Fluorescent detection of amidinium-carboxylate and amidinium formation using a 1,8-diphenylnaphthalene-based diamidine: dicarboxylic acid recognition with high fluorescence efficiency

A 1,8-diphenylnaphthalene-based diamidine (1) ‘turn-on’ fluorescent probe for the detection of dicarboxylic acids has been designed and synthesized. The fluorescence spectra of the diamidine 1 with carboxylic acids that showed two different fluorescence bands, which corresponded to the amidinium-carboxylate (λ_em=410–430 nm) and amidinium (λ_em=440–470 nm as a broad band, which consisted from two peaks) formation, were confirmed by DOSY NMR and TD-DFT calculations. The complexation of diamidine 1 with dicarboxylic acids, which have sufficient distances between the two carboxylic groups for binding to the diamidine 1 (dicarboxylic acids 3, 4, and α,ω-dicarboxylic acids 6 (C₆–C₂₀)), showed the formation of 1:1 complexes (i.e., amidinium-carboxylate formation). On the other hand, for the complexation with monocarboxylic acids and dicarboxylic acids having insufficient distances between the two carboxylic groups (benzoic acid 5, acetic acid 7, and α,ω-dicarboxylic acids 6 (C₃–C₅)), formation of the amidinium (1·2H⁺) was observed. Relatively similar binding constants (10⁻⁵) for the complexation of the diamidine 1 with dicarboxylic acids 6, which depend on their chain length (strain), were observed due to the flexibility of the 1,8-diphenylnaphthalene unit. Additionally, for the complexation of the diamidine 1 with dicarboxylic acids, higher fluorescence quantum yields (Φ_fl: up to 80%) were observed when compared to the binding of the diamidine 2 (Φ_fl: up to 35%).     

(Mesitylene)ruthenium π-complexes with benzo-15-crown-5 and dibenzo-18-crown-6

The reactions of benzo-15-crown-5 and dibenzo-18-crown-6 with 1 equiv. of [(mes)Ru(MeNO₂)₃]²⁺ (mes = 1,3,5-C₆H₃Me₃) give the mononuclear complexes [(mes)Ru(η⁶-benzo-15-crown-5)]²⁺ (1) and [(mes)Ru(η⁶-dibenzo-18-crown-6)]²⁺ (2) in 50% yield. Similar reaction with 2 equiv. of [(mes)Ru(MeNO₂)₃]²⁺ produces the dinuclear complex [(μ-η⁶:η⁶-dibenzo-18-crown-6)Ru₂(mes)₂]⁴⁺ (3) in 96% yield as a 2:3 mixture of cis- and trans-isomers. Structures of 2(OTf)₂ and trans-3(OTf)₄ were confirmed by X-ray diffraction. The NMR titration showed that mononuclear dications 1 and 2 bind Na⁺ ion less effective (K_a = 600 and 250 M^-1) than free benzo-15-crown-5 and dibenzo-18-crown-6 (K_a = 2 × 10⁵ and 5 × 10⁶ M⁻¹). The dinuclear tetracation 3 does not bind Na⁺ within measurable limits of NMR titration method. The electrochemical behaviour of complexes 1-3 was studied in propylene carbonate solution. They exhibit a partially chemically reversible Ru(II)/Ru(I) reduction, which in the case of the dinuclear complex 3 proceeds through two slightly separated steps. The redox activity of the complexes is substantially unaffected by the presence of sodium ion.     

Anion recognition by d-ribose-based receptors

Anion recognition properties of d-ribose-based receptors α- and β-1 were measured by ¹H NMR in CDCl₃ and MeCN-d₃. Receptor β-1 showed effective binding with anions by cooperative hydrogen bonds of cis-diol. The anomeric isomer α-1 is a less effective anion receptor which has similar cis-diol as a recognition site, indicating that the stereo configuration of the anomeric position is of significant influence on the anion recognition ability.     

Novel C1-symmetric chiral crown ethers bearing rosin acids groups: synthesis and enantiomeric recognition for ammonium salts

Four types of novel C₁-symmetric chiral crown ethers including 28-crown-8, 20-crown-6, 17-crown-5 and 14-crown-3 (9a–m) were synthesized and their enantiodiscriminating abilities with protonated primary amines (10–14) were examined by ¹H NMR spectroscopy. 20-crown-6 crown ethers exhibited good chiral recognition properties toward these guests and showed different complementarity to some chiral guests, indicating that 20-crown-6 crown ethers could be used as a chiral NMR solvating agent to determine the enantiopurity of these guests. In addition, the binding model and binding site between the hosts and guests were also studied by the computational modeling and experimental calculation.     

Carboxylic acid to amide hydrogen bonding. 10-Oxo-semirubins

Using their amide (and pyrrole) groups, dipyrrinones act as hydrogen bonding receptors for carboxylic acids, as found in a large number of 10-oxo-semirubins (1-6). The latter can be synthesized readily by Friedel-Crafts coupling of 9-H dipyrrinones with half-ester acid chlorides or diacid dichlorides of α,ω-dicarboxylic acids, ranging from C₂ to C₁₀. With ω-oxo-alkanoic acid chains of C₅ or ≥C₅, intramolecular hydrogen bonding is observed. With acid chains <C₅ hydrogen bonding is not observed. Uncharacteristically (for dipyrrinones), 10-oxo-dipyrrinone acids (1-6) and their corresponding esters (1e-6e) remain monomeric in hydrogen bond promoting solvents.     

Barium ion sensing by a 2,2′-binaphthalene derivative bearing two monoaza-15-crown-5 ethers

A novel fluoroionophore 1 based on 2,2′-binaphthalene bearing two monoaza-15-crown-5 ethers at 8- and 8′-positions was prepared. UV-vis and fluorescence responses of 1 upon the addition of alkali and alkaline earth metal cations were evaluated in 15% MeOH-MeCN. Receptor 1 showed unique response for Ba²⁺ due to the formation of an intramolecular sandwich complex.     

Fluorescent detection of amidinium-carboxylate and amidinium formation using anthracene-based diamidine: an application for the analysis of dicarboxylic acid binding

An anthracene-based diamidine (1) ‘turn-on’ fluorescent probe for the detection of dicarboxylic acids has been designed and synthesized. The fluorescence spectra of the diamidine 1 with carboxylic acids that showed two different fluorescence bands, which corresponded to the amidinium-carboxylate (λ_em=430-440 nm), and amidinium (λ_em=460-470 nm as a broad band) formation, were confirmed by DOSY NMR and TD-DFT calculations. These different fluorescence bands showed the binding mode of carboxylic acids and the stability of formed complexes toward diamidine 1. The fluorescent detection of amidinium-carboxylate formation using diamidine 1 was applicable to the detection of α,ω-dicarboxylic acids (C₆-C₁₃) and succeeded in the detection of α,ω-dicarboxylic acid (adipic acid) in human urine.     

Synthesis of C2-symmetric chiral crown ethers by lipase-catalyzed reactions

Kinetic resolution of a racemic mixture of C₂-symmetric 18-crown-6 diols (rac-1a) and 15-crown-5 diol (rac-1c) was achieved by lipase-catalyzed acetylation. The enantiomeric excess of the chiral crown diols (95% ee and 82% ee) was determined by ¹H NMR spectroscopy, using (R)-(+)-1-(1-naphthyl)ethylammonium hydrochloride as a shift reagent. The C₂-symmetric chiral 15-crown-5 diol (>95% ee) was also obtained by kinetic resolution of the racemic diacetate (rac-2c) using lipase-catalyzed solvolysis.     

Intramolecular charge transfer dual fluorescent sensors from 4-(dialkylamino)benzanilides with metal binding site within electron acceptor

Three fluoroionophores (2a-c) were designed as the intramolecular charge transfer (CT) dual fluorescent sensors for metal cations with metal binding site within the electron acceptor. These sensors were derived from 4-dialkylaminobenzanilides (alkyl=methyl, ethyl, and n-butyl) with the amido phenyl ring being an arm of 15-crown-5 thus bearing binding site for alkaline and alkaline earth metal cations. Compounds 2a-c were expected to have two possible CT channels of opposite direction. The absorption and fluorescence spectra of 2a-c and their crown-ether free model molecules 3a-c in a variety of solvents were recorded. Dual fluorescence was observed with 2a-c and was assigned to the LE and the CT states, respectively. In nonpolar or less polar solvents the CT occurring with 2a-c was identified as that occurred with benzanilides (BA) with the amido anilines being the electron donor (the BA-like CT), while in polar solvents such as acetonitrile (ACN), the CT was still mainly the BA-like. In the presence of alkali and alkaline earth metal cations in ACN, the CT dual fluorescence underwent substantial changes so as increased total quantum yield, red-shifted LE band and enhanced CT to LE intensity ratio. Binding of the metal cations at the 15-crown-5 moiety of 2a-c was shown to turn the CT direction that the dialkylamino group in the binding complexes being the electron donor while the benzo-15-crown-5 moiety now being within the electron acceptor. The occurrence of this CT enhances metal cation binding to 15-crown-5 ether in 2a-c, which was confirmed by the observed higher metal binding constants. Compounds 2a-c as the CT dual fluorescent sensors were shown to operate under the mechanism of the metal cation binding induced switching of the CT character from the BA-like to that occurred with 4-(dimethylamino)benzamides (the DMABA-like). Compounds 2a-c therefore represent successful examples for the CT dual fluorescent sensors for cations with the metal binding site within the electron acceptor and can be employed as sensitive ratiometric fluorescent sensors for metal cations of improved sensing performance.     

Synthesis of Double-Armed Benzo-15-crown-5 and Their Complexation Thermodynamics with Alkali Cations

A series of double-armed benzo-15-crown-5 lariats (3–8) have been synthesized by the reaction of 4′, 5′-bis(bromomethyl)-benzo-15-crown-5 (2) with 4-hydroxybenzaldehyde, phenol, 4-chlorophenol, 4-methoxyphenol, 2-hydroxybenzaldehyde, and 4-acetamidophenol in 43 ~ 82% yields, respectively. The complex stability constants (K _S) and thermodynamic parameters for the stoichiometric 1:1 and/or 1:2 complexes of benzo-15-crown-5 1 and double-armed crown ethers 3–8 with alkali cations (Na⁺, K⁺, Rb⁺) have been determined in methanol–water (V/V=8:2) at 25 °C by means of microcalorimetric titrations. As compared with the parent benzo-15-crown-5 1, double-armed crown ethers 3–8 show unremarkable changes in the complex stability constants upon complexation with Na⁺, but present significantly enhanced binding ability toward cations larger than the crown cavity by the secondly sandwich complexation. Thermodynamically, the sandwich complexations of crown ethers 3-8 with cations are mostly enthalpy-driven processes accompanied with a moderate entropy loss. The binding ability and selectivity of cations by the double-armed crown ethers are discussed from the viewpoints of the electron density, additional binding site, softness, spatial arrangement, and especially the cooperative binding of two crown ether molecules toward one metal ion.     

Lutetium gets a crown: Synthesis, structure and reaction chemistry of the separated ion pair complex, [Li(12-crown-4)2][(C5Me5)2LuMe2]

Reaction of (C₅Me₅)₂Lu(Me)(μ-Me)Li(THF)₃ (2) with excess 12-crown-4 affords the new separated ion pair complex, [Li(12-crown-4)₂][(C₅Me₅)₂LuMe₂] (3), in excellent yield. This complex reacts with 2,6-diisopropylaniline and phenylacetylene to give the methyl amide complex [Li(12-crown-4)₂][(C₅Me₅)₂Lu(Me)(NH-2,6-ⁱPr₂C₆H₃)] (4) and the bis(acetylide) complex [Li(12-crown-4)₂][(C₅Me₅)₂Lu(C≡C-Ph)₂] (5), respectively. Attempts to promote methane loss from complexes 3 and 4 to generate a lutetium methylidene or imido complex, respectively, were unsuccessful. The ability of the bis(acetylide) complex 5 to act as a π-tweezer complex was also explored. Reaction between [Li(12-crown-4)₂][(C₅Me₅)₂Lu(C≡C-Ph)₂] (5) and CuSPh gave only intractable lutetium products and the copper(I) species [Li(12-crown-4)₂][Cu(C≡C-Ph)₂] (8). The new lutetium complexes have been characterized by elemental analysis and NMR spectroscopy. Finally, the X-ray crystal structures of (C₅Me₅)₂Lu(Me)(μ-Me)Li(THF)₃ (2), [Li(12-crown-4)₂][(C₅Me₅)₂LuMe₂] (3), [Li(12-crown-4)₂][(C₅Me₅)₂Lu(Me)(NH-2,6-ⁱPr₂C₆H₃)] (4), [Li(12-crown-4)₂][(C₅Me₅)₂Lu(C≡C-Ph)₂] (5), and [Li(12-crown-4)₂][Cu(C≡C-Ph)₂] (8) are also reported.     

Yttrium thiocyanate-based supramolecular architectures: Synthesis, crystal structures, and thermal properties

The reaction of [Y(H₂O)₅(NCS)₃]·H₂O (1) with crown ether (18-crown-6) and KNCS in methanol afforded the complexes [Y(H₂O)₄(NCS)₃]·1.5(18-crown-6) (2) and [K(18-crown-6)(H₂O)_1.25]_2n{[K(18-crown-6)]₂[Y(NCS)₆]}_n·n(NCS) (3). In mononuclear complex 1, yttrium has a coordination number 8 and forms the coordination unit YO₅N₃. Complexes 1 are linked by hydrogen bonds to form a framework. The crystal structure of 2 contains the centrosymmetric ensembles [Y(H₂O)₄(NCS)₃]₂(18-crown-6)₃ formed via hydrogen bonds. In the crystal structure of 3, the [Y(NCS)₆]³⁻ anions and the [K(18-crown-6)]⁺ cations form one-dimensional polymeric chains (-Y-NCS-K-)_n. The thermal behavior of compounds 1 and 2 was investigated. It was shown that the supramolecular assembly has an effect on the temperature range for the removal of coordinated water molecules from the thiocyanate complex. The oxidative decomposition of the acido ligands in 1 and 2 occurs in a similar way to give Y₂O₂SO₄ as the final product (700 °С).     

Soluble and processable conjugated polyazines with oligo(p-phenylene vinylene)s

An efficient polycondensation reaction between α,ω-diformyl functional aromatics, namely 2,5-diheptyloxy-1,4-diformylbenzene and side-chain substituted α,ω-diformyl oligo(p-phenylene vinylene) (OPV) with hydrazine afforded novel soluble and processable conjugated polymers, P1 and P2, respectively. The reaction conditions were investigated and structural analysis of the polymers was carried out by means of ¹H, ¹³C, ¹⁵N NMR, indicating all-trans configured CN-NC linkages. The molecular weights M_n were observed at ∼1100-1400 g/mol for P1 and ∼8700-10,500 g/mol for P2. The optical properties showed absorption maxima at ∼455 nm and ∼487 nm for P1 and P2 (CHCl₃ solutions), respectively, red shifted by 31-60 nm relative to the monomer aromatics due to conjugation through the azine linkage. The emission maxima are observed at ∼515 nm and ∼560 nm for P1 and P2 (CHCl₃ solutions), respectively. Thin films of P2 readily undergo n-doping.     

New calсium β-diketonate complexes: The monomeric complexes [Ca(PhCOCHCOCF3)2(15-crown-5)], [Ca(AdCOCHCOCF3)2(15-crown-5)] and the binuclear hydrated complex [{Ca(adtfa)(18-crown-6)(H2O)}{Ca(adtfa)3(H2O)}(EtOH)]. Synthesis, characterization and crystal structure

The preparation of the Ca-β-diketonate complexes with crown-ethers, [Ca(btfa)₂(15-crown-5)] (1), [Ca(adtfa)₂(15-crown-5)] (2), [Ca(adtfa)₂(15-crown-5)](C₆H₅CH₃)_0.5 (3) and [{Ca(adtfa)(18-crown-6)(H₂O)}{Ca(adtfa)₃(H₂O)}(EtOH)] (4) (btfa = 1,1,1-trifluoro-4-phenyl-butanedionato-2,4; adtfa = 1,1,1-trifluoro-4-(1-adamantyl)butanedionato-2,4; 15-crown-5 = 1,4,7,10,13-pentaoxacyclopentadecane; 18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane), is described. Complex 1 has been prepared from the reaction of metallic Ca with 2 eq. of Hbtfa and 1 eq. of 15-crown-5 in toluene; complex 2 has been prepared from the reaction of metallic Ca with 2 eq. of Hadtfa and 1 eq. of 15-crown-5 in ethanol. The solvated complex 3 was obtained by cooling of a toluene-hexane solution of 2. The hydrated complex 4 was prepared from the reaction of metallic Ca with 2 eq. of Hadtfa and 1 eq. of 18-crown-6, followed by addition of excess H₂O to the resulting reaction mixture. The all complexes were characterized by elemental analyses, IR-spectroscopy, NMR-spectroscopy, single-crystal X-ray diffraction methods, DSC and TGA. A single-crystal X-ray study of 1 and 3 has show that complexes 1 and 3 are monomeric and contain the calcium atom bonded with two β-diketonate ligands and one molecule of crown-ether. Complex 4, as shown by X-ray analyses, is an ion-paired solvated adduct, containing the cation {Ca(adtfa)(18-crown-6)(H₂O)}⁺ and the anion {Ca(adtfa)₃(H₂O)}⁻. The monomeric complexes 1-3 are volatile and thermally stable in the temperature range 100-260 °C. Complex 4 undergoes decomposition above 110 °C with consecutive loss of ethanol, H₂O, 18-crown-6 and some evaporization of 4.     

Synthesis of Double-Armed Benzo-15-crown-5 and Their Complexation Thermodynamics with Alkali Cations

A series of double-armed benzo-15-crown-5 lariats (3–8) have been synthesized by the reaction of 4′, 5′-bis(bromomethyl)-benzo-15-crown-5 (2) with 4-hydroxybenzaldehyde, phenol, 4-chlorophenol, 4-methoxyphenol, 2-hydroxybenzaldehyde, and 4-acetamidophenol in 43 ~ 82% yields, respectively. The complex stability constants (K _S) and thermodynamic parameters for the stoichiometric 1:1 and/or 1:2 complexes of benzo-15-crown-5 1 and double-armed crown ethers 3–8 with alkali cations (Na⁺, K⁺, Rb⁺) have been determined in methanol–water (V/V=8:2) at 25 °C by means of microcalorimetric titrations. As compared with the parent benzo-15-crown-5 1, double-armed crown ethers 3–8 show unremarkable changes in the complex stability constants upon complexation with Na⁺, but present significantly enhanced binding ability toward cations larger than the crown cavity by the secondly sandwich complexation. Thermodynamically, the sandwich complexations of crown ethers 3-8 with cations are mostly enthalpy-driven processes accompanied with a moderate entropy loss. The binding ability and selectivity of cations by the double-armed crown ethers are discussed from the viewpoints of the electron density, additional binding site, softness, spatial arrangement, and especially the cooperative binding of two crown ether molecules toward one metal ion.Graphical Abstract Synthesis of Double-Armed Benzo-15-crown-5 and Their Complexation Thermodynamics with Alkali CationsYU LIU*, JIAN-RONG HAN, ZHONG-YU DUAN and HENG-YI ZHANG This revised version was published online in July 2005 with a corrected issue number.     

Triazole-based chromogenic and non-chromogenic receptors for halides

We designed and synthesized a series of triazole-based receptors for anion recognition. Our studies demonstrated that an amide-linked triazole unit is a promising moiety for anion recognition. We synthesized various chromogenic and non-chromogenic receptors based on this moiety. Receptor 11 binds very strongly (K = 102,750 M⁻¹) to fluoride. Receptor 18 changes color from faint yellow to orange upon binding to fluoride.     

Complexing properties of two benzocrown-ether moieties arranged at a cyclobutane ring system

Biscrown ethers 2a-c and 3a-c arranged at a cyclobutane ring were prepared by intermolecular [2+2] photocycloaddition of vinylated benzocrown ethers. The complexing behavior of 2a-c toward alkali metal cations was evaluated by ESI-MS analysis, liquid-liquid extraction, and the comparison of complexing stability constant. An intramolecular sandwich-type 1:1 (host/guest) complexation was observed by ESI-MS analysis in the competitive system where 2a-Na⁺, 2b-K⁺, and 2c-Cs⁺ were formed selectively. In the liquid-liquid extraction, however, 2a hardly extracted any cation, while both 2b and 2c efficiently extracted larger cations such as K⁺, Rb⁺, and Cs⁺. It was found that the complexing stability constant of 2a-Na⁺ is lower than that of benzo-15-crown-5-Na⁺ though extraordinarily high values were obtained for 2b-K⁺ and 2c-Cs⁺ complexes compared with those of 18-crown-6-K⁺ and dibenzo-24-crown-8-Cs⁺ complexes, respectively. Hence, the excellent complexing ability was achieved by using the cyclobutane ring, which strongly preorganized two benzocrown-ether moieties for the larger alkali metal cations.     

Synthesis and structures of organoantimony compounds containing intramolecular Sb-N interactions

Stibines containing the pendant arm [2-(Me₂NCHR)C₆H₄] (where R = H or Me) were synthesized, and their reactions with CH3I and HBr have been carried out to obtain the diammonium salt {[2-(Me₂NCHR)C₆H₄] [2-(Me₃N⁺CHR)C₆H₄]}Sb 2[I]⁻ (where R = H 3; Me 4) and triammonium salt {2-[(Me₂HN⁺CH₂)C₆H₄]₃}Sb 3[Br]⁻5, respectively. A novel platinum complex 6 [PtCl₂ · 1] containing stibine 1 as a bidentate ligand has also been prepared. All these compounds show Sb-N interactions. A good conjunction was observed between semi-empirical method and ¹H and ¹³C NMR (at different temperature) data for the diammonium salts of compounds 3 and 4. The structures of all the synthesized compounds were determined by X-ray diffraction analyses. This appears to be the second molecular structure of a Pt stibine complex containing a Pt-Cl bond trans to stibine ligand, as few Pt-Sb X-ray structures are known.     

Di(1H,1H,2H,2H-perfluorooctyl)-dibenzo-18-crown-6: A “light fluorous” recyclable phase transfer catalyst

A series of dibenzo-18-crown-6 lariat ethers containing two C₇H₁₅ (11), (CH₂)₂C₆F₁₃ (14), (CH₂)₂C₈F₁₇ (15), NHC₇H₁₅ (18) and NHCH₂C₆F₁₃ (19) sidearms were prepared and the single crystal X-ray structure of cis-4,4′-di(1H,1H,2H,2H-perfluorodecyl)-dibenzo-18-crown-6 (15a) is reported. The “light fluorous” dibenzo-18-crown-6 ether (14) has emerged as a stable and robust PTC catalyst, which can be recycled efficiently by fluorous solid-phase extraction, and gives better PTC catalytic activity compared to the parent, non-fluorinated PTC catalyst, dibenzo-18-crown-6, and the alkylated derivative (11) in aliphatic and aromatic nucleophilic substitutions.     

Pyrenyl-appended imidazolium receptor for selective fluorescence sensing of oxalic acid

A new fluorescent imidazolium-based cholestane receptor 4 bearing a pyrene moiety was synthesized. The binding ability of 4 toward various dicarboxylic acids was examined by UV-vis and fluorescence spectroscopy. Receptor 4 showed the highest binding constant for oxalic acid among all the tested dicarboxylic acids (K_a = 5.06 × 10⁴ M⁻¹). Oxalic acid formed a complex with 4 with a 1:2 ratio in ethanol.