H3PW12O40-functionalized tip for scanning tunneling microscopy

Song, In Kyu; Kitchin, John R.; Barteau, Mark A.

doi:10.1073/pnas.072514399

Cited by 21 publications

(20 citation statements)

References 28 publications

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“…Therefore, the immobilization of the HPW clusters must take place preferentially in the wide micropores (0.7 nm < pore size < 2.0 nm) to result in a partial block of the supermicroporosity [24], which would be in good agreement with our previous observations on HPAs being mainly adsorbed in the supermicroporous domain of activated carbonaceous supports [21]. These results are consistent with the average size of the [XM12O40] n-Keggin-type POM anions, which display diameters of 0.8-1.0 nm regardless of the addenda metal M or heteroatom X [17,32], and hence they cannot be incorporated into the ultramicropores due to size exclusion. and more specifically, in the domain of the pores with sizes equal to or lower than 0.8 nm.…”

Section: Characterization Of the Supported Catalystssupporting

confidence: 92%

Zirconia-supported tungstophosphoric heteropolyacid as heterogeneous acid catalyst for biodiesel production

Alcañiz-Monge

Bakkali

Trautwein

et al. 2018

Applied Catalysis B: Environmental

135

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Section: Characterization Of the Supported Catalystssupporting

confidence: 92%

Zirconia-supported tungstophosphoric heteropolyacid as heterogeneous acid catalyst for biodiesel production

Alcañiz-Monge

Bakkali

Trautwein

et al. 2018

Applied Catalysis B: Environmental

135

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“…Since the occurrence of a superlattice is closely R332 related to defects, graphite surfaces cleaved with adhesive tape are more likely to exhibit superlattice structures. Mechanically cut Pt/Ir tips were commonly used in experiments, although there were a few exceptions in which etched gold tips [44], etched tungsten tips [31,[44][45][46][47][48], etched Pt/Ir tips [21,49,50], heteropolyacid (HPA)-functionalized Pt/Ir tips [51] and silicon tips [24] were used. Apparently the tip material does not affect the observed superlattice structures.…”

Section: Experimental Procedures and Resultsmentioning

confidence: 99%

A review and outlook for an anomaly of scanning tunnelling microscopy (STM): superlattices on graphite

Pong

Durkan²

2005

J. Phys. D: Appl. Phys.

159

127

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Since its invention in 1981, scanning tunnelling microscopy (STM) is well-known for its supreme imaging resolution enabling one to observe atomic-scale structures, which has led to the flourishing of nanoscience. As successful as it is, there still remain phenomena which are observed using STM but are beyond our understanding. Graphite is one of the surfaces which have been most extensively studied using STM. However, there are a number of unusual properties of graphite surfaces. First reported in the 1980s, superlattices on graphite have since been observed many times and by many groups, but as yet our understanding of this phenomenon is quite limited. Most of the observed superlattice phenomena are widely believed to be the result of a Moiré rotation pattern, arising from the misorientation between two graphite layers, as verified experimentally. A Moiré pattern is a lattice with larger periodicity resulting from the overlap of two lattices with smaller periodicities. As graphite layers are composed of hexagonal lattices with a periodicity of 0.246 nm, as observed using STM, when there are misoriented graphite layers overlapping each other, a Moiré pattern with larger periodicity, depending on the misorientation angle, will be produced and appear as a superperiodic hexagonal structure on top of the graphite atomic lattice of the topmost surface layer. It is important to study graphite superlattices because, firstly, knowledge of this phenomenon will enable us to properly interpret STM images; secondly, it helps us to understand the correlation between electronic structures and atomic-structure rearrangement of graphite which is of tremendous aid for engineering material properties; thirdly, and perhaps most importantly, the observation of the phenomenon exhibits the capability of STM to produce images indicating the nature of internal defects which are below the surface. Over recent years, experimental and modelling techniques have been developed to study this anomalous regime of STM; however, there is a lack of a systematic classification of this scattered information. This review article thus serves the purpose of organizing all these results so as to enable a more comprehensive understanding of this phenomenon. We review the discovery of graphite superlattices, the observation of the associated properties, and the research efforts on this subject. An effort is made to envision the future experimental and theoretical research possibilities to unveil the mystery of this anomaly of STM. Applications of graphite superlattices are also proposed.

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“…They might bind to chromatin and act as a scaffold for the local recruitment of pluripotency transcription factors, similar to other lncRNAs like HOTAIR for histone modification complexes [44] and Xist in the context of X-chromosome inactivation [44-46]. Alternatively, HERV-H might counteract retrovirus spread by interfering with packaging of retroviral genomic RNA [47,48] or by soaking up miRNAs that are required for retrovirus transduction.…”

Section: Discussionmentioning

confidence: 99%

HERV-H RNA is abundant in human embryonic stem cells and a precise marker for pluripotency

2012

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BackgroundCertain post-translational modifications to histones, including H3K4me3, as well as binding sites for the transcription factor STAT1, predict the site of integration of exogenous gamma-retroviruses with great accuracy and cell-type specificity. Statistical methods that were used to identify chromatin features that predict exogenous gamma-retrovirus integration site selection were exploited here to determine whether cell type-specific chromatin markers are enriched in the vicinity of endogenous retroviruses (ERVs).ResultsAmong retro-elements in the human genome, the gamma-retrovirus HERV-H was highly associated with H3K4me3, though this association was only observed in embryonic stem (ES) cells (p < 10-300) and, to a lesser extent, in induced pluripotent stem (iPS) cells. No significant association was observed in nearly 40 differentiated cell types, nor was any association observed with other retro-elements. Similar strong association was observed between HERV-H and the binding sites within ES cells for the pluripotency transcription factors NANOG, OCT4, and SOX2. NANOG binding sites were located within the HERV-H 5′LTR itself. OCT4 and SOX2 binding sites were within 1 kB and 2 kB of the 5′LTR, respectively. In keeping with these observations, HERV-H RNA constituted 2% of all poly A RNA in ES cells. As ES cells progressed down a differentiation pathway, the levels of HERV-H RNA decreased progressively. RNA-Seq datasets showed HERV-H transcripts to be over 5 kB in length and to have the structure 5′LTR-gag-pro-3′LTR, with no evidence of splicing and no intact open reading frames.ConclusionThe developmental regulation of HERV-H expression, the association of HERV-H with binding sites for pluripotency transcription factors, and the extremely high levels of HERV-H RNA in human ES cells suggest that HERV-H contributes to pluripotency in human cells. Proximity of HERV-H to binding sites for pluripotency transcription factors within ES cells might be due to retention of the same chromatin features that determined the site of integration of the ancestral, exogenous, gamma-retrovirus that gave rise to HERV-H in the distant past. Retention of these markers, or, alternatively, recruitment of them to the site of the established provirus, may have acted post-integration to fix the provirus within the germ-line of the host species. Either way, HERV-H RNA provides a specific marker for pluripotency in human cells.

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H₃PW₁₂O₄₀-functionalized tip for scanning tunneling microscopy

Cited by 21 publications

References 28 publications

Zirconia-supported tungstophosphoric heteropolyacid as heterogeneous acid catalyst for biodiesel production

Zirconia-supported tungstophosphoric heteropolyacid as heterogeneous acid catalyst for biodiesel production

A review and outlook for an anomaly of scanning tunnelling microscopy (STM): superlattices on graphite

HERV-H RNA is abundant in human embryonic stem cells and a precise marker for pluripotency

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