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Richard A Bartsch

Publications and source records attributed to Richard A Bartsch.

At least 19 recordsLinked to original sources
PubMed2006

Effect of para-substituents on alkaline earth metal ion extraction by proton di-ionizable calix[4]arene-crown-6 ligands in cone, partial-cone and 1,3-alternate conformations.

Two carboxylic acid or N-(X)sulfonyl carboxamide groups were incorporated into calix[4]arene-crown-6 compounds to afford di-ionizable ligands for use in divalent metal ion separations. Acidities of the N-(X)sulfonyl carboxamide groups were tuned by variation of the electron-withdrawing properties of X. Cone, partial-cone and 1,3-alternate conformations were obtained by different synthetic strategies and their structures verified by NMR spectroscopy. Competitive solvent extractions of alkaline earth metal cations from aqueous solutions into chloroform were performed and the results compared with those reported previously for di-ionizable p-tert-butylcalix[4]arene-crown-6 analogues to probe the influence of the para-substituent on the calix[4]arene scaffold on extraction selectivity and efficiency.

Journal Article↗
PubMed2006

A PCT-based, pyrene-armed calix[4]crown fluoroionophore.

A photoinduced charge transfer (PCT)-based 1,3-alternate calix[4]crown fluoroionophore containing two cation recognition sites, a crown ether ring and two facing pyreneamide groups, is synthesized. Upon addition of K+, Pb2+, or Cu2+, wavelength changes are observed in both the fluorescence and absorption spectra, but with different binding modes. With K+, fluorescence emissions of the ligand scarcely change, while addition of Pb2+ or Cu2+ produces a remarkable change in both the excimer and monomer emissions. The observed data indicate that the metal cation is encapsulated in the crown-5 ring for K+ and by the two facing amide groups in the latter case, which is verified by a metal ion exchange experiment. The wavelength shifts in both fluorescence and absorption spectra upon addition of Cu2+ show that, in contrast to Pb2+, Cu2+ interacts with the nitrogen atoms of the amide groups, resulting in a PCT mechanism.

Journal Article↗
PubMed2006

Additivity in the optical kerr effect spectra of binary ionic liquid mixtures: implications for nanostructural organization.

Low-frequency spectra of binary room-temperature ionic liquid (RTIL) mixtures of 1-pentyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 1-pentyl-3-methylimidazolium bromide in the 0-250 cm(-1) region were studied as a function of mole fraction at 295 K. The spectra were obtained by use of optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The spectra of these binary mixtures are well described by the weighted sums of the spectra for the neat RTILs. This surprising result implies that the intermolecular modes giving rise to the spectra of the neat liquids must also produce the spectra of the mixtures. Additivity of the OKE spectra can be explained by a model in which locally ordered domains are assumed to exist in the neat liquid with the structures of these locally ordered domains preserved upon mixing. Recently published molecular dynamics simulations show that RTILs are nanostructurally organized with ionic networks and nonpolar regions. If ionic networks also exist in the mixture, the additivity of the OKE spectra implies that there are "blocks" along the network of the mixture that are ordered in the same way as in the neat liquids. These "block co-networks" would have a nanostructural organization resembling that of a block copolymer.

Letter↗
PubMed2006

Di-ionizable p-tert-butylcalix[4]arene-1,2-crown-5 and -crown-6 compounds in the cone conformation: synthesis and alkaline earth metal cation extraction.

Di-ionizable p-tert-butylcalix[4]arene-1,2-crown-5 and -crown-6 ethers in the cone conformation were prepared and their conformations and regioselectivities were verified by NMR spectroscopy. The metal ion-complexing properties of these ligands were evaluated by competitive solvent extractions of alkaline earth metal cations from water into chloroform. The ligands were found to be efficient extractants with selectivity for Ba(2+). The maximal loadings were 95-100% as calculated for formation of 1 : 1 ionized ligand-metal ion complexes. With the variation of proton-ionizable groups, which were oxyacetic acid moieties and N-(X)sulfonyl oxyacetamide units with X = methyl, phenyl, 4-nitrophenyl, and trifluoromethyl, "tunable" acidity was obtained.

Journal Article↗
PubMed2006

Synthesis and alkaline earth metal cation extraction by proton di-ionizable p-tert-butylcalix[4]arene-crown-5 compounds in cone, partial-cone and 1,3-alternate conformations.

Synthetic strategies for novel, proton di-ionizable p-tert-butylcalix[4]arene-crown-5 compounds in cone, partial-cone and 1,3-alternate conformations are reported. Selective linkage of the two diametrical phenolic oxygens in p-tert-butylcalix[4]arene with tetraethylene glycol ditosylate gave 1,3-bridged p-tert-butylcalix[4]arene-crown-5. The two remaining phenolic units were alkylated using NaH and KH as the bases to give the cone and partial-cone conformers, respectively. Preparation of the 1,3-alternate conformers utilized a different sequence in which O-alkylation was followed by crown ether ring formation. Structures of these new ligands were elucidated by (1)H and (13)C NMR spectroscopy. These proton-ionizable ligands were tested for their solvent extraction properties toward alkaline earth metal cations. Surprising differences in their extraction behaviors are noted compared to those reported previously for di-ionizable p-tert-butylcalix[4]arenecrown-6 analogues.

Journal Article↗
PubMed2005

Indium(III)-induced fluorescent excimer formation and extinction in calix[4]arene-fluoroionophores.

New fluorogenic or/and chromogenic calix[4]arenes 1-3 with two facing amide groups linked to fluorescent pyrene units are synthesized. Orientations of the pyrene units are remote from each other in 1 and face-to-face pi-stacked in 2, which produces different photophysical properties. In the excited state, the two pyrene units of 2 form a strong intramolecular excimer displaying an emission at 472 nm with a relatively weak monomer emission at 395 nm. In contrast, 1 exhibits only a monomer emission at 398 nm because intramolecular hydrogen bonding between the phenolic OH oxygens and the amide hydrogens prevents pi-stacking of the two pyrene groups. Fluorescence changes upon addition of various metal ions show that 1 has a remarkably high selectivity for In(3+) over the other metal ions tested. Compound 1 forms 2:1 (metal:ligand), as well as 1:1 complexes, with In(3+), with fluorescence varying uniquely with the complex stoichiometry. Compound 3, which possess two pyrene units and two chromogenic azo groups, shows almost the same binding behavior toward metal ions as does 1, together with additional bathochromic shifts of the absorption maximum. Compared with 1, compound 3 emits a considerably weaker fluorescence, which is attributed to electron transfer from the pyrene units to the nitro groups of the phenylazo moieties.

Calixarenes↗
PubMed2005

A fluoride-selective PCT chemosensor based on formation of a static pyrene excimer.

[reaction: see text] Calixarene-based fluorescent chemosensor 1 with two fluorogenic pyrene units conjugated to amide groups as guest recognition sites is synthesized. Complexation of F(-) by 1 causes a red shift of its absorption band to 400 nm (Deltalambda = 54 nm) and a blue shift of the excimer emission to 470 nm (Deltalambda = 12 nm) together with enhanced fluorescence intensity. The blue-shifted excimer emission is attributed to a pyrene dimer formed in the ground state, a so-called static excimer.

Calixarenes↗
PubMed2005

Structural toxicity relationship of 4-alkoxyphenols' cytotoxicity towards murine B16-F0 melanoma cell line.

PURPOSE: The aim of this study was to identify phenolic agents that could form quinone reactive intermediate metabolites in melanocytes in order to be effective as anti-melanoma agents; but were not metabolized by liver P450 metabolizing enzymes in order to have minimal toxicity towards the liver. METHODS: Tyrosinase, an enzyme present abundantly in melanocytes was selected as a molecular target for the treatment of malignant melanoma. Ten alkoxyphenols were investigated for their metabolism by tyrosinase/O2, rat liver P450 microsomal/NADPH/O2 metabolizing systems and for their toxicity towards B16-F0 melanoma cells. RESULTS: All the alkoxyphenols showed a dose- and time-dependent toxicity towards B16-F0 cells except 2-iso-propoxyphenol. 4-n-hexyloxyphenol demonstrated the greatest toxicity towards B16-F0 cells while minimally depleting glutathione in microsomal preparations at its calculated LC10 and LC50 lethal concentrations for B16-F0. At 100 microM concentrations, 4-t-butoxyphenol showed the lowest amount of glutathione depletion by microsomal P450 system. Alkoxyphenols with at least two alkyl groups derivatized at alpha carbon of alkoxy group showed minimal rates of metabolism by tyrosinase/O2 metabolizing system. A quantitative structural toxicity relationship equation was also derived, LogLC50(mM)= -0.265(+/-0.064)LogP + 2.482(+/-0.179). CONCLUSIONS: 4-n-hexyloxy-phenol was identified as a potential lead anti-melanoma agent against B16-F0 melanoma cells with minimal metabolism by rat liver P450 microsomal preparation.

Alcohols↗
PubMed2005

Proton di-ionizable p-tert-butylcalix[4]arene-crown-6 compounds in cone, partial-cone and 1,3-alternate conformations: synthesis and alkaline earth metal cation extraction.

Novel proton di-ionizable p-tert-butylcalix[4]arene-crown-6 compounds in cone, partial-cone and 1,3-alternate conformations are synthesized to compare the efficiency and selectivity with which they extract alkaline earth metal ions. In these ligands, a crown-6 polyether unit links alternate aromatic rings of the calix[4]arene framework. To the remaining lower-rim positions are attached oxyacetic acid or N-(X)sulfonyl oxyacetamide groups. Changing the conformation varies the spatial relationship between a polyether-complexed divalent metal ion and the ionized side arms of the ligands. This is found to markedly affect the efficiency and selectivity in competitive solvent extraction of alkaline earth metal ions from aqueous solutions into chloroform by the di-ionizable calix[4]arene-crown-6 ligands.

Journal Article↗
PubMed2004

An excimer-based, binuclear, on-off switchable calix[4]crown chemosensor.

A new fluorescent chemosensor with two different types of cation binding sites on the lower rims of a 1,3-alternate calix[4]arene (1) is synthesized. Two pyrene moieties linked to a cation recognition unit composed of two amide groups form a strong excimer in solution. For 1, the excimer fluorescence is quenched by Pb2+, but revived by addition of K+ to the Pb2+ ligand complex. Thus, metal ion exchange produces an on-off switchable, fluorescent chemosensor. Computational results show that the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbitals (LUMO) of the two pyrene moieties interact under UV irradiation of 1 and its K+ complex, while such HOMO-LUMO interactions are absent in the Pb2+ complex.

Calixarenes↗
PubMed2004

Rigid versus flexible: how important is ligand "preorganization" for metal ion recognition by lower rim-functionalized calix[4]arenes?

For an assessment of the outcomes from use of an appropriately "preorganized" calixarene-based ionophore versus its conformationally mobile prototype, solvent extraction propensities of flexible calix[4]arene di-[N-(X-sulfonyl)carboxamides] for alkali, alkaline earth metal cations, Pb2+, Ag+ and Hg2+ are compared with those for seven new rigid analogs fixed in the cone, partial cone and 1,3-alternate conformations. For each of the metal ions, the preferred calix[4]arene conformation was determined from the NMR spectra for the metal salt of the flexible ligand. Except for Ag+, flexible calix[4]arene di-[N-(X-sulfonyl)carboxamides] were found to provide greater metal ion extraction efficiency and better selectivity than the corresponding "preorganized" ionophores.

Journal Article↗
PubMed2003

Rapid metal ions shuttling through 1,3-alternate Thiacalix[4]crown tubes.

Several new thiacalix[4]monocrown and thiacalix[4]biscrown compounds were synthesized. Their metal ion extractabilities are found to be lower than those of conventional calix[4]crowns. By use of X-ray crystal structures and (1)H NMR spectroscopy, this result is explained by weaker electrostatic interactions of the polyether ring oxygen atoms with the metal ions and diminished pi-metal ion interactions between the metal ions and the aromatic rings of the thiacalix[4]crowns. Temperature-dependent (1)H NMR spectroscopic measurements reveal coalescence temperatures T(c)(intra) and T(c)(inter) for metal ion exchange. In one case, this exchange was rationalized as metal ion shuttling through a thiacalix[4]biscrown tube. Since the metal ions are less tightly complexed by the polyether units in thiacalix[4]biscrowns than in conventional calix[4]biscrowns, more facile metal ion exchange between the two polyether units takes place in the former.

Journal Article↗
PubMed2003

Ion flotation of cadmium(II) and zinc(II) in the presence of proton-ionizable lariat ethers.

Competitive flotation of Cd(II) and Zn(II) from very dilute aqueous solutions by proton-ionizable lariat ethers in the presence of nonylphenol nona(ethylene glycol) ether as a nonionic foaming agent is reported. Influences of structural variation within the collector (identity of the pendent acidic group and lipophilicity), concentration of the collector, and pH of the aqueous solution are assessed. A monoethyl lariat ether phosphonic acid collector is found to exhibit high Cd(II)/Zn(II) flotation selectivity under certain conditions.

Journal Article↗
PubMed2003

High-intensity ultrasound-promoted reformatsky reactions.

Reformatsky reactions of a phenyl ketone, an alpha-bromoester, zinc dust, and a catalytic amount of iodine in dioxane under high-intensity ultrasound (HIU) irradiation from an ultrasonic probe give high yields of beta-hydroxyesters in short reaction times. A series of alkyl phenyl ketones with increasing steric demands of the alkyl group are evaluated as potential electrophiles for the reactions with several alpha-bromoesters, also having increasing steric demands. The Reformatsky reaction under HIU is found to be concentration dependent.

Journal Article↗
PubMed2003

Evaluation of alkali and alkaline earth metal cation selectivities of lariat ether amides by electrospray ionization mass spectrometry.

Lariat ethers with pendant amide groups have shown promise as new ion sensors because of their selectivity towards particular metal ions. In this study we report alkali and alkaline earth metal binding selectivities of dibenzo-16-crown-5 and fifteen dibenzo-16-crown-5 lariat ether amides (LEAs) as determined by electrospray ionization mass spectrometry (ESI-MS). Additionally, the influence of the acid/base nature of the solution on metal cation selectivity is investigated. The validity of using ESI-MS for determination of selectivities is established by analogous experiments using hosts with known binding constants for the same metal cations and solvent systems. Collisionally activated dissociation (CAD) is used to evaluate the influence of the alkali metal cation binding on the fragmentation of the LEAs.

Journal Article↗