Quantitative studies of block copolymers and their containing homopolymer components by diffusion ordered spectroscopy

Several polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) and polyisoprene-b-PMMA (PI-b-PMMA) block copolymers are studied with high-resolution diffusion ordered spectroscopy (DOSY) in order to quantify the amounts and molar masses of the copolymers and the containing homopolymers. These studies are particularly challenging because these homopolymers and one block of the copolymers consist of the same monomer type with different molar masses and compositions and cause a total overlap of these polymer components in the NMR spectra. However, DOSY can be proven as a powerful tool for separation and quantification of these moieties. Whereas exponential fittings only deliver averaged diffusion data, biexponential fittings of the individual magnetization curves can separate the overlapping polymer parts. This DOSY approach can be successfully tested for different blends of PS as well as PS and PS-b-PMMA of different molar masses and weighed compositions. The DOSY separation is also compared to size exclusion chromatography (SEC). In the case of the PS-b-PMMA and PI-b-PMMA block copolymers, DOSY identifies the contaminations with homopolymers, quantifies their individual amounts as well as determines the molar masses of both the copolymers and homopolymers. Two mathematical evaluations are used for quantifying these homopolymers with DOSY. These results are compared with the online coupling of SEC and NMR

Efficient synthesis of macromolecular DO3A@Gn derivatives for potential application in MRI diagnostics: from polymer conjugates to polymer nanoparticles

Herein, the synthesis of three different macromolecular DO3A@Gn conjugates based on poly(2-oxazoline)s is presented. Therefore, poly(2-methyl-2-oxazoline) is synthesized by a ring-opening, cationic polymerization and the polymerization is terminated with DO3A(tBu)3. The best results are obtained after 48 h at 120 °C with degree of termination of 86%. After deprotection of the DO3A ligand and complexation with Gn3+, relaxivity as measured with a magnetic field strength of 9.4 T (400 MHz) reveals values for r1 of up to 2.32 mm−1 s−1. The concept is extended to a block copolymer based on 2-heptyl-2-oxazoline and 2-methyl-2-oxazoline that is again terminated with DO3A(tBu)3 to form micelles with a size of 12.6 ± 0.7 nm after DO3A(tBu)3 termination and deprotection of the 1,4,7,10-tetraazacyclododecane-N,N,N,N-tetraacetic acid ligand. After complexation with Gn3+, relaxivity r1 is 10.1 mm−1 s−1 as determined from the slope of the plot of 1/T1 against the gadolinium(III) concentration at 9.4 T. Finally, crosslinked nanoparticles are prepared from amphiphilic macro-monomers that form micelles in water and are crosslinked throughout the core in the presence of azoisobutyronitrile (AIBN). The nanoparticle is 32.9 ± 7.8 nm in size after Gn3+ complexation and reveals a relaxivity r1 of 6.77 mm−1 s−1

Synthese, Aufbau und Eigenschaften käfigartiger vinyl- und allylsilylierter Kieselsäuren

Durch Umsatz des Tetramethylammoniumsilicats [N(CH3)4]8Si8O20 · 69 H2O mit Vinyldimethylchlorsilan (I) bzw. Divinyltetramethyldisiloxan oder Allydimethylchlorsilan wurden der Vinyldimethylsilylkieselsäureester [CH2CHCH2(CH3)2Si]8Si8O20 und Allyldimethylsilyl-kieselsäureester [CH2CHCH2(CH3)2Si]8Si8O20 erhalten. Mit Hilfe der Gaschromatographie, Massenspektroskopie sowie 1H-und 29Si-NMR wurden die Verbindungen charakterisiert und eine käfigartig aufgebaute Doppelvierring (D4R)-Struktur des Kieselsäuregerüsts nachgewiesen, an deren 8 terminalen O-Atomen des Kieselsäuregerüsts nachgewiesen, an deren 8 terminalen O-Atomen des Kieselsäuregerüsts Vinyldimethylsiyl- bzw. Allydimethylsilylgruppen gebunden sind. Durch Silylierung mit I und Trimethylchlorsilan sind in Abhängigkeit vom Mischungsverhältnis Vinyldimethylsilytrimethysily1-D4R-Kieselsäureester mit einer mittleren Anzahl ungesättigter Gruppen < 8 herzustellen

Eta invariants for flat manifolds

Using H. Donnelly result from the article "Eta Invariants for G-Spaces" we calculate the eta invariants of the signature operator for almost all 7-dimensional flat manifolds with cyclic holonomy group. In all cases this eta invariants are an integer numbers. The article was motivated by D. D. Long and A. Reid article "On the geometric boundaries of hyperbolic 4-manifolds, Geom. Topology 4, 2000, 171-178Comment: 18 pages, a new version with referees comment

Hierarchical assembly of an interlocked M8L16 container

The self‐assembly of eight PdII cations and sixteen phenanthrene‐derived bridging ligands with 60° bite angles yielded a novel M8L16 metallosupramolecular architecture composed of two interlocked D4h‐symmetric barrel‐shaped containers. Mass spectrometry, NMR spectroscopy, and X‐ray analysis revealed this self‐assembled structure to be a very large “Hopf link” catenane featuring channel‐like cavities, which are occupied by NO3− anions. The importance of the anions as catenation templates became imminent when we observed the nitrate‐triggered structural rearrangement of a mixture of M3L6 and M4L8 assemblies formed in the presence of BF4− anions into the same interlocked molecule. Furthermore, the densely packed structure of the M8L16 catenane was exploited in the preparation of a hexyloxy‐functionalized analogue, which further self‐assembled into vesicle‐like aggregates in a reversible manner

Biosynthetic plasticity enables production of fluorinated aurachins

Room for a halogen: The plasticity of the aurachin biosynthetic pathway in the myxobacterium S. erecta was explored for the use of fluoro- and chloroanthranilic acids. Incorporation of the unnatural precursors was quantified. Three fluorinated aurachin analogues were produced in sufficient quantity to enable their antibacterial activities to be assessed. Enzyme promiscuity has important implications in the field of biocatalysis. In some cases, structural analogues of simple metabolic building blocks can be processed through entire pathways to give natural product derivatives that are not readily accessible by chemical means. In this study, we explored the plasticity of the aurachin biosynthesis pathway with regard to using fluoro- and chloroanthranilic acids, which are not abundant in the bacterial producers of these quinolone antibiotics. The incorporation rates of the tested precursor molecules disclosed a regiopreference for halogen substitution as well as steric limitations of enzymatic substrate tolerance. Three previously undescribed fluorinated aurachin derivatives were produced in preparative amounts by fermentation and structurally characterized. Furthermore, their antibacterial activities were evaluated in comparison to their natural congener aurachin D

Morphological control of heteroleptic cis- and trans-Pd2L2Lʹ2 cages

Control over the integrative self-sorting of metallo-supramolecular assemblies has recently generated significant interest as it opens up possibilities of introducing increased complexity and function into a single self-assembled architecture. Here, the relationship between the geometry of three ligand components and morphology of three self-sorted heteroleptic [Pd2L2Lʹ2]4+ cages is examined. Pd-mediated assembly of two bis-monodentate pyridyl ligands with native bite angles of 75° and 120° affords a cis-[Pd2L2Lʹ2]4+ cage while the same reaction with two ligands bearing bite angles of 75° and 60° forces an anti-conformation for latter ligand, leading to an unprecedented, self-penetrating structural motif; a trans-[Pd2(anti-L)2Lʹ2]4+ heteroleptic cage bearing a “doubly-bridged figure-eight” topology. Each heteroleptic assembly can be accessed through cage-to-cage conversion of their homoleptic precursors, and notably, morphological control of [Pd2L2Lʹ2] cages is achieved through selective ligand displacement transformations in a system of three ligands and at least six possible cage products

Myxococcus xanthus as host for the production of benzoxazoles

Benzoxazoles are important structural motifs in pharmaceutical drugs. Here, we present the heterologous production of 3-hydroxyanthranilate-derived benzoxazoles in the host bacterium Myxococcus xanthus following the expression of two genes from the nataxazole biosynthetic gene cluster of Streptomyces sp. Tü 6176. The M. xanthus expression strain achieved a benzoxazole titer of 114.6±7.4 mg L−1 upon precursor supplementation, which is superior to other bacterial production systems. Crosstalk between the heterologously expressed benzoxazole pathway and the endogenous myxochelin pathway led to the combinatorial biosynthesis of benzoxazoles featuring a 2,3-dihydroxybenzoic acid (2,3-DHBA) building block. Subsequent in vitro studies confirmed that this crosstalk is not only due to the availability of 2,3-DHBA in M. xanthus, rather, it is promoted by the adenylating enzyme MxcE from the myxochelin pathway, which contributes to the activation of aryl carboxylic acids and delivers them to benzoxazole biosynthesis

MeSi(CH2SnRO)3 (R = Ph, Me3SiCH2): Building blocks for triangular-shaped diorganotin oxide macrocycles

The syntheses of the novel silicon-bridged tris(tetraorganotin) compounds MeSi(CH2SnPh2R)3 (2, R=Ph; 5, R=Me3SiCH2) and their halogen-substituted derivatives MeSi(CH2SnPh(3−n)In)3 (3, n=1; 4, n=2) and MeSi(CH2SnI2R)3 (6, R=Me3SiCH2) are reported. The reaction of compound 4 with di-t-butyltin oxide (t-Bu2SnO)3 gives the oktokaideka-nuclear (18-nuclear) molecular diorganotin oxide [MeSi(CH2SnPhO)3]6 (7) while the reaction of 6 with sodium hydroxide, NaOH, provides the trikonta-nuclear (30-nuclear) molecular diorganotin oxide [MeSi(CH2SnRO)3]10 (8, R=Me3SiCH2). Both 7 and 8 show belt-like ladder-type macrocyclic structures and are by far the biggest molecular diorganotin oxides reported to date. The compounds have been characterized by elemental analyses, electrospray mass spectrometry (ESI-MS), NMR spectroscopy, 1H DOSY NMR spectroscopy (7), IR spectroscopy (7, 8), and single-crystal X-ray diffraction analysis (2, 7, 8)

Mechanistic Interplay between Light Switching and Guest Binding in Photochromic [Pd 2 Dithienylethene 4 ] Coordination Cages

Photochromic [Pd2L4] coordination cages based on dithienylethene (DTE) ligands L allow triggering guest uptake and release by irradiation with light of different wavelengths. The process involves four consecutive electrocyclic reactions to convert all chromophores between their open and closed photoisomeric forms. So far, guest affinity of the fully switched species was elucidated, but mechanistic details concerning the intermediate steps remained elusive. Now, a new member of the DTE cage family allows unprecedented insight into the interplay between photoisomerization steps and guest location inside/outside the cavity. Therefore, the intrinsic chirality of the DTE backbones was used as reporter for monitoring the fate of a chiral guest. In its "open" photoisomeric form (o-L, [Pd2(o-L)4] = o-C), the C2-symmetric DTE chromophore quickly converts between energetically degenerate P and M helical conformations. After binding homochiral 1R-(-) or 1S-(+) camphor sulfonate (R-CSA or S-CSA), guest-to-host chirality transfer was observed via a circular dichroism (CD) signal for the cage-centered absorption. Irradiating the R/S-CSA@o-C host-guest complexes at 313 nm produced configurationally stable "closed" photoisomers, thus locking the induced chirality with an enantiomeric excess close to 25%. This value (corresponding to chiral induction for one out of four ligands), together with DOSY NMR, ion mobility mass spectrometry, and X-ray structure results, shows that closure of the first photoswitch is sufficient to expel the guest from the cavity