Effect of Phosphate and Ferritin Subunit Composition on the Kinetics, Structure, and Reactivity of the Iron Core in Human Homo- and Heteropolymer Ferritins.

Ferritins are highly conserved supramolecular protein nanostructures that play a key role in iron homeostasis. Thousands of iron atoms can be stored inside their hollow cavity as a hydrated ferric oxyhydroxide mineral. Although phosphate associates with the ferritin iron nanoparticles, the effect of physiological concentrations on the kinetics, structure, and reactivity of ferritin iron cores has not yet been explored. Here, the iron loading and mobilization kinetics were studied in the presence of 1-10 mM phosphate using homopolymer and heteropolymer ferritins having different H to L subunit ratios. In the absence of ferritin, phosphate enhances the rate of ferrous ion oxidation and forms large and soluble polymeric Fe(III)-phosphate species. In the presence of phosphate, Fe(II) oxidation and core formation in ferritin is significantly accelerated with oxidation rates several-fold higher than with phosphate alone. High-angle annular dark-field scanning transmission electron microscopy measurements revealed a strong phosphate effect on both the size and morphology of the iron mineral in H-rich (but not L-rich) ferritins. While iron nanoparticles in L-rich ferritins have spherical shape in the absence and presence of phosphate, iron nanoparticles in H-rich ferritins change from irregular shapes in the absence of phosphate to spherical particles in the presence of phosphate with larger size distribution and smaller particle size. In the presence of phosphate, the kinetics of iron-reductive mobilization from ferritin releases twice as much iron than in its absence. Altogether, our results demonstrate an important role for phosphate, and the ferritin H and L subunit composition toward the kinetics of iron oxidation and removal from ferritin, as well as the structure and reactivity of the iron mineral, and may have an important implication on ferritin iron management in vivo.

Corrigendum to: GSK-3 Inhibitors in the Regulation and Control of Colon Carcinoma.

The author requested to add a co-author after the publication of the original article [1]. In this correction, the author has been added in the article entitled "GSK-3 Inhibitors in the Regulation and Control of Colon Carcinoma" in the journal "Current Drug Targets" 2021; 22(13), 1485-1495. Details of the error and a correction are provided here. The original editorial can be found online at 10.2174/1389450122666210204203950 We regret any errors and apologize to the readers. Original: Sitansu S. Nanda1, Md Imran Hossain1, Heongkyu Ju2 and Dong Kee Yi1,* 1Department of Chemistry, Myongji University, Yongin, 03674, South Korea; 2Department of Physics, Gachon University, Seongnam-si, Gyeonggi-do, South Korea Corrected: Sitansu S. Nanda1, Md Imran Hossain1, Heongkyu Ju2, Georgia C. Papaefthymiou3 and Dong Kee Yi1,* 1Department of Chemistry, Myongji University, Yongin, 03674, South Korea; 2Department of Physics, Gachon University, Seongnam-si, Gyeonggi-do, South Korea 3Department of Physics, Villanova University, Villanova, Pennsylvania19085, USA.

Micromagnetic and morphological characterization of heteropolymer human ferritin cores.

The physical properties of in vitro iron-reconstituted and genetically engineered human heteropolymer ferritins were investigated. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), electron energy-loss spectroscopy (EELS), and 57Fe Mössbauer spectroscopy were employed to ascertain (1) the microstructural, electronic, and micromagnetic properties of the nanosized iron cores, and (2) the effect of the H and L ferritin subunit ratios on these properties. Mössbauer spectroscopic signatures indicate that all iron within the core is in the high spin ferric state. Variable temperature Mössbauer spectroscopy for H-rich (H21/L3) and L-rich (H2/L22) ferritins reconstituted at 1000 57Fe/protein indicates superparamagnetic behavior with blocking temperatures of 19 K and 28 K, while HAADF-STEM measurements give average core diameters of (3.7 ± 0.6) nm and (5.9 ± 1.0) nm, respectively. Most significantly, H-rich proteins reveal elongated, dumbbell, and crescent-shaped cores, while L-rich proteins present spherical cores, pointing to a correlation between core shape and protein shell composition. Assuming an attempt time for spin reversal of τ 0 = 10-11 s, the Néel-Brown formula for spin-relaxation time predicts effective magnetic anisotropy energy densities of 6.83 × 104 J m-3 and 2.75 × 104 J m-3 for H-rich and L-rich proteins, respectively, due to differences in surface and shape contributions to magnetic anisotropy in the two heteropolymers. The observed differences in shape, size, and effective magnetic anisotropies of the derived biomineral cores are discussed in terms of the iron nucleation sites within the interior surface of the heteropolymer shells for H-rich and L-rich proteins. Overall, our results imply that site-directed nucleation and core growth within the protein cavity play a determinant role in the resulting core morphology. Our findings have relevance to iron biomineralization processes in nature and the growth of designer's magnetic nanoparticles within recombinant apoferritin nano-templates for nanotechnology.

GSK-3 Inhibitors in the Regulation and Control of Colon Carcinoma.

BACKGROUND: Glycogen syntheis kinase (GSK-3) inhibitors are novel therapeutic agents for treating various types of cancer, such as breast, lung, and gastric cancer. No pathological changes have been found by the morphological examination of GSK-3. OBJECTIVES: This review describes recent procedures using GSK-3 inhibitors, primarily in treating colon carcinoma. Furthermore, it also explains the mechanism of action of different GSK-3 inhibitors in treating various types of cancers and proposes some additional mechanisms may be useful for further research on GSK-3 inhibitors for cancers, including colon carcinoma. RESULTS: The majority of the cancerous and pre-cancerous lesions are stimulated by the transformation of membrane-bound arachidonic acid (AA) to eicosanoids, a transformation that promotes for the viability, proliferation, and spread of cancer. GSK-3 inhibitors can reinstate hostility to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) responsiveness in gastric adenocarcinoma cells. GSK-3, the final enzyme in glycogen synthesis, is a serine/threonine kinase that phosphorylates varied sequences that are more than a hundred in number, within proteins in an array of heterogeneous pathways. It is an essential module of an exceptionally large number of cellular processes, playing a fundamental role in many metabolic processes and diseases. Many patients diagnosed with colon cancer achieve long-term remission with outstanding survival through the GSK-3 inhibitors. CONCLUSION: Prior to the extensive application of these proposed mechanisms of GSK-3 inhibitor, further evaluation and clinical studies are needed. Only after the completion of appropriate clinical studies and morphological examinations, would extensive application be apprpriate.

Cancer Cell Detection on the Surface of Top-Gated Monolayer Graphene via Raman Spectroscopy.

A label-free biosensor is described based on the Raman spectroscopic signatures of monolayer graphene, which are modified in the compartment of cancer cells because of electron-phonon coupling in monolayer graphene. Specifically, the Raman spectra of electrostatically gated monolayer graphene on SiO2/Si substrates, in the voltage range from 0 to 5 V, were studied in the absence and the presence of cancer cells. Density functional theory simulations afforded a correlation between cancer cells and the observed Raman spectra, through the regulation of the intensities of the G and 2D Raman vibrational modes with applied voltage. The C-H and N-H bonds of phenylalanine enabled the detection of this biosensing activity. Significantly, this detection can be carried out even in the absence of cancer cell-culturing steps.

Monolayer Quantum-Dot Based Light-Sensor by a Photo-Electrochemical Mechanism.

Monolayer nanocrystal-based light sensors with cadmium-selenium thin film electrodes have been investigated using electrochemical cyclic voltammetry tests. An indium tin oxide electrode system, with a monolayer of homogeneously deposited cadmium-selenium quantum dots was proven to work as a photo-sensor via an electrochemical cell mechanism; it was possible to tune current densities under light illumination. Electrochemical tests on a quantum dot capacitor, using different sized (red, yellow and green) cadmium-selenium quantum dots on indium tin oxide substrates, showed typical capacitive behavior of cyclic voltammetry curves in 2M H2SO4 aqueous solutions. This arrangement provides a beneficial effect in, both, charge separation and light sensory characteristics. Importantly, the photocurrent density depended on quantum yield rendering tunable photo-sensing properties.

N-H Bond Formation at a Diiron Bridging Nitride.

Despite their connection to ammonia synthesis, little is known about the ability of iron-bound, bridging nitrides to form N-H bonds. Herein we report a linear diiron bridging nitride complex supported by a redox-active macrocycle. The unique ability of the ligand scaffold to adapt to the geometric preference of the bridging species was found to facilitate the formation of N-H bonds via proton-coupled electron transfer to generate a µ-amide product. The structurally analogous µ-silyl- and µ-borylamide complexes were shown to form from the net insertion of the nitride into the E-H bonds (E=B, Si). Protonation of the parent bridging amide produced ammonia in high yield, and treatment of the nitride with PhSH was found to liberate NH3 in high yield through a reaction that engages the redox-activity of the ligand during PCET.

Mechanophysical Cues in Extracellular Matrix Regulation of Cell Behavior.

The extracellular matrix (ECM) is a macromolecular network that can provide biochemical and structural support for cell adhesion and formation. It regulates cell behavior by influencing biochemical and physical cues. It is a dynamic structure whose components are modified, degraded, or deposited during connective tissue development, giving tissues strength and structural integrity. The physical properties of the natural ECM environment control the design of naturally or synthetically derived biomaterials to guide cell function in tissue engineering. Tissue engineering is an important field that explores physical cues of the ECM to produce new viable tissue for medical applications, such as in organ transplant and organ recovery. Understanding how the ECM exerts physical effects on cell behavior, when cells are seeded in synthetic ECM scaffolds, is of utmost importance. Herein we review recent findings in this area that report on cell behaviors in a variety of ECMs with different physical properties, i.e., topology, geometry, dimensionality, stiffness, and tension.

A new device concept for bacterial sensing by Raman spectroscopy and voltage-gated monolayer graphene.

Electron-phonon coupling in monolayer graphene results in a modification of its Raman spectra upon charge transfer processes induced by interaction with its chemical environment or the presence of strain or defects in its structure. Modification of Raman spectra is examined in order to develop ultra-sensitive biosensing techniques for the detection, identification, differentiation and classification of bacteria associated with infectious diseases. Specifically, the electrochemical properties of top gated monolayer graphene on SiO2/Si substrates, in the absence and presence of interaction with Gram-positive bacteria (Enterococcus faecalis, Bacillus subtilis) and Gram-negative bacteria (Escherichia coli and Salmonella typhimurium), are probed by Raman spectroscopy in an applied voltage range from 0 V to 3 V. Bacteria and monolayer graphene interactions are thus electrostatically tuned. The resulting correlation of specific bacterial chemical properties and Raman spectral characteristics is reported, along with density functional theory simulations of the charge transfer mechanism. The intensities of the G and D Raman vibrational modes are modulated as a function of the applied voltage in the presence of bacteria, but remain unchanged in bare monolayer graphene. A fingerprint region is also identified in the range of 200 cm-1 to 600 cm-1, with disulfide bonds observed at 490 cm-1, associated with bacterial membrane proteins. Significantly, such observations are detected even in the absence of bacterial culturing, a time-consuming step.

Recent advances in biocompatible semiconductor nanocrystals for immunobiological applications.

Quantum confinement in inorganic semiconductor nanocrystals produces brightly luminescent nanoparticles endowed with unique photo-physical properties, such as tunable optical properties. These have found widespread applications in nanotechnology. The ability to render such nanostructures biocompatible, while maintaining their tunable radiation in the visible range of the electromagnetic spectrum, renders them appropriate for bio-applications. Promising in vitro and in vivo diagnostic applications have been demonstrated, such as fluorescence-based detection of biological interactions, single molecule tracking, multiplexing and immunoassaying. In particular, these fluorescent inorganic semiconductor nanocrystals, generally known as quantum dots, have the potential of remarkable immunobiological applications. This review focuses on the current status of biocompatible quantum dots and their applications in immunobiology - immunosensing, immunofluorescent imaging and immunotherapy.

Combined Mössbauer Spectral and Density Functional Study of an Eight-Coordinate Iron(II) Complex.

The iron-57 Mössbauer spectra of the eight-coordinate complex, [Fe(L(N4))2](BF4)2, where L(N4) is the tetradentate N(1)(E),N(2)(E)-bis[(1-methyl-1H-imidazol-2-yl)methylene]-1,2-benzenediimine ligand, have been measured between 4.2 and 295 K and fit with a quadrupole doublet. The fit at 4.2 K yields an isomer shift, δ(Fe), of 1.260(1) mm/s and a quadrupole splitting, ΔE(Q), of 3.854(2) mm/s, values that are typical of a high-spin iron(II) complex. The temperature dependence of the isomer shift yields a Mössbauer temperature, Θ(M), of 319(27) K and the temperature dependence of the logarithm of the Mössbauer spectral absorption area yields a Debye temperature, Θ(D), of 131(6) K, values that are indicative of high-spin iron(II). Nonrelativistic single point density functional calculations with the B3LYP functional, the full 6-311++G(d,p) basis set, and the known X-ray structures for [Mn(L(N4))2](2+), [Mn(L(N4))2](ClO4)2, 1, [Fe(L(N4))2](2+), and [Fe(L(N4))2](BF4)2, 2, yield small electric field gradients for the manganese(II) complexes and electric field gradients and s-electron densities at the iron-57 nuclide that are in good to excellent agreement with the Mössbauer spectral parameters. The structure of 2 with a distorted square-antiprism C1 iron(II) coordination symmetry exhibits four different Fe-N(imid) bonds to the imidazole nitrogens with an average bond distance of 2.253(2) Å and four different Fe-N(imine) bonds to the benzenediimine nitrogens, with an average bond distance of 2.432(2) Å; this large difference yields the large observed ΔE(Q). An optimization of the [Fe(L(N4))2](2+) structure leads to a highly symmetric eight-coordination environment with S4 symmetry and four equivalent Fe-N(imid) bond distances of 2.301(2) Å and four equivalent Fe-N(imine) bond distances of 2.487(2) Å. In contrast, an optimization of the [Mn(LN4)2](2+) structure leads to an eight-coordination manganese(II) environment with D(2d) symmetry and four equivalent Mn-N(imid) bond distances of 2.350(3) Å and four equivalent Mn-N(imine) bond distances of 2.565(3) Å.

Size- and composition-dependent radio frequency magnetic permeability of iron oxide nanocrystals.

We investigate the size- and composition-dependent ac magnetic permeability of superparamagnetic iron oxide nanocrystals for radio frequency (RF) applications. The nanocrystals are obtained through high-temperature decomposition synthesis, and their stoichiometry is determined by Mössbauer spectroscopy. Two sets of oxides are studied: (a) as-synthesized magnetite-rich and (b) aged maghemite nanocrystals. All nanocrystalline samples are confirmed to be in the superparamagnetic state at room temperature by SQUID magnetometry. Through the one-turn inductor method, the ac magnetic properties of the nanocrystalline oxides are characterized. In magnetite-rich iron oxide nanocrystals, size-dependent magnetic permeability is not observed, while maghemite iron oxide nanocrystals show clear size dependence. The inductance, resistance, and quality factor of hand-wound inductors with a superparamagnetic composite core are measured. The superparamagnetic nanocrystals are successfully embedded into hand-wound inductors to function as inductor cores.

The Mössbauer and magnetic properties of ferritin cores.

BACKGROUND: Mössbauer and magnetization measurements, singly or in combination, extract detailed information on the microscopic or internal magnetism of iron-based materials and their macroscopic or bulk magnetization. The combination of the two techniques affords a powerful investigatory probe into spin relaxation processes of nanosize magnetic systems. The ferritin core constitutes a paradigm of such nano-magnetic system where Mössbauer and magnetization studies have been broadly combined in order to elucidate its composition, the initial steps of iron nucleation and biomineralization, particle growth and core-size distribution. In vivo produced and in vitro reconstituted wild-type and variant ferritins have been extensively studied in order to elucidate structure/function correlations and ferritin's role in iron overloading or neurodegenerative disorders. SCOPE OF REVIEW: Studies on the initial stages of iron biomineralization, biomimetic synthetic analogues and ferrous ion retention within the ferritin core are presented. The dynamical magnetic properties of ferritin by Mössbauer and magnetization measurements are critically reviewed. The focus is on experiments that reveal the internal magnetic structure of the ferritin core. Novel magnetic measurements on individual ferritin molecules via AFM and nanoSQUID investigations are also mentioned. MAJOR CONCLUSIONS: A complex two-phase spin system is revealed due to finite-size effects and non-compensated spins at the surface of the anti-ferromagnetic ferritin core. Below the blocking temperature surface spins participate in relaxation processes much faster than those associated with collective magnetic excitations of interior spins. GENERAL SIGNIFICANCE: The studies reviewed contribute uniquely to the elucidation of the spin-structure and spin-dynamics of anti-ferromagnetic nanolattices and their possible applications to nano/bio-technology.

Stable eight-coordinate iron(III/II) complexes.

The chemistry of unusual coordination numbers of transition-metal complexes has been of interest because of their presence in biology and catalytic systems. Herein we describe a systematic and predictable approach toward isolation of stable eight-coordinate (8C) iron(III/II) systems. The 8C (S = 2; high-spin, HS) complex [Fe(L(N4))(2)](BF(4))(2) (1) has been synthesized and characterized, displaying a distorted square-antiprism structure. Complex 1 is a unique 8C iron complex that exhibits remarkable stability in solution under various unfavorable conditions. The E(1/2) value of 1 (0.430 V vs Ag/AgCl, MeCN) supports the Fe(II) oxidation state; however, the corresponding HS (S = 5/2) 8C Fe(III) analogue [Fe(L(N4))(2)](NO(3))(3) (3) has also been synthesized via the chemical oxidation of 1. The structural, spectroscopic, and theoretical descriptions of these 8C iron complexes are reported in this work.

A comparative Mössbauer study of the mineral cores of human H-chain ferritin employing dioxygen and hydrogen peroxide as iron oxidants.

Ferritins are ubiquitous iron storage and detoxification proteins distributed throughout the plant and animal kingdoms. Mammalian ferritins oxidize and accumulate iron as a ferrihydrite mineral within a shell-like protein cavity. Iron deposition utilizes both O(2) and H(2)O(2) as oxidants for Fe(2+) where oxidation can occur either at protein ferroxidase centers or directly on the surface of the growing mineral core. The present study was undertaken to determine whether the nature of the mineral core formed depends on the protein ferroxidase center versus mineral surface mechanism and on H(2)O(2) versus O(2) as the oxidant. The data reveal that similar cores are produced in all instances, suggesting that the structure of the core is thermodynamically, not kinetically controlled. Cores averaging 500 Fe/protein shell and diameter approximately 2.6 nm were prepared and exhibited superparamagnetic blocking temperatures of 19 and 22 K for the H(2)O(2) and O(2) oxidized samples, respectively. The observed blocking temperatures are consistent with the unexpectedly large effective anisotropy constant K(eff)=312 kJ/m(3) recently reported for ferrihydrite nanoparticles formed in reverse micelles [E.L. Duarte, R. Itri, E. Lima Jr., M.S. Batista, T.S. Berquó and G.F. Goya, Large Magnetic Anisotropy in ferrihydrite nanoparticles synthesized from reverse micelles, Nanotechnology 17 (2006) 5549-5555.]. All ferritin samples exhibited two magnetic phases present in nearly equal amounts and ascribed to iron spins at the surface and in the interior of the nanoparticle. At 4.2 K, the surface spins exhibit hyperfine fields, H(hf), of 436 and 445 kOe for the H(2)O(2) and O(2) samples, respectively. As expected, the spins in the interior of the core exhibit larger H(hf) values, i.e. 478 and 486 kOe for the H(2)O(2) and O(2) samples, respectively. The slightly smaller hyperfine field distribution DH(hf) for both surface (78 kOe vs. 92 kOe) and interior spins (45 kOe vs. 54 kOe) of the O(2) sample compared to the H(2)O(2) samples implies that the former is somewhat more crystalline.

Size-dependent magnetic properties of single-crystalline multiferroic BiFeO3 nanoparticles.

As-prepared, single-crystalline bismuth ferrite nanoparticles show strong size-dependent magnetic properties that correlate with: (a) increased suppression of the known spiral spin structure (period length of approximately 62 nm) with decreasing nanoparticle size and (b) uncompensated spins and strain anisotropies at the surface. Zero-field-cooled and field-cooled magnetization curves exhibit spin-glass freezing behavior due to a complex interplay between finite size effects, interparticle interactions, and a random distribution of anisotropy axes in our nanoparticle assemblies.

Silica-coated nanocomposites of magnetic nanoparticles and quantum dots.

Quantum dots (QDs) and magnetic nanoparticles (MPs) are of interest for biological imaging, drug targeting, and bioconjugation because of their unique optoelectronic and magnetic properties, respectively. To provide for water solubility and biocompatibility, QDs and MPs were encapsulated within a silica shell using a reverse microemulsion synthesis. The resulting SiO2/MP-QD nanocomposite particles present a unique combination of magnetic and optical properties. Their nonporous silica shell allows them to be surface modified for bioconjugation in various biomedical applications.

Magnetic, electronic, and structural characterization of nonstoichiometric iron oxides at the nanoscale.

We have investigated the structural, magnetic, and electronic properties of nonstoichiometric iron oxide nanocrystals prepared by decomposition of iron(II) and iron(0) precursors in the presence of organic solvents and capping groups. The highly uniform, crystalline, and monodisperse nanocrystals that were produced enabled a full structural and compositional survey by electron microscopy and X-ray diffraction. The complex and metastable behavior of nonstoichiometric iron oxide (wüstite) at the nanoscale was studied by a combination of Mossbauer spectroscopy and magnetic characterization. Deposition from hydrocarbon solvents with subsequent self-assembly of iron oxide nanocrystals into superlattices allowed the preparation of continuous thin films suitable for electronic transport measurements.

mu-1,2-Peroxobridged di-iron(III) dimer formation in human H-chain ferritin.

Biomineralization of the ferritin iron core involves a complex series of events in which H(2)O(2) is produced during iron oxidation by O(2) at a dinuclear centre, the 'ferroxidase site', located on the H-subunit of mammalian proteins. Rapid-freeze quench Mössbauer spectroscopy was used to probe the early events of iron oxidation and mineralization in recombinant human ferritin containing 24 H-subunits. The spectra reveal that a mu-1,2-peroxodiFe(III) intermediate (species P) with Mössbauer parameters delta (isomer shift)=0.58 mm/s and DeltaE(Q) (quadrupole splitting)=1.07 mm/s at 4.2 K is formed within 50 ms of mixing Fe(II) with the apoprotein. This intermediate accounts for almost all of the iron in the sample at 160 ms. It subsequently decays within 10 s to form a mu-oxodiFe(III)-protein complex (species D), which partially vacates the ferroxidase sites of the protein to generate Fe(III) clusters (species C) at a reaction time of 10 min. The intermediate peroxodiFe(III) complex does not decay under O(2)-limiting conditions, an observation suggesting inhibition of decay by unreacted Fe(II), or a possible role for O(2) in ferritin biomineralization in addition to that of direct oxidation of iron(II).

Deuterium structural effects in inorganic and bioinorganic aggregates.

Deuterium kinetic isotope effects are widely used in chemical and biological research. Deuterium thermodynamic effects on the aqueous synthesis of inorganic materials, however, seem not to have been recognized. Here we report that the simple replacement of H(2)O with D(2)O in the synthesis of a solid-state manganese complex results in a new structurally and magnetically distinct phase. When iron oxides are synthesized, the relative amount of the mineral phases obtained in H(2)O vs D(2)O is different. The morphology and magnetic properties of the iron core of the iron storage protein ferritin are likewise different when mineralization is carried out in heavy water. The formation of extra inorganic solids, change in the ratio of two phases or alteration of a single phase morphology in D(2)O suggest that new inorganic and bioinorganic metal complexes might be obtained by using the thermodynamic isotope effect.