Sn Ligand Research Articles

Sulfur‐nitrogen bond activation to give polynuclear terbium(III) complexes

AbstractIn recent years the SN ligand platform was progressing toward high performing lanthanide‐based single‐molecule magnets. Especially the sodium and potassium triimidosulfites are the most promising starting materials. Hence, the [Na(thf)6][S(tmsN)3(thf)3Na3{(Ntms)3S}] (1), [S(tBuN)3(thf)3K3{(HNtBu)(NtBu)2S}] (2), and [S(tBuN)3(thf)3Na3{(HNtBu)(NtBu)2S}] (L1) precursors were prepared.L1leads to four different terbium derivatives upon reaction with the terbium halide salts. For the derived complexes [ClTb{Na(thf)}2{(NtBu)3S}2] (3), [{Na(thf)}2{S(tBuN)3}TbSTb{Na(thf)}2{(NtBu)3S}] (4), [(tBuNH)Tb{(NtBu)3S}]2(5), and [{S(tBuN)3}TbSTb{(NtBu)3S}]2(6) the solid‐state structures were determined and compared. Unfortunately, isolation of these four complexes in preparative applicable yields could not yet be accomplished.

Effect of Oxidation and Protonation States on [2Fe-2S] Cluster Nitrosylation Giving {Fe(NO)2}9 Dinitrosyl Iron Complexes (DNICs).

The nitrosylation of biological Fe/S clusters to give protein-bound dinitrosyl iron complexes (DNICs) is physiologically important. Biomimetic studies on the reaction of synthetic [2Fe-2S] clusters with NO have so far been limited to diferric model complexes. This work now compares the nitrosylation of [2Fe-2S] clusters with SN- or NN-chelating benzimidazolate/thiophenolate or bis(benzimidazolate) capping ligands in their diferric (12- and 22-) and mixed-valent (FeIIFeIII, 13-, and 23-) forms. Furthermore, the effect of protonation of the imidazole part of the SN ligand has been probed on both the nitrosylation reaction and properties of the resulting DNIC. The reaction of 12- and 22- with 4 equiv NO yields the new anionic {Fe(NO)2}9 DNICs 3- and 4-, respectively, which have been comprehensively characterized, including X-ray crystallography of their PPN+ salts. Nitrosylation of mixed-valent [2Fe-2S] clusters 13- and 23- first leads to slow oxidation to the corresponding diferric congeners, followed by core degradation and DNIC formation. In the case of 23-, a second diferric intermediate very similar to 22- is detected by UV-vis spectroscopy, but could not be further identified. Nitrosylation of 1H2 gives the neutral, N-protonated DNIC 3H, and acid/base titrations show that interconversion between 3- and 3H is reversible. Peripheral ligand protonation leads to a blue shift of the NO stretching vibrations by about 23 cm-1 and a significant shift of the reduction potential to less negative values (Δ E1/2 = 0.26 V), but no effect on 57Fe Mössbauer parameters is observed. Density functional theory calculations based on the structure of 3- indicate that the electronic ground-state properties of 3- and 3H are similar, although the NO(π*) → Fe 3d π-donation is slightly increased and π-backbonding is slightly decreased upon protonation. As a result, protonation has a significant effect on the NO stretching frequencies, but only minor effects on the Fe-(NO)2 modes. This is confirmed by nuclear inelastic scattering of 3- and 3H, which shows no clear influence of protonation on the energy of the Fe-(NO)2 bending and stretching modes occurring in the range 400-600 cm-1, but characteristic changes below 350 cm-1 that reflect perturbation of free rotary motion of the thiophenolate and benzimidazole ring systems of the capping ligand after N-protonation. These findings add to the understanding of [2Fe-2S] cluster nitrosylation and will help to identify DNICs resulting from the reaction of NO with Fe/S cofactors featuring alternative, proton-responsive histidine ligands such as the Rieske and mitoNEET [2Fe-2S] clusters.

Novel binuclear and polymeric diorganotin (IV) complexes with N-nicotinyl phosphoramides: Synthesis, characterization, structural studies and anticancer activity

Two new diorganotin complexes with formula {SnCl2(CH3)2L1}2 (C1), L1 = N-nicotinyl, N′,N″-bis(diethylamine) phosphoric triamide and {SnCl2(CH3)2L2}n (C2), L2 = N-nicotinyl, N′,N″-bis(cyclopentylamine) phosphoric triamide were synthesized and characterized by IR and NMR spectroscopy, and elemental analysis. Single crystal X-ray diffraction structural analyses confirmed all-trans and cis–trans configurations for distorted octahedral geometry in C1 and C2, respectively. Also, it revealed that the coordination of L1 and L2 to Sn atom results to a binuclear arrangement in C1 and one-dimensional polymeric chain in C2. The relative stability of M1 (SnCl2(CH3)2L1) and M2 (SnCl2(CH3)2L2) units in binuclear and polymeric arrangements were compared using density functional theory (DFT) calculations. Based on theoretical findings, M1 and M2 prefer polymeric chain structure from energy point of view though the stability difference of M1, in two arrangements, was much lower compared to stability difference of M2. Furthermore, nature of bonds and Sn–ligand interactions was studied by NBO analyses. In vitro cytotoxic assay of complexes against breast cancer cell lines MCF-7, MDA-MB-468 and T47-Dhuman, were also reported. MDA-MB-468 cells are exquisitely sensitive to cell death induced by C1 and C2 complexes treatment. C1 complex exhibited higher anticancer activity, compared to C2, which can be attributed to larger ClSnCl angle in C1.

Four- and five-coordinate high-spin iron(II) complexes bearing bidentate soft/hard SN ligands based on 2-aminopyridine

Several new coordinatively unsaturated iron(II) complexes of the types [Fe(SNR-Ph)X2] (X=Cl, Br; R=H, Me, Et) and the dimeric complex [Fe(SNH–Ph)(μ-Cl)Cl]2 containing bidentate N-(2-pyridyl)amino-diphenylphosphine sulfides were prepared and characterized by various methods including X-ray crystallography, 57Fe Mössbauer spectroscopy, SQUID magnetometry, ESI-MS and DFT calculations. All complexes exhibit magnetic moments very close to 4.9μB reflecting the four unpaired d-electrons. In solution, as revealed by ESI MS studies, all compounds appear to be labile and complexes [Fe(SNR-Ph)X2] seem to be in equilibrium with solvated FeX2, free ligand, and the five-coordinate cationic complexes [Fe(SNR-Ph)2X]+. The latter are the most prominent species in the ESI mass spectra. Despite their relatively low formal electron count all iron complexes were inert towards the addition of carbon monoxide.

Synthesis, structural characterization and DFT calculations of a new one-dimensional diorganotin(IV) derivative of N-isonicotinyl phosphoramide

A new diorganotin complex with formula {SnCl2(CH3)2L}n (1), L=N-isonicotinyl, N′,N″-bis(α-methylbenzyl) phosphoric triamide, was synthesized and characterized on the basis of elemental analysis, IR and multinuclear NMR spectroscopy. Solid state structure of 1 was established by single crystal X-ray diffraction, revealing a distorted octahedral geometry for Sn, with trans-(dimethyl), cis-(Cl2) and cis-(L2) configuration. Coordination of L from Ophosphoryl and Npyridine, as a bridging bidentate ligand, resulted in infinite 1D polymeric chains along b axis. Non-covalent interactions, i.e. hydrogen bonding, π–π stacking and CH⋯HC contacts further connected the chains into a 3D framework. The main intermolecular interactions were supported by Hirshfeld surface analysis and fingerprint plots. Density functional theory (DFT) calculations were performed for 1 and its possible all-trans isomer to compare their relative stability and results showed that the latter is the stable form in the gas phase. By using parameters derived from the quantum theory of atoms in molecules, the nature of Sn–ligand interaction is found to be mainly electrostatic with a small amount of covalent character. Natural bond orbital analysis showed donor–acceptor delocalizations from donor atoms to tin center.

Time-Resolved, in Situ, Small- and Wide-Angle X-ray Scattering To Monitor Pt Nanoparticle Structure Evolution Stabilized by Adsorbed SnCl3– Ligands During Synthesis

Understanding and controlling nanoparticle formation mechanisms is important because of increasing reports of unusual material properties in this critical size region in fields ranging from magnetics, electrocatalysis, optics, and heterogeneous synthesis. Here we use real-time, in situ small-angle and wide-angle X-ray scattering to dynamically monitor the production of Pt critical nuclei from Sn–Pt complexes on a length scale approaching 0.6 nm. A time resolution of 20 s is achieved due to the slow reduction and growth processes of this unique system. The structure and evolution of inorganic Sn ligands on these Pt nanoparticle cores is of particular interest because of the ability of Sn to mitigate poisoning of electrocatalyst surfaces by adsorbed CO intermediates (COads) on the anode of direct alcohol fuel cells. Coherent scattering from the stabilizing ligand shell is identified in the wide-angle scattering data and suggests segregation of Sn ligands at the surface of the nanoparticles synthesized using our approach. We correlate the autoreduction kinetics of precursor complexes with number density, polydispersity, and Pt volume fraction, thereby establishing the mechanism of particle size control at the onset of atomic coalescence. Particle growth is shown to terminate when a Sn shell of well-defined thickness (about 0.6 nm) is completed for a range of Pt core diameters in this critical size range.

Sialoadhesin ligand expression identifies a subset of CD4+Foxp3- T cells with a distinct activation and glycosylation profile.

Sialoadhesin (Sn) is a sialic acid-binding Ig-like lectin expressed selectively on macrophage subsets. In a model of experimental autoimmune encephalomyelitis, Sn interacted with sialylated ligands expressed selectively on CD4(+)Foxp3(+) regulatory T cells (Tregs) and inhibited their proliferation. In this study, we examined the induction of Sn ligands (SnL) on all splenic CD4(+) T cells following in vitro activation. Most CD4(+) Tregs strongly upregulated SnL, whereas only a small subset of ~20% CD4(+)Foxp3(-) T cells (effector T cells [Teffs]) upregulated SnL. SnL(+) Teffs displayed higher levels of activation markers CD25 and CD69, exhibited increased proliferation, and produced higher amounts of IL-2 and IFN-γ than corresponding SnL(-) Teffs. Coculture of activated Teffs with Sn(+) macrophages or Sn(+) Chinese hamster ovary cells resulted in increased cell death, suggesting a regulatory role for Sn-SnL interactions. The key importance of α2,3-sialylation in SnL expression was demonstrated by increased binding of α2,3-linkage-specific Maackia amurensis lectin, increased expression of α2,3-sialyltransferase ST3GalVI, and loss of SnL following treatment with an α2,3-linkage-specific sialidase. The induction of SnL on activated CD4(+) T cells was dependent on N-glycan rather than O-glycan biosynthesis and independent of the mucin-like molecules CD43 and P-selectin glycoprotein ligand-1, previously implicated in Sn interactions. Induction of ligands on CD4(+)Foxp3(-) Teffs was also observed in vivo using the New Zealand Black × New Zealand White F1 murine model of spontaneous lupus and SnL levels on Teffs correlated strongly with the degree of proteinuria. Collectively, these data indicate that SnL is a novel marker of activated CD4(+) Teffs that are implicated in the pathogenesis of autoimmune diseases.

In Silico-Aided Design of a Glycan Ligand of Sialoadhesin for in Vivo Targeting of Macrophages

Cell-specific delivery of therapeutic agents using ligand targeting is gaining interest because of its potential for increased efficacy and reduced side effects. The challenge is to develop a suitable ligand for a cell-surface receptor that is selectively expressed on the desired cell. Sialoadhesin (Sn, Siglec-1, CD169), a sialic acid-binding immunoglobulin-like lectin (Siglec) expressed on subsets of resident and inflammatory macrophages, is an attractive target for the development of a ligand-targeted delivery system. Here we report the development of a high-affinity and selective ligand for Sn that is an analogue of the natural ligand and is capable of targeting liposomal nanoparticles to Sn-expressing cells in vivo. An efficient in silico screen of a library of ∼8400 carboxylic acids was the key to identifying novel 9-N-acyl-substituted N-acetylneuramic acid (Neu5Ac) substituents as potential lead compounds. A small panel of targets were selected from the screen and synthesized to evaluate their affinities and selectivities. The most potent of these Sn ligands, 9-N-(4H-thieno[3,2-c]chromene-2-carbamoyl)-Neu5Acα2-3Galβ1-4GlcNAc ((TCC)Neu5Ac), was conjugated to lipids for display on a liposomal nanoparticle for evaluation of targeted delivery to cells. The (TCC)Neu5Ac liposomes were found to target liposomes selectively to cells expressing either murine or human Sn in vitro, and when administered to mice, they exhibited in vivo targeting to Sn-positive macrophages.

Tri- and tetracoordinate copper(i) complexes bearing bidentate soft/hard SN and SeN ligands based on 2-aminopyridine

The coordination properties of the EN ligands N-(2-pyridinyl)amino-diphenylphosphine sulfide, N-(2-pyridinyl)amino-diisopropylphosphine sulfide, N-(2-pyridinyl)amino-diphenylphosphine selenide, N-(2-pyridinyl)amino-diisopropylphosphine selenide towards copper(I) precursors CuX (X = Br, I), [Cu(IPr)Cl] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), and [Cu(CH(3)CN)(4)]PF(6) were studied. Treatment of CuX with EN ligands resulted in the formation of tricoordinate complexes of the type [Cu(κ(2)(E,N)-EN)X]. The reaction of [Cu(IPr)Cl] with EN ligands, followed by halide abstraction with AgSbF(6), afforded cationic tricoordinate complexes [Cu(κ(2)(S,N)-EN)(IPr)](+), while the reaction of [Cu(CH(3)CN)(4)](+) with two equivalents of EN ligands yielded tetrahedral complexes [Cu(κ(2)(E,N)-EN)(2)](+). Halide removal from [Cu(κ(2)(S,N)-SN)I] with silver salts in the presence of L = CH(3)CN and CNtBu afforded dinuclear complexes of the type [Cu(κ(2)(S,N),μ(S)-SN)(L)](2)(2+) containing bridging SN ligands. With the terminal alkynes HC≡CC(6)H(4)Me and HC≡CC(6)H(4)OMe, complexes of the formula [Cu(κ(2)(S,N)-SN-iPr)(η(2)-HC≡CC(6)H(4)Me)](+) and [Cu(κ(2)(S,N)-SN-iPr)(η(2)-HC≡CC(6)H(4)OMe)](+) were obtained. The mononuclear nature of these compounds was supported by DFT calculations. Most complexes were also characterized by X-ray crystallography.

(η6-Arene)RuII/Chiral SN Ligand: A Novel Bifunctional Catalyst System for Asymmetric Transfer Hydrogenation of Aromatic Ketones

A binary catalyst system of [RuCl 2 (η 6 -arene)] 2 and a protic aminothiol (SN) ligand has been found to promote hydrogen transfer between alcohols and carbonyl compounds. The chiral catalyst system with the pipecolinol-derived chiral SN ligand displays excellent stereoselectivity in the asymmetric transfer hydrogenation of aromatic ketones using HCO 2 H―Et 3 N. Novel unsymmetrical bis(thiolate)-bridged binuclear complex, which is relevant to the generation of catalytically active species, has been synthesized and structurally characterized.

Sialoadhesin-Positive Macrophages Bind Regulatory T Cells, Negatively Controlling Their Expansion and Autoimmune Disease Progression

An important regulatory suppressive function in autoimmune and other inflammatory processes has been ascribed to CD4(+)Foxp3(+) regulatory T cells (Tregs), which requires direct cell-cell communication between Tregs, effector T cells, and APCs. However, the molecular basis for these interactions has not yet been clarified. We show here that sialoadhesin (Sn), the prototype of the siglec family of sialic acid-binding transmembrane proteins, expressed by resident and activated tissue-infiltrating macrophages, directly binds to Tregs, negatively regulating their expansion in an animal model of multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE). In this model, macrophages infiltrate the CNS exhibiting tissue-destructing and demyelinating activity, leading to MS-like symptoms. We show here that severity of EAE symptoms is reduced in Sn knockout (KO) mice compared with wild-type littermates due to an up-regulation of CD4(+)Foxp3(+) Treg lymphocytes. Through the use of a Sn fusion protein, Tregs were shown to express substantial amounts of Sn ligand on their cell surface, and direct interaction of Sn(+) macrophages with Tregs specifically inhibited Treg but not effector T lymphocyte proliferation. Conversely, blocking of Sn on macrophages by Sn-specific Abs resulted in elevated proliferation of Tregs. Data indicate that Sn(+) macrophages regulate Treg homeostasis which subsequently influences EAE progression. We propose a new direct cell-cell interaction-based mechanism regulating the expansion of the Tregs during the immune response, representing a "dialogue" between Sn(+) macrophages and Sn-accessible sialic acid residues on Treg lymphocytes.

Trans Influence of Boryl Ligands and Comparison with C, Si, and Sn Ligands

In this paper, the trans influence of boryl ligands, together with that of other ligands commonly believed to have a strong trans influence, has been investigated theoretically via density functional theory (DFT) calculations on a series of square-planar platinum(II) complexes of the form trans-[PtL(Cl)(PMe3)2]. The following order of trans influence has been obtained: -BMe2>-SiMe3>-BH2>-SnMe3 approximately >-Bpin>> approximately -Bcat approximately -BCl2 approximately -BBr2 approximately -SiH3>-CH2CH3>-CH=CH2>-H approximately -Me>-C6H5>-SiCl3>-SnCl3>-CCH. Natural bond order analyses have been used to understand how the substituents at the boron center affect the trans-influence properties of the boryl ligands. The major factor is the sigma-donor strength of the boryl ligand. However, surprisingly, very strong pi acceptors also enhance the trans influence.

Nickel(II), copper(II), palladium(II) and platinum(II) complexes of bidentate SN ligands derived from S-alkyldithiocarbazates and the X-ray crystal structures of the [Ni(tasbz)2] and [Cu(tasbz)2] · CHCl3 complexes

New complexes of general empirical formula, [M(NS)2] · nCHCl3 (M = NiII, CuII, PdII or PtII; NS = anionic form of the thiophene-2-aldehyde Schiff bases of S-methyl- and S-benzyldithiocarbazate; n = 0, 1) have been synthesized and characterized by physico-chemical techniques. Magnetic and spectroscopic evidence support a square-planar structure for these complexes. The crystal structures of the [Ni(tasbz)2] and [Cu(tasbz)2] · CHCl3 complexes (tasbz = anionic form of the thiophene-2-aldehyde Schiff base of S-benzyldithiocarbazate) have been determined by X-ray diffraction. Both complexes have a trans-planar structure in which the two Schiff base ligands are coordinated to the metal(II) ion as uninegatively charged bidentate ligands via the thiolate sulfur and the azomethine nitrogen atoms.

Synthesis, crystal structure and equilibrium studies on the novel bidentate amine adducts of bis[S-benzyl-β-N(p-nitrophenyl)methyldithiocarbazide]nickel(II)

The novel adducts [Ni(SN)2L] formed from chelating bidentate diamines and the square-planar bis[S-benzyl-β-N(p-nitrophenyl)methyldithiocarbazide]nickel(II) complex [Ni(SN)2] have been prepared and characterized. The bidentate diammines are 1,10-phenanthroline (phen), 2,2′-bipyridine (bipy), 5-nitro-1,10-phenanthroline (NO2phen), 4,4′-methyl-2,2′-bipyridine(Mebipy) and 4,5-diazafluoren-9-one (diafo). The addition equilibrium constants, K, determined by u.v.-vis. spectrophotometry in CH2Cl2, were influenced by the coordinating ability of the added ligands in the order: Kphen >; KNO2phen >; Kdiafo; and KMebipy >; Kbipy >; Kdiafo. The structure of the phenanthroline adduct was determined in order to study the mechanism of the addition processes and the [Ni(SN)2phen] complex has been characterized by X-ray crystal structure analysis. The coordination geometry of the nickel atom is distorted octahedral. The four nitrogen atoms of the two SN ligands and the phenanthroline form an equatorial plane with a Ni-N distance of ca. 2.10 AA, and the two sulfur atoms are located at the axial position with an average Ni-S distance of 2.40 AA. From the results of the structural determination and the addition equilibrium studies, a possible addition mechanism is also discussed.

Synthesis, crystal structure and equilibrium studies on bidentate amine adducts of bis(S-benzyl)-β-N-(4-dimethylaminobenzyl)methylendithiocarbazone nickel(II) complex

The novel adducts of chelating diamines to the diamagnetic, square-planar nickel(II) complex bis(S-benzyl)-β-N-(4-dimethylaminobenzyl)methylendithiocarbazone nickel(II) [hereafter abbreviated Ni(SN) 2] have been prepared and characterized, where the chelating diamines are 1,10-phenanthroline (phen), 2,2′-bipyridine (bipy), 5-nitro-1, 10-phenanthroline (NO 2phen), 4,4′-methyl-2,2′-bipyridine (Mebipy) and 4,5-diazafluren-9-one (diafo). The addition equilibrium constants ( K), determined by a UV-vis spectrometer, were influenced by the coordinating ability of the added ligands in the order: K phen > K mebipy > K bipy > K NO 2phen > K diafo. The single crystal structure of the phenanthroline adduct was determined to study the possible mechanism of the addition processes. The coordination geometry of the nickel atom is distorted octahedral The four nitrogen atoms of the two SN ligands and the phenanthroline molecule form the equatorial plane with a NiN distance ca 2.10 Å and the two sulfur atoms site at the axial positions with the NiS distance of 2.40 Å. From the results of structural determination and the addition equilibrium studies, the possible addition mechanisms have been discussed.

Synthesis, crystal structure and equilibrium studies on the bidentate amine adducts of bis(S-methyl-β-N-(4-methyloxyphenyl) methylendithiocarbazide)nickel(II) complex

The crystal structure of the 1,10-phenanthroline bis(S-methyl-β-N-(4-methyloxyphenyl)methylendithiocarbazide)nickel(II) adduct, (Ni(SN) 2phen) [SN = S-methyl-β-N-(4-methyloxyphenyl)methylendithiocarbazide, phen = phenanthroline], has been determined by single crystal X-ray diffraction. The nickel atom is in an octahedral environment, surrounded by two chelating SN ligands and one chelating phen molecule. The nitrogen atoms from phen are in the cis configuration. The other chelating diamines adducts of the parent complex (Ni(SN) 2) were also studied, where the chelating diamnies are 5-nitro-1,10-phenanthroline(NO 2phen), 2,2′-bipyridine (bipy), 4,4′-methyl-2,2′-bipyridine (Mebipy). The equilibria were determined by UV-vis spectrometry in dichloromethane. The coordination ability of the added ligands were influenced by substitute groupings and steric factors. From the structure and addition equilibrium studies, the possible addition mechanisms are also discussed.

The Dynamic Behaviour of η 3-Allyl Palladium and Platinum Complexes Containing the SnCl 3 Ligand

The solution behaviour of [η 3-allylM(PR 3)SnCl 3] (M = Pd, Pt) has been studied. Dissociation of the Sn ligand (either SnCl 2 or SnCl 3) explains the dynamic behaviour observed by NMR. The M-Sn bond is stronger if an alkylphosphine is bound to the metal. According to the observed 1 J(Pt, C) values of the Pt-C bond trans to SnCl 3, tin ligand and olefin have comparable trans influence.

Carbonyl trichlorostannate complexes of platinum: chemistry and 119Sn, 195Pt, and 13C NMR spectroscopy

The reactions of the carbonyl anion [PtCl 3(CO)] - with SnCl 2 in the presence of CO in both methylene chloride and acetone are reported. In the former solvent, only Pt II-SnCl 3 species are formed. These have been identified by 13C, 119Sn and 195Pt NMR measurements as cis-[PtCl 2(SnCl 3)(CO)] -, ( I), trans- [PtCl(SnCl 3) 2(CO)] -, ( II), and [Pt(SnCl 3) 4(CO)] 2-, ( III). Salts of these complexes have been isolated. In contrast, when acetone is the solvent, reduction of the platinum occurs to give two new complexes. On the basis of NMR measurements, we assign one of these as the Pt I dimer [Pt 2(SnCl 3) 4(CO) 2] 2-, ( IV), and the other as a platinum triangle ( VI) containing terminal CO ligands and two types of Sn ligand. The Pt II compound ( IV) can also be generated by treating a CH 2Cl 2 solution of trans-[PtCl(SnCl 3) 2- (CO)] -, ( II), with dihydrogen. NMR spectroscopic data, including those from measurements on samples of the complexes containing 13C-enriched CO, are reported and discussed.

Mitochondrial inclusions in fibroblast culture from a patient with beta-methylcrotonylglycinuria.

Sialoadhesin (Sn) is a sialic acid–binding Ig-like lectin expressed selectively on macrophage subsets. In a model of experimental autoimmune encephalomyelitis, Sn interacted with sialylated ligands expressed selectively on CD4⁺Foxp3⁺ regulatory T cells (Tregs) and inhibited their proliferation. In this study, we examined the induction of Sn ligands (SnL) on all splenic CD4⁺ T cells following in vitro activation. Most CD4⁺ Tregs strongly upregulated SnL, whereas only a small subset of ∼20% CD4⁺Foxp3⁻ T cells (effector T cells [Teffs]) upregulated SnL. SnL⁺ Teffs displayed higher levels of activation markers CD25 and CD69, exhibited increased proliferation, and produced higher amounts of IL-2 and IFN-γ than corresponding SnL⁻ Teffs. Coculture of activated Teffs with Sn⁺ macrophages or Sn⁺ Chinese hamster ovary cells resulted in increased cell death, suggesting a regulatory role for Sn–SnL interactions. The key importance of α2,3-sialylation in SnL expression was demonstrated by increased binding of α2,3-linkage–specific <i>Maackia amurensis</i> lectin, increased expression of α2,3-sialyltransferase ST3GalVI, and loss of SnL following treatment with an α2,3-linkage–specific sialidase. The induction of SnL on activated CD4⁺ T cells was dependent on <i>N</i>-glycan rather than <i>O</i>-glycan biosynthesis and independent of the mucin-like molecules CD43 and P-selectin glycoprotein ligand-1, previously implicated in Sn interactions. Induction of ligands on CD4⁺Foxp3⁻ Teffs was also observed in vivo using the New Zealand Black × New Zealand White F1 murine model of spontaneous lupus and SnL levels on Teffs correlated strongly with the degree of proteinuria. Collectively, these data indicate that SnL is a novel marker of activated CD4⁺ Teffs that are implicated in the pathogenesis of autoimmune diseases.

ENDOR investigations on the superhyperfine interaction of Fe3+ in SnO2

AbstractENDOR measurements on Fe3+ at substitutional lattice sites of SnO2 show a well resolved superhyperfine interaction with the ten nearest Sn ligands and confirm a substitution of Sn4+ by Fe3+. The isotropic and anisotropic parts of the interaction are obtained. The spin Hamiltonian parameters of ESR are redetermined at 4.2 °K.