Abstract:The synthesis methods, physicochemical and structural characteristics, and catalytic reactivity of new macrocyclic proton chelators, N,N',N''-tris(p-tolyl)azacalix[3](2,6)(4-pyrrolidinopyridine) and N,N',N''-tris(p-tolyl)azacalix[3](2,6)(4-piperidinopyridine), are studied. The introduction of pyrrolidino and piperidino groups into the pyridine unit enables the enhancement of the synergistic proton affinity of the cavity of the macrotricycle giving a high basicity (pK(BH+) = 28.1 and 27.1 in CD(3)CN), resulting… Show more
“…1). The resonance of the central proton was observed at >22 ppm, which is comparable to the chemical shift of structurally related macrotricyclic aminopyridines 32 .Fig. 2Synthesis of TQ: TriQuinoline.…”
The bottom-up synthesis of structurally well-defined motifs of graphitic materials is crucial to understanding their physicochemical properties and to elicit new functions. Herein, we report the design and synthesis of TriQuinoline (TQ) as a molecular model for pyridinic-nitrogen defects in graphene sheets. TQ is a trimer of quinoline units concatenated at the 2- and 8-positions in a head-to-tail fashion, whose structure leads to unusual aromatisation behaviour at the final stage of the synthesis. The central atomic-sized void endows TQ with high proton affinity, which was confirmed empirically and computationally. TQ•H
+
is a two-dimensional cationic molecule that displays both π–π and CH–π contact modes, culminating in the formation of the ternary complex ([12]cycloparaphenylene(CPP) ⊃ (TQ•H
+
/coronene)) that consists of TQ•H
+
, coronene (flat), and [12]cycloparaphenylene ([12]CPP) (ring). The water-miscibility of TQ•H
+
allows it to serve as an efficient DNA intercalator for e.g. the inhibition of topoisomerase I activity.
“…1). The resonance of the central proton was observed at >22 ppm, which is comparable to the chemical shift of structurally related macrotricyclic aminopyridines 32 .Fig. 2Synthesis of TQ: TriQuinoline.…”
The bottom-up synthesis of structurally well-defined motifs of graphitic materials is crucial to understanding their physicochemical properties and to elicit new functions. Herein, we report the design and synthesis of TriQuinoline (TQ) as a molecular model for pyridinic-nitrogen defects in graphene sheets. TQ is a trimer of quinoline units concatenated at the 2- and 8-positions in a head-to-tail fashion, whose structure leads to unusual aromatisation behaviour at the final stage of the synthesis. The central atomic-sized void endows TQ with high proton affinity, which was confirmed empirically and computationally. TQ•H
+
is a two-dimensional cationic molecule that displays both π–π and CH–π contact modes, culminating in the formation of the ternary complex ([12]cycloparaphenylene(CPP) ⊃ (TQ•H
+
/coronene)) that consists of TQ•H
+
, coronene (flat), and [12]cycloparaphenylene ([12]CPP) (ring). The water-miscibility of TQ•H
+
allows it to serve as an efficient DNA intercalator for e.g. the inhibition of topoisomerase I activity.
“…Also included in Tables 5 and 6 are the reference bases and acids used in this work. The basicity and acidity of a wide range of neutral heterocyclic and acyclic nitrogen-containing compounds have been measured previously in acetonitrile by several groups, [19][20][21] resulting in well-defined acidity scales covering 24 orders of acidity 20a,b and a base scale covering 28 orders of basicity, 20c,d thus facilitating comparison of the pK a values of the compounds studied in this work with previously measured ones.…”
Section: Basicity and Acidity Determinationmentioning
“…It is interesting that the diamagnetic effect of the aromatic -system on the proton in the [N···H−N] + group in cation 38H + is so great that this species still holds the record for the chemical shift of a chelated proton ( N−H ~ 24 ppm) [55]. Recently synthesized pyridine aza-crown ethers 40a-c (azacalix [3](2,6)pyridines) proved to be very strong bases providing trifurcated hydrogen bonding to a proton reaching the interior of the macrocycle [57,58]. In the solid phase, the internal proton is asymmetrically positioned, while, in solution, it equally belongs to all three pyridine nitrogen atoms.…”
Section: Aza-arene Superbasesmentioning
confidence: 99%
“…These compounds may be characterized as similar to proton sponges, but not really falling into this category, and are called proton-sponge-like compounds. The difficulty in obtaining many representatives of this group has hindered their possible use in organic synthesis [58].…”
The structural principles known to date serving as the basis for the design of heterocyclic compounds with anomalously high basicity (superbasicity) are reviewed. A general classification is given for such superbases as proton sponges, compounds that are similar to proton sponges but are not sponges (proton-sponge-like), and proton traps.
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