PHA-L lectin and carbohydrate relationship: conjugation with CdSe/CdS nanoparticles, radiolabeling and in vitro affinities on MCF-7 cells

This research aims to investigate the interaction between phytohemagglutinin-L (PHA-L) and sialic acid, which is abundant on the breast cancer cell (MCF-7) surface and displays monosaccharide characteristics, by experimental and computational methods. Experimentally, CdSe/CdS nanoparticles (QDs) were synthesized; PHA-L was conjugated with QDs and labeled with ¹²⁵I. Radiolabeling yield was found to be 97 ± 1.2 %. Afterwards, in vitro bioaffinities of radiolabeled PHA-L conjugated QDs have been investigated on MCF-7 cells and it has been observed that the cell incorporation increased with time. The results indicated that ¹²⁵I labeled QD-PHA-L conjugates represent significant affinity on MCF-7 cells. In the second step of the study, the crystal structure of carbohydrate interaction surface of PHA-L was extracted from the crystal structure of PHA-L. The interactions between this surface and sialic acid were calculated by computational tools. These calculations revealed specific interactions between PHA-L and sialic acid. Semi-empirical methods, PM3 and AM1, were used in these calculations. Significant outcomes have been obtained from the experimental and computational studies and these results demonstrated that PHA-L may be an effective agent for imagining MCF-7 cells.     

A Novel pH/Light‐Triggered Surface for DNA Adsorption and Release

A simple strategy for the immobilization of Cy3‐labeled single strand DNA (Cy3‐ssDNA) on a Si(001) surface and its release under control of both light and pH stimuli is presented. In order to prepare a dual pH/light‐triggered surface, positively chargeable azobenzene molecules are self‐assembled on the Si(001) surface. The surface wettability of this substrate can be changed under influence of both light and pH conditions. The substrates can be positively charged under mildly acidic conditions. The pH‐sensitive behavior of the film allows binding of Cy3‐ssDNA on the functionalized Si(001) surface through e?ective electrostatic interactions with the negatively charged polynucleotide backbone. Moreover, irradiation of the film with UVA light induces trans–cis isomerization of the azobenzene units on the surface. As a result, the binding a?nity for DNA decreases due to the changing surface hydrophilicity. In order to understand and control the reversible photoswitchable mechanism of this surface, water contact angles are measured after UVA and visible light irradiation. The release of DNA from a dual pH/light‐sensitive sample is performed using fluorescence microscopy. The results show that irradiation of the film with UVA light induces trans–cis isomerization of the photoresponsive azobenzene units; this leads to significant changes in the surface hydrophilicity and reduces the binding affinity for DNA.     

Light harvesting and efficient energy transfer in a boron-dipyrrin (BODIPY) functionalized perylenediimide derivative

[reaction: see text] Click chemistry has been successfully applied in the synthesis of a bay region tetraboron-dipyrrin (BODIPY) appended perylenediimide (PDI). This light-harvesting molecule presents a large cross section for the absorption of light in the visible region. Excitation energy is efficiently channeled to the perylenediimide core. This novel antenna system is the first demonstration of the efficiency of energy transfer in a BODIPY-PDI bichromophoric system and appears to be highly promising for the design and synthesis of similar dendritic structures.     

Establishment of a quality system for nuclear analytical laboratories

Comprehensive Quality Control (QC) and Quality Assurance (QA) Program is stated on the quality policy, organization, methods and records for nuclear analytical laboratories which are necessary for improvement of productivity, to upgrade the performance, credibility and reputation. The proper and complete identification of quality elements for management and technical requirements are being written in Quality Manual as well as analytical and organizational procedures and working instructions according to ISO 17025 standard. Technical ability of gamma, X-ray and a/b laboratories in the Center has been checked by participation in proficiency test, critical technical variables, and quality results. Performance of quality system has been controlled by external audit inspection, progress reports and service to clients. The present study is a framework of the model project of IAEA, coded RER/2/004, which has resulted self-sustainable accreditation from the national body, TURKAK. This revised version was published online in August 2006 with corrections to the Cover Date.     

Surface-induced self-assembly of dipeptides onto nanotextured surfaces

There is an increasing interest for the utilization of biomolecules for fabricating novel nanostructures due to their ability for specific molecular recognition, biocompatibility, and ease of availability. Among these molecules, diphenylalanine (Phe-Phe) dipeptide is considered as one of the simplest molecules that can generate a family of self-assembly based nanostructures. The properties of the substrate surface, on which the self-assembly process of these peptides occurs, play a critical role. Herein, we demonstrated the influence of surface texture and functionality on the self-assembly of Phe-Phe dipeptides using smooth silicon surfaces, anodized aluminum oxide (AAO) membranes, and poly(chloro-p-xylylene) (PPX) films having columnar and helical morphologies. We found that helical PPX films, AAO, and silicon surfaces induce similar self-assembly processes and the surface hydrophobicity has a direct influence for the final dipeptide structure whether being in an aggregated tubular form or creating a thin film that covers the substrate surface. Moreover, the dye staining data indicates that the surface charge properties and hence the mechanism of the self-assembly process are different for tubular structures as opposed to the peptidic film. We believe that our results may contribute to the control of surface-induced self-assembly of peptide molecules and this control can potentially allow the fabrication of novel peptide based materials with desired morphologies and unique functionalities for different technological applications.     

Responsive microgrooves for the formation of harvestable tissue constructs

Given its biocompatibility, elasticity, and gas permeability, poly(dimethylsiloxane) (PDMS) is widely used to fabricate microgrooves and microfluidic devices for three-dimensional (3D) cell culture studies. However, conformal coating of complex PDMS devices prepared by standard microfabrication techniques with desired chemical functionality is challenging. This study describes the conformal coating of PDMS microgrooves with poly(N-isopropylacrylamide) (PNIPAAm) by using initiated chemical vapor deposition (iCVD). These microgrooves guided the formation of tissue constructs from NIH-3T3 fibroblasts that could be retrieved by the temperature-dependent swelling property and hydrophilicity change of the PNIPAAm. The thickness of swollen PNIPAAm films at 24 °C was approximately 3 times greater than at 37 °C. Furthermore, PNIPAAm-coated microgroove surfaces exhibit increased hydrophilicity at 24 °C (contact angle θ = 30° ± 2) compared to 37 °C (θ = 50° ± 1). Thus PNIPAAm film on the microgrooves exhibits responsive swelling with higher hydrophilicity at room temperature, which could be used to retrieve tissue constructs. The resulting tissue constructs were the same size as the grooves and could be used as modules in tissue fabrication. Given its ability to form and retrieve cell aggregates and its integration with standard microfabrication, PNIPAAm-coated PDMS templates may become useful for 3D cell culture applications in tissue engineering and drug discovery.     

Stabilization ofEscherichia coli penicillin G acylase by polyethylene glycols against thermal inactivation

The effects of five polyethylene glycol (PEG) compounds of different molecular weight on the thermal stability of penicillin G acylase (PGA) obtained from a mutant ofEscherichia coli ATCC 11105 have been investigated. The molecular weights of PEG compounds were 400, 4000, 6000, 10,000, and 15,000. The thermal inactivation mechanisms of both native and PEG-containing PGA were considered to obey first order inactivation kinetics during prolonged heat treatments. Optimal concentrations of PEGs at molecular weights of 400,4000, 6000,10,000, and 15,000 were found to be 250,150,150,100, and 50 mM, respectively. The greatest enhancement of thermostability was observed with PEG 4000 and PEG 6000, as a nearly 20-fold increase above 50°C. PGA showed almost the same temperature activity profile and optimal temperature values both in the presence and absence of PEG. The addition of PEGs did not cause any change in the optimal temperature value of PGA, but the parametersV _m ,K _m , the activation energy, and thek _cat values of enzyme were markedly decreased because of the mixed inhibition by PEG compounds. The type of inhibition was found to be hyperbolic uncompetitive.     

Measurement of absolute intensity of 1001 keV gamma-ray of 234mPa

The sorption behavior of ²³⁵U fission fission products ⁹⁹Mo and ¹³²Te was studied through batch and dynamic experiments when they were dissolved in 1 to 7M HNO₃ solutions. It was found that ⁹⁹Mo is always totally adsorbed on hydrated SnO₂, while ¹³²Te is rather weakly adsorbed, therefore they can be separated from each other although ¹³²Te in the solution still remains contaminated with other radionuclides as well as ⁹⁹Mo does in the solid.