Diquat Derivatives: Highly Active, Two-Dimensional Nonlinear Optical Chromophores with Potential Redox Switchability

In this article, we present a detailed study of structure−activity relationships in diquaternized 2,2′-bipyridyl (diquat) derivatives. Sixteen new chromophores have been synthesized, with variations in the amino electron donor substituents, π-conjugated bridge, and alkyl diquaternizing unit. Our aim is to combine very large, two-dimensional (2D) quadratic nonlinear optical (NLO) responses with reversible redox chemistry. The chromophores have been characterized as their PF_6^− salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Their visible absorption spectra are dominated by intense π → π^* intramolecular charge-transfer (ICT) bands, and all show two reversible diquat-based reductions. First hyperpolarizabilities β have been measured by using hyper-Rayleigh scattering with an 800 nm laser, and Stark spectroscopy of the ICT bands affords estimated static first hyperpolarizabilities β_0. The directly and indirectly derived β values are large and increase with the extent of π-conjugation and electron donor strength. Extending the quaternizing alkyl linkage always increases the ICT energy and decreases the E_(1/2) values for diquat reduction, but a compensating increase in the ICT intensity prevents significant decreases in Stark-based β_0 responses. Nine single-crystal X-ray structures have also been obtained. Time-dependent density functional theory clarifies the molecular electronic/optical properties, and finite field calculations agree with polarized HRS data in that the NLO responses of the disubstituted species are dominated by ‘off-diagonal’ β_(zyy) components. The most significant findings of these studies are: (i) β_0 values as much as 6 times that of the chromophore in the technologically important material (E)-4′-(dimethylamino)-N-methyl-4-stilbazolium tosylate; (ii) reversible electrochemistry that offers potential for redox-switching of optical properties over multiple states; (iii) strongly 2D NLO responses that may be exploited for novel practical applications; (iv) a new polar material, suitable for bulk NLO behavior

Evolution of Linear Absorption and Nonlinear Optical Properties in V-Shaped Ruthenium(II)-Based Chromophores

In this article, we describe a series of complexes with electron-rich cis-{Ru^(II)(NH_3)_4}^(2+) centers coordinated to two pyridyl ligands bearing N-methyl/arylpyridinium electron-acceptor groups. These V-shaped dipolar species are new, extended members of a class of chromophores first reported by us (Coe, B. J. et al. J. Am. Chem. Soc. 2005, 127, 4845−4859). They have been isolated as their PF_6− salts and characterized by using various techniques including ^1H NMR and electronic absorption spectroscopies and cyclic voltammetry. Reversible Ru^(III/II) waves show that the new complexes are potentially redox-switchable chromophores. Single crystal X-ray structures have been obtained for four complex salts; three of these crystallize noncentrosymmetrically, but with the individual molecular dipoles aligned largely antiparallel. Very large molecular first hyperpolarizabilities β have been determined by using hyper-Rayleigh scattering (HRS) with an 800 nm laser and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d → π^* metal-to-ligand charge-transfer (MLCT) and π → π^* intraligand charge-transfer (ILCT) bands. The latter measurements afford total nonresonant β_0 responses as high as ca. 600 × 10^(−30) esu. These pseudo-C_(2v) chromophores show two substantial components of the β tensor, β_(zzz) and β_(zyy), although the relative significance of these varies with the physical method applied. According to HRS, β_(zzz) dominates in all cases, whereas the Stark analyses indicate that β_(zyy) is dominant in the shorter chromophores, but β_(zzz) and β_(zyy) are similar for the extended species. In contrast, finite field calculations predict that β_(zyy) is always the major component. Time-dependent density functional theory calculations predict increasing ILCT character for the nominally MLCT transitions and accompanying blue-shifts of the visible absorptions, as the ligand π-systems are extended. Such unusual behavior has also been observed with related 1D complexes (Coe, B. J. et al. J. Am. Chem. Soc. 2004, 126, 3880−3891)

Differential Reactivity of [TpRu(κ2P,N-iPr2PXPy)Cl] (X = NH, S) Bearing Hemilabile Coligands Towards NaBArF 4, Lithium Acetylide, and Acetylenes

In contrast with [TpRu(κ2P,N-iPr2PNHPy)Cl] (1a, Tp = trispyrazolylborate), [TpRu(κ2P,N-iPr2PSPy)Cl] (1b) reacts with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBArF 4) in fluorobenzene under nitrogen to afford the dinuclear complex [{TpRu(κ2P,N-iPr2PSPy)}2(μ-Cl)][BArF4] (1b ). Through diverse synthetic strategies, a series of neutral acetylides [TpRu(C CR)(κ2P,N-iPr2PXHPy)] [X = NH; R = Ph (2a), SiMe3 (2b); X = S; R = Ph (2c), p-C6H4Br (2d), COOMe (2e)], cationic vinylidene complexes [TpRu(=C=CHR)(κ2P,NiPr2PNHPy)]+ [X = NH; R = Ph (3a), SiMe3 (3b); X = S; R = Ph (3c), p-C6H4Br (3d)] and [TpRu(=C=CH2)(κ2P,N-iPr2PNHPy)]+ (3e), and a cationic η2-alkyne complex [TpRu(η2- HC CCOOMe)(κ2P,N-iPr2PSPy)][BArF 4] have been efficiently synthesized from 1a and 1b. The methoxy(methyl)- carbene complexes [TpRu{=C(OMe)CH3}(κ2P,N-iPr2PXPy)]- [BPh4] [X = NH (5a), S (5b)] were isolated from the reactions of 1a and 1b with acetylene gas in the presence of NaBArF4 in methanol. The deprotonation of the cationic vinylidenes derived from 1b with KtBuO affords the corresponding neutral acetylide complexes, which undergo facile protonation with CF3SO3H to reproduce the cationic vinylidenes quantitatively

Pro-oxidant Induced DNA Damage in Human Lymphoblastoid Cells: Homeostatic Mechanisms of Genotoxic Tolerance

Oxidative stress contributes to many disease etiologies including ageing, neurodegeneration, and cancer, partly through DNA damage induction (genotoxicity). Understanding the i nteractions of free radicals with DNA is fundamental to discern mutation risks. In genetic toxicology, regulatory authorities consider that most genotoxins exhibit a linear relationship between dose and mutagenic response. Yet, homeostatic mechanisms, including DNA repair, that allow cells to tolerate low levels of genotoxic exposure exist. Acceptance of thresholds for genotoxicity has widespread consequences in terms of understanding cancer risk and regulating human exposure to chemicals/drugs. Three pro-oxidant chemicals, hydrogen peroxide (H2O2), potassium bromate (KBrO3), and menadione, were examined for low dose-response curves in human lymphoblastoid cells. DNA repair and antioxidant capacity were assessed as possible threshold mechanisms. H2O2 and KBrO3, but not menadione, exhibited thresholded responses, containing a range of nongenotoxic low doses. Levels of the DNA glycosylase 8-oxoguanine glycosylase were unchanged in response to pro- oxidant stress. DNA repair–focused gene expression arrays reported changes in ATM and BRCA1, involved in double-strand break repair, in response to low-dose pro-oxidant exposure; however, these alterations were not substantiated at the protein level. Determination of oxidatively induced DNA damage in H2O2-treated AHH-1 cells reported accumulation of thymine glycol above the genotoxic threshold. Further, the H2O2 dose-response curve was shifted by modulating the antioxidant glutathione. Hence, observed pro- oxidant thresholds were due to protective capacities of base excision repair enzymes and antioxidants against DNA damage, highlighting the importance of homeostatic mechanisms in “genotoxic tolerance.

ETUDE DE L'EXPRESSION ET DE LA REGULATION DU GENE OGG1 CODANT UNE 8-OXOGUANINE ADN GLYCOSYLASE DANS LES CELLULES DE MAMMIFERE

LE GENE OGG1 EST CONSERVE DEPUIS LA LEVURE JUSQU'A L'HOMME. IL CODE POUR UNE PROTEINE DE REPARATION DE L'ADN QUI EXCISE UNE LESION D'OXYDATION MAJEURE DE L'ADN, LA 8-OXOGUANINE. CETTE LESION EST FORTEMENT MUTAGENE ET CONDUIT A DES TRANSVERSIONS DE G : C VERS T : A. L'ACTION ANTIMUTATRICE DE LA PROTEINE OGG1 A ETE DEMONTREE CHEZ LA LEVURE S. CEREVISIAE ET LA SOURIS. EN REDUISANT LA FREQUENCE DES MUTATIONS, OGG1 POURRAIT PREVENIR LE PROCESSUS DE CANCEROGENESE. POUR VALIDER CETTE HYPOTHESE, NOUS AVONS ENTREPRIS LE CLONAGE DU GENE OGG1 HUMAIN ET L'ETUDE DE SON EXPRESSION DANS LES CELLULES NORMALES ET TUMORALES. LA STRUCTURE ET LA TAILLE DES EXONS DU GENE OGG1 EST IDENTIQUE ENTRE L'HOMME ET LA SOURIS. LE PROMOTEUR D'HOGG1 NE POSSEDE NI BOITE TATA, NI BOITE CCAAT CONSENSUS ET CONTIENT DES ILOTS CPG. CE SONT DES PROPRIETES DE GENES DITS DE MENAGE DONT L'EXPRESSION EST UBIQUITAIRE. CETTE CARACTERISTIQUE EST COHERENTE AVEC LE ROLE D'HOGG1 DANS LA REPARATION DE LESIONS DUES AU STRESS OXYDATIF ENDOGENE. NOUS AVONS DETECTE LA PRESENCE D'HOGG1 ET MOGG1 DANS TOUS LES TISSUS ET LIGNEES CELLULAIRES UTILISES. L'ANALYSE DU TAUX D'ARN MESSAGER, DE PROTEINE ET D'ACTIVITE ENZYMATIQUE D'HOGG1 DANS DIVERSES SITUATIONS A MONTRE QU'ILS SONT CONSTANTS. L'EXPRESSION D'HOGG1 A NOTAMMENT ETE ETUDIEE AU COURS DU CYCLE, DE LA CROISSANCE ET DE LA DIFFERENCIATION CELLULAIRE, MAIS EGALEMENT SUITE A DIVERS STRESS OXYDATIFS INDUISANT LA FORMATION DE LESIONS 8-OXOG. LE PROCESSUS DE CANCEROGENESE S'ACCOMPAGNE SOUVENT D'UNE METHYLATION DE SEQUENCES CPG D'ADN CONDUISANT A L'INACTIVATION DE GENES SUPPRESSEURS DE TUMEURS. NOUS AVONS MONTRE QU'UNE EXTINCTION DE L'EXPRESSION D'HOGG1 PEUT ETRE REALISEE IN VITRO PAR METHYLATION DES ILOTS CPG PRESENTS DANS LE PROMOTEUR DU GENE HOGG1. L'EXPRESSION DU GENE HOGG1 EST DONC UBIQUITAIRE ET NE VARIE PAS DANS LES SITUATIONS DE STRESS OXYDATIF ANALYSEES. ELLE PEUT NEANMOINS ETRE MODULEE PAR METHYLATION DE SON PROMOTEUR CE QUI PEUT ETRE LIE AU PROCESSUS DE CANCEROGENESE.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Identification and characterization of a human DNA glycosylase for repair of modified bases in oxidatively damaged DNA

8-oxoguanine (8-oxoG), ring-opened purines (formamidopyrimidines or Fapys), and other oxidized DNA base lesions generated by reactive oxygen species are often mutagenic and toxic, and have been implicated in the etiology of many diseases, including cancer, and in aging. Repair of these lesions in all organisms occurs primarily via the DNA base excision repair pathway, initiated with their excision by DNA glycosylase/AP lyases, which are of two classes. One class utilizes an internal Lys residue as the active site nucleophile, and includes Escherichia coli Nth and both known mammalian DNA glycosylase/AP lyases, namely, OGG1 and NTH1. E. coli MutM and its paralog Nei, which comprise the second class, use N-terminal Pro as the active site. Here, we report the presence of two human orthologs of E. coli mutM nei genes in the human genome database, and characterize one of their products. Based on the substrate preference, we have named it NEH1 (Nei homolog). The 44-kDa, wild-type recombinant NEH1, purified to homogeneity from E. coli, excises Fapys from damaged DNA, and oxidized pyrimidines and 8-oxoG from oligodeoxynucleotides. Inactivation of the enzyme because of either deletion of N-terminal Pro or Histag fusion at the N terminus supports the role of N-terminal Pro as its active site. The tissue-specific levels of NEH1 and OGG1 mRNAs are distinct, and S phase-specific increase in NEH1 at both RNA and protein levels suggests that NEH1 is involved in replication-associated repair of oxidized bases