A study of the OH- -induced beta-elimination reactions of 2-(4-chloroethyl)pyridine, 2-(2-chloroethyl)pyridine, 1-methyl-2-(4-chloroethyl)pyridinium iodide and 1-methyl-2-(2-chloroethyl)pyridinium iodide in acetonitrile/water

Second-order rate constants have been determined for the title reactions in OH(-)/H(2)O and in OH(-)/ (CH(3)CN/H(2)O) [30/70, 60/40, and 85/15 (v/v) mixtures]. A relatively small increase in reactivity is observed for the four substrates upon increasing the percentage of CH(3)CN in the solvent mixture. The methyl activating factors (/) are also slightly affected by the solvent composition. On the other hand, the high acceleration of the reaction by methylation of the pyridine ring amounts to 10(4)-10(6) according to an E1cb mechanism.     

Synthesis of substituted 2-ethyl-3-(4-hydrazinocarbonylphenyl)-4-quinazo-lones and 2-ethyl-3-(4-hydrazinocarbonylmethylphenyl)-4-quinazolones

Some substituted 2-ethyl-3-(4-hydrazinocarbonylphenyl)-4-quinazolones and 2-ethyl-3-(4-hydrazinocarbonylmethylphenyl)-4-quinazolones were synthesized and characterized by their sharp melting points, elemental analyses and spectral data.     

Laser photolysis of 1-(4-nitrophenyl)-3-methylpyrazole and 1-ethyl-3-(4-nitrophenyl)-5-chloropyrazole

The spectral kinetic characteristics of the triplet states of 1-(4-nitrophenyl)-3-methylpyrazole (1) and 1-ethyl-3-(4-nitrophenyl)-5-chloropyrazole (2) were studied by the laser nanosecond photolysis technique in different solvents. The triplet lifetimes (τ_T) of molecules 1 and 2 were found to depend strongly on the solvent nature. An increase in τ_T by approximately two orders of magnitude on going from nonpolar and polar aprotic solvents (τ_T ≤ 15 ns) to aqueous-acetonitrile solutions (τ_T = 1100 ns for a volume acetonitrile to water ratio of 1 : 3) was analyzed, taking into account the influence of the medium on the relative contribution of the n,π*- and π,π*-configurations to the lowest triplet state. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1115–1119, May, 2005.     

Photoinduced intramolecular charge transfer in 4-(dimethyl)aminobenzonitrile--a theoretical perspective

Recent advances in time-dependent density functional theory (TDDFT) have led to computational methods that can predict properties of photoexcited molecules with satisfactory accuracy at comparably moderate cost. We apply these methods to study the photophysics and photochemistry of 4-(dimethyl)aminobenzonitrile (DMABN). DMABN is considered the paradigm of photoinduced intramolecular charge transfer (ICT), leading to dual fluorescence in polar solvents. By comparison of calculated emission energies, dipole moments, and vibrational frequencies with recent results from transient spectroscopy measurements, a definitive assignment of the electronic and geometric structure of the two lowest singlet excited states of DMABN is possible for the first time. We investigate the mechanism of the ICT reaction by means of minimum energy path calculations. The results confirm existing state-crossing models of dual fluorescence. Our study suggests that analytical TDDFT derivative methods will be useful to predict and classify emissive properties of other donor-acceptor systems as well.     

1-Methyl-2-((1E,3E)-4-phenylbuta-1,3-dienyl)pyridinium iodide: Synthesis,characterization, and X-ray analysis

1-Methyl-2-((1E,3E)-4-phenylbuta-1,3-dienyl)pyridinium iodide (1) is synthesized and characterized by UV-Vis, FT-IR, ¹H and ¹³C NMR, and single crystal X-ray diffraction. Compound 1 crystallizes in an orthorhombic Iba2 space group with the unit cell parameters a = 12.8236(11) Å, b = 20.1216(17) Å, c = 11.2071(10) Å, V = 2891.8(4) ų and Z = 8. X-ray diffraction indicates that the molecule of 1 displays E,E configurations with respect to the two middle C=C double bonds. The molecular structure of 1 is twisted and the dihedral angle between the pyridinium and phenyl rings is 15.0(2)°. In the crystal packing, cations form stacks in an anti-parallel V-shaped manner along the a axis through π-π interactions between pyridinium and phenyl rings.     

A Novel Molecule: 1-(2,6 Dichlorobenzyl)-4-(2-(2-4-hydroxybenzylidene)hydrazinyl)pyridinium Chloride and its Interaction with DNA

Herein, a novel pyridine derivative, 1-(2,6 dichlorobenzyl)-4-(2-(2-4-hydroxybenzylidene)hydrazinyl)-pyridinium chloride (DHPC), was synthesized as a candidate drug molecule. Interaction of DHPC with DNA was used to explore its effect on DNA via Differential Pulse Voltammetry, Cyclic Voltammetry, and Electrochemical Impedance Spectroscopy. We demonstrated that oxidation signal of guanine bases of DNA decreased significantly while that of DHPC increased after its interaction with one another. Our candidate drug molecule exhibits LOD and LOQ, e.g., 1.5 μg/mL and 4.9 μg/mL, respectively. Toxicity effect value for DHPC (S%) was calculated as %31, demonstrating the candidate drug molecule's toxic effect on DNA.     

2-(3-ethyl-2,2-dimethylcyclobutyl-methyl)-4(3H)-quinazolinones

Anthranilic acid and its 5-bromo and 4-chloro derivatives react with pinanoic and pinonoic acid chlorides to give the corresponding N-acyl derivatives. The pinanoyl derivatives give the corresponding 2-(3-ethyl-2,2-dimethyl-cyclobutylmethyl)-4-(3H)-quinazolinones when refluxed in formamide. Pinanoylanthranilic acid reacts with dicyclohexylcarbodiimide to give 2-(3-ethyl-2,2-dimethylcyclobutylmethyl)benz-3,1-oxazin-4(H)-one and subsequently with hydrazine hydrate to give 3-amino-2-(3-ethyl-2,2-dimethylcyclobutylmethyl)-4(3H)-quinazolinone. Refluxing of the pinanoyl- and pinonoylanthranilic acids with acetic anhydride gives acetylanthranilic acid, and pinonoylanthranilic acid gives 4(3H)-quinazolinone with formamide.Riga Technical University, Riga LV-1658, Latvia; e-mail: marina@osi.lanet.lv. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 811–817, June, 1999.     

Dynamics of ultrafast intramolecular charge transfer with 4-(dimethylamino)benzonitrile in acetonitrile

The kinetics of the intramolecular charge-transfer (ICT) reaction of 4-(dimethylamino)benzonitrile (DMABN) in the polar solvent acetonitrile (MeCN) is investigated by fluorescence quantum yield and picosecond time-correlated single photon counting (SPC) experiments over the temperature range from -45 to +75 degrees C, together with femtosecond Sn <-- S1 transient absorption measurements at room temperature. For DMABN in MeCN, the fluorescence from the locally excited (LE) state is strongly quenched, with an unquenched to quenched fluorescence quantum yield ratio of 290 at 25 degrees C. Under these conditions, even very small amounts of the photoproduct 4-(methylamino)benzonitrile (MABN) severely interfere, as the LE fluorescence of MABN is in the same spectral range as that of DMABN. The influence of photoproduct formation could be overcome by a simultaneous analysis of the picosecond and photostationary measurements, resulting in data for the activation barriers Ea (5 kJ/mol) and Ed (32 kJ/mol) of the forward and backward ICT reaction as well as the ICT reaction enthalpy and entropy: DeltaH (-27 kJ/mol) and DeltaS [-38 J/(mol K)]. The reaction hence takes place over a barrier, with double-exponential fluorescence decays, as to be expected in a two-state reaction. From femtosecond transient absorption down to 200 fs, the LE and ICT excited state absorption (ESA) spectra of DMABN in n-hexane (LE) and in MeCN (LE and ICT) and also of 4-aminobenzonitrile in MeCN (LE) are obtained. For DMABN in MeCN, the quenching of the LE and the rise of the ICT ESA bands occurs with a single characteristic time of 4.1 ps, the same as the ICT reaction time found from the picosecond SPC experiments at 25 degrees C. The sharp ICT peak at 320 nm does not change its spectral position after a pump-probe delay time of 200 fs, which suggests that large amplitude motions do not take place after this time. The increase with time in signal intensity observed for the LE spectrum of DMABN in n-hexane between 730 and 770 nm, is attributed to solvent cooling of the excess excitation energy and not to an inverse ICT --> LE reaction, as reported in the literature.     

Spectroscopic characterization of intramolecular charge transfer of sodium 4-(N,N-dimethylamino)naphthalene-1-sulfonate

In this paper, a new dual fluorescent N,N-dimethylaminonaphthalene derivative, sodium 4-(N,N-dimethylamino)naphthalene-1-sulfonate (SDMDNS), was reported. It was found that SDMDNS emits dual fluorescence only in highly polar solvent water but not in organic solvents such as methanol, dioxane and acetonitrile. Only a single broad band emission at ca. 420 nm was observed in the short wavelength region in organic solvents. The dual fluorescence of SDMDNS in water was found at 423 and 520 nm, respectively. Introduction of organic solvent as ethanol into aqueous solution of SDMDNS leads to blue shift of the long-wavelength emission, and this was evidently supported by introduction of cyclodextrin or surfactant in the aqueous solution. It indicates that a highly polar solvent was required to bring out dual fluorescence; furthermore, the short wavelength fluorescence is emitted from locally excited (LE) state and the long wavelength fluorescence is emitted from charge transfer (CT) state. The pH dependence of the dual fluorescence of SDMDNS demonstrates that the neutral form of the molecular has a higher ratio of CT band intensity to LE band. Temperature effect on the excited state of SDMDNS was also examined and gave stabilization enthalpy (-DeltaH ) of the CT reaction 8.7 kJ mol(-1).     

Photoinduced intramolecular charge transfer of sodium 4-(N,N-dimethylamino) benzenesulfonate

A new dual fluorescent N,N-dimethylaniline derivative, sodium 4-(N,N-dimethylamino)-benzenesulfonate (SDMAS), is reported. In SDMAS, the electron acceptor is linked to the phenyl ring via a sulfur atom at the para-position of the electron donor. It was found that SDMAS emits dual fluorescence only in highly polar solvent water but not in organic solvents such as formamide, methanol and acetonitrile. In organic solvents only a single-band emission at ca.360 nm was observed in the short wavelength region. The dual fluorescence of SDMAS in water was found at 365 and 475 nm, respectively. Introduction of organic solvent such as ethanol, acetonitrile, and 1,4-dioxane into aqueous solution of SDMAS leads to blue-shift and quenching of the long-wavelength emission. Measurements of steady-state and picosecond time-resolved fluorescence indicate that the long wavelength fluorescence is emitted from a charge transfer (CT) state that is populated from the locally excited (LE) state, with the latter giving off the