کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
9594179 | 1395486 | 2005 | 10 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
A study of the headgroup motion of sphingomyelin using 31P NMR and an analytically soluble model
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موضوعات مرتبط
مهندسی و علوم پایه
شیمی
شیمی تئوریک و عملی
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چکیده انگلیسی
A 31P NMR investigation has been carried out of the headgroup dynamics of sphingomyelin molecules in bilayers for the Lα and LβⲠphases. The resulting line shapes have been analysed in terms of a reduced-parameter model, using van Faassen's method for obtaining an analytic solution to first-order stochastic differential equations to simulate the line shapes of oriented and non-oriented samples. Our treatment results in good fits to measured data but using fewer parameters than traditional methods. Angles and correlation times (Ï|| and Ïâ¥) describing the geometry and dynamics of the headgroup are obtained by optimising the agreement between simulated and experimental data. The results are contrasted with those obtained for the lecithins DMPC and DPPC using a similar analysis. Not only are Ï|| and Ï⥠now equal in value for the Lα phase, but this value is also found to be nearly four times larger than the longest correlation time for the lecithins. We interpret this as evidence of inter- and intramolecular hydrogen bonding in the Lα phase of sphingomyelin. In the LβⲠphase of sphingomyelin, however, although Ï|| and Ï⥠remain equal their value is now 32% smaller than that of the lecithins in the same phase. This indicates less difference between the fluidities in the headgroup region of the two phases of sphingomyelin as compared to that of the lecithins. Another significant difference between the LβⲠphases is that the tilt angle for sphingomyelin is found to be nearly twice as large as for the lecithins. We argue that these combined observations point to the existence of hydrogen bonding in this phase also. Again in contrast to our previous work on lecithins, our results provide evidence of a negative diamagnetic anisotropy in sphingomyelin molecules, even in the LβⲠphase. This is provided for in our model by the assumption that our unoriented samples consist of prolate ellipsoidal liposomes whose major axes are oriented parallel to the static magnetic field. The apparently different diamagnetic behaviour of sphingomyelin in the present work is due to the higher static field used rather than any intrinsic difference in this respect between sphingomyelin and the lecithins DMPC and DPPC.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Solid State Nuclear Magnetic Resonance - Volume 27, Issue 4, June 2005, Pages 247-256
Journal: Solid State Nuclear Magnetic Resonance - Volume 27, Issue 4, June 2005, Pages 247-256
نویسندگان
I.C. Malcolm, J.C. Ross, J. Higinbotham,