Binding interactions of hydrophobically-modified flavonols with β-glucosidase: fluorescence spectroscopy and molecular modelling study.

Natural flavonoids are capable of inhibiting glucosidase activity, so they can be used for treating diabetes mellitus and hypertension. However, molecular-level details of their interactions with glucosidase enzymes remain poorly understood. This paper describes the synthesis and spectral characterization of a series of fluorescent flavonols and their interaction with the β-glucosidase enzyme.

Complexation of Flavonoids: Spectral Phenomena, Regioselectivity, Interplay with Charge and Proton Transfer.

The review compiles information on the spectral classification of flavonoids, the changes in their electronic structure upon complex formation, and the manifestation of these changes in the absorption and emission spectra. Part of the review is devoted to the regioselectivity of the complex formation process, including types of complexation sites, the structure of chelates and 'open' complexes, and the correlation between the structure of complexes and their spectral properties. The interplay between complex formation and other processes occurring in flavonoids during electronic excitation is also considered, such as intramolecular inter-fragment charge transfer (ICT) and intramolecular proton transfer (ESIPT).

Progress and Achievements in Glycosylation of Flavonoids.

In recent years, the chemistry of flavonoid glycosylation has undergone significant developments. This mini-review is devoted to summarizing existing strategies and methods for glycosylation of natural and synthetic flavonoids. Herein we overviewed the reaction conditions of flavonoid glycosylation depending on the position of hydroxyl groups in a parent molecule, the degree of it conjugation with the π-system, the presence of steric factors, the formation of intramolecular hydrogen bonds, etc.

Aminofluoresceins Versus Fluorescein: Peculiarity of Fluorescence.

In this article, we examined the fluorescent properties of 4'- and 5'-aminofluorescein, unsubstituted fluorescein, and its 4'-nitro derivative in a set of solvent systems. Fluorescence lifetimes, quantum yields, time-resolved fluorescence spectra, and quantum chemical calculations allowed clarifying the reasons of the emitting properties in this dye series. In water, the dianions R of aminofluoresceins are practically nonfluorescent; in alcohols, the quantum yields are low.

Aminofluoresceins Versus Fluorescein: Ascertained New Unusual Features of Tautomerism and Dissociation of Hydroxyxanthene Dyes in Solution.

Within the course of this spectroscopic research, we revealed novel features of the protolytic behavior, which extend the knowledge of the chemistry of xanthene dyes and rationalize the utilization of these compounds. In addition to the well-known tautomerism of the molecular form, HR, of fluorescein dyes, new aspects of tautomeric transformation of anions are disclosed. First, for the dyes bearing the substituents in the phthalic acid residue, 4'- and 5'-aminofluoresceins and 4'-fluorescein isothiocyanate, the monoanion HR exists in non-hydrogen-bond donor solvents not only as a tautomer with the ionized carboxylic and nonionized OH group but also as a "phenolate" ion with a nonionized COOH group.

On the use of acridinium indicators for the chemiluminescent determination of the total antioxidant capacity of dietary supplements.

Acridinium salts, due to their chemiluminogenic properties, have found several applications in biomedical analysis as labels and indicators, where the assessment of emission intensity is used for the end-point detection. This work presents the use of chemiluminescent indicators in the form of selected acridinium esters in order to determine the antioxidant properties of exemplary formulations, namely quercetin, vitamin C and the dietary supplement, Apiextract. The principle of measurements is based on a change in the kinetics of emission decay derived from the acridinium cations in alkaline solutions of hydrogen peroxide in the presence of an antioxidant (the analyte).

Structural and Spectral Features of 4'-Substituted 2'-Hydroxychalcones in Solutions and Crystals: Spectroscopic and Theoretical Investigations.

The article describes investigations of 2'-hydroxychalcone and its three derivatives bearing differently sized alkyloxy groups at position 4'. The compounds are investigated from the point of view of crystal structure, electronic absorption, fluorescence features in solutions and crystals using X-ray diffraction and electronic spectroscopy methods, and quantum chemistry calculations. In general, both in solutions and in the crystal phase, the influence of substituents on absorption spectra of chalcones was found to be insignificant.

Fluorescence of aminofluoresceins as an indicative process allowing one to distinguish between micelles of cationic surfactants and micelle-like aggregates.

Among the vast set of fluorescein derivatives, the double charged R anions of aminofluoresceins are known to exhibit only low quantum yields of fluorescence, [Formula: see text]. The [Formula: see text] value becomes as high as that of the fluorescein dianion when the lone electron pair of the amino group is involved in a covalent bond. According to Munkholm et al (1990 J.

Origin of Spectral Features and Acid-Base Properties of 3,7-Dihydroxyflavone and Its Monofunctional Derivatives in the Ground and Excited States.

Comprehensive spectral investigations of 3,7-dihydroxyflavone and its two derivatives, which each contain a methyl-blocked hydroxyl group, reveal complex radiation absorption in the 300-450 nm range and emission in the 370-650 nm range. The absorption and fluorescence characteristics of these compounds depend on the pH/H0 of the water/methanol media, which is caused by the existence of the compounds in various protolytic (cationic, neutral, anionic) and tautomeric forms. Combined analysis of steady-state, time-dependent and fluorescence decay spectral data enabled the identification of the emitting species, determination of their lifetimes with respect to radiative and nonradiative deactivation processes, fluorescence quantum yields, protolytic and tautomeric abilities under various conditions, and acidic dissociation constants of the cationic, neutral, and anionic forms of the compounds.

7-Hydroxyflavone Revisited. 2. Substitution Effect on Spectral and Acid-Base Properties in the Ground and Excited States.

Three derivatives of 7-hydroxy-2-phenyl-4H-chromen-4-one (7-hydroxyflavone), containing chloro, methoxy, and dimethylamino substituents at position 4', were synthesized and investigated from the view of their ground-state and electronically excited-state behavior. Spectral and fluorescent properties in a wide range of pH/H0, thermodynamics of the ground and S1 states, and kinetics of the excited-state deactivation of the compounds were investigated by means of steady-state electronic absorption, steady-state, and time-resolved fluorescent spectroscopies as well as by computational methods. The results are rationalized from the point of view of the substituent effect.

7-hydroxyflavone revisited: spectral, acid-base properties, and interplay of the protolytic forms in the ground and excited states.

Spectral and acid-base properties of 7-hydroxyflavone (7HF) in the ground and excited states were investigated with a purpose to enable reasonable application of this dye and its derivatives as fluorescent probes. Analysis of solvatochromic and solvatofluorochromic ability of 7HF in 20 solvents, investigations of 7HF spectral properties in the frozen solvents, spectrophotometric and spectrofluorimetric titrations in methanol-water (4:1 v/v) in the wide pH/H0 range (from pH = 11.0 to H0 = -4.

Tautomerism and behavior of 3-hydroxy-2-phenyl-4H-chromen-4-ones (flavonols) and 3,7-dihydroxy-2,8-diphenyl-4H,6H-pyrano[3,2-g]chromene-4,6-diones (diflavonols) in basic media: spectroscopic and computational investigations.

Absorption and emission spectroscopic investigations and computational predictions have shown that neutral molecules of flavonols and diflavonols can exist in the ground and excited states in one or two tautomeric forms stabilized by intramolecular (in aprotic media) or intermolecular (with solvent molecule(s), in protic media) hydrogen bonds. Electronic excitation creates conditions for the transformation of tautomeric forms, accompanied by proton transfer, reflected in fluorescence spectra. Proton transfer is also probable in monoanions of diflavonols in protic media.

2-(4-Hy-droxy-phen-yl)-3-meth-oxy-4H-chromen-4-one.

In the title compound, C16H12O4, the substituent benzene ring and meth-oxy group are twisted relative to the 4H-chromene skeleton by 24.1 (1) and 61.3 (1)°, respectively.

2-(4-Fluoro-phen-yl)-2H-chromen-4(3H)-one.

In the crystal structure of the title compound, C(15)H(11)FO(2), mol-ecules form inversion dimers through pairs of weak C-H⋯O hydrogen bonds. Dimers oriented in parallel, linked by C-H⋯π contacts, are arranged in columns along the b axis. The fluoro-phenyl ring and the benzene ring of the 2H-chromen-4(3H)-one unit are inclined to one another by 70.

3-Hy-droxy-2-(4-meth-oxy-phen-yl)-4H-chromen-4-one.

In the title compound, C(16)H(12)O(4), the benzene ring is twisted at an angle of 12.3 (1)° relative to the 4H-chromene skeleton, and an intramolecular O-H⋯O hydrogen bond occurs. The meth-oxy group is almost coplanar with the benzene ring [1.

Chemiluminogenic features of 10-methyl-9-(phenoxycarbonyl)acridinium trifluoromethanesulfonates alkyl substituted at the benzene ring in aqueous media.

10-Methyl-9-(phenoxycarbonyl)acridinium trifluoromethanesulfonates bearing alkyl substituents at the benzene ring were synthesized, purified, and identified. In the reaction with OOH(-) in basic aqueous media, the cations of the compounds investigated were converted to electronically excited 10-methyl-9-acridinone, whose relaxation was accompanied by chemiluminescence (CL). The kinetic constants of CL decay, relative efficiencies of light emission, chemiluminescence quantum yields, and resistance toward alkaline hydrolysis were determined experimentally under various conditions.

Chemiluminogenic properties of 10-methyl-9-(phenoxycarbonyl)acridinium cations in organic environments.

The chemiluminogenic (CL) properties of aryl esters of 9-carboxy-10-methylacridinium acid and 9-carboxy-2-methoxy-10-methylacridinium acid (AE), variously substituted in the benzene ring (2-H, 2-CH(3), 2-Cl) were investigated in aliphatic alcohols, acetonitrile, and dimethyl sulfoxide in the presence of hydrogen peroxide and different bases-potassium hydroxide, tetra-n-butylammonium hydroxide, and 1,8-diazabicyclo[5.4.0]undec-7-ene.

2,2-Difluoro-4-phenyl-1,3,2-dioxaborolo[4,5-c]chromen-5-ium-2-ide.

In the crystal, the inversely oriented mol-ecules of the title compound, C(15)H(9)BF(2)O(3), form stacks along the a axis via π-π inter-actions between parallel phenyl-chromenium fragments. Linked by a network of C-H⋯F inter-actions, the stacks form layers in the ac plane that are dispersively stabilized in the crystal structure. Two F atoms bonded to the B atom are located in the plane perpendicular to the planar skeleton of the mol-ecule made rigid by two intra-molecular C-H⋯O inter-actions.

2-(4-Fluoro-phen-yl)-3-hy-droxy-4H-chromen-4-one.

In the crystal structure of the title compound, C(15)H(9)FO(3), inversely oriented mol-ecules form inversion dimers through pairs of O-H⋯O hydrogen bonds. The benzene ring is twisted at an angle of 12.0 (1)° relative to the 4H-chromene skeleton of the mol-ecule.

Spectral features of substituted 9-(phenoxycarbonyl)-acridines and their protonated and methylated cation derivatives.

The long-wavelength absorption of eight 9-(phenoxycarbonyl)-acridines and the 10-H-9-(phenoxycarbonyl)-acridinium and 10-methyl-9-(phenoxycarbonyl)-acridinium cations derived from them, substituted with an alkyl or trifluoroalkyl group at the benzene ring, occurs above 300 nm as the superposition of four bands. Three of these bands occupy comparable positions (expressed in nm) in all the compounds; the fourth one, however, changes position, appearing in neutral molecules as a long-wavelength shoulder below 400 nm, but in cations as an almost separate band above 400 nm. The weak fluorescence resulting from excitation within the long-wavelength absorption band is red-shifted relative to absorption, such that Stokes shifts are similar for both neutral molecules and cations.

Two polymorphs of 2-(4-chlorophenyl)-4-methylchromenium perchlorate.

Crystallization (from ethyl acetate solution) of 2-(4-chlorophenyl)-4-methylchromenium perchlorate, C(16)H(12)ClO(+).;ClO(4)(-), (I), yields two monoclinic polymorphs with the space groups P2(1)/n [polymorph (Ia)] and P2(1)/c [polymorph (Ib)]; in both cases, Z = 4. Cations and anions, disordered in polymorph (Ib), form ion pairs in both polymorphs as a result of Cl-O.

Tautomerism of acridin-9-amines substituted at the exocyclic nitrogen atom: spectroscopic investigations and theoretical studies.

In the ground electronic state, the first two (1 and 2) of the compounds investigated--9-(methoxyamino)acridine (1), 9-hydrazinoacridine (2), N-(2-chloroethyl)acridin-9-amine (3) and N-(5-methylpyridin-2-yl)acridin-9-amine (4)--exist principally in the imino tautomeric form, while the other two (3 and 4) can coexist as amino and imino tautomers in solvents of various polarities and abilities to enter into specific interactions. These features of the molecules are reflected in the experimental absorption spectra and the predicted thermodynamic and spectral data. The predicted thermodynamic characteristics suggest that in the S1 state, the imino tautomers of 1, 2 and 4 and the amino tautomer of 3 are more stable than their tautomeric counterparts.