Study On The Interaction Of Small Drug Molecules And Biomacromolecules

The interactions of bovine serum albumin （BSA） with two local anesthetics,procaine hydrochloride （PCH） and tetracaine hydrochloride （TCH）, were studied usingsuch spectroscopic methods as fluorescence and ultraviolet visible （UV-vis） andelectrochemical techniques including cyclic voltammetry （CV） and differential pulsedstripping voltammetry （DPSV）. The results obtained from these techniques turned outthat both PCH and TCH could bind to BSA. The binding constants （KA） and the numberof binding sites （n） of the two drugs with BSA at different temperatures weredetermined, respectively. At291K, KAwas found as2.40×10⁴and1.42×10⁴L mol^-1andn was1.03and0.99for PCH-BSA and TCH-BSA, respectively. According to van’t Hoffequation, the thermodynamic parameters, ΔG, ΔH and ΔS, were obtained, showing theinvolvement of hydrophobic and electrostatic force in these interactions. Based on thetheory of the F rster energy transference, the distance between the acceptor （PCH orTCH） and the donor （BSA） were determined as2.32and3.62nm for PCH and TCH,respectively. The effects of Fe³⁺, Cu²⁺, Mg²⁺, Mn²⁺, Zn²⁺and Ca²⁺on the binding ofPCH or TCH to BSA were also evaluated.The three flavonoids including naringenin, hesperetin and apigenin binding tobovine serum albumin （BSA） at pH7.4was studied by fluorescence quenching,synchronous fluorescence and UV-vis absorption spectroscopic techniques. The resultsobtained revealed that naringenin, hesperetin and apigenin strongly quenched theintrinsic fluorescence of BSA. The Stern–Volmer curves suggested that these quenchingprocesses were all static quenching processes. At291K, the value and the order of thebinding constant were: K_A （naringenin）=4.08×10⁴<KA （hesperetin）=5.40×10⁴≈K_A （apigenin）= 5.32×10⁴L mol1. The main binding force between the flavonoid and BSA washydrophobic and electrostatic force. According to the F rster theory of non-radiationenergy transfer, the binding distances （r0） were obtained as3.36,3.47and3.30nm fornaringenin–BSA, hesperetin–BSA and apigenin–BSA, respectively. The effect of somecommon ions such as Fe³⁺, Cu²⁺, Mg²⁺, Mn²⁺, Zn²⁺and Ca²⁺on the binding was alsostudied in detail. The competition binding was also performed. The apparent bindingconstant （K’_A） obtained suggested that one flavonoid had an obvious effect on thebinding of another flavonoid to protein when they coexisted in BSA solution.The interaction of eugenol （or methyleugenol） with salmon spermdeoxyribonucleic acid （DNA） were explored. To study the binding mechanism, theabsorption, fluorescence, melting temperature, and viscosity measurement were carriedout. It was also found that ionic strength had little effect on the binding of eugenol ormethyleugenol with DNA. The binding mode of eugenol or methyleugenol with DNAwas evaluated to be intercalative binding. Stern–Volmer plots at18,28and38℃showed that the quenching of fluorescence by eugenol or methyleugenol was a staticquenching process. The binding sites number n and binding constants Kaofeugenol–DNA and methyleugenol–DNA at different temperatures were got. Thecorresponding thermodynamic parameters ΔH，ΔG and ΔS at18℃were obtainedaccording to Van’t Hoff equations. Quantum yield of eugenol and methyleugenol wereobtained by comparing fluorescence intensity of them with human serum albumin （HSA,having known quantum yield） under identical condition. Based on the theory of theF rster energy transference, the distance between the acceptor （DNA） and the donor（eugenol or methyleugenol） were determined.The fluorescence characteristic of oleanolic acid （OA） in micellar system ofβ-cyclodextrin （β-CD） was studied. The experiment indicated that β-CD can enhancegreatly the fluorescence signal. Based on this result, a new method of sensitized fluorescence using the micellar system for the trace analysis of OA was developed. Thelinear range was1.0×10-5⁴.0×10-4mol L^-1. The recovery of sample was within therange of93.84%¹06.30%. The inclusion mechanism of β-CD and oleanolic acid wasstudied. The optimum amount of β-CD was determined and the effect of ionic strengthon OA-β-CD system was studied.