Development of a charge-perturbed particle-in-a-sphere model for nanoparticle electronic structure

The complex surface structure of gold-thiolate nanoparticles is known to affect the calculated density functional theory (DFT) excitation spectra. However, as the nanoparticle size increases, it becomes impractical to calculate the excitation spectrum using DFT. In this study, a new method is developed to determine the energy levels of the thiolate-protected gold nanoparticles [Au(25)(SR)(18)](-), Au(102)(SR)(44) and Au(144)(SR)(60). A 3 nm thiolate-protected nanoparticle is also modeled. The particle-in-a-sphere model is used to represent the core while the ligands are treated as point charge perturbations. The electronic structures obtained with this model are qualitatively similar to DFT results. The symmetry of the arrangement of the perturbations around the core plays a major role in determining the splitting of the orbitals. The radius chosen to represent the core also affects the orbital splitting. Increasing the number of perturbations around the core shifts the orbitals to higher energies but does not significantly change the band gaps and orbital splitting as long as the symmetrical arrangement of the perturbations is conserved. This model can be applied to any gold nanoparticle with a spherical core, regardless of its size or the nature of the ligands, at very low computational cost.     

Multivalent Design of Apoptosis‐Inducing Bid‐BH3 Peptide–Oligosaccharides Boosts the Intracellular Activity at Identical Overall Peptide Concentrations

Multivalent peptide–oligosaccharide conjugates were prepared and used to investigate the multivalency effect concerning the activity of Bid‐BH3 peptides in live cells. Dextran oligosaccharides were carboxyethylated selectively in the 2‐position of the carbohydrate units and activated for the ligation of N‐terminally cysteinylated peptides. Ligation through maleimide coupling was found to be superior to the native chemical ligation protocol. Monomeric Bid‐BH3 peptides were virtually inactive, whereas pentameric peptide conjugates induced apoptosis up to 20‐fold stronger at identical peptide concentrations. Comparison of lowly multivalent and highly multivalent peptide dextrans proved a multivalency effect in life cells which was specific for the BH3 peptide sequence.     

Polymeric coatings on silver nanoparticles hinder autoaggregation but enhance attachment to uncoated surfaces

The propensity of silver nanoparticles (AgNPs) having two different polymer coatings (poly(vinylpyrrolidone), PVP, or gum arabic, GA) to aggregate, or to deposit to a reference surface (silica), was explored as a basis for differentiating the effect of surface coating on the stability of nanoparticles in aggregation and in deposition. Surface polymeric coatings stabilize nanoparticles against aggregation as shown by either an increased critical coagulation concentration as for PVP-coated AgNPs (AgPVP) or the absence of observable aggregation even at a high ionic strength as for GA-coated AgNPs (AgGA). In experiments of AgNPs deposition in a silica porous medium, dissimilar surfaces favored deposition, such as the case where polymer coatings were present on the AgNPs but were absent on the porous medium. The increased affinity of the AgNPs for the porous medium in this case may be explained by a shifted contact frontier where electrical double layer interaction is weaker. When coating polymers were introduced to the porous medium and allowed to preadsorb to the silica surfaces, the attachment efficiencies for both the AgPVP and AgGA were reduced due to steric and electrosteric stabilization, respectively. The results suggest that polymeric coatings that are usually deemed as stabilizers (as they indeed are in the case of autoaggregation) might not necessarily stabilize nanoparticles against deposition unless the collector surfaces are also coated with polymer.     

Suppression of parasitic lasing in high energy, high repetition rate Ti:sapphire laser amplifiers

Transverse parasitic lasing is well known for limiting the signal gain and the pulse energy that can be extracted from Ti:sapphire petawatt amplifiers. We have developed a technique for suppressing these parasitic lasing modes based on perfect refractive index-matching liquid doped with a broad-bandwidth absorber to suppress the transverse lasing while ensuring proper heat removal from the Ti:sapphire crystal. The 800 nm laser output with a bandwidth of 41 nm (FWHM) and peak energy of 22.7 J at a repetition rate of 1 Hz is demonstrated.     

An integrated chemical biology approach provides insight into cdk2 functional redundancy and inhibitor sensitivity

1. Download : Download high-res image (204KB)
2. Download : Download full-size image

Highlights? Demonstration that Cdk2 is rate-limiting for DNA replication due to insufficient Cdk1 activity ? A simple bioinformatic approach to design inhibitor resistant mutations in kinases ? Demonstration of distinct binding modes and selectivity of Cdk inhibitors ? Identification of kinetic and structural mechanisms of inhibitor resistance     

Low‐temperature elastic and dielectric properties of K3Na(SO4)2 crystals

Elastic and dielectric properties of glaserite K₃Na(SO₄)₂ single crystal were examined using the method of composite oscillators, Brillouin light scattering methods and dielectric spectroscopy. Measurements were performed in the temperature range from 18 K to 300 K. Anomalies in the temperature dependencies of Brillouin shift and dielectric permittivity at about 70 K confirmed the earlier predicted phase transition at 75 ± 25 K. Temperature dependences of the resonance frequency of the vibrating composite oscillator, Brillouin shift measured in the [110] direction, components of dielectric permittivity tensor reveal an anomaly at about 50 K. Moreover, thermal hysteresis of the dielectric permittivity suggested the presence of an incommensurate state between T ₁ = 50 K and T ₂ = 70 K. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spectral multipliers on a class of NA groups with rank two

We consider a family of real NA groups with rank two, and we prove that these groups have sub-Laplacians with differentiable Lp functional calculus for all p?1.     

From isocyanides to trichloropyruvamides: application to a new preparation of oxamide derivatives

Isocyanides react readily with trichloroacetic acid anhydride forming stable hydrates of trichloropyruvamides. These compounds are valuable intermediates for obtaining oxamides by reaction with TMSCl/NEt₃ followed by addition of an amine.     

Crystallographic structures of two bisphosphonate:1-deoxyxylulose-5-phosphate reductoisomerase complexes

We have obtained the single-crystal X-ray crystallographic structures of the bisphosphonates [(1-isoquinolinylamino)methylene]-1,1-bisphosphonate and [[(5-chloro-2-pyridinyl)amino]methylene]-1,1-bisphosphonate, bound to the enzyme 1-deoxyxylulose-5-phosphate reductoisomerase (DXR, EC 1.1.1.267, also known as 2-C-methyl-d-erythritol-4-phosphate synthase), an important target for the development of antimalarial drugs. Our results indicate that both bisphosphonates bind into the fosmidomycin binding site. The aromatic groups are in a shallow hydrophobic pocket, and the phosphonate groups are involved in electrostatic interactions with Mg2+ or a cluster of carboxylic acid groups and lysine while the fosmidomycin phosphonate-binding site is occupied by a sulfate ion (as also observed in the DXR/NADP+ structure). The availability of these two new crystal structures opens up the possibility of the further development of bisphosphonates and related systems as DXR inhibitors and, potentially, as antiinfective agents.