Electrophilic organic selenium reagents—protonated seleninic acids as precursors for unsymmetrical aromatic selenides

Arylselenylations of methylbenzenes, methoxybenzenes and thiophene were smoothly achieved with selenenium ions generated by comproportionation of 1:1 mixtures of p-toluenesulfonic acid salts of seleninic acids and the corresponding diselenides. A series of p-toluenesulfonic salts of seleninic acids were prepared by hydrogen peroxide oxidation of the corresponding diselenides in the presence of p-toluenesulfonic acid. Novel 2-(organylseleno)thiophenes were obtained by heating the protonated seleninic acids with a 50-fold excess of thiophene in glacial acetic acid.     

Duplex and triplex formation of mixed pyrimidine oligonucleotides with stacking of phenyl-triazole moieties in the major groove

5-(1-Phenyl-1,2,3-triazol-4-yl)-2'-deoxycytidine was synthesized from a modified CuAAC protocol and incorporated into mixed pyrimidine oligonucleotide sequences together with the corresponding 5-(1-phenyl-1,2,3-triazol-4-yl)-2'-deoxyuridine. With consecutive incorporations of the two modified nucleosides, improved duplex formation with a complementary RNA and improved triplex formation with a complementary DNA duplex were observed. The improvement is due to π-π stacking of the phenyl-triazole moieties in the major groove. The strongest stacking and most pronounced positive influence on thermal stability was found in between the uridine analogues or with the cytidine analogue placed in the 3' direction to the uridine analogue. Modeling indicated a different orientation of the phenyl-triazole moieties in the major groove to account for the difference between the two nucleotides. The modified oligonucleotides were all found to be significantly stabilized toward nucleolytic degration.     

Bandgap guidance in hybrid chalcogenide-silica photonic crystal fibers

We report a hybrid chalcogenide-silica photonic crystal fiber made by pressure-assisted melt-filling of molten glass. Photonic bandgap guidance is obtained at a silica core placed centrally in a hexagonal array of continuous centimeters-long chalcogenide strands with diameters of 1.45 μm. In the passbands of the cladding, when the transmission through the silica core is very weak, the chalcogenide strands light up with distinct modal patterns corresponding to Mie resonances. In the spectral regions between these passbands, strong bandgap guidance is observed, where the silica core transmission loss is 60 dB/cm lower. The pressure-assisted fabrication approach opens up new ways of integrating sophisticated glass-based devices into optical fiber circuitry with potential applications in supercontinuum generation, magneto-optics, wavelength selective devices, and rare-earth-doped amplifiers with high gain per unit length.     

Controlled food protein aggregation for new functionality

Globular proteins are an important component of many food products. Heat-induced aggregation of globular proteins gives them new properties that can be useful in food products. In order to optimize functionality, the aggregation process needs to be controlled, which in turn requires good understanding of the mechanism. Heating aqueous solutions of globular proteins leads to the formation of aggregates with one of four distinctly different morphologies: spherical particles, flexible strands, semi-flexible fibrils, and fractal clusters. We review recent research in this area focusing on the parameters that control the morphology including the influence of hydrolysis. The aggregation mechanism and the effect of the morphology on the functionality will be addressed. A distinction is made between primary aggregation leading to roughly spherical particles or more or less flexible strands and secondary aggregation leading to fractal clusters, gels or precipitates. We will discuss how the formation of aggregates with different morphologies is related to the formation of either particulate or fine stranded gels.     

From collisions to clusters: first steps of sulphuric acid nanocluster formation dynamics

The clustering of sulphuric acid with base molecules is one of the main pathways of new-particle formation in the Earth's atmosphere. First step in the clustering process is likely the formation of a (sulphuric acid)₁(base)₁(water)_n cluster. Here, we present results from direct first-principles molecular dynamics collision simulations of (sulphuric acid)₁(water)_{0, 1} + (dimethylamine) → (sulphuric acid)₁(dimethylamine)₁(water)_{0, 1} cluster formation processes. The simulations indicate that the sticking factor in the collisions is unity: the interaction between the molecules is strong enough to overcome the possible initial non-optimal collision orientations. No post-collisional cluster break up is observed. The reasons for the efficient clustering are (i) the proton transfer reaction which takes place in each of the collision simulations and (ii) the subsequent competition over the proton control. As a consequence, the clusters show very dynamic ion pair structure, which differs from both the static structure optimisation calculations and the equilibrium first-principles molecular dynamics simulations. In some of the simulation runs, water mediates the proton transfer by acting as a proton bridge. In general, water is able to notably stabilise the formed clusters by allocating a fraction of the released clustering energy.     

Highly Enantioselective Rhodium(I)‐Catalyzed Activation of Enantiotopic Cyclobutanone C?C Bonds

The selective functionalization of carbon–carbon σ bonds is a synthetic strategy that offers uncommon retrosynthetic disconnections. Despite progress in C C activation and its great importance, the development of asymmetric reactions lags behind. Rhodium(I)‐catalyzed selective oxidative additions into enantiotopic C C bonds in cyclobutanones are reported. Even operating at a reaction temperature of 130 °C, the process is characterized by outstanding enantioselectivity with the e.r. generally greater than 99.5:0.5. The intermediate rhodacycle is shown to react with a wide variety of tethered olefins to deliver complex bicyclic ketones in high yields.     

Structural and spectroscopic characterization of mononuclear copper(I) nitrosyl complexes: end-on versus side-on coordination of NO to copper(I)

Two crystal structures of the mononuclear copper(I)-nitrosyl complexes [Cu(L3)(NO)] (1) and [Cu(L3')(NO)](ClO4) (2) with the related coligands L3- (hydrotris(3-tert-butyl-5-isopropyl-1-pyrazolyl)borate) and L3' (tris(3-tert-butyl-5-isopropyl-1-pyrazolyl)methane) are presented. These compounds are then investigated in detail using a variety of spectroscopic methods. Vibrational spectra show nu(N-O) at 1698 cm(-1) and nu(Cu-NO) split at 365/338 cm(-1) for 1, which translates to force constants of 12.53 (N-O) and 1.31 mdyn/A (Cu-NO), respectively. The weak Cu-NO force constant is in agreement with the observed instability of the Cu-NO bond. Interestingly, complex 2 with the neutral coligand L3' shows a stronger N-O bond, evident from nu(N-O) at 1742 cm(-1). This difference is attributed to a true second coordination sphere effect, where the covalency of the Cu(I)-NO bond is not altered. The EPR spectrum of 1 is in agreement with the Cu(I)-NO(radical) electronic structure of the complexes, as obtained from density functional theory (DFT) calculations. In addition, an interesting trend between g parallel(gz) and the Cu-N-O angle is established. Finally, high-quality MCD spectra of 1 are presented and assigned using TD-DFT calculations. Based on the in-depth spectroscopic characterization of end-on bound NO to copper(I) presented in this work, it is possible to determine the binding mode of the Cu-NO intermediate of Cu nitrite reductase studied by Scholes and co-workers (Usov, O. M.; Sun, Y.; Grigoryants, V. M.; Shapleigh, J. P.; Scholes, C. P., J. Am. Chem. Soc. 2006, 128, 13102-13111) in solution as strongly bent (approximately 135 degrees) but likely not side-on.     

The influence of bond rigidity and cluster diffusion on the self-diffusion of hard spheres with square well interaction

Hard spheres interacting through a square well potential were simulated by using two different methods: Brownian cluster dynamics (BCD) and event driven Brownian dynamics (EDBD). The structure of the equilibrium states obtained by both methods was compared and found to be almost identical. Self-diffusion coefficients (D) were determined as a function of the interaction strength. The same values were found by using BCD or EDBD. Contrary to EDBD, BCD allows one to study the effect of bond rigidity and hydrodynamic interaction within the clusters. When the bonds are flexible, the effect of attraction on D is relatively weak compared to systems with rigid bonds. D increases first with increasing attraction strength, and then decreases for stronger interaction. Introducing intracluster hydrodynamic interaction weakly increases D for a given interaction strength. Introducing bond rigidity causes a strong decrease in D which no longer shows a maximum as function of the attraction strength.     

Scalable Production of Monodisperse Bioactive Spider Silk Nanowires

Elongated protein-based micro- and nanostructures are of great interest for a wide range of biomedical applications, where they can serve as a backbone for surface functionalization and as vehicles for drug delivery. Current production methods for protein constructs lack precise control of either shape and dimensions or render structures fixed to substrates. This work demonstrates production of recombinant spider silk nanowires suspended in solution, starting with liquid bridge induced assembly (LBIA) on a substrate, followed by release using ultrasonication, and concentration by centrifugation. The significance of this method lies in that it provides i) reproducability (standard deviation of length <13% and of diameter <38%), ii) scalability of fabrication, iii) compatibility with autoclavation with retained shape and function, iv) retention of bioactivity, and v) easy functionalization both pre- and post-formation. This work demonstrates how altering the function and nanotopography of a surface by nanowire coating supports the attachment and growth of human mesenchymal stem cells (hMSCs). Cell compatibility is further studied through integration of nanowires during aggregate formation of hMSCs and the breast cancer cell line MCF7. The herein-presented industrial-compatible process enables silk nanowires for use as functionalizing agents in a variety of cell culture applications and medical research.