Yan Lu

Proanthocyanidins are a mixture of monomers, oligomers, and polymers of flavan-3-ols that are widely distributed in the plant kingdom. One of the most widely studied proanthocyanidins is procyanidin B3. In this study, the interaction between procyanidin B3 and bovine serum albumin (BSA) was investigated using isothermal titration calorimetry (ITC), in combination with fluorescence spectroscopy, UV-vis absorption spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, circular dichroism (CD) spectroscopy and molecular docking. Thermodynamic investigations reveal that the electrostatic interaction and hydrophobic interaction are the major binding forces in the binding of procyanidin B3 to BSA. The binding of procyanidin B3 to BSA is synergistically driven by enthalpy and entropy. Fluorescence experiments suggest that procyanidin B3 can quench the fluorescence of BSA through a static quenching mechanism. The obtained binding constants and the equilibrium fraction of unbound procyanidin B3 show that procyanidin B3 can be stored and transported from the circulatory system to reach its target organ. Binding site I is found to be the primary binding site for procyanidin B3, which is consistent with the result of molecular docking studies. Additionally, as shown by the UV-vis absorption, synchronous fluorescence spectroscopy, FT-IR and CD, procyanidin B3 may induce conformational and microenvironmental changes of BSA.

Binding of ascorbic acid (water-soluble antioxidant) and α-tocopherol (lipid-soluble antioxidant) to bovine serum albumin (BSA) has been studied using isothermal titration calorimetry (ITC), in combination with fluorescence spectroscopy, UV-vis absorption spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. Thermodynamic investigations reveal that ascorbic acid/α-tocopherol binding to BSA is driven by favorable enthalpy and unfavorable entropy, and the major driving forces are hydrogen bonding and van der Waals forces. For ascorbic acid, the interaction is characterized by a high number of binding sites, which suggests that binding occurs by a surface adsorption mechanism that leads to coating of the protein surface. For α-tocopherol, one molecule of α-tocopherol combines with one molecule of BSA and no more α-tocopherol binding to BSA occurs at concentration ranges used in this study. Fluorescence experiments suggest that ascorbic acid has predominantly a “sphere of action” quenching mechanism, whereas, for α-tocopherol, the quenching mechanism is “static quenching” and due to the formation of a ground state complex. Additionally, as shown by the UV-vis absorption, synchronous fluorescence spectroscopy, and FT-IR, ascorbic acid and α-tocopherol may induce conformational and microenvironmental changes of BSA.

A rapid, sensitive and selective fluorescence sensor for detection of Pb²⁺ was developed based on a Pb²⁺-induced G-quadruplex and graphene oxide. By using a specific G-rich DNA sequence, this strategy provided a promising alternative to Pb²⁺ determination in the presence of Hg²⁺ escaping from the use of a masking agent of Hg²⁺.

For an ideal solution, an analytical expression for the macromolecule concentration, electrolyte concentration, and solution osmotic pressure is obtained on the basis of the van’t Hoff equation and the Donnan equilibrium. The expression was further applied to a colloid solution of about 3 nm glutathione-stabilized gold nanoparticles. The concentration of the colloid solution and the average net ion charge number for each gold nanoparticle were determined with the measured osmotic pressure data. Meanwhile, the gold contents of the solutions were analyzed by means of atomic absorption spectrophotometry, and the results were combined with the determined concentration of gold nanoparticle colloids to determine that the average number of gold atoms per 3 nm gold nanoparticle is 479, which is 1/1.7 times the number of atoms in bulk metallic gold of the same size. The same proportion also occurred in the 2 nm 4-mercaptobenzoic acid monolayer-protected gold nanoparticles prepared by Ackerson et al., who utilized the quantitative high-angle annular dark-field scanning transmission electron microscope to determine the average number of gold atoms per nanoparticle (Ackerson, C. J.; Jadzinsky, P. D.; Sexton J. Z.; Bushnell, D. A.; Kornberg, R. D. Synthesis and Bioconjugation of 2 and 3 nm-Diameter Gold Nanoparticles. Bioconjugate Chem. 2010, 21, 214–218).

The binding of quercetin to lysozyme (LYSO) in aqueous solution was investigated by fluorescence spectroscopy, UV-vis absorption spectroscopy and molecular simulation at pH 7.4. The fluorescence quenching of LYSO by addition of quercetin is due to static quenching, the binding constants, K _a , were 3.63 × 10⁴, 3.31 × 10⁴ and 2.85 × 10⁴ L·mol⁻¹ at 288, 298 and 308 K, respectively. The thermodynamic parameters, enthalpy change, ∆H, and entropy change, ∆S, were noted to be −7.56 kJ·mol⁻¹ and 61.07 J·mol⁻¹·K⁻¹. The results indicated that hydrophobic interaction may play a major role in the binding process. The distance r between the donor (LYSO) and acceptor (quercetin) was determined as 3.34 nm by the fluorescence resonance energy transfer. The synchronous fluorescence spectroscopy showed the polarity around the tryptophan residues increased and the hydrophobicity decreased. Furthermore, the study of molecular simulation indicated that quercetin could bind to the active site (a pocket made up of 24 amino-acid residues) of LYSO mainly via hydrophobic interactions and that there were hydrogen interactions between the residues (Gln 57, Ile 98) of LYSO and quercetin. The accessible surface area (ASA) calculation verified the important roles of tryptophan (Trp) residues during the binding process.

This study was designed to examine the interaction of 4′-O-(a-L-Cladinosyl) daunorubicin (DNR–D5), a disaccharide anthracycline with calf thymus deoxyribonucleic acid (ctDNA) by UV/Vis in combination with fluorescence spectroscopy and molecular modeling techniques under physiological conditions (Britton–Robinson buffer solutions, pH = 7.4). By the analysis of UV/Vis spectrum, it was observed that upon binding to ctDNA the anthraquinone chromophore of DNR–D5 could slide into the base pairs. Moreover, the large binding constant indicated DNR–D5 had a high affinity with ctDNA. At the same time, fluorescence spectra suggested that the quenching mechanism of the interaction of DNR–D5 to ctDNA was a static quenching type. The binding constants between DNR–D5 and ctDNA were calculated based on fluorescence quenching data at different temperatures. The negative ∆G implied that the binding process was spontaneous, and negative ∆H and negative ΔS suggested that hydrogen bonding force most likely played a major role in the binding of DNR–D5 to ctDNA. Moreover, the results obtained from molecular docking corroborate the experimental results obtained from spectroscopic investigations.