The plasticity of pure single crystals

The theory of the work-hardening curve of a pure single crystal is discussed. An outline is given of the experimental methods available for the study of the mechanism of plastic deformation and work hardening. An attempt is made to correlate existing theories of work hardening. The theory is illustrated by discussions of copper, of other face-centred cubic metals, of the diamond and sphalerite structures, of hexagonal close-packed metals, of ionic face-centred cubic crystals and of body-centred cubic metals.     

New Antibacterial Diterpenes from Pseudopterogorgia elisabethae

From the MeOH extract of Pseudopterogorgia elisabethae, collected from the Bahamas, four new diterpenes, elisabethin E ( 1 ), elisabethin F ( 2 ), pseudopterosin P ( 3 ), and pseudopterosin Q ( 4 ), were isolated and their structures established with the aid of extensive spectroscopic studies. Compounds 3 and 4 showed antibacterial activity selectively against the Gram‐positive bacteria Streptococcus pyogenes, Staphylococcus aureus, and Enterococcus faecalis.     

Unraveling the 13C NMR chemical shifts in single-walled carbon nanotubes: dependence on diameter and electronic structure

The atomic specificity afforded by nuclear magnetic resonance (NMR) spectroscopy could enable detailed mechanistic information about single-walled carbon nanotube (SWCNT) functionalization as well as the noncovalent molecular interactions that dictate ground-state charge transfer and separation by electronic structure and diameter. However, to date, the polydispersity present in as-synthesized SWCNT populations has obscured the dependence of the SWCNT (13)C chemical shift on intrinsic parameters such as diameter and electronic structure, meaning that no information is gleaned for specific SWCNTs with unique chiral indices. In this article, we utilize a combination of (13)C labeling and density gradient ultracentrifugation (DGU) to produce an array of (13)C-labeled SWCNT populations with varying diameter, electronic structure, and chiral angle. We find that the SWCNT isotropic (13)C chemical shift decreases systematically with increasing diameter for semiconducting SWCNTs, in agreement with recent theoretical predictions that have heretofore gone unaddressed. Furthermore, we find that the (13)C chemical shifts for small diameter metallic and semiconducting SWCNTs differ significantly, and that the full-width of the isotropic peak for metallic SWCNTs is much larger than that of semiconducting nanotubes, irrespective of diameter.     

Copper‐Catalyzed Oxy‐Alkenylation of Homoallylic Alcohols to Generate Functional syn‐1,3‐Diol Derivatives

A novel method for the synthesis of a wide range of functionalized 1,3‐diol derivatives is reported. Employing a copper‐catalyzed oxy‐alkenylation strategy, a range of readily available, substituted homoallylic alcohol derivatives and alkenyl(aryl) iodonium salts combine to form syn‐1,3‐carbonates in excellent yield and with high selectivity. Furthermore, the products formed are amenable to an iterative reaction sequence, thus affording highly complex polyketide‐like fragments.     

Diastereoselective synthesis of linear‐fused tricyclic nitrogen heterocycles by a tandem reduction‐reductive amination reaction

A two‐step diastereoselective synthesis of linear‐fused tricyclic nitrogen heterocycles has been developed from cyclic β‐ketoesters. The cyclization substrates are readily prepared by alkylation of the methyl 2‐oxo‐cycloalkanecarboxylates with 2‐nitrobenzyl bromide. Hydrogenation of these substrates initiates a reaction sequence involving (1) reduction of the aromatic nitro group, (2) condensation of the resulting hydroxyl‐amine or aniline nitrogen with the cycloalkanone and (3) reduction of the imine. The products are isolated in high yield as single diastereomers having the trans‐fused ring junction. The observed selectivity is rationalized in terms of a steric effect imposed by the ester group in the final reductive amination step which directs the incoming hydrogen to the opposite face of the molecule. By comparison, reductive cyclizations of substrates lacking the stereodirecting ester group give mixtures of cis and trans products with a preference for the cis‐fused heterocycle.     

The minimal number of solutions to

In 1958, A. Schinzel showed that for each fixed there are at least two solutions to . Using the same method and a computer search, Schinzel and A. Wakulicz extended the bound to all . Here we show that Schinzel's method can be used to further extend the bound when is even, but not when is odd.

     

Dipotassium tristrontium dimanganese tris­(diphosphate)

The structure of the title mixed trimetallic diphosphate, K₂Sr₃Mn₂(P₂O₇)₃, is constructed of a three‐dimensional matrix composed of SrO_8–10, MnO₅ and PO₄ polyhedra. The sharing of O atoms between these polyhedra creates tunnels of large dimensions parallel to (010), in which are found columns of K⁺ ions. Thus, the presence of several cations differing in size in the solid matrix leads to the formation of large tunnels and potential conductivity.     

Photophysical studies on antimalarial drugs

Most drugs used in the treatment of malaria produce phototoxic side effects in both the skin and the eye. Cutaneous and ocular effects that may be caused by light include changes in skin pigmentation, corneal opacity, cataract formation and other visual disturbances including irreversible retinal damage (retinopathy) leading to blindness. The mechanism for these reactions in humans is unknown. We irradiated a number of antimalarial drugs (amodiaquine, chloroquine, hydroxychloroquine, mefloquine, primaquine and quinacrine) with light (lambda > 300 nm) and conducted electron paramagnetic resonance (EPR) and laser flash photolysis studies to determine the possible active intermediates produced. Each antimalarial drug produced at least one EPR adduct with the spin-trap 5,5-dimethyl-1-pyrroline N-oxide in benzene: superoxide/hydroperoxyl adducts (chloroquine, mefloquine, quinacrine, amodiaquine and quinine), carbon-centered radical adducts (all but primaquine), or a nitrogen-centered radical adduct only (primaquine). In ethanol all drugs except primaquine produced some superoxide/hydroperoxyl adduct, with quinine, quinacrine, and hydroxychloroquine also producing the ethoxyl adduct. As detected with flash photolysis and steady-state techniques, mefloquine, quinine, amodiquine and a photoproduct of quinacrine produced singlet oxygen ([symbol: see text]delta = 0.38; [symbol: see text]delta = 0.36; [symbol: see text]delta = 0.011; [symbol: see text]delta = 0.013 in D2O, pD7), but only primaquine quenched singlet oxygen efficiently (2.6 x 10(8) M-1 s-1 in D2O, pD7). Because malaria is a disease most prevalent in regions of high light intensity, protective measures (clothing, sunblock, sunglasses or eye wraps) should be recommended when administering antimalarial drugs.     

Nitropyridyl isocyanates

We hereby report the first preparation of 3‐nitro‐4‐pyridyl isocyanate 9 and 5‐nitro‐2‐pyridyl isocyanate 18 . They were formed by Curtius rearrangement of the corresponding acyl azides 8 and 17 , prepared from methyl 3‐nitro‐4‐pyridinecarboxylate 6 via the hydrazide 7 and 5‐nitro‐picolinic acid 16 , respectively. The substrates 6 and 16 were generated by nitration of methyl 4‐pyridinecarboxylate 5 and nitration and oxidation of 2‐picoline 14 . 3‐Nitro‐4‐pyridyl isocyanate 9 can be stored in dry solution and is stable at room temperature for several weeks while 5‐nitro‐2‐pyridyl isocyanate 18 was less stable and should be used for synthetic purposes immediately.