Lower Rim Substituted tert-Butyl calix[4]arenes (I). The Structure and Complexing Properties in Ion-Selective PVC Membrane Electrodes

Some di- and tetraamide tert-butylcalix[4]areneswere synthesized and described. Their ionophoric properties were studied in liquid membrane ion-selective electrodes. The correlation between thechemical structure (conformation in solution determined by ¹H NMR) and potentiometric ion-selectivity and complex formation constant havebeen studied. The PVC membrane electrodes based on tetraamides 8–11 show high sodium selectivity, are stable and long lasting. Disubstituted amides 1–7 are selective for larger and more lipophilic ions, as for exampleguanidinium ion. The crystal structure of the diamide 4 was determined by single crystal X-ray analysis. Crystals of 4 are triclinic, spacegroup P-1, with: a = 16,669(8), b = 17.795(10), c = 20.984(8) Å, =91.08(4)°, = 91.60(3)°, = 90.73(4)° and Z = 4. Ionophore 4 posseses a distorted cone conformation and is substituted at the proximal phenol rings.     

Synthesis and Structure of Triphenylscandium-bis(tetrahydrofuran)

Metathesis reaction of ScCl₃(THF)₃ with 3 equiv. of phenyllithium in THF/Et₂O solution affords ScPh₃(THF)₂ ( 1 ) in good yield. The crystallographically determined molecular structure of 1 reveals a trigonal-bipyramidal coordination sphere with the THF molecules in the axial positions and Sc–C bonds of 2.245(4)–2.266(4) Å. The σ-bound phenyl groups are only slightly twisted (0, 8, 18°) with respect to the ScC₃ plane. Ab initio calculations suggest that the THF molecules play some direct role in the moderate coplanarity of the phenyl rings.     

Synthesis of dipeptidyl peptidase-4 inhibitors: a brief overview

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Looking glass inhibitors: both enantiomeric N-benzyl derivatives of 1,4-dideoxy-1,4-imino-d-lyxitol [a potent competitive inhibitor of α-d-galactosidase] and of 1,4-dideoxy-1,4-imino-l-lyxitol [a weak competitive inhibitor of α-d-galactosidase] inhibit naringinase,an α-l-rhamnosidase competitively

Benzhydryl protection by diphenyldiazomethane of an alcohol in enantiomeric base-sensitive ribonolactones allows short efficient syntheses of 1,4-dideoxy-1,4-imino-d-lyxitol (DIL) and of 1,4-dideoxy-1,4-imino-l-lyxitol (LIL). DIL showed potent [K_i = 0.13 μM]—and LIL showed weak [K_i = 113 μM]—competitive inhibition of α-d-galactosidase. Both enantiomers N-benzyl-DIL [K_i = 64 μM] and N-benzyl-LIL [K_i = 13 μM] were moderate competitive inhibitors of naringinase, an α-l-rhamnosidase.     

Crystallization kinetics study on higher homologues of benzylidene aniline compounds: impact of phase variant on nucleation process

A systematic kinetic study leading to the crystallization process from the kinetophases (which occur prior to crystal phase) smectic B, crystal G and smectic F is performed on representative compounds of the homologous series p -phenylbenzylidene-p′-alkylanilines (PBnA) and p-n -alkoxybenzylidene-p′-alkylanilines (nO.m) these compounds are p-phenylbenzylidene-p′-nonylaniline (PB9A), p -phenylbenzylidene-p′-tetradecylaniline (PB14A), p-n -pentadecyloxybenzylidene p′-tetradecylaniline (15O.14) and p-n -octadecyloxybenzylidene-p′-nonylaniline (18O.9). The molecular mechanism and dimensionality in crystal growth from the kineto phases are computed from the Avrami equation, while the characteristic crystalline time (t ^*) at each crystallization temperature is deduced from the individual plots of log t vs. Δ H. The low magnitudes of the dimensionality parameter n infers the occurrence of diffusion-controlled transformations leading to the formation of plates or needles of finite size possessing impinged edges. The degree of variation in the value of n at each crystallization temperature also reveals the existence of an independent nucleation mechanism for any individual member of the series. The influence of the terminal alkyl chain lengths on the rate of crystallization is determined from a comparative study with the reported analogous compounds.     

A Mössbauer spectroscopic study of salt lake sediments from Qaidam basin

Mössbauer spectroscopy, X-ray diffractometry and chemical fractionation have been used to study the clay smaples in sediments of Charhan playa and Qinghai lake. The spectral components of the Mossbauer spectra of the samples are attributed to Fe²⁺ ions in chlorite and siderite, Fe³⁺ ions in clay minerals and hematite, and partly in amorphous ferric hydroxides. The essential difference in the mineral composition of the sediments of both lakes is the presence of siderite in the samples of Char han playa, whereas it is absent in the samples of Qinghai lake. The fraction of the amorphous ferric hydroxides is higher in the sediments of Qinghai lake. Total Fe²⁺/Fe³⁺ ratios increase with sediment depth of Charhan playa, whereas these ratios are altogether smaller and run through a maximum at a certain depth for Qinghai lake.     

Elastic electron scattering from 40Ar

Cross sections for elastic electron scattering from ⁴⁰Ar have been measured for the momentum transfer range from 0.59 to 1.31 fm^?1. We have analyzed with the Fourier-Bessel ansatz our data as well as the data of former experiments. The rms charge radius we have found is 3.423(14) fm. The results are in excellent agreement with latest muonic data. Furthermore, we have reanalyzed former ⁴⁰Ca data and have discussed the ⁴⁰Ca- ⁴⁰Ar charge distribution.     

Optical clock distribution with a compact free space interconnect system

Optical clock signal distribution has been widely discussed to be an attractive way to reduce the clock skew in high-speed digital systems. For short interconnect lengths, especially for chip level clock distribution, free space systems using diffractive optical elements (DOEs) have specific advantages. The optoelectronic pathway described in this paper consists of a GaAs laser diode, a microetched silicon mirror, a faceted diffractive element and four silicon photodiodes hybridized to a (dummy) silicon chip. The key element of the clock distribution demonstrator is the diffractive element which matches setup requirements like compactness, off-axis geometry and use of an unshaped laser beam. The whole setup meets the demands of alignment accuracy in an excellent way. This is achieved by the very good imaging characteristic of the DOE and by an alignment technique based on precision mounting of micromachined silicon components. The system was tested with clock rates up to 2.5 GHz, the cut-off frequency is 350 MHz.