Nanosilica-supported polyethoxyamines as low-cost, reversible carbon dioxide sorbents

Nanoparticles capped with amine ligands with different steric properties, dodecylamine and oleylamine, respectively, are investigated in the solid state as well as in solution. A combined X-ray diffraction, small angle X-ray scattering and electron microscopy investigation showed that the nanoparticles exhibit the sphalerite modification of ZnS as crystal phase with a diameter of 3-5 nm. A close packing of the monocrystalline nanoparticles in the solid state is observed. However, in the dodecylamine sample, besides spherical particles, a fraction of the nanoparticles is elongated. The nanoparticles are readily resoluble in apolar solvents like hexane. Dynamic light scattering (DLS) and SAXS investigations of the solutions reveal that the nanoparticles are dissolved as singular particles. In the case of oleylamine-capped ZnS, a defined core-shell structure with a ZnS core with a diameter of 4 nm and an organic shell with a thickness of approximately 2 nm have been found. Dodecylamine-capped nanoparticles slightly tend to form agglomerates with a diameter of approximately 40 nm.     

Zirconium phosphate nano-platelets: a novel platform for drug delivery in cancer therapy

Doxorubicin was intercalated into novel zirconium phosphate nano-platelets (ZrP). The obtained doxorubicin intercalated ZrP nano-platelets had an impressive 34.9% (w/w) drug loading. We used this material to deliver doxorubicin to breast cancer cells (MCF-7). Cellular studies with MCF-7 cells showed higher uptake and cytotoxicity of doxorubicin loaded ZrP compared to free doxorubicin.     

Real-time kinetics of surfactant molecule transfer between emulsion particles probed by in situ second harmonic generation spectroscopy

Emulsions are widely used in industrial and environmental remediation applications. The breaking and reformulation of emulsions, which occur during their use, lead to changes in their surface composition as well as their physical and chemical properties. Hence, a fundamental understanding of the transfer of surfactant molecules between emulsion particles is required for optimization of their applications. However, such an understanding remains elusive because of the lack of in situ and real-time surface-specific techniques. To address this, we designed and synthesized the surfactant probe molecules MG-butyl-1 (2) and MG-octyl-1 (3), which contain an n-butyl and an n-octyl chain, respectively, and a charged headgroup similar to that in malachite green (MG, 1). MG is known to be effective in generating second harmonic generation (SHG) signals when adsorbed onto surfaces of colloidal microparticles. Making use of the coherent nature of SHG, we monitored in real-time the transfer of 2 and 3 between oil-in-water emulsion particles with diameters of ~220 nm. We found that 3 is transferred ~600 times slower than 2, suggesting that an increase in the hydrophobic chain length decreases the transfer rate. Our results show that SHG combined with molecular design and synthesis of surfactant probe molecules can be used to measure the rate of surfactant transfer between emulsion particles. This method provides an experimental framework for examining the factors controlling the kinetics of surfactant transfer between emulsion particles, which cannot be readily investigated in situ and in real-time using conventional methods.     

Wave envelopes method for description of nonlinear acoustic wave propagation

A novel, free from paraxial approximation and computationally efficient numerical algorithm capable of predicting 4D acoustic fields in lossy and nonlinear media from arbitrary shaped sources (relevant to probes used in medical ultrasonic imaging and therapeutic systems) is described. The new WE (wave envelopes) approach to nonlinear propagation modeling is based on the solution of the second order nonlinear differential wave equation reported in [J. Wójcik, J. Acoust. Soc. Am. 104 (1998) 2654-2663; V.P. Kuznetsov, Akust. Zh. 16 (1970) 548-553]. An incremental stepping scheme allows for forward wave propagation. The operator-splitting method accounts independently for the effects of full diffraction, absorption and nonlinear interactions of harmonics. The WE method represents the propagating pulsed acoustic wave as a superposition of wavelet-like sinusoidal pulses with carrier frequencies being the harmonics of the boundary tone burst disturbance. The model is valid for lossy media, arbitrarily shaped plane and focused sources, accounts for the effects of diffraction and can be applied to continuous as well as to pulsed waves. Depending on the source geometry, level of nonlinearity and frequency bandwidth, in comparison with the conventional approach the Time-Averaged Wave Envelopes (TAWE) method shortens computational time of the full 4D nonlinear field calculation by at least an order of magnitude; thus, predictions of nonlinear beam propagation from complex sources (such as phased arrays) can be available within 30-60 min using only a standard PC. The approximate ratio between the computational time costs obtained by using the TAWE method and the conventional approach in calculations of the nonlinear interactions is proportional to 1/N2, and in memory consumption to 1/N where N is the average bandwidth of the individual wavelets. Numerical computations comparing the spatial field distributions obtained by using both the TAWE method and the conventional approach (based on a Fourier series representation of the propagating wave) are given for circular source geometry, which represents the most challenging case from the computational time point of view. For two cases, short (2 cycle) and long (8 cycle) 2 MHz bursts, the computational times were 10 min and 15 min versus 2 h and 8 h for the TAWE method versus the conventional method, respectively.     

Anticancer cyclometalated [Au(III)m(C(wedge)N(wedge)C)mL]n+ compounds: Synthesis and cytotoxic properties

A series of cyclometalated gold(III) compounds [Au(m)(C(wedge)N(wedge)C)mL]n+ (m = 1-3; n = 0-3; HC(wedge)N(wedge)CH = 2,6-diphenylpyridine) was prepared by ligand substitution reaction of L with N-donor or phosphine ligands. The [Au(m)(C(wedge)N(wedge)C)mL]n+ compounds are stable in solution in the presence of glutathione. Crystal structures of the gold(III) compounds containing bridging bi- and tridentate phosphino ligands reveal the presence of weak intramolecular pi pi stacking between the [Au(C(wedge)N(wedge)C)]+ units. Results of MTT assays demonstrated that the [Au(m)(C(wedge)N(wedge)C)mL]n+ compounds containing nontoxic N-donor auxiliary ligands (2) exert anticancer potency comparable to that of cisplatin, with IC50 values ranging from 1.5 to 84 microM. The use of [Au(C(wedge)N(wedge)C)(1-methylimidazole)]+ (2 a) as a model compound revealed that the gold(III)-induced cytotoxicity occurs through an apoptotic cell-death pathway. The cell-free interaction of 2 a with double-stranded DNA was also examined. Absorption titration showed that 2 a binds to calf-thymus DNA (ctDNA) with a binding constant of 4.5 x 10(5) dm3 mol(-1) at 298 K. Evidence from gel-mobility-shift assays and viscosity measurements supports an intercalating binding mode for the 2 a-DNA interaction. Cell-cycle analysis revealed that 2 a causes S-phase cell arrest after incubation for 24 and 48 hours. The cytotoxicity of 3 b-g toward cancer cells (IC50 = 0.04-4.3 microM) correlates to that of the metal-free phosphine ligands (IC50 = 0.1-38.0 microM), with [Au2(C(wedge)N(wedge)C)2(mu-dppp)]2+ (3 d) and dppp (dppp = 1,2-bis(diphenylphosphino)propane) being the most cytotoxic gold(III) and metal-free compounds, respectively. Compound 3 d shows a cytotoxicity at least ten-fold higher than the other gold(III) analogues; in vitro cellular-uptake experiments reveal similar absorptions for all the gold(III) compounds into nasopharyngeal carcinoma cells (SUNE1) (1.18-3.81 ng/cell; c.f., 3 d = 2.04 ng/cell), suggesting the presence of non-gold-mediated cytotoxicity. Unlike 2 a, both gold(III) compounds [Au(C(wedge)N(wedge)C)(PPh3)]+ (3 a) (PPh3 = triphenylphosphine) and [Au2(C(wedge)N(wedge)C)2(mu-dppp)]2+ (3 d) interact only weakly with ctDNA and do not arrest the cell cycle.     

Isotope labeling studies reveal the order of oxygen incorporation into the tryptophan tryptophylquinone cofactor of methylamine dehydrogenase

The bacterial enzyme methylamine dehydrogenase (MADH) contains the protein-derived cofactor tryptophan tryptophylquinone (TTQ). TTQ is generated by the posttranslational modification of two endogenous MADH tryptophans, betaW57 and betaW108. Two oxygens are inserted sequentially into betaW57 to generate the quinone moiety, after which it is cross-linked to betaW108. We have previously shown that the second oxygenation and cross-link formation are catalyzed by the novel di-heme cytochrome MauG. Here we show, using isotopically labeled oxygen and water, that the first addition of oxygen occurs specifically at the C7 position of betaW57 and that MauG then inserts the second oxygen at position C6.     

Infrared line shape of an alpha-carbon deuterium-labeled amino acid

The viability of alpha-carbon deuterated bonds (Calpha-D) as infrared (IR) probes of protein backbone dynamics was explored through a combination of experiment and theory. alpha-Carbon deuterated alanine (Ala-d1) served as a convenient model system for a comparison of experiment, density functional theory (DFT), and combined quantum mechanical/molecular mechanical (QM/MM) simulations of the Calpha-D IR line shape. In addition to the primary Calpha-D absorption, the experimental spectrum contains three features that likely result from Fermi resonances. DFT calculations supported the assignments and identified the lower frequency modes participating in the Fermi resonances. A QM/MM simulation of the Ala-d1 line shape was in qualitative agreement with the experiment, including the presence of classical analogues of Fermi resonances. These studies demonstrated that the Calpha-D line shape is sensitive, via Fermi resonances, to lower frequency collective vibrations that are expected to play a role in protein dynamics and function, and that the QM/MM approach, which is applicable to proteins, is capable of aiding in their interpretation.     

Aggregation and chiroptical behavior of a high molecular weight chirally substituted dialkylpoly(p‐phenyleneethynylene)

The solvent and temperature dependent aggregation of high molecular weight bis[S‐(+)‐3,7‐dimethyloctyl)] substituted poly(p‐phenyleneethynylene) (PPE, 2 ) was examined by absorption, emission and circular dichroism spectroscopy. All herein employed methods strongly support the view that 2 forms ordered aggregates in the solid state and in solvent mixtures. This is the first case in which a chiral high molecular weight PPE displays its aggregation by both optical and chiroptical methods.