Determination of Melatonin Hormone and Neurotransmitters in Cerebrospinal Fluid: Method Validation and Uncertainty Calculations

The uncertainty of measurement for well-known neurotransmitters like serotonin, noradrenalin and gamma-aminobutyric acid (GABA), glutamate and melatonin hormone with high performance liquid chromatography?fluorescence detection was calculated after the method validation. Two methods were developed for the determination of the neurotransmitters. A derivatization step was performed for the determination of GABA and glutamate. Sensitivity, method detection limit, limit of quantification, linearity, recovery, interday and intraday precision values were calculated. Low detection limit values were obtained especially for the determination of GABA and glutamate. Then, bottom-up approach was used to calculate measurement uncertainty. The critical stages of the method were evaluated. The major sources of the uncertainty budget were calibration curves, stock solution and recovery. The calculated percentage relative uncertainty values for the compounds changed between 10.1 and 16.7.     

Photoluminescence and Magnetism Study of Blue Light Emitting the Oxygen-Bridged Open-Cubane Cobalt(II) Cluster

A new cubane-based cobalt(II) cluster, [Co₄L₄] (1), where H₂L?=?2-((E)-(2-hydroxyethylimino) methyl)-4-chlorophenol has been prepared using a solvothermal process and characterized by structural, optical and magnetism. The crystal structure of 1 consists of a tetranuclear Co₄O₄ core in an open-cubane framework. Each cobalt(II) ion is penta-coordinated in a distorted square pyramidal geometry (τ_Co1=Co1i?=?0.030, τ_Co2=Co2i?=?0.023). Furthermore, the photoluminescence analysis indicates that 1 has a strong blue emission which should be attributed to coordination of the metal to the ligand. The temperature dependence of the magnetic susceptibilities of 1 shows antiferromagnetic coupling (J?=???26.61?±?0.01) between cobalt(II) ions.     

Use of Sulfonates as Desorption Agents for Phosphopeptide Elution from an Anion-exchange Material

In general, phosphopeptides are specifically adsorbed to the surface of the material at the initial step of phosphopeptide enrichment methods. Thus, nonphosphopeptides can be removed from the media by following the appropriate washing steps. After sufficient washing, the phosphopeptides are eluted from the surface of the material completely for further analysis. Performing the elution of phosphopeptides fully in the enrichment step is very important in terms of determining the whole phosphoproteome profile of a sample by subsequent mass spectrometric analysis. Materials containing anion exchanger groups such as amines on the surface can be used as a selective stationary phase in phosphopeptide enrichment methods. Positively charged groups on the surface of this type of material interact with the phosphate groups of phosphopeptides through electrostatic interactions. Such interactions can be basically manipulated by changing the pH of the medium or replacing the salts present in the solution. Phosphopeptides attached to the surface of anion-exchange materials may be displaced with the addition of highly acidic compounds such as sulfonates to the enrichment medium. Here, we used various sulfonates as desorption agents for the elution of retained phosphopeptides from the surface of an anion-exchange material. We found that differences in the chemical structures and properties of the sulfonates remarkably affected phosphopeptide retrieval from the anion-exchange material.     

Preparation and Characterization of Small Pore Carbon Molecular Sieves by Chemical Vapor Deposition of Pistachio Shells

Low-cost pistachio shells were used for the production of small pore carbon molecular sieves by the benzene deposition method. The prepared materials were characterized by the Brunauer–Emmett–Teller surface area and scanning electron microscopy. The deposition temperature and the deposition time parameters, which affect the formation of carbon molecular sieves, were examined. The effect of deposition temperature was examined in the range of 700–900°C, while deposition time was examined between 30 and 60?min. The optimum surface area of the carbon molecular sieve prepared by benzene deposition was 895?m²/g at 800°C. The average pore diameter of the carbon molecular sieve was 0.27?nm, principally denoted ultramicropore characteristics. The obtained values of the pore size distributions of the prepared carbon molecular sieves were in the range of 0.26–0.29?nm.     

Crystal structures of mixed ligand complexes containing saccharinate and nicotinamide: [Cu(saccharinato)2 (nicotinamide) (H2O)]⋅(H2O) and [M(nicotinamide)2 (H2O)4]⋅(saccharinate)2 (M = Ni2+, Co2+)

[M(saccharinato)₂(H₂O)₄] (M = Cu²⁺, Ni²⁺, Co²⁺) react with nicotinamide to form mixed ligand complexes, [Cu(saccharinato)₂(nicotinamide)(H₂O)](H₂O) (1) and [M(nicotinamide)₂(H₂O)₄](saccharinate)₂ (2: M = Ni²⁺; 3: M = Co²⁺), and their crystal structures have been determined by X-ray diffraction. In 1, the Cu²⁺ atom in an octahedral configuration is coordinated by two monodentate saccharinato ligands in the trans arrangement through the deprotonated ring nitrogens, by two bidentate nicotinamide ligands, one through the pyridyl ring nitrogen and the other through the amide oxygen, and by a water molecule, thus forming a nicotinamide-bridged one-dimensional extended structure. In the isomorphous complexes 2 and 3, the octahedral metal atom, which rides on a crystallographic center of symmetry, is coordinated by two monodentate nicotinamide ligands through the ring nitrogens and four water molecules to form a discrete [M(nicotinamide)₂(H₂O)₄]^{2 +} structural unit, which captures up and down two saccharinate ions, each through three hydrogen bonds: two hydrogen bonds between two water ligands and the ring N and the carbonyl O atoms and one between the amide N of the nicotinamide ligand and the carbonyl O.     

Stability analysis of time-fractional differential equations with initial data

In this work, we investigate the stability of solution for a class of time-fractional differential equation with initial data by the help of a fractional Duhamel principle; we use it and the superposition principle to obtain the solution of our problem. We present some theoretical results by some scientific theorems and lemmas.     

Frequency dependent conductivity in As2Se3 and As2Se3 + 15% Sb

Dc and ac measurements were performed on bulk samples of undoped and 15% Sb doped As₂Se₃ as a function of temperature (90–400 K) and frequency (10³–10⁶ Hz). The dc results show an activated conductivity dependence on temperature with an activation energy of 0.8 eV above room temperature. The ac results give a temperature dependent frequency exponent s. The temperature dependence of G _ac is discussed in terms of the mechanisms involved. Results are compared with the predictions of the Quantum Mechanical Tunnelling and Correlated Barrier Hopping models. It is found that doping increases the dc conductivity but has no effect on the ac conductivity.     

Phase shift analysis of modulated photocurrent: A new approach to determining the energy scale

One of the major problems of the method of phase shift analysis of modulated photocurrent for studying the density of states in the energy gap of amorphous semiconductors has been the determination of the energy scale corresponding to this DOS profile. This study presents a new way of dealing with this problem. This new method is especially useful in the case where the DOS profile lacks a characteristic peak. A computer analysis is used to confirm the validity of this method and to demonstrate how it can be used.     

Sensitivity analysis of the modulated photocurrent method

This study presents a simulation that is used to determine the sensitivity of the phase shift analysis of the modulated photocurrent method to the differences in the fine scale structures in the density of states (DOS) distributions. Four DOS distributions are considered and the expected data are obtained. The results show that the modulated photocurrent method is very sensitive to such fine features in the DOS distributions. A comparison is also made with the sensitivity of other techniques commonly used in the determination of the DOS profiles.