New trends in the chemistry of condensed heteromacrocycles part B: Macrocyclic formazans

This review article, covering the literature from 1979 to 2002, deals with the main strategies for the synthesis of macrocyclic crown formazans as well as their specific syntheses. Reactivities and applications of these compounds are also in focus.     

New acridine derivatives bearing immobilized azacrown or azathiacrown ligand as fluorescent chemosensors for Hg and Cd

Two new acridine derivatives bearing azacrown or azathiacrown ligand were synthesized as fluorescent chemosensors for Hg²⁺ and Cd²⁺ in aqueous solution. Compounds 1 and 2 displayed selective CHEF (chelation enhanced fluorescence) effects with Hg²⁺ or Cd²⁺ among the metal ions examined. The practical use of these probes was demonstrated by their applications to the detection of Hg²⁺ and Cd²⁺ ions in mammalian cells.     

New trends in the chemistry of α-fluorinated ethers, thioethers, amines and phosphines

Fluorine, the most electronegative element plays nowadays a key role in pharmaceutical, agrochemical and material sciences. About 20% of all pharmaceuticals and about 30% of agrochemicals under development or recently introduced on the market contain fluorine. However, when one examines the relevant structures more closely, one quickly recognizes a structural monotony. The same fluorine bearing aromatic or heterocyclic “cores” appear over and over again. The search for novel molecules having “emergent” fluorinated groups and the development of an efficient access toward them is a challenging task for industrial as well as academic laboratories. For example, the trifluoromethoxy group finds increased utility as a substituent in bioactives, but it is still perhaps the least well understood fluorine substituent in currency. The present review will give an updated overview on the synthesis of α-fluorinated ethers, thioethers, amines and phosphines.     

A molecular mechanics study of conformational trends in simple alcohols and ethers. Part I: Geometric trends

We have modified the MM2(80) molecular mechanics force field for alcohols and ethers to reproduce geometric trends predicted by ab initio calculations with the 4-21G basis set. The results obtained with the modified force field are consistent with experimental evidence.     

Stoichiometry and conformation of the azacrown moiety in sodium complexes of azacrown ethers. A Raman/IR spectroscopic study. Part I: Complexes of 4,13-Diaza-18-crown-6

Three sodium complexes (bromide, iodide and thiocyanate) of 4,13-diaza-18-crown-6 were studied using Raman and IR spectroscopy and normal coordinate calculations to probe the stoichiometry of the complexes and the variation in the conformation of azacrown moiety on complex formation. complex formation is accompanied by characteristic shifts of the bands, especially of those in the 800–900 cm^–1 region. Complexes of both 11 and 21 stoichiometry were observed. Normal coordinate calculations showed the reduction of symmetry of azacrown moiety toC _i , in contrast to theC _2h symmetry known for the parent azacrown and potassium thiocyanate complex.     

Stoichiometry and conformation of the azacrown moiety in sodium complexes of azacrown ethers. A Raman/IR spectroscopic study. Part II: Complexes of 4,13-diaza-15-crown-5

4,13-Diaza-15-crown-5 and three of its sodium complexes (bromide, iodide and thiocyanate) were studied using Raman and IR spectroscopy and normal coordinate calculations, following the corresponding study on the sodium complexes of 4,13-diaza-18-crown-6 in the preceding paper. Complex formation was again accompanied by a characteristic shift of the bands, especially of those in the 800–900 cm^–1 region. The complexes of 4-13-diaza-15-crown-5 were distinct from those of 4-13-diaza-18-crown-6, in that both of the bands at 830 and 890 cm^–1 of the parent azacrown were affected on complex formation and in that only the 11 complex was formed. Normal mode calculations were made to predict conformations of the azacrown ring of the parent 4,13-diaza-15-crown-5 and its sodium complexes. Attention was paid to the different extent of mismatch in size of a sodium ion and azacrown cavities.     

氮杂冠醚研究IV:N-双取代二苯并氮杂冠醚与对甲苯重氮氟硼酸盐的配合作用

本文报道借^1HNMR方法研究了四种新的N-双取代二苯并氮杂冠醚化合物(1-4)和对甲苯重氮氟硼酸盐在CDCl3-CD3CN中的配合作用, 并计算了以上配合物的稳定常数, 简轭讨论了取代基团的改变对配合作用的某些影响.     

Stoichiometry and conformation of the azacrown moiety in sodium complexes of azacrown ethers. a Raman/IR spectroscopic study. Part I: Complexes of 4,13-diaza-18-crown-6

Three sodium complexes (bromide, iodide an thiocyanate) of 4,13-diaza-18-crown-6 were studied using Raman and IR spectroscopy and normal coordinate calculations to probe the stoichiometry of the complexes and the variation in the conformation of azacrown moiety on complex formation. Complex formation is accompaniedby characteristic shifts of the bands, especially of those in the 800–900 cm^–1 region. Complexes of both 1: 1 and 2:1 stoichiometry were observed. Normal coordinate calculations showed the reduction of symmetry of azacrown moiety toC ₂ , in contrast to theC _2h symmetry known for the parent azacrown and potassium thiocyanate complex.     

Synthesis of thiacrown and azacrown ethers based on a spiroacetal framework

A novel class of thiacrown and azacrown ethers incorporating the 1,7-dioxaspiro[5.5]undecane spiroacetal ring system was prepared by reaction of ditosylate 5 with the appropriate dithiols 9a-c or protected diamine 12a. Spiroacetal ditosylate 5 in turn, was prepared from diol 3 via ozonolysis of bisallyl ether 7 followed by tosylation of the derived diol 8.     

New trends in methodological developments in clinical chemistry

Many new techniques have been introduced in clinical chemistry. Three important new methodologies are dry chemistry, gen technology and biosensors. Solid-phase chemistry systems. The two most common solid-phase systems are the Kodak-Ektachem and the Boehringer Mannheim Reflotron. The first one is working with serum and the second one mainly with whole blood. The determination of urea and the determination of the activity of AST (GOT) will be described. The greatest problems of these systems are the quality control of the analysis and the interferences by endogenous and exogenous substances. Analysis with the aid of gen technology. The major diagnostic applications of gen technology in human disease is the detection of genetic disorders and the tumor diagnosis. The beta-thalassemia will be the example for genetic disorders and the chronic myeloid leukemia (CML) for diagnosis of a tumor. Thalassemias are a group of inherited disorders caused by the defective or absent outpout of one of the globin chains of the Hb tetramere. The CML is an example of a specific translocation of a small region of chromosome 9 bearing the abl-oncogene to chromosome 22. Biosensors in biochemical analysis. Biosensors are analytical devices that respond selectively to analytes in an appropriate sample and convert their concentration into an electrical signal. As examples an in-vivo ferrocene-mediated glucose sensor and the determination of the isoenzyme LDH5 based on an antigene-antibody reaction are described.     

Mixed monolayers of alkylated azacrown ethers and palmitic acid at the air-water surface

The Langmuir films of two alkylated azacrown ethers at the air-water surface were characterized using surface pressure-area isotherms, ellipsometry, Brewster angle microscopy, and constant-area surface pressure relaxation. The azacrown ether molecules aggregate in the monolayer, which significantly stabilizes the film against dissolution. Mixed azacrown ether-palmitic acid monolayers were also characterized; results suggest that at high compression the two molecules interact repulsively. The influence of Cu(II) ions present in the aqueous subphase on the single components and mixed monolayer characteristics was also studied.     

N-Cyanomethyl-β-chloro amines: chiral building blocks for the synthesis of azacrown ethers

(1R,2S)-Ephedrine and norephedrine derived N-cyanomethyl-β-chloro amines react with tri-, tetra- and penta-ethylene glycol to stereoselectively give the corresponding amino ethers. Further transformation into chiral monoaza 12-, 15- and 18-crown-4, -5 and -6 ethers was realized in three steps and good overall yields by: (i) mesylation, (ii) deprotection of the N-cyanomethyl group and (iii) intramolecular alkylation. Binding affinities of these azacrown ethers for alkali cations was studied by FAB-MS.     

New chemistry of zwitterionic peroxides arising by photooxygenation of enol ethers

The rosebengal-sensitized photooxygenation of 2-methoxynorborn-2-ene(1)in acetaldehyde gave cis-1-carboxaldehyde-3-carbomethoxycyclopentane (31%) and the cis and trans-Me derivatives of the cis-fuscd exo-1,2,4-trioxanes arising by addition of a molecule of oxygen and acetaldehyde to 1 at C3 and C2 respectively (13%) Similar photooxygenation of 2-(methoxymethylidene)adamantane in the presence of acetaldehyde, propionaldehyde and pivalaldehyde gave adamantanone (31–42%), and the cis and trans tricylo[3.3.1.1^3,7]decane-2-spiro-6'-[3-alkyl-5-methoxy-1,2,4-trioxanes] in yields of 32–53% Trioxane formation under similar conditions was experienced for 1,1-di-t-butyl-2-methoxyethene and 2-(methylmercaptomethylidene) adamantane. The results are discussed in terms of an intermediate zwitterionic peroxide which can either close directly to a 1,2-dioxetane or, if aldehyde is present, condense across the CO function giving the 1,2,4-trioxane.     

Free radical chemistry. Part 5. [1] A new approach to the synthesis of perfluorinated ethers

Fluorinations of the free-radical adducts of fluorinated alkenes, to ethers, over cobalt trifluoride are described and perfluorinated ethers are obtained at temperatures in excess of 400°C. The effect of structure on the formation of perfluoroethers is outlined.     

Synthesis of azacrown ethers and benzocryptands by macrocyclization of podands at high concentrations of reactants

The reactions of 1,2-bis(2-Y-ethoxy)benzenes, N,N-bis(2-Y-ethyl)-N-phenylamines, or 2,6-bis(Y-methyl)pyridines (Y = I, Br, or OTs) with α,ω-polyoxaalkanediamines or diazacrown ethers in the presence or absence of alkali carbonates in a concentrated acetonitrile solution of the reactants afforded the corresponding azacrown ethers or cryptands in high yields.     

Frontiers of positron and positronium chemistry in condensed media

Our work proves that positron annihilation spectroscopy is an excellent tool to follow the structural changes in chemical species. We present four examples to support the above statement. The sizes of defects in electrodeposited chromium layers were studied and estimated on the basis of positron lifetime spectra decomposed into two components. Vacancies, di-vacancies and vacancy-clusters could be identified in the electrodeposites. The changes of the size distribution of the free volume units in poly(methylmetacrylate) on the dependence of molecular weight and dispersity were described by the correlation between the lifetime ofortho-Ps and the free volume units in polymers. It was found that the free volume is affected by both the molecular weight and dispersity. The effect of dispersity was explained by the sample preparation technique, namely by the application of high pressure. The ortho-para conversion ofortho-Ps was used to follow the partial spin-crossover in [Fe(1-ethyl-1H-tetrazole)₆](BF₄)₂. The spin-crossover temperature was identified to be 105 K. A conformal structural transformation was found in [Zn(1-propyl-1H-tetrazole)₆](BF₄)₂ between 170 and 90 K by positronium lifetime measurement and the role of (BF₄)²⁻ anion, in this transformation, was proved by¹⁹F NMR spectroscopy.     

New trends in polyoxometalate photoredox chemistry: from photosensitisation to water oxidation catalysis

Molecular metal oxide clusters, so-called polyoxometalates (POM) have been extensively used as homogeneous photocatalysts in various photoredox reactions such as the oxidation of alkanes, alkenes and alcohols as well as the light-induced mineralisation of various organic and inorganic pollutants. The more general application of POMs as photoactive compounds, in particular in solar energy harnessing, has been hampered as the clusters typically absorb light in the UV-region only. Over the past decade, concepts have been put forward on how the reactivity of this class of compounds can be optimised to improve their overall photoactivity, and a particular focus has been on the design of photocatalytic processes which allow the conversion of solar light into useful chemical reactivity. This perspective gives a brief overview of general aspects of POM photochemistry and critically discusses the advantages and challenges of a range of POM-based systems for photooxidations and photoreductions with a focus on the development of sustainable solar light conversion systems.