No abstract

Hydrazone derivatives possess potential antitumor activities based on modulation of the iron metabolism in cancer cell. A novel hydrazone, N'-(2,4-dimethoxybenzylidene)-2-hydroxybenzohydrazide (DBH), has been synthesized and characterized, which is an analogue of 311 possessing potent anticancer activity. The interactions between DBH and bovine serum albumin (BSA) have been investigated systematically by fluorescence, molecular docking, circular dichroism (CD), UV-vis absorption, and electrochemical impedance spectroscopy (EIS) methods under physiological conditions. The fluorescence quenching observed is attributed to the formation of a complex between BSA and DBH, and the reverse temperature effect of the fluorescence quenching has been found and discussed. The primary binding pattern is determined by hydrophobic interaction occurring in Sudlow's site I of BSA. DBH could slightly change the secondary structure and induce unfolding of the polypeptides of protein. An average binding distance of ~4.0 nm has been determined on the basis of the Förster resonance energy theory (FRET). The effects of iron on the system of DBH-BSA have also been investigated. It is found that iron could compete against BSA to bind DBH. All of these results are supported by a docking study using a BSA crystal model. It is shown that DBH can efficiently bind with BSA and be transported to the focuses needed. Subsequent antitumor test and detailed anticancer mechanism are undergoing in our lab.

Owing to their excellent photoluminescence (PL) properties, good biocompatibility, and low toxicity, graphene quantum dots (GQDs) are widely applied in bioimaging, biosensing, and so forth. However, further development of GQDs is limited by their synthetic methodology and unclear PL mechanism. Therefore, it is urgent to find efficient and universal methods for the synthesis of GQDs with high stability, controllable surface properties, and tunable PL emission wavelength. By coating with polyethyleneimine (PEI) of different molecular weights, blue-, yellow-, and red-emitting GQDs were successfully prepared. By transmission electron microscopy, atomic force microscopy, and dynamic light scattering, the characterization of size and morphology revealed that blue-emitting PEI GQDs were monocoated, like jelly beans, and red-emitting PEI GQDs were multicoated, like capsules. The amidation reaction between carboxyl and amide functional groups played an important role in the coating process, as evidenced by IR spectroscopy and theoretical calculation with density functional theory B3LYP/6-31G*. The PL-tunable GQDs exhibited an excellent chemical stability and extremely low cytotoxicity, and they had been shown to be feasible for bioimaging, making these GQDs highly attractive for a wide variety of applications, including multicolor imaging and bioanalysis.

Nanoparticles (NPs) will inevitably interact with proteins and form protein coronas once they are exposed to biological fluids.

Noble metal nanoclusters (NCs) show great promise as nanoprobes for bioanalysis and cellular imaging in biological applications due to ultrasmall size, good photophysical properties, and excellent biocompatibility. In order to achieve a comprehensive understanding of possible biological implications, a series of spectroscopic measurements were conducted under different temperatures to investigate the interactions of Au NCs (∼1.7 nm) with three model plasmatic proteins (human serum albumin (HSA), γ-globulins, and transferrin). It was found that the fluorescence quenching of HSA and γ-globulins triggered by Au NCs was due to dynamic quenching mechanism, while the fluorescence quenching of transferrin by Au NCs was a result of the formation of a Au NC-transferrin complex. The apparent association constants of the Au NCs bound to HSA, γ-globulins, and transferrin demonstrated no obvious difference. Thermodynamic studies demonstrated that the interaction between Au NCs and HSA (or γ-globulins) was driven by hydrophobic forces, while the electrostatic interactions played predominant roles in the adsorption process for transferrin. Furthermore, it was proven that Au NCs had no obvious interference in the secondary structures of these three kinds of proteins. In turn, these three proteins had a minor effect on the fluorescence intensity of Au NCs, which made fluorescent Au NCs promising in biological applications owing to their chemical and photophysical stability. In addition, by comparing the interactions of small molecules, Au NCs, and large nanomaterials with serum albumin, it was found that the binding constants were gradually increased with the increase of particle size. This work has elucidated the interaction mechanisms between nanoclusters and proteins, and shed light on a new interaction mode different from the protein corona on the surface of nanoparticles, which will highly contribute to the better design and applications of fluorescent nanoclusters.