Effect of aggregation state, temperature and phospholipids on photobleaching of photosynthetic pigments in spinach Photosystem II core complexes

Photosystem II (PSII) complex activity is known to decrease under strong white light illumination, and this photoinhibition phenomenon is connected to the photobleaching of the PSII photosynthetic pigments. In this work the pigment photobleaching has been studied on PSII core complexes, by observing the effects of different factors such as the aggregation state (PSII monomers and dimers were used), temperature (20 degrees C and 10 degrees C temperatures were tested) and the presence of the exogenous phospholipids (cardiolipin and phosphatidylglycerol). In particular, PSII resistance against white light stress was studied by means of UV/VIS Absorption and Fluorescence Emission measurements. It was found that PSII dimers resulted more resistant against photobleaching and that lower temperature reduces the pigment photodestruction. Moreover, the presence of phosphatidylglycerol or cardiolipin enhanced the PSII resistance to the photobleaching phenomenon, mainly at lower temperatures.     

The electrochemical behavior of a system with a limited number of molecules

In this paper, based on Einstein relationship between diffusion and random walk, the electrochemical behavior of a system with a limited number of molecules was simulated and explored theoretically. The transition of the current vs time responses from discrete to continuous was clearly obtained as the number of redox molecules increased from 10 to 10⁶. By correlation analysis between the simulation results and the results of analytical expressions, a quantized extent parameter was proposed to investigate the underlying rules of these discrete signals, which looked stochastic. The results revealed that this parameter would be useful to describe such systems.     

Investigation of the carrier saturation in facilitated transport of unsaturated hydrocarbons

Single-component facilitated transports of ethylbenzene, styrene, cyclohexene and 1-hexene were carried out using the feed concentrations ranging from 0.5 M to pure. Equilibrium constants of the Ag⁺-solute complex formation, determined by distribution method, were 0.7, 2.2, 32.0, 129.1 M⁻¹, respectively. Carrier saturation was not found with the membrane incorporated with 2.67 M Ag⁺-ion. As the carrier concentration was reduced to 0.51 M, increase in the feed concentration beyond 4.5 M had very little effect on ethylbenzene flux, suggesting the onset of carrier saturation. Styrene and cyclohexene underwent the carrier saturation when the carrier loading was 0.25 M, while a complete saturation was not observed with 1-hexene. Extraction of solute from the membranes revealed that less than 50% of Ag⁺-ions were occupied when the carrier saturation occurred. It was also found that the ability of solute to use available Ag⁺-ions in the membrane was dependent on the equilibrium constant.     

Determination of Gossypol in Trace Level by Flow Injection Analysis with Chemiluminescence Detection

Gossypol, [1, 1′, 6, 6′, 7,7′-hexahydroxyl-5,5′-diisopropyl-3,3′-dimethyl-(2,2′-binaphtha- lene)-8,8′-dicarboxaldehyde] is a polyphenolic yellow compound naturally occurring in various parts of cotton plants1. The compound has been associated with     

Fluorescence energy transfer-sensitized photobleaching of a fluorescent label as a tool to study donor-acceptor distance distributions and dynamics in protein assemblies: studies of a complex of biotinylated IgM with streptavidin and aggregates of concanavalin A

A photokinetic method of detection of fluorescence resonance energy transfer (FRET) between special fluorescent labels is applied to study time-averaged spatial distribution of labeled proteins in protein assemblies. Prolonged irradiation of a sample at the absorption maximum of the energy donor initiates FRET-sensitized fluorescence photobleaching of the energy acceptor label, which was monitored by steady-state fluorimetric measurements. Kinetics of the acceptor photobleaching and kinetics of decreasing the efficiency of FRET from donors to unbleached acceptors were determined. The FRET efficiency was found from measuring sensitization of acceptor fluorescence. Analysis of the photokinetic data permits to estimate the time-averaged distribution of acceptors on donor-acceptor distances in the range of characteristic distances of FRET. Dynamic processes influencing donor-acceptor distances can be also investigated by the method. Application of the method is demonstrated by the studies of a complex of biotinylated IgM with streptavidin and aggregates composed of concanavalin A and sodium dodecyl sulphate. A new thiadicarbocyanine dye was used as the acceptor label. R-phycoerythrin and tetramethylrhodamine isothiocyanate were the donor labels. In the IgM-streptavidin complex, 16% of acceptors most contributed to FRET provided 90% of FRET efficiency, whereas acceptors made about the same time-averaged contribution to FRET in the concanavalin A aggregates.     

Dependence on effective saturation of numbers of singlet peaks in one- and two-dimensional separations

The average numbers of singlet peaks in one-dimensional (1D) and two-dimensional (2D) separations of randomly distributed peaks are predicted by statistical-overlap theory and compared against the effective saturation. The effective saturation is a recently introduced metric of peak crowding that is more practitioner-friendly than the usual metric, the saturation. The effective saturation absorbs the average minimum resolution of statistical-overlap theory, facilitating the comparison of 1D and 2D separations by traditional metrics of resolution and peak capacity. In this paper, singlet peaks are identified with maxima produced by a single mixture constituent. Their effective saturations are calculated from published equations for the average minimum resolution of 1D singlet peaks, and from equations derived here for the average minimum resolution of 2D singlet peaks. The fractions of peaks that are singlets in 1D and 2D separations are predicted by statistical-overlap theory as functions of saturation but are compared as functions of effective saturation. The two fractions differ by no more than 0.033 at any effective saturation between 0 and 6, when the distribution of peak heights is exponential and the edge effect is neglected. This result shows that 1D and 2D separations of randomly distributed peaks are about the same in their ability to separate singlet peaks as maxima, when assessed relative to effective saturation. Empirical equations in effective saturation are reported for the fractions of peaks that are singlets. It is argued that the effective saturation is a good metric for comparing separations having different average minimum resolutions.     

Self-assembling bacterial pores as components of nanobiosensors for the detection of single peptide molecules

Nano-sized bacterial pores were inserted into a lipid membrane as a nanobiosensor for the detection of single peptide molecules. Due to the intrinsic properties of single-channel conductance, the transit of individual molecules through the pore can be studied. The analysis of both the blockage current and duration is able to provide specific structural information and allows the detection of specific peptides in bulk mixtures. Supported by the National Natural Science Foundation of China (Grant No. 20875030) and the Shuguang Project of Shanghai (Grant No. 07SG36)     

Spectral imaging of single molecules by transmission grating-based epi-fluorescence microscopy

A spectral imaging method of single protein molecules labeled with a single fluorophore is presented. The method is based on a transmission grating and a routine fluorescence microscope. The bovine serum alubmin (BSA) and antiBSA molecules labeled with Alexa Fluor 488 and Alexa Fluor 594, respectively, are used as the model proteins. The fluorescence of single molecules is dispersed into zeroth-order spectrum and first-order spectrum by the transmission grating. Results show that the fluorescence emission spectrum of single molecule converted from the first-order spectral imaging is in good agreement with the bulk fluorescence spectrum. The spectral resolution of 2.4 nm/pixel is obtained, which is sufficient for identifying the molecular species in a multicomponent system.     

Probing lipid vesicles by bimolecular association and dissociation trajectories of single molecules

Vesicles prepared by DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) and SOPC (1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine) lipid molecules having sizes smaller than the diffraction-limited focused laser beam have been used to confine single molecules in the laser focus. The confinement of single molecules in a volume smaller than the focused laser beam leads to a Gaussian distribution of single molecule fluorescence intensity. The interactions of single Nile Red molecules with DMPC and SOPC lipid bilayers were studied by single molecule fluorescence confocal microscopy. Nile Red molecules were observed to associate with and dissociate from individual DMPC and SOPC vesicles adsorbed on a glass surface, generating on-and-off fluctuations in a fluorescence signal representing a very low noise two-state trajectory. Off-time statistics were used to investigate the mean radius of the vesicles and the size distribution functions. The means of the on-time distributions of Nile Red in DMPC and SOPC vesicles were significantly different. The association and dissociation reactions of single Nile Red molecules with a vesicle have been studied. Features of the bimolecular interaction between the probe Nile Red and the vesicle were evaluated from the uncorrelated mean on-time and vesicle radius distributions, and the linear Nile Red concentration dependence of the mean off-time. Nile Red is shown to be a useful probe of the structural fluctuations and heterogeneity of these membrane structures, and it is a useful model with which to directly study a diffusion-influenced reversible bimolecular reaction.     

Investigation of fluorinated surfaces by means of radio-labelled probe molecules

Acid-base reactions and interactions are at the heart of inorganic fluorine chemistry and are now recognised as forming a very important part of the chemistry, catalytic or non-catalytic, that occurs on inorganic fluorinated surfaces. This review traces the use that has been made of radioactive isotopes, particularly the short-lived β⁺ emitter, fluorine-18, and the very long-lived chlorine-36, which is a β⁻ emitter, to investigate a variety of surface-related phenomena. Attention is concentrated on solid Lewis acids, including aluminium(III) fluoride derivatives, fluorinated γ-alumina and fluorinated chromia.     

Identification of individual DNA molecule of Mycobacterium tuberculosis by nested PCR-RFLP and capillary electrophoresis

The improvement of sensitivity and differentiation in rapidly identifying a small amount of mycobacteria in sputum has significant implications for reducing tuberculosis transmission. We previously applied the conventional PCR and capillary electrophoresis (CE) to establish the restriction fragment length polymorphism (RFLP) pattern of mycobacterial 65-kDa heat shock protein (hsp65) gene from colony specimens. However, the previous analysis did not provide enough sensitivity for sputum specimens in which the limitation of analysis might be hindered by PCR inhibitors and primer-dimers formation during amplification. In the current study, nested PCR (nPCR) had been redesigned for PCR-RFLP analysis (PRA) of mycobacterial hsp65 gene using CE. The results show both Mycobacterium tuberculosis complex and mycobacteria other than tuberculosis could be identified in the presence of PCR inhibitors. The interference due to primer-dimers was also minimized. Based on the Poisson distribution, the repeatability of single DNA molecule detection was greatly affected by sampling probability and might be improved significantly by increasing the sample loading. The PRA using nPCR and CE is not only able to detect the individual mycobacterial DNA molecule but also potentially differentiate the species.     

Controllable distribution of single molecules and peptides within oligomer template investigated by STM

This communication provides a facile method for distributing and dispersing molecules within a molecular template. Using the self-assembled template of oligo(phenylene-ethynylene) (OPE), organic molecules such as coronene (COR) and biomolecules such as tripeptide are controllably distributed and dispersed within this molecular template on highly oriented pyrolytic graphite (HOPG) surfaces. COR molecules were controllably distributed into various regular arrays by simply adjusting the molecular molar ratio, while tripeptide molecules were uniformly positioned at the vacancies of the OPE template.     

Determination of homogeneous vibronic spectra and the inhomogeneous distribution function of impurity molecules in solids by fluorescence saturation

Methods are developed for determining homogeneous vibronic spectra and the inhomogeneous distribution function of impurity molecules in low-temperature solid matrices by optical saturation of no-phonon transitions. The possibilities are demonstrated with solid solutions of perylene in benzophenone and n-hexane at 4.2 K.     

Sub-Doppler laser spectroscopy of molecules and clusters in cold beams

This paper illustrates, with several examples, the spectral resolution and attainable sensitivity reached with sub-Doppler laser spectroscopy in cold argon beams, seeded with molecular or metal vapors. Linear as well as nonlinear spectroscopy has been applied. The detection techniques use either LIF or resonant two-photon ionization. Examples given include NO₂, SO₂ and Na₃-molecules. The advantage of optical double resonance methods is illustrated.     

Investigation of the conformation and electronic spectra of simple organic molecules by the NDDO method

Calculations have been performed by using the semi-empirical all-valence-electron NDDO method for the molecules ethylene, formaldehyde, formyl fluoride, carbonyl fluoride, butadiene, acrolein, glyoxal, acryloyl fluoride, acrylic acid, glyoxalic acid and oxalic acid. The conformational stability of the conjugated systems were correctly reproduced with the exception of acrolein and acryloyl fluoride. The calculated dipole moments are in good qualitative agreement with the experimental values. It has been found that the ionization potentials are higher by a factor of 1.35 than the experimental ones. The singlet—singlet and singlet—triplet transition energies and oscillator strengths of ethylene, formaldehyde and formyl fluoride are presented. A factor of 1.46 is needed for good agreement with the experimental transition energies.     

Ionic effect on combing of single DNA molecules and observation of their force-induced melting by fluorescence microscopy

Molecular combing is a powerful and simple method for aligning DNA molecules onto a surface. Using this technique combined with fluorescence microscopy, we observed that the length of lambda-DNA molecules was extended to about 1.6 times their contour length (unextended length, 16.2 microm) by the combing method on hydrophobic polymethylmetacrylate coated surfaces. The effects of sodium and magnesium ions and pH of the DNA solution were investigated. Interestingly, we observed force-induced melting of single DNA molecules.     

Guided alignment and positioning of single DNA molecules by a structured contact line on a block copolymer surface

A nanostructured dynamical contact line is generated when the meniscus of a droplet of water solution is moving on the structured surface of a thin film of a block copolymer of poly(styrene-b-methyl methacrylate) (PS-b-PMMA) because of the difference in the water contact angles on PS and PMMA. Such a structured receding contact line extends DNA molecules as in the molecular combing process. More importantly, it aligns DNA molecules following the position and orientation of the PMMA domains on the surface. The driving force of this phenomenon is discussed as the lateral motion of the locally modified contact line.     

Detection of electronic and vibrational coherences in molecular systems by 2D electronic photon echo spectroscopy

Two-dimensional optical photon echo spectra are simulated for model systems which exhibit vibrational, electronic and a combination of electronic and vibrational coherent dynamics. The coherent motion manifests itself as periodic beatings of the spectrum cross-peak intensity with the population time. The intensity modulations are compared to evolution of the excited-state population and coordinate expectation value. The advantageous capabilities of the technique as well as possible difficulties in spectra interpretations are outlined. Possibilities for distinguishing electronic and vibrational coherences are discussed.     

Mechanical properties of single motor molecules studied by three-dimensional thermal force probing in optical tweezers.

A new method combining three-dimensional (3D) force measurements in an optical trap with the analysis of thermally induced (Brownian) position fluctuations of a trapped probe was used to investigate the mechanical properties of a single molecule, the molecular motor kinesin. One kinesin molecule attached to the probe was bound in a rigorlike state to one microtubule. The optical trap was kept weak to measure the thermal forces acting on the probe, which were mainly counterbalanced by the kinesin tether. The stiffness of kinesin during stretching and compression with respect to its backbone axis were measured. Our results indicate that a section of kinesin close to the motor domain is the dominating element in the flexibility of the motor structure. The experiments demonstrate the power of 3D thermal fluctuation analysis to characterize mechanical properties of individual motor proteins and indicate its usefulness to study single molecule in general     

Investigation of the self-association of proflavine and acridine orange molecules in aqueous solution by 1H NMR

The chemical shifts of the protons in the proflavine and acridine orange molecules in aqueous solution were measured by ¹H NMR spectroscopy. The equilibrium constants for the association of the molecules and the chemical shifts of the protons in the monomers and associates were obtained from the concentration dependence of the proton chemical shifts. The most probable structures for the dimers of the dyes were calculated on the basis of the obtained chemical shifts, and a comparative analysis was made.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 3, pp. 373–376, May–June, 1987.