Multivariate spectrochemical analysis of interactions of three common Isatin derivatives to calf thymus DNA in vitro

Inhibitory effects of polyphenols on the Maillard reaction in low lactose milk and the underlying mechanism

In this study, low lactose milk (LLM) was heat-treated under different conditions and stored at 4, 25 and 37°C for 15 d, after which the changes in the Maillard reaction (MR) of LLM were investigated. The contents of α-dicarbonyl compounds and 5-hydroxymethylfurfural(5-HMF) in LLM after the addition of polyphenols were determined via HPLC, and the inhibitory effects of 3 different concentrations of epigallocatechin gallate (EGCG), dihydromyricetin (DMY), and procyanidin (PC) on the MR of LLM were studied. The fluorescence intensity of LLM was measured at 290, 300 and 310 K, the fluorescence quenching types and binding constants of PC on casein were investigated, and thermodynamic analysis was carried out. These results suggest that the optimal heat treatment conditions were 80°C for 15 s and that the optimal storage conditions were 4°C. In the α-dicarbonyl compound capture and 5-HMF inhibition tests, PC had the greatest inhibitory effect at a concentration of 0.2 mg/mL, with an inhibition rate of 48.19%. Therefore, PC is more stable than the other 2 polyphenols. The mechanism of inhibition involves the formation of matrix complexes between PC and casein in LLM, resulting in static quenching of the LLM and thus a reduction of the inhibitory effect. The thermodynamic analysis revealed that the binding of PC to casein was an exothermic reaction, and the combination of the 2 was driven mainly by hydrogen bonding and van der Waals forces. This study lays a theoretical foundation for the development of LLM.

Assessment of binding interaction dihydromyricetin and myricetin with bovine lactoferrin and effects on antioxidant activity

The binding interactions of bovine lactoferrin (BLF) with two flavonoids dihydromyricetin (DMY) and myricetin (MY) were investigated by the multi-spectroscopic, microscale thermophoresis (MST) techniques, molecular docking, and then their antioxidant activities were studied by detection of free radical scavenging activity against DPPH. Results of UV-vis and fluorescence spectroscopies showed that DMY/MY and BLF formed the ground state complex through the static quenching mechanism. Moreover, MY with more planar stereochemical structure had higher affinity for BLF than DMY with twisted stereochemical structure, according to the binding constant (K_b), free energy change (ΔG°), dissociation constant (K_d) and donor-acceptor distance (r). Thermodynamic parameters revealed that hydrogen bond and van der Waals force were major forces in the formation of BLF-DMY complex, while hydrophobic interactions played major roles in the formation of BLF-DMY complex. The circular dichroism (CD) study indicated that MY induced more conformational change in BLF than DMY. Furthermore, molecular modeling provided insights into the difference of binding interactions between BLF and two flavonoids. Finally, the radical scavenging activity assays indicated the presence of BLF delayed the decrease in antioxidant capacities of two flavonoids. These results were helpful to understand the binding mechanism and biological effects of non-covalent BLF-flavonoid interaction.

Comprehensive study of the interaction between Puerariae Radix flavonoids and DNA: From theoretical simulation to structural analysis to functional analysis

Puerariae Radix (PR) is a natural herb whose active ingredient is mainly flavonoids. To explore the interaction between PR flavonoids and DNA not only has important biological implications for understanding the mechanism of action, but also helps develop PR products for the design of appropriate dietary interventions to aid cancer treatment. In this work, we comprehensively studied the interaction between six kinds of PR flavonoids and DNA from four different and progressive levels, including molecular docking, multi-spectral analysis, and functional analysis in vitro and in cell. Results show that the DNA binding affinity of six flavonoids is in an order of quercetin > formononetin > daidzein > puerarin > 4'-methoxy puerarin > puerarin 6″-O-xyloside (POS), in which quercetin can significantly inhibit DNA amplification owing to its strongest binding affinity. The binding between quercetin and DNA is further revealed to be intercalated binding, which can cause conformational changes in DNA, thereby exhibiting an activity of cell cycle arrest and anti-proliferative. This property of quercetin can be utilized for the further development of flavonoids with anticancer activity. In addition to the potential application, this work also provides a platform for the comprehensive study of the interaction between micromolecules and DNA.

Photocatalysed decolouration of indigo in solution via in situ generation of an organic hydroperoxide

Indigo, an emblematic violet dye used for thousands of years to colour fabric, is resistant to fading on exposure to sunlight. Prior work has indicated that indigo is reactive towards both hydroperoxyl radicals and superoxide anions in solution. In order to promote photobleaching of indigo, we have utilised a BOPHY-based (BOPHY = aryl fused symmetrical pyrrole-BF₂ complex) chromophore known to form both superoxide ions and a stable alkyl hydroperoxide under illumination in aerated solution. Selective irradiation of the photocatalyst causes relatively fast fading of indigo, with the rate increasing gently with increasing concentration of indigo. Molecular oxygen and light are essential for effective bleaching. One molecule of photocatalyst can bleach more than 40 molecules of indigo. An active component of the photocatalyst is a butylated hydroxytoluene (BHT) residue which itself quenches the triplet excited state of indigo. This provides an ancillary mechanism for effecting photofading of indigo but, because the triplet is formed in very low yield, this route is less practical.

Analysis of DNA protection, interaction and antimicrobial activity of isatin derivatives

Isatin, thiosemicarbazone and their derivatives have been widely used in biological applications such as antimicrobial, antiviral and anticancer therapies. Herein, eight isatin and thiosemicarbazone derivative compounds were re-synthesized and evaluated for DNA binding analysis including DNA protection studies using plasmid DNA (pUC19) and DNA interaction experiments using calf thymus DNA (CT-DNA). All compounds were also utilized in vitro assay to assess the antimicrobial activity of compounds against different pathogenic bacterial strains. All isatin and thiosemicarbazone derivative compounds exhibited DNA protection activity which ranged from 23.5 to 59.5%. Among them, I3-(N-2-MP)-TSC had the greatest DNA protective activity. For DNA binding analysis, all compounds had the same constant concentration (40 μM), which interacts with CT-DNA. It was also observed that DNA interactions gave a high intrinsic binding constant (Kb = 1.72 × 10⁴ M^-1-9.73 × 10⁵ M^-1). Besides, several derivatives of isatin thiosemicarbazone exhibited significant and selective antibacterial activity with low concentration. These compounds primarily affected Gram-positive bacteria, but were not effective against P. vulgaris and E. coli. The Gram-positive methicillin-resistant S. aureus ATCC 43300 (MRSA) was the most influenced strain by these compounds. It was found that methyphenyl group at isatin was essential for its antibacterial activity for MRSA.

Spectroscopic profiling and computational study of the binding of tschimgine: A natural monoterpene derivative, with calf thymus DNA

DNA is a major target for a number of anticancer substances. Interaction studies between small molecules and DNA are essential for rational drug designing to influence main biological processes and also introducing new probes for the assay of DNA. Tschimgine (TMG) is a monoterpene derivative with anticancer properties. In the present study we tried to elucidate the interaction of TMG with calf thymus DNA (CT-DNA) using different spectroscopic methods. UV-visible absorption spectrophotometry, fluorescence and circular dichroism (CD) spectroscopies as well as molecular docking study revealed formation of complex between TMG and CT-DNA. Binding constant (K_b) between TMG and DNA was 2.27×10⁴M^-1, that is comparable to groove binding agents. The fluorescence spectroscopic data revealed that the quenching mechanism of fluorescence of TMG by CT-DNA is static quenching. Thermodynamic parameters (ΔH<0 and ΔS<0) at different temperatures indicated that van der Waals forces and hydrogen bonds were involved in the binding process of TMG with CT-DNA. Competitive binding assay with methylene blue (MB) and Hoechst 33258 using fluorescence spectroscopy displayed that TMG possibly binds to the minor groove of CT-DNA. These observations were further confirmed by CD spectral analysis, viscosity measurements and molecular docking.