Light‐Induced On/Off Switching of the Surfactant Character of the o‐Cobaltabis(dicarbollide) Anion with No Covalent Bond Alteration

Abstract

Cobaltabis(dicarbollide) anion ([o-COSAN] À ) is a well-known metallacarborane with multiple applications in a variety of fields. In aqueous solution, the cisoid rotamer is the most stable disposition in the ground state. The present work provides theoretical evidence on the possibility to photoinduce the rotation from the cisoid to the transoid rotamer, a conversion that can be reverted when the ground state is repopulated. The non-radiative decay mechanisms proposed in this work are coherent with the lack of fluorescence observed in 3D fluorescence mapping experiments performed on [o-COSAN] À and its derivatives. This phenomenon induced by light has the potential to destruct the vesicles and micelles cisoid [o-COSAN] À typically forms in aqueous solution, which could lead to promising applications, particularly in the field of nanomedicine.

Counterion-Induced Aggregation of Metallacarboranes

“…1−22 COSAN is a weakly hydrated and slightly surface-active anion with an ability to rotate alongside the longitudinal axis with three distinct rotational isomers: cisoid, gauche, and transoid. 2,13,21,22 The cisoid rotamer was found to be the most stable species in solution. 13,21,22 The COSAN salts form small multimolecular aggregates above the critical aggregation concentration (CAC), which is temperature-and ionic strength-dependent.…”

“…Thus, the classical hydrophobic effect is not likely to be the main driving force. 13,21,22 The two-process model considering all the COSAN forms in solution provided the total description of the COSAN aggregation (Table 1 and Figure 2, further details in the Supporting Information). Strikingly, the larger aggregates with n = 9 ± 2, and β = 0.54 ± 0.08 (the second process column in Table 1) are more thermodynamically stable than the pentamers as can be deduced from the significantly more exothermic enthalpy of aggregation.…”

“…The metallacarboranes, including the [cobalt­(III) bis­(1,2-dicarbollide)]­(1-) anion, which is called COSAN (CObalt SANdwich) in the further text (Figure , inset), are a peculiar class of nanoions with an uneven structure and charge distribution . They constitute a distinct family of boron cluster compounds with unique structure and properties. − The metallacarboranes have been assigned as hydrophobes, surfactants, amphiphiles, or superchaotropes in the recent literature, − but actually, they did not fit to any classical category. Considering their potential application in medicine, ion-conducting materials, and advanced nanodevices, a proper understanding of their self- and co-assembling properties represents the eminent task for physical chemists and nanochemists. ,,,,− …”

“…The aggregation of sodium salt of COSAN, Na­[COSAN], and other metallacarboranes in aqueous solutions has been discovered by Matějíček et al in 2006 . Since then, a decent number of papers have been published on the topic, mostly by Matějíček, − Teixidor, and Viñas. − First, 100–200 nm compact spherical COSAN aggregates were observed by light scattering measurements in 2006 . Although such aggregates were found unrealistic, the finding pointed out to the role of counterions.…”

Photochemical and thermochemical pathways to S2 and polysulfur formation in the atmosphere of Venus

“…In this work, we identify the main photochemical routes of 1 (SO) 2 isomers by accurately simulating the gas-phase conditions of the Venus atmosphere through non-adiabatic molecular dynamics (NAMD) [25][26][27][28][29][30][31] , a well-established state-of-the-art methodology [32][33][34][35][36][37][38][39][40][41][42] , especially in combination with multiconfigurational quantum chemistry [43][44][45][46][47] . For HOSO 48,49 and HOSO 2 50,51 radical photochemistry, NAMD has recently demonstrated that the ejection of OH is the main photodissociation channel for both systems in Earth's atmosphere 24,52 .…”