-bridged periodic mesoporous organosilica (PMO) powders with crystal-like and amorphous wall structures are investigated. Crystal-like Ph-PMO has a molecular ordering of the bridging organic moieties with intervals of 0.76 and 0.44 nm parallel and perpendicular to the mesochannel direction, respectively, whereas amorphous Ph-PMO has no molecular-level periodicity in the wall. Fluorescence from the exciton and excimer of the Ph moieties and the defect center in the silicate network were detected at room temperature, but fluorescence from the excimer and the defect center were not detected at 77 K for crystal-like Ph-PMO dispersed in a methanol/ethanol mixed solvent. The decay curve of the exciton fluorescence of crystal-like Ph-PMO at room temperature was analyzed successfully using a one-dimensional diffusion model quenched by the defect center and the excimer site. The results were discussed in comparison with those for the crystal-like biphenylene-bridged PMO reported in the preceding paper (Yamanaka et al., Phys. Chem. Chem. Phys., 2010, 12, 11688-11696). The existence of excited states with various conformations including ground state dimers or aggregates of the Ph moieties was suggested for amorphous Ph-PMO. It was clearly apparent that the differences in the excited state dynamics reflected the differences in the molecular-level structure in the wall.     

Effect of organotin compounds on membrane lipids: Fluorescence spectroscopy studies

The temperature dependence of 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) fluorescence anisotropy has been studied to investigate the influence of mono-n-butyltin chloride (MBTC), di-n-butyltin chloride (DBTC) and tri-n-phenyl chloride (TPTC) on the physicochemical state of dipalmitoyl phosphatidylcholine. Below the lipid chain melting transition (T_m), fluorescence anisotropy values of DPH and TMA-DPH are increased by the presence of the organotins, without important modifications of the phase transition temperature. A possible difference in localization of the organotin compounds is suggested by the differential effect of the probes. It is suggested that there is localization in the hydrophobic core of the bilayer for TPTC, and at the head-group level for DBTC, and a homogeneous distribution in the bilayer for MBTC. Similar studies have been performed in liposomal suspensions of cardiolipin, phosphatidylserine and egg phosphatidylcholine.     

Fluorescence studies on the interactions of barbaloin with bovine serum albumin

The fluorescence quenching reactions of barbaloin with bovine serum albumin (BSA) in pH 7.20 Tris-HCl buffer solution were studied. The quenching mechanism of BSA by barbaloin was interpreted using the Stern-Volmer (S-V) mechanism. The binding constant K values were 2.78 x 10(5) (293 K), 1.87 x 10(5) (310 K), 1.25 x 10(5) (318 K), and the number of binding sites (n) were 1.18, 1.14, and 1.09, respectively. In addition, the thermodynamic functions enthalpy (deltaH degrees ) and entropy (deltaS degrees ) for the reaction were also calculated according to Vant's Hoff equation were -23.7 kJ/mol and 23.6 J/mol, respectively. Plausible explanations of the quenching mechanism are discussed on the basis of a hydrophobic interaction between barbaloin and BSA.