Syntheses and micellar properties of well‐defined amphiphilic AB2 and A2B Y‐shaped miktoarm star copolymers of ε‐caprolactone and 2‐(dimethylamino)ethyl methacrylate

Well‐defined amphiphilic PCL‐b‐(PDMA)₂ and (PCL)₂‐b‐PDMA Y‐shaped miktoarm star copolymers and PCL‐b‐PDMA linear diblock copolymer were synthesized via a combination of ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP), where PCL is poly (ε‐caprolactone) and PDMA is poly(2‐(dimethylamino)ethyl methacrylate). All of these three types of copolymers have comparable PCL contents and overall molecular weights. The PCL block is hydrophobic while the PDMA block is hydrophilic, and they behave like polymeric surfactants and self‐assemble into PCL‐core micelles in aqueous media. The chain architectural effects on the micellization properties, including the aggregation number, size, polydispersity, and micelle densities of (PCL₂₉)₂‐b‐PDMA₄₅, PCL₆₁‐b‐(PDMA₂₄)₂, and PCL₅₆‐b‐PDMA₄₉ in dilute aqueous solution, were then explored by dynamic and static laser light scattering (LLS). The intensity–average hydrodynamic radius, 〈R_h〉, the aggregation number per micelle, N_agg, and the core radius, R_core, of the PCL‐core micelles all increased in the order PCL₆₁‐b‐(PDMA₂₄)₂ < (PCL₂₉)₂‐b‐PDMA₄₅ < PCL₅₆‐b‐PDMA₄₉. The surface area occupied per soluble PDMA block at the core/corona interface increased in the order PCL₆₁‐b‐(PDMA₂₄)₂ < PCL₅₆‐b‐PDMA₄₉ < (PCL₂₉)₂‐b‐PDMA₄₅. PCL₆₁‐b‐(PDMA₂₄)₂ micelles had the largest overall micelle density, possibly because of that the presence of two soluble PDMA arms at the junction point favors the bending of the core–corona interface and thus the formation of densely‐packed core‐shell nanostructures. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1446–1462, 2007     

An insight into the surface engineering of colloidal PbSe quantum dots for polymer hybrid photovoltaic applications

Journal of Sol-Gel Science and Technology - In this article, the beneficial effect of surface passivation rendered by the amalgamation of co-ordinating tri-n-octylphophine (TOP), oleylamine (OLA),...     

A Novel Strategy for N-Alkylation of Primary Amines

N-alkyiation of primary amines has been carried out with alkylbromide using commercial Me₂SO and K₂CO₃ as a base. This process offers a method of selection for obtaining either mono or dialkyl amines.     

Solvent Effect on Cocaine and Methyl Benzoate Phosphorescence

In polar, nonhydrogen-bonding solvents, cocaine's phosphorescence differs from that of its model compound, methyl benzoate, in what can be attributed to an amine-benzoate charge transfer interaction and both compounds exhibit long wavelength bands not present in nonpolar media.     

Rapid synthesis of gold nanorods using a one-step photochemical strategy

Rapid synthesis of gold nanorods of controlled dimensions is one of the desired aspects of nanotechnology as a result of the potential of these nanomaterials for biomedical applications. The synthesis of gold nanorods has been achieved using a photoinitiator as an instant source of ketyl radicals, which allows the synthesis of gold nanorods in minutes. This is the first report providing a one-step synthesis of nanorods of controlled dimensions in 20-30 min using photoinitiator I-2959 as a source of ketyl radicals. Furthermore, the role of UV intensity, the concentration of silver ions, and the presence of cosolvents and a cosurfactant have been studied in detail in an effort to produce nanorods with controlled dimensions in higher yields. The role of acetone in nanorod synthesis has been explored in detail, and it has been demonstrated that, for the photochemical synthesis of nanorods using a photoinitiator, acetone is not a critical component and can be replaced by other water-miscible solvents, thus the successful synthesis of nanorods in tetrahydrofuran (THF) has been demonstrated. It has also been found that a cosurfactant and an organic solvent are not required for the synthesis of nanorods; however, their presence is found to improve the monodispersity of nanorod samples, in addition to providing a higher yield.     

Electron paramagnetic resonance study of 3,4,5-trimethoxytetraphenyl porphyrinoxovanadium (IV) complex

3,4,5-Trimetoxytetraphenylporphyrinoxovanadium (IV) complex (3,4,5-TMVOTPP) was synthesized by a new one pot synthetic method. The complex was studied in the form of single crystal, powder (polycrystalline state), solution and frozen solution (glassy state) by electron paramagnetic resonance (EPR) between room temperature (RT) and liquid nitrogen temperature (LNT). Interestingly a well-resolved octet in the EPR spectrum at RT is observed in the pure paramagnetic state of the crystal. This observation is attributed to a greatly reduced dipolar interaction between paramagnetic vanadyl ions due to the large size of the molecule and the resultant stacking in the crystalline state. The line width of the EPR signals in single crystal at RT is approximately 3.3 mT which is more than the usual line width in diluted paramagnets ( approximately 1.5 mT) and is attributed to some kind of broadening effect akin to slow motion broadening. The line width in solvents is more than the crystal value but decreases appreciably at low temperatures. The decrease in line width at low temperature is attributed to the increase in spin-lattice-relaxation time and quenching of RT broadening motion. Only one octet is observed in the crystal EPR spectra which suggests only one formula unit per unit cell or a parallel/antiparallel ordering of V=O vectors in case the formula units per unit cell are more than one. This result needs verification by a detailed X-ray investigation. The crystalline field symmetry around the V(4+) metal ion is revealed to be axial by the observed angular dependence of the EPR spectrum and the powder EPR spectrum. No super hyperfine splitting of the hyperfine lines of the vanadyl ion is observed in solid state or diluted glass up to liquid nitrogen temperature. This suggests an expected weak in-plane pi-bonding with ligands. The spin Hamiltonian parameters for vanadyl ion in crystal, powder, diluted solutions and frozen glasses are evaluated and discussed.     

Effect of donor-acceptor interaction strength on excitation energy migration and diffusion at high donor concentrations

The migration and diffusion modulated excitation energy transfer has been studied in a new dye pair 7-diethylamino-4-methylcoumarin (donor) to 3,3'-dimethyloxacarbocyanine iodide (acceptor) by steady-state and picosecond time-resolved spectroscopy. To reduce the artifact of self-absorption, at high donor concentrations, the time-resolved studies have been carried out in thin films of polyvinyl alcohol (solid matrix) and in methanol (liquid phase) at front-face geometry of excitation. The Forster-type (nonradiative) energy transfer [Discuss. Faraday Soc. 27, 7 (1959)] takes place directly from donor to acceptor in case of solid matrix, while Yokota-Tanimoto model [J. Phys. Soc. Jpn. 22, 779 (1967)] for diffusion has been found to be operating in the liquid phase. It has been found here that the high interaction strength between donor and acceptor molecules as compared to that among donors masks the effect of energy migration and diffusion at high donor concentrations. The rate and efficiency of energy transfer increase with increasing the acceptor concentration. This has been confirmed by the study of acceptor kinetics.     

Generation of high-purity telecom-band entangled photon pairs in dispersion-shifted fiber

We study the purity of correlated photon pairs generated in a dispersion-shifted fiber at various temperatures. The ratio of coincidence to accidental-coincidence counts greater than 100 can be obtained as the fiber is cooled to liquid-nitrogen temperature (77 K). We then generate polarization-entangled photon pairs by using a compact counterpropagating scheme. Two-photon interference with visibility >98% and Bell's inequality violation by >8 standard deviations of measurement uncertainty are observed at 77 K, without subtracting the accidental-coincidence counts due to background Raman photons.     

Chemoenzymatic synthesis of the trans-dihydrodiol isomers of monosubstituted benzenes via anti-benzene dioxides

Enantiopure cis-2,3-dihydrodiols, available from dioxygenase-catalysed cis-dihydroxylation of monosubstituted benzene substrates, have been used as synthetic precursors of the corresponding trans-3,4-dihydrodiols. The six-step chemoenzymatic route from cis-dihydrodiol precursors, involving acetonide, tetraol, dibromodiacetate and diepoxide intermediates, and substitution of vinyl bromide and iodide atoms, has been used in the synthesis of ten trans-dihydrododiol derivatives of substituted benzenes. The general applicability of the method has been demonstrated by its use in the synthesis of both enantiomers of the trans-1,2-and 3,4-dihydrodiol derivatives of toluene.     

Prediction of vapour pressure using descriptors derived from molecular dynamics

Vapour pressures of organic materials can be predicted to high levels of accuracy using cohesive energies and solubility parameters derived from molecular dynamics simulations that use good forcefields. It is found that over 90% of the correlation with vapour pressure is accounted for by a single cross term involving the product of either the molecular weight or molar volume of a molecule and its cohesive energy density.