Templating of inorganic nanomaterials by biomacromolecules and their assemblies

During the past decade biomacromolecules attracted tremendous attention as versatile materials for self-assembly, nanoconstruction, and templating. An increasing number of reports highlights creative applications of DNA, proteins, and their assemblies for construction of materials, which synthesis by traditional top-down techniques is not possible. This review summarizes various aspects of the application of biomacromolecules and their self-organized structures for building-up inorganic nanomaterials of different complicity by metallization or mineralization of natural templates. The central focus of the review is given to DNA-templated and DNA-directed synthesis of nanostructures, as the progress in the utilization of DNA for nanoconstruction is most considerable.     

高压脉冲放电技术成桩法

主要介绍了高压脉冲放电技术的发展现状、成桩机理、成桩特点以及成桩的新工艺。该成桩方法具有高的承载能力和经济效益,具有其它桩所不具有的优点。还对其成桩技术的应用前景进行了展望。     

Effect of bio-optical parameter variability and uncertainties in reflectance measurements on the remote estimation of chlorophyll-a concentration in turbid productive waters: modeling results

Most algorithms for retrieving chlorophyll-a concentration (Chla) from reflectance spectra assume that bio-optical parameters such as the phytoplankton specific absorption coefficient (aPhi*) or the chlorophyll-a fluorescence quantum yield (eta) are constant. Yet there exist experimental data showing large ranges of variability for these quantities. The main objective of this study was to analyze the sensitivity of two Chla algorithms to variations in bio-optical parameters and to uncertainties in reflectance measurements. These algorithms are specifically designed for turbid productive waters and are based on red and near-infrared reflectances. By means of simulated data, it is shown that the spectral regions where the algorithms are maximally sensitive to Chla overlap those of maximal sensitivity to variations in the above bio-optical parameters. Thus, to increase the accuracy of Chla retrieval, we suggest using spectral regions where the algorithms are less sensitive to Chla, but also less sensitive to these interferences. aPhi* appeared to be one of the most important sources of error for retrieving Chla. However, when the phytoplankton backscattering coefficient (bb,Phi) dominates the total backscattering, as is likely during algal blooms, variations in the specific bb,Phi may introduce large systematic uncertainties in Chla estimation. Also, uncertainties in reflectance measurements, which are due to incomplete atmospheric correction or reflected skylight removal, seem to affect considerably the accuracy of Chla estimation. Instead, variations in other bio-optical parameters, such as eta or the specific backscattering coefficient of total suspended particles, appear to have minor importance. Suggestions regarding the optimal band locations to be used in the above algorithms are finally provided.     

Electrochemical and XAFS studies of effects of carbonate on the oxidation of arsenite

Measurements of electrochemical (EC) arsenite oxidation demonstrated thatthe arsenite oxidation current increased in the presence of carbonate while the potential of the onset of EC arsenite oxidation exhibited a strong shift toward less positive values. Examination of pH and total carbonate concentration effects on the EC arsenite oxidation parameters showed that they were affected solely by the concentration of carbonate ion CO3(2-), which appeared to form relatively weak mono- and dicarbonate complexes with arsenite. The EC activity of these complexes was determined to be almost an order of magnitude higher than that of free arsenite. However, X-ray absorption fine-structure (XAFS) measurements did not show any changes in the properties of the As(III) inner complexation shell associated with the presence of the bound carbonate ions. It was accordingly concluded that the strength of bonds between the bound carbonate and As(III) is close to that for As(III)-OH- interactions. The acceleration of the oxidation of carbonate-As(III) complexes was hypothesized to be associated with an additional pathway of the formation of As(IV) intermediates, in which the carbonate group present in the As(III) inner shell provides an electron to form a bound carbonate radical and also a good leaving group for facile cleavage from the transient As(IV) species.     

Modulation of Aptamer–Ligand-Binding by Complementary Oligonucleotides: A G-Quadruplex Anti-Ochratoxin A Aptamer Case Study

Short oligonucleotides are widely used for the construction of aptamer-based sensors and logical bioelements to modulate aptamer–ligand binding. However, relationships between the parameters (length, location of the complementary region) of oligonucleotides and their influence on aptamer–ligand interactions remain unclear. Here, we addressed this task by comparing the effects of short complementary oligonucleotides (ssDNAs) on the structure and ligand-binding ability of an aptamer and identifying ssDNAs’ features that determine these effects. Within this, the interactions between the OTA-specific G-quadruplex aptamer 1.12.2 (5′-GATCGGGTGTGGGTGGCGTAAAGGGA GCATCGGACA-3′) and 21 single-stranded DNA (ssDNA) oligonucleotides complementary to different regions of the aptamer were studied. Two sets of aptamer–ssDNA dissociation constants were obtained in the absence and in the presence of OTA by isothermal calorimetry and fluorescence anisotropy, respectively. In both sets, the binding constants depend on the number of hydrogen bonds formed in the aptamer–ssDNA complex. The ssDNAs’ having more than 23 hydrogen bonds with the aptamer have a lower aptamer dissociation constant than for aptamer–OTA interactions. The ssDNAs’ having less than 18 hydrogen bonds did not affect the aptamer–OTA affinity. The location of ssDNA’s complementary site in the aptamer affeced the kinetics of the interaction and retention of OTA-binding in aptamer–ssDNA complexes. The location of the ssDNA site in the aptamer G-quadruplex led to its unfolding. In the presence of OTA, the unfolding process was longer and takes from 20 to 70 min. The refolding in the presence of OTA was possible and depends on the length and location of the ssDNA’s complementary site. The location of the ssDNA site in the tail region led to its rapid displacement and wasn’t affecting the G-qaudruplex’s integrity. It makes the tail region more perspective for the development of ssDNA-based tools using this aptamer.     

Hydroxylherderite (Ca2Be2P2O8(OH)2) stability under extreme conditions (up to 750°C/100 GPa)

Hydroxylherderite, Ca₂Be₂P₂O₈(OH)₂, is among the most common beryllophosphates in nature and could play a substantial role in Be geochemical cycle. Hydroxylherderite P–T stability and crystal structure behavior were studied under extreme conditions (up to 750°C/100 GPa) using in situ single-crystal and powder X-ray diffraction and Raman spectroscopy. The mineral demonstrated high stability under high-pressure conditions (up to ∼100 GPa) without any phase transitions. Under high-temperature conditions, it was stable up to about 700°C, when it decomposed with the formation of fluorapatite Ca₅(PO₄)₃F and hurlbutite CaBe₂P₂O₈. The beryllophosphate member of the gadolinite supergroup is the most stable mineral (material) under high-pressure conditions, compared to aluminum-, boro- and beryllosilicates.     

Effect of absorbed power and dopant content on densification during rapid microwave sintering of Bi2O3-doped ZnO

ZnO samples with an addition of 0, 0.035, 0.1, and 0.35 mol.% Bi₂O₃ were microwave sintered at heating rates 10 and 50°C/min to a maximum temperature of 1200°C with zero hold time. The densification curves obtained by optical dilatometry have been studied in their dependence on the dopant concentration and the heating rate. Direct volumetric absorption of microwave radiation resulted in a 50–60°C shift of the densification curves toward low temperatures compared to susceptor-assisted heating. An analysis of the effect of the volumetrically absorbed microwave power on the formation of grain-boundary phases that facilitate densification is presented.