Abstract
We have synthesized first novel dihexadecyl phosphate (DHGP-n) gemini surfactants containing alkyl chain ((CnH2n); n = 3, 4, 5, and 6) spacers. Surfactants were used to form monolayers on water surface. Surface tension measurement (STm), Brewster angle microscopy (BAM), and density functional theory (DFT) calculation were used to investigate these monolayers. Surface pressure (π) and molecular area (A); π-A isotherm curves of all DHGP-n gemini surfactants showed a gradual increase in surface pressure without any break points in the curves, confirmed the formation of liquid-expand (LE) type monolayers. BAM observations also supported the STm results. Limited molecular area (A0) of these monolayers depended on the spacer of gemini surfactants without spacer n = 4. Longer alkyl chain spacer in the series had higher value of A0 in π-A isotherm plots. In the series, A0 of spacer n = 4 was smallest among A0 values of other spacers. Density functional theory (DFT) method calculation also confirmed π-A isotherm curves pattern of these surfactants. Calculation showed that both odd and even numbers and length of the alkyl chain spacer influenced the structure of DHGP-n monolayer formation on the water surface.
Highlights
Amphiphilic compounds including phosphate group such as phospholipids are fundamental components of many creatures
Density functional theory (DFT) method calculation confirmed π-A isotherm curves pattern of these surfactants. Calculation showed that both odd and even numbers and length of the alkyl chain spacer influenced the structure of DHGP-n monolayer formation on the water surface
Monolayer of 1-OP was obtained by using dropping method for comparison with DHGP-n surfactants
Summary
Amphiphilic compounds including phosphate group such as phospholipids are fundamental components of many creatures. Monoalkyl phosphate (MAP, Figure 1(a)) is an important candidate for investigation and elucidation of the above phenomena similar to two alkyl chains phospholipid such as dipalmitoyl phosphatidyl choline (DPPC) commonly and commercially known as lecithin. “gemini” surfactant essentially has a structure in which two general or common category monosurfactants having one hydrophobic and one hydrophilic moiety are connected by a spacer group such as an alkyl chain or a peptide group [9] [10] [11]. Gemini surfactants have two hydrophobic alkyl chains, they are better candidates to prepare and investigate model membranes for applications in drug delivery systems (DDS) [12] [13] [14]
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