Untersuchungen zum UV/VIS-Spektralverhalten von Azofarbstoffen. XV. Eine Analyse der Absorptionsspektren von 4,4′-Diaminoazobenzenen

Studies on UV/VIS Absorption Spectra of Azo Dyes. XV. An Analysis of the Absorption Spectra of 4,4′-Diaminoazobenzenes In the visible absorption spectrum 4,4′-bis-diethylaminoazobenzene shows two absorption maxima (λ_max = 426 nm and λ_max = 477 nm) with high intensity. Quantum chemical calculations and examination by peak separation of six 4-substituted azobenzenes and six 4′-substituted 4-diethylaminoazobenzenes ( 1a–k ) indicate that the longest wavelength band is due to a n-π* transition and the other band is due to a π-π*-transition. This is verified using an increment system for n-π* absorption maxima. A linear relation is found between intensity ratios of the two bands and the HAMMETT -σ-constants of the substituents. With increasing electron releasing tendency of the substituents the absorption intensity of the n-π*-band increases.     

1H- und 13C-NMR-spektroskopische Messungen und MO-Berechnungen zur π-Elektronenstruktur von p,p′-disubstituierten trans-Stilbenen und substituierten trans-β-Styryl-methyl-sulfonen

¹H and ¹³C n.m.r. Spectroscopical Measurements and HMO-π-Calculations to the π-Electronic Structure of p,p′-Disubstituted trans-Stilbenes and Substituted trans-β-Styryl-methyl-Sulfones The ¹H and ¹³C n.m.r. spectra have been measured for a series of donator-acceptor-disubstituted trans-stilbenes 1 and monosubstituted β-styryl-methyl-sulfones 2 . The ¹³C n.m.r.-signals have been identified by comparison with empirical calculated chemical shifts and quantum chemical determined HMO-π-electrons densities. The influence of substitutents to the experimental chemical shifts are discussed in detail. For 1 and 2 exist linear correlations between chemical shifts and HAMMETT values, and π-electron densities, respectively.     

Copolymerization of alkyl α-chloroacrylates with methyl methacrylate

Hexyl α-chloroacrylate (HCA) and cyclohexyl α-chloroacrylate (CCA) have been copolymerized with methyl methacrylate (MMA) in toluene at 55°C using azobisisobutyronitrile (AIBN) as initiator. Copolymer compositions have been determined both by ¹H NMR and elemental analyses. For copolymerization of MMA (M1) with HCA (M2), the reactivity ratios (RR) are r₁ = 0.47 ± 0.19 and r₂ = 0.81 ± 0.51 and with CCA the values are r₁ = 0.76 ± 0.31 and r₂ = 2.30 ± 1.73. Thermal properties of these copolymers have also been investigated.     

Substituenteneffekte in den 13C-NMR-Spektren von diastereomeren Chalkondihalogeniden. VIII. Untersuchungen an α- und β-Halogendihydrochalkonen und Berechnung von 13C-chemischen Verschiebungen bei diastereomeren Chalkondihalogeniden und Chalkonhalogenhydrinen

Substituent Effects in ¹³C-N.M.R. Spectra of Diastereomeric Chalcone Dihalogenides. VIII. Investigations of α- and β-Halogene Dihydrochalcones and Calculation of ¹³C-chemical Shifts of Diastereomeric Chalcone Dihalogenides and Chalcone Halogenohydrins The chemical shifts of C-α and C-β in the ¹³C-n.m.r. spectra are determined and compared with calculated values from an incremental system and Taft relationship. The correlations are extended for erythro and threo isomers of halohydrins and diastereometric dihalogenides 6 – 18 . The chemical shifts of C-α and C-β atoms of 6 – 18 are described in the dependence of the shifts calculated by an incremental system. Excellent correlations allowed the computation of chemical shifts of C-α and C-β for diastereomeric α,β-disubstituted dihydrochalcone derivatives likely 6 – 18 in advance.     

Trans- α, β-ungesättigte Fettsäuren und deren Reduktionsprodukte mit Lithium-Aluminium-Hydrid und Diisobutyl-Aluminium-Hydrid

Trans-α,β-Unsaturated Fatty Acids and Products formed by their Reduction with Lithium-Aluminium-Hydride and Di-isobutyl-Aluminium-Hydride A method for the preparation of pure methyl esters of α,β-unsaturated fatty acids is described. The reduction of these esters with LiAlH₄ led to poor yields of α,β-unsaturated alcohols. Saturated alkanols and aldehydes were mainly formed. Di-isobutyl aluminium hydride gave near quantitative yields of α,β-unsaturated alcohols. The reaction was studied with the help of gas chromatography using strongly polar stationary phases.     

Über die γ-strahleninduzierte polymerisation an oberflächen von feststoffpulvern

Experiments with fine grained powders of silica gel, kaolinite and calciumcarbonate have been carried out, in order to prove whether the ⁶⁰Co-γ-preirradiation method is applicable for grafting methylmethacrylate (MMA) and styrene onto the surface of these powders. It is demonstrated that significant amounts of polymer may be grafted by this method. The degree of grafting (PG) increases with increasing absorbed dose and approaches a limiting value (PG^max) at high doses. Measured values of PG_F^max (expressed in units of g polymer per m² surface of powder) are the same within an order of magnitude for all substances. Therefore, it is concluded, that the polymerization is started by activecentersgenerated previously at the powder surface and that the maximum concentration of active centers attainable at the particle surface is about the same for all powders. Differences of PG^max_f-values obtained with the various substances are presumably due to the fact that the grafted powders contain a fraction of not covalently bonded and in spite of this not extractable polymer in narrow pores. Evidence for this was obtained by initiating the polymerization of MMA with AIBN at 50°C in the presence of a highly porous sample of silica gel. In this case PG_F = 2 × 10^?4g polymer/m² was obtained which compares with PG^max_F = 8 × 10^?4g polymer/m² for the preirradiated solid. It is assumed that at least a portion of the polymer grafted by the preirradiation method is not bonded covalently. The polymer portion which is not bonded covalently and is not extractable should be a function of the number and the width of the pores. It should vary, therefore, with the substance.     

Thermal decomposition behavior of γ‐irradiated poly(vinyl acetate)/poly(methyl methacrylate) miscible blends

Miscible polymer blends based on various ratios of poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA) were prepared in film form by the solution casting technique using benzene as a common solvent. The thermal decomposition behavior of these blends and their individual homopolymers before and after γ‐irradiation at various doses (50–250 kGy) was investigated. The thermogravimetric analysis technique was utilized to determine the temperatures at which the maximum value of the rate of reaction (T_max) occurs and the kinetic parameters of the thermal decomposition. The rate of reaction curves of the individual homopolymers or their blends before or after γ‐ irradiation displayed similar trends in which the T_max corresponding to all polymers was found to exist in the same position but with different values. These findings and the visual observations of the blend solutions and the transparency of the films gave support to the complete miscibility of these blends. Three transitions were observed along the reaction rate versus temperature curves; the first was around 100–200°C with no defined T_max, which may arise from the evaporation of the solvent. The second T_max was in the 340–380°C range, which depended on the polymer blend and the γ‐irradiation condition. A third transition was seen in the rate of reaction curves only for pure PVAc and its blends with PMMA with ratios up to 50%, regardless of γ‐ irradiation. We concluded that γ‐irradiation improved the thermal stability of PVAc/PMMA blends, even though the PMMA polymer was degradable by γ irradiation. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1773–1780, 2006     

Synthese und Charakterisierung von O2S2 — und N2S2‐Übergangsmetallkomplexen ausgehend von β‐Chlor) β‐trifluormethylvinylaldehyden

Synthesis and Characterization of O₂S₂ — and N₂S₂‐Transition Metal Complexes Starting from β‐Chloro‐β‐trifluoromethyl Vinylaldehydes The syntheses of complexes 4 and 5 with O₂S₂ ‐and N₂S₂ — donor atom sets are described as one‐step procedures. Their structures were confirmed by NMR, IR, UV‐ VIS and MS spectroscopy. One nickel complex 5a was determined by X‐ray structure analysis whereas the Cu^II complexes were studied by EPR spectroscopy.     

α-Substituierte Phosphonate. XXXIV. Zur Veresterung und N-Formylierung von α-Aminomethan-bisphosphonsäuren mit Orthoameisensäuretriethylester

α-Substituted Phosphonates. XXXIV. Esterification and N-Formylation of α-Aminomethane-bisphosphonic Acids with Triethylorthoformate In contrast to simple mono- and bisphosphonic acids esterification of dialkylaminomethanebisphosphonic acids with orthoformate (OAE) proceeds very slowly. Monoalkyl and monoarylaminomethanebisphosphonic acids, respectively react with OAE in constrast to analogous hydroxy compounds more readily primarily by formylating the N-atom and then esterification to formyl aminomethane bisphosphonictetraesters 10 . Acetaminomethanephosphonic acid ( 12 ) reacts without N-formylation, while the aminomethanebisphosphonic acid ( 14 ) reacted to give a mixture of mono- and bis-formylated products 15 and 16 . By acidic hydrolysis of 10 the ester- and formylgroups are splitt off, while the ester group can selectively be removed by reaction with Me₃SiBr/H₂O. – As shown by ¹H-, ¹³C- and ³¹P-n.m.r. spectroscopy the phosphorylated formamides 10 exists in two rotameres, the ratio depending on the solvent. The n.m.r. signals could be correlated to E-resp. Z-form undoubtedly by using shift-agents or the benzene-diluting technique. A rotational barrier of 22,8 kcal for 10c could be calculated.     

Photochemie von Aminoketonen. IV [1]. Synthese von 3-Aryl-pyrrolidinolen-(3) durch Photocyclisierung von β-Amino-propiophenonen

Photochemistry of Aminoketones. IV. Synthesis of 3-Aryl-pyrrolidinols-(3) via Photocyclization of β-Amino-propiophenones Photolysis (λ_irr ≥ 300 nm) of N-benzyl-N-benzoyl-β-aminopropiophenones 6–9 in abs. ether affords a 47–50% yield of N-benzoyl-pyrrolidinols 12–18 . The relative configurations of the diastereomeric 12–18 are determined by ¹H-n.m.r. spectroscopy. The different behaviour of the N-acylated 6–9 in contrast to N,N-dialkyl-β-aminopropiophenones is explained by assumption of a dipol-dipol interaction between the keto and the amido carbonylgroups in the n,π*-excited state.     

Radiation-induced copolymerization of α,β,β-trifluoroacrylonitrile with α-olefin

Homopolymerization and copolymerization of α,β,β-trifluoroacrylonitrile (FAN) with γ-olefins were carried out in bulk by γ-ray irradiation at 25°C. FAN gives very small quantities of brown and greasy low molecular weight polymer. Cyano groups in FAN polymer were found to be readily hydrolyzed to acid amide groups in the atmosphere. FAN was found to copolymerize with ethylene, propylene, and isobutylene via a radical mechanism to form equimolar copolymers in a wide range of monomer compositions. The polymerization rate increases linearly with FAN fraction in the monomer mixture. These copolymers are also hydrolyzed in the atmosphere, and the hydrolysis proceeds with more difficulty for the copolymer with higher α-olefin. The reactivity ratios r₁ (FAN) and r₂ (α-olefin) were determined to be 0.01 and 0.12 for the FAN/ethylene copolymerization and 0.01 and 0.07 for the FAN/propylene copolymerization. These results confirm that an alternating copolymerization takes place in the FAN/α-olefin system.     

Asymmetric 1,3‐Dipolar Cycloaddition Reaction between α,β‐Unsaturated Aldehydes and Nitrones Catalyzed by Well‐Defined Iridium or Rhodium Catalysts

Reaction of the complexes (S_M,R_C)‐[(η⁵‐C₅Me₅)M{(R)‐Prophos}(H₂O)](SbF₆)₂ (M=Rh, Ir) with α,β‐unsaturated aldehydes diastereoselectively gave complexes (S_M,R_C)‐[(η⁵‐C₅Me₅)M{(R)‐Prophos}(enal)](SbF₆)₂ which have been fully characterized, including an X‐ray molecular structure determination of the complex (S_Rh,R_C)‐[(η⁵‐C₅Me₅)Rh{(R)‐Prophos}(trans‐2‐methyl‐2‐pentenal)](SbF₆)₂. These enal complexes efficiently catalyze the enantioselective 1,3‐dipolar cycloaddition of the nitrones N‐benzylideneaniline N‐oxide and 3,4‐dihydroisoquinoline N‐oxide to the corresponding enals. Reactions occur with excellent regioselectivity, perfect endo selectivity and with enantiomeric excesses up to 94 %. The absolute configuration of the adduct 5‐methyl‐2,3‐diphenylisoxazolidine‐4‐carboxaldehyde was determined through its (R)‐(−)‐α‐methylbenzylamine derivative.     

Preparation and Application of Iron‐substituted (Z)‐Enals: Synthesis of 5‐Substituted α,β‐Butenolides

A reaction sequence furnishing cyclic β‐[η⁵‐C₅H₅(CO)₂Fe]‐substituted enals 5 starting from β‐keto esters 1 is described. Organolithiums were found to react smoothly with the iron‐substituted enals yielding α,β‐butenolides 6 by an intramolecular cyclocarbonylation of the lithiumalkoxide initially formed. The influence of e.g. the reaction temperature and the solvent on the reaction cascade is discussed. A reaction mechanism is proposed.     

Relationship between the mechanical relaxations in the α zone and the calorimetric transitions in low density polyethylene

The α-relaxation spectra of LDPE, irradiated and unirradiated, has been compared with their calorimetric thermograms. There exists a correlation between the two mechanical relaxations that appear in the α zone and the two fusion peaks observed in the calorimetric thermograms, confirming that the parameter that governs the temperature of the relaxations α_I and α_II is the most probable crystallite thickness, whereas the height of the α-relaxation zone, as measured by means of tan δ_max, depends on the total crystalline content of the sample.     

Desaktivierungsverhalten von Arenen und Heteroarenen. XL. Mechanismus der reversiblen intramolekularen [π4s + π4s]-Photocycloaddition von α, ω-Bis-(9-acridiziniumyl)-alkanen

Deactivation Behaviour of Arenes and Heteroarenes. XL. The Mechanism of the Reversible Intramolecular [_π4_s + _π4_s]-Photocycloaddition Reaction of α,ω-Bis-(9-acridiziniumyl)-alkanes. On electronic excitation the bichromophores deactivate by fluorescence and radiationless photophysical processes from its local excited state. Simultaneously, intramolecular interaction occurs between the excited chromophor and that in the ground state (i.e. by reversible energy migration or intramolecular excimer formation). The excimer rapidly collapses to the cyclomer assuming a common pericyclic transition state for the reversible photocycloaddition. In the pericyclic state the reaction is split into cyclomer formation or backformation of bichromophores in the ground state, respectively. This mechanism of the reversible intramolecular [_π4_s + _π4_s]- photo-cycloaddition reaction is discussed on the basis of a potential correlation diagram.     

Photopolymer: synthesis and characterization of poly(4‐methacryloyloxyphenyl‐4′‐chlorostyryl ketone)

Methacrylate monomer containing a photodimerizable α,β‐unsaturated ketone moiety was prepared and polymerized in ethyl methyl ketone at 70 °C using benzoyl peroxide as an initiator. The polymer was characterized by UV, IR, ¹H NMR and ¹³C NMR spectra. The molecular weights (M _w and M _n) of the polymer were determined by gel permeation chromotography. The thermal stability of the polymer was measured by thermogravimetric analysis in air and nitrogen. The glass transition temperature of the polymer was determined by differential scanning calorimetry. The photo reactivity of the polymer was investigated as thin film and in solution. © 2000 Society of Chemical Industry     

Glass transition temperatures of poly(alkyl α-cyanoacrylates)

The glass transition temperatures of the poly(alkyl α-cyanocrylates) were determined by the dilatometric technique, and some of the values were checked by differential thermal analysis. The data indicate that the T_g's appear to decrease with increase in the size of the alkyl group, for a given molecular weight range. It was also found that the T_g of poly(methyl or butyl α-cyanoacrylate) increased with molecular weight. All cyanoacrylates, excepting methyl and ethyl esters, formed only low molecular weight polymers in aqueous surroundings. Therefore, they have characteristic low glass transition temperatures, causing coalescence at low temperatures.     

Bestimmung der Nullfeldparameter optisch angeregter 3(π,π*)-Zustände ausgewählter aromatischer Systeme

Determination of the Zero Field Parameters Optically Excited ³(π,π*)-States in Selected Aromatic Systems Experimental zero field parameters of optically excited naphthalene and quinoxaline derivatives are presented. The (D*), (D) and (E) parameters are determined by the position of the transitions by means of simple approximation formula, magnetophotoselection and simulation of spectra. Possibilities of comparison of the zero field parameters of optically excited ³(π,π*)-states with parameters of ground state for simple aromatic hydrocarbones are presented.     

Photochemie von Aminoketonen. V. Diastereoselektive Synthese von 3-Aryl-azetidin-3-olen durch Photocyclisierung von Aryl-α-amidoalkyl-ketonen

Photochemistry of Aminoketones. V. Diastereoselective Synthesis of 3-Aryl-azetidin-3-ols via Photocyclization of Aryl-α-amidoalkyl-ketones N-Acyl-azetidin-3-ols 3 and 4 are formed by diastereoselective cyclization of n,π*-excited N-benzyl-N-phenacyl-amides 1 and 2 in ether solution. Dependent on the nature of the p-and α-substituents of the phenacyl part and especially of the N-acylgroups in the amides 1 and 2 competing reactions occur, particularly the NORRISH II cleavage and an oxydative cleavage of the intermediate hydroxybiradicals A . N-Acylgroups with low energy barrier ΔG^≠ of internal rotation favour the diastereoselective photocyclization by intramolecular interaction between the amide oxygen atom and the n,π*-CO-group in 1 *, 2 * and the OH group in the biradicals A , respectively. An intramolecular hydrogen bonding enables the N-tosyl-azetidinols 3 to rearrange to the N-tosylamino-methyl-benzhydryl-ketones 6 by 1 -sensitized photoreaction.     

Acetylcholine Promotes Binding of α‐Conotoxin MII at α3β2 Nicotinic Acetylcholine Receptors

α‐Conotoxin MII (α‐CTxMII) is a 16‐residue peptide with the sequence GCCSNPVCHLEHSNLC, containing Cys2–Cys8 and Cys3–Cys16 disulfide bonds. This peptide, isolated from the venom of the marine cone snail Conus magus, is a potent and selective antagonist of neuronal nicotinic acetylcholine receptors (nAChRs). To evaluate the impact of channel–ligand interactions on ligand‐binding affinity, homology models of the heteropentameric α₃β₂‐nAChR were constructed. The models were created in MODELLER with the aid of experimentally characterized structures of the Torpedo marmorata‐nAChR (Tm‐nAChR, PDB ID: 2BG9) and the Aplysia californica‐acetylcholine binding protein (Ac‐AChBP, PDB ID: 2BR8) as templates for the α₃‐ and β₂‐subunit isoforms derived from rat neuronal nAChR primary amino acid sequences. Molecular docking calculations were performed with AutoDock to evaluate interactions of the heteropentameric nAChR homology models with the ligands acetylcholine (ACh) and α‐CTxMII. The nAChR homology models described here bind ACh with binding energies commensurate with those of previously reported systems, and identify critical interactions that facilitate both ACh and α‐CTxMII ligand binding. The docking calculations revealed an increased binding affinity of the α₃β₂‐nAChR for α‐CTxMII with ACh bound to the receptor, and this was confirmed through two‐electrode voltage clamp experiments on oocytes from Xenopus laevis. These findings provide insights into the inhibition and mechanism of electrostatically driven antagonist properties of the α‐CTxMIIs on nAChRs.