Sorption and Conformational Characteristics of Reconstituted Plant Cuticular Waxes on Montmorillonite

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• 作者：Baoliang Chen and Baoshan Xing
• 刊名：Environmental Science & Technology
• 出版年：2005
• 出版时间：November 1, 2005
• 年：2005
• 卷：39
• 期：21
• 页码：8315 - 8323
• 全文大小：398K
• 年卷期：v.39,no.21(November 1, 2005)
• ISSN：1520-5851

文摘

Plant cuticular waxes are essential barriers that regulatethe transport of water and organic molecules to intactcuticular membranes. They also compose a significantfraction of the recalcitrant aliphatic components of soil organicmatter (SOM). In this study, we examined the sorptionand desorption of three polycyclic aromatic hydrocarbons(PAHs), naphthalene (NAPH), phenanthrene (PHEN), andpyrene (PYR), by cuticular waxes of green pepper (Capsicumannuum) that had been reconstituted by loading themonto montmorillonite (at four different loadings). Thereconstituted wax samples, with and without sorbed PAHs,were characterized by solid-state ¹³C NMR to supply theevidence of melting transition. The sorption isotherms fit wellto a Freundlich equation. Sorption isotherms werepractically linear except for that of PYR sorption to the low-load wax-montmorillonite sample. The organic-carbon-normalized sorption coefficients (K_oc) depended on PAH'slipophilicity (e.g., octanol-water partition coefficient)and increased with increasing wax-load on clay. Desorptionwas dependent on PAH's molecular sizes and sorbedamounts and on the wax load of the clay. Desorptionhysteresis was observed only at high loads of NAPH andPHEN, and it decreased with both increasing wax loadand molecular size (i.e. NAPH > PHEN >> PYR). Contributingto hysteresis, the melting transition of the reconstitutedwaxes after sorbing the PAHs was confirmed by solid-state ¹³C NMR data. Upon adsorption, the intensity of theNMR peak at 29 ppm (attributed to mobile amorphousparaffinic domains) increased, and a peak at 167 ppm(-COOH) appeared, reflecting the transition of solidamorphous to mobile amorphous domains in the reconstitutedwaxes. The intensity of melting induced by PAH adsorptiondecreased with increasing PAH molecular size.