Nanoimprint Lithography with UV-Curable Hyperbranched Polymer Nanocomposites

Nano-scale patterns were produced with UV-curable acrylated hyperbranched polymer nanocomposites using nanoimprint lithography with a glass master in a rapid, low-pressure process. The pattern of the glass master was replicated with composites containing up to 25 vol% SiO₂ with a shape fidelity better than 98%. Photo-rheology, interferometry and atomic force microscopy were used to analyze the material behavior. Attention was paid to the relationship between composition, nanoparticle dispersion, kinetics of photo-polymerisation, shrinkage, pressure and shape fidelity of nano-gratings. It was shown that the gel-point of the nanocomposite was an important factor that determined the stability as well as the dimensions of the imprinted structure. Dimensional accuracy also strongly depended on the level of internal stress, which in fact increased with the amount of silica. A resin rich layer on the surface of the composite accounted for the good surface quality of the nano-pattern.     

Direct, preparative enantioselective chromatography of propranolol hydrochloride and thioridazine hydrochloride using carbon dioxide-based mobile phases

In this paper, we describe the direct, preparative enantioselective chromatography of racemic (rac)-propranolol hydrochloride (HCI) and rac-thioridazine.HCl using Chiralpak AD chiral stationary phase and mobile phase systems containing carbon dioxide and methanol without the use of basic or acidic additives. Isolated fractions of propranolol.HCl were positively identified by mass spectrometry, Beilstein flame test, melting point, and chemical analysis to be HCI enantiomers of propranolol-HCl salts exhibited characteristic mass spectra peaks at 36 and 38 mass-to-charge ratio in the expected 3:1 isotopic ratio for the solute that were absent in the mass spectra for the free-base forms. To our knowledge, the direct, preparative enantioselective isolation of HCI enantiomeric salts of rac-propranolol and of rac-thioridazine have not been previously demonstrated and published.     

Bi-Lipschitz parameterization of surfaces

We consider surfaces Z homeomorphic to the plane with complete, possibly singular Riemannian metrics. If we have _ZK⁺<2– for the positive and _ZK^–<C for the negative part of the integral curvature, then Z is L-bi-Lipschitz equivalent to ² with L depending only on >0 and C>0. This result implies a conjecture by J. Fu.Supported by NSF grant DMS-0200566.     

Synthesis and olfactory properties of (−)-(1R,2S)-Georgywood

The enantiomers of Georgywood^® were synthesized from (E)-2-methyl-6-methylene-nona-2,7-diene and methacrylaldehyde followed by oxidation of the Diels–Alder adduct and classical racemate separation of the acid with optically-active N-methylephedrine. Conversion to the final ketone and olfactory evaluation showed that the (−)-(1R,2S)-enantiomer is more powerful by a factor of >100 than its antipode. The absolute configuration was determined by conformational studies and CD-analysis.     

Experiments on the total synthesis of Lysolipin I. Part II. Michael addition of 1,3-cyclohexanedione to quinone acetals

Base-catalyzed reaction of 1,3-cyclohexanedione ( 3 ) with the quinone monoacetals 4 and 7 leads to the polycyclic products 5 and 8 , respectively, and in the case of 4 to variable amounts of dibenzofuranone 6 . The 2-arylcyclohexanedione 9 , on the other hand, is isolated from the reaction of 3 and bisacetal 11 catalyzed by ZnCl₂ (Scheme 2). Treatment of the adduct 8 with (CH₃O)₂SO₂/K₂CO₃ results in cleavage of teh heterocyclic ring by a retro-Michael reaction affording teh liable enone 23 which was further transformed to 24 by selective hydrogenation. The 8-acetoxydibenzofuranone 22 is obtainable from 8 by acid treatment and acetylation (Scheme 4). The reactions of the silylenol ethers 27 and 35 with quinone monoacetals were very complex (Scheme 6). The desired arylcyclohexanone derivatives 28 and 36 were formed in very low yields. Under certain conditions (elevated temperature or strong Lewis acids as catalysts), single-electron transfer or addition to the ene-acetal rather than to the enone function of the quinone monoacetals became predominant. In connection with this study, the sensitive 2-methoxy-p-benzoquinone monoacetals 15 (Scheme 3) and 29 (Scheme 6) have been prepared and characterized.     

An ab initioCI calculation of the triplet–triplet absorption spectrum of naphthalene

The triplet–triplet absorption spectrum of naphthalene (³B_1g ← ³B_2u; ³A_g ← ³B_2u) was calculated using an ab initio method with a STO -3G basis set and moderately large configuration interaction. Eight bands were found in the region 18,000–45,000 cm^?1 and compared with those of the experimental spectrum. The strongest band observed at about 44,000 cm^?1 was assigned to a ³A_g ← ³B_2u tansition. The excited triplet and singlet ground-state electronic charge distributions are compared.     

Versuche zur Synthese von ‘Push-Pull’-Diacetylenen

Attempted Synthesis of Push-Pull Diacetylenes Two alternative synthesis of push-pull diacetylenes of type 1 (5-amino-2,4-alkadiynals) are investigated. A bromination-dehydrobromination sequence starting with 5-dimethylamino-2,4-pentadienal ( 2 ) as well as the application of the well-known Cadiot-Chodkiewicz coupling reaction give new intermediates 3–5 , and 7 and 8 , respectively, but fail to give the target molecules 1 .     

Ionophore extrem hoher Lipophilie als selektive Komponenten für Flüssigmembranelektroden

Selective ionophores of extreme lipophilicity for liquid membrane electrodes Lipophilic ionophores of the type diether diamides have been prepared. Their lipophilicity is up to 7 orders of magnitude higher than the one of the most lipophilic ion carriers used as selective components in liquid membrane electrodes reported so far. For such ion carriers of extremely high lipophilicity kinetic limitations of the carrier induced ion transfer between aqueous and membrane phase usually dominate and heavily disturb the electromotive behavior of the membrane electrode. These limitations are absent only in those cases where most of the lipophilic segments of the carrier may remain in the membrane phase while the segments with the coordination sites are exposed to the aqueous phase during the transfer process.     

Synthese und Circulardichroismus optisch aktiver Carotinoidmodelle

Synthesis and Circular Dichroism of Optically Active Carotenoid Models The synthesis of the following optically active carotenoidic model compounds are described: (—)-(3,S,3′S)-3,3′-diisopropenyl-16,17,18,16′,17,18′-hexanor-β,β-carotene ( 1 ), (3R,3′R)-19,20,19′,20′-Metranor-zeaxanthin ( 2 ) and (6R,6′R)-19,20, 19′,20′-tetranor-ε,ε-carotene ( 3 ). These compounds were synthesized for the following reasons: (1) the presence of methyl groups at C(1), C(1′), C(5), C(5′) of cyclic carotenoids profoundly affects the torsional angle of the C(6), C(7)- and C(6′), C(7′)-bonds. Sign and magnitude of this angle are, according to recent theories [4] [5], responsible for a helical chromophore and for strong conservative [4] Cotton effects. CD. measurements of 1 give experimental support to these state- 1 exhibits weaker and less temperature dependent Cotton effects. Of more significance, the shape of the curve is no longer conservative, as expected. This constitutes experimental evidence for the contention that the β-endgroups and the polyene chain indeed form an inherently dissymmetric chromophore in optically active β, β-carotene derivatives; (2) the slightly S-shaped form of the polyene chain of carotenoids, shown by X-ray analyses [12] [13], is mainly ascribed to the presence of the methyl groups in the chain. Models 2 and 3 therefore are assumed to be linear. CD. studies of these compounds should consequently give information about the influence of deviation from Linearity and planarity of the polyene on the CD. spectra of carotenoids. CD measurements of 2 and 3 show that the lack of methyl groups does not alter the general type of the curve. Only the intensity and to some extent the position of the Cotton effects are influenced. Carotenoids with the ε-endgroup possess inherently symmetric but asymmetrically distorted chromophores. The assumption that non-conservative CD. spectra could become conservative upon cooling [4] is experimentally confirmed by model 3 . The rule stating that pairs of all-(E) and mono-(Z) isomers of carotenoids with only one cyclic endgroup should have CD. spectra with the same sign [5] is disproved by the CD. spectra of four stereoisomeric rubixanthins (s. Fig. 5). The UV./VIS. spectrum of 3, λ_max 447 (ε 216000), 418 (ε 189000) exhibits the highest molecular extinction ever reported for a carotenoid.