Synthesis of new ESIPT-fluorescein: photophysics of pH sensitivity and fluorescence

ESIPT-inspired benzimidazolyl substituted fluorescein dyes were synthesized. PH-sensitivity was determined by the photophysical property measured at a physiological possible pH range. Fluorescence quantum efficiency values were calculated independently at two different emissions. A rational relationship is defined between fluorescence quantum efficiency and calculated HOMO energy.     

Potentiometric Study of Coated Graphite Electrode and Polymeric Membrane Electrode for the Determination of Sm3+ Ion

Preliminary studies on the two Schiff bases N2‐((3H‐indol‐3‐yl)methylene)‐6‐phenyl‐1,3,5‐triazine‐2,4‐diamine (L₁) and N2,N4‐bis((3H‐indol‐3‐yl)methylene)‐6‐phenyl‐1,3,5‐triazine‐2,4‐diamine (L₂) have shown that they can act as Sm³⁺ selective electrodes. The performances of a polymeric membrane electrode and a coated graphite electrode based on L₂ were compared and the CGE proved to be better, as it shows a low detection limit of 1.8×10^?8 mol L^?1, a Nernstian slope of 19.6±0.4 mV decade^?1 of activity with a response time of 11 s in the pH range of 3.0–9.0. The CGE was used to determine Sm³⁺ in medicinal plants and soil samples. It was also used to determine fluoride ions in mouthwash samples and in toothpaste.     

Oligoethylene glycols as highly efficient mutifunctional promoters for nucleophilic-substitution reactions

Herein, we report the promising use of n-oligoethylene glycols (oligoEGs) as mutifunctional promoters for nucleophilic-substitution reactions employing alkali metal salts. Among the various oligoEGs tested, pentaethylene glycol (pentaEG) had the most efficient catalytic activity. In particular, when compared with other nucleophiles examined, a fluorine nucleophile generated from CsF was significantly activated by the pentaEG promoter. We also performed various facile nucleophilic-displacement reactions, such as the halogenation, acetoxylation, thioacetoxylation, nitrilation, and azidation of various substrates with potassium halides, acetate, thioacetate, cyanide, and sodium azide, respectively, in the presence of the pentaEG promoter. All of these reactions provided their desired products in excellent yields. Furthermore, the combination of pentaEG and a tert-alcohol medium showed tremendous efficiency in the nucleophilic-displacement reactions (fluorination and methoxylation) of base-sensitive substrates with basic nucleophiles (cesium fluoride and potassium methoxide, respectively). The catalytic role of oligoEGs was examined by quantum-chemical methods. The oxygen atoms in oligoEGs were found to act as Lewis bases on the metal cations to produce the "flexible" nucleophile, whereas the two terminal hydroxy (OH) groups acted as "anchors" to orientate the nucleophile and the substrate into an ideal configuration for the reaction.     

Oxidative cleavage of alkenes using an in situ generated iodonium ion with oxone as a terminal oxidant

A facile and operationally convenient catalytic procedure for oxidative cleavage of alkenes is described. In situ formed [hydroxy(4-carboxyphenyl)iodonium]ion, 2, from the oxidation of 4-iodobenzoic acid, 1, has been shown to facilitate the cleavage of a variety of alkenes in presence of Oxone as a co-oxidant. Optimization of the reaction conditions using 1-phenyl-1-cyclohexene, 3, and the competitive oxidative cleavage of different substrates using the optimized conditions has uncovered important mechanistic details of the reaction.     

A novel naphthoquinone from <Emphasis Type="Italic">Plumbago zeylanica</Emphasis> roots

A novel naphthoquinone (1) was isolated from the methanol extract of P. zeylanica roots in addition to a known compound plumbagin (2). Their structures were determined by UV, IR, MS, ¹H, and ¹³C NMR spectroscopic analysis, including 2D NMR.     

Covalent microcontact printing of proteins for cell patterning

We describe a straightforward approach to the covalent immobilization of cytophilic proteins by microcontact printing, which can be used to pattern cells on substrates. Cytophilic proteins are printed in micropatterns on reactive self-assembled monolayers by using imine chemistry. An aldehyde-terminated monolayer on glass or on gold was obtained by the reaction between an amino-terminated monolayer and terephthaldialdehyde. The aldehyde monolayer was employed as a substrate for the direct microcontact printing of bioengineered, collagen-like proteins by using an oxidized poly(dimethylsiloxane) (PDMS) stamp. After immobilization of the proteins into adhesive "islands", the remaining areas were blocked with amino-poly(ethylene glycol), which forms a layer that is resistant to cell adhesion. Human malignant carcinoma (HeLa) cells were seeded and incubated onto the patterned substrate. It was found that these cells adhere to and spread selectively on the protein islands, and avoid the poly(ethylene glycol) (PEG) zones. These findings illustrate the importance of microcontact printing as a method for positioning proteins at surfaces and demonstrate the scope of controlled surface chemistry to direct cell adhesion.     

Evaluation of nonlinear quantum time correlation functions within the centroid dynamics formulation

A method to evaluate nonlinear centroid correlation functions is presented that is amenable to simple numerical computation. It can be implemented with the centroid molecular dynamics method for approximate quantum dynamics with no additional assumptions. Two nonlinear correlation functions are evaluated for a model potential using this scheme and compared with results from exact quantum calculations.     

Cleavage of activated cyclic amines: Unprecedented approach toward 2-substituted cyclobutanones

We report, for the first time, ring opening of activated four- to six-membered cyclic amines followed by an intramolecular expansion of cyclopropanol to cyclobutanone via carbocation intermediate. In the case of a N-tosylaziridine ester, a cyclobutanol was formed in a stereospecific manner during the Kulinkovich reaction step.     

Enantioselective one-pot three-component synthesis of propargylamines

[reaction: see text] A copper(I) complex of i-Pr-pybox-diPh has been found to be an efficient catalyst for an enantioselective one-pot three-component synthesis of propargylamines from aldehydes, amines, and alkynes. The reaction has been applied to a wide variety of aromatic aldehydes with excellent yields (up to 99%) and enantiomeric excesses (up to 99% ee). A transition-state model has been proposed to explain the stereochemical outcome of the reaction.