1. 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
7/6/ :50:10 AM
Aravamudhan: Chiral Recognition by NMR

2. Aravamudhan: Chiral Recognition by NMR
In the D3d all oxygen are disposed towards the cavity of the molecule
In the Cs there are interatomic distances for favorable hydrogen bonding
D3d Cs
D3d
JPG Image
Full publication by Bagatur Yants et al
7/6/ :50:10 AM
Aravamudhan: Chiral Recognition by NMR

3. Aravamudhan: Chiral Recognition by NMR
The JPG Image
The several perspective views of the D3d structure which seems to be occurring more in the polar media
The JPG image
Crown Ether-18crown6-D3d-webmo computational result
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Aravamudhan: Chiral Recognition by NMR

4. Aravamudhan: Chiral Recognition by NMR
The JPG Image
The several perspective views of the Cs structure which seems to be occurring more in the nonpolar media
18crown6-Cs form-computational results
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Aravamudhan: Chiral Recognition by NMR

5. 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=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
The JPG Image
Crown Ether-18crown6-D3d-webmo computational result
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Aravamudhan: Chiral Recognition by NMR

6. Aravamudhan: Chiral Recognition by NMR
Job Str-PMR-CMR-C12H24O6-Crownether-form2-65.JPG
Cyclohexane-boat for comparison
18crown6-Cs form-computational results
The JPG Image
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Aravamudhan: Chiral Recognition by NMR

7. Aravamudhan: Chiral Recognition by NMR
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)
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.
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.
The JPG Image
The Full publication by Koylu et al
7/6/ :50:10 AM
Aravamudhan: Chiral Recognition by NMR

8. Aravamudhan: Chiral Recognition by NMR
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?
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
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
The Full publication by Koylu et al
The JPG Image
7/6/ :50:10 AM
Aravamudhan: Chiral Recognition by NMR

9. 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. 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.
The Full publication by Koylu et al
The JPG Image
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Aravamudhan: Chiral Recognition by NMR

10. Aravamudhan: Chiral Recognition by NMR
CYCLOHEXANE-analogous symmetry and conformational disposition
The JPG Image
Computation on Cyclohexane-chair
Return to Slide #4
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Aravamudhan: Chiral Recognition by NMR

11. Aravamudhan: Chiral Recognition by NMR
CYCLOHEXANE-analogous symmetry and conformational disposition
The JPG Image
Computation on
Cyclohexane-boat
Return to Slide #5
7/6/ :50:10 AM
Aravamudhan: Chiral Recognition by NMR