Irreversible Wave Research Articles

Irreversible evolution of a wave packet in the rigged-Hilbert-space quantum mechanics

It is well known that a state with complex energy cannot be the eigenstate of a self-adjoint operator, like the Hamiltonian. Resonances, i.e. states with exponentially decaying observables, are not vectors belonging to the conventional Hilbert space. One can describe these resonances in an unusual mathematical formalism, based on the so-called Rigged Hilbert Space (RHS). In the RHS, the states with complex energy are denoted as Gamow Vectors (GV), and they model decay processes. We study GV of the Reversed Harmonic Oscillator (RHO), and we analytically and numerically investigate the unstable evolution of wave packets. We introduce the background function to study initial data not composed only by a summation of GV and we analyse different wave packets belonging to specific function spaces. Our work furnishes support to the idea that irreversible wave propagations can be investigated by means of Rigged Hilbert Space Quantum Mechanics and provides insights for the experimental investigation of irreversible dynamics.

Zinc and Nickel-Salophen Catalysts in Mediated Electrohydrocyclization Reactions

Electrohydrocyclization (EHC) refers to those processes which undergo an electrochemically promoted reductive cyclization leading to the formation of a new sigma bond between the beta-carbons of alpha, beta-unsaturated esters or nitriles. Moens, Baizer, and Little reported the use of an EHC reaction as the key step in the total synthesis of the natural product 1-sterpurene.1 Nickel-salen compounds have been shown as effective electron transfer agents in mediated electrohydrocyclization reactions.2 Experimental and computational methods have provided evidence that electron transfer occurs primarily through an inner-sphere process, implying the existence of a ligand-centered radical anion as the electron transfer agent.3 Our current study has focused upon changing the identity of the metal and changing the structure of the ligand in hopes of stabilizing the radical anion intermediate, resulting in a more efficient inner sphere electron transfer. The compounds we studied are shown in Figure 1. Figure 2 cyclic voltammetry showed that Zn-salophen 1 gives an irreversible wave at -1.70 V (vs Ag/AgCl) and Ni-salophen 2 gives a reversible wave at -1.60 V (vs Ag/AgCl). The cyclic voltammograms were run using a glassy carbon working electrode, platinum wire counter electrode, and a Ag/AgCl reference electrode. The experiment was run in dimethylformamide (DMF) solvent using 0.1 M tetrabutylammonium hexafluorophosphate as the supporting electrolyte at a scan rate of 0.2 V/sec. Both compounds 1 and 2 exhibited catalytic activity towards mediated EHC (Scheme 1). Controlled potential electrolysis using 5 mol % mediator, dimethyl malonate as proton donor, 0.1 M tetrabutylammonium hexafluorophosphate as supporting electrolyte in dimethylformamide gave cyclized products cis (4) and trans (5). The reactions proceeded with >95% product conversion after 2 hours and yielded similar cis:trans ratios for both catalysts. The cis: trans ratio using Zinc-salophen (1) was 35:65 and for Nickel-salophen (2) was 32:68. These results showed an improvement over previous metal-salen mediated EHC reactions with higher yields and faster reaction times. Future work includes the investigation of other metal-salophens (different metals and varying the ligand structure) to further stabilize the radical anion intermediate. We also wish to develop a solid-phase version of mediated EHC using polymer supported metal-salen catalysts that utilize Merrifield resin or possibly zeolite frameworks for heterogeneous catalysis. References L. Moens, M.M. Baizer, and R.D. Little. J. Org. Chem., 51, 4497 (1986).J. A. Miranda, C.J. Wade, and R.D. Little. J. Org. Chem., 70, 8017 (2005).J.M. Yates, J.S. Fell, J.A. Miranda, B.F. Gherman. J. Electrochem. Soc., 160, G3080 (2013). Acknowledgments We gratefully acknowledge Sacramento State University for their support of this research through the Instructionally Related Activities Grant (ASI), Russell-Forkey Summer Research Award (Chemistry Department), and Faculty Endowment for Student Scholarship Award. We also thank the Sacramento State College of Natural Science and Mathematics for funding this research. Figure 1

Enhancing the Bipolar Redox Cycling Efficiency of Plane-Recessed Microelectrode Arrays by Adding a Chemically Irreversible Interferent.

The individual electrochemical anodic responses of dopamine (DA), epinephrine (EP), and pyrocatechol (CT) were investigated at arrays of recessed gold disk-microelectrodes arrays (MEAs) covered by a gold plane electrode and compared to those of their binary mixture (CT and EP) when the top-plane electrode was operated as a bipolar electrode or as a collector. The interferent species (EP) displays a chemically irreversible wave over the same potential range as the chemically reversible ones of DA or CT. As expected, in the generator-collector (GC) mode, EP did not contribute to the redox cycling amplification that occurred only for DA or CT. Conversely, in the bipolar mode, the presence of EP drastically increased the bipolar redox cycling efficiency of DA and CT. This evidenced that the chemically irreversible oxidation of EP at the anodic poles of the top plane floating electrode provided additional electron fluxes that were used to more efficiently reduce the oxidized DA or CT species at the cathodic poles. This suggests an easy experimental strategy for enhancing the bipolar efficiency of MEAs up to reach a performance identical to that achieved when the same MEAs are operated in a GC mode.

A Chiral Hemiporphyrazine Derivative: Synthesis and Chiroptical Properties.

The synthesis of an optically active hemiporphyrazine with chiral binaphthyl substituents (1) is reported, providing the first example of the incorporation of an intrinsically chiral moiety into the macrocyclic core of a hemiporphyrazine analogue. A negative circular dichroism (CD) signal is observed in the 325-450 nm region of the CD spectrum of (S,S)-1, while mainly positive bands are observed in the 220-325 nm region. Mirror symmetry is observed across the entire wavelength range of the CD spectra of (R,R)-1 and (S,S)-1. An irreversible one-electron oxidation wave with an onset potential at 1.07 V is observed by cyclic voltammetry, along with a reversible one-electron reduction wave at -0.85 V. Density functional calculations reproduce the experimentally observed data and trends, and provide further insight into the nature of the electronic transitions.

Electrochemical oxidation of salicylhydroxamic acid on Pt electrode

Abstract The electrochemical oxidation behavior of salicylhydroxamic acid (SHAM) on a Pt electrode was investigated in aqueous solution of different pHs, containing 10 mM of SHAM, at 25°C, by cyclic voltammetry technique. The results indicate that the SHAM was oxidized more easily in alkaline medium than acidic and neutral mediums, and the oxidation peaks of SHAM shifted toward lower potential values by increasing pH values. The SHAM electrooxidation involves an irreversible transfer of one or two electron, depending on the pH of solution. If solution pH is lower than 3 and higher than 7, the two electron transfer is involved in the electrooxidation. While, from pH=3 to pH=7, the SHAM electrooxidation involves an irreversible transfer of one electron and two protons in the first step, in agreement with the one step one-electron mechanism. The effect of SHAM concentration on the electrode reaction was investigated in artificial saliva solution. SHAM gives a single irreversible oxidation wave over the wide concentration range studied. Possible mechanism of SHAM electrooxidation was proposed.

Electrocatalytic processes promoted by diamond nanoparticles in enzymatic biosensing devices

We have developed a biosensing platform for lactate determination based on gold electrodes modified with diamond nanoparticles of 4nm of nominal diameter, employing the enzyme lactate oxidase and (hydroxymethyl)ferrocene (HMF) as redox mediator in solution. This system displays a response towards lactate that is completely different to those typically observed for lactate biosensors based on other nanomaterials, such as graphene, carbon nanotubes, gold nanoparticles or even diamond nanoparticles of greater size. We have observed by cyclic voltammetry that, under certain experimental conditions, an irreversible wave (E0=+0.15V) appears concomitantly with the typical FeII/FeIII peaks (E0=+0.30V) of HMF. In this case, the biosensor response to lactate shows simultaneous electrocatalytic peaks at +0.15V and +0.30V, indicating the concurrence of different feedback mechanisms. The achievement of a biosensor response to lactate at +0.15V is very convenient in order to avoid potential interferences. The developed biosensor presents a linear concentration range from 0.02mM to 1.2mM, a sensitivity of 6.1μAmM−1, a detection limit of 5.3μM and excellent stability. These analytical properties compare well with those obtained for other lactate-based biosensors that also include nanomaterials and employ HMF as redox mediator.

Antimicrobial and anticancer activities of organoiron melamine dendrimers capped with piperazine moieties

Three generations of a biologically active class of melamine dendrimers containing arene- cyclopentadienyliron cations were synthesized using the divergent method. These dendrimers were decorated with chloro-, hydroxyl-, or piperazine moieties. Cyclic voltammetric studies showed that dendrimers with chloro- or hydroxyl- terminal group exhibit reversible redox activity while dendrimers with piperazine moieties showed two distinct irreversible reductive waves. Organoiron dendrimers were thermally stable with the first degradation step at 200°C associated with the decomplexation of the iron moieties. All dendrimers were evaluated against Gram-positive bacteria [Methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus warneri and vancomycin-resistant Enterococcus faecium (VRE)], and showed significant activities against bacterial strains but were found to be less active in the case of chloro- terminal group. Second generation dendrimer 8 capped with piperazine exhibited inhibitory activity against Gram-positive bacteria generally comparable to that of reference vancomycin and rifampicin. Also, all dendrimers were screened against MCF-7 and HTB-26 breast cancer cell lines and dendrimer 8 exhibited significant inhibitory activity against MCF-7 compared with dendrimers in lower generations.

Tuning the photophysical properties of a (P,N)ReI complex by adding a –NH– fragment into a P,N-bidentate ligand: The case of [P,N-{(C6H5)2(C5H4N)NHPRe(CO)3Br

The spectroscopic, electrochemical and photophysical properties of the new complex [P,N-{(C6H5)2(C5H4N)NHP}Re(CO)3Br] (RePNN) are reported. The UV–Vis spectrum in dichloromethane (DCM) shows an absorption maximum centered at 300nm and a shoulder at 350nm. These absorption bands have been characterized, having a πpy→π∗py and a MLCT character. Excitation at the first wavelength (higher energy) leads to an emission band centered at 365nm. Cyclic voltammetry shows a fully irreversible oxidation wave around +1.45V, assigned to ReI/ReII couple, whereas two irreversible reduction signals centered at −0.75 and −1.20V are assigned to ligand reduction processes. The photophysical results show that emission from the RePNN complex comes exclusively from the ligand. The MLCT excited state shows to be non-emissive by coupling to vibrational modes leading to non-radiative decay path to ground state. The luminescent decay fits to a bi-exponential function. DFT calculations suggest that intra-ligand πpy→π∗py and πpy→π∗ph excited states may account for the existence of these two decay lifetimes. The additional –NH– fragment present in the 2-(diphenylphosphinoamino)pyridine ligand compared to 2-pyridylphosphine, makes it more flexible and in consequence, enhances the non-radiative decay rate constant from the 3MLCT to the ground state in the RePNN complex compared to those of 2-pyridylphosphine, [P,N-{(C6H5)2(C5H4N)PRe(CO)3Br] (RePN).

Mechanism and Thermodynamics of Reductive Cleavage of Carbon-Halogen Bonds in the Polybrominated Aliphatic Electrophiles.

Quantum-mechanical computations revealed that, despite the presence of electron-withdrawing and/or π-acceptor substituents, the lowest unoccupied molecular orbitals (LUMO) of the polybromosubstituted aliphatic molecules R-Br (R-Br = C3Br2F6, CBr3NO2, CBr3CN, CBr3CONH2, CBr3CO2H, CHBr3, CFBr3, CBr4, CBr3COCBr3) are delocalized mostly over their bromine-containing fragments. The singly occupied molecular orbitals in the corresponding vertically excited anion radicals (R-Br(•-))* are characterized by essentially the same shapes and show nodes in the middle of the C-Br bonds. An injection of an electron into the antibonding LUMO results in the barrierless dissociation of the anion-radical species and the concerted reductive cleavages of C-Br bonds leading to the formation of the loosely bonded {R(•)···Br(-)} associates. The interaction energies between the fragments of these ion-radical pairs vary from ∼10 to 20 kcal mol(-1) in the gas phase and from 1 to 3 kcal mol(-1) in acetonitrile. In accord with the concerted mechanism of reductive cleavage, all R-Br molecules showed completely irreversible reduction waves in the voltammograms in the whole range of the scan rates employed (from 0.05 to 5 V s(-1)). Also, the transfer coefficients α, established from the width of these waves and dependence of reduction peak potentials Ep on the scan rates, were significantly lower than 0.5. The standard reduction potentials of the R-Br electrophiles, E(o)R-Br/R·+X(-), and the corresponding R(•) radicals, E(o)R(•)/R(-), were calculated in acetonitrile using the appropriate thermodynamic cycles. In agreement with these calculations, which indicated that the R(•) radicals resulting from the reductive cleavage of the R-Br molecules are stronger oxidants than their parents, the reduction peaks' currents in cyclic voltammograms were consistent with the two-electron transfer processes.

Disassembly of diruthenium(II,III) tetraacetate with P–N donor ligands

Valent-averaged diruthenium(II,III) tetraacetate, [Ru2(μ-O2CCH3)4(H2O)2](PF6), was reacted with various bidentate P–N donor ligands. These reactions led to the partial displacement of bridging carboxylate groups and concomitant cleavage of the Ru–Ru bond, producing novel complexes. Disassembly reactions with the aminophosphines; diphenyl-2-pyridylphosphine (dpppy) and 2-(diphenylphosphino)ethylamine (dppea), produced homoleptic tris-chelated species, fac-[Ru(dpppy-P,N)3](PF6)2 (III) and mer-[Ru(dppea-P,N)3](PF6)2 (VI), respectively. Disassembly reactions with aromatic aminophosphines; 2-(diphenylphosphino)methylpyridine (dppmpy) and 2-(diphenylphosphino)ethylpyridine (dppepy), led to heteroleptic tris-chelated complexes cis,cis,trans-[Ru(dppmpy-P,N)2(η2-O2CCH3)](PF6)·MeOH (IV) and cis,cis,trans-[Ru(dppepy-P,N)2(η2-O2CCH3)](PF6) (V), respectively, whereas reaction with the non-cyclic aminophosphine, 3-(diphenylphosphino)-1-propylamine (dpppa) and the non-cyclic iminophosphine, 2-(diphenylphosphino)benzylidinebenzylamine (dppbba), led to the heteroleptic tris-chelated complexes cis,cis,trans-[Ru(dpppa-P,N)2(η2-O2CCH3)](PF6·EtOH (VII) and cis,cis,trans-[Ru(dppbba-P,N)2(η2-O2CCH3)](PF6)·2MeOH·H2O (VIII), respectively. All complexes were fully characterized. Electrochemical studies (CV, OSWV) showed that the homoleptic tris-chelated complexes had higher oxidation potentials (Epa) than the corresponding heteroleptic tris-chelated complexes, due to the weak π-acceptor ability of the acetate group. Complex (III) has the highest Epa as it contains the strongest combination of π-accepting groups. The Epa values of the heteroleptic complexes were found to be in the order: dppbba (CHN)>dppmpy, dppepy (py)>dpppa (NH2), since amines are much poorer π-acceptors than pyridyl and imino groups. Complexes (III), (VI) and (VII) showed irreversible oxidation waves, while complexes (IV), (V) and (VIII) displayed quasi-reversible one electron processes.

Synthesis, characterization, photophysics and electrochemistry of hexanuclear silver(I) alkynyl phosphine complexes

Hexanuclear silver(I) alkynyl phosphine complexes with anthryl (An) and naphthyl (Np) moieties, [{Ag3(μ-dppm)3(μ3-η1-CC)}2An-9,10](BF4)4 and [{Ag3(μ-dppm)3(μ3-η1-CC)}2Np-1,5](BF4)4, have been synthesized. X-Ray crystallography has been used to study the single crystal structure of one of the complexes. This class of silver(I) complexes was found to be emissive at both room and low temperatures in various media, showing green to orange luminescence at ca. 524–593 nm. The electrochemical properties have also been studied by cyclic voltammetry, and an irreversible anodic wave for the alkynyl-centered oxidation was observed. A computational study has been performed to provide further insight into the spectroscopic origin.

Synthesis and Characterization of Chloridobis(dimethylglyoximato)4-(2-ferrocenylvinyl)pyridinecobalt(III): A New Heterobinuclear Cobaloxime

The synthesis of a new heterobinuclear cobaloxime with 4-(2-ferrocenylvinyl)pyridine, fcvpy, is reported. The complex [CoCl(dmgH)2(fcvpy)], where dmgH2is dimethylglyoxime and dmgH is dimethylglyoximato, has been characterized by1H-NMR, UV-Vis, cyclic voltammetry, and elemental analysis. The cyclic voltammogram of this complex shows a fc/fc+reversible wave at +0.58 V versus Ag/AgCl, one irreversible wave,Epc= −0.54 V versus Ag/AgCl, assigned to the reduction of Co(III) to Co(II), and two quasireversible processes at −1.02 V and −1.10 V versus Ag/AgCl associated with the reduction of Co(II). The complex showed ferrocene-ligand charge transfer bands at 334 nm and 505 nm. TDDFT/B3LYP/6-31G(d) calculations support this assignation.

Synthesis and electron-donating properties of novel norphthalocyanines containing thiacrown ether-linked tetrathiafulvalene moieties

A novel magnesium-base and metal-free norphthalocyanine (6 and 7) containing peripheral thiacrown ether-linked tetrathiafulvalene moieties have been synthesized and fully characterized. Electrochemical investigations showed two quasi-reversible one-electron oxidation waves, one irreversible one-electron oxidation wave and two irreversible one-electron reduction waves, indicating that these triads are good π-electron donors. Triad 6 reacted with 2,3,5,6-tetrafluoro-7,7,8,8-tetra-cyanoquinodimethane (F4TCNQ) to form a charge transfer complex that exhibited absorption bands in the vicinity of 750 and 960nm. Compound 6 showed evident intramolecular charge transfer interactions in ground states and these may be explained on the basis of the density functional theory.

Electrochemistry of the COMT Enzyme Inhibitor Entacapone and Its Determination in Pharmaceutical Formulation and Human Blood-Pharmacokinetic Study

Entacapone (ENT) is a potent inhibitor of catechol-O-methyltransferase enzyme. ENT is reduced via two irreversible cathodic waves over the pH range 2.0–11.5. It has strong interfacial adsorptive behavior onto Hg electrode surface. Langmuir isotherm indicated monolayer adsorption and the equilibrium parameter RL value (0.40 – 0.93) indicated that sorption process was favorable. A monolayer surface coverage of 6.06 × 10−10 mol cm−2 was estimated and each adsorbed ENT molecule occupied an area of 0.27 nm2. Taking advantage of the adsorption features of ENT, a sensitive and selective square-wave adsorptive cathodic stripping voltammetric (SW-AdCSV) method was developed for trace determination of ENT in pure form, commercial formulations (in Comtan tablets; as a single active drug and in Stalevo 200 tablets; as tertiary mixture of ENT, levodopa and carbidopa) and in human serum. Limits of quantification (LOQ) of 5.0 × 10−10 and 1.3 × 10−9 mol L−1 ENT were achieved in pure form and in spiked human serum, respectively. This analysis was carried out without addition of any surfactant, extraction of the drug and interference from some common excipients, co-formulated and co-administrated drugs. The proposed method has also been successfully applied for assay of ENT in real plasma samples and seems to be suitable for therapeutic drug monitoring purposes.

Synthesis and electrochemistry of meso-substitutes dipyrromethene nickel (II) complexes

Metalation of dipyrromethene (dipyrrin) (1a–c) with Ni(OAc)2 provides Ni-dipyrrole complexes (NiL2) (2a–c) in 37–47% yields. The complexes were characterized by mass spectrometry and UV–Vis absorption, 1H NMR spectroscopy and single crystal X-ray. In CH2Cl2, each compound undergoes two reversible one-electron reductions and one irreversible oxidation wave. In DMF, complexes 2a–c also undergoes two reversible one-electron reductions but with three irreversible oxidation waves were observed. The effect of substituents and solvent on redox potentials is discussed.

Electrochemical oxidation of amoxicillin in its pharmaceutical formulation at boron doped diamond (BDD) electrode

In this work, voltammetric andelectrolysis experiments have been carried out on a conductive boron dopeddiamond (BDD) electrode in solution containing amoxicillin in itspharmaceutical formulation. The physical characterization of the BDD surface byscanning electron microscopy (SEM) reveals a polycrystalline structure withgrain sizes ranging between 0.3 and 0.6 µm. With Raman spectroscopy, BDDsurface is composed of diamons (Csp3) type carbon (Csp3)and graphitic type carbon (Csp2). The electrochemical characterization of the BDD electrode in sulfuric acid electrolyte showed a wide potential window worthing 2.74 V. The oxidation of Amoxicillin showed an irreversible anodic wave on the voltammogram in the domain of water stability indicating a direct oxidation of amoxicillin at BDD surface. The treatment of Amoxicillin in the synthetic wastewaters under various constant current densities 20, 50, 100, 135 mA cm-2 on BDD showed that Amoxicillin is highly reducedunder 100 mA cm-2 reaching 92% of the Chemical Oxygen Demand (COD)removal after 5 h of electrolysis. Investigation performed in perchloric acidas supporting electrolyte led to 87% of COD removal after 5 h of electrolysis.Mineralization of amoxicillin occurs on BDD and the chemical oxygen demandremoval was higher in sulfuric acid than in perchloric acid owing to theinvolvement of the in-situ formed persulfate and perchlorate to the degradation process mainly in the bulkof the solution. The instantaneous current efficiency (ICE) presents anexponential decay indicating that the process was limited by diffusion. Thespecific energy consumed after 5h of the amoxicillin electrolysis was 0.096 kWh COD-1and 0.035 kWh COD-1 in sulfuric acid and in perchloric acidrespectively.

Axial Ligand Coordination to the C-H Amination Catalyst Rh2(esp)2: A Structural and Spectroscopic Study.

The compound Rh2(esp)2 (esp = α,α,α',α'-tetramethyl-1,3-benzenediproponoate) is the most generally effective catalyst for nitrenoid amination of C-H bonds. However, much of its fundamental coordination chemistry is unknown. In this work, we study the effects of axial ligand coordination to the catalyst Rh2(esp)2. We report here crystal structures, cyclic voltammetry, UV-vis, IR, Raman, and (1)H NMR spectra for the complexes Rh2(esp)2L2 where L = pyridine, 3-picoline, 2,6-lutidine, acetonitrile, and methanol. The compounds all show well-defined π* → σ* electronic transitions in the 16500 to 20500 cm(-1) range, and Rh-Rh stretching vibrations in the range from 304 to 322 cm(-1). Taking these data into account we find that the strength of axial ligand binding to Rh2(esp)2 increases in the series CH3OH ∼ 2,6-lutidine < CH3CN < 3-methylpyridine ∼ pyridine. Quasi-reversible Rh2(4+/5+) redox waves are only obtained when either acetonitrile or no axial ligand is present. In the presence of pyridines, irreversible oxidation waves are observed, suggesting that these ligands destabilize the Rh2 complex under oxidative conditions.

Pyridine and Pyridinium Electrochemistry on Polycrystalline Gold Electrodes and Implications for CO2 Reduction

We examine the electrochemical behavior of pyridine (py) and pyridinium ion (pyrH+) on gold electrodes in inert nitrogen (N2) and carbon dioxide (CO2) environments to evaluate potential catalytic roles of nitrogen heterocycles in electrochemical CO2 reduction. Analysis of the pyridine and pyridinium systems shows that gold electrodes exhibit unique pyrH+ and CO2 electrochemistry compared with previous work on platinum electrodes or photoelectrode systems. Specifically, analysis of the data shows specific adsorption of pyridine/pyridinium, an irreversible reduction wave at −1.0 V vs Ag/AgCl associated with the one-electron reduction of pyridinium, and an enhanced reductive current when CO2 and pyrH+ are included together in the aqueous solution. Our results show no evidence to support formation of carbon-containing reduction products and implicate CO2 as a possible weak acid catalyst for production of dihydrogen.

Insights on the UV/Vis, Fluorescence, and Cyclic Voltammetry Properties and the Molecular Structures of ZnII Tetraphenylporphyrin Complexes with Pseudohalide Axial Azido, Cyanato‐N, Thiocyanato‐N, and Cyanido Ligands

AbstractThe syntheses, spectroscopic and photophysical properties, and molecular structures of azido‐ (1), cyanato‐N‐ (2), thiocyanato‐N‐ (3), and cyanido‐ (4) (meso‐tetraphenylporphyrinato)zinc(II) complexes are reported. These species were prepared by using cryptand‐222 to solubilize the pseudohalide salts in organic solvents. The UV/Vis spectra of these zinc metalloporphyrins are solvent‐dependent and exhibit large redshifted Soret bands compared with those of the [Zn(Porph)L] derivatives in which Porph is a meso‐porphyrinato ligand and L is a monodentate neutral axial ligand. The room‐temperature fluorescence spectra of the zinc complexes 1–4 indicate that the Q bands are not very affected by the nature of the axial ligands, and their positions are very close to those of previously reported (meso‐porphyrinato)zinc complexes. The quantum yields of the S1 → So fluorescence of 1–4 range between 2.8 and 5.5 %, and their fluorescence lifetimes are the same (1.7 ns). Cyclic voltammetry investigations on 1–4 show that the characteristic potentials for the reduction and the two first oxidations of the porphyrin ring are not very affected by the nature of the axial ligand. A third irreversible oxidation of the porphyrin ring is observed. Additional anodic irreversible waves are observed for the thiocyanato‐N (3) and cyanido (4) species. The solid‐state molecular structures of 1–4 are the first examples of zinc porphyrin complexes with anionic ligands. The average equatorial zinc–pyrrole N atom (Zn–Np) distances for 1–4 range between 2.083(1) and 2.117(2) Å and are much longer than those of the related pentacoordinate zinc porphyrin complexes with monodentate neutral ligands. As a consequence, the displacement of the Zn2+ cation from the mean 24‐atom plan of the porphyrin core is significant (ca. 0.5 Å), and the porphyrin core is very distorted. The crystal structures of 1–4 are stabilized by weak intermolecular π interactions, C–H···Cg (Cg are the centroids of some six‐membered phenyl rings and five‐membered pyrrole rings). The molecular structure of 1 is further stabilized by weak intermolecular C–H···N hydrogen bonds between one carbon atom of cryptand‐222 and the terminal nitrogen atom of the azido ligand.

Effects of Electrolyte, Current Density and Electricity Consumption on the Anodic Oxidation of Cyclic Amides

Anodic oxidation of N-alkylamides in the presence of nucleophiles such as water, alcohol or carboxylic acid, affords the respective alpha- hydroxy, -alkoxy or -carboxy derivatives as final products (Eq. 1). The electrochemical properties of three cyclic amides of the type N-acylazacycloalkanes (I - III) (Scheme 1) have been investigated in acetonitrile by cyclic voltammetry. Each one of them exhibits one irreversible anodic wave (at ~2 V) and one irreversible cathodic wave (at around -1.3 V). Preparative anodic oxidation of I - III in methanol at C anodes under various electrochemical conditions (current density, electricity consumption and supporting electrolytes) led to four major products by all three substrates: alpha-methoxy- and alpha,alpha'-dimethoxy cyclic amides, and two cyclic eneamide derivatives. Their relative ratio was found to be highly dependent on the nature of the electrolyte and current density.