Reaction of alkenes with hydrogen peroxide and sodium iodide: a nonenzymatic biogenic-like approach to iodohydrins

An efficient protocol to synthesize iodohydrins from alkenes is presented. Reactions were conducted in aqueous media using safe and readily available sodium iodide (the most abundant form of the element), and a highly convenient oxidant such as hydrogen peroxide. Addition of a protic acid triggers a faster and efficient process, a role formally related to that played by haloperoxidase enzymes in naturally occurring transformations. The successful application of these conditions to multigram scale preparations and over natural products derivatives is also discussed.     

Concentrated reverse micelles in a random graft block copolymer system: structure and in-situ synthesis of silver nanoparticles

The structure and rheological properties of a poly(dimethylsiloxane)-graft-poly(oxyethylene) copolymer at high concentrations in block-selective solvents were studied by small-angle X-ray scattering (SAXS) and rheometry. Analysis of SAXS data indicates that quasispherical, reverse micellar aggregates (with no ordered packing) are present in concentrated solutions of the copolymer in nonpolar solvents, and that upon addition of water, the size of such aggregates increases due to the solubilization inside the micellar cores. The viscosity of concentrated polymer solutions increases exponentially as water is added, and finally, viscoelastic, gel-like behavior is found in the vicinity of the phase separation limit. It was found that small silver nanoparticles with an average diameter of ≈3 nm can be synthesized inside the copolymer aggregates without the need of a reducing agent; namely, particles embedded in a viscoelastic matrix are obtained. The synthesis seems to follow first-order kinetics. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Unexpected ferromagnetic interaction in a new tetranuclear copper(II) complex: synthesis, crystal structure, magnetic properties, and theoretical studies

The new tetranuclear carbonate complex [Cu2L)2(CO3)] x 8H2O (1 x 8H2O) (H3L = (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) has been obtained by two different synthetic routes and fully characterized. Recrystallization of 1 x 8H2O in methanol yields single crystals of {[(Cu2L)2(CO3)]}2 x 12H2O (1 x 6H2O), suitable for X-ray diffraction studies. The crystal structure of 1 x 6H2O shows two crystallographically different tetranuclear molecules in the asymmetric unit, 1a and 1b. Both molecules can be understood as self-assembled from two dinuclear [Cu2L]+ cations, joined by a mu4-eta(2):eta(1):eta(1) carbonate ligand. The copper atoms of each crystallographically different [(Cu2L)2(CO3)] molecule present miscellaneous coordination polyhedra: in both 1a and 1b, two metal centers are in square pyramidal environments, one displays a square planar chromophore and the other one has a geometry that can be considered as an intermediate between square pyramid and trigonal bipyramid. Magnetic studies reveal net intramolecular ferromagnetic coupling between the metal atoms. Density functional calculations allow the assignment of the different magnetic coupling constants and explain the unexpected ferromagnetic behavior, because of the presence of an unusual NCN bridging moiety and countercomplementarity of the phenoxo (or carbonate) and NCN bridges.     

Biocompatible hydrogels based on chitosan,cellulose/starch,PVA and PEDOT:PSS with high flexibility and high mechanical strength

Fabricating mechanically strong hydrogels that can withstand the conditions in internal tissues is a challenging task. We have designed hydrogels based on multicomponent systems by combining chitosan, starch/cellulose, PVA, and PEDOT:PSS via one-pot synthesis. The starch-based hydrogels were homogeneous, while the cellulose-based hydrogels showed the presence of cellulose micro- and nanofibers. The cellulose-based hydrogels demonstrated a swelling ratio between 121 and 156%, while the starch-based hydrogels showed higher values, from 234 to 280%. Tensile tests indicated that the presence of starch in the hydrogels provided high flexibility (strain at break?>?300%), while combination with cellulose led to the formation of stiffer hydrogels (elastic moduli 3.9–6.6 MPa). The ultimate tensile strength for both types of hydrogels was similar (2.8–3.9 MPa). The adhesion and growth of human osteoblast-like SAOS-2 cells was higher on hydrogels with cellulose than on hydrogels with starch, and was higher on hydrogels with PEDOT:PSS than on hydrogels without this polymer. The metabolic activity of cells cultivated for 3 days in the hydrogel infusions indicated that no acutely toxic compounds were released. This is promising for further possible applications of these hydrogels in tissue engineering or in wound dressings.

Graphical abstract

     

Two New Antiferromagnetic Nickel(II) Complexes Bridged by Azido Ligands in the Cis Position. Effect of the Counteranion on the Crystal Structure and Magnetic Properties

Two new nickel(II) end-to-end azido-bridged compounds, cis-catena-[NiL(2)(&mgr;-N(3))](n)()(ClO(4))(n)().nH(2)O (1) and [Ni(2)L(4)(&mgr;-N(3))(2)](PF(6))(2) (2), were synthesized and characterized; L is 2-(aminoethyl)pyridine. The crystal structures of 1 and 2 were solved. Complex 1: monoclinic system, space group P2(1)/a, a = 8.637(2) ?, b = 18.9995(7) ?, c = 12.3093(7) ?, beta = 105.92(2) degrees, Z = 4. Complex 2: triclinic system, space group P&onemacr;, a = 9.139(7) ?, b = 10.124(3) ?, c = 12.024(2) ?, alpha = 70.407(14) degrees, beta = 84.19(2) degrees, gamma = 67.67(4) degrees, Z = 1. In the two complexes the nickel atom is situated in a similarly distorted octahedral environment. The two complexes are different; 1 is a one-dimensional helicoidal complex with the two L ligands and the two end-to-end azido bridges in a cis arrangement while complex 2 is a dinuclear system with two end-to-end azido bridges, indicating the extreme importance of the counteranion present (ClO(4)(-) for 1 and PF(6)(-) for 2). The magnetic properties of the two compounds were studied by susceptibility measurements vs temperature. The chi(M) vs T plot for 1 shows the shape for a weakly antiferromagnetically coupled nickel(II) one-dimensional complex without a maximum until 4 K. In contrast, for complex 2 the shape of the chi(M) vs T curve shows a maximum near 40 K, indicating medium antiferromagnetic coupling. From the spin Hamiltonian -J(ij)()S(i)()S(j)(), J values for 1 and 2 were less than -1 and -29.1 cm(-)(1), respectively. The magnetic behavior for 1 and 2 may be explained in terms of the overlap between magnetic orbitals, taking into account the torsion of the Ni(II) atoms and azido-bridging ligands in the two structures.     

Analytic correlated wave functions in momentum space and related properties of helium like ions

We obtain analytic correlated wave functions in momentum space as the Fourier transform of correlated wave functions which are able to incorporate almost all of the correlation energy for the ground-state of two-electron atoms. Then we study the atomic momentum-density, the Compton profile and the elastic and inelastic scattering factors for this kind of wave functions. The scattering factors are also compared with the ones provided by a more accurate correlated wave function. All the calculations can be analytically performed, provided the correlated wave function in position space has been determined.     

Xanthate complexes of nickel with nitrogen donor ligands. Part V

Nickel(II) xanthate complexes of general formula, [Ni(Rxa)₂(L)] [R = i-Pr, i-Am, xa = OCS^– ₂, L = 4,7-diphenyl-1,10-phenanthroline(baphen), 4,4-dimethyl-2,2-bipyridyl (me₂bpy), 2-9-dimethyl-1,10-phenanthroline(neo) or trans-1,2-diaminocyclohexane (dch)] and [Ni(Rxa)(cyclam)](Rxa) (= 1,4,8,11-tetraazacyclotetradecane) have been synthesized and characterized by elemental analyses, i.r. and electronic spectroscopy, magnetic and conductivity measurements. The complexes with cyclam were studied by cyclic voltammetry. Values of magnetic moments at room temperature lie within the 3.25–3.51 B.M. range and thus indicate the presence of two unpaired electrons, except for the complexes with cyclam, where the anomalous values of 1.76 and 1.74 B.M. were obtained in respect to the nickel(II) complexes. Magnetic susceptibility data for [Ni(i-Prxa)(cyclam)](i-Prxa) were measured over the 79–298 K range and indicate no exchange interaction between paramagnetic nickel(II) centres.     

Holo- and hemidirected lead(II) in the polymeric [Pb(4)(mu-3,4-TDTA)2(H2O)2]*4H2O complex. N,N,N',N'-tetraacetate ligands derived from o-phenylenediamines as sequestering agents for lead(II)

The coordinating ability of the ligands 3,4-toluenediamine-N,N,N',N'-tetraacetate (3,4-TDTA), o-phenylenediamine-N,N,N',N'-tetraacetate (o-PhDTA), and 4-chloro-1,2-phenylenediamine-N,N,N',N'-tetraacetate (4-Cl-o-PhDTA) (H4L acids) toward lead(II) is studied by potentiometry (25 degrees C, I = 0.5 mol x dm(-3) in NaClO4), UV-vis spectrophotometry, and 207Pb NMR spectrometry. The stability constants of the complex species formed were determined. X-ray diffraction structural analysis of the complex [Pb4(mu-3,4-TDTA)4(H2O)2]*4H2O (1) revealed that 1 has a 2-D structure. The layers are built up by the polymerization of centrosymmetric [Pb4L2(H2O)2] tetranuclear units. The neutral layers have the aromatic rings of the ligands pointing to the periphery, whereas the metallic ions are located in the central part of the layers. In compound 1, two types of six-coordinate lead(II) environments are produced. The Pb(1) is coordinated to two nitrogen atoms and four carboxylate oxygens from the ligand, whereas Pb(2) has an O6 trigonally distorted octahedral surrounding. The lead(II) ion is surrounded by five carboxylate oxygens and a water molecule. The carboxylate oxygens belong to four different ligands that are also joined to four other Pb(1) ions. The selective uptake of lead(II) was analyzed by means of chemical speciation diagrams as well as the so-called conditional or effective formation constants K(Pb)eff. The results indicate that, in competition with other ligands that are strong complexing agents for lead(II), our ligands are better sequestering agents in acidic media.     

A highly reactive mononuclear Zn(II) complex for phosphodiester cleavage

The activity of a Zn(II) complex of a tetradentate, tripodal ligand for catalyzing phosphodiester cleavage is enhanced 750-fold by introducing three hydrogen bond donors to the ligand. Inhibition studies show that the Zn-aqua complex is the kinetically active form and that it binds the transition state with a formal dissociation constant of 3 x 108 M-1. The effect of these ligand modifications on the transition-state affinity is comparable to the rate acceleration provided by the metal ion itself. Overall, this mononuclear complex is more active than the most reactive dinuclear Zn(II) complexes reported to date.     

Ligand adsorption on an activated carbon for the removal of chromate ions from aqueous solutions

The results presented in this work are related to the design of a guideline to develop specific properties at the surface of an activated carbon (AC). For this, two model aromatic compounds have been synthesized and their electrolytic behavior in aqueous solutions was studied by a potentiometric method. The textural characteristics of the activated carbon were determined by porosimetry methods. The nature of oxygen-carrying functions and the acid-base behavior of the AC surface were characterized by TPD and potentiometric titration methods, respectively. The adsorption and desorption equilibria of the aromatic compounds on activated carbon were measured in aqueous solutions, and the hysteresis between adsorption and desorption, which reveals irreversible adsorption, was discussed on the basis of the frontier orbital theory. HOMO and LUMO orbitals of the adsorbent and adsorbates were calculated, and irreversible adsorption was attributed to the small energy difference between HOMO and LUMO of the aromatic adsorbates and the adsorbent. Adsorption equilibria of K2CrO4 in aqueous solution on the AC alone and on the AC-aromatic ligand adsorbents, respectively, prove the efficient development of specific chemical functions at the carbon surface provided by the adsorbed aromatic compounds.