Synthesis and spectroscopic and electrochemical studies of chitosan Schiff base derivatives

Schiff derivatives were prepared by the reactions of salicylaldehyde and its derivatives (5-chloro, 5-methoxy, 5-fluoro, 5-methyl, 5-nitro) with the amino group of chitosan. The Schiff bases were studied by Fourier IR spectroscopy and by UV-visible spectroscopy. The cyclic voltammograms of the Schiff bases were analyzed and compared to those of chitosan and salicylaldehyde. The formal potential of the chitosan Schiff base derivative correlates with the Hammett parameters. The oxidation potential increases and the optical density decreases with enhancement of the electron-acceptor properties of the functional group R in the m-position to the -N=CH-group. Chitosan (Chi) is a polysaccharide whose chains consist of recurrent units of acetamido-2-deoxy-D-glucode linked by the 1,4-β-glycoside bond. This polysaccharide was widely studied as drug carrier [1, 2], because it is nontoxic, biodegradable, and well biocompatible [3].     

Synthesis and electrochemical studies of tetrathiafulvalene derivatives (TTFs) as redox active ligands

A simple route for synthesis of new tetrathiafulvalene dimethyl ester (TTF‐DME) is reported. The tetrathifulvalene dimethylester (TTF‐DME) has been prepared by introducing an ester coordination function as a bifunctional new donor. The redox behavior of the TTF‐DME was investigated in comparison to the well‐known dibenzotetrathiafulvene (DB‐TTF) by cyclic voltammetry. A two‐electron redox behavior was observed as a two waves.     

Synthesis,structure and electrochemical properties of two new unsymmetrical tetrathiafulvalene derivatives

Two new unsymmetrical tetrathiafulvalene (TTF) derivatives, 2,3‐bis(cyanoethylthio)‐6,7‐(methyl‐ethylenedithio)tetrathiafulvalene ( 6a ) and 2,3‐bis(cyanoethylthio)‐6,7‐(cyclopentodithio)tetrathiafulvalene ( 6b ), have been prepared and characterized by NMR, MS, IR and Elemental analyses. The molecular structures have been determined by X‐ray crystallography. Their redox properties have been investigated by cyclic voltammetry in dichloromethane solution and each compound shows two reversible single‐electron redox couples.     

Syntheses,electrochemical studies and crystal structures of new unsymmetrical tetrathiafulvalene carboxylate derivatives

A series of new unsymmetrical tetrathiafulvalene carboxylate derivatives ( 7‐11 ) were synthesized and characterized by NMR, MS, electrochemical studies and X‐ray crystal structural determination. Compound 8 showed obvious changes in redox peak potentials as the concentration of p‐toluenesulfonic acid changes.     

Synthesis of new ethynylbipyridine-linked mono- and bis-tetrathiafulvalenes: electrochemical, spectroscopic, and Ru(II)-binding studies

Two new ethynylbipyridine-linked mono- and bis-tetrathiafulvalene (TTF) derivatives, together with a Ru(II) complex, were synthesized using Sonogashira coupling reactions and characterized by UV/vis spectroscopy and cyclic voltammetry. They display a clear electrochemically amphoteric behavior consisting of two reversible single-electron oxidation waves (typical for TTF derivatives) and one reversible single-electron reduction wave (bpy) and act as donor-acceptor (D-A) systems. Furthermore, for the Ru(II) complex, a quite intense fluorescence originating from the ³MLCT state is observed.     

Donor-acceptor-donor triads incorporating tetrathiafulvalene and perylene diimide units: synthesis, electrochemical and spectroscopic studies

Three donor-acceptor-donor triads 1-3 consisting of tetrathiafulvalene units attached to perylene diimides by flexible and rigid spacers were synthesized and characterized. UV/vis spectroscopic and cyclic voltammetric results indicate that they all show negligible intramolecular charge transfer interaction in their ground states. As compared to the reference compound 21, triads 1-3 display reduced fluorescence and their fluorescence lifetimes are shortened, which is probably owing to the photoinduced electron transfer interactions between the PI units and TTF units. The different photophysical behaviors between 1 and 2 (and 3) might be due to their difference in the spatial separation of TTF and PI units. It is preliminarily found that the steric hindrance of the groups attached to TTF units can affect their photostability.     

Highly selective colorimetric and electrochemical Pb2+ detection based on TTF-pi-pyridine derivatives

[reaction: see text] The pyridineethenyl-substituted tetrathiafulvalene (TTF) compounds, 4-(4-pyridineethenyl)tetrathiafulvalene (1a) and 4,4'(5')-[bis-(4-pyridineethenyl)]tetrathiafulvalene (2a) together with the styryl-substituted TTF compounds, 4-styryltetrathiafulvalene (1b) and 4,4'(5')-bis-styryltetrathiafulvalene (2b), have been designed and synthesized. All these compounds exhibit strong absorption bands in the range of 370 to 550 nm, which are assigned to the intramolecular charge-transfer transition from the HOMO in TTF to the LUMO in the pyridyl or phenyl group. Compared to compounds 1b and 2b, the pyridineethenyl-substituted TTF compounds 1a and 2a show remarkable sensing and coordinating properties to Pb2+. With the addition of micromolar concentrations of Pb2+ to the solution, 1a or 2a displays dramatic changes in the UV-vis absorption spectrum, 1H NMR spectrum, and redox property.     

Synthesis, structural, spectroscopic and electrochemical studies of carborane substituted naphthyl selenides

New unsymmetrical selenides bearing an o-carborane and a naphthalene ring as the substituents were prepared by the cleavage of the corresponding diselenides. The compounds were characterized by means of spectroscopic and analytical methods. (77)Se NMR signals of the selenium atoms attached to the carbon atoms of the carborane cages are shifted downfield in comparison to those bonded only to the aromatic rings, indicating an electron withdrawing effect of the o-carboranyl substituent. Compounds 1-(2-R-1,2-dicarba-closo-carboranyl)naphthyl selenides (R = Me, 1; Ph, 2) were characterized by means of single crystal X-ray diffraction. The influence of the electronic nature of the substituents attached to the selenium atoms on the structural parameters and packing properties of naphthyl selenides are discussed. Theoretical calculations and cyclic voltammetry (CV) studies were carried out to compare the bonding nature of carboranyl and analogous aryl selenium compounds. Cyclic voltammetry studies of naphthyl carboranyl mono and diselenides have shown that the carboranyl fragment polarizes the Se lone pair making it less prone to generate a Se-Se bond.     

Synthesis and spectroscopic studies of 3-carbamoylisonicotinic acid derivatives

An unusual example of the selective hydrolysis of a cyano group to the corresponding carboxyl group under mild reaction conditions in the presence of a carboxamide group is reported. The reaction resulted in the formation of a rare combination of vicinal carboxamide and carboxyl groups on a pyridone ring. The structure of the synthesized products was thoroughly studied using one- and two-dimensional NMR experiments and the reaction pathway was monitored fluorometrically.     

Synthesis of optically active amphiphilic tetrathiafulvalene derivatives

The synthesis and characterization of novel chiral tetrathiafulvalenes bearing two long alkyl chains at one end of the π-electron rich unit and different functional groups—ester, acid or thiolate—at the other extreme is described. The synthetic method requires the preparation of 1,3-dithiol derivatives with two stereogenic centers. Different routes and reaction conditions were explored to form these compounds, whose optimized synthesis involved the nucleophilic substitution of a chiral bromo methylene derivative with tetrabutylammonium bis(2-thioxo-1,3-dithiole-4,5-dithiolate)zincate. The tetrathiafulvalenes were prepared by coupling the 1,3-dithiol derivative with 4,5-bis(methoxycarbonyl)-1,3-dithiol-2-one or 4,5-bis(2-cyanotehylthio)-1,3-dithiol-2-thione. The products were fully characterized, including by circular dichroism spectroscopy, which confirmed their optical activity. They are promising candidates to be used as building blocks in supramolecular materials for molecular electronics, to produce systems with unique electrical, magnetic or optical properties that stem from their chirality.     

Synthesis and spectroscopic studies of some fluorinated 1,3,5-triazine derivatives

Tri-substituted derivatives of 2,4,6-trichloro-1,3,5-triazine have been prepared in good yields by the reaction of 2,4,6-trichloro-1,3,5-triazine with various aromatic amines. These new types of products have been characterised by elemental analysis, IR, ¹H and ¹⁹F NMR spectral studies.     

Synthesis and spectroscopic studies of some new oxazepine derivatives throughout [2+5] cycloaddition reactions (III)

The present work included condensation reactions of o-tolidine with different aromatic aldehydes in absolute ethanol to give Schiff bases (w ₉ –w ₁₂ ) in high yield which, on reaction with maleic and phthalic anhydride by [2+5] cycloaddition reactions in the presence of suitable solvents, give the corresponding [1,3]oxazepine-4,7-dione (w ₉ m–w ₁₂ m) and [1,3]oxazepine-1,5-dione (w ₉ ph–w ₁₂ ph), respectively. The structure of the newly synthesized compounds were monitored by TLC and established on the basis of elemental analysis, FT-IR, and ¹H NMR.     

Potent 5-nitrofuran derivatives inhibitors of Trypanosoma cruzi growth: electrochemical, spectroscopic and biological studies

Cyclic voltammetry and electron spin resonance techniques were used in the investigation of several potential antiprotozoal containing thiosemicarbazone and carbamate nitrofurans. In the electrochemical behaviour, a self-protonation process involving the nitro group was observed. The reactivity of the nitro anion radical for these derivatives with glutathione, a biological relevant thiol, was also studied in means of cyclic voltammetry. These studies demonstrated that glutathione could react with radical species from 5-nitrofuryl system. Furthermore, from the voltammetric results, some parameters of biological significance as E(7)(1) (indicative of the biological nitro anion radical formation), and [Formula: see text] (thermodynamic indicator the of oxygen redox cycling) have been calculated. We also evaluated the stability of the nitro anion radical in terms of the dimerization constant (k(d)). The nitrofuran-free radicals from cyclic voltammetry were characterized by electron spin resonance. A clear dependence between both the thiosemicarbazone or carbamate substructure and the length of the linker, furyl- or furylpropenyl-spacer, and the delocalization of the unpaired electron was observed. Through of biological assays we obtained important parameters that account for the selective anti-trypanosomal activity of these derivatives. The trypomastigote viability study showed that all derivatives are as active as in the epimastigote form of the parasite in a doses dependent manner.     

Synthesis and electrochemical properties of a chiral silyl-substituted tetrathiafulvalene derivative

A new chiral tetrathiafulvalene(TTF) derivative and related silyl-substituted 1,3-dithiole-2-(thi)one compounds were synthesized and characterized by ~1H NMR,~(13)C NMR,MS and IR spectra.Single crystal structure of the silyl-substituted 1,3-dithiole-2-one revealed the high degree of conjugation of the fivemembered ring moiety in the compound.The electrochemical properties of the new TTF derivative were studied by cyclic voltammetry and the results indicated that the electron-donating ability of the chiral TTF derivative was similar to that of BEDT-TTF.The △E value for the new TTF derivative was smaller than those for TTF and BEDT-TTF,indicative of decreased Coulombic repulsion in the dicationic redox state.Formation of charge-transfer(CT) complex between the new donor and electron acceptor 2,3-dichloro-5,6-dicyano-l,4-benzoquinone(DDQ) was demonstrated.     

Synthesis of tetrathiafulvalene derivatives by dimerization of 1,3-dithiolselenones-2 using triphenylphosphine

Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1278–1279, September, 1991.     

Organic high-spin systems: Synthesis,electrochemical and spectroscopic studies of π-extended tetraaryl m-phenylenediamines

Three highly π-extended tetraaryl-1,3-phenylenediamines for charged high-spin molecular systems were successfully synthesized using Suzuki coupling. Their electrochemical and spectroscopic properties were also examined. They showed blue fluorescence. The dications derived from highly π-extended tetraaryl-1,3-phenylenediamines were generated and characterized by electron transfer stopped-flow method.     

CO2 Fixation by Cu2+ and Zn2+ complexes of a terpyridinophane aza receptor. Crystal structures of Cu2+ complexes, pH-metric, spectroscopic, and electrochemical studies

The synthesis of the terpyridinophane-type polyamine 2,6,9,12,16-pentaaza[17]-(5,5' ')-cyclo-(2,2':6',2' ')-terpyridinophane heptahydrobromide tetrahydrate (L.7HBr.4H2O) is described. L presents six protonation constants with values in the range 9.21-3.27 logarithmic units. L interacts with Cu2+ and Zn2+ forming in both cases, neutral, protonated, and hydroxylated mono- and binuclear complexes whose constants have been calculated by potentiometry in 0.15 M NaClO4 at 298.1 K. The crystal structures of the compounds [Cu(HL-carb)(H2O)](ClO4)3.2H2O (1) and [Cu2(H2L)(CO3)]2(ClO4)8.9H2O (2) have been solved by X-ray diffraction. In 1, the metal center presents square pyramidal geometry. The base of the pyramid is formed by the three nitrogen atoms of pyridine and one oxygen atom of a CO2 group which is forming a carbamate bond with the central nitrogen atom of the polyamine chain. The axial position is occupied by a water molecule. In 2, one Cu2+ is bound by the three pyridine nitrogens and the other one by the three central nitrogen atoms of the polyamine chain. The square planar coordination geometry is completed by a carbonate group taken up from the atmosphere that behaves as a bridging mu,mu'-ligand between the two centers. The pH-metric titrations on the ternary Cu2+-L-carbonate and Zn2+-L-carbonate systems show the extensive formation of adduct species which above pH 6 are formed quantitatively in solution. The stoichiometries of the main species formed in solution at pH = 6.8 agree with those found in the crystalline compounds. CO2 uptake by the Zn2+ and Cu2+ 1:1 complexes in aqueous solution has also been followed by recording the variations in the band at ca. 300 nm. The formation of the Zn2+ carbamate moiety has been evidenced by 13C NMR and ESI spectroscopy.     

Synthesis,structural, electrochemical,and spectroscopic studies of some (diimine)ruthenium nitrile complexes

The syntheses of cationic ruthenium(II) complexes [Ru(Me₂-bpy)(PPh₃)₂RR?][PF₆]_x {Me₂-bpy = 4,4?-dimethyl-2,2?-bipyridine, (3) R = Cl, R? = N≡CMe, x = 1, (4) R = Cl, R? = N≡CPh, x = 1, (5) R = R? = N≡CMe, x = 2} and [Ru(Me₂-bpy)(κ²-dppf)RR?][PF₆]_x {dppf = 1,1?-bis(diphenylphosphino)ferrocene, (6) R = Cl, R? = N≡CMe, x = 1, (7) R = Cl, R? = N≡CPh, x = 1, (8) R = R? = N≡CMe, x = 2} are reported, together with their structural confirmation by NMR (³¹P, ¹H) and IR spectroscopy and elemental analysis, and, in the case of trans-[Ru(Me₂-bpy)(PPh₃)₂(N≡CCH₃)Cl][PF₆] (3), by X-ray crystallography. Electronic absorption and emission spectra of the complexes reveal that all complexes except 4 and 6 are emissive in the range 370–400 nm with 8 exhibiting an emission in the blue. Cyclic voltammetry studies of 3–8 show reversible or quasi-reversible redox processes at ca. 1 V, assigned to the Ru(II/III) couple.     

Binding studies between tetrathiafulvalene derivatives and cyclobis(paraquat-p-phenylene)

The complexation between a number of different pi-electron donating TTF derivatives and the pi-electron accepting tetracationic cyclophane cyclobis(paraquat-p-phenylene) (CBPQT(4+)) has been studied by (1)H NMR and UV-vis spectroscopy. The results demonstrate that the strength of association between the donors (TTF derivatives) and acceptor (CBPQT(4+)) is strongly dependent on the pi-electron donating properties (measured by the first redox potential ) of the TTF derivatives. However, the first redox potential () is not the only factor of importance. The extended pi-surface of the TTF derivatives also exerts a stabilizing influence upon complexation. The kinetics for the complexation-decomplexation were studied using (1)H NMR spectroscopy and are related to the bulkiness of the TTF derivatives. These effects may serve to improve the design of interlocked molecular systems, especially (bistable) molecular switches, in which CBPQT(4+) and a derivatized TTF unit are incorporated.