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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis of Spacer-Armed Glucodendrimers Based on the Modification of Poly(propylene Imine) Dendrimers (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1879-1886 
    Details
    ISSN: 1434-193X
    Keywords: Amphiphiles ; Carbohydrates ; Dendrimers ; Cluster glucosides ; Neoglycoconjugates ; Polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of preformed poly(propylene imine) dendrimers [DAB(Pa)x] with reactive primary amine end groups proved to be very useful for the construction of saccharide surface-coated dendrimers. For this purpose, amide bonds were introduced by a reaction between the primary amine end groups of the dendrimers with N-succinimidyl-activated esters of spacer-armed acetyl-protected thioglucopyranoside units. The linear alkyl chain spacers between the dendrimer surface and the saccharide units was increased in length with 1, 5 and 10 carbon atoms. These spacer arms were introduced to determine the influence of local saccharide surface concentration variations on the dendrimer properties. After modification of the dendrimers with these saccharide units, the acetyl protecting groups were removed. Purification of these derivatives was accomplished by using dialysis either in water or in aqueous methanol. The solubility behavior of the resulting glucodendrimers proved to be strongly dependent on the hydrophobic part, i.e. the alkyl chain spacers in the molecule. Therefore, these nanosized multivalent structures, appropriate for studying carbohydrate-protein interactions, are also proposed useful for investigating amphiphilic properties.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Enantiopure Dendrimers Derived from the 1,1′-Binaphthyl Moiety: A Correlation Between Chiroptical Properties and Conformation of the 1,1′-Binaphthyl Template (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 61-71 
    Details
    ISSN: 1434-193X
    Keywords: Binaphthyls ; Chirality ; Circular dichroism ; Dendrimers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The absorption and CD spectra of a series of Fréchet (compounds 7-10) and backfolding (compounds 11-12) dendrimers derived from enantiopure (S)-2,2′-dihydroxy-1,1′-binaphthalene have been recorded (THF) in the range 200-350 nm. All the compounds examined show a positive couplet between 200 and 240 nm (1B transition of the 2-naphthol chromophore), the intensity of which (Δεmax of the low-energy branch) ranges between 100 and 40. By means of the DeVoe polarizability model the intensity of the 1B couplet has been calculated vs. the dihedral angle θ. This analysis provides θ angles of 95-110° for the Fréchet dendrimers and 100-110° for the backfolding compounds. These values clearly indicate that the torsional angle θ, defined by the two naphthalene planes, never exceeds the critical value of 110°. This investigation confirms the wide utility of CD spectroscopy to provide geometrical information that cannot be obtained by other types of structural analysis.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Enantioselective Discrimination in the Self-Assembly of [2]Pseudorotaxanes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 983-986 
    Details
    ISSN: 1434-193X
    Keywords: Chirality ; Host-guest chemistry ; Enantioselective receptors ; CD spectroscopy ; Self-assembly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The combination of (i) an optically active, axially chiral π-electron-deficient tetracationic cyclophane derivative of cyclobis(paraquat-p-phenylene), in which both of the p-phenylene spacers have been replaced by axially-chiral 3,3′-disubstituted binaphthol spacers, and (ii) enantiomeric, π-electron-rich substrates, in which a hydroquinone ring is inserted into the polyether backbone terminated by carboxyl groups and substituted in a C2-symmetric manner by two methyl groups, thus creating two equivalent chiral centers in the substrate, produces in solution 1:1 complexes in which the π-electron-rich substrates are inserted into the π-electron-deficient cavities of the cyclophanes in a pseudorotaxane-like manner. The differences in the free energies of complexation for (RR) and (SS) enantiomers of the π-electron-rich substrates span the range from 0.1 to 0.7 kcal mol-1. Chiral recognition becomes more effective the closer the chiral centers are to the hydroquinone templating unit. CD spectroscopy reveals that the different modes of binding of the enantiomeric substrates by the axially chiral tetracationic cyclophane are not accompanied by drastically different core geometries for the [2]pseudorotaxanes. Thus, the chirality of the complex is governed primarily by the properties of the rigid receptor. The combination of the D2 symmetry of the receptor with the C2 symmetry of the substrates has been found to be particularly effective, considering that the chiral centers on the substrates are located on polyether chains which possess a high degree of conformational freedom.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Extended-Core Discotic Liquid Crystals Based on the Intramolecular H-Bonding in N-Acylated 2,2′-Bipyridine-3,3′-diamine Moieties (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 300-307 
    Details
    ISSN: 0947-6539
    Keywords: bipyridines ; discotic liquid crystals ; hydrogen bonds ; liquid crystals ; mesophases ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new type of disc-shaped molecule (1 a-c) has been synthesised and characterised. The molecules were built up by linking three lipophilic, N-monoacylated 2,2′-bipyridine-3,3′-diamine wedges to a central 1,3,5-benzenetricarbonyl unit. They show liquid crystalline behaviour, as shown by DSC, polarisation microscopy and X-ray diffraction. In all cases the mesophase was characterised as a Dho phase. From 1H NMR results it was shown that the interior of compounds 1 a-c preferentially adopts a C3 symmetrical conformation owing to strong intramolecular H-bonding, which gives rise to an extended core. This large core induces strong interactions between molecules, leading to mesophases of enhanced thermal stability.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030220
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  • 5
    Electronic Resource
    Electronic Resource
    Synthesis of Glycodendrimers by Modification of Poly(propylene imine) DendrimersSynthetic carbohydrate dendrimers, part 3. For part 2, see: P. R. Ashton, S. E. Boyd, C. L. Brown, N. Jayaraman, J. F. Stoddart, Angew. Chem. Int. Ed. Engl. 1997, 36, issue 7. A list of abbreviations used in this paper is given in ref. [37]. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 974-984 
    Details
    ISSN: 0947-6539
    Keywords: carbohydrates ; dendrimers ; glycosides ; neoglycoconjugates ; polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of preformed poly-(propylene imine) dendrimers (DAB-dendr-(NH2)x) for the rapid and facile construction of high molecular weight carbohydrate-coated dendrimers (glyco-dendrimers) is presented. An efficient attachment of spacer-armed derivatives of D-galactose and lactose to the primary amino end groups of DAB-dendr-(NH2)x has been achieved by means of amide bond formation, using the N-hydroxysuccinimide coupling procedure. Acetate protecting groups have been employed in order to avoid side reactions at the coupling stage. Deacetylation leads to the target glycodendrimers. The reactivity of all the available DAB-dendr-(NH2)x (generations 1-5) has been investigated and a series of homologous carbohydrate-coated dendrimers have been synthesized. In addition, the attachment of larger saccharide moieties has been demonstrated by the condensation of a trisgalactoside cluster with DAB-dendr-(NH2)x carrying both four and eight primary amino groups. The regularity of the glycodendrimers has been proven by NMR spectroscopy, and the molecular weights of the low-generation carbohydrate-coated dendrimers have been determined by mass spectrometry. Modifications of DAB-dendr-(NH2)x with biologically active carbohydrates affords a new and simple approach to high molecular weight compounds that may be considered as neoglycoconjugates with perfectly symmetrical structures and that offer much promise as multivalent ligands involved in carbohydrate-protein interactions.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030620
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  • 6
    Electronic Resource
    Electronic Resource
    Chirality in Dendritic ArchitecturesThis concepts article is a personal reflection on the many issues raised by the combination of chirality and dendrimers. The concepts presented here are partly based on several recent reports in the published literature and partly on the highly appreciated discussions with colleagues on as yet undisclosed results. In particular Bert Meijer would like to express his gratitude to Professor Hans Wynberg who stimulated him to explore all aspects of stereochemistry.Dedicated to Professor Hans Wynberg on the occasion of his 75th birthday (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1563-1570 
    Details
    ISSN: 0947-6539
    Keywords: catalysis ; chirality ; dendrimers ; molecular recognition ; surfaces ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: At first glance the topic of chiral dendrimers seems to be a contradiction in terms. However, recent studies reveal that both the building blocks of the dendrimer and the overall dendritic architecture can be chiral and that chirality can be introduced at various levels. The expression of optical activity in these enantiomerically pure dendrimers as a result of conformational (dis)order has proven to be of special interest. In this Concepts article we present the different approaches to introducing chirality in dendritic architectures, organized through their possible impact in fields such as biocompatibility, catalysis, molecular recognition, and surface chemistry. Also, the relation between molecular chirality of core or building block and the macroscopic chirality of dendritic objects is discussed.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031005
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  • 7
    Electronic Resource
    Electronic Resource
    Polystyrene-Poly(propylene imine) Dendrimers: Synthesis, Characterization, and Association Behavior of a New Class of Amphiphiles (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1616-1626 
    Details
    ISSN: 0947-6539
    Keywords: amphiphiles ; block copolymers ; dendrimers ; micelles ; surfactants ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new class of amphiphilic macromolecules has successfully been synthesized by creating well-defined diblock copolymers of polystyrene (PS, Mn=3.2 × 103, Mw/Mn=1.04) with poly-(propylene imine) dendrimers. A poly-styrene core molecule with a primary amine end-group was prepared by a quantitative three-step modification procedure of acid-functionalized polystyrene. On this core molecule, five different generations from PS-dendr-NH2 up to PS-dendr-(NH2)32 were constructed in high yields. The molecular structure of the block co-polymers was analyzed in detail with NMR and IR spectroscopy and electrospray mass spectrometry. With conductivity measurements and monolayer pressure-area isotherm determinations, we observed generation-dependent amphiphilic behavior. Dynamic light scattering and transmission electron microscopy showed that amphiphile geometry had a distinct effect on aggregation behavior; this is in qualitative agreement with Israelachvili's theory. Critical association concentrations determined with the pyrene probe luminescence technique were as low as 5 × 10-7 M. The amphiphiles presented here, therefore, show a resemblance to traditional block copolymers with regard to size and stability, and are similar to surfactants with respect to tuning of the shape.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021221
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  • 8
    Electronic Resource
    Electronic Resource
    Electrospray Mass Spectrometry of Poly(propylene imine) Dendrimers - The Issue of Dendritic Purity or Polydispersity (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1489-1493 
    Details
    ISSN: 0947-6539
    Keywords: defects ; dendrimers ; electrospray ; mass spectrometry ; polydispersity ; selectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electrospray mass spectrometry (ESI-MS) is used to analyze in detail the structure of the first five generations of the poly(propylene imine) dendrimers with 4-64 end groups. Although the reaction sequence to prepare these dendrimers is highly optimized, an accumulation of statistical defects is observed at higher generations. A simple statistical simulation allows the assignment of all peaks in the deconvoluted spectrum and the determination of yields for each side reaction in the formation of each generation. The fifth generation of the poly(propylene imine) dendrimer containing amine end groups, which is formed after 248 consecutive reaction steps, possesses a dendritic purity of approx. 20%, which corresponds to a polydispersity of approximately 1.002. The defects in the divergent growth patterns of dendrimers are compared to those observed in the Merrifield synthesis of polypeptides.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030916
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesis and Characterization of Axially Chiral Molecules Containing Dendritic Substituents (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 573-577 
    Details
    ISSN: 1434-193X
    Keywords: Chirality ; Dendrimers ; Chiral auxiliaries ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiomerically pure, axially chiral (S)-1,1′-bi-2-naphthol has been used as a core material to which Fréchet-type dendritic wedges of the zeroth up to the fourth generation were attached, yielding the first axially chiral dendrimers 1-5. The chiroptical features of these compounds were studied and revealed an increasing molar optical activity for higher generations of dendrimers. This effect can be explained by a larger torsional angle between the naphthyl units, caused by steric repulsions between the dendritic wedges. However, the effect is marginal, indicating a high degree of flexibility present in the axially chiral dendrimers.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    „Sergeants-and-Soldiers“-Prinzip in chiralen, säulenförmigen Stapeln scheibenförmiger Moleküle mit C3-SymmetrieWir danken Dr. H. Fischer und Dr. R. Hikmet für stimulierende Diskussionen sowie Philips Research und DSM Research für uneingeschränkt nutzbare Forschungsmittel. (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 109 (1997), S. 2763-2765 
    Details
    ISSN: 0044-8249
    Keywords: Chiralität ; Circulardichroismus ; Helicale Strukturen ; Stapelwechselwirkungen ; Supramolekulare Chemie ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19971092328
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