Search

Graphdiyne-based nanotubes (GDNTs) are a novel type of carbon nanotubes. While conventional carbon nanotubes (CNTs) are generated by rolling graphene sheets, GDNTs are generated by rolling sheets that are similar to graphene but where the edges are elongated by the introduction of additional acetylene bonds between vertices (C 6 aromatic rings). Such nanotubes are predicted to have many useful practical applications, but a thorough understanding of the relationship between their structure and their physical properties is still missing. We present a theoretical study of the electronic and optical properties of GDNTs. The structural, electronic, and optical properties of GDNTs with different diameters (i.e., 2-10 additional acetylene bonds) have been studied systematically by using density function theory (DFT) and self-consistent charge density functional tight-binding (SCC-DFTB) and by solving the Bethe-Salpeter equation (BSE), with and without considering the electron-hole interactions. The results indicate that the GDNTs are semiconductors with the direct band gap in close range, which is beneficial for photoelectronic devices and applications. Moreover, the absorption spectra of the GDNTs with different edge structures, (armchair, and zigzag) revealed little differences between the optical spectra of armchair and zigzag GDNTs, which could mean that fine separation between those structures (a process that is likely difficult and expensive in practice) will not be necessary. Importantly, the nanotubes were highly stable based on their cohesive energies, and their exciton binding energies were as large as about ~ 1 eV. From a methodological point of view, SCC-DFTB was found to be in agreement with more elaborate DFT calculations for most systems. Graphical abstract.

Interaction of the alkali metals (AMs) like lithium (Li), sodium (Na), and potassium (K) with defective and non-defective (8,0) C3N nanotubes (C3NNT) have been investigated using the first-principles study. In addition to structural properties, we have also studied the electronic properties, charge transfer, and work function of the AM-C3NNT complexes. AMs are adsorbed on hollow sites, regardless of the initial positions. Upon the adsorption of AMs, the structures exhibit semiconducting behavior. Furthermore, interaction of Li atom can be explained by Dewar model, whereas for the other atoms there are different explanations. For all metal adsorbates, the direction of the charge transfer is from adsorbate to adsorbent, because of their high surface reactivity. The results showed that the nanotube with carbon vacancy is the most favorite adsorbent. Our findings also indicated that the enhancement in absolute adsorption energy is in order of Li > K > Na. It is noteworthy that clustering of AM atoms on the nanotubes with and without defects is not expected. It is worthy that C3NNT is a better adsorbent for AM atoms than CNT, graphene, C60, and B80.

Infective endocarditis (IE) can be diagnosed in the clinical microbiology laboratory by culturing explanted heart valve material. We present a service evaluation that examines the sensitivity and specificity of a broad-range 16S rDNA polymerase chain reaction (PCR) assay for the detection of the causative microbe in culture-proven and culture-negative cases of IE. A clinical case-note review was performed for 151 patients, from eight UK and Ireland hospitals, whose endocardial specimens were referred to the Microbiology Laboratory at Great Ormond Street Hospital (GOSH) for broad-range 16S rDNA PCR over a 12-year period. PCR detects the causative microbe in 35/47 cases of culture-proven IE and provides an aetiological agent in 43/69 cases of culture-negative IE. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the 16S rDNA PCR assay were calculated for this series of selected samples using the clinical diagnosis of IE as the reference standard. The values obtained are as follows: sensitivity = 67 %, specificity = 91 %, PPV = 96 % and NPV = 46 %. A wide range of organisms are detected by PCR, with Streptococcus spp. detected most frequently and a relatively large number of cases of Bartonella spp. and Tropheryma whipplei IE. PCR testing of explanted heart valves is recommended in addition to culture techniques to increase diagnostic yield. The data describing the aetiological agents in a large UK and Ireland series of culture-negative IE will allow future development of the diagnostic algorithm to include real-time PCR assays targeted at specific organisms.

Homocysteine thiolactone (HCTL) is a cyclic thioester of homocysteine, showing high reactivity toward lysine residues of proteins. In the present study the structural properties and aggregation propensity of bovine pancreatic insulin were studied in the presences of increasing concentration of HCTL (0-500 μM), using different spectroscopic techniques. As shown in this study, HCTL induces gross structural alterations and subsequently aggregation of insulin in a dose dependent manner. Also induction of insulin aggregation by HCTL occurs in a sequential process, where native protein with alpha-helical abundant structure gradually transforms into partially folded conformations with the significant amount of beta-sheet. Since C-terminal B-chain of insulin plays a critical role in stability of this protein, the structural alteration/aggregation induced by HCTL can be consequence of homocysteinylation of the only Lysine residue (Lys29) on its B-chain. This study may have important implications regarding the effect of HCTL on structure of insulin particularly in the pathological states linked to hyperhomocysteinemia.

The effect of stabilizing and destabilizing salts on the catalytic behavior of ribonuclease A (RNase A) was investigated at pH 7.5 and 25 degrees C, using spectrophotometric, viscometric and molecular dynamic methods. The changes in the distance between N(epsilon2) of His(12) and N(delta1) of His(119) at the catalytic center of RNase A upon the addition of sodium sulfate, sodium hydrogen sulfate and sodium thiocyanate were evaluated by molecular dynamic methods. The compactness and expansion in terms of Stokes radius of RNase A upon the addition of sulfate ions as kosmotropic salts, and thiocyanate ion as a chaotropic salt, were estimated by viscometric measurements. Enzyme activity was measured using cytidine 2', 3'-cyclic monophosphate as a substrate. The results from the measurements of distances between N(epsilon2) of His(12) and N(delta1) of His(119) and Stokes radius suggest (i) that the presence of sulfate ions decreases the distance between the catalytic His residues and increases the globular compactness, and (ii) that there is an expansion of the enzyme surface as well as elongation of the catalytic center in the presence of thiocyanate ion. These findings are in agreement with activity measurements.