A series of isoreticular, highly stable, porous zirconium oxide based metal-organic frameworks

Brolly good MOFs: A new series of hydrophobic isoreticular porous Zr oxide dicarboxylate MOFs have been prepared (see picture, Zr?blue polyhedra, O?red, C?black). They have a one-dimensional pore system, a rare combination of Lewis acidity and hydrophobic character, and a higher hydrothermal and mechanical stability than their UiO MOF polymorph counterparts.     

Structure determination of neutral MgO clusters--hexagonal nanotubes and cages

Structural information for neutral magnesium oxide clusters has been obtained by a comparison of their experimental vibrational spectra with predictions from theory. (MgO)(n) clusters with n = 3-16 have been studied in the gas phase with a tunable IR-UV two-color ionization scheme and size-selective infrared spectra have been measured. These IR spectra are compared to the calculated spectra of the global minimum structures predicted by a hybrid ab initio genetic algorithm. The comparison shows clear evidence that clusters of the composition (MgO)(3k) (k = 1-5) form hexagonal tubes, which confirm previous theoretical predictions. For the intermediate sizes (n≠ 3k) cage-like structures containing hexagonal (MgO)(3) rings are identified. Except for the cubic (MgO)(4) no evidence for bulk like structures is found.     

Patchy worm-like micelles: solution structure studied by small-angle neutron scattering

Triblock terpolymers exhibit a rich self-organization behavior including the formation of fascinating cylindrical core-shell structures with a phase separated corona. After crystallization-induced self-assembly of polystyrene-block-polyethylene-block-poly(methyl methacrylate) triblock terpolymers (abbreviated as SEMs = Styrene-Ethylene-Methacrylates) from solution, worm-like core-shell micelles with a patchy corona of polystyrene and poly(methyl methacrylate) were observed by transmission electron microscopy. However, the solution structure is still a matter of debate. Here, we present a method to distinguish in situ between a Janus-type (two faced) and a patchy (multiple compartments) configuration of the corona. To discriminate between both models the scattering intensity must be determined mainly by one corona compartment. Contrast variation in small-angle neutron scattering enables us to focus on one compartment of the worm-like micelles. The results validate the existence of the patchy structure also in solution.     

Structural variability in transition metal oxide clusters: gas phase vibrational spectroscopy of V3O(6-8)+

We present gas phase vibrational spectra of the trinuclear vanadium oxide cations V(3)O(6)(+)·He(1-4), V(3)O(7)(+)·Ar(0,1), and V(3)O(8)(+)·Ar(0,2) between 350 and 1200 cm(-1). Cluster structures are assigned based on a comparison of the experimental and simulated IR spectra. The latter are derived from B3LYP/TZVP calculations on energetically low-lying isomers identified in a rigorous search of the respective configurational space, using higher level calculations when necessary. V(3)O(7)(+) has a cage-like structure of C(3v) symmetry. Removal or addition of an O-atom results in a substantial increase in the number of energetically low-lying structural isomers. V(3)O(8)(+) also exhibits the cage motif, but with an O(2) unit replacing one of the vanadyl oxygen atoms. A chain isomer is found to be most stable for V(3)O(6)(+). The binding of the rare gas atoms to V(3)O(6-8)(+) clusters is found to be strong, up to 55 kJ/mol for Ar, and markedly isomer-dependent, resulting in two interesting effects. First, for V(3)O(7)(+)·Ar and V(3)O(8)(+)·Ar an energetic reordering of the isomers compared to the bare ion is observed, making the ring motif the most stable one. Second, different isomers bind different number of rare gas atoms. We demonstrate how both effects can be exploited to isolate and assign the contributions from multiple isomers to the vibrational spectrum. The present results exemplify the structural variability of vanadium oxide clusters, in particular, the sensitivity of their structure on small perturbations in their environment.     

Circular, nanostructured and biofunctionalized hydrogel microchannels for dynamic cell adhesion studies

We report on a method to fabricate biofunctionalized polyethylene glycol hydrogel microchannels with adjustable circular cross-sections. The inner channel surfaces are decorated with Au-nanoparticle arrays of tunable density. These Au-nanoparticles are functionalized with biomolecules whereas the hydrogel material provides an inert and biocompatible background. This technology provides control over flow conditions, channel curvature and biomolecule density on the channel surface. It can be applied for biophysical studies of cell-surface interactions mimicking, for example, leukocyte interactions with the endothelial lining in small vessels.     

Chlorinated corroles

Fully β-pyrrole chlorinated corrole was obtained via reaction of the cobalt(iii) complex of 5,10,15-tris(pentafluorophenyl)corrole with chlorine. The structural and electronic effects of chlorination are reported, together with the coordination chemistry of this complex.     

Scaffold tailoring by a newly detected Pictet-Spenglerase activity of strictosidine synthase: from the common tryptoline skeleton to the rare piperazino-indole framework

The Pictet-Spenglerase strictosidine synthase (STR1) has been recognized as a key enzyme in the biosynthesis of some 2000 indole alkaloids in plants, some with high therapeutic value. In this study, a novel function of STR1 has been detected which allows for the first time a simple enzymatic synthesis of the strictosidine analogue 3 harboring the piperazino[1,2-a]indole (PI) scaffold and to switch from the common tryptoline (hydrogenated carboline) to the rare PI skeleton. Insight into the reaction is provided by X-ray crystal analysis and modeling of STR1 ligand complexes. STR1 presently provides exclusively access to 3 and can act as a source to generate by chemoenzymatic approaches libraries of this novel class of alkaloids which may have new biological activities. Synthetic or natural monoterpenoid alkaloids with the PI core have not been reported before.     

Unfavorable electrostatic and steric interactions in DNA polymerase β E295K mutant interfere with the enzyme's pathway

Mutations in DNA polymerase β (pol β) have been associated with approximately 30% of human tumors. The E295K mutation of pol β has been linked to gastric carcinoma via interference with base excision repair. To interpret the different behavior of E295K as compared to wild-type pol β in atomic and energetic detail, we resolve a binary crystal complex of E295K at 2.5 ? and apply transition path sampling (TPS) to delineate the closing pathway of the E295K pol β mutant. Conformational changes are important components in the enzymatic pathway that lead to and ready the enzyme for the chemical reaction. Our analyses show that the closing pathway of E295K mutant differs from the wild-type pol β in terms of the individual transition states along the pathway, associated energies, and the active site conformation in the final closed form of the mutant. In particular, the closed state of E295K has a more distorted active site than the active site in the wild-type pol β. In addition, the total energy barrier in the conformational closing pathway is 65 ± 11 kJ/mol, much higher than that estimated for both correct (e.g., G:C) and incorrect (e.g., G:A) wild-type pol β systems (42 ± 8 and 45 ± 7 kJ/mol, respectively). In particular, the rotation of Arg258 is the rate-limiting step in the conformational pathway of E295K due to unfavorable electrostatic and steric interactions. The distorted active site in the closed relative to open state and the high energy barrier in the conformational pathway may explain in part why the E295K mutant is observed to be inactive. Interestingly, however, following the closing of the thumb but prior to the rotation of Arg258, the E295K mutant complex has a similar energy level as compared to the wild-type pol β. This suggests that the E295K mutant may associate with DNA with similar affinity, but it may be hampered in continuing the process of chemistry. Supporting experimental data come from the observation that the catalytic activity of wild-type pol β is hampered when E295K is present: this may arise from the competition between E295K and wild-type enzyme for the DNA. These combined results suggest that the low insertion efficiency of E295K mutant as compared to wild-type pol β may be related to a closed form distorted by unfavorable electrostatic and steric interactions between Arg258 and other key residues. The active site is thus less competent for proceeding to the chemical reaction, which may also involve a higher reaction barrier than the wild-type or may not be possible in this mutant. Our analysis also suggests further experiments for other mutants to test the above hypothesis and dissect the roles of steric and electrostatic factors on enzyme behavior.     

A polymer surfactant corona dynamically replaces water in solvent-free protein liquids and ensures macromolecular flexibility and activity

The observation of biological activity in solvent-free protein-polymer surfactant hybrids challenges the view of aqueous and nonaqueous solvents being unique promoters of protein dynamics linked to function. Here, we combine elastic incoherent neutron scattering and specific deuterium labeling to separately study protein and polymer motions in solvent-free hybrids. Myoglobin motions within the hybrid are found to closely resemble those of a hydrated protein, and motions of the polymer surfactant coating are similar to those of the hydration water, leading to the conclusion that the polymer surfactant coating plasticizes protein structures in a way similar to hydration water.