Hydrothermal reactions of a lead(II) salt with 3-aminopyrazine-2-carboxylic acid (HL1) gave rise to a series of lead(II) coordination compounds (1–6) having zero, one, two and three dimensional ...structures. X-ray diffraction structural analyses reveal that complexes Pb(L1)22 (1) and Pb(L1)(OCHNH2)(η-OCHO)2 (2) possess dinuclear structures, containing a centre of symmetry. Complexes Pb2(L1)4(NHMeCHO)2n (3) and Pb2(L1)4n·(H2O)n·(2.5DMF)n (4) have 1D chain like structures, and Pb5(L1)7(η-NO3)(μ-HCOO)(η-HCOO)n·(DMF)n·(MeOH)n (5) shows a 2D sheet like structure constructed by the Pb5O5(HCOO) cluster and 3-aminopyrazine-2-carboxylate anions. The hydrothermal reaction of lead(II) nitrate with HL1 in DMF led to in situ formation of 3,3′-(methylenebis(azanediyl))bis(pyrazine-2-carboxylic acid) H2L2 which produces the 3D framework Pb2(L2)2n·(2DMF)n·(H2O)n (6). The L1(−) and L2(2−) ligands bind the metal cations by means of a pyrazine N-atom and one, or both, carboxylate O-atoms. The carboxylate group of L1(−) presents a diversity of coordination modes, viz., monodentate (1 and 3), bridging μ2 (3) and bridging μ3 (4), monodentate bridging μ2 (1, 2, 4, 5 and 6) and bridging chelate μ2 (5). The carboxylate moiety of L2(2−) in 6 binds the metal in a bridging μ2 fashion. The Pb(II) ions display coordination numbers from 5 to 8 with hemi- or holodirected coordination environments. The Pb(II) complexes act as heterogeneous catalysts for the cyanosilylation reaction, at 15 °C, of different aldehydes with trimethylsilyl cyanide (TMSCN) and can be recycled at least three times without losing activity.
Three novel coordination compounds, Cu(ca)
2
(Hbae)
2
(
1
), Cu(va)
2
(Hbae)
2
(
2
) and Cu
4
(va)
4
(bae)
4
·H
2
O (
3
), have been prepared by self-assembly reactions of copper(
ii
) chloride (
1
...and
2
) or tetrafluoroborate (
3
) and CH
3
OH (
1
and
3
) or CH
3
CN (
2
) solution of 2-benzylaminoethanol (Hbae) and cinnamic (Hca,
1
) or valeric (Hva,
2
and
3
) acid. Crystallographic analysis revealed that both
1
and
2
have mononuclear crystal structures, wherein the complex molecules are H-bonded forming extended supramolecular chains. The tetranuclear structure of
3
is based on the {Cu
4
(μ
3
-O)
4
} core, wherein the metal atoms are bound together by μ
3
oxygen bridges from 2-benzylaminoethanol forming an overall cubane-like configuration. The strong hydrogen bonding in
1-3
leads to the joining of the neighbouring molecules into 1D chains. Concentration-dependent ESI-MS studies disclosed the equilibria between di-, tri- and tetranuclear species in solutions of
1-3
. All three compounds act as catalysts for the aerobic oxidation of
o
-aminophenol to the phenoxazinone chromophore (phenoxazinone synthase-like activity), with the maximum reaction rates of 4.0 × 10
−7
, 2.5 × 10
−7
and 2.1 × 10
−7
M s
−1
for
1
,
2
and
3
, respectively, supported by the quantitative yield of the product after 24 h. The dependence of the reaction rates on catalyst concentrations is evidence of reaction orders higher than one relative to the catalyst. Kinetic and ESI-MS data allowed us to assume that the tetranuclear species, originating from
1
,
2
and
3
in solution, possess considerably higher activity than the species of lower nuclearity. Mechanistic and isotopic
18
O-labelling experiments suggested that
o
-aminophenol coordinates to Cu
II
species with the formation of reactive intermediates, while the oxygen from
18
O
2
is not incorporated into the phenoxazinone chromophore.
Three novel copper coordination compounds bearing aminoalcohol and carboxylate ligands have been synthesized and applied for mild aerobic oxidation of
o
-aminophenol to the phenoxazinone chromophore.
The role of substituents on resonance assisted hydrogen bonding (RAHB) vs. intermolecular hydrogen bonding is highlighted in known arylhydrazones of active methylene compounds (AHAMCs) and in their ...new representatives – ( E / Z )-2-(2-( para -substitutedphenyl)hydrazineylidene)- N , N -diethyl-3-oxobutanamides (–C 2 H 5 , –H, –COOH, –CN). The strength of the H-bond depends on the attached functional groups to both the active methylene fragment and the aromatic moiety of the AHAMC. For instance, attachment of the strong electron donor group –N(C 2 H 5 ) 2 ( σ p = −0.72) to the active methylene fragment of AHAMC allows to isolate this class of compounds without RAHB but with strong intermolecular H-bonds, which are the first examples reported herein.
In this work, two new 1D Cd(II) coordination polymers (CPs), Cd(L1)(NMF)
(
) and Cd(L2)(DMF)(H
O)
·n(H
O) (
), have been synthesized, characterized and employed as catalysts for the ...microwave-assisted solvent-free Strecker-type cyanation of different acetals. Solvothermal reaction between the pro-ligand, 5-{(pyren-1-ylmethyl)amino}isophthalic acid (
) or 5-{(anthracen-9-ylmethyl)amino}isophthalic acid (
), and Cd(NO
)
.6H
O in the presence of NMF or DMF:THF solvent, produces the coordination polymer
or
, respectively. These frameworks were characterized by single-crystal and powder X-ray diffraction analyses, ATR-FTIR, elemental and thermogravimetry analysis. Their structural analysis revealed that both CPs show one-dimensional structures, but CP
has a 1D double chain type structure whereas CP
is a simple one-dimensional network. In CP
the dinuclear {Cd
(COO)
} unit acts as a secondary building unit (SBU) and the assembly of dinuclear SBUs with deprotonated ligand (L1
) led to the formation of a 1D double chain framework. In contrast, no SBU was observed in CP
. To test the catalytic effectiveness of these 1D compounds, the solvent-free Strecker-type cyanation reactions of different acetals in presence of trimethylsilyl cyanide (TMSCN) was studied with CPs
and
as heterogenous catalysts. CP
displays a higher activity (yield 95%) compared to CP
(yield 84%) after the same reaction time. This is accounted for by the strong hydrogen bonding packing network in CP
that hampers the accessibility of the metal centers, and the presence of the dinuclear Cd(II) SBU in CP
which can promote the catalytic process in comparison with the mononuclear Cd(II) center in CP
. Moreover, the recyclability and heterogeneity of both CPs were tested, demonstrating that they can be recyclable for at least for four cycles without losing their structural integrity and catalytic activity.
A benzimidazole–based chemosensor (DFB) for Cu2+ and Zn2+ was developed, and its sequential anions (CN− and P2O74-) and DNA sensing capability and its live-cell imaging, as well as its PPi detection ...in PCR-amplified DNA products, has been demonstrated.
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•A benzimidazole-based chemosensor (DFB) shows “off-on” responses upon differential detection of Cu2+ and Zn2+.•The DFB derived Cu2+ & Zn2+ complexes act as efficient sensors toward CN−, PPi and DNA in an aqueous medium.•DFB acts as a sequential fluorescent probe to detect Cu2+, Zn2+ and PPi in living cancer cells.•DFB-Zn2+ can detect the PPi in the PCR amplified DNA products.
Differential chemosensors have emerged as next-generation systems due to their simplicity and favourable responsive properties to produce different signals upon selective binding of various analytes simultaneously. Nevertheless, given their inadequate fluorescence response and laborious synthetic procedures, only a few differential chemosensors have been developed so far. In this work, we have employed a single pot synthesis strategy to establish a new benzimidazole-based Schiff base type fluorogenic chemosensor (DFB) which differentially detects Cu2+ (detection limit (LOD) = 24.4 ± 0.5 nM) and Zn2+ (LOD = 2.18 ± 0.1 nM) through fluorescence “off-on” manner over the library of other metal cations in an aqueous medium. The DFB-derived ‘in situ’ complexes DFB-Cu2+ and DFB-Zn2+ showed fluorescence revival “on-off” responses toward cyanide (CN−) and bio-relevant pyrophosphate (P2O74--PPi) ions with a significantly low LOD of 9.43 ± 0.2 and 2.9 ± 0.1 nM, respectively, in water. We have demonstrated the phosphate group-specific binding capability of DFB-Zn2+, by testing it with both ssDNA and dsDNA samples which displayed fluorescence “turn-off” response (LOD ∼10-7 M), similar to the PPi binding in an aqueous medium, indicating that it interacts explicitly with the phosphate backbone of DNA. We have also harnessed the DFB as a sequential fluorescent probe to detect Cu2+, Zn2+, CN− and P2O74- ions in human cervical (HeLa) and breast (MCF-7 and MDA-MB-231 (aggressive and invasive)) cancer cell lines. Moreover, we have explored the PPi recognition capability of DFB-Zn2+ in the polymerase-chain-reaction (PCR) products where PPi is one of the primary by-products during amplification of DNA.
A one‐pot template condensation of 2‐(2‐(dicyanomethylene)hydrazinyl)benzenesulfonic acid (H2L1, 1) or 2‐(2‐(dicyanomethylene)hydrazinyl)benzoic acid (H2L2, 2) with methanol (a), ethylenediamine (b), ...ethanol (c) or water (d) on copper(II), led to a variety of metal complexes, that is, mononuclear Cu(H2O)2(κO1,κN2 L1a (3) and Cu(H2O)(κO1,κN3 L1b) (4), tetranuclear Cu4(1 κO1,κN2:2 κO1 L2a)3‐(1 κO1, κN2:2 κO2 L2a) (5), Cu2(H2O)(1 κO1, κN2:2 κO1 L2c)‐(1 κO1,1 κN2:2 κO1,2 κN1‐ L2c)2 (6) and Cu2(H2O)2(κO1,κN2‐ L1dd)‐(1 κO1,κN2:2 κO1 L1dd)(μ‐H2O)2⋅ 2 H2O (7⋅2 H2O), as well as polymer‐ ic Cu(H2O)(κO1,1 κN2:2 κN1 L1c)n (8) and Cu(NH2C2H5)(κO1,1 κN2:2 κN1L2a)n (9). The ligands 2‐SO3H‐C6H4‐(NH)NC{(CN)C(NH2)‐(NCH2CH2NH2)} (H2L1b, 10), 2‐CO2H‐C6H4‐(NH)N{C(CN)C(OCH3)‐(NH)} (H2L2a, 11) and 2‐SO3H‐C6H4‐(NH)NC{C(O)‐(NH2)}2 (H2L1dd, 12) were easily liberated upon respective treatment of 4, 5 and 7 with HCl, whereas the formation of cyclic zwitterionic amidine 2‐(SO3−)C6H4NNC(C(NH+)CH2CH2NH)(CNHCH2CH2NH) (13) was observed when 1 was treated with ethylenediamine. The hydrogen bond‐induced E/Z isomerization of the (HL1d)− ligand occurs upon conversion of {Na(H2O)2(μ‐H2O)2}(HL1d)n (14) to Cu(H2O)6HL1d2⋅2 H2O (15) and {CuNa(H2O)‐(κN1,1 κO2:2 κO1 L1d)2}K0.5(μ‐O)2n⋅H2O (16). The synthesized complexes 3–9 are catalyst precursors for both the selective oxidation of primary and secondary alcohols (to the corresponding carbonyl compounds) and the following diastereoselective nitroaldol (Henry) reaction, with typical yields of 80–99 %.
An effective assistant: CuII complexes containing arylhydrazones from methylene‐active nitriles are effective catalysts and appear to act as suitable Lewis acids for the unprecedented possibility of a resonance‐assisted hydrogen bond (RAHB)/coordination‐controlled E/Z isomeric transition (see scheme).
Transition metal complexes, of which the platinum(II) complex cisplatin is an example, have been used in medicine to treat cancer for more than 40 years. Although many successes have been achieved, ...there are problems associated with the use of these drugs, such as side effects and drug resistance. Converting them into prodrugs, to make them more inert, so that they can travel to the tumour site unchanged and release the drug in its active form only there, is a strategy which is the subject of much research nowadays. The new prodrugs may be activated and release the cytotoxic agent by differences in oxygen concentration or in pH, by the action of overexpressed enzymes, by differences in metabolic rates, etc., which characteristically distinguish cancer cells from normal ones, or even by the input of radiation, which can be visible light. Converting a metal complex into a prodrug may also be used to improve its pharmacological properties. In some cases, the metal complex is a carrier which transports the active drug as a ligand. Some platinum prodrugs have reached clinical trials. So far platinum, ruthenium and cobalt have been the most studied metals. This review presents the recent developments in this area, including the types of complexes used, the mechanisms of drug action and in some cases the techniques applied to monitor drug delivery to cells.
Three new compounds bearing different flexible side functional groups, viz. 2-acetamidoterephthalic acid (H2L1), 2-propionamidoterephthalic acid (H2L2) and 2-benzamidoterephthalic acid (H2L3), were ...synthesized and their coordination reactions with zinc(II) were studied. X-ray crystallography showed the formation of novel metal organic frameworks with different dimensionalities, where the side functional groups of amidoterephthalic acid and/or auxiliary ligands were found to play significant roles. These frameworks Zn2(L1)2(4,4'-bipyridine)2(H2O)(DMF)n (1), Zn4(L2)3(OH)2(DMF)2(H2O)2n (2) and Zn(L3)(H2O)2n·n/2(1,4-dioxane) (3) act as heterogeneous polymeric solid catalysts not only for the diastereoselective nitroaldol (Henry) reaction of different aldehydes with nitroalkanes but also for transesterification reactions. These MOF-based heterogeneous catalysts can be recycled without losing their activity.
Three novel bioactive silver–organic networks, namely, the 2D polymer Ag(μ3-PTA)(chc) n ·n(Hchc)·2nH2O (1), the 3D bioMOF Ag2(μ3-PTA)2(μ2-chdc) n ·5nH2O (2), and the 2D polymer ...Ag2(μ2-PTA)2(μ4-H2chtc) n ·6nH2O (3), were constructed from 1,3,5-triaza-7-phosphaadamantane (PTA) and various flexible cyclohexanecarboxylic acids as building blocks {cyclohexanecarboxylic (Hchc), 1,4-cyclohexanedicarboxylic (H2chdc), and 1,2,4,5-cyclohexanetetracarboxylic (H4chtc) acid, respectively}. The obtained products 1–3 were fully characterized by IR and NMR spectroscopy, ESI-MS(±) spectrometry, elemental and thermogravimetric (TGA) analyses, and single-crystal and powder X-ray diffraction. Their structural diversity originates from distinct coordination modes of cyclohexanecarboxylate moieties as well as from the presence of unconventional N,N,P-tridentate or N,P-bidentate PTA spacers. Topological classification of underlying metal–organic networks was performed, disclosing the hcb, 4,4L28, and a rare fsc-3,4-Pbcn-3 topology in 1, 2, and 3, respectively. Moreover, combination of aqueous solubility (S 25°C ≈ 4–6 mg mL–1), air stability, and appropriate coordination environments around silver centers favors a release of bioactive Ag+ ions by 1–3, which thus act as potent antibacterial and antifungal agents against Gram-positive (S. aureus) and Gram-negative (E. coli and P. aeruginosa) bacteria as well as a yeast (C. albicans). The best normalized minimum inhibitory concentrations (normalized MIC) of 10–18 (for bacterial strains) or 57 nmol mL–1 (for a yeast strain) were achieved. Detailed ESI-MS studies were performed, confirming the relative stability of 1–3 in solution and giving additional insight on the self-assembly formation of polycarboxylate Ag–PTA derivatives and their crystal growth process.
Chiral halogenated substances have many applications in pharmaceuticals, agrochemicals, and materials, such as polymers, liquid crystals and as intermediates in synthesis. The presence of a halogen ...atom in a molecule can have a large effect in its properties; for instance, halogens are used in drugs to improve lipophilicity, membrane permeability and absorption, and even the blood‐brain barrier permeability. As highlighted in this review, there are nowadays a range of highly selective, versatile halogenating reagents, electrophilic, nucleophilic or radical in nature, which operate under mild conditions, allowing late‐stage functionalization of complex molecules in cascade reactions. Recent developments in organocatalyst design revealed novel Cinchona alkaloids derivatives, chiral phosphoric acids, amines, phosphines and several bifunctional catalysts, mostly thiourea‐ or squaramide‐based, which introduced chirality, with high levels of enantio‐ and diastereoselection, in the formation of one or multiple chiral centers in a single synthetic operation, as shown. In this review we survey the literature published in this field from 2014 to 2020.
Cascade reactions, either induced by halogenation or involving halogenated synthetic building blocks, have been utilized in recent years to obtain a variety of cyclic compounds, of interest for many applications. In this review the literature on enantioselective catalytic methods of synthesis is surveyed for the period 2014–2020.
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