Exploring ion-ion preferences through structure-property correlations: amino acid-derived, bis(guanidinium) disiloxane salts

Abstract

present study that valuable information could be obtained from comparative analysis of series of compounds: complicated enough to include more than one functionality, yet simple enough to allow for differentiation of their individual impact on bulk physicochemical properties. Starting with the abovementioned lysozyme/ionic liquid behaviour discrepancy and wanting to also investigate the structuring effect of anions on the separating organic phase, we decided to synthesize amino acid-linked bis(guanidines), in which the polar moieties are separated by a siloxane bridge. This idea stemmed from a previous study, which revealed an abnormally low water solubility of the prepared 1,3-bis(3-guanidinopropyl)-t etramethyldisiloxane nitrate (parent chloride was fully water-miscible) 17. Addition of amide bonds seemed very attractive, as they often co-exist with guanidine moieties in many polypeptides and are a key ingredient in their higher-than-primary structure. Guanidines, on the other hand, have well-established "chaotropic" properties in their own right 18. Siloxane bridges, though fairly chemically and very thermally resistant, impart a strong tendency for disorganization and non-crystallinity on the molecule, which stems from the extremely low energy barrier for rotation around the Si-O bond 19. This results in most siloxanes presenting as liquids, oils or waxy solids at room temperature (a point of connection with ionic liquids). The apparent crystallinity of the abovementioned nitrate was yet another reason for choosing that particular class of compounds. Apart from the obvious advantage of easily comparable results, one of the drawbacks of articles referring to Hofmeister series as a common denominator is the limitation of studied anions to those with well-established places on that spectrum: phosphate, sulphate, halides, nitrate, perchlorate and thiocyanate. In an effort to find more subtle differences, we expanded our search. For example, while the charge density difference between sulphate and perchlorate explains why these two geometrically similar oxoanions exert significantly different influences on water solutions, we chose chromate and molybdate (same geometry and charge) instead. Azide, an ion very rarely studied in this context, was also included-due to its specific linear geometry (similar to thiocyanate) and significant electronic contribution from the characteristic − N = N + = N − resonance structure. Results and Discussion Design and synthesis. The intramolecular hydrogen bonding between amide moieties determines the

Guanidinium-Based Ionic Covalent-Organic Nanosheets for Sequestration of Cr(VI) and As(V) Oxoanions in Water

“…Interestingly, the Q e Cr /(IEC/2) values were comparable between iCONs with syn- ( III ) and anti- hydrogen bonding conformations ( II ) at the guanidinium sites, suggesting that the parallel bidentate hydrogen bonding interactions with tetrahedral oxoanion are not essential to chromate adsorption . Instead, the high binding affinity of chromate with iCONs is likely a result of the strong ion–ion interaction between chromate and guanidinium units. , …”

“…53 Instead, the high binding affinity of chromate with iCONs is likely a result of the strong ion−ion interaction between chromate and guanidinium units. 60,61 In contrast, the structural variations in iCONs had pronounced impacts on the arsenate uptake (Q e As , Figure 4a, blue bars). First, the conformation of the guanidinium hydrogen bond donors appeared to play a decisive role in the adsorption of arsenate.…”

Quantitative and biosafe modification of bifunctional groups onto carbon dots by click chemistry

“…7.61 ppm corresponds to the N–H proton. 26 The peaks in the range of 2.55–3.12 ppm and at ca. 1.80 ppm correspond to the methylene proton of 3-azido-1-propanamine.…”