Synthesis of 13c-labelled [s]-proline and its conformational analysis by nuclear magnetic resonance

In order to analyze completely the ring conformation of [S]-Proline (l-thiazolidine-4-carboxylic acid) this compound has been synthesized with its C_δ atom enriched at 90% in ¹³C. The ¹H-¹H, ¹³C-¹H, ¹³C-¹³C vicinal coupling constants measured at several pH values describe well the geometry of the thiazolidine ring. The results suggest that the ring has an average planar conformation only in a narrow range of pH close to the pK of the amine group. Above and below this pH the ring tends to adopt preferentially the S_γendo and S_γexo puckered conformations respectively. It is concluded that a good correlation exists between the value of the dihedral angle ø and the character S_γendo or S_γexo of the ring.     

Nuclearity controlled cyanide-bridged bimetallic CrIII-MnII compounds: synthesis, crystal structures, magnetic properties and theoretical calculations

The preparation, X-ray crystallography and magnetic investigation of the compounds PPh4[Cr(bipy)(CN)4].2 CH3CN.H2O (1) (mononuclear), [[Cr(bipy)(CN)4]2Mn-(H2O)4].4H2O (2) (trinuclear), [[Cr(bipy)(CN)4]2Mn(H2O)2] (3) (chain) and [[Cr(bipy)(CN)4]2Mn(H2O)].H2O.CH3CN (4) (double chain) [bipy=2,2'-bipyridine; PPh4 (+)=tetraphenylphosphonium] are described herein. The [Cr(bipy)(CN)4]- unit act either as a monodentate (2) or bis-monodentate (3) ligand toward the manganese atom through one (2) or two (3) of its four cyanide groups. The manganese atom is six-coordinate with two (2) or four (3) cyanide nitrogens and four (2) or two (3) water molecules building a distorted octahedral environment. In 4, two chains of 3 are pillared through interchain Mn-N-C-Cr links which replace one of the two trans-coordinated water molecules at the manganese atom to afford a double chain structure where bis- and tris-monodenate coordination modes of [Cr(bipy)(CN)4]- coexist. The magnetic properties of 1-4 were investigated in the temperature range 1.9-300 K. A Curie law behaviour for a magnetically isolated spin quartet is observed for 1. A significant antiferromagnetic interaction between CrIII and MnII through the single cyanide bridge [J=-6.2 cm(-1), the Hamiltonian being defined as H=-J(SCr1.SMn+SCr2.SMn] occurs in 2 leading to a low-lying spin doublet which is fully populated at T <5 K. A metamagnetic behaviour is observed for 3 and 4 [the values of the critical field Hc being ca. 3000 (3) and 1500 Oe (4)] which is associated to the occurrence of weak interchain antiferromagnetic interactions between ferrimagnetic Cr2III MnII chains. The analysis of the exchange pathways in 2-4 through DFT type calculations together with the magnetic bevaviour simulation using the quantum Monte Carlo methodology provided a good understanding of their magnetic properties.     

mer-[Fe III(bpca)(CN)3]-: a new low-spin iron(III) complex to build heterometallic ladder-like chains

The novel mononuclear complex PPh(4)-mer-[Fe(III)(bpca)(3)(CN)(3)].H(2)O (1) [PPh(4)(+) = tetraphenylphosphonium cation and bpca = bis(2-pyridylcarbonyl)amidate anion] and ladder-like chain compound [[Fe(III)(bpca)(micro-CN)(3)Mn(II)(H(2)O)(3)] [Fe(III)(bpca)(CN)(3)]].3H(2)O (2) have been prepared and characterized by X-ray diffraction analysis. Compound 1 is a low-spin iron(III) compound with three cyanide ligands in mer arrangement and a tridentate N-donor ligand building a distorted octahedral environment around the iron atom. Compound 2 is an ionic salt made up of cationic ladder-like chains [[Fe(III)(bpca)(micro-CN)(3)Mn(II)(H(2)O)(3)]](+) and uncoordinated anions [Fe(III)(bpca)(3)(CN)(3)](-). The magnetic properties of 2 correspond to those of a ferrimagnetic chain with significant intrachain antiferromagnetic coupling between the low-spin iron(III) centers and the high-spin manganese(II) cations. This compound exhibits ferrimagnetic ordering below 2.0 K.     

Interactions in Aqueous Mixtures of Alkylammonium Chlorides and Sodium Cholate

The interactions of alkylammonium chlorides (the number of carbon atom per chain was either 12, 14, or 16) with sodium cholate have been investigated by a combination of techniques including light and electron microscopy, surface tension, conductivity, light scattering, and microelectrophoretic measurements. The phase behavior has strongly depended on the molar ratio and actual concentration of oppositely charged surfactants. The change in the composition of the aggregates leads to a shape transformation from globular to elongated micelles to open and/or closed bilayers (vesicles) and precipitation. The length of micelles has been found to decrease dramatically with the concentration shift to the micellar regions of either surfactant. Upon a moderate excess of one surfactant, the mean hydrodynamic diameter of aggregates increases and wormlike micelles and/or open and closed bilayers are formed. Microscopic observations of alkylammonium cholates (novel catanionic surfactants precipitated in and/or close to equimolar region) have shown the presence of a variety of morphologies including twisted ribbons, tubules and bundles of tubules.     

Michael addition of thiols to alpha-enones in ionic liquids with and without organocatalysts

Seventeen organocatalyts were tested for their ability to catalyst the addition of thiophenols to chalcones in [bmim]PF6. The products were isolated in high yield after a short reaction time, but no stereoselectivity was observed. The reactions also proceeded (without any stereoselectivity) in four other ionic liquids. In contrast, 16% and 26% ee were observed when L-proline and cinchonine, respectively, were used as the catalysts in CH2Cl2. Addition of thiophenols is also catalysed by HCl, as well as D-mandelic and L-tartaric acids. Addition of thiophenols to chalcones also occurred in neat ionic liquids, without any additional catalyst, but the rate of the reaction depended considerably on the structure of ionic liquid. The scope of the non-catalysed reaction in ionic liquids was tested by the reactions of 5 different thiols and 3 different alpha-enones.     

Protein alignment: Exact versus approximate. An illustration

We illustrate solving the protein alignment problem exactly using the algorithm VESPA (very efficient search for protein alignment). We have compared our result with the approximate solution obtained with BLAST (basic local alignment search tool) software, which is currently the most widely used for searching for protein alignment. We have selected human and mouse proteins having around 170 amino acids for comparison. The exact solution has found 78 pairs of amino acids, to which one should add 17 individual amino acid alignments giving a total of 95 aligned amino acids. BLAST has identified 64 aligned amino acids which involve pairs of more than two adjacent amino acids. However, the difference between the two outputs is not as large as it may appear, because a number of amino acids that are adjacent have been reported by BLAST as single amino acids. So if one counts all amino acids, whether isolated (single) or in a group of two and more amino acids, then the count for BLAST is 89 and for VESPA is 95, a difference of only six. © 2015 Wiley Periodicals, Inc.     

Unexpected Synthesis of a 5H‐chromeno[3,4‐c]pyridine Derivative from 4‐Chlorocoumarin‐3‐carbaldehyde and Malononitrile

In the reaction of 4‐chlorocoumarin‐3‐carbaldehyde with malononitrile in the presence of piperidine, a piperidinium salt of a novel tricyclic chromeno[3,4‐c]pyridine derivative was isolated instead of the expected “tert‐amino effect” product. When hexamethyleneimine (azepane) was used as a base, the corresponding azepanium salt (same anion) was obtained. Both structures have been formulated on the basis of their spectral (IR, NMR, MS) behavior and elemental analyses. In addition, the structure of the piperidinium salt was confirmed by means of X‐ray crystallographic analysis.     

Pushing the surface-enhanced Raman scattering analyses sensitivity by magnetic concentration: A simple non core–shell approach

A simple and accessible method for molecular analyses down to the picomolar range was realized using self-assembled hybrid superparamagnetic nanostructured materials, instead of complicated SERS substrates such as core–shell, surface nanostructured, or matrix embedded gold nanoparticles. Good signal-to-noise ratio has been achieved in a reproducible way even at concentrations down to 5 × 10⁻¹¹ M using methylene blue (MB) and phenanthroline (phen) as model species, exploiting the plasmonic properties of conventional citrate protected gold nanoparticles and alkylamine functionalized magnetite nanoparticles. The hot spots were generated by salt induced aggregation of gold nanoparticles (AuNP) in the presence of those analytes. Then, the aggregates of AuNP/analyte were decorated with small magnetite nanoparticles by electrostatic self-assembly forming MagSERS hybrid nanostructured materials. SERS peaks were enhanced up to 100 times after magnetic concentration in a circular spot using a magnet in comparison with the respective dispersion of the nanostructured material.