Self-assembly of amphiphilic hexapyridinium cations at the air/water interface and on HOPG surfaces.

Mono- and multilayers of a novel amphiphilic hexapyridinium cation with six eicosyl chains (3) are spread at the air/water interface as well as on highly ordered pyrolytic graphite (HOPG). On water, the monolayer of 3 is investigated by recording surface pressure/area and surface potential/area isotherms, and by Brewster angle microscopy (BAM). Self-organized tubular micelles with an internal edge-on orientation of molecules form at the air/water interface at low surface pressure whereas multilayers are present at high surface pressure, after a phase transition. Packing motifs suggesting a tubular arrangement of the constituting molecules were gleaned from atomic force microscopy (AFM) investigations of Langmuir-Blodgett (LB) monolayers being transferred on HOPG at different surface pressures. These LB film structures are compared to the self-assembled monolayer (SAM) of 3 formed via adsorption from a supersaturated solution, which is studied by scanning tunnelling microscopy (STM). On HOPG the SAM of 3 consists of nanorods with a highly ordered edge-on packing of the aromatic rings and an arrangement of alkyl chains which resembles the packing of molecules at the air/water interface at low surface pressure. Additional details of the molecular packing were gleaned from single-crystal X-ray structure analysis of the hexapyridinium model compound 2b, which possesses methyl instead of eicosyl residues.     

Elektronenstoss-induzierter zerfall von benzol-tricarbonyl-chrom- und -wolfram-derivaten; ein vergleich

The Electron impact mass spectra of (CO)₃ MC₆H₅—X complexes (M = Cr, W; X = OCH₃, OC₄H₉, CO₂CH₃, CO₂C₄H₉) were recorded. From metastable transitions and by high-resolution measurements complete fragmentation diagrams were obtained; in some cases comparative structure determinations of fragment ions were carried out by collisional activation. The fragmentation of the tungsten complexes considerably differs from that of the chromium compounds. The differences may be attributed to the stronger-electrophilic character as well as to the more pronounced tendency of tungsten to attain higher oxidation states.     

Structure and Thermodynamics of NaF-AlF(3) Melts with Addition of CaF(2) and MgF(2)

The NaF-AlF(3) system with additions of CaF(2) and MgF(2) has been studied with Raman and vapor pressure measurements for 3 >/= CR (NaF/AlF(3) molar ratio) >/= 1 and up to 50 mol % additive. The results show that the binary melt can be described using the two equilibria AlF(6)(3)(-) = AlF(6)(2)(-) + F(-) and AlF(5)(2)(-) = AlF(4)(-) + F(-) with equilibrium constants 0.25 and 0.05, respectively, at 1293 K. Both reactions have positive reaction enthalpies. The first equilibrium is strongly shifted to the right resulting in a melt mixture with very low AlF(6)(3)(-) concentrations even at the Na(3)AlF(6) composition. Evidence for nonideal mixing of anions was found. For the ternaries, models based on Raman data are presented and compared with vapor pressure measurements. Good agreement is observed when association between the additives, CaF(2) or MgF(2), with the AlF(5)(2)(-) ions in the melt was considered. This association could be experimentally observed through a band broadening and a slight shift in the AlF(5)(2)(-) band frequency. Our vapor pressures and Raman data both indicate that MgF(2) clearly acts as an acid when added to NaF-AlF(3) melts of any composition. When CaF(2) is added, a slight decrease of vapor pressure occurs. Raman data indicate a decrease of AlF(4)(-) concentration, corresponding to a dissociation of CaF(2) with liberation of F(-) ions. All these results are, however, very much dependent on the initial melt composition. These data are explained in terms of acid-base, dilution, and association reactions of the solute with the solvent.     

Cation-crown ether complex formation in water. II. Alkali and alkaline earth cations and 12-crown-4, 15-crown-5, and 18-crown-6

The stability constants and the partial molal volume and isentropic partial molal compressibility changes of complex formation between cations and crown ethers in water at 25°C are presented. The cations involved are Na⁺, K⁺, Rb⁺, Cs⁺, Ca²⁺, and Ba²⁺, and the crown ethers are 12-crown-4, 15-crown-5, and 18-crown-6. Values of V of complex formation have been discussed in terms of two simple models, one based on the scaled particle theory, and the others on the Drude-Nernst continuum model. The results indicate that the charge of the potassium cation in 18-crown-6 is especially well screened from the water. On this basis hydration numbers of complexed cations have been calculated. This shows that the size of the cation compared to the crown ether hole is important for the contacts between complexed cations and water.     

X‐Ray Single Crystal Refinement and Superconductivity of La3Ni2B2N3

Crystalline samples of La₃Ni₂B₂N₃ were synthesized using solid state metathesis reactions from combinations of La, LaCl₃, NiCl₂ together with Li₃BN₂. The structure was determined by single crystal X‐ray diffraction (I4/mmm (No. 139), a = 372.95(2) pm, c = 2056.3(2) pm, R₁ = 0.027, wR₂ = 0.062) and confirmed earlier results from neutron powder diffraction. La₃Ni₂B₂N₃ contains BN units capping square planar Ni layers. Isolated nitrogen atoms reside in La₆ octahedra. Magnetic measurements on several bulk samples exhibit superconductivity at temperatures below 14.6 K.     

Chiral synthesis of (2s,3s,7s)-3,7-dimethylpentadecan-2-yl acetate and propionate,potential sex pheromone components of the pine saw-fly neodiprion sertifer (geoff.)

A synthesis of (2S,3S,7S)-3,7-dimethylpentadecan-2-yl acetate ($\text{2}$) and propionate ($\text{3}$) is described. (2S)-2-Methyldecan-1-yl lithium ($\text{5}$) was reacted with (3S,4S)-3,4-dimethyl-γ-butyrolactone ($\text{6}$) to yield the ketoalcohol $\text{19}$ which upon Huang-Minlon reduction furnished (2S,3S,7S)-3,7-dimethylpentadecan-2-ol ($\text{1}$). Acylations gave the esters $\text{2}$ and $\text{3}$. The (2S)-2-methyldecan-1-yl lithium was obtained via asymmetric synthesis. The chiral lactone $\text{6}$ was obtained from (2S,3S)-trans-2,3-epoxybutane and dimethyl malonate.     

Solid-phase synthesis of lipidated peptides

Characteristic partial structures of lipidated proteins embodying different lipid groups as well as additional fluorescent tags or a maleimide for coupling to proteins can be synthesized readily by means of a new solid-phase technique employing the oxidative cleavage of the hydrazide linker as well as on-resin farnesylation and palmitoylation after appropriate deprotection of cysteine thiol groups as the key steps.     

A microcomputer aided microwave spectrometer controlled by a larger computer

Hewlett-Packard 8460A microwave spectrometer has been connected to a microcomputer based on the Motorola MC6800 microprocessor. The microcomputer is programmed to control frequency and Stark voltage and to perform $\text{A}\text{D}$ conversion, storage and accumulation of intensities.The microcomputer is connected to a larger local computer, the RC4000, from which it may be loaded with a program, started and stopped, and from which data transfer between the storages of the two computers is controlled. This transfer may be performed, while the microcomputer is running a spectrum.     

Classification of wheat varieties: use of two-dimensional gel electrophoresis for varieties that can not be classified by matrix assisted laser desorpiton/ionization-time of flight-mass spectrometry and an artificial neural network

Analyzing a gliadin extract by matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) combined with an artificial neural network (ANN) is a suitable method for identification of wheat varieties. However, the ANN can not distinguish between all different wheat varieties. Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) was applied to three pairs of wheat varieties, which can not be classified correctly by ANN. By 2-D PAGE the varieties in the three pairs can be discriminated and these six wheat varieties can be separated from each other, which could not be separated by MALDI-TOF-MS and NN.     

Isentropic partial molal compressibilities of alcohols in propylene carbonate at 25°C

The isentropic coefficients of compressibility of the homologous series of alcohols and diols R _n CH₂OH (n=2–6), CH₃CHOHR _n (n=1–5), 1,2-propanediol, 1,3- 1,4- and 2,3-butanediol, 1,5-pentanediol, and 1,7-heptanediol dissolved in propylene carbonate have been measured at 25°C. Isentropic partial molal compressibilities and group partial molal compressibilities at infinite dilution have been evaluated. The isentropic partial molal compressibilities of these alcohols and diols have been compared with the corresponding values in water. This comparison shows that the values in propylene carbonate are higher than in water by a factor of 10 due to an increased compressibility of the solvation sheath around nonpolar groups in PC.