Effect of structural modifications of diaza-18-crown-6 on the extractability and selectivity of univalent metal picrates

The solvent extraction of univalent metal cations with N,N'-dibenzyl-1,4,10,13-tetraoxa-7,16 diaza-2,3,11,12-dibenzocycloocta deca-2,11-diene (L(1)), N,N' didodecyl-1,4,10,13-tetraoxa-7,16-diaza-2,3-benzocylooctadeca-2 ene (L(2)) and N,N'-dibenzyl-1,4,10,13-tetraoxa-7,16 diaza-2,3,11,12-dibenzocyclo octadeca-2,11-diene (L(3)) with picrate anion into dichloromethane has been studied at 25 degrees C by UV-visible spectroscopy. The extractability and selectivity of univalent metal picrates (Li(+), Na(+), Ag(+), PhCH(2)NH(3)(+), NH(4)(+)) was evaluated as a function of [ligand]/[metal cation]. L(2) showed the highest extractability and selectivity for Li(+) over the larger studied cations, and also exhibited the highest [Li(+)]/[NH(4)(+)] selectivity as L/M=1.     

Extraction equilibria of various metal picrates with 19-crown-6 between benzene and water. Effect of the extra methylene group on extraction ability and selectivity

The overall extraction equilibrium constants (K(ex)) of picrates of Li(+), Na(+), K(+), Rb(+), Cs(+), Ag(+), Tl(+), and Sr(2+)with 19-crown-6 (19C6) were determined between benzene and water at 25 degrees C. The K(ex) values were analyzed into the constituent equilibrium constants, i.e. the extraction constant of picric acid, the distribution constant of the crown ether, the formation constant of the metal ion-crown ether complex in water, and the ion-pair extraction constant of the complex cation with the picrate anion. The effects of an extra methylene group of 19C6 on the extraction ability and selectivity are discussed in detail by comparing the constituent equilibrium constants of 19C6 with those of 18-crown-6 (18C6). The K(ex) value of 19C6 for each metal ion is lower than that of 18C6, which is mostly attributed to the higher lipophilicity of 19C6. The extraction ability of 19C6 for the univalent metal ions decreases in the order Tl(+)>K(+)>Rb(+)>Ag(+)>Cs(+)>Na(+)Li(+), which is the same as that observed for 18C6. The difference in logK(ex) between the univalent metals is generally smaller for 19C6 than for 18C6. The extraction selectivity of 19C6 is governed by the selectivity in the ion-pair extraction, whereas that of 18C6 depends on both the selectivities in the ion-pair extraction and in the complexation in water.     

Photometric reagents for alkali metal ions, based on crown-ether complex formation--III. 4'-picrylaminobenzo-15-crown-5 derivatives

An extraction study of alkali metal cations has been made with crown-ether reagents, 4'-picrylaminobenzo-15-crown-5 derivatives (HL). On dissociation in alkaline medium, the orange HL gives the blood-red anion L(-) and extracts alkali metal ions into chloroform as coloured complexes of composition ML.HL or ML. The ease of extraction decreases in the order, K(+) > Rb(+) > Cs(+) > Na(+) > Li(+). The extracted complexes are ML.HL for K(+) and Rb(+), and both ML.HL and ML for Na(+). The Li(+) complex is not extracted. The photometric determination of 10-800 ppm of K(+) is possible in the presence of other alkali and alkaline earth metal ions.     

UV and IR spectroscopic studies of cold alkali metal ion-crown ether complexes in the gas phase

We report UV photodissociation (UVPD) and IR-UV double-resonance spectra of dibenzo-18-crown-6 (DB18C6) complexes with alkali metal ions (Li(+), Na(+), K(+), Rb(+), and Cs(+)) in a cold, 22-pole ion trap. All the complexes show a number of vibronically resolved UV bands in the 36,000-38,000 cm(-1) region. The Li(+) and Na(+) complexes each exhibit two stable conformations in the cold ion trap (as verified by IR-UV double resonance), whereas the K(+), Rb(+), and Cs(+) complexes exist in a single conformation. We analyze the structure of the conformers with the aid of density functional theory (DFT) calculations. In the Li(+) and Na(+) complexes, DB18C6 distorts the ether ring to fit the cavity size to the small diameter of Li(+) and Na(+). In the complexes with K(+), Rb(+), and Cs(+), DB18C6 adopts a boat-type (C(2v)) open conformation. The K(+) ion is captured in the cavity of the open conformer thanks to the optimum matching between the cavity size and the ion diameter. The Rb(+) and Cs(+) ions sit on top of the ether ring because they are too large to enter the cavity of the open conformer. According to time-dependent DFT calculations, complexes that are highly distorted to hold metal ions open the ether ring upon S(1)-S(0) excitation, and this is confirmed by extensive low-frequency progressions in the UVPD spectra.     

Extraction of sodium and potassium picrates with 15-(2,5-dioxahexyl)-15-methyl-16-crown-5 (lariat 16C5) into various organic solvents. Elucidation of fundamental equilibria which determine the extraction ability for Na(+) and K(+) and the selectivity

To quantitatively elucidate the effects of the side chains and diluents on the extraction selectivity for sodium and potassium picrates of 15-(2,5-dioxahexyl)-15-methyl-16-crown-5 (L16C5) from the viewpoint of equilibrium, the constants for the overall extraction (K(ex)), the partition for various diluents of low dielectric constants (K(D,MLA)), and the aqueous ion-pair formation (K(MLA)) of L16C5-sodium and -potassium picrate 1:1:1 complexes were determined at 25 degrees C; the distribution constants of L16C5 were also measured at 25 degrees C. The log K(MLA) values for Na(+) and K(+) are 2.74+/-0.29 and 1.70+/-0.36, respectively. In going from 16-crown-5 (16C5) to L16C5, the side chains decrease the K(MLA) value, but do not increase the difference in K(MLA) between Na(+) and K(+). The distribution behavior of L16C5 and its 1:1:1 complexes with the alkali metal picrates closely obeys regular solution theory, except for chloroform. Molar volumes and solubility parameters of L16C5 and the 1:1:1 complexes were determined. The magnitude of K(ex) is mainly governed by the K(M(L16C5)A) value. For every diluent, L16C5 shows Na(+) extraction selectivity over K(+). The Na(+) extraction selectivity of L16C5 is determined completely by K(M(L16C5)A). The extraction ability and selectivity for sodium and potassium picrates by L16C5 are compared with those of 16C5 on the basis of the fundamental equilibrium constants.     

UV and IR spectroscopy of cold 1,2-dimethoxybenzene complexes with alkali metal ions

We report UV photodissociation (UVPD) and IR-UV double-resonance spectra of 1,2-dimethoxybenzene (DMB) complexes with alkali metal ions, M(+)·DMB (M = Li, Na, K, Rb, and Cs), in a cold, 22-pole ion trap. The UVPD spectrum of the Li(+) complex shows a strong origin band. For the K(+)·DMB, Rb(+)·DMB, and Cs(+)·DMB complexes, the origin band is very weak and low-frequency progressions are much more extensive than that of the Li(+) ion. In the case of the Na(+)·DMB complex, spectral features are similar to those of the K(+), Rb(+), and Cs(+) complexes, but vibronic bands are not resolved. Geometry optimization with density functional theory indicates that the metal ions are bonded to the oxygen atoms in all the M(+)·DMB complexes. For the Li(+) complex in the S(0) state, the Li(+) ion is located in the same plane as the benzene ring, while the Na(+), K(+), Rb(+), and Cs(+) ions are located off the plane. In the S(1) state, the Li(+) complex has a structure similar to that in the S(0) state, providing the strong origin band in the UV spectrum. In contrast, the other complexes show a large structural change in the out-of-plane direction upon S(1)-S(0) excitation, which results in the extensive low-frequency progressions in the UVPD spectra. For the Na(+)·DMB complex, fast charge transfer occurs from Na(+) to DMB after the UV excitation, making the bandwidth of the UVPD spectrum much broader than that of the other complexes and producing the photofragment DMB(+) ion.     

Adduct formation between alkali metal ions and anionic LV(V)O(2)(-) (L(2-) = tridentate ONS ligands) species: syntheses, structural investigation, and photochemical studies

Syntheses of alkali metal adducts [LVO(2)M(H(2)O)(n)] (1-7) (M = Na(+), K(+), Rb(+), and Cs(+); L = L(1)(-)L(3)) of anionic cis-dioxovanadium(V) species (LVO(2)(-)) of tridentate dithiocarbazate-based Schiff base ligands H(2)L (S-methyl-3-((5-(R-2-hydroxyphenyl))methyl)dithiocarbazate, R = H, L = L(1); R = NO(2), L = L(2); R = Br, L = L(3)) have been reported. The LVO(2)(-) moieties here behave like an analogue of carboxylate group and have displayed interesting variations in their binding pattern with the change in size of the alkali metal ions as revealed in the solid state from the X-ray crystallographic analysis of 1, 3, 6, and 7. The compounds have extended chain structures, forming ion channels, and are stabilized by strong Coulombic and hydrogen-bonded interactions. The number of coordinated water molecules in [LVO(2)M(H(2)O)(n)] decreases as the charge density on the alkali metal ion decreases (n = 3.5 for Na(+) and 1 for K(+) and Rb(+), while, for Cs(+), no coordinated water molecule is present). In solution, compounds 1-7 are stable in water and methanol, while in aprotic solvents of higher donor strengths, viz. CH(3)CN, DMF and DMSO, they undergo photoinduced reduction when exposed to visible light, yielding green solutions from their initial yellow color. The putative product is a mixed-oxidation (mu-oxo)divanadium(IV/V) species as revealed from EPR, electronic spectroscopy, dynamic (1)H NMR, and redox studies.     

Solvent effects on extraction of alkali metal picrates with 15-crown-5 into various organic solvents. Elucidation of fundamental equilibria which govern extraction-efficiency and -selectivity

Extractions of alkali metal (Na-Cs) picrates (MA) with 15-crown-5 (15C5) into various diluents of low dielectric constant were conducted at 25 degrees C. Using the extraction data, the ion-pair formation constants (K(MLA)) in water of 15C5-MA 1:1:1 complexes were determined by an equation derived from the regular solution theory (logK(MLA)=4.43+/-0.27 for Na, 3.27+/-0.42 for K, 3.58+/-0.35 for Rb, and 2.78+/-0.41 for Cs). The actual overall extraction equilibrium constants were obtained by considering the concentrations of the 1:1:1 15C5 complexes and the ion-pair formation between uncomplexed alkali metal and picrate ions in the aqueous phase. The distribution constants of the 15C5 complexes were calculated and their partition behavior is explained by the regular solution theory. Molar volumes and solubility parameters of 15C5 itself and the complexes were determined. Extraction-efficiency and -selectivity of 15C5 for alkali metal picrates were completely elucidated from the standpoint of equilibrium.     

Infrared multiple photon dissociation spectroscopy of cationized histidine: effects of metal cation size on gas-phase conformation

The gas phase structures of cationized histidine (His), including complexes with Li(+), Na(+), K(+), Rb(+), and Cs(+), are examined by infrared multiple photon dissociation (IRMPD) action spectroscopy utilizing light generated by a free electron laser, in conjunction with quantum chemical calculations. To identify the structures present in the experimental studies, measured IRMPD spectra are compared to spectra calculated at B3LYP/6-311+G(d,p) (Li(+), Na(+), and K(+) complexes) and B3LYP/HW*/6-311+G(d,p) (Rb(+) and Cs(+) complexes) levels of theory, where HW* indicates that the Hay-Wadt effective core potential with additional polarization functions was used on the metals. Single point energy calculations were carried out at the B3LYP, B3P86, and MP2(full) levels using the 6-311+G(2d,2p) basis set. On the basis of these experiments and calculations, the only conformation that reproduces the IRMPD action spectra for the complexes of the smaller alkali metal cations, Li(+)(His) and Na(+)(His), is a charge-solvated, tridentate structure where the metal cation binds to the backbone carbonyl oxygen, backbone amino nitrogen, and nitrogen atom of the imidazole side chain, [CO,N(α),N(1)], in agreement with the predicted ground states of these complexes. Spectra of the larger alkali metal cation complexes, K(+)(His), Rb(+)(His), and Cs(+)(His), have very similar spectral features that are considerably more complex than the IRMPD spectra of Li(+)(His) and Na(+)(His). For these complexes, the bidentate [CO,N(1)] conformer in which the metal cation binds to the backbone carbonyl oxygen and nitrogen atom of the imidazole side chain is a dominant contributor, although features associated with the tridentate [CO,N(α),N(1)] conformer remain, and those for the [COOH] conformer are also clearly present. Theoretical results for Rb(+)(His) and Cs(+)(His) indicate that both [CO,N(1)] and [COOH] conformers are low-energy structures, with different levels of theory predicting different ground conformers.     

冠醚配合物的热力学性质的研究 III. 碱金属离子与18C6甲基衍生物配位反应的电导研究

The coordination reaction of Na+, K+, Rb+ and Cs+ with benzo- 15-crown-5, 18-crown-6 and the newly synthesized cyclic polyethers 2, 3-benzo-8, 15-dimethyl-18-crown-6, 2, 3-benzo-8, 11, 15-trimethyl-18-crown-6 in methanol at 25`C has been studied by conductometric titration. The stability constants for the 1:1 coordination compounds were calculated. The marked selectivity of 18-crown-6 toward alkali metal ions was not found in its methyl derivatives. The induction effect of the benzene ring and methyl group on polyether ring reduced the stability of the coordination compounds. In methanol, the stability sequence of te compounds of alkali metal ions with 18-crown-6 was K+>Rb+>Cs+>Na+, that of its dimethyl derivative was K+>Rb+>Na+>Cs+ and that of its trimethyl derivative was K+>Na+>Rb+>Cs+, that is, the methyl substituent had a weaker influence on the stability of Na+ compound than on that of Rb+ or Cs+ compound. In the range of concentration studied, decrease in equivalent conductance is in agreement with the prediction on the basis of the structure of the complexes. The above results may give a clue for modifying the structure of a crown ether for specified selectivity.     

Oligoether-strapped calix[4]pyrrole: an ion-pair receptor displaying cation-dependent chloride anion transport

A ditopic ion-pair receptor (1), which has tunable cation- and anion-binding sites, has been synthesized and characterized. Spectroscopic analyses provide support for the conclusion that receptor 1 binds fluoride and chloride anions strongly and forms stable 1:1 complexes ([1·F](-) and [1·Cl](-)) with appropriately chosen salts of these anions in acetonitrile. When the anion complexes of 1 were treated with alkali metal ions (Li(+), Na(+), K(+), Cs(+), as their perchlorate salts), ion-dependent interactions were observed that were found to depend on both the choice of added cation and the initially complexed anion. In the case of [1·F](-), no appreciable interaction with the K(+) ion was seen. On the other hand, when this complex was treated with Li(+) or Na(+) ions, decomplexation of the bound fluoride anion was observed. In contrast to what was seen with Li(+), Na(+), K(+), treating [1·F](-) with Cs(+) ions gave rise to a stable, host-separated ion-pair complex, [F·1·Cs], which contains the Cs(+) ion bound in the cup-like portion of the calix[4]pyrrole. Different complexation behavior was seen in the case of the chloride complex, [1·Cl](-). Here, no appreciable interaction was observed with Na(+) or K(+). In contrast, treating with Li(+) produces a tight ion-pair complex, [1·Li·Cl], in which the cation is bound to the crown moiety. In analogy to what was seen for [1·F](-), treatment of [1·Cl](-) with Cs(+) ions gives rise to a host-separated ion-pair complex, [Cl·1·Cs], in which the cation is bound to the cup of the calix[4]pyrrole. As inferred from liposomal model membrane transport studies, system 1 can act as an effective carrier for several chloride anion salts of Group 1 cations, operating through both symport (chloride+cation co-transport) and antiport (nitrate-for-chloride exchange) mechanisms. This transport behavior stands in contrast to what is seen for simple octamethylcalix[4]pyrrole, which acts as an effective carrier for cesium chloride but does not operates through a nitrate-for-chloride anion exchange mechanism.     

A solid-state 23Na NMR study of monovalent cation binding to double-stranded DNA at low relative humidity

We report a solid-state (23)Na NMR study of monovalent cation (Li(+), Na(+), K(+), Rb(+), Cs(+) and NH(4) (+)) binding to double-stranded calf thymus DNA (CT DNA) at low relative humidity, ca 0-10%. Results from (23)Na--(31)P rotational echo double resonance (REDOR) NMR experiments firmly establish that, at low relative humidity, monovalent cations are directly bound to the phosphate group of CT DNA and are partially dehydrated. On the basis of solid-state (23)Na NMR titration experiments, we obtain quantitative thermodynamic parameters concerning the cation-binding affinity for the phosphate group of CT DNA. The free energy difference (DeltaG degrees ) between M(+) and Na(+) ions is as follows: Li(+) (-1.0 kcal mol(-1)), K(+) (7.2 kcal mol(-1)), NH(4) (+) (1.0 kcal mol(-1)), Rb(+) (4.5 kcal mol(-1)) and Cs(+) (1.5 kcal mol(-1)). These results suggest that, at low relative humidity, the binding affinity of monovalent cations for the phosphate group of CT DNA follows the order: Li(+) > Na(+) > NH(4) (+) > Cs(+) > Rb(+) > K(+). This sequence is drastically different from that observed for CT DNA in solution. This discrepancy is attributed to the different modes of cation binding in dry and wet states of DNA. In the wet state of DNA, cations are fully hydrated. Our results suggest that the free energy balance between direct cation-phosphate contact and dehydration interactions is important. The reported experimental results on relative ion-binding affinity for the DNA backbone may be used for testing theoretical treatment of cation-phosphate interactions in DNA.     

Substitution effect,absorption, and fluorescence behaviors of 11,12-benzo-1,7,10,13-tetraoxa-4-aza- cyclopentadec-11-ene (benzoaza-15-crown-5) derivatives upon cation complexation in solvent extraction

Substitution effect, absorption, and fluorescence behaviors of some benzoaza-15-crown-5 derivatives upon cation complexation in solvent extraction were studied. The introduction of a substituent on the nitrogen atom in benzoaza-15-crown-5 enhanced extractabilities in the solvent extraction of aqueous alkali metal picrates. The nondonating substituents raised the cation selectivity for Na(+) over K(+), but the donating substituents reduced the cation selectivity. The absorption and fluorescence spectral behavior was different with the alkali metal cations.     

Extraction of sodium and potassium perchlorates with benzo-18-crown-6 into various organic solvents. Quantitative elucidation of anion effects on the extraction-ability and -selectivity for Na(+) and K(+)

To investigate quantitatively the anion effect on the extraction-ability and -selectivity of benzo-18-crown-6 (B18C6) for alkali metal ions, the constants for overall extraction into various diluents having low dielectric constants (K(ex)) and aqueous ion-pair formation (K(MLA)) of B18C6-sodium and potassium perchlorate 1:1:1 complexes (MLA) were determined at 25 degrees C. The K(ex) value was analyzed by the four fundamental equilibrium constants. The K(MLA) values were determined by applying our established method to this perchlorate extraction system. The K(M(B18C6)A) value of the perchlorate is much larger for K(+) than for Na(+), and is much smaller than that of the picrate. The K(M(B18C6)A) value makes a minor contribution to the magnitude of K(ex) for the perchlorate system, but a major contribution to that for the picrate one. The distribution behavior of the B18C6 1:1:1 complexes with the alkali metal perchlorates follows the regular solution theory. For the diluent with a high dipole moment, however, the 1:1:1 complexes somewhat undergo the dipole-dipole interaction. B18C6 always shows very high extraction selectivity for KClO(4) over NaClO(4), which is determined mostly by the much greater log/(log K(MLA)) value for K(+) than for Na(+). The extraction-ability and -selectivity of B18C6 for Na(+) and K(+) ions with a perchlorate ion were compared with those with a picrate ion in terms of the fundamental equilibrium constants. The K(+) extraction-selectivity of B18C6 over Na(+) for the perchlorate system is superior to that for the picrate one, which is caused largely by the greater log/(log K(K(B18C6)A))-log/(log K(Na(B18C6)A)) value for the perchlorate than for the picrate. The perchlorate system is recommended for extraction separation of K(+) from Na(+).     

Extraction mechanism of monovalent ion-pairs by polyurethane foams

The extractability sequence of K(+) approximately Rb(+) > Cs(+) > Na(+) > Li(+) for the extraction with polyether foam suggests that the cation chelation mechanism might be operative. However, the same order was obtained for the extraction with 100% polypropylene oxide polyether foam which does not normally adopt a helical structure to form oxygen-rich cavities as easily or as effectively as polyethylene oxide to accommodate alkali metal ions. This result indicates that a hole-size/cation-diameter relationship may not be required for the high extraction of K(+). The extraction of alkali metal DPAs and hydroxides from methanol demonstrates the importance of the solvent effect. It indicates that the water-structure enforced ion-pairing (WSEIP) is the driving force for extraction of the ion-pairs. The extraction mechanism for ionic species can be described as an ion-pair extraction process. The overall effect of ion-pair formation in water and interaction of the extracted ions with foam appears to determine the extractability of the ions of the extractable ion-pair.     

Determination of stability constants of valinomycin complexes with ammonium and alkali metal ions by capillary affinity electrophoresis

Capillary affinity electrophoresis (CAE) has been employed to investigate quantitatively the interactions of valinomycin, macrocyclic depsipeptide antibiotic ionophore, with univalent cations, ammonium and alkali metal ions, K(+), Cs(+), Na(+), and Li(+), in methanol. The study involved measuring the change in effective electrophoretic mobility of valinomycin while the cation concentrations in the BGE were increased. The corresponding apparent stability (binding) constants of the valinomycin-univalent cation complexes were obtained from the dependence of valinomycin effective mobility on the cation concentration in BGE using a nonlinear regression analysis. The calculated apparent stability constants of the above-mentioned complexes show the substantially higher selectivity of valinomycin for K(+) and Cs(+) ions over Li(+), Na(+), and NH(4)(+) ions. CAE proved to be a suitable method for the investigation of both weak and strong interactions of valinomycin with small ions.     

Investigation of homo- and heterodimer alkali metal cation complexes of resorc[4]arenes by electrospray ionization mass spectrometry

Resorc[4]arenes are compounds with interesting properties, mainly because of their ability to form host-guest complexes with the guest located inside the cavity. The size of the guest limits the complexation, as shown by a competition experiment with tetraalkylammonium ions of different size. By electroscopy ionization tandem mass spectrometric experiments on resorc[4]arene heterodimers bearing an alkali metal ion as guest, it was found that there must be two different binding mechanisms for alkali metal ions with high surface charge density (Li(+) and Na(+)) on the one hand compared with those with a lower surface charge density on the other hand (K(+), Rb(+), Cs(+)).     

Extraction of Alkali Metal (Na—Cs) Picrates with Dibenzo-18-crown-6 into Various Organic Solvents. Elucidation of Fundamental Equilibria which Govern the Extraction-Ability and -Selectivity

In order to quantitatively investigate effects of the size, the structuralrigidity, and the lipophilicity of dibenzo-18-crown-6 (DB18C6) on itsextraction-ability and -selectivity for alkali metal ions, constants of theoverall extraction (Kex), the distribution for various diluents of lowdielectric constants (K_D,MLA), and the aqueous ion-pairformation (K_MLA) of DB18C6-alkali metal (Na-—Cs) picrate 1:1:1 complexes were determined at 25°C; the partition constants of DB18C6 itself were also measured at 25°C. The log K_MLA of Na, K, Rb, and Cs are -0.14 ± 0.11, 1.30 ± 0.10, 1.00 ± 0.09, and 0.24 ± 0.11, respectively. The partition behavior of DB18C6 and its1:1:1 complexes with the alkali metal picrates can be clearly explained byregular solution theory, except for chloroform. The molar volumes andsolubility parameters of DB18C6 and the 1:1:1 complexes were determined.A relation between molar volumes of the complexes and K_MLAis discussed. The magnitude of Kex is largely determined by that ofK_D,MLA. For every diluent, the extraction selectivity of DB18C6increases in the order Na > Cs > Rb > K. The K extraction-selectivity of DB18C6 over Na is the highest among all the combinations of the two neighboring alkali metals in the periodic table. The extraction-ability and -selectivity for the alkalimetal picrates and their change with the diluent of DB18C6 were completely elucidated by the four fundamental equilibria and regular solution theory.     

Selectivity of bis(calix[4]diquinone) ionophores towards metal ions in solvent dimethylsulfoxide: a molecular mechanics and molecular dynamics study

Molecular modelling studies have been carried out on two bis(calix[4]diquinone) ionophores, each created from two (calix[4]diquinone)arenes bridged at their bottom rims via alkyl chains (CH(2))(n), 1: n = 3, 2; n = 4, in order to understand the reported selectivity of these ligands towards different sized metal ions such as Na(+), K(+), Rb(+), and Cs(+) in dmso solution. Conformational analyses have been carried out which show that in the lowest energy conformations of the two macrocycles, the individual calix[4]diquinones exhibit a combination of partial cone, 1,3-alternate and cone conformations. The interactions of these alkali metals with the macrocycles have been studied in the gas phase and in a periodic box of solvent dmso by molecular mechanics and molecular dynamics calculations. Molecular mechanics calculations have been carried out on the mode of entry of the ions into the macrocycles and suggest that this is likely to occur from the side of the central cavity, rather than through the main axis of the calix[4]diquinones. There are energy barriers of ca. 19 kcal mol(-1) for this entry path in the gas phase, but in solution no energy barrier is found. Molecular dynamics simulations show that in both 1 and 2, though particularly in the latter macrocycle, one or two solvent molecules are bonded to the metal throughout the course of the simulation, often to the exclusion of one or more of the ether oxygen atoms. By contrast the carbonyl oxygen atoms remain bonded to the metal atoms throughout with bond lengths that remain significantly less than those to the ether oxygen atoms. Free energy perturbation studies have been carried out in dmso and indicate that for 1, the selectivity follows the order Rb(+) approximately K(+) > Cs(+) > Na(+), which is partially in agreement with the experimental results. The energy differences are small and indeed the ratio between stability constants found for Cs(+) and K(+) complexes is only 0.60, showing that has only a slight preference for K(+). For the larger receptor , which is better suited to metal complexation, the binding affinity follows the pattern Cs(+) > Rb(+) > K(+) > Na(+), with energy differences of 5.75, 2.61, 2.78 kcal mol(-1) which is perfectly consistent with experimental results.     

Design and synthesis of luminescence chemosensors based on alkynyl phosphine gold(I)-copper(I) aggregates

Receptor-containing polynuclear mixed-metal complexes of gold(I)-copper(I) 1-3 based on a [{Au(3)Cu(2)(C≡CPh)(6)}Au(3){PPh(2)-C(6)H(4)-PPh(2)}(3)](2+) (Au(6)Cu(2)) core with benzo-15-crown-5, oligoether and urea binding sites were designed and synthesized, respectively. These complexes exhibited remarkably strong red emission at ca. 619-630 nm in dichloromethane solution at room temperature upon photoexcitation at λ > 400 nm, with the emission quantum yield in the range 0.59-0.85. The cation-binding properties of 1 and 2 and the anion-binding properties of 3 were studied using UV-vis, emission and (1)H NMR techniques. Complex 1, with six benzo-15-crown-5 pendants, was found to show a higher binding preference for K(+), with a selectivity trend of K(+)? Cs(+) > Na(+) > Li(+). The addition of metal ions (Li(+), Na(+), K(+) and Cs(+)) to complex 1 led to a modest emission enhancement with a concomitant slight blue shift in energy and well-defined isoemissive points, which is attributed to the rigidity of the structure and the inhibited PET (photo-induced electron transfer) process from the oxygen to the aggregate as a result of the binding of the metal ion. The six urea receptor groups on complex 3 were found to form multiple hydrogen bonding interactions with anions, with the positive charge providing additional electrostatic interaction for anion-binding. The anion selectivity of 3 follows the trend F(-) > Cl(-)≈ H(2)PO(4)(-) > Br(-) and the highest affinity towards F(-) is attributed to the stronger basicity of F(-), as well as its good size match with the cavity of the urea pocket.