Stable Langmuir monolayers

Shimomura and Kunitake have reported that stable monolayers and LB films were obtained by electrostatic interaction of water soluble anionic polymers with cationic amphiphiles [58]. This polyion-complexation was also a useful method for stabilization of monolayers of unstable [59] or water soluble anionic surfactants [60]. Mixtures of water soluble cationic and anionic surfactants (1 1) also formed stable Langmuir monolayers at the air/ water interface [60]. 

Fig. 4.11 The asymmetric rod-coil molecules form stable Langmuir monolayers at the air-water interface as shown by it-A isotherms for molecule 1 (solid line) and molecule 2 (dashed line) with deposition points indicated by arrows. (From ref. [73])...

The Bingel macrocyclization has been increasingly exploited in the construction of molecular building blocks for supramolecular systems. For this purpose, cis-2 bis-adducts, such as 43 with a m-xylylene tether (Scheme 7-8), have been particularly useful. Thus, bis-adducts 55 [70], a fullerene-glycodendron conjugate, and 56 [71] were shown to form stable Langmuir monolayers at the air-water interface (Scheme 7-9). 

The same group showed that pure Pluronics produced reasonably stable Langmuir monolayers, which seemed, however, to be far from thermodynamic equilibrium due to the fact that high compression rates were applied [55]. The monolayers were of liquid expanded character, and a short pseudo-plateau at 12mNm was only observed for the polymers with short PEO blocks. This result does not seem consistent with the interpretation of the monolayer morphology, where the plateau is described as the result of PEO desorption from the air-water... 

However, transfer of the monolayers to solid substrates was inefficient because of the small size of the hydrophilic anchor, which imparted a hydrophobic/hydrophilic imbalance. Accordingly, increasing the size of the hydrophilic anchor facilitated the formation of stable Langmuir films that could be transferred to sohd substrates with a transfer ratio of 1 (Nierengarten et al. 2001). Bayer s research group reported a related approach in which the fullerene was modified with carboxylate-terminated dendrons and alkyl chains (Maierhofer et al. 2000). This amphiphilic fullerene derivative formed stable monolayers that could be compressed and expanded without hysteresis (Fig. 11.46d Maierhofer et al. 2000). 

Langmuir monolayers play some part in the preparation of multi-layer systems, now mostly referred to as self-assembled monolayers or multilayers (SAM s). However, this role is modest because it is difficult to make Langmuir-Blodgett layers sufficiently perfect and stable to function in new materials, such as electronic and bio-mimetic devices. One approach of stabilizing LB films is by working with molecules having double bonds that, after deposition, are polymerized. Such layers are stable enough to serve as a substrate for protein adsorption ). 

Three common film architectures can result from vertical deposition (Fig. 6). In X-type LB films, a Langmuir monolayer is consistently transferred onto a hydrophobic substrate so that it maintains head-tail interactions. In Z-type LB films, the monolayer is transferred onto a hydrophilic substrate that also forms head-tail interactions. X- and Z-type films are not common but can be prepared on a specially designed trough. However, some amphiphiles prefer this type of interaction, and upon regular dipping these structures form spontaneously. Y-type multilayers are most common, can be prepared on either hydrophilic or hydrophobic substrates, and are typically the most stable due to the strength of the head-head and tail-tail interactions. Even when films of some amphiphiles have been deliberately transferred by an X or Z method, the spacing between the hydrophilic... 

In order to determine the infants lung maturity and the necessity of surfactant therapy it is of great importance to substantiate the functionality of the alveolar surfactant, derived via invasive techniques [13], Several techniques and models have been largely used to investigate inteifacial physicochemical properties in vitro and to assess clinical efficiency of ES in vivo the Langmuir monolayer technique in combination with Wilhelmy plate method for surface tension measurements and black foam film method for determination of the ability of ES for stable film formation [14]. The pendant drop method combined with the Axisym-metric Drop Shape Analysis (ADSA) has been also used for similar purposes [4,15-18]. 

The majority of studies conducted on Langmuir films have, until recently, been performed on small amphiphilic molecules (17). These materials form highly ordered and oriented films at the air-water interface and upon transfer to a solid substrate. In the case of more complex materials with a variety of chemical functionalities, such as the PAC and polymer, the morphology of monolayers formed at an air-water interface and after transfer is not well-characterized. Although both materials form stable Langmuir films that can be transferred to the quartz substrates, the details of the orientation and morphology of these films are not known and may in fact, be highly disordered. 

In the recent past, combinatorial chemistry has revolutionized medicinal chemistry and this approach has emerged as a powerful technique to discover novel materials. For the first time, we have attempted to combine Langmuir monolayer and combinatorial chemistry techniques to create proteinlike su-pramolecular structures. We synthesized a peptide lipid library and three sublibraries and studied their monolayer properties at the air-water interface. It was found that the peptide lipid libraries readily formed stable monolayers at the air-water interface and exhibited different binding activities toward carbohydrate molecules from the aqueous subphase. Our study suggests that combinatorial surface chemistry is a possible novel technique in the design and creation of artificial proteins. 

Guldi D M, Tian Y, Fendler J H, Hungerbuhler H and Asmus K-D 1995 Stable monolayers and Langmuir-Blodgett films of functionalized fullerenes J. Phys. Chem. 99 17 673-6... 

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