Preparation Of Dialdehyde Cellulose 3, 5-Dinitrobenzoate And Its Adsorption For Uremic Toxins

Urea and creatinine are two of the major toxins in patints suffering from chronic renalfailure (CRF). Removal of the excess toxins is the key problem for the treatments of CRF. Inthis work, a new multi-effect oral adsorbent named dialdehyde cellulose 3, 5-dinitrobenzoate(DCNB) was prepared and its adsorption for urea and creatinine was studied. The oraladsorbent was desgined based on the reaction of shift base between aldehyde group and ureaand complex reaction between 3, 5-dinitrobenzoic acid and creatinine, so it can adsorb ureaand creatinine simultaneously. The research was supported by grants from SpecializedResearch Fund for the Doctoral Program of Higher Education (SRFDP) (No. 20060225008).Microcrystalline cellulose (MCC) was activated with ultrasonic waves. The influence ofultrasonic treatment on the changes of supramolecular structure and morphology structure wasstudied by XRD, SEM and degree of polymerization (DP). The accessibility of the MCC wascharacterized by water retention value (WRV) and specific surficial area. The influence ofultrasonic treatment on the regioselective oxidation reactivity of MCC was investigated and themechanism of the reactivity change of ultrasonically treated MCC was examined. The resultsshowed that the degree of crystallinity of MCC decreased and DP showed little change aftertreatment with ultrasonic waves. The morphologial variation of the treated MCC wassignificant compared to the untreated MCC. These changes were contributed to the increase ofspecific surface area and WRV, which implied the improvement of accessibility. The aldehydecontent of dialdehyde cellulose (DAC) prepared from ultrasonically treated MCC wasimproved from 64.19% to 85.00%, indicating that the regioselective oxidation reactivity ofMCC was significantly improved.DAC was prepared from alkali activated MCC with periodate sodium as oxidant. Theinfluences of oxidant concentration, reaction temperature, reaction time and pH of solution onthe aldehyde content were investigated. DAC was characterized by XRD, FTIR, elementanalysis and measuring the aldehyde group. The relation between the aldehyde content of DACand the urea adsorption capacity was discussed. The adsorption equilibrium and kinetics ofurea onto dialdehyde cellulose were studied. The results showed that the optimal syntheticalcondition was that the ration of NaIO₄ to MCC was 2.4 to 1 by weight, the reactiontemperature was 35℃, the reaction time was 3.5 hours and pH was 2, with aldehyde content of92.95 % and a yield of 75.67 % under this condition. As the increase of aldehyde content, theadsorption capacity (AC) of urea first increased and then decreased: When the adsorptiontemperature was 37℃and pH was 7, the max AC of urea was 59.23 mg/g and adsorptionequilibrium reached after 4 hours. The adsorption isotherm curve of DAC fit with Freundich equation.The milti-effect oral adsorbent DCNB was prepared by esterification of DAC and 3,5-dinitrobenzoic chloride (DNBZ-Cl) with pyridine as solvent and catalyst. The product wascharacterized by XRD, FTIR, SEM and element analysis. The effects of molar ratio of thematerials, reaction temperature, reaction time, amount of pyridine and activated temperature onthe degree of substitution (DS) were investigated. The adsorption properties of DCNB for ureaand creatinine were studied under simulated biological conditions. The results showed that ahigh DS of 0.93 was obtained when the molar ratio of DNBZ-C; to DAC was 3 to 1, thereaction time was 3 hours, the reaction temperature was 80℃, the amount of pyridine was 40mL per gram of DAC and the activated temperature was room temperature. The yield ofDCNB was 69.78% under this condition. All of the DS, dose of DCNB, adsorptiontemperature and pH value had a great influence on the adsorption properties of DCNB. Theoptimum dose was 0.1g adsorbents for 10 mL urea or creatinine dialysate. The equilibriumtime of urea was 5 hours, while that of creatinine was 6 hours. When the DS of DCNB was0.93, the saturated AC of urea and creatinine reached 14.75 mg/g and 2.974 mg/g respectivelyat 37℃, pH=7. Equilibrium data of urea and creatinine within temperature range of 20 to 50℃and investigative concentration range fit well with Freundich equation. Values of isostericadsorption enthalpy, Gibbs adsorption energy, and adsorption entropy were calculatedaccording to the relationship of thermodynamic function and the adsorption behaviors arereasonably interpreted. The adsorption of urea on DCNB was a chemically endothermicprocess and that of creatinine was a spontaneous exothermic process.To avoid the side effect of aldehyde, DCNB Ca-alginate microspheres were prepared byfirst mixing DCNB with sodium alginate, and then coagulation of sodium alginate in CaCl₂solutions. The formability and swelling behavior of DCNB Ca-alginate microspheres werestudied. Comparing to DCNB, the adsorption properties of DCNB Ca-alginate microsphereswere investigated. The results showed that DCNB Ca-alginate microspheres had pH senstivifies.It didn't swell in stomach and swelled in intestines, which was favorable to adsorbe. TheDCNB Ca-alginate microspheres had good adsorption properties. When used at 37℃, pH=7,the AC of urea of DCNB Ca-alginate microspheres was 37.34 mg/g for 5 hours, and AC ofcreatinine was 1.458 mg/g for 6 hours.