A Synthetic Method to Access Symmetric and Non-Symmetric 2-(<em>N</em>,<em>N</em><em>'</em>-disubstituted)guanidinebenzothiazoles

Symmetric and non-symmetric 2-(N-H, N-methyl, N-ethylenyl and N-aryl)guanidinebenzothiazoles were synthesized from the reaction of ammonia, methylamine, pyrrolidine and aniline with dimethyl benzo[d]thiazol-2-yl-carbono-dithioimidate (5) as intermediate. The products were characterized by ¹H-, ¹³C-NMR spectroscopy and three of them by X-ray diffraction analysis. HN-phenyl protons formed intramolecular hydrogen bonds that assist the stereochemistry of the second substituent, whereas the HN-alkyl protons were involved in intermolecular hydrogen bonding.     

High NIR-purity index single-walled carbon nanotubes for electrochemical sensing in microfluidic chips

Single-walled carbon nanotubes (SWCNTs) should constitute an important natural step towards the improvement of the analytical performance of microfluidic electrochemical sensing. SWCNTs inherently offer lower detection potentials, higher surfaces and better stability than the existing carbon electrodes. However, pristine SWCNTs contain some carbonaceous and metallic impurities that influence their electrochemical performance. Thus, an appropriate processing method is important for obtaining high purity SWCNTs for analytical applications. In this work, a set of 0.1 mg mL(-1) SWCNT dispersions with different degrees of purity and different dispersants (SDBS; pluronic F68 and DMF) was carefully characterized by near infrared (NIR) spectroscopy giving a Purity Index (NIR-PI) ranging from 0.039 to 0.310. The highest purity was obtained when air oxidized SWCNTs were dispersed in SDBS, followed by centrifugation. The SWCNT dispersions were utilized to modify microfluidic chip electrodes for the electrochemical sensing of dopamine and catechol. In comparison with non-SWCNT-based electrodes, the sample with the highest NIR-PI (0.310) exhibited the best analytical performance in terms of improved sensitivity (3-folds higher), very good signal-to-noise ratio, high resistance-to-fouling in terms of relative standard deviation (RSD 7%; n = 15), and enhanced resolution (2-folds higher). In addition, very well-defined concentration dependence was also obtained with excellent correlation coefficients (r ≥ 0.990). Likewise, a good analytical sensitivity, suitable detection limits (LODs) and a very good precision with independence of the concentration assayed (RSDs ≤ 5%) was achieved. These valuable features indicate the suitability of this material for quantitative analysis. NIR-PI and further TEM and XRD characterization demonstrated that the analytical response was driven and controlled by the high NIR-PI of the SWCNTs used. The significance of this work is the demonstration for the first time of the sensitivity-purity relationship in SWCNT microfluidic chips. A novel and valuable analytical tool for electrochemical sensing has been developed: SWCNTs with high purity and a rich surface chemistry with functional groups, both essential for analytical purposes. Also, this work helps to better understand the analytical potency of SWCNTs coupled to microfluidic chips and it opens new gates for using these unique dispersions in real-world applications.     

Density-functional theory (hyper)polarizabilities of push-pull pi-conjugated systems: treatment of exact exchange and role of correlation

The performance of the optimized effective potential procedure for exact exchange in calculating static electric-field response properties of push-pull pi-conjugated systems has been studied, with an emphasis on NO2-(CH=CH)n-NH2 chains. Good agreement with Hartree-Fock dipole moments and (hyper)polarizabilities is obtained; particularly noteworthy is the chain length dependence for beta/n. Thus, the problem that conventional density-functional theory functionals dramatically overestimate these properties is largely solved, although there remains a significant correlation contribution that cannot be accounted for with current correlation functionals.     

Inherent instabilities of some W5Si3-type binary phases with large electropositive metal atoms: Six examples in the Ba-Pb, Ca-Sn-Mg,Cu,Zn, and La-Ga-Al,Zn systems

A particular pathology of certain W₅Si₃-type A₅B₃ structures (I4/mcm) appears to arise because of unduly close approaches of the A1-type atoms on the cell faces at , 0, () that occur with the larger and more electropositive A and/or in the presence of smaller B atoms. A structure refinement of binary Ba_4.81Pb₃ indicates such a marginal stability in that the Ba atoms in the facial Ba_0.81 chains exhibit an extreme displacement ellipsoid along . Although Ca₅Sn₃ and La₅Ga₃ binaries are unknown in this structure type, five stable ternary derivatives of these have been synthesized via substitution reactions and characterized by single crystal X-ray diffraction means: Ca₄Sn_3.223(4)Mg_0.777, Ca₄Sn₃Cu_1.30(4), Ca_4.66(6)Sn₃Zn_0.704(4), La_4.81(1)Ga_1.38(2)Al_1.62, and La_4.762(5)Ga_1.5(1)Zn_1.5. Only the Ca-Sn-Zn phase exhibits lower symmetry, P4/mbm. The problematic A1 sites exhibit diverse changes in these, whereas the surrounding B2 tetrahedra are largely unaltered. The Ca-Sn results are, respectively: direct Mg/Sn substitution at the Ca1 site; mixed fractional distribution of the smaller Cu at two sites around the A1 position with an unresolved disorder; a pair of apparently independent modes, fractional Ca in the normal position and fractional Zn rectangles thereabout. The two La-Sn phases contain normal Ga,Al (Ga,Zn) tetrahedral chains with pairs of fractional disordered La atoms along , 0, z. Each can be rationalized in terms of a reasonable incommensurate structure. Electronic effects may also be operable.     

Electrochemical technologies for treating petroleum industry wastewater

This review focuses on recent developments in electrochemical technology (with special emphasis on electrocoagulation, electro-oxidation, and electro-Fenton) to treat petroleum industry effluents (offshore and hydraulic fracturing extraction, as well as refinery effluents). In addition, an overview is given of what these processes face to position themselves as consolidated technologies.     

Structure and dynamics of biological liquid crystals

A review of thermodynamic and flow liquid crystal models is presented and applied to a wide range of biological liquid crystals (BLCs), including helicoidal plywoods, biopolymer solutions and in vivo liquid crystals. The key characteristics of liquid crystals (self-assembly, packing, defects, functionalities, processability) are discussed in relation to biological materials and the strong correspondence between different synthetic and biological materials is discussed. Viscoelastic models for nematic and chiral nematics are reviewed and discussed in terms of key parameters that facilitate understanding and quantitative information from experimental measurements. The range and consistency of the predictions demonstrates that the use of mesoscopic liquid crystal models is an efficient tool to develop the science and biomimetic applications of mesogenic biological materials.     

Structural Diversity from the Transannular Cyclizations of Natural Germacrone and Epoxy Derivatives: A Theoretical–Experimental Study

Treatment of germacrone ( 1 ) with different electrophiles, and of its epoxy derivatives germacrone‐4,5‐epoxide ( 2 ), germacrone‐1,10‐epoxide ( 3 ) and isogermacrone‐4,5‐epoxide ( 4 ) with Brönsted/Lewis acids and Ti^III, gives rise to a great structural diversity. Thus, by using a maximum of two steps, the production of more than 40 compounds corresponding to 14 skeletons is described. Computational calculations rationalizing the structural divergence produced are also described. Finally, since some of the compounds generated are bioactive natural sesquiterpenes, the mechanisms of formation of these substances will provide new insights in their biosynthesis.     

Synthesis and Characterization of Metal Complexes of two Novel Pyridine‐Derived Macrocyclic Ligands Bearing o‐ and p‐Nitrobenzyl Pendant Groups

The pendant‐armed ligands L¹ and L² were synthesized by N‐alkylation of the two secondary aminic groups of the oxaazamacrocyclic precursor L with o‐nitrobenzylbromide (L¹) or p‐nitrobenzylbromide (L²). Metal complexes of L¹ and L² have been synthesized and characterized by microanalysis, MS‐FAB, conductivity measurements, IR, UV‐Vis, ¹H and ¹³C NMR spectroscopy and magnetic studies. Crystal structures of ligands L¹ and L², as well as complexes [CdL¹(NO₃)₂]·2CH₃CN and [Ag₂Br(L²)₂](ClO₄)·2CH₃CN have been determined by single crystal X‐ray crystallography.