Henning Eickmeier

Reversible Adhesion Switching of Porous Fibrillar Adhesive Pads by Humidity

We report reversible adhesion switching on porous fibrillar polystyrene-block-poly(2-vinyl pyridine) (PS-b-P2VP) adhesive pads by humidity changes. Adhesion at a relative humidity of 90% was more than nine times higher than at a relative humidity of 2%. On nonporous fibrillar adhesive pads of the same material, adhesion increased only by a factor of ~3.3. The switching performance remained unchanged in at least 10 successive high/low humidity cycles. Main origin of enhanced adhesion at high humidity is the humidity-induced decrease in the elastic modulus of the polar component P2VP rather than capillary force. The presence of spongelike continuous internal pore systems with walls consisting of P2VP significantly leveraged this effect. Fibrillar adhesive pads on which adhesion is switchable by humidity changes may be used for preconcentration of airborne particulates, pollutants, and germs combined with triggered surface cleaning.

Ultrafine sanding paper: a simple tool for creating small particles.

A top-down approach, i.e., creating small particles by mechanical force starting from bulk materials, probably presents the most logical approach to particle size reduction and, therefore, top-down techniques are among the first to achieve small particles. A new solvent-free, amazingly simple approach is reported, suitable to achieve nanoparticles and sub-micro particles.

Synthesis and Characterization of Upconversion FluorescentYb3+,Er3+Doped CsY2F7Nano- and Microcrystals

Cs: 78%, 20%, 2% nanocrystals with a mean diameter of approximately 8 nm were synthesized at in the high boiling organic solvent N-(2-hydroxyethyl)-ethylenediamine (HEEDA) using ammonium fluoride, the rare earth chlorides and a solution of caesium alkoxide of N-(2-hydroxyethyl)-ethylenediamine in HEEDA. In parallel with this approach, a microwave assisted synthesis was carried out which forms nanocrystals of the same material, about 50 nm in size, in aqueous solution at /8 bar starting from ammonium fluoride, the rare earth chlorides, and caesium fluoride. In case of the nanocrystals, derived from the HEEDA synthesis, TEM images reveal that the particles are separated but have a broad size distribution. Also an occurred heat-treatment of these nanocrystals ( for 45 minutes) led to bulk material which shows highly efficient light emission upon continuous wave (CW) excitation at 978 nm. Besides the optical properties, the structure and the morphology of the three products were investigated by means of powder XRD and Rietveld method.

3-Bromo-1-(2-deoxy-β-d-erythro-pento­furan­osyl)-1H-pyrazolo­[3,4-d]­pyrimidine-4,6-di­amine: a nucleoside which strongly enhances DNA duplex stability

The title compound, C10H13BrN6O3, exhibits an anti glycosylic bond conformation, with an O-C-N-C torsion angle of -105.0 (6) degrees . The pseudorotation phase angle and the amplitude [P = 5.8 (5) degrees and tau(m) = 30.0 (3) degrees , respectively] indicate N-type sugar puckering (3T2).

5-Methyl-6-aza-2'-deoxyisocytidine.

: In the title compound, 3-amino-2-(2-deoxy-beta-D-erythro-pentofuranosyl)-6-methyl-1,2,4-triazin-5(2H)-one, C(9)H(14)N(4)O(4), the conformation of the N-glycosidic bond is high-anti and the 2-deoxyribofuranosyl moiety adopts a North sugar pucker ((2)T(3)). The orientation of the exocyclic C-C bond between the -CH(2)OH group and the five-membered ring is ap (gauche, trans). The crystal packing is such that the nucleobases lie parallel to the ac plane; the planes are connected via hydrogen bonds involving the five-membered ring.

Synthesis and characterization of upconversion fluorescent Yb 3+ , Er 3+ doped CsY2F7 nano- and microcrystals

Cs: 78%, 20%, 2% nanocrystals with a mean diameter of approximately 8 nm were synthesized at in the high boiling organic solvent N-(2-hydroxyethyl)-ethylenediamine (HEEDA) using ammonium fluoride, the rare earth chlorides and a solution of caesium alkoxide of N-(2-hydroxyethyl)-ethylenediamine in HEEDA. In parallel with this approach, a microwave assisted synthesis was carried out which forms nanocrystals of the same material, about 50 nm in size, in aqueous solution at /8 bar starting from ammonium fluoride, the rare earth chlorides, and caesium fluoride. In case of the nanocrystals, derived from the HEEDA synthesis, TEM images reveal that the particles are separated but have a broad size distribution. Also an occurred heat-treatment of these nanocrystals ( for 45 minutes) led to bulk material which shows highly efficient light emission upon continuous wave (CW) excitation at 978 nm. Besides the optical properties, the structure and the morphology of the three products were investigated by means of powder XRD and Rietveld method.

Methyl 1-deoxy-1-(N1-thyminyl)-β-D-psicofuranoside

In the structure of the title compound, C12H18N2O7, the furanosyl ring adopts the S-type sugar pucker with the following pseudorotational parameters: PS = 159.6° (C2′-endo according to the designation of the ribofuranose ring of natural nucleosides; C3′-endo according to the numbering of the title compound) and νmax = 35.9°. The conformation around the C5′—C6′ bond is ap (gauche–trans; gt; −g), with a torsion angle γ of −170.3 (2)°. The structure of the thymine base is very similar to that of thymidine. There are intermolecular N—H...O and O—H...O hydrogen bonds.

2′-Deoxy-5-fluorotubercidin

In the title compound, 4-amino-7-(2-deoxy-beta-D-erythro-pentofuranosyl)-5-fluoro-7H-pyrrolo[2,3-d]pyrimidine, C11H13FN4O3, the conformation of the glycosyl bond lies between anti and high anti [chi = -101.1 (3) degrees ]. The furanose moiety adopts the S-type sugar pucker (2T3), with P = 164.7 (3) degrees and tau = 40.1 (2) degrees . The extended structure is a three-dimensional hydrogen-bond network involving a C-H...F, two N-H...O and two O-H...O hydrogen bonds.

O 2,1 ′ -Anhydro-( β -D-Psicofuranosyl)Thymine and 1-(1 ′ ,4 ′ -O-Anhydro- β -D-Psicofuranosyl)Thymine: The Crystal Structures Versus the 1H NMR and AB Initio Data

The crystal structures of the title compounds 1 and 2 have been determined. Relation between the stereochemistry of both nucleosides in the crystal state and the 1H NMR data in solution as well as the ab initio calculations is discussed.

7-Vinyl-8-aza-7-deaza-2'-deoxyadenosine monohydrate.

In the title compound, 4-amino-1-(2-deoxy-beta-D-eythro-pentofuranosyl)-3-vinyl-1H-pyrazolo[3,4-d]pyrimidine monohydrate, C12H15N5O3.H2O, the conformation of the glycosyl bond is anti. The furanose moiety is in an S conformation with an unsymmetrical twist, and the conformation at the exocyclic C-C(OH) bond is +sc (gauche, gauche). The vinyl side chain is bent out of the heterocyclic ring plane by 147.5 (5) degrees . The three-dimensional packing is stabilized by O-H...O, O-H...N and N-H...O hydrogen bonds.