Implantation of tellurium in iron and measurement of the magnetic moment of the first excited state in123Te

By means of an isotope separator, the¹²³Te^m activity has been implanted in iron. The attenuation of thee—γ angular correlation was measured using a randomly oriented magnetic hyperfine interaction. From this the magnetic moment of the 159 keV first excited 3/2⁺ state has been obtained to be ¦μ¦=0.72±0.12 n.m. This value was found to be in agreement with the Kisslinger-Sorensen prediction and consistent with the systematics observed for the character of the 3/2⁺–1/2⁺ transitions in the odd tellurium isotopes.     

The magnetic moment of the lowest 3/2− state in57Co

The reaction⁵⁴Fe(α, n)⁵⁷Ni has been used to implant⁵⁷Co isotopes in ferromagnetic iron. Theg-factor of the lowest 3/2^? state is determined using the internal field in a constant angle reversed field method. The angular correlation of the 127–1,378 keV cascade is also measured. The result of the angular correlation measurement together with reaction data is consistent withp _3/2 andp _1/2 single particle assignments to the lowest 3/2^? resp. 1/2^? state. In view of this statement the quenching of the magnetic moment is discussed.     

Carbosilane dendrimeric carbodiimides: site isolation as a lactamization tool

The convergent syntheses of three generations of carbosilane dendrimeric carbodiimides are described. The wedge-type building blocks were synthesized in a divergent way, starting from allyl chloride and a repetitive sequence of hydrosilylation with HSiCl3 and a Grignard reaction with allylmagnesium bromide. Hydrogenation of the terminal double bonds led to inert and stable wedges. The chloride substituent at the focal point was transformed into several functional groups that eventually led to dendrimeric structures with a carbodiimide core. The extent of the site isolation effect of the dendrimers was studied with dilution experiments monitored by FT-IR spectroscopy on the corresponding dendrimeric ureas. These studies showed that only the first generation self-aggregates via hydrogen bonding, while the second and the third do not, implying isolation of core-bound moieties. The dendrimeric carbodiimides mediated lactamization reactions to obtain homodiketopiperazines.     

slate: A method for the superposition of flexible ligands

A novel program for the superposition of flexible molecules, slate, is presented. It uses simulated annealing to minimise the difference between the distance matrices calculated from the hydrogen-bonding and aromatic-ring properties of two ligands. A method for generating a molecular stack using multiple pairwise matches is illustrated. These stacks are used by the program doh to predict the relative positions of receptor atoms that could form hydrogen bonds to two or more ligands in the dataset. The methodology has been applied to ligands binding to dihydrofolate reductase, thermolysin, H₃ histamine receptors, ₂ adrenoceptors and 5-HT_1D receptors. When there are sufficient numbers and diversity of molecules in the dataset, the prediction of receptor-atom positions is applicable to compound design.     

Effect of chain length on the glyme-separated ion-pair formation in bolaform salts of α,ω-(9-fluorenyl)polymethylenes

Formation constants of tetraglyme (glyme 5) separated ion pairs of bolaform electrolytes of the type Na⁺,^–Fl(CH₂) _n Fl^–, Na⁺ (Fl^– denoting a fluorenyl carbanion) were measured spectrophotometrically in tetrahydrofuran (THF) and tetrahydropyran (THP) at 25°C as a function of the chain lengthn, withn=2, 3, 4, or 6. The ratiosK ₁/K ₂ of the first and second glyme ion-pair separation steps were found to be equal to the statistical factor 4 in all cases except in THP for the compoundn=2, where the ratio is 15. Values ofK ₁ as well as K ₂ increase considerably with chain length, the former by a factor 19 asn increases from 2 to 6. The ion-pair separation with glyme 5 is easier in THP than in THF. The results are discussed in terms of differences in external cation solvation and the possible involvement of cyclized structures or curled conformations as a result of interactions between the terminal ion pairs.     

Intramolecular energy transfer in a tetra-coumarin perylene system: influence of solvent and bridging unit on electronic properties

The synthesis and characterisation of a novel coumarin donor-perylene bisimide acceptor light-harvesting system is reported, in which an energy-transfer efficiency of >99% is achieved. Comparison of the excited-state properties of the donor-acceptor system with model compounds revealed that although the photophysical properties of the perylene bisimide acceptor unit are affected considerably by the nature of the substituent at the imide positions and the solvent employed, through-bond interaction between the donor and acceptor units is negligible. Energy transfer in the present system can be described as occurring via a through-space energy-transfer mechanism. Careful consideration of the redox properties of the donor relative to the acceptor units allows for avoidance of potentially deleterious excited-state electron-transfer processes.     

Self‐Orienting Hydrogel Micro‐Buckets as Novel Cell Carriers

Hydrogel microparticles are important in materials engineering, but their applications remain limited owing to the difficulties associated with their manipulation. Herein, we report the self‐orientation of crescent‐shaped hydrogel microparticles and elucidate its mechanism. Additionally, the microparticles were used, for the first time, as micro‐buckets to carry living cells. In aqueous solution, the microparticles spontaneously rotated to a preferred orientation with the cavity facing up. We developed a geometric model that explains the self‐orienting behavior of crescent‐shaped particles by minimizing the potential energy of this specific morphology. Finally, we selectively modified the particles’ cavities with RGD peptide and exploited their preferred orientation to load them with living cells. Cells could adhere, proliferate, and be transported and released in vitro. These micro‐buckets hold a great potential for applications in smart materials, cell therapy, and biological engineering.     

Access to Metastable Gel States Using Seeded Self‐Assembly of Low‐Molecular‐Weight Gelators

Here we report on how metastable supramolecular gels can be formed through seeded self‐assembly of multicomponent gelators. Hydrazone‐based gelators decorated with non‐ionic and anionic groups are formed in situ from hydrazide and aldehyde building blocks, and lead through multiple self‐sorting processes to the formation of heterogeneous gels approaching thermodynamic equilibrium. Interestingly, the addition of seeds composing of oligomers of gelators bypasses the self‐sorting processes and accelerates the self‐assembly along a kinetically favored pathway, resulting in homogeneous gels of which the network morphologies and gel stiffness are markedly different from the thermodynamically more stable gel products. Importantly, over time, these metastable homogeneous gel networks are capable of converting into the thermodynamically more stable state. This seeding‐driven formation of out‐of‐equilibrium supramolecular structures is expected to serve as a simple approach towards functional materials with pathway‐dependent properties.     

Molecular patterning at a liquid/solid interface: the foldamer approach

Molecular patterning has received a lot of attention in the past decade; however, the functionalization of these surface-confined 2D patterns on the nanoscale level remains a challenge. Assembling 2D patterns from oligomeric foldamers turns out to be an interesting approach to accomplishing the controlled positioning of functional elements. We designed a family of peptidomimetic foldamers bearing a 2D turn element folding at the liquid/solid interface. The turning element was developed while studying derivatives with one turning unit. Furthermore, folding was found to be induced by the confinement of the surface. This achievement paves the way for the design of foldamers with multiple turns, providing a higher versatility in the functionalization of nanopatterns.