Effect of Temperature On Re-entrant Condensation of Globular Protein in Presence of Tri-Valent Ions

Globular proteins play several essential roles in functioning different mechanisms of the living organisms, and the stability of such protein molecules in an aqueous solution is strongly affected by multivalent ions. In this article, we have systematically studied the effect of temperature (between 5 and 25ºC) on the re-entrant condensation behaviour of bovine serum albumin (BSA) in the presence of trivalent ions, Yttrium (Y3+), and Lanthanum (La3+). The effect of temperature is explained considering the optical properties of the protein, i.e., from the optical absorption and emission behaviours. The absorption in the visible region and the fluorescence emission of BSA becomes maximum at the lowest temperature. The decrement of mobility at lower temperature is responsible for fluorescence enhancement. Moreover, the activation energy of the turbid or viscus phase of the BSA protein under re-entrant condensation is enhanced in comparison with the transparent phase and the corresponding energy value is estimated from the fluorescence study.

Fluorescence Study of Riboflavin Interactions with Graphene Dispersed in Bioactive Tannic Acid

The potential of tannic acid (TA) as a dispersing agent for graphene (G) in aqueous solutions and its interaction with riboflavin have been studied under different experimental conditions. TA induces quenching of riboflavin fluorescence, and the effect is stronger with increasing TA concentration, due to π-π interactions through the aromatic rings, and hydrogen bonding interactions between the hydroxyl moieties of both compounds. The influence of TA concentration, the pH, and the G/TA weight ratio on the quenching magnitude, have been studied. At a pH of 4.1, G dispersed in TA hardly influences the riboflavin fluorescence, while at a pH of 7.1, the nanomaterial interacts with riboflavin, causing an additional quenching to that produced by TA. When TA concentration is kept constant, quenching of G on riboflavin fluorescence depends on both the G/TA weight ratio and the TA concentration. The fluorescence attenuation is stronger for dispersions with the lowest G/TA ratios, since TA is the main contributor to the quenching effect. Data obey the Stern–Volmer relationship up to TA 2.0 g L−1 and G 20 mg L−1. Results demonstrate that TA is an effective dispersant for graphene-based nanomaterials in liquid medium and a green alternative to conventional surfactants and synthetic polymers for the determination of biomolecules.

Synthesis of Dense 1,2,3-Triazole Polymers Soluble in Common Organic Solvents

Aiming at synthesis of dense 1,2,3-triazole polymers soluble in common organic solvents, a new 3-azido-1-propyne derivative, i.e., t-butyl 4-azido-5-hexynoate (tBuAH), was synthesized and polymerized by copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) and Huisgen cycloaddition (HC). CuAAC polymerization produced poly(tBuAH) composed of 1,4-disubstituted 1,2,3-triazole units (1,4-units), whereas HC polymerization gave poly(tBuAH) composed of 1,4- and 1,5-disubstituted 1,2,3-triazole units (1,4- and 1,5-units). In HC polymerization, the fraction of 1,4-unit (f1,4) decreased with the permittivity of solvent used. Differential scanning calorimetry data indicated that the melting point of poly(tBuAH) increased from 61 to 89 °C with increasing f1,4 from 0.38 to 1.0, indicative of higher crystallinity of poly(tBuAH) composed of 1,4-unit. Preliminary steady-state fluorescence study indicated that all the poly(tBuAH) samples of different f1,4 emitted weak but significant fluorescence in DMF. The maximum of fluorescence band shifted from ca. 350 to ca. 450 nm with varying the excitation wavelength from 300 to 400 nm.