Synthesis of silver nanoparticles for remote opening of polyelectrolyte microcapsules

Silver nanoparticles of 10, 18, and 23 nm were synthesized in aqueous medium by chemical reduction of silver nitrate in excess of sodium borohydride. Modification of polyelectrolyte shells with synthesized silver nanoparticles was performed using the layer-by-layer approach. Remote opening of the polyelectrolyte/silver capsules was performed with a CW Nd:YAG FD laser with an average incident power output up to 70 mW. Capsules with a mixture of 10 and 18 nm silver nanoparticles in its polyelectrolyte shell were ruptured after less than 7 s of laser irradiation, while microcapsules with 23 nm silver nanoparticles in the shell were broken after 11 s of laser treatment and 10 nm silver nanoparticles were broken after 26 s.     

Diboryl and Diboranyl Porphyrin Complexes: Synthesis,Structural Motifs,and Redox Chemistry: Diborenyl Porphyrin or Diboranyl Isophlorin?

The syntheses of diboryl porphyrin complexes [(BX2)2(ttp)] (ttp: dianion of tetra-p-tolylporphyrin) and the B-B single-bond diboranyl complexes [(BX)2(ttp)] (X=F, Cl, Br, I) are given. The former are prepared from the reactions of BX3 (X=F, Cl) with [Li2(ttp)] and the latter from B(2)Cl(4) (X=Cl), the reaction of SbF3 with [(BCl)2(ttp)] (for X=F), and, in the cases of X=Br or I, in a remarkable reductive coupling reaction resulting directly from the reaction of BBr3 or BI3 with [Li2(ttp)]. Density functional theory (DFT) calculations on the thermochemical parameters for the reductive coupling reactions (and those calculated for related dipyrromethene complexes) indicate that a combination of the reducing ability of bromide and iodide ions combined with the constrained environment of the porphyrin ligand contribute to the driving force. The reductive coupling is also observed in the reaction of [(BCl2)2(ttp)] with nBuLi to give [(BnBu)2(ttp)], which was characterised crystallographically. The reaction of [(BCl)2(ttp)] with catechol gives a boron catecholato porphyrin complex, [B2(O(2)C(6)H(4))(ttp)]. Chloride abstraction from [(BCl)2(ttp)] gives the planar dication [B2(ttp)]2+, whereas chemical reduction of [(BCl)2(ttp)] by using magnesium anthracenide gives a neutral complex, [B(2)(ttp)], in which the TTP ligand has been reduced by two electrons to give an unusual example of an isophlorin complex. The cationic and neutral complexes [B2(ttp)]2+ and [B2(ttp)] were characterised through a combination of spectroscopic data that is supported by DFT calculations on the porphine analogues.     

Viral MRI contrast agents: coordination of Gd by native virions and attachment of Gd complexes by azide-alkyne cycloaddition

Icosahedral virus particles decorated with a Gd(DOTA) analogue by Cu-mediated azide-alkyne cycloaddition (CuAAC) and/or with Gd(3+) ions by coordination to the viral nucleoprotein show increased T(1) relaxivity relative to free Gd(DOTA) complexes in solution.     

Single-molecule force spectroscopy of β-peptides that display well-defined three-dimensional chemical patterns

Oligomers of β-amino acids ("β-peptides") can be designed to fold into stable helices that display side chains with a diverse range of chemical functionality in precise arrangements. We sought to determine whether the predictable, three-dimensional side-chain patterns generated by β-peptides could be used in combination with single-molecule force spectroscopy to quantify how changes in nanometer-scale chemical patterns affect intermolecular interactions. To this end, we synthesized β-peptides that were designed to be either globally amphiphilic (GA), i.e., display a global segregation of side chains bearing hydrophobic and cationic functional groups, or non-globally amphiphilic (iso-GA), i.e., display a more uniform distribution of hydrophobic and cationic functional groups in three-dimensions. Single-molecule force measurements of β-peptide interactions with hydrophobic surfaces through aqueous solution (triethanolamine buffer, pH 7.2) reveal that the GA and iso-GA isomers give rise to qualitatively different adhesion force histograms. The data are consistent with the display of a substantial nonpolar domain by the GA oligomer, which leads to strong hydrophobic interactions, and the absence of a comparable domain on the iso-GA oligomer. This interpretation is supported by force measurements in the presence of methanol, which is known to disrupt hydrophobic interactions. Our ability to associate changes in measured forces with changes in three-dimensional chemical nanopatterns projected from conformationally stable β-peptide helices highlights a contrast between this system and conventional peptides (α-amino acid residues): conventional peptides are more conformationally flexible, which leads to uncertainty in the three-dimensional nanoscopic chemical patterns that underlie measured forces. Overall, we conclude that β-peptide oligomers provide a versatile platform for quantifying intermolecular interactions that arise from specific functional group nanopatterns.     

Synthesis of enantiopure substituted piperidines via an aziridinium ring expansion

Herein we report a novel methodology for the asymmetric synthesis of 3-substituted piperidines from readily available chiral building blocks. This method, which features a novel irreversible dihydropyrole-tetrahydropyridine ring expansion, allows the introduction of a large variety of substituents at the 3-position and permits substitution at the 2- and 6-position giving mono-, di-, or trisubstituted piperidines with high diastereocontrol.     

Cembradienes from the Caribbean sea whip Eunicea sp.

A new cembradiene diterpenoid 1, together with the known antiplasmodial cembradiene 2, was isolated from the sea whip Eunicea sp. collected from Santa Marta Bay on the Colombian Caribbean sea. The structures and absolute stereochemistry of 1-2 were determined by extensive spectroscopic analysis, chemical transformation of 2 to the new diterpenoid 3, and by using modified Mosher’s method. This is the first known report regarding the determination of the absolute configuration of 2.     

Ultrasonic approach for formation of erbium oxide nanoparticles with variable geometries

Ultrasound (20 kHz, 29 W·cm(-2)) is employed to form three types of erbium oxide nanoparticles in the presence of multiwalled carbon nanotubes as a template material in water. The nanoparticles are (i) erbium carboxioxide nanoparticles deposited on the external walls of multiwalled carbon nanotubes and Er(2)O(3) in the bulk with (ii) hexagonal and (iii) spherical geometries. Each type of ultrasonically formed nanoparticle reveals Er(3+) photoluminescence from crystal lattice. The main advantage of the erbium carboxioxide nanoparticles on the carbon nanotubes is the electromagnetic emission in the visible region, which is new and not examined up to the present date. On the other hand, the photoluminescence of hexagonal erbium oxide nanoparticles is long-lived (μs) and enables the higher energy transition ((4)S(3/2)-(4)I(15/2)), which is not observed for spherical nanoparticles. Our work is unique because it combines for the first time spectroscopy of Er(3+) electronic transitions in the host crystal lattices of nanoparticles with the geometry established by ultrasound in aqueous solution of carbon nanotubes employed as a template material. The work can be of great interest for "green" chemistry synthesis of photoluminescent nanoparticles in water.     

Chromium-mediated stereoselective synthesis of carbohydrate-derived (E)-α,β-unsaturated esters or amides

A chromium-mediated novel synthesis of carbohydrate-derived di- and trisubstituted (E)-α,β-unsaturated esters or amides from a range of dichloroesters or amides and a variety of sugar aldehydes is reported. The process took place with total stereoselectivity and in high yields. A mechanism based on a sequential chromium-promoted aldol-type reaction and a completely stereoselective β-elimination reaction is proposed to explain these results.     

Dynamic modeling and simulation of a real world billiard

Gravitational billiards provide an experimentally accessible arena for testing formulations of nonlinear dynamics. We present a mathematical model that captures the essential dynamics required for describing the motion of a realistic billiard for arbitrary boundaries. Simulations of the model are applied to parabolic, wedge and hyperbolic billiards that are driven sinusoidally. Direct comparisons are made between the model?s predictions and previously published experimental data. It is shown that the data can be successfully modeled with a simple set of parameters without an assumption of exotic energy dependence.     

Electrically detected electron-spin-echo envelope modulation: a highly sensitive technique for resolving complex interface structures

We show that the electrical detection of electron-spin-echo envelope modulation (ESEEM) is a highly sensitive tool to study interfaces. Taking the Si/SiO2 interface defects in phosphorus-doped crystalline silicon as an example, we find that the main features of the observed echo modulation pattern allow us to develop a microscopic model for the dangling-bond-like P(b0) center by comparison with the results of ab initio calculations. The ESEEM spectrum is found to be far more sensitive to the defect characteristics than the spectrally resolved hyperfine splitting itself.