Surprising secondary photochemical reactions observed on conventional photolysis of diazotetrahydrofuranones

The formation of C-H insertion products of the terminal N-atom of a diazo group into the α-СН-bond of tetrahydrofuran during direct photolysis of regioisomeric 2,2-dimethyl-5,5-diphenyl and 5,5-dimethyl-2,2-diphenyl-substituted 3-diazotetrahydrofuran-4-ones in THF is dictated by photochemical cycloelimination of the originally formed (1,1-dimethyl-2-oxa-3,3-diphenyl-propano)ketene and oxetanecarboxylic acid derivatives to yield benzophenone. The latter, under subsequent UV irradiation of the reaction mixture, initiates sensitized photolysis of the starting diazoketones resulting in the appearance of the insertion products with the solvent.     

Vortex lattice matching effects in a washboard pinning potential induced by Co nanostripe arrays

An advanced mask-less nanofabrication technique, focused electron beam-induced deposition (FEBID), has been employed on epitaxial Nb thin films to prepare ferromagnetic decorations in the form of an array of Co stripes. These substantially modify the non-patterned films’ superconducting properties, providing a washboard-like pinning potential landscape for the vortex motion. At small magnetic fields B ? 0.1 T, vortex lattice matching effects have been investigated by magneto-transport measurements. Step-like drops in the field dependencies of the films resistivity ρ(B) have been observed in particular for the vortex motion perpendicular to the Co stripes. The field values, corresponding to the middle points of these drops in ρ(B), meet the vortex lattice parameter matching the pinning structure’s period. These disagree with the results of Jaque et al. (2002) [11], who observed matching effects corresponding to the stripe width in Nb films grown on periodically distributed submicrometric lines of Ni.     

Formation and Deposition of Langmuir-Blodgett Films with Thiol-Stabilized CdTe Nanoparticles

Incorporation of the thiol-stabilized CdTe nanoparticles into mono- and multilayer films produced by Langmuir-Blodgett (LB) technique was investigated using “pressure-area” isotherms, Quartz Crystal Microbalance, FTIR, UV/Vis absorption and photoluminescence spectroscopy. LB films were formed from cationic (octadecyltrinonylammonium iodide—ODTNA) and anionic (behenic acid) surfactants. Both noticeable increase of limiting surface area of behenic acid monolayer and simultaneous decrease of film strength have been established when the aqueous solution of CdTe nanoparticles was used as a subphase. LB films deposition on solid substrates depends on the type of stabilizing ligands (1-thioglycerol or 2-mercaptoethanol) for CdTe nanoparticles. Optical absorption and photoluminescence properties of the films obtained from behenic acid monolayers that has thioglycerol-stabilized CdTe nanoparticles incorporated into them acquire the same properties as the size-quantized CdTe nanoparticles. The bonding of the cadmium ions, that released as a result of a partial dissociation of ligand-stabilized CdTe nanoparticles with carboxylic group, is considered to be responsible for the incorporation in case of behenic acid surfactant, and in case of ODTNA the incorporation proceeds by means of a weak “nanoparticle-LB matrix” interaction.     

Conformational energetics of interpolyelectrolyte complexation between ι-carrageenan and poly(methylaminophosphazene) measured by high-sensitivity differential scanning calorimetry

The interaction of poly(methylaminophosphazene) hydrochloride (PMAP·HCl) of varying degrees of ionization (f) with the potassium salt of ι-carrageenan was studied by high-sensitivity differential scanning calorimetry at a KCl concentration of 0.15 M, which is included for the purpose of stabilizing the helix conformation of the polysaccharide up to 55 °C. The conditions of strong (pH 3.8, I = 0.15), moderate (pH 7.4, I = 0.15), and weak (pH 7.4, I = 0.25) electrostatic interactions of the polyelectrolytes were considered. The thermodynamic parameters of the helix-coil transition of ι-carrageenan were determined as a function of the polycation/polyanion ratio. We show that the interpolyelectrolyte reaction between PMAP·HCl and ι-carrageenan results in a complete unfolding of the polysaccharide helix under conditions of strong electrostatic interaction and increases its stability under conditions of medium and weak electrostatic interactions. The formation of stoichiometric PMAP-carrageenan interpolyelectrolyte complexes proceeded via a cooperative mechanism at pH 3.8 (f = 0.5) and pH 7.4 (f = 0.2) at an ionic strength of 0.15. In contrast, the complexation at pH 7.4 and an ionic strength of 0.25 could be considered to be a consecutive competitive binding of charged units of poly(methylaminophosphazene) to the oppositely charged polysaccharide matrix in the helix or coil conformation. Binding constants of the polycation to the helix and coil forms of ι-carrageenan were estimated. They revealed a preferential binding of the polycation to the helix form of the polysaccharide.     

On-line fractionation and characterization of aquatic humic substances by means of sequential-stage ultrafiltration

A five-stage tangential-flow ultrafiltration (UF) device equipped with advanced membrane filters (molecular weight cut-off: 1, 5, 10, 50 and 100 kDalton) of the polyethersulfone type is described and applied for the analytical on-line fractionation of a series of aquatic humic substances (HS) originating from surface or groundwaters. Fractionation patterns of HS (6 fractions each) evaluated by this UF device exhibit their particular dependence on the HS concentration, the pH-value and the salt content of the sample (10 ml) to be analyzed. Fundamental parameters (e.g., washing volume) governing the molecular-size fractionation of HS by means of multistage UF are discussed, too. The fractionation of an aquatic reference HS (BOC 3/9.5) by means of the above UF procedure reveals considerable differences preferably characterized by the UV-VIS absorption ratio E₃₅₀/E₄₅₀ and metal complexing capacity (Cu(II)) of the produced fractions. Moreover, molecular spectroscopy investigations (FTIR, ¹H-NMR) of the fraction series of this HS indicate that carbohydrate substructures (preferably found in fractions >50 k Dalton) and aromatic ones (preferably in fractions <5 k Dalton) are unevenly distributed.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Observation and simulation of PbS nonocrystal formation at the initial steps

Ultrafine lead sulfide clusters are produced by the reaction of long-chain thiols with lead ions in non-aqueous medium, and according to X-ray diffraction (XRD) data reveal the different steps of he bulk-like rocksalt lattice growth. XRD pattern is simulated by the Debye formula for four model clusters (27, 75, 125, 729 atoms) and the correspondence of model and experimental clusters is shown that allows to estimate their size. Ab initio MOLCAO calculations result in energetical parameters and charge distribution for the clusters with 27 atoms. The value of energy gap indicates the true tendency of variation for the clusters of different size but left yet higher than maxima in the optical absorption at the fixed steps.     

Synthesis of 4-fluoroalkyl-substituted pyridazines from fluorinated diazodiketones

Two approaches are reported for the preparation of 3,4,6-trisubstituted pyridazines from fluoroalkyl-containing diazodiketones: the sequence of Wittig/Staudinger/diaza-Wittig and Staudinger/Wittig/diaza-Wittig reactions. The implementation of the Wittig reaction at the first stage gives rise to considerably higher yields of the targeted pyridazines than through initial phosphazines. In both approaches the final stages of the synthesis (the formation of vinylphosphazines and the subsequent diaza-Wittig reaction) occur as a tandem process. R^F-activated carbonyls are much more reactive in Wittig olefination of diazodicarbonyl and 1,3-dioxophosphazine molecules, than non-fluorinated acyl and aroyl carbonyl groups (R^FCO ? COAlk, COAr), and as a result non-fluorinated diazodiketones and their phosphazines do not produce pyridazines under the same conditions.