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J. J. LaBrecque Z. A. De Benzo E. Marcano C. A. Peña 《Journal of Radioanalytical and Nuclear Chemistry》1984,84(2):407-413
The comparison of an ambient temperature mercuric iodide spectrometer (HgI2) with a conventional cooled Si(Li) spectrometer is presented for the determination of niobium in Venezuelan laterites in the laboratory. The energy resolution of the HgI2 spectrometer was only about 590 eV (FWHM) at 5.9 keV compared to about 150 eV for the conventional Si(Li) spectrometer. The efficiency was about 5 times lower in the region of the NbK
peak as compared to the Si(Li) detector. Even though its energy resolution and efficiency is much poorer than the conventional Si(Li), the results it produced for the determination of niobium were acceptable for use in the exploration and exploitation of a niobium-rich deposit such as Cerro Impacto, Estado Bolívar, Venezuela. 相似文献
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David E. Salazar Marcano Mhamad Aly Moussawi Alexander V. Anyushin Sarah Lentink Luc Van Meervelt Ivana Ivanovi-Burmazovi Tatjana N. Parac-Vogt 《Chemical science》2022,13(10):2891
Hybrid structures incorporating different organic and inorganic constituents are emerging as a very promising class of materials since they synergistically combine the complementary and diverse properties of the individual components. Hybrid materials based on polyoxometalate clusters (POMs) are particularly interesting due to their versatile catalytic, redox, electronic, and magnetic properties, yet the controlled incorporation of different clusters into a hybrid structure is challenging and has been scarcely reported. Herein we propose a novel and general strategy for combining multiple types of metal-oxo clusters in a single hybrid molecule. Two novel hybrid POM structures (HPOMs) bis-functionalised with dipentaerythritol (R–POM1–R; R = (OCH2)3CCH2OCH2C(CH2OH)) were synthesised as building-blocks for the formation of heterometallic hybrid triads (POM2–R–POM1–R–POM2). Such a modular approach resulted in the formation of four novel heterometallic hybrids combing the Lindqvist {V6}, Anderson–Evans {XMo6} (X = Cr or Al) and trisubstituted Wells–Dawson {P2V3W15} POM structures. Their formation was confirmed by multinuclear Nuclear Magnetic Resonance (NMR), infrared (IR) and UV-Vis spectroscopy, as well as Mass Spectrometry, Diffusion Ordered Spectroscopy (DOSY) and elemental analysis. The thermal stability of the hybrids was also examined by Thermogravimetric Analysis (TGA), which showed that the HPOM triads exhibit higher thermal stability than comparable hybrid structures containing only one type of POM. The one-pot synthesis of these novel compounds was achieved in high yields in aqueous and organic media under simple reflux conditions, without the need of any additives, and could be translated to create other hybrid materials based on a variety of metal-oxo cluster building-blocks.A versatile modular approach has been developed for incorporating different metal-oxo nanoclusters with characteristic structures into a single hybrid molecule by covalently linking them with polyol ligands. 相似文献
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Barral P J Hasmy A Jiménez J Marcano A 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》2000,61(2):1812-1815
Using a simple computational procedure, we examine DNA chains from different species in order to prove their nonlinear deterministic structures. This procedure applies a nonlinear modeling technique based upon quantitative comparison of the neighborhoods from similar DNA subsegments of size d. Our results reveal that noncoding regions exhibit a deterministic signature at sizes larger than a characteristic dimension d(c). Applications to evolutionary categories and recognition of different DNA regions are discussed. 相似文献
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The optical phonon spectrum of the semiconductor Cu2SnTe3, that crystallizes in the orthorhombic structure with space group Imm2 (), have been studied by measuring unpolarized Raman scattering between 10 and 300 K. The experimental frequencies of the phonon modes observed were compared to those calculated by using simplified lattice dynamical models reported in the literature. From combined analysis of these results together with the factor group analysis of the zone-center vibrational modes, valuable information about these modes was obtained and their possible symmetry was assigned. A1 modes at 71, 123, 167, 176 and 190 cm−1; A2 modes 115 and 131 cm−1; B1 modes at 76, 142 and 152 cm−1; B2 modes at 89, 100 and 206 cm−1; a overtone at 246 cm−1, and combinations at 218, 270 and 292 cm−1; have been observed in this compound. 相似文献
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Deanna De Marcano Bernardo Mndez Jeannette De Mndez Jos Monasterios Aníbal C. Rojas Thomas G. Halsall 《Magnetic resonance in chemistry : MRC》1983,21(8):524-525
The 13C NMR spectra of a series of some Δ4(20),11-taxadiene derivatives are reported. A detailed analysis of their assignments is presented. 相似文献
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Deanna Marcano Jeannette De Mndez Ana C. Ortiz Mirna Salinas 《Magnetic resonance in chemistry : MRC》1984,22(11):736-738
The 13C chemical shift data of several D-homoandrostanes with heteroatoms (N,O) in the 17a-position are reported. Heteroatom effects on the shieldings of the carbons of rings C and D are discussed. 相似文献
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Dr. Cui-Lian Liu Dr. Mhamad Aly Moussawi Givi Kalandia Dr. David E. Salazar Marcano Dr. William E. Shepard Prof. Dr. Tatjana N. Parac-Vogt 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(19):e202401940
The artificial microenvironments inside coordination cages have gained significant attention for performing enzyme-like catalytic reactions by facilitating the formation of labile and complex molecules through a “ship-in-a-bottle” approach. Despite many fascinating examples, this approach remains scarcely explored in the context of synthesizing metallic clusters such as polyoxometalates (POMs). The development of innovative approaches to control and influence the speciation of POMs in aqueous solutions would greatly advance their applicability and could ultimately lead to the formation of elusive clusters that cannot be synthesized by using traditional methods. In this study, we employ host–guest stabilization within a coordination cage to enable a novel cavity-directed synthesis of labile POMs in aqueous solutions under mild conditions. The elusive Lindqvist [M6O19]2− (M=Mo or W) POMs were successfully synthesized at room temperature via the condensation of molybdate or tungstate building blocks within the confined cavity of a robust and water-soluble Pt6L4(NO3)12 coordination cage. Importantly, the encapsulation of these POMs enhances their stability in water, rendering them efficient catalysts for environmentally friendly and selective sulfoxidation reactions using H2O2 as a green oxidant in a pure aqueous medium. The approach developed in this paper offers a means to synthesize and stabilize the otherwise unstable metal-oxo clusters in water, which can broaden the scope of their applications. 相似文献
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Emildo Marcano Emilio Squitieri Juan Murgich Humberto Soscún 《Journal of Molecular Structure》2009,911(1-3):81-87
Hatree–Fock calculations at ab initio and semiempirical levels were carried out for the averaged polarizability α and second hyperpolarizability γ of two pairs of quadrupolar isomers with different donor and acceptor groups. These properties were correlated with the antibonding/bonding π occupation number (π*/π ratio). It was found that isomers with extended π systems had low π*/π ratios and high α and γ values, while low α and γ values were obtained for isomers with large π*/π ratios and no extended π system. The PM3 and PM6 α values were found to be in excellent agreement with the HF/6-31+G(d,p) ones. The PM3 values for γ were significantly larger than those calculated by HF/6-31+G(d,p), with an average PM3/HF ratio of 1.43. The PM6 results were noticeably better with a ratio of 0.85. The calculation of α and γ at MP2/6-31+G(d,p) level for representative isomers showed that the contribution of the electron correlation to their values was small and that the HF/6-31+G(d,p) method provides reliable values at much lower computational cost. 相似文献