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The digital image correlation method has been applied to directly observe the local strain and crack formation in mooring chain steel during tensile tests in air or when simultaneously charging hydrogen in different ways, viz. including/excluding the notch root. Interestingly, hydrogen accumulation promoted crack initiation on the surface when the local strain reached approximately 0.9%, while strain of 19% to 20% was reached in the hydrogen-free specimens before visible crack formation. Even through the stress–strain curves prior to the sudden drop indicate a negligible effect of hydrogen, its presence can greatly reduce the stress-induced crack initiation. In addition, hydrogen introduced while avoiding the notch root can disorganize the regular distribution of strain produced by the notch before crack initiation. Therefore, hydrogen-induced embrittlement below the critical stress criterion can be explained by hydrogen-enhanced localized plasticity, while above the critical stress criterion, hydrogen-enhanced decohesion provides a better explanation.

In the current work, the nitroxide radical groups are utilized to functionalize the nucleobases, obtaining the nucleobase diradical building blocks for magnetic DNA with significant ferromagnetic or antiferromagnetic coupling characteristics. The nitroxide functionalization strategies include introduction of nitroxide radical group to the carbon site and oxidization of the amino group in nucleobases, and the diradical-functionalized nucleobases are denoted by 2NOX, where X = A, G, T, and C bases. The density functional theory calculations reveal that these nitroxide diradicalized nucleobases are stable and have large magnetic spin coupling magnitudes. Almost all of them possess antiferromagnetic-like spin coupling characteristics with considerably large spin coupling constants [J = −671.7 (2NOA1), −463.3 (2NOA3), −370.5 (2NOG), −494.9 (2NOC1), −3265.5 (2NOT), and −2445.5 cm–1 (2NOC3)] expect for 2NOC2 and 2NOA2 which have the ferromagnetic-like spin coupling characteristics (J = 149.1 and 440.7 cm–1), res...

The spin-coupling properties of a series of radicalized uracil (rU) dimer diradicals with different H-bonding modes is examined. Each rU has four double H-bonding sites [the amide units: two at the Watson-Crick face (upper site WC1 and lower site WC2 ), a Hoogsteen site (HO), and a minor-groove site (MI)], and ten homogeneous dimers (rU-rU) can self-pair with well-defined diradical characters and comparable stability to the native U dimers. More interestingly, all these dimers exhibit distinctly different spin-coupling characters (ferromagnetic (FM) versus antiferromagnetic (AFM) and large- versus small-magnitude spin couplings), indicative of remarkable magnetic-coupling anisotropy of rU. This observation originates from the fusion of a cyclopentadienyl radical to U, which leads to uneven spin-density distribution. In rU, the fused five-membered radical ring can spin-polarize to the edge in the minor groove, and thus dimerization of rU leads to different H-bonded structures with remarkably different magnetic couplings. The calculated larger magnetic coupling constants J are 1003.7 and 540.2 cm-1 for the WC2 -HO and MI-HO H-bonding modes between rU, which exhibit considerably large FM couplings, the MI-MI, WC1 -WC2 and WC2 -WC2 modes show moderate FM couplings (J=0.4-77 cm-1 ), and the other modes exhibit moderate or weak AFM couplings. These observations indicate that the HO and MI sites are favorable spin-coupling sites. In addition, the H-bond lengths and electronic structures of the H-bonding sites, proton transfer, and extra H-bonding interaction with the surroundings can also affect the magnetic couplings of the base pairs. Clearly, the unique magnetic coupling anisotropy of rU provides a promising application basis for the design and assembly of bio-inspired anisotropically magnetic membranes and even magnetism-tunable building blocks for novel magnetic nanoscale devices.

Detection of targets in real samples with high sensitivity and accuracy is very important and a challenge for the application of developed biosensors. Herein, a novel and efficient cathodic aptasensor coupling photoelectrochemical (PEC) enhancement of photoanodes with signal amplification of nanocatalysts was elaborated. The model target of carcinoembryonic antigen (CEA) was employed to demonstrate the performance. A three-dimensional (3D) PEDOT/Bi2S3/ZnO photoanode was fabricated via successive modification of bismuth sulfide (Bi2S3) nanosheets and a poly(3,4-ethylenedixythiophene) (PEDOT) layer on vertical zinc oxide (ZnO) nanorods. For the aptasensing cathode, after reduced graphene oxide (RGO) was deposited, the CEA aptamer was anchored on the cathodic substrate via the linking of chitosan. Part of the complementary DNA (cDNA) was labeled with Pt nanocatalyst to form the Pt-cDNA conjugate, which amplified the signal via DNA hybridization with the CEA aptamer. Target detection depended on a dramatic decrease in the current signal produced by both the escape of the signal amplifier and obvious steric hindrance of the captured CEA. Benefiting from the superior cosensitization structure of the photoanode and excellent catalytic ability for oxygen reduction of the labeled Pt nanocatalyst, the cathodic aptasensor demonstrated high sensitivity. Owing to the separation of the photoanode with biorecognition, the aptasensor also exhibited good selectivity in the biomatrix. This kind of cathodic aptasensor has offered an effective way to explore other high-performance biosensors for real applications.

Experimental studies showed that high energy radiation induced base release and DNA backbone breaks mainly occur at the neighboring 5' nucleotide when a single-stranded DNA is modified by radiosensitizing 5-halogenated deoxyuridines. However, no mechanism can be used to interpret these experimental observations. To better understand the radiosensitivity of 5-halogenated deoxyuridines, mechanisms involving hydrogen abstraction by the uracil-5-yl radical from the C2' and C3' positions of an adjacent nucleotide separately followed by the C3'-O3' or N-glycosidic bond rupture and the P-O3' bond breakage are investigated in the DNA sequence 5'-TU(•)-3' employing density functional theory calculations in the present study. It is found that hydrogen abstractions from both positions are comparable with the one from the C2' site slightly more favorable. The N-glycosidic bond cleavage in the neighboring 5' nucleotide following the internucleotide C2'-Ha abstraction is estimated to have the lowest activation free energies, indicating that the adjacent 5' base release dominates electron induced damage to single-stranded DNA incorporated by 5-halogenated deoxyuridines. Relative to the P-O3' bond breakage after the internucleotide C3'-H abstraction, the C3'-O3' bond rupture in the neighboring 5' nucleotide following the internucleotide C2'-Ha abstraction is predicted to have a lower activation free energy, implying that single-stranded DNA backbone breaks are prone to occur at the C3'-O3' bond site. The 5'-TU(•)-3' species has substantial electron affinity and can even capture a hydrated electron, forming the 5'-TU(-)-3' anion. However, the electron induced C3'-O3' bond rupture in 5'-TU(-)-3' anion via a pathway of internucleotide proton abstraction is only minor in both the gas phase and aqueous solution. The present theoretical predictions can interpret rationally experimental observations, thereby demonstrating that the mechanisms proposed here are responsible for high energy radiation induced damage to single-stranded DNA incorporated by radiosensitizing 5-halogenated deoxyuridines. By comparing with previous results, our work proves that the radiosensitizing action of 5-bromo-2-deoxyuridine is not weaker but stronger than its isomer 6-bromo-2-deoxyuridine on the basis of the available data.

Graphene oxide (GO) and polyaniline (PANI) are very unique materials with broad potential in corrosion protection coating. To achieve the maximum stability and anti-corrosion effect in a polar medium, firstly itaconic acid doped PANI (DP) was readily prepared by a one-step method, followed by forming a GO and DP composite (GODP). Characterization by Fourier transform infrared spectroscopy and ultraviolet-visible absorption spectra provides evidence for the successful doping of itaconic acid in PANI. X-ray diffraction analysis shows that the d-spacing of the GO sheets increases slightly with the intercalation of DP. The morphological studies show disordered structures in GODP compared with the original GO sheets due to the introduction of PANI molecules and the interaction of functional groups on the surface of the GO sheets. Thermogravimetric analysis reveals the good thermal stability of DP and GODP. Quantum calculation further confirms the successful doping of itaconic acid, and the effective complex of GO and DP, providing a quantitative understanding of the curing mechanism. The crosslinking interaction among the GODP, curing agent, and epoxy resin facilitates the formation of a compact coating, leading to excellent corrosion resistance toward Mg alloy.

In this work, we computationally design radical nucleobases which possess improved electronic properties, especially diradical properties through introducing a cyclopentadiene radical. We predict that the detailed electromagnetic features of base assemblies are based on the orientation of the extra five-membered cyclopentadiene ring. Broken symmetry DFT calculations take into account the relevant structures and properties. Our results reveal that both the radicalized DNA bases and the base pairs formed when they combine with their counterparts remain stable and display larger spin delocalization. The mode of embedding the cyclopentadiene free radical in the structures has some influence on the degree of π-conjugation, which results in various diradical characteristics. Single-layered radical base pairs all have an open-shell singlet ground state, but the energy difference between singlet and triplet is not significant. For two-layered radical base pairs, the situation is more complex. All of them have an open-shell state as their ground state, including an open-shell singlet state and an open-shell triplet state. That is, the majority of radical base pairs possess anti-ferromagnetic or ferromagnetic characteristics. We present here a more in-depth discussion and analyses to study the magnetic characteristics of radical bases and base pairs. As an important factor, two-layered radical base pairs also have been carefully analyzed. We hope that all the measurements and results presented here will stimulate further detailed insights into the related mechanisms in modified DNA bases and the design of better ring-expanded DNA magnetic materials.

Possible electron-induced ruptures of C3'-O3', C5'-O5', and N1-C1' bonds in O4-hydrogenated 2'-deoxythymidine-3'-monophosphate (3'-dT(O4H)MPH) and 2'-deoxythymidine-5'-monophosphate (5'-dT(O4H)MPH) are investigated using density functional theory calculations, and efficient pathways are proposed. Electron attachment causes remarkable structural relaxation in the thymine C6 site. A concerted process of intramolecular proton transfer (IPT) from the C2' site of 2'-deoxyribose to the C6 site and the C3'-O3' bond rupture is observed in [3'-dT(O4H)MPH](-). A low activation barrier (9.32 kcal/mol) indicates that this pathway is the most efficient one as compared to other known pathways leading to backbone breaks of a single strand DNA at the non-3'-end thymine, which prevents the N1-C1' bond cleavage in [3'-dT(O4H)MPH](-). However, essentially spontaneous N1-C1' bond cleavage following similar IPT is predicted in [5'-dT(O4H)MPH](-). A moderate activation barrier (13.02 kcal/mol) for the rate-controlling IPT step suggests that base release from the N1-C1' cleavage arises readily at the 3'-end of single strand DNA with the strand ended by a thymine. The C5'-O5' bond has only an insignificant change in the IPT process. Solvent effects are found to increase slightly the energy requirements for either bond ruptures (11.23 kcal/mol (C3'-O3') vs 16.18 kcal/mol (N1-C1')), but not change their relative efficiencies.