Spectroscopic Evidence for Ligand Substitution Reactions at the Solid–Liquid Interface of a Sub‐micrometer Gold(I) Carbene Complex

Colloidal coordination compounds in the sub‐micrometer range were synthesized from a chloro gold(I) carbene complex via the anti‐solvent procedure and stabilized by a surfactant shell of Tween 20. This compound was successfully applied as model system to monitor heterogeneous multiphase ligand substitution reactions at the solid–liquid interface.     

Experimental and numerical investigation of flow separation in a supersonic nozzle

The flow in a two-dimensional symmetric convergent-divergent supersonic nozzle with and without a deflector at the exit plane was tested experimentally and numerically. Combined optoelectronic devices were used to demonstrate the possibilities of the shadow and schlieren methods and holographic interferometry for the flow visualization especially in the separation region. A series of experiments was performed in a trisonic wind tunnel (VTI, Beograd). The experimental results obtained using optical methods are compared with the pressure measurements and numerical calculations. Numerical results were obtained using a code for solving the average Navier-Stokes equations. Five structured meshes with different resolutions and two turbulent models were employed. The coupled influence of the mesh resolution and the order of accuracy of the used numerical scheme is analyzed.     

Synthesis of Some Novel Fused 7-Oxanorbornenes

Synthesis of fused 7-oxanorbomenes 1 - 4 from readily available furandimethyl acetylenedicarboxylate bis-Diels-Alder adducts is described.     

Ultrasound‐Assisted Synthesis of 3‐(Arylamino)‐1‐ferrocenylpropan‐1‐ones

A successful aza‐Michael addition of arylamines to a conjugated enone, acryloylferrocene, has been achieved by ultrasonic irradiation of the mixture of these reactants and the catalyst, i.e., montmorillonite K‐10. This solvent‐free reaction, yielding ferrocene containing Mannich bases, 3‐(arylamino)‐1‐ferrocenylpropan‐1‐ones, considered as valuable precursors in organic synthesis, has been performed by using a simple ultrasonic cleaner. Among 17 synthesized β‐amino ketones, three were new ones, and these were fully characterized by spectroscopic means. X‐Ray crystallographic analysis of three of these crystalline products enabled the insight into the conformational details of these compounds. All compounds were evaluated for their antibacterial activities against six Gram‐positive and five Gram‐negative strains in a microdilution assay. The observed promising antibacterial activity (with a MIC value of 25 μg/ml (ca. 0.07 μmol/ml) as the best result for almost all tested compounds against Micrococcus flavus) seems not only to be compound but also bacterial species‐specific.     

Click Mechanochemistry: Quantitative Synthesis of “Ready to Use” Chiral Organocatalysts by Efficient Two‐Fold Thiourea Coupling to Vicinal Diamines

Mechanochemical methods of neat grinding and liquid‐assisted grinding have been applied to the synthesis of mono‐ and bis(thiourea)s by using the click coupling of aromatic and aliphatic diamines with aromatic isothiocyanates. The ability to modify the reaction conditions allowed the optimization of each reaction, leading to the quantitative formation of chiral bis(thiourea)s with known uses as organocatalysts or anion sensors. Quantitative reaction yields, combined with the fact that mechanochemical reaction conditions avoid the use of bulk solvents, enabled solution‐based purification methods (such as chromatography or recrystallization) to be completely avoided. Importantly, by using selected model reactions, we also show that the described mechanochemical reaction procedures can be readily scaled up to at least the one‐gram scale. In that way, mechanochemical synthesis provides a facile method to fully transform valuable enantiomerically pure reagents into useful products that can immediately be applied in their designed purpose. This was demonstrated by using some of the mechanochemically prepared reagents as organocatalysts in a model Morita–Baylis–Hillman reaction and as cyanide ion sensors in organic solvents. The use of electronically and sterically hindered ortho‐phenylenediamine revealed that mechanochemical reaction conditions can be readily optimized to form either the 1:1 or the 1:2 click‐coupling product, demonstrating that reaction stoichiometry can be more efficiently controlled under these conditions than in solution‐based syntheses. In this way, it was shown that excellent stoichiometric control by mechanochemistry, previously established for mechanochemical syntheses of cocrystals and coordination polymers, can also be achieved in the context of covalent‐bond formation.     

Photoluminescence of anatase and rutile TiO2 particles

Nonaqueous reactions between titanium(IV) chloride and alcohols (benzyl alcohol or n-butanol) were used for the synthesis of anatase TiO2 particles, while rutile TiO2 particles were synthesized in aqueous media by acidic hydrolysis of titanium(IV) chloride. The X-ray diffraction measurements proved the exclusive presence of either the anatase or the rutile phase in prepared samples. The photoluminescence of both kinds of particles (anatase and rutile) with several well-resolved peaks extending in the visible spectral region was observed, and the quantum yield at room temperature was found to be 0.25%. Photon energy up-conversion from colloidal anatase and rutile TiO2 particles was observed at low excitation intensities. The energy of up-converted photoluminescence spans the range of emission of normal photoluminescence. The explanation of photon energy up-conversion involves mid-gap energy levels originating from oxygen vacancies.     

On the Laplacian energy of a graph

In this paper we consider the energy of a simple graph with respect to its Laplacian eigenvalues, and prove some basic properties of this energy. In particular, we find the minimal value of this energy in the class of all connected graphs on n vertices (n = 1, 2, ...). Besides, we consider the class of all connected graphs whose Laplacian energy is uniformly bounded by a constant α ⩾ 4, and completely describe this class in the case α = 40.     

Evaluation of the Fourier transform of e^{ - ux^2 } for imaginary u

It is shown that the Fourier integral of the function exp(−ux ²) exists not only for u satisfying Re u > 0 but also for u that satisfies Re u ≥ 0. The proof is given by evaluating this integral for imaginary u.