Intramolecular Frustrated Lewis Pair with the Smallest Boryl Site: Reversible H2 Addition and Kinetic Analysis

Ansa‐aminoborane 1 (ortho‐TMP? C₆H₄? BH₂; TMP=2,2,6,6‐tetramethylpiperid‐1‐yl), a frustrated Lewis pair with the smallest possible Lewis acidic boryl site (? BH₂), is prepared. Although it is present in quenched forms in solution, and BH₂ represents an acidic site with reduced hydride affinity, 1 reacts with H₂ under mild conditions producing ansa‐ammonium trihydroborate 2 . The thermodynamic and kinetic features as well as the mechanism of this reaction are studied by variable‐temperature NMR spectroscopy, spin‐saturation transfer experiments, and DFT calculations, which provide comprehensive insight into the nature of 1 .     

Synthesis of tricarbonyl(N-methylisatin)chromium(0) and an unanticipated transformation of a N-MEM to a N-MOM group

The synthesis of tricarbonyl(N-methylisatin)chromium(0) (6) was achieved by protection of the keto functionality of the ligand as an acetal followed by complexation with tricarbonyl(naphthalene)chromium(0) and subsequent deprotection with formic acid. In order to obtain a removable substituent at nitrogen, N-methoxyethoxymethyl (N-MEM) substituted isatin 12 was prepared. Upon acetalization with trimethylformiate in methanol under acidic reaction conditions the corresponding methoxymethyl (N-MOM) derivative was unexpectedly obtained. This substitution was highly accelerated by microwave irradiation. Complexation of the N-MEM and N-MOM substituted isatin afforded only poor yields. The addition of vinylmagnesium bromide at 6 takes place not only at the keto group but also at the lactam carbonyl group. Divinylation at either one of the carbonyl functions was also achieved with the product distribution being highly dependent on the reaction time.     

Self-limited oxygen exchange kinetics at SnO2 surfaces

The oxygen exchange at SnO(2) surfaces strongly depends on surface termination, which is affected by the oxygen chemical potential. At low oxygen chemical potential, the surface adopts its reduced termination which allows oxygen exchange, while exchange is suppressed by the stoichiometric surface termination.     

Rapid determination of 239Pu in urine samples using molecular recognition technology product AnaLig®Pu-02 gel

This paper describes the use of IBC′s AnaLig^®Pu-02 molecular recognition technology product to effectively and selectively pre-concentrate, separate and recover plutonium from urine samples. This method uses two-stage column separations consisting of two different commercial products, Eichrom’s Pre-filter Material and AnaLig^®Pu-02 resin from IBC Advanced Technologies. By eliminating the co-precipitation techniques and the ashing steps to remove residual organics, the analysis time was reduced significantly. The method was successfully tested by adding known activities of reference solutions of ²⁴²Pu and ²³⁹Pu to urine samples.     

Modal Analysis of Vehicle Power Trains

In this study, modal analysis of vehicle power trains is based on the linearization of the underlying equations of motions at specified time instants. The equations of motion represent a flexible multi-body system where force-elements (joints) connect different bodies. Whenever the linearization leads to an ordinary differential equation with constant coefficients, a standard eigenvalue procedure is used, to compute eigenvalues and mode shapes. The concept is applied to a vehicle power train. Comparison of the results with a commercial software product provide good agreement. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the Mechanism of Bifunctional Squaramide‐Catalyzed Organocatalytic Michael Addition: A Protonated Catalyst as an Oxyanion Hole

A joint experimental–theoretical study of a bifunctional squaramide‐amine‐catalyzed Michael addition reaction between 1,3‐dioxo nucleophiles and nitrostyrene has been undertaken to gain insight into the nature of bifunctional organocatalytic activation. For this highly stereoselective reaction, three previously proposed mechanistic scenarios for the critical C?C bond‐formation step were examined. Accordingly, the formation of the major stereoisomeric products is most plausible by one of the bifunctional pathways that involve electrophile activation by the protonated amine group of the catalyst. However, some of the minor product isomers are also accessible through alternative reaction routes. Structural analysis of transition states points to the structural invariance of certain fragments of the transition state, such as the protonated catalyst and the anionic fragment of approaching reactants. Our topological analysis provides deeper insight and a more general understanding of bifunctional noncovalent organocatalysis.     

External and internal plasticization of cellulose acetate with caprolactone: Structure and properties

Cellulose acetate was modified with caprolactone in an internal mixer at temperatures between 120 and 220 °C, and reaction times between 5 and 45 min in the presence of tinoctoate catalyst. The effect of plasticization on the properties of the polymer was studied by dynamic mechanical analysis and tensile testing. The dynamic mechanical spectrum of cellulose acetate exhibits three main relaxation transitions. These can be assigned to segments (α), to smaller structural units of the main chain, probably individual glucose rings (β), and to hydroxyl or hydroxylmethyl groups (γ). Plasticization by caprolactone leads to the decrease of the glass transition temperature of CA, but also to the breakdown of relatively large segments to smaller structural units. Free hydroxyl groups interact with the plasticizer forming larger units with higher transition temperature. Grafting decreases the intensity of the γ‐transition peak. External plasticization creates a larger number of small structural units, but the external plasticizer is less efficient in the decrease of stiffness than grafted polycaprolactone chains. Internal plasticization is more advantageous because it leads to higher flexibility at larger strength than external plasticization, and the migration of the plasticizer is prevented at the same time. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 873–883, 2007     

A Genetically Encoded Isonitrile Lysine for Orthogonal Bioorthogonal Labeling Schemes

Bioorthogonal click-reactions represent ideal means for labeling biomolecules selectively and specifically with suitable small synthetic dyes. Genetic code expansion (GCE) technology enables efficient site-selective installation of bioorthogonal handles onto proteins of interest (POIs). Incorporation of bioorthogonalized non-canonical amino acids is a minimally perturbing means of enabling the study of proteins in their native environment. The growing demand for the multiple modification of POIs has triggered the quest for developing orthogonal bioorthogonal reactions that allow simultaneous modification of biomolecules. The recently reported bioorthogonal [4 + 1] cycloaddition reaction of bulky tetrazines and sterically demanding isonitriles has prompted us to develop a non-canonical amino acid (ncAA) bearing a suitable isonitrile function. Herein we disclose the synthesis and genetic incorporation of this ncAA together with studies aiming at assessing the mutual orthogonality between its reaction with bulky tetrazines and the inverse electron demand Diels–Alder (IEDDA) reaction of bicyclononyne (BCN) and tetrazine. Results showed that the new ncAA, bulky-isonitrile-carbamate-lysine (BICK) is efficiently and specifically incorporated into proteins by genetic code expansion, and despite the slow [4 + 1] cycloaddition, enables the labeling of outer membrane receptors such as insulin receptor (IR) with a membrane-impermeable dye. Furthermore, double labeling of protein structures in live and fixed mammalian cells was achieved using the mutually orthogonal bioorthogonal IEDDA and [4 + 1] cycloaddition reaction pair, by introducing BICK through GCE and BCN through a HaloTag technique.     

Chemical Swarming: Depending on Concentration,an Amphiphilic Ruthenium Polypyridyl Complex Induces Cell Death via Two Different Mechanisms

The crystal structure and in vitro cytotoxicity of the amphiphilic ruthenium complex [ 3 ](PF₆)₂ are reported. Complex [ 3 ](PF₆)₂ contains a Ru?S bond that is stable in the dark in cell‐growing medium, but is photosensitive. Upon blue‐light irradiation, complex [ 3 ](PF₆)₂ releases the cholesterol–thioether ligand 2 and an aqua ruthenium complex [ 1 ](PF₆)₂. Although ligand 2 and complex [ 1 ](PF₆)₂ are by themselves not cytotoxic, complex [ 3 ](PF₆)₂ was unexpectedly found to be as cytotoxic as cisplatin in the dark, that is, with micromolar effective concentrations (EC₅₀), against six human cancer cell lines (A375, A431, A549, MCF‐7, MDA‐MB‐231, and U87MG). Blue‐light irradiation (λ=450 nm, 6.3 J cm^?2) had little influence on the cytotoxicity of [ 3 ](PF₆)₂ after 6 h of incubation time, but it increased the cytotoxicity of the complex by a factor 2 after longer (24 h) incubation. Exploring the unexpected biological activity of [ 3 ](PF₆)₂ in the dark elucidated an as‐yet unknown bifaceted mode of action that depended on concentration, and thus, on the aggregation state of the compound. At low concentration, it acts as a monomer, inserts into the membrane, and can deliver [ 1 ]²⁺ inside the cell upon blue‐light activation. At higher concentrations (>3–5 μm ), complex [ 3 ](PF₆)₂ forms supramolecular aggregates that induce non‐apoptotic cell death by permeabilizing cell membranes and extracting lipids and membrane proteins.