Influence of an Amide Group in Methyl Octadecanoates on the Monolayer Stability
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- 作者：Katharina Dreger ; Li Zhang ; Hans-Joachim Galla ; Harald Fuchs ; Lifeng Chi ; Ernst-Ulrich Wü ; rthwein ; and Hans Jü ; rgen Schä ; fer
- 刊名：Langmuir
- 出版年：2006
- 出版时间：February 14, 2006
- 年：2006
- 卷：22
- 期：4
- 页码：1586 - 1594
- 全文大小：504K
- 年卷期：v.22,no.4(February 14, 2006)
- ISSN：1520-5827
文摘
The influence of a hydrogen bond donor and acceptor in the hydrophobic part of an amphiphile on the monolayerstability at the air/water interface is investigated. For that purpose, the amide group is integrated into the alkyl chain.Eight methyl octadecanoates have been synthesized with the amide group in two orientations and in different positionsof the alkyl chain, namely, CH3O2C(CH2)mNHCO(CH2)nCH3 (n + m = 14): 1 (m = 1), 3 (m = 2), 5 (m = 3), 7 (m= 14); and CH3O2C(CH2)mCONH(CH2)nCH3: 2 (m = 1), 4 (m = 2), 6 (m = 3), 8 (m = 14). The monolayers havebeen characterized by their 
/A isotherms, their temperature dependence and Brewster angle microscopy (BAM).Amphiphile 1 with the amide group close to the ester group (m = 1) behaves like an unsubstituted fatty acid ester,while 3, 5, and 7, with the amide group in an intermediate and terminal position, exhibit a two-phase region. Theamphiphiles 2, 4, 6, and 8, with a reversed orientation of the amide group, all exhibit a two-phase region with higherplateau pressures and lower collapse pressures than those of 1, 3, 5, and 7. For 7 and 8, domains of the liquid condensed(LC) phase are visualized by BAM in the two-phase region. The liquid expanded (LE)/LC-phase transitions are allexothermic with enthalpies 
H ranging from -31 to -12 kJ/mol. Comparison with other bipolar amphiphiles indicatesthat the LC phase is better stabilized by the hydroxy and dihydroxy groups than by the amide group. For modelcompounds of 1-4, optimized conformers in the LE and LC phases have been determined by density functional theory(DFT) calculations.
/A isotherms, their temperature dependence and Brewster angle microscopy (BAM).Amphiphile 1 with the amide group close to the ester group (m = 1) behaves like an unsubstituted fatty acid ester,while 3, 5, and 7, with the amide group in an intermediate and terminal position, exhibit a two-phase region. Theamphiphiles 2, 4, 6, and 8, with a reversed orientation of the amide group, all exhibit a two-phase region with higherplateau pressures and lower collapse pressures than those of 1, 3, 5, and 7. For 7 and 8, domains of the liquid condensed(LC) phase are visualized by BAM in the two-phase region. The liquid expanded (LE)/LC-phase transitions are allexothermic with enthalpies H ranging from -31 to -12 kJ/mol. Comparison with other bipolar amphiphiles indicatesthat the LC phase is better stabilized by the hydroxy and dihydroxy groups than by the amide group. For modelcompounds of 1-4, optimized conformers in the LE and LC phases have been determined by density functional theory(DFT) calculations.