Langmuir monolayers of fractions of cork suberin extract.

The wide variability in composition and molecular weight of natural polymers has hampered understanding of their physicochemical properties and ultimately their use in noble applications, especially in the cases where surface properties need to be probed at the molecular level. A useful approach to analyse data from surface monolayers of complex mixtures is to try distinguishing the effects from the distinct fractions in such mixtures. The cork suberin extract investigated here is known to contain aliphatic monomers with terminal carboxylic acid and methyl ester groups as well as long esterified aliphatic chains dispersed in a polymeric aliphatic matrix. The role of such terminal groups was studied and the results showed that depending on the nature of the terminal groups the monolayers present distinct isotherms due to the different interactions with the water subphase. Fractionation strategies based on different solubilities of the cork suberin components in chloroform were also employed to probe their effect on the monolayer characteristics. From the two sets of experiments it is clear that the presence of monomers with terminal carboxylic acids in the suberin extract affects considerably the monolayer-forming ability. This approach may be used as a complementary, relatively simple route to assess suberin genetic engineering strategies towards resistance to environmental stress.

Modern physicochemical research on Langmuir monolayers.

Recent developments in characterising Langmuir monolayers of a variety of film-forming materials and employing several physicochemical techniques are reviewed. The extension of the LB method to non-amphiphilic substances, especially macromolecular systems, has increased the need of a thorough understanding of Langmuir film properties, which requires characterising techniques that provide complementary information. Since there is vast literature in the subject, only selected examples are given of results that illustrate the potential of the techniques discussed.

Langmuir Monolayers from Substituted 5'-Phenyl-m-terphenyl Carboxylic Acids.

A series of 5'-phenyl-m-terphenyl carboxylic acid (PTCA) derivatives with methyl, chloro, and fluoro substituents at both side phenyl rings have been synthesized and characterized as Langmuir monolayers at the air/water interface. A comparative analysis, based on the surface pressure and electric surface potential measurements under a variety of experimental conditions, is complemented with BAM images. Copyright 2001 Academic Press.

Structural Modification Influences the Characteristics of Langmuir Monolayers from Aromatic Carboxylic Acids.

The molecular organization of purely aromatic, polyphenyl carboxylic acids, as Langmuir monolayers at the air/water interface, has been investigated by means of surface pressure and electric surface potential measurements upon film compression. The monolayer characteristics of the basic compound, a symmetrical triphenylbenzene (5'-phenyl-m-terphenyl) ring with a carboxylic group at the 4 position (namely 5'-phenyl-1,1' : 3',1"-terphenyl-4-carboxylic acid), are compared with those of its derivatives containing hydrophilic (nitro) or hydrophobic (phenyl) substituents. The nature of the substituent as well as its position (2' or 4') has a profound influence on the monolayer properties. The results are discussed in view of molecular orientation deduced from values of effective dipole moments. Copyright 2001 Academic Press.