Synthesis and Properties of a Decacyclene Monoimide and a Naphthalimide Derivative as Three‐Dimensional Acceptor–Donor–Acceptor Systems

A method involving the Diels–Alder (DA) cycloaddition of diacenaphtheno[1,2‐b;1′,2′‐d]thiophenes (DATs) with N‐alkylacenaphthylene‐5,6‐dicarboximides (AIs) was developed to synthesize decacyclene monoimides (DCMIs). The reactions generate the corresponding 1:2 adducts (BAIAs) as major products together with 1:1 adducts (the DCMIs). The molecular structure of BAIAb (N‐octyl derivative) was unambiguously assigned as the bis‐adduct having an endo,endo spatial disposition of the two acenaphthylene‐5,6‐dicarboximide moieties by using X‐ray crystallographic analysis. Relative to the absorption spectrum of decacyclene triimide (DCTIa, N‐2‐ethylhexyl derivative), that of the analogous N‐2‐ethylhexyl‐substituted monoadduct, DCMIa, is bathochromically shifted despite the fact that it possesses a less delocalized π‐electron system. DCMIa does not fluoresce in various organic solvents, whereas DCTIa emits yellow fluorescence in CH₂Cl₂ with a low quantum yield (Φ_SN). Moreover, DCMIa in CDCl₃ displays concentration‐dependent ¹H NMR spectroscopy behavior, which suggests that it self‐aggregates with an association constant (K_a) of (193±50) m ^?1 at 20 °C. Despite the presence of four bulky tert‐butyl groups in DCMIa, its K_a value for aggregate formation is comparable to that of DCTIa [(495±42) m ^?1], which does not contain tert‐butyl substituents. Spectroscopic studies with the bis‐adduct BAIAa (N‐2‐ethylhexyl derivative) show that it displays remarkable solvatofluorochromism corresponding to an emission maximum shift (Δλ_EM) of 100 nm. The results of density functional theory calculations on BAIAc (N‐methyl derivative) demonstrate that a considerable spatial separation exists between the HOMO and LUMO coefficient distributions, which indicates that the ground‐to‐excited state transition of the novel three‐dimensional acceptor–donor–acceptor BAIAa system should have intramolecular charge‐transfer character.     

Effect of accelerated thermal ageing on the thermal behaviour of the recently made parchments

To reveal the fire injuring of parchment, the changes in the thermal behaviour of some goat parchments, obtained from skins originating from different animals, as a result of thermal aging were determined by thermal analysis methods (DSC; simultaneous TG/DTG, DSC; micro hot table (MHT)). Thermal aging of parchments was revealed to bring about the decrease in shrinkage temperature, absolute value of enthalpy of denaturation in water and some changes in non-isothermal parameters characteristic for dehydration process in static air atmosphere. The results obtained by DSC analysis performed in N₂ and O₂ flows as well as those obtained by simultaneous TG/DTG, DSC analyses have shown that both softening (melting) process parameters and parameters of thermo-oxidative processes have not been changed by thermal ageing. The results obtained by thermal analysis methods were correlated with those obtained by microscopic investigation of parchment samples immersed in water and scanning electron microscopy (SEM). The application of these microscopic techniques has revealed the morphology changes in the investigated parchments as a result of thermal degradation.     

Stepwise construction of manganese-chromium carbonyl chalcogenide complexes: synthesis, electrochemical properties, and computational studies

When trigonal-bipyramidal clusters, [PPN][E(2)Mn(3)(CO)(9)] (E = S, Se), were treated with Cr(CO)(6) and PPNCl in a molar ratio of 1:1:2 or 1:2:2 in 4 M KOH/MeCN/MeOH solutions, mono-Cr(CO)(5)-incorporated HE(2)Mn(3)-complexes [PPN](2)[HE(2)Mn(3)Cr(CO)(14)] (E = S, [PPN](2)[1a]; Se, [PPN](2)[1b]), respectively, were formed. X-ray crystallographic analysis showed that 1a and 1b were isostructural and each displayed an E(2)Mn(3) square-pyramidal core with one of the two basal E atoms externally coordinated with one Cr(CO)(5) group and one Mn-Mn bond bridged by one hydrogen atom. However, when the TMBA(+) salts for [E(2)Mn(3)(CO)(9)](-) were mixed with Cr(CO)(6) in a molar ratio of 1:1 in 4 M KOH/MeOH solutions and refluxed at 60 °C, mono-Cr(CO)(3)-incorporated E(2)Mn(3)Cr octahedral clusters [TMBA](3)[E(2)Mn(3)Cr(CO)(12)] (E = S, [TMBA](3)[2a]; Se, [TMBA](3)[2b]), respectively, were obtained. Clusters 2a and 2b were isostructural, and each consisted of an octahedral E(2)Mn(3)Cr core, in which each Mn-Mn or Mn-Cr bond of the Mn(3)Cr plane was semibridged by one carbonyl ligand. Clusters 1a and 1b (with [TMBA] salts) underwent metal core closure to form octahedral clusters 2a and 2b upon treatment with KOH/MeOH at 60 °C. In addition, 1a and 1b were found to undergo cluster expansion to form di-Cr(CO)(5)-incorporated HE(2)Mn(3)-clusters [HE(2)Mn(3)Cr(2)(CO)(19)](2-) (E = S, 3a; Se, 3b), respectively, upon the addition of 1 or 2 equiv of Cr(CO)(6) heated in refluxing CH(2)Cl(2). Clusters 3a and 3b were structurally related to clusters 1a and 1b, but with the other bare E atom (E = S, 3a; Se, 3b) further externally coordinated with one Cr(CO)(5) group. The nature, cluster transformation, and electrochemical properties of the mixed manganese-chromium carbonyl sulfides and selenides were systematically discussed in terms of the chalcogen elements, the introduced chromium carbonyl group, and the metal skeleton with the aid of molecular calculations at the BP86 level of the density functional theory.     

Synthesis and Characterization of Alumina R Chemically Modified with n-Octyl for Use as a Stationary Phase in TLC

JPC – Journal of Planar Chromatography – Modern TLC - A stationary phase for thin-layer chromatography has been prepared by attaching 1-octene to alumina R. This stationary phase has...     

Sextic centrifugal distortion constants of ozone

Theoretical expressions for the sextic centrifugal distortion constants of triangular triatomic molecules, as given by Sumberg and Parker, have been evaluated for the ozone molecule. For this calculation, the harmonic frequencies and cubic anharmonic potential constants determined by Barbe, Secroun, and Jouve were used. The calculated distortion constants were compared to complete sets of measured distortion constants recently determined by Maki, and by Barbe et al. Even though the measured constants range over more than four orders of magnitude, we find that the theory reproduces the relative magnitudes and the algebraic signs of the constants quite well. Absolute quantitative agreement is considerably better than order-of-magnitude.     

Thermal degradation of collagen-based materials that are supports of cultural and historical objects

The thermal analysis methods (TG, DTG and DTA) were used for the investigation of the thermal degradation of some recent manufactured tanned leathers, leathers that are supports of cultural or historical objects (leather from book covers (XVII-XIX centuries); leather from an Austrian belt (Franz Joseph period), Cordoba leather (XVII century), lining leathers), recent and patrimonial parchments and recent extracted collagen (sorts of collagen obtained from bovine leather at different pH-values, bovine collagen with different hydration degree). At progressive heating, all investigated materials exhibit two main successive processes, associated with the dehydration and thermo-oxidative degradation. Each analyzed material has a characteristic thermal analysis curve (TG, DTG and DTA) that can be considered a material 'fingerprint'. This result suggests the use of the thermal analysis methods to identify of leathers from which the patrimonial objects are manufactured. The rate of thermo-oxidation of recent manufactured tanned leathers is substantially higher than the rate of the same process corresponding to naturally aged leathers that exhibit values of the thermo-oxidation rate appropriate to those obtained for parchments and collagens. The rate of thermo-oxidation of leather can thus be used as a criterion to distinguish between recent manufactured leather and patrimonial one. This revised version was published online in July 2006 with corrections to the Cover Date.     

Copper(I)-picolinic acid catalyzed N-arylation of hydrazides

An efficient copper-catalyzed carbon-nitrogen bond formation is described. The copper(I) complex with commercially available 2-picolinic acid ligand was found to be effective in N-arylation of N-Boc-hydrazine. This methodology offers a regioselective N-arylation of hydrazides using a variety of substituted aryl iodides.     

物理教学中实施科学方法教育的途径

在中学物理教学中，对学生进行科学方法教育是素质教育的基本要求，也是物理新课程三维目标的要求之一；它有利于提高学生的科学素质，有利于培养创新型人才，有利于培养学生分析和解决实际问题的能力．     

Origin of the fast magnetization relaxation at low temperatures in HTS with strong pinning

The temperature T variation of the normalized magnetization relaxation rate S in high-temperature superconductors (HTS) with strong vortex pinning exhibits a maximum in the low-T range. This was reported for various HTS, and the origin of the faster relaxation at low T appearing in standard magnetization relaxation measurements was usually related to specific pinning properties of the investigated specimens. Since the observed behaviour seems to be characteristic to all HTS with enhanced pinning (generated by random and/or correlated disorder), we show that the S(T) maximum can be explained in terms of classic collective vortex creep. The influence of thermo-magnetic instabilities in the low-T range is also evidenced. The collective (elastic) creep regime is generated by the T dependent macroscopic currents induced in the sample during standard magnetization measurements.