香豆素衍生物的TICT态和荧光介质效应

研究了八种７－氨基香豆素衍生物在纯溶剂和二元溶剂体系中的荧光特性。这些衍生物因氨基上Ｈ的取代程度的不同，在溶液中可以形成两种不同的氢键。一种是由溶剂分子提供Ｈ，在香豆素环的２位氧原子上形成的氢键；另一种是由溶质分子提供Ｈ，在香豆素衍生物的７－氨基酸上形成的氢键。     

Spectral properties of substituted coumarins in solution and polymer matrices

The absorption and fluorescence spectra of substituted coumarins (2-oxo-2H-chromenes) were investigated in solvents and in polymer matrices. The substitutions involved were: (1) by groups with varying electron donating ability such as CH?, OCH? and N(CH?)?, mainly, but not exclusively, in positions 7 and (2), by either CHO or 4-PhNHCONHN=CH- in position 3. While the spectra of non-substituted coumarin-3-carbaldehyde has absorptions at approximately 305 and 350 nm, substitution at position 7 leads to remarkable changes in the shape of the absorption spectrum and shifts the absorption to a longer wavelength. Similarly, the replacement of the formyl group with a semicarbazide group substantially influences the shape of the absorption spectrum, and coumarins which have only N(CH?)? in position 7 experience small changes. These changes are associated with the increasing intramolecular charge transfer (ICT) character and increasing conjugation length of the chromophoric system, respectively, in the studied molecules. The fluorescence is almost negligible for derivatives which have H in this position. With increasing electron donating ability, and the possibility of a positive mesomeric (+M) effect of the substituent in position 7 of the coumarin moiety, the fluorescence increases, and this increase is most intense when N(CH?)? substitutes in this position, for both 3-substituted derivatives. Spectral measurements of the studied coumarins in polymer matrices revealed that the absorption and fluorescence maxima lay within the maxima for solvents, and that coumarins yield more intense fluorescence in polymer matrices than when they are in solution. The quantum yield of derivatives which have a dimethylamino group in position 7 in polymer matrices approaches 1, and the fluorescence lifetime is within the range of 0.5-4 ns. The high quantum yield of 7-dimethylamino derivatives qualifies them as laser dyes which have k(F) higher than k(nr) in the given medium. This is caused by stiffening of the coumarin structure in polar polymer matrices, such as PMMA and PVC, due to higher micro-viscosity than in solution and intermolecular dipole-dipole interaction between chromophore (dopant) and matrix.     

Fluorescence properties of recombinant tropomyosin containing tryptophan, 5-hydroxytryptophan and 7-azatryptophan

Tropomyosin mutants containing either tryptophan (122W), 5-hydroxytryptophan (5OH122W) or 7-azatryptophan (7N122W) have been expressed in Escherichia coli and their fluorescence properties studied. The fluorescent amino acids were located at position 122 of the tropomyosin primary sequence, corresponding to a solvent-exposed position c of the coiled-coil heptapeptide repeat. The emission spectrum of the probe in each mutant is blue-shifted slightly with respect to that of the probe in water. The fluorescence anisotropy decays are single exponential, with a time constant of 2-3 ns while the fluorescence lifetimes of the probes incorporated into the proteins, in water, are nonexponential. Because tryptophan in water has an intrinsic nonexponential fluorescence decay, it is not surprising that the fluorescence decay of 122W is well described by a triple exponential. The fluorescence decays in water of the nonnatural amino acids 5-hydroxytryptophan and 7-azatryptophan (when emission is collected from the entire band) are single exponential. Incorporation into tropomyosin induces triple-exponential fluorescence decay in 5-hydroxytryptophan and double-exponential fluorescence decay in 7-azatryptophan. The range of lifetimes observed for 5-hydroxyindole and 5-hydroxytryptophan at high pH and in the nonaqueous solvents were used as a base with which to interpret the lifetimes observed for the 5OH122W and indicate that the chromophore exists in several solvent environments in both its protonated and unprotonated forms in 5OH122W.     

Design of a coumarin-based triketone as a fluorescent protecting group for primary amines

A series of 3-acetyl-4-hydroxycoumarin and its derivatives were prepared and evaluated for their potential to function as a fluorescent primary amine protection group. When primary amines or amino acids react with the protecting group 3-acetyl-4-methoxy-7- N, N-dimethylaminocoumarin, the resulting compounds emit blue fluorescence with a quantum yield of 0.25-0.50 in methylene chloride. These protected compounds display satisfactory acid/base stability, and the protecting group can be removed with 5% hydrazine hydrate in DMF within 5 min at ambient temperature.     

Researches on allo- and isoalloxazines

The reaction of 7-aminoallo- and isoalloxazines with ethylene oxide is investigated, and its optimum conditions are found. Addition of ethylene oxide to 7-aminoisoalloxazine involves only the cyclic amino group at position 3, while addition to 7-aminoalloxazine involves the cyclic imino group at position 3 and the amino group at position 7.     

ON THE FLUORESCENCE OF KETONES OF THE ANDROSTANE SERIES

Abstract— The fluorescence spectrum and relative intensity of several ketoandrostanes is investigated as a function of the position of the carbonyl group on the steroid skeleton. The fluorescence intensity, though very low, depends rather strongly on the position. No dependence on solvent, excitation wavelength (in the vicinity of the first absorption peak), cooling or presence of oxygen was found. No phosphorescence was observed. The fluorescence decay time of the strongest fluorescing compound was measured to be 4·4 ± 0·2 nsec. For diketoandrostanes deactivation interactions between the carbonyl groups were found, depending on the position of the groups. The results are considered to be closely related to the vibrational pattern of the steroid frame.     

Tuning the photoinduced electron transfer in near-infrared heptamethine cyanine dyes

An efficient photoinduced electron transfer (PET) system in near-infrared region was described. The PET in heptamethine cyanine dyes was tuned by changing the electron-donating ability of the substituent at the central position of the polymehine chain. 4-Aminophenylthio-substitution led to an efficient PET and the lowest fluorescence quantum yield. The acetylation, protonation or transition metal cation coordination of the amino group could recover fluorescence greatly via suppressing the PET.     

Photophysics and Photochemical Studies of the Vitamin B6 Group and Related Derivatives

The photophysics and photochemical properties of vitamin B6 constituents and analogs were studied as function of pH and solvent. The p K of the phenolic oxygen and the pyridine ring nitrogen depends on the electron donor-acceptor ability of the 4-substituent, and agrees with the calculated proton affinity. For all studied compounds, the fluorescence properties showed that the phenolic oxygen is 8 units more acidic in the lowest singlet excited state than in the ground state. The pyridine N-atom is slightly more basic in the excited state. At pH of biological significance, pH 6–8, pyridoxamine and 4-pyridoxic acid are the more efficient chromophores with higher fluorescence yield and longer lifetime. Spectroscopic studies showed that the tautomeric equilibrium depends on the nature of the 4-substituent. The quenching of the singlet excited state of pyridoxamine and 4-pyridoxic acid by amino acids, free or in a peptide, and DNA bases at pH 7 was studied by time-resolved fluorescence techniques. The quenching rate constants are well correlated with the redox properties of the pyridoxinic compound and amino acids, and are related to the free energy change in the electron transfer process. Guanosine and pyrimidine bases also are efficient quenchers, involving an electron transfer reaction.     

Synthesis, dual fluorescence, and fluoroionophoric behavior of dipyridylaminomethylstilbenes

The synthesis, dual fluorescence, and fluoroionophoric behavior of two donor-sigma spacer-acceptor (D-s-A) compounds, trans-4-(N,N-bis(2-pyridyl)amino)methylstilbene (1H) and trans-4-(N,N-bis(2-pyridyl)amino)methyl-4'-cyanostilbene (1CN), are reported and compared to that of trans-4-(N,N-bis(2-pyridyl)amino)methyl-4'-(N,N-dimethylamino)stilbene (1DPA). To gain insights into the dual fluorescence properties for 1H and 1CN in polar but not in nonpolar solvents, model compounds resulting from a replacement of the stilbene group by alkyl (2R) or xylyl (2X) groups or from a replacement of the dipyridylamino (dpa) group by dianisoleamino (3AA), diethylamino (3EE), methylanilino (3MP), or diphenylamino (3PP) groups also have been investigated. In addition to 1H and 1CN, all four compounds of 3 display dual fluorescence. The locally excited (LE) fluorescence mainly results from the stilbene group and the ICT fluorescence from the through-bond interactions between the amino donor and the stilbene acceptors. In the presence of transition metal ions such as Zn(II), Ni(II), Cu(II), and Cd(II), the ICT processes are switched from dpa (D) --> stilbene (A) in 1H and 1CN to stilbene (D) --> dpa/metal ion (A) in their complexes. Whereas the ICT states for the complexes are generally nonfluorescent, an exception was found for the case of 1H/Zn(II). As a result, substituent-dependent fluoroionophoric behavior has been demonstrated by 1H, 1CN, and 1DPA in response to Zn(II).     

Fragmentation sous l'Impact Electronique de Diamino-4,5 Triazoles-1,2,4 et d'Amino-4 Mercapto-5 Triazoles-1,2,4

The mass spectra of several 4-amino 1,2,4-triazoles with an amino, methylamino, mercapto or methylmercapto group in position 5 are reported and analysed. Five different fragmentation pathways of the molecular ion are observed in the heterocylic ring but the amino group in position 4 also involves some other specific cleavages.     

Synthesis of alkylated aminofluorenes by palladium-catalyzed substitution at halofluorenes

New N-substituted 2-amino-9,9-dialkylfluorenes optionally bearing electron-withdrawing substituents such as nitro or cyano in position 7 can be synthesized starting from 2-halo-9,9-dialkylfluorenes by Pd-catalyzed substitution with amines. Chiral amino groups can be introduced by this method too. 2-N,N-Dimethylamino-7-nitro-9H-fluorene was obtained in a convenient way by reductive amination. The N-substituted 2-amino-7-nitro-9H-fluorenes are promising candidates for fluorescence probes for femtosecond solvation dynamics.     

Low-lying excited states of C120 and C151: a multireference perturbation theory study

Excited states of two 7-aminocoumarin derivatives, coumarin 120 (7-amino-4-methylcoumarin) and coumarin 151 (7-amino-4-trifluoromethylcoumarin), were investigated using generalized multiconfigurational quasidegenerate perturbation theory (GMC-QDPT), multiconfigurational quasidegenerate perturbation theory (MC-QDPT) and time-dependent density functional theory (TDDFT) with the B3LYP and CAM-B3LYP functionals. The absorption and fluorescence spectra of C120 and C151 were calculated. We elucidated the characters of the low-lying states of C120 and C151. The absorption spectra calculated with GMC-QDPT and TDDFT B3LYP agreed well with the experimental data, while for the fluorescence spectra, the TDDFT calculations overestimated the fluorescence spectra compared to GMC-QDPT calculations. Utilizing active spaces with large numbers of electrons and orbitals for reference functions, GMC-QDPT showed a better performance than MC-QDPT with a complete active space self-consistent field (CASSCF) reference of active space with smaller number of electrons and orbitals. In our gas phase calculation, we found that the optimized structures for the first excited states have a planar amino group with a CN single bond, while the amino group is pyramidal in the ground state.     

Electronic spectra of adenine and 2-aminopurine: an ab initio study of energy level diagrams of different tautomers in gas phase and aqueous solution

Ground and lowest two singlet excited state geometries of four tautomeric forms (N9H, N7H, N3H and N1H) of each of adenine and 2-aminopurine (2AP) were optimized using an ab initio approach employing a mixed basis set (6-311 + G* on the nitrogen atom of the amino group and 4-31G basis set on the other atoms). Excited states were generated employing configuration interaction involving single electron excitations (CIS). Subsequently, the different species were solvated in water employing the self-consistent reaction field (SCRF) approach along with the corresponding gas phase optimized geometries. Thus the observed absorption and fluorescence spectra of adenine and 2AP have been explained successfully. It is concluded that both the N9H and N7H forms of 2AP would contribute to absorption and fluorescence spectra. Further, the fluorescence of 2AP would be absorbed by its cation in which both the N9 and N7 atoms are protonated, the fluorescence of which can have an anti-Stokes component. Among the different tautomers of adenine, the N9H form would be present dominantly in the ground state in aqueous solutions but the N7H form would be produced by energy transfer and subsequent fluorescence. The N3H form of adenine appears to be responsible for the observed absorption near 300 nm by its solutions intermittently exposed to ultraviolet radiation. The rings of the different species related to 2AP and adenine remain almost planar in the pi-pi* and n-pi* singlet excited states as in the ground state. The pyramidal character of the amino group is usually less in the pi-pi* excited states than that in the corresponding ground or n-pi* excited states. Molecular electrostatic potential (MEP) maps of the molecules provide useful clues regarding phototautomerism.     

Structure and medium effects on the photochemical behavior of nonfluorinated quinolone antibiotics

The photophysical behavior of the quinolone antibiotics, oxolinic (OX), cinoxacin (CNX) and pipemidic (PM) acids was studied as a function of pH and solvent properties. The ground state of these compounds exhibits different protonated forms, which also exist in the first excited states. Theoretical calculations of the Fukui indexes allowed to assigning the different protonation equilibria. The pK values indicate that the acidity of the 3-carboxylic and 4-carbonyl groups increases with the N-atom at position 2 in CNX. It has been found that fluorescence properties are strongly affected by pH, the more fluorescent species is that with protonated carboxylic acid, protonated species at the carbonyl group and the totally deprotonated form present very low fluorescence. The fluorescence behavior also depends on the chemical structure of the quinolone and on the solvent properties. The analysis of the solvent effect on the maximum and the width of the fluorescence band of OX, using the linear solvent-energy relation solvatochromic equation, indicates that the polarizability and hydrogen bond donor ability are the parameters that condition the spectral changes. The hydrogen bond acceptor ability of the solvents also contributes to the spectral shifts of CNX. The compound bearing the piperazinyl group at the position 7, PM only is fluorescent in high protic solvents. These results are discussed in terms of the competition between the intra- and intermolecular hydrogen bonds. The irradiation of OX, CNX and PM using 300 nm UV light led to a very low photodecomposition rate. Under the same conditions the nalidixic acid (NA), a structurally related quinolone, photodecomposes two orders of magnitude faster.     

Influence of polarity of solvents on the spectral properties of bichromophoric coumarins

Absorption and fluorescence spectra of bichromophoric coumarins were investigated in different solvents and in polymer matrices. These bichromophoric coumarins were composed of a coumarin dimethylamino-substituted at position 7 or unsubstituted coumarin and phthalimide or a 1,8-naphthylimide linked with an iminomethyl bridge to the position 3 or 8 of the coumarin ring. Absorption spectra of 7-dimethylamino derivatives in position 3 of coumarin were quite similar, exhibiting broad bands around 430-440 nm like the parent compound 7-dimethylaminocoumarin-3-carbaldehyde. For coumarin derivatives substituted in position 8, the absorption maximum was shifted to shorter wavelength as for derivatives without position 7 dimethylamino substitution. The most intense fluorescence was observed for 7-(N,N-dimethylamino)-3-[(N-phtalimidoyl)iminomethyl]coumarin in polar solvent, while intense fluorescence was observed for 7-(N,N-dimethylamino)-3-[N-(1,3-dioxobenz[de]isoquinolinyl)iminomethyl]-coumarin in non polar solvent (chloroform), comparable with the fluorescence of 7-amino-4-methylcoumarin. Spectral measurements of bichromophoric coumarins in polymer matrices revealed that the maxima lies in between those for chloroform and methanol yielding more intense fluorescence then in solutions. Completely different solvent effects were observed for 7-(N,N-dimethylamino)-3-[N-(1,3-dioxobenz[de]isoquinolinyl)imino-methyl]coumarin and 7-(N,N-dimethylamino)-3-[(N-phtalimidoyl)iminomethyl]coumarin. With addition of polar methanol the intensity of fluorescence decreases, yielding a Stern-Volmer-like constant of 0.54 dm3 mol?1 for 7-(N,N-dimethylamino)-3-[N-(1,3-dioxo-benz[de]isoquinolinyl)iminomethyl]coumarin and an even higher one of 1.08 dm3·mol?1 for 7-dimethylaminocoumarin-3-carbaldehyde compared to the rather low one of 0.024 dm3 mol?1 for 7-amino-4-methylcoumarin. Contrary to this, addition of methanol under identical conditions brings about an increase in fluorescence intensity of 7-(N,N-dimethylamino)-3-[(N-phtalimidoyl)iminomethyl]coumarin (about 60-fold). The reasons for these different solvent effects are discussed.     

Fluorescence properties of some 2-(4-amino-substituted-3-nitrophenyl)-3-hydroxyquinolin-4(1H)-ones

2-(4-Amino-substituted-3-nitrophenyl)-3-hydroxyquinolin-4(1H)-ones have been studied to evaluate their fluorescence properties and possible use as molecular fluorescent probes. The amino group was substituted with various alkyl moieties possessing a suitable terminal functional group (such as hydroxy or amino group) that could serve to bind a 3-hydroxyquinolin-4(1H)-one (3HQ) fluorescence label to a biomolecule. Besides simple hydrocarbon chains, ligands containing ethylenoxy units as optimal spacers were also tested. The structure-fluorescence properties and theoretical applicability of the studied molecules are discussed.     

Intensely Fluorescent Azobenzenes: Synthesis,Crystal Structures,Effects of Substituents,and Application to Fluorescent Vital Stain

2‐[Bis(pentafluorophenyl)boryl]azobenzenes bearing hydrogen, methoxy, dimethylamino, trifluoromethyl, fluoro, n‐butyl, and tert‐butyldimethylsiloxy groups at the 4′‐position or methoxy and bromo groups at the 4‐position have been synthesized. The 4‐bromo group of the 2‐boryl‐4‐bromoazobenzene derivative was converted to phenyl and diphenylamino groups by palladium‐catalyzed reactions. The absorption and fluorescence properties have been investigated using UV/Vis and fluorescence spectroscopy. The 2‐borylazobenzenes emitted an intense green, yellow, and orange fluorescence, in marked contrast to the usual azobenzene fluorescence. The 4′‐siloxy derivative showed the highest fluorescence quantum yield (0.90) among those reported for azobenzenes to date. The correlation between the substituent and the fluorescence properties was elucidated by studying the effect of the substituent on the relaxation process and from DFT and TD‐DFT calculations. An electron‐donating group at the 4′‐position was found to be important for an intense emission. Application of fluorescent azobenzenes as a fluorescent vital stain for the visualization of living tissues was also investigated by microinjection into Xenopus embryos, suggesting these compounds are nontoxic towards embryos.     

Structural factors influencing the reaction rates of 4-aryloxy-7-nitrobenzofurazans with amino acids

An interesting observation was made when studying the S _N Ar reaction between several 4-aryloxy-7-nitrobenzofurazans (2) and several amino acids leading to the apparition of detectable fluorescence from the substitution products3. Acidic amino acids reacted very slowly=while basic amino acids react fastest with2 having an unsubstituted phenyl or a 4-formyl-phenyl Ar group. Amongst neutral amino acids, proline reacts fastest at room temperature after 100 min. With2 having a methoxy-subtituted Ar group.     

Triazolylbenzimidazolthiones and derivatives of the new 1,2,3‐triazolo[ 1,5‐a][ 1,3,5]benzotriazepine heterocycle

Four new triazolylbenzimidazolthione derivatives (2a‐d), analogous to triazolylbenzimidazolone derivatives previously tested as activators of the BK_Ca potassium channels, were prepared and assayed without success. Some derivatives of a new tricyclic nitrogen heterocycle, 1,2,3‐triazolo[1,5‐a][1,3,5]benzo‐triazepine, bearing a carboxamido group in the 3 position, other substituents in the 8 position and a carbonyl (5a‐d) or thione (6a‐c) or methylthio (7a‐c) function in the 5 position were synthesised. The nucleophilic displacement of the methylthio substituent with morpholine or cyclopentylamine provided the 5‐amino‐substituted tricyclic derivatives 8a‐d. Starting from the l‐(2‐nitrophenyl)‐4‐cyano‐5‐amino‐1,2,3‐triazole (9), the 3‐cyano‐triazolobenzotriazepin‐5‐one derivative 12 was also obtained. The majority of the new compounds were tested towards the BK_Ca potassium channels, the benzodiazepine and adenosine A₁ and A_2a receptors, but no remarkable activity was detected.