Search results for "Mono"

Influence of a hydrophilic spacer on the structure of a phospholipid monolayer

1994

We present the results of thermodynamical and X-ray grazing incidence diffraction experiments performed on Langmuir monolayers of ether lipids with hydrophilic spacers between the glycerol backbone and the phosphatidylcholine head group: DHPC, DH-E01-PC, and DH-E02-PC. As a spacer the oxy-ethylene group is used, which is a typical hydrophilic unit of non-ionic tensides. It turns out that the introduction of the hydrophilic spacers leads to a fluidization of the monolayer and reduces the tilt angle of the chains.

Low-energy decay pathways of doubly charged silver clusters $Ag_{n}^{2+}$ (n = 9 - 24)

1997

The low-energy dissociation channels of mass selected silver cluster ions Ag n 2+ (n = 9–24) are determined by collision induced dissociation (CID) in a Penning trap. While all clusters of the size n ≥ 17 evaporate neutral monomers, most smaller clusters undergo asymmetric fission of the form Ag n 2+ → Ag −3 + + Ag {3} + . However, Ag 15 2+ and Ag 11 2+ emit monomers which indicates shell or odd-even effects. The observed fragmentation pathways are different from previous reports of measurements with sputtered Ag n 2+ .

IR Spectroscopy of Monoclinic Tungsten Oxide

2000

Stoichiometric tungsten trioxide WO3 has several polimorphous crystal phases [1] in the temperature region from 4 up to 1200K. These WO3 phases have more or less distorted ReO3 — type crystal structures, and ReO3 lattice topology is identical to topology of the BO3 sublattice of perovskite ABO3.

ChemInform Abstract: Nb4Te17I4, a New Pseudo One-Dimensional Solid-State Polytelluride.

2010

The new ternary compound Nb4Te17I4 has been prepared and structurally characterized. It crystallizes in the monoclinic system, space group C2/c with unit-cell parameters a = 16.199(4), b = 8.128(2), c = 27.355(6) A, β = 110.84(2)°, Z = 4. The structure consists of infinite one-dimensional niobium/tellurium chains running parallel to the crystallographic c direction. The chains are separated by iodine atoms. Short and long metal–metal distances alternate in the sequence of three consecutive short bonds ([d ≈ 3.1 – 3.2 A) and one long (d = 4.268 A) metal–metal separation. Each Nb atom is eight-coordinate. The composition of the chain is ∞11[(Nb5+)2(Nb4+)2(Te22−)4(Te32−)3(I−)4].

1993

A macromonomer was prepared from succinimido methacrylate and poly(N-isopropylacrylamide) (PIPA) with an amino end group. The macronomer (MA-PIPA) obtained shows a temperature-responsive transition phenomenon from coil to globule in water at about 36°C. For the copolymer of MA-PIPA with acrylamide (ratio of monomer residues of N-isopropylacrylamide (IPA) and acrylamide (AAm) 10:3), the transition temperature of the PIPA chain was the same as that of the macromonomer, whereas the transition temperature of a linear copolymer of IPA and AAm (ratio of the monomer residues 10:3) was much higher than that of PIPA (52°C). Microspheres were prepared by emulsion polymerization of the macromonomer an…

ChemInform Abstract: Homogeneous Metal-Based Catalysis in Supercritical Carbon Dioxide as Reaction Medium

2016

Above 31.1 °C and 73.8 bar, carbon dioxide reaches the supercritical state, being transformed into a fluid (scCO2) that has attracted interest in the last few decades as reaction medium for several transition-metal-catalyzed organic transformations. The main feature of this fluid rests on its capability to dissolve large amounts of other gases such as hydrogen, carbon monoxide, ethylene, or even methane and light alkanes. In this manner, very high concentrations of these reactants are available for catalysis. In this contribution a review of the main achievements of the use of transition-metal complexes as catalysts in scCO2 is presented.

On the occurrence of ClO in cirrus clouds and volcanic aerosol in the tropopause region

1997

Airborne observations during descents of the ER-2 through layers of volcanic aerosol (Mount Pinatubo eruption of 1991) and a cirrus cloud are utilized to study the the abundance of ClO and its relation to aerosol surface area in the midlatitude tropopause region. During a cirrus event near the tropopause ClO mixing ratios up to 2.7 pptv were detected and near the tropopause ClO levels from a few to 70 pptv were found. These measurements are associated with large experimental uncertainties but demonstrate the possible presence of ClO inside cirrus clouds and near the tropopause. Model calculations show that possible enhancements of ClO by heterogeneous chemistry on cirrus cloud particles cou…

Monomeric vs. polymeric bonded iminodiacetate silica supports in high-performance ligand-exchange chromatography

1983

The synthesis of monomeric and polymeric bonded iminodiacetate-groups on silica supports is described. The polymeric support offers advantages over the monomeric, such as (i) preparation is much simpler, (ii) higher surface concentration of functional groups can be achieved without loss of efficiency and (iii) hydrolytic stability. Cu2+ loaded supports were examined for their kinetic performance, in particular for the C-parameter of the Knox equation, and for their hydrolytic stability. Calculation of the surface coverage shows that only a rather thin polymeric layer is formed; this is in agreement with the results of the kinetic performance. The retention of α-amino acids on the Cu2+ loade…

Die acidolytische depolymerisation von trioxan in stationärer phase. 21. Mitt. über polyoxymethylene1

1964

Die Depolymerisation von Trioxan mit verschiedenen Phosphorsauren wurde im Temperaturbereich von 100–160°C untersucht. Sie fuhrt zu einem temperaturabhangigen Gleichgewicht zwischen Trioxan und Formaldehyd, das oberhalb 180°C weitgehend auf der Seite des Formaldehyds liegt. Zu einer schnellen Einstellung des Gleichgewichtes eignen sich Ortho- und Pyrophosphorsaure. Die bevorzugte Nebenreaktion ist die Bildung von Methylformiat; die Ausbeute an Methylformiat wird durch Erhohung der Reaktionszeit und der Katalysatoroberflache vergrosert. Das geschilderte Verfahren eignet sich zur Darstellung von monomerem Formaldehyd (Reinheitsgrad etwa 99,8%) im Laboratorium. Depolymerization of trioxane by …

Liposomes from α,ω-dipolar amphiphiles with a polymerizable diyne moiety in the hydrophobic chain

1982

Symmetric polymerizable α,ω-dipolar C22-diacetylenes were prepared by oxidative coupling of 10-undecynoic acid and 10-undecynol, respectively, by means of copper II salts in ethanolic solution. 10,12-Docosadiyne-1,22-diphosphate (3)—by reaction of 10,12-docosadiyne-1,22-diol (2) with POCl3—was polymerized in aqueous solution using UV irradiation to form deep blue, thermochromic solutions. By consonication of 3 with cholesterol, monolayer vesicles were formed. This was proven by encapsulation of 6-carboxyfluorescein. These monomeric vesicles were polymerized by UV light to yield stable, deep blue polymeric vesicle suspensions.