scholarly journals Bimodal 1H Double Quantum Build-Up Curves by Fourier and Laplace-like Transforms on Aged Cross-Linked Natural Rubber

Polymers ◽  
2021 ◽  
Vol 13 (20) ◽  
pp. 3523
Author(s):  
Dumitrița Moldovan ◽  
Radu Fechete

The 1H DQ Fourier and Laplace-like spectra for a series of cross-linked natural rubber (NR) samples naturally aged during six years are presented and characterized. The DQ build-up curves of these samples present two peaks which cannot be described by classical functions. The DQ Fourier spectra can be obtained after a numeric procedure which introduces a correction time which depends less on the chosen approximation, spin-½ and isolated CH2 and CH3 functional groups. The DQ Fourier spectra are well described by the distributions of the residual dipolar coupling correlated with the distribution of the end-to-end vector of the polymer network, and with the second and fourth van Vleck moments. The deconvolution of DQ Fourier spectra with a sum of four Gaussian variates show that the center and the width of Gaussian functions increase linearly with the increase in the cross-link density. The Laplace-like spectra for the natural aged NR DQ build-up curves are presented. The centers of four Gaussian distributions obtained via both methods are consistent. The differences between the Fourier and Laplace-like spectra consist mainly of the spectral resolution in the favor of Laplace-like spectra. The last one was used to discuss the effect of natural aging for cross-linked NR.

2016 ◽  
Vol 49 (7) ◽  
pp. 574-594 ◽  
Author(s):  
Chaiwute Vudjung ◽  
Sayant Saengsuwan

A series of interpenetrating polymer network (IPN) hydrogels based on cross-linked natural rubber (XNR) and cassava starch (CSt) as biodegradable membrane material were synthesized via free radical polymerization in latex state using N, N′-methylene bisacrylamide (MBA) and maleic acid as cross-linkers. The IPN XNR/CSt hydrogels were confirmed and characterized by infrared spectroscopy, thermal analysis, and X-ray diffraction. The results showed that with increasing MBA content from 1.0 to 2.5 phr, cross-link density and gel fraction of XNR increased from 0.80 to 0.90 mol M−3 and from 19.7% to 30.5%, respectively. The gel fraction and tensile strength of the IPN XNR/CSt hydrogels also gradually increased as a function of MBA content but the water swelling and elongation at break decreased slightly. The IPN XNR/CSt containing 1.0 phr MBA displayed the highest water swelling of 82%. The weight retentions of IPN XNR/CSt hydrogels after soil degradations for 90 days increased from 48% to 56% with increasing MBA from 1.0 phr to 2.5 phr. The IPN XNR/CSt exhibited not only a good biodegradation but also high mechanical strength and flexibility. Also, the IPN XNR/CSt could be a promising candidate as a biodegradable membrane for longer released fertilizer application.


Biochemistry ◽  
2015 ◽  
Vol 54 (46) ◽  
pp. 6876-6886 ◽  
Author(s):  
Francisco N. Newby ◽  
Alfonso De Simone ◽  
Maho Yagi-Utsumi ◽  
Xavier Salvatella ◽  
Christopher M. Dobson ◽  
...  

2018 ◽  
Vol 4 (3) ◽  
pp. 33 ◽  
Author(s):  
Tsuyoshi Konuma ◽  
Aritaka Nagadoi ◽  
Jun-ichi Kurita ◽  
Takahisa Ikegami

Nuclear magnetic resonance relaxation dispersion (rd) experiments provide kinetics and thermodynamics information of molecules undergoing conformational exchange. Rd experiments often use a Carr-Purcell-Meiboom-Gill (CPMG) pulse train equally separated by a spin-state selective inversion element (U-element). Even with measurement parameters carefully set, however, parts of 1H–15N correlations sometimes exhibit large artifacts that may hamper the subsequent analyses. We analyzed such artifacts with a combination of NMR measurements and simulation. We found that particularly the lowest CPMG frequency (νcpmg) can also introduce large artifacts into amide 1H–15N and aromatic 1H–13C correlations whose 15N/13C resonances are very close to the carrier frequencies. The simulation showed that the off-resonance effects and miscalibration of the CPMG π pulses generate artifact maxima at resonance offsets of even and odd multiples of νcpmg, respectively. We demonstrate that a method once introduced into the rd experiments for molecules having residual dipolar coupling significantly reduces artifacts. In the method the 15N/13C π pulse phase in the U-element is chosen between x and y. We show that the correctly adjusted sequence is tolerant to miscalibration of the CPMG π pulse power as large as ±10% for most amide 15N and aromatic 13C resonances of proteins.


2021 ◽  
Vol 8 ◽  
Author(s):  
Ana Poveda ◽  
Giulio Fittolani ◽  
Peter H. Seeberger ◽  
Martina Delbianco ◽  
Jesús Jiménez-Barbero

The intrinsic flexibility of glycans complicates the study of their structures and dynamics, which are often important for their biological function. NMR has provided insights into the conformational, dynamic and recognition features of glycans, but suffers from severe chemical shift degeneracy. We employed labelled glycans to explore the conformational behaviour of a β(1-6)-Glc hexasaccharide model through residual dipolar couplings (RDCs). RDC delivered information on the relative orientation of specific residues along the glycan chain and provided experimental clues for the existence of certain geometries. The use of two different aligning media demonstrated the adaptability of flexible oligosaccharide structures to different environments.


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