Fluorescence properties of Phycocyanin and Phycocyanin-human serum albumin complex

In this work, the fluorescence properties of Phycocyanin (PC) and the corresponding quenching effects are investigated in attendance of human serum albumin (HSA). At first, PC is excited at 532 nm using CW SHG Nd:YAG laser, then the emission wavelength, Stokes shift, quantum yield, extinction constant and self-quenching coefficient are obtained based on the modified Beer-Lambert equation. It is shown that a notable red shift appears in terms of PC concentration. According to the fluorescence spectra, the addition of HSA in PC solution leads to a significant reduction in the fluorescence signal via quenching events, however a lucid blue shift takes place in the same time. Stern-Volmer formalism is used to determine the quenching constant (K_S), the number of binding sites (n) between PC and HSA as well as the association constant K_a for the purpose of facile transportation to the target in the context of drug delivery. Eventually, temperature dependent coefficients and corresponding spectral shifts are investigated over a wide range of temperatures at a couple of distinct PC concentrations to attest the dominant static quenching takes place. The rate of conjugate formations elevates at low temperatures leading to a certain blue shift. Furthermore, large K_S is measured in the course of signal reduction, particularly at low PC populations. In fact, PC conjugation to HSA is essential interaction to enhance chemo drug transportation. Here, at the body temperature, the quenching coefficient decreases to facilitate the drug release. Moreover, the spectral shift of fluorescence emission can be useful for simultaneous monitoring and drug delivery treatment.

A comparative study of the photosynthetic capacity in two green tide macroalgae using chlorophyll fluorescence

Green tides have occurred in the Yellow Sea, China, every year from 2007 to 2015. The free-floating Ulva prolifera (Müller) J. Agardh was the causative macroalgal species. The co-occurring, attached U. intestinalis was also observed. Photosynthetic capacities were determined using chlorophyll fluorescence in situ and after 7 days lab acclimation, and a significant differences were noted. Pigment composition showed no obvious differences, but concentrations varied significantly, especially chlorophyll b in U. prolifera two times increase was observed after acclimation. The optimal photochemical efficiency of PS II (Fv/Fm) was significantly higher in U. prolifera. Photosynthetic rate (α), maximum relative electron transport rate (rETRmax), and minimum saturating irradiance (Ek), obtained from rapid light response curves (RLCs), showed almost the same photosynthetic physiological status as Fv/Fm. Quenching coefficients and low temperature (77 K) chlorophyll fluorescence emission spectra of thylakoid membranes analysis showed U. prolifera has a better recovery activity and plasticity of PSII than U. intestinalis. Furthermore, energy dissipation via non-photochemical quenching (NPQ) and state transitions showed efficacious photoprotection solution especially in U. prolifera suffered from the severe stresses. Results in the present study suggested that U. prolifera’s higher photosynthetic capacity would contribute to its free-floating proliferation, and efficacious photoprotection in addition to favorable oceanographic conditions and high nutrient levels support its growth and aggregation.