Effect of nanostructured MoS2 morphology on the glucose sensing of electrochemical biosensors

In this study, the effects of the morphological characteristics of MoS₂ nanomaterials on the glucose sensing of electrochemical biosensors were explored. Nanostructured MoS₂ materials, including nanoparticles (NPs), nanoflowers (NFs), and nanoplatelets (NPLs), were prepared via a simple hydrothermal method. The structure and morphological characteristics of MoS₂ nanomaterials were examined through X-ray diffraction, field emission scanning electron microscopy, and Raman spectroscopy. Electrochemical properties were analyzed through cyclic voltammetry. Results showed that the obtained sensitivity was 64, 68.7, and 77.6 μAmM⁻¹ cm⁻² for MoS₂ NP-, MoS₂ NF-, and MoS₂ NPL-based biosensors, respectively. The limit of detection (LOD) of all MoS₂-based glucose biosensors was 0.081 mM. In addition, the pH, temperature, glucose oxidase (GOx) concentration, reproducibility, specificity, and stability of glucose biosensors with different MoS₂ morphologies were also investigated and indicated the oxidation current response of the MoS₂ NPL-based glucose biosensor was higher than that of MoS₂ NF- and NP-based biosensors.     

Investigation of radiation resistance of fullerenes under irradiation with fast neutrons

Fullerenes C₆₀ and C₇₀ synthesized by the electric arc method and fractionated (purity grades of 99.99 and 99.90 wt %, respectively) were irradiated in a solid phase in the WWR-M reactor (Konstantinov Petersburg Nuclear Physics Institute, National Research Centre “Kurchatov Institute,” Gatchina, Russia) with the aim of determining the survivability in the range of fast neutron fluences Φ = 4 × 10¹⁵?3 × 10¹⁷ n/cm². The irradiated samples were dissolved in carbon disulfide, and intact fullerenes were extracted. With an increase in the fluence, their weight fraction in the samples S(Φ), a measure of radiation resistance of molecules, decreased, to a first approximation, exponentially: S(Φ) = exp(?Φ/Φ _D ). The estimated characteristic fluences were Φ _D = 2.4 × 10¹⁷ and 4.0 × 10¹⁷ n/cm² for C₆₀ and C₇₀, respectively.     

Photoinduced intramolecular electron-transfer reactions in carbazole-fullerene and phenothiazine-fullerene linked compounds in benzene and benzonitrile as studied by fluorescence, transient absorption, time-resolved EPR, and magnetic field effects

Photoinduced intramolecular electron-transfer reactions in carbazole (Cz)-fullerene (C₆₀) (Cz(8)C₆₀) and phenothiazine (Ph)-C₆₀ (Ph(n)C₆₀ (n=8, 10, 12)) linked compounds have been investigated in benzene and benzonitrile by fluorescence, transient absorption, and time-resolved electron paramagnetic resonance measurements, and by magnetic field effects on the decay rate constants of the photogenerated biradicals. In benzonitrile, photoinduced intramolecular electron transfer from Cz to the singlet excited state of C₆₀ (¹C₆₀ ^*) occurred in Cz(8)C₆₀, but not to the triplet excited state (³C₆₀ ^*), while the intramolecular electron-transfer to both¹C₆₀ ^* and³C₆₀ ^* occurred in Ph(n)C₆₀ (n=8, 10, 12). In benzene, on the other hand, no electron transfer to both¹C₆₀ ^* and³C₆₀ ^* took place in all linked compounds. These results were interpreted in terms of the different Gibbs free energy changes in the two solvents.     

The infrared spectra of 12C32S, 12C34S, 13C32S,and 12C33S

Using a tunable diode laser spectrometer, the infrared absorption spectra of four isotopic species of carbon monosulfide have been observed in the positive column of a dc discharge of CS₂ and Ar. The wavenumbers of 115 vibration-rotation transitions between 1180.5 and 1266.1 cm^?1 have been measured. These lines were assigned to the 1-0, 2-1, 3-2, and 4-3 bands of ¹²C³²S, the 1-0 and 2-1 bands of ¹²C³⁴S and ¹³C³²S, and the 1-0 band of ¹²C³³S. These new data have been combined with the previous infrared and microwave results to determine Dunham coefficients (Y_ij), the Dunham potential expansion constants (a₀,a₁,a₂,a₃, and a₄), and the classical turning points by the RKR method.     

Normalization of the p-3H and n-3He tails of 4He and the 4He charge from factor

It is known that suitable Eckart parametrizations of the nucleon-trinucleo n overlap functions are able to reproduce the charge form factor of ⁴He. The extracted relative normalization constants of the asymptotic nucleon functions are C_n ≈ 4.1 and C_p ≈ 4.0.     

Effect of sodium citrate as complexing on electrochemical behavior and speciation diagrams of CoFeNiCu baths

In this study, the effects of addition of sodium citrate dosages and different pH levels on the electrochemical behavior of CoFeNiCu alloy baths (electrolytes containing metal ions) were investigated. Stability (Pourbiax) diagrams and also speciation diagrams of cobalt, iron, nickel and copper, in conventional and citrate-added CoFeNiCu bath, were calculated by ChemEQL V.3.0 software. Stability diagrams showed that addition of 20 g?L^?1 sodium citrate to the bath increased the pH of formed detrimental metal hydroxides (especially Fe(OH)₃ from pH 3.4 to pH?~?6.9) through forming stable complexed species that were more stable than metal hydroxides at low pH levels (< ~3). According to the speciation diagrams, both pH level and sodium citrate dosage had noticeable effect on the distribution of species in the baths. Generally, at low pH level and/or sodium citrate dosage, Co⁺⁺, Fe⁺⁺, Ni⁺⁺, and Cu⁺⁺ species were dominant. The concentration of complexed species of Co(C₆H₅O₇)^? ( at pH?>?~ 7.5 or sodium citrate dosage?>?~ 30 g?L^?1), Fe(C₆H₅O₇)^? (at pH?>?~ 5.5 or sodium citrate dosage?>?~ 25 g?L^?1), Ni(C₆H₅O₇)^? (at pH?>?~ 6 or sodium citrate dosage?>?~ 30 g?L^?1), and Cu(OHC₆H₅O₇)^2? ( at pH?>?~ 8 or sodium citrate dosage?>?~ 20 g?L^?1) became significant. The effects of sodium citrate and reverse potential (E _λ) on cyclic voltammetry curves were also studied. The addition of sodium citrate in the bath shifted the reduction potential of metals towards more negative potentials. Moreover, in order to deposit cobalt, iron, and nickel simultaneously with copper, it was necessary to increase E _λ value gradually with sodium citrate dosage; otherwise, only copper would have deposited from citrate-added CoFeNiCu bath. The study of speciation diagrams showed that reduction of metals from CoFeNiCu bath with natural pH (no acid or base is added to adjust pH and it was?~?5.2) and containing 20 g?L^?1 of sodium citrate mainly occurred directly from complexed species.     

13C MAS NMR investigations of alkali doped C60

Results of¹³C MAS NMR measurements of the Rb _x C₆₀ system (x=2.75, 3, 4, 6) and the A₆C₆₀ compounds (A=K, Rb, Cs) are presented. Special attention was paid to sample preparation in order to suppress effects of impurities and lattice defects due to imperfect C₆₀ starting material. The¹³C MAS NMR measurements of the Rb _x C₆₀ system demonstrate the usefulness of this method to reveal valuable information about its phase diagram. The existence of underdoped Rb₃C₆₀ is proved. Well resolved lines in all investigated A₆C₆₀ compounds confirm the orientational order of the C₆₀ ions. An assignment of the signals to the three magnetically inequivalent carbon atom positions in the crystal structure is proposed.     

Sensitive voltammetric determination of cysteamine using promazine hydrochloride as a mediator and modified multi-wall carbon nanotubes carbon paste electrodes

This paper presents a sensitive electrochemical method for the determination of cysteamine (CA) using promazine hydrochloride-modified multi-wall carbon nanotubes carbon paste electrode (PrH/MWCNTs CPE). Because of the good electrochemical activity of MWCNTs and the acceptable performance of promazine hydrochloride (PrH) as an electrocatalytic mediator, the modified electrode significantly enhanced the sensitivity for the detection of CA in comparison to the bare carbon paste electrode (CPE). All chemical parameters such as pH of solution, concentration of PrH and kinetic parameters of the system were investigated. Linear sweep voltammetric (LSV) method was used to follow the electrocatalytic effect of CA on the current–potential response of PrH. Under optimum conditions, the obtained net peak current ?I _p(I _sample???I _blank) was linear with CA concentrations in two dynamic ranges of 2.0–346.5 μmol l^?1 (?I _p?=?(0.0195?±?0.0043)C _CA?+?(0.7648?±?0.0397) (r ²?=?0.9948)) and 346.5–1,912.5 μmol l^?1 (?I _p?=?(0.0100?±?0.0026)C _CA?+?(3.8981?±?0.0828) (r ²?=?0.9911)) with a detection limit of 0.8 μmol l^?1. Finally, the PrH/MWCNTs CPE was successfully applied for the determination of CA in urine and drug samples with satisfactory results.     

Complete pentagon orientational ordering in C60 fullerite charged with NO

Solid C₆₀ was stored in NO under high pressure, and the gas molecules NO were found to diffuse into the octahedral interstitial sites in its fcc crystal lattice. Its ¹³C NMR MAS spectra are composed of a primary resonance at 143.7 ppm accompanied by two minor peaks shifted 0.4 and 0.8 ppm downfield, respectively. The dopant was found to depress its phase transition temperature at 260 K in pure C₆₀ and to substantially reduce the drop Δ?′ at the phase transition temperature. Furthermore, the spectral features associated with relaxation during glass transition at lower temperature, as observed in impedance spectra, were smeared. The fraction of P-orientation below T _c was calculated to be larger than 11/12. These results show that a completely P-oriented phase occurred in (NO)_0.1C₆₀ and that this phase is favored by a negative pressure on the C₆₀ lattice exerted by NO, as well as by the electrostatic interaction between the two.     

Electronic and geometric structure of acetylide carbon on the surface of lithium

The reaction products formed on clean evaporated lithium films exposed to acetylene gas under UHV conditions were examined with ultraviolet photoelectron and Auger electron spectroscopies. Good agreement was obtained between the observed ultraviolet photoelectron spectrum and a spectrum simulated from ab initio calculations for C₂Li₂ in D_2h symmetry. The components of the C(KW) Auger signal were also consistent with carbon being present as C₂^n? units (acetylide) rather than as carbonaceous aggregates or as monomeric carbon. The observed carbon AES structure was fit in good agreement by a simulation using experimental electronic binding energies and Auger transition intensities calculated for C₂Li₂. Saturation of the ultraviolet and Auger electron signals with increasing exposure to HC₂H was not found, although thin films of lithium were slowly consumed on long exposure to acetylene. A loss of the reaction product from the interfacial region was indicated. Cluster models of acetylide on the (100) face of lithium, C₂/Li₈(6, 2)-(100), were used to investigate geometric arrangement of C₂^n? relative to lithium. The results show that acetylide resident in the interface below the first layer of lithiums of the model was energetically favored compared to C₂^n? resident on top of the first layer of lithium. The stability of this conformation was calculated to be further increased by a small expansion of lithiums near neighbor to C₂Li₂. The restructuring calculated for the model complements the absent saturation and suggests that C₂^n? units diffuse into the actual film via a local expansion.     

A quantum-chemical study of intermediates of the 1O2 photogeneration sensitized by buckminsterfullerene and accompanying photochemical reactions

The intermediates of hypothetical photochemical reactions that accompany the quenching of the ³C ₆₀ ^* triplet state by triplet oxygen are studied by the (U)PBE0 quantum-chemical method. The diradical C₆₀-O-O formed from ³O₂ and photoexcited buckminsterfullerene ³C ₆₀ ^* is characterized by a negative binding energy ?1.11 eV (with respect to C₆₀ and ³O₂), the singlet-triplet splitting ΔE _ST of 0.07 eV, and the dipole moment of 3.2 D at the equilibrium internuclear separations 1.522 Å (CO) and 1.294 Å (OO). Its decay produces ¹O₂. The formation of a dioxetane circle lowers the energy by 0.8 eV. The ground-state energy of diketone C₅₈(C=O)₂ is 2.0 eV lower than the energy of C₆₀-O-O. The metastable centrosymmetric diradical C₆₀-C₆₀, formed upon ineffective light absorption by clusters (C₆₀)_N, has a single interpolyhedral C-C bond (1.657 Å). Its triplet state T ₁ lies 0.16 eV higher than the S ₁ singlet. The S ₁ → S ₀ relaxation leads to the formation of a stable C₆₀-C₆₀ dimer with a shorter (1.584 Å) bis-single exothermic (+0.24 eV) bond of polyhedra. The photoexcited C₆₀-C₆₀ dimer is able to form isomeric metastable diradicals C₆₀-C₆₀-O-O.     

The effect of gamma irradiation on electrical and dielectric properties of Al-TiW-Pd2Si/n-Si Schottky diode at room temperature

The effects of ⁶⁰Co (γ-ray) irradiation on the electrical and dielectric properties of Al-TiW-Pd₂Si/n-Si Schottky diodes (SDs) have been investigated by using capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements at room temperature and 500 KHz. The corrected capacitance and conductance values were obtained by eliminating the effect of series resistance (R_s) on the measured capacitance (C_m) and conductance (G_m) values. The high-low frequency capacitance (CHF-CLF) method given in [12] as N_ss = (1/qA) [((1/C_LF) − (1/C_ox))⁻¹ −  ((1/C_HF) − (1/C_ox))⁻¹] was successfully adapted to the before-after irradiation capacitance given in this report as N_ss = (1/qA) [((1/C_bef) − (1/C_ox))⁻¹ − ((1/C_after) − (1/C_ox))⁻¹] for the analyzing the density of interface states. The N_ss-V plots give a distinct peak corresponding to localized interface states regions at metal and semiconductor interface. The experimental values of the ac electrical conductivity (σ_ac), the real (M′) and imaginary (M″) parts of the electrical modulus were found to be strong functions of radiation and applied bias voltage, especially in the depletion and accumulation regions. The changes in the dielectric properties in the depletion and accumulation regions stem especially from the restructuring and reordering of the charges at interface states and surface polarization whereas those in the accumulation region are caused by series resistance effect.     

Low temperature heat capacities and thermal properties of DyAl2, ErAl2 and LuAl2

The heat capacities of the compounds DyAl₂, ErAl₂ and LuAl₂ were measured in an adiabatic calorimeter from approximately 5 to 300 K. The compounds DyAl₂ and ErAl₂ show C_P anomalies at 58.0 and 10.2 K, respectively, which are attributed to the destruction of magnetic order. In order to separate the crystal field and magnetic contributions from the measured heat capacities, it was necessary to evaluate the lattice heat capacity. The lattice term, C_L was obtained from the C_P data of LuAl₂ by a method of interpolation which gave values of C_L for an arbitrary R Al₂ compound. Using this “interpolated lattice blank”, excess entropies associated with the crystal field and magnetic terms were computed throughout the series. These values are quite close to R In (2J + 1). The results also indicate that, for the compounds studied, the degeneracy of the lowest ground state is completely lifted. In addition, the magnetic contribution to the heat capacity of the magnetically ordered R A1₂ phases was found to exhibit an exponential dependence below the temperature corresponding to the spin wave energy gap and a T^{$\text{3}\text{2}$} dependence above this temperature.Detailed calculations were performed to characterize the influence of cubic crystal field in ErAl₂ on the ⁴I_{$\text{15}\text{2}$} ground state multiplet of the Er³⁺ ion. It is concluded that the magnetic ordering in ErAl₂ takes place within the Γ₈³ quartet state. Smoothed values of heat capacity, entropy and related thermodynamic functions are tabulated.     

The12 C+12 C →8 Be gs+16 O gs reaction atE cm=27 to 36 MeV

The¹² C+¹² C→⁸ Be _gs+¹⁶ O _gs reaction has been experimentally investigated at c.m. energies between 27 and 36 MeV. A resonance is present at 32.5 MeV,i.e. at the same energy of the resonance previously observed [1] in the¹² C(0 ₂ ⁺ )+¹² C(0 ₂ ⁺ ) exit channel, but its width is about three times narrower. Moreover the data indicate an enhancement of the cross section at a c.m. energy close to 29 MeV. These results are discussed and compared to the predictions of the Band Crossing Model obtained for different exit channels of the¹² C+¹² C reaction.     

Heterodyne measurements of 12C18O, 13C16O,and 13C18 O laser frequencies; mass dependence of Dunham coefficients

Difference frequencies between rare isotope CO lasers and a ¹²C¹⁶O laser have been measured by optical heterodyne techniques. These data for ¹²C¹⁸O, ¹³C¹⁶O, and ¹³C¹⁸O have been used together with the 15 previously reported Dunham coefficients Y_kl for ¹²C¹⁶O to determine a set of mass independent parameters Δ_kl and U_kl defined by Y_kl = μ^-(k/2+l)[1+m_e(Δ^C_kl/M_C + Δ^O_kl/M_O)] U_kl. The 01, 1 0, and 20 correction terms were found to be statistically significant. Line frequencies calculated from the resulting 15 Dunham coefficients for the rare isotopes are accurate to a few MHz in the measured laser bands.     

QCD analysis of the Bjorken sum rule revisited

We present extended analysis of the polarized Bjorken sum rule using the four-loop expression for the coefficient function C _Bj(α_s) available now and the recent low Q ²-data from the Jefferson Lab and COMPASS experiments. We demonstrate that the perturbative series for the function C _Bj gives a hint to its asymptotic nature manifesting itself in the region Q ² ? 1 GeV². It is confirmed by the considered integral model for the perturbative QCD correction. We analyze values of higher-twist terms extracted from the mentioned data and discuss the interplay between higher orders perturbative and higher-twist contributions. We extend our consideration to the Gross-Llewellyn Smith sum rule and investigate the relation between higher twist coefficients in these two sum rules.     

Microwave spectra of the ground vibrational state of formaldehyde substituted with 17O and 18O

Pure rotational transitions in the ground vibrational state have been measured for H₂¹²C¹⁸O, H₂¹²C¹⁷O, H₂¹³C¹⁸O, and H₂¹³C¹⁷O in the frequency region 8–75 GHz. These have included both Q- and R-branch transitions, and have permitted accurate evaluation of rotational constants and several quartic centrifugal distortion constants for each species. These in turn have permitted the prediction of several transitions of possible use in radioastronomy.     

Study of alkyl chain length dependent characteristics of imidazolium based ionic liquids [CnMIM]+[TFSA]− by Brillouin and dielectric loss spectroscopy

This study examined the acoustic phonon mode of ionic liquids consisting of 1-alkyl-3-methyl-imidazolium family (C_nMIM) cations with n values ranging from 2 to 10 and bis(trifluoromethylsulfonyl)amide (TFSA) anion in the temperature range from 300 K to 100 K. [C_nMIM]⁺[TFSA]^? showed depolarized (VH) components of Brillouin peaks at temperatures below the glass transition temperature when n is larger than 4. On the other hand, in the case of ionic liquids with different anions, such as [C₄MIM]⁺[BF₄]^?, [C₄MIM]⁺[PF₆]^? and [C₈MIM]⁺[BF₄]^?, the VH component of Brillouin peaks was not observed in the temperature range investigated. The dielectric loss spectra showed that the temperature dependence of alkyl chain domain relaxation of all ionic liquids followed the Arrhenius law and showed an increase in activation energy at the temperature where the VH component of Brillouin peak appeared. These results suggest that the observed depolarized component of Brillouin peak might originate from uniquely induced polarization in the 2nd domain composed of head groups of cations and anions.     

The elastic constants for single-crystal bismuth and tin from room temperature to the melting point

The six adiabatic elastic stiffness constants of bismuth and tin have been determined over a range of temperatures extending from room temperature to the melting point. These constants were computed from measurements of the ultrasonic wave velocity in high-purity, single crystal specimens. The constants for bismuth at the melting point are C₁₁ = 56·l C₁₃ = 24·2 C₁₄ = 60 C₃₃ = 34·9 C₄₄ = 90 C₆₆= 16·1 in units of 10¹⁰ dynes/cm². The constants for tin at the melting point (in the same units) are C₁₁ = 61·3 C₁₂ = 38·5 C₁₃ = 38·0 C₃₃ = 75·6 C₄₄ = 16·9 C₆₆ = 19·0.     

Coherent-anomaly method in self-avoiding walk problems

Self-avoiding walk (SAW), being a nonequilibrium cooperative phenomenon, is investigated with a finite-order-restricted-walk (finite-ORW or FORW) coherent-anomaly method (CAM). The coefficient β_1r in the asymptotic form C_nr≅ β_1r λⁿ_1r for the total number C_nr of r- ORW's with respect to the step number n is investigated for the first time. An asymptotic form for SAW's is thus obtained form the series of FORW approximants, C_nr≅ br^gμⁿ(1 + a/r)ⁿ, as the envelope curve C_n≅b(ae/g)^gμⁿn^g. Numerical results are given by C_n≅1.424n^0.27884.1507ⁿ and C_n≅1.179n^0.158710.005ⁿ for the plane triangular lattice and f.c.c. lattice, respectively. A good coincidence of the total numbers estimated from the above simple formulae with exact enumerations for finite-step SAW's implies that the essential nature of SAW (non-Markov process) can be understood from FORW (Markov process) in the CAM framework.