RESUMO
We have synthesized single crystals of a highly stable Ag8 nanocluster protected by six ligands of diphenyl-2-phosphinic pyridine (DPPY) plus six ligands of phenylacetylene (PhCîC). This Ag8(DPPY)6(PhCîC)6 cluster bears a triangular superatomic Ag8 core, with the vertex and edge Ag atoms (quasi-triangle Ag6) being protected by both P and N bidentate coordination of the six DPPY ligands; meanwhile, the six PhCîC ligands via µ3-C coordination form coordination on the two central Ag atoms capped on both sides of the triangle facet. Apart from the well-organized coordination of the two ligands pertaining to the balanced interactions with the Ag8 core, this Ag8 nanocluster exhibits superatomic stability with two delocalized valence electrons (1S2||1P0), assuming that the six PhCîC ligands fix 6 localized electrons from the Ag atoms. Interestingly, the Ag8(DPPY)6(PhCîC)6 NCs display temperature-dependent dual emissions at 330 and 535 nm under deep ultraviolet excitation. TD-DFT calculations reproduced the experimental spectrum, shedding light on the nature of excitation states and metal-ligand interactions in such a superatomic metal cluster.
RESUMO
We have synthesized single crystals of a highly stable Cu6 nanocluster protected by six ligands of 2-mercapto-5-n-propylpyrimidine (SMPP). This Cu6(SMPP)6 cluster has a quasi-octahedral superatomic Cu6 core, with the Cu atoms being protected by both -S- and N-bidentate coordination of the SMPP ligands. Interestingly, each Cu atom is linked with an N atom, while the two neighboring Cu atoms on the same triangular facet are linked by the -S- bridge of the ligand. Single-crystal parsing results show that the altered orientation of the SMPP ligands give rise to three packing modes (named as 1, 2, and 3) of the Cu6(SMPP)6 NCs. Apart from the well-organized coordination, this Cu6(SMPP)6 nanocluster exhibits superatomic stability with a metallic core of 4 valence electrons (1S22S2||3S2), enabling to largely balance the interactions between the polynuclear core and delocalized electrons. Interestingly, the Cu6(SMPP)6 NCs display dual emissions in both ultraviolet-visible (UV-Vis) and near-infrared (NIR) regions. First-principles calculations well reproduce the experimental spectrum, shedding light on the nature of excitation states and metal-ligand interactions in the Cu6(SMPP)6 cluster.
Assuntos
COVID-19 , Pneumonia , Corticosteroides , Humanos , Imunossupressores , Pneumonia/tratamento farmacológico , SARS-CoV-2RESUMO
We have synthesized single crystals of a highly stable Cu-doped undeca-gold cluster protected by both triphenylphosphine (PPh3) and 2-pyridinethiol (-SPy) ligands, formulated as [Au11Cu1(PPh3)7(SPy)3]+. This cluster (Au11Cu1 NCs for short) has a metallic core of C3v Au@Au10 with the Cu atom capped on one of the nine triangular facets and it is triply-coordinated to three N atoms of the SPy ligands of which the sulfur atom simultaneously binds to three adjacent Au atoms via singly-coordinated S-Au bonds, respectively. The other seven gold atoms form a crown structure by a link of three orthogons with common sides and are protected by seven PPh3 ligands. Besides the well-organized coordination, this Au11Cu1 nanocluster is demonstrated to exhibit superatom stability of the metallic core within 8 valence electrons (assuming that the 3 electrophilic-SPy ligands capture 3 electrons from the metal center). More interestingly, this Au11Cu1 nanocluster shows interesting emissions in both ultraviolet visible (UV-Vis) and near infrared (NIR) regions, and the emissions display novel anti-Stokes up-conversion lasing characteristics. TD-DFT calculated UV-vis and emission spectra well reproduce the experimental results, shedding light on the nature of excitation states and underlying mechanism of electronic transitions between diverse energy levels of such a monolayer-protected bimetallic cluster.
RESUMO
We report the single-crystal synthesis of a chlorine-centered bimetallic cluster, Cl@Ag22 Au6 (4-TBBT)28 (PPh4 ), which bears a quatrefoil-structured Cl@Ag22 (SR)16 core studded by six Au(SR)2 staples showing a quasi Td symmetry. This cluster bears 28 metal atoms and 28 ligands, with a chlorine atom hosted in the center of the metallic Ag22 Au6 core. Single-crystal analysis shows that this cluster possesses essentially a different bonding nature compared with other monolayer-protected metal clusters (MPCs) or traditional metal-sulfur complexes. We fully dissect the structure evolution in forming such a chlorine-centered cluster. Interestingly, this cluster, Cl@Ag22 Au6 (4-TBBT)28 (PPh4 ), displays a fluorescence emission at 570â nm and supports the solid emission with a minor red shift at 574â nm. On the other hand, we have tested the nonlinear optical property and observed unambiguous nonlinear optical property with a normal valley-shaped transmittance curve corresponding to reverse saturated absorption (RSA) of the cluster.
Assuntos
Resistência Microbiana a Medicamentos , Mycobacterium tuberculosis/efeitos dos fármacos , Tuberculose Pulmonar/tratamento farmacológico , Adolescente , Adulto , Antituberculosos/farmacologia , População Negra , Criança , Pré-Escolar , Feminino , Humanos , Quênia , Masculino , Pessoa de Meia-IdadeAssuntos
Ácidos Aminossalicílicos/farmacologia , Resistência Microbiana a Medicamentos , Isoniazida/farmacologia , Mycobacterium tuberculosis/efeitos dos fármacos , Estreptomicina/farmacologia , Tioacetazona/farmacologia , África , Animais , Catalase/análise , Cobaias , Fígado/enzimologia , Pulmão/enzimologia , Linfonodos/enzimologia , Mycobacterium tuberculosis/enzimologia , Mycobacterium tuberculosis/patogenicidade , Baço/enzimologia , VirulênciaAssuntos
Tuberculose Pulmonar/diagnóstico , África , Meios de Cultura , Humanos , Microscopia de Contraste de Fase , Mycobacterium tuberculosis/isolamento & purificação , Escarro/microbiologia , Coloração e Rotulagem , Fatores de Tempo , Tuberculose Pulmonar/microbiologia , Tuberculose Pulmonar/patologiaAssuntos
Resistência Microbiana a Medicamentos , Mycobacterium tuberculosis/patogenicidade , Ácidos Aminossalicílicos/farmacologia , Animais , Catalase/metabolismo , Meios de Cultura , Cobaias , Isoniazida/farmacologia , Pulmão/efeitos dos fármacos , Testes de Sensibilidade Microbiana , Mycobacterium tuberculosis/efeitos dos fármacos , Mycobacterium tuberculosis/enzimologia , Especificidade da Espécie , Baço/efeitos dos fármacos , Estreptomicina/farmacologia , VirulênciaRESUMO
In tropical and subtropical countries, the presence of non-tuberculosis mycobacteria may invalidate case-finding programmes; experience has shown that many of the acid-fast bacilli discovered on examination of sputum specimens are non-tuberculosis mycobacteria-either photochromogens, scotochromogens, unpigmented or rapid growers (Groups I to IV, respectively, of Runyon's classification) or saprophytes.Studies have recently been undertaken to determine the frequency of various types of non-tuberculosis strains in different parts of Africa. This paper describes the first of these studies, devoted to the isolation and identification of non-tuberculosis mycobacteria from seven countries.Of 18 568 cultures examined at the Central Tuberculosis Laboratory, Nairobi, in 1961-64, 1.9% were non-tuberculosis strains. However, valid conclusions as to prevalence cannot be drawn from this figure, since some specimens came from tuberculosis patients and others from general population surveys. An earlier comparison, based on 7580 cultures from tuberculosis patients and 657 from a random survey, had shown a significant difference in the frequency of non-tuberculosis strains, the figures being 1.1% and 19.8%, respectively.Of the identification tests studied, the formamidase test was found very useful for differentiating saprophytic mycobacteria from the other non-tuberculosis mycobacteria, particularly the rapid growers. This test is discussed in greater detail in the third study of the series.