Can multivalency be expressed kinetically? The answer is yes

Inspired by the concept of multivalency and in pursuit of ever more intricate artificial molecular machines, we investigated the strict self-assembly of a triply threaded two-component superbundle, starting from a tritopic receptor in which three benzo[24]crown-8 macrorings are fused onto a triphenylene core and a trifurcated trication wherein three bipyridinium units are linked 1,3,5 to a central benzenoid core. The result of the investigation was quite unexpected and surprising. It transpired that the rapid formation of a doubly threaded two-component complex was followed by an extremely slow conversion (a week at 253 K in CD3COCD3 to reach equilibrium) of this kinetically controlled product into a thermodynamically controlled one, namely a triply threaded two-component superbundle. This intriguing observation begs the question: are there instances in nature where multivalency is expressed as a kinetically controlled process, prior to an equilibrium state being reached, and if so, what are the biological implications, if any?     

[Zn3(PO4)2(H2O)0.8(NH3)1.2]

The structure of the title compound, ammineaquadi‐μ₅‐phosphato‐trizinc(II), [Zn₃(PO₄)₂(H₂O)_0.8(NH₃)_1.2], consists of two parts: (i) PO₄ and ZnO₄ vertex‐sharing tetrahedra arranged in layers parallel to (100) and (ii) ZnO₂(N/O)₂ tetrahedra located between the layers. Elemental analysis establishes the ammine‐to‐water ratio as 3:2. ZnO₂(N/O)₂ tetrahedra are located at special position 4e (site symmetry 2) in C2/c. The two O atoms of ZnO₂(N/O)₂ are bonded to neighbouring P atoms, forming two Zn—O—P linkages and connecting ZnO₂(N/O)₂ tetrahedra with two adjacent bc plane layers. A noteworthy feature of the structure is the presence of NH₃ and H₂O at the same crystallographic position and, consequently, qualitative changes in the pattern of hydrogen bonding and weaker N/O—H...O electrostatic interactions, as compared to two closely related structures.     

Effect of atmospheric pressure pulsed discharge spatial inhomogeneity on Ar I and H I lines: Electron number density study

The spatial inhomogeneity of pulsed atmospheric pressure discharge in argon is investigated using the electron number density N_e diagnostics procedure applied to asymmetrically broadened Ar I lines. A dedicated fitting procedure is used for describing Ar I 703.0 nm line shape recorded from argon gas discharge and H I (at 486.13 and 656.28 nm) lines recorded from Ar-H₂ gas mixture discharge. The results revealed the change in N_e in both axial and radial directions. The additional Ar I lines at 614.5, 710.7, 731.2, and 731.6 nm, recorded from integral spatial radiation, are analysed as well to confirm the results from the plasma column region. The possibility of using AlO (B²∑⁺–X²∑⁺) and CN (B²∑⁺–X²∑⁺) molecular bands for gas temperature T_g measurements in this type of gas discharge source is demonstrated and T_g used as an input parameter for the N_e diagnostics procedure. For the proper identification of molecular band spectral lines, the Fortrat parabolas are constructed. The results obtained from Ar I 703.0 nm line indicate three different N_e values, with N_e1 ≈ 0.6 × 10¹⁶ cm⁻³, N_e2 ≈ 3.6 × 10¹⁶ cm⁻³, and N_e3 ≈ 19 × 10¹⁶ cm⁻³ measured from the plasma column. These N_e values increase in the cathode and anode region.     

Controlling the dynamics of molecular encapsulation and gating

This critical review describes mechanisms by which guest molecules enter and depart molecular capsules. The discussion focuses on presenting gated molecular encapsulation, i.e., trapping and releasing of guest molecules at rates that are controlled by conformational changes in the host's structure. Developing quantitative rules that describe the gating are, at present, a matter of scientific curiosity but could play an important role in building more effective catalysts, drug-delivery devices or membranes (105 references).     

Template-directed synthesis of mechanically interlocked molecular bundles using dynamic covalent chemistry

Mixing the dipyrido[24]crown-8 derivatives carrying one or two formyl group(s) on the 4 position(s) of their pyridine ring(s) with a 3-fold symmetrical trisammonium ion template in a 3:1 ratio in CD3NO2 results in the formation of thermodynamically stable [4]pseudorotaxanes which, upon addition of a 1,3,5-trisaminobenzene cap, form mechanically interlocked molecular bundles with one and two caps, respectively, by virtue of dynamic imine bond formation.     

Stress Integration of the Hoek-Brown Material Model Using Incremental Plasticity Theory

This paper presents the formulation of the stress integration procedure for the Hoek-Brown (HB) material model with non-associative yielding condition by using the incremental plasticity method. Main idea of this method is to reach the solution by calculating the plastic matrix according to the method of incremental plasticity (used for elastic constitutive matrix corrections), and with the use of the total strain increment. Computational procedure is implemented within the PAK program package. Results of this procedure were compared with the solutions obtained by other program that contains this material model. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cd2Cu(PO4)2

During an investigation of the insufficiently known system M1O–M2O–X₂O₅–H₂O (M1 = Cd²⁺, Sr²⁺ and Ba²⁺; M2 = Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺ and Mg²⁺; X = P⁵⁺, As⁵⁺ and V⁵⁺), single crystals of the novel compound dicadmium copper(II) bis[phosphate(V)], Cd₂Cu(PO₄)₂, were obtained. This compound belongs to a small group of compounds adopting a Cu₃(PO₄)₂‐type structure and having the general formula M1₂M2(XO₄)₂ (M1/M2 = Cd²⁺, Cu²⁺, Mg²⁺ and Zn²⁺; X = As⁵⁺, P⁵⁺ and V⁵⁺). The crystal structure is characterized by the interconnection of infinite [Cu(PO₄)₂]_n chains and [Cd₂O₁₀]_n double chains, both extending along the a axis. Exceptional characteristics of this structure are its novel chemical composition and the occurrence of double chains of CdO₆ polyhedra that were not found in related structures. In contrast to the isomorphous compounds, where the M1 cations are coordinated by five O atoms, the Cd atom is coordinated by six. The dissimilarity in the geometry of M1 coordination between Cd₂Cu(PO₄)₂ and the isomorphous compounds is mostly due to the larger ionic radius of the Cd cation in comparison with the Cu, Mg and Zn cations. Sharing a common edge, two CdO₆ polyhedra form Cd₂O₁₀ dimers. Each such dimer is bonded to another dimer sharing common vertices, forming [Cd₂O₁₀]_n double chains in the [100] direction. The Cu atoms, located on an inversion centre (site symmetry ), form isolated CuO₄ squares interconnected by PO₄ tetrahedra, forming [Cu(PO₄)₂]_n chains similar to those found in related structures. Conversely, the [Cd₂O₁₀]_n double chains, which were not found in related structures, are an exclusive feature of this structure.     

Supramolecular catalysis at work: diastereoselective synthesis of a molecular bowl with dynamic inner space

The supramolecular assistance to Pd(0)/Cu(I)-catalyzed cyclotrimerization of stannylated norbornene 7 has been investigated to give molecular bowl 1syn in a stereoselective fashion. Following a divergent strategy, racemic norbornene 7 was synthesized in satisfactory yield. Self-coupling, promoted by Pd(0)/Cu(I) catalysis acting in synergy with CsF, yielded molecular bowl 1syn in a moderate 30% yield. The reaction diastereoselectivity is affected by the concentration of Cu(I) and Cs+: increasing quantities of the cations enhanced the syn/anti ratio of the isolated cyclotrimer from statistical (1:3) to a more desirable (4.5:1) ratio, in favor of the molecular bowl 1syn. 1H NMR spectroscopic studies suggested the coordinating affinity of 1syn toward transition metals Cu(I), Ag(I), and Au(I), to account for the observed templation effect. In particular, the tridentate 1syn has been shown to bind to one Ag(I) cation in the assembly process that is driven with enthalpy (Delta H degrees = -19 +/- 2 kcal/mol, Delta S degrees = -45 eu). The complete coordination was not cooperative, and was hypothesized to be impeded with the adverse entropy. Accordingly, density functional theory (BP86) calculations of 1syn and its mono-, bis-, and tris-Ag(I) complexes suggested that the coordination of one to three silver cations is highly exothermic. The calculations also revealed that the bowl constriction is necessary for the aromatic arms to become preorganized and bind to a silver cation(s) (Delta E approximately 8 kcal/mol). Ultimately, Ag(I) has been shown to assist the diastereoselective formation of 1syn, lending support to the notion of template-directed synthesis.