A novel technique using chronic infusion of small extracellular vesicles from gestational diabetes mellitus causes glucose intolerance in pregnant mice.

Small extracellular vesicles (sEVs) play a central role in cell-to-cell communication in normal physiology and in disease, including gestational diabetes mellitus (GDM). The goal of the present study was to test the hypothesis that chronic administration of sEVs isolated from GDM causes glucose intolerance in healthy pregnant mice. Small EVs were isolated from plasma between 24 and 28 weeks gestation from healthy pregnant women (controls) and GDM, and infused intravenously for 4 days in late pregnant mice using a mini-osmotic pump. Subsequently in vivo glucose tolerance was assessed, and muscle and adipose tissue insulin sensitivity and islet glucose stimulated insulin secretion (GSIS) were determined in vitro. Mice infused with sEVs from GDM developed glucose intolerance. Administration of sEVs from controls, but not sEVs from GDM women, stimulated islet GSIS and increased fasting insulin levels in pregnant mice. Neither infusion of sEVs from controls nor from GDM women affected muscle insulin sensitivity, placental insulin or mTOR signaling, placental and fetal weight. Moreover, these results were not associated with immunomodulatory effects as human sEVs did not activate mouse T cells in vitro. We suggest that circulating sEVs regulate maternal glucose homeostasis in pregnancy and may contribute to the attenuated islet insulin secretion and more pronounced glucose intolerance in GDM as compared with healthy pregnancy.

Circulating extracellular vesicles exhibit a differential miRNA profile in gestational diabetes mellitus pregnancies.

We undertook a prospective temporal study collecting blood samples from consenting pregnant women, to test the hypothesis that circulating extracellular vesicles (EVs) carrying specific non-coding microRNA signatures can underlie gestational diabetes mellitus (GDM). To test this hypothesis, miRNA cargo of isolated and characterized EVs revealed contributions from the placenta and differential expression at all three trimesters and at delivery between pregnant and non-pregnant states. Many miRNAs originate from the placental-specific chromosome 19 microRNA cluster (19MC) and chromosome 14 microRNA cluster (14MC). Further a positive correlation emerged between third trimester and at delivery EVs containing miRNAs and those expressed by the corresponding post-parturient placentas (R value = 0.63 to 0.69, p value = 2.2X10-16), in normal and GDM. In addition, distinct differences at all trimesters emerged between women who subsequently developed GDM. Analysis by logistic regression with leave-one-out-cross validation revealed the optimal combination of miRNAs using all the circulating miRNAs (miR-92a-3p, miR-192-5p, miR-451a, miR-122-5p), or using only the differentially expressed miRNAs (has-miR-92a-3p, hsa-miR-92b-3p, hsa-miR-100-5p and hsa-miR-125a-3p) in GDM during the first trimester. As an initial step, both sets of miRNAs demonstrated a predictive probability with an area under the curve of 0.95 to 0.96. These miRNAs targeted genes involved in cell metabolism, proliferation and immune tolerance. In particular genes of the P-I-3-Kinase, FOXO, insulin signaling and glucogenic pathways were targeted, suggestive of placental connectivity with various maternal organs/cells, altering physiology along with pathogenic mechanisms underlying the subsequent development of GDM. We conclude that circulating EVs originating from the placenta with their miRNA cargo communicate and regulate signaling pathways in maternal organs, thereby predetermining development of GDM.

Extracellular vesicles and their role in gestational diabetes mellitus.

Gestational diabetes mellitus (GDM) is a complex disorder that is defined by glucose intolerance with onset during pregnancy. The incidence of GDM is increasing worldwide. Pregnancies complicated with GDM have higher rates of maternal and fetal morbidity with short- and long-term consequences, including increased rates of cardiovascular disease and type II diabetes for both the mother and offspring. The pathophysiology of GDM still remains unclear and there has been interest in the role of small extracellular vesicles (sEVs) in the maternal metabolic adaptations that occur in pregnancy and GDM. Small EVs are nanosized particles that contain bioactive content, including miRNAs and proteins, which are released by cells to provide cell-to-cell communication. Pregnancy induces an increase in total and placental-secreted sEVs across gestation, with a further increase in sEV number and changes in the protein and miRNA composition of these sEVs in GDM. Research has suggested that these sEVs have an impact on maternal adaptations during pregnancy, including targeting the pancreas, skeletal muscle and adipose tissue. Consequently, this review will focus on the differences in total and placental sEVs in GDM compared to normal pregnancy, the role of sEVs in the pathophysiology of GDM and their clinical application as potential GDM biomarkers.

Regulation of glucose homeostasis by small extracellular vesicles in normal pregnancy and in gestational diabetes.

The mechanisms underpinning maternal metabolic adaptations to a healthy pregnancy and in gestational diabetes mellitus (GDM) remain poorly understood. We hypothesized that small extracellular vesicles (sEVs) isolated from healthy pregnant women promote islet glucose-stimulated insulin secretion (GSIS) and peripheral insulin resistance in nonpregnant mice and that sEVs from GDM women fail to stimulate insulin secretion and cause exacerbated insulin resistance. Small EVs were isolated from plasma of nonpregnant, healthy pregnant, and GDM women at 24-28 weeks of gestation. We developed a novel approach in nonpregnant mice involving a mini-osmotic pump for continuous 4-day jugular venous infusion of sEVs and determined their effects on glucose tolerance in vivo and islets and skeletal muscle in vitro. Fasting insulin was elevated in mice infused with pregnant sEVs as compared to sEVs from nonpregnant and GDM women. Mice infused with sEVs from GDM women developed glucose intolerance. GSIS was increased in mice infused with healthy pregnancy sEVs compared to mice receiving nonpregnant sEVs. GSIS and muscle basal insulin signaling, and insulin responsiveness were attenuated in mice infused with GDM sEVs. sEVs represent a novel mechanism regulating maternal glucose homeostasis in pregnancy and we speculate that altered sEV content contributes to the development of GDM.

Changes in Placental Nutrient Transporter Protein Expression and Activity Across Gestation in Normal and Obese Women.

Fetal growth and development are dependent on placental nutrient transport. The syncytiotrophoblast (ST) and its two polarized plasma membranes, the maternal-facing microvillous membrane (MVM) and fetal-facing basal membrane (BM), represent the primary barrier in the human placenta, controlling transplacental transfer of small solutes. MVM and BM nutrient transporter expression and activity are increased in obese mothers delivering large babies. However, placental nutrient transporter expression and activity in early gestation in normal and obese women are largely unknown. Placentas from normal BMI and obese women at 6-24 weeks of gestation, and term placentas from normal BMI women, were collected and ST plasma membranes isolated. The activity and protein expression of amino acid, glucose, and fatty acid transporters was assessed. No significant differences were observed in placental nutrient transporter protein expression between normal BMI and obese women in early pregnancy. In the MVM, system A amino acid activity (p = 0.02), SNAT2 (p < 0.0001), SNAT4 (p < 0.001), and GLUT1 (p = 0.01) protein expression were higher at term compared with early gestation. In contrast, MVM system L activity (p = 0.001), FATP4 (p = 0.03), and FATP6 (p = 0.009) protein expression were lower at term compared with early pregnancy. In the BM, there was no change in system L activity across gestation; however, BM FATP6 (p = 0.002) protein expression was lower at term compared with early pregnancy. These results suggest that placental transport of amino acids, glucose, and fatty acids are subjected to coordinated regulation across gestation to meet a fetal nutrient demand that changes with advancing pregnancy.

The phenotype of decidual CD56+ lymphocytes is influenced by secreted factors from decidual stromal cells but not macrophages in the first trimester of pregnancy.

During the first trimester of pregnancy the decidua is comprised of decidual stromal cells (DSC), invading fetal trophoblast cells and maternal leukocytes, including decidual natural killer (dNK) cells and macrophages. dNK cells are distinct from peripheral blood NK cells and have a role in regulating trophoblast invasion and spiral artery remodelling. The unique phenotype of dNK cells results from the decidual environment in which they reside, however the interaction and influence of other cells in the decidua on dNK phenotype is unknown. We isolated first trimester DSC and decidual macrophages and investigated the effect that DSC and decidual macrophage secreted factors have on CD56+ decidual lymphocyte receptor expression and cytokine secretion (including dNK cells). We report that DSC secreted factors induce the secretion of the cytokines IL-8 and IL-6 from first trimester CD56+ cells. However, neither DSC nor decidual macrophage secreted factors changed CD56+ cell receptor expression. These results suggest that secreted factors from DSC influence CD56+ decidual lymphocytes during the first trimester of pregnancy and therefore may play a role in regulating the unique phenotype and function of dNK cells during placentation.

Insulin Stimulates GLUT4 Trafficking to the Syncytiotrophoblast Basal Plasma Membrane in the Human Placenta.

CONTEXT: Placental transport capacity influences fetal glucose supply. The syncytiotrophoblast is the transporting epithelium in the human placenta, expressing glucose transporters (GLUTs) and insulin receptors (IRs) in its maternal-facing microvillous plasma membrane (MVM) and fetal-facing basal plasma membrane (BM). OBJECTIVE: The objectives of this study were to (i) determine the expression of the insulin-sensitive GLUT4 glucose transporter and IR in the syncytiotrophoblast plasma membranes across gestation in normal pregnancy and in pregnancies complicated by maternal obesity, and (ii) assess the effect of insulin on GLUT4 plasma membrane trafficking in human placental explants. DESIGN, SETTING, AND PARTICIPANTS: Placental tissue was collected across gestation from women with normal body mass index (BMI) and mothers with obesity with appropriate for gestational age and macrosomic infants. MVM and BM were isolated. MAIN OUTCOME MEASURES: Protein expression of GLUT4, GLUT1, and IR were determined by western blot. RESULTS: GLUT4 was exclusively expressed in the BM, and IR was predominantly expressed in the MVM, with increasing expression across gestation. BM GLUT1 expression was increased and BM GLUT4 expression was decreased in women with obesity delivering macrosomic babies. In placental villous explants, incubation with insulin stimulated Akt (S473) phosphorylation (+76%, P = 0.0003, n = 13) independent of maternal BMI and increased BM GLUT4 protein expression (+77%, P = 0.0013, n = 7) in placentas from lean women but not women with obesity. CONCLUSION: We propose that maternal insulin stimulates placental glucose transport by promoting GLUT4 trafficking to the BM, which may enhance glucose transfer to the fetus in response to postprandial hyperinsulinemia in women with normal BMI.

Improving the handover and transport of critically ill pediatric patients.

AIMS AND OBJECTIVES: The aims of this project were to (a) determine barriers to current handover and transport process, (b) develop a new protocol and process for team-to-team handover, and (c) evaluate staff satisfaction with the new process. BACKGROUND: The handover and transport of critically ill patients from the paediatric emergency department to the paediatric intensive care unit is a period of vulnerability associated with adverse events. DESIGN: A mixed-methods study using a quasi-experimental design and qualitative approach. METHODS: Focus groups were conducted to determine the barriers and facilitators of the current handover and transport process. Using these themes, a multidisciplinary team developed and implemented a new process including establishment of eight patient criteria for specialised transport and a standardised, interdisciplinary handover tool for team-to-team handover. Staff satisfaction was examined pre- and postintervention. RESULTS: Content analysis of focus groups revealed five categories: need for improved communication, cultural dissonance among units, defects in system and processes, need for standardisation and ambiguity between providers regarding acuity. Staff members reported improvements in their perceptions of satisfaction, safety, communication and role understanding associated with the new process. CONCLUSIONS: Standardisation through the establishment of severity of illness criteria and communication tools creates shared mental models and decreases risks to safety. A paradigm shift of team-to-team handover and transport is recommended. RELEVANCE TO CLINICAL PRACTICE: This paper suggests the importance of improving communication during the handover and transport process through establishing standardised patient severity of illness criteria, use of standardised tools and team-to-team handover processes.

Development of monoclonal anti-PDGF-CC antibodies as tools for investigating human tissue expression and for blocking PDGF-CC induced PDGFRα signalling in vivo.

PDGF-CC is a member of the platelet-derived growth factor (PDGF) family that stimulates PDGFRα phosphorylation and thereby activates intracellular signalling events essential for development but also in cancer, fibrosis and neuropathologies involving blood-brain barrier (BBB) disruption. In order to elucidate the biological and pathological role(s) of PDGF-CC signalling, we have generated high affinity neutralizing monoclonal antibodies (mAbs) recognizing human PDGF-CC. We determined the complementarity determining regions (CDRs) of the selected clones, and mapped the binding epitope for clone 6B3. Using the monoclonal 6B3, we determined the expression pattern for PDGF-CC in different human primary tumours and control tissues, and explored its ability to neutralize PDGF-CC-induced phosphorylation of PDGFRα. In addition, we showed that PDGF-CC induced disruption of the blood-retinal barrier (BRB) was significantly reduced upon intraperitoneal administration of a chimeric anti-PDGF-CC antibody. In summary, we report on high affinity monoclonal antibodies against PDGF-CC that have therapeutic efficacy in vivo.

Global conformational changes in IgG-Fc upon mutation of the FcRn-binding site are not associated with altered antibody-dependent effector functions.

Antibody engineering is important for many diagnostic and clinical applications of monoclonal antibodies. We recently reported a series of fragment crystallizable (Fc) mutations targeting the neonatal Fc receptor (FcRn) site on a Lewis Y (Ley) binding IgG1, hu3S193. The hu3S193 variants displayed shortened in vivo half-lives and may have potential for radioimaging or radiotherapy of Ley-positive tumors. Here, we report Fc crystal structures of wild-type hu3S193, seven FcRn-binding site variants, and a variant lacking C1q binding or complement-dependent cytotoxicity (CDC) activity. The Fc conformation of the FcRn-binding sites was similar for wild-type and all mutants of hu3S193 Fc, which suggests that FcRn interactions were directly affected by the amino acid substitutions. The C1q-binding site mutant Fc was nearly identical with the wild-type Fc. Surprisingly, several hu3S193 Fc variants showed large changes in global structure compared with wild-type Fc. All hu3S193 Fc mutants had similar antibody-dependent cellular cytotoxicity, despite some with conformations expected to diminish Fc gamma receptor binding. Several hu3S193 variants displayed altered CDC, but there was no correlation with the different Fc conformations. All versions of hu3S193, except the C1q-binding site mutant, bound C1q, suggesting that the altered CDC of some variants could result from different propensities to form IgG hexamers after engaging Ley on target cells. Overall, our findings support the concept that the antibody Fc is both flexible and mobile in solution. Structure-based design approaches should take into account the conformational plasticity of the Fc when engineering antibodies with optimal effector properties.

The role of decidual NK cells in pregnancies with impaired vascular remodelling.

The pathologies of the dangerous pregnancy complications pre-eclampsia (PE) and fetal growth restriction (FGR) are established in the first trimester of human pregnancy yet we know little of how this happens. Finely tuned interactions between maternal and placental cells are essential for pregnancy to progress without complications; however, the precise nature of this cross-talk and how it can go wrong are crucial questions that remain to be answered. This review summarises recent studies examining the role played by natural killer cells in regulating normal placentation and remodelling. Their involvement when it is impaired in PE/FGR pregnancies will additionally be discussed.

Cross-species analysis of Fc engineered anti-Lewis-Y human IgG1 variants in human neonatal receptor transgenic mice reveal importance of S254 and Y436 in binding human neonatal Fc receptor.

IgG has a long half-life through engagement of its Fc region with the neonatal Fc receptor (FcRn). The FcRn binding site on IgG1 has been shown to contain I253 and H310 in the CH2 domain and H435 in the CH3 domain. Altering the half-life of IgG has been pursued with the aim to prolong or reduce the half-life of therapeutic IgGs. More recent studies have shown that IgGs bind differently to mouse and human FcRn. In this study we characterize a set of hu3S193 IgG1 variants with mutations in the FcRn binding site. A double mutation in the binding site is necessary to abrogate binding to murine FcRn, whereas a single mutation in the FcRn binding site is sufficient to no longer detect binding to human FcRn and create hu3S193 IgG1 variants with a half-life similar to previously studied hu3S193 F(ab')2 (t1/2ß, I253A, 12.23 h; H310A, 12.94; H435A, 12.57; F(ab')2, 12.6 h). Alanine substitutions in S254 in the CH2 domain and Y436 in the CH3 domain showed reduced binding in vitro to human FcRn and reduced elimination half-lives in huFcRn transgenic mice (t1/2ß, S254A, 37.43 h; Y436A, 39.53 h; wild-type, 83.15 h). These variants had minimal effect on half-life in BALB/c nu/nu mice (t1/2ß, S254A, 119.9 h; Y436A, 162.1 h; wild-type, 163.1 h). These results provide insight into the interaction of human Fc by human FcRn, and are important for antibody-based therapeutics with optimal pharmacokinetics for payload strategies used in the clinic.

Engineering anti-Lewis-Y hu3S193 antibodies with improved therapeutic ratio for radioimmunotherapy of epithelial cancers.

BACKGROUND: The aim of the study was to explore Fc mutations of a humanised anti-Lewis-Y antibody (IgG1) hu3S193 as a strategy to improve therapeutic ratios for therapeutic payload delivery. METHODS: Four hu3S193 variants (I253A, H310A, H435A and I253A/H310A) were generated via site-directed mutagenesis and radiolabelled with diagnostic isotopes iodine-125 or indium-111. Biodistribution studies in Lewis-Y-positive tumour-bearing mice were used to calculate the dose in tumours and organs for therapeutic isotopes (iodine-131, yttrium-90 and lutetium-177). RESULTS: (111)In-labelled I253A and H435A showed similar slow kinetics (t 1/2ß, 63.2 and 62.2 h, respectively) and a maximum tumour uptake of 33.11 ± 4.05 and 33.69 ± 3.77 percentage injected dose per gramme (%ID/g), respectively. (111)In-labelled I253A/H310A cleared fastest (t 1/2ß, 9.1 h) with the lowest maximum tumour uptake (23.72 ± 0.85 %ID/g). The highest increase in tumour-to-blood area under the curve (AUC) ratio was observed with the metal-labelled mutants ((90)Y and (177)Lu). (177)Lu-CHX-A" DTPA-hu3S193 I253A/H310A (6:1) showed the highest tumour-to-blood AUC ratio compared to wild type (3:1) and other variants and doubling of calculated dose to tumour based on red marrow dose constraints. CONCLUSIONS: These results suggest that hu3S193 Fc can be engineered with improved therapeutic ratios for (90)Y- and (177)Lu-based therapy, with the best candidate being hu3S193 I253A/H310A for (177)Lu-based therapy.

The value of SPaCE in delivering patient feedback.

BACKGROUND: The use of simulated patients (SPs) within undergraduate medical curricula is an established and valued learning opportunity. Within the context of simulation, it is imperative to capture feedback from all participants within the simulation activity. The Simulated Patient Candidate Evaluation (SPaCE) tool was developed to deliver SP feedback following a simulation activity. SpaCE is a closed feedback tool that allows SPs to rate a student's performance, using a five-point Likert scale, in three domains: attitude; interaction skills; and management. This research study examined the value of the SPaCE tool and how it contributes to the overall feedback that a student receives. METHODS: Classical test theory was used to determine the reliability of the SPaCE tool. An evaluation of all SP responses was conducted to observe trends in scoring patterns for each question. Qualitative data were collected via a free-text questionnaire and subsequent focus group discussion. It is imperative to capture feedback from all participants within the simulation activity RESULTS: Classical test theory determined that the SPaCE tool had a reliability co-efficient of 0.89. A total of 13 SPs replied to the questionnaire. A thematic analysis of all questionnaire data identified that the SPaCE tool provides a structure that allows patient feedback to be given effectively following a simulation activity. These themes were discussed further with six SPs who attended the subsequent focus group session. DISCUSSION: The SPaCE tool has been shown to be a reliable closed feedback tool that allows SPs to discriminate between students, based on their performance. The next stage in the development of the SPaCE tool is to test the wider applicability of this feedback tool.

Integral membrane protease fibroblast activation protein sensitizes fibrosarcoma to chemotherapy and alters cell death mechanisms.

Fibroblast activation protein (FAP), an integral membrane serine protease, is found on fibro- and osteo-sarcoma and on myofibroblasts in epithelial carcinoma, but rarely on other adult tissue. FAP has been demonstrated to be an excellent target for tumor imaging in clinical trials, and antibodies and other FAP-targeting drugs are in development. Here we have shown that FAP overexpression increased the growth of HT1080 fibrosarcoma cells in vitro and in vivo, and found that the expression of FAP affects response to chemotherapy. When treated with doxorubicin, expression of FAP increased susceptibility to the drug. In spite of this, FAP-HT1080 cells had fewer markers of classical apoptosis than HT1080 cells and neither necrosis nor necroptosis were enhanced. However, levels of early mitochondrial and lysosomal membrane permeability markers were increased, and autophagy switched from a protective function in HT1080 cells to part of the cell death mechanism with FAP expression. Therefore, FAP may affect how the tumor responds to chemotherapeutic drugs overall, which should be considered in targeted drug development. The overexpression of FAP also alters cell signaling and responses to the environment in this cell line. This includes cell death mechanisms, changing the response of HT1080 cells to doxorubicin from classical apoptosis to an organelle membrane permeability-dependent form of cell death.

Fibroblast activation protein increases metastatic potential of fibrosarcoma line HT1080 through upregulation of integrin-mediated signaling pathways.

The serine protease fibroblast activation protein (FAP) is selectively expressed on tumour-associated fibroblasts in most human epithelial tumours, as well as on some mesenchymal tumours such as sarcoma. High FAP expression is most often associated with poor outcome and increased metastasis. Here, we compare the in vitro metastatic potential of HT1080 fibrosarcoma cells with and without FAP expression in order to elucidate the mechanism by which FAP may influence metastasis. In the presence of FAP, cells were more adhesive to extracellular matrix proteins and migrated and invaded through Matrigel to a greater degree. The anti-FAP antibody ESC11, which caused internalization of FAP, decreased adhesion and migration, but only when cells expressed FAP. It was also found that blocking activity of integrins ß1 and αvß3 reduced both cell adhesion and migration and this effect was much more marked in FAP-expressing HT1080 cells than mock-transfected HT1080 cells. The expression or activation of intracellular proteins that form part of the downstream signaling of integrins, including integrin-linked kinase, Rac1 and focal adhesion kinase, was also upregulated when FAP was expressed, suggesting that FAP not only upregulates metastatic-like cell behaviours through interaction with integrins, but also influences the intracellular signaling of integrins. This was confirmed using both PI3 kinase and Src kinase inhibitors, which decreased adhesion and migration in FAP-expressing cells, but did not affect mock-transfected HT1080 cells. FAP is therefore a useful target for anti-cancer therapy, as not only is its expression tumour-selective, but its downregulation has the potential to reduce incidence of metastasis.

Tuning ligand electronics and peripheral substitution on cobalt salen complexes: structure and polymerisation activity.

A series of cobalt salen complexes, where salen represents an N2O2 bis-Schiff-base bis-phenolate framework, are prepared, characterised and investigated for reversible-termination organometallic mediated radical polymerisation (RT-OMRP). The salen ligands contain a cyclohexane diimine bridge and systematically altered para-substituted phenoxide moieties as a method to examine the electronic impact of the ligand on complex structure and reactivity. The complexes are characterised by single crystal X-ray diffraction, cyclic voltammetry, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy and computational methods. Structural studies all support a tailorable metal centre reactivity altered by the electron-donating ability of the salen ligand. RT-OMRP of styrene, methyl methacrylate and vinyl acetate is reported and suggests that cobalt-carbon bond strength varies with the ligand substitution. Competing ß-hydrogen abstraction affords long-chain olefin-terminated polymer chains and well controlled vinyl acetate polymerisations, contrasting with the lower temperature associative exchange mechanism of degenerative transfer OMRP.

Organometallic mediated radical polymerization of vinyl acetate using bis(imino)pyridine vanadium trichloride complexes.

The synthesis and characterization of one novel proligand and six novel vanadium(III) trichloride complexes is described. The controlled radical polymerization activity towards vinyl acetate of these, and eight other bis(imino)pyridine vanadium trichloride complexes previously reported, is investigated. Those complexes possessing variation at the N-aryl para-position with no steric protection offered by ortho-substituents (4 examples) result in poor control over poly(vinyl acetate) polymerization. Control is improved with increasing steric bulk at the ortho-position of the N-aryl substituent (4 examples) although attempts to increase steric bulk past isopropyl were unsuccessful. Synthesizing bis(imino)pyridine vanadium trichloride complexes with substituted imine backbones restores polymerization control when aliphatic substituents are used (4 examples) but ceases to make any drastic improvements on catalyst lifetime. Modification of the polymerization conditions is also investigated, in an attempt to improve the catalyst lifetime. Expansion of the monomer scope to include other vinyl esters, particularly those derived from renewable resources, shows promising results.

Controlled radical polymerization mediated by amine-bis(phenolate) iron(III) complexes.

Tetradentate amine-bis(phenolate) iron(III) halide complexes containing chloro substituents on the aromatic ring are extremely efficient catalysts for controlled radical polymerization. Molecular weights are in good agreement with theoretical values and polydispersity indexes (PDIs) are as low as 1.11 for styrene and methyl methacrylate polymerizations. Complexes containing alkyl substituents on the aromatic ring are less efficient. Kinetic data reveal activity for styrene polymerization among the fastest reported to date and initial studies implicate a multimechanism system. Despite the highly colored polymerization media, simple work-up procedures yield pure white polymers.

Origins of stereoselectivity in optically pure phenylethaniminopyridine tris-chelates M(NN')3(n+) (M = Mn, Fe, Co, Ni and Zn).

One-pot reactions of 2-pyridinecarboxaldehyde, chiral phenylethanamines and Fe(II) give single diastereomer fac diimine complexes at thermodynamic equilibrium so that no chiral separations are required (d.r. > 200 : 1). The origins of this stereoselectivity are partly steric and partly a result of the presence of three sets of inter-ligand parallel-offset π-stacking interactions. Mn(II), Co(II), Co(III), Ni(II) and Zn(II) give similar fac structures, alongside the imidazole analogues for Fe(II). While most of the complexes are paramagnetic, the series of molecular structures allows us to assess the influence of the π-stacking present, and there is a strong correlation between this and the M-N bond length. Fe(II) is close to optimal. For the larger Zn(II) ion, very weak π-stacking leads to poorer measured stereoselectivity (NMR) but this is improved with increased solvent polarity. The mechanism of stereoselection is further investigated via DFT calculations, chiroptical spectroscopy and the use of synthetic probes.