Добірка наукової літератури з теми "Electron-deficient complexes"

This chapter explains in simple terms the background physics of imaging using standard X-rays, computed axial tomography (CT), nuclear medicine (including positron emission tomography-PET), and magnetic resonance imaging (MRI). It covers the basics of ionising radiation, and also discusses lasers, which are a form of non-ionising radiation (imaging using ultrasound is covered in Chapter 10). X-rays, CT, aspects of nuclear medicine, and lasers are covered briefly. MRI is examined in more detail as this is a newer modality that is often difficult to comprehend, and in any case often involves the presence of the anaesthetist. Some isotopes are naturally occurring but many of the radioactive nuclides used in medicine are produced artificially by a nuclear reactor or cyclotron. Each of these will provide isotopes that are useful for different purposes. Unstable radioactive nuclides achieve stability by radioactive decay, during which they can lose energy. This occurs in a number of ways. For example, atoms can lose energy by ejection of an alpha particle (an extremely tightly bound basic atomic structure of 2 protons and 2 neutrons, which is equivalent to a helium nucleus). This occurs if they have too many nucleons (protons or neutrons) and results in the atomic number being reduced by two and the atomic mass by 4. Other ways that unstable radionuclides decay include: emission of an electron (β−) from the nucleus if the atoms have an excess of neutrons, or by, either emitting a positron (β+) or capturing an electron if they are neutron deficient. Normally isotopes produced by a reactor will be neutron rich and decay by emitting an electron and the cyclotron will tend to produce isotopes that are proton rich and the decay will then be by emitting a positron. This is illustrated in Table 29.1. The new nuclide formed by the decay process (the daughter nuclide) may be left in an excited nuclear state and can release this excess energy by emission of gamma (γ) radiation as shown in Figure 29.1. This example is where the electron (β−) has been emitted. The situation is more complex when a positron has been emitted.

A variety of antibiotics and immune-suppressive agents contain extended arrays of all- ( E )-polyenes. Samir Bouzbouz of CNS Rouen and Janine Cossy of ESPCI ParisTech devised ( Synlett 2009, 803) a simple iterative route to polyacetates such as 1 and demonstrated that after cross-metathesis, elimination, in this case to give Navenone B 3, was facile. Both ketones and esters can promote the elimination. Daesung Lee of the University of Illinois at Chicago designed (Organic Lett. 2009, 11 , 571) a clever chain-walking ring-closing ene-yne metathesis, cyclizing 4 to 5. Deprotection led to (+)-asperpentyn 6. This should be a general entry to such polyoxygenated cyclohexenes. For the structures of H2 and G2, see Organic Highlights, September 13, 2004. One of the challenges in the synthesis of (-)-amphidinoloide K 10 is the assembly of the complex conjugated diene. Eun Lee of Seoul National University found (Angew. Chem. Int. Ed. 2009, 48, 2364) a solution to this problem in the Ru-catalyzed cross-metathesis between the alkyne 7 and the alkene 8. Note that the cross-metathesis proceeded with high regioselectivity and with substantial (7.5:1) control of the product alkene geometry. For the construction of complex natural products such as norhalichondrin B 14, it is important to employ a convergent synthetic strategy. For this to be successful, efficient methods for convergent coupling are required. In the course of a synthesis of 14, Andrew J. Phillips of the University of Colorado showed (Angew. Chem. Int. Ed. 2009, 48, 2346) that Ru-mediated cross-metathesis could be used to couple the enone 11 with the alkene 12. A less congested version of H2, designed by Robert H. Grubbs of Caltech, was used for the coupling. The electron-deficient alkene of 11 and the more electron-rich alkene of 12 made a matched set, promoting the cross-coupling. Note again, in this context, the desirability of leaving the allylic alcohol of 12 unprotected to facilitate Ru-catalyzed alkene cross-metathesis.

Huanfeng Jiang at the South China University of Technology developed (J. Am. Chem. Soc. 2013, 135, 5286) the palladium-catalyzed dehydrogenative aminohalogenation of methyl acrylate with aniline 1. A 1,3-hydrogen shift/ chlorination catalyzed by an iridium complex was reported (Angew. Chem. Int. Ed. 2013, 52, 6273) by Belén Martín- Matute at Stockholm University. Robert M. Waymouth discovered (J. Am. Chem. Soc. 2013, 135, 7593) the chemoselective oxidation of polyol 5 by a cationic palladium species. A ruthenium(II) hydride was found to catalyze the conversion of alcohols such as 7 to carboxylic acids using water as the oxygen source as disclosed (Nature Chem. 2013, 5, 122) by David Milstein at the Weizmann Institute of Science in Israel. Susan K. Hanson at the Los Alamos National Laboratory in New Mexico reported (Org. Lett. 2013, 15, 650) the acceptorless dehydrogenation of alcohols catalyzed by cobalt complex 12 to form imines such as 13 upon reaction with an amine. A collabo­ration led by Pedro J. Pérez at the University of Huelva in Spain studied (J. Am. Chem. Soc. 2013, 135, 3887) the oxidation of alkanes under catalysis with copper complex 15, primarily yielding alcohols and ketones, such as in the conversion of cyclohexane (14) to cyclohexanol (16) and cyclohexanone (17). A remarkable symmetry-breaking Wacker oxidation of diene 18 to produce 19 was the key step in the total synthesis of (+)-obolactone reported (Org. Lett. 2013, 15, 1294) by Reinhard Brückner at the University of Freiburg in Germany. Kiyotomi Kaneda at the University of Osaka found (Angew. Chem. Int. Ed. 2013, 52, 5961) that a palladium salt catalyzes the conversion of electron-deficient internal olefin 20 to ketone 21. As part of a program to develop environmentally sustainable procedures, Caterina Fusco at the University of Bari in Italy described (Tetrahedron Lett. 2013, 54, 515) the oxidative cleavage of lactam 22 by methyl(trifluoromethyl)dioxirane in water to pro­duce ω-nitro acid 24. Motomu Kanai at the University of Tokyo reported (Org. Lett. 2013, 15, 1918) the β-functionalization of tertiary aromatic amine 25 with nitroolefin 26 to produce 27 by iron catalysis.

Although it is recognized that glycoprotein (GP) Ib/IX complexes are deficient in the platelets of patients with the Bernard-Soulier syndrome (BSS), the nature of the genetic defect remains unknown. We have looked for these GPs in permeabilized megakaryocytes (MK) of a BSS patient employing immunofluorescence (IF) or immunocytochemical procedures combined with electron microscopy. The study involved the use of monoclonal antibodies AP-1 (anti-GP Ib), AP-2 (anti-GP IIb-IIIa) and FMC 25 (anti-GP IX), gifts from Drs. T. Kunicki and M. Berndt respectively. Bound IgG were revealed by biotinylated a

Elemental boron has many interesting properties, such as high melting point, low density, high hardness, high Young’s modulus, good oxidation resistance, resulting from its complex crystalline structure from its electron-deficient nature. Boron forms complex crystalline structures according to the various arrangements of B12 icosahedra in the lattice, such as α (B12)- and β (B105)-rhombohedral and α (B50)- and β (B196)-tetragonal boron polymorphs, among others. Even though considerable materials research has been conducted over the past half century on boron and boron-based compounds, investig