A fluorescence polarisation molecular imprint sorbent assay for 2,4-D: a non-separation pseudo-immunoassay

The first pseudo-immunoassay which employs a molecularly imprinted receptor and a fluorescent probe, and quantifies the bound analyte directly using the fluorescence anisotropy of the polymer-probe-analyte suspension, is described.     

Solid phase extraction of penicillins from milk by using sacrificial silica beads as a support for a molecular imprint

We have prepared molecularly imprinted beads with molecular recognition capability for target molecules containing the penicillanic acid substructure. They were prepared by (a) grafting mesoporous silica beads with 6-aminopenicillanic acid as the mimic template, (b) filling the pores with a polymerized mixture of methacrylic acid and trimethylolpropane trimethacrylate, and (c) removing the silica support with ammonium fluoride. The resulting imprinted beads showed good molecular recognition capability for various penicillanic species, while antibiotics such as cephalosporins or chloramphenicol were poorly recognized. The imprinted beads were used to extract penicillin V, nafcillin, oxacillin, cloxacillin and dicloxacillin from skimmed and deproteinized milk in the concentration range of 5–100 μg·L⁻¹. The extracts were then analyzed by micellar electrokinetic chromatography by applying reverse polarity staking as an in-capillary preconcentration step, and this resulted in a fast and affordable method within the MRL levels, characterized by minimal pretreatment steps and recoveries of 64–90 %.

Penicillanic acid-imprinted beads prepared in preformed porous silica by an imprinting &; etching approach show selectivity towards β-lactams antibiotics. Molecularly imprinted solid phase extraction/micellar electrokinetic chromatography coupled with in-capillary preconcentration resulted in a fast and affordable method for penicillins in milk at MRL levels.

     

Solid phase extraction of penicillins from milk by using sacrificial silica beads as a support for a molecular imprint

We have prepared molecularly imprinted beads with molecular recognition capability for target molecules containing the penicillanic acid substructure. They were prepared by (a) grafting mesoporous silica beads with 6-aminopenicillanic acid as the mimic template, (b) filling the pores with a polymerized mixture of methacrylic acid and trimethylolpropane trimethacrylate, and (c) removing the silica support with ammonium fluoride. The resulting imprinted beads showed good molecular recognition capability for various penicillanic species, while antibiotics such as cephalosporins or chloramphenicol were poorly recognized. The imprinted beads were used to extract penicillin V, nafcillin, oxacillin, cloxacillin and dicloxacillin from skimmed and deproteinized milk in the concentration range of 5–100 μg·L^?1. The extracts were then analyzed by micellar electrokinetic chromatography by applying reverse polarity staking as an in-capillary preconcentration step, and this resulted in a fast and affordable method within the MRL levels, characterized by minimal pretreatment steps and recoveries of 64–90 %.

Thermally-regulated molecular selectivity of organosilica sol-gels

The feasibility of using temperature as a control mechanism for altering the selectivity of organosilica sol-gels for a specific molecule is demonstrated in this communication. The porous organosilica sol-gels act as reversible thermoresponsive materials which become hydrophobic at higher temperature and hydrophilic at lower temperature. When exposed to a mixture of molecules, the gels selectively intake the more hydrophobic species at higher temperature. A particularly remarkable feature of these gels is their ability to preferentially sequester the hydrophobic molecule at high temperature and the hydrophilic species at low temperature. Finally, these gels selectively intake hydrophobic molecules at high temperature and then preferentially release them when the temperature is lowered.     

N,S-containing soft ligands for extractive separation of f-metals: synthesis and unexpected inverse selectivity

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Phosphonomethylation of 2-aminoethanethiol and thiazolidine. An unexpected product

Phosphonomethylation of 2-aminoethanethiol and thiazolidine gives the unexpected dimethylene diphosphonic acid 6.     

Mechanistic understanding of the unexpected meta selectivity in copper-catalyzed anilide C-H bond arylation

DFT calculations suggest that the unexpected meta product in the copper-catalyzed arylation of anilide is formed via a Heck-like four-membered-ring transition state involving a Cu(III)-Ph species. A competitive electrophilic substitution mechanism delivers the ortho product when a methoxy group is present at the meta position of pivanilide. A series of experiments including kinetic studies support the involvement of a Cu(I) catalyst.     

Synthesis of heterocyclic compounds XLIX. An unexpected synthesis of isoxazolamines

Reaction of 3-aryl-1-phenyl-2-nitropropenones 1 with potassium cyanide leads to 4-aryl-3-benzoyl-5-isoxazo-lamines 5 in a one-step process involving the formal reduction of the nitro group followed by nucleophilic attack at the cyano group. Treatment of the isoxazolamine with an aromatic aldehyde yields the corresponding N-arylideneisoxazolamine.     

An unexpected synthesis of ketene monothioacetals

Some dithiocarbonates (xanthates) can be converted into ketene monothioacetals through extrusion of sulfur upon treatment with base and an alkylating agent.     

An unexpected base-induced rearrangement of tritylamine

An unexpected rearrangement was observed during the treatment of tritylamine with n-butyllithium, leading to the formation of an imine.     

Encapsulation of guests within a gated molecular basket: thermodynamics and selectivity

Molecular basket 1 has been designed to contain a set of aromatic gates, each with rotational mobility restricted via intramolecular hydrogen bonding. This structural, yet dynamic, feature of the host has been revealed to permit the formation of a transient enclosed space capable of containing haloalkanes, whose size/shape, electronic and entropic attributes contributed to the thermodynamics of binding. Markedly, the basket is capable of mediating the trafficking of a broad range of molecules.     

An unexpected generation of magnetically separable Se/Fe3O4 for catalytic degradation of polyene contaminants with molecular oxygen

Selenization of Fe₂O₃ with NaHSe led to Se/Fe₃O₄. The unexpected generation of Fe₃O₄ attributed to the reduction conditions of the reaction, and the resulted magnetic features of the material facilitated its separation in practical applications. Owning to the synergistic effect of Se with Fe, the material was especially active to catalyze the oxidative C=C scission using O₂ as mild oxidant. The technique has been successfully applied in polyene degradation project, which is of profound practical values for the treatment of the polyene pigment pollution and may be applied in the food and pharmaceutical industry.     

Topologies of metal-organic frameworks based on pyrimidine-5-carboxylate and unexpected gas-sorption selectivity for CO(2)

A simple and multitopic ligand, pyrimidine-5-carboxylate (pmc), has been used to obtain a series of metal-organic frameworks (MOFs) based on Co(2+), Cd(2+), and Cu(2+). The networks possess well-defined topologies of body-centered-cubic, rutile, and interpenetrated NbO structures, respectively. Among those, [Cu(pmc)(2)] possesses a permanent porosity resulting from straight one-dimensional channels of 5.5 ? free passages. Unexpectedly, this porous MOF displays a highly selective sorption behavior for CO(2), and the sorptions of N(2), Ar, O(2), H(2), and CH(4) at two different temperatures are found to be negligible. The results of diffraction and spectroscopic analyses exclude framework dynamics or incomplete evacuation as the origin of the gas-sorption selectivity.     

Regioselective cyclomanganation of Schiff bases. An unexpected effect of chloro substituents

In this paper we describe the synthesis of new metallacycles by the cyclomanganation reaction of benzyl-benzylidene-amines by using [MnMe(CO)₅] as metallating agent. These ligands can undergo metallation on different aromatic carbon atoms but no important differences have been found in the regioselectivity of the process, that can be related to the electronic effect of the substituents, and in all the cases studied the endo-cyclomanganated complexes of para-substituted imines have been obtained. The corresponding exo-metallacycles were obtained by reaction of [MnMe(CO)₅] on the imine 2,6-Cl₂C₆H₃CHNCH₂Ph and 2,4,6-Me₃C₆H₂CHNCH₂Ph, derived from 2,6-dichlorobenzaldehyde and 2,4,6-trimethylbenzaldehyde, respectively.The results described suggest that the mechanism of the cyclomanganation is similar to that of cyclopalladation and it can be proposed that cyclomanganation takes place by the formation of a four-centered transition state, involving the C-H and Mn-C_acetyl bonds, in the acetyl coordination complex formed in the first step of the reaction.     

Preparation and phenol-recognizing ability of a poly(methacrylic acid) molecular imprint on the surface of a silica gel

Molecularly imprinted solid phase extraction is an excellent tool for the preconcentration of trace analytes. We report on the preparation of such a material by firstly graft-polymerizing methacrylic acid onto the surface of silica gel particles, and then imprinting it by using phenol as a template and ethylene glycol diglycidyl ether as a crosslinker. The binding and recognition of phenol were examined by static methods. The binding capacity at saturation is 160?mg·g^?1 in 9?h at pH 6. The selectivity coefficients relative to o-cresol and chlorophenol are 22 and 23, respectively. The pH value has a large effect. Adsorbed phenol can be eluted easily from the imprint with diluted sodium hydroxide solution, and the material is reusable.

An unexpected ring-opening in the reissert reaction on 2,3-diphenylquinoxaline-n-oxide.

When quinoxaline-N-oxide 1 is reacted with KCN and benzoyl chloride in water (the Reissert reaction) or methanol, the products are 2-,5- and 6- chloroquinoxaline (the latter being the major product: 42±6 %) and small amounts of 2-cyanoquinoxaline. Using three equivalents of trimethylsilyl cyanide instead of KCN, and dichloromethane as the solvent, leads to a 72 % yield of 2-cyanoquinoxaline. The reaction of trimethylsilyl cyanide and benzoyl chloride with 2,3-diphenylquinoxaline-N-oxide 2 leads to an unexpected ring-opening product 13; its structure is based on spectroscopic data and on an X-ray crystallographic analysis.