Synthesis,molecular and crystalline architectures,and magnetic properties of neutral nickel(II)dicyanamide coordination polymers containing a symmetrical/unsymmetrical 1,2-diamine as an end-capping ligand

Two neutral nickel(II) coordination polymers [Ni(en)(dca)₂]_n (1) and [Ni(dmen)(dca)₂]_n (2) (en = ethylenediamine; dmen = N,N-dimethylethylenediamine; dca = dicyanamide) have been synthesized and X-ray crystallographically characterized. Each nickel(II) center in 1/2 adopts a distorted octahedral coordination environment with a NiN₆ chromophore ligated by two amine N atoms of the bidentate amine (en/dmen) and four nitrile N atoms of μ_1,5 bridged dca. The metal(II) centers are connected with each other through single μ_1,5 M–NCNCN–M bridges, resulting in a 2D layer structure with a (4,4) topology in 1 and a 3D network of topology (6,6) in 2. Multiple lateral N–H···N and C–H···N hydrogen bondings promote dimensionality. The magnetic susceptibility results of 1 and 2 at very low temperature support the zero-field splitting effect of the nickel(II) ions.     

Decarboxylative homocoupling of (hetero)aromatic carboxylic acids

A variety of hetero(aromatic) carboxylic acids are shown to undergo decarboxylative homocoupling, mediated by a Pd/Ag system. This novel methodology for the synthesis of symmetrical biaryls avoids the use of haloarenes and organometallic compounds as starting materials.     

Hapten synthesis, monoclonal antibody generation, and development of competitive immunoassays for the analysis of picoxystrobin in beer

This paper describes the original synthesis of a functionalized derivative of the fungicide picoxystrobin and the generation of the first reported monoclonal antibodies against this strobilurin pesticide. The synthetic hapten was prepared by total synthesis from commercial chemicals and incorporating the spacer arm through a carbon-carbon single bond. Also, to obtain the immunogen, an uncommon hapten activation strategy based on N,N'-disuccinimidyl carbonate was employed, affording high activation yields and clean and reproducible coupling results. With these immunoreagents, two enzyme-linked immunosorbent assays (ELISAs) were developed: a competitive one-step assay using the antibody-coated direct ELISA format and a competitive two-step assay with the conjugate-coated indirect ELISA procedure. Both immunoassays were characterized in terms of sensitivity, selectivity, tolerance to solvents and matrix effects, achieving limits of detection below 0.2 μgL(-1). The optimized assays were used for the determination of picoxystrobin residues in beer, with recovery values ranging between 90 and 121% for the direct assay and from 79 to 122% for the indirect assay.     

Supramolecular coordination chemistry of aromatic polyoxalamide ligands: A metallosupramolecular approach toward functional magnetic materials

The impressive potential of the metallosupramolecular approach in designing new functional magnetic materials constitutes a great scientific challenge for the chemical research community that requires an interdisciplinary collaboration. New fundamental concepts and future applications in nanoscience and nanotechnology will emerge from the study of magnetism as a supramolecular function in metallosupramolecular chemistry. Our recent work on the rich supramolecular coordination chemistry of a novel family of aromatic polyoxalamide (APOXA) ligands with first-row transition metal ions has allowed us to move one step further in the rational design of metallosupramolecular assemblies of increasing structural and magnetic complexity. Thus, we have taken advantage of the new developments of metallosupramolecular chemistry and, in particular, the molecular-programmed self-assembly methods that exploit the coordination preferences of paramagnetic metal ions and suitable designed polytopic ligands. The resulting self-assembled di- and trinuclear metallacyclic complexes with APOXA ligands, either metallacyclophanes or metallacryptands, are indeed ideal model systems for the study of the electron exchange mechanism between paramagnetic metal centers through extended π-conjugated aromatic bridges. So, the influence of different factors such as the topology and conformation of the bridging ligand or the electronic configuration and magnetic anisotropy of the metal ion have been investigated in a systematic way. These oligonuclear metallacyclic complexes can be important in the development of a new class of molecular magnetic devices, such as molecular magnetic wires (MMWs) and switches (MMSs), which are major goals in the field of molecular electronics and spintronics. On the other hand, because of their metal binding capacity through the outer carbonyl-oxygen atoms of the oxamato groups, they can further be used as ligands, referred to as metal–organic ligands (MOLs), toward either coordinatively unsaturated metal complexes or fully solvated metal ions. This well-known “complex-as-ligand” approach affords a wide variety of high-nuclearity metal–organic clusters (MOCs) and high-dimensionality metal–organic polymers (MOPs). The judicious choice of the oligonuclear MOL, ranging from mono- to di- and trinuclear species, has allowed us to control the overall structure and magnetic properties of the final oxamato-bridged multidimensional (nD, n = 0–3) MOCs and MOPs. The intercrossing between short- (nanoscopic) and long-range (macroscopic) magnetic behavior has been investigated in this unique family of oxamato-bridged metallosupramolecular magnetic materials expanding the examples of low-dimensional, single-molecule (SMMs) and single-chain (SCMs) magnets and high-dimensional, open-framework magnets (OFMs), which are brand-new targets in the field of molecular magnetism and materials science.     

Exploring the rotational isomerism in non-classical Wells-Dawson anions {W18X}: a combined theoretical and mass spectrometry study

We present a combined theoretical and mass spectrometry study of the rotational isomerism of the non-classical Wells-Dawson anions. The structure is larger than the Keggin anion and six geometric isomers are predicted (α, β, γ, α*, β*, γ*) on the basis of structural arguments. This work explores the geometrical differences between the isomers and evaluates the stability of these unusual clusters based upon the inclusion of the different heteroatoms. We connect the theoretical results with experimental studies by exploring the fragmentation of the parent clusters by electrospray-ionisation mass spectrometry (ESI-MS). Both approaches show a general stability trend that can be postulated as follows: γ* > β* > α* > α ? β > γ where the isomers γ*, β* and α are the only anions of this type known to have been synthesised.     

The exohedral Diels-Alder reactivity of the titanium carbide endohedral metallofullerene Ti2C2@D(3h)-C78: comparison with D(3h)-C78 and M3N@D(3h)-C78 (M=Sc and Y) reactivity

The chemical functionalization of endohedral (metallo)fullerenes has become a main focus of research in the last few years. It has been found that the reactivity of endohedral (metallo)fullerenes may be quite different from that of the empty fullerenes. Encapsulated species have an enormous influence on the thermodynamics, kinetics, and regiochemistry of the exohedral addition reactions undergone by these species. A detailed understanding of the changes in chemical reactivity due to incarceration of atoms or clusters of atoms is essential to assist the synthesis of new functionalized endohedral fullerenes with specific properties. Herein, we report the study of the Diels-Alder cycloaddition between 1,3-butadiene and all nonequivalent bonds of the Ti(2)C(2)@D(3h)-C(78) metallic carbide endohedral metallofullerene (EMF) at the BP86/TZP//BP86/DZP level of theory. The results obtained are compared with those found by some of us at the same level of theory for the D(3h)-C(78) free cage and the M(3)N@D(3h)-C(78) (M=Sc and Y) metallic nitride EMFs. It is found that the free cage is more reactive than the Ti(2)C(2)@D(3h)-C(78) EMF and this, in turn, has a higher reactivity than M(3)N@D(3h)-C(78). The results indicate that, for Ti(2)C(2)@D(3h)-C(78), the corannulene-type [5,6] bonds c and f, and the type B [6,6] bond 3 are those thermodynamically and kinetically preferred. In contrast, the D(3h)-C(78) free cage has a preference for addition to the [6,6] 1 and 6 bonds and the [5,6] b bond, whereas M(3)N@D(3h)-C(78) favors additions to the [6,6] 6 (M=Sc) and [5,6] d (M=Y) bonds. The reasons for the regioselectivity found in Ti(2)C(2)@D(3h)-C(78) are discussed.     

Chiral-symmetry selection in soft monolayers under vortical flow

Herein, we report and interpret a new chiral-selection phenomenon in the orientational ordering of soft-assembled domains that arise spontaneously in Langmuir monolayers of an azobenzene derivative at the air/water interface. The orientational chirality of isolated sub-millimeter domains was unambiguously assessed by optical microscopy. The selection process, quantified by using an enantiomeric excess parameter, was controlled by stirring the aqueous subphase. We have studied the dependence of this process on stirring rate and handedness, stirring time, temperature, and on the initial state of the monolayer. The influence of the concomitant cis/trans isomerization on the reported chiral-selection process is also discussed.     

New identification of proanthocyanidins in cinnamon (<Emphasis Type="Italic">Cinnamomum zeylanicum</Emphasis> L.) using MALDI-TOF/TOF mass spectrometry

The inner bark of Ceylon cinnamon (Cinnamomum zeylanicum L.) is commonly used as a spice and has also been widely employed in the treatment and prevention of disease. The positive health effects associated with the consumption of cinnamon could in part be due to its phenolic composition; proanthocyanidins (PA) are the major polyphenolic component in commercial cinnamon. We present a thorough study of the PA profile of cinnamon obtained using matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI-TOF/TOF) mass spectrometry. In addition to the advantages of MALDI-TOF as a sensitive technique for the analysis of high-molecular-weight compounds, the tandem arrangement allows the identification of the compounds through their fragmentation patterns from MS/MS experiments. This is the first time that this technique has been used to analyze polymeric PA. The results show that cinnamon PA are more complex than was previously thought. We show here for the first time that they contain (epi)gallocatechin and (epi)catechingallate units. As gallates (galloyl moieties) and the pyrogallol group in gallocatechins have been related to the biological activity of grape and tea polyphenols, the presence of these substructures may explain some of the properties of cinnamon extracts. MALDI-TOF/TOF reveals that cinnamon bark PA include combinations of (epi)catechin, (epi)catechingallate, (epi)gallocatechin, and (epi)afzelechin, which results in a highly heterogeneous mixture of procyanidins, prodelphinidins, and propelargonidins.