Cuboidal Structure Research Articles

Inactivated LMBV vaccine with nano‑aluminum adjuvant provided immune protection in largemouth bass (Micropterus Salmoides)

Largemouth bass ranavirus (LMBV) has caused severe economic losses in largemouth bass (Micropterus salmoides) aquaculture. Vaccination is acknowledged as an efficient strategy to prevent viral diseases in fish. In this study, an inactivated virus vaccine with nano‑aluminum adjuvant was successfully developed to protect largemouth bass effectively against LMBV. LMBV was inactivated by formalin and mixed with nano‑aluminum adjuvant under moderate agitation. The nano‑aluminum hydroxide adjuvant showed a cuboidal structure under the scanning transmission electron microscope (STEM), scanning electron microscope (SEM), and transmission electron microscope (TEM), and LMBV antigen-adsorbing rate was 39.49 % superior to those of micro‑aluminum hydroxide and IMS1312 adjuvants. The results from both external and internal damage assessments indicated that the nano‑aluminum vaccine had good safety for Micropterus salmoides. The relative percentage of survival was 80 % with a booster immunization in largemouth bass. The expression levels of immune-related genes such as TNF-α, IFN, and IL-8 were significantly up-regulated in the spleen of fish immunized by nano‑aluminum adjuvant vaccine compared to those in inactivated LMBV and control groups. The neutralizing antibody in nano‑aluminum adjuvant vaccine group showed higher abundance and lasted for a longer period. Lymphocytes from the head kidney of largemouth bass in the nano‑aluminum adjuvant vaccine group showed stronger proliferation activity in vitro post-stimulation with ConA. Moreover, stronger migration of the dendritic cells was induced by the nano‑aluminum adjuvant vaccine. Collectively, our findings suggested that the inactivated LMBV vaccine with nano‑aluminum adjuvant could provide efficient protection for largemouth bass against LMBV infection. The nano‑aluminum adjuvant has potential application with inactivated viral vaccines in fish.

A Periodic Comparison of Harderian Gland in Henna Partridge (Alectoris chukar) According to Different Developmental Stages

Background: The present study aimed at determining histological structure and histochemical properties of the henna partridge (Alectoris chukar) Harderian gland periodically. Objectives: For this purpose, the Harderian glands of 12 (6 females + 6 males) healthy henna partridges aged 3 and 6 months were used. Methods: Totally removed Harderian gland tissue samples were kept in 10% neutral formolin for 36 hours and fixed. After washing, dehydrating, and polishing with known histological techniques, tissue pieces were blocked in paraffin. Results: We found that a thin connective tissue capsule surrounds the Harderian gland of the henna partridge and that the capsule sends septums into the gland and divides the gland into lobes and lobules. It was observed that the corpus glandulae consist of low or high prismatic epithelial cells. Within each lobe, there is a single main draining channel which has a very large lumen along with primary draining channels. Primary and main draining channel epithelial cells have a single-layered cuboidal structure. By Gordon-Sweet staining, it was found that reticular fiber bundles started from the connective tissue capsule that surrounded the organ and spread by branching. The reticular fiber bundles extended in thin strands to the periphery of the corpus glandulae. These reticular fiber bundles in the regions where the connective tissue septums widened are thicker and form a network. The reticular fiber bundles are seen in the basal part of the epithelial cells forming the main draining channel and especially in the crypt areas. Reticular fibers are also found around blood vessels. Strong Alcian blue (AB)-positive epithelial cells are observed in the corpus glandulae in AB pH=2.5 staining, but no periodic acid-Schiff (PAS)-positive epithelial cells are observed in PAS staining. While the majority of primary draining channel cells show a strong AB-positive reaction, a few cells showed a weak PAS-positive reaction. Regarding the main draining channel epithelium, goblet cells show a weak and strong AB-positive reaction in AB pH=2.5 staining method, respectively and a weak PAS-positive reaction in PAS staining method. Conclusion: In line with these findings, no significant difference was found in terms of general histological structure and histochemical properties of the 3- and 6-month-old henna partridge Harderian gland.

Hazardous 2,4,6-Trinitrophenol (TNP) Detection in Water by Amine and Azine Functionalized Metal-Organic Framework.

A Zn(II)-based metal-organic framework (MOF) decorated with amine and azine functionalities, TMU-17-NH2 (formulated as [Zn(H2ata)(L)].2DMF; L = 1,4-bis(4-pyridyl)-2,3-diaza-2,3-butadiene and H2ata = 2-aminoterephthalic acid) has been successfully synthesized via a solvothermal method. According to crystallographic studies, the synthesized TMU-17-NH2 has three dimensional cuboidal structure with the pore surface decorated with free amine (-NH2) and azine (= N-N =) functional groups. The photoluminescence investigations proved that the synthesized MOF can be effectively utilized for selective detection of 2,4,6-trinitrophenol (TNP) in water with an apparent turn-off quenching response. Its limits of detection (LOD) for TNP was 9.4ppb and competitive nitro explosive testing confirmed its higher selectivity towards TNP (over other nitro explosives). Calculations based on density functional theory (DFT) and spectrum overlap were utilized to evaluate the sensing mechanisms. This MOF-based fluorescence sensing technique for TNP had a high sensitivity (Ksv = 3.26 × 104M-1).

Cobalt and copper-based metal-organic frameworks synthesis and their supercapacitor application

In this study, two different metal-organic frameworks (MOFs) were synthesized using copper and cobalt metal ions with benzenedicarboxylic acid (bdc) as a common ligand. The prepared MOFs were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy-energy dispersive spectroscopy. Also, the electrochemical characteristics were analyzed using cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy methods. Structural characterizations indicate that Co-bdc MOF is composed of three-dimensional non-uniform colloids and Cu-bdc MOF has a regular three-dimensional cuboidal structure, possessing good crystalline structure. The Cu-bdc MOF exhibited a maximum specific capacitance of 171 F/g, while Co-bdc MOF showed 368 F/g at the current density of 1 A/g. The solution resistance for the Co-bdc MOF was 0.09 Ω in comparison to 1.25 Ω for the Cu-bdc MOF. Also, the Co-bdc MOF demonstrated better cycling performance by retaining 85 % of its capacity after 2000 charge-discharge cycles. In contrast, the stability of the Cu-bdc MOF was lower, with only 78 % retention in capacity. Conclusively, the Co-bdc MOF demonstrated superior specific capacitance, lower resistance, and enhanced cyclic stability in 3 M KOH electrolyte system.

Mechanical behaviour of reconstructed defected skull with custom PEEK implant and Titanium fixture plates under dynamic loading conditions using FEM

Skull reconstruction using cranial implants is often required for repairing skull defects caused due to trauma, diseases, or malignancy to protect intracranial structures. For relieving Intracranial Pressure (ICP) surgeons restore cranial defects either using natural bones or fabricated custom cranial implants. With the increase in Traumatic Brain Injuries (TBI) and challenges faced by TBI patients to regain normalcy, it is imperative to analyse the mechanical behaviour of skull-implant assemblies under some Head Injury Criteria (HIC). Medical grade materials including Titanium Alloys (Ti-6Al-4V) and Polyether-ether-ketone (PEEK) are used by fabricating Patient-Specific Implants (PSI) manufactured using 3D imaging, modelling and printing techniques. 3D technologies are preferred over conventional manufacturing methods, as they enable fabrication of custom shapes, sizes and properties for these PSI.For an effective attachment of PSI with a defective skull, a stable joint and plate arrangement as fixture plates is necessary at their interface. These fixtures can have variable numbers, design shapes, materials and location arrangements.This paper presents the Finite Element Method/Analysis (FEM/FEA) study of PSI attached to a defected skull for reconstruction, with linear shaped fixture configuration, when subjected to an external dynamic loading at 5 m/s, strain rate of 10s−1 to 243s−1 and ICP of 15mm Hg from three sides of the skull faces. Three different materials as Neoprene (soft), Concrete (medium rigid) and E-Glass (highly rigid) have been used, in the form of a rectangular thin cuboidal wall structure, at an angle of 45° with the skull face. Four linear shaped fixture plates which were simplest to design, were used to attach the PSI-skull assembly, to ensure that weight of the PSI-fixation assembly on the patient remains minimal, overall assembly has symmetrical fixations and efforts required by a surgeon for fitment of these plates remain minimal. Placement of these fixture plates has been optimized to encompass the complete PSI-skull interface section, due to which the stresses within all the assembly components (PSI, fixture plate and skull) reduced by nearly 2.5 times than the initial design and remained within yielding limits, thereby, averting any failure under heavy external dynamic loading.

Optimizing the microstructure and mechanical performance of Fe-Ni-Cr-Al high entropy alloys via Ti addition

The effect of Ti content on the microstructure and mechanical properties regulation for Fe45Ni30−xCr15Al10Tix high entropy alloys (HEAs) with a duplex FCC/BCC structure is investigated. The as-cast Fe45Ni30−xCr15Al10Tix HEAs have typical dendrite and inter-dendrite structure, where dendric and inter-dendric regions are FCC and BCC phases, respectively. After introducing Ti, the inter-dendric structure transforms into coexistence of disordered BCC and ordered B2/L21 phases. And the morphology of B2/L21 precipitates gradually changes from a regular maze-like mesh and cuboidal structure to elliptical structures due to the increase of the lattice mismatch. The change of precipitate type and volume fraction lead to that the ultimate tensile strength of the HEAs increases from 540 MPa to 1292 MPa. Meanwhile, it keeps the uniform elongation of 13.29%, showing outstanding strength-plasticity synergy.

Numerical Analysis on Effects of Wall Structures on Bubble Groups

With the volume of fluid (VOF) method for a dam-break problem, the effects of wall structures on compressible bubble groups were studied through measurement of the spatial average pressure on the wall. An obstacle was set up at the bottom of the tank, which helps create air bubbles in the collapsing water impacting on it. Three kinds of structures were set up on the left wall, namely, a cuboidal structure, an ellipsoidal structure and a conical structure. It is found that when water hits the left wall, the topology of the bubble wrapped in the water will be changed by the wall structure, which leads to the change of pressure on the wall. The example analysis shows that, the cuboidal structure has the maximum effect in reducing the average pressure amplitude on the wall among those three kinds of wall structures. Especially, a proper adjustment of the position and the size of the cuboidal structure can eliminate the oscillation of the wall pressure.

Spectroscopic, density functional theory, cytotoxicity and antioxidant activities of sulfasalazine and naproxen drugs combination

In this study, we reported preparation and characterization of a new nano product consisting of the combination of two anti-inflammatory drugs: naproxen and sulfasalazine (Sulfoxen) where both are currently used for the treatment of inflammatory disorders. The nano combination product and its structural characterization were obtained by the Fourier transform infrared (FT-IR) spectroscopy, X-ray powder diffraction (XRPD), Thermogravimetric analysis (TGA), Differential scanning calorimetry (DSC), Dynamic light scattering (DLS), Atomic force microscopy (AFM), and Field emission scanning electron microscopy (FE-SEM), respectively.The hydrogen bonding between the COOH groups of naproxen (NPX) and sulfasalazine (SSZ) drugs were evaluated by the experimental and theoretical spectra. FESEM and AFM techniques represent that the most particles of Sulfoxen have a solid dense cubical or cuboidal structure and they also have size range of 50–100 nm. The objective was to prepare the nano-formulation of the Sulfoxen with improved antioxidant properties with respect to the two compounds administered separately. We have evaluated the anti-cancer effect of Sulfoxen in comparison to sulfasalazine and naproxen drugs on MCF-7 and KYSE30 cell lines. Interestingly, exposure of the zebrafishes to Sulfoxen (12.5 mM) did not exhibit lethal toxicity compared to the control groups. Therefore, Sulfoxen could contribute to more studies for the possible future clinical use.

Effect of alloying on the γ-γ′ microstructure of W-free Co-based superalloys

The effect of niobium and molybdenum on the formation and morphology of γ′-phase with L12 ordering was studied in three single crystals of the Co-rich corner of the Co-Al-Mo-Nb system. It was shown that the diffraction lines of the γ′- phase were not detected in X-ray diffraction patterns, but reflections of this phase were visible in transmission electron-microscopic images (SAED patterns). Cuboidal structure of the γ′ -phase was presented in TEM images of studied alloys. It was found that in compare with molybdenum, the adding of niobium shows a stronger effect on the amount of the ordered γ′-phase formed in Co-Al-Mo-Nb alloys. Molybdenum content effects on the lattice mismatch between γ and γ′ phases, that is manifested in the loss of the cuboidal shape of the γ′- precipitations in the γ - matrix in the studied Co-Al-Mo-Nb alloy.

Vehicle–road interaction analysis for pounding between cargo and trailer-bed

The study is aimed at understanding the likelihood of occurrence of vertical separation between the cargo and the trailer of a truck resulting from the amplified vertical vibrational response of the vehicle. Certain road geometries can induce excessive amplification in suspension response of the heavy vehicles leading to large vertical accelerations in the cargo. The cargo of interest is a modular building unit (MBU) which is a long cuboidal structure that requires to be transported from the factory to the building site. The current work deploys an experimentally validated mathematical pitch-plane model of a trailer and a road undulation (road bump) geometry for the analysis. Parameters such as suspension stiffness, damping, vehicular speed, road undulation geometry and tie-down strap strength are used to quantify the probability of vertical separation that can occur between the MBU and the trailer-bed by employing Monte-Carlo simulations. Vertical separation is converted to vertical pounding (impact) velocity and values reaching up to 1.5 ms−1 have been found to be probable at the end of the study.

Antibacterial and Anticancer Activities of Biogenic Synthesized Ag and ZNO NPS

Biogenic synthesis of Ag and ZnO nanoparticles has been proposed as an environmental friendly and cost effective method. Curcuma longa tuber extract was used to reduce silver nitrate and zinc acetate to Ag NPs and ZnO NPs. The extract acts as each reducing capping agent. Synthesis process be standardized by modifying various parameters like salt concentrations, C. longa tuber extract concentration, and temperature and incubation period. The formation of Silver and ZnO NPs was observed among color transition. The morphology of the amalgamate Ag and ZnO NPs be characterized with various experimental techniques (FESEM, TEM). The face-centered cuboidal structure of Ag and ZnO NPs be studied using X-ray optical phenomenon. Further Ag in addition to ZnO NPs were tested for antibacterial and anticancer activities.

Template free synthesis of CdSnO3 micro-cuboids for dye sensitized solar cells

Mesoporous transparent conducting oxide, CdSnO3 has been synthesized using ultrasonication assisted co-precipitation method. Rather employing any template or structure directing agent, the co-precipitation effect of sodium hydroxide and citric acid were able to form cuboid shaped CdSnO3 during the sonochemical treatment as investigated by a systematic X-ray diffraction and field emission scanning electron microscopy studies. An optimum 3:1 molar concentration of NaOH and citric acid leads to form cuboidal structure of CdSnO3 on calcined at 700 °C. Further calcination at 800 °C converted cuboids to nanoparticles. Comparative studies have been carried out between the cuboid and particle morphology to understand the physico-chemical properties related to the morphology using various characterization techniques. Further, the CTO cuboids and the decomposed nanoparticles have been tested as photoanode for dye sensitized solar cell applications. The cuboid based photoanode exhibited an enhanced efficiency of 3.23% with a VOC of 0.72 V than its decomposed nanoparticle which exhibited a lower efficiency of 2.67%. The electrochemical impedance and incident photon to electron conversion efficiency results also support enhanced performance of cuboid based device than particle. The overall results show the advantage of cuboidal CdSnO3 in rapid electron injection and higher light reflection leading to improved current density of the DSSC device than the decomposed nanoparticle form. The results establish the application of less explored CdSnO3 as a photoanode in DSSCs application.

Structure of Phospholipid Mixed Micelles (Bicelles) Studied by Small-Angle X-ray Scattering.

Mixed phospholipid micelles (bicelles) are widely applied in nuclear magnetic resonance (NMR) studies of membrane proteins in solution, as they can solubilize these proteins and provide a membrane-like environment. In this work, the structure of bicelles of dihexanoyl phosphatidyl choline (DHPC) and dimyristoyl phosphatidyl choline (DMPC) at different ratios was determined by small-angle X-ray scattering (SAXS) at 37 °C. Samples with concentrations as applied for NMR measurements with 28 wt % lipids were diluted to avoid concentration effects in the SAXS data. The DMPC/DHPC ratio within the bicelles was kept constant by diluting with solutions of finite DHPC concentrations, where the concentration of free DHPC is the same as in the original solution. Absolute-scale modeling of the SAXS data using molecular and concentration constraints reveals a relatively complex set of morphologies of the lipid aggregates as a function of the molar ratio Q of DMPC to DHPC. At Q = 0 (pure DHPC lipids), oblate core-shell micelles are present. At Q = 0.5, the bicelles have a tablet-shaped core-shell cylindrical form with an ellipsoidal cross section. For Q = 1, 2, 3.2, and 4, the bicelles have a rectangular cuboidal structure with a core and a shell, for which the overall length and width increase with Q. At Q = ∞ (pure DMPC), there is coexistence between multilamellar structures and free bilayers. For Q = 1-4, the hydrocarbon core is relatively narrow and the headgroup thickness on the flat areas is larger than that of, respectively, pure DHPC and DMPC, suggesting some mixing of DHPC into these areas and staggering of the molecules. This is further supported by comparisons of the ratio of the areas of rim and flat parts and estimates of the composition of the flat areas.

Synthesis, Structural and Morphological Property of BaSnO3 Nanopowder Prepared by Solid State Ceramic Method

BaSnO3 is a cubic perovskite-type oxide that behaves as an n-type semiconductor with a wide band gap of 3.4 eV and remains stable at temperatures up to 1000°C. It has wide applications such as thermally stable capacitors, humidity sensors, gas sensors, etc. Barium stannate has also been used in optical applications, in capacitors and ceramic boundary layers, and as a promising material to produce gas phase sensors for the detection of carbon monoxide and carbon dioxide. BaSnO3 powder was prepared by solid state ceramic method. X-ray diffraction pattern of the prepared sample presents all the characteristic peaks of cubic phase of BaSnO3 (JCPDScard no: 15 -0780). The lattice constant for the compound was calculated and found to be 4.101A0 which is in agreement with the reported value (4.112A0). The average size of the crystallites estimated by Debye Scherrer’s formula was found to be 49 nm shows the nanostructured nature. The Raman bands observed ~ 139, 833 and 1122 cm−1 can be assigned on the basis of the fundamental vibrations of SnO6 octahedron which has Oh symmetry, in the distorted perovskite structure. The SEM image shows a porous surface morphology with grains of cuboidal structure with well-defined grain boundaries. UV-Visible spectra shows BaSnO3powder exhibit high reflectance in the 400-700 nm range.

Extraordinary high strength Ti-Zr-Ta alloys through nanoscaled, dual-cubic spinodal reinforcement.

The current research details microstructural, mechanical, and biological investigations into four novel biomedical alloys in a hitherto uninvestigated region of the Ti-Zr-Ta alloy system; Ti-45Zr-10Ta, Ti-40Zr-14Ta, Ti-35Zr-18Ta and Ti-30Zr-22Ta. We find that the investigated alloys display 0.2% yield strengths of up to 1.40GPa and elastic admissible strains of up to 1.48%, along with biological properties comparable to that seen in the conventional metallic biomaterial ASTM Grade-2 CP-Ti, achieved in the complete absence of traditional thermomechanical processing techniques. This is attributed to the presence of a dual-BCC cuboidal nanostructure, achieved via spinodal decomposition; while similar structures have been reported in e.g. Ni-based superalloys, we believe this is the first such structure investigated in a Ti-based material. As such, this work is felt to be of great interest in aiding the design and manufacture of highly-biocompatible, porous, metallic biomaterials for orthopedic application.

Antimony-Supported Cu4I4 Cuboid with Short Cu-Cu Bonds: Structural Premise for Near-Infrared Thermoluminescence.

Herein we report the synthesis, temperature-dependent X-ray structures (100, 150, 200, 250, 273, and 300 K), and solid-state emissive properties of the antimony-copper(I)-iodo cluster [Cu4(I)4(Sb(i)Pr3)4] (1), supported by the trialkylantimony donor Sb(i)Pr3. Overall, 1 exhibits a distorted cuboidal structure, wherein a twisting of the "cube" generates an interconnected Cu4 tetrahedron, as well as long Cu-I and Cu-Sb bonds [e.g., 2.707(2) and 2.571(2) Å]; in the 100 K X-ray structure, the Cu-Cu bonds are quite short [2.761(3) Å]. Solid-state emission spectra of 1 were obtained over a range of temperatures (163-298 K), wherein 1 exhibits only a low-energy emission feature centered near 700 nm (λEm = 711 nm, fwhm = 150 nm, and λEx = 390 nm). Because 1 contains no aryl units, the emission spectrum (and absorption) can be unambiguously attributed to the Cu4I4 core [no L (pnictogen ligand) component]. The luminescence is sharply attenuated upon warming from 150 to 200 K. An overlaid plot of the emissive properties of 1 and its Cu-Cu bond distances [2.761(3)-2.836(4) Å] reveal that ∼2.80 Å represents a critical crossing point for low-energy thermoluminescence in Cu4-based clusters.

Photocatalytic decoloration of three commercial dyes in aqueous phase and industrial effluents using TiO2 nanoparticles

TiO2 sol was synthesized under mild conditions (25 ± 1°C and ambient pressure) by hydrolysis of titanium isopropoxide in aqueous solution and subsequent reflux to enhance crystallization. The material was characterized by X-ray diffraction, transmission electron microscopy, and Fourier transform infrared. The synthesized sample presented a pure phase anatase with nanometric particle size. The photodegradation of reactive dyes (malachite green, methylene blue, and rhodamine B) and industrial effluents was elucidated in aqueous suspension containing titania nanoparticles under UV irradiation. Also, the effect of pH in nanoparticle synthesis and role of catalyst dose and dye concentration were evaluated. The experimental result showed that particles synthesized by sol–gel method are of 20–40nm anatase form with cuboidal structure and OH− as a major functional group. These particles showed efficiency to degrade dyes up to 98% and industry (paint and textile) effluents can be decolorized in the TiO2/UV system.

μ2-Acetato-κ(2) O:O'-(4,4'-bipyridyl-κN)tris-(diethyl di-thio-phosphato-κ(2) S,S')-μ3-sulfido-tri-μ2-sulfido-trimolybdenum(IV) diethyl ether monosolvate.

In the title compound, [Mo3(CH3COO)(C4H10O2PS2)3S4(C10H8N2)]·C4H10O, the complex mol­ecule has a trinuclear incomplete cuboidal structure which is coordinated by three kinds of ligands, namely, diethyl di­thio­phosphate, acetate and 4,4′-bipyridyl. If Mo—Mo bonds are ignored, each Mo atom can be considered as six-coordinated in a distorted octa­hedral geometry. The Mo—Mo distance of 2.6880 (5) Å for two the Mo atoms bridged by the acetate ligand is shorter than the other two Mo—Mo distances [2.7490 (5) and 2.7566 (5) Å]. One ethyl group is disordered between two conformations in a 0.65 (3):0.35 (3) ratio. In the crystal, weak C—H⋯O inter­actions link the trinuclear mol­ecules related by translation in [100] into chains. The crystal packing exhibits short inter­molecular S⋯S contacts of 3.1886 (13) Å. In other words, in this crystal packing, a supramolecular structure is constructed by the C—H⋯O and S⋯S interactions.

Effects of Alloying Elements on Physical and Mechanical Properties of Co-Al-W-Based L1<sub>2</sub>/fcc Two-Phase Alloys

The changes in the γ’ solvus temperature and the volume fraction of Co-Al-W based alloys with fcc / L12 two-phase microstructures upon alloying with quaternary elements have been investigated. All investigated quaternary elements, except for Fe and Re, increase the γ’ solvus temperatures of Co-Al-W based alloys with varying efficiencies depending on quaternary element. On the other hand, the variation of the γ’ volume fraction with alloying depends on the alloying element. Of the investigated quaternary elements, Ta is found to be the most effective in increasing the γ’ solvus temperature of Co-Al-W based alloys. The lattice mismatch significantly increase upon alloying with Ta of 4at.%, which destroys the coherent cuboidal structure.

Water Oxidation Mechanism for Synthetic Co–Oxides with Small Nuclearity

Hybrid DFT model calculations have been performed for some cobalt complexes capable of oxidizing water. Since a very plausible mechanism for the oxygen-evolving complex involving the cuboidal Mn4Ca structure in photosystem II (PSII) has recently been established, the most important part of the present study concerns a detailed comparison between cobalt and manganese as water oxidation catalysts. One similarity found is that a M(IV)-O(•) state is the key precursor for O-O bond formation in both cases. This means that simply getting a M(IV) state is not enough; a formal M(V)═O state is required, with two oxidations on one center from M(III). For cobalt, not even that is enough. A singlet coupled state is required at this oxidation level, which is not the ground state. It is shown that there are also more fundamental differences between catalysts based on these metals. The favorable low-barrier direct coupling mechanism found for PSII is not possible for the corresponding cobalt complexes. The origin of this difference is explained. For the only oxygen-evolving cubic Co4O4 complex with a defined structure, described by Dismukes et al., the calculated results are in good agreement with experiments. For the Co4 models of the amorphous cobalt-oxo catalyst found by Nocera et al., higher barriers are found than the one obtained experimentally. The reasons for this are discussed.