Controllable growth of chains and grids from polyoxomolybdate building blocks linked by silver(I) dimers

Molecular growth processes utilizing a beta-octamolybdate synthon and {Ag2} dimers are described and the directing influence of "encapsulating" cations and coordinating solvent is also demonstrated. The growth of two 1D chains, (nBu4N)2n[Ag2Mo8O26]n (1) and (nBu4N)2n[Ag2Mo8O26(CH3CN)2]n (2), is achieved when nBu4N+ ions are used, and the diameter of the chains can be expanded by the coordination of CH3CN solvent (2). The formation of a type of gridlike structure in which 1D chains are crossed-over each other in alternatively packed layers is achieved in DMSO as the solvent; DMSO acts as a linking group to give (nBu4N)2n[Ag2Mo8O26(dmso)2]n (3), which, similar to 1 and 2, still incorporates the Bu4N+ ions that exert an "encapsulating" influence. However, in (HDMF)n[Ag3(Mo8O26)(dmf)4]n (4) the relatively bulky Bu4N+ ions are exchanged for protonated DMF cations, thereby allowing the chains to condense to a 2D array. The building block concept is further enforced by the isolation of a "monomeric" unit (Ph4P)2[Ag2Mo8O26(dmso)4] (5), which is isolated when the Ph4P+ ions are so "encapsulating" as to prevent aggregation of the {Ag-Mo8-Ag} building blocks. The nature of the AgAg dimers in each of the compounds 1-4 is examined by DFT calculations and the interplay between these Ag-Ag interactions and the structure types is described.     

微孔和介孔材料中的热化学

这篇论文综述了美国加州大学戴维斯分校科学院院士Navrotsky课题组多年来在多孔材料上取得的一系列热化学研究结果。讨论了热化学对微孔、介孔材料的结构稳定性和合成过程的影响。借助多种测热手段对影响骨架结构的热焓、热熵和自由能进行了系统的测量和计算。研究数据表明一系列纯硅分子筛、介孔材料和磷酸铝多孔材料同相应的石英相和块磷铝矿相相比能量上最多只高出15 kJ·mol-1。一系列纯硅分子筛的熵值比石英相高出3.2—4.2 J·K-1·mol-1；在0—12.6 J·K-1·mol-1范围内相对应的自由能几乎没有差别。因此，对不同微孔、介孔材料，其骨架结构在能量上是几乎没有区别的。另外，本文通过介绍一种新型测热方法——原位测热，揭示了分子筛合成过程中的动力学和成核/结晶机理。     

In vivo optical analysis of quantitative changes in collagen and elastin during arterial remodeling

Altered collagen and elastin content correlates closely with remodeling of the arterial wall after injury. Optical analytical approaches have been shown to detect qualitative changes in plaque composition, but the capacity for detection of quantitative changes in arterial collagen and elastin content in vivo is not known. We have assessed fluorescence spectroscopy for detection of quantitative changes in arterial composition in situ, in rabbit models of angioplasty and stent implant. Fluorescence emission intensity (FEI) recorded at sites remote from the primary implant site was correlated with immunohistochemical (IH) analysis and extracted elastin and collagen. FEI was significantly decreased (P<0.05) after treatment with anti-inflammatory agents, and plaque area decreased on comparison with saline-treated rabbits after stent implant or angioplasty (Por=0.961) analysis were detected by multiple regression (MR) analysis. Good correlations also were found for FEI with elastin and collagen measured by high-performance liquid chromatography; MR analysis provided highly predictive values for collagen and elastin (R2>or=0.994). Fluorescence spectroscopic analysis detects quantitative compositional changes in arterial connective tissue in vivo, demonstrating changes at sites remote from primary angioplasty and stent implant sites.     

Time-resolved chemically induced dynamic nuclear polarization studies of structure and reactivity of methionine radical cations in aqueous solution as a function of pH

Using time-resolved chemically induced dynamic nuclear polarization (CIDNP) techniques, we have studied the mechanism of the photoreactions of triplet excited 4-carboxybenzophenone (CBP) with l-methionine (Met) and 3-(methylthio)propylamine (MTPA) in aqueous solution and the details of the formation of CIDNP at pH from 6.7 to 13.6. At a pH below the pKa of the nitrogen atom of Met, the CIDNP is strongly affected by degenerate electron exchange between the S-S cationic radical dimer and the zwitterionic form of Met with the rate constant kex = 3.4 x 10(8) s(-1) providing an exhaustive explanation of the pH dependence of steady-state CIDNP that was previously interpreted as a manifestation of fast interconversion among three different methionine radical species (Goez, M.; Rozwadowski, J. J. Phys. Chem. A 1998, 102, 7945-7953). By analyzing the polarization of different protons formed in geminate recombination as a function of the pH, we obtained the branching ratio between two reaction pathways for oxidative quenching of (T)CBP via electron transfer from the sulfur and nitrogen atoms of Met and MTPA. Nuclear spin-lattice relaxation times were determined in the dimeric cation radical of Met (T1,S = 8.5 micros). In the cyclic radical cation of MTPA with a three-electron two-center S-N bond, the estimated paramagnetic relaxation is comparatively slow for all protons. Fast deprotonation of the primary aminium radical cation of MTPA and Met in strongly basic solution takes place on the submicrosecond time scale leading to efficient formation of CIDNP in the neutral aminyl radical.     

Synthetic studies related to diketopyrrolopyrrole (DPP) pigments. Part 2: The use of esters in place of nitriles in standard DPP syntheses: Claisen-type acylations and furopyrrole intermediates

Ethyl 2-aryl-4,5-dihydro-5-oxopyrrole-3-carboxylates react with esters or acyl halides in the presence of a strong base to give 4-acyl derivatives, which exist predominantly as either E- or Z-enols. These are cyclised, either in solution at temperatures >200 °C or by microwave irradiation, to 3,6-disubstituted 1H-furo[3,4-c]pyrrolediones which, after N-protection, are convertible by reaction with primary amines into novel N,N′-disubstituted DPP derivatives.     

Virus Particles Monitored by Fluorescence Spectroscopy: A Potential Detection Assay for Macromolecular Assembly¶

Native fluorescence spectroscopy was used for in situ investigations of two lipid‐containing bacteriophages from the cystovirus family as well as their Pseudomonad host cells. Both the viruses φ6 and φ12 and their bacterial host proteins contain the amino acid tryptophan (trp), which is the predominant fluorophore in UV. Within proteins, trp's structural environment differs, and the differences are reflected in their spectroscopic signatures. It was observed that the peak of the trp emission from both viruses was at 330 nm, a significantly shorter wavelength than trp in either the Pseudomonad host cells or the amino acid's chemical form. This allowed us to monitor the viral attachment process and subsequent lytic release of progeny virus particles by measurement of the trp emission spectra during the infection process. This work demonstrates that fluorescence may offer a novel tool to detect viruses and monitor viral infection of cells and may be part of a biodefense application.     

The ortho effect in the mass spectra of ortho/para isomers of bisphenol a derivatives and related compounds

New examples of the ortho effect in bisphenol A derivatives including interaction of the hydrogen of the ortho-hydroxy group with the neighbouring aromatic ring have been observed. The characteristic ions [M ? PhOH]^+middot; (m/z = 134) and [M ? CH₃ ? PhOH]⁺ (m/z = 119) were shown to form through the hydrogen transfer from hydroxy and isopropyl groups, respectively. The spectra of cyclic derivatives having ortho-hydroxy functions show [M ? 43]⁺, [M ? C₈H₉O]⁺, m/z = 147, m/z = 135 and [M ? C₉H₁₀O]⁺ ions. The proposed mechanims of the corresponding transformations were supported by mass spectra of deuterated analogues, methyl and trimethyl silyl ethers.