1. Provide the structure of arginine at different pH as...

1. Provide the structure of arginine at different pH as below: ? pH < pKa1 ? pKa1 < pH < pKa2 ? pKa2 < pH < pKa3 ? pH > pKa3 Relate your answer to the buffering region in the titration curve. What happens to arginine protonation/deprotonation when the pH is > or < particular pKa value? Are they protonated or deprotonated? You can hand-draw the structure for this question. If you obtain the structures from literature, remember to cite them (12 m)

Transcript

00:01 Hello everyone in this question we will be studying about the structure of arginine at different ph so let us make the structure of arginine okay so here it is the h3 n positive and the r group is the gonadineum group present here okay so c h2 is here here and h is here this is c double bond n plus h2 and n h2 so we can see that we have three ionic group present here okay this zero and n plus hrude that means three charges are present on arjunine and pk value is the isoelectric point this is the ph at which there is zero charge present on a molecule say the pk value of of c .o.

01:02 Negative is p .k .a .1.

01:05 Let's denote it like this.

01:06 And the pk value of coo is basically 2.

01:10 This, the pk value is very acidic.

01:13 And this as p .k .a.

01:16 2.

01:17 And the value here is 9.

01:19 And this is p .k .a 3.

01:22 And this is approximately equals to 12 .8.

01:26 Okay.

01:27 So now in the first part of the question it is saying that the ph is less than p -k -a -1 that means the ph is less than 2 so if the ph is less than 2 then coo will get protonated and will become this okay this will become the edge as it is acidic so more h is present so it will become protonated and it will lose the charge here okay so only two charges are present here and here.

02:04 So the charge here will be, the charge here will be plus two.

02:11 Now in second part of the question, it is saying that pca1 is less than ph and the ph is less than pkk 2.

02:23 Okay, so ph basically is more than 2 because pga 1 first 2, so it is more than 2, but it is less than 9.

02:35 That means if it is more than 2, then the cooh will donate its proton and it will become coo minus.

02:45 Okay, so this will be present and as it is ph 9, so nh3 will be like this only and nh2 will be like this only.

02:55 So here we have 2 plus charge and 1 minus charge.

03:00 So the charge here will be 2 minus 1 that is 1...

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