From pico to nano: biofunctionalization of cube-octameric silsesquioxanes by peptides and miniproteins

Polyhedral silsesquioxanes are considered valuable conjugation scaffolds. Nevertheless, only a few examples of silsesquioxane-assembled peptide oligomers have been reported to date. We developed a new bioorthogonal cube-octameric silsesquioxane (COSS) scaffold bearing eight aminooxy coupling sites allowing for the conjugation of diverse peptides via oxime ligation. We found that the coupling efficacy depends on the ligand in view of steric hindrance and electrostatic repulsion. For the first time scaffold-based conjugation of cystine-knot miniproteins having a backbone of about thirty amino acids was successfully accomplished without loss of bioactivity. Atomic force microscopy (AFM) provided further knowledge on the size of COSS verifying them as picoscaffolds growing upon bioconjugation to nano-dimension.     

Orbital-resolved partial charge transfer from the methoxy groups of substituted pyrenes in complexes with tetracyanoquinodimethane--a NEXAFS study

It is demonstrated that the near-edge X-ray absorption fine structure (NEXAFS) provides a powerful local probe of functional groups in novel charge transfer (CT) compounds and their electronic properties. Microcrystals of tetra-/hexamethoxypyrene as donors with the strong acceptor tetracyano-p-quinodimethane (TMP/HMP-TCNQ) were grown by vapor diffusion. The oxygen and nitrogen K-edge spectra are spectroscopic fingerprints of the functional groups in the donor and acceptor moieties, respectively. The orbital selectivity of the NEXAFS pre-edge resonances allows us to precisely elucidate the participation of specific orbitals in the charge transfer process. Upon complex formation, the intensities of several resonances change substantially and a new resonance occurs in the oxygen K-edge spectrum. This gives evidence of a corresponding change of hybridization of specific orbitals in the functional groups of the donor (those derived from the frontier orbitals 2e and 6a(1) of the isolated methoxy group) and acceptor (orbitals b(3g), a(u), b(1g), and b(2u), all located at the cyano group) with π*-orbitals of the ring systems. Along with this intensity effect, the resonance positions associated with the oxygen K-edge (donor) and nitrogen K-edge (acceptor) shift to higher and lower photon energies in the complex, respectively. A calculation based on density functional theory qualitatively explains the experimental results. NEXAFS measurements shine light on the action of the functional groups and elucidate charge transfer on a submolecular level.     

Solid-state syntheses of coordination polymers by thermal conversion of molecular building blocks and polymeric precursors

The syntheses and crystal structures of a mononuclear cadmium complex and five novel coordination polymers based on 1,2,4-triazolyl benzoates are presented. The compounds (∞)(3)[Cd(H-Me-trz-pba)(2)] (2), (∞)(3)[Cd(Me-3py-trz-pba)(2)] (4), and (∞)(3)[Zn(H-Me-trz-pba)(2)] (6) can be obtained by solvothermal synthesis or simple heating of the starting materials in appropriate solvents, and are also accessible by thermal conversion of the complex [Cd(H-Me-trz-pba)(2)(H(2)O)(4)] (1), the one-dimensional (1D) coordination polymer (∞)(1)[Cd(Me-3py-trz-pba)(2)(H(2)O)(2)]·H(2)O (3), and the porous three-dimensional (3D) framework (∞)(3)[Zn(H-Me-trz-pba)2]·4H(2)O (5), respectively. The driving force for these conversions is the formation of thermally stable, nonporous, crystalline 3D coordination polymers. The structural transformations are accompanied by the loss of water and reveal significant changes of the coordination spheres of the metal ions caused by a rearrangement of the triazolyl benzoate ligands. Compounds 2, 4, 5, and 6 exhibit 4- and 5-fold interpenetration of diamondoid networks (dia) and are thermally stable up to 380 °C.     

Selective synthesis and derivatization of alkali metal silanides MSi(SiH3)3

Greetings from silicon valley: Alkali metal silanides (H(3)Si)(3)Si(-)M(+) were shown to be selectively accessible for the first time by the reaction of neopentasilane Si(SiH(3))(4) with tBuOM or iPr(2)NLi. The method allows the convenient derivatization of higher silicon hydrides and provides a simple access for unprecedented systematic studies on the chemical behavior of hydropolysilanes (see scheme).     

New Trioxane Copolymers

Abstract

A review is given on two types of trioxane copolymers: trioxane/dioxolane copolymers and copolymers of trioxane with polar monomers. It has been possible to find reaction conditions that influence the transacetalization reaction and, hence, the molecular weight distribution and the sequence length of trioxane/dioxolane copolymers. Trioxane copolymers with varying dioxolane content show an unusual behavior with respect to density, specific volume, and melting point as a function of composition. This is possibly caused by the formation of at least four different crystal structures in such copolymers. The synthesis of polyoxymethylenes carrying reactive groups is possible by copolymerizing trioxane with substituted phenylglycidyl ethers. These copolymers can be subjected to further chemical modification leading to poly-oxymethylenes with aldehyde, carboxy, and amino groups or derivatives thereof.     

Self-Dual Noncommutative {\phi^4} -Theory in Four Dimensions is a Non-Perturbatively Solvable and Non-Trivial Quantum Field Theory

We study quartic matrix models with partition function \({\mathcal{Z}[E, J] = \int dM}\) exp(trace \({(JM - EM^{2} - \frac{\lambda}{4} M^4)}\) ). The integral is over the space of Hermitean \({\mathcal{N} \times \mathcal{N}}\) -matrices, the external matrix E encodes the dynamics, \({\lambda > 0}\) is a scalar coupling constant and the matrix J is used to generate correlation functions. For E not a multiple of the identity matrix, we prove a universal algebraic recursion formula which gives all higher correlation functions in terms of the 2-point function and the distinct eigenvalues of E. The 2-point function itself satisfies a closed non-linear equation which must be solved case by case for given E. These results imply that if the 2-point function of a quartic matrix model is renormalisable by mass and wavefunction renormalisation, then the entire model is renormalisable and has vanishing β-function. As the main application we prove that Euclidean \({\phi^4}\) -quantum field theory on four-dimensional Moyal space with harmonic propagation, taken at its self-duality point and in the infinite volume limit, is exactly solvable and non-trivial. This model is a quartic matrix model, where E has for \({\mathcal{N} \to \infty}\) the same spectrum as the Laplace operator in four dimensions. Using the theory of singular integral equations of Carleman type we compute (for \({\mathcal{N} \to \infty}\) and after renormalisation of \({E, \lambda}\) ) the free energy density (1/volume) log \({(\mathcal{Z}[E, J]/\mathcal{Z}[E, 0])}\) exactly in terms of the solution of a non-linear integral equation. Existence of a solution is proved via the Schauder fixed point theorem. The derivation of the non-linear integral equation relies on an assumption which in subsequent work is verified for coupling constants \({\lambda \leq 0}\) .