Synthesis of Pyridyl and N-Methylpyridinium Analogues of Rosamines: Relevance of Solvent and Charge on Their Photophysical Properties

A series of pyridyl analogues of rosamines was prepared by employing two methodologies: (i) the conventional-heating condensation of a pyridinecarboxaldehyde with 3-(diethylamino)phenol in propionic acid, and (ii) the novel ohmic-heating assisted condensation under “on water” conditions, followed by oxidation. The 4-pyridyl substituted rosamine was further converted into the N-methylpyridinium derivative through N-alkylation using methyl iodide. The influence of the position and cationization of the nitrogen atom of the pyridyl ring in the physicochemical properties of fluorophores was investigated by ¹H, ¹³C, ¹⁵N NMR spectral analysis, UV/Vis and fluorescence spectroscopy, single-crystal X-ray diffraction (4-pyridyl and N-methylpyridinium derivatives) and thermal-behavior analysis. Curiously, for ethanolic solutions of 4-pyridyl and N-methylpyridinium derivatives an extinction of color and fluorescence over time was observed. This phenomenon was further studied and the data revealed that it is the result of nucleophilic addition of ethoxide ion to the central 9-position of the xanthene. The kinetics of the process is slower for the 4-pyridyl rosamine, which emphasizes the importance of the charge in the N-methylpyridinium analogue in the reactivity of the molecule towards a nucleophile agent. This phenomenon is reversible, meaning that the compounds can be rapidly recovered by decreasing the pH, opening new avenues in the sensing applications of this class of rosamines.     

2- and 2,7-Substituted para-N-Methylpyridinium Pyrenes: Syntheses,Molecular and Electronic Structures,Photophysical, Electrochemical,and Spectroelectrochemical Properties and Binding to Double-Stranded (ds) DNA

Two N-methylpyridinium compounds and analogous N-protonated salts of 2- and 2,7-substituted 4-pyridyl-pyrene compounds were synthesised and their crystal structures, photophysical properties both in solution and in the solid state, electrochemical and spectroelectrochemical properties were studied. Upon methylation or protonation, the emission maxima are significantly bathochromically shifted compared to the neutral compounds, although the absorption maxima remain almost unchanged. As a result, the cationic compounds show very large apparent Stokes shifts of up to 7200 cm⁻¹. The N-methylpyridinium compounds have a single reduction at ca. −1.5 V vs. Fc/Fc⁺ in MeCN. While the reduction process was reversible for the 2,7-disubstituted compound, it was irreversible for the mono-substituted one. Experimental findings are complemented by DFT and TD-DFT calculations. Furthermore, the N-methylpyridinium compounds show strong interactions with calf thymus (ct)-DNA, presumably by intercalation, which paves the way for further applications of these multi-functional compounds as potential DNA-bioactive agents.     

Aggregation Behavior of Pyridinium-Based Ionic Liquids in Aqueous Solution

Aggregation of the ionic liquids 1-butylpyridinium tetrafluoroborate, 1-butylpyridinium triflate, 1-butyl-2-methylpyridinium tetrafluoroborate, 1-butyl-3-methylpyridinium tetrafluoroborate, 1-butyl-4-methylpyridinium tetrafluoroborate, 1-butyl-3-methylpyridinium dicyanamide, and 1-octyl-3-methylpyridinium tetrafluoroborate in aqueous solution has been characterized at 298.15 K through density, ρ, speed of sound, u, and conductivity, σ, measurements. In addition, apparent molar volumes, V _φ , and isentropic compressibilities, κ _s , have been calculated from the experimental data. To characterize the formation of aggregates, the critical aggregation concentration of the ionic liquids, cac, the degree of ionization of the aggregates, β, and the standard Gibbs energy of aggregation, DG_m^°\Delta G_{\mathrm{m}}^{\circ}, have been obtained, with good agreement between results derived from the different methods. The dependence on the structural variation of these ions has been analyzed by comparing the results obtained for this series of ionic liquids.     

Quaternary salts from 2-(methylpyridyl or quinolyl)benzimidazoles and related polymethine dyes

The quaternisation of 2-(methylpyridyl or quinolyl)benzimidazoles with methyl iodide leads to a variety of salts depending on the relative position of the nuclei and on the experimental conditions: N-methylpyridinium, N-methylquinolinium, methyl and 1,3-dimethylbenzimidazolium iodides, and hydroiodides were isolated. Cyanine dyes were prepared from N-methylpyridinium and N-methylquinolinium methiodides. The main spectrospcopic features of these compounds are briefly discussed.     

Synthesis and Properties of a New Two-photon-absorbed Material Heasps

Abstract

A new dye Trans-4-[p-(N-hydroxyethyl-N-ethyiamino)styryl]-N-methylpyridinium p-toluene sulfonate (HEASPS) was synthesized, and the two-photon absorption (TPA), TPA-induced frequency up-conversion emission, and two-photon pumped (TPP) frequency up-converted lasing properties of this new dye were experimentally studied. This new dye has a moderate TPA cross-section of\sigma₂ = 4.7 × 10^?48 cm⁴ .s/photon at 1064nm, but exhibits a high lasing efficiency. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the 626 nm up-converted lasing energy is 18.2% at the pump energy level of 1.9 mJ.     

Mimesis of peroxidase by Mn-TMPyP in the catalytic fluorescence reaction of the homovanillic acid-hydrogen peroxide system

The fluorescence produced by the catalytic effect of the manganese (III)-tetrakis-(N-methylpyridinium)porphyrin complex (Mn-TMPyP) on the oxidation of homovanillic acid by hydrogen peroxide has been studied. The reaction product fluoresces at 424 nm (with excitation at 316 nm). Traces of hydrogen peroxide (1.3 × 10^–7–2.4 × 10^–6 M) and glucose (1.5–5.0 g/ml) can be determined with good accuracy and reproducibility. The characteristics of the mimetic enzyme Mn-TMPyP have been compared with those of horseradish peroxidase.     

Application des mesures de couplages 15N?H à la détermination de configurations d'oximes

Several ¹⁵N enriched oximes of heterocyclic aldehydes have been prepared in syn and anti forms. The less stable form may be obtained by UV irradiation of the other one. The geminal ¹⁵N? H coupling in the R? CH?¹⁵N? OH fragment allows an immediate and unambiguous assignment of the configuration to be made, being 13 to 16 Hz and 2 to 3 Hz for the anti and syn forms, respectively. Whereas oximes 1 to 4 are preferentially in the anti form, the N-methylpyridinium aldoxime iodides (2-PAM, 3-PAM, 4-PAM) are found to be syn in the stable form and not anti as previously thought. This reassignment is of special interest, since 2-PAM ( 8 ), which is an excellent antidote against alkyl phosphate nerve poisoning, has been used to study the geometry of the acetylcholinesterase active site of the enzyme.     

Reduction of n-(1,3-dioxolan-2-yl)-1-methylpyridinium ions: Molecular structure of the 4-(l,3-dioxolan-2-yl)-1-methyl-1,2,3,6-tetrahydropyridine-borane complex

The reduction of the n-(1,3-dioxolan-2-yl)-1-methylpyridinium ions with sodium borohydride has been studied to prepare N-methylformylpiperidines. Deuterium oxide was used as the solvent in order to assign the protons in the nmr spectra. As a product of the reaction, the 4-(1,3-dioxolan-2-yl)-1-methyl-1,2,3,6-tetrahy-dropyridine-borane complex, was isolated and crystallized. A X-ray study of this borane complex has been carried out.     

N-Methyl chemical shifts in some 2-, 3- and 4-substituted N-methylpyridinium salts

The chemical shifts of the N-methyl group in a series of 2-, 3- and 4-substituted N-methylpyridinium salts have been measured in DMSO solution. The shift is primarily affected by resonance interaction between the substituent and aza group, and the results suggest that the resonance effect from a 2-substituent is at least as great as from the corresponding 4-substituent.     

Phase equilibria study of the binary systems (ionic liquid + thiophene): Desulphurization process

(Solid + liquid) equilibria (SLE) and (liquid + liquid) equilibria (LLE) for the binary systems: {ionic liquid (IL) N-butyl-4-methylpyridinium tosylate (p-toluenesulfonate) [BM⁴Py][TOS], or N-butyl-3-methylpyridinium tosylate [BM³Py][TOS], or N-hexyl-3-methylpyridinium tosylate [HM³Py][TOS], or N-butyl-4-methylpyridinium bis{(trifluoromethyl)sulfonyl}imide [BM⁴Py][NTf₂], or 1,4-dimethylpyridinium tosylate [M^1,4Py][TOS], or 2,4,6-collidine tosylate [M^2,4,6Py][TOS], or 1-ethyl-3-methylimidazolium thiocyanate [EMIM][SCN], or 1-butyl-3-methylimidazolium thiocyanate [BMIM][SCN], or 1-hexyl-3-methylimidazolium thiocyanate [HMIM][SCN], or triethylsulphonium bis(trifluoromethylsulfonyl)imide [Et₃S][NTf₂] + thiophene} have been determined at ambient pressure. A dynamic method was used over a broad range of mole fractions and temperatures from (270 to 390) K. In the case of systems (pyridinium IL, or sulphonium IL + thiophene) the mutual immiscibility with an upper critical solution temperature (UCST) was detected at the very narrow and low mole fraction of the IL. For the binary systems containing (imidazolium thiocyanate IL + thiophene), the mutual immiscibility with the lower critical solution temperature (LCST) was detected at the higher mole fraction range of the IL. The basic thermal properties of the pure ILs, i.e. melting and glass-transition temperatures as well as the enthalpy of fusion have been measured using a differential scanning microcalorimetry technique (DSC). The well-known NRTL equation has been used to correlate experimental SLE/LLE data sets.     

1H and 7Li NMR Study on the Complex Formation of Lithium Cations with Pyridinium Derivatives of Calix[4]arenes

Complexation of lithium ions by three chromoionophoric calix[4]arenes has been studied by ¹H and ⁷Li NMR spectroscopy. The signalling unit of the chromoionophores is the N-methylpyridinium(methyleneimino) group in conjugation with a phenolic group of the calixarene ring while the coordination spheres contain esteric (ethoxycarbonylmethoxy) or etheric (ethoxy, propoxy) units. ¹H NMR and NOESY measurements suggest the dominance of cone conformations of the calixarene rings with slight, solvent-dependent distortions. Complexation occurs only in the presence of a weak base. The interaction with lithium ions causes a broadening of both the ¹H and ⁷Li NMR signals. Analysis of the chemical shifts in the three complexes indicates a different coordination environment for the lithium with the calixarene containing esteric groups from those having etheric groups. This explains the differences in the stabilities of the lithium complexes of the two types of calixarenes.     

Thermal decompositions of N-methylpyridinium,quinolinium, isoquinolinium and phenanthridinium salts in a mass spectrometer. Evidence for a specific HI elimination and for an oxidation to amides

The mass spectra of some N-methylpyridinium, quinolinium, isoquinolinium and phenanthridinium salts (R⁺X^?)

1 The salt will be represented by R⁺X^? or RX, R⁺ being the organic moiety, with its associated mass and X- the inorganic anion.

are analyzed (X^? = I^? or ClO₄^?). For X^? = I^?, thermal decomposition gives rise mainly to the superimposed spectra of CH₃I and the free base. Hence, iodide salts cannot be determined specifically by their mass spectra. When an α-methyl group is present, e.g. 2-methylpyridinium methiodide, elimination of HI becomes an important thermal process. For X^? = ClO₄^?, the same pattern is observed, but in addition a generally important peak at [R + 15] is present. This peak is due to the oxidation, mainly α to the nitrogen of the organic moiety by the ClO₄^? ion, giving rise to the corresponding amide. In some cases, chlorination of the organic moiety has been observed as well as double oxidation. The thermal processes for the perchlorate salts are characteristic and are useful in the elucidation of the quaternary structure.     

N-alkoxy-pyridinium and N-alkoxy-quinolinium salts as initiators for cationic photopolymerizations

The polymerization of n-butyl vinyl ether (BVE), cyclohexene oxide (CHO) and 3,4-epoxycyclohexyl(methyl)-3′,4′-epoxycyclohexane carboxylate (EEC) was initiated upon UV irradiation (λ_inc > 300 nm) of dichloromethane solutions containing N-ethoxy-2-methylpyridinium ( V ), N-ethoxy-4-phenyl-pyridinium ( VI ) or N-ethoxy-isoquinolinium hexafluorophosphate ( VII ). Whereas the bifunctional EEC was converted into an insoluble gel, BVE and CHO formed polymers of molar mass: M_w = 2 X 10⁴?2 X 10⁵ (PCHO) and M_w ≈ 2 X 10⁴ (PBVE). Protons are formed with a rather high quantum yield [ø(H+) = 0.48 on irradiating VII in dichloromethane; titration with sodium p-nitrophenolate] and it is, therefore, assumed that the polymerization is initiated by photochemically generated protons. © 1992 John Wiley & Sons, Inc.     

Development and rheological investigation of novel alginate/N‐succinylchitosan hydrogels

In the present article alginate hydrogels and novel hydrogels based on blends of alginate/N‐succinylchitosan have been realized in water solution at neutral conditions. The gels have been obtained by crosslinking via the internal setting method using calcium carbonate (CaCO₃) as calcium ions source. A rheological investigation of both the plain alginate and the alginate/N‐succinylchitosan blend hydrogels has been performed by means of oscillatory dynamic measurements. The effect of the inclusion of different amounts of CaCO₃ on the critical deformation (γ_c) characterizing the limit of the linear viscoelastic regime has been studied for the plain alginate gels. The frequency response in small amplitude oscillatory experiments of the plain alginate gels has been investigated in terms of the storage (G′) and loss (G″) modulus behavior. The dynamic data have been interpreted in terms of the Friedrich and Heymann model. The inclusion of the N‐succinylchitosan, in the range 10–50% w/w, had no effect on the γ_c values. On the contrary, when the 10% w/w of the N‐succinylchitosan is added to the plain alginate gels, a significant increase in the storage modulus values is recorded for all the systems analyzed. The gelation kinetics has been investigated and the results indicate that the kinetics process can be accelerated increasing the percentage of Ca⁺² ions and/or including the N‐succinylchitosan in the plain alginate systems. Finally, the morphological analysis of scaffolds obtained from the hydrogels through freeze‐drying revealed an interconnected porous structure. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1167–1182, 2008     

Highly effective binding and inverse fluorescent behavior of palmatine and l-tetrahydropalmatine alkaloids by p-sulfonatocalixarenes

The effects of pressure and solvent were examined for the inclusion complexation of phenothiazine dyes and trans-4-[4-(dimethylamino)styryl]-1-methylpyridinium (St-4Me) with water-soluble p-sulfonatocalix[8]arene (Calix-S8). Depending on the bulkiness of the guest dyes, external pressures and solvent polarity increase the inclusion equilibrium constants of dyes with Calix-S8. From the pressure dependence of the inclusion equilibria, the reaction volumes for inclusion by Calix-S8 in the alcohol-water mixtures were estimated to be negative values (?19.8 to ?5.29 cm³ mol^?1 for the phenothiazine dyes and ?13.1 to ?9.85 cm³ mol^?1 for St-4Me). Analysis of the results of the high pressure indicated that the intrinsic volume change related to inclusion into the Calix-S8 cavity plays an important role in the inclusion of Calix-S8, depending on the bulkiness of the guest molecules. Based on ¹H NMR measurements, the structures of the inclusion complexes of Calix-S8 with phenothiazine dyes have been established and the differences in the inclusion behaviors of the phenothiazine dyes and St-4Me are discussed.     

Excellent correlation between substituent constants and pyridinium N-methyl chemical shifts

Substituents on the pyridinium ring of N-methylpyridinium derivatives, especially those on the 2- or 4-position, have a large effect on the ¹H and ¹³C NMR chemical shifts of the N-methyl group. Reasonable correlations between the chemical shift changes and the resonance substituent constants are observed. The dual substituent parameter approach provides an excellent correlation when a combination of polar and resonance substituent constants is employed.     

Complexation and Self-Assembling of Sulfonatomethylated Calix[4]resorcinarene with Both Organic and Lanthanide Ions in Aqueous Media

The stoichiometry and binding constant of the paramagnetic lanthanide ion(Gd³⁺) with sulfonatomethylated calix[4]resorcinarene (H₈Xna₄) were evaluated from the NMR relaxation data. Both ¹H NMR spectroscopy and NMR relaxation data indicate that interaction of tetramethylammonium (TEMA) and N-methylpyridinium (MePy) cations with H₈Xna₄ in the presence of Ln³⁺ (Lu³⁺ or Gd³⁺) results in theformation of ternary complexes [Ln(G)H₈X] with lanthanide ions,coordinated via sulfonate groups and organic cation included intothe cavity of H₈Xna₄. The inclusion of long-chainedN-decyl-(DePy) and N-cetylpyridinium (CPy) ions into H₈Xna₄ cavity leads to self-assembling which can be revealed by NMR relaxation method with Gd³⁺ probe ions. The excess of alkylpyridinium or TEMA cations leads to disassembling of (Gd)_n(H₈X)_m(RPy)_maggregates.     

Synthesis of Five-Membered Ring Heteroaryl Pyridines from Heteroaryllithium and N-Ethoxycarbonylpyridinium Chlorides

Furylpyridines, thienylpyridines, and imidazolylpyridines were obtained regioselectively in 40-67% yields from the reaction of heteroaryllithiums with N-ethoxycarbonylpyridinium chloride or N-ethoxycarbonyl-3-methylpyridinium chloride in the presence of Cul in a catalytic amount at ?78 °C or ?50°C, then followed by oxidation. The regioselectivity of this reaction depended upon temperature of the reaction and the nature of heteroaryllithiurn.     

Formation and decay of N,N, N′, N′-tetraethyl-p-phenylenediamine radical cation in aqueous solution. A kinetic study by stopped-flow technique

A kinetic study has been carried out on the oxidation of N, N, N′, N′,-tetraethyl-p-phenylenediamine (TEPD) by metal ion like Ce⁴⁺, oxoanions viz., MnO₄^? and Cr₂O₇^2?; peroxides such as peroxomonosulphate (PMS), peroxodisulphate (PDS), and H₂O₂; and halogens namely Cl₂, Br₂, and I₂. The fast kinetics of the formation and decay of the radical cation TEPD^˙+ have been analyzed at 565 nm by the stopped-flow technique under pseudo-first-order conditions. From the kinetic data, it has been inferred that the reactions were found to be of first-order with respect to [TEPD] and [oxidant] but over all it has been of second-order. The observed second-order rate constants in both the formation and decay of TEPD^˙+ has been correlated with the oxidation potentials of the various oxidants employed in this study. The effect of pH on the oxidation has been investigated in the formation and decay of TEPD^˙+ as well as reduction studies have also been carried out using dithionite which has been found to regenerate the TEPD from the TEPD^˙+ and the corresponding rate constant has also been determined. Besides these, this article also explains how the TEPD, which forms TEPD^˙+ acts as a better electron relay than TMPD(N, N, N′, N′-tetramethyl-p-phenylenediamine) which forms TMPD^˙+, even though both of them undergo one-electron oxidation and are used in the chemical routes to solar energy conversions. The observed rate constants for electron transfer were correlated theoretically using Marcus theory. The observed and calculated rate constants have good correlation. © 1995 John Wiley & Sons, Inc.     

Bridgehead nitrogen heterocycles. VI. The reaction of 1-amino- and 1,2-diaminopyridinium salts with β-dicarbonyl compounds

1,2-Diaminopyridinium iodide underwent reaction with ethyl acetoacetate to form 1,4-dihydro-2-methyl-4-oxopyrido[1,2-a]pyrimidin-1-ium iodide, and with acetyl acetone it gave 2,4-dimethylpyrido[1,2-a]pyrimidin-5-ium iodide. Though 2-acetylcyclohexanone gave the corresponding 5-methyl-1,2,3,4-tetrahydropyrido[1,2-a]quinazolin-11-ium iodide, no reaction was observed with 2,6-dimethyl-3,5-heptanedione, 1-benzoylacetone, 1,3-diphenyl-1,3-propanedione and its p-methoxyphenyl derivative. However, 1-aminopyridinium iodide and acetyl acetone in the presence of base gave 3-acetyl-2-methylpyrazolo[1,5-a]pyridine and 1-amino-2-methylpyridinium iodide yielded the corresponding 3-acetyl-2,7-dimethylpyrazolo[1,5-a]pyridine. With ethyl acetoacetate, the latter salt formed 3-ethoxycarbonyl-2,7-dimethylpyrazolo[1,5-a]pyridine but with 2,6-dimethyl substituents in the pyridine ring no condensation occurred. Reaction of 1-amino-2-methylpyridinium iodide with benzaldehyde gave N-benzalimino-2-methylpyridinium iodide which, on treatment with base, resulted in the formation of 2-picoline and benzonitrile, providing a convenient method of deamination.