Ashish Kumar Ghosh

Electronic Spectroscopic Study of the Formation of a Molecular Complex Between Asphaltene and o-Chloranil in SDS Aqueous Micellar Medium

Ultraviolet-visible absorption and steady-state fluorescence of asphaltene in sodium dodecyl sulphate (SDS) micellar medium containing o-chloranil have been studied. Spectroscopic results indicate formation of a complex between asphaltene and o-chloranil. The absorption spectrum of the complex has been detected by difference spectral method. The position of maximum absorption of the complex in micellar medium agrees well with that of the complex in the carbon tetrachloride medium studied previously. The formation constant (K) has been determined using Benesi-Hildebrand equation utilizing absorption spectral data. Formation of ground state complex involving asphaltene and o-chloranil has also been evidenced from the study of quenching of asphaltene fluorescence by o-chloranil. The value of K, as obtained by Stern-Volmer plot, agrees well with that obtained by absorption spectrophotometric method.

Study of Molecular Complex Formation of Coal-Derived Asphaltene with TCNQ in Homogeneous and Heterogeneous Media by UV-Vis and Fluorescence Spectroscopic Studies

Coal-derived asphaltene (CDA) has been shown to form electron donor–acceptor-type molecular complexes with electron acceptor such as 2,5-cyclohexadiene-1,4-diylidene also known as tetracyanoquinodimethane (TCNQ) in homogeneous medium of carbon tetrachloride and heterogeneous medium of aqueous SDS. This has been investigated both by UV-Vis and fluorescence spectrophotometric method. The Charge transfer (CT) absorption peaks have been detected by difference spectral method and the wavelengths of the CT peaks are close in both the medium. The formation constants (K) have been determined using the Benesi–Hildebrand equation. The magnitudes of K are in the order of 103 L mol−1 that are comparable to some supramolecular or inclusion complexes. The study reveals the presence of π-donor (i.e., aromatic) type of compounds in CDA molecule. It also supports the view that CDA molecules exist in solution forming micellar aggregate, in the cavities of which the TCNQ molecules are included. The remarkable increase (three fold) in the formation constant in the SDS medium compared to CCl4 further indicates that the CDA aggregate in SDS undergoes some preorganization to further facilitate inclusion. GRAPHICAL ABSTRACT

Spectroscopic Investigation of Asphaltene Aggregation in Carbon Tetrachloride Medium Containing Microquantities of Water

By fluorescence spectroscopy it has been established that coal derived asphaltene (CDA) forms aggregates in CCl4 medium. The new feature of this compound is that even before aggregate formation it can incorporate water molecules and the critical aggregation concentration (CAC) in nonaqueous medium increases with increase in ω (= water:CDA mole ratio). The fluorescence spectroscopic determination of the equilibrium constant (K) of the molecular complex of [60] fullerenes with CDA in carbon tetrachloride medium has revealed that K increases on addition of microquantities of water. This observation has been rationalized by assuming that the nitrogenatoms at one end of CDA molecules attach themselves to the water micropool and thus producing a different conformation with a wider distance at the other end. This pre-organization further facilitates inclusion. By utilizing fluorescence variation of [60]fullerene/CDA complex in CCl4 as continuous medium with change in ω a critical ω (=5) has been found. The formation of CDA/[60]fullerene complex has also been established by NMR spectroscopy. GRAPHICAL ABSTRACT

The Role of Water in the Aggregation of Coal-Derived Asphaltene: Dominance of π-π Interaction

The effect of water to the self-aggregational phenomenon of coal-derived asphaltene (sourced from coal liquefaction plant at CIMFR, Dhanbad, India) has been studied tensiometrically and fluorimetrically in CCl4 medium. Although asphaltene molecule contains small number of hydrophilic groups such as –NH, –SH, and sometimes –OH, the main force behind the aggregation of asphaltene is π-π stacking interaction between the asphaltene molecules. This has been established by showing that critical micelle concentration (CMC) of asphaltene/CCl4 system increases with addition of microquantity of water and also by studying the variation of surface tension (ST) with addition of water to asphaltene solution above its CMC.