Results 1 - 10 of 1645
Results 1 - 10 of 1645. Search took: 0.025 seconds
|Sort by: date | relevance|
[en] Reactivity of 1,3,2,5-dioxaboraphosphorinates towards borane is studied, stability of the complexes prepared is compared with stability of aminoalkylphosphine complexes with borane. The reaction products are studied by the methods of 31P NMR and IR-spectroscopy, data of the element analysis are given, melting points are determined. It is shown that 2,5-diphenyl-4,6-di-P-1,3,2,5-dioxaboraphosphorinates provide complexes with borane with the formation of P-B coordination bond
[en] The long-term stability of metal nanoparticle–molecule junctions in molecular electronic devices based on nanoelectrodes (NEL) is a major challenge in the effort to bring related molecular electronic devices to application. To optimize the reproducibility of molecular electronic nanodevices, the time-dependent modification of such junctions as exposed to different media needs to be known. Here, we have studied (1) the stability of Au-NEL and (2) the electrical stability of molecule–Au nanoparticle (AuNP) junctions themselves with the molecule being 1,8-octanedithiol (ODT). Both the NELs only and the junctions were exposed to air and liquids such as deionized water, tetrahydrofuran, toluene and tetramethylethylenediamine (TMEDA) over a period of 1 month. The nanogaps remained stable in width when stored in either deionized water or toluene, whereas the current through 1,8-octanedithiol–NP junctions remained most stable when stored in TMEDA as compared to other solvents. Although it is difficult to follow the chemical processes in such devices in the 10-nm range with analytical methods, the behavior can be interpreted from known interactions of solvent molecules with electrodes and ODT
[en] Polydiacetylene (PDAs) have received great attention as colorimetric sensors since these conjugated polymers undergo a blue-to-red color change upon various chemical/biochemical and physical stimuli. PDAs have been reported to display thermochromism (heat), solvatochromism (solvent), mechanochromism (mechanical strain) as well as magnetochromism (magnetic force) electrochromism (electric current), and affinochromism (ligand-receptor interaction). The solvent induced color change of PDA is generally non-specific and irreversible. For instance, the PDA derived from 10,12-pentacosadiynoic acid (PCDA) undergoes a blue-to-red (or purple) color change upon exposure to many common organic solvents including tetrahydrofuran (THF), chloroform, dichloromethane, acetone, methanol (MeOH), ethyl acetate (EA), and diethyl ether. The results obtained from Raman spectral analysis suggests that exposure to THF causes the distortion of the backbone of the polymer main chain and some conformational changes in the aliphatic side chain. Solvatochromism of a PDA is closely related to the solubility of a diacetylene monomer. PDA undergoes a color change when the dissolution of unpolymerized monomers causes some void in the PDA supramolecules. Since PCDA-mBzA has a good solubility only in THF, colorimetric transition of PDA occurs only in response to THF. Since solubility of a diacetylene monomer can be manipulated by structural change of the monomer, we believe the strategy described in current investigation should be useful for the development of solvent-specific PDA sensor systems
[en] Full text: In case of lanthanide (Ln) compounds the bis(trimethylsilyl)amido (btmsa) ligand is considered as a steric and electronic equivalent of the bis(trimethylsilyl)methanido (btmsm) group . Because of their extreme air and moisture sensitivity the chemistry of Ln(btmsm)3 is very poor, whereas that of comparatively stable Ln(btmsa)3 is much more developed. As we wish to extend the chemistry of Ln(btmsm)3 and plan to derive and to parameterize the crystal field (CF) splitting patterns of the target molecules, it is recommended to study in advance the electronic structures of the corresponding compounds derived from Ln(btmsa)3 . Beside (btmsa)3 Nd(m-Cl)Li(THF)3 a number of mono base adducts [(btmsa)3 Ln.B] with sterically less demanding bases such as OPPh3 , NCtBu or CNtBu have been described and were partly structurally characterized. Considering only the immediately coordinating atoms, the effective CF is of C3v symmetry. According to recent spectroscopic investigations, Nd(btmsa)3 dissolved in Tetrahydrofuran (THF)/MeTHF (ratio 1:3) adds quantitatively THF and forms a transparent hydrocarbon glass at low temperatures. On the basis of absorption measurements run at ambient and at low temperatures the CF splitting pattern of (btmsa)3Nd.THF was derived. Subsequently the parameters of an empirical Hamiltonian were fitted to the experimental CF splitting pattern to give an r.m.s. deviation of 26.5 cm -1 for 76 assignments. The parameters obtained are compared with those of base-free Nd(btmsa)3 and (btmsa)3 Nd(λ-Cl)Li(THF)3
[en] Aldol condensation of furfural with acetone and a series of aldehydes in the presence of PAF-SO3H acid catalyst based on mesoporous aromatic frameworks was studied. The reaction course depending on the process temperature, catalyst amount, and reactant ratio was studied for the furfural condensation with acetone as an example. The catalyst can be reused in several cycles without appreciable activity loss.
[en] Present chapter of book is devoted to study of de-solvation process of elements of borohydrides of II A group. The de-solvation process of initial substances Me(BH4)2· tetrahydrofurane, where Me is Mg, Ca, Sr was studied. The temperature interval of the end of de-solvation process of studied compounds was determined.