Studies of an Fe9 tridiminished icosahedron

The synthesis and structural characterization of a nonanuclear FeIII cage complex is reported. The nine iron centers in [Fe9(mu3-O)4(O3PPh)3(O2CCMe3)13] lie on the vertices of an incomplete icosahedron, with the P atoms of triphenylphosphonate at the other three vertices. The paramagnetic core therefore describes a tridiminished icosahedron. Magnetic studies suggest an S=1/2 ground state for the molecule. Analysis of exchange paths and the susceptibility data point to the interpretation that the cluster can be divided into two nearly decoupled sections: an {Fe6O3} section, with an S=0 ground state, in which three oxo-centered triangles bound a central triangle that is not oxo-centered; and an {Fe3O} triangle with S=1/2. The analysis of the susceptibility data leads to a Heisenberg model based on three significant antiferromagnetic exchange interactions, with values of 173.7 cm-1 in the {Fe3O} triangle, and 30.9 and 19.1 cm-1 within the {Fe6O3} section, while the exchange between them is <1 cm-1. With these assignments, the theoretical low-temperature differential susceptibility is also in very good agreement with measurements up to 50 T. Magnetic measurements in the milli-kelvin range reveal striking hysteresis loops and magnetization reversals associated with a Landau-Zener-Stückelberg (LZS) transition as enhanced by the occurrence of a phonon bottleneck.     

Reactions of 4-acetoxy-2H-1,4-benzoxazin-3-ones with some nucleophiles

O-Acetates of 4-hydroxy and 4-hydroxy-7-methoxy-2H-1,4-benzoxazin-3-ones reacted with nucleophiles such as phenols, indoles and ethanethiol. The major reaction center is the positively-charged nitrogen atom. In the reaction with 2-methylindole, 6-position of the benzoxazinone ring is another major reaction center.     

Kristall- und Molekülstruktur von 6-Ethoxy-12,12-dimethyldibenzo[d,g]-1,3,2,6-dioxaphosphasilocin-6-oxid

Synthesis and Crystal Structure of the Bis(amidinatochelate) Complex ClSb[Ph? C(NSiMe₃)₂]₂ The antimony(III) amidinato complex ClSb[Ph? C(NSiMe₃)₂]₂ was obtained by the reaction of antimony trichloride and N,N,N′-tris(trimethylsilyl)benzamidine in dichloromethane in form of pale-yellow, moisture sensitive crystals. X-ray crystal structure determinations were performed at 20°C and at ?93°C. Crystal data at 20°C: space group P1 , Z = 2, a = 1160.3(2), b = 1305.4(2), c = 1336.5(2) pm, α = 68.32(1), β = 79.79(1), γ = 71.47(1)°; at ?93°C the lattice vectors are 1.20 to 0.85% shorter. In the molecule two Ph? C(NSiMe₃)₂ groups are attached with their N atoms in a chelate manner to the Sb atom. Together with the Cl atom they form an irregular coordination polyhedron about the Sb atom with a stereochemically strongly effective lone electron pair. The SiMe₃ groups show considerable twisting vibrations about the N? Si axes even at ?93°C.     

Tuning the Surface of Nanoparticles: Impact of Poly(2‐ethyl‐2‐oxazoline) on Protein Adsorption in Serum and Cellular Uptake

Due to the adsorption of biomolecules, the control of the biodistribution of nanoparticles is still one of the major challenges of nanomedicine. Poly(2‐ethyl‐2‐oxazoline) (PEtOx) for surface modification of nanoparticles is applied and both protein adsorption and cellular uptake of PEtOxylated nanoparticles versus nanoparticles coated with poly(ethylene glycol) (PEG) and non‐coated positively and negatively charged nanoparticles are compared. Therefore, fluorescent poly(organosiloxane) nanoparticles of 15 nm radius are synthesized, which are used as a scaffold for surface modification in a grafting onto approach. With multi‐angle dynamic light scattering, asymmetrical flow field‐flow fractionation, gel electrophoresis, and liquid chromatography‐mass spectrometry, it is demonstrated that protein adsorption on PEtOxylated nanoparticles is extremely low, similar as on PEGylated nanoparticles. Moreover, quantitative microscopy reveals that PEtOxylation significantly reduces the non‐specific cellular uptake, particularly by macrophage‐like cells. Collectively, studies demonstrate that PEtOx is a very effective alternative to PEG for stealth modification of the surface of nanoparticles.

     

Solvent-induced dual chirality switching in the optical resolution of tropic acid via diastereomeric salt formation with (1R,2S)-2-amino-1,2-diphenylethanol

Solvent-induced chirality switching in the optical resolution of racemic tropic acid (TA) with (1R,2S)-2-amino-1,2-diphenylethanol has been demonstrated. Recrystallization of the diastereomeric salt mixture from i-PrOH or EtOH afforded the (S)-TA salt, while the (R)-TA salt was deposited from 1,4-dioxane and water-enriched alcohol solutions. Dual chirality switching was achieved by using two different types of solvents. The X-ray crystal structures of both diastereomeric salts showed that incorporation of the crystallization solvent played a crucial role in stabilizing each diastereomeric salt crystal. The mechanism of chirality switching has been discussed on the basis of the relative stability of the salt, as deduced from their structures.     

Attracting cavities for docking. Replacing the rough energy landscape of the protein by a smooth attracting landscape

Molecular docking is a computational approach for predicting the most probable position of ligands in the binding sites of macromolecules and constitutes the cornerstone of structure‐based computer‐aided drug design. Here, we present a new algorithm called Attracting Cavities that allows molecular docking to be performed by simple energy minimizations only. The approach consists in transiently replacing the rough potential energy hypersurface of the protein by a smooth attracting potential driving the ligands into protein cavities. The actual protein energy landscape is reintroduced in a second step to refine the ligand position. The scoring function of Attracting Cavities is based on the CHARMM force field and the FACTS solvation model. The approach was tested on the 85 experimental ligand–protein structures included in the Astex diverse set and achieved a success rate of 80% in reproducing the experimental binding mode starting from a completely randomized ligand conformer. The algorithm thus compares favorably with current state‐of‐the‐art docking programs. © 2015 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.     

Correlation between energy levels of linear and bent X2Y2 molecules

The permutation-inversion group developed by Longuet-Higgins is extended to a classification of the vibronic, torsional, and rotational wavefunctions of a nonrigid X₂Y₂ molecule by introducing a symmetry operation $\text{T}\text{?}$, which rotates the top half of the molecule by 2π and, accordingly, the molecule-fixed x axis by π. Since the energy levels of linear (D_∞h) and bent (C_2h, C_2h, and C₂) forms of X₂Y₂ are classified according to a set of common symmetry operations of this extended permutation-inversion group, their energy levels can be correlated, including those of nonrigid forms such as a quasilinear system or a free internal rotor. Nuclear spin weights and selection rules are derived.     

Comparison of the lattice Λ parameter with the continuum Λ parameter in massless QCD

The ratio of the scale parameter Λ in massless QCD defined on a lattice to the one in the continuum theory is determined by performing one-loop renormalization of the coupling constant. Our calculation method on a lattice directly relates Λ^lattice to the continuum one in the minimal subtraction scheme. The effect of incorporation of massless quarks depends on a parameter λ which is introduced to avoid trouble with fermions on a lattice. For λ=1, which is Wilson's value, the ratio previously calculated by Hasenfratz in the pure gauge theory is changed as follows:

$\text{Δ}{}_{\mathrm{\alpha =1}}{}^{\mathrm{MOM}}\text{Δ}{}^{\mathrm{lattice}}\text{=83.5}\text{for pure SU(3) gauge theory;}$

$\text{Δ}{}_{\mathrm{\alpha =1}}{}^{\mathrm{MOM}}\text{Δ}{}^{\mathrm{lattice}}\text{=105.7}\text{for QCD with 3 flavors;}$

$\text{Δ}{}_{\mathrm{\alpha =1}}{}^{\mathrm{MOM}}\text{Δ}{}^{\mathrm{lattice}}\text{=105.7}\text{117.0 for QCD with 4 flavors.}$

Critical properties of the lattice QCD will also be discussed briefly.