On the 1,4‐cis‐Polymerization of Butadiene with the Highly Active Catalyst Systems Nd(C3H5)2Cl·1.5 THF/Hexaisobutylaluminoxane (HIBAO), Nd(C3H5)Cl2· 2 THF/HIBAO and Nd(C3H5)Cl2·2 THF/Methyl‐aluminoxane (MAO) – Degree of Polymerization,Polydispersity, Kinetics and Catalyst Formation

The allylneodymium chloride complexes Nd(C₃H₅)₂Cl·1.5 THF and Nd(C₃H₅)Cl₂·2 THF can be activated by adding hexaisobutylaluminoxane (HIBAO) or methylaluminoxane (MAO) in a ratio of Al/Nd = 30 for the catalysis of butadiene 1,4‐cis‐polymerization. A turnover frequency (TOF) of about 20 000 mol butadiene/(mol Nd·h) and cis‐selectivity of 95–97% are achieved under standard conditions ([BD]₀ = 2 m, 35°C, toluene). Molecular weight determinations indicate a low polydispersity (M̄_w (LS)/M̄_n (LS) = 1–1.5), the formation of only one polymer chain per neodymium and the linear increase of the degree of polymerization (DP) with the butadiene conversion, as observed for living polymerizations. First indications of chain‐transfer reaction occur only at the highest conversion or degree of polymerization. The rate law r_P = k_P[Nd][C₄H₆]^1.8 is derived for the catalyst system Nd(C₃H₅)₂Cl·1.5 THF/HIBAO and for the system Nd(C₃H₅)Cl₂·2 THF/MAO the rate law r_P = k_P[Nd] [C₄H₆]² with k_P = 3.24 L²/(mol²·s) (at 35°C). Taking into account the Lewis acidity of the alkylaluminoxanes and the characteristic coordination number of 8 for Nd(III) in allyl complexes the formation of an η³‐butenyl‐bis(η⁴‐butadiene)neodymium(III) complex of the composition [Nd(η³‐RC₃H₄)(η⁴‐C₄H₆)₂(X‐{AlOR}_n)₂] is assumed to be a single‐site catalyst for the chain propagation by reaction of the coordinated butadiene via the π‐allyl insertion mechanism and the anti‐cis and syn‐trans correlation to explain the experimental results.     

Steroidumwandelnde Enzyme aus Mikroorganismen X. Anreicherung einer 4-En-3-oxosteroid-5α-Reduktase aus Mycobacterium smegmatis sowie Abtrennung und Anreicherung des Apoenzyms mit Hilfe der Affinitätschromatographie

The 4-en-3-oxosteroid-5α-reductase from Mycobacterium smegmatis was bound biospecifically on the affinant containing an immobilized testosterone ligand. The enzyme obtained by elution with ethylene glycol and urea in a 32 fold purity has a S. A. of 8.73 × 10^?3 μM androstenedione min^?1 mg^?1. The coenzyme (FAD) could be separated from the immobilized enzyme substrate complex on the affinity matrix, in the presence of (NH₄)₂SO₄ at pH 3.0. After elution of the apoenzyme 97% of the initial enzyme activity was obtained by incubation with FAD. The reactivated enzyme results in a 40 fold enrichment.     

Cationic polymerization of α·β-disubstituted olefins. Part XI. Polymerization of 2-chloroethyl propenyl ether catalyzed by BF3·O(C2H5)2

2-Chloroethyl propenyl ether (CEPE) was synthesized, and its cationic polymerizability by BF₃·O(C₂H₅)₂ and the steric structure of the resulting polymer were studied. In the polymerization in toluene at ?78°C, the rate of consumption of monomers decreased in the following order: cis-CEPE > 2-chloroethyl vinyl ether > trans-CEPE. The steric structure of the β-methyl group of the resulting polymer was determined quantitatively on the basis of the NMR spectrum of the β-methyl protons decoupled from β-methine protons. In the polymerization of CEPE in toluene at ?78°C, the polymer obtained from trans-CEPE was rich in threo-meso structure whilst cis-CEPE gave a polymer containing almost the same amount of threo-meso and erythro-meso structures. With methylene chloride as solvent, the amount of threo-meso structure increased and that of erythro-meso structure decreased for the polymer obtained from cis-CEPE. The steric structure of the polymer obtained from trans-CEPE was independent of the nature of the solvent used. The effect of polymerization temperature on the steric structure of the polymers was also investigated.     

Beiträge zur lösungsviskosität. I. Über zusammenhänge zwischen kH (HUGGINS) und dem ausdehnungs-koeffizienten αη und zwischen den verschieden definierten grenzviskositätszahlen [η]Θ, [η]T und [η]R untereinander

On the basis of literature results and considerations established on these, a relation is given between k_H (HUGGINS) and α_η (FLORY ): and another between intrinsic viscosities [η]Θ, [η]_T and [η]_R which are differently defined and differently determinable: The applicability of this last relation for the calculation of the real density of a coil at the Θ-point is discussed.     

Darstellung und [η]-M̄-Beziehung von Mikrogelen aus polyvinylalkohol

Microgels were prepared by crosslinking of poly(vinylalcohol)s with different molecular weights (saponification degree: 88 mole-%) with glutaraldehyde in aqueous solutions. The degree of crosslinking was varied between 0 and 10% (i.e. 10 crosslinks per 100 structural units). Viscosity measurements showed that the viscosity number [η] of the microgels decreases considerably with increasing degree of crosslinking — as to be expected with increasing mean density of the random coils: The mean coil volume in aqueous solution shrinks by introducing 10 crosslinks per 100 structural units to 1/10 of the primary volume. A comparison of the logarithmic [η]-M?-plots of our microgels showed a linear decrease of the exponent a, from a = 0,73 (uncrosslinked) to a = 0,16, with increasing degree of crosslinking. By extrapolation, with a degree of crosslinking of 13% (i.e. 13 cross-links per 100 structural units of polymer chain), it was found that [η] becomes independent of the molecular weight of the primary PVAl-samples.     

Über den thermischen abbau des poly(ε-caprolacton)s

The thermal and electron impact induced degradation reactions of poly(ε-caprolactone) {poly[oxy(1-oxohexamethylene)]} were investigated in a mass spectrometer. It can be shown that the favorated thermal degradation reaction is the cleavage of the ester bond and formation of ω-hydroxyl and ketene endgroups (Eq. (iii)) and with a lower intensity the cleavage of the O? CH₂-bond and formation of carboxyl-and pentenyl endgroups (Eq. (vii)). After electron impact and fragmentation of the pyrolysis products to carboxonium ions an elimination of caprolactone via a “zip”-mechanism can be observed (Eq. (v)).     

Zur copolymerisation von α-methylstyrol und butadien III. Das NMR-spektrum der sequenzen mit zentraler α-methylstyroleinheit

220 MHz proton resonance spectra of copolymers from α-methylstyrene and butadiene have been investigated. Model compounds have been prepared by a lithiumbutyl initiated copolymerisation in tetrahydrofurane at ?75°C. The NMR spectra of the phenyl and α-methyl group are interpreted by signals from configurational and compositional triads with a central χ-methylstyrene unit. The chemical shift of the triads, possessing a central α-methyl styrene unit, takes place to lower field in the α-methyl region to such an extend that no strong overlapping with the signals of the configurational triads takes place. In the region of the phenyl protons configurational and compositional triads are overlapping each other. Using 3,4,5-trideuterio-α-methylstyrene it is possible to assign configurational and compositional triads in the resonance spectrum of the ortho-phenylprotons.     

Polymere aus cyclischen Dilactamen. II. Copolymerisation des 2.5-dioxopiperazins mit ε-Caprolactam

The copolymerization of 2.5-dioxopiperazine (DOP) and ε-caprolactam (CL) has been studied for mole ratios DOP/CL between 1:0.75 and 1:0.25 at temperatures between 150 and 170°C using benzoic acid and AH salt (salt of hexamethylenediamine and adipic acid) as initiators (between 0.5 and 5 mole-%). The dependence of conversion on time is very complicated due to the strong differences in reactivity of the monomers and the accompanying side reactions (degradation). The calculated equilibrium constants approach a limiting value at infinite high initiator concentration. The limiting value for caprolactam is identical with the equilibrium constant of the homopolymerization reported in literature. The equilibrium constant for DOP is estimated to be smaller than 0.4 kg/mole at 160°C.     

Zur Taktizität von Poly(α-methylstyrol), 5. Die Abhängigkeit der Taktizität von der Reaktionstemperatur und der Anfangsmonomerkonzentration

The tacticity of poly(α-methylstyrene) was measured by ¹H NMR spectroscopy. The polymerisation initiated in tetrahydrofuran by butyllithium gives a dependence on the initial monomer concentration and a S-shaped plot of log(m/r) vs. 1/T, which is not influenced by a stronger reaction medium like 1,2-dimethoxyethane or hexamethylphosphoric triamid or by addition of LiB(C₆H₅)₄. The activation parameters of the two straight lines A and B limiting the experimental curve are according to the equation The temperature dependence of the propagation rate constant k_w measured dilatometricly between ?11°C and ?75°C gives a linear Arrhenius plot. The rate constant of depolymerisation k_d was calculated using the equilibrium monomer concentration. The activation parameters are The influence of ionic dissociation on the tacticity is discussed. The results lead to the conclusion, that the contact ion pair, the solvent separated ion pair, and the free anion generate tacticities, which are undistinguishable by the applied experimental methods.     

Molecular Motions in the Supramolecular Complexes between Poly(ε‐caprolactone)‐Poly(ethylene oxide)‐Poly(ε‐caprolactone) and α‐ and γ‐Cyclodextrins

The structure and molecular motions of the triblock copolymer PCL‐PEO‐PCL and its inclusion complexes with α‐ and γ‐cyclodextrins (α‐ and γ‐CDs) have been studied by solid‐state NMR. Different cross‐polarization dynamics have been observed for the guest polymer and host CDs. Guest–host magnetization exchange has been observed by proton spin lattice relaxation T₁, proton spin lattice frame relaxation T_1ρ and 2D heteronuclear correlation experiments. A homogeneous phase has been observed for these complexes. Conventional relaxation experiments and 2D wide‐line separation NMR with windowless isotropic mixing have been used to measure the chain dynamics. The results show that for localized molecular motion in the megahertz regime, the included PCL block chains are much more mobile than the crystalline PCL blocks in the bulk triblock copolymer. However, the mobility of the included PEO block chains is not very different from the amorphous PEO blocks of the bulk sample. The cooperative, long chain motions in the mid‐kilohertz regime for pairs of PCL‐PEO‐PCL chains in their γ‐CD channels seem more restricted than for the single PCL‐PEO‐PCL chains in the α‐CD channels, however, they are not influencing the more localized, higher frequency megahertz motions.     

Zur Taktizität von Poly(α-methylstyrol), 6. Zum stereoregulierenden Mechanismus der Polyreaktion des α-Methylstyrols mit Butyllithium in Tetrahydrofuran

Some models of the stereoregulating mechanism of the polymerisation of α-methylstyrene with butyllithium in tetrahydrofuran are discussed. A mechanism is proposed, in which the depolymerisation of the polymer chain and an isomerisation reaction of the active site change the tacticity generated by each propagation step. The isomerisation reaction is interpreted as a dissociation of the active lithiumorganic compound occurring with racemisation. The quantitative calculation of the tacticity based on the mechanism without depolymerisation using kinetic data agrees well with the experimental dependence of the tacticity on reaction temperature and initial monomer concentration. The activation parameters of the isomerisation reaction used in this treatment are (index r = racemic, m = meso):      

Polykondensationen mit α-aminocarbonsäureestern. IV. Komplexe des zinntetrachlorids mit den äthylestern und dioxopiperazinen des glycins und des L-leucins

Tin tetrachloride forms a 1:2 complex with glycine ethylester, 1:1 complexes with L-leucine ethylester, 2,5-dioxopiperazine resp. 3,6-diisobutyl-2,5-dioxopiperazine. Complex formation takes place via the amine groups as well as via the ester carbonyl groups as could be shown by IR spectroscopy. The relative amount of each type of bonding depends on temperature (+22 to ?80°C.) and solvent (n-hexane and benzene) from which the complexes were precipitated. A coordination number of 5 seems to be probable for the 1:1 complexes.     

Synthesis of polypropene-graft-poly(ε-caprolactone)

The copolymerization of polypropene (PP) with maleic anhydride (MA) was carried out at 120°C in xylene with benzoyl peroxide (BPO) as initiator. The resulting product was identified as poly(propene-co-maleic anhydride) obtained by reaction of the double bond of maleic anhydride with free radicals created on the PP chain. In the next step this copolymer was reacted with functional poly(ε-caprolactone) (PCL) by a co-melting method to give rise to a graft copolymer. The optimum time for the second step was found to be around 6 h (at 120°C). X-ray diffraction measurements and DSC characterization of PP-g-PCL have shown that the melting point of the PP phase in the graft copolymers is lower than that of homopolypropene and that its glass transition temperature increases with increasing of PCL grafts.     

Vinylpolymerisation mit reduzierenden Übergangsmetallverbindungen, 3. Polymerisation in gegenwart von initiatorsystemen aus vanadium(II)- und vanadium (III)-chlorid sowie organischen halogenverbindungen

The polymerization of methyl methacrylate initiated by the redox system vanadium(III) chloride/carbon tetrachloride was studied. The rate of polymerization can be described by the equation R_p = k · [VCl₃]^0,5·[CCl₄]^0,5·[MMA]^1,0. The overall activation energies were estimated to be 74,5 kJ·mol^?1 for VCl₃/CCl₄ and 59,5 kJ·mol^?1 for VCl₂/CCl₄. Vanadium (II) chloride acts as a retarder in the polymerization of styrene initiated by 2,2′-azoisobutyronitrile (AIBN). The polymerization of acrylonitrile and methyl methacrylate is inhibited by vanadium (II) chloride. The polymerization of acrylonitrile initiated by AIBN is retarded by vanadium (III) chloride.     

Spaltung des α-L-Arabinofuranosids, β-D-Glucopyranosids und β-Cellobiosids von 4-Nitrophenol durch Enzyme verschiedener Pilze — ein Beitrag in Verbindung mit Versuchen zur Steigerung der Selektivität der Tumortherapie

To carry out long-term experiments as part of a therapy concept of malignant tumours using inactive transport forms of cancerostatic substances and their specific cleavage in the acidic pH region of the tumours by application of extraneous enzymes, we require enzymes with similar catalytic and pharmacokinetic properties which differ from each other in immunological respect. In the search for such enzymes, the α-L-arabinofuranosidases from 12 different fungi, among them 9 basidiomycetes, were studied. The enzymes mentioned were demonstrable in all fungi. Optimum pH values ranged between 2.5 and 5.5. The Km values for the cleavage of α-L-arabinofuranoside were, in most cases, 0.5 to 1.8 moles · liter^?1 · 10^?3. With regard to pH dependence, the α-L-arabino-furanosidases of most of the fungi investigated proved adequate for the long-term trials envisaged. 4-nitrophenyl-β-D-glucopyranoside and -β-cellobioside were also cleaved by enzyme preparations of all the 11 fungi investigated. The β-D-glucopyranosidases showed a less favourable pH dependence than the α-L-arabinofuranosidases. The cleavage of 4-nitrophenyl-β-cellobioside, on the contrary, showed mostly a comparatively favourable pH dependence. On the basis of the coinciding optimal pH values and the occurrence of 4-nitrophenyl-β-D-glucopyranoside as an intermediate product in the cleavage of the corresponding cellobioside, we assume that both substrates are cleaved by β-glucosidase. Because the occurrence of the glucoside during the cleavage of cellobioside is undesirable for the therapeutic trial, a method is proposed for selection of an appropriate cellobioside splitting enzyme basing on the present studies and the relevant literature.     

Recognition of E-cadherin on epithelial cells by the mucosal T cell integrin αM290β7 (αEβ7)

The integrin α_M290β7 on the surface of a T cell hybridoma, MTC-1, mediated adhesion of these cells to the mouse epithelial cell line CMT93. This interaction was critically dependent on the presence of divalent cations; Mn²⁺ strongly promoted adhesion, Ca²⁺ was ineffective and Mg²⁺ gave intermediate results. Antibodies to molecules on the surface of CMT93 cells were tested for inhibition of adhesion. One monoclonal antibody (mAb) against E-cadherin, ECCD-2, was found to have significant inhibitory activity. Other mAb to E-cadherin and antibodies to other molecules had no effect. To show that inhibition by ECCD-2 was specific for adhesion mediated by α_M290β7, MTC-1 cells were induced to adhere to CMT93 via the LFA-1/ICAM-1 pathway. For this purpose, the epithelial cells were treated with interferon-γ and tumor necrosis factor-α to induce ICAM-1 expression and, in addition, α_M290β7 on MTC-1 cells was down-regulated by culturing the cells in the absence of transforming growth factor β. Under these circumstances adhesion of MTC-1 cells to CMT93 was inhibited by an antibody to LFA-1 but not by ECCD-2. Transfection of mouse L cells with cDNA for mouse E-cadherin enabled MTC-1 cells to adhere to them through the α_M290β7 integrin; this interaction was inhibited both by ECCD-2 and by blocking antibody against the integrin. These data strongly suggest that E-cadherin is a principal ligand for α_M290β7.     

The production of 3aα-H-4α-(3′-propionic acid)-5α-hydroxy-7aβ-methylhexahydro-1-indanone-δ-lactone by Nocardia restricta mutants

Two mutants of Nocardia restricta breakdown androst-4-ene-3,17-dione into 3aα-H-4α-(3′-propionic acid)-5α-hydroxy-7aβ-methylhexahydro-l-indanone-δ-lactone. The metabolic intermediates formed are very different in each mutant. One uses certain aromatic compounds very slowly. A degradation pathway for steroids by Nocardia restricta has been proposed.