Holmium-Containing Metal-Organic Frameworks as Modifiers for PEBA-Based Membranes.

Recently, there has been an active search for new modifiers to create hybrid polymeric materials for various applications, in particular, membrane technology. One of the topical modifiers is metal-organic frameworks (MOFs), which can significantly alter the characteristics of obtained mixed matrix membranes (MMMs). In this work, new holmium-based MOFs (Ho-MOFs) were synthesized for polyether block amide (PEBA) modification to develop novel MMMs with improved properties. The study of Ho-MOFs, polymers and membranes was carried out by methods of X-ray phase analysis, scanning electron and atomic force microscopies, Fourier transform infrared spectroscopy, low-temperature nitrogen adsorption, dynamic and kinematic viscosity, static and dynamic light scattering, gel permeation chromatography, thermogravimetric analysis and contact angle measurements. Synthesized Ho-MOFs had different X-ray structures, particle forms and sizes depending on the ligand used. To study the effect of Ho-MOF modifier on membrane transport properties, PEBA/Ho-MOFs membrane retention capacity was evaluated in vacuum fourth-stage filtration for dye removal (Congo Red, Fuchsin, Glycine thymol blue, Methylene blue, Eriochrome Black T). Modified membranes demonstrated improved flux and rejection coefficients for dyes containing amino groups: Congo Red, Fuchsin (PEBA/Ho-1,3,5-H3btc membrane possessed optimal properties: 81% and 68% rejection coefficients for Congo Red and Fuchsin filtration, respectively, and 0.7 L/(m2s) flux).

Interpolymer Complexes of Poly(methacryloyloxyethyl phosphorylcholine) and Polyacids.

It has been shown that macromolecules of poly(methacryloyloxyethyl phosphorylcholine) can form hydrogen bonded interpolymer complexes with homo- and copolymers of carboxylic acids and with poly(vinylphosphonic) acid in aqueous solutions. Polarized luminescence and IR spectroscopy were applied in the investigation. Nanosecond relaxation times characterizing the mobility of the chain fragments for the initial luminescent labeled polymers were determined and their changes by a factor of 2-50 were established during the formation of an interpolymer complex. Hydrogen bonds play a dominant role in the formation of these complexes. Hydrophobic interactions serve as an additional stabilizing factor. It is established that poly(methacryloyloxyethyl phosphorylcholine)/poly(vinylphosphonic acid) complex forms a looser structure in comparison with those for polycarboxylic acids as result of electrostatic repulsion between charged groups.

New Copolymers of Vinylphosphonic Acid with Hydrophilic Monomers and Their Eu3+ Complexes.

Free radical copolymerization is used for the synthesis of novel water-soluble copolymers of vinylphosphonic acid with 2-deoxy-2-methacrylamido-D-glucose or 4-acryloylmorpholine, with varied compositions and molecular masses, as well as for the synthesis of copolymers of vinylphosphonic acid with acrylamide. The obtained copolymers contain 6-97 mol.% of vinylphosphonic acid units, and their molecular masses vary from 5 × 103 to 310 × 103. The monomer reactivity ratios of vinylphosphonic acid and 2-deoxy-2-methacrylamido-D-glucose in copolymerization are determined for the first time, and their values are 0.04 and 9.02, correspondingly. It is demonstrated that the synthesized copolymers form luminescent mixed-ligand complexes with Eu3+, thenoyltrifluoroacetone, and phenanthroline. The influence of the comonomer's nature on the intensity of the luminescence of complex solutions is revealed.

Synthesis of Water-Soluble Copolymers of N-vinylpyrrolidone with N-vinyldithiocarbamate as Multidentate Polymeric Chelation Systems and Their Complexes with Indium and Gallium.

Dithiocarbamate (DTC) derivatives of N-vinylpyrrolidone-N-vinylamine (VP-VA) copolymers were synthesized via reaction between the copolymers and carbon disulfide in alkaline medium; molecular masses of the products were 12 and 29 kDa; the VP:VDTC ratios were 94:6 and 83:17 mol.%. Complexation between the obtained DTC derivatives and metal ions (indium and gallium) was investigated. It was demonstrated that metal-DTC ligand complexes with 1:3 ratio between components were formed. Gallium metal-polymer complexes (MPC) were unstable in solution. Individual indium MPC were isolated and characterized by spectral and chromatographic methods. Unlike similar gallium MPC, they appeared to be stable in histidine challenge reaction.

Wheat germ agglutinin is involved in the protective action of 24-epibrassinolide on the roots of wheat seedlings under drought conditions.

The involvement of wheat germ agglutinin (WGA) in the protective action of 24-epibrassinolide (EBR) against drought stress was studied in the seedling roots of two wheat cultivars differing in drought tolerance. Under dehydration conditions, the contents of ABA and WGA were shown to change significantly in the roots of either drought-tolerant cultivar Omskaya 35 or drought-sensitive cultivar Salavat Yulaev. Meanwhile, accumulation of either ABA or WGA started earlier and was two times greater in plants of drought-tolerant cultivar. Since WGA is an excreted protein, it is not surprising that the level of lectin in the roots gradually decreased by the 7th day of treatment due to its exudation into root environment. Pre-sowing treatment with EBR contributed to additional accumulation of lectin as compared to the control variants of either cultivar, while the hormone treatment did not change ABA content. Meanwhile, under conditions of drought, EBR-pretreated seedlings were characterized by lower level of accumulation of ABA and WGA in the roots. EBR application was found to prevent drought-induced inhibition of cell division in the root apical meristem, while WGA excreted into the root environment may contribute significantly to the effect.

Involvement of dehydrins in 24-epibrassinolide-induced protection of wheat plants against drought stress.

In this study, we performed a comparative analysis of the physiological and biochemical parameters of wheat cultivars with contrasting drought resistance, drought-resistant Omskaya 35 (O-35) and less drought-resistant Salavat Yulaev (SYu), during 7-day germination under drought stress simulated by 5% mannitol. In addition, we evaluated the effectiveness of pre-sowing seed treatment with 0.4 µM 24-epibrassinolide (EBR) used to increase the resistance of plants of both cultivars to drought stress. It was revealed that mannitol has caused significant changes in the hormonal balance of the plants of both cultivars, associated with abscisic acid (ABA) accumulation and decrease in the contents of indoleacetic acid (IAA) and cytokinins (CKs). It should be noted that more dramatic changes in the content of phytohormones were characteristic for seedlings of SYu cultivar, which was reflected in a stronger growth inhibition of these plants. Pretreatment with EBR mitigated the negative effect of drought on the hormonal status and growth of seedlings during their germination. Furthermore, we found that drought caused accumulation of dehydrin (DHN) proteins, especially of low molecular weight DHNs, whose abundance was 2.5 times greater in O-35 cultivar than in SYu plants. EBR-pretreated plants of both cultivars were characterized by the additional accumulation of DHNs, indicating their involvement in the development of the EBR-induced wheat drought resistance. The use of fluridone allowed us to demonstrate ABA-dependent and ABA-independent pathways of regulation of low molecular mass dehydrins accumulation by EBR in wheat plants of both cultivars under drought conditions.

Cytokinin oxidase is involved in the regulation of cytokinin content by 24-epibrassinolide in wheat seedlings.

Fast and stable 2-fold accumulation of cytokinins (CKs) was detected initially in roots and then in shoots of 4-day-old wheat (Triticum aestivum L.) seedlings in the course of their treatment with 0.4µM 24-epibrassinolide (EBR). Elevated cytokinin level has been maintained only in the presence of EBR, while the hormone removal has led to return of cytokinin concentration to the control level initially in the roots and then in the shoots. EBR-induced accumulation of cytokinins was accompanied by inhibition of both cytokinin oxidase (CKX) (cytokinin oxidase/dehydrogenase, EC 1.5.99.12) activity and expression of the gene coding for this enzyme, and on the contrary the decline in CKs level resulted in increase in these characteristics up to the control level in roots and then in shoots. Sharp accumulation of cytokinin O-glucosides has been discovered in response to EBR-treatment suggesting fast EBR-induced activation of production of cytokinins, which excessive amounts were transferred into the storage forms. The obtained data provide evidence for the involvement of EBR in regulation of cytokinin level in wheat seedlings.