Reactivity of tert‐butylperoxyl radical with manganese(III), cobalt(II), and nickel(II) salicylidene Schiff base chelates

Salicylidene Schiff base chelates (R,R)‐(–)‐N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediaminomanganese(III) chloride, (R,R)‐(–)‐N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediaminocobalt(II), N,N′‐bis(salicylidene)‐ethylenediaminocobalt(II), N,N′‐bis(salicylidene)ethylenediaminonickel(II), and N,N′‐bis(salicylidene)ethylenediaminoaquacobalt(II), as well as (R,R)‐(–)‐N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)1,2‐cyclohexanediamine, were kinetically examined as antioxidants in the scavenging of tert‐butylperoxyl radical (tert‐butylOO^?). Absolute rate constants and corresponding Arrhenius parameters were determined for reactions of tert‐butylOO^? with these chelates in the temperature range ?52.5 to ?11°C. High reactivity of tert‐butylOO^? with Mn(III) and Co(II) salicylidene Schiff base chelates was established using a kinetic electron paramagnetic resonance method. These salicylidene Schiff base chelates react in a 1:1 stoichiometric fashion with tert‐butylOO^? without free radical formation. Ultraviolet–visible spectrophotometry and differential pulse voltammetry established that the rapid removal rate of tert‐butylOO^? by these chelates is the result of Mn(III) oxidation to Mn(IV) and Co(II) oxidation to Co(III) by tert‐butylOO^?. It is concluded that removal of alkylperoxyl radical by Mn(III) and Co(II) salicylidene Schiff base chelates may partially account for their biological activities. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 431–439, 2007     

A natural extension for the greedy β-transformation with three arbitrary digits

We construct a planar version of the natural extension of the piecewise linear transformation T generating greedy β-expansions with digits in an arbitrary set of real numbers A = {a ₀, a ₁, a ₂}. As a result, we derive in an easy way a closed formula for the density of the unique T-invariant measure µ absolutely continuous with respect to Lebesgue measure. Furthermore, we show that T is exact and weak Bernoulli with respect to µ.     

The transfer of tin and germanium atoms from N-heterocyclic stannylenes and germylenes to diazadienes

New N-heterocyclic stannylenes and germylenes were synthesized by transamination of E[N(SiMe3)2] (E = Ge, Sn) with alpha-amino-aldimines or ethylidene-1,2-diamines and were characterized by spectroscopic methods and in the case of the germylene 10 g by X-ray diffraction. The reactions of several germylenes and stannylenes with diazadienes were studied by using dynamic NMR and computational methods. Experimental and theoretical studies confirmed that metathesis with exchange of the Group 14 atom is feasible for both stannylenes and germylenes, with exchange rates being generally higher for stannylenes. The metathesis of the diazadiene 3 b and the stannylene 1 b follows second-order kinetics and exhibits a sizeable negative entropy of activation. The transfer reaction is inhibited by bulky substituents in both reactants and surprisingly coincides with a suppression of the fragmentation of the stannylene into tin and diazadiene. A connection between oxidative addition and ring fragmentation was also observed in the reaction of 1 f with sulfur. Density functional theory (DFT) calculations suggest that all metathesis reactions proceed via transient spirocyclic [1+4] cycloaddition products, the formation of which is generally endothermic and endergonic. The spirostannanes display a distorted Psi-tbp geometry at the tin atom and their cycloreversion requires low or nearly negligible activation energies; spirogermanes exhibit distorted tetrahedral central atoms and sizeable energy barriers with respect to the same reaction. Complementary studies of cycloadditions of diazadienes to triplet germylenes or stannylenes indicate that these reactions are exothermic. The lowest triplet state in the carbene homologues results from promotion of an electron from an n(N) orbital with pi character rather than the n(C)-sigma orbital as in carbenes, and singlet-triplet excitation energies decrease from carbon to tin. Spirostannanes exhibit a triplet ground-state multiplicity that implies that the energy hypersurfaces for the reactions of singlet and triplet stannylenes with diazadienes intersect; for germylenes, the singlet hypersurface is always lower in energy. A reaction mechanism explaining the different thermal stabilities of N-heterocyclic germylenes and stannylenes, and the coincidence between ring metathesis and thermal decomposition of the latter, is proposed based on the different separation of the singlet and triplet energy hypersurfaces.     

Ion concentration of external solution as a characteristic of micro- and nanogel ionic reservoirs

Ion-sensitive hydrogel is regarded as an ionic reservoir, i.e., a system capable of changing the external pH or ionic strength by accumulating or releasing ions. The concept of a hydrogel ionic reservoir was demonstrated for hydrogel particles of three different size ranges: macrogel (1000-6000 microm), microgel (approximately 20-200 microm), and nanogel (approximately 0.2 microm). Ion sensitivity of poly(N-isopropylacrylamide-co-1-vinylimidazole) (PNIPA-VI) microgels with imidazolyl (ionizable) groups was confirmed by the pH dependence of their volume, while nanogels were characterized by dynamic light scattering. On the contrary, the volume of poly(N-isopropylacrylamide) (PNIPA) microgels without ionizable groups was pH independent in the whole range of pH from 10 to 2. Four distinct regions of pH-behavior were observed for PNIPA-VI hydrogel micro- and nanoparticles using potentiometric titration of their suspensions. Time-resolved measurements of ion concentrations in the suspension of hydrogel particles revealed a substantial difference in kinetics of pH equilibration for (i) ion-sensitive hydrogels (PNIPA-VI) vs hydrogels without ionizable groups (PNIPA) and (ii) PNIPA-VI hydrogels of different sizes. On the basis of the experimental observations, a two-step mechanism affecting the kinetics of proton uptake into the hydrogel particles with ionizable groups was proposed: (1) fast binding of ions to the immediate surface of each particle and (2) a slower successive diffusion of bound sites into the next inner layer of polymer network. In accord with the mechanism proposed, a quasi-chemical kinetic model of pH relaxation to equilibrium was developed to fit the experimental data for the time course of proton uptake by macro-, micro-, and nanogels into two exponentials with the characteristic times of tau(1) and tau(2). We believe the same kinetic model will be pertinent to describe phenomenological and molecular mechanisms controlling proton transport in/out bacteria, cells, organelles, drug delivery vehicles, and other natural or artificial multifunctional ionic containers. The approach can be easily extended for the other ions (e.g., Na(+), K(+), and Ca(2+)).     

A new characterization of arithmeticity

We prove that an equivalence lattice is arithmetical whenever for every and there exists a compatible choice function modulo , having a as a fixed point. The converse holds if L is finite. Received September 30, 1998; accepted in final form December 1, 1998.     

Ligand entrapment in twofold interpenetrating PtS matrixes by metallo-organic frameworks

Single-crystal X-ray crystallography was used to determine the structures of four metallo-organic frameworks (MOFs). A dendritic tetradentate ligand (tetrakis(isonicotinoxymethyl)methane, TINM) was used with first-row transition-metal elements copper, nickel, and cobalt to synthesize MOFs with a PtS interpenetration, due to both planar and tetrahedral junctions being present in the framework. Two different polymeric complexes, 1 and 2, were obtained from similar starting materials, TINM and Cu(NO(3))(2).3H(2)O, but different solvents. The use of dichloromethane in addition to methanol and water promoted the coordination of nitrate ions to the copper. With only methanol and water used as solvent, the copper atom was coordinated to water molecules instead. Compound 1 has pores going through the structure in two dimensions, along crystallographic axes a and c with diameters of the pores (the diameters correspond to the minimum distances between van der Waals surfaces of opposing walls defined by projection along channel axis) approximately 1.0 x 3.1 and 2.5 x 3.7 A, respectively. Compound 2 has channels along all crystallographic axes. The dimensions of the channels are 3.2 x 3.7, 3.7 x 5.0, and 2.8 x 4.1 A, respectively. The structures of 3 and 4 entrap a large guest ligand molecule in the framework. The guest ligand is uncoordinated, although the pattern that the entrapped guests form brings the two arms of any two guests within close range. The lack of 3-fold penetration is due to only two arms being close to each other and also the fact that there is no space for an additional set of metal centers.     

Interaction of modified liposomes with Bacillus spores

The interaction between liposomes modified with a particular peptide sequence and Bacillus subtilis spores was experimentally observed as (1) an increase in the average diameter of spore-related particles, and (2) the formation of dense and structured shells around the spores at higher concentrations of liposomes.     

Liquid phase oxidation of transition metals. Part 6. iron and copper complexes containing dimethylsulphoxide,dimethylformamide, and acetonitrile. Anomalous states of ligands

Summary Direct oxidation of iron and copper in a donor-acceptor medium, L + CCl₄, where L is dimethylsulphoxide, dimethylformamide or acetonitrile was employed to obtain complex compounds:cis-[FeCl₂(DMSO)₄]Cl] (3), 2 FeCl₃ · 3 DMSO (5), [FeCl(DMSO)₅][FeCl₄]₂] (6), [FeCl(DMSO)₅][Fe₂Cl₆O] (7),cis-[FeCl₂(DMF)₄][FeCl₄] (8), [Fe(MeCN)₆][FeCl₄]₂ (9) andcis-[CuCl₂(DMF)₂]₂ (10), The structures of complexes (9) and (10) have been established by x-ray diffraction analysis and compared with those of (3), (6), (7) and (8) which are reported elsewhere.The [FeCl(DMSO)₅][Fe₂Cl₆O] complex (7) is formed by oxidation of iron fromcis-[Fe^IIICl₂(DMSO)₄]₂[Fe^IICl₄] (4) in ethanol. One of the 5 DMSO molecules of (7) was found to be disordered; the Mössbauer spectroscopy data suggest that it can move within the cation coordination sphere.Mössbauer spectroscopy and x-ray diffraction analysis indicate electron isomerism in one of the complexes.For papers 4 and 5 of these series see refs. 1 and 2.     

Structurally diverse second-generation [2.2]paracyclophane ketimines with planar and central chirality: syntheses, structural determination, and evaluation for asymmetric catalysis

A set of 20 novel [2.2]paracyclophane ketimines with planar and central chirality has been synthesized from enantiomerically pure and racemic 5-acyl-4-hydroxy[2.2]paracyclophane and alpha-branched chiral amines. Their X-ray structures were determined to elucidate the three-dimensional structures and the absolute configuration. The ketimines were used as catalysts in the asymmetric 1,2-addition reactions of diethylzinc with substituted benzaldehydes to furnish chiral alcohols in up to 95 % ee.