Co-Aggregation of Two Anionic Azo Dyestuffs at a Well-Defined Stoichiometry

Abstract

The present work investigates the formation of well-defined heteroaggregates from a binary mixture of a red and a yellow azo-dyestuff in the presence of Mg(2+) ions. Combined static and dynamic light scattering together with laser induced liquid bead ion desorption mass spectrometry (LILBID-MS) has been applied to characterize the states of the pure red dye and the pure yellow dye as well as of their mixture in aqueous solution without Mg(2+). These experiments indicated that a structural reorganization on a molecular scale takes place as soon as the two dyes are combined. Solutions of the combined red and yellow dye contain micelle-like mixed entities with a size of a few tenths of nanometers. Upon the addition of Mg(2+), these micelles vanish in favor of elongated heteroaggregates, which grow by a stepwise addition of smaller building units. As unraveled by UV/vis spectroscopy, the heteroaggregates that are formed from the red and yellow azo dye in the presence of Mg(2+) obey a stoichiometric ratio of the two components of 1:1. A new multiangle scattering instrument allowed us for the first time to follow this aggregation process at the stoichiometric ratio by time-resolved combined static and dynamic light scattering, thereby providing further aspects of the worm-like nature of the growing heteroaggregates.

Kinetic and Structural Features of a Dyestuff Coaggregation Studied by Time-Resolved Static Light Scattering

“…This is plausible since micellar aggregates are present in solutions of RD and YD even when Mg 2+ is absent. 8 TEM images, the analysis of scattering patterns and the correlation of size parameters suggest a wormlike shape of the growing dyestuff aggregates. Thereby, a constant persistence length of about 200 nm could be established accompanied with a decrease of polydispersity toward increasing contour length of the dyestuff aggregates.…”

“…The growing fibers adopt a distinct stoichiometry of RD/YD = 1:1. 8 The growth process was analyzed by means of timeresolved static light scattering at variable Mg 2+ content and at variable dyestuff concentration, where the composition of the dyestuff mixture prior to the addition of Mg 2+ was kept at the stoichiometric point. Successively, two kinetic growth models, the INE model and the Lomakin model, 21 have been applied to describe the evolution of aggregate mass values with time.…”

Lateral association and elongation of vimentin intermediate filament proteins: A time-resolved light-scattering study

“…Further details on the instrument can be found in ref. 27. Cylindrical quartz cuvettes of 20 mm diameter, washed with freshly distilled acetone, were used as scattering cells.…”

“…Compared with singleangle setups, where assumptions about the morphology and size distribution of the particles are necessary to extract structural parameters, multiangle light scattering permits reliable extraction of the molecular weight (M w ), radius of gyration (R g ), and hydrodynamic radius (R H ) without specific assumptions about the shape and the degree of polydispersity of the particles, as previously demonstrated for the aggregation of dyestuff molecules and for nucleation and growth of silica particles (27,28). Application of this in situ technique provides us with a consistent set of M w , R g , and R H of assembling filaments and enables us to follow quantitatively and in real time the longitudinal growth of ULFs toward filaments of lengths up to 600 nm.…”

Inducing Hetero‐aggregation of Different Azo Dyes through Electrostatic Self‐Assembly

“…It is well known that H‐ and J‐aggregation of identical dye molecules (homoaggregates) can be described by exciton theory, but only a few investigations on heteroaggregation exist. For example, stacking of different dyes has been achieved using specifically synthesized DNA derivatives as support or by addition of ions such as Mg 2+ …”