Studies On Synthesis, Interface Electrochemical Properties And Drug Carrier Of Structurally Charged Layered Materials

Hydrotalcite-like compounds (HTlc), a kind of new material possessing permanently positive charges, contains brucite (magnesium hydroxide)-like layers where some divalent metal cations are substituted by trivalent metal cations to form positively structurally charged layers. The structural positive charges in the layers are compensated by the hydrated interlayer anions. The HTlcs have important application values in the industry fields such as catalysts, antacids, the treatment of the wastewater, antisettling agents, medicine, anionic exchangers, and rheology modifiers.HTlc have the general formula: [M²⁺_1-xM³⁺_x(OH)₂]_<sup>x+A^n-_x/n·mH₂O, where M²⁺ is divalent metal cation, M³⁺ is divalent metal cation, A^n- is the charge compensating anion, m is the number of moles of moles of co-intercalated water per formula weight of the compound and x is the number of moles of M³⁺ per formula weight of the compound. Different M²⁺ and M³⁺ formed a class of layered materials which has been paid a good deal of attention in recent years.Recently, interest has grown tremendously on the preparation, characterization, and application in the fields of colloid and interface chemistry. In this paper, the synthesis, the characterization, and the interface electrochemical properties of Zn-Al-Fe HTlc were systematically studied; on the other hand, he interface electrochemical properties of montmorillonite and kaolinite possessing negative charge were also studied; finally, the absorption properties of ketoprofen on HTlc, the intercalation of ketoprofen into HTlc and the controlled release of Mg-Al-KEP HTlc were systematically studied. Scetion 1. The synthesis and characterization of Zn-Al-Fe HTlcThe synthesis and the characterization of HTlc containing three kinds of metal cations with the general formula [Zn1-x(Al,Fe)_x(OH)₂]^x+A^n-x/n·mH₂O were studied in this chapter, and the following conclusions were obtained.(1) The hydrotalcite-like compounds containing Zn²⁺, Al³⁺ and Fe³⁺ were synthesized by a co-precipitation method. The samples were characterized by element chemical analysis, powder X-ray diffraction and transmission electron microscope. The results show that molar ratio of Zn/Zn+Al+Fe in prepared Zn-Al-Fe HTlc samples is lower than that of the material, and molar ratio of Fe/Zn+Al+Fe in prepared Zn-Al-Fe HTlc samples is higher than that of the material. The result may attribute to the small value of K_{sp,Fe(OH)3·}(2) It was found that pure HTlc phase could be got when x (M³⁺/M²⁺+M³⁺)is between 0.59 and 0.82. The study showed that there was no concentration superposition effect between Fe³⁺ and Al³⁺ on the crystalline state of the samples. In our previous work, the concentration superposition effect between Zn²⁺ and Mg²⁺ in the synthesis of Zn-Mg-Al-HTlc was found.(3) For the prepared Zn-Al-Fe HTlc samples, the value of lattice parameter α is between 0.306 and 0.308 nm; and the value of lattice parameter c is between 2.302 and 2.341 nm, the basal spacing is in the range of 0.765 and 0.789 nm. The height of gallery is about 0.30nm. It was found that the particles of prepared samples are comparatively complete hexagonal plate particles. The particle size is determined respectively by TEM and particle-size instrument.Section 2. The electrical properties of colloid particles possessing structural chargeThe interface electrochemistry of colloid is a traditional project in the field of colloid and interface chemistry and tremendous attention has been paid on it. There is a debate on the existence of point of zero net charge (PZNC) of the permanent charged materials just like the oxide. In this study, the electrical properties of hydrotalcite-like compounds possessing positive structural charge and clay samples (montmorillonite and kaolinite) possessing negative structural charge were studied and some conclusion can be drawn:(1) Montmorillonte and kaolinite possessing negative structural charge, as well as hydrotalcite-like compounds possessing positive structural charge, have PZNC independent of the concentration of electrolyte c. A common intersection point (CIP) should appear among the acid-base titration curves at different c and the pH at the CIP is pH_PZNC.(2) pH_PZNC of Zn-Al-Fe HTlc samples possessing positive structural charge appear at the acidic region, and clay samples possessing negative structural charge appear at the basic region. The pH_PZNC values of Zn-Al-Fe HTlc samples range from9.29 to 10.00, and the pH_PZNC values of montmorillonite and kaolinite are 2.66 and 2.16 respectively.(3) The pH_PZNC decrease with increasing structural positive charge and increase with increasing structural negative charge. For five HTlc samples studied, there is a relationship between the pH_PZNC values and σ_st values, pHpzNc=-2.42σ_st+11.27 (12=0.9892).(4) The structural charge density will influence the affinity between H⁺ and the surface of HTlc, so the intrinsic surface reaction equilibrium constants (pK, pAT_al^int and pK_a2^int) decrease with increasing σ_st. For five Zn-Al-Fe HTlc samples, there are relationships between the intrinsic surface reaction equilibrium constants and the σ_st values:pK=-0.38σ_st+11.47 (R=0.9898)pKa₁^int=-0.44fσ_st+10.82 (R=0.9901)pKa₂^int=-0.32σ_st+12.10 (R=0.9890).(5) For five Zn-Al-Fe HTlc samples, there are relationships between the intrinsic surface reaction equilibrium constants and the pH_PZNC values:pK = 1.64pH_PZNC- 6.91 (R=0.9940) pKa₁^int= 1 .89pH_PZNC - 10.28 (R=0.9892)pKa₂^int = 1.40pH_PZNC - 3.52 (R=0.9990)the pK, pKa₁^int and pKa₂^int values all increase with increasing pH_PZNC.(6) Point of zero net proton charge (PZNPC) is dependent on the concentration of electrolyte c. The PZNPC of HTlc increase with increasing c and the PZNPC of montmorillonite and kaolinite decrease with increasing c.Section 3. The synthesis and Characterization of Mg-Al-KPF HTlcRecently, HTlc possessing structural positive charge has been paid much attention as drug carrier because HTlc have large ionic exchangeable content to carry the large molecule, such as DNA. But the studies on synthesis and characterization of drug-HTlc with the controllable release ability have been little reported. DNA was intercalated into HTlc by Choy etc. in 1999, and this progeny aroused great attention. Ketoprofen is a non-steroidal antiinflammatory drug used for the relief of symptoms of rheumatoid arthritis and osteoarthritis. It is used both in the treatment of acute flares and in longterm management of these diseases. Its use is often limited by the frequent side effects affecting the gastrointestinal tract. This side effect is also a consequence of high plasma levels following the administration of conventional formulations. These problems could be reduced by a formulation able to control the drug release. As matrices to prepare a controlled release formulation, HTlc has been taken into account. The idea was to store the drug in the interlayer region of the HTlc and allow the drug release as a consequence of a de-intercalation process.In this paper, ketoprofen has been intercalated into Mg-Al-HTlc, and Mg-Al-KPF HTlc has been gotten. The effects of reaction time, the initial concentration of ketoprofen and the pH value of dispersion on the amount of KPF involved in Mg-Al-HTlc have been studied. The ketoprofen-release of Mg-AI-KPF HTlc in buffer solution have also been studied and some conclusions have been drawn: (1) The ketoprofen was intercalated into the Mg-Al-HTlc and by co-precipitation, anion exchange and "memory effect", respectively. The Mg-Al-KPF HTlc had fine crystal structure with the ketoprofen anion between layers, and the interlayer spacing was about 2.36nm. According to Hartree-Fock3-21g* quanta chemistry de novo calculation method, the molecular length of ketoprofen was about 1.03nm. The interlayer spacing of Mg-Al-KPF HTlc studied in the research was about 2.36nm, subtraction the thickness of brucite-like layer (0.48 nm), the result got was that ketoprofen molecular in Mg-Al-KPF HTlc gallery area ranged in bilayer perpendicularity to brucite-like layer.(2) The effects of the reaction time, the initial concentration of ketoprofen, the temperature and the pH value of dispersion on the amount of KPF involved in Mg-Al-HTlc have been studied. The research indicated that the reaction time and the temperature had little effect on the on the amount of KPF involved in Mg-Al-HTlc, but the initial concentration of ketoprofen and the pH value of dispersion affected that much.(3) The study showed that the Mg-Al-KPF HTlc have good controllable ketoprofen-release function, and the release rate decrease obviously with increasing pH value. When the pH of buffer solution was 4.00, the dissolution of the Mg-Al-layer contributed to the release of ketoprfen mostly and the diffusion of ketoprofen between the layers proffered much; when the pH of buffer solution was 6.86, the release of ketoprfen attributed to the diffusion of ketoprofen between the layers only.