- Molecular Origin of the Odd-Even Effect of Macroscopic Properties of n-Alkanethiolate Self-Assembled Monolayers: Bulk or Interface?
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Elucidating the influence of the monolayer interface versus bulk on the macroscopic properties (e.g., surface hydrophobicity, charge transport, and electron transfer) of organic self-assembled monolayers (SAMs) chemically anchored to metal surfaces is a challenge. This article reports the characterization of prototypical SAMs of n-alkanethiolates on gold (CH3(CH2)nSAu, n = 6-19) at the macroscopic scale by electrochemical impedance spectroscopy and contact angle goniometry, and at the molecular level, by infrared reflection absorption spectroscopy. The SAM capacitance, dielectric constant, and surface hydrophobicity exhibit dependencies on both the length (n) and parity (nodd or neven) of the polymethylene chain. The peak positions of the CH2 stretching modes indicate a progressive increase in the chain conformational order with increasing n between n = 6 and 16. SAMs of nodd have a greater degree of structural gauche defects than SAMs of neven. The peak intensities and positions of the CH3 stretching modes are chain length independent but show an odd-even alternation of the spatial orientation of the terminal CH3. The correlations between the different data trends establish that the chain length dependencies of the dielectric constant and surface hydrophobicity originate from changes in the polymethylene chain conformation (bulk), while the odd-even variation arises primarily from a difference in the chemical composition of the interface related to the terminal group orientation. These findings provide new physical insights into the structure-property relation of SAMs for the design of ultrathin film dielectrics as well as the understanding of stereostructural effects on the electrical characteristics of tunnel junctions.
- Ben Amara, Fadwa,Dionne, Eric R.,Kassir, Sahar,Pellerin, Christian,Badia, Antonella
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supporting information
p. 13051 - 13061
(2020/09/01)
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- Synthesis, critical micelle concentrations, and antimycobacterial properties of homologous, dendritic amphiphiles. Probing intrinsic activity and the "cutoff" effect
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Newkome-type, 1→3 C-branched dendrons make an excellent headgroup for amphiphiles with ultralong, saturated, linear alkyl chains. Synthesis of a homologous series of five such amphiphiles from 14 to 22 carbons- RNHCONHC(CH2CH2CO2H)3, R = n-C nH2n+1, n = 14, 16, 18, 20, 22-proceeds readily. These amphiphiles are soluble in aqueous solutions of triethanolamine. Surface-tension measurements on this homologous series reveal an unusually gradual decrease in log critical micelle concentration (CMC) as the chain length increases. In fact, the tetradecyl homologue does not appear to form micelles. Further, measurements of minimal inhibitory concentration (MIC) by broth microdilution against Mycobacterium smegmatis as a function of the initial cell density provide a direct measure of the intrinsic activity (MIC0) of each homologue. The hexadecyl homologue is the most active at inhibiting growth with an MIC0 equal to 3.5 × 10-5 M, which is 100-fold below the CMC.
- Sugandhi, Eko W.,Macri, Richard V.,Williams, André A.,Kite, Brett L.,Slebodnick, Carla,Falkinham III, Joseph O.,Esker, Alan R.,Gandour, Richard D.
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p. 1645 - 1650
(2008/02/01)
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- SYNTHESIS OF HIERRIDIN, A PHENOL FROM THE LICHEN, RAMALINA HIERRENSIS
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A five-step reaction sequence was used to synthesize hierridin (2,4-dimethoxy-6-heneicosanylphenol), a new compound isolated from the lichen Ramalina hierrensis. Key Word Index: Ramalina hierrensis; lichen; hierridin; 2,4-dimethoxy-6-heneicosanylphenol.
- a Rodriguez
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p. 1436 - 1439
(2007/10/02)
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