Adding impurities or defects destroys crystalline order. Occasionally, however, extraordinary behaviour emerges that cannot be explained by perturbing the ordered state. One example is the Kondo ...effect, where magnetic impurities in metals drastically alter the temperature dependence of resistivity. In Type-II superconductors, disorder generally works to pin vortices, giving zero resistivity below a critical current j
. However, peaks have been observed in the temperature and field dependences of j
. This peak effect is difficult to explain in terms of an ordered Abrikosov vortex lattice. Here we test the widespread paradigm that an order-disorder transition of the vortex ensemble drives the peak effect. Using neutron scattering to probe the vortex order in superconducting vanadium, we uncover an order-disorder transition from a quasi-long-range-ordered phase to a vortex glass. The peak effect, however, is found to lie at higher fields and temperatures, in a region where thermal fluctuations of individual vortices become significant.
The Chemistry of Griseofulvin Petersen, Asger B; Rønnest, Mads H; Larsen, Thomas O ...
Chemical reviews,
12/2014, Letnik:
114, Številka:
24
Journal Article
Hyperglucagonemia is a common observation in both obesity and type 2 diabetes, and the etiology is primarily thought to be hypersecretion of glucagon. We investigated whether altered elimination ...kinetics of glucagon could contribute to the hyperglucagonemia in type 2 diabetes and obesity. Individuals with type 2 diabetes and preserved kidney function (8 with and 8 without obesity) and matched control individuals (8 with and 8 without obesity) were recruited. Each participant underwent a 1-hour glucagon infusion (4 ng/kg/min), achieving steady-state plasma glucagon concentrations, followed by a 1-hour wash-out period. Plasma levels, the metabolic clearance rate (MCR), half-life (T
) and volume of distribution of glucagon were evaluated and a pharmacokinetic model was constructed. Glucagon MCR and volume of distribution were significantly higher in the type 2 diabetes group compared to the control group, while no significant differences between the groups were found in glucagon T
Individuals with obesity had neither a significantly decreased MCR, T
, nor volume of distribution of glucagon. In our pharmacokinetic model, glucagon MCR associated positively with fasting plasma glucose and negatively with body weight. In conclusion, our results suggest that impaired glucagon clearance is not a fundamental part of the hyperglucagonemia observed in obesity and type 2 diabetes.
Griseofulvin (1) is an important antifungal agent that has recently received attention due to its antiproliferative activity in mammalian cancer cells. Comprehensive SAR studies have led to the ...identification of 2′-benzyloxy griseofulvin 2, a more potent analogue with low micromolar anticancer potency in vitro. Analogue 2 was also shown to retard tumor growth through inhibition of centrosomal clustering in murine xenograft models of colon cancer and multiple myeloma. However, similar to griseofulvin, compound 2 exhibited poor metabolic stability and aqueous solubility. In order to improve the poor pharmacokinetic properties, 11 griseofulvin analogues were synthesized and evaluated for biological activity and physiological stabilities including SGF, plasma, and metabolic stability. Finally, the most promising compounds were investigated in respect to thermodynamic solubility and formulation studies. The 2′-benzylamine analogue 10 proved to be the most promising compound with low μM in vitro anticancer potency, a 200-fold increase in PBS solubility over compound 2, and with improved metabolic stability. Furthermore, this analogue proved compatible with formulations suitable for both oral and intravenous administration. Finally, 2′-benzylamine analogue 10 was confirmed to induce G2/M cell cycle arrest in vitro.
Progress of development of a novel griseofulvin-derived anti-cancer lead compound. Display omitted
•Synthesis of six new griseofulvin analogues.•Biological and physico-chemical evaluation of 11 griseofulvin analogues.•The 2′-benzylamine analogue exhibited improved potency, solubility, and stability.•2′-Benzylamine griseofulvin was confirmed to induce G2/M cell arrest in vitro.
We describe the first example of the synthesis of a tetraoxa8circulene with only four substituents by means of BF3·OEt2 mediated tetramerisation of tert‐butyl‐1,4‐benzoquinone. Two of the four ...regioisomers of tetra‐tert‐butyltetraoxa8circulene have been isolated and characterised by single‐crystal X‐ray analysis. It was found that the tetra‐tert‐butyltetraoxa8circulenes aggregate in solution through a cooperative polymerisation mechanism despite functionalisation with bulky tert‐butyl substituents.
Despite bulky tert‐butyl substituents, tetra‐tert‐butyltetraoxa8circulene aggregates into a supramolecular aggregate in solution through a cooperative mechanism.
In continuation of previous studies showing promising metal−molecule contact properties a variety of C60 end-capped “molecular wires” for molecular electronics were prepared by variants of the Prato ...1,3-dipolar cycloaddition reaction. Either benzene or fluorene was chosen as the central wire, and synthetic protocols for derivatives terminated with one or two fullerocpyrrolidine “electrode anchoring” groups were developed. An aryl-substituted aziridine could in some cases be employed directly as the azomethine ylide precursor for the Prato reaction without the need of having an electron-withdrawing ester group present. The effect of extending the π-system of the central wire from 1,4-phenylenediamine to 2,7-fluorenediamine was investigated by absorption, fluorescence, and electrochemical methods. The central wire and the C60 end-groups were found not to electronically communicate in the ground state. However, the fluorescence of C60 was quenched by charge transfer from the wire to C60. Quantum chemical calculations predict and explain the collapse of coherent electronic transmission through one of the fulleropyrrolidine-terminated molecular wires.
We present a strategy for chemical preparation of multiple copies of single-molecule electronic devices that is based on chemical self-assembly under equilibrium conditions in aqueous solution. As a ...first step in the realization of this, we show that thiol end-capped oligo(phenylenevinylene)s (OPVs) can be rendered water-soluble by forming well-defined stoichiometric supramolecular complexes with α-cyclodextrins. On the basis of fluorescence intensity measurements in water, a 1:3 stoichiometry was determined for the complexes with equilibrium constants of the order of 5 × 10−2 M−2. The photophysical properties of the OPV3s as free molecules in solution, as nanoaggregates in aqueous suspension, and embedded in cyclodextrins in water, are reported, and the prospects of using these complexes as nucleation sites for growth of gold nanorods bridged by electronically active thiol end-capped molecules is discussed.
Pseudo-complementary oligonucleotide analogues and mimics provide novel opportunities for targeting duplex structures in RNA and DNA. Previously, a pseudo-complementary A-T base pair has been ...introduced. Towards sequence unrestricted targeting, a pseudo-complementary G-C base pair consisting of the unnatural nucleobases N6-methoxy-2,6-diaminopurine (previously described in a DNA context), and N4-benzoylcytosine is now presented for design of pseudo-complementary PNA oligomers (pcPNAs).
Treatment of 1,2-diols with diphenylphosphinoyl chloride in pyridine produces beta-chloroethyl phosphinates which react with complete control of stereochemistry to give epoxides and azido-alcohols, ...useful intermediates in cyclopropane synthesis.
The Chemistry of Griseofulvin Petersen, Asger B; Rønnest, Mads H; Larsen, Thomas O ...
Chemical reviews,
12/2014, Letnik:
114, Številka:
24
Journal Article
Recenzirano
The chemistry of the antifungal agent griseofulvin is examined. Topics discusses include its biological activity and biosynthesis.
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