Cu(II)-nitroxyl radicals as catalytic galactose oxidase mimics

Results from Hammett correlation studies and primary kinetic isotope effects for the CuCl-TEMPO catalysed aerobic benzyl alcohol oxidations are inconsistent with an oxoammonium based mechanism. We postulate a copper-mediated dehydrogenation mechanism, in which TEMPO regenerates the active Cu(II)-species. This mechanism is analogous to that observed for Galactose Oxidase and mimics thereof.     

Highly atom efficient catalytic reactions utilizing water and alcohols as reagents

In this accounts, we describe our recent studies on hydrolysis, alcoholysis, and addition of alcohols to organic molecules. The reactions utilizing water and alcohols as a reagent are one of the most basic and simple reactions. The palladium-catalyzed asymmetric hydrolysis and alcoholysis of vinyl ethers gave valuable axially chiral 1,1′-bi-2-naphthol and 1,1′-bi-2-phenol derivatives and chiral P-chirogenic compounds in optically active form. The reaction is applied for hydrolytic deallylation of N-allyl amide and allyl esters. The later one was achieved by palladium/ruthenium dual catalysts which is the first example of catalytic irreversible ester hydrolysis. Gold complexes also catalyzed vinyl ether alcoholysis and hydroalkoxylation of olefins. In the later reaction, simple unactivated olefins can be used as substrates and gave the product in 92% yield. The copper-DTBM-SEGPHOS complex catalyzed alcoholysis of azlactones which is the first example showing zero-order kinetic resolution.     

Selective catalytic monoreduction of dichlorooligosilanes with Grignard reagents

Transition metal-catalyzed monoreduction of dichlorooligosilanes with Grignard reagents is reported. Among the examined catalysts, group 4 metal chlorides such as TiCl₄ and Cp₂TiCl₂ gave the highest reactivity and good selectivity. The reducing power is effectively controlled by changing the catalysts and Grignard reagents to achieve sufficient selectivity depending on the oligosilane substrates.     

Polymer-supported organotin reagents in the catalytic Stille reaction

Polymer-supported dibutyltin chloride and dimethyltin chloride resins were synthesised and used in Maleczka's catalytic Stille reaction.     

Added-metal-free catalytic nucleophilic addition of Grignard reagents to ketones

On the basis of the investigation of the combinational effect of quaternary ammonium salts and organic bases, an added-metal-free catalytic system for nucleophilic addition reactions of a variety of Grignard reagents to diverse ketones in THF solvent has been developed to produce tertiary alcohols in good to excellent yields. By using tetrabutylammonium chloride (NBu(4)Cl) as a catalyst and diglyme (DGDE) as an additive, this system strongly enhances the efficiency of addition at the expense of enolization and reduction. NBu(4)Cl should help to shift the Schlenk equilibrium of Grignard reagents to the side of dimeric Grignard reagents to favor the additions of Grignard reagents to ketones via a favored six-membered transition state to form the desired tertiary alcohols, and DGDE should increase the nucleophilic reactivities of Grignard reagents by coordination. This catalytic system has been applied in the efficient synthesis of Citalopram, an effective U.S. FDA-approved antidepressant, and a recyclable version of this catalytic synthesis has also been devised.     

Chiral N-acylethylenediamines as new modular ligands for the catalytic asymmetric addition of alkylzinc reagents to aldehydes

Chiral N-acylethylenediamines represent a new class of modular ligands for the catalytic asymmetric addition of alkylzinc reagents to aldehydes. The N-acylethylenediamine moiety serves as a metal binding site, while attached amino acids provide the source of chirality. Three sites of diversity on the ligands were optimized to enhance the enantioselectivity of the catalysts using an iterative optimization procedure. The most effective ligand, 4k, was synthesized in a single reaction step from inexpensive and commercially available starting materials. This ligand (10 mol %) catalyzed the addition of Me2Zn to 2-naphthaldehyde, benzaldehyde, and 4-chlorobenzaldehyde to give the corresponding alcohol products in 86%, 84% and 81% ee, respectively.     

Aptamers as analytical reagents

Many important analytical methods are based on molecular recognition. Aptamers are oligonucleotides that exhibit molecular recognition; they are capable of specifically binding a target molecule, and have exhibited affinity for several classes of molecules. The use of aptamers as tools in analytical chemistry is on the rise due to the development of the "systematic evolution of ligands by exponential enrichment" (SELEX) procedure. This technique allows high-affinity aptamers to be isolated and amplified when starting from a large pool of oligonucleotide sequences. These molecules have been used in flow cytometry, biosensors, affinity probe electrophoresis, capillary electrochromatography, and affinity chromatography. In this paper, we will discuss applications of aptamers which have led to the development of aptamers as chromatographic stationary phases and applications of these stationary phases; and look towards future work which may benefit from the use of aptamers as stationary phases.     

Hyperbranched polyselenides as glutathione peroxidase mimics

Novel hyperbranched polyselenides with multi-catalytic sites at the branching units have been synthesized which may provide a new approach towards glutathione peroxidase mimics.     

New catalytic cycle for couplings of aldehydes with organochromium reagents

[reaction: see text] A new catalytic cycle has been developed to effect all three subgroups of Cr-mediated couplings, i.e., (1) Ni/Cr-mediated alkenylation, alkynylation, and arylation, (2) Co/Cr-mediated 2-haloallylation, alkylation, and propargylation, and (3) Cr-mediated allylation. In the presence of chiral sulfonamide ligands, good asymmetric inductions can be achieved for some of the Ni/Cr-mediated alkenylation, Co/Cr-mediated 2-haloallylation and propargylation, and Cr-mediated allylation.     

Highly efficient catalytic system for electrophilic amination of arylzinc reagents

The effect of catalyst on the yield of amine in the amination of three classes of arylzinc reagents with acetone oxime O‐tosylate was investigated. Since they allowed the preparation of arylamines in excellent yields in the presence of a minimum amount of copper (I) or copper (II) compounds, the catalytic systems using copper (I) or copper (II) combined with a P‐, N‐ or S‐donor ligand were revealed to be the best catalysts for the electrophilic amination of arylzinc reagents with acetone oxime O‐tosylate in the presence of DMPU. Copyright © 2009 John Wiley & Sons, Ltd.     

3,4,5-Trihydroxyfluorones as analytical reagents

Acid-base, spectrophotometric, and chromaticity characteristics of 3,4,5-trihydroxy-9-(2′-sulfophenyl)-6-isoxanthone (Pyrogallol Red, PR) and its 2,7-dibromo derivative (Dibromopyrogallol Red, BPR) were considered. The effect of the ionic strength, solvents, and surfactants on these characteristics was discussed. The complexation of the reagents with metal ions in the presence of second and third components (surfactants of different natures and organic reagents) was considered. The analytical characteristics of two-, three-, and four-component complexes were compared. The selectivity of the reagents, methods for changing the selectivity, and applications in analytical chemistry were considered. It was noted that chromaticity measurements are promising for studying the complexation of ions and their determination.     

Hydroxamic acids as colorimetric reagents

Thirty-three hydroxamic acids and three N-substituted hydroxamic acids or structurally similar compounds have been studied as possible colorimetric reagents for metal ions. They were tested with 78 ions under varying conditions of acidity and basicity. Aliphatic, substituted aliphatic, aromatic, substituted aromatic, and heterocyclic hydroxamic acids were represented in the compounds studied. An attempt was made to correlate the activity towards metal ions with variations in the molecular structure of the hydroxamic acids. The studies with C-substituted hydroxamic acids indicate that the preferential formation of a colour or a precipitate depends on pH, the solvent, and reagent concentration, and is not a function of the presence or absence of a substituent on the nitrogen atom. A number of the compounds offer promise of being useful colorimetric reagents under proper reaction conditions.     

Immobilized enzymes as analytical reagents

Immobilized enzymes are becoming increasingly popular as analytical reagents because of their reusability, stability, and sensitivity to many inhibitors that would seriously interfere in assays using soluble enzymes. In this article, some of the kinetic and catalytic effects of immobilized enzymes in analysis will be discussed. The shift of the activity-pH profile curves on immobilization, the changes in temperature dependence. the inhibitor constants (K₁). Michaelis constants (K _m ), and the maximum velocity (V_max). plus others, will be discussed. Finally, the use of these immobilized enzymes in fluorometric and electrochemical monitoring systems will be shown, and the future of these reagents in various areas will be discussed. A survey of enzyme electrodes will be presented as an example of the use of immobilized enzymes. Application of immobilized enzyme technology to the assay of BUN, glucose, uric acid, amino acids, ethanol. and other metabolites will be discussed.     

Substituted hydroxylamines as analytical reagents

The review deals with analytical applications of hydroxylamine derivatives. The defects of cupferron and versatility of N-benzoyl-N-phenylhydroxylamine in reaction with various metal ions is discussed. The application of the latter in chemical analysis is summarized and separation factors for some pairs of elements included. Suggestions for further use of this compound and other hydroxylamines are given.     

Porphyrin-fullerene linked systems as artificial photosynthetic mimics

We have prepared a variety of porphyrin-fullerene linked systems to mimic photoinduced energy and electron transfer (ET) processes in photosynthesis. Photodynamical studies on porphyrin and analogs-fullerene linked systems have revealed the acceleration of photoinduced electron transfer and charge-shift and the deceleration of charge recombination, which is reasonably explained by the small reorganization energies of electron transfer in fullerenes. In this context, we have proposed two strategies, photoinduced single-step and multi-step electron transfers, for prolonging the lifetime of a charge-separated state in donor-acceptor linked systems. The single-step ET strategy allowed a zinc chlorin-fullerene linked dyad to extend the lifetime up to 120 seconds in frozen PhCN at 123 K, which is the longest value of charge separation ever reported for donor-acceptor linked systems. Unfortunately, however, the quantum yield of formation of the charge-separated state was as low as 12%, probably due to the decay of the precursor exciplex state to the ground state rather than to the favorable complete charge-separated state. In contrast, the multi-step ET strategy has been successfully applied to porphyrin-fullerene linked triads, tetrads, and a pentad. In particular, a ferrocene-porphyrin trimer-fullerene pentad revealed formation of a long-lived charge-separated state (0.53 s in frozen DMF at 163 K) with an extremely high quantum yield (83%), which is comparable to natural bacterial reaction centers. These results not only provide valuable information for a better understanding of photoinduced energy and electron transfer processes in photosynthesis, but also open the door for the development of photoinitiated molecular devices and machines.     

Fruit waste (Pulp) decorated CuO NFs as promising platform for enhanced catalytic response and its peroxidase mimics evaluation

Herein, we report for the first time, an eco-compatible hydrothermal route for the synthesis of carbon enriched mesoporous material (CuO NFs@MP) using fruit waste (Pulp) obtained from Citrus limetta’s (Mausambi) decorated irregular shaped CuO nanoflakes (NFs). The CuO NFs@MP nanocomposite was fully characterized through several spectroscopic-cum-analytical techniques such as TEM and XPS, which further confirmed the presence of CuO NFs. CuO NFs@MP could serve as an excellent catalyst for N-Arylation reaction and also paves promising peroxidase mimic activity. The preliminary results indicated that CuO NFs@MP shows the catalytic advantage of higher yields, shorter reaction time and greener conditions. Simultaneously, the oxidation of colorless TMB with H₂O₂ into blue-green colored ox-TMB was also observed in 60 s with CuO NFs@MP. The present nanocomposite is easy to synthesize, economical, retrievable and a reusable catalyst for synthesizing a varied range of N-Arylated products and could also mimic peroxidase without significant loss of activity.     

The catalytic oxidation of phenol with H2O2 by metalloporphyrins as peroxidase mimics

Summary Three metalloporphyrin complexes are used as peroxidase mimics in the oxidation of phenol by hydrogen peroxide.A kinetic model for the titled reaction is constructed.     

Polymeric enzyme mimics: catalytic activity of ribose-containing polymers for a phosphate substrate

The polymers containing ribose rings: poly(5'-acrylamido-5'-deoxy-1',2'-O-isopropylidene-alpha-D-ribose) (11), poly(5'-acrylamido-5'-deoxy-alpha-D-ribose) (12) and poly(5'-acrylamido-5'-deoxy-1'-O-methyl-D-ribose) (13) were prepared as enzyme mimics. Polymers 12 and 13 with free vic-cis-diol groups catalyzed the hydrolysis of phosphodiester (ethyl p-nitrophenyl phosphate and N-methylpyridinium 4-tert-butylcatechol cyclic phosphate) and phosphomonoester substrates with a rate acceleration of 10 approximately equal to 10(3) compared with the uncatalyzed reaction. They also catalyzed the reverse reactions, i.e., the esterification of phosphomonoester to phosphodiester and the phosphorylation of alcohols with phosphate ions. The catalytic activity was attributable to the vic-cis-diols of riboses on polymer chains, which formed hydrogen bonds with two phosphoryl oxygen atoms of phosphates so as to activate the phosphorus atoms to be attacked by nucleophiles. The catalytic activity was negligible for polymer 11 where vic-cis-diol groups were blocked with isopropylidene groups. The catalytic activity was attributable to the vic-cis-diols of riboses on polymer chains, which formed hydrogen bonds with two phosphoryl oxygen atoms of phosphates so as to activate the phosphorus atoms to be attacked by nucleophiles.