Facile Synthesis of Bis(crown ether)benzils: Prospective Building Blocks for Metal Ion Sensors

A new facile synthetic route to benzils containing fragments of 12-crown-4, 15-crown-5, and 18-crown-6 by oxidation of corresponding stilbenes was developed. The first representative of a new family of fluorescent sensors was obtained by reaction of bis(15-crown-5)benzil with o-phenylenediamine. The latter exhibits great fluorescence enhancement upon association with K⁺ and Rb⁺ compared to Na⁺ and Cs⁺.     

Complexation Studies of Phosphorus Containing Bis and Tris (Benzocrown Ether) Moieties

The complexation behaviour between salts of Li⁺-Rb⁺ in CD₃CN and tris(benzocrown ether)s 2a,bX=P(NMeN=CH-B15C5)₃ (X = O, S) and tri[bis(benzocrown ether)][N=P(NMeN=CH-B15C5)₂]₃ 3 was investigated by ¹³ C NMR spectroscopy. Using the program RMNSTAB, the complexation constants for the different possible complexes (M₂L, ML andML₂ were L represents one benzo-15-crown-5) were obtained and were compared with those of the corresponding monomer material. A remarkable ``biscrown effect' for compounds 2a,b and 3 was found, especially for potassium and rubidium by the predominant formation of stable ML₂ complexes. The strong chelate effect make these ligands highly efficient extracting agents for alkali metal picrate salts of K⁺, Rb⁺ and Cs⁺,as shown by UV-Vis spectroscopy.     

Complexation between Methyl Viologen (Paraquat) Bis(Hexafluorophosphate) and Dibenzo[24]Crown‐8 Revisited

Paraquat bis(hexafluorophosphate) undergoes stepwise dissociation in acetone. All three species—the neutral molecule, and the mono‐ and dications—are represented significantly under the experimental conditions typically used in host–guest binding studies. Paraquat forms at least four host–guest complexes with dibenzo[24]crown‐8. They are characterized by both 1:1 and 1:2 stoichiometries, and an overall charge of either zero (neutral molecule) or one (monocation). The monocationic 1:1 host–guest complex is the most abundant species under typical (0.5–20 mM ) experimental conditions. The presence of the dicationic 1:1 host–guest complex cannot be excluded on the basis of our experimental data, but neither is it unambiguously confirmed to be present. The two confirmed forms of paraquat that do undergo complexation—the neutral molecule and the monocation—exhibit approximately identical binding affinities toward dibenzo[24]crown‐8. Thus, the relative abundance of neutral, singly, and doubly charged pseudorotaxanes is identical to the relative abundance of neutral, singly, and doubly charged paraquat unbound with respect to the crown ether in acetone. In the specific case of paraquat/dibenzo[24]crown‐8, ion‐pairing does not contribute to host–guest complex formation, as has been suggested previously in the literature.     

Bis(Dialkylphosphinylmethyl)Alkylamines as the Liquid and Membrane Extractants of Rare Earth and Trace Metal Ions

Abstract

A large number of new lipophilic mono- and bisphosphinylamines were synthesized on the basis of the Kabachnik–Fields reaction and extraction and membrane transport properties of the synthesized compounds toward the rare earth and alkaline metal were studied. Aminophosphonyls demonstrate extracting efficiency and selectivity toward Sc(III), In(III), Y(III), and Ga(III) rare earth elements. The mixture of reactants bis(dialkylphosphinylmethyl)alkylamine, and thio- and dithiophosphoric acid shows selectivity toward lithium ions.     

Alkali and Alkaline Earth Metal Ions Complexes with a Partial Peptide of the Selectivity Filter in K+ Channels Studied by a Cold Ion Trap Infrared Spectroscopy

The infrared (IR) spectra of alkali and alkaline earth metal ion complexes with the Ac-Tyr-NHMe (GYG) peptide have been measured by laser photodissociation in a cold ion trap coupled with an electrospray mass spectrometer. The GYG peptide corresponds to a portion of the ion selectivity filter in the KcsA K⁺ channel that allows K⁺ to pass, but blocks Na⁺ even though it has a smaller ionic radius than K⁺. This current study extends a previous investigation on Na⁺ and K⁺ to the entire set of alkali metaI ions and alkaline earth dications. IR-IR hole-burning (IR² dip) spectroscopy has established the coexistence of several conformers of the GYG-metal ion complexes. The structures of the conformers were assigned by comparison between the isomer-selected IR spectra and theoretical IR spectra obtained from quantum chemical calculations. It was found that the structure of the dominant conformer correlates with the ability of the ion to permeate through the K⁺ channel.     

Adsorption Studies of Radionuclides and Toxic Metal Ions on a Modified Mesoporous Lanthanum(III) Silicate

A new adsorbent, modified mesoporous lanthanum(III) silicate, has been prepared with various molar ratios of Si/La (10, 20, 40, 80) and cethyltrimethylammonium bromide (CTAB) as structure directing agent. XRD, nitrogen sorption, SEM, IR, thermogravimetry and sorption of radionuclides and toxic metal ions have been studied. The results show that adsorption amount of some element such as Pb(II) and Th(IV) has been increased significantly by incorporation of lanthanum ions in the framework of adsorbent. Separation of Co(II)‐Th(IV), Co(II)‐U(VI) and Mo(VI)‐U(VI) has been developed on columns of this adsorbent.     

Inclusion of Ethyl Acetoacetate Bearing 7‐Hydroxycoumarin Dye by β‐Cyclodextrin and its Cooperative Assembly with Mercury(II) Ions: Spectroscopic and Molecular Modeling Studies

The inclusion of the fluorescent organic dye, ethyl 3‐(7‐hydroxy‐2‐oxo‐2H‐chromen‐3‐yl)‐3‐oxopropanoate ( 1 ) by the host β‐cyclodextrin (β‐CD), and its response toward mercuric ions (Hg²⁺), was studied by UV/Vis, fluorescence, and ¹H NMR spectroscopic analyses, mass spectrometry and molecular modeling studies. ¹H NMR measurements together with molecular modeling studies for dye 1 demonstrate that it exhibits two tautomeric forms (keto and enol); however, when the dye is included into the β‐CD cavity, the enol form predominates. Moreover, by using spectroscopic and spectrometry techniques, a 1:1 stoichiometry was determined for the complexes formed between dye 1 (enol form) and β‐CD, with a binding constant (K_b1=1.8×10⁴ m ^?1) and for the dye 1 (keto form)‐Hg²⁺ (K_b2=2.3×10³ m ^?1). Interestingly, in the presence of 1 –β‐CD complex and mercuric ions, a ternary supramolecular system (Hg– 1 –β‐CD complex) was established, with a 1:1:1 stoichiometry and a K_b3 value of 4.3×10³ m ^?1, with the keto form of the dye being the only one present in this assembly. The three‐component system provides a starting point for the development of novel and directed supramolecular assemblies.     

Synthesis of a Resorcylic Acid Lactone (RAL) Library Using Fluorous‐Mixture Synthesis and Profile of its Selectivity Against a Panel of Kinases

A library of resorcylic acid lactones (RAL) containing a cis‐enone moiety targeting kinases bearing a cysteine residue within the ATP‐binding pocket was prepared using a fluorous‐mixture synthesis and evaluated against a panel of 19 kinases thus providing important structure–activity trends. Two new analogues were then profiled for their selectivity against a panel of 402 kinases providing the broadest evaluation of this pharmacophores’ selectivity.     

Alleno‐Acetylenic Cage (AAC) Receptors: Chiroptical Switching and Enantioselective Complexation of trans‐1,2‐Dimethylcyclohexane in a Diaxial Conformation

Four enantiopure 1,3‐diethynylallenes (DEAs) with OH termini were attached to the rim of a resorcin[4]arene cavitand. The system undergoes conformational switching between a cage form, closed by a circular H‐bonding array, and an open form, with the tertiary alcohol groups reaching outwards. The cage form is predominant in apolar solvents, and the open conformation in small, polar solvents. Both states were confirmed in solution and in X‐ray co‐crystal structures. ECD spectra of the alleno‐acetylenic cages (AACs) are highly conformation sensitive, the longest wavelength Cotton effect at 304 nm switches from Δ?=+191 m ^?1 cm^?1 for open (P)₄‐AAC?acetonitrile to Δ?=?691 m ^?1 cm^?1 (ΔΔ?=882 m ^?1 cm^?1) for closed (P)₄‐AAC?cyclohexane. Complete chiral resolution of (±)‐trans‐1,2‐dimethylcyclohexane was found in the X‐ray structures, with (P)₄‐AAC exclusively bound to the (R,R)‐ and (M)₄‐AAC to the (S,S)‐guest. Guest inclusion occurs in a higher energy diaxial conformation.     

DFT Study of a 5‐endo‐trig‐Type Cyclization of 3‐Alkenoic Acids by Using Pd–Spiro‐bis(isoxazoline) as Catalyst: Importance of the Rigid Spiro Framework for Both Selectivity and Reactivity

The reaction pathway of an enantioselective 5‐endo‐trig‐type cyclization of 3‐alkenoic acids catalyzed by a chiral palladium–spiro‐bis(isoxazoline) complex, Pd–SPRIX, has been studied by density functional theory calculations. The most plausible pathway involves intramolecular nucleophilic attack of the carboxylate moiety on the C?C double bond activated by Pd–SPRIX and β‐H elimination from the resulting organopalladium intermediate. The enantioselectivity was determined in the cyclization step through the formation of a π‐olefin complex, in which one of the two enantiofaces of the olefin moiety was selected. The β‐H elimination occurs via a seven‐membered cyclic structure in which the acetate ligand plays a key role in lowering the activation barrier of the transition state. In the elimination step, the SPRIX ligand was found to behave as a monodentate ligand due to the hemilability of one of the isoxazoline units thereby facilitating the elimination. Natural population analysis of this pathway showed that the more weakly electron‐donating SPRIX ligand, compared with the bis(oxazoline) ligand, BOX, facilitated the formation of the π‐olefin complex intermediate, leading to a smaller overall activation energy and a higher reactivity of the Pd–SPRIX catalyst.     

Synthesis and Characterization of a New (E,E)-Dioxime and its Homonuclear Complexes

N′-(4′-Benzo[15-crown-5]naphthylaminoglyoxime (H₂L) and its sodium chloride complex (H₂L·NaCl) have been prepared from 2-naphthylchloroglyoxime, 4′-aminobenzo[15-crown-5] and sodium bicarbonate or sodium bicarbonate and sodium chloride. Nickel(II), cobalt(II) and copper(II) complexes of H₂L and H₂L·NaCl have a metal–ligand ratio of 1:2 and the ligand coordinates through the two N atoms, as do most of the vic-dioximes. The BF₂⁺-capped Ni(II), Co(III) and mononuclear complexes of thevic-dioxime were prepared. The macrocyclic ligands and their transition metal complexes have been characterized on the basis of IR, ¹H NMR spectroscopy and elemental analyses data.