The Structure of the Antibiotic Hedamycin. I. Chemical,Physical and Spectral Properties

Interpretation of the chemical and spectral (IR., UV., ¹H- and ¹³C-NMR.) properties of the antitumor antibiotic hedamycin (C₄₁H₅₀N₂O₁₁) suggests that the molecule contains a methyl substituted 1-hydroxyanthraquinone nucleus, an α, β-unsaturated ketone, two sugar-like tetrahydropyran rings ( 4 and 8 ) and an aliphatic chain 2 , presumably with an epoxy group (see the Scheme).     

Quadratically constrained least squares and quadratic problems

Summary We consider the following problem: Compute a vectorx such that Ax–b₂=min, subject to the constraint x₂=. A new approach to this problem based on Gauss quadrature is given. The method is especially well suited when the dimensions ofA are large and the matrix is sparse.It is also possible to extend this technique to a constrained quadratic form: For a symmetric matrixA we consider the minimization ofx ^T A x–2b ^T x subject to the constraint x₂=.Some numerical examples are given.This work was in part supported by the National Science Foundation under Grant DCR-8412314 and by the National Institute of Standards and Technology under Grant 60NANB9D0908.     

A Theoretical Study of Complex Formation between Formaldehyde and Lithium

Ab initio SCF and CI calculations on the cationic and neutral complexes of formaldehyde and lithium are reported. For the cationic complex CH₂O/Li⁺, the stabilization energy of 41.7 kcal/mol obtained from the SCF calculation increases to 51.6 kcal/mol if a configuration interaction is introduced. For the neutral complex CH₂O^?/Li⁺, the C_2v-conformer of the ²A₁-state with the equilibrium bond distances of d(C? O) = 1.23 Å and d (O? Li) = 1.90 Å is calculated to be more stable than the ₂B₁-state with d (C? O) = 1.34 Å, and d (O? Li) = 1.65 Å. Charge transfer and polarization effects upon complex formation are discussed.     

Bestimmung des Metabolismus und der Produktionsrate von Testosteron, Dehydroepiandrosteron und Dehydroepiandrosteronsulfat

Zusammenfassung Nach i.v. Injektion von 4–6 Ci¹⁴C-Testosteron und 7–8 Ci³H-Androstendion oder entsprechenden Mengen¹⁴C-Dehydroepiandrosteron und³H-Dehydroepiandrosteronsulfat wurden die Glucuronide von Testosteron, Androsteron, Ätiocholanolon und Dehydroepiandrosteron sowie Dehydroepiandrosteronsulfat säulen- (Al₂O₃), papier- (Bush A₂) und dünnschicht-chromatographisch (Chloroform/Äthylacetat 41) aus Urin abgetrennt und gas-chromatographisch (1% XE-60, Flammenionisationsdetektor) bestimmt. Nach splitting des Trägergases und Kondensation der gasförmigen Steroide in einem wattegefüllten Glasröhrchen eines Gasfraktionskollektors wurde die¹⁴C- und³H-Aktivität der einzelnen Androgenmetaboliten mit einem Müssigkeitsszintillationszähler gemessen und aus der spezifischen Aktivität (Impulse/Mikrogramm) die Produktions- und Interkonversionsraten von Testosteron, DHEA und DHEA-Sulfat berechnet.

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Determination of the metabolism and production rates androstendione of testosterone, dehydroepiandrosterone, and dehydroepiandrosterone sulphate

After the i.v. application of 4–6 Ci¹⁴C-testosterone and 7–8 Ci³H-androstendione or equivalent dosages of tritium dehydroepiandrosterone sulphate and dehydroepiandrosterone the gluouronides of testosterone, etiocholanolone, androsterone and dehydroepiandrosterone and dehydroepiandrosterone sulphate were separated from urine by column (Al₂O₃), paper (system Bush A₂) and thin-layer (chloroform:ethylacetate=41) chromatography. After a final gas-liquid chromatography on 1% XE-60 the androgen metabolites were estimated quantitatively by flame-ionisation detector. The radioactivity (³H and¹⁴C impulses) of the compounds was measured after splitting the carrier gas and condensation of the steroids in a gas-fraction collector. From the specific activity (Imp/g) the production and interconversion rates of testosterone, dehydroepiandrosterone and dehydroepiandrosterone sulphate were calculated.

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Die Arbeit wurde mit Mitteln des Bundesministeriums für Wissenschaftliche Forschung gefördert.     

Chemistry of (Carbonyl)(nitrosyl)[bis(phosphorus donor)]rhenium Complexes

The chemistry of [Re(CO)(NO)L₂] fragments (L ? phosphorus donor) was explored. Starting from [Re(CO)₅Cl] the synthesis of [Re₂Cl₂(μ-Cl)₂(CO)₄(NO)₂] ( 1 ) was accomplished via the preparation of [Et₄N]₂[Re₂Cl₂(μ-Cl)₂(CO)₆] and nitrosylation of this compound with [NO][BF₄]. Complex 1 was converted to [RecL₂(CO)(NO)L₂] complexes 2 ( a L = (MeO)₃P; b L = (EtO)₃P; c L = (i-PrO)₃P; d L ? Me₃P; e L ? Et₃P; f L ? Cy₃P) by heating with L in MeCN. In the case of the reaction of L = (MeO)₃P, a trisubstitued compound mer-{ReCl₂(NO)[P(OMe)₃]₃} 3 was also obtained. Replacement of the Cl ligands in 2a–e with Me groups was achieved by reacting them with MeLi in Et₂O yielding cis, trans-[Re(CO)(NO)Me₂L₂]complexes 4a–e . Reaction of 2a–e with Li[BHEt₃] led to substitution of one Cl by an H ligand with formation of [ReCl(CO)H(NO)L₂] compounds 5a–;e , displaying trans-H,NO geometries. The hydride-transfer agent Na[AlH₂(OCH₂CH₂OCH₃)₂] transformed 2 into the cis-dihydride systems [Re(CO)H₂(NO)L₂] 6a–f . Reductive carbonylation of 2a–d in the presence of Na/Hg and CO gave pentacoordinate [Re(CO)₂(NO)L₂] complexes 7b–d , and under comparable conditions the Cl substituents of 2b–f were replaced by tolane using Mg or t-BuLi giving trigonal bipyramidal [Re(CO)(NO)L₂(PhC?CPh)] compounds 8b–f . Complexes 5c , 6a , and 8d were characterized by X-ray crystal-structure analysis.     

The asymptotic Plateau problem in Gromov hyperbolic manifolds

We solve the asymptotic Plateau problem in every Gromov hyperbolic Hadamard manifold (X,g) with bounded geometry. That is, we prove existence of complete (possibly singular) k-dimensional area minimizing surfaces in X with prescribed boundary data at infinity, for a large class of admissible limit sets and for all . The result also holds with respect to any riemannian metric on X which is lipschitz equivalent to g. Received: 23 January 2001 / Accepted: 25 October 2001 Published online: 28 February 2002     

Mo基多组分催化剂催化丙烷选择氧化制丙烯醛

用共沉淀法制备了不同比例的MoCrTeO、MoCoTeO和MoCrTeCoO复合氧化物催化剂,考察其对丙烷选择氧化制丙烯醛反应的催化性能,并对反应温度、空速、原料气比例等条件进行优化,得到丙烯醛最高产率为22．96％．实验结果表明,Te元素的添加对提高丙烯醛的选择性和产率起了十分重要的作用,但过高的Te含量却不利于丙烷的转化率．X射线衍射表征结果表明,催化剂中正交系TeMo5O16相可能是丙烷选择氧化制丙烯醛反应的重要的活性相．     

Exponential decay lifetimes of excitons in individual single-walled carbon nanotubes

The dynamics of excitons in individual semiconducting single-walled carbon nanotubes was studied using time-resolved photoluminescence (PL) spectroscopy. The PL decay from tubes of the same (n,m) type was found to be monoexponential, however, with lifetimes varying between less than 20 and 200 ps from tube to tube. Competition of nonradiative decay of excitons is facilitated by a thermally activated process, most likely a transition to a low-lying optically inactive trap state that is promoted by a low-frequency phonon mode.