Studies on some experimental parameters of radiometric flow injection analysis (RFIA) using137Cs and60Co

A simple radiometric flow injection analyzer with NaI(Tl) detector was used for the study of some experimental parameters of¹³⁷Cs and⁶⁰Co determination. A sample transfer system was developed employing both merging zone and sample injection principle.     

Simultaneous determination of60Co,131I and137Cs in model radioactive waste water by reverse radiometric flow injection analysis with the aid of a multichannel analyzer

Reverse radiometric flow injection analysis was used for the simultaneous determination of⁶⁰Co,¹³¹I and¹³⁷Cs in model radioactive waste water. A NaI (Tl) scintillation detector coupled to a Canberra MCA was used for measuring the activity of¹³⁷Cs at 662 keV,⁶⁰Co at 1173 keV and 1332 keV, and¹³¹I at 364 keV.     

Lens alpha-crystallin and hypericin: a photophysical mechanism explains observed lens

Determining whether alpha-crystallin (the major lens protein) affects the photophysics of hypericin, a photosensitizing agent found in various plants, such as St. John's Wort, is important. Hypericin shows promise in cancer and human immunodeficiency virus therapy but may harm individuals taking St. John's Wort extracts (for mild to moderate depression). Hypericin causes hypericism, which is characterized by cellular damage in light-exposed areas. Ocular tissues are at risk for photosensitized damage; thus, we investigated the effects on hypericin photophysics by alpha-crystallin. We measured the transient absorption spectra and the 1270 nm luminescence of singlet (1Deltag) oxygen produced from hypericin in the presence of alpha-crystallin. alpha-Crystallin complexes hypericin, extending the lifetime of its triplet excited state; the Stern-Volmer slope is negative, but not linear, after a saturation curve. Damage to the lens protein by hypericin is known to occur via singlet oxygen, which oxidizes methionine, tryptophan and histidine residues. Binding to alpha-crystallin does not inhibit singlet oxygen formation by hypericin. alpha-Crystallin reacts with singlet oxygen with a rate constant of 1.3 x 10(8) M(-1) s(-1). Thus, we anticipate that hypericin will be an effective photosensitizer in the lens.     

Light-Responsive Hexagonal Assemblies of Triangular Azo Dyes

The rational design of small building block molecules and understanding their molecular assemblies are of fundamental importance in creating new stimuli-responsive organic architectures with desired shapes and functions. Based on the experimental results of light-induced conformational changes of four types of triangular azo dyes with different terminal functional groups, as well as absorption and fluorescence characteristics associated with their molecular assemblies, we report that aggregation-active emission enhancement (AIEE)-active compound (1) substituted with sterically crowded tert-butyl (t-Bu) groups showed approximately 35% light-induced molecular switching and had a strong tendency to assemble into highly stable hexagonal structures with AIEE characteristics. Their sizes were regulated from nanometer-scale hexagonal rods to micrometer-scale sticks depending on the concentration. This is in contrast to other triangular compounds with bromo (Br) and triphenylamine (TPA) substituents, which exhibited no photoisomerization and tended to form flexible fibrous structures. Moreover, non-contact exposure of the fluorescent hexagonal nanorods to ultraviolet (UV) light led to a dramatic hexagonal-to-amorphous structure transition. The resulting remarkable variations, such as in the contrast of microscopic images and fluorescence characteristics, were confirmed by various microscopic and spectroscopic measurements.     

Modeling and simulation of chemo-electro-mechanical behavior of pH-electric-sensitive hydrogel

A chemo-electro-mechanical multi-field model, termed the multi-effect-coupling pH-electric-stimuli (MECpHe) model, has been developed to simulate the response behavior of smart hydrogels subject to pH and electric voltage coupled stimuli when the hydrogels are immersed in a pH buffer solution subject to an externally applied electric field. The MECpHe model developed considers multiphysics effects and formulates the fixed charge density with the coupled buffer solution pH and electric voltage effects, expressed by a set of nonlinear partial differential governing equations. The model can be used to predict the hydrogel displacement and the distributive profiles of the concentrations of diffusive ionic species and the electric potential and the fixed charge density in both the hydrogels and surrounding solution. After validation of the model by comparison of current numerical results with experiment data extracted from the literature, one-dimensional steady-state simulations were carried out for equilibrium of the smart hydrogels subject to pH and electric coupled stimuli. The effects of several important physical conditions, including the externally applied electric voltage, on the distributions of the concentrations of diffusive ionic species, the electric potential, the fixed charge density, and the displacement of the hydrogel strip were studied in detail. The effects of the ionic strength on the bending deformation of the hydrogels under the solution pH and electric voltage coupled stimuli are also discussed.     

Peptide mimotopes of phomopsins: Identification, characterization and application in an immunoassay

Peptide mimotopes of plant-associated toxins offer the potential for improving analytical and diagnostic methodologies as well as providing candidates for potential protective vaccines against plant poisoning diseases. Monoclonal antibody (mAb) C₃C₁₁, which recognizes the antimicrotubule phomopsin mycotoxins, was used to isolate peptide mimics of phomopsin A from a random 15-mer phage display peptide library. A total of 46 clones were isolated that showed specific reactivity with the mAb. Amino acid sequence analysis revealed four different types of mimotope sequences, all of which contained a common motif V-A-L/V-C. Of the 46 clones isolated, 44 contained the motif V-A-L-C while 2 contained the V-A-V-C motif. All four types of phage clones inhibited the reactivity of the mAb with phomopsin A in a competition ELISA. The clone with the mimotope sequence CT VALCNMYFGAKLD demonstrated the strongest binding. It was further shown that synthetic peptides containing these mimotope amino acid sequences were able to inhibit the mAb-phomopsin A interaction, indicating that the peptide mimotopes were responsible for the specific binding, independent of the phage framework. The results also suggest that the mimotope peptides bind to mAb C₃C₁₁ at the same site as phomopsin A. The application of recombinant phage particles carrying phomopsin mimotopes in immunoassay was evaluated and the results demonstrated approximately 100-fold increase in sensitivity in comparison with a conventional immunoassay using a chemically linked phomopsin-horseradish peroxidase conjugate.     

Fully coupled channel approach to doubly strange s-shell hypernuclei

We describe ab initio calculations of doubly strange, S = -2, s-shell hypernuclei (4(LambdaLambda)H, 5LambdaLambda)H, 5(LambdaLambda)He, and 6(LambdaLambda)He) as a first attempt to explore the few-body problem of the full-coupled channel scheme for these systems. The wave function includes LambdaLambda, LambdaSigma, NXi, and SigmaSigma channels. Minnesota NN, D2' YN, and simulated YY potentials based on the Nijmegen hard-core model are used. Bound-state solutions of these systems are obtained. We find that a set of phenomenological B8B8 interactions among the octet baryons in S = 0,-1, and -2 sectors, which is consistent with all of the available experimental binding energies of S = 0,-1, and -2 s-shell (hyper)nuclei, can predict a particle stable bound state of 4(LambdaLambda)H. For 5(LambdaLambda)H and 5(LambdaLambda)He, LambdaN-SigmaN and XiN-LambdaSigma potentials significantly affect the net LambdaLambda-NXi coupling, and a large Xi probability is obtained even for a weaker LambdaLambda-NXi potential.     

Production and Accumulation of 4-<Emphasis Type="Italic">O</Emphasis>-Methyl-α-<Emphasis Type="SmallCaps">d</Emphasis>-Glucuronosyl-Xylotriose by Growing Culture of Thermophilic <Emphasis Type="Italic">Anoxybacillus</Emphasis> sp. Strain JT-12

A thermophilic Anoxybacillus sp. strain JT-12, isolated from soil, produced acidic xylotriose, 4-O-methyl-α-d-glucuronosyl-xylotriose (MeGlcAX₃), as a main product from birchwood xylan and accumulated them in the culture under optimum conditions at pH 7.0 and 55 °C using 0.75% (w/v) birchwood xylan as a carbon source for 42–72 h. The acidic xylotriose was purified by ethanol precipitation and high-performance liquid chromatography using NH₂ Lichosher® 100 column. The results of electrospray ionization mass spectrometry, mass to charge ratio (m/z) 603.23, confirmed that the purified sample was acidic xylotriose that had benefits and applications in many fields.     

Plasmonic gold nanocrosses with multidirectional excitation and strong photothermal effect

We report a facile chemical synthesis of well-defined gold nanocrosses through anisotropic growth along both <110> and <001>, whereas gold nanorods grow only along either <110> or <001>. The multiple branching was achieved by breaking the face-centered-cubic lattice symmetry of gold through copper-induced formation of single or double twins, and the resulting gold nanocrosses exhibited pronounced near-IR absorption with a great extension to the mid-IR region. As studied by discrete dipole approximation (DDA) simulations, the entire nanocross gets excited even when one of the branches is exposed to incident light. The above properties make them useful as octopus antennas for capturing near-IR light for effective photothermal destruction of cells. The cell damage process was analyzed using the Arrhenius model, and its intrinsic thermodynamic characteristics were determined quantitatively. Besides effective photothermal treatment and two-photon luminescence imaging, the near- and mid-IR-absorbing gold nanocrosses may also find applications in IR sensing, thermal imaging, telecommunications, and the like.