Miller–Urey Spark-Discharge Experiments in the Deuterium World

We designed and conducted a series of primordial-soup Miller-Urey style experiments with deuterated gases and reagents to compare the spark-discharge products of a “deuterated world” with the standard reaction in the “hydrogenated world”. While the deuteration of the system has little effect on the distribution of amino acid products, significant differences are seen in other regions of the product-space. Not only do we observe about 120 new species, we also see significant differences in their distribution if the two hydrogen isotope worlds are compared. Several isotopologue matches can be identified in both, but a large proportion of products have no equivalent in the corresponding isotope world with ca. 43 new species in the D world and ca. 39 new species in the H world. This shows that isotopic exchange (the addition of only one neutron) may lead to significant additional complexity in chemical space under otherwise identical reaction conditions.     

A Total Synthesis of Spirastrellolide A Methyl Ester

A concise total synthesis of spirastrellolide A methyl ester ( 1 a , R¹=Me) as the parent compound of a series of highly cytotoxic marine macrolides is disclosed, which exploits and expands the flexibility of a synthesis plan previously developed by our group en route to the sister compound spirastrellolide F methyl ester ( 6 a , R¹=Me). Key to success was the masking of the signature Δ^15,16‐bond of 1 a as a C16‐carbonyl group until after the stereogenic center at C24 had been properly set by a highly selective hydrogenation of the C24 exo‐methylene precursor 66 . Conformational control over the macrocyclic frame allowed the proper stereochemical course to be dialed into this reduction process. The elaboration of the C16 ketone to the C15–C16 double bond was accomplished by a chemoselective alkenyl triflate formation followed by a palladium‐catalyzed hydride delivery. The role of the ketone at C16 as a strategic design element is also evident up‐stream of the key intermediate 66 , the assembly of which hinged upon the addition of the polyfunctionalized dithiane 37 to the similarly elaborate aldehyde fragment 46 . Other crucial steps of the total synthesis were an alkyl‐Suzuki coupling and a Yamaguchi lactonization that allowed the Northern and the Southern sector of the target to be stitched together and the macrocyclic perimeter to be forged. The lateral chain comprising the remote C46 stereocenter was finally attached to the core region by a modified Julia–Kocienski olefination. The preparation of the individual building blocks led to some methodological spin‐offs, amongst which the improved procedure for the N–O‐bond cleavage of isoxazolines by zero‐valent molybdenum and the ozonolysis of a double bond in the presence of other oxidation‐prone functionality are most noteworthy. Preliminary biological data suggest that the entire carbon framework, that is the macrocyclic core plus the lateral chain, might be necessary for high cytotoxicity.     

Substrate‐Independent Magnetic Bistability in Monolayers of the Single‐Molecule Magnet Dy2ScN@C80 on Metals and Insulators

Magnetic hysteresis is demonstrated for monolayers of the single‐molecule magnet (SMM) Dy₂ScN@C₈₀ deposited on Au(111), Ag(100), and MgO|Ag(100) surfaces by vacuum sublimation. The topography and electronic structure of Dy₂ScN@C₈₀ adsorbed on Au(111) were studied by STM. X‐ray magnetic CD studies show that the Dy₂ScN@C₈₀ monolayers exhibit similarly broad magnetic hysteresis independent on the substrate used, but the orientation of the Dy₂ScN cluster depends strongly on the surface. DFT calculations show that the extent of the electronic interaction of the fullerene molecules with the surface is increasing dramatically from MgO to Au(111) and Ag(100). However, the charge redistribution at the fullerene‐surface interface is fully absorbed by the carbon cage, leaving the state of the endohedral cluster intact. This Faraday cage effect of the fullerene preserves the magnetic bistability of fullerene‐SMMs on conducting substrates and facilitates their application in molecular spintronics.     

Observation of metastable erbium trihydride

The γ phase of the erbium-hydrogen system is a hexagonal trihydride that is not predicted to be stable at room temperature without an overpressure of hydrogen gas. Herein, we report the creation of both, a thin film and powder of erbium trihydride that is metastable at ambient conditions. The presence of the hexagonal γ phase was determined by X-ray diffraction (XRD). The ratio of the total moles of hydrogen isotopes (hydrogen and deuterium) to moles of erbium, (H + D):Er, have been confirmed by elastic recoil detection (ERD)/Rutherford backscattering spectroscopy (RBS). Auger electron spectroscopy (AES) depth profiles and X-ray photoelectron spectroscopy (XPS) revealed the presence of an oxide layer that may account for the metastable behavior of the thin film.     

Hydrogen adsorption strength and sites in the metal organic framework MOF5: Comparing experiment and model calculations

Hydrogen adsorption in porous, high surface area, and stable metal organic frameworks (MOF’s) appears a novel route towards hydrogen storage materials [N.L. Rosi, J. Eckert, M. Eddaoudi, D.T. Vodak, J. Kim, M. O’Keeffe, O.M. Yaghi, Science 300 (2003) 1127; J.L.C. Rowsell, A.R. Millward, K. Sung Park, O.M. Yaghi, J. Am. Chem. Soc. 126 (2004) 5666; G. Ferey, M. Latroche, C. Serre, F. Millange, T. Loiseau, A. Percheron-Guegan, Chem. Commun. (2003) 2976; T. Loiseau, C. Serre, C. Huguenard, G. Fink, F. Taulelle, M. Henry, T. Bataille, G. Férey, Chem. Eur. J. 10 (2004) 1373]. A prerequisite for such materials is sufficient adsorption interaction strength for hydrogen adsorbed on the adsorption sites of the material because this facilitates successful operation under moderate temperature and pressure conditions. Here we report detailed information on the geometry of the hydrogen adsorption sites, based on the analysis of inelastic neutron spectroscopy (INS). The adsorption energies for the metal organic framework MOF5 equal about 800 K for part of the different sites, which is significantly higher than for nanoporous carbon materials (550 K) [H.G. Schimmel, G.J. Kearley, M.G. Nijkamp, C.T. Visser, K.P. de Jong, F.M. Mulder, Chem. Eur. J. 9 (2003) 4764], and is in agreement with what is found in first principles calculations [T. Sagara, J. Klassen, E. Ganz, J. Chem. Phys. 121 (2004) 12543; F.M. Mulder, T.J. Dingemans, M. Wagemaker, G.J. Kearley, Chem. Phys. 317 (2005) 113]. Assignments of the INS spectra is realized using comparison with independently published model calculations [F.M. Mulder, T.J. Dingemans, M. Wagemaker, G.J. Kearley, Chem. Phys. 317 (2005) 113] and structural data [T. Yildirim, M.R. Hartman, Phys. Rev. Lett. 95 (2005) 215504].     

Liquid chromatography-mass spectrometry method for quantification of caspofungin in clinical plasma samples

Caspofungin [(CASPO) MK-0991] is the first broad-spectrum anti-fungal agent of the echinocandin class approved for clinical use. Measurement of CASPO levels in blood might help monitor therapy in patients who are critically ill, in particular, if high-dose regimens or combinations of CASPO with other anti-fungals are used. The objective of this study was to develop a fast method for the measurement of CASPO levels in clinical blood samples using liquid chromatography coupled to a triple-quadrupole mass spectrometer. Stock solutions were prepared in plasma to avoid CASPO adsorption to glass and plastic surfaces during processing. CASPO and the internal standard (IS) were extracted from 100 microl of plasma using acetonitrile protein precipitation. The supernatant was diluted and directly injected into an analytical column (C8; 2.1 x 30 mm). The total run time was 15 min. CASPO was ionized by electrospray in the positive mode. CASPO and IS [M + 2H]2+ parent ions (m/z 547.3 and 547.8, respectively) and specific product ions (m/z 137.1 and 62.2, respectively) were used for the ion transitions. No carry over or cross-talk was observed on the column. The mean method recovery was 90 +/- 3%. Neither blood from different individuals (n = 6) nor the presence of concomitant drugs (n = 33) in plasma samples interfered with CASPO quantification. Quantification over time of the CASPO levels in plasma and whole blood was investigated at different pre-analysis storage conditions. The calibration curve included the clinically relevant CASPO concentration range from 0.04 to 20 microg/ml. Mean intra- and inter-day accuracy was 96.1 +/- 2.2% and 102.5 +/- 2.4%, respectively. Mean intra- and inter-day precision was 7.9 +/- 3.2% and 6.3 +/- 1.8%, respectively. This simple and robust liquid chromatography-tandem mass spectrometry (LC-MS/MS) method may easily be implemented for monitoring CASPO therapy.     

ChemInform Abstract: SrZn2Sn2 and Ca2Zn3Sn6 — Two New Ae—Zn—Sn Polar Intermetallic Compounds (Ae: Alkaline Earth Metal).

The title compounds are synthesized from the elements (950—1000 °C, 45 min—48 h) and characterized by single crystal XRD and DFT electronic structure calculations.