DT Molecules Research Articles

Study on potential energy curves and ro-vibrational energies of DT, HT and T2 molecules

Accurately monitoring and effectively controlling the tritium compounds based on their ro-vibrational energy structure are important issues in various nuclear systems. Because of their radioactivity, it is difficult to obtain the corresponding energies directly through experiments. In this paper, the potential energy curves and the corresponding ro-vibrational full spectrum of DT, HT and T2 systems are derived by ab initio methods. However, it is difficult to verify the reliability of the calculated results due to the lack of direct experimental support. Therefore, a data-driven reliability analysis method is proposed, which can confirm the reliability by extracting information from the relevant calculations and multiple experimental data (the vibrational level, rotational level, and molar heat capacity) of similar systems (HD, H2, D2). The results show that: 1) The potential energy curves obtained by the ab initio method can provide the full ro-vibrational energy spectrum with an accuracy of approximately 10 cm−1; 2) Macroscopic heat capacity information can be used to distinguish and calibrate the overall reliability of microscopic ro-vibrational energies; 3) For the isotopic energy level structure of hydrogen, the influence of isotopes is mainly mass effect.

Low energy (6-18 eV) electron scattering from condensed thymidine (dT) III: absolute electronic excitation cross sections.

Absolute cross sections (CSs) for electronic excitation by low-energy electron (LEE) scattering, from condensed thymidine (dT) in the 6-18 eV incident energy range, were measured by high-resolution electron energy loss spectroscopy (HREELS). Various electron energy loss (EEL) spectra were acquired using 1 ML of dT condensed on a multilayer film of Ar held at about 20 K under ultra-high vacuum (∼1 × 10-11 Torr). dT is one of the most complex DNA constituents to be studied by HREELS and these spectra provide the first LEE energy-loss data for electronic excitation of a nucleoside. CSs for transitions to the states 13A', 13A'', 23A', 21A', 33A', 23A'', 43A', 33A'', 53A' and 51A' of dT were extracted from the EEL spectra. These states correlate to those previously measured for the thymine moiety. Two broad resonances are observed in the energy dependence of the CSs at around 8 and 10 eV; these energies are close to those found in earlier gas- and solid-phase studies on the interaction of LEEs with dT, thymine and related molecules. A quantitative comparison between the electronic CSs of dT and those of thymine and tetrahydrofuran indicates that no variation is induced in the electronic CSs of thymine upon chemically binding to a deoxyribose group.

Precision tests of nonadiabatic perturbation theory with measurements on the DT molecule

This paper presents new measurements and calculations on the rovibrational transitions of DT, an istopolog of the hydrogen molecule composed of deuterium and tritium. The authors show an improved accuracy with respect to previous results and a good agreement between experiment and theory.

Textile with Janus wetting properties via copper deposition and subsequent chemical vapor deposition of 1-dodecanethiol

Textile with Janus wetting properties, viz., one side super-nonwetting (abridged as SNW) and the other side super-wetting (SW), was fabricated via copper (Cu) deposition and subsequent chemical vapor deposition (CVD) of 1-dodecanethiol (DT). To facilitate or hinder the deposition of DT molecules onto the SNW or SW side, three measures were taken. Firstly, less Cu particles were electroless deposited onto the adhered side of the textile to the vessel bottom. Secondly, the side with less Cu particles were adhered to the bottom of the vessel in the CVD process and was wetted by water. Thirdly, the DT molecules on the cap of the vessel spread downward and deposited on the exposed side and could not go through the textile and deposit on the bottom side due to the water sealing and evaporating.

Isotope dependence of the c 3Πu−b 3Σ and D 1Π−B′ 1Σ predissociation rates of molecular hydrogen

The state-specific predissociation rates of the (v,N,J) state by and the (v,J) state by the continuum of various isotopologues of molecular hydrogen have been calculated from accurate ab initio potential energy curves and electronic coupling matrix elements. Lifetimes and predissociation rates of the (v,N,J) and (v,J) levels and accurate energies of the (v,N) and (v,J) levels of the isotopologues have been obtained. Significant isotope dependence of state specific predissociation rate has been found even after adjustment for Franck-Condon factors and reduced mass. The use of average electronic matrix elements of H2 for other isotopologues underestimates the − predissociation rates of the HD, HT, D2, DT and T2 molecules by ∼12%, ∼16%, ∼30%, ∼40%, ∼52%, respectively, and the − rates of the HD, HT, D2, DT and T2 molecules by ∼10%, ∼15%, ∼26%, ∼35% and ∼45%, respectively. When compared at similar rotation, vibration and kinetic energies, the underestimation is nearly independent of the kinetic energy. The absolute value of the average electronic coupling matrix element increases with the reduced mass while that of the vibrational overlap integral decreases with the reduced mass. This accidental substantial cancellation in the − system is responsible for the experimental observation that the relative predissociation rate of two isotopologues approximately equals the squared inverse reduced mass ratio. The origin and implications of the isotope dependence of the averaged electronic coupling matrix elements are discussed.

Low energy (1-19 eV) electron scattering from condensed thymidine (dT) I: absolute vibrational excitation cross sections.

Absolute cross sections (CSs) for vibrational excitation by electrons of energy between 1-19 eV scattering from condensed thymidine (dT) were measured by means of high-resolution electron energy loss spectroscopy (HREELS). The CSs were extracted from electron energy loss spectra of dT condensed on multilayers film of Ar held at about 20 K under ultra-high vacuum (∼1 × 10-11 Torr). dT is one of the most complex molecules to be studied in condensed phase by HREELS. The magnitudes of the vibrational CSs lie within the 10-17 cm2 range. Structures observed in the energy dependence of the vibrational CSs under 3 eV and around 4 eV were compared with previous results of gas- and solid-phase studies on dT and related molecules (e.g., thymine and tetrahydrofuran). These structures were attributed to the formation of shape resonances.

Nuclear Spin-Spin Coupling in HD, HT, and DT.

The interaction between nuclear spins in a molecule is exceptionally sensitive to the physics beyond the standard model. However, all present calculations of the nuclear spin-spin coupling constant J are burdened by computational difficulties, which hinders the comparison to experimental results. Here, we present a variational approach and calculate the constant J in the hydrogen molecule with the controlled numerical precision, using the adiabatic approximation. The apparent discrepancy with experimental result is removed by an analysis of nonadiabatic effects based on the experimental values of the J constant for HD, HT, and DT molecules. This study significantly improves the reliability of the NMR theory for searching new physics in the spin-spin coupling.

Probing the excited state relaxation dynamics of pyrimidine nucleosides in chloroform solution

Ultrafast transient electronic and vibrational absorption spectroscopy (TEAS and TVAS) of 2'-deoxy-cytidine (dC) and 2'-deoxy-thymidine (dT) dissolved in chloroform examines their excited-state dynamics and the recovery of ground electronic state molecules following absorption of ultraviolet light. The chloroform serves as a weakly interacting solvent, allowing comparisons to be drawn with prior experimental studies of the photodynamics of these nucleosides in the gas phase and in polar solvents such as water. The pyrimidine base nucleosides have some propensity to dimerize in aprotic solvents, but the monomer photochemistry can be resolved clearly and is the focus of this study. UV absorption at a wavelength of 260 nm excites a 1ππ* ← S0 transition, but prompt crossing of a significant fraction (50% in dC, 17% in dT) of the 1ππ* population into a nearby 1nπ* state is too fast for the experiments to resolve. The remaining flux on the 1ππ* state leaves the vertical Franck-Condon region and encounters a conical intersection with the ground electronic state of ethylenic twist character. In dC, the 1ππ* state decays to the ground state with a time constant of 1.1 ± 0.1 ps. The lifetime of the 1nπ* state is much longer in the canonical forms of both molecules: recovery of the ground state population from these states occurs with time constants of 18.6 ± 1.1 ps in amino-oxo dC and ∼114 ps in dT, indicating potential energy barriers to the 1nπ*/S0 conical intersections. The small fraction of the imino-oxo tautomer of dC present in solution has a longer-lived 1nπ* state with a lifetime for ground state recovery of 193 ± 55 ps. No evidence is found for photo-induced tautomerization of amino-oxo dC to the imino-oxo form, or for population of low lying triplet states of this nucleoside. In contrast, ∼8% of the UV-excited dT molecules access the long-lived T1 (3ππ*) state through the 1nπ* state. The primary influence of the solvent appears to be the degree to which it destabilizes the states of 1nπ* character, with consequences for the lifetimes of these states as well as the triplet state yields.

Lifetimes of Vibro-Rotational Levels in Excited Electronic States of Diatomic Hydrogen Isotopologues

The current situation in studies of lifetimes of excited rovibronic levels for the H2, D2, T2, HD, HT, and DT molecules is analyzed. All measured lifetime values (792 entries for 618 different vibro-rotational levels of 33 electronic states) reported in 61 publications before April 2015 are compiled and listed in tabular format together with an annotated bibliography. Experimental data are only available for the H2, HD, and D2 molecules. The data collected in the present work show fragmentariness of experimental data. For the vast majority of the levels, the lifetime values were reported in one paper only and up to now are without independent experimental verification. A complete bibliography of publications concerning semiempirical determination and nonempirical calculations of the lifetimes is presented. Numerical results obtained in the framework of these two approaches are listed only in cases when experimental data are available. For more than half of the levels, the differences between measured and calculated values are three times higher than experimental errors. These discrepancies show necessity of more precise experimental and nonempirical studies. For some 79 rovibronic levels, our analysis makes it possible to propose certain set of recommended lifetime values.

Study of the inhibitive effect of mixed self-assembled monolayers on copper with SECM

Mixed self-assembled monolayers (SAMmix) were formed by 2-(Pyridin-2-yliminomethyl)-phenol (HL) and 1-dodecanethiol (DT) molecules on copper surface. The inhibitive ability of SAMmix in sodium chloride solution was characterized in situ by the scanning electrochemical microscope (SECM). The results show that the compactness and the stability of SAMmix, formed by the two organic materials in an appropriate sequence, are improved and the inhibition efficiency (η%) increases markedly. They also verify that SAMmix are formed due to the existence of collapsed sites and pinhole defects on SAMs of single materials on the surface of copper. The re-arrangement and the competitive adsorption of HL and DT molecules may have impact on the quality of SAMmix. Possible structures of SAMmix are suggested based on the experimental results.

Polarization: A must for fusion

The complete polarization of DT fuel would increase the fusion reactivity by 50% in magnetic as well as in inertial confinements. The persistence of polarization in a fusion process could be tested, using a terawatt laser hitting a polarized HD target. The polarized deuterons heated in the plasma induced by the laser can fuse producing a 3He and a neutron in the final state. The angular distribution of the emitted neutrons and the change in the corresponding total Cross Section (CS) can sign the polarization persistence. The polarization of solid H2, D2 or T2 Hydrogen isotopes is very difficult. However, it has been possible to polarize HD, a hetero-molecular form of Hydrogen, by static polarization, at very low temperature and very high field. The radioactivity of DT molecules forbids there high polarization by the static method, therefore one has to develop the Dynamic Nuclear Polarization (DNP) by RF transitions. The DNP of HD has been investigated in the past. The magnetic properties of HD and DT molecules are very similar, it is therefore expected that any polarization result obtained with HD could be extrapolated to DT.

Effect of small interfering RNA 3'-end overhangs on chemosensitivity to thymidylate synthase inhibitors

BackgroundSmall interfering RNAs (siRNAs) are double-stranded RNAs that effectively inhibit expression of its complimentary target mRNA. Standard siRNAs contain two nucleotide overhangs on their 3' end. While these overhangs are usually comprised of deoxythymidines (dT), it has been shown that any nucleotide can be used on the 3' end without affecting RNAi silencing.ResultsIt was recently shown that extension of the 3' end to five or eight dT molecules allows siRNAs to be effectively complexed with linear polyethylenimine (PEI), leading to enhanced cellular uptake and intracellular release. Here, we provide further evidence that only extended or 'sticky' siRNAs complexed with PEI result in significant target knockdown. However, when investigating the potential effects of these extended siRNAs on growth of human colon cancer RKO cells, we observed a dose-dependent reversal of cytotoxicity of a thymidylate synthase-targeted siRNA. In contrast, siRNAs with uridine overhangs maintained their growth inhibitory effects. We further demonstrated that dT-containing siRNAs prevented the cytotoxic effects of thymidylate synthase (TS) inhibitor compounds, such as ZD1694 and 5'-fluoro-deoxyuridine, while having no deleterious effect on cisplatin toxicity. We show that this rescue effect results from the rapid degradation of the siRNA.ConclusionsGiven that TS is an important enzyme for cell growth and proliferation and that its expression is controlled by multiple pathways, the rescue of its growth inhibitory effects may have unintended consequences. As siRNAs are being developed as therapeutic molecules, it will be important to avoid such off-target effects due to dT release. Hence, siRNAs should contain only uridine residues in their 3'-end overhangs.

Studies on corrosion inhibition of copper by alkanethiol SAMs prepared in aqueous micellar solution

AbstractThe character of 1‐dodecanethiol (DT) self‐assembled monolayers (SAMs) formed on copper surface in aqueous micellar solution is investigated by means of contact angle measurement, electrochemical impedance spectroscopy (EIS), and polarization curves. The contact angle measurement shows that the SAMs formed in aqueous micellar solution are oriented and compact. According to the electrochemical measurements, it is found that both the concentration of DT and temperature can significantly affect the property of SAMs. The DT SAMs can prevent the corrosion of copper in chloride‐containing solution effectively because the inhibition efficiency can reach 99.59% at the DT concentration of 10−2 M. The adsorption of DT in aqueous micellar solution obeys to the Langmuir adsorption isotherm, and the value of the free energy of adsorption calculated indicates that the adsorption of DT molecule is a spontaneous process and a typical of chemical adsorption.

Electrochemical behavior of silver single-crystal electrodes in 1 M NaNO3 solution in the absence and in the presence of decanethiol films

The surface properties of silver single-crystal faces (111) and (210) in 1 M NaNO3 aqueous solution in the absence and in the presence of monolayer n-decanethiol (DT) films are studied by the methods of cyclic voltammetry and electrochemical impedance using the meniscus contact technique. It is experimentally shown that, in the potential range from 0 to −0.5 V, the faradaic processes are absent and low currents are recorded on the unmodified silver surfaces. It is shown that the DT molecules, which are adsorbed on the nonoxidized surfaces of silver faces, spontaneously form (during 72 h) compact structurized films. The films are stable in the air and in the electrolyte solutions and totally block the surfaces of both faces. The impedance spectra, which were measured for each interface in a wide range of frequencies, are analyzed and interpreted. The measurements were performed by the use of the corresponding empirical equivalent circuits containing perfect and imperfect analogs of electrical circuits; complex nonlinear least squares (CNLS) regression method was applied for the calculations. The capacitance, ohmic resistance, and adsorbed monolayer thickness were estimated.

Towards the polarization of DT molecules

The polarization of D and T nuclei should increase the reactivity of DT molecules in HIIF processes. At IPN Orsay, we have developed the static polarization of HD samples using “brute force” (BF). It has been demonstrated, that the ageing technique or the double distillation allow to get nuclear relaxation times larger than 1 h, even at 1.5 K and 1 T. It is advocated that it is possible to achieve by RF the conventional Dynamic Nuclear Polarization (DNP) of the proton and the deuteron contained in the HD molecule, using HD samples distilled at Orsay and suitably irradiated. The persistence after irradiation of the long nuclear relaxation times resulting from the double distillation has already been demonstrated. If feasible, the DNP of HD would open the possibility to polarize DT, which has the same magnetic structure as HD and is the ideal fuel for HIIF.

Molecular (H/D/T) sources in JET

Molecular Fulcher-α spectroscopy is used for the investigation of the HD and DT molecule formation in JET during H2 and T2 puffs, respectively. In the hydrogen case, the HD fraction in the outer divertor was about 10% of the molecular D2 flux, resulting in a 1% contribution of H2 to the D2 flux using the law of mass action which is a very sensitive means to measure low quantities of H2 or T2 respectively via the detection of the isotopomeres HD and DT. Since the puffed tritium was about one order of magnitude smaller than the H flux introduced, a DT-flux of only ∼1% is expected, resulting in a T2 flux of 0.1%. Evidence will be presented that similar levels have indeed been detected, although the signals were near the detection limit, demonstrating that this type of spectroscopy offers an interesting potential tool as a fuelling and recycling rate diagnostic.

Investigation of the quenching efficiency of diatoxanthin in cells of Phaeodactylum tricornutum (Bacillariophyceae) with different pool sizes of xanthophyll cycle pigments

A. Schumann, R. Goss, T. Jakob and C. Wilhelm. 2007. Investigation of the quenching efficiency of diatoxanthin in cells of Phaeodactylum tricornutum (Bacillariophyceae) with different pool sizes of xanthophyll cycle pigments. Phycologia 46: 113–117. DOI: 10.2216/06-30.1In the present study, the content of diadinoxanthin (Dd) + diatoxanthin (Dt) in the diatom Phaeodactylum tricornutum was manipulated by low-light (LL) and high-light (HL) growth conditions. Cells grown in HL almost doubled the pool size of Dd cycle pigments compared to cells from a LL culture. HL-grown cultures exhibited a stronger de-epoxidation and higher amounts of Dt during actinic HL illumination. However, the correlation between Dt and the corresponding nonphotochemical quenching (NPQ) revealed that the quenching efficiency of Dt was drastically decreased in these HL-grown cells compared to cells from the LL cultivation. The correlation between the de-epoxidation state of the Dd cycle and NPQ implied that in HL-grown cells a part of the Dt molecules had lost their ability to contribute to the NPQ. A precise quantification of the amount of free Dd + Dt by anion exchange chromatography and high-performance liquid chromatography showed that only 10% of the additionally synthesized Dd cycle pigments existed as free pigment in the thylakoid membrane and that most of the Dd + Dt was still bound to the light-harvesting proteins. The possible function of the additional free Dt in photo-protection and the antenna-bound Dt in the synthesis of the light-harvesting pigment fucoxanthin is discussed.

Synergistic effect of 1‐dodecanethiol upon inhibition of Schiff bases on carbon steel corrosion in sulphuric acid media

PurposeIn this paper, the main aim is to study the synergistic effects of alkanethiols upon inhibition of Schiff bases, N,N′‐ethylen‐bis and N,N′‐ortho‐phenylen‐bis in 0.5 M sulphuric acid solutions.Design/methodology/approachMeasurements were carried out in a three‐electrode cell assembly connected to the corrosion measurement system using software for Tafel polarization. Impedance measurements were carried out at open circuit potential using an electrochemical interface and frequency response analyzer at frequencies from 100 kHz to 10 MHz.FindingsResults obtained revealed that at high concentrations, each of the investigated Schiff bases and 1‐dodecanethiol (DT) were good inhibitors when added separately to the corrosive media. The decrease in corrosion rate was associated with an increase in their concentrations. It was found that the presence of DT together with Schiff bases in corrosive medium increased inhibition effect, especially at low concentrations. Synergistic effect is discussed from viewpoint of their co‐adsorption. The adsorption of combined inhibitors was found to follow Langmuir isotherm. Thermodynamic calculations revealed that adsorption of combined inhibitors had a physical nature.Research limitations/implicationsIn order to improve further the performance of Schiff bases and identifying their synergistic effects with other additives it is suggested that some more researches on other Schiff bases with other alkanethiol molecules must be done.Practical implicationsThe results of this paper can be used for acid cleaning of carbon steel in which suitable inhibitor systems with the highest efficiency is required.Originality/valueThis paper reveals that the presence of DT molecules in solution encourage the adsorption of Schiff bases by facilitating the electrostatic co‐adsorption of Schiff base molecules through a synergistic effect.

Molecular effects in investigations of tritium molecule β decay endpoint experiments

The final state distribution of the first six electronic states of $^{3}\mathrm{HeT}{}^{+},^{3}\mathrm{HeD}{}^{+}$ and $^{3}\mathrm{HeH}{}^{+}$ resulting from the \ensuremath{\beta} decay of ${T}_{2}$, DT, and HT are calculated, to satisfy the higher-resolution requirements and increased sensitivity of the future tritium neutrino mass experiments. The sensitivity of the initial temperature, ortho-para ratio, and isotopic composition of the source is considered. Estimates of the error in the value of the neutrino mass deduced from fitting, due to uncertainties in the temperature, the ortho-para ratio of ${T}_{2}$, and the percentage of DT molecules in the source are presented.

Progress in the polarization of HD

The static polarization of HD samples has been achieved using “brute force”, for HD samples purified by double distillation. Proton polarization in excess of 60% and deuteron vector polarization higher than 14% have been reached. It has been demonstrated that the ageing technique allows to get relaxation times at 1.5 K and 1 T larger than a week. It is advocated that the conventional dynamic polarization of HD should be feasible for the proton and the deuteron contained in the HD molecule. This would create the possibility of polarizing DT molecules, increasing their reactivity when used as fuel in HIIF processes.