Studies On The Interaction Of Drug Molecules And Biomolecules By Spectrometric Methods

It is well known that the serum albumin can reversibly bind drugmolecules to affect the drugs distribution. The strong fluorescencecharacteristics of the serum albumins provide a sensitive spectrometric methodto study their interactions with various drug molecules. The intracellular targetfor the majority of anticancer and antibiotic drugs is DNA and the interactionbetween DNA and drug can affect DNA replication and synthesis in cancer cells,inhibit the growth of cancer cells. So, the study on the interaction of drug withserum albumin or DNA plays a key role in pharmacology.The interactions of flavonoids, including quercetin, rutin, hyperin andbaicalin, with human serum albumin (HSA) were studied. Fluorescenceemission spectra of HSA in the presence of the investigated compounds,recorded at the excitation and emission wavelength of 280 and 290-500nm,respectively, clearly showed that these compounds quenched the fluorescenceof HSA. The binding constants and the number of binding sites of theflavonoids with HSA were obtained by three different calculation methods andthe results obtained by these methods were compared. The effects of variousmetal ions on the binding constants of these flavonoids with HSA were alsostudied. Based on the mechanism of the F?rster energy transference, theenergy transfer efficiency between the acceptors and HSA were found. Therelationship between the structure characteristics of these compounds andbinding properties of the flavonoids and HSA was explored.The interactions of serum albumins such as human serum albumin (HSA)and bovine serum albumin (BSA) with emodin, rhein, aloe-emodin and aloinwere assessed employing fluorescence quenching and absorption spectroscopictechniques. The results obtained revealed that there are relatively strongbinding affinity for the four anthraquinones with HSA and BSA and the bindingconstants for the interactions of anthraquinones with HSA or BSA at 20oC wereobtained. Anthraquinone-albumin interactions were studied at differenttemperatures and in the presence of some metal ions. And the competitionbinding of anthraquinones with serum albumins was also discussed. TheStern-Volmer curves suggested that the quenching occurring in the reactionswas the static quenching process. The binding distances and transferefficiencies for each binding reactions were calculated according to the F?stertheory of non-radiation energy transfer. Using thermodynamic equations, themain action forces of these reactions were also obtained. The reasons of thedifferent binding affinities for different anthraquinone-albumin reactions wereprobed from the point of view of molecular structures.A molecular spectroscopic investigation of the interaction betweentetracyclines antibiotics and human serum albumin or bovine serum albuminwas reported. The influences of some metal ions on the interaction were alsostudied. When tetracyclines drugs were added into the solution containingserum albumins, the fluorescence intensity of serum albumins decreased withthe increasing of the drugs concentrations, which is due to the formation of newnon-fluorescence complexes of drug-serum albumin. The tetracyclines acted asquenchers and quenched the fluorescence of the serum albumins. The bindingconstants and the number of the binding sites of the reaction of tetracyclinesand serum albumins were obtained. The main sorts of acting force between thedrugs and serum albumins were found and the action distances and the energytransfer efficiencies between donor-acceptor were calculated based on theF?ster energy transference.The binding characteristics of antibiotics, cefotaxime sodium, oxacillin,amoxicillin, norfloxacin and enoxacin with human serum albumin (HSA) werestudied by fluorescence spectrometry. These drugs quenched the HSAfluorescence via a nonradiative energy transfer mechanism. The bindingconstants and binding sites for drug-HSA were obtained by an improvedanalysis method to process the experimental data. The effects of Cu2+, Al3+,Mg2+ and Zn2+ on the binding constants of drug-HSA were also discussed. Theelectrostatic interaction was found to be main acting force in the studiedsystems. The binding distances r0 were 1.89 nm for cefotaxime sodium-HSAand, 1.77, 1.65, 2.15 and 2.43 nm for oxicillin-HSA, amoxicillin-HSA,norfloxacin-HSA and enoxacin-HSA, respectively.The interactions of flavonoids, such as quercetin, kaempferide and luteolin,with fish sperm deoxyribonucleic acid (DNA) were explored by using acridineorange (AO) as a fluorescence probe. The variations in the spectroscopiccharacteristics of DNA-AO in an aqueous medium upon addition of the threedrugs were observed. Measurements of ultraviolet absorption and fluorescencespectra, determination of binding constants for flavonoids-double strandedDNA (dsDNA) or flavonoids-single stranded DNA (ssDNA), studies oncompetitive bindings among these drugs interacting with DNA-AO systems,melting temperature (Tm) curves and viscosity measurements were carried outto investigate binding mechanism of these flavonoids with DNA. The bindingmode of quercetin, kaempferide and luteolin with DNA was evaluated to begroove binding. The binding constants of quercetin, kaempferide, and luteolinwith DNA-AO complex were 3.19×104, 5.63×104 and 2.33×104 L mol-1,respectively.Emodin, rhein, aloe-emodin and aloin interacting with DNA was studiedby different spectroscopic techniques, such as fluorescence, ultraviolet andvisible (UV-vis), and fourier transform infared (FT-IR) spectroscopies, usingethidium bromide (EB) as a nucleic acid probe. The decrease in fluorescence ofDNA-EB system on addition of the drugs shows that the fluorescencequenching of DNA-EB complex by emodin, rhein, and aloe-emodin occurs. At20 °C, the binding constants of emodin, rhein, and aloe-emodin with DNA inthe presence of EB are 6.02×104, 1.05×104, 5.94×104 L mol-1, respectively.FT-IR spectra further suggested that both the phosphate groups and the bases ofDNA could react with the anthraquinones. The reaction of DNA withanthraquinone in the presence of EB was affected by ionic strength andtemperature. The melting temperature of DNA-EB and anthraquinone-DNA-EBwere determined, respectively, and the results revealed that the stability ofDNA-EB decreased.