7/6/2012 11:49:36 AM Aravamudhan: Chiral Recognition by NMR 1 Distiguishing features for Chirality crowmether- host1.ppt Such small chiral molecules are complexed with larger host molecules and the NMR spectra of the resulting complex is used for recognizing the chiral form, the R or S. Amino acids are designated by L or D optical isomers (equivalent to R,S designation) that corresponds to the presence of asymmetric carbon / a chiral centre. Most of them experimental studies and not much Computational chemistry is reported on such systems for the calculation of chemical shifts of un complexed host and ligand, for a comparison with the complexes. Thus this presentation is a study reporting a small molecule docking with a larger molecule and the use of calculation of chemical shifts on certain model systems. Just as much as experimentalists use NMR spectroscopy as an analytical tool for structure determination, it is being pointed out that trends using Chemical shift calculations can be so much useful in modeling studies even if the calculated shift values do not reproduce the experimental shift values. Chiral Recognition by NMR Spectroscopy- A Theoretical approach. Illustrating modeling strategies with organic molecules with overtones for Modeling of Bio-molecules An Abstract S.Aravamudhan This material may be available as Internet Resource: Display the web subdirectory: http://www.ugc-inno-nehu.com/CRNMR/ Some of the linked files in this .ppt file require the Software “ARGUSLAB” be installed in your system. Download the MS Windows installer “setup.exe” file by clicking on the link below: http://www.ugc-inno-nehu.com/arguslab/ And download the all the contents of this directory into the same and single folder in the resident disc of the P.C. for the hyperlinks in the presentation file to display the appropriate file. Download these presentation files from my internet resource: http://www.ugc-inno-nehu.com/wmbs-II-mzu/ S.Aravamudhan Department of Chemistry North Eastern Hill University SHILLONG 793022 Meghalaya
crowmether-host1.ppt. Distiguishing features for Chirality. Such small chiral molecules are complexed with larger host molecules and the NMR spectra of the resulting complex is used for recognizing the chiral form, the R or S. - PowerPoint PPT Presentation
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Slide 11
crowmether-host1.ppt
Such small chiral molecules are complexed with larger host
molecules and the NMR spectra of the resulting complex is used for
recognizing the chiral form, the R or S.
Amino acids are designated by L or D optical isomers (equivalent to
R,S designation) that corresponds to the presence of asymmetric
carbon / a chiral centre.
Most of them experimental studies and not much Computational
chemistry is reported on such systems for the calculation of
chemical shifts of un complexed host and ligand, for a comparison
with the complexes.
Thus this presentation is a study reporting a small molecule
docking with a larger molecule and the use of calculation of
chemical shifts on certain model systems.
Just as much as experimentalists use NMR spectroscopy as an
analytical tool for structure determination, it is being pointed
out that trends using Chemical shift calculations can be so much
useful in modeling studies even if the calculated shift values do
not reproduce the experimental shift values.
Chiral Recognition by NMR Spectroscopy- A Theoretical
approach.
Illustrating modeling strategies with organic molecules
with overtones for Modeling of Bio-molecules
Display the web subdirectory:
http://www.ugc-inno-nehu.com/CRNMR/
Some of the linked files in this .ppt file require the Software
“ARGUSLAB” be installed in your system. Download the MS Windows
installer “setup.exe” file by clicking on the link below:
Download these presentation files from my internet resource:
Cs
D3d
D3d
In the D3d all oxygen are disposed towards the cavity of the
molecule
In the Cs there are interatomic distances for favorable hydrogen
bonding
Crown Ether
18Crown6 Ether
Aravamudhan: Chiral Recognition by NMR
The several perspective views of the D3d structure which seems to
be occurring more in the polar media
Aravamudhan: Chiral Recognition by NMR
The several perspective views of the Cs structure which seems to be
occurring more in the nonpolar media
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
Cyclohexane- CHAIR conformation with similar two line spectrum,
requires 5.9 secs CPU time (a fctor of 9 times less). Crown Ether
has 42 atoms and Cyclohexane has 18 atoms in the molecule (atom
count includes oxygen hetero atom in Crown ether)
Job106639-Str-PMR-CMR-C12H24O6-Crownether-form2-65.JPG
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.
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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