Effect of chelating functional polymer on the size of CdS nanocluster formation

Chelating poly(acrylates-co-2-methylacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester) microspheres of diameter 250-310 nm were prepared by the soap-free emulsion polymerization method for varying amounts of GMA-IDA. Then CdS/copolymer composite was generated by chemical deposition on the surface of the copolymer microspheres. By XRD analysis it is found that the chelated CdS nanoparticles are a pure cubic zinc blende structure. The CdS/copolymer composite is examined by UV-vis absorbance, photoluminescence, and TEM observation. Average CdS nanoparticle size calculated from Henglein's empirical curve is in the range of 3.0-8.0 nm and varies according to the GMA-IDA molar ratio during polymerization, pH value during chelation, and postchelation annealing temperature. Higher ratio of chelating group, pH value, and annealing temperature produce larger CdS nanoparticles. As GMA-IDA ratio increases, photoluminescence exhibits a red shift from 510 to 520 nm, photoluminescence increases, and bandwidth decreases. Photoluminescence of the CdS nanoparticle becomes negligible when diameter exceeds 5 nm.     

Study of molecular behavior in a water nanocluster: size and temperature effect

Temperature and size effects on the behavior of nanoscale water molecule clusters are investigated by molecular dynamics simulations. The flexible three-centered (F3C) water potential is used to model the inter- and intramolecular interactions of the water molecule. The differences between the structural properties for the surface region and those for the interior region of the cluster are also investigated. It is found that as the temperature rises, the average number of hydrogen bonds per water molecule decreases, but the ratio of surface water molecules increases. After comparing the water densities in interior regions and the average number of hydrogen bonds in those regions, we find there is no apparent size effect on water molecules in the interior region, whereas the size of the water cluster has a significant influence on the behavior of water molecules at the surface region.     

Critical nucleus size effects on nanoparticle formation in microemulsions: a comparison study between experimental and simulation results

Monte Carlo simulations were performed to study the influence of critical nucleus size on nanoparticle formation in microemulsions. It was found that critical nucleus size strongly affected nucleation and growth rates, as well as final nanoparticle sizes. An increase of critical nucleus leads to a slower nucleation process. In contrast, it gives rise to acceleration of the growth process. Final nanoparticle sizes increase as the critical nucleus value increases. It is predicted that this dependence will be less pronounced when a high reactant concentration is used. We have compared the simulation results with experimental data taken from different authors. Good agreement between the two kinds of results supports the conclusions of this paper.     

Gold nanocluster confined within a cage: template-directed formation of a hexaporphyrin cage and its confinement capability

A novel container complex in which a 1.4 nm gold cluster is confined within a hexaporphyrin cage was synthesized; the cage showed notable confinement capability for the cluster core, but allowed the interpenetration of small molecules into the interstitial space.     

Predicting retention data using the slope of the log adjusted retention time vs. carbon number plot for n-alkanes

Summary The slope of the n-alkane log plot dt′_R/dn_c (t′_R=adjusted retention time; n_c=carbon number) for a stationary phase can be used to obtain the retention index of an unidentified substance in a chromatogram containing only one peak with a known retention index, or to predict the retention time of a substance from that of a different homolog in the same series. It can also be used to translate retention indices into relative retention time, partition coefficient or specific retention volume. Published values of the slope are collected and critically evaluated. Equations are deduced that predict its approximate value at a specified temperature given the value at only one other temperature.     

Investigation of a convergent route to purpuromycin: benzofuran formation vs spiroketalization

[Structure: see text] A mild and efficient [3+2] nitrile oxide/olefin cycloaddition allows coupling of the highly functionalized naphthalene and isocoumarin hemispheres of purpuromycin. A rationale of the inability of advanced keto alcohols to spirocyclize is presented based upon a systematic examination of the electronic factors present in these systems and suggests that the biosynthesis of purpuromycin does not proceed through open-chain intermediates.     

Substrate-promoted formation of a catalytically competent binuclear center and regulation of reactivity in a glycerophosphodiesterase from Enterobacter aerogenes

The glycerophosphodiesterase (GpdQ) from Enterobacter aerogenes is a promiscuous binuclear metallohydrolase that catalyzes the hydrolysis of mono-, di-, and triester substrates, including some organophosphate pesticides and products of the degradation of nerve agents. GpdQ has attracted recent attention as a promising enzymatic bioremediator. Here, we have investigated the catalytic mechanism of this versatile enzyme using a range of techniques. An improved crystal structure (1.9 A resolution) illustrates the presence of (i) an extended hydrogen bond network in the active site, and (ii) two possible nucleophiles, i.e., water/hydroxide ligands, coordinated to one or both metal ions. While it is at present not possible to unambiguously distinguish between these two possibilities, a reaction mechanism is proposed whereby the terminally bound H2O/OH(-) acts as the nucleophile, activated via hydrogen bonding by the bridging water molecule. Furthermore, the presence of substrate promotes the formation of a catalytically competent binuclear center by significantly enhancing the binding affinity of one of the metal ions in the active site. Asn80 appears to display coordination flexibility that may modulate enzyme activity. Kinetic data suggest that the rate-limiting step occurs after hydrolysis, i.e., the release of the phosphate moiety and the concomitant dissociation of one of the metal ions and/or associated conformational changes. Thus, it is proposed that GpdQ employs an intricate regulatory mechanism for catalysis, where coordination flexibility in one of the two metal binding sites is essential for optimal activity.     

Influence of fluorine substitution on the properties of CdO nanocluster : a DFT approach

Fluorine substituted cadmium oxide (Cd _n O _n?1F) cluster for n = 2–6 of linear, ring and three dimensional structures were studied using B3LYP exchange correlation function with LanL2DZ as basis set. Different isomers were optimized to obtain structural stability and various parameters such as dipole moment, HOMO–LUMO gap, ionization potential, electron affinity, stability factor, binding energy, vibrational studies and optical absorption were studied and reported. The stability of the cluster depends on the binding energy and vibrational intensity.     

Effect of size of catalytically active phases in the dehydrogenation of alcohols and the challenging selective oxidation of hydrocarbons

The size of the active phase is one of the most important factors in determining the catalytic behaviour of a heterogeneous catalyst. This Feature Article focuses on the size effects in two types of reactions, i.e., the metal nanoparticle-catalysed dehydrogenation of alcohols and the metal oxide nanocluster-catalysed selective oxidation of hydrocarbons (including the selective oxidation of methane and ethane and the epoxidation of propylene). For Pd or Au nanoparticle-catalysed oxidative or non-oxidative dehydrogenation of alcohols, the size of metal nanoparticles mainly controls the catalytic activity by affecting the activation of reactants (either alcohol or O(2)). The size of oxidic molybdenum species loaded on SBA-15 determines not only the activity but also the selectivity of oxygenates in the selective oxidation of ethane; highly dispersed molybdenum species are suitable for acetaldehyde formation, while molybdenum oxide nanoparticles exhibit higher formaldehyde selectivity. Cu(II) and Fe(III) isolated on mesoporous silica are highly efficient for the selective oxidation of methane to formaldehyde, while the corresponding oxide clusters mainly catalyse the complete oxidation of methane. The lattice oxygen in iron or copper oxide clusters is responsible for the complete oxidation, while the isolated Cu(I) or Fe(II) generated during the reaction can activate molecular oxygen forming active oxygen species for the selective oxidation of methane. Highly dispersed Cu(I) and Fe(II) species also function for the epoxidation of propylene by O(2) and N(2)O, respectively. Alkali metal ions work as promoters for the epoxidation of propylene by enhancing the dispersion of copper or iron species and weakening the acidity.     

Metal switch for amyloid formation: insight into the structure of the nucleus

The role of Zn2+ in pre-organizing Abeta(10-21) amyloid formation is shown to preferentially alter the relative rate of fibril nucleation and to have little influence on fibril propagation. Fibril morphology, as determined by small angle neutron scattering (SANS) and transmission electron microscopy (TEM), was unchanged in the presence and absence of Zn2+ in Abeta(10-21), as well as in a series of site-specifically altered variants. The metal-independence of the Abeta(10-21)H13Q peptide suggested that the increase in nucleation rate in Abeta(10-21) is due to Zn2+-mediated inter-sheet interactions, involving both histidine 13 and histidine 14.     

Oriented attachment: an effective mechanism in the formation of anisotropic nanocrystals

In this article, we report the formation of dispersed anisotropic nanostructures by the oriented attachment mechanism, under hydrothermal conditions and in a system that all other growth processes are improbable. The comparison of dilute and agglomerated experimental conditions indicate that oriented attachment is an effective mechanism for the formation of anisotropic nanocrystals, and the conclusions can be extended to other nanometric systems.     

The splitting of atomic orbitals with a common principal quantum number revisited: np vs. ns

Atomic orbitals with a common principal quantum number are degenerate, as in the hydrogen atom, in the absence of interelectronic repulsion. Due to the virial theorem, electrons in such orbitals experience equal nuclear attractions. Comparing states of several-electron atoms that differ by the occupation of orbitals with a common principal quantum number, such as 1s(2) 2s vs. 1s(2) 2p, we find that although the difference in energies, ΔE, is due to the interelectronic repulsion term in the Hamiltonian, the difference between the interelectronic repulsions, ΔC, makes a smaller contribution to ΔE than the corresponding difference between the nuclear attractions, ΔL. Analysis of spectroscopic data for atomic isoelectronic sequences allows an extensive investigation of these issues. In the low nuclear charge range of pertinent isoelectronic sequences, i.e., for neutral atoms and mildly positively charged ions, it is found that ΔC actually reverses its sign. About 96% of the nuclear attraction difference between the 6p (2)P and the 6s (2)S states of the Cs atom is cancelled by the corresponding interelectronic repulsion difference. From the monotonic increase of ΔE with Z it follows (via the Hellmann-Feynman theorem) that ΔL > 0. Upon increasing the nuclear charge along an atomic isoelectronic sequence with a single electron outside a closed shell from Z(c), the critical charge below which the outmost electron is not bound, to infinity, the ratio ΔC/ΔL increases monotonically from lim(Z→Z(c)(+))ΔC/ΔL=-1 to lim(Z→∞)ΔC/ΔL=1. These results should allow for a more nuanced discussion than is usually encountered of the crude electronic structure of many-electron atoms and the structure of the periodic table.     

A wheel-shaped indium-telluride nanocluster [In18Te30(dach)6]6-: its formation and structure

The preparation and crystal structure of a large wheel-shaped indium-telluride compound are reported. The inorganic cluster is decorated with 1,2-diaminocyclohexane molecules that play an important role in the formation of the nanoring. A related new 1D polymeric InTe compound is also presented in order to understand the effect of acidity on the formation of the ring structure.     

Accuracy vs time dilemma on the prediction of NMR chemical shifts: a case study (chloropyrimidines)

The nuclear magnetic shieldings of two chloropyrimidine species have been predicted and analyzed by means of ab initio and DFT methods. The results have been compared with the experimental values and with those from other database-related approaches. These dataset-based techniques are found to be particularly valuable because of the accurate and instantaneous prediction of the 13C chemical shifts. On the other hand, only a few quantum chemistry based approaches were showed to be the most precise to predict 1H chemical shifts and to elucidate unequivocally the 1H NMR spectra of the regioisomeric mixture under study. Special emphasis was put on incorporating the solvent effect, implicitly, or explicitly. The influence of the level of theory and basis set in the predicted values has also been discussed.     

Polynuclear crystal growth in electrocrystallization of silver: Determining the nucleus size via the nucleation theorem

We employ the nucleation theorem for a model-independent determination of the size of the two-dimensional (2D) Ag nucleus with the aid of experimental data for nucleation-mediated electrochemical crystal growth. The growth is investigated of a screw dislocation-free Ag(100) single crystal face in aqueous solution of AgNO₃ at 318 K. The data are for the stationary values of the overpotential during galvanostatic pulses with sufficiently high amplitudes to ensure polynuclear growth mechanism. It is found that the Gibbs-Thomson equation of the classical theory of 2D nucleation describes very well the experimentally obtained overpotential dependence of the size of the 2D Ag nucleus. Published in Russian in Elektrokhimiya, 2008, vol. 44, No. 6, pp. 698–703. The text was submitted by the authors in English.     

Boron nitride nanocluster as a carrier for lomustine anticancer drug delivery: DFT and thermodynamics studies

Monatshefte für Chemie - Chemical Monthly - Previous reports were shown that boron nitride nanostructures can be biocompatible and nontoxic. Therefore, interaction of lomustine as an...     

Solvothermal vs. bench-top reactions: control over the formation of discrete complexes and coordination polymers

The formation of discrete complexes [M(mcoe)2S2] (M = Cu, Ni; S = MeOH, H2O) vs. a nitroso-bridged ferromagnetically-coupled Cu(II) coordination polymer [Cu(mcoe)2] is influenced by the use of solvothermal reaction conditions.     

Phosphine-phosphite ligands: chelate ring size vs. activity and enantioselectivity relationships in asymmetric hydrogenation

A series of new phosphine-phosphite ligands P(C)(n)OP (n = 1-4) have been synthesized and used for rhodium-catalyzed asymmetric hydrogenation of prochiral olefins in order to study the effect of the chelate ring size. Excellent ees (up to 97.5%) were obtained in the hydrogenation of dimethyl itaconate and an increase of activity and enantioselectivity was observed in the hydrogenation of (Z)-α-acetamidocinnamic acid methyl ester with the increasing length of the backbone of the ligands.     

Correlation energy functionals dependent on an effective number of electrons: charged species and equilibrium geometries

Recently proposed spin-dependent and spin-independent correlation energy functionals [Perez-Jimenez et al., J. Chem. Phys. 116, 10571 (2002)] based on an effective number of electrons N are extended to deal with charged systems. By introducing the concept of an effective atomic number Z analogous to N, the spin-dependent functional in combination with Becke's exchange [Becke, Phys. Rev. A 38, 3098 (1988)] yields a mean absolute error (MAE) of 5.4 kcal/mol for the 88 ionization potentials and 58 electron affinities included in the extended G2 set, and a MAE of 4.1 kcal/mol for the 312 data comprising the above plus the 148 enthalpies of formation of the extended G2 set and the 18 total energies of the neutral atoms H through Ar. Geometry optimizations performed on the 53 molecules of the G2-1 test set with the above combination of exchange and correlation functionals yield MAEs of 0.017 A and 1.5 degrees for the 68 bond lengths and 29 angles analyzed as compared with the experimental estimates.