Combined voltammetric and spectroscopic investigation of binding interaction between nifedipine and human serum albumin on polyelectrolyte modified ITO electrode

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.

Introduction of a thrombin sensor based on its interaction with dabigatran as an oral direct thrombin inhibitor

Dabigatran (DAB) is a direct thrombin inhibitor used for preventing blood clots and emboli after orthopedic surgery. The DAB - thrombin interaction was followed by fluorescence and UV-Vis spectroscopic methods. The binding of DAB to thrombin was also modeled by the molecular docking method. The obtained experimental results were consistent with theoretical results. The voltammetric method was also tested for DAB - thrombin interaction. Based on voltammetric findings, carbon paste electrode containing graphite powder, paraffin oil, MWCNTs, and DAB was constructed and used for thrombin monitoring after investigation of the DAB oxidation mechanism for the first time. The decrease in the linear sweep voltammetric (LSV) peak current of DAB in the presence of thrombin was utilized for the thrombin analysis. The calibration plot was linear in the concentration range of 1 to 70 nM (R² = 0.9992) by LSV technique with a detection limit of 0.3 nM. The applicability of the proposed sensor was evaluated by the determination of thrombin in human serum as a real sample.

Competitive binding of Chlorin p6 and Dansyl-l-Proline to Sudlow's site II of human serum albumin

The binding of chlorin p6, a model photosensitizer for photodynamic therapy (PDT), to the Sudlow's site II of Human Serum Albumin (HSA) has been monitored by different spectroscopic methods. Displacement of Dansyl-l-Proline (DP) from its conjugate with HSA is manifested in the spectral shift and decrease in its fluorescence intensity as well as the emergence of component with lifetime of 2-3ns, which is characteristic of free DP. As DP is known to bind specifically to the Sudlow's site II of human serum albumin, its displacement by chlorin p6 indicates the residence of the photosensitizer in the same site, in addition to Sudlow's site I. The binding constants for Sudlow's site II, determined by the stopped-flow technique, are found to be two orders of magnitude smaller than that for Sudlow's site I.

Magnetic nanoparticles-serum proteins bioconjugates for binding of irinotecan

The binding of irinotecan to serum proteins (hemoglobin, globulin and human serum albumin) was studied on the surface of epoxide modified superparamagnetic iron oxide nanoparticles (GPTS-SPIONs), which were synthesized by the coprecipitation of ferrous and ferric salts with NH4OH and then modified with [3-(2,3-epoxypropoxy)propyl] trimethoxy silane (GPTS) to obtain functional epoxide groups on the SPIONs' surface. Results were compared to find an alternative as drug carries system. Data showed that binding amount of human serum albumin (HSA), globulin (Glb) and hemoglobin (Hb) found to be as 44, 21.2 and 32.6 μg per 20 mg of GPTS modified SPIONs, respectively. The thermal behavior of the serum protein-Ir interaction on GPTS-SPIONs was also studied by using thermo gravimetric analysis (TGA) technique and then the kinetic parameters for the thermal decomposition were determined using Horowitz-Metzger method.

Biosensor utilizing a liquid crystal/water interface functionalized with poly(4-cyanobiphenyl-4'-oxyundecylacrylate-b-((2-dimethyl amino) ethyl methacrylate))

The interface between the nematic liquid crystal, 4-cyano-4'-pentylbiphenyl (5CB) and water within a transmission electron microscopy (TEM) grid cell coated with the pH-dependent weak cationic amphiphilic block copolymer poly((4-cyanobiphenyl-4'-oxyundecylacrylate)-b-((2-dimethyl amino) ethyl methacrylate)) (LCP-b-PDMAEMA) (which was successfully synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization) was subsequently evaluated for protein and deoxyribonucleic acid (DNA) detection. The LCP-b-PDMAEMA monolayer was fabricated using a Langmuir Blodgett trough, transferred to the 5CB-filled TEM grid, and placed on the octadecyltrichlorosilane-coated glass (TEMPDMAEMA) in such a way that the LCP chains were immersed in the 5CB while the PDMAEMA chains were pointed away from the 5CB surface and immersed in water. Several model proteins such as bovine serum albumin (BSA), hemoglobin (Hb), and chymotrypsinogen (ChTg) were tested at pH values ranging from 2 to 12 to determine the role of the charge state of the protein on protein detection by a weak polyelectrolyte such as PDMAEMA. PDMAEMA contains cationic and neutral states below and above the pKa value, respectively, and is thus able to absorb proteins below its pKa threshold through electrostatic interactions. BSA exhibited a homeotropic to planar (H-P) change in orientation within the TEMPDMAEMA grid cell at concentrations greater than 0.02wt% within the pH range between the isoelectric point (pI) of BSA and the pKa of PDMAEMA, where the charge states of BSA and PDMAEMA were negative and positive, respectively. However, this change in orientation did not occur with other proteins that exhibited a pI higher than the pKa of PDMAEMA due to the electrostatic repulsions resulting from their same cationic charges. This result indicates that the electrostatic interactions between proteins and PDMAEMA are a major contributing factor for protein detection by the H-P transformation within the TEMPDMAEMA grid cell. DNA, a pH-independent strong anionic polyelectrolyte, was also tested with the TEMPDMAEMA grid cell, and it exhibited an H-P transformation at the charged state of PDMAEMA below its pKa threshold at concentrations higher than 0.01wt%. Thus, we demonstrated that the TEMPDMAEMA grid cell effectively facilitated the detection of negatively charged biomaterials (i.e.; protein and DNA) through the H-P transformation using the polarized optical microscope. This simple and inexpensive experimental set-up for non-specific biomaterial detection lays the basic groundwork for developing effective biosensors using polyelectrolytes.