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  • 1
    ISSN: 0947-6539
    Keywords: ionophores ; impedance spectroscopy ; membrane models ; monolayers ; self-assembly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel ion-binding monolayers on gold surfaces are presented where the molecular design is based upon the natural ion binder ferrichrome. The new ion binders possess hydroxamate coordinating groups arranged in C2 symmetry (bishydroxamate binder, BHB) or C3 symmetry (trishydroxamate binder, THB), and a separate dialkyl sulfide moiety, which serves as an anchor to the gold substrate. The separation between the ion-binding cavity and the attachment site to the gold allows each parameter to be controlled separately, namely, cavity size, its symmetry and external envelope, as well as the functional group used for immobilization. The monolayers were characterized with respect to ellipsometric thickness, wettability (advancing and receding contact angles (CAs) for water), and surface coverage; the latter is determined by metal underpotential deposition (UPD). It is shown that the introduction of hydrophobic side chains (i-butyl) improves the CAs, thickness, and surface coverage of the monolayers. A detailed analysis of the alternating-current (AC) impedance spectra is presented for THB monolayers on gold electrodes, where the impedance data are fitted to an equivalent circuit model. It is shown that the AC response in a wide frequency range can be used to probe ion binding and release in monolayer systems on electrodes.
    Additional Material: 7 Ill.
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  • 2
    ISSN: 0947-6539
    Keywords: amphiphiles ; glucophospholipids ; self-assembly ; tubules ; vesicles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new family of amphiphiles that form tubules (i.e., hollow cylindrical bilayer-based microstructures) by self-aggregation has been identified, namely, anionic glucophospholipids of type 1, in which a double-tailed hydrophobe is grafted through a phosphate linkage to the O-6 position of a polar glucose head group. Compounds 1a-c self-assemble into stable, hollow tubular microstructures when dispersed in water and cooled below the temperature at which the transition between crystal and liquid-crystal phases takes place (estimated from change in turbidity). The diameter of the microstructures appears to depend on the nature of the hydrophobic tail, significantly smaller diameters being obtained for fluorinated tails. No tubules were obtained when galactose (2a-c, pH〈11) or mannose (3a-c) derivatives were used instead of glucose derivatives, or when glucose was derivatized at the O-3 (4b) rather than O-6 position; in these cases only vesicles were formed. Tubules made of 1 converted rapidly into giant vesicles when heated; they spontaneously formed again upon cooling. The presence of a fluorinated chain, as in 1b and 1c, increased the temperature at which the tubule-vesicle interconversion occurred to above room temperature. Because the amphiphiles are negatively charged, the formation of tubules is pH-dependent and is favored at higher pH. These findings support the view that hydration of and hydrogen bonds between polar heads play a major role in tubule formation. Hydration of the sugar-derived head groups decreases as the number of intermolecular hydrogen bonds increases; this favors membrane crystallization and tubule formation.
    Additional Material: 4 Ill.
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  • 3
    ISSN: 0947-6539
    Keywords: bipyridine ligands ; helicates ; kinetics ; mass spectrometry ; self-assembly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The self-assembly of the pentanuclear double helicates Hh, Ha and He from the corresponding oligobipyridine strands Lh, La and Le and Cu1 ions has been investigated by NMR and electrospray mass spectrometry (ESMS). Where as Hh is assembled rapidly (in less than 20 min), He (about 20 h) and especially Ha (about 60 h) form much more slowly. The rate decreases strongly with increasing steric bulk of the substituents in the 4,4′-positions on the bipyridine units; this indicates that the search processes (wrapping, unwrapping) that lead to the final helicate are strongly hindered by the size of the substituents. The ESMS data give information about the species present in solution under different conditions and allow the formulation of possible formation pathways, which may involve, in particular, helicates of hairpin type.
    Additional Material: 6 Ill.
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  • 4
    ISSN: 0947-6539
    Keywords: helical structures ; lipids ; liposomes ; self-assembly ; tubules ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The development of functional supramolecular devices built by self-assembly of elementary molecules and with bioactive properties arouses considerable interest in the field of nanotechnology and new materials. We report here the formation of a new class of lipid tubules exhibiting both properties of molecular recognition and crystal formation for the protein streptavidin. These lipid tubules, made of biotin-containing dioctadecylamine molecules, are straight hollow cylinders with a constant diameter of 27 nm and variable length up to several micrometers. They are unilamellar with an inner diameter of about 16 nm, as shown by cryoelectron microscopy. Streptavidin binds to the biotinylated tubules and assembles spontaneously into ordered helical arrays at the tube surface. These crystals exhibit regular order up to about 1.5 nm resolution. In addition, the helical streptavidin arrays act as functionalized supramolecular devices that bind a wide variety of biotinylated objects, as demonstrated here with proteins and liposomes.
    Additional Material: 5 Ill.
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  • 5
    ISSN: 0947-6539
    Keywords: luminescence ; photochemistry ; redox chemistry ; self-assembly ; self-complexation ; template syntheses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photochemical control of a self-assembled supramolecular 1:1 pseudorotaxane (formed between a tetracationic cyclophane, namely the tetrachloride salt of cyclobis(paraquat-p-phenylene), and 1,5-bis[2-(2-(2-hydroxy)ethoxy)ethoxy]naphthalene) has been achieved in aqueous solution. The photochemical one-electron reduction of the cyclophane to the radical trication weakens the noncovalent bonding interactions between the cyclophane and the naphthalene guest - π-π interactions between the π-electron-rich and π-electron-poor aromatic systems, and hydrogen-bonding interactions between the acidic α-bipyridinium hydrogen atoms of the cyclophane and the polyether oxygen atoms of the naphthalene derivative - sufficiently to allow the guest to dethread from the cavity; the process can be monitored by the appearance of naphthalene fluorescence. The radical tricationic cyclophane can be oxidized back to the tetracation in the dark by allowing oxygen gas into the system. This reversible process is marked by the disappearance of naphthalene fluorescence as the molecule is recomplexed by the tetracationic cyclophane. This supramolecular system can be chemically modified such that the π-electron-rich unit, either a naphthalene derivative or a hydroquinone ring, and the tetracationic cyclophane are covalently linked. We have demonstrated that the π-electron-rich residue in this system is totally “self-complexed” by the cyclophane to which it is covalently attached. Additionally, the self-complexation can be switched “off” and “on” by electrochemical two-electron reductions and oxidations, respectively, of the tetracationic cyclophane component. Thus, we have achieved the construction of two switches at the nanoscale level, one driven by photons and the other by electrons.
    Additional Material: 15 Ill.
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  • 6
    ISSN: 0947-6539
    Keywords: iron ; metallacryptands ; metalla-cryptates ; self-assembly ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and structural characterisation of two dinuclear iron(III) complexes are reported. The compounds of general structure [Fe2L13] [8; L1 = dianion of 2,2′-dicyano-2,2′-isophthaloyldi(isopropyldicarboxylate)] and [K ⊂ Fe2L23]+ (PF6)- [10; L2 = dianion of 1,1′-(2,6-pyridylene)bis-1,3-(4-dimethyl)-pentanedione] are formed by the deprotonation of ligands 7 and 9 with triethylamine and potassium hydride respectively, followed by addition of iron(III) chloride and work up with water or aqueous potassium hexafluorophosphate. X-ray crystallographic studies reveal that 8 is a racemic mixture composed of triple helicates with (Δ,Δ)-fac and (Δ,Δ)-fac configuration at the two iron bridgeheads. In contrast to racemic 8, the two iron centres in the meso-10 [(Δ,Δ)-fac] have opposite configuration. Investigations of the redox-active iron centres in {2}-metallacryptand 8 and {2}-metallacryptate 10 by cyclic voltammetry show slightly different behaviour. The peaks for the two consecutive reductions of the two iron centres of 8 can hardly be resolved, whereas 10 shows two well-separated peaks. Mössbauer measurements were performed on 8 and 10 between 4.2 and 300 K, with and without a field applied perpendicular or parallel to the γ-beam. All zero-field and 20 mT spectra exhibit a broad and unresolved absorption pattern. Application of 5.3 T at 4.2 K results in well-resolved magnetic hyperfine patterns which are practically the same for 8 and 10.
    Additional Material: 5 Ill.
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  • 7
    ISSN: 0947-6539
    Keywords: catenanes ; polycatenanes ; polyrotaxanes ; rotaxanes ; self-assembly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The self-assembly of three bis[2]catenanes and a bis[2]rotaxane, by two complementary strategies, is reported. A synthetic route to derivatives of bis-para-phenylene[34]crown-10 (BPP34C10) and 1,5-naphtho-para-phenylene[36]-crown-10 (1/5NPP36C10) containing a fused five-membered ring with a secondary amine function is described. These intermediate N-allylimido macrocyclic polyethers undergo template-directed reactions with 1,1′-[1,4-phenylenebis-(methylene)]bis-4,4′-bipyridinium bis-(hexafluorophosphate) and 1,4-bis(bromo-methyl)benzene to produce [2]catenanes containing an N-allyl functionality. The N-allylimido macrocyclic polyethers have also been reduced and deprotected to afford macrocycles possessing a free NH group, which are then linked through a 4,4′-biphenyldicarbonyl spacer to produce bis(crown ether)s, in which each crown ether moiety has two recognition sites. These ditopic BPP34C10 and 1/5NPP36C10 derivatives are capable of sustaining self-assembly reactions at both recognition sites to yield bis[2]catenanes. The self-assembly of a complementary bis[2]catenane, in which two tetracationic cyclophanes are linked together with a flexible hexyl chain, has also been achieved by treating 1,1′-[1,4-phenylenebis(methylene)]bis-4,4′-bipyridinium bis-(hexafluorophosphate) with a compound containing two linked 1,4-bis(bromomethyl)benzene units in the presence of BPP34C10. Replacing BPP34C10 with a dumbbell-shaped compound containing a linear polyether unit intercepted by a naphthalene residue and terminated by two bulky adamantoyl groups has led to the self-assembly of a bis[2]rotaxane. The X-ray crystal structures of one of the catenanes and its associated crown ether component are reported, together with solution state dynamic 1H NMR spectroscopic studies, showing that there is substantial degree of order characterizing the molecular structure of the catenanes.
    Additional Material: 10 Ill.
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  • 8
    ISSN: 0947-6539
    Keywords: catenanes ; macrocycles ; rotaxanes ; self-assembly ; tetrathiafulvalenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general stepwise approach is described for the preparation of tetrathiafulvalene (TTF)-based linear and monoand dimacrocyclic compounds incorporating one or two 1,4-dioxyphenylene, 9,10-dioxyanthrylene, or 1,5- or 2,6-dioxynaphthylene units from readily available starting materials. By utilizing the π-π stacking interactions of the TTF unit with the dipyridinium dication of 1,1′-[1,4-phenylenebis (methylene)] bis-4,4′-bipyridinium bis(hexafluorophosphate), a rotaxane and two [2]catenanes were synthesized starting from the linear and monomacrocyclic compounds, respectively. From the dioxyphenylene-based dimacrocycle, three [3]pseudocatenanes (trans, cis, and a mixture of cis/trans isomers) were obtained with the trans compound as the major product. From the dioxyanthrylene dimacrocycle, only the trans-[3]pseudocatenane was obtained. Catenane products were formed quantitatively from the 1,5-dioxynaphthylene dimacrocycle in a template-directed reaction, affording a trans-[3]pseudo-catenane together with a [4]pseudocatenane (mixture of cis/trans isomers). From the 2,6-dioxynaphthylene dimacrocycle, a cis-[3]pseudocatenane was obtained as the major product and a trans-[3]pseudocatenane as the minor one. For the [3]pseudocatenanes (i.e., both the cis and trans catenanes), in which the TTF units were clamped by the tetracationic macrocycle, isomerizations were completely prevented even in the presence of trifluoroacetic acid. All new rotaxanes and catenanes were characterized by electrospray mass spectrometry, and the cis- and trans- [3]pseudocatenanes were additionally investigated by 1H NMR spectroscopy. The electrochemical and spectral properties of the rotaxane and the catenanes are reported. Catenane formation increases the redox potentials of the TTF unit. The results demonstrate the versatility of TTF as a building block in the construction of supramolecular structures.
    Additional Material: 4 Ill.
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  • 9
    ISSN: 0947-6539
    Keywords: lactam ; macrocycles ; rotaxanes ; self-assembly ; template syntheses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two new rotaxane types, the [2]rotaxanes 12a,b and the [3]rotaxane 13, have been synthesised by treating the “axle” 7 with the stopper component 9 in the presence of the “wheel” 8. A nonionic template intermediate of type 10 is proposed. The [3]rotaxane 13 was only obtained when the chain of the “axle” had a certain length: with n = 1 only [2]rotaxane 12 a was isolated, whereas with n = 2 the [3]rotaxane 13 was formed besides the [2]rotaxane 12 b. This suggests that more extended rotaxanes and polyrotaxanes can be synthesised by the template strategy.
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  • 10
    ISSN: 0947-6539
    Keywords: catenanes ; chirality ; enantioselection ; receptors ; self-assembly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The design of a new class of chiral [2]catenanes is reported. The self-assembly of [2]catenanes comprising one or two 3,3′-bitolyl spacers in the π-electron-deficient component, and bis-p-phenylene-34-crown-10 (BPP 34 C 10) as the π-electron-rich component, is described. The X-ray crystal structures, together with solution-state dynamic 1H NMR spectroscopic studies, show that the degree of order characterizing the molecular structures is substantially different from that of the “parent” [2]-catenane, comprising cyclobis(paraquat-p-phenylene) and BPP34C 10. When appropriately substituted in their ortho positions, bitolyl compounds can support axial chirality: the self-assembly of axially chiral [2]catenanes, comprising one or two 3,3′-disubstituted-2,2′-dihydroxy-1,1′-binaphthyl spacers, has been achieved in good yields, showing that the introduction of the bulky, axially chiral spacer and the consequent distortion of the cavity of the π-electron-deficient component still permits good molecular recognition between the components leading to efficient catenane production. X-ray crystallography suggests that this recognition is driven by hydrogen bonding and π-π stacking interactions between the complementary subunits. The hydroxyl groups on the chiral spacer were further functionalized as benzoyl esters in a [2]catenane as well as in the tetracationic cyclophanes; that is, chemistry can be done on these catenanes. The chiral tetracationic cyclophanes exhibit good enantiomeric differentiation toward the D- and L-enantiomers of aromatic amino acids in water and their N-acetylated derivatives in organic solvents.
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