HEPES, 4-hydroxyethyl piperazine ethanesulfonic acid were used to prepare gold nanoparticles by HEPES NaOH reduction method. The method is simple in operation, quick in reaction, easy to control, few by-products and environmentally friendly.
The purity (> 99%) is water-soluble, the process is stable, and the appearance of the product can be guaranteed to be pure white crystal powder.
Preparation of gold nanoparticles
1. Prepare 0.05-10mmol/l chloroauric acid solution;
2. Prepare HEPES buffer with a concentration of 5-50mmol / L, and adjust the pH value of HEPES buffer to 7.0-8.0 with sodium hydroxide;
3. Add surfactant to HEPES buffer prepared in step 2 to prepare surfactant solution with concentration of 1-2mmol / L;
4. The surfactant solution prepared in step 3 is introduced into the reaction tank, and the chloroauric acid solution prepared in step 1 is slowly added to the reaction tank according to the molar ratio of chloroauric acid solution and surfactant solution of 1:1-1:10, and stirred at a constant speed of 200-300r / min for 5-30min to obtain the mixed solution containing nano gold colloid;
5. The mixture prepared in step 4 is dried and purified to obtain gold nanoparticles.
Take the preparation of 200L HEPES buffer solution with a concentration of 50mmol / L as an example. The configuration method is as follows: first, weigh 2.38kg HEPES and dissolve it in 180L deionized water, and then use ultrasonic wave and vibration until it is completely dissolved; then use pH meter to measure the pH value of the solution at this time is about 5.4, then slowly add 0.1mol/l sodium hydroxide solution and continuously stir until the pH is adjusted to 7.4; finally, continue to add deionized water to 200 L.
Preparation of HEPES
Directly use 1,2-dichloroethane as solvent, add hydroxyethyl piperazine (5.00g, 0.02mol), potassium carbonate K2CO3 (6.00g, 0.04mol), 50ml1,2-dichloroethane into a 100ml three bottle equipped with mechanical agitation and thermometer, heat it in oil bath for 90 ℃ (1,2-dichloroethane boiling point 85 ℃), and stir it for 20h. Stop the reaction, filter and wash the filtered salt with 200ml ethyl acetate (EA). The filtrate was dried to obtain 2.6g HEPES solid.
Add 11.0g (84.5mmol) of anhydrous sodium sulfite, 27.0ml (343.6mmol) of dichloroethane, 120ml of water, 110ml of ethanol, 50mg of copper powder into a three port bottle equipped with a magnetic stirrer and a reflux condensing tube. Stir and heat in an oil bath until reflux occurs. After refluxing for 22h, the reaction liquid was evaporated to remove water under reduced pressure until all white solids were separated out. The solid is mainly composed of product, unreacted raw material and generated salt. Add the solid and 500ml ethanol into 1L flask, heat and reflux for 40min. After the filtrate is cooled, place it at 0 ℃ for one night. The yield of flake crystal is 11.40 g and the yield is 81.0%.
Add sodium chloroethanesulfonate (15.10g, 0.08mol), hydroxyethyl piperazine (9.88g, 0.075mol), 60ml water and oil bath to the four bottles equipped with magnetic stirrer, reflux condenser and thermometer, stir the reaction at 105 ℃. As the reaction proceeds, the pH of the reaction solution will decrease. Drop 5mol/LNaOH water solution, control the pH at about 9, add 15ml in total, and continue the reaction for 5h.
At the end of the reaction, dilute the reaction solution to 500ml with water, and conduct desalting and purification on the ion exchange resin column (about 500g). After the reaction solution is completely loaded on the column, wash it with distilled water to the pH value of the effluent solution is 6, and then wash it with 1mol/L ammonia water, and collect the effluent solution with product point detected by TLC (pH value is about 5-9). Steam and concentrate to 150ml, add active carbon for decolorization, oil bath for 110 ℃, heat and stir for 0.5h, filter, spin dry the filtrate, add 50ml ethanol, heat and reflux for 0.5h, heat filter, the white solid obtained is 8.63g after drying. The filtrate was dripped with glacial acetic acid, adjusted to pH 5, cooled overnight at 0 ℃, filtered, and the resulting solid dried to 2.80g. The solid content of HEPES was 11.43g, and the yield was 64.5%.
The preparation method of 10mmol/L HEPES buffer solution is as follows: accurately weigh 2.383g HEPES and add fresh triple distilled water to constant volume to 1L. Filter and sterilize, and store at 4 ℃ after repacking. If it is used to be added to cell culture medium as buffer, it is recommended that the culture medium be kept away from light.
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