Robinson Michelle D, Cistola David P
Nanoparticle Diagnostics Research Laboratory, Division of Research & Innovation, and Department of Integrative Physiology, University of North Texas Health Science Center , Fort Worth, Texas 76107, United States.
Biochemistry. 2014 Dec 9;53(48):7515-22. doi: 10.1021/bi5011859. Epub 2014 Nov 26.
The functional properties of lipid-rich assemblies such as serum lipoproteins, cell membranes, and intracellular lipid droplets are modulated by the fluidity of the hydrocarbon chain environment. Existing methods for monitoring hydrocarbon chain fluidity include fluorescence, electron spin resonance, and nuclear magnetic resonance (NMR) spectroscopy; each possesses advantages and limitations. Here we introduce a new approach based on benchtop time-domain (1)H NMR relaxometry (TD-NMR). Unlike conventional NMR spectroscopy, TD-NMR does not rely on the chemical shift resolution made possible by homogeneous, high-field magnets and Fourier transforms. Rather, it focuses on a multiexponential analysis of the time decay signal. In this study, we investigated a series of single-phase fatty acid oils, which allowed us to correlate (1)H spin-spin relaxation time constants (T2) with experimental measures of sample fluidity, as obtained using a viscometer. Remarkably, benchtop TD-NMR at 40 MHz was able to resolve two to four T2 components in biologically relevant fatty acids, assigned to nanometer-scale domains in different segments of the hydrocarbon chain. The T2 values for each domain were exquisitely sensitive to hydrocarbon chain structure; the largest values were observed for pure fatty acids or mixtures with the highest cis-double bond content. Moreover, the T2 values for each domain exhibited positive linear correlations with fluidity. The TD-NMR T2 and fluidity measurements appear to be monitoring the same underlying phenomenon: variations in hydrocarbon chain packing. The results from this study validate the use of benchtop TD-NMR T2 as a nanofluidity meter and demonstrate its potential for probing nanofluidity in other systems of biological interest.
富含脂质的聚集体（如血清脂蛋白、细胞膜和细胞内脂滴）的功能特性受烃链环境流动性的调节。现有的监测烃链流动性的方法包括荧光法、电子自旋共振法和核磁共振（NMR）光谱法；每种方法都有其优缺点。在此，我们介绍一种基于台式时域（1）H NMR弛豫测量法（TD-NMR）的新方法。与传统的NMR光谱法不同，TD-NMR不依赖于由均匀的高场磁体和傅里叶变换实现的化学位移分辨率。相反，它专注于对时间衰减信号进行多指数分析。在本研究中，我们研究了一系列单相脂肪酸油，这使我们能够将（1）H自旋-自旋弛豫时间常数（T2）与使用粘度计获得的样品流动性实验测量值相关联。值得注意的是，40 MHz的台式TD-NMR能够分辨生物相关脂肪酸中的两到四个T2成分，这些成分对应于烃链不同片段中的纳米级区域。每个区域的T2值对烃链结构极为敏感；在纯脂肪酸或顺式双键含量最高的混合物中观察到最大的T2值。此外，每个区域的T2值与流动性呈正线性相关。TD-NMR的T2测量值和流动性测量值似乎在监测相同的潜在现象：烃链堆积的变化。本研究结果验证了使用台式TD-NMR T2作为纳米流动性计的可行性，并证明了其在探测其他具有生物学意义的系统中的纳米流动性方面的潜力。
