Theoretical study of hydrazine adsorption on Pt(111): Anti or cis?

Hydrazine (N₂H₄) adsorption on metal surface is important due to its application in the direct hydrazine fuel cell technology. First principles DFT calculations have been carried out to understand the structure and mechanism of hydrazine adsorption on Pt(111). Calculations revealed that configuration with hydrazine adsorbed on its anti-conformation yields the largest adsorption energy suggesting it to be the most stable structure on Pt(111). This result was found to be in disagreement with available XPS results which favor the adsorption on cis-conformation as the most stable configuration. However, by taking into account the energy cost for orbital re-hybridization and internal rotation involves in the adsorption, it was found that the interaction strength between adsorbate and substrate is comparably equal for adsorption on both anti and cis-conformations that indicates the feasibility of the adsorption in cis-conformation to occur. Charge transfers from lone-pair orbitals belong to the highest occupied molecular orbital (HOMO) and second highest occupied molecular orbital (S-HOMO) were found to be important in the formation of the bonding. The π-anti-bonding HOMO lone-pair transfers its charge to the surface which stabilizes the internal structure of the molecule and responsible for the stable anti-conformation adsorption structure. The interaction of the π-bonding S-HOMO lone pair with the surface was found to be dative type and plays an important role in the stabilization of cis-conformation adsorption structure.     

Synthesis of Cysteine Modified MoS2 Nanocomposite: A Biocompatible Electrochemical Sensor Material and its Application to the Determination of Antidiabetic Dapagliflozin

Herein, for the first time, a new generation cysteine modified MoS₂ (Cys@MoS₂) based electrochemical sensor was reported. The electrochemical behaviour of dapagliflozin (DAP) was investigated through differential pulse voltammetry (DPV) on the developed sensor (Cys@MoS₂/GCE). The transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR), x‐ray diffraction spectroscopy (XRD) and x‐ray photoelectron spectroscopy (XPS) methods were performed for structural and morphological characterizations of Cys@MoS₂ nanocomposite. On the surface of Cys@MoS₂/GCE, an irreversible anodic peak was observed at 1324 mV. Under the optimal conditions, linear calibration curve with two working ranges between 2.0–60.0 μM and 60.0–110.0 μM were obtained and limit of detection was found to be 1.6 μM. The developed sensor was successfully applied to determine the content of DAP in pharmaceutical sample with satisfying recovery results. It is concluded that Cys@MoS₂/GCE is a reliable, easy to apply and cost‐effective sensor for the routine DAP analysis in pharmaceutical samples.     

Evaluating students’ conceptual and procedural understanding of sampling distributions

Introductory statistics courses, which are important in preparing students for their daily lives, generally derive inferential statistics from informal knowledge. In this transition process, sampling distributions have an important place, yet research has shown that students often have difficulties with this concept. In order to increase their understanding of sampling distributions, students should have a strong conceptual foundation that is balanced with procedural knowledge. To address this issue, this study was designed to examine the relationship between college students’ procedural and conceptual knowledge of sampling distributions. With this aim in mind, an achievement test consisting of two sections – procedural and conceptual knowledge – was prepared. In answering the questions related to procedural knowledge, the participants were more successful in identifying the relationship between standard deviation of a population and sample means. However, they lacked theoretical knowledge about statements that they had heard or knew intuitively. Simulation activities provided in statistics courses may support students in developing their conceptual understanding in this regard.     

Zur quantitativen Bestimmung des Isopropylalkohols

Ohne Zusammenfassung     

A bio-imprinted urease biosensor: Improved thermal and operational stabilities

Despite the increasing number of applications of biosensors in many fields, the construction of a steady biosensor remains still challenging. The high stability of molecularly bio-imprinted enzymes for its substrate can make them ideal alternatives as recognition elements for sensors. Urease (urea aminohydrolase, EC 3.5.1.5), which catalysis the hydrolysis of urea to ammonia and carbon dioxide, has been used in immobilized form in artificial kidney for blood detoxification. According to one report approximately half a million patients worldwide are being supported by haemodialysis. In this study, the enzyme of urease was first complexed by using a substrate analogue, thiourea, in aqueous medium and then this enzyme was immobilized on gelatin by crosslinking with glutaraldehyde on a glass electrode surface. Similarly, urease noncomplexed with thiourea was also immobilized on a glass electrode in the same conditions. The aim of the study was to compare the two biosensors in terms of their repeatability, pH stability and thermal stability, and also, linear ranges of two biosensors were compared with each other.     

Effect of the presence of strong and weak electrolytes on the existence of uniaxial and biaxial nematic phases in lyotropic mixtures

The lyotropic mixture of potassium laurate/decanol/water presenting only the uniaxial nematic calamitic phase was doped with one strong (potassium chloride, KCl) and 11 weak electrolytes with phenyl-rings (DL-mandelic acid, benzoic acid, DL-phenyllactic acid, phenylacetic acid, phenol and phenylmethanol) and with cyclohexyl-ring (RS-hexahydromandelic acid, cyclohexanecarboxylic acid, cyclohexaneacetic acid, cyclohexanol and cyclohexylmethanol), separately. We also chose two nonpolar dopant molecules, benzene and cyclohexane, for the comparison of them with weak electrolytes, since they are located in the hydrocarbon core of the micelle. The nematic phase sequences, in particular the presence of the biaxial nematic phase, were investigated as a function of the dopant molar concentration and temperature. The laser conoscopy and small-angle X-ray scattering techniques were used to characterise the different nematic phases. Weak electrolytes having –COOH group as polar part were found to be very effective in stabilising the three nematic phases (two uniaxial and a biaxial). Guest molecules with only the –OH group did not show any effect on the stabilisation of other nematic phases. The experimental results are interpreted considering the screening effect of the hydrophilic parts of the dopants on the repulsion between the polar heads of the main amphiphilic molecules at micelle surfaces. This process favours the increase of the more flat micellar surfaces of micelles, which triggers the orientational fluctuations responsible for the biaxial and discotic nematic phases.     

Problem types used in math lessons: the relationship between student achievement and teacher preferences

The purpose of this study was to determine the relationship between the problems teachers preferred in mathematics lessons and student achievement in different types of problems. In accordance with this purpose, nine mathematics teachers were interviewed, and corresponding problems were prepared and administered to 225 eighth-grade students. The findings indicate that problem types are dependent on teacher preferences. It was found that curriculum-dependent and routine problems were dominant for teacher preferences. Students are more successful at with missing data, problems that are visual and do not require the use of different strategies. They have lower success at long problems, those that contain irrelevant data, problems that require the use of different strategies and difficult problem types. It was found that problem types at which students were successful and which teachers preferred were related. These results relay information about problems used in the learning environment and effect of problem-solving experiences on students' success.     

Fabrication of Electrochemical Immunosensor for Detection of Interleukin 8 Biomarker via Layer-by-layer Self-assembly Process on Cost-effective Fluorine Tin Oxide Electrode

A highly sensitive impedimetric immunosensor for the determination of interleukin 8 (IL 8) cancer biomarker was fabricated via simple fabrication process. A silane agent with isocyanate groups, 3-(triethoxysilyl)propyl isocyanate (IPTES), were utilized for binding of IL 8 antigen specific antibodies and self-assembled on the fluorine tin oxide (FTO) substrate with a standard silanization chemistry. Under optimum experimental conditions, the designed immunosensor had a wide linear detection range of 0.02–4 pg/mL, a low limit of detection of 11.9 fg/mL and a high sensitivity of 4.42 kΩ pg⁻¹ mL cm⁻². The designed biosensor displayed high reproducibility and repeatability, good selectivity against interference biomarkers.     

A mathematical model for personalized advertisement in virtual reality environments

We consider a personalized advertisement assignment problem faced by the manager of a virtual reality environment. In this online environment, users log in/out, and they spend time in different virtual locations while they are online. Every time a user visits a new virtual location, the site manager can show the ad of an advertiser. At the end of a fixed time horizon, the manager collects revenues from all of the advertisers, and the total revenue depends on the number of ads of different advertisers she displays to different users. In this setup, the objective of the manager is to find an optimal dynamic ad display policy in order to maximize her expected revenue. In the current paper, we formulate this problem as a continuous time stochastic optimization problem in which the actions of users are represented with two-state Markov processes and the manager makes display decisions at the transition times of these processes. To our best knowledge, no formal stochastic model and rigorous analysis has been given for this practical problem. Such a model and its analysis are the major contributions of this paper along with an optimal solution.     

Molecularly imprinted cryogel as a pH-responsive delivery system for doxorubicin

In this study, implantable and degradable molecularly imprinted cryogel was prepared for pH-responsive delivery of doxorubicin. Cryogel discs were synthesized using amino acid-based functional monomer with HEMA and gelatin. The molecularly imprinted discs were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, degradation and swelling tests. In vitro delivery experiments were carried out in order to examine the effects of medium pH and drug content. The degree of degradation of composite cryogels was found to be 83.45±1.86% after 56 days. The release profiles of DOX from molecularly imprinted cryogel discs exhibit a biphasic delivery. It was observed that an initial burst release step from 0 to 12 h was followed by a slower and sustained release. Release rate of DOX from cryogel discs increased in more acidic conditions. Kinetic studies showed that a combination of diffusion and erosion control is mainly responsible from the general release behaviors of molecularly imprinted cryogel discs.