Carotenoid radical anions and their protonated derivatives

In this study, we report the protonation reactions for astaxanthin and canthaxanthin radical anions in methanol, alkaline methanol, and aqueous 2% Triton X-100 at different pH values. The pKa values for the corresponding alpha-hydroxy radical derivatives of astaxanthin, canthaxanthin, and beta-apo-8'-carotenal were estimated in 2% Triton X-100. Also, the effects of the microenvironment and the structure of the carotenoids on the protonation rate constant are discussed.     

Derivatives of hydroxybenzoic acids and their salts: Synthesis and pharmacological activity

Russian Journal of General Chemistry - Preparation of salicylic and acetylsalicylic acid esters via esterification and alkylation of the salts with alkyl halides has been examined. The effect of...     

Electronic absorption of carboxylic acids and their anions

Electronic spectra of formic, acetic, mono-, di-, trichloro- and trifluoroacetic, glycolic, cyanoacetic, pivalic, α-methoxyacetic, lactic, oxalic, tartaric and citric acids and betaine and of corresponding anions were recorded. The acid forms of all the carboxylic acids studied show a medium-strong π → π^* and a weak n → π^* absorption band, the latter in the 220–250-nm region. The corresponding anions (or the completely dissociated forms of polybasic acids) show the π → π^* absorption bands, but no indication of a shoulder corresponding to a n → π^* transition. Changes in the absorbance in the wavelength region corresponding to the n → π^* transition with addition of alkali metal hydroxides can be used for end-point detection in titrations. Changes of these absorbances in solutions of buffers or strong acids can be used for pK determinations. A pK value of 0.89 (at μ = 0.5) was found for dichloroacetic acid; approximate pK values were established by means of the H_o acidity scale for trichloroacetic acid (—0.80) and trifluoroacetic acid (—0.92). Finally, absorbances in the 220–250-nm region can be used for determination of carboxylic acids in solutions of strong acids, and some buffers, like phosphate or borate.     

Photodissociation dynamics of hydroxybenzoic acids

Aromatic amino acids have large UV absorption cross-sections and low fluorescence quantum yields. Ultrafast internal conversion, which transforms electronic excitation energy to vibrational energy, was assumed to account for the photostability of amino acids. Recent theoretical and experimental investigations suggested that low fluorescence quantum yields of phenol (chromophore of tyrosine) are due to the dissociation from a repulsive excited state. Radicals generated from dissociation may undergo undesired reactions. It contradicts the observed photostability of amino acids. In this work, we explored the photodissociation dynamics of the tyrosine chromophores, 2-, 3- and 4-hydroxybenzoic acid in a molecular beam at 193 nm using multimass ion imaging techniques. We demonstrated that dissociation from the excited state is effectively quenched for the conformers of hydroxybenzoic acids with intramolecular hydrogen bonding. Ab initio calculations show that the excited state and the ground state potential energy surfaces change significantly for the conformers with intramolecular hydrogen bonding. It shows the importance of intramolecular hydrogen bond in the excited state dynamics and provides an alternative molecular mechanism for the photostability of aromatic amino acids upon irradiation of ultraviolet photons.     

Flavonoids from Lupinus texensis and their free radical scavenging activity

Seventeen flavonoids including one new compound were isolated from Texas bluebonnet (Lupinus texensis), the state flower of Texas. Their structures were determined by extensive nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry analyses. High-performance liquid chromatography analytic method for simultaneous determination of the 17 compounds was established and validated. Eleven isolated flavonoids were first evaluated for their free radical scavenging activity using α,α-diphenyl-β-picrylhydrazyl scavenging assay and they showed activity with EC(50) 48.6-172.5 μg mL(-1).     

Investigation of the dimerization of acridine radical anions by electrochemical methods

The electrochemical reduction of acridine (dimethylformamide (DMF) and Bu₄NClO₄) was investigated by differential cyclic voltammetry and controlled-potential electrolysis. The experimental data (dimerization rate constant and yield of the 9,9 dimer) agreed with the theoretically calculated ones.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1284–1286, June, 1990.     

Tensor magneto-optical properties of some carboxylate anions

The Cotton—Mouton effect was used for the study of benzoate, phthalate. isophthalate, and terephthalate anions. The additive tensor characteristics of optical polarizability and magnetic susceptibility ellipsoids have been calculated for C(Ar)-COO^– and . The spatial structures of mono- and deprotonated phthalate anions have been discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 874–876, May, 1993.     

Polyphenolic compounds from Malus hupehensis and their free radical scavenging effects

One new 4-chromanone glycoside, 5-O-β-d-glucopyranoside-4-chromanone (1), together with 21 known polyphenols, was isolated from the leaves of Malus hupehensis. Their structures were elucidated on the basis of extensive spectroscopic methods including NMR (1D and 2D), mass (ESIMS and HRESIMS), IR, and by comparison with the data reported in the literature. Some of the isolated compounds were screened for antioxidant activity. Compounds 18 and 14 exhibited significant antioxidant activities with SC₅₀ values 2.73 and 2.91 μg/mL, respectively, while 17, 19, 11, 7, 20, 22, 12 and 13 exhibited moderate activities with SC₅₀ values ranging from 5.24–11.86 μg/mL. The HPLC fingerprint profiles of the leaves and fruits extracts were also analysed, which showed that the constituents were almost the same in both the extracts except for the content of phlorizin which was present in higher amount in the leaves.     

Flavanol derivatives from Rhizophora stylosa and their DPPH radical scavenging activity

A new acetylated flavanol, 3,7-O-diacetyl (-)-epicatechin (3), and seven known flavanol derivatives, (-)-epicatechin (1), 3-O-acetyl (-)-epicatechin (2), 3,3',4',5,7-O-pentaacetyl (-)-epicatechin (4), (+)-afzelechin (5), (+)-catechin (6), cinchonain Ib (7), and proanthocyanidin B2 (8), were isolated from the stems and twigs of the mangrove plant Rhizophora stylosa and identified. The crude extract, the different fractions and all of the purified compounds were evaluated for DPPH radical scavenging activity.     

Dinuclear zinc(II) complexes of tetraiminodiphenol macrocycles and their interactions with carboxylate anions and amino acids. Photoluminescence, equilibria, and structure

The reaction equilibria [H(4)L](2+) + Zn(OAc)(2) right harpoon over left harpoon [Zn(H(2)L)](2+) + 2HOAc (K(1)) and [Zn(H(2)L)](2+) + Zn(OAc)(2) right harpoon over left harpoon [Zn(2)L](2+) + 2HOAc (K(2)), involving zinc acetate and the perchlorate salts of the tetraiminodiphenol macrocycles [H(4)L(1)(-)(3)](ClO(4))(2), the lateral (CH(2))(n)() chains of which vary between n = 2 and n = 4, have been studied by spectrophotometric and spectrofluorimetric titrations in acetonitrile. The photoluminescence behavior of the complexes [Zn(2)L(1)](ClO(4))(2), [Zn(2)L(2)(H(2)O)(2)](ClO(4))(2), [Zn(2)L(2)(mu-O(2)CR)](ClO(4)) (R = CH(3), C(6)H(5), p-CH(3)C(6)H(4), p-OCH(3)C(6)H(4), p-ClC(6)H(4), p-NO(2)C(6)H(4)), and [Zn(2)L(3)(mu-OAc)](ClO(4)) have been investigated. The X-ray crystal structures of the complexes [Zn(2)L(2)(H(2)O)(2)](ClO(4))(2), [Zn(2)L(3)(mu-OAc)](ClO(4)), and [Zn(2)L(2)(mu-OBz)(OBz)(H(3)O)](ClO(4)) have been determined. The complex [Zn(2)L(2)(mu-OBz)(OBz)(H(3)O)](ClO(4)) in which the coordinated water molecule is present as the hydronium ion (H(3)O(+)) on deprotonation gives rise to the neutral dibenzoate-bridged compound [Zn(2)L(2)(mu-OBz)(2)].H(2)O. The equilibrium constants (K) for the reaction [Zn(2)L(2)(H(2)O)(2)](2+) + A(-) right harpoon over left harpoon [Zn(2)L(2)A](+) + 2H(2)O (K), where A(-) = acetate, benzoate, or the carboxylate moiety of the amino acids glycine, l-alanine, l-histidine, l-valine, and l-proline, have been determined spectrofluorimetrically in aqueous solution (pH 6-7) at room temperature. The binding constants (K) evaluated for these systems vary in the range (1-8) x 10(5).     

Fabrication of hyaluronic acid-based nanoparticles and studies on their radical scavenging activity

The purpose of this paper is to study the stability, radical scavenging activities, and bio-safety of cysteine-conjugated hyaluronic acid nanoparticles (Cys-conj-HA NPs). Additionally, the feasibility of utilizing these NPs as drug delivery systems is discussed. The structures of synthesized Cys-conj-HA polymers were analyzed using ¹H nuclear magnetic spectrum (¹H NMR) and Fourier transform infrared spectroscopy (FTIR) spectra. The stability, radical scavenging activity, and bio-safety of fabricated Cys-conj-HA NPs were investigated. Transmission electron microscopy (TEM) photograph illustrated that Cys-conj-HA NPs possessed spherical shapes with an average diameter of approximately 230 nm. Furthermore, these NPs exhibited high stability at temperatures of 4, 25, and 37°C. Notably, Cys-conj-HA NPs demonstrated significant free radical scavenging capabilities. The high cell viability observed indicated the absence of cytotoxicity from Cys-conj-HA NPs. Additionally, bio-safety studies revealed that these NPs did not induce acute toxicity in the blood and viscera of cargo-free NPs treated mice. Elisa assays indicated that there was no significant difference in the concentrations of interferon-γ (INF-γ) and tumor necrosis factor-α (TNF-α) between Cys-conj-HA NPs and normal saline (NS) treated mice (ns, p > 0.05), suggesting the absence of an inflammatory reaction caused by these NPs. Consequently, it can be concluded that Cys-conj-HA NPs are sufficiently safe to be employed as a vehicle for delivering oxidizing drugs.     

Synthesis of water-soluble C_(60) derivatives and their scavenging free radical activity

Four piperazine-appended [60] fuilerenes (1a-1d) were synthesized and characterized. Their activities of scavenging radical were studied via UV-Vis and EPR. The results indicate that light irradiation is of advantage to increase the activity of scavenging radical.     

Investigation of the influence of hydroxy groups on the radical scavenging ability of polyphenols

Recently, O-H bond dissociation enthalpies (BDEs) have been successfully used to express the free radical scavenging ability of polyphenolic antioxidants. In this work, the BDEs of phenol, catechol, resorcinol, hydroquinone, pyrogallol, phloroglucinol, 1,2,4-benzenetriol, and 5-hydroxypyrogallol have been calculated at B3LYP/6-311G++(3df, 3pd) and used to elucidate the effect of OH groups. Increasing the number of OH groups in the adjacent (vicinal) position decreases the BDE of phenols. Increasing the number of O-H groups in the alternative position C(1,3) as in resorcinol and C(1,3,5) as in phloroglucinol does not show any notable change in the BDEs when compared to that of OH in C(1) as in phenol. 5-Hydroxypyrogallol has the smallest BDE (250.3 kJ mol(-1)) followed by pyrogallol (289.4 kJ mol(-1)), then 1,2,4-benzenetriol (294.8 kJ mol(-1)), and then catechol (312.8 kJ mol(-1)). Overall, our results indicated that the presence of ortho and para hydroxy groups reduces the BDEs. An intramolecular hydrogen bond (IHB) develops due to the ortho arrangement of OH's and plays a dominant role in decreasing the BDEs. This key study on phenols showed that the reactive order of OH position in the benzene ring is the following: 5-hydroxypyrogallol > pyrogallol > 1,2,4-benzenetriol > catechol > hydroquinone > phenol approximately resorcinol approximately phloroglucinol.     

A quantum chemical study of small beryllium hydrides and their radical anions

Molecular structures of neutral and anionic beryllium hydrides have been investigated using ab initio calculations at the MP 2 (geometries) and MP 4 (energies)/6 – 31⁺⁺G** levels. ZPE and (if possible) BSSE correction have been included. While BeH₂^? is not stable, the radical anion of the beryllium hydride dimer is significantly stabilized with respect to the neutral Be₂H₄ system. Moreover, this anion can appear in two isomeric forms with comparable stability. © 1995 John Wiley & Sons, Inc.