Interactions of Hydrogen with Pd@MOF Composites

Physisorption and chemisorption of hydrogen on solid-state materials are two fundamentally different interactions, both of which display advantages and drawbacks for hydrogen storage. It has been hypothesised that their combination by merging two classes of materials showing different sorption behaviour towards hydrogen in the same composite may synergistically combine their desirable properties. As representatives of such composites, palladium nanoparticles, nanoclusters, and single atoms have been encapsulated in a metal-organic framework matrix, embedded, or immobilised in its pores, respectively. In this minireview, we review advances on the understanding and potential applications of the combination of Pd with metal-organic framework matrices through the analysis of the nanocomposite materials’ interaction with hydrogen and sorption properties.     

Influence type of natural rubber on properties of green biodegradable thermoplastic natural rubber based on poly(butylene succinate)

Green biodegradable thermoplastic natural rubber (GB‐TPNR) based on simple blend of natural rubber (NR) and poly(butylene succinate) (PBS) was prepared using three NR alternatives: unmodified NR and epoxidized NR with 25‐ or 50‐mol% epoxide (ie, ENR‐25 or ENR‐50). It was found that ENR‐50/PBS blend showed the best compatibility, which resulted in superior mechanical and thermal properties with the highest crystallinity of the PBS phase, on comparing with the ENR‐25/PBS and NR/PBS blends. This might be attributed to stronger chemical interactions between the epoxide groups in ENR‐50 and the polar functional groups in PBS, which were confirmed by Fourier transform infrared (FTIR). Furthermore, scanning electron microscopy (SEM), atomic force microscopy (AFM), and polarizing optical microscopy (POM) micrographs of ENR‐50/PBS blend revealed phase separation with finer‐grained cocontinuous structure than in ENR‐25/PBS and NR/PBS simple blends. Furthermore, the chemical interactions in ENR‐50/PBS blend enhanced the resistance to accelerated weathering.     

C−I‐Selective Cross‐Coupling Enabled by a Cationic Palladium Trimer

While there is a growing interest in harnessing synergistic effects of more than one metal in catalysis, relatively little is known beyond bimetallic systems. This report describes the straightforward access to an air‐stable Pd trimer and presents unambiguous reactivity data of its privileged capability to differentiate C?I over C?Br bonds in C?C bond formations (arylation and alkylation) of polyhalogenated arenes, which typical Pd⁰ and Pd^I‐Pd^I catalysts fail to deliver. Experimental and computational reactivity data, including the first location of a transition state for bond activation by the trimer, are presented, supporting direct trimer reactivity to be feasible.     

Discovery of Elusive K4O6, a Compound Stabilized by Configurational Entropy of Polarons

Synthesis of elusive K₄O₆ has disclosed implications of crucial relevance for new solid materials discovery. K₄O₆ forms in equilibrium from K₂O₂ and KO₂, in an all‐solid state, endothermic reaction at elevated temperature, undergoing back reaction upon cooling to ambient conditions. This tells that the compound is stabilized by entropy alone. Analyzing possible entropic contributions reveals that the configurational entropy of “localized” electrons, i.e., of polaronic quasi‐particles, provides the essential contribution to the stabilization. We corroborate this assumption by measuring the relevant heats of transformation and tracking the origin of entropy of formation computationally. These findings challenge current experimental and computational approaches towards exploring chemical systems for new materials by searching the potential energy landscape: one would fail in detecting candidates that are crucially stabilized by the configurational entropy of localized polarons.     

Electronic and vibrational properties of fluorenone in the channels of zeolite L

Fluorenone (C13H8O) was inserted into the channels of zeolite L by using gas-phase adsorption. The size, structure, and stability of fluorenone are well suited for studying host-guest interactions. The Fourier transform IR, Raman, luminescence, and excitation spectra, in addition to thermal analysis data, of fluorenone in solution and fluorenone/zeolite L are reported. Normal coordinate analysis of fluorenone was performed, based on which IR and Raman bands were assigned, and an experimental force field was determined. The vibrational spectra can be used for nondestructive quantitative analysis by comparing a characteristic dye band with a zeolite band that has been chosen as the internal standard. Molecular orbital calculations were performed to gain a better understanding of the electronic structure of the system and to support the interpretation of the electronic absorption and luminescence spectra. Fluorenone shows unusual luminescence behavior in that it emits from two states. The relative intensity of these two bands depends strongly on the environment and changes unexpectedly in response to temperature. In fluorenone/zeolite L, the intensity of the 300 nm band (lifetime 9 micros) increases with decreasing temperature, while the opposite is true for the 400 nm band (lifetime 115 micros). A model of the host-guest interaction is derived from the experimental results and calculations: the dye molecule sits close to the channel walls with the carbonyl group pointing to an Al3+ site of the zeolite framework. A secondary interaction was observed between the fluorenone's aromatic ring and the zeolite's charge-compensating cations.     

Comparison of three sequential extraction procedures (original and modified 3 steps BCR procedure) applied to sediments of different origin

The 3 steps sequential extraction procedure proposed by the Standards Measurements and Testing program (SM&T--formerly BCR) of the European Union has been applied for the speciation of metals in sediments. Results obtained by the application of the BCR standardized procedure were compared to those of two four step sequential extraction procedures, which are different from the BCR procedure only for the introduction of an additional step with NaOCl, as 2nd and 3rd step respectively. Five different metals have been taken into consideration: Cd, Cu, Ni, Pb and Zn. The analytical performances of the laboratory have been evaluated using three certified reference materials: the BCR 601 lake sediment for the BCR sequential extraction procedure, PACS-1 and MESS-1 for total metal concentration. Results showed that the efficiency of NaOCl treatment is higher or at least equal to that of H2O2 treatment and that its selectivity is quite satisfying. Moreover the NaOCl treatment doesn't significantly influence the extraction of the easily reducible fraction.     

Toward efficient Zn(II)-based artificial nucleases

A series of cis-cis-triaminocyclohexane Zn(II) complex-anthraquinone intercalator conjugates, designed in such a way to allow their easy synthesis and modification, have been investigated as hydrolytic cleaving agents for plasmid DNA. The ligand structure comprises a triaminocyclohexane platform linked by means of alkyl spacers of different length (from C(4) to C(8)) to the anthraquinone group which may intercalate the DNA. At a concentration of 5 microM, the complex of the derivative with a C(8) alkyl spacer induces the hydrolytic stand scission of supercoiled DNA with a rate of 4.6 x 10(-6) s(-1) at pH 7 and 37 degrees C. The conjugation of the metal complex with the anthraquinone group leads to a 15-fold increase of the cleavage efficiency when compared with the anthraquinone lacking Zn-triaminocyclohexane complex. The straightforward synthetic procedure employed, allowing a systematic change of the spacer length, made possible to gain more insight on the role of the intercalating group in determining the reactivity of the systems. Comparison of the reactivity of the different complexes shows a remarkable increase of the DNA cleaving efficiency with the length of the spacer. In the case of too-short spacers, the advantages due to the increased DNA affinity are canceled due to the incorrect positioning of the reactive group, thus leading to cleavage inhibition.     

Rapid calculation of protein chemical shifts using bond polarization theory and its application to protein structure refinement

Although difficult to analyze, NMR chemical shifts provide detailed information on protein structure. We have adapted the semi-empirical bond polarization theory (BPT) to protein chemical shift calculation and chemical shift driven protein structure refinement. A new parameterization for BPT amide nitrogen chemical shift calculation has been derived from MP2 ab initio calculations and successfully evaluated using crystalline tripeptides. We computed the chemical shifts of the small globular protein ubiquitin, demonstrating that BPT calculations can match the results obtained at the DFT level of theory at very low computational cost. In addition to the calculation of chemical shift tensors, BPT allows the calculation of chemical shift gradients and consequently chemical shift driven geometry optimizations. We applied chemical shift driven protein structure refinement to the conformational analysis of a set of Trypanosoma brucei (the causative agent of African sleeping sickness) tryparedoxin peroxidase Px III structures. We found that the interaction of Px III with its reaction partner Tpx seems to be governed by conformational selection rather than by induced fit.     

Structural evolution in the isotropic channel of a water-nonionic surfactant system that has a disconnected lamellar phase: a 1H NMR self-diffusion study

We showed in a previous study that a water-nonionic surfactant system, where the surfactant is a 9:1 mixture of tetraethylene glycol monodecyl ether (C(10)E(4)) and pentaethylene glycol monodecyl ether (C(10)E(5)), forms a disconnected lamellar (L(α)) phase. Thus, the isotropic phase spans the whole concentration range from the water-rich L(1) region to the surfactant-rich L(2) region of the phase diagram. The L(1) and L(2) regions are connected via an isotropic channel that separates the two regions of the L(α) phase. In this letter, we monitored the structural evolution of the isotropic phase along a path through this isotropic channel via (1)H NMR self-diffusion measurements. We used this technique because it enables us to distinguish between discrete and bicontinuous structures by comparing the relative self-diffusion coefficients (obstruction factors) D/D(0) of the solvents (i.e. of water and surfactant in the present case). We found that the obstruction factor of water decreases whereas the obstruction factor of the surfactant increases with increasing surfactant concentration and increasing temperature. This trend is interpreted as the transition from a water-continuous L(1) region, which contains discrete micelles, to a bicontinuous structure, which may extend to very high surfactant concentrations. Although there is good evidence of bicontinuity over a broad concentration range, there is no evidence of inverse micelles or any other microstructure at the highest concentration studied in the surfactant-rich L(2) phase.