Electrophilic Behavior of the "Nucleophilic" Pyramidane: Reactivity of Ge-Pyramidane towards Organolithium Reagents.

The particular reactivity of the recently discovered class of the main group element polyhedral clusters, pyramidanes, remains largely unexplored. In this communication, we report the reaction of the germapyramidane with tert-butyllithium leading to the rather unusual organogermanium compound [Li+(thf)2]⋅2-, as the product of the formal insertion of a Ge-apex into the C-Li bond. This reactivity mode exemplifies unusual electrophilic behaviour of a pyramidane, which is a priori considered as a nucleophilic reagent. Being highly reactive, [Li+(thf)2]⋅2- readily undergoes reactions with electrophiles (MeI, EtBr), initially forming intermediate germahousenes, which isomerize to the thermodynamically more favourable germoles.

Heavy Tetrel Clusters Based on the Bicyclobutane Framework: Bicyclo[1.1.0]butanes, [1.1.1]Propellanes, and Tricyclo[2.1.0.02,5 ]pentanes.

In this review, the current state of affairs in the novel field of the group 14 element clusters based on the bicyclo[1.1.0]butane framework, namely, bicyclo[1.1.0]butane, [1.1.1]propellane, and tricyclo[2.1.0.02,5 ]pentane derivatives, are overviewed. Structural similarities and differences between these three classes of highly strained polycyclic compounds are considered from the viewpoint of the critically important nature of their bridgehead bonds. Synthetic strategies towards bicyclo[1.1.0]butanes, [1.1.1]propellanes, and tricyclo[2.1.0.02,5 ]pentanes, as well as their peculiar structural and bonding features, and specific reactivity, are also presented and discussed in this review.

Pyramidanes: newcomers to the anti-van't Hoff-Le Bel family.

In this feature article, an overview of the chemistry of pyramidanes, as a novel class of main group element clusters, is given. A general introduction sets the scene, briefly presenting the non-classical pyramidal geometry of tetracoordinate carbon, as opposed to the classical tetrahedral configuration. Pyramidanes, as the simplest organic compounds possessing a pyramidal carbon atom, are then discussed from both computational and experimental viewpoints, to show the theoretical predictions on the stability and thus the feasibility of pyramidanes has finally culminated in the isolation of the first stable representatives of the pyramidane family featuring heavy main group elements at the apex of the square pyramid. Synthetic strategies towards pyramidanes, as well as their peculiar structural features, non-classical bonding situations, and specific reactivity, are presented and discussed in this review.

Organogermanium Analogues of Alkenes, Alkynes, 1,3-Dienes, Allenes, and Vinylidenes.

In this review, the latest achievements in the field of multiply bonded organogermanium derivatives, mostly reported within the last two decades, are presented. The isolable Ge-containing analogues of alkenes, alkynes, 1,3-dienes, allenes, and vinylidenes are discussed, and for each class of unsaturated organogermanium compounds, the most representative examples are given. The synthetic approaches toward homonuclear multiply bonded combinations solely consisting of germanium atoms, and their heteronuclear variants containing germanium and other group 14 elements, both acyclic and cyclic, are discussed. The peculiar structural features and nonclassical bonding nature of the abovementioned compounds are discussed based on their spectroscopic and structural characteristics, in particular their crystallographic parameters (double bond length, trans-bending at the doubly bonded centers, and twisting about the double bond). The prospects for the practical use of the title compounds in synthetic and catalytic fields are also briefly discussed.

Probe-based confocal laser endomicroscopy in COVID-19.

Probe-based confocal laser endomicroscopy (pCLE) is a method that produces microscopic imaging of a lung tissue during bronchoscopy. We report a case ot a patient with negative nasopharyngeal swabs and suspected lung cancer who underwent pCLE. The diagnosis of COVID-19 was confirmed by PCR analyses of lavage fluid and transbrohial biopsy. The pCLE image shows density of alveolar thickened fibres, disorganization of elastin network, and multiple large drops of intraalveolar secretions. As far as we know, this is the first pCLE image discribed in patient with COVID-19 at that moment.

From SiO2 to Alkoxysilanes for the Synthesis of Useful Chemicals.

The transformation of silica (SiO2) to useful chemicals is difficult to explore because of the strength of the Si-O bond and thermodynamic stability of the SiO2 structure. The direct formation of alkoxysilanes from SiO2 has been explored as an alternative to the carbothermal reduction (1900 °C) of SiO2 to metallic silicon (Simet) followed by treatment with alcohols. The base-catalyzed depolymerization of SiO2 with diols and monoalcohols afforded cyclic silicon alkoxides and tetraalkoxysilanes, respectively. SiO2 can also be converted to alkoxysilanes in the presence of organic carbonates, such as dimethyl carbonate. Alkoxysilanes can be further converted to useful chemicals, such as carbamates, organic carbonates, and chlorosilanes. An interesting and highly efficient pathway to the direct conversion of SiO2 to alkoxysilanes has been discussed in detail along with the corresponding economic and environmental implications. The thermodynamic and kinetic aspects of SiO2 transformations in the presence of alcohols are also discussed.

Titanium Germylidenes.

Two novel 18-electron titanium germylene complexes, Cp2 Ti(L)=Ge[Si3 (SiMet Bu2 )4 ] 3 b (L=Me3 P) and 3 c (L=XylNC), were synthesized, isolated, and structurally characterized. The length of the titanium-germanium bonds of 2.5387(3) Šand 2.5276(3) Š(in 3 b and 3 c, respectively) well match those expected for the double bond, which was further supported by the DFT study. Based on their structural characteristics, as well as their atomic charges calculations which revealed Ti(δ+)=Ge(δ-) bond polarization, both 3 b and 3 c are classified as the Schrock-type titanium germylidenes, as the germanium analogues of the widely known titanium alkylidenes. By contrast, germylene complexes of the group 6 metals 8 a (M=Mo) and 8 b (M=W) are better described as Fischer-type germylene complexes.

Sustainable Catalytic Synthesis of Diethyl Carbonate.

New sustainable approaches should be developed to overcome equilibrium limitation of dialkyl carbonate synthesis from CO2 and alcohols. Using tetraethyl orthosilicate (TEOS) and CO2 with Zr catalysts, we report the first example of sustainable catalytic synthesis of diethyl carbonate (DEC). The disiloxane byproduct can be reverted to TEOS. Under the same conditions, DEC can be synthesized using a wide range of alkoxysilane substrates by investigating the effects of the number of ethoxy substituent in alkoxysilane substrates, alkyl chain, and unsaturated moiety on the fundamental property of this reaction. Mechanistic insights obtained by kinetic studies, labeling experiments, and spectroscopic investigations reveal that DEC is generated via nucleophilic ethoxylation of a CO2 -inserted Zr catalyst and catalyst regeneration by TEOS. The unprecedented transformation offers a new approach toward a cleaner route for DEC synthesis using recyclable alkoxysilane.

From a (Silatrigerma)cyclobutenylium Ion to a (Silatrigerma)cyclobutenyl Radical and Back.

(Silatrigerma)cyclobutenylium ion salt 2+·[B(C6F5)4]- was readily prepared by the reaction of cyclotrigermene 1 with an equimolar amount of [Et3Si(benzene)]+·[B(C6F5)4]- in benzene. The homoaromatic nature of 2+ was firmly established by its crystallographic analysis, which revealed a highly folded SiGe3 four-membered ring (40.4°) and a remarkably short transannular Ge-Ge distance of 2.9346(3) Å. The homoaromaticity of 2+ was supported by DFT calculations, which confirmed an extensive transannular bonding orbital interaction. One-electron reduction of 2+·[B(C6F5)4]- with potassium graphite resulted in the selective formation of (silatrigerma)cyclobutenyl free radical 2·, which has an allylic-type structure as confirmed by its X-ray and EPR studies. Cation 2+ and free radical 2· can be readily interconverted, thus constituting a fully reversible redox pair.

Tuning Philicity of Dichlorosilylene: Nucleophilic Behavior of the Dichlorosilylene-NHC Complex Cl2Si-IPr.

Novel unsaturated four-membered ring disilene, 3,3-dichloro-1,2,4,4-tetrakis[di-tert-butyl(methyl)silyl]-1Δ-1,2,3,4-trisilagermetene, was synthesized by the ring expansion reaction of the three-membered ring 1-disilagermirene with the silylene-NHC complex Cl2Si-IPr. The mechanism of the unexpected formation of this compound was verified by high-level density functional theory computations, which revealed nSi:(HOMO)-πSi=Si(LUMO) * as the dominant orbital interaction.

The vaginal microbiome and preterm birth.

The incidence of preterm birth exceeds 10% worldwide. There are significant disparities in the frequency of preterm birth among populations within countries, and women of African ancestry disproportionately bear the burden of risk in the United States. In the present study, we report a community resource that includes 'omics' data from approximately 12,000 samples as part of the integrative Human Microbiome Project. Longitudinal analyses of 16S ribosomal RNA, metagenomic, metatranscriptomic and cytokine profiles from 45 preterm and 90 term birth controls identified harbingers of preterm birth in this cohort of women predominantly of African ancestry. Women who delivered preterm exhibited significantly lower vaginal levels of Lactobacillus crispatus and higher levels of BVAB1, Sneathia amnii, TM7-H1, a group of Prevotella species and nine additional taxa. The first representative genomes of BVAB1 and TM7-H1 are described. Preterm-birth-associated taxa were correlated with proinflammatory cytokines in vaginal fluid. These findings highlight new opportunities for assessment of the risk of preterm birth.

Racioethnic diversity in the dynamics of the vaginal microbiome during pregnancy.

The microbiome of the female reproductive tract has implications for women's reproductive health. We examined the vaginal microbiome in two cohorts of women who experienced normal term births: a cross-sectionally sampled cohort of 613 pregnant and 1,969 non-pregnant women, focusing on 300 pregnant and 300 non-pregnant women of African, Hispanic or European ancestry case-matched for race, gestational age and household income; and a longitudinally sampled cohort of 90 pregnant women of African or non-African ancestry. In these women, the vaginal microbiome shifted during pregnancy toward Lactobacillus-dominated profiles at the expense of taxa often associated with vaginal dysbiosis. The shifts occurred early in pregnancy, followed predictable patterns, were associated with simplification of the metabolic capacity of the microbiome and were significant only in women of African or Hispanic ancestry. Both genomic and environmental factors are likely contributors to these trends, with socioeconomic status as a likely environmental influence.

Genomic comparison of Trypanosoma conorhini and Trypanosoma rangeli to Trypanosoma cruzi strains of high and low virulence.

BACKGROUND: Trypanosoma conorhini and Trypanosoma rangeli, like Trypanosoma cruzi, are kinetoplastid protist parasites of mammals displaying divergent hosts, geographic ranges and lifestyles. Largely nonpathogenic T. rangeli and T. conorhini represent clades that are phylogenetically closely related to the T. cruzi and T. cruzi-like taxa and provide insights into the evolution of pathogenicity in those parasites. T. rangeli, like T. cruzi is endemic in many Latin American countries, whereas T. conorhini is tropicopolitan. T. rangeli and T. conorhini are exclusively extracellular, while T. cruzi has an intracellular stage in the mammalian host. RESULTS: Here we provide the first comprehensive sequence analysis of T. rangeli AM80 and T. conorhini 025E, and provide a comparison of their genomes to those of T. cruzi G and T. cruzi CL, respectively members of T. cruzi lineages TcI and TcVI. We report de novo assembled genome sequences of the low-virulent T. cruzi G, T. rangeli AM80, and T. conorhini 025E ranging from ~ 21-25 Mbp, with ~ 10,000 to 13,000 genes, and for the highly virulent and hybrid T. cruzi CL we present a ~ 65 Mbp in-house assembled haplotyped genome with ~ 12,500 genes per haplotype. Single copy orthologs of the two T. cruzi strains exhibited ~ 97% amino acid identity, and ~ 78% identity to proteins of T. rangeli or T. conorhini. Proteins of the latter two organisms exhibited ~ 84% identity. T. cruzi CL exhibited the highest heterozygosity. T. rangeli and T. conorhini displayed greater metabolic capabilities for utilization of complex carbohydrates, and contained fewer retrotransposons and multigene family copies, i.e. trans-sialidases, mucins, DGF-1, and MASP, compared to T. cruzi. CONCLUSIONS: Our analyses of the T. rangeli and T. conorhini genomes closely reflected their phylogenetic proximity to the T. cruzi clade, and were largely consistent with their divergent life cycles. Our results provide a greater context for understanding the life cycles, host range expansion, immunity evasion, and pathogenesis of these trypanosomatids.

Arsagermene, a compound with an -As[double bond, length as m-dash]Ge[double bond splayed right] double bond.

The first compound featuring an As[double bond, length as m-dash]Ge double bond, arsagermene Mes*As[double bond, length as m-dash]Ge(SiMetBu2)2, was synthesized, isolated and fully characterized. Crystallographic studies revealed that arsagermene has a planar Ge[double bond, length as m-dash]As bond of 2.2731(8) Å, which is notably shorter than the standard Ge-As single bond. The double bond character of arsagermene was further supported by computational data.

From Borapyramidane to Borole Dianion.

Nonclassical pyramidanes with their inverted tetrahedral configuration of the apical atom are among the most challenging synthetic targets in cluster chemistry. In this Communication, we report on the synthesis and structure of the first representative of pyramidal compounds with the group 13 element at the apex, namely, chloroborapyramidane 2. Reduction of 2 with excess of lithium metal unexpectedly produced the cage-opening product, borole dianion derivative {32-·[Li(thf)+]2}, a 6π-electron aromatic system.

Bis(stibahousene).

Strained hydrocarbons constitute one of the most prominent classes of organic compounds. Among them, bicyclo[2.1.0]pentene ("housene") derivatives represent a highly challenging and very attractive class. Although organic housenes have been known for more than five decades, there are still very few of them containing heavier main group elements. In this paper, we report on the two housene-type structures, novel monomeric stibahousene and dimeric bis(stibahousene). The bonding natures of both compounds were approached from both experimental and computational directions to reveal their peculiar structural features.

The Evolutionary Loss of RNAi Key Determinants in Kinetoplastids as a Multiple Sporadic Phenomenon.

We screened the genomes of a broad panel of kinetoplastid protists for genes encoding proteins associated with the RNA interference (RNAi) system using probes from the Argonaute (AGO1), Dicer1 (DCL1), and Dicer2 (DCL2) genes of Leishmania brasiliensis and Crithidia fasciculata. We identified homologs for all the three of these genes in the genomes of a subset of these organisms. However, several of these organisms lacked evidence for any of these genes, while others lacked only DCL2. The open reading frames encoding these putative proteins were structurally analyzed in silico. The alignments indicated that the genes are homologous with a high degree of confidence, and three-dimensional structural models strongly supported a functional relationship to previously characterized AGO1, DCL1, and DCL2 proteins. Phylogenetic analysis of these putative proteins showed that these genes, when present, evolved in parallel with other nuclear genes, arguing that the RNAi system genes share a common progenitor, likely across all Kinetoplastea. In addition, the genome segments bearing these genes are highly conserved and syntenic, even among those taxa in which they are absent. However, taxa in which these genes are apparently absent represent several widely divergent branches of kinetoplastids, arguing that these genes were independently lost at least six times in the evolutionary history of these organisms. The mechanisms responsible for the apparent coordinate loss of these RNAi system genes independently in several lineages of kinetoplastids, while being maintained in other related lineages, are currently unknown.

A Cationic Phosphapyramidane.

Pyramidanes C[C4 R4 ] constitute a novel class of highly strained and reactive polyhedral clusters that attracted a great deal of attention of both theoreticians and experimentalists. Although well-studied from the theoretical viewpoint, pyramidanes were synthetically inaccessible, and only very recently their very first isolable representatives have been described. In this Communication, we report on the synthesis and structural studies of the cationic pyramidane with the Group 15 element at the apex, namely, phosphapyramidane, an isoelectronic analogue of the neutral pyramidanes of the Group 14 elements.

From a Si3-Cyclopropene to a Si3S-Bicyclo[1.1.0]butane to a Si3S-Cyclopropene to a Si3S2-Bicyclo[1.1.0]butane: Back-and-Forth, and In-Between.

Compact and highly reactive bicyclo[1.1.0]butanes constitute one of the most fascinating classes of organic compounds. Furthermore, interplay of bicyclo[1.1.0]butanes with their valence isomers, such as buta-1,3-dienes and cyclobutenes, is among the fundamental pericyclic transformations in organic chemistry. Herein we report the back-and-forth interconversion between the cyclotrisilenes and thiatrisilabicyclo[1.1.0]butanes, allowing for the synthesis of novel representatives of such classes of highly reactive organometallics. The peculiar structural and bonding features of the newly synthesized compounds, as well as the mechanism of their isomerization, were verified both experimentally and computationally.

Pentagermapyramidane: crystallizing the "transition-state" structure.

The first example of the homonuclear pyramidanes, pentagermapyramidane, was synthesized, fully characterized, and computationally studied to reveal its peculiar structural features and the nature of its apex-to-base bonding interactions. Both solid-state and solution structures of pentagermapyramidane are discussed based on the computed stabilities of its square-pyramidal and distorted forms.