1,721,007 research outputs found
Naphthalene diimides as selective naked-eye chemosensor for copper(II) in aqueous solution
No full textSubstituted and water-soluble naphthalene diimides (NDIs) exhibiting (CH2)2NMe2 coordinating moieties have been shown to be selective and fast responding mono- and di-nuclear colorimetric Cu(II) chemosensor
Photochemistry of transition metal complexes (2017–2018)
No full textThis chapter reviews the major advances in the field of photochemistry and photocatalysis by transition metal compounds published in 2017–2018. Particular attention has been given to (i) photocatalysis in synthesis (ii) photoreactivity; (iii) biomedical applications of photoactive transition metal complexes, e.g. as photo-CORMs and PDT (photodynamic therapy) agents
Synthesis and study in solution of a new dansyl-modified azacryptand
Full text linkThe synthesis of a new asymmetric azacryptand (L1), characterized by three p-xylyl spacers, one of which carries a dansyl
side arm is reported. The fluorescent sensor has been studied by potentiometric, UV-Vis, and emission studies in MeOH: water 3 : 2 mixture
(0.07M NaNO3), determining, in particular, the protonation constants of the free ligand and metal ion complexation equilibria.
Interestingly, the obtained results revealed that the new receptor is fluorescent at neutral pH with a typical emission band of the
dansyl group. Metal addition induced a partial quenching of the dansyl emission band; this behavior is more pronounced with
Cu(II) that reduces the receptor’s emission by 60%. With all the studied cations, quenching follows the formation of a dimetallic
complex. Similar studies on the model compound L2 confirmed that fluorescence quenching ismainly driven by a static mechanism,
attributable to the formation of the inclusion dicopper complex [L1Cu2]4+. In order to test the stability of copper complexes under
physiological conditions, spectrofluorimetric titrations with Cu(II) were performed in water buffered at pH = 8 (HEPES 0.07 M)
and the values of binding constants, K11 and K12, were determined
The Interaction of Fluoride with Fluorogenic Ureas: An ON1–OFF–ON2Response
No full textThe anion binding tendencies of the two fluorogenic ureas L1H and L2H, containing the 2-anthracenyl and 1-pyrenyl moieties as signaling units, respectively, have been investigated in MeCN and DMSO by absorption, emission, and 1H NMR spectroscopies. The formation of stable 1:1 receptor:anion H-bond complexes has been confirmed by structural studies on the crystalline [Bu4N][L1···Cl] and [Bu4N][L2H···CH3COO] salts. Complexation induces significant variations of the emission properties of L1H and L2H according to a multifaceted behavior, which depends upon the fluorogenic substituent, the solvent, and the basicity of the anion. Poorly basic anions (Cl–, Br–) cause a red shift of the emission band(s). Carboxylates (CH3COO–, C6H5COO–) induce fluorescence quenching due to the occurrence of an electron-transfer process taking place in the locally excited complex [*L-H···X]−. However, this excited complex may undergo an intracomplex proton transfer from one urea N–H fragment to the anion, to give the tautomeric excited complex [L···H–X]−*, which emits at higher wavelength. F– displays a unique behavior: It forms with L1H a stable [L–H···F]− complex which in the excited state undergoes intracomplex proton transfer, to give the poorly emissive excited tautomer [L···H–F]−*. With L2H, on moderate addition of F–, the 1:1 H-bond complex forms, and the blue fluorescence of pyrene is quenched. Large excess addition of F– promotes deprotonation of the ground-state complex, according to the equilibrium [L2H···F]− + F– [L2]− + HF2–. The deprotonated receptor [L2]− is distinctly emissive (yellow fluorescence), which generates the fluorimetric response ON1–OFF–ON2 of receptor L2H with respect to F–
Bistren cryptands and cryptates: Versatile receptors for anion inclusion and recognition in water
No full textBistren cryptands can be easily synthesised through the Schiff base condensation of two molecules of tren and three molecules of a dialdehyde, followed by hydrogenation of the six C=N double bonds to give octamine cages, whose ellipsoidal cavity can be varied at will, by choosing the appropriate dialdehyde, in order to include substrates of varying sizes and shapes. Bistrens can operate as effective anion receptors in two ways: (i) in their protonated form, providing six secondary ammonium groups capable of establishing hydrogen bonding interactions with the anion; (ii) as dicopper(II) cryptates, in which the two coordinatively unsaturated metal centres can be bridged by an ambidentate anion. Representative examples of the two approaches, as well as the design of an anion molecular dispenser, in which a dicopper(II) bistren cryptate acts as a bottle will be illustrated
The squaramide versus urea contest for anion recognition
No full textThe interaction of a neutral squaramide-based receptor, equipped with two 4-nitrophenyl substituents, with halides and oxoanions has been studied in MeCN. UV/Vis and 1H NMR spectroscopy titration experiments clearly indicated the formation of 1:1 hydrogen bonding complexes with all the investigated anions. X-ray diffraction studies on the chloride and bromide complex salts confirmed the 1:1 stoichiometry and indicated the establishment of bifurcated hydrogen-bond interactions between the squaramide-based receptor and the halide anion that involved both 1) amide NH and 2) aryl proximate CH fragments, for a total of four bonds. Probably due to the contribution of CH fragments, complexes of squaramide with halides are 1 to 2 orders of magnitude more stable than the corresponding ones with the analogous urea-based receptor that contains two 4-nitrophenyl substituents. In the case of oxoanions, squaramide forms complexes, the stability of which decreases with the decreasing basicity of the anion, and is comparable to that of complexes of the urea-based receptor. Such a behaviour is ascribed to the predominance of different contributions: electrostatic interaction for halides, acid-to-base ‘frozen’ proton transfer for oxoanions. Finally, with the strongly basic anions F− and CH3COO−, squaramide first gives genuine hydrogen-bond complexes of 1:1 stoichiometry; then, upon addition of a second anion equivalent, it undergoes deprotonation of one NH fragment, with the simultaneous formation of the dianion hydrogen-bond complexes. In the case of the urea-based derivative, deprotonation takes place with fluoride but not with acetate. The apparently higher Brønsted acidity of squaramide with respect to urea reflects the capability of the squaramide receptor to delocalise the negative charge formed on NH deprotonation over the cyclobutene-1,2-dione ring and the entire molecular framewor
Recognition and Sensing of Nucleoside Monophosphates by a Dicopper(II) Cryptate
Full text linkThe dicopper complex of a bis-tren cryptand in which the spacer consists of two furane subunits
connected in 2,2' by a -CH2- fragment selectively recognizes guanosine monophosphate with respect
to other nucleoside monophospates (NMPs) in a MeOH/water solution at pH 7. Recognition is efficiently
signaled through the displacement of the indicator 6-carboxyfluorescein bound to the receptor, monitoring
its yellow fluorescent emission. Titration experiments evidenced the occurrence of several simultaneous
equilibria involving 1:1 and 2:1 receptor/NMP and receptor/indicator complexes. It was demonstrated that
the added NMP displaces the indicator from the 2:1 receptor/indicator complex, forming the 1:1 receptor/
analyte inclusion complex. Recognition selectivity is thus ascribed to the nature of nucleotide donor atoms
involved in the coordination and their ability to encompass the CuII-CuII distance within the cryptate
Azacryptands as molecular cages for anions and metal ions
No full textThis is a short overview on azacryptands, as molecular receptors for cations and anions. A particular
attention was devoted to the results obtained by women researchers working in the field. The terms
‘cryptand’ and ‘cryptate’ were coined by Lehn. Since then, much work has been done to improve
the knowledge on this class of receptors. Small azacryptands, as free bases, were found to bind a
single metal ion within their cavities. When fully protonated, the same systems could also behave
as selective hosts for anions, through the cooperation of H-bonding and electrostatic interactions.
Proceeding to systems with larger cavities, the inclusion of two metal ions and a bridging anion
was possible, forming the so-called ‘cascade’ complexes. Azacryptates carrying fluorescent spacers
or exploiting the indicator displacement paradigm allowed the sensing of anionic species in water
at micromolar concentrations. Moreover, immobilisation on solid matrices and surfaces yielded
new materials for the solid-phase extraction of anionic pollutants and the construction of selective
electrodes for analytes in water
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