Does phenazine form triplet excimer and dimer anion radical?

Laser flash photolysis of phenazine (PZ) solution reveals the existence of a stable species with a long lifetime at 380 nm in addition to the usual triplet PZ at 440 nm. The former is suggested to be due to formation of triplet PZ excimer. The triplet excimer also undergoes photoinduced electron transfer with some aromatic amines. The formation of PZ dimer anion radical and amine cation radicals are confirmed by external magnetic field effect studies. Measurement of B_1/2, which estimates hyperfine present in the system, also supports this assignment.     

Preparation of Aryl‐Substituted E‐Homoallylic Bromides from Cyclopropylcarbinol and PBr3

An expeditious synthesis of aryl substituted E‐homoallylic bromides has been accomplished by the cleavage of cyclopropylcarbinols with phosphorus tribromide.     

Thermal studies of furosemide–caffeine binary system that forms a cocrystal

Thermal techniques, differential scanning calorimetry (DSC), and hot stage microscopy (HSM) have been used to study the interactions between furosemide and caffeine that are known to form a 1:1 cocrystal. This system has been used as an example to study the probable mechanism of cocrystal formation when the individual components, which are polymorphic, are heated. The study indicates that the phase transition of the low temperature stable polymorph of furosemide initiates cocrystal formation. This result suggests increased mass transfer rate can trigger cocrystal formation. The binary phase diagram (composition–temperature plots) of furosemide–cocrystal–caffeine system was determined from the DSC curves. The results imply that the cocrystal forms eutectic with caffeine but not with furosemide. This study has thus exemplified the use of DSC in understanding binary phase system where the two components form a cocrystal.     

Tunneling Assists the 1,2‐Hydrogen Shift in N‐Heterocyclic Carbenes

At room temperature, 1,2‐hydrogen‐transfer reactions of N‐heterocyclic carbenes, like the imidazol‐2‐ylidene to give imidazole is shown to occurr almost entirely (>90 %) by quantum mechanical tunneling (QMT). At 60 K in an Ar matrix, for the 2, 3‐dihydrothiazol‐2‐ylidene→thiazole transformation, QMT is shown to increase the rate about 10⁵ times. Calculations including small‐curvature tunneling show that the barrier for intermolecular 1,2‐hydrogen‐transfer reaction is small, and QMT leads to a reduced rate of the forward reaction because of nonclassical reflections even at room temperature. A small barrier also leads to smaller kinetic isotope effects because of efficient QMT by both H and D. QMT does not always lead to faster reactions or larger KIE values, particularly when the barrier is small.     

Medium-dependent electron and H atom transfer between 2'-deoxyadenosine and menadione: a magnetic field effect study

The interaction between 2'-deoxyadenosine and the model antitumor drug menadione has been studied in organic solvent and in micellar medium. The aim of the work is to elucidate the mechanism of this drug-nucleoside interaction and to determine the environmental effects. Laser flash photolysis and magnetic field effect are used to detect the transients and their spin states. The results indicate that H atom transfer and electron transfer are the operative mechanisms depending upon the medium.     

Surfactant-induced aggregation patterns of thiazole orange: a photophysical study

The aggregation behavior of the DNA marker dye thiazole orange (TO), has been investigated in two types of surfactant assemblies, namely, premicelles/micelles of sodium dodecyl sulfate (SDS) and pre reverse micelles/reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT). In the case of an SDS/water system, absorption spectral changes of TO signify the formation of H-aggregates and H-dimers of the dye at premicellar concentrations, which subsequently convert to the monomeric form beyond the critical micellar concentration (cmc). Interestingly, the observed changes in the absorption and emission characteristics due to the surfactant-induced formation of H-aggregates/dimers of TO are found to be useful to estimate the surfactant concentration parameters for premicellar aggregation of SDS. In the case of an AOT/n-heptane system, similarly, H-aggregates/dimers are observed at low AOT concentrations, below the cmc. However, in this case, the H-dimers persist even beyond the cmc. This is attributed to the strong tendency of TO for self-aggregation and its favorable electrostatic interactions with the AOT head groups. With increasing water content in the AOT reverse micelles, the hydration of the dye leads to the conversion of H-dimers to the monomeric form. The steady-state fluorescence results are nicely corroborated with those from time-resolved fluorescence studies and demonstrate the interesting behavior of the surfactant-induced aggregation of TO dye.     

Surface functionalized silver nanoparticle conjugates: demonstration of uptake and release of a phototherapeutic porphyrin dye

A facile supramolecular approach to prepare surface functionalized silver nanoparticle conjugates has been established and their enhanced molecular recognition features have been explored to demonstrate the uptake and stimulus responsive release of a phototherapeutic porphyrin dye, the TMPyP.     

Interaction of 4-nitroquinoline-1-oxide with indole derivatives and some related biomolecules: a study with magnetic field

Laser flash photolysis and an external magnetic field have been used for the study of the interaction of 4-nitroquinoline-1-oxide (4NQO) with some indole derivatives, amino acids, tyrosine and tryptophan, and model proteins, lysozyme and bovine serum albumin. In an aprotic medium, photoinduced electron transfer (PET) from indoles to 4NQO is accompanied by proton transfer from the indole moieties irrespective of the substitution at the N-1 position. For 1,2-dimethylindole, however, proton abstraction is hindered possibly due to steric effects. In a protic medium, obviously proton transfer is possible from the medium and is the dominating reaction following PET. The effect of an external magnetic field is very small for all the systems studied. This is attributed to a competition between geminate proton abstraction by the 4NQO radical anion from the partner radical cation and escape of the 4NQO radical anion to the medium followed by proton transfer. The latter process is more predominant, and the former one, which produces a small population of geminate spin-correlated radical pairs, leads to a minor field effect. Another interesting observation is the affinity of 4NQO toward the tryptophan residues in a protein environment. It is seen that PET takes place preferably from the tryptophan residues rather than from the tyrosine residues.     

Structural and magnetic study of swift heavy ion irradiated W/Fe multilayer structure

The present study reports the effect of swift heavy ion irradiation on structural and magnetic properties of sputtered W/Fe multilayer structure (MLS) having bilayer compositions of [W(10 Å)/Fe(20 Å)]_10BL. The MLS is irradiated by 120 MeV Au⁹⁺ ions of fluences 1×10¹³ and 4×10¹³ ions/cm². Techniques like X-ray reflectivity (XRR), cross-sectional transmission electron microscopy (X-TEM) and DC magnetization with a vibrating sample magnetometer (VSM) are used for structural and magnetic characterization of pristine and irradiated MLS. Analysis of XRR data using Parratt’s formalism shows a significant increase in W/Fe layer roughness. X-TEM studies reveal that intra-layer microstructure of Fe layers in MLS becomes nano-crystalline on irradiation. DC magnetization study shows that with spacer layer thickness interlayer coupling changes between ferromagnetic to antiferromagnetic.     

Design and synthesis of fluorescent symmetric bis-triazolylated-1,4-dihydropyridines as potent antibreast cancer agents

Herein, we report the synthesis of fluorescent 1,4-dihydropyridine-linked bis-triazoles (2a–2n) through Hantzsch synthesis by the condensation of o/m-chloro-substituted benzaldehyde, ethyl 3-oxo-4(prop-2-yn-1-yloxy)butanoate, and ammonium acetate in the presence of Ba(NO₃)₂ as a catalyst followed by the click reaction of resultant Hantzsch product (1) with various aromatic as well as aliphatic azides. All the synthesized compounds were well characterized by ¹H-NMR, ¹³C-NMR, FTIR, and HRMS spectral techniques. Antibreast cancer evaluation of all the synthesized derivatives revealed that the compounds 2f (IC₅₀?=?7?±?0.02?µM) and 2g (IC₅₀?=?5?±?0.03?µM) showed better anticancer activity (lower IC₅₀) than the standard drug tamoxifen (IC₅₀?=?11.2?±?0.01?µM) against breast carcinoma (MDA-MB-231) cell line. The synthesized compounds were also screened against normal human embryonic kidney (HEK-293) cell line and found to be nontoxic. The fluorescent nature and cytotoxicity assay of these newly synthesized hybrids recommend their utility in tumor cell imaging.