Studies on Intramolecular Charge Transfer Fluorescence Probe and DNA Binding Characteristics

An intramolecular charge transfer fluorescence probe of 4′-N,N-dimethylamino-4-amino-chalcone(DMAC) exhibits characteristics clearly correlated with the polarity of solvents. The interaction of this fluorescence probe with calf thymus DNA has been investigated. Generally, DMAC bound to DNA shows marked changes in fluorescence and absorbance properties compared to the spectral characteristics of the free form in solution phase. In the presence of DNA the fluorescence intensity of DMAC is greatly increased with a large bathochromic shift of excitation and emission wavelengths. A hypochromism in absorption spectrum was also observed. The absorption and fluorescence spectra, salt concentration effect, and KI quenching experiments demonstrate that DMAC molecule as an intercalator is inserted into the base-stacking domain of DNA double helix, and the interaction of the nucleobases with DMAC molecule causes the increase of fluorescence intensity and hypochromism in absorption spectrum. The intrinsic binding constant and the binding site number were estimated to be 7.04 × 10⁶ mol L⁻¹ in base pairs and 0.065, respectively. The I/I₀ vs DNA concentration plot shows a linear range covering 1.98 × 10⁻⁶ to 2.08 × 10⁻⁴ mol L⁻¹ in base pairs which can be used for determining DNA with a detection limit of 6.0 × 10⁻⁷ mol L⁻¹ in base pairs (0.6 μg ml⁻¹).     

Evidence for Two‐Photon Absorption‐Induced ESIPT of Chromophores Containing Hydroxyl and Imino Groups

This paper presents experimental and theoretical investigations into excited‐state intramolecular proton transfer (ESIPT) in new chromophores with hydroxyl and imino groups under one‐ and two‐photon excitation. The results show that internal hydrogen bonding exhibits a remarkable influence on the maximum absorption wavelength of 2‐[(4′‐N,N‐diethylaminodiphenylethylene‐4‐ylimino)methyl]phenol ( C1 ) and 2‐[(4′‐methoxyl‐diphenylethylene‐4‐ylimino)methyl]phenol ( C3 ). Compounds C1 and C3 exhibit well‐separated dual fluorescence emission bands under one‐ and two‐photon excitation. The second fluorescence peaks of C1 and C3 are characterized by much larger Stokes shift than the first normal peaks (ca. 140 vs. 30 nm). 4‐[(4′‐N,N‐Diethylaminodiphenylethylene‐4‐ylimino)methyl]phenol ( C2 ) and 4‐[(4′‐methoxyldiphenylethylene‐4‐ylimino)methyl]phenol ( C4 ) display single emission bands with small Stokes shifts (ca. 30 nm) in various solvents under one‐ and two‐photon excitation. Furthermore, the first emission maxima of C1 and C3 are almost identical to the maximum fluorescence emission wavelengths of C2 and C4 , respectively. These results show that C1 and C3 can undergo ESIPT via a reasonable six‐membered ring, while there is no ESIPT in C2 and C4 under one‐ and two‐photon excitation. Compounds C1 and C2 have larger two‐photon absorption cross‐sections under various near‐infrared laser frequencies tuned from 700 to 880 nm. Molecular geometry optimization of the phototautomers (enol and keto) was performed to analyze the experimental results. The possibility of using these chromophores for metal ions as chemosensors of was thoroughly investigated. In DMF C3 exhibits excellent sensing responses to Zn²⁺ and Fe³⁺ ions through a greatly increased greatly and a largely reduced emission, respectively. In methanol disappearance of ESIPT emission with added Zn²⁺ ions confirms its existence. The binding constants of C3 with Zn²⁺ and Fe³⁺ ions in DMF are also estimated.     

4-Cyano-2-oxo-1,2,4-oxadiazolo[2,3-a]quinoxaline 5-N-oxides. New synthetic method and reaction with alcohols. Potential cytotoxic activity

Several quinoxaline 1,4-di-N-oxides have been shown to be efficient and selective cytotoxins for hypoxic cells. We present now a series of 4-cyano-2-oxo-1,2,4-oxadiazolo[2,3-a]quinoxaline 5-N-oxides 2a-2k . They were prepared starting from 3-amino-2-quinoxalinecarbonitrile 1,4-di-N-oxides 1a-1k and 2-chloroethyl isocyanate in dry dioxane at 100–110°. A reaction mechanism is proposed. The treatment of 1a with phenyl isocyanate afforded 2a . Reaction of 2c with silica gel yielded 1c . Compounds 2a-2g were heated in the presence of ethanol and 2-propanol giving the corresponding carbamates 3a-3g and 4a-4g . Compound 2d was already obtained by heating a mixture of 1d and ethyl chloroformiate. Compound 2b was prepared when the carbamate 3b was heated at 150°. Quinoxalines were tested as cytotoxic agents both in oxic and hypoxic cells. The most interesting compounds were 3g and 4g .     

LUMINESCENCE STUDIES ON FORMYCIN, ITS AGLYCONE, AND THEIR N-METHYL DERIVATIVES: TAUTOMERISM, SITES OF PROTONATION AND PHOTOTAUTOMERISM

Abstract— A detailed study has been made of the luminescence spectra of 3-β-d -ribofuranosyl-7-amino-pyrazolo(4,3-d)pyrimidine (formycin A), 3-propyl-7-aminopyrazolo(4,3-d)pyrimidine (7APP), and their various N-methyl derivatives, at room temperature and in methanol-water glasses at 77 K. Comparisons of the foregoing, together with the observed dependence of the emission spectra of formycin and 7APP on excitation wavelength, demonstrated that these consist of two tautomeric species, N(1)H and N(2)H, both of which emit at 300 and 77 K. The two tautomers may be distinguished by the location of the emission maxima, especially for phosphorescence, and quantum yields for emission. Comparisons of the emission spectra of the protonated forms of 7APP and its N-methyl derivatives showed that the fluorescence of the cations of 7APP and its N,- and N₂-methyl derivatives originates from the forms protonated on N(4). By contrast, the forms protonated on N(6) contribute appreciably to the phosphorescence at 77 K. On the basis of the emission spectra at 77 K, it is concluded that the major tautomeric form of the formycin cation is N(1)H,N(4)H₊, but there is also some contribution by the form N(2)H,N(4)H₊. In acid medium at room temperature, there is photodissociation of a proton from the pyrazole ring of the formycin cation. This leads to formation in the state S! of the tautomeric species N(4)H, which does not exist in the ground state. This conclusion, similar to that previously reported for the analogous isomeric 4-aminopyrazolo(3,4-d)pyrimidines, is derived from a comparison of the fluorescence spectra of the cations of formycin and N₄-methylformycin, which exhibit two bands at 375 and 440 nm, the latter corresponding to the emission of the neutral form of N,i-methylformycin. The proposed mechanism of phototautomerization is supported by a study of solvent and salt effects.     

Synthesis of N-Substituted Azetidin-3-ones

Addition of RC(0)Cl (R = OEt, Me, or Ph) across the highly strained N-C(3) o-bond in 3-bromomethyl-l-azabicyclo[1.1.0]butane (1) afforded the corresponding N-acyl-3-bromomethyl-3-chloroazetidines (2a-2c, respectively). Subsequent zinc promoted eliminative dehalogenation of 2a-2c produced the corresponding N-acyl-3-methyleneazetidines (3a-3c, respectively). Finally, ozonolysis of 3a-3c afforded the corresopnding N-acylazetidin-3-ones (4a-4c, respectively).     

Cyclodehydration of N-(2-nitroaryl)-1,2,3,4-tetrahydroisoquinoline derivatives

Compounds 1a-1g gave the corresponding N-oxide derivatives 3a-3g when heated with acetic or propionic acid.     

Ring-opening reactions of halogenated N-aryl-1,2,3,4-tetrahydroisoquinoline and 2,3,4,5-tetrahydro-1H-2-benzazepine derivatives

Compounds 4a-4d, 4f and 10 were prepared and their ring-opening reactions with N-bromosuccinimide (NBS) investigated. Compounds 4a and 4b gave a mixture of products which did not contain any significant quantity of the corresponding aldehydes 5a and 5b whereas compounds 4c, 4d and 4f gave exclusively the aldehydes 5c, 5d and 5f respectively. Compound 10 similarly gave the aldehyde 11 when treated with NBS.     

Synthesis,Crystal Structure,and Photophysical Properties of (1E,3E,5E)‐1,3,4,6‐Tetraarylhexa‐1,3,5‐trienes: A New Class of Fluorophores Exhibiting Aggregation‐Induced Emission

Double Horner–Wadsworth–Emmons reaction of (E)‐2,3‐diaryl‐1,4‐bis(diethylphosphonyl)but‐2‐ene with (p‐substituted) benzaldehydes gave (1E,3E,5E)‐1,3,4,6‐tetraarylhexa‐1,3,5‐trienes in moderate to good yields. Substitution of electron‐withdrawing or ‐donating groups at the para position of the 1,6‐diphenyl groups induced a slight bathochromic shift of UV spectra measured in CHCl₃ compared with that of the parent 1,3,4,6‐tetraphenylhexa‐1,3,5‐triene. Although fluorescence was not observed with all the trienes in CHCl₃, they markedly emitted visible light in powder forms with quantum yields of 0.15–0.44. Introduction of amino groups at the para position of the 3,4‐diphenyl groups induced a bathochromic shift of emission maxima with good solid‐state quantum yields. Thus, the tetraarylated triene framework is found to serve as a new class of fluorophores that exhibit aggregation‐induced emission.     

Photochromism of an <Emphasis Type="Italic">N</Emphasis>-aminofulgimide-derived Schiff base

A Schiff base was synthesized from 5-methoxysalicylaldehyde and N-aminofulgimide, viz., 1-amino-3-[1-(2,5-dimethylthiophen-3-yl)ethylidene]-4-isopropylidenepyrrolidine-2,5-dione. The compound synthesized undergoes photochromic transformations typical of those of N-aminofulgimide studied earlier. A bathochromic shift of the absorption bands of the open and cyclic forms of the obtained Schiff base compared to the starting N-aminofulgimide was observed.     

The synthesis and fluorescence of novel N‐substituted‐1,8‐naphthylimides

The synthesis and characterisation of a series of novel 4‐acylamino and 4‐alkylamino‐N‐1,8‐naphthalimides is described. The UV‐visible absorption and emission properties of the compounds are reported. Significant solvent effects are noted for 4‐n‐butyl‐9‐n‐butyl‐1,8‐naphthylimide. The incorporation of acetyl and chloroacetyl groups into the 4‐substituent markedly increases the fluorescence quantum yield compared with 4‐alkylamino substituemnts.     

含萘并呋喃基团冠醚的合成及离子选择性研究

以2-羟基-1-萘甲醛和2-羟甲基冠醚为原料,合成3种新的含萘并呋喃基团冠醚(3a-3c),并经1 H NMR,13C NMR,MS及元素分析确证.碱金属和碱土金属离子的加入对体系的最大吸收波长影响不大.Li+使3b摩尔吸光度变大,Ca2+和Ba2+引起3a-3c最大发射波长λem发生相对较大红移,同时使其荧光强度降低.     

New hypoxia-selective cytotoxines derived from quinoxaline 1,4-dioxides

A new series of quinoxaline 1,4-dioxides, structurally related to the benzotriazine tirapazamine 1 have been prepared starting from 5,6-dichlorobenzofuroxane 2 . The Beirut reaction between 2 and alkyl or aryl thiopropanones afforded the 2-methyl-3-alkyl(aryl)thioquinoxaline 1,4-dioxides 3a-3e . Selective oxidation of 3 with m-chloroperbenzoic acid yielded the sulphinyl 4a-4c and sulphonyl 5a-5b derivatives. Replacement of the sulphonyl group of 5a by chlorine or bromine gave 6 or 7 , while nucleophilic displacement by 3-(N,N-dimethylamino)propylamine afforded 8 . A dimer 9 was prepared from 5a and hydrazine hydrate. The methylthio group of 3a was replaced by using formamidine acetate giving the amino compound 10 . Bromination of the methyl group of 3b afforded 11 , which reacted with 2-aminoethanol giving 12 . Compounds were tested as cytotoxic agents both in oxic and in hypoxic cells.     

Excited State Intramolecular Proton Transfer of New Diphenylethylene Derivatives Bearing Imino Group: A Combination of Experimental and Theoretical Investigation

In this paper, we described the synthesis and characterization of new diphenylethylene bearing imino group. We concentrated particularly on the investigation of the possibility of the excited state intramolecular charge transfer (ESIPT) of the new dyes experimentally and theoretically. The absorption and fluorescence spectroscopy of the dyes were determined in various solvents. The results showed that the maximal absorption wavelength of 2‐[(4′‐N,N‐dimethylamino‐diphenylethylene‐4‐ylimino)methyl]phenol ( C1 ) and 4‐[(4′‐N,N‐dimethylamino‐diphenylethylene‐4‐ylimino)methyl]phenol ( C2 ) exhibited almost independence on the solvent polarity. While as contrast, the maximal fluorescence wavelength of the dyes showed somewhat dependence on the solvent polarity. In particular, C1 displayed well‐separated dual fluorescence spectroscopy. The second fluorescence peak was characterized with an "abnormal" fluorescence emission wavelength in aprotic solvents with large Stokes shift (ca. 140 nm in THF), which was much more than normal Stokes shift (ca. 30 nm in THF). This emission spectroscopy could be assigned to ESIPT emission. On the other hand, the ESIPT fluorescence of C1 was much reduced or lost in the protic solvents. While, only normal fluorescence emission was detected in various solvents. Although the absorption maxima of C1 exhibited about 10 nm red‐shift with respect to those of C2 , the normal fluorescence maxima of C1 and C2 were almost identical in various solvents. These results suggested that C1 could undergo ESIPT, but C2 was not able to proceed ESIPT. The molecular geometry optimization of phototautomers in the ground electronic state (S₀) was carried out with HF method (Hartree‐Fock) and at DFT level (Density Functional Theory) using B3LYP both, while the CIS was employed to optimize the geometries of the first singlet excited state (S₁) of the phototautomers of C1 and C2 respectively. The properties of the ground state and the excited state of the phototautomers of C1 and C2 , including the geometrical parameter, the energy, the frontier orbits, the Mulliken charge and the dipole moment change were performed and compared completely. The data were analyzed further based on our experimental results. Furthermore, the absorption and fluorescence spectra were calculated in theory and compared with the measured ones. The rate constant of internal proton transfer (9.831×10¹¹ s^?1) of C1 was much lower than that of salicylidene methylamine ( C3 , 2.045×10¹⁵ s^?1), which was a typical Schiff base compound and was well demonstrated to undergo ESIPT easily under photoexcitation.     

Reaction of 6‐aryl‐ or styryl‐4‐methylsulfanyl‐2‐oxo‐2H‐pyrans with active methylene compounds and fluorescence properties of the products

New 2‐pyrone derivatives, dialkyl 3‐cyano‐6‐phenyl‐2‐oxo‐2H‐pyran‐4‐ylmalonates and alkyl 3‐cyano‐6‐phenyl‐2‐oxo‐2H‐pyran‐4‐ylacetates, which were easily prepared by the reaction of 6‐aryl‐4‐methyl‐sulfanyl‐2‐oxo‐2H‐pyran‐3‐carbonitriles with active methylene compounds in the presence of potassium carbonate, show fluorescence emission radiation. The light‐emitting region of dimethyl 3‐cyano‐6‐(4‐N,N‐dimethylamino)styryl‐2‐oxo‐2H‐pyran‐4‐ylmalonate ( 7h ) was 620 nm in dichloromethane, making this compound a typical red fluorescent compound. Methyl 8‐hydroxy‐6‐methyl‐1‐oxo‐3‐phenyl‐1H‐pyrano‐[3,4‐c]pyridine‐5‐carboxylate deriv‐atives also showed fluorescence in the solid state. This is the first example of fluorescence in fused 2‐pyrone derivatives.     

Synthesis of piperidine analogs of 1-(3-chlorophenyl)piperazine,a well known serotonin ligand

Synthesis of arylpiperideines 3a-3d and arylpiperidines 4a-4d as analogs of a well known serotonin ligand 1-(3-chlorophenyl)piperazine is reported. Starting aryllithium derivatives were treated with 1-methyl-piperdin-4-one to provide the corresponding hydroxy derivatives 6a and 6b. N-Methylpiperideine derivatives 3a and 3c were obtained by their dehydration while the corresponding N-unsubstituted compounds 3b and 3d were prepared indirectly by a three-step procedure. Hydrogenation of piperideine 3a provided the corresponding piperidine derivative 4a which after demethylation yielded 4b. Similar 4-pyridyl derivatives 4c and 4d were prepared by a similar strategy via the corresponding methoxy derivatives.     

UV/Vis Spectroscopic Properties of N -(2′-Hydroxy-4′- N , N -dimethyl-aminobenzylidene)-4-nitroaniline in Various Solvents and Solid Environments

 N-(2′-Hydroxy-4′-N,N-dimethylaminobenzylidene)-4-nitroaniline [HDBN] has been used as a model for investigating intra- and intermolecular D–A (donor–acceptor) interactions in various environments by means of UV/Vis spectroscopy. UV/Vis spectra of HDBN have been measured in various solvents, ethanolic solutions of different pH, adsorbed on silica, and in the solid state. A bathochromic shift of ν_max is observed with increasing the dipolarity/polarizability and HBD (hydrogen bond donor) capacity of the solvent, which is described by means of a multiple LSE (linear solvation energy) relationship in terms of the empirical Kamlet-Taft solvent polarity parameters. The adsorption of HDBN on Aerosil^? 300-silica particles in non-HBA (hydrogen bond acceptor) solvents is explained in the same sense. Mobile protons and sol–gel entrapping cause a hypsochromic shift due to protonation of the lone electron pair of the 4′-N,N-dimethylamino group. Hydroxide ions attack the 2′-hydroxy group which causes a bathochromic shift. A strong intramolecular hydrogen bond between the 2′-hydroxyl hydrogen and the imine nitrogen atom is present in the solid-state structure causing an unprecedented bathochromic shift.     

UV/Vis Spectroscopic Properties of <Emphasis Type="Italic">N</Emphasis>-(2′-Hydroxy-4′-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethyl-aminobenzylidene)-4-nitroaniline in Various Solvents and Solid Environments

Summary.  N-(2′-Hydroxy-4′-N,N-dimethylaminobenzylidene)-4-nitroaniline [HDBN] has been used as a model for investigating intra- and intermolecular D–A (donor–acceptor) interactions in various environments by means of UV/Vis spectroscopy. UV/Vis spectra of HDBN have been measured in various solvents, ethanolic solutions of different pH, adsorbed on silica, and in the solid state. A bathochromic shift of ν_max is observed with increasing the dipolarity/polarizability and HBD (hydrogen bond donor) capacity of the solvent, which is described by means of a multiple LSE (linear solvation energy) relationship in terms of the empirical Kamlet-Taft solvent polarity parameters. The adsorption of HDBN on Aerosil^? 300-silica particles in non-HBA (hydrogen bond acceptor) solvents is explained in the same sense. Mobile protons and sol–gel entrapping cause a hypsochromic shift due to protonation of the lone electron pair of the 4′-N,N-dimethylamino group. Hydroxide ions attack the 2′-hydroxy group which causes a bathochromic shift. A strong intramolecular hydrogen bond between the 2′-hydroxyl hydrogen and the imine nitrogen atom is present in the solid-state structure causing an unprecedented bathochromic shift. Corresponding author. E-mail: stefan.spange@chemie.tu-chemnitz.de Received July 8, 2002; accepted (revised) September 30, 2002     

An imidazole functionalized copper(II)-organic framework for highly selective sensing of picric acid and metal ions in water

An imidazole functionalized metal–organic framework (MOF), [Cu(HL)(H₂O)]·(H₂O)·(DMA) ( HBU-166 , H₃L = 4,4′,4″-(1H-imidazole-2,4,5-triyl)tribenzoic acid, DMA = N,N-dimethylacetamide) was synthesized and characterized by single-crystal X-ray diffraction. HBU-166 was observed as a two-dimensional MOF and showed good stability in water, an acidic solution (pH = 4), and an alkaline solution (pH = 9). HBU-166 exhibited ligand-based luminescence with a blue shift, which could be attributed to the coordination effect. Moreover, HBU-166 could be applied to detect nitroaromatic compounds (NACs) and metal ions in water with preferable selectivity and sensitivity. In particular, HBU-166 could be used as a promising luminescent sensor for picric acid (PA) with enhancement of emission intensity. The mechanism for PA detection likely involved electron transfer and weak interaction between ligand and electron-deficient of NACs at the beginning to increase the emission intensity. Additionally, HBU-166 exhibited excellent selectivity in the sensing of 4-nitrophenol and Fe³⁺ through fluorescence quenching.     

Synthesis of Azo-Sulfa Drugs Based on 2-Pyridinone and 2-Pyridinethione

Some new azo sulfa drugs 3-cyano-4,6-diphenyl-1-[4-(N-substituted)sulfamyl]phenylazo-2-pyridinone dyes (1-6) and 3-cyano-4,6-diphenyl-1-[4-(N-substituted)sulfamyl]phenylazo-2-pyridinethione dyes (1′-6′) were synthesized by coupling of 4-(N-substituted)sulfamylbenzene diazonium salts with 3-cyano-4,6-diphenyl-2-pyridinone and/or with 3-cyano-4,6-diphenyl-2-pyridin-ethione. The corresponding iron (1a-6a, 1′a-6′a), copper (1b-6b, 1′b-6′b) and mercury (1c-6c, 1′c-6′c) chelates wvere also prepared. All synthesized compounds were screened in vitro for antibacterial and antifungal activities.     

Cadmium‐1,3,6,8‐tetrakis(4‐carboxylphenyl)pyrene Framework as a Thermometer for Fluorescence Sensing of Temperature

Compounds exhibiting tunable fluorescence emission upon adjusting the temperature are considered smart materials. Herein a three‐dimensional structure of {[Cd(TBAPy)(H₂O)₂] · 4(H₂O)}_n ( 1 ) constructed from Cd^II and 1,3,6,8‐tetrakis(4‐carboxylphenyl)pyrene (TBAPy^4–) ligand was synthesized and characterized. Temperature‐dependent fluorescence studies showed the emission intensities for compound 1 decrease as temperature increasing. The emission intensity is linearly related to temperature in the range of 100 to 300 K. This findings demonstrate that compound 1 is a good candidate for temperature sensitive sensor over a wide temperature range. Such a fluorescence behavior is closely related to the highly conjugated organic ligand with a pyrene core.