ORGLIST: Re: Everybody Digest, Vol 12, Issue 1

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From: Lakshmipathi Pandarinathan (plpathi$##$hotmail.com)
Date: Thu Sep 01 2005 - 14:57:44 EDT



Excess triphosgene can be removed out of organic layer by washing the org
layer with cold aqeuos 5% NaOH solution and I think this should not affect
your isocyanate.
good luck
Pathi
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Sent: Thursday, September 01, 2005 1:47 PM
Subject: Everybody Digest, Vol 12, Issue 1


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> Today's Topics:
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> 1. FW: ORGLIST: Quantification of SH group (Ismail, Fyaz)
> 2. Removing excess Triphosgene (Kamal)
> 3. esterification (Rajeshri Mehta and Dr.Tushar)
>
>
> ----------------------------------------------------------------------
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> Message: 1
> Date: Wed, 31 Aug 2005 13:15:58 +0100
> From: "Ismail, Fyaz" <F.M.Ismail$##$livjm.ac.uk>
> Subject: FW: ORGLIST: Quantification of SH group
> To: <everybody$##$orglist.net>, "Anil Saini" <sainianil3$##$rediffmail.com>
> Message-ID: <03DFED21847B3C4FB7C047193B5FD65A018C8B55$##$exch4.jmu.ac.uk>
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> Ellman's Reagent
>
> In order to quantitative available sulphydryl groups, the classic reagent
> is Ellman's reagent, (DTNB), which is used for the modification of free
> thiols in proteins and peptides[1]. It typically reacts with the thiol
> containing molecule to releasing the 5-thio-2-nitrobenzoate (TNB) anion,
> which absorbs at 412 nm (absorption coefficient of 13600 M?1cm?1 [2]).
> It's presence can be plotted against a standard curve to determine the
> total amount of free thiols in proteins or peptide. Typically reactions
> arte conducted in phosphate buffer, (0.1 M pH 7.2) at 25 C under
> strictly anaerobic conditions. Around 3.6 x 10-5 M of free thiol is
> relatively easy to detect. Ten fold further dilution appears to be the
> limit of thee assay using 1 cm pathlength cells. A double vacuum manifold
> system (under Argon) and a stoppered sidearm cuvette are routinely used in
> our laboratory to maintain strictly anaerobic conditions. Otherwise,
> oxidation to disulphides may occur preventing accurate quantification of
> the thiol groups present.
>
> References
>
> [1] Riddles, P. W.; Blakely, R.; Zerner, B. Reassessment of Ellman's
> reagent. Methods Enzymol. 1983;91:49-60.
>
> [2] Li, T.-Y.; Minkel, D. T.; Shaw III, C. F.; Petering, D. H. Biochem.
> J. (1981) 193, 441-446.
>
> Dr. Fyaz M. D. Ismail
> Laboratory of Medicinal Chemistry
> Liverpool John Moores University,
> Byrom Street,
> Liverpool L3 3AF
>
>
> -----Original Message-----
> From: everybody-bounces$##$orglist.net
> [mailto:everybody-bounces$##$orglist.net]On Behalf Of Anil Saini
> Sent: 31 August 2005 10:59
> To: everybody$##$orglist.net
> Subject: ORGLIST: Quantification of SH group
>
>
>
> Helo to every one
> I want to know how to quantitate the sulfahydrl group (-SH) in a linear
> peptide chain spectrophotometrically. and if there is any other method to
> quantitate it what will be the strategy for that.
>
> another thing i want to know is that how to precipitate urea from a
> solution of denatured protiens.
> I thanks in advance
>
>
> Anil
>
>
>
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> Message: 2
> Date: Wed, 31 Aug 2005 19:12:12 +0530
> From: "Kamal" <mailbox$##$invalid>
> Subject: ORGLIST: Removing excess Triphosgene
> To: <everybody$##$orglist.net>
> Message-ID: <000b01c5ae31$cab5f4c0$1864fea9$##$kamal>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Hi to all my orglist friends !
>
> I'm still struggling with my developement of an aliphatic Isocyanate.
> (Sorry to Yuehui & Lakshmipathiji, again disturbing you !!)
>
> As per the advice given to me by you, I performed procedure of ORGANIC
> SYNTHESIS by using Amine HCl, Triphosgene, Dichloromethane & aq.
> bicarbonate. The reaction goes so well but I'm feeling difficulties in
> removing the excess triphosgene after completion of reaction.
>
> I used 0.35.......to......0.5 eq. of triphosgene in different experiments
> & all give almost similar results. In all of them, excess triphosgene
> remains in the organic layer & generates a lot of amount of acidic solids.
> It still remains in the distilled isocyanate also ! If I use lower ratio
> of triphosgene (0.33 eq. or less), then some Amine HCl remains unconverted
> & it makes other urea/hydantoin based impurities in significant amounts !
>
> Is it possible to remove this excess triphosgene ?
>
> Pls...................give some advice to me.
>
>
>
>
> Thanking you,
> Kamal
> (mailbox$##$invalid)
>
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> ------------------------------
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> Message: 3
> Date: Thu, 1 Sep 2005 03:51:43 -0700 (PDT)
> From: "Rajeshri Mehta and Dr.Tushar" <rajtush$##$yahoo.com>
> Subject: ORGLIST: esterification
> To: everybody$##$orglist.net
> Message-ID: <20050901105144.48946.qmail$##$web30603.mail.mud.yahoo.com>
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>
> Dear All
>
> How to selectively esterify carboxylic acid on phenyl
> ring bearing boronic acid on 4 position.
>
> i tried with HCl. H2SO4 and Thionyl methanol
>
> not working
>
> Any ans
>
> Tushar
>
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> End of Everybody Digest, Vol 12, Issue 1
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