Bicarbonate Activation of Monomeric Photosystem II-PsbS/Psb27 Complex

In thylakoid membranes, Photosystem II monomers from the stromal lamellae contain the subunits PsbS and Psb27 (PSIIm-S/27), while Photosystem II monomers from granal regions (PSIIm) lack these subunits. Here, we have isolated and characterised these two types of Photosystem II complexes. The PSIIm-S/27 showed enhanced fluorescence, the near-absence of oxygen evolution, as well as limited and slow electron transfer from QA to QB compared to the near-normal activities in the granal PSIIm. However, when bicarbonate was added to the PSIIm-S/27, water splitting and QA to QB electron transfer rates were comparable to those in granal PSIIm. The findings suggest that the binding of PsbS and/or Psb27 inhibits forward electron transfer and lowers the binding affinity for the bicarbonate. This can be rationalized in terms of the recently discovered photoprotection role played by bicarbonate binding via the redox tuning of the QA/QA?- couple, which controls the charge recombination route, and this limits chlorophyll triplet mediated 1O2 formation (Brinkert K et al. (2016) Proc Natl Acad Sci U S A. 113(43):12144-12149). These findings suggest that PSIIm-S/27 is an intermediate in the assembly of PSII in which PsbS and/or Psb27 restrict PSII activity while in transit, by using a bicarbonate-mediated switch and protective mechanism.

Single Molecule Techniques Can Distinguish the Photophysical Processes Governing Metal-Enhanced Fluorescence

<p>Plasmonic metal nanoparticles can impact the behaviour of organic molecules in a number of ways, including enhancing or quenching fluorescence. Only through a comprehensive understanding of the fundamental photophysical processes regulating nano-molecular interactions can these effects be controlled, and exploited to the fullest extent possible. Metal-enhanced fluorescence (MEF) is governed by two underlying processes, increased rate of fluorophore excitation and increased fluorophore emission, the balance between which has implications for optimizing hybrid nanoparticle-molecular systems for various applications. We report groundbreaking work on the use of single molecule fluorescence microscopy to distinguish between the two mechanistic components of MEF, in a model system consisting of two analogous boron dipyrromethene (BODIPY) fluorophores and triangular silver nanoparticles (AgNP). We demonstrate that the increased excitation MEF mechanism occurs to approximately the same extent for both dyes, but that the BODIPY with the higher quantum yield of fluorescence experiences a greater degree of MEF via the increased fluorophore emission mechanism, and higher overall enhancement, as a result of its superior ability to undergo near-field interactions with AgNP. We foresee that this knowledge and methodology will be used to tailor MEF to meet the needs of different applications, such as those requiring maximum enhancement of fluorescence intensity or instead prioritizing excited-state photochemistry. </p>

Single Molecule Techniques Can Distinguish the Photophysical Processes Governing Metal-Enhanced Fluorescence

<p>Plasmonic metal nanoparticles can impact the behaviour of organic molecules in a number of ways, including enhancing or quenching fluorescence. Only through a comprehensive understanding of the fundamental photophysical processes regulating nano-molecular interactions can these effects be controlled, and exploited to the fullest extent possible. Metal-enhanced fluorescence (MEF) is governed by two underlying processes, increased rate of fluorophore excitation and increased fluorophore emission, the balance between which has implications for optimizing hybrid nanoparticle-molecular systems for various applications. We report groundbreaking work on the use of single molecule fluorescence microscopy to distinguish between the two mechanistic components of MEF, in a model system consisting of two analogous boron dipyrromethene (BODIPY) fluorophores and triangular silver nanoparticles (AgNP). We demonstrate that the increased excitation MEF mechanism occurs to approximately the same extent for both dyes, but that the BODIPY with the higher quantum yield of fluorescence experiences a greater degree of MEF via the increased fluorophore emission mechanism, and higher overall enhancement, as a result of its superior ability to undergo near-field interactions with AgNP. We foresee that this knowledge and methodology will be used to tailor MEF to meet the needs of different applications, such as those requiring maximum enhancement of fluorescence intensity or instead prioritizing excited-state photochemistry. </p>

A Practical Hydrazine-Carbothioamide-Based Fluorescent Probe for the Detection of Zn2+: Applications to Paper Strip, Zebrafish and Water Samples

A practical hydrazine-carbothioamide-based fluorescent chemosensor TCC (N-(4-chlorophenyl)-2-(thiophene-2-carbonyl)hydrazine-1-carbothioamide) was applied for Zn2+ detection. TCC exhibited selective fluorescence emission for Zn2+ and did not show any interference with other metal ions. In particular, TCC was utilized for the detection of Zn2+ in paper strips, zebrafish and real water samples. TCC could detect Zn2+ down to 0.39 μM in the solution phase and 51.13 μM in zebrafish. The association ratio between TCC and Zn2+ was determined to be 2:1 by ESI-mass and Job plot. The sensing mechanism of TCC for Zn2+ was illustrated to be a chelation-enhanced fluorescence process through spectroscopic experiments and theoretical calculations.

A pyridine based Schiff base as a selective and sensitive fluorescent probe for cadmium ions with “turn-on” fluorescence responses

A new fluorescent probe based on pyridine Schiff base (2-(pyridine-2-ylmethylene)phenoxyaniline, PMPA) working with PET mechanism and chelation enhanced fluorescence (CHEF) was designed and synthesized for the selective detection of cadmium...

Nanoparticle Tracers in Reservoir-On-A-chip by Surface-Enhanced Raman Scattering - Fluorescence SERS-SEF Imaging Technology

Nanoparticles or nanocomposite fluids are injected into oil reservoirs for reservoir tracing or to improve injectivity or recovery of oil. Effective application of nanoparticles in fluid flooding still needs to be investigated. Dual-mode surface-enhanced Raman scattering (SERS) - surface-enhanced fluorescence (SEF) composite nanoparticles have been developed as nanoparticle reservoir tracers. This presentation discusses their transport and detectability in porous media, providing valuable information for understanding the role of nanoparticles in EOR process. The dual-mode surface-enhanced Raman scattering (SERS) - surface-enhanced fluorescence (SEF) composite nanoparticles are synthesized composed of Ag or Au metal cores, specific dye molecules, and a SiO2 shell materials. To optimize maximum signal enhancement of both phenomena such as SERS and SEF, the distance between core metal nanoparticles and dye molecules are precisely controlled. The synthesized composite nanoparticles barcoded with dye molecules are detectable by both fluorescence and Raman spectroscopies due to the SERS-SEF phenomena. Both fluorescence and Raman microscopic images of dye embedded surfaceenhanced Raman scattering (SERS) surface-enhanced fluorescence (SEF) composite nanoparticles in water phase successfully were collected within microfluidic reservoir-on-a-chip. The reservoir-on-a-chip utilized in this study fabricated based on reservoir rock geometry and coated with calcium carbonate. The synthesized SERS-SEF composite nanoparticles in water solution have been flooded into the microfluidic reservoir-on-a-chip and imaged for probing interfacial behavior of fluids such as liquid-liquid interfaces and studying the behavior of nanoparticles at liquid-rock interfaces. The precise synthesis method to produce the composite nanoparticles has been developed for the embedded dye molecules to generate noticeably enhanced detectability due to the strong SERS phenomenon. In conclusion, SERS-SEF nanoparticles barcoded with the fingerprinted Raman and fluorescence signals can provide a possible pathway toward SERS-SEF nanoprobe as various barcoded tracers to understand fluid behavior in porous media. Composite nanoparticle synthesis and its detection in flow technologies have been developed for visualization of the fluid flow behavior in porous media representing reservoir rock geometry. The results of the high-resolution nanoparticle fluid imaging data in reservoir-on-a-chip can be applied to understand mechanism of nanoparticle fluid assisted chemical enhanced oil recovery.

Synthesis and Spectral Characterisation of (E)-3-(3-(4 (Dimethylamino)Phenyl)Acrylo-yl)-4-Hydroxy-2H-Chromen-2-One and Their Antibacterial Activity and Acetylcholinesterase Inhibition

A new coumarin derivative, (E)-3-(3-(4-(dimethylamino) phenyl) acrylo-yl)-4-hydroxy-2H-chromen-2-one (3), was synthesized by the condensation of 3-acetyl-4-hydroxycoumarin (1) with 4-N,N-dimethylaminobenzaldehyde (2) in the presence of piperidine in ethanol. The structure of the synthesized compound was characterized using spectroscopic data (IR and 1H NMR) and elemental analysis. The antimicrobial properties and acetylcholinesterase inhibition activity (AChEI) of coumarin 3 were investigated, with the highest observed AChEI activity providing 48.25% inhibition. The electronic absorption and emission spectra revealed that 3 exists as two, main keto-enol tautomers. The ratios of these tautomers in both protic and aprotic solvents with different polarities and dielectric constants were calculated. The fluorescence of coumarin 3 was enhanced upon increasing the medium viscosity, which was due to the resultant molecular rigidity. This criterion was further investigated using DNA, whereby 3 showed enhanced fluorescence upon its uptake in DNA grooves and was therefore tested as a novel DNA fluorescent stain.