User:Sarah Burkhard/Notebook/471 Nano Notebook/2017/03/21

Project name

Main project page Previous entry      Next entry

Objectives UV-Vis prepared solutions Prepare ~ 50mM His solution Observations The capped and the non-capped Arg at pH 14 show purple color Cys-Arg 10 times ratio and the 5 times ratio show white precipitate capped pH 8 and 10 show yellow/orange color The non-capped shows a peak at 580 nm. The capped shows a peak at the same wavelength, but with muss less intensity. The Cys-Arg mix absorbs at a wavelength around 370 nm, and shows a shoulder around 240 nm. The capped pH absorbs at 290 nm. Discussion The yellow color from the capped Arg may come from a reaction of the N-cap, which has a carboxamide group. Yellow in specific often indicates amino groups (N=O) . This could be further confirmed using IR spectroscopy. Further, the fact that NPs formed above pK2, where the amino acid is negatively charged (above pH 13.2) , leads us to run further tests with Histidine, which has a lower pK2 and therefore a wider range of pH we can test. Histidine will have a negative one charge at pH above 8.97. pKa1 1.78 (carboxylic group will be protonated only at pH below 1.78 ) pKa2 8.97 (amine will be protonated only at pH values below 8.97 ) pKaR 5.97 (amine in R chain will be protonated at pH values below 5.97) charges: below 1.78: charge is 2+ 1.78 - 5.97 : +1 5.97 - 8.97 : 0 above 8.97  : -1 We will run Histidine at pH 4, 7 , 10, 12, and 14 . Make graph of Arg absorbance at different pH