Liquid-phase characterization of molecular interactions in polyunsaturated and n-fatty acid methyl esters by1H low-field nuclear magnetic resonance

Biotechnology for Biofuels

Nitzan Meiri³  Paula Berman³  Luiz Alberto Colnago²  Tiago Bueno Moraes¹  Charles Linder⁴  Zeev Wiesman³ 

[1] Instituto de Física de São Carlos, Universidade de São Paulo, Av. Trabalhador Sao-Carlense 400, São Carlos 13566-590, SP, Brazil

[2] Embrapa Instrumentação, Rua 15 de Novembro 1452, São Carlos 13560-970, SP, Brazil

[3] The Phyto-Lipid Biotechnology Lab, Departments of Biotechnology, Energy and Environmental Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel

[4] Zuckerberg Center for Water Sciences and Technology and Department of Biotechnology, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel

关键词: Translational motion;    Segmental motion;    Molecular packing;    Melting point;    Fatty acid methyl esters;    Biodiesel physical properties;    1H low-field nuclear magnetic resonance relaxometry;   

Others  :  1219145
DOI  :  10.1186/s13068-015-0280-5

 received in 2015-04-22, accepted in 2015-06-29,  发布年份 2015

【 摘 要 】

Background

To identify and develop the best renewable and low carbon footprint biodiesel substitutes for petroleum diesel, the properties of different biodiesel candidates should be studied and characterized with respect to molecular structures versus biodiesel liquid property relationships. In our previous paper,¹ H low-field nuclear magnetic resonance (LF-NMR) relaxometry was investigated as a tool for studying the liquid-phase molecular packing interactions and morphology of fatty acid methyl esters (FAMEs). The technological potential was demonstrated with oleic acid and methyl oleate standards having similar alkyl chains but different head groups. In the present work, molecular organization versus segmental and translational movements of FAMEs in their pure liquid phase, with different alkyl chain lengths (10–20 carbons) and degrees of unsaturation (0–3 double bonds), were studied with¹ H LF-NMR relaxometry and X-ray,¹ H LF-NMR diffusiometry, and¹³ C high-field NMR.

Results

Based on density values and X-ray measurements, it was proposed that FAMEs possess a liquid crystal-like order above their melting point, consisting of random liquid crystal aggregates with void spaces between them, whose morphological properties depend on chain length and degree of unsaturation. FAMEs were also found to exhibit different degrees of rotational and translational motions, which were rationalized by chain organization within the clusters, and the degree and type of molecular interactions and temperature effects. At equivalent fixed temperature differences from melting point, saturated FAME molecules were found to have similar translational motion regardless of chain length, expressed by viscosity, self-diffusion coefficients, and spin-spin (T₂ )¹ H LF-NMR. T₂distributions suggest increased alkyl chain rigidity, and reduced temperature response of the peaks’ relative contribution with increasing unsaturation is a direct result of the alkyl chain’s morphological packing and molecular interactions.

Conclusions

Both the peaks’ assignments for T₂distributions of FAMEs and the model for their liquid crystal-like morphology in the liquid phase were confirmed. The study of morphological structures within liquids and their response to temperature changes by¹ H LF-NMR has a high value in the field of biodiesel and other research and applied disciplines in numerous physicochemical- and organizational-based properties, processes, and mechanisms of alkyl chains, molecular interactions, and morphologies.

【 授权许可】

   
2015 Meiri et al.

【 图 表 】

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