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Reactions of a cyclotrisilane with styrene derivatives and diarylacetylenes - evidence for nucleophilic silylenes
No full textSilaindanes were obtained by reaction of hexakis[2-(dimethylaminomethyl)phenyl]cyclotrisilane (3) with 3 equiv. of various styrenes. Analogous treatment of 3 with p-methoxystryrene yielded a mixture of the corresponding silaindane and a 2:1 adduct between bis[2-(dimethylaminomethyl)phenyl]silylene (4) and the styrene. Competition experiments show that the addition rate of 4 to the triple bond of diarylacetylenes is accelerated by electron-withdrawing substituents. The reaction constant (p=+0.85+/-0.21) indicates that 4 acts as a nucleophile in these reactions. The rate determining step in these reactions of cyclotrisilane 3 is the formation of silylene 4. The rate constant for this first order process was determined to be (6.3+/-0.4)x10(-4) s(-1) at 60 degreesC. (C) 2001 Elsevier Science Ltd. All rights reserved
Indolo[2,3-b]-quinolizinium bromide: an efficient intercalator with DNA-photodamaging properties
No full textThe associative interactions of indolo[2,3-b]-quinolizinium bromide with DNA and its DNA photocleavage properties were studied in detail. Absorption and emission spectroscopy, linear dichroism, and energy-transfer measurements indicate that the indoloquinolizinium binds to DNA primarily by intercalation, with a preference for GC base pairs. In agreement with this data, the results of primer extension analysis indicate that photocleavage occurrs prevalently at the GC nucleotides. Molecular modeling studies confirm that intercalative stacking between adjacent base pairs is energetically favorable. However, it is also observed that the location of the dye in the minor groove of the DNA is energetically even more favorable. Upon UVA irradiation, the indoloquinolizinium causes single-strand cleavage with an efficiency that varies with the dye-DNA ratio. This observation is rationalized in terms of more efficient photocleavage by the externally bound dye compared with the intercalated one. The kinetics of strand degradation under aerobic and anaerobic conditions suggest that a Type I reaction occurs, that is, radical-mediated DNA damage
Comparative studies on the DNA-binding properties of linear and angular dibenzoquinolizinium ions
No full textThe interaction of the linear dibenzo[b,g]quinolizinium (5a) and the angular dibenzo[a,f]quinolizinium (6) with DNA was studied in detail in order to evaluate the influence of the shape of polycyclic quinolizinium ions on their DNA-binding properties. First, the synthesis and the thermally induced dimerization of 5a were reinvestigated because the preparation and isolation of the bromide salt of 5a according to literature procedures turned out to be problematic. The dibenzo[b,g]quinolizinium bromide [5a(Br)] tends to dimerize in solution with a highly selective and unprecedented formation of the corresponding anti-head-to-head dimer. Nevertheless, it was observed that careful exclusion of bromide ions from the reaction mixture suppresses the formation of the dimer. Moreover, the dimer may be transformed to the monomer by a remarkably rapid photoinduced electron-transfer reaction with 1-methoxynaphthalene. The association of 5a and 6 with nucleic acids was investigated by spectrophotometric and spectrofluorimetric DNA titrations, CD and LD spectroscopy, DNA thermal denaturation studies, and competition-dialysis techniques. Both dibenzoquinolizinium ions 5a and 6 exhibit an intercalative mode of binding to double-stranded DNA with moderate binding constants (K = 1-7 x 10(5) M(-1)) and a slight preference for association with GC-rich DNA regions. The structures of the intercalation complexes were calculated by molecular modeling methods. Competition-dialysis studies reveal that the isomers 5a and 6 bind selectively to triple-helical DNA (poly[dA]-poly[dT]2) as compared to selected synthetic and native double-stranded nucleic acids. Notably, the selectivity of the linear dibenzo[b,g]quinolizinium 5a toward triplex DNA is higher than the one of the angular derivative 6. In contrast, the DNA thermal denaturation studies reveal a higher stabilization of triple-helical DNA in the presence of 6 (DeltaTm3-->2 = 28 degrees C at r = 0.5) as compared to the stabilization by 5a (DeltaTm3-->2 = 14 degrees C at r = 0.5). This comparison emphasizes the importance of the extended pi system for the interaction of annelated quinolizinium ions with DNA. Moreover, the comparison between 5a and 6 demonstrates the significant influence of the shape of the pi system on the duplex- and triplex-stabilizing properties of the dibenzoquinolizinium ions
Intercalation of Organic Dye Molecules into Double-Stranded DNA; Part 2: The Annelated Quinolizinium Ion as a Structural Motif in DNA Intercalators
No full textDNA intercalators represent an important class of compounds with a high potential as DNA-targeting drugs. In this review it is demonstrated that annelated quinolizinium derivatives such as coralyne and derivatives thereof intercalate into DNA and that this structural motif allows several variations of the substitution pattern without loss of intercalating properties. The commonly applied methods for the evaluation of the DNA association, mainly spectroscopic studies, are pointed out. In addition, studies on the biological activities of annelated quinolizinium derivatives, such as topoisomerase poisoning or cell toxicity, are highlighted
DNA-binding and DNA-photocleavaging properties of 12a,14a-diazoniapentaphene
No full textThe association of 12a,14a-diazoniapentaphene dibromide (5) with DNA and its ability to
photoinduce DNA damage was studied. Spectrophotometric and fluorimetric titrations show that
the title compound (5) binds to DNA (K ≈ 5·105 M–1) with the highest affinity towards GC-rich
regions. The highest affinity was observed for GC base pairs. Compound 5 binds to DNA
primarily by intercalation as shown by LD spectroscopy and energy-transfer experiments.
Moreover, efficient DNA damage was observed on UVA irradiation in the presence of 5.
Preliminary experiments suggest that singlet oxygen may be involved in the photoinduced DNA
damage
Naftoquinolizinium derivatives as a novel platform for DNA-binding and DNA-photodamaging chromophores
No full textThe association of the naphtho[1,2-b]quinolizinium bromide (5a) and naphtho[2,1-b]quinolizinium bromide (5b) with DNA and the propensity of these cationic arenes to damage DNA after UV-A irradiation have been studied. Spectrophotometric and fluorimetric titrations show that the two isomers 5a and 5b bind to DNA (K approximately 10(5) M(-1)). The highest affinity was observed for GC base pairs. The mode of binding was investigated by CD and LD spectroscopy. Whereas quinolizinium 5a exclusively intercalates in DNA, the isomer 5b exhibits a deviation from perfect intercalation into the double helix. Moreover, efficient DNA damage was observed on UV-A irradiation in the presence of the quinolizinium salts. Primer extension analysis indicates that the photocleavage takes place preferentially at guanine-rich regions
Synthesis and investigation of the DNA-binding and DNA-photodamaging properties of indolo[2,3-b] quinolizinium bromide
No full textThe readily available cationic dye 3-Br binds to DNA as was shown by UV, fluorescence and CD spectroscopy. The electronic spectra of the quinolizinium salt 3 exhibit significant bathochromic shifts and a decrease of the absorbance and emission intensity on addition of calf thymus DNA. Moreover, fluorometric titration of [poly(dCdG)]2 with salt 3 resulted in a significant decrease of the emission intensity, whereas addition of [poly(dAdT)]2 led only to a marginal perturbation of the emission spectrum. Analysis of the binding constants with the different polynucleotides revealed that quinolizinium 3-Br binds preferentially to GC base pairs. Irradiation of DNA in the presence of quinolizinium 3-Br resulted in efficient single-strand cleavage of the nucleic acid
6-aminoacridizinium bromide: a fluorescence probe which lights up in AT-rich regions of DNA
No full textAn overview is given of a useful fluorescence probe for DNA detection. Its emission properties are drastically switched by a change of the base composition within the binding pocket because of a delicate balance between emission and redox properties. Thus, this compound constitutes a useful platform for a new generation of selective DNA-sensing probes
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