For HSQC spectra, broadband decoupling during acquisition was obtained with the standard GARP scheme, and unless otherwise specified interpulse INEPT delay was optimized for a 145 Hz J value for the cyclosporin sample and 132 Hz for polymer samples.
13C spectral window was 12 or 4 ppm for cyclosporin and polymer sample, respectively, and 256 t 1 increments were used. Bs 2D HSQC and HMBC spectra were acquired using following parameters: 1H spectral window was 9.2 or 8.0 ppm for cyclosporin and polymer samples, respectively, resulting in acquisition time of 0.44 or 0.51 s, respectively (TD 4096). Acquisition time was 1.05 s and relaxation delay D1 2.00 s. 1D 13C spectra were acquired using Bruker standard zgpg30 sequence (30° flip angle, bilevel 1H Waltz-16 decoupling). Polymer samples were prepared by dissolving about 35 mg of solid in ca. The cyclosporin sample was a sealed sample containing 50 mg of cyclosporin A in 0.5 mL of C 6D 6. Herein is reported an evaluation of various bs-HSQC and bs-HMBC sequences, first from a methodological point of view (selectivity, dependence to INEPT interpulse delay or relaxation delay), using the cyclic peptide cyclosporin selected as a model compound, and then from an applicative approach, comparing tacticity determined from bs-HSQC and bs-HMBC experiments to the one obtained from 1D 13C on the carbonyl region.ġD and 2D NMR spectra were recorded on a 500 MHz Bruker Av III HD spectrometer (Billerica, MA, USA), fitted with a direct broadband 5 mm probehead (BBO) carefully tuned on both 1H and 13C channels. Band-selective (bs) HSQC, improving spectral resolution by restriction of the heteronuclear dimension without inducing spectral folding, has been recently used for polymer tacticity determination.
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