Development of a ratiometric fluorescent probe for the detection of peroxynitrite.

Peroxynitrite is one of the important reactive oxygen species in the human body and is closely related to the physiological and pathological processes of many diseases. Therefore, the development of probes to detect peroxynitrite is important for diagnostic and pathologic studies of many diseases. In this work, a ratiometric probe was designed using benzopyran as the recognition site, and the sensitivity and selectivity of the probe were tuned by modification of substituents on benzopyran. Upon reaction with peroxynitrite, the color of the solution changes to the naked eye (from blue to yellow), and the fluorescence changes from red to blue. The probe SJ has the advantages of large Stokes shift (237 nm), fast response (≤10 s), wide linear range, good selectivity, low detection line (21.3 nm), and low cytotoxicity. Probe SJ has been successfully used for bioimaging of endogenous and exogenous peroxynitrite.

Interpretation of vaginal metagenomic characteristics in different types of vaginitis.

Although vaginitis is closely related to vaginal microecology in females, the precise composition and functional potential of different types of vaginitis remain unclear. Here, metagenomic sequencing was applied to analyze the vaginal flora in patients with various forms of vaginitis, including cases with a clue cell proportion ranging from 1% to 20% (Clue1_20), bacterial vaginitis (BV), vulvovaginal candidiasis (VVC), and BV combined with VVC (VVC_BV). Our results identified Prevotella as an important biomarker between BV and Clue1_20. Moreover, a gradual decrease was observed in the relative abundance of shikimic acid metabolism associated with bacteria producing indole as well as a decline in the abundance of Gardnerella vaginalis in patients with BV, Clue1_20, and healthy women. Interestingly, the vaginal flora of patients in the VVC_BV group exhibited structural similarities to that of the VVC group, and its potentially functional characteristics resembled those of the BV and VVC groups. Finally, Lactobacillus crispatus was found in high abundance in healthy samples, greatly contributing to the stability of the vaginal environment. For the further study of L. crispatus, we isolated five strains of L. crispatus from healthy samples and evaluated their capacity to inhibit G. vaginalis biofilms and produce lactic acid in vitro to select the potential probiotic candidate for improving vaginitis in future clinical studies. Overall, we successfully identified bacterial biomarkers of different vaginitis and characterized the dynamic shifts in vaginal flora between patients with BV and healthy females. This research advances our understanding and holds great promise in enhancing clinical approaches for the treatment of vaginitis. IMPORTANCE: Vaginitis is one of the most common gynecological diseases, mostly caused by infections of pathogens such as Candida albicans and Gardnerella vaginalis. In recent years, it has been found that the stability of the vaginal flora plays an important role in vaginitis. Furthermore, the abundant Lactobacillus-producing rich lactic acid in the vagina provides a healthy acidic environment such as Lactobacillus crispatus. The metabolites of Lactobacillus can inhibit the colonization of pathogens. Here, we collected the vaginal samples of patients with bacterial vaginitis (BV), vulvovaginal candidiasis (VVC), and BV combined with VVC to discover the differences and relationships among the different kinds of vaginitis by metagenomic sequencing. Furthermore, because of the importance of L. crispatus in promoting vaginal health, we isolated multiple strains from vaginal samples of healthy females and chose the most promising strain with potential probiotic benefits to provide clinical implications for treatment strategies.

Solubility determination and thermodynamic model analysis of L-α-glyceryl phosphorylcholine in different organic solvents of 278.15 K to 323.15 K.

L-α-glyceryl phosphorylcholine, also referred to as choline ethanol phosphate and phosphocholine glycerophosphate, is a naturally occurring metabolite of water-soluble phospholipids in animals. This molecular property is important for informing the crystallization and purification of drugs. The solubility of L-α-glyceryl phosphorylcholine was determined in ten pure solvents and three mixed solvents under atmospheric pressure. The experimental results indicate that L-α-glyceryl phosphorylcholine is most soluble in methanol and least soluble in acetone. Additionally, the solubility of L-α-glyceryl phosphorylcholine was found to increase with temperature within the experimental range. Furthermore, the solubility of L-α-glyceryl phosphorylcholine in binary solvents is dependent on the proportion of positive solvent and temperature. The solubility of L-α-glyceryl phosphorylcholine increases with the proportion of positive solvent. XRD and DSC results indicate that the crystal form of L-α-glyceryl phosphorylcholine remains unchanged before and after dissolution in the reagent, and its melting point temperature is 413.15 K. Various models, including the modified Apelblat model, λh model, Jouyban-Acree model, SUN model, and CNIBS/R-K model, were used to fit the solubility data of L-α-glyceryl phosphorylcholine in different solvents. The study found that the modified Apelblat model and CNIBS/R-K model were the most appropriate for fitting the data. The KAT-LSER model was used to analyze the molecular interactions between solvents and solutes, revealing that the solvent step method with non-specific polarity/polarization interaction had the greatest impact on solubility.

Microbial carbonate reservoir characteristics and their depositional effects, the IV Member of Dengying Formation, Gaoshiti-Moxi area, Sichuan Basin, Southwest China.

Previous scientific research on reservoirs of the Deng IV Member in the Gaoshiti-Moxi area, the main production area of the Anyue gas field with reserves of tens of billions of cubic metres, has focused on karst palaeogeomorphology reconstruction, the facies distribution on platform margins, and their effects on creating favourable reservoirs. However, the quality of microbial carbonate reservoirs is also closely related to their original depositional environments on both inner and marginal platforms. Therefore, this paper attempts to reveal favourable microbial carbonate reservoir characteristics and the sedimentary effects on their distribution and prediction based predominantly on a synthetic analysis of the sequence stratigraphy and depositional facies. The results show that favourable reservoirs of the Deng IV Member are classified into three types according to their reservoir spaces: fracture-cavity, pore-cavity and pore reservoirs. Secondary dissolution pores and cavities are primary reservoir spaces developed mainly in nonskeletal grain dolomites with sparry cements, thrombolites, and stromatolites. The physical properties of the fracture-cavity and pore-cavity types of reservoirs are better than those of pore reservoirs and have porosities between 1 and 5% and permeabilities between 0.01 × 10-3 and 1 × 10-3 µm2. Vertically, favourable reservoirs are developed mainly in parasequence set 6 (PSS6) and PSS7 and are laterally distributed in well zone MX9-MX19-MX1 for the fracture-cavity type, MX105-MX110-GS20 for the pore-cavity type and MX17-MX107-MX41-MX102-GS102 for the pore type. Moreover, depositional effects on reservoirs in terms of depositional sequences, seismic facies, microfacies and microfacies associations indicate that to some extent, the fracture-cavity type of reservoir is constrained by the top boundaries of PSS7, PSS2, parasequence 17 (PS17) and PS14; the pore-cavity type of reservoir is constrained by the top boundaries of PSS7, PSS4, PS18 and PS12; and the pore type of reservoir is constrained by the top boundaries of PSS7, PSS6, PSS3, PSS2, PS18, PS17, PS14, and PS12. Seismic facies associated with shoals and mound-flat complexes are related to the facies distributions of pore cavities and pore reservoirs. MA1, MA3, MA7, and MA8 are predominant microfacies associations of favourable reservoirs of the Deng IV Member in the Gaoshiti-Moxi area. The above results are significant for further petroleum exploration and exploitation of ultradeep microbial carbonate reservoirs in this area.

Water extract from Ligusticum chuanxiong delays the aging of Saccharomyces cerevisiae via improving antioxidant activity.

Ligusticum chuanxiong is a common traditional edible-medicinal herb that has various pharmacological activities. However, its effects on Saccharomyces cerevisiae (S. cerevisiae) remains unknown. In this study, we found that water extract of Ligusticum chuanxiong (abbreviated as WEL) exhibited excellent free radical scavenging ability in-vitro. Moreover, WEL treatment could delay the aging of S. cerevisiae, an important food microorganism sensitive to reactive oxygen species (ROS) stress. Biochemical analyses revealed that WEL significantly increased the activity of antioxidant enzymes in S. cerevisiae, including superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR), as well as their gene expression. As a result, ROS level was significantly decreased and accompanied with the decline of malondialdehyde (MDA), which represented a state of low oxidative stress. The reduction of oxidative stress could elevate S. cerevisiae's ethanol fermentation efficiency. Taken together, WEL plays a protective role against S. cerevisiae aging via improving antioxidant activity.

Omics analysis revealed the possible mechanism of streptococcus disease outbreak in tilapia under high temperature.

High temperature is a main cause to result in the outbreak of tilapia streptococcal disease. However, the underlying mechanisms are not well understood. In this study, we first confirmed that tilapia infected with Streptococcus agalactiae (S. agalactiae) had a higher mortality at high temperature (35 °C) than that at normal temperature (28 °C). Subsequently, the effects of high temperature on gene expression pattern of S. agalactiae and intestinal microbiota of tilapia were respectively detected by RNA-seq and 16S rDNA sequencing. RNA-seq identified 357 differentially expressed genes (DEGs) in S. agalactiae cultured at 28 °C and 35 °C. GO and KEGG analysis showed that these DEGs were highly involved in metabolic processes, including glucose, lipid and amino acid metabolisms, which indicates that S. agalactiae have stronger vitality and are likely to be more infectious under high temperature. Microbiota analysis revealed that high temperature could influence the bacterial community composition of tilapia intestine, accompanied by changes in intestinal structure. Compared to feed at 28 °C, the total bacterial species as well as pathogens, such as norank_f__Rhizobiales_Incertae_Sedis, Pseudorhodoplanes, Ancylobacter, in tilapia intestine were significantly increased at 35 °C, which may weaken the immune resistance of tilapia. Taken together, our results suggest that high temperature evoked tilapia susceptible to S. agalactiae should be the combined effect of enhanced S. agalactiae metabolism and dysregulated tilapia intestinal microbiota.

Recent advances in neuropeptide-related omics and gene editing: Spotlight on NPY and somatostatin and their roles in growth and food intake of fish.

Feeding and growth are two closely related and important physiological processes in living organisms. Studies in mammals have provided us with a series of characterizations of neuropeptides and their receptors as well as their roles in appetite control and growth. The central nervous system, especially the hypothalamus, plays an important role in the regulation of appetite. Based on their role in the regulation of feeding, neuropeptides can be classified as orexigenic peptide and anorexigenic peptide. To date, the regulation mechanism of neuropeptide on feeding and growth has been explored mainly from mammalian models, however, as a lower and diverse vertebrate, little is known in fish regarding the knowledge of regulatory roles of neuropeptides and their receptors. In recent years, the development of omics and gene editing technology has accelerated the speed and depth of research on neuropeptides and their receptors. These powerful techniques and tools allow a more precise and comprehensive perspective to explore the functional mechanisms of neuropeptides. This paper reviews the recent advance of omics and gene editing technologies in neuropeptides and receptors and their progresses in the regulation of feeding and growth of fish. The purpose of this review is to contribute to a comparative understanding of the functional mechanisms of neuropeptides in non-mammalians, especially fish.

Design of choline chloride modified USY zeolites for palladium-catalyzed acetylene hydrochlorination.

USY zeolites (USY) were applied to design and synthesize palladium-based heterogeneous catalysts for exploring an efficient non-mercuric catalyst for acetylene hydrochlorination. Choline chloride (ChCl) was selected as the nitrogen-containing ligand to modify the Pd@USY catalysts and the proposed Pd@15ChCl@USY catalyst exhibited obviously the best catalytic performance with a stable acetylene conversion and vinyl chloride selectivity of over 99.0% for more than 20 h. According to the results of characterization and the density functional theory calculations, it is indicated that the addition of ChCl can significantly inhibit the agglomeration and loss of the Pd active species, prevent carbon deposition and enhance the ability of HCl and C2H2 adsorption and C2H3Cl desorption, resulting in promoting the catalytic performance of Pd@USY catalysts during the acetylene hydrochlorination reaction.

Long-Chain Non-Coding RNA (lncRNA) MT1JP Suppresses Biological Activities of Lung Cancer by Regulating miRNA-423-3p/Bim Axis.

BACKGROUND This study aimed to explain the effects and mechanism of MT1JP in lung cancer development and treatment. MATERIAL AND METHODS Thirty non-small cell lung cancer (NSCLC) (stages I-II, 17 cases; stages III-IV, 13 cases) and adjacent normal tissues were obtained. MT1JP and miRNA-423-3p levels were assessed by in situ hybridization and Bim protein expression by immunohistochemistry, and the correlations determined were analyzed. Cell proliferation was determined using MTT and colony formation assay, and cell apoptosis was measured using flow cytometry. A549 cell invasion and migration were assessed by Transwell migration and scratch wound healing assays. Relative mRNA and protein expressions were assessed using real-time polymerase chain reaction and western blotting. Correlations between miRNA-423-3p and Bim protein were investigated using luciferase activity assay, and Bim protein expression was evaluated using western blotting. RESULTS MT1JP, miRNA-423-3p, and Bim expressions in NSCLC cancer tissues and those in adjacent cancer tissues were significantly different (P<0.01 or P<0.001) with increasing stage. Compared with those in the normal control (NC) group, cell proliferation rates were significantly suppressed (P<0.01 or P<0.001) and cell apoptosis rates significantly increased (P<0.01 or P<0.001) in the miRNA inhibitor and lncRNA+miRNA inhibitor groups. Invasion cell numbers and wound healing rates were also significantly inhibited in the miRNA inhibitor and lncRNA+miRNA inhibitor groups (P<0.01 or P<0.001) compared with those in the NC group. CONCLUSIONS The lncRNA MT1JP suppresses NSCLC biological activities by regulating the miRNA-423-3p/Bim axis.

Acetylene hydrochlorination over boron-doped Pd/HY zeolite catalysts.

A novel boron-doped Pd/HY zeolite catalyst for acetylene hydrochlorination was prepared and exhibited an outstanding catalytic performance (the acetylene conversion was maintained at >95% for about 30 h). The boron species can stabilize catalytically active Pd2+ species and weaken carbon deposition and Pd2+ reduction during the reaction, thus improving the catalytic stability.

The effect of a liver-X-receptor ligand on bleomycin induced pulmonary fibrosis in mice.

The liver-X-receptors have shown anti-fibrosis ability in several animal models. Our purpose was to investigate the effect of LXRs in bleomycin induced lung fibrosis in mice. Bleomycin was intratracheally delivered to mice. Some mice were administered a LXR agonist, T0901317. Then mice were evaluated for the development of lung inflammation and fibrosis. T0901317 was able to attenuate the inflammation and fibrosis induced by bleomycin. T0901317 treatment evidently abolished the high level of TGF-ß1 and inhibited NF-κB DNA-binding activity in lung. So LXRs may attenuate the progressing of lung fibrosis, providing a potential treatment of IPF.

Increased risk of developing lung cancer in Asian patients carrying the TERT rs2736098 G>A polymorphism: evidence from 3,354 cases and 3,518 controls.

BACKGROUND: The association between telomerase reverse transcriptase (TERT) rs2736098 G>A and risk of lung cancer (LC) remains inconclusive. To explore the association more precisely, we performed a comprehensive search and conducted a meta-analysis on all eligible case-control studies involving 3,354 cases and 3,518 controls. METHODS: The 95% confidence interval (95% CI) and the pooled odds ratio (OR) were calculated using a random or fixed effect model. Publication bias, heterogeneity, and sensitivity analysis were also explored. RESULTS: All studies were case-control studies on LC in patients of Asian descent, consisting of one Korean study and five Chinese studies. Overall, the variant A allele of TERT rs2736098 G>A was found to significantly increase the risk of LC in all genetic models (GA vs GG: OR =1.13, 95% CI =1.02-1.25, P=0.017; AA vs GG: OR =1.78, 95% CI =1.53-2.07, P<0.001; GA/AA vs GG: OR =1.25, 95% CI =1.14-1.38, P<0.001; AA vs GA/GG: OR =1.66, 95% CI =1.45-1.92, P<0.001). In the subgroup analysis, significant associations were found in Chinese group and hospital-based studies. Different genotype test methods showed no influence on the final results. CONCLUSION: Our study identified that TERT rs2736098 G>A polymorphism significantly increased the risk of LC in Asian populations.

Association between BIM deletion polymorphism and clinical outcome of EGFR-mutated NSCLC patient with EGFR-TKI therapy: A meta-analysis.

AIM: BIM deletion polymorphism was deemed to be associated with downregulation of BIM, resulting in a decreased apoptosis induced by epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) in EGFR mutation-positive non-small cell lung cancer (NSCLC). However, accumulating evidences concerning the association between BIM deletion polymorphism and efficacy of EGFR-TKI and survival in EGFR-mutation-driven NSCLC patient reported contradictory results. MATERIALS AND METHODS: A meta-analysis was conducted by combing six original eligible studies including 871 NSCLC patients. RESULTS: Our study showed that BIM deletion polymorphism was significantly associated with poor response to EGFR-TKI therapy in mutant EGFRNSCLC patients (P(h) = 0.309, P(z) = 0.001, OR = 0.39, 95% confidence interval (CI) = 0.23-0.67). Disease control rate (DCR) in mutant EGFRNSCLC patient with treatment of EGFR-TKI was significantly decreased in patients with BIM deletion polymorphism comparing to patients harbored BIM wild variant (P(h) = 0.583, P(Z) = 0.007, OR = 0.46, 95%CI = 0.25-0.85). EGFR mutation-derived NSCLC patient carrying BIM deletion polymorphism had a shorter progression-free survival (PFS; P(h) < 0.001, P(z) < 0.001, hazard ratio (HR) = 1.37, 95%CI = 1.09-1.71) and overall survival (OS; P(h) = 0.90, P(z) = 0.003, HR = 1.25, 95%CI = 1.08-1.45), than those harbored BIM wild variant. CONCLUSION: These results suggested that BIM deletion polymorphism might be a cause that contributes to primary EGFR-TKI resistance, and it could be used as a genetic predictor for EGFR-TKI outcome and an independent prognostic factor of EGFR mutation-driven NSCLC patient.

Rs895819 within miR-27a might be involved in development of non small cell lung cancer in the Chinese Han population.

MicroRNA-27a (miR-27a) is deemed to be an oncogene that plays an important role in development of various cancers, and single nucleotide polymorphism (SNP) of miR-27a can influence the maturation or aberrant expression of hsa-miR27a, resulting in increased risk of cancer and poor prognosis for non-small cell lung cancer (NSCLC). This study aimed to assess the effects of rs895819 within miR-27a on susceptibility and prognosis of NSCLC patients in 560 clinical confirmed cases and 568 healthy check-up individuals. Adjusted odds/hazard ratios (ORs/HRs) and 95% confidential intervals (CIs) were calculated to evaluate the association between rs895819 and the risk and prognosis of NSCLC. The results showed that allele A and genotype GG of rs895819 were significantly associated with an increased risk of NSCLC (38.9% vs 30.8%, adjusted OR=1.26, 95%CI=1.23-1.29 for allele G vs A; 18.1% vs 11.7%, adjusted OR=1.67, 95%CI=1.59-1.75 for genotype GG vs AA). Moreover, positive associations were also observed in dominant and recessive models (53.7% vs 49.9%, adjusted OR=1.17, 95%CI=1.13-1.20 for GG/AG vs AA; 18.1% vs 11.7%, adjusted=1.65, 95%CI=1.58-1.73). However, no significant association was found between rs895819 and the prognosis of NSCLC in genotype, dominant and recessive models. These results suggested that miR-27a might be involved in NSCLC carcinogenesis, but not in progression of NSCLC. The allele G, genotype GG and allele G carrier (GG/AG vs AA) of rs895819 might be genetic susceptible factors for NSCLC. Further multi-central, large sample size and well-designed prospective studies as well as functional studies are warranted to verify our findings.

Expression and significance of circulating microRNA-31 in lung cancer patients.

BACKGROUND: The aim of this study was to investigate the expression level of circulating microRNA-31(miRNA-31) in lung cancer patients and its clinical significance. MATERIAL AND METHODS: Real-time fluorescent quantitative PCR was utilized to detect the circulating miRNA-31 expression levels in 300 lung cancer patients and 300 health control subjects. The ROC curve was drawn to evaluate the diagnostic value of the circulating miRNA-31 expression levels in lung cancer. The 300 lung cancer patients were divided into a miRNA-31 low-expression group and a miRNA-31 high-expression group. A survival curve was drawn according to the Kaplan-Meier method to evaluate the prognostic value of the circulating microRNA-31 expression levels for lung cancer. RESULTS: The circulating miRNA-31 expression levels in the lung cancer patients (l.88±0. 67) increased significantly (P<0.001) compared to the healthy controls (0.58±0. 44). The area under the ROC curve drawn according to the circulating miRNA-31 expression levels was 0.785 (95% CI=0.486-0.763). When the critical value was 1.27, the sensitivity and specificity for lung cancer diagnosis according to the circulating miRNA-31 expression levels were 0.769 and 0.745, respectively. The difference in the survival curve between the miRNA-31 low-expression group (123 cases) and high-expression group (177 cases) was statistically significant (P=0.004). Median survival period of the low-expression group (38.44 months) was longer than that of the high-expression group (25.23 months). CONCLUSIONS: miRNA-31 may be a molecular marker for the diagnostic and prognostic evaluation of primary lung cancer.

Electron transport in all-carbon molecular electronic devices.

Carbon has always been an important electrode material for electrochemical applications, and the relatively recent development of carbon nanotubes and graphene as electrodes has significantly increased interest in the field. Carbon solids, both sp(2) and sp(3) hybridized, are unique in their combination of electronic conductivity and the ability to form strong bonds to a variety of other elements and molecules. The Faraday Discussion included broad concepts and applications of carbon materials in electrochemistry, including analysis, energy storage, materials science, and solid-state electronics. This introductory paper describes some of the special properties of carbon materials useful in electrochemistry, with particular illustrations in the realm of molecular electronics. The strong bond between sp(2) conducting carbon and aromatic organic molecules enables not only strong electronic interactions across the interface between the two materials, but also provides sufficient stability for practical applications. The last section of the paper discusses several factors which affect the electron transfer kinetics at highly ordered pyrolytic graphite, some of which are currently controversial. These issues bear on the general question of how the structure and electronic properties of the carbon electrode material control its utility in electrochemistry and electron transport, which are the core principles of electrochemistry using carbon electrodes.

Neuron specific enolase and prognosis of non-small cell lung cancer: a systematic review and meta-analysis.

PURPOSE: The predictive and prognostic role of neuron-specific enolase (NSE) in non-small cell lung cancer (NSCLC) is still under debate. The present meta-analysis aimed to evaluate the relation between serum NSE levels and the prognosis of NSCLC. METHODS: We performed a meta-analysis of published studies assessing the association of NSE with the prognosis of NSCLC. Literature retrieval, trials' selection and assessment, data collection, and statistical analysis were performed according to the Revman 5.0 guidelines. A fixed-effect model was used to pool the hazard ratio (HR) and 95% confidence intervals (95% CIs). RESULTS: A total of 8 eligible studies that included 2389 NSCLC patients were analyzed. We did not find prognostic value of NSE for NSCLC (HR=1.17, 95% CI: 0.95-1.44, p=0.14). CONCLUSION: The present study indicated that serum NSE level is of no prognostic significance in patients with NSCLC.

Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions.

In this work, we bridge the gap between short-range tunneling in molecular junctions and activated hopping in bulk organic films, and greatly extend the distance range of charge transport in molecular electronic devices. Three distinct transport mechanisms were observed for 4.5-22-nm-thick oligo(thiophene) layers between carbon contacts, with tunneling operative when d < 8 nm, activated hopping when d > 16 nm for high temperatures and low bias, and a third mechanism consistent with field-induced ionization of highest occupied molecular orbitals or interface states to generate charge carriers when d = 8-22 nm. Transport in the 8-22-nm range is weakly temperature dependent, with a field-dependent activation barrier that becomes negligible at moderate bias. We thus report here a unique, activationless transport mechanism, operative over 8-22-nm distances without involving hopping, which severely limits carrier mobility and device lifetime in organic semiconductors. Charge transport in molecular electronic junctions can thus be effective for transport distances significantly greater than the 1-5 nm associated with quantum-mechanical tunneling.

A critical perspective on molecular electronic junctions: there is plenty of room in the middle.

The promise of molecular electronic devices stems from the possibilities offered by the rich electronic structure of organic molecules. The use of molecules as functional components in microelectronic devices has long been envisioned to augment or even replace silicon. However, the understanding of what controls charge transport in these devices involves complexities stemming from numerous variables that are often interactive and exert a controlling influence on transport, confounding the role of the molecular component. This perspective discusses various aspects of molecular electronics, from the initial "vision quests" of single molecule, functional electronic elements, to the molecular tunnel junctions that have been studied and characterized in-depth. Aspects of energy level alignment are discussed in the context of charge transport mechanisms, as are important electronic interactions when molecules are bonded to conducting "contacts". In addition, integration of molecular components with microelectronic processing is considered, as are the prospects for functional, real-world devices.

Charge transport in molecular electronic junctions: compression of the molecular tunnel barrier in the strong coupling regime.

Molecular junctions are essentially modified electrodes familiar to electrochemists where the electrolyte is replaced by a conducting "contact." It is generally hypothesized that changing molecular structure will alter system energy levels leading to a change in the transport barrier. Here, we show the conductance of seven different aromatic molecules covalently bonded to carbon implies a modest range (< 0.5 eV) in the observed transport barrier despite widely different free molecule HOMO energies (> 2 eV range). These results are explained by considering the effect of bonding the molecule to the substrate. Upon bonding, electronic inductive effects modulate the energy levels of the system resulting in compression of the tunneling barrier. Modification of the molecule with donating or withdrawing groups modulate the molecular orbital energies and the contact energy level resulting in a leveling effect that compresses the tunneling barrier into a range much smaller than expected. Whereas the value of the tunneling barrier can be varied by using a different class of molecules (alkanes), using only aromatic structures results in a similar equilibrium value for the tunnel barrier for different structures resulting from partial charge transfer between the molecular layer and the substrate. Thus, the system does not obey the Schottky-Mott limit, and the interaction between the molecular layer and the substrate acts to influence the energy level alignment. These results indicate that the entire system must be considered to determine the impact of a variety of electronic factors that act to determine the tunnel barrier.