2.7- Diazapyrenium

A similar, but covalent, approach was employed by Raymo and Cejas, who functionalized the surface of commercially available silica nanoparticles (20 nm diameter) with 2,7-diazapyrenium dications and used them for the detection of dopamine in... 

Figure 9 Molecular structures of ethidium bromide (EB+), protonated acridinium orange (AOH+), and yV,yV -dimethyl-2,7-diazapyrenium dichloride (DAP2+). Each of these molecules is known to intercalate into duplex DNA.

The monofunctional complexes [PtCl(dien)]+, [PtCl(NH3)3]+, and the active d.v-compounds cA-[PtCl(NH3)2 (Am)]+, where Am is an heterocyclic or aromatic amine ligand like pyridine, pyrimidine, purine, or aniline, only form stable monoadducts with DNA [50][51]. However, when Am = A-methyl-2,7-diazapyrenium (a strong intercalator), the monoadduct is stable only on single-stranded DNA. On double-stranded DNA it is hydrolyzed with release of c T-[Pt(NH3)2(Am)(H20)]3+ or of Am generating the aqua monoadduct of cisplatin [52],... 

Substantial efforts have been devoted to the development of molecular sensors for dopamine. Raymo et al.70 reported a two-step procedure to coat silica particles with fluorescent 2,7-diazapyrenium dications sensing toward dopamine. The analysis of the fluorescence decay with multiple-equilibria binding model revealed that the electron deficient dications and the electron-rich analytes form 1 1 and 1 2 complexes at the particle/water interface. The interfacial dissociation constants of the 1 1 complexes were 5.6mM and 3.6mM for dopamine and catechol, respectively. Dopamine was dominated by the interaction of its electron-rich dioxyarene fragment with the electron-deficient fluorophore in neutral aqueous environments. Ahn et al.71 reported tripodal oxazoline-based artificial receptors, capable of providing a preorganized hydrophobic environment by rational design, which mimics a hydrophobic pocket predicted for a human D2 receptor. A moderate binding affinity, a dissociation constant of 8.2 mM was obtained by NMR titrations of tripodal oxazoline-based artificial receptor with dopamine in a phosphate buffer solution (pH 7.0). Structurally related ammonium ions, norepinephrine, 2-phenylethylamine,... 

EB) and -dimethyl-2,7-diazapyrenium dichloride (DAP) intercalate between base pairs in... 

N-Debenzylation. N-Benzylpyrrolidine and a little 9,10-dicyanoanthracene as electron acceptor in 7 3 acetonitrile/water irradiated for 6-10 h in a Pyrex tube with a 450 W Hanovia lamp (405 nm) fitted with a CuS04 NH3 soln. filter - pyrrolidine, Y 90%. The method is not applicable to deprotection of a-aminoacids. F.e.s. G. Pandey, K.S. Rani, Tetrahedron Letters 29, 4157-8 (1988) N-demethylation with N,N -dimethyl-2,7-diazapyrenium fluoroborate as electron acceptor s. J. Santamaria et al., ibid. 30, 2927-8 (1989) review of photo-induced electron transfer s, J, Mattay, Synthesis 1989, 233-52 review of single electron transfer (SET) s. E.C. Ashby, Acc. Chem. Res. 21, 414-21 (1988) review of new developments in photochemical synthesis s. M. Demuth, G. Mikhail, Synthesis 1989, 145-62. 

The role of photochemistry and photophysics in most applications of supramolecular chemistry is all important also with organic compounds. As an example, the system composed of a crown ether containing re-electron donating naphthalene units and a 2,7-diazapyrenium re-electron acceptor (see formulae below) associates with a large equilibrium constant in organic solution and yields a pseudorotaxane-type complex. 

Leventis N, Elder lA, Rolison DR, Anderson ML, Merzbacher Cl (1999) Durable Modification of Silica Aerogel Monoliths with Fluorescent 2,7-Diazapyrenium Moieties. Sensing Oxygen near the Speed of Open-Air Diffusion. Chem Mater 11 2837-2845... 

Leventis, N, Elder, I A, Rolison, D R, Anderson, M L, Merzbacher, CI (1999) Durable modiheatitm of sUica aerogel monoliths with fluorescent 2,7-diazapyrenium moieties sensing oxygen near the speed of open-air diffusion. Chem Mater 11 2837-2845. 

Initially, PET in DNA was studied using the electron donors and acceptors intercalated in DNA in a random manner. In 1992, Harriman and Brun reported fluorescence lifetimes of calf thymus DNA using ethidium bromide (EB+) and V,V -dimethyl-2,7-diazapyrenium dichloride (DAP +) as intercalators. They found the short fluorescence lifetime components to be due to PET between EB+ and DAP +. On the basis of the assumption that PET occurred between EB+ and DAP + separated by 3-5 base pairs, PET rates were estimated. Since the electron transfer rate ( et) can be expressed as a function of the donor-acceptor distance (r) in (7), the value was evaluated to be 0.88 a value close to that estimated for proteins. 

A series of tryptycene-derived homooxacalixarenes (6) was conveniently prepared by a one-pot approach starting from 2,7-dihydroxytriptycene and l,3-bis(bromomethyl)benzene derivatives under mild conditions (13JOC981).Tryptycene-derived macrotricyclic polyethers containing two dibenzo [30] crown-10 cavities and different functionalized paraquat derivatives, diquat, and a 2,7-diazapyrenium salt in both the solid state and in solution were studied (13JOC3235). The first organometallic (Pd) complexes of an oxacalixarene were prepared by oxidative addition of the C-I bond on the lower rim (13IC6779). 

The practical and effective synthesis of photoactive lanthanide cryptates (1), capable of effective light conversion, has found application in the design of novel fluorescent immunoassay systems. The macrobicyclic bipyridyl cryptands prevent the normal solvation quenching of these cations. Remarkably effective DNA cleavage was accomplished using intercalators (2) based on 2,7-diazapyrenium cations. 

Highly-polymerized deoxyribonucleic acid, (DNA), from calf-thymus, was purchased from Sigma Chem. Co. and used as received. Stock solutions of DNA were prepared by dissolution overnight in 5 mM phosphate pH 7 buffer and were stored at 4°C in the dark for short periods only. Concentrations of DNA per nucleotide phosphate were determined by absorption spectroscopy using a molar extinction coefficient of 6,600 M cm at 260 nm [4]. N,N -Dimethyl-2,7-diazapyrenium dlchloride (DAP " ") was prepared and purified according to the method of HUnig et al. [5] whereas ethidium bromide (EB ) was purchased from Sigma Chem. Co. and used as received. 

Intercalation of ethidium bromide (EB ) into calf-thymus DNA (5 mM phosphate buffer, pH 7) occurs with a saturation of 0.4/base-pair and, at [EB ] = 67 nK and [DNA-bases] = 1.4 mM, more than 99% of EB will be intercalated. Assuming a nonrandom distribution, the average distance between chro-mophores is 10 base-pairs ( 34 A). Fluorescence from Intercalated EB decays with a lifetime (tq) of (21.1 0.1) ns, compared to (1.6 0.1) ns in water. Upon addition of N,N -dimethyl-2,7-diazapyrenium dichloride (DAP ), which intercalates with high affinity, fluorescence from EB was quenched and decay profiles became markedly non-exponential, even at very low concentrations of quencher. 

A covalent capsule 251 (Scheme 6.31) exhibits an ON/OFF caging ability relative to guest 2,7-diazapyrenium derivatives, forming the corresponding cage complexes with only a cis-isomer of the ligand. The photocontrolled process... 

Fig. 5.14 The self-assembly of the 2,7-diazapyrenium dication r and the crown ether 2 to give the pseudorotaxane [1 2] ...

Chart 6.1 Structural formulas of the wheel CX and N,N -di(iecyl-2,7-diazapyrenium thread-like molecule 1-2PF6... 

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