Facile electrochemical generation of polyoxyethyl-vinylogous tetrathiafulvalene films

Electropolymerization of substituted dithiafulvenes is a convenient way to produce conjugated TTF electroactive films. When flexible polyoxyethyl chains link a conjugated TTF, the properties of the electroactive units in the film are the same as those observed in solution. This is illustrated with the existence of molecular movements in the TTF core that were previously described in solution and are clearly detected in the film. With this linker, morphologic investigations performed by in situ EC-AFM show a regular film formation leading to a continuous deposit with no special structures.     

Unsymmetrically substituted furoxans. Part 11. Methylfuroxancarbaldehydes

The two isomeric 3-methyl-4-furoxancarbaldehydes ( 2a ) and 4-methyl-3-furoxancarbaldehyde ( 2b ) have been prepared. Discussion of their structures, thermal equilibration and kinetic of thermal conversion from the 3-methyl to the 4-methyl isomer are also reported. (Phenylsulfonyl)hydrazones 3a and 3b have been prepared as derivatives in view of their potential antitumoral properties.     

1-Hydrazinophthalazine based hydrazones and their transition metal complexes: Structure and biological activity

Structure, tautomeric rearrangements, acid-base properties and complex formation ability of 1-hydrazinophthalazine hydrazones and their coordination compounds with transition metals are considered. The main factors influencing the structure and physicochemical properties of the complexes, biological activity of phthalazine hydrazones and their complexes are discussed.     

Proton transfer and coordination properties of aromatic α-hydroxy hydrazones

The prototropic properties of two nitro derivatives of aromatic α-hydroxy hydrazones [2,4-dinitro-N-phenyl-N′(2-hydroxy-1-phenylmethylene hydrazine) and 2,4-dinitro-N-phenyl-N′(2-hydroxy-1-naphthylmethylene hydrazine] have been analysed through electronic absorption, ¹H and ¹³C NMR and semiempirical molecular orbital methods. The metal binding properties of both compounds and of the unsubstituted hydrazones were evaluated from potentiometric and spectrophotometric data in dioxane-water mixtures. On the basis of the spectral analysis and PM3 semiempirical calculations, the structures of the formed complexes were proposed.     

Luminescence and photochemical properties of hydrazones of aromatic aldehydes

Luminescence and photochemical properties found by us earlier for several hydrazones of aromatic aldehydes have been shown to be characteristic also of other compounds of this class. The structure of the product of reversible photochemical reaction of hydrazones of aromatic aldehydes is explained by specific interactions between the lone electron pairs of the two vicinal nitrogen atoms in the molecule of hydrazine. Compounds possessing photochromic properties have been suggested and prerequisites of application of luminescent hydrazones as luminophors have been formulated.     

Protolitic complexing properties of acylhydrazones of substituted salicylaldehydes and stability constants of their cooper(II) complexes

The acid-base properties of acetyl-and heptoylhydrazones of substituted salicylaldehyde derivatives and the stability of their copper(II) complexes have been studied. For both sets of compounds, the ionization constants of the hydrazones and the stability constants of hydrazone complexes are linear functions of the substituent constants σ. An analogous tendency is found for the antiferromagnetic exchange interaction parameters in dimeric copper(II) nitrate complexes of heptoylhydrazones of substituted salicylaldehyde derivatives. A correlation between the protolytic properties of hydrazones and the magnetic properties of their complexes is suggested.     

3‐(Arylhydrazono)pentane‐2, 4‐diones and their Complexes with Copper(II) and Nickel(II) — Synthesis and Crystal Structures

A series of new 3‐(arylhydrazono)pentane‐2, 4‐diones ( 1 ‐ 6 ) synthesized from pentane‐2, 4‐dione and diazonium salts of respective anilines using the procedure of Japp‐Klingemann are described. Complexes with Cu^II and Ni^II salts are prepared ( 7 ‐ 10 , respectively). Spectroscopic properties of these compounds have been studied and X‐ray crystal structures of selected hydrazones ( 3 , 4 , 6 ) and of the hydrazone complexes ( 7 ‐ 10 ) are reported. The structures of the uncomplexed hydrazones feature an intramolecular N‐H···O interaction to yield a six‐membered H‐bond ring reflecting preference of the hydrazone tautomeric structure. All the complexes are mononuclear 2:1 (L:M) structures of six‐membered chelate type involving N₂O₂ binding sites that are quadratic arranged but differ in the entire coordination environment dependent on the metal and the ligand substitution including distorted octahedral and quadratic pyramidal coordination geometries in the Cu^II complexes 7 and 8 or nearly regular square planar coordination geometry in the Ni^II complexes 9 and 10 , respectively. In the crystal packings, strong and weak H‐bond interactions cause supramolecular network structures.     

Pyrroloquinoxaline hydrazones as fluorescent probes for amyloid fibrils

Here we describe the identification and preliminary characterization of a new class of pyrrolo(imidazo)quinoxaline hydrazones as florescent probes for Aβ(1-42) fibrils. All the newly developed compounds were able to bind amyloid fibrils formed in vitro and some of them displayed an increase of their fluorescence upon binding. When tested on brain tissue preparations presenting Aβ deposits, the described hydrazones selectively stained amyloid structures and did not display aspecific binding. The hydrazones did not show antifibrillogenic activity and electron microscopy analysis revealed that they do not interfere with fibrils structure. The described pyrrolo(imidazo)quinoxalines could be useful for studying amyloid structures in vitro. Moreover, their experimentally proven ability to cross the blood-brain barrier in mouse opens the possibility of developing these compounds as potential amyloid imaging agents for in vivo applications.     

Comparison of properties of aniline and o-aminophenol polymers obtained using hydrogen peroxide

Powders of electroactive polymers are obtained using the reaction of hydrogen peroxide with acidic solutions containing aniline, o-aminophenol, or their mixture. These polymers are considered as counterparts of polyaniline obtained in the course of cathodic oxygen reduction, which is confirmed by the similarity of their electrochemical properties. IR-spectra of the obtained powders prove that their structures are in many ways similar.     

Protolytic properties of 8-quinolylhydrazones of substituted salicylaldehydes and physicochemical properties of their copper(II) complexes

Acid-base properties of hydrazones derived from 8-hydrazinoquinoline and substituted salicylaldehydes were studied. Under the experimental conditions, only the first step of ionization of the hydrazones is realized. The ionization constants were calculated quantum-chemically. Copper(II) complexes of these hydrazones, (HL)Cu(X)(CH₃OH)_n, were isolated (HL^? is the monodeprotonated form of hydrazones, and X^? is the acid residue). According to the data of elemental analysis, IR spectroscopy, conductometry, and magnetochemistry, the majority of the complexes have a binuclear structure. The copper(II) ions in the dimeric complex show antiferromagnetic exchange coupling. The ionization constants of the hydrazones and the exchange parameters strongly depend on the substituent in the salicylaldehyde moiety.     

Experimental and theoretical study on the absorption and fluorescence properties of substituted aryl hydrazones of 1,8-naphthalimide

Absorption and fluorescence spectra in acetonitrile for a series of substituted aryl hydrazones of N-hexyl-1,8-naphthalimide are studied with the aim of potential application of the compounds for enzyme activity localization. The influence of the substituents on the spectral characteristics has been evaluated. The absorption and fluorescence energies of substituted aryl-1,8-naphthalimide hydrazones have been calculated with the PCM TDDFT formalism. The M06 and PBE0 functionals, combined with the 6-31+G(d) atomic basis set, have been found to accurately model the excited state properties of the present set of solvated fluorophores. Absorption and fluorescence spectral characteristics have been rationalized in terms of experimental and theoretical electronic indices in order to assess their predictive abilities for application in designing analogues with good emitting properties. An excellent linear dependence is established between the experimental fluorescence and Hammett σ(p)(+) substituent constants and on the other hand σ(p)(+) constants correlate with the theoretically calculated values for the electrostatic potential at nuclei (EPN). A model for predicting the fluorescence properties of substituted hydrazones by means of EPN is drawn, including the polysubstituted derivatives, where Hammett constants are not applicable.     

Sensitive RP-HPLC Enantioseparation of (<Emphasis Type="Italic">RS</Emphasis>)-Ketamine via Chiral Derivatization Based on (<Emphasis Type="Italic">S</Emphasis>)-Levofloxacin

Enantioseparation of (RS)-ketamine has been achieved in the form of its diastereomeric hydrazones. A new chiral reagent was synthesized from enantiomerically pure (S)-levofloxacin by converting its carboxyl group into a hydrazide derivative: the reagent provided a reaction site for the ketonic group present in (RS)-ketamine. Because of the structural feature of the chiral reagent formation of diastereomeric hydrazones of (RS)-ketamine was successful without protection of its amino group. The diastereomeric hydrazones were separated on a reversed-phase C₁₈ column with a mobile phase consisting of MeCN and 0.1% TFA under gradient elution from 35 to 65% of MeCN. The limit of detection was found to be 3.2 and 3.4 nmol for first and second eluting diastereomeric hydrazones, respectively. The separation mechanism and elution order of the diastereomeric hydrazones were proposed and supported by developing the geometry optimized ‘lowest energy’ structures of the two diastereomeric hydrazones using DFT-based Gaussian software.     

Hydrazones from hydroxy naphthaldehydes. Part 2. Condensations with aromatic N-aminoheterocycles and elucidation of tautomeric structures

This paper extends previous studies on hydrazones derived from hydroxyl naphthaldehydes to aromatic N-aminoheterocycles (exemplified herein by triazole derivatives), in an attempt to freeze enamine structures either by altering the electronic properties of the non-iminic nitrogen or through steric hindrance leading to coplanar dispositions between the lone pairs. By comparing experimentally obtained results (NMR in solution and crystal data) to computationally simulated ones (via DFT calculations in the gas phase and CHCl₃), the structures of the preferential conformers and tautomers can be confidently assigned. All data are consistent with enhanced stability of imine forms with respect to their enamine counterparts. DFT calculations have the ability to identify the orbital interactions responsible for electron delocalization and the energy of intramolecular hydrogen bonding. In addition, all transition structures for conformational and tautomeric equilibria are located and characterized.     

Potential‐Driven Chirality Manifestations and Impressive Enantioselectivity by Inherently Chiral Electroactive Organic Films

The typical design of chiral electroactive materials involves attaching chiral pendants to an electroactive polyconjugated backbone and generally results in modest chirality manifestations. Discussed herein are electroactive chiral poly‐heterocycles, where chirality is not external to the electroactive backbone but inherent to it, and results from a torsion generated by the periodic presence of atropisomeric, conjugatively active biheteroaromatic scaffolds, (3,3′‐bithianaphthene). As the stereogenic element coincides with the electroactive one, films of impressive chiroptical activity and outstanding enantiodiscrimination properties are obtained. Moreover, chirality manifestations can be finely and reversibly tuned by the electric potential, as progressive injection of holes forces the two thianaphthene rings to co‐planarize to favor delocalization. Such deformations, revealed by CD spectroelectrochemistry, are elastic and reversible, thus suggesting a breathing system.     

The structure of the protonated forms of 1-hydrazinophthalazine and phthalazone hydrazone derivatives

Phthalazone derivatives Ia–h are protonated at the exocyclic nitrogen and phthalazine derivatives IIa–c at the N-2 of the ring. The cations of hydrazones Va–e have the cyclic structures VIa–e.     

Dihydro-1,2-diazaphenazines

Derivatives of dihydro-1,2-diazaphenazines were obtained by cyclization of the phenylhydrazones and hydrazones of 2-acetonyl- and 2-phenacyl-3-quinoxalones by refluxing in glacial acetic acid. Data characterizing their structures are presented.     

Photoinduced processes in interlocked structures containing porphyrins

The recent literature on photoactive interlocked structures containing porphyrins is reviewed. Catenanes and rotaxanes studied both in the author's laboratory and by other groups, displaying either photoinduced energy or electron transfer processes are reported. In addition to porphyrins, the examined structures contain photo or electroactive components as C₆₀, paraquat, ferrocene, aromatic amines. Both metal catenanes/rotaxanes and free catenanes/rotaxanes are discussed and the differences in their behavior is outlined with respect to structural rigidity and electronic coupling properties. The role of different conformations and their effect on photophysical properties is examined. In spite of their uncommon topology, these arrays behave similarly to covalently or self-assembled photoactive multi-component architectures and display fast energy/electron transfer rates and high charge separation efficiency. A rationale for this behavior is provided.     

Synthesis and metallochromic properties of some hydrazones of 2-, 3- and 8-hydrazinoquinoline

Twenty-two new hydrazones were synthesized for evaluation as possible calorimetric reagents for trace determinations of iron, cobalt, nickel, copper and zinc. Spectrophotometric studies revealed that several show promise as sensitive reagents, with possible utility for simultaneous determinations of two or more of the metals. Conclusions regarding geometric structures of some of the hydrazones and chelates were deduced from mole-ratio studies.     

Planarization-Induced Activation Wavelength Red-Shift and Thermal Half-Life Acceleration in Hydrazone Photoswitches

The optimization and modulation of the properties of photochromic compounds, such as their activation wavelengths and thermal relaxation half-lives (τ_1/2), are essential for their adaptation in various applications. In this work, we studied the effect of co-planarization of the rotary fragment of two photochromic hydrazones with the core of the molecule on their switching properties. The Z and E isomers of both compounds exhibit red-shifted absorption bands relative to their twisted versions, allowing for their photoswitching using longer wavelengths of light. Additionally, the thermal half-lives of both hydrazones are drastically shortened from hundreds of years to days.     

Reaction of 2-acyl-3-aminobenzofurans with hydrazines

While 2-acetyl and 2-benzoyl-3-aminobenzofurans did not react with hydrazine, monomethyl- and N,N-dimethylhydrazine to give the related hydrazones, their 3-N-(p-toluenesulfonyl) derivatives afforded them smoothly in good yields. Depending upon reaction conditions, products arising from hydrazone cyclization to benzofuropyrazoles and/or from furan ring cleavage at the C2 O bond to give 5-(2-hydroxyphenyl)pyrazoles were also formed. The formation of these products depends upon hydrazones configuration and is discussed. Only (E)-isomers appear to undergo furan ring opening. In acidic media at room temprature either the hydrazones or the monomethylhydrazones gave the same related α-azines. Microanalyses, ir, uv, ¹H-nmr and ms spectra are in agreement with the proposed structures.