Palladium‐Catalyzed Stereoselective Intramolecular Oxidative Amidation of Alkenes in the Synthesis of 1,3‐ and 1,4‐Amino Alcohols and 1,3‐Diamines

An efficient and practical Pd‐catalyzed intramolecular oxidative allylic amidation provides facile access to derivatives of 1,3‐ and 1,4‐amino alcohols and 1,3‐diamines. The method operates under mild reaction conditions (RT) with molecular oxygen (1 atm) as the sole reoxidant of Pd. Excellent diastereoselectivities were attained with substrates bearing a secondary stereogenic center     

Variability in the Formation and Framework Polymorphism of Metal-organic Frameworks based on Yttrium(III) and the Bifunctional Organic Linker 2,5-Dihydroxyterephthalic Acid

Depending on the solvothermal reaction conditions, we obtained three different metal-organic frameworks with yttrium(III) as metal component and 2,5-dihdyroxyterepthalic acid (Hgt;4gt;dhtp) as bifunctional organic linker: Ygt;2gt;(Hgt;2gt;dhtp)gt;3gt;(dmf)gt;4gt; · (dmf)gt;2gt; (CPO-29) contains dinuclear, paddle-wheel like inorganic secondary building units (SBUs) connected by the organic linker to a network with α-Po topology, while Ygt;2gt;(Hgt;2gt;dhtp)(dhtp)(dmf)gt;2gt; (CPO-30) and Ygt;2gt;(Hgt;2gt;dhtp)(dhtp)(dmf)gt;2gt;(Hgt;2gt;O)gt;2gt; · (Hgt;2gt;O)gt;4gt; (CPO-31) contain one-dimensional inorganic SBUs that differ in how the half- and fully deprotonated ligands are connected to and arranged around them. Only the carboxylic acid groups of the organic linker are deprotonated in CPO-29, while CPO-30 and CPO-31 contain both 2,5-dihydroxyterephthalate (Hgt;2gt;dhtpgt;2–gt;) linkers and fully deprotonated 2,5-dioxidoterephthalate (dhtpgt;4–gt;) linkers. All three compounds contain large volumes filled with solvent, but we were able to demonstrate permanence of porosity only for CPO-30. Variable temperature powder X-ray diffraction reveals that CPO-29 and CPO-31 undergo discontinuous phase transitions upon heating, and the flexibility of the framework structure indicated by these might be the reason for the inability to access the pore volume. Desolvated CPO-30 and CPO-31 are polymorphs, whose network structures differ in whether the Hgt;2gt;dhtpgt;2–gt; and dhtpgt;4–gt; linkers are located in gt;cisgt; or gt;transgt; arrangement around the inorganic SBU.     

The spectrum of the random environment and localization of noise

We consider random walk on a mildly random environment on finite transitive gt;dgt;-regular graphs of increasing girth. After scaling and centering, the analytic spectrum of the transition matrix converges in distribution to a Gaussian noise. An interesting phenomenon occurs at gt;dgt; = 2: as the limit graph changes from a regular tree to the integers, the noise becomes localized. gt; gt; g src="/static-content/0.5898/images/810/art%253A10.1007%252Fs00440-009-0225-7/MediaObjects/440_2009_225_Figa_HTML.gif" class="a-plus-plus" alt=">g> gt; gt; The graphs of the noise covariance structure for gt;dgt; = 4, 3, 2.1 from above.     

Efficient J=0-1 soft-X-ray lasing in neon-like ions at pump powers below 250 GW

2 . By using a 0.7% prepulse that precedes the main pulse by 5 ns and applying a total pump energy of 100 J or less, the J=0-1 lasing is at least one order of magnitude higher than the non-lasing background. For the 32.6-nm line of Ti, the 25.5-nm line of Fe, and the 23.1-nm line of Ni, gain coefficients of (±) 4.20.4cmgt;-1gt;, (±) 3.90.3cmgt;-1gt;, and (±) 3.60.6cmgt;-1gt;, respectively, were measured for 2.4-cm-long curved targets, resulting in gain–length products of ∼10. Angle-resolved spectra indicate a beam divergence of 3 mrad (FWHM), typically. The space-resolved spectra show that the J=0-1 lasing lines are emitted from an approximately 60-μm-wide (FWHM) plasma region, whereas the nearby continuum emission is produced in a considerably broader plasma region of ∼250 μm. Lasing at 25.5 nm in neon-like iron was observed at a pump power as low as 180 GW (∼9 TW/cmgt;2gt;), with, however, considerable shot-to-shot scatter in the absolute laser output. Received: 5 September 1997/Revised version: 10 November 1997     

Structural phase stability studies on MBeH3 (M = Li, Na, K, Rb, Cs) from density functional calculations

Density functional theory calculations within the generalized-gradient approximation are used to establish the ground-state structure, equilibrium structural parameters, and electronic structure for MBeH(3) phases. From the 24 structural arrangements used as inputs for structural optimization calculations, the ground-state crystal structures of MBeH(3) phases have been predicted. At ambient conditions, LiBeH(3) and NaBeH(3) crystallize with perovskite-related orthorhombic and cubic structures, respectively. The remaining phases KBeH(3), RbBeH(3), and CsBeH(3) crystalize in a monoclinic structure. In the predicted phases one can store up to 15.93 wt % of hydrogen. The formation energy for the MBeH(3) phases have been investigated along different reaction pathways. The electronic structures reveal that all these phases are insulators with estimated band gaps varying between 1.79 and 3.44 eV.     

Molecular orbital interpretation of X-ray emission spectra of ClCN and ONCl

Ab initio as well as semi-empirical SCF MO calculations are presented for ClCN and ONCl. The relative intensities for Cl Kβ emission in the two molecules were calculated. The calculated spectra from the ab initio wavefunctions are in excellent agreement with experiments.     

High-throughput screening of pKa values of pharmaceuticals by pressure-assisted capillary electrophoresis and mass spectrometry

A high-throughput pKa screening method based on pressure-assisted capillary electrophoresis (CE) and mass spectrometry (MS) is presented. Effects of buffer type and ionic strength on sensitivity and pKa values were investigated. Influence of dimethyl sulfoxide (DMSO) concentration present in the sample on effective mobility measurement was examined. A series of ten volatile buffers, covering a pH range from 2.5 to 10.5 with the same ionic strength, was employed. The application of volatile background electrolytes resulted in significant signal increase as compared with commonly used non-volatile phosphate buffers. In general, the CE/MS system provided a ten-fold higher sensitivity than conventional UV detection. The newly developed CE/MS method offers high-throughput capacity by pooling a number of compounds into a single sample. Simultaneous measurement of more than 50 compounds was readily achieved in less than 150 min. The measured pKa values are consistent with the published data obtained from the CE/UV method and are also in good agreement with data generated by other methods. Other advantages of using CE/MS for pKa screening are illustrated with typical examples, including poorly soluble compounds and non-UV-absorbing compounds.     

Photofragmentations, state interactions, and energetics of Rydberg and ion-pair states: two-dimensional resonance enhanced multiphoton ionization of HBr via singlet-, triplet-, Ω = 0 and 2 states

Mass spectra were recorded for one-colour resonance enhanced multiphoton ionization (REMPI) of H(i)Br (i = 79, 81) for the two-photon resonance excitation region 79,040-80,300 cm(-1) to obtain two-dimensional REMPI data. The data were analysed in terms of rotational line positions, intensities, and line-widths. Quantitative analysis of the data relevant to near-resonance interactions between the F(1)Δ(2)(v' = 1) and V(1)Σ(+)(v' = m + 7) states gives interaction strengths, fractional state mixing, and parameters relevant to dissociation of the F state. Qualitative analysis further reveals the nature of state interactions between ion-pair states and the E(1)Σ(+) (v' = 1) and H(1)Σ(+)(v' = 0) Rydberg states in terms of relative strengths and J' dependences. Large variety in line-widths, depending on electronic states and J' quantum numbers, is indicative of number of different predissociation channels. The relationship between line-widths, line-shifts, and signal intensities reveals dissociation mechanisms involving ion-pair to Rydberg state interactions prior to direct or indirect predissociations of Rydberg states. Quantum interference effects are found to be important. Moreover, observed bromine atom (2 + 1) REMPI signals support the importance of Rydberg state predissociation channels. A band system, not previously observed in REMPI, was observed and assigned to the k(3)Π(0)(v' = 0) ←← X transition with band origin 80,038 cm(-1) and rotational parameter B(v('))=7.238 cm(-1).     

Structure and Polymorphism of M(thd)3 (M = Al,Cr, Mn,Fe, Co,Ga, and In)

Formation, crystal structure, polymorphism, and transition between polymorphs are reported for gt;Mgt;(thd)gt;3gt;, (gt;Mgt; = Al, Cr, Mn, Fe, Co, Ga, and In) [(thd)gt;–gt; = anion of H(thd) = Cgt;11gt;Hgt;20gt;Ogt;2gt; = 2, 2, 6, 6‐tetramethylheptane‐3, 5‐dione]. Fresh crystal‐structure data are provided for monoclinic polymorphs of Al(thd)gt;3gt;, Ga(thd)gt;3gt;, and In(thd)gt;3gt;. Apart from adjustment of the gt;Mgt;–Ogt;kgt; bond length, the structural characteristics of gt;Mgt;(thd)gt;3gt; complexes remain essentially unaffected by change of gt;Mgt;. Analysis of the gt;Mgt;–Ogt;kgt;, Ogt;kgt;–Cgt;kgt;, and Cgt;kgt;–Cgt;kgt; distances support the notion that the gt;Mgt;–Ogt;kgt;–Cgt;kgt;–Cgt;kgt;–Cgt;kgt;–Ogt;kgt;– ring forms a heterocyclic unit with σ and π contributions to the bonds. Tentative assessments according to the bond‐valence or bond‐order scheme suggest that the strengths of the σ bonds are approximately equal for the gt;Mgt;–Ogt;kgt;, Ogt;kgt;–Cgt;kgt;, and Cgt;kgt;–Cgt;kgt; bonds, whereas the π component of the gt;Mgt;–Ogt;kgt; bonds is small compared with those for the Ogt;kgt;–Cgt;kgt;, and Cgt;kgt;–Cgt;kgt; bonds. The contours of a pattern for the occurrence of gt;Mgt;(thd)gt;3gt; polymorphs suggest that polymorphs with structures of orthorhombic or higher symmetry are favored on crystallization from the vapor phase (viz. sublimation). Monoclinic polymorphs prefer crystallization from solution at temperatures closer to ambient. Each of the gt;Mgt;(thd)gt;3gt; complexes subject to this study exhibits three or more polymorphs (further variants are likely to emerge consequent on systematic exploration of the crystallization conditions). High‐temperature powder X‐ray diffraction shows that the monoclinic polymorphs convert irreversibly to the corresponding rotational disordered orthorhombic variant above some 100–150 °C (depending on gt;Mgt;). The orthorhombic variant is in turn transformed into polymorphs of tetragonal and cubic symmetry before entering the molten state. These findings are discussed in light of the current conceptions of rotational disorder in molecular crystals.     

Homo- and hetero-nuclear chromium(III) complexes with natural ligands. Part 2. Oxo- and hydroxo-bridged chromium(III)/vanadium(V) species

Six new heteropolynuclear chromium(III)/vanadium(V) complexes with natural ligands: glycine, glutaminic, nicotinic and asparginic acids, have been isolated and physicochemically characterised. The complexes have been analysed using spectroscopic (diffuse reflectance u.v.–vis., i.r.), magnetic methods and by FAB mass spectra. Spectral analyses with the digital filter and band deconvolution methods are presented. Additionally, preliminary toxicity studies have been performed.