CP dynamics of heterogeneous organic material: characterization of molecular domains in coals

Simplified equations are used in common approaches to describe cross polarization (CP) dynamics of solids. The CP behavior may be modulated by several nuclei interactions and physicochemical sample properties. At high magnetic fields and spinning speeds, these modulations can obscure the results. To elucidate their impact on the CP behavior of natural organic materials variable contact time (VCT) experiments were acquired with a high temporal resolution for two coal samples. The measurements were distinctly influenced by interfering fluctuations. Conventional approaches showed insufficient flexibility in terms of degrees of freedom to calculate the CP dynamics. The use of an original fundamental equation as model resulted in sufficient flexibility for such heterogeneous systems. The best results were obtained assuming a two component system. On these conditions a differentiation between amorphous and crystalline domains within the coal samples was enabled.     

First crystal structure of a pentacyclic biomarker: 4,4,6a,12b,14b-Pentamethyl-1,2,3,4,4a,5,6,6a,6b,7, 8,12b,13,14,14a,14b-hexadecahydropicen-3β-ol

The crystal structure of the title compound (1, C₂₇H₄₀O 1/8 H₂O) synthesized via photo-induced electron transfer promoted biomimetic cascade cyclization, is reported. Compound 1 crystallizes in the monoclinic space group C2/c, with cell parameters a = 53.982(4), b = 7.1889(6), c = 11.170(1) Å, = 96.86(1). The structure adopts a fully trans-fused ring junction with all methyl groups axially oriented. The geometrical aspects associated with 1 were discussed and compared with the previously determined X-ray data for structurally analogous compounds.     

Rapid Analysis of Cell–Nanoparticle Interactions using Single‐Cell Raman Trapping Microscopy

Iron oxide nanoparticles have been used in preclinical studies to label stem cells for non‐invasive tracking and homing. The search continues for novel particle candidates that are suitable for clinical applications. Since standard analyses to investigate cell–particle interactions and safety are labor‐intensive, an efficient procedure is required to guide future particle development and to exclude adverse health effects. The application of combined Raman trapping microscopy with fluidic chips is reported for the analysis of single cells labeled with different types of aminated iron oxide particles. Multivariate data analysis revealed Raman signal differences that could be clearly assigned to cell–particle interactions and cytotoxicity, respectively. A validation dataset verified that more than 95 % of the spectra were correctly classified. Thus, our approach enables rapid discrimination of non‐hazardous from cytotoxic nanoparticles as a prerequisite for safe clinical applications.     

Stereoselective synthesis of 2-aminocyclobutanols via photocyclization of alpha-amido alkylaryl ketones: mechanistic implications for the Norrish/Yang reaction.

A series of chiral N-acylated alpha-amino p-methylbutyrophenone derivatives 1a-1h was synthesized from alpha-amino acids via a three-step procedure. These substrates were photolyzed in benzene and gave Norrish II and Norrish I cleavage products as well as the N-acylated 2-aminocyclobutanols that derive from gamma-hydrogen abstraction and 1,4-triplet biradical combination (Yang cyclization). The products were formed with characteristic Yang/cleavage ratios. The quantum yields for the photodecomposition of the N-acetyl-protected substrates 1b,e,f were moderate (12-26%); the diastereoselectivities of the cyclobutanol formation were remarkably high for all substrates. High diastereospecificity was observed for the isoleucine derivatives (2S,3S)-1g and allo-(2S,3R)-1g; the Yang reaction dominated the photochemistry of allo-1g, whereas 1ggave preferentially Norrish II cleavage. The role of hydrogen bonding as one of the stereodirecting effects was demonstrated by comparison of the cyclization efficiency of the valine derivative 1e with 1h,i,j. Also, aromatic beta-keto esters gave the Yang cyclization products in low yields. The diastereoselectivity of the cyclobutanol formation was rationalized by a three-step mechanism where every step is connected with one distinct stereochemical induction mechanism: (a) diastereoselective hydrogen abstraction, (b) conformational equilibration of the 1,4-tetramethylene biradicals (as calculated by semiempiric methods) controlled by hydrogen bonding, and (c) diastereoselective biradical combination (versus cleavage) influenced by spin-orbit coupling controlled intersystem crossing geometries.     

Stereochemie von Metallocenen, 14. Mit.: Chemische Korrelation und absolute Konfiguration von optisch aktiven α- und β-substituierten Methylcymantrenen

Zusammenfassung Die optisch aktiven Methylcymantren-- und--carbonsäuren (2a bzw.2b) wurden über die Methylcymantrenoyl-propionsäuren (4) in die isomeren -(Methylcymantrenyl)-buttersäuren (5) umgewandelt. Die aktiven Ketosäuren4 konnten auch durch Succinylierung von Methylcymantren, Isomerentrennung und Racematspaltung erhalten werden. Beim Ringschluß lieferten die Buttersäuren5 (a, b) isomere Methylcymantreno[1.2]cyclohexenone (6, 10, 12), deren Strukturen durchNMR geklärt wurden. ORD-Vergleiche der methylierten Ringketone mit Cymantrenocyclohexenon (8) bekannter Absolutkonfiguration ermöglichten den Schluß auf die Konfigurationen aller - und -substituierten Methyleymantrene: (1 S) für (+)-2 a, (–)-2 b und ihre Folgeprodukte. Dieses im Vergleich zu den entsprechenden Ferrocenderivaten gegensätzliche Verhalten — hier habenbeide rechtsdrehenden Säuren die gleiche Konfiguration (1 S) — wird diskutiert.

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The optically active methylcymantrene-- and--carboxylic acids (2 a and2 b, resp.) were transformed into the isomeric -(methylcymantrenyl) butyric acids (5) via the methylcymantrenoyl propionic acids (4). The latter could also be obtained by succinylation of methylcymantrene, separation of the isomers and resolution. On cyclization, the butyric acids5 (a, b) afforded isomeric methylcymantreno[1.2]cyclohexenones (6, 10, 12), the structures of which were elucidated byNMR.Comparison of theORD-curves of the methylated ring ketones with cymantrenocyclohexenone (8) of known absolute configuration allowed a reliable conclusion to the configurations of all - and -substituted methylcymantrenes: (1S) for (+)-2 a, (–)-2 b and their subsequent products. This opposite behaviour as compared with the corresponding ferrocene derivatives [whereboth dextrorotatory carboxylic acids have the same configuration (1S] is discussed.

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Mit 1 Abbildung

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Herrn Prof. Dr.L. Schmid in herzlicher Verbundenheit zum 70. Geburtstag gewidmet (K. S)

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Auszugsweise vorgetragen (vonK. S.) beim 3. Internat. Symposium über Metallorganische Chemie, München, 28. August bis 1. September 1967.

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13. Mitt.:Heike Gowal undK. Schlögl, Mh. Chem.98, 2302 (1967).     

Organosilicon hypersilylchalcogenolates and related compounds

Reaction of potassium hypersilylchalcogenolates (Me₃Si)₃SiEK (E = S, Se, Te) with organochlorosilanes R_4 − xSiCl_x (R = Me, Ph; x = 1-4) and methylchlorodisilanes (Si₂Me₅Cl, 1,2-Si₂Me₄Cl₂) yields organosilicon hypersilylchalcogenolates [(Me₃Si)₃SiE]_xSiR_4 − x (x = 1-4) and [(Me₃Si)₃SiE]_xSi₂Me_6 − x (x = 1, 2). A partial substitution product, [(Me₃Si)₃SiSe]₂SiPhCl (2) has been obtained by reaction of PhSiCl₃ with 1.5 equivalents (Me₃Si)₃SiSeK. Besides characterization by ¹H, ¹³C, ²⁹Si, ⁷⁷Se and ¹²⁵Te NMR spectroscopy the compounds [(Me₃Si)₃SiTe]₂SiPh₂ (1), [(Me₃Si)₃SiSe]₂SiPhCl (2) and [(Me₃Si)₃SiSe]₂Si₂Me₄(3) have also been analyzed by crystal structure analyses.Starting from (Me₃Si)₅Si₂K treatment with sulfur gave the highly branched potassium heptasilanylthiolate (Me₃Si)₅Si₂SK. Reactions with methylchlorosilanes Me_4 − xSiCl_x (x = 1, 2, 3) yielded organosilicon heptasilanylthiolates [(Me₃Si)₃Si-(Me₃Si)₂Si-S]_xSiMe_3 − x.     

Nucleophilic 1,2-Shifts of Carboxamide Groups in the Benzil-Benzilic Acid Type Rearrangement of 4-Aryl-2,3-dioxobutyramides and of Quinisatine

4-Aryl-2,3-dioxobutyramide hydrates 1 , undergo the benzil-benzilic acid rearrangement to form (substituted) benzyltartronate monoamides 2 . For compound 1a (Ar = Ph), it is demonstrated by isotopic labelling that the reaction occurs exclusively by migration of the CONH₂ group. Kinetic measurements with 1a-c and with the cyclic amide quinisatine 6 show that the rearrangement of the carboxamide group, proceeding via an alkali-catalysed step, can reach a plateau in the k_obs./[OH^?] diagram (cf. the Fig.), due to complete formation of a mono-anion, and a further increase of rate attributable to the rearrangement of a bis-anion. Comparisons suggest that rearrangements involving an amide group are slower than those involving an ester group, and that, for this effect (as for others), the pre-equilibrium deprotonation of the hydrate is more important than a specific migration tendency.     

Über die 1,2-Verschiebung von Carbonestergruppen bei der Benzilsäureumlagerung von α,β-Dioxobuttersäure-estern. 25. Mitteilung über Reduktone und Tricarbonylverbindungen [1]

In the benzilic acid type rearrangement of t-butyl α,β-dioxobutyrate (VII) the intact t-butoxycarbonyl group is shifted to the β-carbonyl carbon atom.