在TiO2纳米阵列上电沉积RuO2用于CO2电还原

传统上,RuO₂/TiO₂复合电极制备是通过在TiO₂/Ti基体上多次涂覆含Ru前驱体溶液和随后热分解（TD）来实现的. 为克服上述方法中Ru用量大和利用率低之不足, 本工作主要基于循环伏安法（CV）在TiO₂纳米管阵列（TNA）上电沉积RuO₂制备RuO₂^CV/TNA复合电极. SEM、GIXRD和CV结果表明, 电沉积的RuO₂为无定型结构, 所制备电极中的Ru用量约为传统的RuO₂^TD/TNA电极中Ru用量的1/30. 尽管两电极催化CO₂还原产物的法拉第效率接近, 但是RuO₂^CV/TNA电极比RuO₂^TD/TNA电极展示了更高的还原电流, 较正的初始还原电位和更好的稳定性. 与磷酸盐缓冲溶液中电还原CO₂相比,RuO₂^CV/TNA电极在0.1 mol•L^-1 KHCO₃中电还原CO₂除生成更高法拉第效率的甲酸根和甲烷外,还检测到CO的生成.     

DNA polymerase-mediated DNA synthesis on a TNA template

TNA, or threose nucleic acid, is capable of Watson-Crick base pairing with DNA, RNA, and TNA; coupled with its chemical simplicity, this suggests that TNA is a possible progenitor of RNA. As an initial step toward developing the molecular tools necessary to investigate the functional capabilities of TNA by in vitro selection, we have screened a variety of DNA polymerases for activity on a TNA template. We report that despite having a repeating unit that is one atom shorter than that of DNA, several polymerases showed surprisingly good ability to copy limited stretches of TNA.     

TNA synthesis by DNA polymerases

Threose nucleic acid (TNA), which has a repeat unit one atom shorter than that of DNA, is capable of Watson-Crick base pairing with DNA, RNA, and TNA. Because of its chemical simplicity, TNA is considered to be a possible progenitor of RNA. As an initial step toward developing the molecular tools necessary to investigate the functional capabilities of TNA by in vitro selection, we have screened a variety of DNA polymerases for TNA synthesis activity on a DNA template. We wish to report that several polymerases show surprisingly good ability to synthesize TNA using alpha-l-threofuranosyl thymidine-3'-triphosphate as a substrate.     

Highly Stable Duplex Formation by Artificial Nucleic Acids Acyclic Threoninol Nucleic Acid (aTNA) and Serinol Nucleic Acid (SNA) with Acyclic Scaffolds

The stabilities of duplexes formed by strands of novel artificial nucleic acids composed of acyclic threoninol nucleic acid (aTNA) and serinol nucleic acid (SNA) building blocks were compared with duplexes formed by the acyclic glycol nucleic acid (GNA), peptide nucleic acid (PNA), and native DNA and RNA. All acyclic nucleic acid homoduplexes examined in this study had significantly higher thermal stability than DNA and RNA duplexes. Melting temperatures of homoduplexes were in the order of aTNA>PNA≈GNA≥SNA?RNA>DNA. Thermodynamic analyses revealed that high stabilities of duplexes formed by aTNA and SNA were due to large enthalpy changes upon formation of duplexes compared with DNA and RNA duplexes. The higher stability of the aTNA homoduplex than the SNA duplex was attributed to the less flexible backbone due to the methyl group of D ‐threoninol on aTNA, which induced clockwise winding. Unlike aTNA, the more flexible SNA was able to cross‐hybridize with RNA and DNA. Similarly, the SNA/PNA heteroduplex was more stable than the aTNA/PNA duplex. A 15‐mer SNA/RNA was more stable than an RNA/DNA duplex of the same sequence.     

An in vitro selection system for TNA

(3'-2')-alpha-l-Threose nucleic acid (TNA) is an unnatural polymer that possesses the rare ability to base-pair with RNA, DNA, and itself. This feature, coupled with its chemical simplicity, makes TNA of interest as a possible progenitor of RNA during the early history of life. To evaluate the functional potential of TNA, we have developed a system for the in vitro selection of TNA. We identified the Therminator DNA polymerase as a remarkably efficient DNA-dependent TNA polymerase capable of polymerizing more than 50 tNTPs. We have also developed a method of covalently linking a DNA template to the TNA strand that it encodes, thus obviating the need for a TNA-dependent DNA polymerase during cycles of selection.     

Kinetic analysis of an efficient DNA-dependent TNA polymerase

alpha-l-Threofuranosyl nucleoside triphosphates (tNTPs) are tetrafuranose nucleoside derivatives and potential progenitors of present-day beta-d-2'-deoxyribofuranosyl nucleoside triphosphates (dNTPs). Therminator DNA polymerase, a variant of the 9 degrees N DNA polymerase, is an efficient DNA-directed threosyl nucleic acid (TNA) polymerase. Here we report a detailed kinetic comparison of Therminator-catalyzed TNA and DNA syntheses. We examined the rate of single-nucleotide incorporation for all four tNTPs and dNTPs from a DNA primer-template complex and carried out parallel experiments with a chimeric DNA-TNA primer-DNA template containing five TNA residues at the primer 3'-terminus. Remarkably, no drop in the rate of TNA incorporation was observed in comparing the DNA-TNA primer to the all-DNA primer, suggesting that few primer-enzyme contacts are lost with a TNA primer. Moreover, comparison of the catalytic efficiency of TNA synthesis relative to DNA synthesis at the downstream positions reveals a difference of no greater than 5-fold in favor of the natural DNA substrate. This disparity becomes negligible when the TNA synthesis reaction mixture is supplemented with 1.25 mM MnCl(2). These results indicate that Therminator DNA polymerase can recognize both a TNA primer and tNTP substrates and is an effective catalyst of TNA polymerization despite changes in the geometry of the reactants.     

Adsorption of the nitrosamine and thionitrosamine molecules as carcinogen compounds on the BN and B3Al N nanotubes: A DFT study

DFT calculations were performed to investigation of the influence of doping three atoms of aluminum on the electronic properties of the (4,0) zigzag boron nitride nanotube (BNNT). Also, adsorption properties of nitrosamine (NA) and thionitrosamine (TNA) molecules as carcinogen agents onto BN and B_Al3N nanotubes were studied. The results show that the B_3AlN nanotube is the most energetically favorable candidates for adsorption of these molecules. Also, B(B_3Al)NNT/TNA complexes are more stable than B(B_3Al)NNT/NA complexes. The HOMO–LUMO gap, electronic chemical potential (μ), hardness (?), softness (S), the maximum amount of electronic charge (ΔN_max) and electrophilicity index (ω) for monomers and complexes in the gas and polar solvent phases were calculated. The results show that the conductivity and reactivity of BNNT increase by doping Al atoms instead of B atoms. Also, the interaction of NA and TNA molecules with BN and B_Al3N nanotubes results in significant changes in the electronic properties of nanotubes. Based on the natural bond orbital (NBO) analysis, in all complexes charge transfer occurs from NA and TNA molecules to nanotubes. Theory of atoms in molecules (AIM) was applied to characterize the nature of interactions in nanotubes. It is predicted that, BN and B_3AlN nanotubes can be used to as sensor for detection of NA and TNA molecules.     

Pulse radiolysis of thionicotinamide in aqueous solutions: formation of resonance stabilized species on one electron oxidation

Pulse radiolysis studies on thionicotinamide (TNA) have been carried out in aqueous solutions at pH 6.8 and 1. The initial species formed by OH radical reaction with TNA at pH 6.8 was found to react with the parent molecule to give a dimer radical species (_max = 420-440 nm). Reaction of Br₂ ^- radicals with TNA was found to give a transient species having _max at 380 nm. This spectrum has been assigned to a resonance stabilized species with free electron delocalised over the -N-C-S bond. Reactions of OH and Cl2₂ ^- radicals with TNA at pH 1 were found to give identical transient species with _max at 420 nm, which decayed by first-order kinetics at a rate of about 8.0 × 10³ s^-1. This species is suggested to be the protonated form of the resonance-stabilized species formed at pH 6.8 in the reaction of Br₂ ^- with TNA. The rate constant for the reaction was 4 × 10⁹ dm³ mol^-1 s^-1. Semi-reduced species formed by the reaction of e-_aq with TNA (k = 1.6 × 10¹⁰ dm³ mol^-1 s^-1) was found to be a good reductant which could transfer electron to methyl viologen. CO₂ ^- radicals also reacted with TNA to give a reducing species. Although, the absorption peaks in the two cases were at the same wavelengths viz. 380 and 480 nm, the ratios of the peak heights were different suggesting the formation of different species. Hydrogen atoms and (CH₃)₂COH radicals were found to transfer an electron to TNA at pH 1, as seen by quantitative electron transfer to methyl viologen from the transient species.     

The structure of a TNA-TNA complex in solution: NMR study of the octamer duplex derived from alpha-(L)-threofuranosyl-(3'-2')-CGAATTCG

TNA (alpha-( l)-threofuranosyl-(3'-2') nucleic acid) is a nucleic acid in which the ribofuranose building block of the natural nucleic acid RNA is replaced by the tetrofuranose alpha-( l)-threose. This shortens the repetitive unit of the backbone by one bond as compared to the natural systems. Among the alternative nucleic acid structures studied so far in our laboratories in the etiological context, TNA is the only one that exhibits Watson-Crick pairing not only with itself but also with DNA and, even more strongly, with RNA. Using NMR spectroscopy, we have determined the structure of a duplex consisting entirely of TNA nucleotides. The TNA octamer (3'-2')-CGAATTCG forms a right-handed double helix with antiparallel strands paired according to the Watson-Crick mode. The dominant conformation of the sugar units has the 2'- and 3'-phosphodiester substituents in quasi-diaxial position and corresponds to a 4'-exo puckering. With 5.85 A, the average sequential P i -P i+1 distances of TNA are shorter than for A-type DNA (6.2 A). The helix parameters, in particular the slide and x-displacement, as well as the shallow and wide minor groove, place the TNA duplex in the structural vicinity of A-type DNA and RNA.     

Thionicotinamide SAM on Gold: Adsorption Studies and Electroactivity

STM and impedance results of the self‐assembled monolayer (SAM) formed with thionicotinamide (TNA) on gold indicate the presence of defects that increase with the immersion time of the electrode in the TNA solution affecting the SAM electroactivity toward the electron transfer reaction of the cytochrome c metalloprotein and [Fe(CN)₆]^4? and [Ru(NH₃)₆]³⁺ complexes. It was observed that this electroactivity was also affected by the pH of the electrolyte solution. SERS and STM data indicate sulfur coordination to the surface with contribution of the NH₂ group. From the dependence of the TNA surface coverage on the temperature and concentration in solution, thermodynamic parameters of adsorption were determined.     

不同吸附类型有机物在TiO2纳米管阵列电极表面的光电催化性能和反应机制

利用有机物在薄层反应器中发生的耗竭氧化反应,研究了弱吸附型的葡萄糖和强吸附型的邻苯二甲酸氢钾在TiO2纳米管阵列(TNA)电极表面的光电催化反应性能和反应机制.研究表明,光电催化反应电流-时间(I-t)曲线的变化趋势能够很好地反映有机物在TNA电极表面的反应性能.对于弱吸附型的葡萄糖,由于其在TNA电极表面吸附能力弱,从溶液本体被吸附至电极表面较慢,致使葡萄糖在高浓度光催化反应时出现I-t曲线瞬时升高然后迅速下降,再呈现缓慢下降的变化趋势.对于强吸附型的邻苯二甲酸氢钾,其吸附性强且难降解,因而在电极表面总是存在着大量的邻苯二甲酸氢钾,导致溶液中邻苯二甲酸氢钾浓度升高时,光电催化反应的I-t曲线在瞬时升高,然后依然持续升高,之后才呈缓慢下降的变化趋势.本文还对有机物的吸附类型、吸附系数、反应机制等进行了分析.研究表明,利用薄层反应器的耗竭氧化反应,有助于深入了解有机物在电极表面的反应过程及其微观机制.     

Base-pairing systems related to TNA: alpha-threofuranosyl oligonucleotides containing phosphoramidate linkages

(3'NH)- and (2'NH)-TNA, two isomeric phosphoramidate analogues of TNA (alpha-threofuranosyl-(3'-->2') oligonucleotides), are shown to be efficient Watson-Crick base-pairing systems and to undergo intersystem cross-pairing with TNA, RNA, and DNA. [reaction: see text]     

分子印迹TiO2纳米管阵列的制备与选择性光电催化降解邻苯二甲酸二乙酯

以邻苯二甲酸二乙酯(DEP)为模板分子,在TiO2纳米管阵列(TNA)上沉积了能识别DEP分子的TiO2纳米颗粒,制备了DEP分子印迹型TNA(DM-TNA)。X射线衍射(XRD)测试表明,DM-TNA的晶体结构是锐钛矿。扫描电镜(SEM)测试显示颗粒大小约为20 nm的TiO2纳米颗粒均匀地涂覆在TNA的管壁上。光电催化降解DEP和2,4-二氯苯酚(DCP)的结果表明,DM-TNA降解DEP的活性高于非分子印迹TNA(NM-TNA),而DM-TNA降解DCP的活性低于NM-TNA。DM-TNA降解DEP的速率常数是NM-TNA的2.76倍。     

Crystal structure of a B-form DNA duplex containing (L)-alpha-threofuranosyl (3'-->2') nucleosides: a four-carbon sugar is easily accommodated into the backbone of DNA

(L)-alpha-Threofuranosyl-(3'-->2')-oligonucleotides (TNA) containing vicinally connected phosphodiester linkages undergo informational base pairing in an antiparallel strand orientation and are capable of cross-pairing with RNA and DNA. TNA is derived from a sugar containing only four carbon atoms and is one of the simplest potentially natural nucleic acid alternatives investigated thus far in the context of a chemical etiology of nucleic acid structure. Compared to DNA and RNA that contain six covalent bonds per repeating nucleotide unit, TNA contains only five. We have determined the atomic-resolution crystal structure of the B-form DNA duplex [d(CGCGAA)Td(TCGCG)](2) containing a single (L)-alpha-threofuranosyl thymine (T) per strand. In the modified duplex base stacking interactions are practically unchanged relative to the reference DNA structure. The orientations of the backbone at the TNA incorporation sites are slightly altered in order to accommodate fewer atoms and covalent bonds. The conformation of the threose is C4'-exo with the 2'- and 3'-substituents assuming quasi-diaxial orientation.     

Improving the contact properties of CdS-decorated TiO<Subscript>2</Subscript> nanotube arrays using an electrochemical/thermal/chemical approach

Decoration of TiO₂ nanotube films (TiO₂ nanotube arrays (TNAs)) with CdS nanoparticles has been pursued for a broad range of applications that goes from solar cells to biological sensors. In most synthesis methods, the scale-up of devices has been challenging due to the poor contact at the chalcogenide/oxide interface. In this work, we validate the electrochemical/thermal/chemical route as a superior strategy to sensitize TNAs with CdS nanoparticles when compared with conventional methods. The process consisted of (i) electrodeposition of cadmium on TNAs to ensure strong bonding between TiO₂ and Cd precursor particles, (ii) air annealing of Cd-decorated TNAs to thermally oxidize cadmium to cadmium oxide, and (iii) total sulfurization of cadmium oxide to obtain CdS in an hexagonal phase matching that of TNAs. X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analyses indicated the complete transformation of cadmium precursor particles into CdS and a good surface coverage of the internal/external walls of TNAs. When compared to samples prepared by successive ionic layer adsorption and reaction (SILAR), electrochemical impedance spectroscopy data revealed the improvement of the electrical properties of the TNA matrix due to the sulfurization process and a lower contact resistance at the CdS/TNA interface. These improvements explain the superior photoelectrochemical response of CdS/TNA photoelectrodes obtained by the electrochemical/thermal/chemical route.     

A novel photoelectrochemical immunosensor by integration of nanobody and TiO2 nanotubes for sensitive detection of serum cystatin C

Cystatin C (CysC) is a sensitive marker for the estimation of the glomerular filtration rate and the clinical diagnosis of different diseases. In this paper, CysC-specific nanobodies (Nbs) were isolated from a phage display nanobody library. A simple and sensitive photoelectrochemical immunosensor based on TiO₂ nanotube arrays (TNAs) was proposed for the sensitive detection of CysC. The TiO₂ nanotube arrays deposited by electrochemical anodization displayed a high and stable photocurrent response under irradiation. After coupling CysC-specific nanobody to TNA (Nb/TNA), the proposed immunosensor for CysC can be utilized for tracking the photocurrent change of Nb/TNA caused by immunoreactions between CysC and the immobilized CysC-specific Nb. This allowed for the determination of CysC with a calibration range from 0.72 pM to 7.19 nM. The variation of the photocurrent was in a linear relationship with the logarithm of the CysC concentration in the range of 0.72 pM–3.6 nM. The immunosensor had a correlation coefficient of 0.97 and a detection limit of 0.14 pM at a signal-to-noise ratio of 3. The proposed immunosensor showed satisfactory intra- and inter-assay accuracy, high selectivity and good stability. As a result, this proposed strategy would offer a novel and simple approach for the detection of immunoreactions, provide new insights in popularizing the diagnosis of CysC, and extend the application of TiO₂ nanotubes.     

The α‐L‐Threofuranosyl‐(3′→2′)‐oligonucleotide System (‘TNA'): Synthesis and Pairing Properties

Our studies of α‐L ‐Threofuranosyl‐(3′→2′)‐oligonucleotides (‘TNA') are part of a systematic experimental inquiry into the base‐pairing properties of potentially natural nucleic acid alternatives taken from RNA's close structural neighborhood. TNA is an efficient Watson‐Crick base‐pairing system and has the capability of informational cross‐pairing with both RNA and DNA. This property, together with the system's constitutional and (presumed) generational simplicity, warrants special scrutiny of TNA in the context of the search for chemical clues to RNA's origin.     

Nonenzymatic oligomerization of RNA by TNA templates

Cytosine TNA promotes nonenzymatic, template-directed oligomerization of complementary activated rGMP, leading to selective and efficient formation of RNA products. This process models "genetic takeover" of a pre-RNA by RNA. [reaction: see text]     

An Organic Nitrogen Specific Detector for High Pressure Liquid Chromatography

Abstract

The Thermal Nitrogen Analyzer (TNA), a new highly sensitive and nitrogen-selective detector for high pressure liquid chromatography, is described.     

Detection of Potential TNA and RNA Nucleoside Precursors in a Prebiotic Mixture by Pure Shift Diffusion‐Ordered NMR Spectroscopy

In the context of prebiotic chemistry, one of the characteristics of mixed nitrogenous‐oxygenous chemistry is its propensity to give rise to highly complex reaction mixtures. There is therefore an urgent need to develop improved spectroscopic techniques if onerous chromatographic separations are to be avoided. One potential avenue is the combination of pure shift methodology, in which NMR spectra are measured with greatly improved resolution by suppressing multiplet structure, with diffusion‐ordered spectroscopy, in which NMR signals from different species are distinguished through their different rates of diffusion. Such a combination has the added advantage of working with intact mixtures, allowing analyses to be carried out without perturbing mixtures in which chemical entities are part of a network of reactions in equilibrium. As part of a systems chemistry approach towards investigating the self‐assembly of potentially prebiotic small molecules, we have analysed the complex mixture arising from mixing glycolaldehyde and cyanamide, in a first application of pure shift DOSY NMR to the characterisation of a partially unknown reaction composition. The work presented illustrates the potential of pure shift DOSY to be applied to chemistries that give rise to mixtures of compounds in which the NMR signal resolution is poor. The direct formation of potential RNA and TNA nucleoside precursors, amongst other adducts, was observed. These preliminary observations may have implications for the potentially prebiotic assembly chemistry of pyrimidine threonucleotides, and therefore of TNA, by using recently reported chemistries that yield the activated pyridimidine ribonucleotides.