A novel blue luminescent high-spin iron(III) complex with interlayer O–H⋯Cl bridging: Synthesis,structure and spectroscopic studies

A blue luminescent high-spin (s = 5/2) iron(III) complex, [Fe^III(HL¹)₂]Cl (2), was synthesized with the acyclic tridentate salicylaldehyde 2-pyridyl hydrazone ligand, H₂L¹ (1), and it can subsequently be deprotonated and methylated into blue luminescent iron(III) complexes, [Fe^III(L²)₂]Cl (3) and [Fe^III(MeL¹)₂]Cl (4) respectively. On excitation at 390 nm, the ligand and the complexes display fluorescence in the blue region (λ_em = 440–450 nm) of the spectrum. The association constant, (K_ass = 4.6421 × 10⁴ at 298 K) and the thermodynamic parameters for complex 2 have been determined by UV–Vis spectroscopy. The iron(III)–iron(II) reduction potentials lie near – 0.2 V versus SCE. The X-ray crystal structure of the complex, [Fe^III(HL¹)₂]Cl · H₂O (2), was determined, revealing meridional binding of the two ligands affording a cis-FeN₄O₂ geometry with alternate chlorine and water molecules at the interface of the main molecule, resulting in interesting interlayer O–H?Cl bridging.     

Nanoparticle formation in water-in-oil microemulsions: experiments, mechanism, and Monte Carlo simulation

The dynamics of nanoparticle formation in water-in-oil microemulsions via temporal size evolution has been followed from UV-visible absorption spectra of CdS nanoparticles. Existing Monte Carlo (MC) simulations of nanoparticle formation are primarily based on the mechanism of nuclei formation and their growth by coalescence-exchange of drops, which alone do not predict particles of large size as observed in some experiments. Hence, we have included an additional size enlargement process, namely coagulation of nanoparticles during drop coalescence. We find that particle coagulation, constrained by microemulsion drop size, shows very good agreement with our experimental data on CdS nanoparticle size evolution, for different drop sizes. Thus a combined approach of spectroscopy and MC simulation is helpful in elucidating the mechanism of nanoparticle formation in these confined systems, leading to prediction of size-controlled nanoparticle synthesis.     

Phase behavior and dewetting for polymer blend films studied by in situ AFM and XPS: from thin to ultrathin films

In this work, the film thickness (l0) effect on the phase and dewetting behaviors of the blend film of poly(methyl methacrylate)/poly(styrene-ran-acrylonitrile) (PMMA/SAN) has been studied by in situ atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The thinner film shows the more compatibility of the blend, and the phase separation of the film occurs at l0>5Rg (radius of gyration). An initially time-independent q*, the characteristic wavenumber of the phase image, which is in good agreement of Cahn's linearized theory for the early stage of spinodal decomposition, has been obtained in real space and discussed in detail. For 5Rg>l0>3Rg, a "pseudo-dewetting/(phase separation+wetting)" behavior occurs, where the pseudo-wetting is driven by the concentration fluctuation mechanism. For l0<3Rg, a "real dewetting/(phase separation+wetting)" behavior occurs.     

Bis(trimethylsilyl)chromate catalyzed oxidations of alcohols to aldehydes and ketones with periodic acid

A facile, selective and high yielding bis(trimethylsilyl) chromate (BTSC) catalyzed selective oxidation of alcohols to aldehydes and ketones with periodic acid is reported.     

Synthesis of a ‐shaped amphiphilic block copolymer by the combination of atom transfer radical polymerization and living anionic polymerization

The functionalization of monomer units in the form of macroinitiators in an orthogonal fashion yields more predictable macromolecular architectures and complex polymers. Therefore, a new ‐shaped amphiphilic block copolymer, (PMMA)₂–PEO–(PS)₂–PEO–(PMMA)₂ [where PMMA is poly(methyl methacrylate), PEO is poly (ethylene oxide), and PS is polystyrene], has been designed and successfully synthesized by the combination of atom transfer radical polymerization (ATRP) and living anionic polymerization. The synthesis of meso‐2,3‐dibromosuccinic acid acetate/diethylene glycol was used to initiate the polymerization of styrene via ATRP to yield linear (HO)₂–PS₂ with two active hydroxyl groups by living anionic polymerization via diphenylmethylpotassium to initiate the polymerization of ethylene oxide. Afterwards, the synthesized miktoarm‐4 amphiphilic block copolymer, (HO–PEO)₂–PS₂, was esterified with 2,2‐dichloroacetyl chloride to form a macroinitiator that initiated the polymerization of methyl methacrylate via ATRP to prepare the ‐shaped amphiphilic block copolymer. The polymers were characterized with gel permeation chromatography and ¹H NMR spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 147–156, 2007     

Phagocytic activity of alveolar macrophages toward polystyrene latex microspheres and PLGA microspheres loaded with anti-tuberculosis agent

Phagocytosis of alveolar macrophages (Ms) toward poly(lactic-co-glycolic acid) (PLGA) microspheres (MS) loaded with the anti-tuberculosis agent rifampicin (RFP-PLGA MS) has been shown to be effective for the treatment of tuberculosis. The phagocytosis should be evaluated in terms of that toward reference MS. We chose polystyrene latex (PSL) MS as a reference. In this study, phagocytic activity of cell line NR8383, derived from rat alveolar M, toward PSL MS with various diameters was examined by incubating the cells for 4 h at 37 °C with various numbers of PSL MS per M cell (MS/M = 0.1–10). The results were then compared with those of the phagocytosis toward RFP-PLGA MS. We determined the phagocytic activity by counting the population of M cells that had phagocytosed MS (N) and the number of particles phagocytosed (n) in microscopic fields. Both N and n for PSL and RFP-PLGA MS increased in general with an increase in MS/M, but both of these values for PSL MS were smaller than those for RFP-PLGA MS. Phagocytosis of the particles were dependent on the particle size; i.e., of the PSL MS the 6-μm ones were taken up by M the most, and the RFP-PLGA MS 3 μm in diameter seemed to be phagocytosed the most efficiently, although we were not able to determine exactly the phagocytosis of 6- and 10-μm RFP-PLGA MS. From the changes in N and n values with MS/M, the phagocytosis of RFP-PLGA MS was likely to enhance the phagocytic activity of M cells, but this effect did not seem to be significant for PSL MS.     

Poly(vinylpyrrolidone): Configurational assignments by one- and two-dimensional NMR spectroscopy

The configurational assignment of poly(vinylpyrrolidone) (PVP) prepared by peroxide-initiated solution polymerization was studied by the combination of one- and two-dimensional NMR spectroscopy. The broad and overlapping ¹H-NMR and ¹³C{¹H}-NMR spectra of PVP were assigned to the configurational triad, pentad (CH, ²CH₂, ³CH₂, and ⁴CH₂ regions), and tetrad (β-CH₂ region) sequences. The configurational assignments of the various carbon resonances were confirmed with the help of two-dimensional experiments such as heteronuclear single quantum correlation (HSQC), heteronuclear single quantum correlation–total correlation spectroscopy (2-D HSQC–TOCSY). The various geminal and vicinal couplings within the configurational sequences were assigned with the help of total correlation spectroscopy (TOCSY low mixing time). The propagation pathway was studied using the ¹³C{¹H}-NMR (carbonyl carbon) and ¹⁵N{¹H}-NMR spectra. The ¹⁵N{¹H} resonance signals were assigned to pentad-level configurational sequences. The results obtained by the analysis of the area under the resonance signals confirmed that poly(vinylpyrrolidone) obeys Bernoullian statistics. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3922–3928, 1999     

Applications of a local grid method for modeling chemical dynamics at a mean-field level

A local grid method proposed earlier is used to model chemical dynamical events in more than one dimension. Two different mean-field routes are applied to model problems representing dynamics of isomerization, H⁺-ion transfer, energy transfer, etc. The methods are seen to work with equal facility for both time-dependent and time-independent potentials. © 1996 John Wiley & Sons, Inc.     

MD simulations and QM/MM calculations reveal the key mechanistic elements which are responsible for the efficient C–H amination reaction performed by a bioengineered P450 enzyme

An enzyme which is capable of catalyzing C–H amination reactions is considered to be a dream tool for chemists due to its pharmaceutical potential and greener approach. Recently, the Arnold group achieved this feat using an engineered CYP411 enzyme, which further undergoes a random directed evolution which increases its efficiency and selectivity. The present study provides mechanistic insight and the root cause of the success of these mutations to enhance the reactivity and selectivity of the mutant enzyme. This is achieved by means of comprehensive MD simulations and hybrid QM/MM calculations. The study shows that the efficient C–H amination by the engineered CYP411 is a combined outcome of electronic and steric effects. The mutation of the axial cysteine ligand to serine relays electron density to the Fe ion in the heme, and thereby enhances the bonding capability of the heme-iron to the nitrogen atom of the tosyl azide. In comparison, the native cysteine-ligated P450 cannot bind the tosyl azide. Additionally, the A78V and A82L mutations in P411 provide ‘bulk’ to the active site which increases the enantioselectivity via a steric effect. At the same time, the QM/MM calculations elucidate the C–H amination by the iron nitrenoid, revealing a mechanism analogous to Compound I in the native C–H hydroxylation by P450.

Computer simulation method reveals the mechanism of C–H amination reaction due to a single site mutation.