Octadecylamine Monolayer Research Articles

Monolayer Characteristics of Mixed Octadecylamine and Stearic Acid at the Air/Water Interface

Mixed monolayers of stearic acid (SA) and octadecylamine (ODA) at the air/water interface were investigated in this article. The miscibility of the two compounds was evaluated by the measurement of surface pressure-area per molecule (pi-A) isothems and the direct observation of Brewster angle microscopy (BAM) on the water surface. The two compounds were spread individually on the subphase (method 1) or premixed first in the spreading solvent and then cospread (method 2). The effect of spreading method on the miscibility of the two compounds was also studied. The results show that the mixed monolayers prepared by method 1 cannot get a well-mixed state. The isotherms of mixed monolayers preserve both characteristics of SA and ODA and exhibit two collapse points. The calculated excess surface area is very small. Besides, distinguished domains corresponding to those of pure SA and ODA can be inspected from the BAM images. Such results indicate that SA and ODA cannot get a well-mixed phase via 2-dimensional mixing. On the contrary, in the mixed monolayer prepared by cospreading, the two compounds exhibit high miscibility. In the pi-A isotherms, the individual characteristics of SA and ODA disappear. The calculated excess area exhibits a highly positive deviation which indicates the existence of special interaction between the two compounds. The low compressibility of isotherm implies the highly rigid characteristic of the mixed monolayer. which was also sustained by the striplike collapse morphology observed from the BAM. The rigid characteristic of SA/ODA mixed monolayer was attributed to the formation of "catanionic surfactant" by electrostatic adsorption of headgroups of SA and ODA or to the formation of salt by acid-base reaction.

Elaboration of odorant biosensors based on Langmuir-Blodgett technique

The advent of electronic noses opened a new kind of analytical approach, which offers an easy, quick, and cheap measurement comparing to conventional analytical approaches. It has potential applications on many different fields, such as assessment of various foodstuffs and beverages, environmental contamination monitoring and medical diagnostics etc. In this study, we used odorant binding protein (OBP) as odor-sensing material for developing such kind of artificial odorant biosensor. And biological films of OBP-1F (rat OBP) were deposited by Langmuir-Blodgett (LB) technique on gold electrode previously functionalised with 1-octadecanethiol (ODT) by self-assembled monolayers (SAMs). It is known that successful immobilization of the Langmuir-Blodgett films depends strongly on the characteristics, particularly stability, of the corresponding Langmuir films at the air/water interface. Hence the characteristics of monolayer of amphiphile octadecylamine (ODA) and the mixed monolayer of ODA/OBP were studied. Electrochemical impedance spectroscopy (EIS) was used to monitor the response of the system to a specific odorant molecule, isoamyl acetate.

Interactions of lipid monolayers with the natural biopolymer hyaluronic acid

The interaction of the natural mucopolysaccharide hyaluronic acid with different lipids, present in the natural membranes, was studied at the lipid/water interface using thermodynamic methods and X-ray diffraction. The results show that this biopolymer modifies the properties and the structure of the lipid monolayer. The two-dimensional crystalline lattice and domain structure of the charged octadecylamine monolayer are strongly disturbed by the hyaluronic acid, the monolayer compressibility increases and the monolayer collapse pressure drops down. In addition, the presence of charged lipid interfaces influences the structural organisation of the hyaluronic acid at the membrane/water interfaces. The impacts of these results on the structural organisation at the membrane interface are discussed.

Interaction of Bauhinia monandra lectin (BmoLL) with lipid monolayers

The interfacial behavior of the hypoglycemia lectin BmoLL purified from the leaves of Bauhinia monandra, and its ability to interact with lipid monolayers has been studied by surface tension ( γ) measurements. The results of these experiments revealed that in the solution concentration range comprised between 0.2 and 1.0 mg/ml, there was an extremely pronounced increase in the BmoLL adsorption at the interface with the air phase. This adsorption at the higher studied BmoLL concentrations gave rise to a more gradual increase in the surface pressure ( π = γ 0− γ). The results showed also that the surface pressure of adsorbed films was pH dependent and it substantially increased at low pHs (between pH 4.0 and pH 2.5). Independently carried out ξ potential measurements demonstrated that BmoLL was negatively charged at all pHs and borne the highest charge at the pH around 5.5. The penetrant ability of BmoLL into the two different in chemical nature monolayers: (dioleoylphosphatidylcholine and octadecylamine) have been assessed measuring Δ π increments at constant area. It was observed that, whereas the monolayers of either pure dioleoylphosphatidylcholine (DOPC) or pure octadecylamine (ODA) stimulated BmoLL adsorption, the lectin adsorption within their mixtures strongly depended on both the content of positively charged octadecylamine in a mixture and on the monolayer compressibility. These findings are discussed in terms of both the electrostatic interaction involved in adsorption of BmoLL and of changes in monolayer compressibilities brought up by the addition of ODA molecules to the phospholipid. The relevance of this work to liposome preparations is indicated in the concluding remarks.

Effect of salt on the hybridization of DNA by sequential immobilization of oligonucleotides at the air-water interface in the presence of ODA/DOTAP monolayers

The effect of low ionic strength on the binding of preformed DNA duplexes and the hybridization of single-stranded oligonucleotides at the air–water interface in the presence of cationic Langmuir monolayers of octadecylamine (ODA), as well as 1,2-dioleoyloxytrimethylammonium propane (DOTAP), is investigated. The complexation of the single-stranded DNA molecules and preformed duplexes with NaCl in solution with ODA/DOTAP Langmuir monolayers was followed in time by monitoring the pressure–area isotherms, wherein a very large and rapid expansion of the ODA/DOTAP monolayer was observed. In the case of sequential immobilization of complementary oligonucleotides, after addition of the complementary strand and intercalator, there was not much expansion, indicative of the fact that equilibrium had been rapidly achieved. Langmuir–Blodgett (LB) films of the ODA/DOTAP–DNA complex were formed on different substrates and characterized using quartz-crystal microgravimetry (QCM), fluorescence spectroscopy, and thermal melting studies. These measurements clearly showed that the preformed duplexes retained their native form as double helices and further, hybridization of the complementary single-stranded DNA molecules had occurred at the air–water interface, leading to the characteristic double-helical structure.

Relaxation Behaviors of Monolayers of Octadecylamine and Stearic Acid at the Air/Water Interface

This study investigated the relaxation behaviors of octadecylamine (ODA), stearic acid (SA), and SA/ODA mixed monolayers at the air/water interface. Area relaxations of monolayers at constant surface pressure were studied by a nucleation and growth mechanism and by direct observation using a Brewster angle microscope (BAM). The results showed that ODA and SA monolayers exhibit different characteristics in the area loss and in the BAM morphology. In the initial relaxation stage, SA monolayer illustrates a more stable characteristic than ODA. But at the later stage, the area loss of SA monolayer increases more quickly than that for ODA due to significant nucleation and growth of 3D aggregates. The BAM results demonstrated that 3D aggregates of large scale domains are likely to form on a SA monolayer even when the area loss is insignificant. On the contrary, only dotlike aggregates of low density were found on the ODA monolayer when relaxation is carried out at higher surface pressure. The relaxation behavior of SA monolayer can be described by the Vollhardt model. However, the relaxation of ODA monolayer does not follow the nucleation model described by Vollhard but can reasonably be attributed to the effect of dissolution. For the SA/ODA mixed monolayers, the relaxation behaviors in the initial and final stages follow different mechanisms, which is attributed to the formation of distinct phases as observed from the BAM. This result also implied that SA and ODA are not completely miscible to be a homogeneous phase. Phases of various compositions were formed in the mixed monolayers, and thus, the relaxation mechanism was shifted during the relaxation process as dominated by different relaxation behaviors of various phases.

Time-dependent complexation of glucose-reduced gold nanoparticles with octadecylamine Langmuir monolayers

We report on the reduction of aqueous chloroaurate ions by glucose to form gold nanoparticles of uniform size. We further demonstrate the complexation of these particles with octadecylamine (ODA) monolayers at the air–water interface. Pressure–area ( π– A) isotherms as a function of time of complexation revealed a significant expansion of the monolayer. Surface pressure variation with time for constant areas after spreading of the monolayer was carried out to observe the kinetics of complexation of the colloidal particles at the interface. The kinetics of complexation of the particles at the interface was also monitored by Brewster angle microscopy (BAM) measurements. Langmuir–Blodgett films of the particles complexed with ODA were formed at a subphase pH of 9 onto different substrates. Quartz crystal microgravimetry (QCM) was used to quantify the amount of particles deposited per immersion cycle of the quartz crystal. The LB films were further characterized by UV–vis and transmission electron microscopy (TEM) measurements. TEM measurements indicate a close packed and equidistant arrangement of colloidal particles in the LB film, probably due to hydrogen-bonding interactions.

Time-Dependent Complexation of Cysteine-Capped Gold Nanoparticles with Octadecylamine Langmuir Monolayers at the Air−Water Interface

In this paper, we present time-dependent studies on the complexation of cysteine-capped gold nanoparticles with octadecylamine (ODA) Langmuir monolayers. The cysteine molecules bound to the colloidal gold surface via thiolate linkages impart a net negative charge to the particles due to deprotonated carboxylic acid groups. Strong attractive electrostatic interaction between the negatively charged gold nanoparticles and positively charged ODA monolayer drives the complexation process. The extent of complexation of the gold nanoparticles and subsequent Langmuir−Blodgett (LB) film formation is a function of charge on the particles/monolayer. The charge on the nanoparticles/monolayer may be controlled by simple variation of the subphase pH. At pH 9, the carboxylic acid groups on the particles are highly ionized leading to strong electrostatic attraction with the protonated ODA monolayer, while at pH 12, the ODA monolayer is deprotonated leading to a reduction in the electrostatic interaction. The nanoparticle...

Growth of cubic crystals of cobalt-hexacyanoferrate under the octadecyl amine monolayer

Highly oriented cubic crystals of Cobalt (II)-hexacyanoferrate (III) (Co-hcf) are formed at the air–water interface under the compressed Langmuir monolayer of octadecyl amine (ODA) when we react K 3Fe(CN) 6 solution with cobalt (II) chloride solution in the sub-phase, while no crystals are formed at the air–water interface without the ODA monolayer. X-ray diffraction and electron diffraction studies indicate that these Co-hcf crystals are oriented with their {1 0 0} plane parallel to the monolayer. Transmission electron microscopy and atomic force microscopy reveal that cubic crystals with sides of 50–300 nm are initially formed, which grow further with time and coalesce to form a thin film. Cyclic voltammetry on those Co-hcf films, transferred on gold coated glass, indicates the presence of a surface couple corresponding to Fe(CN) 6 3−/Fe(CN) 6 4− system. Present study gives an insight into the in situ growth behaviour of crystals and has implications in the design and development of advanced materials for devices.

Thermodynamics of Phase Transitions in Langmuir Monolayers Observed by Vibrational Sum Frequency Spectroscopy

Vibrational sum-frequency spectroscopy (VSFS) was used to study gauche defects in octadecylamine (ODA) monolayers at the air/water interface. The VSFS spectra provide unique insights into phase transitions that occur as a result of changes in the structure of the monolayer's hydrophobic region. These changes can be attributed to the increased presence of gauche conformers in the ODA alkyl chains during the monolayer's transition from the solid to liquid phase. Temperature-dependent spectra from monolayers at several different pressures were used to assign the phase transition temperature based on the observed changes in microscopic structure. Through application of a two-dimensional form of the Clapeyron equation, the first in situ measurements of the entropy and enthalpy changes associated with gauche conformers in a monolayer were made.

Studies on the formation of Langmuir monolayer and Langmuir–Blodgett films of octadecyl amine-bromocresol purple dye complex

Properties of the monolayer of octadecyl amine (ODA) molecules on aqueous solution of bromocresol purple (Bcp) dye have been studied over a wide range of pH by measuring the surface pressure-area isotherms. A strong interaction of ODA molecule was observed with the dye molecule in the pH range of 4–9. Under the present study, the dye molecules were adsorbed on the ODA monolayer at the water surface and subsequently a Langmuir–Blodgett (LB) film of ODA–dye complex was transferred from the air–water interface onto a solid substrate. Alternatively, dye molecules were incorporated into LB film by immersing the predeposited LB film of pure ODA into the dye solution, i.e. by adsorption of dye molecule at the solid–liquid interface. The adsorption behavior of ODA–Bcp dye complexes obtained through these two different routes was characterised with the help of UV–Visible spectroscopy. The nature of the ODA–dye complex deposited from air–water interface using the LB technique was found to be quite different from that of the complex formed by the adsorption of the dye into the pure ODA LB film. The adsorption spectra of the ODA–dye complex obtained from the air–water interface did not change with pH, while those of the ODA–dye complex formed from the solid–liquid interface showed pH dependence.

Adsorption of glucose oxidase into lipid monolayers: effect of a lipid headgroup charge

The effect of both lipid headgroup charge and of aqueous subphase pH on adsorption of glucose oxidase molecules (GOx) into dibehenoylphosphatidylcholine (DBPC) and octadecylamine (ODA) monolayers has been studied by surface tension and surface pressure measurements. The results revealed that whereas the extent of GOx adsorption into pure DBPC monolayers essentially depended on the area in a monolayer available to harbor adsorbing GOx molecules, enhanced enzyme penetration into a monolayer occurred at high surface densities. The kinetics of enzyme penetration was found to be dependent of the initial surface pressure of a spread monolayer. The addition of ODA to DBPC monolayers gave a dramatic boost to GOx penetration and at high molecular surface densities largely depended on the ratio of ODA in the mixed monolayers. This increase in GOx penetration was attributed to the strong attractive electrostatic interaction between the positively charged ODA and the negatively charged enzyme.

Molecular Packing Changes of Octadecylamine Monolayers on Mica Induced by Pressure and Humidity

The molecular packing structure of octadecylamine molecules forming self-assembled monolayers on mica has been studied by AFM as a function of mechanical pressure and humidity. Upon increasing the load applied by the AFM tip, the thickness of the monolayer was observed to change discretely, which we explain as the result of stepwise tilting of the molecules. Thickness changes were also observed when the films were exposed to high humidity. In this case, we propose that the driving force for such a behavior is the relaxation of electrostatic repulsions between protonated amino groups.

Crystallization of Prussian Blue Analogues at the Air−Water Interface Using an Octadecylamine Monolayer as a Template

We demonstrate the use of a Langmuir monolayer as a templating agent for growth of oriented crystals of metal(II) −hexacyanoferrate(III) (where metal can be Ni, Co, or Cu), popularly known as the Prussian Blue analogues, crystals of which are difficult to grow by conventional means. Crystalline films of metal(II) −hexacyanoferrate(III) are deposited at the air−water interface, under an octadecylamine (ODA) monolayer in a Langmuir trough, upon addition of K3Fe(CN)6 solution into the subphase containing aqueous metal chloride solution. Template action to promote crystallization at the air−water interface appears to be provided by the protonated ODA molecules. In the absence of the template (without ODA), no crystals are deposited and instead a precipitation reaction occurs resulting in the formation of a nonoriented cubic M3[Fe(CN)6]2·nH2O (M = Ni, Co, or Cu) precipitate. Crystalline Ni−hexacyanoferrate films formed through the template action were characterized using X-ray diffraction (XRD), transmission electron microscopy, X-ray photoelectron spectroscopy, and so forth. We also report initial results on the formation of crystalline Co(II)− and Cu(II)−hexacyanoferrate(III) films by XRD results.

PNA−DNA Hybridization at the Air−Water Interface in the Presence of Octadecylamine Langmuir Monolayers

Sequential immobilization of single-stranded complementary DNA and peptide nucleic acid (PNA) molecules at the air−water interface with cationic Langmuir monolayers is demonstrated. The complexation of the single-stranded DNA/PNA molecules with octadecylamine (ODA) Langmuir monolayers was followed in time by monitoring the pressure−area isotherms. A large (and slow) expansion of the ODA monolayer was observed during immobilization of single-stranded DNA at the air−water interface, and interestingly, no further expansion was detected on addition of PNA to the subphase. However, quartz crystal microgravimetry and UV-melting analysis of Langmuir−Blodgett films of the ODA−PNA−DNA hybrid monolayer clearly showed that the sequential immobilization process had resulted in hybridization of the complementary single-stranded DNA molecules with PNA at the air−water interface.

Preparation and Characterization of Self-Assembled Monolayers of Octadecylamine on Mica Using Hydrophobic Solvents

The formation of self-assembled monolayers of octadecylamine on mica from chloroform solutions has been studied ex situ with atomic force microscopy (AFM). Growth occurs in the form of islands with structure and properties that depend critically on preparation conditions. Inside the islands, the molecules are oriented such that they expose the terminal CH3 group and are tilted with respect to the normal direction of the surface. The weak bond between mica and the polar amino (−NH2) group results in weak mechanical stability of the islands, which are easily damaged by the AFM tip during repetitive scans. The influence of several preparation parameters on the islands' structure has been analyzed and discussed on the basis of a model involving residual water molecules on the mica substrate.

Spectroscopic and Structural Studies on Adsorption of Azo Dye in Cationic Langmuir–Blodgett Films

Abstract The monolayer properties of octadecylamine at various pHs on the Naphthalene Red (NR) aqueous solution were studied from the measurements of surface pressure–area isotherms. It was observed that the presence of the azo dye substituted with the –OH group (NR) in the subphase affects the compressibility of the octadecylamine monolayer. The adsorbability of the cationic Langmuir–Blodgett (LB) films was investigated by NR as an adsorbate. The cationic LB films before and after the azo dye adsorption were characterized by UV–vis absorption and emission spectroscopy, polarized visible absorption, X-ray diffraction, FTIR spectroscopy, and atomic force microscopy. Strong dipole–dipole interaction between the NR molecules in functionalized LB films was observed in accordance with the exciton model. It was found that the adsorption of the azo dye induced rearrangement of the layer structure of the cationic LB films where the hydrocarbon chains of the amine molecules exhibited an interdigitated structure and the azo dye molecules adsorbed in the LB films were oriented in an edge-on configuration. Furthermore, the substituent position of the –OH group of NR plays a crucial role in the different ways on the orientation of the other azo dyes in organized assembly.

Adsorption behaviour of alizarine violet molecules onto the Langmuir–Blodgett films of octadecylamine

The monolayer properties of a long-chain amine were investigated at the air–water interface on addition of an anionic anthraquinone dye in the aqueous subphase. From the pressure–area isotherms at various pHs, hydroxide ions of NaOHaq and the sulfonate ions of Alizarine Violet (AV) in the subphase were found to interact competitively with the octadecylamine monolayer. The adsorbability of the cationic Langmuir–Blodgett (LB) films was investigated using AV as an adsorbate. Steady-state absorption and emission spectroscopy indicated the difference in order, arrangement and orientation of the AV molecule in the restricted geometry of the LB films depending upon the adsorption conditions. Structural characteristics of the LB films were realized by low-angle X-ray diffraction and FTIR spectroscopy. AFM images provided information on the topography of the film surface and rearrangement of the layer structure during the adsorption process.

Study of the mechanism for controlled crystallization of BaF2 under two kinds of monolayers

Controlled crystallization of BaF2 under two different kinds of monolayers, octadecylamine [CH3(CH2)17NH2] and hexadecanol [CH3(CH2)14CH2OH], has been studied by using x-ray diffraction (XRD) and scanning electron microscope. It was found that the monolayer headgroup, the degree of ionization of the headgroup, etc., had a complicated effect on the selectivity of monolayers for crystal and on the morphology and orientation of crystals grown under the compressed monolayers. At pH = 7.0, XRD analysis showed that (100)-oriented BaF2 crystals were formed under the octadecylamine monolayer, while several kinds of crystals were found under the hexadecanol monolayer. In comparison, at pH = 8.5, both (100)-oriented BaF2 and (111)-oriented Ba(NO3)2 crystals were obtained under the monolayer of octadecylamine. However, crystals formed under hexadecanol monolayer consist of BaF2, Ba(NO3)2, etc. The detailed mechanism for crystallization was discussed in terms of the specific interaction and lattice matching between the monolayer headgroup and the nucleating species.

Hybridization of DNA by Sequential Immobilization of Oligonucleotides at the Air−Water Interface

The hybridization of DNA by sequential electrostatic and hydrogen-bonding immobilization of single-stranded complementary oligonucleotides at the air−water interface with cationic Langmuir monolayers is demonstrated. The complexation of the single-stranded DNA molecules with octadecylamine (ODA) Langmuir monolayers was followed in time by monitoring the pressure−area isotherms. A large (and slow) expansion of the ODA monolayer was observed during each stage of complexation in the following sequence: primary single-stranded DNA followed by complementary single-stranded DNA followed by the intercalator, ethidium bromide. Langmuir−Blodgett (LB) films of the ODA−DNA complex were formed on different substrates and characterized using quartz-crystal microgravimetry (QCM), Fourier transform infrared spectroscopy (FTIR), polarized-UV−vis and fluorescence spectroscopy, as well as thermal melting studies. These measurements clearly showed that hybridization of the complementary single-stranded DNA molecules had occ...