Tailor made synthesis of amphiphilic azoaromatics via regioselective C–N bond fusion. Comparative studies of surface properties of the two positional isomers and cobalt complexes

Abstract

Tailor made synthesis of the isomeric azoaromatics, HL(1)-HL(4) [HL = (arylamino)phenylazopyridine] containing a single hydrophobic tail (C(n) = C(10) and C(12)) is described. The coordination induced C-N bond fusion synthetic protocol has been successfully used for the synthesis of the compounds, which are subsequently characterized using various spectroscopic techniques. The single crystal X-ray structure of compound HL(4) has revealed that the hydrophobic chain in it orients itself with all-trans conformation of alkyl groups. Studies of their surface properties clearly demonstrate that these behave as surfactants. Amphiphilic properties of the compounds are followed by the studies of compression isotherms and their surface morphologies are studied with the use of high resolution field emission scanning electron microscopy (FE-SEM) as well as atomic force microscopy (AFM). Distinct differences in surface properties in the two HL isomers are observed and disposition of the hydrophobic tail with respect to the head group is shown to play a significant role in the organization process of the molecules at the air-water interface. Transferred monolayers of the above two isomeric compounds show agglomerated nano-domain structures. This phenomenon has been explained considering hydrophobic tail-tail repulsive interaction within the adjacent molecules. Surface properties of the double tail complex, [Co(L(1))(2)]ClO(4) (1) along with that of the single tail complex, [Co(L(1))(L(5))]ClO(4) (3) are also reported. Amphiphilic behavior of the above azoaromatics are distinctly different than those in their metal free state. Notably, the double tail complex (1) favors bi-layer formation even at low surface pressure region (approximately 10 mN m(-1)). The single tail cobalt complex (3), on the other hand, forms a monolayer at high surface pressure region leading finally to the collapse at a very high pressure approximately 60 mN m(-1).

Synthesis of Amphiphilic Azo‐Anion‐Radical Complexes of Chromium(III) and the Development of Ultrathin Redox‐Active Surfaces by the Langmuir–Schaefer Technique

“…[26] We ascribed the grain-like surface morphology of these monolayer and multilayer films to agglomeration of the amphiphiles. [13] Moreover the FE-SEM images of these three representative LS films also depicted a similar trend.…”

“…However, at higher pressures (at 20 or 40 mN m À1 ), there was significant variation of the surface area, thereby indicating reorganization of the molecules. The curve in the low-pressure region can be fitted to the empirical single-exponential given in Equation (1), [13,24] A t =A 0 ¼ aexp ðÀt=tÞþc ð1Þ…”

“…[12] The former approach has been used with impressive results in the design of responsive thin films. [11,13,14] This fact points to the potential role of discrete metallosurfactant materials (i.e. surfactants containing transition-metal ions) in the emerging field of molecular devices.…”

Interaction of glucose with hemoglobin: a study in aqueous solution and at the air–water interface using the Langmuir–Blodgett technique

“…Recently the Langmuir-Blodgett (LB) technique has been recognized to mimic various biological systems especially to study the weak biomolecular interactions at the air/water interface and subsequently allow it to transfer onto a solid substrate for further characterization as well as applications. 14,[21][22][23][24][25] The surface activity of proteins can be well studied by the LB technique. 14,25,26 Also some other properties in relation to proteins/enzymes such as aggregation/dissociation, denaturation, unfolding etc.…”

Influence of KCl on the interfacial activity and conformation of hemoglobin studied by Langmuir–Blodgett technique

“…8,9 There are several techniques to immobilize biomolecules onto solid matrix surfaces such as sol-gel processes, self-assembly, Langmuir-Blodgett (LB) techniques, etc. [10][11][12][13][14][15][16][17] Among these, the LB technique is useful not only for the formation of molecular organization onto a solid substrate, but also on the study protein/enzyme at the molecular level. [11][12][13][14][18][19][20] On the other hand, the study of denaturation, aggregation, dissociation, as well as unfolding in different physiochemical environments has some relevance to the understanding of the molecular mechanism of various diseases such as thalassemia, neurodegenerative diseases, Alzheimer's etc.…”