Fluorescent diazapyrenium films and their response to dopamine

Experimental protocols for the preparation of 2,7-diazapyrenium films on glass, quartz, and silica in one or two steps have been developed. The one-step procedures involve the adsorption of preformed 2,7-diazapyrenium dications with trimethoxysilane appendages to the hydroxylated substrates. The two-step procedures consist in the formation of interfacial polysiloxanes with pendent chloromethyl groups and their subsequent coupling to monoalkylated 2,7-diazapyrene derivatives. For the modification of the glass slides, the silane building blocks have been copolymerized with Si(OEt)4. The transmission absorption spectra of the coated glass and quartz slides all reveal the characteristic bands of the 2,7-diazapyrenium chromophores. Combustion analyses confirm the adsorption of the 2,7-diazapyrenium dications on the silica particles. A comparison of the surface coverages of all films indicates that the one-step procedures are significantly more efficient than their two-step counterparts. Furthermore, the copolymerization of the silane building blocks with Si(OEt)4 translates into an increase in 2,7-diazapyrenium surface coverage of approximately 1 order of magnitude. The emission and excitation spectra of all modified substrates reveal the characteristic bands of the 2,7-diazapyrenium fluorophores. The fluorescence quantum yield, however, decreases as the surface coverage increases. Presumably, interactions between adjacent fluorophores encourage nonradiative deactivation pathways. With the exception of the glass slides modified in two steps, all films respond to the presence of dopamine, in aqueous environments at neutral pH, with pronounced decreases in emission intensity. The association of the 2,7-diazapyrenium acceptors and dopamine donors at the solid/liquid interface is responsible for fluorescence quenching. The glass slides and silica particles modified in one step are the most sensitive substrates and respond to sub-millimolar concentrations of dopamine with large changes in emission intensity. Furthermore, their fluorescence is not affected by relatively large concentrations of ascorbic acid, which is the main interferent in conventional dopamine detection protocols. Thus, these results demonstrate that the supramolecular association of 2,7-diazapyrenium dications and pi-electron rich substrates can be reproduced successfully at solid/liquid interfaces and suggest that the unique properties of 2,7-diazapyrenium films might lead to dopamine-sensing schemes based on fluorescence measurements

Supramolecular association of dopamine with immobilized fluorescent probes

We have designed a two-step procedure to coat silica particles with fluorescent 2,7-diazapyrenium dications. The electron-deficient character of the dications encourages the association of dopamine at the particle/water interface. The supramolecular event produces a significant decrease in the fluorescence intensity. Model binding studies with catechol and propylamine revealed that the interfacial complexation of dopamine is dominated by the interaction of its electron-rich dioxyarene fragment with the electron-deficient fluorophore in neutral aqueous environments

Photoinduced proton exchange between molecular switches

The identification of strategies to establish communication between independent molecules is an essential requirement for the development of operating principles to manipulate information at the molecular level. In this context, we have devised a strategy to exchange signals between pairs of complementary molecular switches. It is based on the photoinduced ring closing of a merocyanine to produce a spiropyran with the concomitant release of a proton. The liberated proton is captured by either one of two pyridine derivatives with the formation of their conjugate acids. This transformation induces a significant increase in chemical shift for the resonances of the pyridyl protons and, in one instance, also a pronounced color change. The overall process is fully reversible and the pair of communicating molecules reverts to the original state in the dark. Relying on this mechanism, an optical input is transduced into a detectable spectroscopic output after the controlled intermolecular exchange of protons. A simple analysis of the signal transduction operated by the communicating molecular switches reveals that a binary digit is passed unaltered from the input to the output even although the nature of the signal carrying the information changes at each step. Furthermore, the different nature of input and output implies that the state of the ensemble of molecules can be probed non-destructively at any point in time. The timescales of the switching steps, however, are seriously limited by the slow reaction kinetics. The photoinduced transformation occurs within minutes, but the thermal reaction reverts the switch state only after several hours. Graphical Abstrac

Memory effects based on intermolecular photoinduced proton transfer

We have identified a strategy to communicate a chemical signal between two independent molecular components. One of them is a photoactive merocyanine that switches to a spiropyran, releasing a proton, when stimulated with visible light. The other is a 4,4'-pyridylpyridinium monocation that captures the released proton, producing an electroactive 4,4'-bipyridinium dication. Under the irradiation conditions employed, the photoinduced transformation requires ca. 15 min to reach a photostationary state. In the dark, the ensemble of communicating molecules reequilibrates to the original state in ca. 5 days. These processes can be monitored following the photoinduced enhancement and thermal decay, respectively, of the current for the monolectronic reduction of the 4,4'-bipyridinium dication. The pronounced difference in time scale for the current enhancement and decay steps can be exploited to implement a memory element with a bit retention time of 11 h. A bit of information can be written optically in the chemical system and it can be read electrically and nondestructively. The memory can be reset, extending its permanence in the dark beyond the bit retention time. A binary logic analysis of the signal transduction operated by the communicating molecules reveals the characteristic behavior of sequential logic operators, which are the basic components of digital memories

Supramolecular assembly of 2,7-dimethyldiazapyrenium and cucurbit[8]uril: a new fluorescent host for detection of catechol and dopamine

The formation of a highly stable inclusion complex between 2,7-dimethyldiazapyrenium (Me(2)DAP(2+)) and the cucurbit[8]uril host (CB8) was demonstrated by X-ray crystallography; MALDI-TOF mass spectrometry; and (1)H NMR, electronic absorption, and emission spectroscopy. The equilibrium association constant was determined to be 8.9(+/-0.2)x10(5) L mol(-1) from UV-visible data and 8.4(+/-1.5) x 10(5) L mol(-1) from fluorescence data. The Me(2)DAP(2+).CB8 inclusion complex acted as a host to bind compounds containing aromatic pi-donor moieties (D), such as catechol and dopamine. This point was demonstrated by (1)H NMR spectroscopy, and electrochemical and emission measurements. Fluorescence detection of the Me(2)DAP(2+).D.CB8 ternary complexes was evident in aqueous solution and on the surface of silica particles, to which fluorescent diazapyrenium units had been covalently immobilized

A unique mucin immunoenhancing peptide with antitumor properties

Implantation of DA-3 mammary tumor cells into BALB/c mice results in tumor growth, metastatic lesions, and death. These cells were transfected with genes encoding for either the transmembrane (DA-3/TM) or secreted (DA-3/sec) form of human mucin 1 (MUC1). Although the gene for the secreted form lacks the transmembrane and cytoplasmic domains, the 5' sequences of these mucins are identical; however, the gene for the secreted mucin isoform ends with a sequence encoding for a unique 11 amino acid peptide. The DA-3/TM or DA-3 cells transfected with the neomycin vector only (DA-3/neo) have the same in vivo growth characteristics as the parent cell line. In contrast, DA-3/sec cells fail to grow when implanted in immunocompetent BALB/c animals. DA-3/sec cells implanted in nude mice resulted in tumor development verifying the tumorigenic potential of these cells. Pre-exposure of BALB/c mice to DA-3/sec cells afforded protection against challenge with DA-3/TM or DA-3/neo mammary tumors and the unrelated tumors K7, an osteosarcoma, and RENCA, a renal cell carcinoma. Partial protection against subsequent tumor challenges was also achieved by substituting the 11 amino acid peptide found only in the secreted MUC1 isoform, for the live DA-3/sec cells. Notably, the efficacy of this peptide is not strain restricted because it also retarded the growth of Lewis lung carcinoma cells in C57 BL/6 mice. These findings reveal that a unique peptide present in the secreted MUC1 has immunoenhancing properties and may be a potential agent for use in immunotherapy