Investigations of interaction mechanism and conformational variation of serum albumin affected by artemisinin and dihydroartemisinin.

In this work, binding interactions of artemisinin (ART) and dihydroartemisinin (DHA) with human serum albumin (HSA) and bovine serum albumin (BSA) were investigated thoroughly to illustrate the conformational variation of serum albumin. Experimental results indicated that ART and DHA bound strongly with the site I of serum albumins via hydrogen bond (H-bond) and van der Waals force and subsequently statically quenched the intrinsic fluorescence of serum albumins through concentration-dependent manner. The quenching abilities of two drugs on the intrinsic fluorescence of HSA were much higher than the quenching abilities of two drugs on the intrinsic fluorescence of BSA. Both ART and DHA, especially DHA, caused the conformational variation of serum albumins and reduced the α-helix structure content of serum albumins. DHA with hydrophilic hydroxyl group bound with HSA more strongly, suggesting the important roles of the chemical polarity and the hydrophilicity during the binding interactions of two drugs with serum albumins. These results reveal the molecular understanding of binding interactions between ART derivatives and serum albumins, providing vital information for the future application of ART derivatives in biological and clinical areas.

Investigation on conformational variation and enzymatic activity of trypsin affected by Ti3C2 QDs via spectroscopic technique and molecular modeling.

In this paper, Ti3C2 quantum dots (Ti3C2 QDs) were synthesized by simply treating Ti3C2 MXene powder with acid and base via hydrothermal method. Ti3C2 QDs exhibited superior fluorescence property and were used for the fluorescent imaging of living HeLa cells successfully. In order to evaluate the influence of Ti3C2 QDs on protease with specific biological functions, binding interaction of Ti3C2 QDs with trypsin was studied comprehensively and deeply through spectroscopic strategies and molecular modeling technique. The intrinsic fluorescence of trypsin was spontaneously quenched by Ti3C2 QDs through static quenching mode under van der Waals interaction force, and Ti3C2 QDs bound with the inactive residue domain of trypsin firmly with stoichiometric ratio of 1:1. Ti3C2 QDs induced the microenvironmental variation of the amino acid residues in trypsin, reducing the thermal stability of trypsin significantly. Gel electrophoresis experiments and microscopic imaging experiments demonstrated that Ti3C2 QDs inhibited the enzymatic activity of trypsin on the digestion of human serum albumin and HeLa cells obviously. These results revealed not only the deep interaction mechanism between Ti3C2 QDs and protease but also the influence of Ti3C2 QDs on the enzymatic activity of trypsin, paving the way for the safe biological application of Ti3C2 QDs in the diagnosis and the therapy of protease-related diseases.

Investigation on conformational variation and fibrillation of human serum albumin affected by molybdenum disulfide quantum dots.

In this work, binding interaction between molybdenum disulfide quantum dots (MoS2 QDs) and human serum albumin (HSA) was researched deeply to dissect the conformational variation and fibrillation of HSA affected by MoS2 QDs. The results revealed that MoS2 QDs bound strongly with HSA with molar ratio of 1:1 under the joint actions of hydrogen bond and van der Waals force, leading to the static fluorescence quenching of HSA. MoS2 QDs caused the secondary structure transition of HSA from α-helix stepwise to ß-turn, ß-sheet, and random coil gradually. MoS2 QDs reduced both the molar enthalpy change and the melting temperature of HSA, reducing the thermal stability of HSA significantly. It is worth noting that MoS2 QDs inhibited the fibrillation process of HSA according to the reduced hydrophobic environment and the disturbance of disulfide bonds in HSA network structure. These results reveal the precise binding mechanism of MoS2 QDs with HSA at molecular level, providing indispensable information for the potential application of MoS2 QDs in biological fields.

Comparison on binding interactions of quercetin and its metal complexes with calf thymus DNA by spectroscopic techniques and viscosity measurement.

Quercetin (Qu) and its metal complexes have received great attention during the last years, due to their good antioxidant, antibacterial, and anticancer activities. In this contribution, binding interactions of Qu and Qu-metal complexes with calf thymus DNA (ctDNA) were investigated and compared systematically by using spectroscopic techniques and viscosity measurement. UV-vis absorption spectra of ctDNA-compound systems showed obvious hypochromic effect. Relative viscosity and melting temperature of ctDNA increased after the addition of Qu and Qu-metal complexes, and the change tendency is Qu-Cr(III) > Qu-Mn(II) > Qu-Zn(II) > Qu-Cu(II) > Qu. Fluorescence competition experiments show that hydrogen bonds and van der Waals interaction play an important role in the intercalative binding of Qu and Qu-metal complexes with ctDNA. Qu and Qu-metal complexes could unwind the right-handed B-form helicity of ctDNA and further affect its base pair stacking. Space steric hindrance might be responsible for the differences in the intercalative binding between ctDNA and different Qu-metal complexes. These results provide new information for the molecular understanding of binding interactions of Qu-metal complexes with DNA and the strategy for research of structural influences.

Investigation on conformational variation and activity of trypsin affected by black phosphorus quantum dots via multi-spectroscopy and molecular modeling.

Binding interaction between black phosphorus quantum dots (BPQDs) and trypsin was researched deeply to illustrate the variations on conformation and activity of trypsin affected by BPQDs via multi-spectroscopy and molecular modeling. Experimental results implied that inherent fluorescence of trypsin was quenched by BPQDs via static fluorescence quenching mode. BPQDs bound with trypsin to construct ground-state complex under the binding forces of van der Waal interaction and hydrophobic interaction, resulting in the conformational change of trypsin to be more hydrophilic and incompact. The result of molecular modeling indicated that BPQDs interacted with trypsin at its allosteric site and inhibited the activity of trypsin via non-competitive manner. Finally, BPQDs efficiently inhibited the digestion activity of trypsin on human serum albumin, human cervical carcinoma HeLa cells, and human lung adenocarcinoma A549 cells. This work not only explores the in-depth understanding on the influence of BPQDs on proteinases but also paves the way for further application of BPQDs on human beings for diseases treatments.

Comparative study of binding interactions between three organometallic rhodium(III) complexes with curcuminoid ligands and human serum albumin.

Organometallic rhodium(III) complexes with curcuminoid ligands attracted considerable attention in biological-related fields and the variation of curcuminoid ligands may regulate the biological activity of these organometallic rhodium(III) complexes. To deeply evaluate the biological influences of these complexes, the binding interactions between three rhodium(III) complexes with curcuminoid ligands and human serum albumin (HSA) were comparably investigated by spectroscopic and electrochemical techniques. The results suggested that the intrinsic fluorescence of HSA was quenched by three complexes through static fluorescence quenching mode. Three complexes bonded with Sudlow's site I of HSA to form ground-state compounds under the binding forces of van der Waals interactions, hydrogen bonds formation, and protonation. Finally, the native conformational structure and the thermal stability of HSA were all changed. Space steric hindrance of complexes took part in the differences of the fluorescence quenching processes, and the chemical polarity of the complexes played a vital role in the variations of the structure and biological activity of HSA. These results illustrated the molecular interactions between protein and organometallic rhodium(III) complexes with curcuminoid ligands, offering new insight about the prospective applications of analogical rhodium(III) complexes in biomedicine areas.

Conformational structure variation of human serum albumin after binding interaction with black phosphorus quantum dots.

Herein, binding interaction between black phosphorus quantum dots (BPQDs) and human serum albumin (HSA) was systematically characterized for deep illustration of conformational structure variation of HSA affected by BPQDs. The results confirmed that the intrinsic fluorescence of HSA was statically quenched by BPQDs mainly through van der Waals interaction and hydrogen bond. BPQDs bound strongly with the site I of HSA to form ground state complex with molar ratio of 1 to 1. The secondary structure of HSA was changed obviously after its binding interaction with BPQDs, and the α-helix structure of HSA was transformed to the ß-sheet structure. The melting temperature of HSA was decreased after its binding interaction with BPQDs, suggesting that BPQDs promoted the thermal denaturation process of HSA. BPQDs could also reduce the molar enthalpy change and the thermal stability of HSA. These results explored the exact conformational structure variation of HSA after its binding interaction with BPQDs, which provides vital information for possible biological influence of BPQDs on human beings.

Effect of composite biological preservative containing Lactobacillus plantarum on postharvest litchi quality.

Biological preservatives containing live microorganisms are environmentally friendly and non-toxic substances used to preserve the quality of fresh fruits. This study investigated whether a composite biological preservative containing live Lactobacillus plantarum (designated as DN003) could preserve the quality of postharvest litchi fruits at high temperature and in humid environment. Postharvest litchi fruits were briefly soaked in DN003, then dried and stored at 29-33°C with 95-98% relative humidity; prochloraz treatment was included as positive control and non-treatment as negative control. In comparison with negative control group, litchi fruits in both DN003-treated and positive control groups better retained their appearance with lower polyphenol oxidase and peroxidase activities and showed higher concentrations of vitamin C, titratable acids, and total sugar content. These data demonstrated that the new composite biological preservative containing L. plantarum is promising to be used in the preservation of postharvest litchi fruit, particularly in high-temperature and humid environment.