Fig. 2: 1H NMR and 13C NMR spectra of the polyisoprene extracted from P. sepium. | Communications Biology

Fig. 2: 1H NMR and 13C NMR spectra of the polyisoprene extracted from P. sepium.

From: Characterization of cis-polyisoprene produced in Periploca sepium, a novel promising alternative source of natural rubber

Fig. 2

a Four major signals appeared at 2.04, 5.12, 2.05, and 1.68 ppm, which were assigned to the methylene (-CH2-), methyne (-CH=), methylene (-CH2-), and methyl (-CH3) protons (H1, H3, H4, and H5) in the 1H-NMR spectra, while five major signals appeared at 39.35, 135.18, 125.00, 26.37, and 23.40 ppm, which were assigned to the methylene, olefinic (-Ċ=), methyne, methylene, and methyl carbons (C1, C2, C3, C4, and C5) in the 13C-NMR spectra, respectively, indicating that the central isoprene units of the polyisoprene are linked in the cis-1,4-configuration; The signals at 4.57 and 62.28 ppm in the 1H-NMR and 13C-NMR spectra were assigned to the methylene proton or carbon (H4 or C4) in the α-terminal isoprene unit, and the signals at 3.64 and 45.36 ppm in the 1H-NMR and 13C-NMR spectra were assigned to the trimethyl (-(CH3)3) structure; These signals suggest that the α-terminal isoprene unit of the polyisoprene may consist of monophosphate and diphosphate (cis-α(cis)-(OPO3)1-2) linked with phospholipids (N+(CH3)3). b Four minor signals at 1.57, 1.58, 1.59, 1.60 ppm in the 1H-NMR spectra and at 19.74, 15.95, 16.00, 16.13 ppm in the 13C-NMR spectra, which were assigned to the methyl protons or carbons (H5 or C5) in the ω-terminal (ω(trans)), trans-1 (ω-trans-trans), trans-2 (trans-trans-trans), and trans-3 (trans-trans-cis) isoprene units; These signals were distinctly different from the signals at 1.68 or 23.40 ppm in corresponding proton or carbon (H5 or C5) of the central isoprene units in the 1H-NMR or 13C-NMR spectra that were assigned to cis-configuration, indicating that the ω-terminal isoprene units of the polyisoprene are followed by 2-3 isoprene units in the trans-1,4-configuration. c Four minor signals appeared at 4.73, 2.03, 1.26, and 1.60 ppm, which were assigned to the methylene, methyne, methylene, and methyl protons (H1, H3, H4, and H5) in the 1H-NMR spectra, and five minor signals appeared at 109.33, 150.52, 42.81, 29.34, and 19.74 ppm, which were assigned to the methylene, olefinic, methyne, methylene, and methyl carbons (C1, C2, C3, C4, and C5) in the 13C-NMR spectra, respectively. These signals corresponded to the 3,4-isoprene unit, indicating that the polyisoprene contains an abnormal 3,4-isoprene side group.

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