The investigation of interaction between Thioguanine and human serum albumin by fluorescence and modeling

Using fluorescence and circular dichroism (CD) spectroscopy to investigate the interaction between di-n-butyl phthalate and bovine serum albumin

The interaction between di-n-butyl phthalate (DBP) and bovine serum albumin (BSA) in physiological Tris-HCl buffer at pH 7.4 was investigated by fluorescence quenching technique. By analyzing the fluorescence spectrum and intensity, it was observed that the DBP had a strong ability to quench the intrinsic fluorescence of BSA through a static quenching procedure. The binding constants K and the number of binding sites n of DBP with BSA were calculated to be 0.11 × 10² L·mol^-1 and 0.52 at 298 K, respectively. The thermodynamic parameters of enthalpy change (ΔH) and entropy change (ΔS) were also calculated to be positive showing that hydrophobic forces might play a major role in the binding of DBP to BSA. The binding process was spontaneous in which Gibbs free energy change (ΔG) was negative. The distance (r) between the donor (BSA) and acceptor (DBP) was calculated to be 2.02 nm based on Forster's non-radiative energy transfer theory, which indicated that the energy transfer from BSA to DBP occurs with a high possibility. The synchronous fluorescence, three-dimensional fluorescence, and circular dichroism (CD) spectra showed that the binding of di-n-butyl phthalate to BSA induced conformational changes in BSA. The interaction between DBP and BSA can help researchers better understand the nature of poisons and serve people in the right way with first aid and detoxification.

Quenching of Protein Fluorescence by Fullerenol C60(OH)36 Nanoparticles

The effect of the interaction between fullerenol C60(OH)36 (FUL) and alcohol dehydrogenase (ADH) from Saccharomyces cerevisiae and human serum albumin (HSA) was studied by absorption spectroscopy, fluorescence spectroscopy, and time-resolved fluorescence spectroscopy. As shown in the study, the fluorescence intensities of ADH and HSA at excitation wavelengths λex = 280 nm (Trp, Tyr) and λex = 295 nm (Trp) are decreased with the increase in the FUL concentration. The results of time-resolved measurements indicate that both quenching mechanisms, dynamic and static, are present. The binding constant Kb and the number of binding sites were obtained for HSA and ADH. Thus, the results indicated the formation of FUL complexes and proteins. However, the binding of FUL to HSA is much stronger than that of ADH. The transfer of energy from the protein to FUL was also proved.

Elucidation on inhibition and binding mechanism of bovine liver catalase by nifedipine: multi-spectroscopic analysis and computer simulation methods

Nifedipine (NDP), a dihydropyridine calcium antagonist, is widely used for the treatment of hypertension and angina pectoris. Catalase is a key antioxidant enzyme that is closely relevant to the level of reactive oxygen species (ROS) in vivo. Here, the research explored the effects of NDP on the conformation and catalytic function of bovine liver catalase (BLC) through enzymatic reaction kinetic techniques, multi-spectroscopic analysis and computer simulation method. Kinetic studies clarified that the NDP debased the activity of BLC by non-competitive inhibition mechanism. Based on the data of trials, it was a static quenching mechanism that functioned in the quenching of intrinsic fluorescence of BLC. The binding constant value was (4.486 ± 0.008) × 10⁴ M^-1 (298 K) and BLC had one binding site for NDP. Tyr was prone to be exposed more to a hydrophilic environment in wake of a shift in fluorescence value. The binding reaction of BLC to NDP caused the conformational alteration of BLC, which in turn led to increase of the α-helix and decline of β-sheet contents. Furthermore, several amino acids residues interacted with NDP by means of van der Waals forces, whereas Gln397, Asn368, Gln371, Asn384 and Pro377 formed several Hydrogen Bonds with NDP.

Protein-Mediated Fluorescence Resonance Energy Transfer (P-FRET) Probe: Fabrication and Hydroxyl Radical Detection

Fluorescent probes based on fluorescence resonance energy transfer (FRET) are highly promising for diverse bioapplications. The key to constructing FRET probes is to confine the donor and acceptor within a sufficiently close distance. However, the commonly used covalent linkage often requires elaborate design and complex organic synthesis, and sometimes causes changes in the fluorescence properties of the donor and acceptor. Inspired by the binding between small molecules and protein in nature, herein, we propose a protein-mediated strategy to fabricate FRET probe. In such protein-mediated FRET (P-FRET) probe, protein acts as a carrier to simultaneously confine donor and acceptor in its cavity. As a proof of concept, we use bovine serum albumin (BSA) as a model protein, coumarin derivative as a donor and hydroxyl radical (·OH)-responsive dye fluorescein as an acceptor. Through a series of investigations, including binding parameters, fluorescence properties and detection performance, we prove that the construction of P-FRET probe is simple and feasible and the detection is sensitive. Our P-FRET strategy will provide new insights for the design of FRET probes.

Development of 6-Thioguanine conjugated PLGA nanoparticles through thioester bond formation: Benefits of electrospray mediated drug encapsulation and sustained release in cancer therapeutic applications

Polymeric nanoparticle-based successful delivery of hydrophobic drugs is highly desirable for its controlled and sustained release at the disease site, which is a challenge with the current synthesis methods. In the present study, an electrospray mediated facile one-step synthesis approach is explored in which a solution mixture of a hydrophobic drug, 6-thioguanine (Tg) and a biocompatible FDA approved polymer, Poly (d, l-lactide-co-glycolide) (PLGA) is injected in an applied electric field of suitable intensity to prepare drug encapsulated PLGA nanoparticles, PLGA-Tg with high yield. In order to explore the effect of external electric field on Tg loading and delivery applications, the nanoparticles are characterized using EDX, AFM, FESEM, TEM, FTIR, Raman, fluorescence, and mass spectroscopy techniques. The characterization studies indicate that the electric field mediated synthesis exhibits spherical nanoparticles with a homogenous core size distribution of ~60 nm, high encapsulation (~97.22%) and stable conjugation of Tg (via thioester linkages) with PLGA molecules in the presence of the applied electric field. The kinetic study demonstrates the 'anomalous diffusion' (non-Fickian diffusion) release mechanism in which Tg escapes from PLGA matrix with a slow, but steady diffusion rate and the sustained drug release profile continues for 60 days. To check the biological activity of the encapsulated Tg, in-vitro cell studies of the PLGA-Tg are performed on HeLa cells. The MTT assay shows significant cell death after 48 h of treatment, and the cellular internalization of the drug-loaded nanoparticles occurs through pinocytosis mediated uptake, which is established by the AFM analysis. The Raman and mass spectroscopy studies suggest that the PLGA-Tg nanoparticles are rapidly hydrolyzed inside cell cytoplasm to release Tg which initiates apoptosis-mediated cell death confirmed by as DNA fragmentation and membrane blebbing studies. The results clearly emphasize the benefits of electrospray based synthesis of polymeric nanodrug formulation through the formation of chemical bonds between polymer and drug molecules that could be easily implemented in the design and development of an effective nanotherapeutic platform with no typical 'burst effect,' prolonged release profile, and significant toxicity to the cancer cells.

Interaction of tebuconazole with bovine serum albumin: determination of the binding mechanism and binding site by spectroscopic methods

This study investigates the interaction between tebuconazole and bovine serum albumin (BSA) in a physiological buffer (pH = 7.4) using the fluorescence quenching method to obtain the apparent binding constants (K) and number of binding sites (n) in the interaction between tebuconazole and BSA. The results revealed that tebuconazole can quench the intrinsic fluorescence of BSA through a static quenching procedure. It also shows that the thermodynamic parameters of enthalpy change (ΔH) and entropy change (ΔS) are negative, indicating that the interaction of tebuconazole with BSA is mainly driven by van der Waals forces and hydrogen bonds. The process of binding was a spontaneous process in which Gibbs free energy change was negative. The distance of r between the donor (BSA) and acceptor (tebuconazole) was calculated to be 0.68 nm based on Forster's non-radiative energy transfer theory. Analysis of synchronous fluorescence, three-dimensional fluorescence and circular dichroism (CD) spectra demonstrates that tebuconazole can induce conformational changes of BSA.