Aravamudhan: Chiral Recognition by NMR 17/6/2012 11:50:10 AM

Chiral Recognition by NMR Spectroscopy- A Theoretical approach.Illustrating modeling strategies with organic molecules

with overtones for Modeling of Bio-molecules

An Abstract

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S.Aravamudhan

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JPG Image

Full publication by Bagatur Yants et al

7/6/2012 11:50:10 AM Aravamudhan: Chiral Recognition by NMR

Cs D3d

D3dIn the D3d all oxygen are disposed towards the cavity of the molecule

In the Cs there are interatomic distances for favorable hydrogen bonding

3Crown Ether-18crown6-D3d-webmo computational result

The JPG image

The JPG Image

7/6/2012 11:50:10 AM Aravamudhan: Chiral Recognition by NMR

The several perspective views of the D3d structure which seems to be occurring more in the polar media

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18crown6-Cs form-computational results

The JPG Image

7/6/2012 11:50:10 AM Aravamudhan: Chiral Recognition by NMR

The several perspective views of the Cs structure which seems to be occurring more in the nonpolar media

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The JPG Image Crown Ether-18crown6-D3d-webmo computational result

7/6/2012 11:50:10 AM Aravamudhan: Chiral Recognition by NMR

The two-line spectrum of the 18-crown-6 ether, due to the fluctuations and conformational dynamics in solution gives a single averaged line spectrum as much as the cyclohexane (Chair) . The experimental PMR spectrum of 18crown6ether displays a single line spectrum at 3.691ppm, this value is higher than the average value of the two-line theoretical spectrum {~(2.0+2.5 )/2=2.25ppm}. Such differences can be reconciled by using a better QM method of calcualtion (-and a scaling seems inevitable in any case) . Link:- data base experimental spectrum

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The JPG Image 18crown6-Cs form-computational results

7/6/2012 11:50:10 AM Aravamudhan: Chiral Recognition by NMR

Job106639-Str-PMR-CMR-C12H24O6-Crownether-form2-65.JPG

Cyclohexane-boat for comparison

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The JPG Image The Full publication by Koylu et al

7/6/2012 11:50:10 AM Aravamudhan: Chiral Recognition by NMR

The variety of Derivatives of 18-crown-6 ether which are used in the experimental methods; For complexing with chiral molecules and proceed to obtain NMR of the complex.

The 18crown6ether in the PMR spectrum has simply a single line; it is not necessary that the derivatives should also have similar single line.Characteristic variations in certain specific nmr line is often possible to recognize the chirality (of the host) dependent variations (as in next slide #7)

Typically referred to as NMR titration: A specific line in the spectrum of the complex displays a variation with the relative guest/host concentration ratio.

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The JPG Image The Full publication by Koylu et al

7/6/2012 11:50:10 AM Aravamudhan: Chiral Recognition by NMR

The specific NMR line position variation for the S and R conformers.

The actual complex (the Host and gust) can be seen in the next slide #8

What makes these kind of studies tedious and prone with ambiguities is: the experimental search for appropriate Guest and Host molecules which would enable some line in the spectrum to be tagged on to distinguish chiral -dependence

Hence the query as to whether theoretical calculations would reduce the uncertainties; the quest for appropriate theoretical method is duly the initiative required; Is it then simply a matter of calculating chemical shifts accurately, or the better G.O . possibilities?

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The JPG Image The Full publication by Koylu et al

7/6/2012 11:50:10 AM Aravamudhan: Chiral Recognition by NMR

This docked complex does indicate that a Theoretical Calculation would entail the complications of docking studies in the macromolecular regime (the hyperlinks should display the AGL files and the

corresponding exported images). Thus such a supra molecule studies could derive benefit by modeling with small molecules for favorable features to know the specifics which can then be integrated into a set of conditions for a tangible study of the large molecule. This indication for the necessity for a modeling was pursued to gain some insight and the full comprehension of the actualities, regarding the Chiral Recognition by NMR using theoretical methods, would require several compilations of the type presented now, and in the remaining parts.

Hyperlink-1Hyperlink-2

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The JPG Image

Computation on Cyclohexane-chair

7/6/2012 11:50:10 AM Aravamudhan: Chiral Recognition by NMR

CYCLOHEXANE-analogous symmetry and conformational disposition

Return to Slide #4

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The JPG Image

Computation onCyclohexane-boat

7/6/2012 11:50:10 AM Aravamudhan: Chiral Recognition by NMR

CYCLOHEXANE-analogous symmetry and conformational disposition

Return to Slide #5