Fano Resonance in Single-Molecule Junctions.

The Fano resonance in single-molecule junctions could be created by interaction with discrete and continuous molecular orbitals and enables effective electron transport modulation between constructive and destructive interference within a small energy range. However, direct observation of Fano resonance remains unexplored because of the disappearance of discrete orbitals by molecule-electrode coupling. We demonstrated the room-temperature observation of Fano resonance from electrochemical gated single-molecule conductance and current-voltage measurements of a para-carbazole anion junction. Theoretical calculations reveal that the negative charge on the nitrogen atom induces a localized HOMO on the molecular center, creating Fano resonance by interfering with the delocalized LUMO on the molecular backbone. Our findings demonstrate that the Fano resonance in electron transport through single-molecule junctions opens pathways for designs of interference-based electronic devices.

Electrostatic gating of single-molecule junctions based on the STM-BJ technique.

The gating of charge transport through single-molecule junctions is considered a critical step towards molecular circuits but remains challenging. In this work, we report an electrostatic gating method to tune the conductance of single-molecule junctions using the scanning tunneling microscope break junction (STM-BJ) technique incorporated with a back-gated chip as a substrate. We demonstrated that the conductance varied at different applied gating voltages (Vgs). The HOMO-dominated molecules show a decrease in conductance with an increase in Vg, and the LUMO-dominated molecules show the opposite trend. The measured conductance trends with Vg are consistent with the transition voltage spectroscopy measurements. Moreover, the transmission functions simulated from density functional theory (DFT) calculations and the finite element analysis all suggest that Vg changed the energy alignment of the molecular junction. This work provides a simple method for modulating the molecular orbitals' alignment relative to the Fermi energy (Ef) of metal electrodes to explore the charge transport properties at the single-molecule scale.

Mechanical single-molecule potentiometers with large switching factors from ortho-pentaphenylene foldamers.

Molecular potentiometers that can indicate displacement-conductance relationship, and predict and control molecular conductance are of significant importance but rarely developed. Herein, single-molecule potentiometers are designed based on ortho-pentaphenylene. The ortho-pentaphenylene derivatives with anchoring groups adopt multiple folded conformers and undergo conformational interconversion in solutions. Solvent-sensitive multiple conductance originating from different conformers is recorded by scanning tunneling microscopy break junction technique. These pseudo-elastic folded molecules can be stretched and compressed by mechanical force along with a variable conductance by up to two orders of magnitude, providing an impressively higher switching factor (114) than the reported values (ca. 1~25). The multichannel conductance governed by through-space and through-bond conducting pathways is rationalized as the charge transport mechanism for the folded ortho-pentaphenylene derivatives. These findings shed light on exploring robust single-molecule potentiometers based on helical structures, and are conducive to fundamental understanding of charge transport in higher-order helical molecules.

Electric Field-Induced Assembly in Single-Stacking Terphenyl Junctions.

Molecular assembly is crucial in functional molecular materials and devices. Among the molecular interactions that can form assemblies, stacking among π-conjugated molecular backbones plays an essential role in charge transport through organic materials and devices. The single-molecule junction technique allows for the application of an electric field of approximately 108 V/m to the nanoscale junctions and to investigate the electric field-induced assembly at the single-stacking level. Here, we demonstrate an electric field-induced stacking effect between two molecules using the scanning tunneling microscope break junction (STM-BJ) technique and we found an increase in the stacking probability with increasing intensity of the electric field. The combined density functional theory (DFT) calculations suggest that the molecules become more planar under the electric field, leading to the energetically preferred stacking configuration. Our study provides a new strategy for tuning molecular assembly by employing a strong electric field.

Yttrium dialkyl supported by a silaamidinate ligand: synthesis, structure and catalysis on cyclotrimerization of isocyanates.

A sterically demanding silaamidine (ArN = Si(L)NHAr) ligand was synthesized and employed for the preparation of a yttrium dialkyl complex, which catalytically enabled the cyclotrimerization of isocyanate with high activity and excellent functional group tolerance.

Cis-1,4-Polymerization of Isoprene by 1,3-Bis(oxazolinymethylidene)isoindoline-Ligated Rare-Earth Metal Dialkyl Complexes.

A series of novel chiral nonmetallocene pincer-type rare-earth metal dialkyl complexes bearing the chiral monoanionic tridentate C2-symmetric 1,3-bis(oxazolinymethylidene)isoindoline (BOXMI-H) ligand (BOXMI)Ln(CH2SiMe3)2 1⁻3 (1: Ln = Sc, yield = 57%; 2: Ln = Lu, yield = 55%; 3: Ln = Y, yield = 62%) have been prepared in moderate yields via the acid-base reaction between the BOXMI ligand and rare-earth metal tri(trimethylsilylmethyl) complexes. The X-ray diffractions show that both of the complexes 1 and 2 contain one BOXMI ligand and two trimethylsilylmethyl ligands, adopting a distorted trigonal bipyramidal configuration. In the presence of a cocatalyst such as borate and AlR3, these complexes 1⁻3 exhibit high activities of up to 6.8 × 104 (g of polymer)/(molLn h) and high cis-1,4 selectivities of up to 97% in the polymerization of isoprene in toluene, yielding the cis-1,4-polyisoprenes with heavy molecular weights (Mn of up to 710,000 g/mol) and bimodal molecular weight distributions (Mw/Mn = 2.0⁻4.5).

RBP2 induces stem-like cancer cells by promoting EMT and is a prognostic marker for renal cell carcinoma.

Renal cell carcinoma (RCC), one of the most common kidney cancers, has a poor prognosis. Epithelial to mesenchymal transition (EMT) is a hallmark of carcinoma invasion and metastasis. Several studies have examined the molecular regulation of EMT, but the relationship between histone demethylases and EMT is little understood. In this study, we investigated the role of retinoblastoma-binding protein-2 (RBP2), a histone demethylase that is highly expressed in RCC and is positively correlated with poor RCC prognosis in the regulation of EMT. We found that ectopic overexpression of RBP2 can induce cancer stem cell-like (CSC) phenotypes through EMT in RCC cells by converting them to a more mesenchymal phenotype. This results in increased resistance to apoptosis, which leads to enhanced tumor growth in xenograft models. Together, our data show that RBP2 is an epigenetic regulator that has an important role in the initiation of CSC phenotypes through EMT, leading to tumor progression. RBP2 is also a novel biomolecule for RCC diagnosis, and prognosis and may be a therapeutic target.

VHL gene mutation analysis of a Chinese family with non- syndromic pheochromocytomas and patients with apparently sporadic pheochromocytoma.

OBJECTIVE: The Von Hippel-Lindau syndrome (VHLD), an inherited neoplastic syndrome predisposing to central nervous system hemangioblastoma (CNS), pheochromocytoma (PCC), renal cell carcinoma(RCC), retinal hemangioma (RA) and renal cysts, is caused by mutations or deletions of the VHL tumor-suppressor gene. To assess VHL genotype-phenotype correlations with function of pVHL a gene mutation analysis of members in a Chinese family with non-syndromic PCCs and individuals with apparently sporadic pheochromocytoma (ASP) was performed. MATERIALS AND METHODS: DNA samples of 20 members from the Chinese family with non-syndromic PCCs and 41 patients with ASP were analyzed by polymerase chain reaction and direct sequencing, confirmed by Taqman probe. RESULTS: Three novel mutations (H125P, 623(?TTTGTtG) and R120T) were identified in the Chinese family and in 3 among 41 ASP patients. The mutations were all located in exon 2 of VHL gene encoding ß-domain of pVHL. The tumor type in H125P carriers and R120T carriers was VHL type 2C. And 623(?TTTGTtG) carriers presented VHL type 2B or type 2C. CONCLUSIONS: VHL gene abnormalities were identified in the Chinese family with non-syndromic PCCs and patients with APS, resulting in dysfunction of pVHL. H125P and R120T could be associated with VHL type 2C, while 623(?TTTGTtG) might be linked with VHL type 2B or type 2C. Not only is the genetic analysis helpful for early diagnosis and treatment of patients with VHLD, it is also benefitial for research into VHLD pathogenesis.

[Genetic detection and analysis of the VHL gene in patients with sporadic pheochromocytoma].

OBJECTIVE: To carry out a genetic detection and analysis of Von Hippel-Lindau (VHL) gene in Chinese patients with sporadic pheochromocytoma. METHODS: DNA samples were extracted from peripheral blood cells and fresh pheochromocytoma specimens from 41 patients with sporadic pheochromocytoma were assayed by polymerase chain reaction and direct sequencing. The DNA samples of 50 healthy volunteers were extracted from peripheral blood as a control. The PCR products of exon 1, exon 2 and exon 3 were used for molecular analysis of the VHL gene. The genetic detection of family members of VHL gene mutations was also performed. RESULTS: One of mutations was located at nucleotide 572 (G-->C) in exon 2, presenting a codon 120 from arginine (R) to threonine (T). Tow small insertions were locatated at nucleotide 623T (TTTGTtG) in exon 2, leading to a frameshift mutation. There were also three carriers of G572C and three carriers of 623T (TTTGTtG) in family members of the three cases. CONCLUSION: There are some Chinese patients with sporadic pheochromocytoma with tumorigenic VHL gene mutations. It is recommended to use the genetic detection and analysis of VHL gene as a routine examination for patients with sporadic pheoehromoeytoma under the age of 50 years with questionable family history. The genetic detection and analysis of VHL gene may be useful as a marker for the diagnosis of hereditary pheochromocytoma.

[Mutation screening of VHL gene in a Chinese family with nonsyndromic pheochromocytoma].

OBJECTIVE: To detect the VHL gene mutations in a Chinese family with nonsyndromic pheochromocytoma. METHODS: Mutations of VHL gene were detected in a Chinese family with nonsyndromic pheochromocytoma. Five patients and fifteen relatives were involved in this study. Peripheral blood was collected and total genomic DNA was prepared for polymerase chain reaction (PCR). PCR products of all the three exons of VHL gene were purified and a direct gene sequence analysis was performed. RESULTS: All the five patients presented a codon 125 from Histidine (H) to Proline (P) change at nucleotide 587 (A --> C) in exon 2. Seven members of fifteen relatives were carriers with the same VHL gene mutation. Two carriers were detected with bilateral adrenal tumors and right renal cyst respectively by ultrasonic inspection. CONCLUSION: The novel VHL gene mutation detected in this kindred may be the causative gene. Genetic test can detect the carriers in an early period. It is recommended as a routine method of genetic test in nonsyndromic pheochromocytoma patients.