Topologically knotted Lagrangians in simply connected four-manifolds

Vidussi was the first to construct knotted Lagrangian tori in simply connected four-dimensional manifolds. Fintushel and Stern introduced a second way to detect such knotting. This note demonstrates that similar examples may be distinguished by the fundamental group of the exterior.

     

Controlled Annealing in Adaptive Multicomponent Gels

We use a pH-driven annealing process to convert between co-assembled and self-sorted networks in multicomponent gels. The initially formed gels at low pH are co-assembled, with the two components coexisting within the same self-assembled structures. We use an enzymatic approach to increase the pH, resulting in a gel-to-sol transition, followed by a hydrolysis to lower the pH once again. As the pH decreases, a self-sorted network is formed by a two-stage gelation process determined by the pK_a of each component. This approach can be expanded to layered systems to generate many varied systems by changing composition and rates of pH change, adapting their microstructure and so allowing access to a far greater range of morphologies and complexity than can be achieved in single component systems.     

Stability of self-assembled monolayers on titanium and gold

Methyl- and hydroxyl-terminated phosphonic acid self-assembled monolayers (SAMs) were coated on Ti from aqueous solution. Dodecyl phosphate and dodecyltrichlorosilane SAMs were also coated on Ti using solution-phase deposition. The stability of SAMs on Ti was investigated in Tris-buffered saline (TBS) at 37 degrees C using X-ray photoelectron spectroscopy, contact angle goniometry, and atomic force microscopy. For comparison purposes, a hydroxyl-terminated thiol SAM was coated on Au, and its stability was also investigated under similar conditions. In TBS, a significant proportion of phosphonic acid or phosphate molecules were desorbed from the Ti surface within 1 day, while the trichlorosilane SAM on Ti or thiol SAM on Au was stable for up to 7 days under similar conditions. The stability of hydroxyl-terminated phosphonic acid SAM coated Ti and thiol SAM coated Au was investigated in ambient air and ultraviolet (UV) light. In ambient air, the phosphonic acid SAM on Ti was stable for up to 14 days, while the thiol SAM on Au was not stable for 1 day. Under UV-radiation exposure, the alkyl chains of the phosphonic acid SAM were decomposed, leaving only the phosphonate groups on the Ti surface after 12 h. Under similar conditions, decomposition of alkyl chains of the thiol SAM was observed on the Au surface accompanied by oxidation of thiolates.     

Tris(2,2'-bipyridyl)ruthenium(II) chemiluminescence enhanced by silver nanoparticles

Mixtures of silver(I) and citrate that are used to produce silver nanoparticles evoke intense chemiluminescence with tris(2,2'-bipyridyl)ruthenium(II) and cerium(IV), which can be exploited for the determination of citrate ions and other analytes over a wide concentration range.     

Porous organic cage nanocrystals by solution mixing

We present here a simple method for the bottom-up fabrication of microporous organic particles with surface areas in the range 500-1000 m(2) g(-1). The method involves chiral recognition between prefabricated, intrinsically porous organic cage molecules that precipitate spontaneously upon mixing in solution. Fine control over particle size from 50 nm to 1 μm can be achieved by varying the mixing temperature or the rate of mixing. No surfactants or templates are required, and the resulting organic dispersions are stable for months. In this method, the covalent synthesis of the cage modules can be separated from their solution processing into particles because the modules can be dissolved in common solvents. This allows a "mix and match" approach to porous organic particles. The marked solubility change that occurs upon mixing cages with opposite chirality is rationalized by density functional theory calculations that suggest favorable intermolecular interactions for heterochiral cage pairings. The important contribution of molecular disorder to porosity and surface area is highlighted. In one case, a purposefully amorphized sample has more than twice the surface area of its crystalline analogue.     

1,3‐Dimethyl‐2‐oxo‐4,6‐diphenyl‐1,2,3,4‐tetrahydropyridine‐3‐carbonitrile

The crystal structure of the title compound, C₂₀H₁₈N₂O, reveals a distorted half‐chair conformation of the central tetra­hydro­pyridine (THP) ring, with the cyano‐ and adjacent phenyl‐substituted C atoms displaced by 0.329 (1) and ?0.315 (1) Å, respectively, from the THP best plane. Steric interactions force the phenyl rings out of the THP plane by 49.21 (9) and 65.76 (5)°. The cyano moiety is coplanar with the THP plane.     

Fluxional processes in diamagnetic and paramagnetic allyl dicarbonyl and 2-methylallyl dicarbonyl molybdenum histidinato complexes as revealed by spectroscopic data and density functional calculations

This work describes a detailed study on the structure and dynamics of pseudooctahedral low-valent complexes of the type [Mo(His-N(epsilon)-R)(eta-2-R'-allyl)(CO)(2)] (His=N(delta),N,O-L-histidinate; R=H, R'=H (1); R=C(2)H(4)CO(2)Me, R'=H (2); R=H, R'=Me (3); R=C(2)H(4)CO(2)Me, R'=Me (4)). These diamagnetic 18-electron complexes were comprehensively characterized spectroscopically and by X-ray crystallography. In the solid state, the (substituted) allyl ligand is in an endo position in all compounds, but it is trans to the His-N(delta) atom in 1 and 2, whereas it is trans to the carboxylate O atom for the 2-Me-allyl compounds 3 and 4. In solution, both isomers are present in a solvent-dependent equilibrium. The third isomer (allyl trans to His-NH(2)) is not spectroscopically observed in solution. This is in agreement with the results from density functional (DFT) computations (BPW 91 functional) for 1 and 3, which predict a considerably higher energy (+6.3 and +5.9 kJ mol(-1), respectively) for this isomer. A likely path for isomerization is calculated, which is consistent with the activation energy determined by variable temperature NMR measurements. At least for 3, the preferred path involves several intermediates and a rotation of the 2-Me-allyl ligand. For the paramagnetic 17-electron congeners, DFT predicts the exo isomer of 3(+) with the 2-Me-allyl ligand trans to the carboxylate O atom to be by far the most stable isomer. For 1(+), an endo-exo equilibrium between the isomers with the allyl ligand trans to the carboxylate O atom is suggested. These suggestions are confirmed by EPR spectroscopy on the electrochemically generated species, which show signals for one- (4) and two- (2) metal-containing compounds. The appearance of the EPR spectra may be rationalized by inspection of the SOMOs from DFT calculations of the species in question. The notion of a metal-centered oxidation is also substantiated by IR spectroelectrochemistry and by UV/Vis spectra of the 17-electron complexes. Upon depleting the metal of electron density, the stretching vibrations of the carbonyl ligands shift more than 100 cm(-1) to higher wavenumbers, and the carbonyl vibration of the metal-coordinated carboxylate shifts by about 50 cm(-1). A color change from yellow to green upon oxidation is observed visually and quantified by the appearance of a new band at 622 nm (2(+)) and 546 nm (4(+)), respectively.     

Magnetically Aligned Supramolecular Hydrogels

The magnetic‐field‐induced alignment of the fibrillar structures present in an aqueous solution of a dipeptide gelator, and the subsequent retention of this alignment upon transformation to a hydrogel upon the addition of CaCl₂ or upon a reduction in solution pH is reported. Utilising the switchable nature of the magnetic field coupled with the slow diffusion of CaCl₂, it is possible to precisely control the extent of anisotropy across a hydrogel, something that is generally very difficult to do using alternative methods. The approach is readily extended to other compounds that form viscous solutions at high pH. It is expected that this work will greatly expand the utility of such low‐molecular‐weight gelators (LMWG) in areas where alignment is key.     

Environmentally benign nanomixing by sonication in high-pressure carbon dioxide

Due to the increased use of nanocomposites, mixing at nanoscale has become important. Current mixing techniques can be classified into: (a) dry mixing (mechanical mixing), (b) wet mixing, and (c) simultaneous production of mixed nanoparticles (when possible). Dry mixing is in general not effective in achieving desired mixing at nanoscale, whereas wet mixing suffers from different disadvantages like nanomaterial of interest should be insoluble, has to wet the liquid, and involves additional steps of filtration and drying. This paper examines the use of pressurized carbon dioxide having high density and low viscosity to replace the liquids (e.g., n-hexane, toluene). Ultrasound is applied to the suspension of nanopowders in gaseous and supercritical carbon dioxide where high impact collisions during sonication help mixing and the final mixture is obtained by simple depressurization. The method is tested for binary mixture of alumina/silica, silica/titania, MWNT (multiwalled carbon nanotubes)/silica, and MWNT/titania. The effects of sonication intensity and pressure on the degree of mixing are studied. Comparative study is also done with liquid n-hexane as a mixing media. Quantitative characterization (e.g., mean composition standard deviation, intensity of segregation) of mixing of alumina/silica and silica/titania is done with energy-dispersive X-ray spectroscopy, and that of MWNT/silica and MWNT/titania is done using field-emission scanning electron microscopy and day-light illumination spectrophotometry. Results show that mixing in carbon dioxide at higher ultrasound amplitudes is as good as in liquid n-hexane, and the final mixed product does not contain any residual media as in the case of liquid n-hexane.     

From workplace air measurement results toward estimates of exposure? Development of a strategy to assess exposure to manufactured nano-objects

In the past few years, an increasing number of studies on workplace air measurements on manufactured nano-materials and -objects have been published. Most of the studies had a more explorative character, so a direct interpretation to workers” exposure for a given exposure situation, activity, or process is not a straight-forward process. In general, the studies use a quite similar package of devices for near real-time monitoring of particle number- and mass concentration in size ranges <100 nm up to 10 μm, and the collection of samples for off-line characterization of air samples. Various approaches for addressing background concentrations and its use to indicate the potential for exposure to nano-objects could be observed. Within the EU-sponsored NANOSH project, a harmonized approach for measurement strategy, data analysis and reporting was developed. In addition to time/activity–concentration profiles as reported by most studies, this approach enables a first step to estimate the potential for exposure to manufactured nano-objects, more quantitatively. The NANOSH data will be collated into a base, which may form the starting point for a harmonized database facilitating overall analysis in near future, to derive estimates for exposure for several exposure situations.