Synthetic, crystallographic, computational, and biological studies of 1,4-difluorobenzo[c]phenanthrene and its metabolites

1,4-Difluorobenzo[c]phenanthrene (1,4-DFBcPh) and its putative metabolites, the dihydrodiol and diol epoxides, have been synthesized and structurally characterized, and the extent of DNA binding by the metabolites has been assessed. 1,4-DFBcPh and 1,4-difluoro-10-methoxybenzo[c]phenanthrene were prepared by photochemical cyclization of appropriate naphthylphenylethylenes. The dihydrodiol was synthesized from 1,4-difluoro-10-methoxybenzo[c]phenanthrene, and the diol epoxides were diastereoselectively synthesized from the dihydrodiol. Interesting differences were noted in 1H NMR spectra of the series 1 (syn) diol epoxides of benzo[c]phenanthrene (BcPh) and 1,4-DFBcPh; the BcPh diol epoxide displays a quasi-diequatorial orientation of the hydroxyl groups, but in the 1,4-DFBcPh case these are diaxially disposed. This difference probably stems from the presence of the fjord-region fluorine atom in 1,4-DFBcPh. A through-space, fjord-region H-F coupling has also been observed for 1,4-DFBcPh and its derivatives. Comparative X-ray crystallographic analyses of BcPh and 1,4-DFBcPh and their dihydrodiols show that introduction of fluorine increases the molecular distortion by about 6-7 degrees . As a guide to estimating the molecular distortion and its effects, and for comparison with the X-ray structures in known cases, optimized structures of BcPh, 1,4-DFBcPh, and 1,4-DMBcPh (the dimethyl analogue) as well as their dihydrodiols and diol epoxides were computed. Relative aromaticities of these compounds were assessed by nucleus-independent chemical shift calculations, and 13C NMR chemical shifts were computed by gauge-inducing atomic orbital calculations. 1,4-DFBcPh and its dihydrodiol were subjected to metabolism, and the amount of DNA binding in human breast cancer MCF-7 cells was assessed. The extent of DNA binding was then compared with that for BcPh and its dihydrodiol and the potent carcinogen benzo[a]pyrene. The 1,4-DFBcPh series 2 (anti) diol epoxide-derived DNA adducts were also compared with those arising from intracellular oxidation of the dihydrodiol with subsequent DNA binding. These experiments showed that increased molecular distortion decreased metabolic activation to the terminal metabolites but that diol epoxide metabolites that are formed are the DNA-damaging species.     

On the corrosion behavior of Al2Cu by local electrochemical impedance spectroscopy using droplet cell microscopy

Journal of Solid State Electrochemistry - In this short communication, we study the electrochemical behavior of an individual Al2Cu intermetallic phase (coexisting with α-Al) in 0.1 M...     

Scolecite as an efficient heterogeneous catalyst for the synthesis of 2,4,5-triarylimidazoles

Natural scolecite has been found as an effective catalyst for the one-pot synthesis of 2,4,5-triarylimidazole derivatives via a three component reaction using benzil or benzoin, aldehydes and ammonium acetate. This method provides several advantages such as being environmentally benign, reusable, possessing high yields with increased variations of the substituents in the product and preparative simplicity.      

Mixed cation effect and iodide ion conductivity in electrolytes for dye sensitized solar cells

Dye-sensitized solar cells (DSSCs) offer an alternative to conventional silicon solar cell because of low cost and easy fabrication. However, one major drawback in DSSCs is their low efficiency. This paper reports the effect of using a binary iodide salt mixture with different size cations on the efficiency enhancement in dye sensitized solar cells based on polymer gel electrolytes. Several different polymers, such as polyacrylonitrile (PAN), polymethylmethacrylate (PMMA), poly (vinylidenefluoride (PVdF)), and polyethylene oxide (PEO) have been used as host polymers. A binary iodide mixture consisting of an alkaline iodide salt (small cation) and a quaternary ammonium iodide salt such as tetrapropyl ammonium iodide (Pr₄NI) (large cation) has been used as the iodide ion source. In some of these systems, efficiency enhancement of more than 25% has been reached due to the “mixed cation effect”. From these studies, it was established that the variation of the power conversion efficiency with the concentration ratio of the two iodide salts follows the same trend as the short circuit current density (J _sc) and goes through a maximum at a particular salt concentration ratio. The maximum efficiency was found to be higher than the efficiencies of the DSSCs with only a single iodide salt in the electrolyte. The J _sc in these DSSCs appears to be governed by the iodide ion conductivity of the gel electrolyte. The observed efficiency enhancement has been explained on the basis of the electrode effects as well as electrolyte effects where the cations play a dominant role.

     

An Efficient Fluorescence “Turn-On” Chemosensor Comprising of Coumarin and Rhodamine Moieties for Al<Superscript>3+</Superscript> and Hg<Superscript>2+</Superscript>

A potent fluorescence ‘turn-on’ receptor (HL) based on rhodamine and coumarin moieties for the detection of Hg²⁺ and Al³⁺ is synthesized by condensation of rhodamine 6G hydrazide and 4-hydroxy-3-acetylcoumarin. In presence of Al³⁺ and/or Hg²⁺ the receptor (HL) exhibits deep pink colouration and a sharp band at 528 nm is appeared in UV–vis titration. Upon gradual addition of Al³⁺ and/or Hg²⁺ to the solution of HL significant enhancement of fluorescence intensity is observed at 564 nm in MeCN:H₂O (1:5, v/v) medium. The receptor is strongly bound to Al³⁺ and/or Hg²⁺ and the association constants (K_a) are found to be 1.74?×?10⁴ and 1.04?×?10⁴ M^??1 for Al³⁺ and Hg²⁺ respectively.

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Graphical Abstract A potent fluorescence ‘turn-on’ receptor (HL) based on rhodamine and coumarin moieties for the detection of Hg²⁺ and Al³⁺ is synthesized and characterized. In presence of Al³⁺ and/or Hg²⁺ the receptor (HL) exhibits deep pink colouration and significant enhancement of fluorescence intensity is observed at 564 nm in MeCN:H₂O (1:5, v/v) medium. The receptor is strongly bound to Al³⁺ and/or Hg²⁺ and the association constants (K_a) are found to be 1.74?×?10⁴ and 1.04?×?10⁴ M^??1 for Al³⁺ and Hg²⁺ respectively.

     

Tertiary Butyl Nitrite Triggered Nitration of Phenols: Solvent‐ and Structure‐Dependent Kinetic Study

Nitration of phenols with tertiary butyl nitrite (TBN) obeyed second‐order kinetics with a first‐order dependence on [TBN] and [phenol] under acid‐free conditions. Reaction rates were significantly altered by a change in the dielectric constant and other physical properties of solvent. The rate of nitration increased with an increase in temperature (303–323 K) in different solvent media (acetonitrile, dichloroethane, CCl₄, dimethyl formamide (DMF), and toluene). The rates of nitration (log k) could not fit into either Amis or Kirkwood plots [log k’ vs. (1/D) or [(D – 1)/(2D + 1)], but the trends were better explained by the basic form of multivariate linear solvent energy relationships (MLSER) suggested by the Koppel and Palm approach on the one hand and the Kamlet and Taft approach on the other hand. These observations probably substantiate that cumulative contributions of basic solvent parameters (equilibrium as well as frictional solvent effects) and solvent–solute interactions for solvation of transition state during nitration of phenols. Reaction rates accelerated with the introduction of electron‐donating groups and retarded with electron‐withdrawing groups. Accordingly, the reactivity of structurally different phenols was found to follow the following sequence: p‐OH > p‐MeO > p‐Me > H > m‐Me > p‐Cl > p‐Br > m‐Cl > p‐NO₂ > m‐OH. The results are interpreted by Hammett's theory of linear free energy relationship. The reaction constant (Hammett's ρ) is a measure of the sensitivity of the reaction toward the electronic effects of the substituent. The rho (ρ) values obtained from the present experiments are fairly large negative values (ρ < 0), indicating attack of an electrophile on the aromatic ring. An increase in temperature decreases the reaction constant (ρ) values. According to Exner, ρ values for a given reaction are influenced by the temperature according to the following relation: ρ = A [1 – β/T]. Obtained “isokinetic temperature (β)” values are in the range of 225–290. These values are far below the experimental temperature range (303–323 K), indicating that the entropy factors are probably more important in controlling the reaction. This point can be seen from the negative entropy values and linearity of multiple linear regression analysis (MLRA). Furthermore, in the present study, rate constants for TBN nitration of ortho‐substituted phenols could not fit into Taft's plots of log(k/k_CH3) versus σ* or, E_s or combined Taft's relationship. However, Charton's MLRA of the log k with polar, resonance, steric, hydrophobicity, and molar refractivity showing a very good linear relationship was obtained. It is of interest to note that when log k_exp values are correlated with log k_cal a perfect linearity is obtained with a correlation coefficient of unity, indicating the consonance between experimental and calculated rate constants in the present work.     

Synthesis and reactions of 2-chloro- and 2-tosyloxy-2'-deoxyinosine derivatives

Convenient syntheses of 2-chloro- and 2-tosyloxy-2'-deoxyinosine as their tert-butyldimethylsilyl ethers are described. Both compounds can be synthesized via a common route and rely on commercially available 2'-deoxyguanosine. The present method leading to the chloro nucleoside is operationally simpler compared to previously reported glycosylation techniques where isomeric products were obtained. Both electrophilic nucleosides can be used for the preparation of N-substituted 2'-deoxyguanosine analogues via displacement of the leaving groups, and a comparison of their reactivities shows the chloro analogue to be superior. Interestingly, a Pd catalyst-mediated, two-step, one-pot conversion of an allyl-protected chloro nucleoside intermediate to the final modified 2'-deoxyguanosine derivatives is also feasible. On the basis of these observations, initial assessments of Pd-catalyzed aryl amination as well as a C-C cross-coupling have also been performed with the chloro and tosyloxy nucleoside substrates. Results indicate a potentially high synthetic utility of 2-chloro-2'-deoxyinosine and in many instances this derivative can supplant the bromo and fluoro analogues that are more cumbersome to prepare or are not readily available.     

Facile Pd-catalyzed cross-coupling of 2'-deoxyguanosine O6-arylsulfonates with arylboronic acids

[reaction: see text]. The O6-(2-mesitylenesulfonyl) derivative of 2'-deoxyguanosine undergoes a facile palladium-mediated C-C cross-coupling with arylboronic acids. Demonstrating the general applicability of this method, the synthesis of a previously undescribed class of 2-amino-6-arylpurine 2'-deoxynucleosides has been accomplished. The study also describes an evaluation of the O6-(2,4,6-triisopropylphenylsulfonyl) and the O6-(4-toluenesulfonyl) derivatives for the cross-coupling.     

Application of symmetry coupling coefficients in the evaluation of the electronic spectra of d 7 ions

The optical absorption spectrum of cobalt chloride thiourea has been studied at room and liquid air temperatures. The results have been interpreted using group theoretical methods taking into account all the quartet states and several doublet states. Crystal field, electrostatic, and spin-orbit coupling interactions were included to yield the allowed transitions with the relative transition probabilities. The experimental results were interpreted for the following set of parameters: B = 750cm^–1, C = 3100cm^–1, = 7370cm^–1, = -200 cm^–1, = 500cm^–1, and = 450 cm^–1.     

Synthetic utility of an isolable nucleoside phosphonium salt

The reaction of O6-benzyl-3',5'-bis- O-( tert-butyldimethylsilyl)-2'-deoxyxanthosine with 1H-benzotriazol-1-yloxy-tris(dimethylamino)phosphonium hexafluorophosphate (BOP) yielded the nucleoside C-2 tris(dimethylamino)phosphonium hexafluorophosphate salt as a stable, isolable species. This is in contrast to reactions of inosine nucleosides with BOP, where the in situ formed phosphonium salts undergo subsequent reaction to yield O6-(benzotriazol-1-yl)inosine derivatives. The phosphonium salt obtained from the 2'-deoxyxanthosine derivative can be effectively used to synthesize N2-modified 2'-deoxyguanosine analogues. Using this salt, a new synthesis of an acrolein-2'-deoxyguanosine adduct has also been accomplished.