[Study on the aggregation behavior of cationic porphyrins and their interaction with ctDNA].

Interest in the interaction between cationic porphyrins, particularly derivatives of meso-tetra(N-methylpyridinium-4-yl) porphyrin(TMPyP), and DNA abounds because they are versatile DNA-binding agents that could find application in photodynamic therapy, cancer detection, artificial nucleases, virus inhibition and so on. The interaction of two water-soluble cationic porphyrins, meso-tetrakis(4-N, N, N-trimethylanilinium) porphyrin (TMAP) and 5-phenyl-10,15,20-tris[4-(N-methyl) pyridinium]porphyrin (TriMPyP), with calf thymus DNA (ctDNA) was studied by UV-Vis absorption spectroscopy, fluorescence spectroscopy and resonance light scattering technique. TriMPyP forms aggregate in water due to the molecular asymmetry while TMAP exists as monomers. At lower concentrations of ctDNA (R > 1, R = c(TMAP)/c(DNA) base pair), the interaction of TMAP with DNA leads to significant hypochromicity and bathochromic shift of absorption spectra. And the fluorescence of TMAP was quenched while it showed enhanced resonance light scattering signals. But the extent of enhancement of resonance light scattering signals is very small, so the aggregate of TMAP is not very high. These observations indicate the self-stacking of TMAP along the DNA surface. At higher concentrations of ctDNA (R < 1), TMAP association with DNA is via outside binding which is accompanied with hyperchromic effect and fluorescence enhancement while the resonance light scattering signals is reduced. DNA addition decreases the fluorescence intensity of TriMPyP and it shifts the peak to the higher wavelengths (red shift). The interaction with DNA promotes the aggregation of TriMPyP and no simple outside binding is observed even at higher concentrations of ctDNA. The steric effect of molecular distortion constrains the intercalation or further binding to DNA. The effect of ionic strength on the interaction was investigated at two DNA concentrations, 1.2 and 24.0 micromol x L(-1), for TMAP. The Interactions of both porphyrins with DNA show high sensitivity to ionic strength. By addition of NaCl, electrostatic attraction is decreased, resulting in the change of binding mode.

[Study on binding mechanism of meso-tetra-(3,5-dibromo-4-hydroxyphenyl) porphyrin with protein by fluorescence method].

Studies on the binding mechanism between protein and small molecules could give us lots of useful information. For example, a detailed characterization of drug-protein binding properties was essential for understanding the function of delivery, hence, interest in the mechanism of the interaction between them has attracted much research using different methods. In the present paper, the interaction mechanism between meso-tetra-(3,5-dibromo-4-hydroxyphenyl) porphyrin [T(DBHP)P] and bovine serum albumin (BSA) was investigated using fluorescence method. Based on the mechanisms of fluorescence quenching of BSA caused by T(DBHP)P, the binding constants between T(DBHP)P and BSA were measured at different temperatures. The experiment showed that T(DBHP)P and BSA have strong interactions. The binding constants of the reaction at 27 and 48 degrees C were calculated by fluorescence method, respectively. The binding constants are K = 1.30 x 10(6) L x mol(-1) at 27 degrees C, and K = 6. 32 x 10(5) L x mol(-1) at 48 degrees C. Because the binding constants decreased with increasing the temperature, the sort of quenching between T(DBHP)P and BSA was determined as static quenching. By the theory of Forster non-radiation energy transfer, the binding distance and the energy transfer efficiency at 27 degrees C between T(DBHP)P (accepter of energy) and BSA (donor of energy) were obtained to be 2.39 nm and 0.91, respectively. The binding distance was less than 7 nm, therefore, the interaction was similar to the non-radiation energy transfer, and the static quenching was further proved. According to the thermodynamic parameters, the main sorts of binding force between T(DBHP)P and BSA could be judged as electrostatic force when deltaG <0, deltaH <0 and deltaS >0. Using the synchronous fluorescence spectra, the effect of T(DBHP)P on the conformation of BSA was studied. The results indicated that the conformation of BSA was changed when T(DBHP)P was added, and the hydrophobic properties of the environment of residues in BSA decreased. It was proved that fluorescence quenching of BSA was induced by static quenching and non-radiation energy transfer.

[Study and application of determination of protein with meso-tetra-(3,5-dibromo-4-hydroxyphenyl) porphyrin fading spectrophotometry].

In the present paper, the binding characteristics and spectral behavior of interaction of meso-tetra-(3, 5-dibromo-4-hydroxyphenyl) porphyrin [T(DBHP)P] as a new-style probe with protein were studied by the techniques of spectrophotometry. The experiment showed that Tween-80 microemulsion was efficiently used to enhance the sensibility and stability of the system at pH 4. 17(Britton-Robinson buffer solution). Under optimum conditions, the characteristics of absorption spectral of meso-tetra-(3,5-dibromo-4-hydroxyphenyl) porphyrin-protein were investigated, the maximum absorption was located at 425 nm, and the reducing value of absorbance A was in proportion to the concentration of proteins in the range 0.50-6.00 microg x mL(-1) for bovine serum albumin, 0.05-0.60 microg x mL(-1) for ovalbumin, and the limits of detection were 0.106 microg x mL(-1) for bovine serum albumin and 0.039 microg x mL(-1) for ovalbumin. The experiments indicated that the proposed method featured high sensitivity and good selectivity and stability, and was simple and relatively free from interference of coexistent substances. It has been applied to the determination of protein in milk samples with satisfactory. The recovery for the investigated protein from milk was 99.56%-100.2% and the relative standard deviations were less than 2.2%. The sensitive method for the quantitative determination of proteins was proposed and may be applicable to the determination of ultra amounts of protein in food analysis. The effect of ionic strength on the system was investigated, and the result indicated that the binding force between meso-tetra-(3, 5-dibromo-4-hydroxyphenyl) porphyrin and protein was judged as electrostatic force. The influence of protein denaturation was also studied, under higher temperature the structure of protein was destroyed, and thermodynamic movement of the molecular of protein was intensified as the heating time extended.

[Study on spectral behavior of meso-tetra-(3, 5-dibromo-4-hydroxyphenyl) porphyrin with calf thymus DNA].

The binding characteristics of meso-tetra-(3, 5-dibromo-4-hydroxphenyl) porphyrin [T(DBHP)P] with calf thymus DNA (ct DNA) in pH 4.92 HAc-NaAc buffer solution were studied by the techniques of spectrophotometry. At the maxium absorption wavelength for T(DBHP)P, the decrease in the absorbance was linear with the amount of ct DNA. The experiments indicated that under optimum conditions, ct DNA obeys Beer's law in the range of 0.20-1.80 microg x mL(-1), and the limit of detection is 0.024 microg x mL(-1). Tween-80 microemulsion was commended in the experiment for better sensitivity. Furthermore, the association number is also determined by molar ratio method. The interactional mechanism between ct DNA and (T(DBHP)P was investigated as well.

[Study on the mechanism of interaction between TH-PF-Mo(VI) complex and bovine serum albumin by fluorimetric method].

The mechanism of interaction between bovine serum albumin (BSA) and trihydroxylphenylfluorone (TH-PF)-Mo(VI) complex in neutral solution was studied by fluorimetric method. The mechanism of fluorescence quenching of BSA caused by (TH-PF)-Mo(VI) complex probe was investigated and the binding constants under different temperature were measured. The binding constants of the reaction at 25 degrees C and 40 degrees C were calculated by fluorimetric method to be 4.78 x 10(4) L x mol(-1) and 3.72 x 10(4) L x mol(-1), respectively. According to the theory of Forster non-radiation energy transfer, the binding distance and transfer efficiency at 25 degrees C were calculated to be 2.89 nm and 0.314, respectively. Furthermore, the thermodynamic parameters were measured and the results indicated that electrostatic force played a major role in the interaction between TH-PF-Mo(VI) complex and BSA.