In modern, high resolution NMR spectroscopy, anisotropic parameters play an important role. They can be measured with the help of liquid crystalline mesophases or stretched polymer gels as so-called alignment media. Biologically occurring chiral polymers are of special interest as alignment media for this technique because they allow enantiomers to be distinguished.
Methods
Biopolymers have been studied by deuterium 1D and J-BIRDd,X-HSQC NMR experiments with respect to their ability to distinguish enantiomers and a summary of existing biopolymers for the task is given.
Results
Gelatin is shown to distinguish D-proline from L-proline and next to already known biopolymers, gellan gum is introduced as a novel biologically derived polymer that is able to partially align solute molecules.
Conclusions
Biologically occurring and biodegradable polymers are well suited as alignment media and in many cases are able to distinguish enantiomers. As the orienting properties are different for different media and solute molecules, the bandwidth of corresponding polymers will be further increased in the future.
BaxA.Weak alignment offers new NMR opportunities to study protein structure and dynamics. Protein Sci.2003; 12 (1): 1–16. Medline. doi: 10.1110/ps.0233303
2.
KummerlöweG., LuyB.Residual dipolar couplings as a tool in determining the structure of organic molecules. TrAC. Trends Anal Chem.2009; 28 (4): 483–493. doi: 10.1016/j.trac.2008.11.016
3.
KummerlöweG., LuyB.Residual dipolar couplings for the configurational and conformational analysis of organic molecules. Annu Rep NMR Spectrosc.2009; 68: 193–232. doi: 10.1016/S0066-4103(09)06804-5
4.
SarfatiM., LesotP., MerletD., CourtieuJ.Theoretical and experimental aspects of enantiomeric differentiation using natural abundance multinuclear NMR spectroscopy in chiral polypeptide liquid crystals. Chem Commun (Camb).2000; 21: 2069–2081. doi: 10.1039/b006244h
5.
LuyB.Distinction of enantiomers by NMR spectroscopy using chiral orienting media. J Indian Inst Sci2010; 90: 119–132.
6.
DelocheB., SamulskiE.T.Short-range nematic-like orientational order in strained elastomers: a deuterium magnetic-resonance study. Macromolecules1981; 14 (3): 575–58. doi: 10.1021/ma50004a024
7.
TyckoR., BlancoF.J., IshiiY.Alignment of biopolymers in strained gels: a new way to create detectable dipole-dipole couplings in high-resolution biomolecular NMR. J Am Chem Soc2000; 122 (38): 9340–9341. doi: 10.1021/ja002133q
8.
SassH.J., MuscoG., StahlS.J., WingfieldP.T., GrzesiekS.Solution NMR of proteins within polyacrylamide gels: diffusional properties and residual alignment by mechanical stress or embedding of oriented purple membranes. J Biomol NMR2000; 18 (4): 303–309. Medline. doi: 10.1023/A: 1026703605147
9.
CierpickiT., BushwellerJ.H.Charged gels as orienting media for measurement of residual dipolar couplings in soluble and integral membrane proteins. J Am Chem Soc2004; 126 (49): 16259–16266. Medline. doi: 10.1021/ja046054g
10.
FreudenbergerJ.C., KnörS., KobzarK.. Stretched poly(vinyl actetate) gels as NMR alignment media for the measurement of residual dipolar couplings in polar organic solvents. Angew Chem Int Ed2005; 44 (3): 423–426. doi: 10.1002/anie.200461241
11.
HaberzP., FarjonJ., GriesingerC.A DMSO-compatible orienting medium: towards the investigation of the stereochemistry of natural products. Angew Chem Int Ed2005; 44 (3): 427–429. doi: 10.1002/anie.200461267
12.
KummerlöweG., AuernheimerJ., LendleinA., LuyB.Stretched poly(acrylonitrile) as a scalable alignment medium for DMSO. J Am Chem Soc2007; 129 (19): 6080–6081 Medline. doi: 10.1021/ja071248s
13.
LuyB., KobzarK., KesslerH.An easy and scalable method for the partial alignment of organic molecules for measuring residual dipolar couplings. Angew Chem Int Ed2004; 43 (9): 1092–1094. doi: 10.1002/anie.200352860
14.
FreudenbergerJ.C., SpitellerP., BauerR., KesslerH., LuyB.Stretched poly(dimethylsiloxane) gels as NMR alignment media for apolar and weakly polar organic solvents: An ideal tool for measuring RDCs at low molecular concentrations. J Am Chem Soc2004; 126: 14690–14691. Medline. doi: 10.1021/ja046155e
15.
LuyB., KobzarK., KnörS., FurrerJ., HeckmannD., KesslerH.Orientational properties of stretched polystyrene gels in organic solvents and the suppression of their residual 1H NMR signals. J Am Chem Soc2005; 127 (17): 6459–6465. Medline. doi: 10.1021/ja043344o
BayleJ.P., CourtieuJ., GabettyE., LoewensteinA., PéchinéJ.M.Enantiomeric analysis in a polypeptide lyotropic liquid-crystal through proton decoupled deuterium NMR. N J Chem1992; 16 (8-9): 837–838.
18.
AroulandaC., SarfatiM., CourtieuJ., LesotP.Investigation of the enantioselectivity of three polypeptide liquid-crystalline solvents using NMR spectroscopy. Enantiomer2001; 6 (5): 281–287. Medline.
19.
ThieleC.M.Simultaneous assignment of all diastereotopic protons in strychnine using RDCs: PELG as alignment medium for organic molecules. J Org Chem2004; 69 (22): 7403–7413. Medline. doi: 10.1021/jo049867w
20.
EliavU., NavonG.Collagen fibers as a chiral agent: a demonstration of stereochemistry effects. J Am Chem Soc2006; 128 (50): 15956–15957 Medline. doi: 10.1021/ja065047k
21.
KobzarK., KesslerH., LuyB.Stretched gelatin gels as chiral alignment media for the discrimination of enantiomers by NMR spectroscopy. Angew Chem Int Ed 2005; 44 (20): 3145–3147. Corrigendum. Angew Chem Int Ed2005; 44 (23): 3509. doi: 10.1002/anie.200590079
22.
KuchelP.W., ChapmanB.E., MüllerN., BubbW.A., PhilpD.J., TorresA.M.Apparatus for rapid adjustment of the degree of alignment of NMR samples in aqueous media: verification with residual quadrupolar splittings in 23Na and 133Cs spectra. J Magn Reson2006; 180 (2): 256–265 Medline. doi: 10.1016/j.jmr.2006.03.002
23.
NaumannC., BubbW.A., ChapmanB.E., KuchelP.W.Tunable-alignment chiral system based on gelatin for NMR spectroscopy. J Am Chem Soc2007; 129 (17): 5340–5341. Medline. doi: 10.1021/ja070348v
24.
KummerlöweG., HalbachF., LauferB., LuyB.Precise measurement of RDCs in water and DMSO based gels using a silicone rubber tube for tunable stretching. Open Spectros J2008; 2: 29–33. doi: 10.2174/1874383800802010029
25.
KummerlöweG., McCordE.F., CheathamS.F., NissS., SchnellR.W., LuyB.Tunable alignment for all polymer gel/solvent combinations for the measurement of anisotropic NMR parameter. Chem Eur J2010; 16 (24): 7087–7089. Medline. doi: 10.1002/chem.201000108
26.
NaumannC., KuchelP.W.Prochiral and chiral resolution in 2H NMR spectra: solutes in stretched and compressed gelatin gels. J Phys Chem A2008; 112 (37): 8659–8664. Medline. doi: 10.1021/jp802982t
27.
KummerlöweG., KiranM.U., LuyB.Covalently cross-linked gelatin allows chiral distinction at elevated temperatures and in DMSO. Chem Eur J2009; 15 (45): 12192–12195. Medline. doi: 10.1002/chem.200902193
