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We seek a theoretical method which is capable of predicting trends in the binding affinity of macrocyclic receptors for various anions in aqueous solution. Success has been achieved in this endeavor by employing semiempirical methodology to compute the energetics of certain exchange reactions whereby anions are exchanged between a macrocyclic receptor and a cluster of water molecules. The method is computationally tractable with workstation-class computing hardware and is applicable to a wide range of guest/host systems. Computations for several anion/receptor systems are reported.

Novel three-dimensional benzene-bridged macrobicyclic polyether 1 and macrotricyclic polyether 2 have been prepared. Macrobicyclic triply bridged cyclophane crown compound 1 was synthesized by atripode-tripode coupling of 1,3,5-tris[7'-(tosyloxy)-2',5'-dioxa-1'-heptyl]benzene (19) with 1,3,5-tris(hydroxymethyl)benzene (5). Macrotricyclic quadruply bridged cyclophane crown ether 2 was obtained by a quadrupode-quadrupode coupling of 1,2,4,5-tetrakis(7'-tosyloxy-2',5'-dioxa-1'-heptyl)-benzene (20) with 1,2,4,5-tetrakis(hydroxymethyl)benzene (6). These ligands could have suitable rigidity and cavity sizes for the coordination of metal cations. They appear to have selectivities for cesium over sodium and lead ions, and 2 shows a log K value of 3.50 for interaction with cesium ion in 80% CH 3 OH/20% water (v/v). Macrotricyclic polyether 2 containing benzene bridgeheads is a new type of ligand, and its structure was confirmed by an X-ray crystallographic study

The macrocycles 1,4-dithia-19-crown-6 and 1,4,7,10-tetrathia-18-crown-6 were chemically bonded to silica gel. Binding constants for the interaction of Pd 2+ , Au 3+ , Ag + , and Hg 2+ with the immobilized macrocycles were determined using a strongly complexing anion or NH 3 so the concentration of uncomplexed cation would be low enough to prevent quantitative loading of the column. Binding constants for Cu 2+ , Fe 3+ , and other base metals were at least 10 orders of magnitude less than constants for Pd 2+ , Au 3+ , Ag + , and Hg 2+

A new method for the simultaneous deactivation and coating of porous silica particles for supercritical fluid chromatography (SFC) has been developed. This method is based on a dehydrocondensation reaction between polymeric silicon hydride reagents and the silanol groups on the surface of the particles. The procedure produces a less active surface than conventional silica packings, which results in less adsorption and improved peak shapes for polar analytes. In SFC, more polar analytes can be chromatographed without the need for mobile phase modifiers. Furthermore, the sensitive and universal flame ionization detector (FID) can be used, since modifiers are not necessary. To avoid splitting of the column effluent before FID detection, packed capillary columns were utilized in this study. The ability to use packed capillary columns for the analysis of polar compounds, while at the same time allowing the use of a wide range of detection methods, serves to expand the number of useful applications for packed column SFC.

Two new dithia-crowns containing a hydroxy group and 1,4,7,10-tetrathia-18-crown-6 containing an allyl-oxymethyl substituent were prepared in good yields. Two of these crowns were covalently attached to silica gel. The silica gel-bound thia-crowns were used to separate gold(III), palladium(II), silver(I) and mercury(II) ions from an aqueous 0.1 M nitric acid solution which also contained 1.0 M ferric chloride.

Current textbooks deal only briefly with the chemistry of starch. A short review with 21 references is presented, describing the structure of starch and indicating the double helix structure of A-type and B-type starch. The structure of the starch granule is examined, pointing out the existence of growth rings of alternating crystalline and noncrystalline starch, with growing amylopectin molecules extending from the hilum (point of origin) to the surface of the starch granule. The swelling of starch granules in water, above the gelatinization temperature of about 60 °C, is discussed. The process of gelatinization involves unraveling of the starch helix and a manyfold increase in volume of the starch granule as water is imbibed and bound to the unraveled starch polymer by hydrogen bonding. Baking bread or pastries causes unraveling of the starch helix, and the process by which these products become stale corresponds primarily to the re-forming of the starch helix. The importance of this phenomenon in food ...

Contemporary methods for the synthesis of alkyl- and arylsubstituted polysiloxane stationary phases are reviewed. A new, moderately polar phase containing the 3-(4-methoxyphenyl)-propyl group is reported.

A method is described for surface deactivation and modification of fused silica capillary columns with a cyanopropyl-containing reagent. The deactivation procedure involved a dehydrocondensation reaction between a bis(cyanopropyl)methylhydropolysiloxane reagent and surface silanol groups at an optimum temperature of only 250°C. Actual critical surface tension measurements were made using the capillary rise method. Excellent deactivation for acidic and basic compounds at the low ng level, and wettability for nonpolar and polar polysiloxane stationary phases were obtained. A procedure was developed to remove acidic impurities that are present in polar stationary phases.

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.

Mesomorphic biphenylcarboxylate esters were coupled via flexible aliphatic hydrocarbon spacers to a polysiloxane backbone. The influence of spacer length, percent mesomorphic substitution, and crosslinking of the stationary phase on liquid-crystalline transition temperatures and on chromatographic performance was investigated. Unique selectivity and good efficiency over a wide temperature range for gum and cross-linked liquid-crystalline phases were demonstrated by the separation of various isomeric polycyclic aromatic compounds.

Polysiloxane polymers, containing polarizable biphenyl, naphtyl and phenoxyphenyl side groups, were synthesized and evaluated for capillary column gas chromatography. Although the more polar cyanopropyl stationary phase demonstrated better resolution of components in a wide-polarity-range mixture, the polarizable phases demonstrated better resolution of polar isomers. The “softer” dipole—induced dipole interaction between the solute and stationary phase, as compared to the dipole—dipole interaction with a polar stationary phase, is more sensitive to slight molecular differences in isomeric structures. The biphenyl polysiloxane, on the whole, demonstrated the best selectivity in a number of isomer separations.

Description des parametres importants dans le choix du solvant revetant et de la temperature de revetement. Influence du solvant sur les viscosites et tensions de surface

New p-cyanophenylethylpolysiloxane and p-cyanophenylpolysiloxane stationary phases exhibiting high efficiency, cross-Iinkability, and thermal stability up to 300°C are reported in this paper. These stationary phases possess a unique blend of polar and polarizable character that has resulted in excellent selectivities for compounds having delocalized nelectrons. Another advantage of the p-cyanophenyl phases is their demonstrated relatively low elution temperatures for polar materials compared with the typical cyanopropyl polysiloxane phases.

Several selective polysiloxane stationary phases were evaluated for the resolution of nitrogen-containing polycyclic aromatic compounds (N-PAC) in coal tar fractions by capillary column gas chromatography. A new liquid crystalline polysiloxane exhibited the highest selectivity for isomeric alkylated 3- and 4-ring N-PAC, whereas a polarizable biphenyl polysiloxane and a moderately polar crown ether-substituted polysiloxane were more applicable for the analysis of 2- and 3-ring N-PAC. The thermal stabilities of these phases made them suitable for GC-MS applications.

Factors affecting gas chromatographic retention on smectic liquid-crystalline phenyl and biphenyl carboxylate ester polysiloxane stationary phases were studied for neutral polycyclic aromatic hydrocarbons (PAHs) and slightly polar sulfur heterocycles. Retention was greatly affected by the molecular geometry of the solutes in addition to other contributions such as solute vapor pressure and polarity. The major geometrical factor was the length-to-breadth ( L/B ) ratio of the solutes, while of less importance, but still significant, was the solute molecular shape. The effect of solute ( L/B ) on selectivity was larger in the smectic region than in the nematic region. Furthermore, the selectivity of the smectic phase was generally better than that of the nematic phase. Compounds with at least four aromatic rings annelated in a straight line were retained much longer, and compounds with aromatic rings annelated in a curved or arc-like arrangement were retained much less, than predicted by the ( L/B ) ratios for these compounds. Arc-like molecules with groups attached to the outer curved side were, however, retained longer than predicted. Lower chromatographic efficiencies were measured for the arc-like molecules as compared to the latter type of molecules. The latter appear to penetrate the laminar arrangement of the polymer liquid-crystalline side groups more easily, thus leading to better solute diffusion and improved mass transfer.

Utilisation des allyloxymethyl dialkyl diaza-18-crowns-6 prepares pour separer les ions Hg(II) de Cd(II) et Zn(II) dans une solution aqueuse de leurs nitrates

Six new polysiloxane materials containing chiral amide side-chains have been prepared by the hydrosilylation of appropriate amide-containing alkenes onto polyhydromethylsiloxane. The alkenes were prepared from either 4-allyloxybenzoic acid or 4-vinylbenzoic acid and the following chiral amines: (S) -1-(1 -naphthyl)ethylamine, (R) -α-methylbenzylamine, the 4-methoxyphenyl ester of alanine and the isopropyl ester of isoleucine. The polysiloxane containing about 7% of the chiral amide prepared from (R) - N -(α-methylbenzyl)-4-allyloxybenzamide proved to be an efficient stationary phase for the capillary gas chromatographic separation of the enantiomers of the N -pentafluoropropionyl isopropyl esters of amino acids of which one example is given. This stationary phase was stable to 280°C.

A series of oligoethylene oxide-containing polysiloxanes were prepared by hydrosilylating the appropriate oligoethylene oxide-containing alkene onto a well-defined polymethylhydrosiloxane polymer. The most convenient oligoethylene oxide-containing alkenes were prepared from eugenol and the tosylate of di- or triethylene glycol monomethyl ether. The polysiloxane phase prepared from 1-(4-allyl-2-methoxyphenoxy)-5-methoxy-3-oxapentane was found to possess desirable chromatographic properties when used in capillary supercritical-fluid chromatography and is suggested as a substitute for Carbowax 20 M . The phase was usable at temperatures from 20°C to 300°C. The synthetic rationale and the effects of structural changes in the polymers on chromatographic performance are discussed in this paper. This paper also contains a systematic study of the influence of chemical structure on chromatographic properties of the resulting polysiloxane phases.

Silica gel-bound crown ethers and aza macrocycles have been synthesized with the attaching arm connected to the carbon framework of the macrocycles. The interactions of these bound macrocycles with cations are almost identical to those involving the analogous free macrocycles. This has allowed for predictable cation separation, concentration, and removal processes to be performed on a small scale. Quantum mechanical calculations and NMR measurements indicate that similarly bound chiral macrocycles will be capable of use in separating chiral organic amines.

Several polyaza-crowns and cyclams, each containing an allyl-oxymethyl or other monofunctional group capable of further reaction to attach it to silica gel, have been prepared. As an example of an attachment of a crown to silica gel, allyloxymethyl-substituted diaza-18-crown-6 was reacted with triethoxysilane to form the crown-substituted triethoxysilane This crown-silane material was heated on silica gel to effect a covalent attachment of the crown. The silica gel-bound macrocyclic ligands were found to interact with various metal cations with log K ( H2O) values similar to those of the same cations with unbound macrocycles. A tetraaza-crown bound to silica gel was found to quantitatively remove toxic heavy metal ions, such as Pb2+, Hg2+ Cd2+ Ag+and others at the ppb level, from large volumes of aqueous solutions containing those metal ions and much larger amounts of Na+Mg2+and Ca2+ions

Solid materials bearing bonded organic functional groups are reviewed. The properties of the oxide supporting materials, silica gel in particular, their chemical and physical properties and the nature of the surface residues are part of this review. Processes leading to modification of the silica gel surface with mono- and polylayers of other oxides resulting in materials with modified properties as well as their susceptibility to chemical modification are also presented. Data on silanization procedures to bond supporting materials with commercial or synthesized organosilicon compounds have been carefully collected and discussed. Special emphasis has been paid to reactions which change the chemical nature of the bonded organic residues leading to valuable materials for partition, ion, ion-exchange, and affinity chromatography as well as for specific separation methods. Data on the collection, separation and preconcentration of inorganic species using these materials are an important part of this ...

The recent permanent attachment of macrocycles such as the crown ethers to silica gel via a hydrocarbon-type linkage has made possible the design of systems capable of the selective and quantitative removal of cations from aqueous solutions. These systems can be operated indefinitely without loss of the expensive macrocycle and maintain the selectivity shown toward metal ions in aqueous solution by the particular macrocycle in the free state. These systems are of potential value in concentrating cations present at the nanogram-per-milliliter level, making their analysis by conventional procedures possible, and in selectively removing either wanted or unwanted metal cations from solutions in which they are present in the milligram-per-milliliter to the nanogram-per-milliliter range. The latter application is treated in this correspondence using the alkaline-earth cations, Ag/sup +/, Hg/sup 2 +/, Tl/sup +/, and Pb/sup 2 +/.

Values of log K for the association of several metal cations with 15-crown-5, 18-crown-6, and N,N′-dibenzyldiaza-18-crown-6, each covalently bonded to silica gel, were found to be nearly the same as those for the association of the same cations with the unbound macrocycles; this observation indicates the possibility of building pre-determined cation selectivity into these permanent macrocycle-bound silica gel systems.