Fluorogenic sensing of CH3CO2- and H2PO4- by ditopic receptor through conformational change

Cyclo-bis-(urea-3,6-dichlorocarbazole) (1) forms a 1 : 2 complex with CH(3)CO(2)(-) and H(2)PO(4)(-) through hydrogen bonding with the two urea moieties, resulting in fluorescence enhancement via a combined photoinduced electron transfer (PET) and energy transfer mechanism. The binding mechanism involves a conformational change of the two urea receptors to a trans orientation after binding of the first anion, which facilitates the second interaction.     

Design and development of an optical beam splitter assembly and high precision colinearity measurements of laser beams

Laser beams with extremely high colinearity are often required where precision position monitoring is important. In order to achieve the said objective, a special type of Laser Beam Splitter Assembly (BSA) has been designed and fabricated in a very small volume due to space constraints. The main features and details of such a system are described here. This type of beam splitter assembly coupled with a diode laser through fibers can be remotely used for alignment or position monitoring of different medium to large size structures with a reconstruction accuracy of 10 μm. In this way, BSA generates two counter propagating laser beams from a single diode laser coupled to an optical fiber. In the present work, the colinearity between two beams within 1 mrad with the variation of 50 μrad has been achieved. The laser's power in the two arms may be controlled precisely, which is an important feature of this BSA. The BSA has been tested to work over a temperature range between ?20 °C to +40 °C. It has also been exposed to 1.0 MeV neutrons at a flux of ～5.0×10¹⁰ n/cm²/s and found compatible.     

Shape-directing role of cetyltrimethylammonium bromide in the preparation of silver nanoparticles

We report a simple chemical reduction method for the synthesis of different colored silver nanoparticles, AgNP, using tyrosine as a reducing agent. Effects of cetyltrimethylammonium bromide, CTAB, and tyrosine concentrations are analyzed by UV-visible measurements and scanning electron microscopy (SEM) to evaluate the mode of AgNP aggregation. The position and shape of the surface resonance plasmon absorption bands strongly depend on the reaction conditions, i.e., [CTAB], [tyrosine], and reaction time. Sub-, post-, and dilution-micellar effects are accountable for the fast and slow nucleation and growth processes. Spectrophotometric measurement also shows that the average size and the polydispersity of AgNP increase with [CTAB] in the solution. CTAB acted as a shape-directing agent.     

Synthesis and Antibacterial Activity of Certain Fused Azoles and Oxazinones

2‐Phenyl‐4‐benzylidene‐5(4H)‐oxazolones ( 1a‐e) were used as versatile starting materials for the synthesis of fused compounds such as: 4H‐3,1‐benoxazin‐4‐ones (2a,b), imidazo[4,3‐b]benzimidazoles (3,4), imidazo[1,5‐b]1,2,4‐triazoles (5a,b), and 7 .     

Synthesis and antimicrobial activity of substituted [(pyrazol‐4‐yl)methylene]hydrazono‐2,3‐dihydrothiazoles and their sugar derivatives

A number of new [(pyrazol‐4‐yl)methylene]hydrazono‐2,3‐dihydrothiazole derivatives, their sugar hydrazones and N‐glycosides were synthesized. Furthermore, N‐substituted oxygenated alkyl and hydroxyl derivatives and 1,3,4,‐oxadiazoline acyclic nucleoside analogs were prepared. The newly synthesized compounds were tested for their antimicrobial activities and showed moderate to high inhibition activities. J. Heterocyclic Chem., (2012).     

Antimicrobial agents as photostabilizers for rigid poly(vinyl chloride)

Some amide derivatives of ethylene glycol‐bis(2‐aminoethylether)‐N,N,N^′,N^′‐tetraacetic acid (EGTA) have been prepared via their coupling with different aniline derivatives: amino, methyl, chloro, and hydroxy aniline. The EGTA amide derivatives were characterized, and their antimicrobial activities were evaluated. These antimicrobial agents have been investigated as photostabilizers for rigid poly(vinyl chloride) (PVC), suspension PVC, with a K value of 70. Their stabilizing efficiencies were evaluated by determining the percentage of weight loss, the intrinsic viscosities, as well as the amount of formed gel of the photodegraded PVC. The extent of discoloration and the change in the mechanical properties of the photodegraded polymer were also evaluated. The applied materials reduced the loss in weight that resulted from HCl evolution during photodegradation. Both viscosity and gel content measurements showed also a decrease in their values during the degradation process. The decrease in the percentage of gel formation upon applying the investigated photostabilizers reflects the lowering in extent of cross‐linking of the polymer, which implies preserving the mechanical properties of PVC. The extent of discoloration was also improved in the presence of the investigated compounds. The results have proved a greater stabilizing efficiencies of the antimicrobial EGTA amide derivatives than that of the phenyl salicylate ultraviolet (UV) absorber, which is commonly used as an industrial stabilizer. A radical mechanism was proposed to account for the stabilizing action of the investigated products. Copyright © 2011 John Wiley & Sons, Ltd.     

Energetics of anionic surfactant-additive systems at the cloud point

The energetics of clouding in anionic surfactant (SDBS) and tetrabutylammonium bromide system in the presence of additives, such as ureas, amino acids and sugars is reported. The change of standard Gibbs energy of solubilization (ΔG _s ^o) for all of the additives was found to be negative. The values of change of standard enthalpy (ΔH _s ^o) and that of standard entropy (TΔS _s ^o) values were found to depend on the type and chemistry of the additive. The results were explained on the basis including chemistry of additives, their effect on water structure, and solubilization of additives either in the micellar or in aqueous phases.     

The interaction of <Superscript>99m</Superscript>Tc with pyrimidine compounds

The reaction of ^99mTc of different oxidation states (+7, +4) with 2-thiouracil and 5-nitrobarbituric acid have been studied at different temperatures, pH and concentrations. The reaction mixtures have been analyzed at different times using thin layer chromatography (TLC) and a radio detector to show the peaks at the plates. ^99mTc is obtained from the Mo generators with oxidation state (+7). The use of SnCl₂ as a reducing agent gave ^99mTc with oxidation state (+4). It is very difficult to separate the complexes formed from the reactions in very small concentration. The percentage of ^99mTc and its oxidation state involved in the complexes can be determined. The labeling efficiencies (percentage of complex) in the reaction of ^99mTc⁺⁷ with 5-nitro-barbituric-acid increases mostly at pH  10. Both oxidation states of ^99mTc(+7, +4) can be detected at pH’s 4 and 10, but at pH  4, the reduced form ^99mTCO₂, is more pronounced. At pH  7 no complexes were detected and most of ^99mTc remains as ^99mTCO₄ ⁻ . By increasing the ligand concentration, the labeling efficiencies of the complex increases. For the reaction of ^99mTc of oxidation states (+4, +7) with 2-thiouracil at different temperatures and analytical times it is concluded that several complexes with different R_f values were observed in equilibrium and most of these complexes were unstable.     

Labeling of new formulation of tin–sucralfate freeze-dried kit with technetium-99m and its biological evaluation

The present investigation deals with a simple preparation of new formulation of tin?Csucralfate freeze-dried kit (F.D.K.), to be directly labeled with ^99mTc at optimal pH value of 7.0. The lyophilized form containing 100?mg sucralfate and 11.3?mg dihydrated stannous chloride. Other optimal pH values of the preparation were found to be from 4.0 to 11.0. The range of sucralfate amount studied (50?C500?mg) not affected the radiochemical purity of the labeled complex. The radiochemical purity and the stability of the labeled preparation that assessed by filtration were more than 95%. ^99mTc sucralfate was radiochemical stable up to a specific activity of 1,000?mCi per gram which was more stable than earlier published value (700?mCi per gram) without any radiolytic decomposition. The biological behavior of ^99mTc-pertechnetate was evaluated in two groups of animals, the first group (neither fasted nor ulcerated) and the second group (fasted and ulcerated mice). The data of organ distribution of ^99mTc?Csucralfate in ulcerated fasted mice showed that more than 99% of the administered dose was accumulated in the stomach (87.92%) and intestine (11.43%). The radioanalytical results together with the in vivo-biological behavior of the labeled preparation demonstrate it??s stability, efficacy and usefulness in medical applications for the detection of gastrointestinal ulcers.     

Spectroscopic and Electrochemical Study of the Interconversion and Decomplexation of Cobalt(II) Sandwich Polyoxometalates Based on a Dawson-Type Anion

The reaction of the trivacant Dawson polyoxometalate α-[P(2)W(15)O(56)](12-) and the divalent cations Co(2+) is known to form a symmetrically derived sandwich complex of formula ββ-[Co(4)(H(2)O)(2)(P(2)W(15)O(56))(2)](16-) [symbolized as ββ-Co(4)(P(2)W(15))(2)] at low pH (ca. pH 3). We have shown previously that, by a slight modification of the reaction conditions, trinuclear αβ-[(NaOH(2))Co(3)(H(2)O)(P(2)W(15)O(56))(2)](17-) and dinuclear [(NaOH(2))(2)Co(2)(P(2)W(15)O(56))(2)](18-) complexes [symbolized as αβ-NaCo(3)(P(2)W(15))(2) and Na(2)Co(2)(P(2)W(15))(2), respectively] can be synthesized as aqueous-soluble sodium salts. αβ-NaCo(3)(P(2)W(15))(2) is a "lacunary" sandwich complex that can add a Co(2+) cation to form nearly quantitatively an unsymmetrical Dawson tetracobalt sandwich polyoxometalate, αβ-[Co(4)(H(2)O)(2)(P(2)W(15)O(56))(2)](16-) [symbolized as αβ-Co(4)(P(2)W(15))(2)]. Thus, for Co(4)(P(2)W(15))(2), the junctions between the trivacant {P(2)W(15)} subunits and the central tetrameric unit can be either both β type or β and α types. The interconversion between αβ-Co(4)(P(2)W(15))(2) and ββ-Co(4)(P(2)W(15))(2) and the decomplexation process at low pH, leading to the formation of αβ-NaCo(3)(P(2)W(15))(2) and/or Na(2)Co(2)(P(2)W(15))(2), have been followed in aqueous solution at various pH values by electrochemistry, UV-visible absorption spectroscopy, and (31)P NMR spectroscopy.