Excited state intramolecular proton transfer in a new o-hydroxy Schiff base in non polar solvents at room temperature and 77 K

A new orthohydroxy Schiff base, 7-ethylsalicylidenebenzylamine (ESBA) has been synthesised. The excited state intramolecular proton transfer (ESIPT) processes have been investigated by means of absorption, emission and nanosecond spectroscopy at room temperature and at 77 K in non polar solvents. The ESIPT is evidenced by a large Stokes shifted emission (11 000 cm⁻¹) only at 77 K. From fluorescence and excitation spectra it is suggested that at least three different species are present in the excited state at room temperature. Our theoretical calculation at AM1 level confirm the cis-isomer to be the only viable form in the ground state.     

Highly efficient water promoted allylation and propargylation of arylepoxides via rearrangement-carbonyl addition

A simple and highly efficient one-pot procedure for allylation and propargylation of arylepoxides has been developed. A combination of SnCl₂ and catalytic Pd(0) or Pd(II) promotes the reaction of organic halides and epoxides in DMSO with controlled water addition, leading to the regioselective formation of the corresponding homoallyl and homopropargyl alcohols in good yields.     

Absorption and fluorescence behavior of cytosine irradiated at different pH and in the presence of Cu(II) ions at neutral pH

Dilute aqueous solutions of cytosine were irradiated with⁶⁰Co -rays under N₂O saturated conditions at different pH and in the presence of Cu(II) ions at neutral pH. The base degradation decreased from neutral to acidic and basic conditions. In the presence of metal ions at neutral pH conditions there was a significant increase in the base degradation compared to that in the absence of metal ions under similar conditions. From the difference absorption spectra and fluorescence behavior of the irradiated solutions it was observed that the major radiolytic products of cytosine under different conditions are cytosine glycols, 5-hydroxycytosine, hydroxy-hydrocytosine and cytosine dimers. The yields of dimers is maximum in neutral conditions and it decreased from basic to acidic conditions. However, in the presence of Cu(II) ions formation of cytosine dimers is completely restricted and there is an increase in the yields of cytosine glycol, hydroxy-hydrocytosine and 5-hydroxycytosine. From the post-radiolytic changes in absorption and fluorescence behavior of irradiated solutions, it is revealed that some of the radiolytic products, namely cytosine glycol and hydroxy-hydrocytosine decompose to 5-hydroxycytosine and cytosine, respectively.     

Preparation, XRD and Raman spectroscopic studies on new compounds RE2Hf2O7 (RE=Dy, Ho, Er, Tm, Lu, Y): Pyrochlores or defect-fluorite?

A series of compositions with the general formula RE₂Hf₂O₇ (RE=Dy, Ho, Er, Tm, Y and Lu) was prepared by a standard solid-state route and characterized by powder X-ray diffraction (XRD) and Raman spectroscopy. As per theoretical modeling reported in literature, some of these materials were predicted to exist in pyrochlore lattice. However, a careful X-ray diffraction, Raman spectroscopic and synchrotron radiation-XRD study revealed that under the experimental conditions used in the present investigation, out of all the RE₂Hf₂O₇ samples only Dy₂Hf₂O₇ has got a tendency to form a pyrochlore structure. All the other (Ho, Er, Tm, Lu, Y) hafnates crystallize in a defect-fluorite structure. In order to further ascertain these inferences, a few more RE₂Hf₂O₇ samples (La, Nd, Sm) i.e., with larger RE³⁺ ions were also prepared and the results were compared.     

Graph theoretical procedure for obtaining analytical expressions of eigenspectra of linear chains and cycles with alternant vertex weights and same edge weight: Application to some complicated graphs

A graph theoretical procedure for obtaining eigenvalues of linear chains and cycles having alternant vertex weights (h₁, h₂, h₁, h₂, h₁, h₂, …) and the same edge weight (k) have been developed. The eigenvalues of some complicated graphs, such as graphs of linear polyacenes, methylene‐substituted linear polyacenes and cylindrical polyacene strips, stack graphs, and reciprocal graphs have been shown to be generated in closed analytical forms by this procedure. Many such graphs represent chemically important molecules or radicals. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Honeycomb nets with interpenetrating frameworks involving iminodiacetato-copper(II) blocks and bipyridine spacers: syntheses, characterization, and magnetic studies

Three coordination polymers of copper(II), viz. ([Cu(ida)(4,4'-bipyH)]ClO(4))( proportional, variant ) (1), ([Cu(2)(ida)(2)(micro-4,4'-bipy)].2H(2)O)( proportional, variant ) (2), and [Cu(2)(ida)(2)(bpa)]( proportional, variant ) (3) have been synthesized by the process of self-assembly using Cu(ida) [ida = iminodiacetate(2-)] as the building block and 4,4'-bipyridyl and 1,2-bis(4-pyridyl)ethane (bpa) as linkers. Crystals of 1 are orthorhombic, of space group Pna2(1), with a = 13.8956(12) A, b = 16.3362(16) A, c = 7.3340(12), and Z = 4. Both compounds 2 and 3 crystallize in monoclinic space group P2(1)/a with a = 10.1887(8) A (9.6779(10) A for 3), b = 8.0008(11) A (9.1718(10) A), c = 11.6684(9) A (12.9144(12) A), beta = 98.307(11) degrees (102.796(18) degrees ), and Z = 2 (2). Compound 1 has a zigzag chain structure with an extensive hydrogen-bonded network while compounds 2 and 3 are honeycomb (6,3) nets with interpenetrating structures. Variable temperature (2-300 K) magnetic study indicates the presence of weak antiferromagnetic interactions (J = 0.82 +/- 0.01 cm(-)(1)) in 1 and ferromagnetic in 2 (J = -0.45 +/- 0.05 cm(-)(1)) and 3 (J = -0.21 +/- 0.02 cm(-)(1)). The extent of planarity of the bridging "Cu-O-C-O-Cu" moiety, acting as the super-exchange pathway between the neighboring copper centers, probably controls the sign of the magnetic exchange coupling in these compounds.     

Enhanced magnetic anisotropy of nickel nanosheet prepared in Na-4 mica

Nanosheets of nickel with thickness equal to 0.6 nm have been grown within the interlayer spaces of Na-4 mica. The sheets are made up of percolative clusters of nanodisks. Magnetization characteristics indicate a superparamagnetic behavior with a blocking temperature of 428 K. The magnetic anisotropy constant as extracted from the coercivity data has been found to be higher than that of bulk nickel by two orders of magnitude. This is ascribed to a large aspect ratio of the nickel nanophase. The Bloch exponent is also found to be considerably different from that of bulk nickel because of a size effect. The Bloch equation is still found to be valid for the two dimensional structures.     

Flower-shaped ZnO nanoparticles as an efficient, heterogeneous and reusable catalyst in the synthesis of N-arylhomophthalimides and benzannelated isoquinolinones

A simple and green protocol, developed utilizing an efficient, heterogeneous and recyclable catalyst, i.e. zinc oxide nanoparticles (ZnO NPs)-mediated synthesis of N-arylhomophthalimides and benzannelated isoquinolinones, is reported. The structures of the desired products were characterized by FTIR, ¹H NMR, ¹³C NMR, and HRMS techniques. The ZnO NPs exhibited excellent catalytic activity and the proposed methodology is capable of providing the desired products in good yield and purity.     

Peptide‐poly(ε‐caprolactone) biohybrids by grafting‐from ring‐opening polymerization: Synthesis,aggregation, and crystalline properties

Well‐defined peptide‐poly(ε‐caprolactone) (Pep‐PCL) biohybrids were successfully synthesized by grafting‐from ring‐opening polymerization (ROP) of ε‐caprolactone (CL) using designed amine‐terminated sequence‐defined peptides as macroinitiators. MALDI‐TOF‐MS and ¹H NMR analyses confirmed the successful attachment of peptide to the PCL chain. The gel permeation chromatography (GPC) measurement showed that the Pep‐PCL biohybrids with controllable molecular weights and low polydispersities (PDI <1.5) were obtained by this approach. The aggregation of Pep‐PCL hybrid molecules in THF solution resulted in the formation of micro/nanospheres as confirmed through FESEM, TEM, and DLS analyses. The circular dichroism study revealed that the secondary structure of peptide moiety was changed in the peptide‐PCL biohybrids. The crystallization and melting behavior of Pep‐PCL hybrids were somewhat changed compared with that of neat PCL of comparable molecular weight as revealed by DSC and XRD measurements. In Pep‐PCL biohybrids, extinction rings were observed in the PCL spherulites, in contrast with the normal spherulite morphology of the neat PCL. There was a substantial decrease (4–5 folds) in the spherulitic growth rate after the incorporation of peptide moiety at the end of PCL chain as measured by polarizing optical microscopy. Pseudomonas lipase catalyzed enzymatic degradation was studied for Pep‐PCL hybrids and neat PCL. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012