COLNAGO, L. A.

VENANCIO, T.

RCAAP - Repositório Científico de Acesso Aberto de Portugal

Improvements in the CWFP method for solvent suppression in high resolution NMR.

Repository Open Access to Scientific Information from Embrapa

iz"NUCLEARMAGNETICRESONANCE USERS MEETING3rdIBEROAMERICANNMRMEETINGMAY46 - OS6, 2009 -HOTEL DO FRADE, ANGRA DOS REIS,RJ,BRAZIL- o', .. '.. '.EXTENDEDABSTRACTSBOOK12.hNUCLEAR MAGNETIC RESONANCE USERS MEETTNG II3" IBEROAMERJCAN NMR MEETlNG !EXTENDED ABSTRACTS BOOK iTr 31IMPROVEMENTS IN THE CWFP METHOD FOR SOLVENT SUPPRESSIONIN HIGH RESOLUTION NMRTiago Venánciot':", Luiz Alberto Colnaqo"1Departamento de Química - UFSCar; 2Embrapa - Instrumentação Agropecuária,venancío@dq.ufscar.brKeywords: Solvent suppression, CWFP, High Resolution NMRWhen the analyte is present in a very dilute solution, the solvent signal cancause serious problems in NMR spectrum. The large solvent signal reduces the qualityof digitalization of analyte signals, causing a dynamic range problem. When it usedpure deuterated solvent also can be a critical problem, for example in protein studies,because the chemical exchange that occurs in amide groups leads to lose informationabout amino acids sequencing. It is worse in "in vivo" expcrimenls whcre is nolpossible to use deuterated solvents. Then, the solvent suppression is ano oí lho 1110:;1important techniques in high resolution NMR. There are sevoral rnothods for' olvr 111suppression based on saturation, magnetization deslroying 1l1rollçlll {lrmllwll pul li 1data post processing [1]. Nowadays, the most efficient melhods for solvont : uppru 1(111are those ones that use gradient pulses, but il could nol 00 nVt111111J11J Ir, nvnt ymachines. Recently, a sim pie technique based on a varialion of lho stoady stll10 frullprecession (SSFP), called continuous wave free précession (CWFP), was dov: IOpOfl 10perform the solvent suppression. It demonstrated to be useful, especially for "in vivo"measurements [2]. However, some problems need to be solved to improve the resultobtained by using CWFP technique. These problems are mainly the intensity andphase anomalies. The purpose of this work is to try to solve these problems.The experiments were performed in equipment consisted of a 2T Oxfordmagnet with a 30cm bore and electronic based on an Apollo-Tecmag spectrometer, apower amplifier AMT 2035 and a pre amplifier Miteq 1054. It was also employed a 1cmdiameter home-made solenoidal coil, covered with an epoxy resin to keep it rigid.Neither plastic tube nor epoxy resin exhibit NMR signal in such conditions. The sampleused is a 1:1 mixture of CHCI3:CH3COOH, to guarantee a big distance betweenchemical shifts observed. The measurements were performed without shimming andlocking. It was employed CWFP technique as in previous works [3], but now varyingthe phase cycfing and pulse width of the train of .the pulses. These modifications werebased on a methodology proposed by Rudakov et ai [4], and also in the excitationprofile of the CWFP pulse sequence.The 1H NMR spectrum of this sample exhibits signafs at 7.3ppm rolatod luCHCI3 and 2.0 and 11.7ppm related to CH3COOH, as shown in fig.1 (a). Wl10n tl10CWFP pulse sequence is applied to suppress the CHCL3 signal, at 7.3 ppm, wlthoutphase cycling it can be observed a phase anomaly in the spectrum. Tl10 CHCI" lli nottotally suppressed and the signals related to CH3COOH are 180(1 invertod to onchother, as can be observed in the fig.1 (b). The phase anomaly can be correclod whonthe CWFP pulse sequence is applied with a phase cycling, but anolher problernpersists, which is related to intensity anomaly, as in the fig.1 (c). Based on theexcitation profile, the pulse width of the pulse from the train was varied and the bestresult was obtained when it was used a pulse width of 15°. In the fig.1 (d) it wasobtained a spectrum with phase and intensity anomalies corrected, and it must beobserved a total suppression of the CHCI3 signal in 7.3ppm.li AUREMN! MAY 4'" - 08'" 2009, HOTEL DO FRADE,j ANGRA DOS REIS, RJ, BRAZILowithout CHCI3suppression CHCI3 suppressionwithout phase cycling3 o -36ppm(a)91215 15 12 9 6ppmb3 o--p1=90CHCI3 suppressionp1=1S0CHCI3 suppression3 o -36ppm9 15 12 9c6ppm(d)3Figure 1: 'H NMR spectrum of a mixture CHCI~CH3COOH: (a) without CHCI3 suppression,using FID; (b) CHCI3 supgressed using CWFP without phase cycling - (900cTP-)n 900x; (c)CHCh suppressed with 90 pulse width CWFP and phase cycling - (90 cTp-900y- Tp-900_cTp-900.y-Tp-)n900_~; (d) CHCI3 suppressed with 15° pulse width CWFP and phase cycling - (1Soc° o o ° .' .Tp-15 r:Tp-15 -rTp-1S _y-Tp-)n90 -y' Tp = 300jJs for ali the expenments.From the obtained results, it could be concluded that the CWFP can be used asa good technique for solvent suppression, taking account some adjustments to improveits efficiency. These adjustments must be done in its phase cycling and also in thepulse width. The advantage of the CWFP method is that it is not necessary to usegradient pulses and it is easy to be implemented. Another possible interference, suchchemical exchange, is being investigated.REFERENCES[1] PRICE, W.S. Annual Reports on NMR Spectroscopy, 38, 289-354 (1999).[2] VENANCIO, T.; AZEREDO, R. B. V.; ENGELSBERG, M.; COLNAGO, L. A Annals of Magn.Res., 2,122-124 (2003).[3] VENÂNCIO, T.; ENGELSBERG, M.; AZEREDO, R. B. V.; ALEM, N. E. R.; COLNAGO, L. AJ. Magn. Res., 173, 34-39 (2005).[4] RUDAKOV, T.N.; BELlAKOV, AV. J. of Phys. O: Applied Phys., 31,1251-1256 (1998).FAPESP, CNPq and CAPES~+-78-3-3

http://www.alice.cnptia.embrapa.br/alice/bitstream/doc/48903/1/Proci09.00025.pdf

Improvements in the CWFP method for solvent suppression in high resolution NMR.

Abstract

Similar works

Full text

Available Versions

RCAAP - Repositório Científico de Acesso Aberto de Portugal

Repository Open Access to Scientific Information from Embrapa