Properties and potential applications of bioconjugates of R-phycoerythrin with Ag° or CdS nanoparticle synthesized in its tunnel cavity: A review.

Green synthesis is a promising method for the preparation of nanoparticles (NPs) due to its simplicity, low cost, low toxicity, and environmental friendliness. Biosynthesized NPs exhibit multifunctional activity, good biocompatibility, and higher anticancer and antibacterial activity compared to chemically synthesized NPs. R-phycoerythrin, a photosynthetic light-harvesting pigment of protein nature (M.w. 290 kDa), is an attractive platform for the synthesis of small sizes NPs due to its structural features, non-toxicity, water solubility. Photosensitive bioconjugates of R-phycoerythrin with NPs were prepared by synthesizing Ag° and CdS NPs in tunnel cavities of R-phycoerythrin (3.5 × 6.0 nm) isolated from the red seaweed Callithamnion rubosum. The review is devoted to the physical processes and chemical reactions that occur in the native protein macromolecule of a complex structure during the synthesis of a NP in its cavity. The influence of Ago and CdS NPs on the electronic processes caused by the absorption of photons, leading to reversible and irreversible changes in R-phycoerythrin has been analyzed. Properties of R-phycoerythrin bioconjugates Ag° and CdS with NPs combined with the literature data suggest potential applications of Ag°â‹…PE and CdS⋅PE bioconjugates for cancer diagnosis, treatment, and monitoring as well as for realizing theranostic strategy in the future. The use of these bioconjugates in anticancer therapy may have synergistic effects since both R-phycoerythrin and NPs induce cancer cell death.

Two Distinct Photoprocesses in Cyanobacterial Bilin Pigments: Energy Migration in Light-Harvesting Phycobiliproteins versus Photoisomerization in Phytochromes.

The evolution of oxygenic photosynthesis, respiration and photoperception are connected with the appearance of cyanobacteria. The key compounds, which are involved in these processes, are tetrapyrroles: open chain - bilins and cyclic - chlorophylls and heme. The latter are characterized by their covalent bond with the apoprotein resulting in the formation of biliproteins. This type of photoreceptors is unique in that it can perform important and opposite functions-light-harvesting in photosynthesis with the participation of phycobiliproteins and photoperception mediated by phycochromes and phytochromes. In this review, cyanobacterial phycobiliproteins and phytochrome Cph1 are considered from a comparative point of view. Structural features of these pigments, which provide their contrasting photophysical and photochemical characteristics, are analyzed. The determining factor in the case of energy migration with the participation of phycobiliproteins is blocking the torsional relaxations of the chromophore, its D-ring, in the excited state and their freedom, in the case of phytochrome photoisomerization. From the energetics point of view, this distinction is preconditioned by the height of the activation barrier for the photoreaction and relaxation in the excited state, which depends on the degree of the chromophore fixation by its protein surroundings.

Ag0 Nanoparticles Synthesized in R-phycoerythrin: Change in Bioconjugate Properties upon Ripening of Nanoparticles.

BACKGROUND: Bioconjugates prepared from photoactive molecules and metal nanoparticles are suitable for the development of new optoelectronic devices and for theranostic applications in medicine. METHODS: We produced a bioconjugate of R-phycoerythrin (R-PE), a photosynthetic pigment of red algae, with Ag0 nanoparticles (Ag0 NPs) synthesized in its tunnel cavities by mixing aqueous solutions of AgNO3 and R-PE without exogenous reductant. In freshly prepared bioconjugate (Ag0⋅R-PE), the diameter of Ag0 NPs measured in electron microscopic images was 6.5 ± 0.5 nm, being commensurate with the length of R-PE tunnel cavity, and they were found to emit bright visible fluorescence. RESULT: The initial aggregation temperature (T0) of freshly prepared Ag0⋅R-PE was decreased, compared to that of native R-PE (33 vs. 44°C). Upon the ripening of Ag0 NPs, their fluorescence was almost entirely quenched, and giant surface-enhanced Raman scattering was recorded. The bioconjugate self-assembled into nanorods 25 ± 5 nm long and could withstand heating to 90°C. Further heating (90°C → 100°C) resulted in the formation of filaments which are 0.5 ± 0.2 µm long and spherical aggregates 60 ± 10 nm in diameter. CONCLUSION: These data can contribute to the development of practical applications for the Ag0⋅R-PE bioconjugate.

The Photovoltaic Effect of CdS Quantum Dots Synthesized in Inverse Micelles and R-Phycoerythrin Tunnel Cavities.

CdS quantum dots (CdS QDs) 4.3 nm in diameter synthesized in an AOT/isooctane/water microemulsion and in R-phycoerythrin tunnel cavities (3.5 × 6.0 nm) were analyzed for photoelectrochemical properties. The CdS QDs preparations were applied onto a platinum electrode to obtain solid films. Experiments were performed in a two-section vessel, with one section filled with ethanol and the other, with 3 M KCl. The sections were connected through an agar stopper. It was found that illumination of the films resulted in a change of the electrode potential. The magnitude of this change and the kinetics of the appearance and disappearance of the photopotential, i.e., the difference between the electrode potential on the light and in dark, depended on the nature of the QD shell. The photovoltaic effect of CdS QDs in R-phycoerythrin, compared to that of CdS QDs in AOT/isooctane micelles, is three to four times greater due to the photosensitizing action of R-phycoerythrin. The photosensitized effect was markedly higher than the photoelectric sensitivity of R-phycoerythrin and had the opposite polarity. Changes in the potential upon turning the light on and off could be observed repeatedly.