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1.
Dalton Trans ; 50(19): 6463-6476, 2021 May 18.
Artigo em Inglês | MEDLINE | ID: mdl-34002748

RESUMO

Complex polymorphic relationships in the LnSiP3 (Ln = La and Ce) family of compounds are reported. An innovative synthetic method was developed to overcome differences in the reactivities of the rare-earth metal and refractory silicon with phosphorus. Reactions of atomically mixed Ln + Si with P allowed for selective control over the reaction outcomes resulting in targeted isolation of three new polymorphs of LaSiP3 and two polymorphs of CeSiP3. In situ X-ray diffraction studies revealed that the developed method bypasses formation of the thermodynamic dead-end, the binary SiP. Careful re-determination of the crystal structure ruled out the previously reported ordered centrosymmetric structure of CeSiP3 and showed that the main LnSiP3 polymorphs crystallize in the non-centrosymmetric Pna21 and Aea2 space groups featuring distinct distortions of the regular P square net to yield either cis-trans 1D phosphorus chains (Pna21) or disordered-2D phosphorus layers (Aea2). The disordered 2D nature of the P layers in the Aea2 LaSiP3 polymorph was confirmed by Raman spectroscopy. A unique centrosymmetric P21/c polymorph was observed for LaSiP3 and has a completely different crystal structure lacking P layers. Consecutive polymorphic transformations at increasing temperatures for LaSiP3(Pna21 → P21/c → Aea2) were derived from optimized synthetic profiles and confirmed by a combination of phonon computations and experimental in situ and ex situ annealings. Crystal structures of the LaSiP3 polymorphs were verified via advanced solid state NMR analysis using 31P MAS and 31P{139La} double resonance techniques. A combination of phonon and electronic structure calculations, NMR T1 relaxation times, UV/Vis/NIR spectroscopy, and resistivity measurements revealed that all the reported polymorphs are semiconductors with resistivities and thermal conductivities strongly dependent on the degree of distortion of P square layers in the crystal structure. Reported here, non-centrosymmetric LnSiP3 polymorphs with tunable resistivity and thermal conductivity provide a platform for the development of novel functional materials with a wide range of applications.

2.
Chemistry ; 27(26): 7383-7390, 2021 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-33523500

RESUMO

Three novel isostructural equiatomic gold tetrel pnictides, AuSiAs, AuGeP, and AuGeAs, were synthesized and characterized. These phases crystallize in the noncentrosymmetric (NCS) monoclinic space group Cc (no. 9), featuring square-planar Au within cis-[AuTt2 Pn2 ] units (Tt=tetrel, Si, Ge; Pn=pnictogen, P, As). This is in drastic contrast to the structure of previously reported AuSiP, which exhibits typical linear coordination of Au with Si and P. Chemical bonding analysis through the electron localization function suggests covalent two-center two-electron Tt-Pn bonds, and three-center Au-Tt-Au and Au-Pn-Au bonds with 1.6 e- per bond. X-ray photoelectron spectroscopy studies support the covalent and nonionic nature of Au-Pn and Au-Tt bonds. The title materials were found to be n-type narrow-gap semiconductors or semimetals, with nearly temperature-independent electrical resistivities and low thermal conductivities. A combination of the semimetallic properties with tunable NCS structure provides opportunities for the development of materials based on gold tetrel pnictides.

3.
Cell Host Microbe ; 26(5): 591-600.e4, 2019 11 13.
Artigo em Inglês | MEDLINE | ID: mdl-31668877

RESUMO

Maternal infection with Zika virus (ZIKV) can lead to microcephaly and other congenital abnormalities of the fetus. Although ZIKV vaccines that prevent or reduce viremia in non-pregnant mice have been described, a maternal vaccine that provides complete fetal protection would be desirable. Here, we show that adenovirus (Ad) vector-based ZIKV vaccines induce potent neutralizing antibodies that confer robust maternal and fetal protection against ZIKV challenge in pregnant, highly susceptible IFN-αßR-/- mice. Moreover, passive transfer of maternal antibodies from vaccinated dams protected pups against post-natal ZIKV challenge. These data suggest that Ad-based ZIKV vaccines may be able to provide protection in pregnant females against fetal ZIKV transmission in utero as well as in infants against ZIKV infection after birth.


Assuntos
Anticorpos Neutralizantes/sangue , Imunidade Materno-Adquirida/imunologia , Receptor de Interferon alfa e beta/genética , Vacinas Virais/imunologia , Infecção por Zika virus/prevenção & controle , Zika virus/imunologia , Adenoviridae/genética , Adenoviridae/imunologia , Animais , Anticorpos Neutralizantes/imunologia , Anticorpos Antivirais/sangue , Anticorpos Antivirais/imunologia , Linhagem Celular , Chlorocebus aethiops , Modelos Animais de Doenças , Feminino , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Endogâmicos C57BL , Camundongos Knockout , Gravidez , Vacinação , Células Vero , Infecção por Zika virus/imunologia
4.
J Am Chem Soc ; 141(33): 13017-13021, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31386348

RESUMO

Over 20 years after the last inorganic ternary B-P compound was reported, Na2BP2, a new compound containing one-dimensional B-P polyanionic chains has been synthesized. Common high-temperature synthetic methods required for the direct reaction of boron and phosphorus negate the possible formation of metastable or low temperature phases. In this study, oxidative elimination was used to successfully condense 0D BP23- anionic monomers found in a Na3BP2 precursor into unique 1D BP22- chains consisting of five-member B2P3 rings connected by bridging P atoms in the crystal structure of Na2BP2. The synthesis was guided by in situ X-ray powder diffraction studies, which revealed the metastable nature of the products of oxidative elimination reactions. Na2BP2 is predicted to be an electron balanced semiconductor which was confirmed by UV-vis spectroscopy with the experimentally determined band gap of 1.1 eV.

5.
J Am Chem Soc ; 141(30): 11976-11983, 2019 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-31276390

RESUMO

A novel barium silicon phosphide was synthesized and characterized. Ba2Si3P6 crystallizes in the noncentrosymmetric space group Pna21 (No. 33) and exhibits a unique bonding connectivity in the Si-P polyanion not found in other compounds. The crystal structure is composed of SiP4 tetrahedra connected into one-dimensional double-tetrahedra chains through corner sharing, edge sharing, and covalent P-P bonds. Chains are surrounded by Ba cations to achieve an electron balance. The novel compound exhibits semiconducting properties with a calculated bandgap of 1.6 eV and experimental optical bandgap of 1.88 eV. The complex pseudo-one-dimensional structure manifests itself in the transport and optical properties of Ba2Si3P6, demonstrating ultralow thermal conductivity (0.56 W m-1 K-1 at 300 K), promising second harmonic generation signal (0.9 × AgGaS2), as well as high laser damage threshold (1.6 × AgGaS2, 48.5 MW/cm2) when compared to the benchmark material AgGaS2. Differential scanning calorimetry reveals that Ba2Si3P6 melts congruently at 1373 K, suggesting that large single crystal growth may be possible.

6.
Chemistry ; 25(25): 6392-6401, 2019 May 02.
Artigo em Inglês | MEDLINE | ID: mdl-30887569

RESUMO

Lithiation of van der Waals tetrel-arsenides, GeAs and SiAs, has been investigated. Electrochemical lithiation demonstrated large initial capacities of over 950 mAh g-1 accompanied by rapid fading over successive cycling in the voltage range 0.01-2 V. Limiting the voltage range to 0.5-2 V achieved more stable cycling, which was attributed to the intercalation process with lower capacities. Ex situ powder X-ray diffraction confirmed complete amorphization of the samples after lithiation, as well as recrystallization of the binary tetrel-arsenide phases after full delithiation in the voltage range 0.5-2 V. Solid-state synthetic methods produce layered phases, in which Si-As or Ge-As layers are separated by Li cations. The first layered compounds in the corresponding ternary systems were discovered, Li0.9 Ge2.9 As3.1 and Li3 Si7 As8 , which crystallize in the Pbam (No. 55) and P2/m (No. 10) space groups, respectively. Semiconducting layered GeAs and SiAs accommodate the extra charge from Li cations through structural rearrangement in the Si-As or Ge-As layers and eventually by replacement of the tetrel dumbbells with sets of Li atoms. Ge and Si monoarsenides demonstrated high structural flexibility and a mild ability for reversible lithiation.

7.
Materials (Basel) ; 12(2)2019 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-30642116

RESUMO

The synthesis, structural characterization, and optical properties of the binary Zintl phases of α-EuP3, ß-EuP3, EuP2, and α-K4P6 are reported in this study. These crystal structures demonstrate the versatility of P fragments with dimensionality varying from 0D (P6 rings in α-K4P6) to 1D chains (EuP2) to 2D layers (both EuP3). EuP2 is isostructural to previously reported SrP2 and BaP2 compounds. The thermal stabilities of the EuP2 and both EuP3 phases were determined using differential scanning calorimetry (DSC), with melting temperatures of 1086 K for the diphosphide and 1143 K for the triphosphides. Diffuse reflectance spectroscopy indicated that EuP2 is an indirect semiconductor with a direct bandgap of 1.12(5) eV and a smaller indirect one, less than 1 eV. Both EuP3 compounds had bandgaps smaller than 1 eV.

8.
BMJ Case Rep ; 20172017 Mar 16.
Artigo em Inglês | MEDLINE | ID: mdl-28302658

RESUMO

This case report considers the psychosocial burden of caring for an infant with a severe congenital heart defect (CHD) on parents. Improved prenatal diagnostics and postnatal surgical intervention have created a new and increasing demographic of children and adults with CHDs that require lifelong medical care. For this reason, primary caregivers spend excessive amounts of time in hospitals and medical facilities, and must regularly decipher vast amounts of unfamiliar medical terminology and concepts with varying levels of assistance from medical personnel. This often leads to marked psychological morbidities in parental caregivers, such as stress, anxiety and depression. The financial cost of caring for infants with CHD, including loss of employment opportunities, is another important factor that impacts the quality of life of caregivers. Frequent and extended travel to seek specialised medical care, often at distant medical centres, represents an additional burden.


Assuntos
Cuidadores/psicologia , Pais/psicologia , Tetralogia de Fallot/cirurgia , Adulto , Cuidadores/economia , Feminino , Humanos , Recém-Nascido , Masculino , Qualidade de Vida/psicologia , Estresse Psicológico/economia , Estresse Psicológico/psicologia , Tetralogia de Fallot/diagnóstico , Tetralogia de Fallot/economia
9.
J Theor Biol ; 266(4): 504-15, 2010 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-20659478

RESUMO

Does natural selection favor veridical perceptions, those that more accurately depict the objective environment? Students of perception often claim that it does. But this claim, though influential, has not been adequately tested. Here we formalize the claim and a few alternatives. To test them, we introduce "interface games," a class of evolutionary games in which perceptual strategies compete. We explore, in closed-form solutions and Monte Carlo simulations, some simpler games that assume frequency-dependent selection and complete mixing in infinite populations. We find that veridical perceptions can be driven to extinction by non-veridical strategies that are tuned to utility rather than objective reality. This suggests that natural selection need not favor veridical perceptions, and that the effects of selection on sensory perception deserve further study.


Assuntos
Percepção , Seleção Genética , Animais , Evolução Biológica , Meio Ambiente , Teoria do Jogo , Distribuição Normal
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