Ionic liquids (ILs) are considered in the majority of cases green solvents, due to their virtually null vapor pressure and to the easiness in recycling them. In particular, imidazolium ILs are widely used in many fields of Chemistry, as solvents or precursors of N-heterocyclic carbenes (NHCs). The latter are easily obtained by deprotonation of the C2-H, usually using strong bases or cathodic reduction. Nevertheless, it is known that weaker bases (e.g., triethylamine) are able to promote C2-H/D exchange. From this perspective, the possibility of deprotonating C2-H group of an imidazolium cation by means of a basic counter-ion was seriously considered and led to the synthesis of imidazolium ILs spontaneously containing NHCs. The most famous of this class of ILs are N,N'-disubstituted imidazolium acetates. Due to the particular reactivity of this kind of ILs, they were appointed as “organocatalytic ionic liquids” or “proto-carbenes.” Many papers report the use of these imidazolium acetates in organocatalytic reactions (i. e., catalyzed by NHC) or in stoichiometric NHC reactions (e.g., with elemental sulfur to yield the corresponding imidazole-2-thiones). Nevertheless, the actual presence of NHC in N,N'-disubstituted imidazolium acetate is still controversial. Moreover, theoretical studies seem to rule out the presence of NHC in such a polar environment as an IL. Aim of this Mini Review is to give the reader an up-to-date overview on the actual or potential presence of NHC in such an “organocatalytic ionic liquid,” both from the experimental and theoretical point of view, without the intent to be exhaustive on N,N'-disubstituted imidazolium acetate applications.
The cathodic reduction of dicationic imidazolium bromides, whose spacer is either an aliphatic chain or a xylyl group, leads to the formation of the corresponding N‐heterocyclic carbenes (NHCs), which were isolated as the corresponding thiones, after reaction with elemental sulfur. The behaviour of the dications was compared with the corresponding monocations. The behaviour of dicarbenes depends on the nature of the spacer. This study evidenced that dicarbenes deriving from xylyl dications are less stable than the corresponding aliphatic ones (giving lower yields in thiones), due to a debenzylation reaction. On the other hand, the yields in thiones starting from aliphatic dications are higher than the corresponding monocations, suggesting a cooperative reduction at the electrode of the two imidazolium moieties. The cathodic process was confirmed using the co‐electrogenerated hydrogen to reduce 2,2,2‐trifluoroacetophenone to the corresponding alcohol.
The electrochemical oxidation of theophylline was investigated by controlled potential electrolysis in two different organic solvents and in water for comparison. The anodic oxidation was monitored by cyclic voltammetry in situ and UV‐Vis spectrophotometry ex situ and the final electrolyzed solutions were analyzed by tandem mass spectrometry after chromatographic separation with an HPLC‐PDA‐ESI‐MS/MS system. The main oxidation products evidenced as the main diode array chromatographic peaks were tentatively assigned to dimeric forms of theophylline, two of which have never been reported before, on the base of retention time, UV‐Vis spectrum, m/z ratio in both positive and negative ESI modes and fragmentation pattern. Two chemical paths following the primary mono‐electronic anodic oxidation of theophylline to the final evidenced oxidation products have been proposed.
A new series of pyrimidine
and pyridine diamines was designed as
dual binding site inhibitors of cholinesterases (ChEs), characterized
by two small aromatic moieties separated by a diaminoalkyl flexible
linker. Many compounds are mixed or uncompetitive acetylcholinesterase
(AChE) and/or butyrylcholinesterase (BChE) nanomolar inhibitors, with
compound
9
being the most active on
Electrophorus
electricus
AChE (
Ee
AChE) (
K
i
= 0.312 μM) and compound
22
on equine BChE (
eq
BChE) (
K
i
= 0.099 μM). Molecular docking and molecular dynamic
studies confirmed the interaction mode of our compounds with the enzymatic
active site. UV–vis spectroscopic studies showed that these
compounds can form complexes with Cu
2+
and Fe
3+
and that compounds
18
,
20
, and
30
have antioxidant properties. Interestingly, some compounds were
also able to reduce Aβ
42
and tau aggregation, with
compound
28
being the most potent (22.3 and 17.0% inhibition
at 100 μM on Aβ
42
and tau, respectively). Moreover,
the most active compounds showed low cytotoxicity on a human brain
cell line and they were predicted as BBB-permeable.
We discovered novel and selective sulfonamides/amides acting as inhibitors of the a-carbonic anhydrase\ud
(CA, EC 4.2.1.1) from the pathogenic bacterium Vibrio cholerae (VchCA). This Gram-negative bacterium is\ud
the causative agent of cholera and colonises the upper small intestine where sodium bicarbonate is present\ud
at a high concentration. The secondary sulfonamides and amides investigated here were potent, low\ud
nanomolar VchCA inhibitors whereas their inhibition of the human cytosolic isoforms CA I and II was in\ud
the micromolar range or higher. The molecules represent an interesting lead for antibacterial agents with\ud
a possibly new mechanism of action, although their CA inhibition mechanism is unknown for the moment
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