Direct oxidimetric determination of thiocarbonate sulphur with ferricyanide, using iron(II)-dimethylglyoxime or sodium nitroprusside as indicator

Direct determination of 15-50 mg of thiocarbonate sulphur can be achieved by a one-step titration with potassium ferricyanide, using iron(II)-dimethylglyoxime or sodium nitroprusside as indicator. Only one sulphur atom of the thiocarbonate ion undergoes oxidation to elemental sulphur, the other two separating as carbon disulphide.     

Microwave-assisted synthesis,characterization, and antimicrobial activity of some odorant Schiff bases derived from naturally occurring carbonyl compounds and anthranilic acid

Nine odorant Schiff bases, namely 2-(4-methoxybenzylideneamino) benzoic acid, 2-(benzylideneamino) benzoic acid, 2-(3-phenylallylidene amino) benzoic acid, 2-(3,7-dimethyloct-2,6-enylideneamino) benzoic acid, 2-(3,7-dimethyloct-6-enylideneamino) benzoic acid, 2-(4-isopropylbenzylideneamino)benzoic acid, 2-(3,4-dimethoxybenzylideneamino) benzoic acid, 2-(1-phenylethylideneamino) benzoic acid, and 2-[(4-(2,6,6-trimethylcyclohex-2-enyl)-but-2-enylideneamino)benzoic acid, were prepared by condensation of anthranilic acid with corresponding naturally occurring carbonyl compounds (anisaldehyde, benzaldehyde, cinnamaldehyde, citral, citronellal, cuminaldehyde, veratraldehyde, acetophenone, and α-ionone) employing conventional and microwave irradiation methods. These compounds were characterized with the aid of elemental and spectral (FT-IR, ¹H NMR, and ¹³C NMR) analysis. Microwave irradiation method was efficient in terms of reduced reaction time, solvent use, and increased yields of these compounds without affecting their olfactory characteristics. These Schiff bases also exhibited olfactory characteristics for various fragrance compositions and varied antimicrobial activity against Aspergillus niger, Penicillium chrysogenum, Staphylococcus aureus, and Escherichia coli.     

Pinchings and Norms of Scaled Triangular Matrices

Suppose U is an upper-triangular matrix, and D a nonsingular diagonal matrix whose diagonal entries appear in nondescending order of magnitude down the diagonal. It is proved that $$\|D^{-1}UD\|\ge\|U\|$$ for any matrix norm that is reduced by a pinching. In addition to known examples -weakly unitarily invariant norms - we show that any matrix norm defined by $$\| A \|^{\underline{\underline {{\rm def}}} } \mathop {\max }\limits_{x \ne 0,y \ne 0} {{{\mathop{\rm Re}\nolimits} (x^*Ay)} \over {\phi (x)\psi (y)}},$$ where θ (.) and y (.) are two absolute vector norms, has this property. This includes l p operator norms as a special case.     

Existence of dynamic tautomerism and divalent N(I) character in N‐(pyridin‐2‐yl)thiazol‐2‐amine

N‐(Pyridin‐2‐yl)thiazol‐2‐amine is a versatile chemical functional unit present in many therapeutically important species. Quantum chemical analysis shows that there are six competitive isomeric structures possible for this class of compounds within a relative energy difference of ～4 kcal/mol. Some of the isomeric structures possess divalent N(I) character. There appears to be a competition between the thiazole and pyridine groups to accommodate the tautomeric hydrogen, and consequently show electron donating property in the structure with R‐N←L representation. Details of electron distribution, tautomeric preferences, protonation energy, and divalent N(I) character, and so on, of this class of compounds are presented in this article. Subsequently, upon protonation, (L→N←L)^⊕ character is clearly evident in these moieties as molecular orbital analysis clearly shows two lone pairs of electrons on the central nitrogen, in this system. © 2013 Wiley Periodicals, Inc.     

Local heating of discrete droplets using magnetic porous silicon-based photonic crystals

This paper describes a method for local heating of discrete microliter-scale liquid droplets. The droplets are covered with magnetic porous Si microparticles, and heating is achieved by application of an external alternating electromagnetic field. The magnetic porous Si microparticles consist of two layers. The top layer contains a photonic code and it is hydrophobic, with surface-grafted dodecyl moieties. The bottom layer consists of a hydrophilic silicon oxide host layer that is infused with Fe3O4 nanoparticles. The amphiphilic microparticles spontaneously align at the interface of a water droplet immersed in mineral oil, allowing manipulation of the droplets by application of a magnetic field. Application of an oscillating magnetic field (338 kHz, 18 A rms current in a coil surrounding the experiment) generates heat in the superparamagnetic particles that can raise the temperature of the enclosed water droplet to >80 degrees C within 5 min. A simple microfluidics application is demonstrated: combining complementary DNA strands contained in separate droplets and then thermally inducing dehybridization of the conjugate. The complementary oligonucleotides were conjugated with the cyanine dye fluorophores Cy3 and Cy5 to quantify the melting/rebinding reaction by fluorescence resonance energy transfer (FRET). The magnetic porous Si microparticles were prepared as photonic crystals, containing spectral codes that allowed the identification of the droplets by reflectivity spectroscopy. The technique demonstrates the feasibility of tagging, manipulating, and heating small volumes of liquids without the use of conventional microfluidic channel and heating systems.