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Synthesis and Characterization of the New Copper Tetraphosphonate Cu2[(HO3PCH2)4C6H2]·2H2O

Following the strategy of using polyfunctional phosphonic acids for the synthesis of three‐dimensional metal phosphonates, the ethyl ester of a tetraphosphonic acid, i. e. 1,2,4,5‐(Et₂O₃PCH₂)₄C₆H₂, was used in the hydrothermal synthesis of the new copper tetraphosphonate, Cu₂[(HO₃PCH₂)₄C₆H₂]·2H₂O ( 1 ). The in situ hydrolysis of the ethyl ester leads to the acid (1,2,4,5‐(H₂O₃PCH₂)₄C₆H₂) which reacts with the Cu²⁺ ions to form the green coarse‐crystalline product. The title compound is the first fully characterized copper tetraphosphonate. Its structure was solved from single crystal data ( 1 : triclinic, , a = 4.9262(10), b = 8.1890(16), c = 11.800(2) Å, α = 71.17(3), β = 89.15(3), γ = 88.56(3)°, V = 450.39(16) ų, Z = 2, R1 = 0.0284, wR₂ = 0.0682). The structure is built up from edge‐sharing CuO₅ polyhedra each containing a single H₂O molecule. Thus, dimeric [Cu₂O₈] units are formed. In the second coordination sphere of each of the Cu²⁺ ions four HO₃PCH₂R units are observed. The [Cu₂O₈] polyhedra are connected to eight other [Cu₂O₈] polyhedra by these organic linkers and a three‐dimensional framework structure is formed. Thermogravimetric, magnetic, and temperature dependent powder XRD measurements and the Raman‐spectrum are also presented.     

Structural flexibility of a helical peptide regulates vibrational energy transport properties

Applying ultrafast vibrational spectroscopy, we find that vibrational energy transport along a helical peptide changes from inefficient but mostly ballistic below approximately 270 K into diffusive and significantly more efficient above. On the basis of molecular dynamics simulations, we attribute this change to the increasing flexibility of the helix above this temperature, similar to the glass transition in proteins. Structural flexibility enhances intramolecular vibrational energy redistribution, thereby refeeding energy into the few vibrational modes that delocalize over large parts of the structure and therefore transport energy efficiently. The paper outlines concepts how one might regulate vibrational energy transport properties in ultrafast photobiological processes, as well as in molecular electronic devices, by engineering the flexibility of their components.     

Synthesis of bifunctional core–shell particles with a porous zeolite core and a responsive polymeric shell

The aim of our work is the synthesis and characterization of colloidal core–shell particles with a zeolite core and an environmentally responsive shell. We have synthesized colloidal ZSM-5 zeolite and modified the surface with 3-(trimethoxysilyl)propyl methacrylate in order to introduce double bonds at the surface. The cross-linked polymeric shell was prepared by precipitation polymerization using the functionalized zeolite particles as seeds. We employed thermoresponsive poly(N-isopropylacrylamide) and pH-responsive poly(vinylpyridine) as the polymeric shell, respectively. The temperature- and pH-depending swelling and deswelling of the core–shell particles were characterized with dynamic light scattering techniques. Transmission electron microscopy pictures show the morphology of the synthesized particles. It is proposed that these types of bifunctional core–shell particles could be of use for controlled uptake and release applications and separation of molecules.     

Maximum Caliber: a variational approach applied to two-state dynamics

We show how to apply a general theoretical approach to nonequilibrium statistical mechanics, called Maximum Caliber, originally suggested by E. T. Jaynes [Annu. Rev. Phys. Chem. 31, 579 (1980)], to a problem of two-state dynamics. Maximum Caliber is a variational principle for dynamics in the same spirit that Maximum Entropy is a variational principle for equilibrium statistical mechanics. The central idea is to compute a dynamical partition function, a sum of weights over all microscopic paths, rather than over microstates. We illustrate the method on the simple problem of two-state dynamics, A<-->B, first for a single particle, then for M particles. Maximum Caliber gives a unified framework for deriving all the relevant dynamical properties, including the microtrajectories and all the moments of the time-dependent probability density. While it can readily be used to derive the traditional master equation and the Langevin results, it goes beyond them in also giving trajectory information. For example, we derive the Langevin noise distribution rather than assuming it. As a general approach to solving nonequilibrium statistical mechanics dynamical problems, Maximum Caliber has some advantages: (1) It is partition-function-based, so we can draw insights from similarities to equilibrium statistical mechanics. (2) It is trajectory-based, so it gives more dynamical information than population-based approaches like master equations; this is particularly important for few-particle and single-molecule systems. (3) It gives an unambiguous way to relate flows to forces, which has traditionally posed challenges. (4) Like Maximum Entropy, it may be useful for data analysis, specifically for time-dependent phenomena.     

Structure and dynamics of the homologous series of alanine peptides: a joint molecular dynamics/NMR study

The phi,psi backbone angle distribution of small homopolymeric model peptides is investigated by a joint molecular dynamics (MD) simulation and heteronuclear NMR study. Combining the accuracy of the measured scalar coupling constants and the atomistic detail of the all-atom MD simulations with explicit solvent, the thermal populations of the peptide conformational states are determined with an uncertainty of <5 %. Trialanine samples mainly ( approximately 90%) a poly-l-proline II helix-like structure, some ( approximately 10%) beta extended structure, but no alphaR helical conformations. No significant change in the distribution of conformers is observed with increasing chain length (Ala(3) to Ala(7)). Trivaline samples all three major conformations significantly. Triglycine samples the four corner regions of the Ramachandran space and exists in a slow conformational equilibrium between the cis and trans conformation of peptide bonds. The backbone angle distribution was also studied for the segment Ala3 surrounded by either three or eight amino acids on both N- and C-termini from a sequence derived from the protein hen egg white lysozyme. While the conformational distribution of the central three alanine residues in the 9mer is similar to that for the small peptides Ala(3)-Ala(7), major differences are found for the 19mer, which significantly (30-40%) samples alphaR helical stuctures.     

Synthese und Kristallstruktur der Übergangsmetalltrimetaphosphimate Zn3[(PO2NH)3]2 · 14 H2O und Co3[(PO2NH)3]2 · 14 H2O

Synthesis and Crystal Structure of the Transition Metal Trimetaphosphimates Zn₃[(PO₂NH)₃]₂ · 14 H₂O and Co₃[(PO₂NH)₃]₂ · 14 H₂O The transition metal trimetaphosphimates Zn₃[(PO₂NH)₃]₂ · 14 H₂O and Co₃[(PO₂NH)₃]₂ · 14 H₂O were obtained by the reaction of an aqueous solution of Na₃(PO₂NH)₃ · 4 H₂O with the respective metal nitrate or halide (molar ratio 1 : 4). The structure of Zn₃[(PO₂NH)₃]₂ · 14 H₂O was solved by single crystal X‐ray methods. The structure of isotypic Co₃[(PO₂NH)₃]₂ · 14 H₂O was refined from X‐ray powder diffraction data using the Rietveld method (Zn₃[(PO₂NH)₃]₂ · 14 H₂O ( 1 ): P 1, a = 743.7(2), b = 955.9(2), c = 980.1(2) pm, α = 102.70(3), β = 90.46(3), and γ = 100.12(3)°, Z = 1; Co₃[(PO₂NH)₃]₂ · 14 H₂O ( 2 ): P 1, a = 746.05(1), b = 957.06(2), c = 988.51(2) pm, α = 102.162(1), β = 90.044(1), and γ = 99.258(1)°, Z = 1). In 1 and 2 the P₃N₃ rings of the trimetaphosphimate ions attain a conformation which can be described as a combination of an ideal boat and an ideal twist conformation. The trimetaphosphimate ions act as bridging ligands. Thus chains of alternating M²⁺ and (PO₂NH)₃^3– ions are formed which are interconnected by additional M²⁺ ions forming electro‐neutral double chains. In the solid these double chains are connected by hydrogen bonds.     

[Al4(OH)2(OCH3)4(H2N‐bdc)3]⋅x H2O: A 12‐Connected Porous Metal–Organic Framework with an Unprecedented Aluminum‐Containing Brick

Al together now! A new stable aluminum aminoterephthalate system contains octameric building blocks that are connected by organic linkers to form a 12‐connected net (see picture). The structure adopts a cubic centered packing motive in which octameric units replace individual atoms, thus forming distorted octahedral (red sphere) and tetrahedral cages (green spheres) with effective accessible diameters of 1 and 0.45 nm, respectively.

     

A Continuous-Wave Electron Paramagnetic Resonance Study of Carbon Dioxide Adsorption on the Metal–Organic Frame-Work MIL-53

Continuous-wave electron paramagnetic resonance spectroscopy is applied to explore the adsorption of carbon dioxide (CO₂) over the metal organic framework (MOF) MIL-53. Therefore, paramagnetic Cr³⁺ ions, which replace a small amount of the bulk Al³⁺ ions in MIL-53(Al/Cr), are used as magnetically active probes. CO₂ was adsorbed on samples of MIL-53(Al/Cr) at equilibrium pressures between 0 and 2.5 bar. The transformation from the large pore phase to the narrow pore phase of MIL-53 was observed by electron paramagnetic resonance spectroscopy at small CO₂ pressures between 0.2 and 0.4 bar, which is in accordance with adsorption results reported in literature. By analyzing the electron paramagnetic resonance signal intensities of the corresponding Cr³⁺ probes, the ratio between the amount of the narrow pore phase and the large pore phase before and after this phase transformation was quantified. A small fraction of the large pore phase remains even after this phase transition. CO₂ adsorption at 77  K indicates the occurrence of the transformation of this MOF from a narrow pore phase to a large pore phase triggered by the adsorbed CO₂. Similar observations were already made using powder X-ray diffraction or infrared spectroscopy. But in contrast to these methods electron paramagnetic resonance spectroscopy on Cr³⁺ seems to be very sensitive not only to large differences between crystallographic conformations like large pores and narrow pores but also to different amounts and configurations of CO₂ molecules trapped in the same structural phase of MIL-53, taking advantage of the high sensitivity of the fine structure interaction of Cr³⁺.