Sintering of ferrite materials requires sensitive control of homogeneity that affects electromagnetic properties. The paper proposes a method for analysis of chemical homogeneity of ferrite ceramics ...based on mathematical analysis of differential temperature dependences of the initial permeability near the Curie point. The method was tested on model samples of LiTiZn ferrite ceramics doped with Al2O3 or ZrO2 of 0.10, 0.25, 0.5 0.75, and 1 wt%. It was found the effect of doping agents on the ferrite lattice parameter is insignificant, and they are not indicated on the diffraction patterns as separate peaks. SEM data show a weak effect of Al2O3 doping agent on the average grain size of ferrite ceramics. At the same time, the effect is more pronounced for ZrO2 due to secondary recrystallization. In this case, the coercive force shows a particular increase as compared with undoped samples: by 23% and 60% for Al2O3 and ZrO2 respectively of doping agents’ concentration increased to 1 wt%. The paramagnetic-to-ferrimagnetic transition of ferrites near the Curie point is highly sensitive to chemical homogeneity of the material. It was shown that the width of the differential temperature dependence peak of the initial permeability can be used to assess chemical homogeneity of ferrimagnetic ceramics. The peak width was found to increase by 75%. Therefore, the proposed method revealed a higher sensitivity compared to XRD and hysteresis loops.
•The study revealed the effect of doping agents Al2O3 or ZrO2 on microstructural and magnetic properties of LiTiZn ferrites.•The paramagnetic transition of ferrites is characterized by the rate of the decrease in the initial permeability.•The transition highly sensitive to chemical homogeneity of LiTiZn ferrite ceramics.•A highly sensitive method has been developed for analysis of chemical homogeneity.•A decrease in the peak width is the most sensitive characteristic of chemical homogeneity increases.
In this work, the effect of ball milling of synthesized LiFe
5
O
8
ferrite powders on the microstructure and properties of ferrite ceramics was studied by XRD, laser diffraction and SEM analysis as ...well as thermal analysis. The mechanical milling of LiFe
5
O
8
was carried out in a Fritsch Pulverisette 7 planetary mill using the zirconia or steel grinding balls. The process of ferrite sintering was investigated using dilatometric analysis. In addition, ferrite ceramics electromagnetic properties, including magnetization, Curie point and electrical resistivity, were investigated. The results showed a strong difference in the structure of ferrite ceramics obtained from ferrite powders pre-milled by zirconia or steel grinding balls. Thus, the milling results in a decrease in the particle size of the ferrite powders to ultrafine range. The ferrite ceramics, obtained from powder milled by steel balls, is characterized by high density and low porosity as well as good electromagnetic properties and the main presence of a disordered β-LiFe
5
O
8
phase. However, the mechanical milling using zirconia balls leads to the contamination of ferrite by zirconia, resulting in the formation of β-LiFe
5
O
8
/ZrO
2
composite ceramics during sintering.
The approach based on molecular modeling was developed to study dNTP derivatives characterized by new polymerase-specific properties. For this purpose, the relative efficiency of PCR amplification ...with modified dUTPs was studied using Taq, Tth, Pfu, Vent, Deep Vent, Vent (exo-), and Deep Vent (exo-) DNA polymerases. The efficiency of PCR amplification with modified dUTPs was compared with the results of molecular modeling using the known 3D structures of KlenTaq polymerase–DNA–dNTP complexes. The dUTPs were C5-modified with bulky functional groups (the Cy5 dye analogs) or lighter aromatic groups. Comparing the experimental data and the results of molecular modeling revealed the decrease in PCR efficiency in the presence of modified dUTPs with an increase in the number of non-covalent bonds between the substituents and the DNA polymerase (about 15% decrease per one extra non-covalent bond). Generalization of the revealed patterns to all the studied polymerases of the A and B families is discussed herein. The number of non-covalent bonds between the substituents and polymerase amino acid residues is proposed to be a potentially variable parameter for regulating enzyme activity.
Modification of DNA aptamers is aimed at increasing their thermodynamic stability, and improving affinity and resistance to biodegradation. G-quadruplex DNA aptamers are a family of affinity ligands ...that form non-canonical DNA assemblies based on a G-tetrads stack. Modification of the quadruplex core is challenging since it can cause complete loss of affinity of the aptamer. On the other hand, increased thermodynamic stability could be a worthy reward. In the current paper, we developed new three- and four-layer modified analogues of the thrombin binding aptamer with high thermal stability, which retain anticoagulant activity against alpha-thrombin. In the modified aptamers, one or two G-tetrads contained non-natural anti-preferred alpha-deoxyguanosines at specific positions. The use of this nucleotide analogue made it possible to control the topology of the modified structures. Due to the presence of non-natural tetrads, we observed some decrease in the anticoagulant activity of the modified aptamers compared to the natural prototype. This negative effect was completely compensated by conjugation of the aptamers with optimized tripeptide sequences.
The effect of the diamagnetic ZrO
2
addition on the microstructure and magnetic properties of LiTiZn ferrite ceramics, including the shape and parameters of the temperature dependence of the initial ...permeability, has been investigated. The defect structure of ferrite ceramic samples is assessed according to our earlier proposed method based on the mathematical treatment of the experimental temperature dependencies of the initial permeability. It was found that the defect structure of ferrite ceramics increased by 350% with an increase in the concentration of the ZrO
2
additive in the range of (0–0.5) wt.%. In this case, for the same samples, the increase in the true physical broadening of diffraction peaks is only 20%, and the coercive force by 50%. Simultaneously, the maximum of the experimental temperature dependence of the initial permeability dropped by 45%. The microstructure of all samples is characterized with a similar average grain size according to the SEM data. However, samples with 0.5 wt.% of ZrO
2
are characterized by the formation of conglomerates. A linear relationship was obtained between the defect structure and the width of the diffraction peaks, which indicates that this parameter is related to the elastic stress of ferrite ceramics. These results suggest that the high sensitive proposed method can be recommended for impurity and defect monitoring of soft ferrite products.
The influence of the degree of dispersion of a nickel–zinc ferrite powder of a Ni
0.7
Zn
0.3
Fe
2
O
4
composition on its magnetic properties has been considered. The material has been synthesized ...using the ceramic technology with preliminary mechanical activation of precursors. The degree of dispersion has been varied using different modes of its dry grinding in a ball mill. The patterns of the changes in saturation magnetization and the coercive force as a function of grinding modes and a specific surface area of the ferrite powder have been established. The changes in the pattern of the magnetic phase transition in the region of the Curie temperature of materials with different degrees of dispersion have been determined.
Oligonucleotide-peptide conjugates (OPCs) are a promising class of biologically active compounds with proven potential for improving nucleic acid therapeutics. OPCs are commonly recognized as an ...efficient instrument to enhance the cellular delivery of therapeutic nucleic acids. In addition to this application field, OPCs have an as yet unexplored potential for the post-SELEX optimization of DNA aptamers. In this paper, we report the preparation of designer thrombin aptamer OPCs with peptide side chains anchored to a particular thymidine residue of the aptamer. The current conjugation strategy utilizes unmodified short peptides and support-bound protected oligonucleotides with activated carboxyl functionality at the T3 thymine nucleobase. The respective modification of the oligonucleotide strand was implemented using N3-derivatized thymidine phosphoramidite. Aptamer OPCs retained the G-quadruplex architecture of the parent DNA structure and showed minor to moderate stabilization. In a series of five OPCs, conjugates bearing T3-Ser-Phe-Asn (SFN) or T3-Tyr-Trp-Asn (YWN) side chains exhibited considerably improved anticoagulant characteristics. Molecular dynamics studies of the aptamer OPC complexes with thrombin revealed the roles of the amino acid nature and sequence in the peptide subunit in modulating the anticoagulant activity.
In a present work, a comparative study of two types of LiTiZn samples of ferrite ceramics, which were sintered using conventional ceramic technology at a temperature of 1010 °C for 2 h and which were ...made with preliminary mechanical treatment in a ball planetary mill, was carried out. It is shown that mechanical treatment in a ball mill leads to a decrease in the defects level, an increase in the Curie point and a demagnetizing factor of ferrite ceramics. The growth of the demagnetizing factor is associated with an increase in the porosity of ferrite ceramics samples pre-grinded in ball. According to the X-ray phase analysis data, the lattice parameter and the coherent scattering region decrease in this case, and the microstrain is reduced by an order of magnitude. The defects level was assessed by the results of mathematical processing of the temperature dependences of the initial permeability using the previously proposed phenomenological expression. Measuring TG/DTG curves in a magnetic field allowed, on the one hand, to confirm a significant difference in Curie points for different types of samples, on the other hand, to detect the presence of an additional magnetic phase in ball-milled ferrite ceramics samples.
Currently, oligonucleotide therapy has emerged as a new paradigm in the treatment of human diseases. In many cases, however, therapeutic oligonucleotides cannot be used directly without modification. ...Chemical modification or the conjugation of therapeutic oligonucleotides is required to increase their stability or specificity, improve their affinity or inhibitory characteristics, and address delivery issues. Recently, we proposed a conjugation strategy for a 15-nt G-quadruplex thrombin aptamer aimed at extending the recognition interface of the aptamer. In particular, we have prepared a series of designer peptide conjugates of the thrombin aptamer, showing improved anticoagulant activity. Herein, we report a new series of aptamer-peptide conjugates with optimized peptide sequences. The anti-thrombotic activity of aptamer conjugates was notably improved. The lead conjugate, TBA-GLE, was able to inhibit thrombin-induced coagulation approximately six-fold more efficiently than the unmodified aptamer. In terms of its anticoagulant activity, the TBA-GLE conjugate approaches NU172, one of the most potent G-quadruplex thrombin aptamers. Molecular dynamics studies have confirmed that the principles applied to the design of the peptide side chain are efficient instruments for improving aptamer characteristics for the proposed TBA conjugate model.
PDF
