Observation of new bands in the N2 Herman infrared system and kinetic study of its formation in a pulsed-discharge apparatus

Four new bands of the unassigned N₂ Herman infrared system (HIR) are observed in a pulsed-discharge apparatus. The upper HIR state is produced by the N₂(A) + N₂(A) energy pooling reaction which is studied by time-resolved spectroscopy; its production rate constant is found to be ?4 × 10^?11 cm³ molecule^?1 s^?1 and its energy $\text{}\text{?}$12eV.     

Bacterial membranes as predictors of antimicrobial potency

A wide range of chemical structures having antimicrobial activity have been studied in an effort to treat the increasing emergence of bacteria that are resistant to traditional antibiotics. These agents have varying degrees of toxicity against different bacterial species. We demonstrate, using members of a novel class of antimicrobial agents, the oligomers of acyllysine, that one cause for the difference in species selectivity is the ability to induce the clustering of anionic lipids, resulting in their segregation into domains. This phenomenon occurs only in bacterial membranes composed of both anionic and zwitterionic lipids and not with bacteria whose membrane lipids are largely anionic. As a consequence it can be predicted which bacterial species will be most affected by antimicrobial agents that function principally by this mechanism. This finding allows for the design of new antibiotics with selective toxicity against different groups of bacteria.     

Protein detection by nanopores equipped with aptamers

Protein nanopores have been used as stochastic sensors for the detection of analytes that range from small molecules to proteins. In this approach, individual analyte molecules modulate the ionic current flowing through a single nanopore. Here, a new type of stochastic sensor based on an αHL pore modified with an aptamer is described. The aptamer is bound to the pore by hybridization to an oligonucleotide that is attached covalently through a disulfide bond to a single cysteine residue near a mouth of the pore. We show that the binding of thrombin to a 15-mer DNA aptamer, which forms a cation-stabilized quadruplex, alters the ionic current through the pore. The approach allows the quantification of nanomolar concentrations of thrombin, and provides association and dissociation rate constants and equilibrium dissociation constants for thrombin·aptamer interactions. Aptamer-based nanopores have the potential to be integrated into arrays for the parallel detection of multiple analytes.     

Integrating proteomics with electrochemistry for identifying kinase biomarkers

We present an integrated approach for highly sensitive identification and validation of substrate-specific kinases as cancer biomarkers. Our approach combines phosphoproteomics for high throughput cancer-related biomarker discovery from patient tissues and an impedimetric kinase activity biosensor for sensitive validation. Using non-small-cell lung cancer (NSCLC) as a proof-of-concept study, label-free quantitative phosphoproteomic analysis of a pair of cancerous and its adjacent normal tissues revealed 198 phosphoproteins that are over-phosphorylated in NSCLC. Among the differentially regulated phosphorylation sites, the most significant alteration was in residue S165 in the Hepatoma Derived Growth Factor (HDGF) protein. Hence, HDGF was selected as a model system for the electrochemical studies. Further motif-based analysis of this altered phosphorylation site revealed that extracellular-signal-regulated kinase 1/2 (ERK1/2) are most likely to be the corresponding kinases. For validation of the kinase–substrate pair, densely packed peptide monolayers corresponding to the HDGF phosphorylation site were coupled to a gold electrode. Phosphorylation of the monolayer by ERK2 and dephosphorylation by alkaline phosphatase (AP) were detected by electrochemical impedance spectroscopy (EIS) and surface roughness analysis. Compared to other methods for quantification of kinase concentration, this label-free electrochemical assay offers the advantages of ultra-sensitivity as well as higher specificity for the detection of cancer-related kinase–substrate pair. With implementation of multiple kinase–substrate biomarker pairs, we expect this integrated approach to become a high throughput platform for discovery and validation of phosphorylation-mediated biomarkers.     

The azaquinone-methide elimination: comparison study of 1,6- and 1,4-eliminations under physiological conditions

The azaquinone-methide elimination is a powerful and efficient reaction useful for disassembly of spacers in prodrug systems. We and others have used the spacer-technique to develop dendritic and polymeric self-immolative molecular systems that can disassemble through a domino-like mechanism upon a stimulus event. In this report, we study the disassembly of a system that can disintegrate through para- and ortho-azaquinone-methide eliminations. The disassembly was evaluated with molecules that undergo single 1,6- or 1,4-elimination and with molecules that undergo double 1,6- and 1,4-elimination. The 1,6-elimination was slightly faster than the 1,4-elimination under physiological conditions. This study sheds light on the disassembly-behavior of prodrug systems.     

Diffusion-weighted imaging (DWI) of the spleen in patients with liver cirrhosis and portal hypertension

Objective

The purpose of this study was to assess the influence of liver cirrhosis and portal hypertension on diffusion coefficients of the spleen.

Material and Methods

We retrospectively evaluated 50 patients with liver cirrhosis and 50 patients without any history of liver disease who underwent magnetic resonance imaging of the upper abdomen, including echo planar diffusion-weighted imaging using b values of 50, 300 and 600 mm²/s. Spleen apparent diffusion coefficient (ADC), liver ADC, muscle ADC and normalized spleen ADC (defined as the ratio of spleen ADC to muscle ADC) were compared between cirrhotic patients and patients in the control group and correlated with Child–Pugh stages. Reproducibility was assessed by measuring interclass correlation coefficient (n = 11). Additionally, in eight patients, ADC measurements were performed 1 day before and 3 days after transjugular intrahepatic portosystemic shunt (TIPSS) implantation.

Results

Compared with control subjects, patients with cirrhosis and portal hypertension had significantly higher spleen ADCs (P = .0001). There was a statistically significant correlation between Child–Pugh grade and spleen ADC (Pearson correlation coefficient, observer 1 r = 0.6, P = .0001; observer 2 r = 0.5, P = .0001). After TIPSS implantation, we observed a reduction in spleen ADC values. Spleen ADC measurements showed a high reproducibility (interclass correlation coefficient 0.75, P = .001).

Conclusion

Our data suggest that different stages of liver cirrhosis and portal hypertension correlate with ADC values of the spleen. Furthermore, ADC values of the spleen decrease after TIPSS implantation. Further studies are required to understand the potential clinical values of these observations.     

Double-hybrid functionals for thermochemical kinetics

We propose two new double-hybrid functionals, denoted B2K-PLYP and mPW2K-PLYP, which yield thermochemical performance comparable to existing double-hybrid functionals but offer superior performance for barrier heights of various kinds. We show that the new functionals yield excellent performance for all of the following: (a) main-group thermochemistry; (b) main-group thermochemical kinetics; (c) late transition metal reactions. In addition, B2K-PLYP performs well for weak interactions.