Bischelated complexes of a dithiocarbazate <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">S</Emphasis> Schiff base ligand: synthesis,characterization and antimicrobial activities

The N,S bidentate proligand S-hexyl-β-N-(4-methoxybenzylidene)dithiocarbazate (HL), obtained by condensation of S-hexyldithiocarbazate with 4-methoxybenzaldehyde, has been used to synthesize six metal complexes, namely NiL₂, CuL₂, ZnL₂, CdL₂, PdL₂ and PbL₂, which have been characterized by physicochemical techniques and spectroscopic methods. Single crystal structural analyses for NiL₂, CuL₂ and PdL₂ show that these are square-planar complexes with each metal bischelated by the Schiff base in its deprotonated monoanionic form. In all three cases, the ligands show a trans configuration, although they crystallize in different space groups. All the metal complexes with the exception of the nickel derivative show a significant decrease in fluorescence intensity with respect to the free proligand HL. Free HL and all six complexes were tested for antibacterial activity against three pathogenic gram-negative organisms. The metal complexes show moderate although diverse activities; however, free HL as well as the copper(II) complex did not reveal any antibacterial activity against the tested organisms.     

N‐Boc‐Indolylbenzothiadiazole Derivatives: Efficient Full‐Color Solid‐State Fluorescence and Self‐Recovering Mechanochromic Luminescence

Herein, the solid‐state emission with good fluorescence quantum yields of N‐Boc‐indolylbenzothiadiazoles as a new class of fluorophores is described. Their solid‐state emission covers the wide range of the visible spectrum and the emission color can be tuned easily by changing the substituents on the two heteroaromatic rings. Among these, 3‐methylindolyl derivatives exhibit moreover autonomously self‐recovering mechanochromic luminescence, whereby the original solid‐state emission could be recovered spontaneously at room temperature after exposure to a mechanical stimulus. The emission color, as well as the recovery time for the color change could be tuned via the introduction of different substituents on the benzothiadiazole ring. We propose that the mechanism of the autonomously self‐recovering mechanochromic luminescence of 3‐methylindolylbenzothiadiazoles is based on a partial amorphization of the crystals upon exposure to the mechanical stimulus, followed by autonomous recovering in the form of recrystallization.     

Chromatographic behavior of small organic compounds in low‐temperature high‐performance liquid chromatography using liquid carbon dioxide as the mobile phase

Low‐temperature high‐performance liquid chromatography, in which a loop injector, column, and detection cell were refrigerated at –35ºC, using liquid carbon dioxide as the mobile phase was developed. Small organic compounds (polyaromatic hydrocarbons, alkylbenzenes, and quinones) were separated by low‐temperature high‐performance liquid chromatography at temperatures from –35 to –5ºC. The combination of liquid carbon dioxide mobile phase with an octadecyl‐silica (C₁₈) column provided reversed phase mode separation, and a bare silica‐gel column resulted in normal phase mode separation. In both the cases, nonlinear behavior at approximately –15ºC was found in the relationship between the temperature and the retention factors of the analytes (van't Hoff plots). In contrast to general trends in high‐performance liquid chromatography, the decrease in temperature enhanced the separation efficiency of both the columns.     

Reaction of a diaryldigermyne with ethylene

Reaction of the stable digermyne BbtGeGeBbt (Bbt = 2,6-[CH(SiMe₃)₂]₂-4-[C(SiMe₃)₃]-C₆H₂) with ethylene initially afforded the corresponding 1,2-digermacyclobutene. Depending on the reaction conditions applied, further reaction of this 1,2-digermacyclobutene with ethylene furnished two different reaction products: a 1,4-digermabicyclo[2.2.0]hexane or a bis(germiranyl)ethane. Combined experimental and theoretical results suggested that the 1,4-digermabicyclo[2.2.0]hexane and the bis(germiranyl)ethane are the thermodynamic and kinetic reaction products, respectively. A reaction mechanism in agreement with these results was proposed.     

Boron‐ and Phosphorus‐Hyperdoped Silicon Nanocrystals

Hyperdoping silicon nanocrystals (Si NCs) to a concentration exceeding the solubility limit of a dopant may enable their novel applications. Here, the successful hyperdoping of Si NCs with boron (B) and phosphorus (P) is demonstrated, which are the most important dopants for Si. Despite the hyperdoping, the diamond structure of Si NCs is hardly modified. There are both electrically active B and P in hyperdoped Si NCs. It is proposed that the hyperdoping is made possible mainly by the kinetics in the nonthermal plasma synthesis of Si NCs. Collision between Si NCs and B or P atoms and the binding energy of B or P at the NC surface are critical to the understanding on the differences in the doping efficiency and dopant distribution between B and P. B‐hyperdoping‐induced tensile stress needs to be taken into account in the investigation on the doping and oxidation of Si NCs.     

Design of an anaerobic sample chamber for fluorescence measurements compatible with the Lytle detector

A sample chamber has been developed that is compatible with the commercially available Lytle ion chamber with soller slits. The key features are (i) the sample position can be shifted vertically without changing the geometry with respect to the soller slits and ion chamber, (ii) the gas‐tight structure makes it possible for experiments to work with samples that require anaerobic conditions.     

Alternating copolymer based on sulfonamide‐substituted phenylmaleimide and vinyl monomers as polymer electrolyte membrane

The alternating copolymerization of phenylmaleimide (PMI) with a pendant sulfonamide acid group (sa‐PMI) and n‐butyl vinyl ether (BVE) as the aliphatic vinyl monomer afforded proton‐conducting polymer electrolytes—sa‐PMI‐BVEs—and their properties were compared with those of sa‐PMI‐STs that were synthesized from sa‐PMI and styrene. The ion exchange capacities (IECs) can be easily controlled by partly replacing sa‐PMI with unsubstituted PMI. sa‐PMI‐BVE is more flexible than sa‐PMI‐ST, and therefore, forms thin membranes even at high IECs, while sa‐PMI‐ST membranes are rigid and brittle. However, sa‐PMI‐BVE exhibits rather low thermal and oxidative stability. To realize polymer electrolyte membranes with reliable mechanical strength and a high IEC, gel‐filled membranes were prepared by polymerization in the presence of a small amount of a crosslinker, divinylbenzene, in porous polytetrafluoroethylene membranes. By using the gel‐filled membrane, H₂/O₂ fuel cells could be operated at 80 °C with reasonable performance. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013