Добірка наукової літератури з теми "Magnetic Hysteresis -Small Molecular Organic Ligands"

Structural information pertaining to the interactions between biological macromolecules and ligands is of potential significance for understanding of molecular mechanisms in key biological processes. Recently, nuclear magnetic resonance (NMR) spectroscopic techniques has come of age and has widened its scope to characterize binding interactions of small molecules with biological macromolecules especially, proteins. NMR spectroscopy-based techniques are versatile due to their ability to examine weak binding interactions and for rapid screening the binding affinities of ligands with proteins at atomic resolution. In this review, we provide a broad overview of some of the important NMR approaches to investigate interactions of small organic molecules with proteins.

The cobalt(II) compounds ([Co(imid)2]x (1), [Co(2-meimid)2]x (2), [Co(4-meimid)2]x (3), [Co(benzimid)2]x (4), and [Co3(imid)6(imidH)2]x (5) (imid = imidazolate, 2-meimid = 2-methylimidazolate, 4-meimid = 4-methylimi dazolate, benzimid = benzimidazolate)), have been synthesized and structurally and magnetically characterized. Electronic and vibrational spectroscopy and thermogravimetric studies on all five compounds support structures involving tetrahedrally coordinated cobalt centers with single-bridging 1,3-diazolate ligands forming extended polymeric lattices. Moreover, X-ray powder diffraction studies on 1 and 5 established, through isomorphism with published structures, that the molecular connectivity in these materials is 3-D. Variable temperature and applied field magnetization studies revealed antiferromagnetism as the primary magnetic exchange process in all five compounds. In addition, 1, 4, and 5 show magnetic phase transitions to ferromagnetically ordered states below critical temperatures of 16, 13, and 15 K, respectively. Magnetization measurements at 4.8 K as the applied field was cycled between +55 000 and –55 000 G revealed typical hysteresis behavior and gave remnant magnetizations of 334, 257, and 175 cm3 G mol–1 and coersive fields of 6620, 5280, and 4140 G for 1, 4, and 5, respectively. No evidence for long-range magnetic order was obtained for either 2 or 3. A comparison of the magnetic properties of three pairs of isostructural iron(II) and cobalt(II) molecule-based magnets shows that while the coersive fields are in general larger for cobalt over iron, the magnitude of the difference varies significantly suggesting that one cannot conclude that cobalt analogues will always be harder magnets.Key words: cobalt(II), 1,3-diazolates, canted spins, molecule-based magnets.

The study of the inherent factors that influence the isolation of one type of metallosupramolecular architecture over another is one of the main objectives in the field of Metallosupramolecular Chemistry. In this work, we report two new neutral copper(II) helicates, [Cu2(L1)2]·4CH3CN and [Cu2(L2)2]·CH3CN, obtained by means of an electrochemical methodology and derived from two Schiff-based strands functionalized with ortho and para-t-butyl groups on the aromatic surface. These small modifications let us explore the relationship between the ligand design and the structure of the extended metallosupramolecular architecture. The magnetic properties of the Cu(II) helicates were explored by Electron Paramagnetic Resonance (EPR) spectroscopy and Direct Current (DC) magnetic susceptibility measurements.

Dual water and organic solvent soluble 3-aryl-3-(trifluormethyl) diazirine-functionalized gold nanoparticles (AuNPs) were prepared through a place exchange reaction from triethylene glycol monomethyl ether (EG3-Me) capped AuNPs. These nanoparticles were fully characterized using 1H and 19F nuclear magnetic resonance (NMR) spectroscopy, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). TGA along with 1H NMR data allowed the determination of 15% incorporation of diazirine (Diaz) ligands onto mixed monolayer AuNPs, while TEM images showed an average diameter of 2.3 ± 0.5 nm. This information led to the estimated molecular formula of Au400 (S-EG4-Diaz)40 (S-EG3-Me)230 for these AuNPs. It is noteworthy that high-resolution XPS was a powerful tool for quantitative analysis. Irradiation of the diazirine capped AuNPs resulted in nitrogen extrusion and the formation of a highly reactive carbene with evidence of a portion of the reaction proceeding via the diazo intermediate and thus requiring a second photon for activation. The carbene species generated was utilized to tether the attached AuNPs via insertion into C=C or O–H functionality inherent on various substrates. Here, we demonstrated that photolysis of the diazirine modified AuNPs in the presence of a variety of model carbene scavengers led to clean and efficient insertion products while maintaining their solubility in polar solvents.

As for ligand fishing, the current immobilization approaches have some potential drawbacks such as the small protein loading capacity and difficult recycle process. The core–shell metal–organic frameworks composite (Fe3O4-COOH@UiO-66-NH2), which exhibited both magnetic characteristics and large specific surface area, was herein fabricated and used as magnetic support for the covalent immobilization of porcine pancreatic lipase (PPL). The resultant composite Fe3O4-COOH@UiO-66-NH2@PPL manifested a high loading capacity (247.8 mg/g) and relative activity recovery (101.5%). In addition, PPL exhibited enhanced tolerance to temperature and pH after immobilization. Then, the composite Fe3O4-COOH@UiO-66-NH2@PPL was incubated with the extract of Scutellaria baicalensis to fish out the ligands. Eight lipase inhibitors were obtained and identified by UPLC-Q-TOF-MS/MS. The feasibility of the method was further confirmed through an in vitro inhibitory assay and molecular docking. The proposed ligand fishing technique based on Fe3O4-COOH@UiO-66-NH2@PPL provided a feasible, selective, and effective platform for discovering enzyme inhibitors from natural products.

The complex [Cp2Ti(μ-PEt2)]2 (1) crystallizes in the monoclinic space group P21/n with a = 16.591(3) Å, b = 8.662(2) Å, c = 37.407(2) Å, β = 102.40(1)°, Z = 8, and V = 5250(2) Å3. The Ti2P2 core of the dimeric complex is planar and the angles at Ti and P are close to 90°. The Ti … Ti separations were found to be 3.732(1) and 3.706(1) Å in the two independent molecules in the unit cell. Bulk magnetic susceptibility measurements on solid 1 show that the species is diamagnetic over the range 5–340 K. The coupling constant for the antiferromagnetic interaction between the Ti centers of 1 is found to be at least −300 cm−1. Extended Hückel Molecular Orbital calculations suggest that mixing of the frontier 1a1 orbitals of the Cp2Ti fragments with the p orbitals of the phosphide fragments affords a mechanism for super-exchange through the ligands. In THF solution, variable temperature 1H, and 31P{1H} NMR and EPR spectra for 1 are consistent with the generation of the paramagnetic monomeric species Cp2TiPEt2, 3. As well, the data suggest thermal populations of the paramagnetic triplet state of the dimer may occur to a small extent at 340 K. In contrast, the analogous Zr dimer 2 shows no evidence of dissociation or of thermal population of the triplet state at temperatures to 340 K. Key words: titanium phosphides, structures, magnetic properties.

Abstract Superparamagnetic iron oxide nanoparticles (SPIONs) have attracted the particular interest of scientists from various disciplines since their obtaining to the present day. The physicochemical and pharmacokinetic properties of SPIONs-containing magnetic nanofluids, and their applicability in biomedicine, largely depend on the stability of the colloidal system, particle size, size distribution, net magnetic moment, phase composition, and type and properties of stabilizers. Also, in some cases, when using magnetic nanoparticles for biomedical purposes, it is necessary that the stabilizing ligands of nanoparticles should not significantly change the magnetic properties. From this point of view, the preparation of stable colloidal systems containing bare iron oxide nanoparticles (BIONs) in water at physiological pH attracts particular attention and becomes increasingly popular in scientific circles. This study is focused on the development of the synthesis of aqueous suspensions of SPIONs stabilized with various organic molecules (oleic acid [OA] and poly(ethylene glycol) monooleate - with molecular weights 460 and 860) using a modified controlled chemical coprecipitation reaction, as well as stable nanofluids containing BIONs in an aqueous medium at neutral pH (near-physiological). The obtained samples were characterized using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy, small-angle x-ray scattering (SAXS), dynamic light scattering (DLS), electrophoretic light scattering (ELS), and Vibrating Sample Magnetometry.

A new film material capable of transforming UV radiation into visible light was obtained from a highly anisometric EuIII complex with organic ligands in a polymethylmethacrylate (PMMA) matrix and then structurally characterized. An important advantage of the synthesized complex is its good solubility in organic solvents such as dichloromethane, chloroform, THF, toluene, etc. The ligand environment (flexible alkyl and cyclohexyl substituents) of the EuIII complex was selected to prevent crystallization, to inhibit the formation of defects in the structure of films and to provide its uniform distribution in the polymer during polymerization. As a result we obtain an EuIII complex of the film with remarkable thermal behavior: the complex melts to isotropic liquid without decomposition, it supercools at ambient temperature and it forms a stable amorphous material at low (up to −30°C) temperatures. The films were prepared by two methods: bulk polymerization and spin coating. A comparison of the differences of luminescent and optical characteristics of micro- and nanosized PMMA films doped with the anisometric EuIII complex is given. Based on X-ray powder diffraction and small-angle scattering data, it has been supposed that the association of EuIII complex molecules occurs in the voids of the PMMA matrix and is accompanied by the formation of a nanocrystalline phase. For films obtained by spin coating, a deeper microphase separation is demonstrated than by bulk polymerization. The dimensional characteristics of the nano-associates were determined and a correlation between the method of preparation and the type of distribution of the EuIII complex in the PMMA matrix is established.

Trypanosoma brucei is a species of kinetoplastid causing sleeping sickness in humans and nagana in cows and horses. One of the peculiarities of this species of parasites is represented by their redox metabolism. One of the proteins involved in this redox machinery is the monothiol glutaredoxin 1 (1CGrx1) which is characterized by a unique disordered N-terminal extension exclusively conserved in trypanosomatids and other organisms. This region modulates the binding profile of the glutathione/trypanothione binding site, one of the functional regions of 1CGrx1. No endogenous ligands are known to bind this protein which does not present well-shaped binding sites, making it target particularly challenging to target. With the aim of targeting this peculiar system, we carried out two different screenings: (i) a fragment-based lead discovery campaign directed to the N-terminal as well as to the canonical binding site of 1CGrx1; (ii) a structure-based virtual screening directed to the 1CGrx1 canonical binding site. Here we report a small molecule that binds at the glutathione binding site in which the binding mode of the molecule was deeply investigated by Nuclear Magnetic Resonance (NMR). This compound represents an important step in the attempt to develop a novel strategy to interfere with the peculiar Trypanosoma Brucei redox system, making it possible to shed light on the perturbation of this biochemical machinery and eventually to novel therapeutic possibilities.

Magnetic nanofluids can be remotely heated by alternating magnetic field and have significant potential for cancer hyperthermia therapy. The heat generated by magnetic nanoparticles is typically quantified by the specific absorption rate (SAR), which represents the thermal power per unit mass of magnetic material generated in the presence of an alternating magnetic field. During hyperthermia treatment, heat dosage of tumor tissue correlates with slowing tumor growth. The therapeutic ratios of cancer can be increased with the use of biofunctionalized magnetic nanoparticles that have higher SAR for modest amplitudes of magnetic field[1]. Hence, understanding the factors that control the heat generation of magnetic nanoparticle suspensions is important to design fluids with optimized biocompatibility and functionality. In all biomedical applications, the nanoparticles must be coated on the surface to prevent their agglomeration [2], enhance biocompatibility and allow targeting to a specific area. Existing studies have shown that the SAR of nanoparticles may change in the presence of functional coating[3–5]. However, while these studies show that the coating may affect the heat generation rate, there is a limited understanding on the mechanisms that cause that changes of SAR. Hence, it is important to carry out a systematic investigation of nanoparticles similar in size but with different organic coating relevant to biomedical applications to obtain a more complete picture of the mechanisms contributing to changes in SAR. In this work, we present a review of our efforts in this area. Specifically, in our studies we are investigating the correlation between the magnetic and physical properties of commercially available nanoparticles systems and their heat generation rate. The susceptibility and SAR of suspensions of coated and uncoated iron oxide nanoparticles of similar particle size are measured. The coatings selected are highly relevant to biomedical applications and include amine and carboxyl functionalization as well as bioaffine ligands such as protein and biotin. The particle and cluster size was determined from transmission electron microscope (TEM), X-Ray diffraction (XRD) and Dynamic light scattering (DLS). TEM and DLS studies suggested that clusters exist in samples. A summary of all morphological properties together with pH of each suspension is shown in Table.1. The AC magnetic susceptibility of the suspensions was measured as a function of frequency with an in-house made apparatus. Finally SAR was determined by heating the suspension in a commercial induction system and measuring the temperature rise as function of time with a fiber optic sensor. Following these measurements, the SAR values were predicted in two ways: 1) based on measured AC susceptibility and 2) based on particle physical and magnetic properties, starting from Debye model for susceptibility. The normalized predicted and experimental SAR values for all samples are also shown in Table 1. From Table 1, it was found that pH may influence aggregation as described in Ref [6], which indicated that at pH about 2 nanoparticles are highly charged preventing their aggregation while in pH in 6–10 suspensions aggregations are more significant. Normalized SAR of nanoparticle system with aggregations seems to be not related to concentration, different from the well dispersed system[7]. The carboxyl coated sample has smallest diameter and show the lowest SAR, as reported in Ref[8]. The results of suspensions of uncoated iron oxide nanoparticles as well as particles coated with amine groups show that normalized experimental SAR (NSARE) agrees relatively well with calculated SAR using experimental susceptibility (NSARC_χ″E); poor agreement was found when experimental susceptibility was substituted with calculated one (NSART_χ″C) using Debye model, which is developed for non-interacting magnetic particles. These results suggest that the coating do not have a direct effect on SAR. On the other hand, agglomeration, which was present in both samples, may lead to dipolar interaction between nanoparticles and enhancement in magnetic properties and SAR. For carboxyl coated sample which has negligible clustering, showed no temperature increase and zero imaginary part of susceptibility. Therefore, good agreement between Debye-model based predictions of SAR and experimental results were obtained in this sample. However, unexpected results were obtained for bioaffine ligands coated sample, where the experimental SAR values are higher than the SAR values determined based on experimental susceptibility. Protein coated sample, which has the larger clusters among the two samples, has a heat generation rate is 6 times higher than the prediction. Meanwhile, the biotin coated sample which has relatively smaller clusters show only a small increase in heat generation rate. A possible explanation for these results is the loss of superparamagnetic character and an opening in hysteresis loop at test frequency for suspensions with large clusters, which may increase the dissipated power above that produced by the relaxation heat losses [9]. Above results show that coating had little effect on SAR. On the other hand, aggregations and clusters may significantly affect SAR, possibly due to dipolar interaction between nanoparticles in suspensions with relatively small clusters or loss of superparmagnetic characters when very large clusters are present.