Preparation and characterization of persistent maltose-conjugated triphenylmethyl radicals

The condensation reaction of D-maltose to free radicals of the series of tris(2,4,6-trichlorophenyl)methyl (TTM) and tris(perchlorophenyl)methyl (PTM) has been described for the first time. The new persistent radicals 1 and 2 are very stable and have been characterized by EPR. Their cyclic voltammograms show a quasi-reversible process in the cathode, being reduced to the corresponding anions, with redox potentials a little lower than those of TTM and PTM, respectively. Their oxidant activity is in close relation with their reduction potentials. Therefore, while 2 is reduced by ascorbic acid, 1 remains unaltered.     

Highly stereoselective synthesis of tertiary propargylic centers and their isomerization to enantiomerically enriched allenes

Center of attention: A new approach for the synthesis of enantiomerically enriched allenes by isomerization of 2-p-tolylsulfinylphenyl propargylic derivatives is presented, which in turn are prepared by reaction of sulfinylated lithium benzylcarbanions with arylsulfonylacetylenes. The high control of stereoselectivity in both steps is exerted by the sulfinyl group.     

Arylsulfonylacetylenes as alkynylating reagents of Csp2-H bonds activated with lithium bases

Chameleon: a new strategy for the synthesis of a wide variety of alkynyl derivatives by the reaction of substituted arylsulfonylacetylenes with organolithium species is described. The high yields, the simplicity of the experimental procedure, the broad scope of this reaction, and the formation of C(sp)-C(sp2) bonds without using transition metals are the main features of this methodology.     

Synthesis and conformational studies of peptido-squaramide foldable modules: a new class of turn-mimetic compounds

The β-turn unit is one of the most important secondary structure elements in proteins. The access to new conformationally controlled foldable modules can afford compounds with interesting bioactivities. Here, we describe a new family of peptido-squaramide foldable modules based on the considerable potential of the squaramide unit as a hydrogen bond donor and acceptor as well as the low rotational barrier of the C-N bond. The conformational analysis by NMR of these modules in chloroform and acetonitrile solution shows that a disecondary squaramide with the 4-aminobutyric acid in one of its substituents can mimic the β-turn structure driven by the formation of an intramolecular hydrogen bonded ten-membered ring. This structure, although flexible, has been successfully combined with dipeptide chains to induce the formation of a hairpin-like structure driven by the formation of several cross-strand intramolecular hydrogen bonds.     

Molecularly imprinted SPE and MEKC with in-capillary sample preconcentration for the determination of digoxin in human urine

Molecularly imprinted solid-phase extraction (MISPE) combined with MEKC was used for clean-up, preconcentration and determination of digoxin in the presence of its aglycon digoxin (digoxigenin) in human urine samples. In addition, the use of an in-capillary sample concentration electrophoretic technique by sweeping was investigated to enhance the concentration sensitivity in MEKC. The highly selective, fast and effective sample pretreatment by MISPE along with the preconcentration by sweeping could overcome the low sensitivity of the highly efficient capillary electrophoresis separation with UV detection. The optimization of the variables affecting the separation as well as MISPE conditions procedure was carried out to select the best conditions of selectivity and sensitivity to determine digoxin at low concentration levels in urine. To demonstrate the suitability of the developed method several analytical characteristics (selectivity, linearity, accuracy, precision, and LOD) were evaluated. Satisfactory results were obtained in terms of linearity (r > 0.99), recovery (95.4-96.5% with RSD from 1.3% to 2.6%), precision (RSD from 0.3% to 1.7% for migration times and from 2.1% to 7.3% for corrected peak areas), and sensitivity (LODs of 6 μg/L with 5 mL of sample or 1.2 μg/L with 25 mL). The proposed MISPE-MEKC method was satisfactorily applied to the analysis of spiked human urine samples achieving a concentration factor up to 7500-fold.     

Integration of gold nanoparticles in optical resonators

The optical absorption of one-dimensional photonic crystal based resonators containing different types of gold nanoparticles is controllably modified by means of the interplay between planar optical cavity modes and localized surface plasmons. Spin-casting of metal oxide nanoparticle suspensions was used to build multilayered photonic structures that host (silica-coated) gold nanorods and spheres. Strong reinforcement and depletion of the absorptance was observed at designed wavelength ranges, thus proving that our method provides a reliable means to modify the optical absorption originated at plasmonic resonances of particles of arbitrary shape and within a wide range of sizes. These observations are discussed on the basis of calculations of the spatial and spectral dependence of the optical field intensity within the multilayers.     

Axial and equatorial ligand effects on biomimetic cysteine dioxygenase model complexes

Density functional theory (DFT) calculations are presented on biomimetic model complexes of cysteine dioxygenase and focus on the effect of axial and equatorial ligand placement. Recent studies by one of us [Y. M. Badiei, M. A. Siegler and D. P. Goldberg, J. Am. Chem. Soc. 2011, 133, 1274] gave evidence of a nonheme iron biomimetic model of cysteine dioxygenase using an i-propyl-bis(imino)pyridine, equatorial tridentate ligand. Addition of thiophenol, an anion - either chloride or triflate - and molecular oxygen, led to several possible stereoisomers of this cysteine dioxygenase biomimetic complex. Moreover, large differences in reactivity using chloride as compared to triflate as the binding anion were observed. Here we present a series of DFT calculations on the origin of these reactivity differences and show that it is caused by the preference of coordination site of anion versus thiophenol binding to the chemical system. Thus, stereochemical interactions of triflate and the bulky iso-propyl substituents of the ligand prevent binding of thiophenol in the trans position using triflate. By contrast, smaller anions, such as chloride, can bind in either cis or trans ligand positions and give isomers with similar stability. Our calculations help to explain the observance of thiophenol dioxygenation by this biomimetic system and gives details of the reactivity differences of ligated chloride versus triflate.     

Mineral content and botanical origin of Spanish honeys

Eleven elements (Zn, P, B, Mn, Mg, Cu, Ca, Ba, Sr, Na and K) were determined by inductively plasma coupled spectrometry in 40 honey samples from different places of Spain and four different botanical origins: Eucalyptus (Eucalyptus sp.), Heather (Erica sp.), Orange-blossom (Citrus sinensis) and Rosemary (Rosmarinus officinalis). K, Ca and P show the higher levels with average concentrations ranged between 434.1-1935 mg kg⁻¹ for K; 42.59-341.0 mg kg⁻¹ for Ca and 51.17-154.3 mg kg⁻¹ for P. Levels of Cu (0.531-2.117 mg kg⁻¹), Ba (0.106-1.264 mg kg⁻¹) and Sr (0.257-1.462 mg kg⁻¹) are the lowest in all honey samples. Zn (1.332-7.825 mg kg⁻¹), Mn (0.133-9.471 mg kg⁻¹), Mg (13.26-74.38 mg kg⁻¹) and Na (11.69-218.5 mg kg⁻¹) concentrations were found strongly dependent on the kind of botanical origin.Results were submitted to pattern recognition procedures, unsupervised methods such as cluster and principal components analysis and supervised learning methods like linear discriminant analysis in order to evaluate the existence of data patterns and the possibility of differentiation of Spanish honeys from different botanical origins according to their mineral content. Cluster analysis shows four clusters corresponding to the four botanical origins of honey and PCA explained 71% of the variance with the first two PC variables. The best-grouped honeys were those from heather; eucalyptus honeys formed a more dispersed group and finally orange-blossom and rosemary honeys formed a less distinguishable group.