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Zn–salophen complexes are a promising class of fluorescent chemosensors for nucleotides and nucleic acids. We have investigated, by means of steady state UV–Vis, ultrafast transient absorption, fluorescence emission and time dependent density functional theory (TD-DFT) the behavior of the excited states of a salicylidene tetradentate Schiff base (Sal), its Zn(II) coordination compound (Zn–Sal) and the effect of the interaction between Zn–Sal and adenosine diphosphate (ADP). TD-DFT shows that the deactivation of the excited state of Sal occurs through torsional motion, due to its rotatable bonds and twistable angles. Complexation with Zn(II) causes rigidity so that the geometry changes in the excited states with respect to the ground state structure are minimal. By addition of ADP to a freshly prepared Zn–Sal ethanol solution, a longer relaxation constant, in comparison to Zn–Sal, was measured, indicative of the interaction between Zn–Sal and ADP. After a few days, the Zn–Sal–ADP solution displayed the same static and dynamic behavior of a solution containing only the Sal ligand, demonstrating that the coordination of the ADP anion to Zn(II)leads to the demetallation of the Sal ligand. Fluorescence measurements also revealed an enhanced fluorescence at 375 nm following the addition of ADP to the solution, caused by the presence of 2,3-diamino naphthalene that is formed by demetallation and partial decomposition of the Sal ligand. The efficient fluorescence of this species at 375 nm could be selectively detected and used as a probe for the detection of ADP in solution. Graphical abstract

Even if laboratory practice is essential for all scientific branches of knowledge, it is often neglected at High School, due to lack of time and/or resources. To establish a closer contact between school and experimental sciences, the University Sapienza of Roma and the Istituto Nazionale di Fisica Nucleare (INFN) launched the Lab2Go project, with the goal of spreading laboratory practice among students and teachers in high schools., in Italian

Click chemistry is used to functionalize simple lipophilic and water-soluble molecules, a complex PEGylated phospholipid (DSPE-PEG2000), and two benzylic substrates with the 2-(hydroxyimino)aldehyde (HIA) group. To this end, two terminal alkynes bearing the HIA moiety were synthesized and coupled to different azides through copper(I)-catalyzed azide alkyne cycloaddition (CuAAC). Norrish-Yang photoisomerization (?= 365 nm, LED source) is successfully obtained, with no interference by the triazole linker, except when the forbidden n-?* carbonyl transition is screened by a remote substituent such as salicylaldehyde. UV-Vis spectrometry suggests a specific interaction of HIAs with Cu(II), whereas no such evidence is found with Cu(I). We thereby show that the CuAAC methodology can be used successfully to obtain HIA-based UV-responsive hydrophilic or lipophilic ligands, phospholipidic components for the construction of liposomes, and macrocycle precursors.

The synthesis of two novel Uranyl-salophen complexes, 1 and 2, decorated with ethynyl substituents, and the study in chloroform of their binding properties toward three different tetrabutylammonium halide salts, i.e. fluoride, chloride, bromide, are here reported. Such derivatives proved to be efficient halide receptors. The presence of two ethynyl groups in the para position, with respect to the phenoxide oxygens, seemed to be accountable for the moderate emission shown by complex 1. Surprisingly, instead, complex 2 does not show such property. The possibility of 1 to form dimers in non-coordinating solvents provides an explanation for such difference, since emission can be induced by the aggregation. This finding provides an unprecedented example of aggregation induced emission (AIE) for metal salophen derivatives. Moreover DFT calculations provide theoretical insight to the formation of host-guest complexes. Their stabilities were calculated in vacuum and in chloroform and the results are perfectly in agreement with the experimental data.

We report the rational design and synthesis of a supramolecular gelator based on a Zn(ii)-salophen derivative functionalized with l-valine residues. This compound is able to gelate acetonitrile by self-assembly into helical long fibers that further aggregate into bundles. The fibers are stabilized by a network of hydrogen bonds and ?-? stacking interactions established by gelator units stacked one on the top of another. The gel is responsive to the presence of anions. Moreover the zinc center remains available for the coordination of an external guest without causing gel disruption.

Many advanced synthetic, natural, degradable or non-degradable materials have been employed to create scaffolds for cell culture for biomedical or tissue engineering applications. One of the most versatile material is poly-lactide (PLA), commonly used as 3D printing filament. Manufacturing of multifunctional scaffolds with improved cell growth proliferation and able to deliver oligonucleotides represents an innovative strategy for controlled and localized gene modulation that hold great promise and could increase the number of applications in biomedicine. Here we report for the first time the synthesis of a novel Rhodamine derivative of a poly-amidoamine dendrimer (G = 5) able to transfect cells and to be monitored by confocal microscopy that we also employed to coat a 3D-printed PLA scaffold. The coating do not modify the oligonucleotide binding ability, toxicity or transfection properties of the scaffold that is able to increase cell proliferation and deliver miRNA mimics (i.e., pre-mir-503) into human cells. Although further experiments are required to optimize the dendrimer/miRNA ratio and improve transfection efficiency, we demonstrated the effectiveness of this promising and innovative 3D-printed transfection system to transfer miRNAs into human cells for future biomedical applications.

We explore the possibility that protonated molecular ions might be an unexpected source of interference in the recognition process of anions and neutral species by Zn-salophen receptors. Zn-salophen complexes are known to bind anions and neutral molecules in solution. We present here evidence (from computational work and IRMPD spectroscopy) that these complexes can also be the binding site for protonated pyridine or quinuclidine. The resulting binding pattern does not involve the Zn ion, but one of the oxygen atoms directly attached to it. The resulting complex therefore turns out to have a positive charge adjacent to the Zn-salophen binding site. This finding seems to point to the existence of an interfering factor in the quantification of the experimental data about the association constant.

Drawing inspiration from the structural features of some natural polyphenols, the synthesis of two different model compounds as potential inhibitors of HIV integrase (IN) has been described. The former was characterised by a diketo acid (DKA) bioisostere, such as a β-hydroxycarbonyl moiety, between two fragments containing aromatic groups, while in the latter an epoxide linked two polyoxygenated aromatic residues. The moieties present in the structures are thought to function by chelating divalent metal ions on the enzyme catalytic site. Overall, 10 compounds were prepared and some of that submitted to molecular modelling studies (to investigate their interactions with the active site of IN), to metal titration studies (to detect their chelating capability) and to biological assays.

The synthesis of a series of non-symmetrically substituted zinc(II)-salophenpyridyl [salophenpyridyl = N,N′-2-pyridylenebis-(salicylideneimine)] complexes obtained by reacting RO-substituted salicylaldehydes (R = C10H21 or C16H33) and 2,3-diaminopyridine is here reported. The molecular aggregation behaviour of these derivatives has been thoroughly studied in the solid state. Five new structures have been isolated and analysed. Interestingly, the crystal structure of the complex 2a@4,4′-bipyridine shows the formation of a porous material, whose structure is formed by neutral open boxes potentially able to host guests of suitable dimensions.

Zn-salophen complexes are a promising class of fluorescent chemosensors for nucleotides and nucleic acids. We have investigated, by means of IRMPD spectroscopy experiments and quantum chemical calculations, the structure of the host-guest complexes formed by two efficient Zn-salophen receptors and dihydrogen phosphate or adenosine 5′-monophosphate (AMP) anions. In the host-guest complexes the phosphate group is bound with a Zn O(phosphate) bond. In addition, a hydrogen bond can be formed between the PO H group and one of the oxygen atoms of the salophen structure. The complexes with AMP anions are endowed with a hydrogen bonded coordination motif together with a weaker π⋯π interaction. It is thus confirmed that the marked changes of the spectroscopic emission properties of Zn-salophen when complexed with AMP can be associated with the existence of π⋯π stacking interactions between the salophen aromatic rings and those of the adenosine nucleobase.

Two series of ternary assemblies comprising metal-salophen [salophen = N,N′-phenylenebis(salicylideneimine)] complexes (M = Zn2+ or UO22+) and 4,4′-bipyridine have been synthesized. Their absorption and emission data have been compared with those of the corresponding mononuclear derivatives. The dinuclear zinc species present lower emission intensities than those corresponding to the mononuclear precursors, while the emission of the analogous uranyl complexes is observed to increase. Absorption and emission titrations indicate that the ternary species are obtained in two independent coordination steps. The important role of the electron donating/withdrawing properties of the substituents is analyzed regarding their photophysical properties and the association constants. A MLCT transition (recorded by emission spectra) is expected and supported by the increase in the emissive properties of the complexes containing the higher electron donating substituent (methoxy). Nevertheless, this electron donating character disfavors the coordination to bipyridine as shown by the lower calculated association constants. DFT calculations have been performed on the zinc derivatives in order to estimate the relative stability of the dinuclear complexes.

Two series of ternary assemblies comprising metal-salophen [salophen = N,N0-phenylenebis(salicylideneimine)] complexes (M = Zn2+ or UO2 2+) and 4,40-bipyridine have been synthesized. Their absorption and emission data have been compared with those of the corresponding mononuclear derivatives. The dinuclear zinc species present lower emission intensities than those corresponding to the mononuclear precursors, while the emission of the analogous uranyl complexes is observed to increase. Absorption and emission titrations indicate that the ternary species are obtained in two independent coordination steps. The important role of the electron donating/withdrawing properties of the substituents is analyzed regarding their photophysical properties and the association constants. A MLCT transition (recorded by emission spectra) is expected and supported by the increase in the emissive properties of the complexes containing the higher electron donating substituent (methoxy). Nevertheless, this electron donating character disfavors the coordination to bipyridine as shown by the lower calculated association constants. DFT calculations have been performed on the zinc derivatives in order to estimate the relative stability of the dinuclear complexes.

The enhancement of the binding between halide anions and a Lewis acidic uranyl-salophen receptor has been achieved by the introduction of pendant electron- deficient arene units into the receptor skeleton. The association and the occurrence of the elusive anion-p interaction with halide anions (as tetrabutylammonium salts) have been demonstrated in solution and in the solid state, providing unambiguous evidence on the interplay of the concerted interactions responsible for the anion binding.

The synthesis and characterization of two new uranyl-salen complexes, 1–2, based on a 1,2-diaminomaleonitrile unit, is described. Spectroscopic studies to evaluate their potential as colorimetric probes for fluoride detection in chloroform and dichloromethane were undertaken. Compound 2 exhibits a ‘turn-on’ response characterized by a naked-eye colorimetric change for the selective recognition of fluoride in both solvents. DFT calculations show that the stabilization energy for the formation of the host:guest complex follows the trend F− > Cl− > Br− hence supporting the experimental data.

Herein we report on the self-assembly, in a low polarity solvent, of a pseudorotaxane species comprising binaphthyl-26-crown-8 (BN26C8) as the macrocyclic host and anthracenyl-benzylammonium as the threadlike positively charged guest (ABH+). Absorption and luminescence data reveal a very efficient energy transfer process occurring from the binaphthyl to the anthracene singlet excited states. The self-assembly is highly dependent on the nature of the counteranion confirming the crucial role played by it in the competition between the self-assembly process and the formation of ion pairs (ABH+X-). This behavior can be readily evidenced in dilute solutions from the analysis of the luminescence properties of the system. The complexation of chloride, sulfate and hexafluorophosphate salts of ABH+ by racemic BN26C8 as well as the complexation of ABH+ salts of the chiral anion tris[tetrachlorobenzenediolato]phosphate(V) (TRISPHAT-) by (+)BN26C8 are described. The efficiency in complexation follows the trend PF6- > TRISPHAT- > Cl-, SO42-. The use of the chiral anion TRISPHAT allowed us to investigate the possibility of inducing stereoselective control on the formation of the interpenetrating assembly. Preliminary 1H NMR spectroscopic evidence supports the fact that the chiral anion is paired to the supramolecular complex and that its configuration influences the recognition process.

International audience; The phenylurea moiety is a ubiquitous synthon in supramolecular chemistry. Here we report that the introduction of chlorine or bromine atoms in the ortho positions to the urea unit is a simple and very efficient way to improve its intermolecular hydrogen bond (HB) donor character. This effect was demonstrated in solution both in the context of bis-ureas self-association and of mono-ureas hydrogen bonding to strong HB acceptors.

Three novel polyoxyethylene bridged bis phenol A derived cyclophanes, {\rm 2 -- 4,} with additional aromatic units in the bridge to increase the number of cation–π interactions with guest cations, were synthesized and characterized by means of X-ray crystal structure determinations. The binding properties of these receptors toward tetramethylammonium (TMA), N-methylpyridinium (NMP), acetylcholine (ACh) and N-methylquinolinium (NMQ) salts were evaluated by means of 1H NMR spectroscopy and compared with those of the previously reported receptor 1.

A thorough kinetic investigation of the triethylamine-catalyzed addition of benzenethiol to 2-cyclopenten-1-one in chloroform shows that the highest energy transition state is a complex of thiol, enone, and base in a 1:1:1 ratio, but whether formation or disruption of the enolate-triethylammonium ion-pair intermediate is rate-limiting is uncertain. Intervention of a second thiol molecule in the assembly of the transition-state complex is ruled out, at least at thiol concentrations not exceeding 0.1-0.2 M. Thiol addition is accelerated significantly by uranyl-salophen complex I and its di-Ph derivative II. The complicated kinetics are described to high precision by means of ad hoc integrated rate equations in which associations to the metal catalyst of the enone reactant and addition product are taken into account. The kinetics are consistent with a four-body transition-state complex, whose formation results from the reaction of a (weak) thiol-base complex with a (strong) enone-uranyl-salophen complex. Open-chain and cyclic enones react at similar rates and respond to the presence of metal catalyst in much the same way. The relative catalytic efficiencies of ethyldimethylamine, triethylamine, and quinuclidine are determined essentially by differences in base strength, rather than steric bulk, in both the presence and absence of a metal complex. Only with the use of the relatively bulky Hunig's base is an adverse steric influence apparent, which is particularly severe in the reaction catalyzed by the sterically demanding II.

The use of micelles to transpose lipophilic receptors, such as uranyl-salophen complexes, into an aqueous environment is a valuable and versatile tool. Receptor 1 incorporated into CTABr micelles forms a supramolecular system that exhibits excellent binding properties towards fluoride in water, despite the competition of the aqueous medium. To fully evaluate the potential of micellar nanodevices, we extended our previous study to other types of surfactants and to a uranyl-salophen receptor with a more extended aromatic surface. Paramagnetic relaxation enhancement experiments were used to obtain information on the location of the two receptors within the micelles and complementary information was obtained from dynamic light scattering experiments. With these data it is possible to account for the key factors necessary to obtain an efficient supramolecular device for anion binding in water., SCOPUS: ar.j, info:eu-repo/semantics/published

We report the synthesis, characterization, and binding properties of a Zn–salophen complex, 1a, functionalized with a 1,8-naphthalimide unit. Unexpectedly, the emission spectrum of 1a shows a remarkable quenching of the band assigned to the naphthalimide unit. To better understand this phenomenon, a supramolecular model system constituted by a symmetric Zn–salophen and a pyridyl derivative of 1,8-naphthalimide, 1b·2a, was investigated. We propose the existence of a photoinduced energy transfer process between the naphthalimide (donor) and the salophen (acceptor) units in 1b·2a. A similar process must be operative in the covalent receptor 1a. Nevertheless, the results deriving from steady-state fluorescence experiments do not rule out the occurrence of a photoinduced electron transfer process as alternative pathway for the quenching. We also describe the chemosensing properties of receptor 1a and the supramolecular system 1b·2a towards acetate. The nonsymmetrically substituted salophen receptor 1a only transduces the binding of the anion to the Zn metal center in significant spectroscopic changes in its absorption spectrum. On the other hand, we exploit the strong emission quenching experienced by the naphthalimide component in the supramolecular complex 1b·2a to detect anions (e.g. acetate) by means of a typical “turn-on” fluorescent indicator displacement assay.

Four Zn-salophen complexes that differ for the electrodonating/electrowithdrawing character of the substituents located in the positions para to the phenolic oxygens have been used for the molecular recognition of several anions. Spectrophotometric and spectrofluorimetric titrations carried out in ethanol show for three of them strong binding affinity and also marked selectivity in the recognition of ATP4-, when methoxy electrodonating substituents are present. The finding that a Zn-salophen derivative with overall electrodonating (-I < +R) substituents is a more selective receptor for this anion than those decorated with electron withdrawing groups, support the occurrence in this case of supramolecular ?-? stacking interactions between the adenosine residue and the aromatic ligand surface that counterbalance the decrease in electrophilicity of the metal center.

This themed collection highlights some of the exciting research in supramolecular chemistry in water.

Diquats—which are important electron transfer agents in biological and photocatalytic systems, as well as structural templates for efficient supramolecular synthesis—are noteworthy for their axial chirality and have been so far reported only in racemic form due to the rapid interconversion between the atropoisomers. We now report the first example of configurational ordering of chiral diquats through their asymmetric ion pairing with novel hexacoordinated phosphate anions TRISPHAT, HYPHAT and BINPHAT.

The vibrational features and molecular structures of complexes formed by a series of uranyl-salophen receptors with simple anions, such as Cl(-) , H(-) , and HCOO(-) , have been investigated in the gas phase. Spectra of the anionic complexes were studied in the $\tilde \nu $=800-1800 cm(-1) range by mass-selective infrared multiple photon dissociation (IRMPD) spectroscopy with a continuously tunable free-electron laser. The gas-phase decarboxylation of the formate adducts produces uranyl-salophen monohydride anions, which have been characterized for the first time and reveal a strong UH bond, the nature of which has been elucidated theoretically. The spectra are in excellent agreement with the results obtained from high-quality ab initio calculations, which provided the structure and binding features of the anion-receptor complexes.

Two novel neutral polyoxyethylene bridged cyclophanes (2a and 2b) incorporating bisphenol A units were synthesized and characterized by means of x-ray crystal structure determination. The binding properties of 2a and 2b toward tetramethylammonium, N-methylpyridinium, and acetylcholine cations were evaluated by means of 1H NMR spectroscopy. Consistent with indications provided by the molecular structure, the cavity in the basket-like cyclophanes is large enough to accommodate the given guest cations conveniently. Circumstantial evidence was obtained that 1,1,2,2-tetrachloroethane is too large to enter the cavity of the smaller cyclophane 2a, but can be included in the cavity of the larger cyclophane 2b. Copyright © 2001 John Wiley & Sons, Ltd.

The synthesis and structural characterisation of three new macrocyclicbis-phenol A cyclophane ethers are described. The solid state structuresof two of the cyclophanes were determined by single crystal X-raydiffraction. Cyclophane 3 crystallises in the orthorhombic spacegroup Pbca with unit cell dimensions of a = 11.533(7), b = 29.383(8),c = 14.927(8) A and cyclophane 4 in the monoclinic spacegroup P21/n with cell dimensions of a = 11.585(4), b = 11.839(2), c = 18.866(2) A, β = 94.48(2)°.The X-ray crystalstructures reveal distorted conformations, thus supporting the weak bindingof quats in solution observed by the NMR studies. In the crystalline state bothmacrocycles were found to form self-complementary dimers held together byweak intermolecular π-π and CH-π interactions. The bindingbehaviour towards a series of tetralkylammonium cations was determinedby 1H NMR titration in CDCl3 solution. The interactions between the hosts and the quats were clearly detectable but too weak to be translated into meaningful equilibrium constants.

The triethylamine-catalyzed addition reactions of benzenethiol to 2-cyclopenten-1-one and its 2- and 3-methyl derivatives have been found to be appreciably reversible in chloroform solution. Rates and equilibria have been carefully measured at 25 degrees C in order to assess the negative influence on addition exerted by methyl groups substituted on the carbon-carbon double bond. 2-Methyl-2-cyclopenten-1-one has been found to react with benzenethiol under kinetic control to give the cis adduct as the sole detectable product in a highly stereoselective anti addition process. However, on prolonged reaction times the system slowly evolved toward a new state of equilibrium in which the more stable trans adduct, derived from a syn addition mode, was the predominant isomer.

The binding properties of the 1,3-bridged calix[5]crowns 1–3 towards a number of quaternary ammonium, phosphonium, and iminium ions have been investigated by 1H NMR in CDCl3 solution, where the sole driving force for association is provided by cation-π interactions. We have found that the cavity of a calix[5]arene fixed in a cone-like conformation provides a fairly efficient, but rather unselective, receptor site for quaternary salts. The conformationally mobile p-tert-butylcalix[5]arene (4) is in general a much less efficient binder than the more preorganized calixcrowns, but displays a remarkable selectivity towards N-methylquinuclidinium ion that is believed to arise from a good complementarity between the globe-shaped guest and the highly adaptable host. The adverse effect on complexation of the p-tert-butyl groups at the upper rim has been assessed by comparing the binding properties of 1 vs. its de-tert-butylated analogue 3. Furthermore, some information on the importance of counterion and solvent effects have been obtained.

The synthesis, characterization, and luminescent properties of a series of 5,5'-X-substituted salophen ligands, X = OCH3, Br, and NO2, and the corresponding Zn(II) complexes are reported here. Their biological activity has been analyzed and related to the different Lewis acid character of the complexes. In vitro studies (AFM and absorption and emission titrations) show that the strongest interaction with free plasmid DNA is observed for 5,5'-dinitro-substituted Zinc-salophen complex 3b. Semiempirical theoretical calculations together with redox potential measurements suggest that this might be interpreted as a direct consequence of this compound having the hardest Lewis acid character. Cellular uptake and cytotoxicity studies undertaken with these metal complexes show that they enter the cells but are not cytotoxic.

In this paper, we report the synthesis and physico-chemical investigation of two uranyl–salophen receptors, bearing either one or two anthracenyl moieties appended to the salophen skeleton. Despite the presence of the anthracenyl fluorophores, no fluorescence emission was detected. Photophysical data and cyclic voltammetric experiments show that photoinduced electron transfer from the anthracene-localised first singlet excited state to the metal centre is strongly exergonic, thus suggesting that this is the main fluorescence quenching mechanism in these complexes. The investigated compounds are photoreactive upon UV irradiation, yielding either anthracene photooxidation or photodimerisation products depending on the specific complex and the experimental conditions.

Micellar incorporation of hydrophobic molecular receptors is a promising strategy to obtain efficient nanodevices that work in water. In order to fully evaluate the potential of this approach, information on the localization and orientation of the receptor inside the micelle are necessary. Systematic studies undertaken on a uranyl-salophen receptor incorporated into CTABr and CTACl micelles show that nuclear magnetic resonance paramagnetic relaxation enhancement (NMR-PRE) experiments are particularly suitable to provide this type of information. The effect on the measurements of surfactant concentration, nature of the surfactant polar head, and ionic strength is also reported. Notably the normalization procedure applied to the obtained data can be considered of general application, thus enabling the comparison of information collected for different types of supramolecular micelle/receptor systems.

A simple and general synthetic protocol to obtain oligosaccharide-appended salicylaldehydes, key intermediates for the synthesis of water-soluble metal-salophen complexes, is here reported. Six new aldehydes have been prepared and fully characterized as well as the corresponding zinc- and uranyl-salophen complexes. These new derivatives show very good solubility in water. Preliminary studies on the association of compound 19-U, that is, the uranyl maltotetraose derivative, with hydrogen phosphate and fluoride provide very encouraging results and open up the possibility of using such compounds for the efficient recognition of anions in pure water.

A Zn–salophen complex has been incorporated into POPC large unilamellar liposomes (LUV) obtained in phosphate buffer at pH 7.4. Fluorescence optical microscopy and anisotropy measurements show that the complex is located at the liposomal surface, close to the polar headgroups. The interaction of the POPC phosphate group with Zn 2 + slowly leads to demetallation of the complex. The process follows first order kinetics and rate constants have been measured fluorimetrically in pure water and in buffered aqueous solution. The coordination of the phosphate group of monomeric POPC with salophen zinc also occurs in chloroform as detected by ESI-MS measurements. The effect of the Zn–salophen complex on the stability of POPC LUV has been evaluated at 25 °C by measuring the rate of release of entrapped 5(6)-carboxyfluorescein (CF) in the presence and in the absence of Triton X-100 as the perturbing agent. It turns out that the inclusion of the complex significantly increases the stability of POPC LUV.

This chapter focuses on the emerging field of supramolecular chemistry concerning ion-pair recognition. The recent progress in the design of receptors that simultaneously bind both cationic and anionic guests is reported here. The different synthetic strategies adopted to accommodate ion pairs within receptors are discussed, and the advantages in terms of affinity and selectivity that can be obtained by this approach are compared with those of simple ion receptors. Keywords: ion-pair recognition; supramolecular chemistry; host–guest chemistry; heteroditopic receptors; ion pairing; association constants

A new water-soluble uranyl-salophen complex incorporating two glucose units has been synthesized. This neutral derivative shows noteworthy binding affinity for fluoride in water thanks to the Lewis acid-base interaction occurring between the metal and the anion. Such interaction is strong enough to overcome the high hydration enthalpy of fluoride. Moreover this complex effectively binds hydrogen phosphate and exhibits remarkably strong association for nucleotide polyanions ADP(3-) and ATP(4-).

In this critical review the use of metal–salophen complexes as anion receptors is discussed with an emphasis on the supramolecular control of selectivity derived by the presence of additional interaction sites on the ligand skeleton. Some examples of application in sensing are also reported (112 references).

A new water soluble zinc-salophen complex with appended D-glucose moieties was synthesized and characterized. Its binding properties toward six aminoacids were investigated by UV-vis spectrophotometric titrations. Association constants showed to be unfavorably affected by increasing steric hindrance of the side chain. Quite surprisingly, different association constants were measured for the L and D enantiomers. These data suggest that aminoacids are bound via two interactions, zinc-carboxylate coordination and two hydrogen bonds between the ammonium group of the aminoacid and two oxygen atoms of one D-glucose moiety. Such conclusion is supported by the result of semiempirical (PM3) calculations. Notably, the KL/KD value of 9.6 observed for the association of phenylalanine rivals with the highest values found for the chiral recognition of aminoacids in water. Chirality, 2009. © 2008 Wiley-Liss, Inc.

Recognition of inorganic phosphates PO(4)(3-), P(2)O(7)(4-), and P(3)O(10)(5-) and nucleotides AMP(2-), ADP(3-), and ATP(4-) by Zn(2+)-salophen complexes 1 and 2 in ethanol was investigated by different spectroscopic techniques. (31)P NMR and mass spectrometry showed that anions of both series are bound by 1 and 2, while absorption and emission studies revealed that only nucleotides produce relevant changes in the spectral properties of the two hosts. (1)H NMR studies proved that the adenine aromatic group is involved in the complexation, thus pointing out the role of supramolecular ditopic receptors played by salophen derivatives toward this class of biologically relevant substrates. The lifetime of the photogenerated triplet state of the Zn(2+)-salophen compounds was measured by nanosecond laser flash photolysis, and the observed changes upon increasing the concentration of nucleotides allowed the identification of the formation of a 1:0.5 host/guest intermediate complex additionally to the formation of a 1:1 complex.

The Et(3)N-assisted addition of beta-ketoester 3 to MVK in chloroform is catalyzed with high turnover efficiency by the phenyl-substituted uranyl-salophen compound 2b but not by the parent compound 1b. A plausible mechanism is suggested, involving concomitant nucleophilic attack at the beta-carbon and hydrogen bonding between the Et(3)NH(+) countercation and the carbonyl oxygen of the s-cis conformation of the enone reactant. The role of the van der Waals interactions with the aromatic side arm of 2b as a crucial driving force for catalysis is discussed.

This short review highlights recent results in the chemistry of nonsymmetrically substituted uranyl-salophen complexes with specific reference to their synthesis and properties. Their use as receptors and catalysts is also emphasized. The possibility of modulating their structure within wide limits by choosing the proper substituted aldehydes and/or ketones as starting materials, coupled with their inherent chirality offers new appealing opportunities for their applications.

The design and synthesis of a novel fluoride receptor that uses a salen-complexed Lewis acidic uranyl center as the sole binding site is reported here. This receptor binds fluoride anions in DMSO with a high affinity constant (K > 106 M-1) and exhibits a negligible affinity (K < 10 M-1) towards otherwise effective competitors, such as acetate, phosphate and cyanide anions.

In the search for configurationally stable inherently chiral uranyl-salophen complexes, the newly synthesized compound 3 featuring a dodecamethylene chain was expected to be a promising candidate. Unexpectedly, dynamic HPLC on a enantioselective column showed that it still undergoes enantiomerization at high temperature. By comparison with the dynamic behavior of compounds 4 and 5, it was found that the enantiomerization rate is independent of the size of the ligand. This finding definitely rules out a jump rope-type mechanism for the enantiomerization process and points to reaction pathways involving preliminary rupture of one of the O· · ·U coordinative bonds. This provides unprecedented evidence of the occurrence of ligand hemilability in metal-sal(oph)en complexes. Such findings inspired the synthesis of compound 6 endowed with a more rigid spacer, i.e., that derived from 4,4′-(1,4- phenylenediisopropylidene)bisphenol. DHPLC investigations showed that the new structural motif impartsa higher configurational stability, thus raising the half-life for the enantiomerization to more than 2 months at room temperature. This clearly establishes that this compound represents the first member of a new class of inherently chiral receptors, whose potential in chiral recognition and catalysis now can be feasibly explored.

(Figure Presented) Binding in a micelle: In the presence of CTABr micelles (see picture), the salophen-UO2 complex 1 binds fluoride in water with the highest affinity ever recorded for a neutral receptor (K≈ ca. 104M-1). The receptor's location and its orientation within the micellar system are determined by PRE and NOE NMR experiments. © 2008 Wiley-VCH Verlag GmbH& Co. KGaA., SCOPUS: ar.j, FLWNA, info:eu-repo/semantics/published

Cleavage of silyl ethers can be efficiently effected using FeCl3, SnCl2, Cu(NO3)2 and Ce(NO3)3 at room temperature.

The Al(III)-salophen complex 1 exhibited strong spectroscopic changes specifically upon addition of polyG and GpG, while double stranded DNA and RNA, and single stranded polyA, polyU and polyC induced negligible spectral changes of 1. Titrations with mono-nucleotides yielded no spectroscopic changes, revealing that there must be at least two consecutive guanines in single stranded oligonucleotide structure for a measurable spectroscopic change of 1. Preliminary results show that 1 has moderate antiproliferative effect on a number of human tumour cell lines.