Increasing risk aversion and life-cycle investing

Mathematics and Financial Economics - We derive the optimal portfolio for an investor with increasing relative risk aversion in a complete continuous-time securities market. The IRRA assumption...     

Recent advances of group 14 dimetallenes and dimetallynes in bond activation and catalysis

Since the first heavy alkene analogues of germanium and tin were isolated in 1976, followed by West''s disilene in 1981, the chemistry of stable group 14 dimetallenes and dimetallynes has advanced immensely. Recent developments in this field veered the focus from the isolation of novel bonding motifs to mimicking transition metals in their ability to activate small molecules and perform catalysis. The potential of these homonuclear multiply bonded compounds has been demonstrated numerous times in the activation of H₂, NH₃, CO₂ and other small molecules. Hereby, the strong relationship between structure and reactivity warrants close attention towards rational ligand design. This minireview provides an overview on recent developments in regard to bond activation with group 14 dimetallenes and dimetallynes with the perspective of potential catalytic applications of these compounds.

This minireview highlights the recent advances in small molecule activation and catalytic applications of homonuclear dimetallenes, dimetallynes and interconnected bismetallylenes of heavier group 14 elements.     

Kinetic Analysis of the Reactions between GG-Containing Oligonucleotides and Platinum Complexes. 1. Reactions of Single-Stranded Oligonucleotides with cis-[Pt(NH(3))(2)(H(2)O)(2)](2+) and [Pt(NH(3))(3)(H(2)O)](2+)

Using concentration measurements based on high performance liquid chromatography, we have investigated the kinetics of reaction between single-stranded oligonucleotides containing a d(GpG) sequence, i.e., d(GG), d(TGG), d(TTGG), and d(CTGGCTCA), and the platinum complexes cis-[Pt(NH(3))(2)(H(2)O)(2)](2+) (1) and [Pt(NH(3))(3)(H(2)O)](2+) (2). The rate constants for the substitution of one aqua ligand of platinum in 1 or 2 by each guanine of the oligonucleotides were individually measured, as well as, for 1, those for the subsequent conversion of the monoadducts to the diadduct. For the platination of d(GG) and d(TGG), the rate constants are similar for the 5'- and 3'-guanines. The longer oligonucleotides d(TTGG) and d(CTGGCTCA) are platinated slightly faster on the 5'-G than on the 3'-G. 2 shows a similar slight preference for the 5'-guanine, but it reacts by a factor of 4-10 more slowly than 1. For both complexes, the platination rate constants increase with increasing oligonucleotide length. Platination of the 5'-G by 1 is 1 order of magnitude faster on d(CTGGCTCA) than on d(GG). Concerning the chelation step giving the GG diadduct of 1, the longer the oligonucleotide, the larger is the ratio between the rates of the cyclization of the 3'- and 5'-monoadducts k(3)(')(c) and k(5)(')(c): k(3)(')(c)/k(5)(')(c) equals 1.4 for d(GG) and 3.3 for d(CTGGCTCA).     

Mechanochemical Synthesis of 3d Transition‐Metal–1,2,4‐Triazole Complexes as Precursors for Microwave‐Assisted and Thermal Conversion to Coordination Polymers with a High Influence on the Dielectric Properties

The complexes [MCl₂(TzH)₄] (M=Mn ( 1 ), Fe ( 2 ); TzH=1,2,4‐1H‐triazole) and [ZnCl₂(TzH)₂] ( 3 ) have been obtained by mechanochemical reactions of the corresponding divalent metal chloride and 1,2,4‐1H‐triazole. They were successfully used as precursors for the formation of coordination polymers either by a microwave‐assisted reaction or by thermal conversion. For manganese, the conversion directly yielded [MnCl₂TzH] ( 4 ), whereas for the iron‐containing precursor, [FeCl₂TzH] ( 6 ), was formed via the intermediate coordination polymer [FeCl(TzH)₂]Cl ( 5 ). For cobalt, the isotypic polymer [CoCl(TzH)₂]Cl ( 7 ) was obtained, but exclusively by a microwave‐induced reaction directly from CoCl₂. The crystal structures were resolved from single crystals and powders. The dielectric properties were determined and revealed large differences in permittivity between the precursor complexes and the rigid chain‐like coordination polymers. Whereas the monomeric complexes exhibit very different dielectric behaviour, depending on the transition metal, from “low‐k” to “high‐k” with the permittivity ranging from 4.3 to >100 for frequencies of up to 1000 Hz, the coordination polymers and complexes with strong intermolecular interactions are all close to “low‐k” materials with very low dielectric constants up to 50 °C. Therefore, the conversion procedures can be used to deliberately influence the dielectric properties from complex to polymer and for different 3d transition‐metal ions.     

Fabrication of Thermo‐Responsive Hybrid Hydrogels by In‐Situ Mineralization and Self‐Assembly of Microgel Particles

Summary: An in‐situ mineralization process in the presence of thermo‐responsive microgels leads to the formation of well‐defined hybrid materials. Experimental data suggest that control of the mineralization process in the presence of the microgels offers the possibility to obtain sub‐micrometer‐sized hybrid particles or macroscopic hybrid hydrogels. The rapid formation of CaCO₃ crystals in the microgel structure favors the preparation of the hybrid particles wherein inorganic crystals cover the shell layer of the microgel. The slow formation of CaCO₃ crystals leads to the simultaneous self‐assembly of the microgel particles on the bottom of the reaction vessel, and the formation of a physical network. It has been demonstrated that hybrid hydrogel materials with different calcium carbonate contents and temperature‐dependent swelling‐deswelling properties can be prepared.

Formation of a hybrid hydrogel by the vapor diffusion method.     

Phase transition in Tl2TeO3: influence and origin of the thallium lone pair distortion

A new modification of thallium tellurite, beta-Tl(2)TeO(3), has been synthesized by methanolothermal reaction, and its phase transition has been studied by single-crystal X-ray diffraction. At a temperature of 440(10) degrees C an irreversible phase transition from a monoclinic structure (beta-Tl(2)TeO(3): P2(1)/c (No. 14), Z = 4, a = 8.9752(18) A, b = 4.8534(6) A, c = 11.884(2) A, beta = 109.67(2) degrees, V = 487.47(15) A3 at 25 degrees C) to an orthorhombic structure (alpha-Tl(2)TeO(3): Pban (No. 50), Z = 8, a = 16.646(2) A, b = 11.094(2) A, c = 5.2417(8) A, V = 968.0(3) A3 at 25 degrees C) is observed. Both structures are characterized by psi-tetrahedral TeO(3)(2-) anions. In the orthorhombic structure psi-trigonal bipyramidal [TlO(4)] units are found together with psi-tetrahedral [TlO(3)] units whereas in the monoclinic structure the coordination polyhedron around Tl(I) can be best described as a psi-square pyramide, psi-[TlO(4)]. The electronic structure of Tl(2)TeO(3) in both modifications has been studied to explain the influence of the lone pairs. It can be conclusively shown that the minimization of antibonding ns-metal/2p-oxygen interactions is the driving force for "lone pair" distortions which determines the structures of Tl(2)TeO(3).     

The presence of high level soluble herpes virus entry mediator in sera of gastric cancer patients

The development of gastric cancer (GC) is closely related to chronic inflammation caused by Helicobacter pylori infection, and herpes virus entry mediator (HVEM) is a receptor expressed on the surface of leukocytes that mediates potent inflammatory responses in animal models. However, the role of HVEM in human GC has not been studied. Previously, we showed that the interaction of HVEM on human leukocytes with its ligand LIGHT induces intracellular calcium mobilization, which results in inflammatory responses including induction of proinflammatory cytokine production and anti-bacterial activities. In this study, we report that leukocytes from GC patients express lower levels of membrane HVEM (mHVEM) and have lower LIGHT-induced bactericidal activities than those from healthy controls (HC). In contrast, levels of soluble HVEM (sHVEM) in the sera of GC patients were significantly higher than in those of HC. We found that monocyte membrane-bound HVEM is released into the medium when cells are activated by proinflammatory cytokines such as TNF-α and IL-8, which are elevated in the sera of GC patients. mHVEM level dropped in parallel with the release of sHVEM, and release was completely blocked by the metalloprotease inhibitor, GM6001. We also found that the low level of mHVEM on GC patient leukocytes was correlated with low LIGHT-induced bactericidal activities against H. pylori and S. aureus and production of reactive oxygen species. Our results indicate that mHVEM on leukocytes and sHVEM in sera may contribute to the development and/or progression of GC.     

Self-assembly of supramolecular architectures and polymers by orthogonal metal complexation and hydrogen-bonding motifs

A modular construction kit with two orthogonal noncovalent binding sites for self-assembly of supramolecular architectures is presented. The heteroditopic building blocks contain a terpyridine (tpy) unit for coordination of metal ions and a Hamilton receptor for multiple H-bonding of cyanuric acid derivatives. The association constants of ligand binding of M(II) complexes (M=Ru, Zn, Fe, and Pt) with a dendritic end cap were determined to be in the range of 10(2) and 10(4) L mol(-1) in chloroform. The capabilities for binding of metal ions were investigated by (1)H NMR and UV/Vis spectroscopy. The Fe complexes are most appropriate for the generation of discrete and high-ordered architectures due to their strong tendency to form FeL(2) complexes. Superstructures are readily formed in a one-pot procedure at room temperature. No mutual interactions between the orthogonal binding motifs were observed, and this demonstrates the highly specific nature of each binding process. Decomplexation experiments were carried out to examine the reversibility of Fe-tpy coordination. Substitution of the terminal end cap with a homoditopic bis-cyanurate linkage leads to formation of an iron-containing supramolecular strand. Formation of coordination polymers was confirmed by viscosity measurements. The supramolecular polymer strands can be reversibly cleaved by addition of a terminating cyanuric acid building block, and this proves the dynamic nature of this noncovalent polymerization process.