Influence of defect locations and nitrogen doping configurations on the mechanical properties of armchair graphene nanoribbons

The effect of defect locations on the mechanical properties of armchair graphene nanoribbons (AGNRs) and the various configurations of nitrogen (N) doping on the mechanical properties of AGNRs were examined using molecular dynamics (MD) simulations. The variation of the Young’s modulus (YM) and the ultimate tensile strength (UTS) of pyridinic-N, graphitic-N, and pyrrolic-N by increasing the concentration of N doping was investigated. The results of MD simulations show that the defect location has a significant effect on the UTS and failure strain (FS) of AGNRs in both vertical and horizontal directions. In the horizontal direction, variations of the UTS and FS are lower than in the vertical direction. On the other hand, the variations of the YM is almost similar in vertical and horizontal directions. The results of this work indicate that the UTS and FS of AGNRs are more sensitive than the YM of AGNRs for different defect directions. Pyridinic-N improves the mechanical properties of the defective AGNR and performs better YM and UTS values than the graphitic-N. Substitution N atoms, which are located at the defective sites and/or at the edges of AGNRs, are mechanically more favorable. Pyrrolic-N configuration has the lowest mechanical properties among the other configurations. Furthermore, pyrrolic-N with Stone-Wales-1 (SW-1) type of defect has higher mechanical properties than pyrrolic-N with Stone-Wales-2 (SW-2) type of defect.     

Effects of the nitrogen doping configuration and site on the thermal conductivity of defective armchair graphene nanoribbons

The influence of the nitrogen (N) doping configuration on the thermal conductivity (TC) of armchair graphene nanoribbons (AGNRs) of size 15.7 nm × 7.26 nm was investigated using classical molecular dynamics (MD) simulations with the optimized Tersoff potential at room temperature. The effect of changing the N-doping site in defects on the TC of AGNRs was also investigated in detail. The variations with N concentration of the TCs of AGNRs presenting graphitic N (quarternary N), pyridinic N, and pyrrolic N doping configurations were studied. Results of MD simulations showed that, among these three doping configurations, pyridinic N was associated with the highest TC, and pyrrolic N with the lowest TC. The highest TC values were obtained when the N dopant atoms were located at the edges and at defects in the AGNR. The presence of both pyrrolic N and Stone–Wales type 1 (SW-1) defects led to a higher TC than the presence of both pyrrolic N and SW-2 defects. Phonon–defect scattering was found to be influenced by changes in C–C bond orientation. SW-1 defects were found to exert a greater influence on the TC than graphitic N doping. Furthermore, the influence on the TC of the N-doping site location in SW-1 defects was examined. Doping the central sites of SW-1 defects was found to yield higher TC values than doping the edge sites of defects. Graphitic-N doping of the more central sites in a SW-1 defect led to a higher TC than the random graphitic-N doping of sites in a SW-1 defect.     

Mechanical properties of armchair silicene nanoribbons with edge cracks: a molecular dynamics study

Silicene has been proven to be a promising material with attractive electronic properties. During the synthesis of silicene, structural defects such as edge crack are likely to be generated and such defects in silicene have impacts on its properties. Herein, molecular dynamics simulations were performed to investigate the mechanical properties of the armchair silicene nanoribbons (ASiNRs) with edge cracks. Our results showed that the mechanical properties of the ASiNRs decrease because of the existence of edge crack. Both the pristine ASiNRs and the ASiNRs with edge cracks show brittle fracture behaviours. The crack length plays an important role in determining the critical strain and fracture strength of the ASiNRs. Moreover, we investigated the effects of strain rate and temperature on the mechanical properties of the ASiNRs with edge cracks. We observed that the increasing strain rate increases the critical strain and fracture strength while decreasing the Young’s modulus. Low-strain rates also changes the expanded directions of cracks in the ASiNRs. We also found that the increasing temperature could significantly decrease the mechanical properties of the ASiNRs with edge cracks.     

Magneto-controlled electrochemical immunoassay of brevetoxin B in seafood based on guanine-functionalized graphene nanoribbons

A facile and feasible magneto-controlled immunosensing platform was designed for sensitive electrochemical immunoassay of brevetoxin B (BTX-2) in seafood by using guanine-assembled graphene nanoribbons (GGNRs) as molecular tags on a home-made magnetic carbon paste electrode. Initially, monoclonal mouse anti-BTX-2 antibodies were covalently immobilized on the surface of magnetic beads, which were used as the immunosensing probes for the capture of BTX-2. The recognition elements were prepared by chemical modification of bovine serum albumin-BTX-2 conjugates (BTX-2-BSA) with the GGNRs. Based on a competitive-type immunoassay format, the formed magnetic immunocomplex was integrated on the electrode with an external magnet, followed by determination in pH 6.5 phosphate-buffered solution containing 2μM Ru(bpy)(3)Cl(2). Under optimal conditions, the electrochemical signals decreased with the increasing BTX-2 concentrations in the sample. The dynamic concentration range spanned from 1.0pgmL(-1) to 10ngmL(-1) with a detection limit of 1.0pgmL(-1) BTX-2. Inter- and intra-batch assay precisions were substantially improved by resorting to the GGNR manifold. The method featured unbiased identification of negative (blank) and positive samples. No significant differences at the 95% confidence level were encountered in the analysis of 12 spiked samples including S. constricta, M. senhousia and T. granosa between the electrochemical immunoassay and commercially available enzyme-linked immunosorbent assay (ELISA) for determination of BTX-2.     

Polyamidoamine dendrimers with different surface charge as carriers in anticancer drug delivery

Second-generation (G2) polyamidoamine (PAMAM) dendrimers are branched polymers containing 16 surface primary amine groups. Due to their structural properties, these polymers can be used as universal carriers in various drug delivery systems. Amine-terminated PAMAM dendrimers are characterized by a high positive surface charge, leading to effective but nonspecific interactions with negatively charged cell plasmatic membranes. To reduce the nonspecific internalization of PAMAM dendrimers, their primary amine groups are often modified by acetic or succinic anhydrides, polyethylene glycol derivatives and other compounds. In this work, the role of primary amine groups, which are localized on the surface of doxorubicin-conjugated (Dox) dendrimers, was studied with regard to their intracellular distribution and internalization rates using SKOV3 human ovarian adenocarcinoma cells. It was demonstrated that all Dox-labeled G2-derivatives containing different numbers of acetamide groups synthesized in this work show high rates of cellular uptake at 37°С. As expected, the conjugate carrying the maximum number of primary amine groups demonstrated the highest rates of binding and endocytosis. At the same time, the G2-Dox conjugate containing the maximum number of acetamide groups showed colocalization with LAMP2, a marker of lysosomes and late endosomes, as well as the highest level of cytotoxic activity against SKOV3 cells. We conclude that second-generation PAMAM dendrimers are characterized by varied pathways of internalization and intracellular distribution due to the number of primary amine groups on their surface and, as a consequence, a different surface charge.     

The nature of the charge carriers in solvated biomacromolecules

Solid state electrolysis experiments were performed on the biomolecules, hemoglobin, cytochromec, collagen, lecithin and melanin at various hydration states; and for hemoglobin at various solvation states with methanol adsorbate. The evolved hydrogen was measured and compared with theoretical (Faraday's Law) expectations for the known amount of charge passed through the adsorbents. The difference between the theoretical and actual is a measure of the contributions of electronic charge carriers to the total current. Thus the protonic/electronic conduction ratios are determined.All biomolecules tested appear to be mixed semiconductors. That is, both electronic and protonic charge carriers make significant contributions to the currents over hydration ranges from 6% to above 50%. The constant temperature conductivity increases exponentially with hydration (solvation) but the ratio of protonic to electronic conduction increases linearly with hydration for the globular proteins, hemoglobin and cytochromec. The fibrous protein, collagen, may be a protonic semiconductor in the dry state, with an electronic component that increases linearly with hydration. The hemoglobin-methanol system shows only electronic conductivity below 2 BET monolayers, with a sharp onset to 70% protonic conductivity above this value. This result is similar to the DNA-water system previously reported. The protonic/electronic ratio in hydrated hemoglobin may be a function of the applied voltage; being predominantly electronic below 30 volts (300 volts/cm), and a constant mixed value above 100 volts (1000 volts/cm). Our results suggest that both electronic and protonic conduction are intrinsic processes in these substances and subject to control by a number of techniques.     

Dynamics of transfer of charge carriers in DNA molecule

An equivalent electrical circuit of DNA molecule is suggested and used to model the charge transfer dynamics in the molecule. Its switching time is shown to be in the femtosecond time range and to depend on the frequency of input electric signal. Raising the input signal frequency from 1 GHz to 4 THz and lowering the temperature decrease the current through DNA. The switching rate of DNA molecule is determined by the processes of delocalization and localization of holes, which is achieved by variation in the base sequence and length.     

Complexes of graphene nanoribbons with porphyrins and metal-encapsulated C28 as molecular rectifiers: a theoretical study

The rectification properties of porphyrin–graphene nanoflake complexes and endohedral complexes of C28 fullerene with metal atoms have been studied using the fully ab initio method. D3 dispersion-corrected PBE/-def2-SVP model was used for the optimisations and the electronic energy evaluation. In porphyrin–graphene nanoflake complexes dispersion dominates, while in the endohedral complexes of C28 dispersion does not play an important role. All studied systems do rectify. In the case of fullerenes, the rectification is possible due to the reduction in the molecular symmetry of the fullerene caused by the interaction with electrodes and the endohedral complex formation. The origin of the rectification is the asymmetrical deformation of the electron density under direct and inverse voltages which creates different currents in opposite directions. It seems that peculiar geometry of Au-TPP-Cd/NF diode is responsible for its high rectification ratio. The Cd ion is notably out of the porphyrin plane making close contact with the neighbouring electrode, increasing the asymmetry of the diode compared to other TPP/NF complexes.     

Inactivation pattern of the fragile X in heterozygous carriers

Summary Chromosome analysis with conventional staining, G-banding, and R-banding with 5-bromodeoxyuridine (BrdU) incorporation were performed on the lymphocytes of ten females, who were heterozygous for the fragile X-chromosome. Mental development of these females varied greatly: moderate to severe mental retardation was found in one and moderate mental retardation in four females. Normal to borderline intelligence was found in three and normal intelligence was noted in two further females. The discrepancy in percentage of active fragile X-chromosomes in the five females with moderate mental retardation was found to be 60–100% (mean value: 80%). The three women with normal to borderline intelligence showed a corresponding discrepancy from 57 to 86% (mean value: 77%) of active fragile X-chromosomes. Finally, two female heterozygotes for fragile X with normal intelligence showed 70 and 76% (mean value 73%) of active fragile X-chromosomes. The phenotypic features also did not seem to correspond with the X-chromosome inactivation pattern. Based on the data obtained, we suggest that there is no evident correlation between the frequency of the active fragile X chromosomes and the mental status of these females.     

Photophosphorylation associated with synchronous turnovers of the electron-transport carriers in chloroplasts

Two saturating single-turnover flashes spaced 100 ms apart are sufficient to achieve ATP formation in isolated chloroplast thylakoids. Two turnovers of the electron carriers result in the accumulation of about 7 nmol H⁺ / mg chlorophyll. Under the same conditions (i.e., ΔG_ATP = 38 kJ/mol) a solitary flash is inadequate to produce ATP. The electron flux from the third or any subsequent flash is coupled to ATP formation as efficiently as is observed in continuous light (i.e., ) and produces 0.8 molecules of ATP per coupling factor on each turnover. The yield of ATP per flash increases with declining temperature being largest near 4°C, the lowest value tested. The number of H⁺ accumulated per flash is independent of temperature so the greater yields of ATP near 4°C indicate that fewer H⁺ are existing the membrane via nonproductive pathways. The yield of ATP per flash near 4°C is largely independent of flash frequency between 1 and 30 Hz. When the formation of an electrical potential difference is prevented by adequate amounts of valinomycin and potassium the accumulated effects of about eight flashes are required before ATP formation is achieved (i.e., about 26 nmol H⁺/mg chlorophyll), indicating an average ΔpH/flash in excess of 0.3 units. In the presence of the exchange carrier nigericin, the electrical component of the driving force for ATP formation is enhanced at the expense of the ΔpH. In this case, ATP formation is efficiently coupled to electron flux only at flash frequencies rapid enough to allow a summation of the electrical field. These results clearly demonstrate that any processes which are prerequisites for ATP synthesis (i.e., activation of coupling factor or generation of Δp) are fulfilled by a remarkably small number of charge separations.     

Proton conduction in lecithins. III. Nature of charge carriers

The nature of charge carriers was studied in hydrated lecithin using different techniques. The current-voltage characteristics confirmed the ionic nature of conduction. Attempts to determine the charge mobility were unsuccessful. From measurements of the thermovoltage at different hydration levels the charge carrier was found to be positive. The value of the thermo electromotive force (thermo e.m.f.) depends on the phase state of the lipid but is independent of its water content. The mechanism of charge generation is discussed. The activation energy of conduction does not reflect the phase change directly. Its dependence on water content is attributed to charge mobility which involves the motion of the head groups. Electrolysis experiments were carried out and the amount of hydrogen evolved was determined by gas chromatography. A proton mechanism of conduction is suggested.     

Ternary complexes comprising polyphosphoramidate gene carriers with different types of charge groups improve transfection efficiency

To understand the influence of charge groups on transfection mediated by polymer complexes, we have synthesized a series of biodegradable and cationic polyphosphoramidates (PPAs) with an identical backbone but different side chains. Our previous study showed that PPA with a spermidine side chain (PPA-SP) showed high transfection efficiency in culture, whereas PPAs with secondary, tertiary, and quaternary amino groups were significantly less efficient. To investigate whether the coexistence of 1 degrees amino charge groups with 3 degrees and 2 degrees amino charge groups in the DNA/polymer complexes would enhance their transfection efficiency, we evaluated a ternary complex system containing DNA and PPAs with 1 degrees amino groups (PPA-SP) and 3 degrees amino groups (PPA-DMA) and a quaternary complex system containing DNA and PPAs with 1 degrees and 2 degrees and 3 degrees amino groups (PPA-EA/PPA-MEA/PPA-DMA), respectively. Ternary complexes mediated 20 and 160 times higher transfection efficiency in COS-7 cells than complexes of DNA with PPA-SP or PPA-DMA alone, respectively. Similarly, quaternary complexes exhibited 8-fold higher transfection efficiency than PPA-EA/DNA complexes. The mechanism of enhancement in transfection efficiency by the mixture carriers appears to be unrelated to the particle size, zeta potential, or DNA uptake. The titration characterization and the transfection experiments using a proton pump inhibitor suggest that the enhancement effect is unlikely due to the slightly improved buffering capacity of the mixture over PPA-SP. This approach represents a simple strategy of developing polymeric gene carriers and understanding the mechanisms of polymer-mediated gene transfer.     

Shared environmental factors associated with telomere length maintenance in elderly male twins

During aging, chromosome ends, or telomeres, gradually erode or shorten with each somatic cell division. Loss of telomere length homeostasis has been linked to age-related disease. Remarkably, specific environmental assaults, both physical and psychological, have been shown to correlate with shortened telomeres. However, the extent that genetic and/or environmental factors may influence telomere length during later stages of lifespan is not known. Telomere length was measured in 686 male US World War II and Korean War veteran monozygotic (MZ) and dizygotic (DZ) twins (including 181 MZ and 125 DZ complete pairs) with a mean age of 77.5 years (range 73-85 years). During the entire process of telomere length measurement, participant age and twin status were completely blinded. White blood cell mean telomere length shortened in this elderly population by 71 base pairs per year (P < 0.0001). We observed no evidence of heritable effects in this elderly population on telomere length maintenance, but rather find that telomere length was largely associated with shared environmental factors (P < 0.0001). Additionally, we found that individuals with hypertension and cardiovascular disease had significantly shorter telomeres (P = 0.0025 and 0.002, respectively). Our results emphasize that shared environmental factors can have a primary impact on telomere length maintenance in elderly humans.     

Isoperoxidase pattern and internode length genotype in Pisum

Inbred Pisum sativum lines of known constitution for the intemode length genes Le, La and Cry, and representing four height phenotypes, were grown to the 7-intemode stage in the light. Six cationic isoperoxidases, making up ca. 90% of the activity of stem extracts, were resolved by concave gradient elution from Dowex 50 columns and shown to run as single peroxidase bands on starch gel electrophoresis. They were all able to oxidise IAA in the presence of 2,4-dichlorophenol, but fell into two groups with widely differing IAA oxidase/peroxidase ratios. The isoperoxidase patterns were independent of both genotype and phenotype for internode length, thus making it unlikely that these loci exert their effect on internode extension via control of synthesis of a particular isoperoxidase. Amongst the lines screened polymorphism was detected involving two of the isoperoxidases, and limited F₂ data suggest that these two variants fire determined by alleles of a single gene. Isoperoxidase patterns of stem extracts of 6 other Pisum species did not differ significantly from the two found in P. sativum.     

Inbreeding is associated with shorter early-life telomere length in a wild passerine

Inbreeding can have negative effects on survival and reproduction, which may be of conservation concern in small and isolated populations. However, the physiological mechanisms underlying inbreeding depression are not well-known. The length of telomeres, the DNA sequences protecting chromosome ends, has been associated with health or fitness in several species. We investigated effects of inbreeding on early-life telomere length in two small island populations of wild house sparrows (Passer domesticus) known to be affected by inbreeding depression. Using genomic measures of inbreeding we found that inbred nestling house sparrows (n?=?371) have significantly shorter telomeres. Using pedigree-based estimates of inbreeding we found a tendency for inbred nestling house sparrows to have shorter telomeres (n?=?1195). This negative effect of inbreeding on telomere length may have been complemented by a heterosis effect resulting in longer telomeres in individuals that were less inbred than the population average. Furthermore, we found some evidence of stronger effects of inbreeding on telomere length in males than females. Thus, telomere length may reveal subtle costs of inbreeding in the wild and demonstrate a route by which inbreeding negatively impacts the physiological state of an organism already at early life-history stages.

     

A PCR-RFLP for KIT associated with tobiano spotting pattern in horses

An MspI polymorphism was identified in intron 13 of the equine homologue of proto-oncogene c-kit (KIT) by comparing DNA sequences from horses with solid coat colour and horses homozygous for the tobiano spotting (To) gene. The allele associated with solid coat colour was designated KM0, while the allele associated with the tobiano pattern created an additional MspI restriction site and was designated KM1. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) studies using DNA from hair follicles demonstrated that all 129 of 129 tobiano patterned horses possessed the KM1 allele. However, three of 104 solid-coloured thoroughbred horses also possessed the KM1 allele. Therefore, while KM1 is strongly associated with the gene for To, the association is not absolute. However, this test appears more efficacious to identify putative homozygotes for To than current biochemical testing methods using albumin (Alb) and vitamin D binding protein (Gc) haplotypes.