Copper(II) Complexes of Cyclams Containing Nitrophenyl Substituents: Push–Pull Behavior and Scorpionate Coordination of the Nitro Group

The three nitrophenyl–cyclam derivatives (nitrocyclams): 1-(4-nitrophenyl)-1,4,8,11-tetraazacyclotetradecane (2), 1-(2-nitrophenyl)-1,4,8,11-tetraazacyclotetradecane (3), and 1-(2,4-dinitrophenyl)-1,4,8,11-tetraazacyclotetradecane (4), in an MeCN solution, specifically incorporate the CuII ion according to an irreversible process signaled by disappearance of the yellow color for a concentration c < 1 × 10–4 M and by a yellow-to-red color change for c ≥ 1 × 10–3, and must be considered efficient and specific dosimeters of copper(II) salts. When present in the ortho position of the nitrophenyl substituent, the −NO2 group coordinates the CuII according to a scorpionate mode, while the metallocyclam system exhibits a trans-I configuration. In an MeCN solution the red trans-I-[CuII(3)]2+ and trans-I-[CuII(4)]2+ scorpionate complexes slowly convert into the violet trans-III scorpionate complexes. Kinetic aspects of the trans-I-to-trans-III configurational rearrangement were investigated in detail for the [CuII(4)]2+ system. In particular, the conversion is spectacularly accelerated by catalytic amounts of Cl–, NCO–, and F–. While for Cl– and NCO– the effect can be associated with the capability of the anion to stabilize through coordination a possible dissociative intermediate, the amazingly powerful effect of F– must be related to the preliminary deprotonation of one N–H fragment of the macrocycle, driven by the formation of the HF2– ion. Most of the metal complex species studied in solution were isolated in a crystalline form, and their molecular structures were elucidated through X-ray diffraction studies. This study documents the first examples of effective metal coordination by the nitro groupThe financial support of the Italian Ministry of University and Research (PRIN−InfoChem) is gratefully acknowledgedS

Terpyridine derivatives functionalized with (hetero)aromatic groups and the corresponding Ru complexes: synthesis and characterization as SHG chromophores

Push–pull terpyridine derivatives were synthesized and characterized in order to study the variations produced in their optical and electronic properties by linking different (hetero)aromatic electron donor moieties at position 4 of the electron deficient terpyridine moiety. The final donor-acceptor systems were synthesized in fair to good yields by Kröhnke condensation of the precursor aldehydes, with 2-acetylpyridine. Hyper-Rayleigh scattering in dioxane solutions using a fundamental wavelength of 1064 nm was employed to evaluate their second-order nonlinear optical properties. Terpyridine derivative functionalized with the 9-ethyl-9H-carbazolyl group exhibited the largest first hyperpolarizability (beta = 610 × 10-30 esu, using the T convention) thus indicating its potential application as a second harmonic generation (SHG) chromophore. Terpyridine derivatives were also used as ligands for the synthesis of novel [RuII(tpy)(NCS)3]– complexes, prepared in good yields by a two-step procedure involving the preparation of [RuIII(tpy)(Cl3] as precursors. RutheniumII complexes display a broad absorption in the visible range, accounting for their very dark color. Their redox behaviour is mainly characterized by the RuII-RuIII oxidation and by the ligand-centred reduction, whose potentials can be finely tuned by the electronic properties of the aromatic substituents on the terpyridine ligand. Hyper-Rayleigh scattering in methanol solutions using a fundamental wavelength of 1064 nm was also employed to evaluate their second-order nonlinear optical properties.Thanks are due to Fundação para a Ciência e a Tecnologia and FEDERCOMPETE for financial support through Centro de Química (UID/QUI/ 00686/2013 and UID/QUI/0686/2016), and a PhD grant to S. S. M. Fernandes (SFRH/BD/87786/2012). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased with funds from FCT and FEDER. The pulsed laser system was acquired within the framework of the grant (PTDC/CTM/105597/2008) from the Portuguese Foundation for Science and Technology (FCT) with funding from FEDER-COMPETE.info:eu-repo/semantics/publishedVersio

Acute Delta Hepatitis in Italy spanning three decades (1991–2019): Evidence for the effectiveness of the hepatitis B vaccination campaign

Updated incidence data of acute Delta virus hepatitis (HDV) are lacking worldwide. Our aim was to evaluate incidence of and risk factors for acute HDV in Italy after the introduction of the compulsory vaccination against hepatitis B virus (HBV) in 1991. Data were obtained from the National Surveillance System of acute viral hepatitis (SEIEVA). Independent predictors of HDV were assessed by logistic-regression analysis. The incidence of acute HDV per 1-million population declined from 3.2 cases in 1987 to 0.04 in 2019, parallel to that of acute HBV per 100,000 from 10.0 to 0.39 cases during the same period. The median age of cases increased from 27 years in the decade 1991-1999 to 44 years in the decade 2010-2019 (p &lt; .001). Over the same period, the male/female ratio decreased from 3.8 to 2.1, the proportion of coinfections increased from 55% to 75% (p = .003) and that of HBsAg positive acute hepatitis tested for by IgM anti-HDV linearly decreased from 50.1% to 34.1% (p &lt; .001). People born abroad accounted for 24.6% of cases in 2004-2010 and 32.1% in 2011-2019. In the period 2010-2019, risky sexual behaviour (O.R. 4.2; 95%CI: 1.4-12.8) was the sole independent predictor of acute HDV; conversely intravenous drug use was no longer associated (O.R. 1.25; 95%CI: 0.15-10.22) with this. In conclusion, HBV vaccination was an effective measure to control acute HDV. Intravenous drug use is no longer an efficient mode of HDV spread. Testing for IgM-anti HDV is a grey area requiring alert. Acute HDV in foreigners should be monitored in the years to come

Electrochemically Driven Swinging of a Nitrobenzyl Pendant Arm in a Nickel Scorpionand Complex

A radical anion -NO2.- is formed upon an electrochemically reversible one-electron reduction of the square-planar Ni-II complex of N-nitrobenzylcyclam. The -NO2.- group goes to occupy an axial position of the metal ion, thus establishing a significant electronic interaction with the metal center. In particular, the ESR spectrum supports the occurrence of an electron transfer from -NO2.- to the metal, which therefore presents a significant Ni-I character. On re-oxidation, the nitrobenzyl side chain detaches and the Ni-II complex is restored, providing an example of a fully reversible redox driven intramolecular motion

Dicopper Double-Strand Helicates Held Together by Additional π–π Interactions

The bis-bidentate ligand, obtained from Schiff base condensation of RR-1,2-cyclohexanediamine and 8-naphthylmethoxyquinoline-2-carbaldehyde (L−L), forms with [CuI (MeCN)4]ClO4 a double strand helicate complex, made especially stable by the presence of four definite interstrand π−π interactions involving a quinoline subunit and a naphthylmethoxy substituent of the two strands. The [CuI2(L−L)2]2+ complex, which does not decompose even on excess addition of either L−L or CuI, undergoes a two electron oxidation in MeCN, through two one-electron fully reversible steps, separated by 260 mV, as shown by cyclic voltammetry (CV) studies. The high stability of the mixed valence complex [CuICuII(L−L)2]3+ with respect to disproportionation to [CuI 2(L−L)2]2+ and [CuII2(L−L)2]4+ is essentially due to a favorable electrostatic term. CuII forms with L−L a stable species, with a 1:1 stoichiometric ratio,but, in the absence of crystallographic data, it was impossible to assess whether it is of mono- or dinuclear nature. However, CV studies on an MeCN solution containing equimolar amounts of CuII and L−L showed the presence in the reduction scan of two fully reversible waves, separated by about 250 mV, which indicated the presence in solution of a dicopper(II) double strand helicate complex, [CuII2(L−L)2]4+. This work demonstrates that additional interstrand π−π interactions can favor the formation of unusually stable dicopper(I) and dicopper(II) helicate complexes

Copper(II) complexes of cyclams containing nitrophenyl substituents: push−pull behavior and scorpionate coordination of the nitro group

ABSTRACT: The three nitrophenyl−cyclam derivatives (nitrocyclams): 1-(4-nitrophenyl)-1,4,8,11-tetraazacyclotetradecane (2), 1-(2-nitrophenyl)-1,4,8,11-tetraazacyclotetradecane (3), and 1-(2,4-dinitrophenyl)-1,4,8,11-tetraazacyclotetradecane (4), in an MeCN solution, specifically incorporate the CuII ion according to an irreversible process signaled by disappearance of the yellow color for a concentration c < 1 × 10−4 M and by a yellow-to-red color change for c ≥ 1 × 10−3, and must be considered efficient and specific dosimeters of copper(II) salts. When present in the ortho position of the nitrophenyl substituent, the −NO2 group coordinates the CuII according to a scorpionate mode, while the metallocyclam system exhibits a trans-I configuration. In an MeCN solution the red trans-I-[CuII(3)]2+ and trans-I-[CuII(4)]2+ scorpionate complexes slowly convert into the violet trans-III scorpionate complexes. Kinetic aspects of the trans-I-to-trans-III configurational rearrangement were investigated in detail for the [CuII(4)]2+ system. In particular, the conversion is spectacularly accelerated by catalytic amounts of Cl−, NCO−, and F−. While for Cl− and NCO− the effect can be associated with the capability of the anion to stabilize through coordination a possible dissociative intermediate, the amazingly powerful effect of F− must be related to the preliminary deprotonation of one N−H fragment of the macrocycle, driven by the formation of the HF2− ion. Most of the metal complex species studied in solution were isolated in a crystalline form, and their molecular structures were elucidated through Xray diffraction studies. This study documents the first examples of effective metal coordination by the nitro group

Enhancing the Anion Affinity of Urea-Based Receptors with a Ru(terpy)₂²⁺ Chromophore

Covalent linking of a Ru­(terpy)₂²⁺ substituent improves recognition and sensing properties of the urea subunit toward anions. Urea’s anion affinity is enhanced by the electrostatic attraction exerted by the Ru^II cation and by the electron-withdrawing effect exerted by the entire polypyridine–metal complex. Such an enhancement of the anion affinity, which results from the combination of a through-space and a through-bond effect, is greater than that exerted by the classical neutral electron-withdrawing substituent nitrophenyl. Small yet significant modifications of π–π* and MLCT bands of the Ru­(terpy)₂²⁺ chromophore, detected through UV–vis spectrophotometric titrations, allowed the determination of the constants for the formation of receptor–anion H-bond complexes in diluted MeCN solution. On ¹H NMR titration experiments, carried out under more concentrated conditions, the interaction of a second Cl^– ion was observed, taking place through an outer-sphere mechanism. The Ru­(terpy)₂²⁺ substituent favors the deprotonation of a urea N–H fragment on addition of a second equivalent of fluoride, with formation of HF₂^–

Fluorogenic Detection of Sulfite in Water by Using Copper(II) Azacyclam Complexes

Copper(II) azacyclam complexes (azacyclam = 1,3,5,8,12-pentaazacyclotetradecane) containing naphthyl or dansyl subunits can be prepared by template synthesis involving proper sulfonamide derivatives as locking fragments. The macrocyclic complexes are very poorly emissive due to the fluorescence-quenching behavior displayed by Cu2+ ions. However, the fluorescence can be recovered as a result of the decomposition of the complexes, which induces the release of free light-emitting subunits to the solution. This reaction takes place very slowly in neutral water but its rate is increased by the presence of sulfite. Therefore, [Cu(azacyclam)]2+ derivatives have been investigated as simple chemical probes for the fluorogenic detection of sulfite both on laboratory and real samples. Preliminary tests performed on samples of white wine provided sulfite concentration values that are in agreement with those obtained by a standard analytical method