HEPES, 4-hydroxyethyl piperazine ethanesulfonic acid, utilizes the reducibility of HEPES to excess metals at specific pH values, and uses HEPES-NaOH reduction method to prepare gold nanoparticles. This method is simple to operate, fast to react, easy to control, less by-products, and environmentally friendly.
Preparation of gold nanoparticles
1. Prepare chloroauric acid solution with concentration of 0.05-10 mmol/L;
2. Prepare HEPES buffer with concentration of 5-50 mmol/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 step2 to prepare surfactant solution with a concentration of 1-2 mmol/L;
4. The surfactant solution prepared in step3 is introduced into the reaction tank, and the chloroauric acid solution prepared in step1 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 speed of 200-300r/min. The reaction lasts for 5-30 min to obtain a mixture containing nanogold colloids;
5. The mixture prepared in step4 is dried and purified to obtain nanogold particles.
Taking the HEPES buffer with a concentration of 50 mmol/L as an example, the configuration method is as follows: firstly, 2.38 kg of HEPES is weighed and dissolved in 180 L of deionized water, and then the pH value of the solution is about 5.4 by using a pH meter, then 0.1 mol/L of sodium hydroxide solution is added slowly and stirred continuously until the pH is adjusted to 7.4; finally, deionized water is added to 200L.
Preparation of HEPES
Using 1,2-dichloroethane as solvent, hydroxyethyl piperazine (5.00g, 0.02mol), potassium carbonate K2CO3 (6.00g, 0.04mol), 50mL 1,2-dichloroethane were added into a 100mL three-port bottle equipped with mechanical stirring and thermometer. The oil bath was heated at 90℃ (1,2-dichloroethane boiling point 85℃), and the reaction was stirred for 20h.Stop the reaction, filter and wash the filtered salt with 200 mL ethyl acetate (EA).The filtrate was dried to obtain 2.6 g HEPES solid.
11.0g (84.5mmol) anhydrous sodium sulfite, 27.0 mL(343.6mmol) dichloroethane, 120mL water, 110mL ethanol, 50mg copper powder were added into three bottles with magnetic stirrer and reflux condensation tube in turn. The oil bath was heated and heated to reflux.After reflux for 22h, the reaction liquid was evaporated under reduced pressure to remove water until all white solids were precipitated.This solid is mainly composed of products, unreacted raw materials and salt produced.The obtained solid and 500mL ethanol were added into a 1L flask and heated for reflux for 40min.Drain and filter while hot, and let the filtrate cool down, then leave it at 0℃ overnight.Drainage filtration and vacuum drying resulted in flake crystallization with yield of 11.40 g and yield of 81.0%.
Sodium chloroethyl sulfonate (15.10 g, 0.08 mol), hydroxyethyl piperazine (9.88 g, 0.075 mol), 60 mL water and oil bath were added into four flasks with magnetic stirrer, reflux condensation tube and thermometer to stir the reaction at 105℃. As the reaction proceeded, the pH of the reaction solution would decrease, and 5 mol/LNaOH aqueous solution was added dropwise to control the pH at about 9. A total of 15 mL was added and the reaction continued for 5h.
At the end of the reaction, the reaction solution was diluted to 500mL with water, and the upper ion exchange resin column (about 500g) was desalted and purified. After the reaction solution was all loaded on the column, it was washed with distilled water until the effluent pH was 6, and then washed with 1mol/L ammonia water. The effluent with product points (pH about 5-9) was collected for TLC detection.Rotary evaporation was concentrated to 150 mL, activated carbon decolorization was added, oil bath was 110℃, heating and stirring for 0.5h, filtration, rotary drying of filtrate, adding 50mL ethanol, heating reflux for 0.5 h, thermal filtration, the white solid obtained after drying was 8.63G.The filtrate was dripped with glacial acetic acid, adjusted to pH 5, cooled overnight at 0℃, and filtered. The solid obtained was 2.80G after drying.A total of 11.43g of HEPES solid was obtained in 64.5% yield.
The preparation method of 10mmol/L HEPES buffer is as follows: weigh 2.383g of HEPES accurately, add fresh three-steamed water to constant volume to 1 L.Filtration sterilization, storage at 4℃ after sub-packaging.If used as a buffer when added to the cell culture medium, it is recommended that the culture medium be kept away from light.
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