Equilibrium Formation of Stable All-Silicon Versions of 1,3-Cyclobutanediyl.

Main group analogues of cyclobutane-1,3-diyls are fascinating due to their unique reactivity and electronic properties. So far only heteronuclear examples have been isolated. Here we report the isolation and characterization of all-silicon 1,3-cyclobutanediyls as stable closed-shell singlet species from the reversible reactions of cyclotrisilene c-Si3 Tip4 (Tip=2,4,6-triisopropylphenyl) with the N-heterocyclic silylenes c-[(CR2 CH2 )(NtBu)2 ]Si: (R=H or methyl) with saturated backbones. At elevated temperatures, tetrasilacyclobutenes are obtained from these equilibrium mixtures. The corresponding reaction with the unsaturated N-heterocyclic silylene c-(CH)2 (NtBu)2 Si: proceeds directly to the corresponding tetrasilacyclobutene without detection of the assumed 1,3-cyclobutanediyl intermediate.

Reactivity patterns for the activation of CO2 and CS2 with alumoxane and aluminum hydrides.

Carbon dioxide is readily fixed when reacting with either alumoxane dihydride [{MeLAl(H)}2(µ-O)] (1) or aluminum dihydride [MeLAlH2] (2) (MeL = HC[(CMe)N(2,4,6-Me3C6H2)]2-) to produce bimetallic aluminum formates [(MeLAl)2(µ-OCHO)2(µ-O)] (3) and [(MeLAl)2(µ-OCHO)2(µ-H)2] (5), respectively. Furthermore, [(MeLAl)2(µ-OCHO)2(µ-OH)2] (4) is easily obtained upon the reaction of 3 or 5 with H2O. The stability of the unusual dialuminum diformate dihydride core observed in 5 stems from the proximity of the Al centers allowing the formation of two Al-HAl bridges and precluding further hydride transfer to the HCO2 moieties. Contrary to this behavior, 1 and 2 react with CS2 giving cyclic alumoxane and aluminum sulfides [(MeLAl)2(µ-S)(µ-O)] (6) and [{MeLAl(µ-S)}2] (7), respectively. The molecular structures of 3-7 were characterized by IR, Raman, solution or solid-state (MAS) NMR spectroscopy and mass spectrometry and for 4-7 were characterized by X-ray diffraction studies. NMR kinetic studies and DFT calculations suggest that the mechanisms for the formation of 6 and 7 involve the transfer of a hydride group forming transient aluminum thioformate intermediates which proceed to form Al-S-Al moieties through the cleavage of C-S bonds and insertion of a sulfur atom, followed by the elimination of thioformaldehyde.

Tris(3,5-dimethylpyrazolyl)methane-based heterobimetallic complexes that contain Zn - and Cd - transition-metal bonds: synthesis, structures, and quantum chemical calculations.

Reactions of the tris(3,5-dimethylpyrazolyl)methanide amido complexes [M'{C(3,5-Me2 pz)3 }{N(SiMe3 )2 }] (M'=Mg (1 a), Zn (1 b), Cd (1 c); 3,5-Me2 pz=3,5-dimethylpyrazolyl) with two equivalents of the acidic Group 6 cyclopentadienyl (Cp) tricarbonyl hydrides [MCp(CO)3 H] (M=Cr (2 a), Mo (2 b)) gave different types of heterobimetallic complex. In each case, two reactions took place, namely the conversion of the tris(3,5-dimethylpyrazolyl)methanide ligand (Tpmd*) into the -methane derivative (Tpm*) and the reaction of the acidic hydride M = H bond with the M' = N(SiMe3 )2 moiety. The latter produces HN(SiMe3 )2 as a byproduct. The Group 2 representatives [Mg(Tpm*){MCp(CO)3 }2 (thf)] (3 a/b) form isocarbonyl bridges between the magnesium and chromium/molybdenum centres, whereas direct metal-metal bonds are formed in the case of the ions [Zn(Tpm*){MCp(CO)3 }](+) (4 a/b; [MCp(CO)3 ](-) as the counteranion) and [Cd(Tpm*){MCp(CO)3 }(thf)](+) (5 a/b; [Cd{MCp(CO)3 }3 ](-) as the counteranion). Complexes 4 a and 5 a/b are the first complexes that contain Zn - Cr, Cd - Cr, and Cd - Mo bonds (bond lengths 251.6, 269.8, and 278.9 pm, respectively). Quantum chemical calculations on 4 a/b* (and also on 5 a/b*) provide evidence for an interaction between the metal atoms.

A metallacyclic alkyl-amido carbene complex (MCAAC).

The activation of the C≡N moiety in the redox-active metalloligand [CpRu{κ(3)N(pz)-1}][PF6] (2) (1: ambidentate hybrid ligand, N≡C-C(pz)3, with pz = pyrazolyl) was observed in the reaction with [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene). By performing detailed NMR spectroscopic and X-ray crystallographic investigations the product was found to be a bimetallic Ru(II)-Ir(III) complex of the composition [CpRu{µ-1}Ir(cod)Cl2][PF6] (3) consisting of a chemically modified ligand 1'. Most notably, the heterobimetallic complex 3 features an unprecedented metallacyclic alkyl-amido carbene (MCAAC) core structure, which is coordinated to an Ir(III) centre. Density functional theory (DFT) calculations as well as cyclic voltammetry (CV) studies were performed in an effort to establish the formal oxidation states of the metal atoms in 3. Indeed, a quasi-reversible oxidation wave was detected at E(1/2)(0) = 0.36 V, which was attributed to the Ru(II)/Ru(III) redox couple, while two irreversible reduction processes were observed at very negative potentials and have been assigned to the stepwise reduction of Ir(III) to Ir(I). First efforts to elucidate the reaction mechanism have also been performed.

Heterobimetallic cuprates consisting of a redox-switchable, silicon-based metalloligand: synthesis, structures, and electronic properties.

A series of bimetallic silyl halido cuprates consisting of the new tripodal silicon-based metalloligand [κ(3)N-Si(3,5-Me2pz)3Mo(CO)3](-) is presented (pz = pyrazolyl). This metalloligand is straightforwardly accessible by reacting the ambidentate ligand tris(3,5-dimethylpyrazolyl)silanide ({Si(3,5-Me2pz)3}(-)) with [Mo(CO)3(η(6)-toluene)]. The compound features a fac-coordinated tripodal chelating ligand and an outward pointing, "free" pyramidal silyl donor, which is easily accessible for a secondary coordination to other metal centers. Several bimetallic silyl halido cuprates of the general formula [CuX{µ-κ(1)Si:κ(3)N-Si(3,5-Me2pz)3Mo(CO)3}](-) (X = Cl, Br, I) have been synthesized. The electronic and structural properties of these complexes were probed in detail by X-ray diffraction analysis, electrospray mass spectrometry, infrared-induced multiphoton dissociation studies, cyclic voltammetry, spectroelectrochemistry, gas-phase photoelectron spectroscopy, as well as UV/Vis and fluorescence spectroscopy. The heterobimetallic complexes contain linear two-coordinate copper(I) entities with the shortest silicon-copper distances reported so far. Oxidation of the anionic complexes in methylene chloride and acetonitrile solutions at E(1/2)(0( = -0.60 and -0.44 V (vs. ferrocene/ferrocenium (Fc/Fc(+))), respectively, shows substantial reversibility. Based on various results obtained from different characterization methods, as well as density functional theory calculations, these oxidation events were attributed to the Mo(0)/Mo(I) redox couple.

Preparation of telluro- and selenoalumoxanes under mild conditions.

Syntheses of the heavy chalcogen-containing alumoxanes [(Me)LAl(SeH)]2(µ-O) (4) and ((Me)LAl)2(µ-Te)(µ-O) (7) were accomplished by the reaction of ((Me)LAlH)2(µ-O) (2; (Me)L = HC[(CMe)N(2,4,6-Me3C6H2)]2(-)) with either red selenium or metallic tellurium. The aluminum hydrogenselenide [(Me)LAl(SeH)]2(µ-Se) (3) was also prepared from the reaction of red selenium and (Me)LAlH2 (1). All compounds were characterized by spectroscopic methods and X-ray diffraction studies. Density functional theory calculations were performed on 4 and 7.

Cyclic alumosiloxanes and alumosilicates: exemplifying the Loewenstein rule at the molecular level.

The cyclic alumosiloxane [{LAl(µ-O)(Ph(2)Si)(µ-O)}(2)] (3) and alumosilicate [{LAl(µ-O){((t)BuO)(2)Si}(µ-O)}(2)] (4) were obtained by reaction of the appropriate R(2)Si(OH)(2) precursor (R = Ph, O(t)Bu) with [{LAl(H)}(2)(µ-O)] (1), providing a nice illustration of the Loewenstein rule at work at the molecular level.

[Herpetic encephalitis: case series of 15 patients confirmed by polymerase chain reaction]. / Encefalitis herpética: serie clínica de 15 casos confirmados por reacción de polimerasa en cadena.

Encephalitis by herpes simplex virus (HSV) is an sporadic and the most important cause of encephalitis in the western world. The aim of this study was to describe the main clinical features and response to therapy in a representative series of cases. Fifteen cases confirmed by polymerase chain reaction were identified in two university hospitals in Santiago. Average age was 41 years (range 5-78) being 80% over 30 years old. Most cases presented with fever and sensorial involvement (80%) or headache (67%) and only a minority with seizures or focal signs (< or =15%). Extracerebral herpetic lesions were present in two patients (13%). Average length of symptoms was 3. 8 days and most cases were associated to type 1 HSV (86.7%). Changes were detected in 91.7% of those evaluated with electroencephalogram, in 81.8% of those evaluated with nuclear magnetic resonance and in only 13.3% of those evaluated with a cerebral CT-scan. All patients were treated with acyclovir and case-fatality ratio was 13.3%, although one death in a patient with AIDS and CNS lymphoma could not be related to HSV. Six patients (40%) showed neurological deficit at discharge. Death or neurological deficit at discharge was associated with a delay > 3 days before acyclovir therapy. (p = 0.01, two-tailed Fisher test).

Aislamiento de Candida dubliniensis en Venezuela / Candida dubliniensis isolation in Venezuela

En las dos últimas décadas, las enfermedades producidas por hongos han ido en aumento, especialmente las causadas por el género Candida. Siendo el grupo más afectado los individuos inmunocomprometidos, principalmente aquellos afectados con VIH/SIDA. Recientemente se ha demostrado una nueva especie de Candida denominada Candida dubliniensis, la cual ha adquirido importancia desde el punto de vista clínico, debido a que comparte características fenotípicas similares a C. albicans, trayendo como consecuencia una inadecuada identificación de especie y posibles errores terapéuticos al tratar a los pacientes que presentaron candidiasis, ya que Candida dubliniensis desarrolla con más facilidad resistencia a los diferentes antifúngicos utilizados para su tratamiento. En Venezuela hasta los momentos no ha sido publicado el hallazgo de esta especie, por tal motivo el objetivo de este trabajo fue el aislamiento de Candida dubliniensis a partir de 111 cepas identificadas como C. albicans provenientes de Micoteca de la Sección de Micología Médica del IMT de la UCV y del Hospital "Dr. Domingo Luciani", utilizando el medio de Staib agar, CHROMagar Candida y el uso de la prueba de Termotolerancia a 45 grados centígrados, siendo estos métodos de identificación fenotípica; además se empleo el panel de Identificación Rápida de Levaduras MicroScan Dade Behring. Se demostró que 16 (14,4 por ciento) cepas de las 111 cepas estudiadas presentaron características fenotípicas compatibles con C. dubliniensis, siendo esta la primera vez, a la luz de nuestros conocimientos que se identifica en Venezuela esta especie, mediante el uso de los caracteres fenotípicos de las cepas evaluadas