Aggregation-deaggregation

Guarise, C., PasquatoJ.., et al. Reversible aggregation/deaggregation of gold nanoparticles induced by a cleavable dithiol linker. Langmuir,21(12), 5537-5541 (2005). 

In a related phenomenon, the spectral shifts which accompany aggregation-deaggregation have been reported as a basis of yet another erasable medium.24 The active layer consists of discrete particles of a cocrystalline complex of a pyrylium dye with a polymer such as polycarbonate. Pulsed irradiation of this aggregated film resulted in an instantaneous deaggregation process which was accompanied by a hypsochromic shift of about 100 nm. The recording mechanism is believed to be thermal and a thermal erasure (reaggregation of the dye-polymer complex) was also demonstrated. 

Since Lewis base additives and basic solvents such as tetrahydrofuran are known to deaggregate polymeric organolithium compounds, (21,23,26) it was postulated that ketone formation would be minimized in the presence of sufficient tetrahydrofuran to effect dissociation of the aggregates. In complete accord with these predictions, it was found that the carbonation of poly(styryl)lithium (eq. 9), poly(isoprenyl)-lithium, and poly(styrene-b-isoprenyl)lithium in a 75/25 mixture (by volume) of benzene and tetrahydrofuran occurs quantitatively to produce the carboxylic acid chain ends (8 ). 

The temperature dependence (296-330 K) of the ring methyl proton resonances of these monomeric heme complexes in the hydrophobic micellar cavity shows [22] a small deviation from the Curie law as in the low-spin complexes in organic and simple aqueous solvents [1, 52]. The origin of such deviation has been variously ascribed [3, 1, 53] either to aggregation or second order Zeeman (SOZ) effect or presence of low-lying spin-quartet state. Since these low-spin hemes in micellar solutions are in deaggregated form, the deviation may be due to the SOZ and/or presence of low-lying excited state. 

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