Linker effect of ferrocenylnaphthalene diimide ligands in the interaction with double stranded DNA

A novel signal amplification strategy for label-free electrochemical DNA sensor based on the interaction between α-cyclodextrin and ferrocenyl indicator

The synthesized ferrocene appended naphthalimide derivative (FND) exhibited great binding ability toward dsDNA, while its usage as the electrochemical hybridization indicator was restricted by the poor water solubility. Herein, a simple and effective signal amplification strategy for FND based label-free DNA biosensors was developed based on the interaction between FND and cyclodextrin. α-Cyclodextrin (α-CD), β-cyclodextrin (β-CD) and γ-cyclodextrin (γ-CD) were helpful to amplify the signal of the DNA biosensor, while the signal amplification effect of α-CD was better than that of β-CD and γ-CD. Under the optimum conditions, there was a 3-fold increase in the sensitivity of the DNA biosensor after the addition of α-CD. The interaction between FND and α-/β-/γ-CD was investigated by differential pulse voltammetry and fluorescence experiment. Experimental results showed that α-CD not only minimized the impact on the electrochemical activity of FND but also improved the dispersity of FND in aqueous solution. That was why the proposed biosensor showed higher sensitivity in the presence of α-CD. This strategy was universal for other ferrocenyl indicators with similar structures as used in this work.

One-stage synthesis of FcP(O)(OC2H5)2from ferrocene and α-hydroxyethylphosphonate

A new approach is proposed for ferrocene phosphorylation using α-hydroxylalkylphosphonate as a “masked” phosphorylating agent, by electrochemical reduction of a ferrocene and (Me)₂C(OH)P(O)(OC₂H₅)₂mixture at −50 °C.

Highly sensitive nuclease assays based on chemically modified DNA or RNA

Nucleolytic enzymes are associated with various diseases, and several methods have been developed for their detection. DNase expression is modulated in such diseases as acute myocardial infarction, transient myocardial ischemia, oral cancer, stomach cancer, and malignant lymphoma, and DNase I is used in cystic fibroma therapy. RNase is used to treat mesothelial cancer because of its antiproliferative, cytotoxic, and antineoplastic activities. Angiogenin, an angiogenic factor, is a member of the RNase A family. Angiogenin inhibitors are being developed as anticancer drugs. In this review, we describe fluorometric and electrochemical techniques for detecting DNase and RNase in disease. Oligonucleotides having fluorescence resonance energy transfer (FRET)-causing chromophores are non-fluorescent by themselves, yet become fluorescent upon cleavage by DNase or RNase. These oligonucleotides serve as a powerful tool to detect activities of these enzymes and provide a basis for drug discovery. In electrochemical techniques, ferrocenyl oligonucleotides with or without a ribonucleoside unit are used for the detection of RNase or DNase. This technique has been used to monitor blood or serum samples in several diseases associated with DNase and RNase and is unaffected by interferents in these sample types.

Interactions of cyclic and non-cyclic naphthalene diimide derivatives with different nucleic acids

Recently, strategy based on stabilization of G-quadruplex telomeric DNA by small organic molecule has been realized by naphthalene diimide derivatives (NDIs). At the same time NDIs bind to DNA duplex as threading intercalators. Here we present cyclic derivative of naphthalene diimide (ligand 1) as DNA-binding ligand with ability to recognition of different structures of telomeric G-quadruplexes and ability to bis-intercalate to double-stranded helixes. The results have been compared to non-cyclic derivative (ligand 2) and revealed that preferential binding of ligands to nucleic acids strongly depends on their topology and structural features of ligands.

Oral cancer diagnosis via a ferrocenylnaphthalene diimide-based electrochemical telomerase assay

BACKGROUND

Telomerase is regarded as a good marker for cancer because it is unregulated in most tumor cells compared with normal cells. We evaluated telomerase activity in the lysate of tumor tissue and surrounding cells of oral cancer patients by an electrochemical technique, dubbed the electrochemical telomerase assay (ECTA).

METHODS

The assay used ferrocenylnaphthalene diimide (FND) as the probe. Electrochemical telomerase substrate (ETS) primer immobilized on the electrode was elongated by telomerase and FND bound to the product to give rise to a current. The data were standardized with the change in current before and after the elongation, respectively.

RESULTS

The change in current increased more than 30% in biopsy samples from most cancer patients, whereas the increase was 20% or lower in most healthy individuals. On the basis of this difference individual clinical samples were judged telomerase positive, ambiguous, or negative. The positive rates in the cancerous tissues and exfoliated cells (EOCs) of the patients were 85% and 90%, respectively, whereas the corresponding values were 50% and 10% by the telomerase repeat amplification protocol. Furthermore, the positive rate for the ECTA was 100% in early tumors smaller than 2 cm, and 95% and 82% of biopsy and exfoliated cells of healthy individuals were correctly judged as negative. Fifty-six unknown samples with EOCs tested were correctly judged to be cancerous or normal in 84% of cases.

CONCLUSIONS

The ECTA yielded high hit rates for cancerous and normal cells, especially in EOCs, results indicating that this minimally invasive test is suitable for oral cancer diagnosis.

Selective immobilization of double stranded DNA on a gold surface through threading intercalation of a naphthalene diimide having dithiolane moieties

Newly synthesized naphthalene diimide 1 having two dithiolane moieties at its substituted termini bound to double stranded DNA by threading intercalation and the resulting complex was immobilized on the gold surface through a dithiolane-gold linkage as revealed by quartz crystal microbalance (QCM) experiments. DNA with 20-meric double stranded and 24-meric single stranded regions was indirectly immobilized on the gold electrode using this characteristic of 1. Hybridization efficiency was 92%, a value higher than 50% for a thiolated oligonucleotide under identical conditions. When this electrode was subjected to hybridization with a 124-meric target DNA in the presence of ferrocenylnaphthalene diimide (FND) as an electrochemical hybridization indicator, a large current increase was observed deriving from FND bound in the double stranded region newly formed between the probe and target DNA.

Substituted heterocyclic naphthalene diimides with unexpected acidity. Synthesis, properties, and reactivity

Naphthalene bisimides (NDIs) with a heterocyclic 1,4-dihydro-2,3-pyrazinedione moiety have been synthesized from both 2,6-dibromonaphthalene and 2,3,6,7-tetrabromonaphthalene bisanhydrides by means of a stepwise protocol including imidization, nucleophilic displacement of the bromine atoms by ethane-1,2-diamine, in situ reductive dehalogenation, and further oxidation. These heterocycles (R = n-pentyl, cyclohexyl) are yellow dyes with green emission in organic solvent, where the acid form dominates. The orange nonfluorescent conjugate base can be generated quantitatively by CH(3)COONBu(4) addition in DMSO, where it exhibits a pK(a) = 7.63. The conjugate base becomes the only detectable species (by UV-vis spectroscopy), in water solution, even under acid conditions (pH 1). In aqueous DMSO the acid/base equilibrium is a function of the DMSO/water ratio. The unexpected acidity of these heterocyclic NDIs, which justifies the reactivity with CH(2)N(2), has been rationalized by DFT computational means [PBE0/6-31+G(d,p)] in aqueous solvent (PCM models) as a result of a strong specific solvation effect, modeled by the inclusion of three water molecules.