Synthesis of U(IV) imidos from Tp*2U(CH2Ph) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) by extrusion of bibenzyl

Addition of organic azides, N(3)R (R = 2,4,6-trimethylphenyl (Mes), phenyl (Ph), 1-adamantyl (Ad)), to a solution of the uranium(III) alkyl complex, Tp*(2)U(CH(2)Ph) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) (1), results in the formation of a family of uranium(iv) imido derivatives, Tp*(2)U(NR) (2-R). Notably, these complexes were synthesized in high yields by coupling of the benzyl groups to form bibenzyl. The uranium(IV) imido derivatives, 2-Mes, 2-Ph, and 2-Ad, were all characterized by both (1)H NMR and IR spectroscopy, and 2-Mes and 2-Ad were also characterized by X-ray crystallography. In the molecular structure of 2-Mes, typical κ(3)-coordination of the Tp* ligands was observed; however in the case of 2-Ad, one pyrazole ring of a Tp* ligand has rotated away from the metal centre, forcing a κ(2)-coordination of the pyrazoles. This results in a uranium-hydrogen interaction with the Tp* B-H. Treating these imido complexes with para-tolualdehyde results in multiple bond metathesis, forming the terminal uranium(IV) oxo complex, Tp*(2)U(O), and the corresponding imine.     

Tracking Injectable Microspheres in Dynamic Tissues With Encapsulated Superparamagnetic Iron Oxide Nanoparticles

Trackable spheres of similar size to those typically used for sustained protein delivery are prepared by incorporating superparamagnetic iron oxide (SPIO) nanoparticles into the core of poly(lactide‐co‐glycolide) microspheres. The visibility of injections in static and temporally in dynamic tissue systems is demonstrated. This method improves upon other, less sensitive imaging modalities in their ability to track injectable delivery systems. The results obtained confirm the localization of microspheres to the injected target area and highlight the novelty of tracking delivery vehicles for other applications.

     

Construction of Heterometallic Clusters in a Small Peptide Scaffold as [NiFe]-Hydrogenase Models: Development of a Synthetic Methodology

[NiFe]-hydrogenases are enzymes that catalyze the reversible interconversion of protons and hydrogen at a heterobimetallic site containing Ni and Fe. This organometallic site has served as an inspiration for the synthesis of a number of biomimetic complexes, but, unfortunately, most close structural mimics have shown little to no reactivity with either of the substrates for hydrogenases. This suggests that interactions between the metallo-active site and the protein scaffold are crucial in tuning reactivity. As a first step toward development of peptide-based models, in this paper we demonstrate a synthetic strategy for construction of peptide coordinated, cysteinyl thiolate bridged Ni-M complexes in which M is a hetero-organometallic fragment. We utilize the seven amino acid peptide ACDLPCG as a scaffold for construction of these peptide-coordinated metallocenters. This peptide binds Ni in an N(2)S(2) environment consisting of the amino terminus, an amide nitrogen, and the two cysteinyl thiolates. We show that these thiolates serve as reactive sites for formation of heterometallic complexes in which they serve as bridging ligands. The method is general, and a number of heterometallic fragments including Ru(η(6)-arene)(2+), M(CO)(4)(piperidine) for M = Mo and W, and Fe(2)(CO)(6) were successfully incorporated, and the resulting metallopeptides characterized via a range of spectroscopic techniques. This methodology serves as the first step to construction of hydrogenase peptidomimetics that incorporate defined outer coordination sphere interactions intended to tune reactivity.     

Preparation and characterization of chloroaluminum phthalocyanine-loaded solid lipid nanoparticles by thermal analysis and powder X-ray diffraction techniques

Solid lipid nanoparticles (SLN) without drug and SLN loaded with chloroaluminum phthalocyanine (AlClPc) were prepared by solvent diffusion method in aqueous system and characterized by thermal analyses and X-ray diffraction (XRD) in this study. Determination of particle size, zeta potential (ZP), and encapsulation efficiency were also evaluated. SLN containing AlClPc of nanometer size with high encapsulation efficiency and ZP were obtained. The results indicated that the size of SLN loaded with AlClPc is larger than that of the inert particle, but ZP is not changed significantly with incorporation of the drug. In differential scanning calorimetry (DSC) curves, it was observed that the melting point of stearic acid (SA) isolated and in SLN occurred at 55 and 64 °C, respectively, suggesting the presence of different polymorphs. DSC also shows that the crystallinity state of SLN was much less than that of SA isolated. The incorporation of drug in SLN may have been favored by this lower crystallinity degree of the samples. XRD techniques corroborated with the thermal analytic techniques, suggesting the polymorphic modifications of stearic acid.     

A high throughput glucocerebrosidase assay using the natural substrate glucosylceramide

Glucocerebrosidase is a lysosomal enzyme that catalyzes the hydrolysis of glucosylceramide to form ceramide and glucose. A deficiency of lysosomal glucocerebrosidase due to genetic mutations results in Gaucher disease, in which glucosylceramide accumulates in the lysosomes of certain cell types. Although enzyme replacement therapy is currently available for the treatment of type 1 Gaucher disease, the neuronopathic forms of Gaucher disease are still not treatable. Small molecule drugs that can penetrate the blood-brain barrier, such as pharmacological chaperones and enzyme activators, are new therapeutic approaches for Gaucher disease. Enzyme assays for glucocerebrosidase are used to screen compound libraries to identify new lead compounds for drug development for the treatment of Gaucher disease. But the current assays use artificial substrates that are not physiologically relevant. We developed a glucocerebrosidase assay using the natural substrate glucosylceramide coupled to an Amplex-red enzyme reporting system. This assay is in a homogenous assay format and has been miniaturized in a 1,536-well plate format for high throughput screening. The assay sensitivity and robustness is similar to those seen with other glucocerebrosidase fluorescence assays. Therefore, this new glucocerebrosidase assay is an alternative approach for high throughput screening.     

Further eleganolone-derived diterpenes from the brown alga Bifurcaria bifurcata

Four new diterpenes (1–4) together with six known members of this family were isolated from the brown alga Bifurcaria bifurcata collected off the coast near Roscoff, France. The structures of the new compounds were established in a comprehensive study on the basis of 1D and 2D NMR spectroscopic and mass spectrometric (ESI-MS) analyses. Our assignment is supported by a comparison of the ¹³C NMR chemical shifts to known compounds and predicted values. The new diterpenes are derivatives of the diterpene eleganolone (5). The structural relation and hypothetical metabolic pathway of the new diterpenes (1–4) with the co-isolated known diterpenes are discussed.     

Inquiry Learning of High School Students Through a Problem‐Based Environmental Health Science Curriculum

The purpose of this study was to examine the degree to which high school students improved their inquiry capabilities in relation to scientific literacy through their experience of a problem‐based environmental health science curriculum. The two inquiry capabilities studied were scientific questioning and approaches to inquiry into their own questions. A total of 129 high school students taught by two teachers in one school wrote responses to environmental health issues at the beginning and at the end of a 10‐week long inquiry curriculum. An additional group of 46 students of one of the two teachers learned an alternative curriculum and participated as a comparison group. The students using the inquiry curriculum performed significantly better than those using the alternative curriculum in posing active inquiry questions and generating hypothesis‐driven approaches to inquiry into their questions. The inquiry curriculum students also improved significantly from the pretest to the posttest in both measures of inquiry capacity. Among the students who were less prepared for inquiry in the beginning, 68% improved inquiry‐questioning capability, while among the students who were more prepared for inquiry, 36% improved in generating hypotheses‐driven approaches. Implications for curriculum design and implementation were provided along with further research suggestions.     

Synthesis of (4R,8R)- and (4S,8R)-4,8-dimethyldecanal: the common aggregation pheromone of flour beetles

The synthesis of (4R,8R)- and (4S,8R)-4,8-dimethyldecanal 1 and 1a has been achieved connecting the chiral building block (R)-2-methyl-1-bromobutane 4 with (R)- and (S)-citronellol derivatives. The key intermediate 4 was obtained optically pure in five steps from methyl (S)-3-hydroxy-2-methylpropionate 2.     

Enzymatic generation of the antimetabolite gamma,gamma-dichloroaminobutyrate by NRPS and mononuclear iron halogenase action in a streptomycete

Four adjacent open reading frames, cytC1-C4, were cloned from a cytotrienin-producing strain of a Streptomyces sp. by using primers derived from the conserved region of a gene encoding a nonheme iron halogenase, CmaB, in coronamic acid biosynthesis. CytC1-3 were active after expression in Escherichia coli, and CytC4 was active after expression in Pseudomonas putida. CytC1, a relatively promiscuous adenylation enzyme, installs the aminoacyl moieties on the phosphopantetheinyl arm of the holo carrier protein CytC2. CytC3 is a nonheme iron halogenase that will generate both gamma-chloro- and gamma,gamma-dichloroaminobutyryl-S-CytC2 from aminobutyryl-S-CytC2. CytC4, a thioesterase, hydrolytically releases the dichloroaminobutyrate, a known streptomycete antibiotic. Thus, this short four-protein pathway is likely the biosynthetic source of this amino acid antimetabolite. This four-enzyme system analogously converts the proS-methyl group of valine to the dichloromethyl product regio- and stereospecifically.     

Reaktionen des metalloiden Clusteranions {Ge9[Si(SiMe3)3]3}– in der Gasphase. Oxidations‐ und Reduktionsschritte geben Einblicke in den Bereich zwischen metalloiden Clustern und Zintl‐Ionen

The cluster anion {Ge₉[Si(SiMe₃)₃]₃}^– ( 1 ) is transferred intact into the gas phase via the electro spray method. Subsequently the fragmentation of 1 after resonant excitation as well as the oxidation reaction with O₂ and Cl₂ are investigated in an FT‐ICR mass spectrometer (Fourier Transform Ion Cyclotron Resonance). Unlike former results with off‐resonant excitation the fragmentation leads mainly to the end‐product Ge₉^–. Moreover, applying an on‐resonant excitation the dissociation experiment can be quantified; 2.0 ± 0.15 eV (193 ± 15kJ · mol^–1) for the elimination of the first two ligands and 2.7 ± 0.15 eV (261 ± 15 kJ · mol^–1) for all ligands, respectively. Particular attention is turned on the first step, where sterically encumbered Si₂(SiMe₃)₆ molecules are formed in a concerted reaction. This result, which is also important for elemental reactions on metal surfaces in catalyses, is based on experimentally determined threshold energies, DFT calculations and calculations on the lifetime of the involved species., In contrast to the high reactivity of crystalline 1 ·Li(THF)₄, gaseous 1 is inert against oxygen. The analogy to recently published spin forbidden reactions of Al₁₃^– with O₂ hints to a general importance of spin conversion during gas phase reactions of larger cluster molecules. The oxidation of 1 with Cl₂ proceeds through different reaction channels. DFT calculations give a first insight on the complex primary oxidation steps. These calculations also reveal that the delocalized bonding situation in the Ge₉ core is distorted upon oxidation. This result together with the dissociation experiments shed more light on differences and similarities between metalloid clusters and Zintl ions.