distiguishing features for chirality
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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 PresentationTRANSCRIPT
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?
9
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?
9