Beta‐hairpin restraint potentials for calculations of potentials of mean force as a function of beta‐hairpin tilt,rotation, and distance

We have developed a set of restraint potentials for β‐hairpin tilt relative to the membrane normal, β‐hairpin rotation around the β‐hairpin axis, and hairpin–hairpin distance. Such restraint potentials enable us to characterize the molecular basis of specific β‐hairpin tilt and rotation in membranes and hairpin–hairpin interactions at the atomic level by sampling their conformational space along these degrees of freedom, i.e., reaction coordinates, during molecular dynamics simulations. We illustrate the efficacy of the β‐hairpin restraint potentials by calculating the potentials of mean force (PMFs) as a function of tilt and rotation angles of protegrin‐1 (PG‐1), a β‐hairpin antimicrobial peptide, in an implicit membrane model. The peptide association in the membrane is also examined by calculating the PMFs as a function of distance between two PG‐1 peptides in various dimer interfaces. These novel restraint potentials are found to perform well in each of these cases and are expected to be a useful means to study the microscopic driving forces of insertion, tilting, and rotation of β‐hairpin peptides in membranes as well as their association in aqueous solvent or membrane environments particularly when combined with explicit solvent models. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009     

Self-assembled peptide architecture with a tooth shape: folding into shape

Molecular self-assembly is the spontaneous association of molecules into structured aggregates by which nature builds complex functional systems. While numerous examples have focused on 2D self-assembly to understand the underlying mechanism and mimic this process to create artificial nano- and microstructures, limited progress has been made toward 3D self-assembly on the molecular level. Here we show that a helical β-peptide foldamer, an artificial protein fragment, with well-defined secondary structure self-assembles to form an unprecedented 3D molecular architecture with a molar tooth shape in a controlled manner in aqueous solution. Powder X-ray diffraction analysis, combined with global optimization and Rietveld refinement, allowed us to propose its molecular arrangement. We found that four individual left-handed helical monomers constitute a right-handed superhelix in a unit cell of the assembly, similar to that found in the supercoiled structure of collagen.     

Nanodiamonds as photocatalysts for reduction of water and graphene oxide

Detonated nanodiamonds (NDs) exhibit remarkable photocatalytic activity towards the hydrogen gas generation upon 532 nm laser pulse irradiation. Hydrogenation dramatically increases the quantum yield, suggesting that hydrogen-terminated sites work as electron reservoirs. NDs can also be used as effective photocatalysts to reduce graphene oxide. The resulting composites exhibit high and stable photocurrent generation upon visible light irradiation.     

Imageable antigen-presenting gold nanoparticle vaccines for effective cancer immunotherapy in vivo

Delivery tracking: Goldnanoparticles (AuNPs) were functionalized with a red fluorescent protein (RFP, pink shapes in picture) as model antigen and an oligonucleotide (CpG) that stimulates the immune response. These functionalized AuNPs were used as cancer vaccines in a tumor model, where they enabled efficient delivery of an antigen to target sites, tracking of the vaccines using noninvasive clinical imaging, and cancer prevention and therapy.     

Immobilization of large, aliovalent cations in the small-pore zeolite K-natrolite by means of pressure

High-pressure ion exchange of small-pore zeolite K-natrolite allows immobilization of nominally non-exchangeable aliovalent cations such as trivalent europium. A sample exchanged at 3.0(1) GPa and 250 °C contains about 4.7 Eu(III) ions per unit cell, which is equivalent to over 90 % of the K(+) cations being exchanged.     

Two‐Dimensional Infrared Correlation Spectroscopy and Principal Component Analysis on the Carbonation of Sterically Hindered Alkanolamines

Despite the academic and industrial importance of the chemical reaction between carbon dioxide (CO₂) and alkanolamine, the delicate and precise monitoring of the reaction dynamics by conventional one‐dimensional (1D) spectroscopy is still challenging, due to the overlapped bands and the restricted static information. Herein, we report two‐dimensional infrared correlation spectroscopy (2D IR COS) and principal component analysis (PCA) on the reaction dynamics of a sterically hindered amine, 2‐[(1,1‐dimethylethyl)amino]ethanol (TBAE) and CO₂. The formation of carbonate rather than carbamate species, which contribute to the unusual high working capacity of ～1 mole CO₂ per mole of TBAE at 40 °C, occurs through deprotonation of the hydroxyl group, protonation on the nitrogen atom of the amino group, and formation of a carbonate species due to the steric hindrance of the tert‐butyl group. In particular, PCA captures the chemical transition into a carbonate species and the main contributions of ${\nu _{{\rm{CO}}_2 } }$ , ${\nu _{{\rm{OH}}} }$ , ${\nu _{{\rm{C - N}}} }$ , and ${\nu _{{\rm{C}} = {\rm{O}}} }$ bands to the carbonation, while 2D IR COS verifies the interrelation of four bands and their changes. Therefore, these results provide a powerful analytic method to understand the complex and abnormal reaction dynamics as well as the rational design strategy for the CO₂ absorbents.     

The effects of Mo doping on 0.3Li[Li0.33Mn0.67]O2·0.7Li[Ni0.5Co0.2Mn0.3]O2 cathode material

Mo doped Li excess transition metal oxides formulated as 0.3Li[Li(0.33)Mn(0.67)]O(2)·0.7Li[Ni(0.5-x)Co(0.2)Mn(0.3-x)Mo(2x)]O(2) were synthesized using the co-precipitation process. The effects of the substitution of Ni and Mn with Mo were investigated for the density of the states, the structure, cycling stability, rate performance and thermal stability by tools such as first principle calculations, synchrotron X-ray diffraction, field-emission SEM, solid state (7)Li MAS nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), elemental mapping by scanning TEM (STEM), inductively coupled plasma atomic emission spectrometry (ICP-AES) and a differential scanning calorimeter (DSC). It was confirmed that high valence Mo(6+) doping of the Li-excess manganese-nickel-cobalt layered oxide in the transition metal enhanced the structural stability and electrochemical performance. This increase was due to strong Mo-O hybridization inducing weak Ni-O hybridization, which may reduce O(2) evolution, and metallic behavior resulting in a diminishing cell resistance.     

Simultaneous determination of phoxim and its photo-transformation metabolite residues in eggs using liquid chromatography coupled with electrospray ionization tandem mass spectrometry

The principal objective of this study was to develop an appropriate, sensitive, and selective method for the simultaneous quantitative determination of phoxim and its photo-transformation product, O,O-diethyl α-cyanobenzylideneamino-thiophosphonate (DCTP) in both chicken and quail eggs. Eggs (1 g) were blended with anhydrous magnesium sulfate (1 g) for sample pretreatment and extracted with acetonitrile. The extracts were then further purified with SPE silica gel tubes deactivated with trimethylamine. Residues were analyzed via a reversed phase-liquid chromatography-tandem mass spectrometry (RP-LC-MS/MS) in positive-ion electrospray ionization (ESI) mode. Tebufenozide was utilized as an internal standard for the quantification of phoxim and its metabolite residues. The identification and quantification of analytes were based on ion transitions monitored by multiple reaction monitoring (MRM). LC-MS/MS analysis was performed from 0.02 to 1 mg kg⁻¹ and correlation coefficients (r²) ranging from 0.998 to 0.999 were obtained for both analytes in blank egg extracts. The relative standard deviations (RSDs) of intra- and inter-day variations ranged from 2.1% to 6.7% and from 2.8% to 6.4% for phoxim and DCTP in chicken and quail eggs. At all levels of fortification (0.02, 0.05, and 0.125 mg kg⁻¹), the recoveries fell within a range of 81.3% to 93.6% for phoxim and 83.3% to 90.1% for DCTP. The matrix effect was <2%, due to the partial dilution of the sample. Decision limits (CCα) and detection capabilities (CCβ) were in the range of 0.0005-0.0044 and 0.0054-0.0224 mg kg⁻¹, respectively. The method was evaluated further by analyzing real samples purchased from markets. All chicken and quail egg samples were free from residues of the target compounds.     

Experimental demonstration of similariton pulse compression in a comblike dispersion-decreasing fiber amplifier

Self-similar propagation of linearly chirped hyperbolic-secant pulses in a comblike decreasing-dispersion fiber amplifier has been observed experimentally for the first time to our knowledge. The scheme takes advantage of an exact solution of the generalized nonlinear Schr?dinger equation with distributed coefficients.     

Optical pseudogap from iron states in filled skutterudites AFe4Sb12 (A=Yb, Ca, Ba)

Optical investigations are presented of the filled skutterudites AFe4Sb12 with divalent cations A=Yb, Ca, Ba. For each of these compounds a very similar pseudogap structure in the optical conductivity develops in the far-infrared spectral region at temperatures below 90 K. Highly accurate local-density approximation electronic band structure calculations can consistently explain the origin of the pseudogap structure generated largely by transition metal 3d states. In particular, a 4f-conduction electron hybridization or strong correlations can be ruled out as origin for the pseudogap.