Magnetic anisotropy of a CoII single ion magnet with distorted trigonal prismatic coordination: theory and experiment

The single ion magnetic properties of Co(II) are affected by the details of the coordination geometry of the ion. Here we show that a geometry close to trigonal prismatic which arises when the ligand 6,6′-((1Z)-((piperazine-1,4-diylbis(propane-3,1-diyl))bis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol) coordinates to Co(II) does indeed lead to enhanced single-ion behaviour as has previously been predicted. Synthesis of the compound, structural information, and static as well as dynamic magnetic data are presented along with an analysis using quantum chemical ab initio calculations. Though the complex shows a slight deviation from an ideal trigonal prismatic coordination, the zero-field splitting as well as the g-tensor are strongly axial with D = −41 cm−1 and E < 0.01 cm−1. For the lowest Kramers doublet (S = 1/2) g∥ = 7.86 and g⊥ < 0.05 were found. In contrast, the second Kramers doublet possesses a rhombic g-tensor with g∥ = 2.75 and g⊥ = 4.35. Due to large spin–orbit coupling resulting in very different g tensors, it is not possible to simulate the temperature dependence of the magnetic susceptibility with a spin Hamiltonian of the form H = D(Sz2 − S(S + 1)/3) + E(Sx2 − Sy2) + μBgS·B using an effective spin S = 3/2. Calculations on model complexes show the influence of the coordinating atoms and the deviation from the ideal trigonal prismatic coordination. As the distortion is reduced towards idealised D3h, the zero field splitting increases and the g-tensor of the second Kramers doublet also becomes axial

SARS-CoV-2 Omicron triggers cross-reactive neutralization and Fc effector functions in previously vaccinated, but not unvaccinated, individuals

The SARS-CoV-2 Omicron variant escapes neutralizing antibodies elicited by vaccines or infection. However, whether Omicron triggers cross-reactive humoral responses to other variants of concern (VOCs) remains unknown. We used plasma from 20 unvaccinated and 7 vaccinated individuals infected by Omicron BA.1 to test binding, Fc effector function, and neutralization against VOCs. In unvaccinated individuals, Fc effector function and binding antibodies targeted Omicron and other VOCs at comparable levels. However, Omicron BA.1- triggered neutralization was not extensively cross-reactive for VOCs (14- to 31-fold titer reduction), and we observed 4-fold decreased titers against Omicron BA.2. In contrast, vaccination followed by breakthrough Omicron infection associated with improved cross-neutralization of VOCs with titers exceeding 1:2,100. This has important implications for the vulnerability of unvaccinated Omicron-infected individuals to reinfection by circulating and emerging VOCs. Although Omicron-based immunogens might be adequate boosters, they are unlikely to be superior to existing vaccines for priming in SARS-CoV-2-naive individuals.The South African Research Chairs Initiative of the Department of Science and Innovation, the National Research Foundation of South Africa, the South African Medical Research Council Strategic Health Innovation Partnerships (SHIP) program, the Centre for the AIDS Programme of Research in South Africa (CAPRISA), the Bill and Melinda Gates Foundation through the Global Immunology and Immune Sequencing for Epidemic Response (GIISER) program and L’Oreal/UNESCO Women in Science South Africa Young Talents award.http://www.cell.com/cell-host-microbe/homeam2023ImmunologyMedical Virolog

Field-Induced Co(II) Single-Ion Magnets with <i>mer</i>-Directing Ligands but Ambiguous Coordination Geometry

Three air-stable Co­(II) mononuclear complexes with different aromatic substituents have been prepared and structurally characterized by single-crystal X-ray diffraction. The mononuclear complexes [Co­(H₂L1)₂]·2THF (<b>1</b>), [Co­(HL2)₂] (<b>2</b>), and [Co­(H₂L3)₂]·CH₂Cl₂ (<b>3</b>) (where H₃L1, H₂L2, and H₃L3 represent 3-hydroxy-naphthalene-2-carboxylic acid (6-hydroxymethyl-pyridin-2-ylmethylene) hydrazide, nicotinic acid (6-hydroxymethyl-pyridin-2-ylmethylene) hydrazide, and 2-hydroxy-benzoic acid (6-hydroxymethyl-pyridin-2-ylmethylene) hydrazide, respectively) feature a distorted <i>mer</i> octahedral coordination geometry. Detailed magnetic studies of <b>1</b>–<b>3</b> have been conducted using direct and alternating current magnetic susceptibility data. Field-induced slow magnetic relaxation was observed for these three complexes. There are few examples of such behavior in (distorted) octahedral coordination geometry (OC) Co­(II) mononuclear complexes with uniaxial anisotropy. Analysis of the six-coordinate Co­(II) mononuclear single-ion magnets (SIMs) in the literature using the SHAPE program revealed that they all show what is best described as distorted trigonal prismatic (TRP) coordination geometry, and in general, these show negative <i>D</i> zero-field splitting (ZFS) values. On the other hand, all the Co­(II) mononuclear complexes displaying what is best approximated as distorted octahedral (OC) coordination geometry show positive <i>D</i> values. In the new Co­(II) mononuclear complexes we describe here, there is an ambiguity, since the rigid tridentate ligands confer what is best described for an octahedral complex as a <i>mer</i> coordination geometry, but the actual shape of the first coordination sphere is between octahedral and trigonal prismatic. The negative <i>D</i> values observed experimentally and supported by high-level electronic structure calculations are thus in line with a trigonal prismatic geometry. However, a consideration of the rhombicity as indicated by the <i>E</i> value of the ZFS in conjunction with the SHAPE analysis shows that in this case it is difficult to distinguish between the OC and TRP descriptions

T cell responses to SARS-1 CoV-2 spike cross-recognize Omicron

The SARS-CoV-2 Omicron variant has multiple Spike (S) protein mutations1,2 that contribute to escape from antibody neutralization3–6 and reduce vaccine protection from infection7,8. The extent to which other components of the adaptive response such as T cells may still target Omicron and contribute to protection from severe outcomes is unknown. We assessed the ability of T cells to react with Omicron spike in participants who were vaccinated with Ad26.CoV2.S, BNT162b2, or unvaccinated convalescent COVID-19 patients (n=70). We found that 70-80% of the CD4+ and CD8+ T cell response to spike was maintained across study groups. Moreover, the magnitude of Omicron cross-reactive T cells was similar to Beta and Delta variants, despite Omicron harboring considerably more mutations. In Omicron-infected hospitalized patients (n=19), there were comparable T cell responses to ancestral spike, nucleocapsid and membrane proteins to those patients hospitalized in previous waves dominated by the ancestral, Beta or Delta variants (n=49). Thus, despite Omicron’s extensive mutations and reduced susceptibility to neutralizing antibodies, the majority of T cell responses, induced by vaccination or infection, cross-recognize the variant. It remains to be determined whether well-preserved T cell immunity to Omicron contributes to protection from severe COVID-19, and is linked to early clinical observations from South Africa and elsewhere9–12