The synthesis of di- and tetramethyl substituted macrocyclic polyether-diester ligands

Three series of macrocyclic polyether-diester ligands have been prepared from dimethyl triethylene glycol ( 20 ), two dimethyl tetraethylene glycols ( 21,23 ), dimethyl pentaethylene glycol ( 22 ) and tetramethyl tetraethylene glycol ( 24 ) and diglycolyl chloride (products 5–9 ), thiadiglycolyl chloride (products 10–14 ) and 2,6-pyridine dicarbonyl chloride (products 15–19 ). The eighteen-membered rings ( 6 and 16 ) formed solid potassium thiocyanate complexes. The eighteen- and twenty-one-membered ring compounds 6–8 and 16–18 complexed with benzylammonium perchlorate in methylene chloride-d₂ as shown by significant chemical shift changes in the ¹H nmr spectra.     

Polarizable biphenyl polysiloxane stationary phase for capillary column gas chromatography

A crosslinkable biphenylmethylpolysiloxane stationary phase was synthesized for capillary column gas chromatography and compared with methyl, phenyl, and cyanopropyl polysiloxane stationary phases for the separation of isomeric polycyclic aromatic compounds. While the new phase gave similar separations of nonpolar isomers when compared to the nonpolar phases, separations of polar isomers were greatly improved because of the induced polarity of the biphenyl group of the stationary phase by the solute molecules. This polarizable stationary phase offers a unique selectivity which is not available in other stationary phases.     

Preparation of crown compounds containing allyloxymethyl or butenyl groups for attachment to silica gel or containing long chain lipophilic groups for use in liquid membrane systems

Several new macrocyclic polyether ligands have been prepared for use in the separation of metal ions from aqueous solutions. Four of the crown ethers reported contain 1,2,4-triazole or 4-pyridone protonionizable subcyclic units and lipophilic groups. The remaining crown ethers are not proton-ionizable but contain alkene groups and were prepared for attachment to silica gel. The crowns were prepared by reacting the appropriate glycols with the appropriate ditosylates or dichloride in the case of the 1,2,4-triazole subcyclic unit. The crowns with proton-ionizable and lipophilic substituents were tested in liquid membrane transport systems and some of the crowns with alloxymethyl or butenyl substituents were attached to silica gel. The log K values for the interaction of these silica gel-bound macrocycles with certain metal ions were nearly the same (± 10%) as those for the association of the unbound macrocycles with the same metal ions.     

Chiral Pyridine-Based Macrobicyclic Clefts: Synthesis and Enantiomeric Recognition of Ammonium Salts

An achiral (3) and two chiral pyridine-based macrobicyclic clefts (4 and 5) have been prepared by treating 2,6-bis[[2',6'-bis(bromomethyl)-4'-methylphenoxy]methyl]pyridine (2) with the appropriate achiral and chiral glycols. Starting 2 was prepared by first treating 2,6-bis(hydroxymethyl)-4-methylphenol with 2,6-[(tosyloxy)methyl]pyridine followed by phosphorus tribromide. Achiral macrobicyclic cleft 3 formed a complex at 25 degrees C in 50% CH(3)OH/50% CHCl(3) (v/v) with a primary ammonium salt (log K = 3.15) as evidenced by a significant change in the (1)H NMR spectrum. Highly organized (S,S,S,S)-4, prepared by treating 2 with (1S,5S)-3-oxapentane-1,5-diol, exhibited recognition at 25 degrees C in 20% C(2)H(5)OH/80% 1,2-C(2)H(4)Cl(2) (v/v) for the (S)-enantiomer of alpha-(1-naphthyl)ethylammonium perchlorate (NapEt) over its (R)-form (Delta log K = 0.85). This high recognition factor probably reflects an increase in molecular rigidity by the introduction of a second macro ring on the monocyclic pyridinocrown ligand.     

Analytical and spectral features of gas-phase chemiluminescence spectrometry of arsenic and antimony

Intense emissions are produced in the u.v. and visible regions when arsine and stibine are introduced into a flow-type furnace—hydrogen diffusion flame system, when the flame is surrounded by oxygen. The emissions in the range 240–300 nm are attributed to AsO and SbO. The emission characteristics seem to be due to chemiluminescence based on the reaction between atomic analyte and oxygen. The detection limits are 0.05 μAs (10 ppb) at 429 nm and 0.1 μ Sb (20 ppb) at 369 nm.     

Delayed onset of intermolecular bonding in the water adlayer on Ru(001) due to the presence of preadsorbed oxygen

Infrared reflection absorption spectroscopy has been employed to study adsorption of water on Ru(001) at liquid nitrogen temperatures. For even the lowest H₂O coverages a broad absorption band at ≈3400 cm^?1 is observed on the clean surface, indicating formation of hydrogen-bonded clusters Small amounts of preadsorbed oxygen delay the clustering process.     

Spatial resolution and measurement of turbulence in the viscous sublayer using subminiature hot-wire probes

Measurements in the viscous sublayer of a flat-plate turbulent boundary layer in air, using single hot-wire sensors with lengths from 1–60 viscous length scales show that, at a given distance from the surface, the turbulence intensity, flatness factor, and skewness factor of the longitudinal velocity fluctuation are nearly independent of wire length when the latter is less than 20–25 times the viscous length scale (i.e. 20–25 wall units), and decrease significantly and abruptly for larger wire lengths. This conclusion is consistent with other workers' probability density functions of streak spacing: the lateral spacing of streaks in the viscous sublayer is 80–100 wall units on average with minimum spacing of 20–25 wall units, which implies that signals would be strongly attenuated by wires whose length exceeds 20–25 wall units. To achieve wire lengths of less than 20–25 wall units, subminiature hot wire probes like those described by Ligrani and Bradshaw (1987), having lengths as small as 150 m, are necessary for sublayer measurements in typical laboratory wind tunnels. As well as the measurements mentioned above, dissipation spectra are presented, to show the effect of spanwise averaging on the high-frequency motions, which is necessarily more severe than the effect on overall intensities.     

Proton-ionizable crown compounds. 3. Synthesis and structural studies of macrocyclic polyether ligands containing a 4-pyridone subcyclic unit

New proton-ionizable macrocyclic polyether ligands containing the 4-pyridone subcyclic unit have been prepared by reacting 4-THP blocked-2,6-pyridinedimethanol with various oligoethylene glycol ditosylates. The 18-crown-6 ligand containing the 4-pyridone subcyclic unit, 4 , forms stable complexes with alkali metal and organic ammonium cations. The crystal structure of 4 proves the 4-pyridone structural unit. The crystal structure of the potassium thiocyanate complex of 4 is also reported and shows the complex to contain the 4-hydroxypyridine unit.     

Synthesis of monoalkenylated crown ethers and C-pivot cryptands

The synthesis of two N-(2-allyloxy)ethyl-substituted diaza-crowns and two C-pivot (allyloxy)methyl-substi-tuted cryptands is described. Controlled etherization of N,N-bis(2-hydroxyethyl)-4,13-diaza-18-crown-6 with allyl bromide and sodium hydride gave N-(2-allyloxy)ethyl-N-(2-hydroxyethyl)-4,13-diaza-18-crown-6 in a good yield. This macrocycle was reacted with sodium hydride and tetrahydrofurfuryl chloride or 3,3-dimeth-ylbutyl tosylate to give expected N-(2-allyloxy)ethyl-N'-tetrahydrofurfuryloxy)ethyl-[or (3,3-dimethylbutoxy)-ethyl]-substituted products 3 or 4 . 6,13-Dimethylenyl-14-crown-4 ( 9 ) and 9,19-dimethylenyl-20-crown-6 ( 10 ) were treated with mercuric acetate, followed by sodium borohydride in strong base to give macrocyclic diols 11 and 12 , respectively. These diols were reacted with sodium hydride and the ditosylate derivative of allyloxymethyl-substituted triethyleneglycol 13 to produce the C-pivot (allyloxy)methyl-substituted macrotri-cycles 6 and 7 .     

Permanent microporosity and enantioselective sorption in a chiral open framework

A homochiral microporous material is presented. The phase has 47% permanently porous void volume and is shown to have >1 nm diameter pores with three-dimensional channels using probe molecule sorption. Enantioselective guest sorption is strongly dependent on guest size. The homochiral microporous phase was identified by reactive selection from a first-generation chiral but nonporous framework. Chiral permanent porosity is established by directional noncovalent interactions between framework-forming and nonframework forming components of the stable second-generation material, which become stronger upon loss of the guests from the pore system.