Lipid profile of circulating placental extracellular vesicles during pregnancy identifies foetal growth restriction risk.

Small-for-gestational age (SGA) neonates exhibit increased perinatal morbidity and mortality, and a greater risk of developing chronic diseases in adulthood. Currently, no effective maternal blood-based screening methods for determining SGA risk are available. We used a high-resolution MS/MSALL shotgun lipidomic approach to explore the lipid profiles of small extracellular vesicles (sEV) released from the placenta into the circulation of pregnant individuals. Samples were acquired from 195 normal and 41 SGA pregnancies. Lipid profiles were determined serially across pregnancy. We identified specific lipid signatures of placental sEVs that define the trajectory of a normal pregnancy and their changes occurring in relation to maternal characteristics (parity and ethnicity) and birthweight centile. We constructed a multivariate model demonstrating that specific lipid features of circulating placental sEVs, particularly during early gestation, are highly predictive of SGA infants. Lipidomic-based biomarker development promises to improve the early detection of pregnancies at risk of developing SGA, an unmet clinical need in obstetrics.

Fibronectin and JMJD6 Signature in Circulating Placental Extracellular Vesicles for the Detection of Preeclampsia.

Preeclampsia (PE) is a major obstetric complication that is challenging to predict. Currently, there are limited tools to assess placental health/function in crucial gestational periods for diagnosis and early prediction. The glycoprotein fibronectin (FN) is augmented in PE placentae, and associated with reduced activity of JMJD6, an oxygen sensor that regulates placental FN processing. Evidence implicates placenta-derived small extracellular vesicles (sEVs) in the pathogenesis of pregnancy-associated disorders. Here, we examined the utility of FN and JMJD6 in placental sEVs as putative markers for early- and late-onset PE (E-PE and L-PE). Maternal plasma was obtained from venous blood collected longitudinally during pregnancy (10-14, 16-22, and 26-32 weeks of gestation and at delivery) in normotensive term control, preterm control, L-PE, E-PE, and gestational hypertensive individuals. Placenta-derived sEVs were isolated and their FN and JMJD6 content and JMJD6 activity were measured. In women that went on to develop preeclampsia, FN content of circulating placental sEVs was significantly elevated as early as 10 to 14 weeks of gestation and remained augmented until the time of delivery. This was accompanied by a depletion in JMJD6 content. Multivariate receiver operating characteristic analysis revealed high predictive power for FN and JMJD6 as early markers of E-PE and L-PE. In vitro, hypoxia or JMJD6 loss promoted FN accumulation in sEVs that was reverted on restoring cellular iron balance with the natural compound, Hinokitiol. Elevated FN, along with diminished JMJD6 in circulating placental sEVs, serves as an early molecular signature for the detection of different hypertensive disorders of pregnancy and their severity.

HIF1 inhibitor acriflavine rescues early-onset preeclampsia phenotype in mice lacking placental prolyl hydroxylase domain protein 2.

Preeclampsia is a serious pregnancy disorder that lacks effective treatments other than delivery. Improper sensing of oxygen changes during placentation by prolyl hydroxylases (PHDs), specifically PHD2, causes placental hypoxia-inducible factor-1 (HIF1) buildup and abnormal downstream signaling in early-onset preeclampsia, yet therapeutic targeting of HIF1 has never been attempted. Here we generated a conditional (placenta-specific) knockout of Phd2 in mice (Phd2-/- cKO) to reproduce HIF1 excess and to assess anti-HIF therapy. Conditional deletion of Phd2 in the junctional zone during pregnancy increased placental HIF1 content, resulting in abnormal placentation, impaired remodeling of the uterine spiral arteries, and fetal growth restriction. Pregnant dams developed new-onset hypertension at midgestation (E9.5) in addition to proteinuria and renal and cardiac pathology, hallmarks of severe preeclampsia in humans. Daily injection of acriflavine, a small molecule inhibitor of HIF1, to pregnant Phd2-/- cKO mice from E7.5 (prior to hypertension) or E10.5 (after hypertension had been established) to E14.5 corrected placental dysmorphologies and improved fetal growth. Moreover, it reduced maternal blood pressure and reverted renal and myocardial pathology. Thus, therapeutic targeting of the HIF pathway may improve placental development and function, as well as maternal and fetal health, in preeclampsia.

Comparing the Electronic Structure of Iron, Cobalt, and Nickel Compounds That Feature a Phosphine-Substituted Bis(imino)pyridine Chelate.

It was recently discovered that (Ph2PPrPDI)Mn (PDI = pyridine diimine) exists as a superposition of low-spin Mn(II) that is supported by a PDI dianion and intermediate-spin Mn(II) that is antiferromagnetically coupled to a triplet PDI dianion, a finding that encouraged the synthesis and electronic structure evaluation of late first row metal variants that feature the same chelate. The addition of Ph2PPrPDI to FeBr2 resulted in bromide dissociation and the formation of [(Ph2PPrPDI)FeBr][Br]. Reduction of this precursor using excess sodium amalgam afforded (Ph2PPrPDI)Fe, which possesses an Fe(II) center that is supported by a dianionic PDI ligand. Similarly, reduction of a premixed solution of Ph2PPrPDI and CoCl2 yielded the cobalt analog, (Ph2PPrPDI)Co. EPR spectroscopy and density functional theory calculations revealed that this compound features a high-spin Co(I) center that is antiferromagnetically coupled to a PDI radical anion. The addition of Ph2PPrPDI to Ni(COD)2 resulted in ligand displacement and the formation of (Ph2PPrPDI)Ni, which was found to possess a pendent phosphine group. Single-crystal X-ray diffraction, CASSCF calculations, and EPR spectroscopy indicate that (Ph2PPrPDI)Ni is best described as having a Ni(II)-PDI2- configuration. The electronic differences between these compounds are highlighted, and a computational analysis of Ph2PPrPDI denticity has revealed the thermodynamic penalties associated with phosphine dissociation from 5-coordinate (Ph2PPrPDI)Mn, (Ph2PPrPDI)Fe, and (Ph2PPrPDI)Co.

Ceramide-Induced Lysosomal Biogenesis and Exocytosis in Early-Onset Preeclampsia Promotes Exosomal Release of SMPD1 Causing Endothelial Dysfunction.

Aberrant ceramide build-up in preeclampsia, a serious disorder of pregnancy, causes exuberant autophagy-mediated trophoblast cell death. The significance of ceramide accumulation for lysosomal biogenesis in preeclampsia is unknown. Here we report that lysosome formation is markedly increased in trophoblast cells of early-onset preeclamptic placentae, in particular in syncytiotrophoblasts. This is accompanied by augmented levels of transcription factor EB (TFEB). In vitro and in vivo experiments demonstrate that ceramide increases TFEB expression and nuclear translocation and induces lysosomal formation and exocytosis. Further, we show that TFEB directly regulates the expression of lysosomal sphingomyelin phosphodiesterase (L-SMPD1) that degrades sphingomyelin to ceramide. In early-onset preeclampsia, ceramide-induced lysosomal exocytosis carries L-SMPD1 to the apical membrane of the syncytial epithelium, resulting in ceramide accumulation in lipid rafts and release of active L-SMPD1 via ceramide-enriched exosomes into the maternal circulation. The SMPD1-containing exosomes promote endothelial activation and impair endothelial tubule formation in vitro. Both exosome-induced processes are attenuated by SMPD1 inhibitors. These findings suggest that ceramide-induced lysosomal biogenesis and exocytosis in preeclamptic placentae contributes to maternal endothelial dysfunction, characteristic of this pathology.

Full Conformational Analyses of the Ultrafast Isomerization in Penta-coordinated Ru(S2C2(CF3)2)(CO)(PPh3)2: One Compound, Two Crystal Structures, Three CO Frequencies, 24 Stereoisomers, and 48 Transition States.

The stereodynamics of an ultrafast (picosecond) isomerization in a penta-coordinated ruthenium complex, Ru(S2C2(CF3)2)(CO)(PPh3)2, were characterized by density functional theory (DFT). The ruthenium complex crystallizes in two almost-square pyramidal (SP) forms. The violet form has an apical PPh3 ligand, the orange form has an apical CO ligand, and their solution displays three CO stretching frequencies. With 4 possible centers of chirality (1 ruthenium, 2 phosphines, and 1 dithiolate), there are 24 stereoisomers. DFT calculations of these stereoisomers show structures ranging from almost-perfect SP (τ5 ≈ 0) to structures significantly distorted toward trigonal bipyramidal (TBP) (τ5 ≈ 0.6). The stereoisomers fall neatly into three groups, with νCO ≈ 1960 cm-1, 1940 cm-1, and 1980 cm-1. These isomers were found to interconvert over relatively small barriers via Ru-S bond twisting, CF3 rotation, phenyl twisting, PPh3 rotation, and, in some cases, by coupled motions. The composite energy surface for each CO frequency group shows that interconversions among the low-energy structures are possible via both the direct and indirect pathways, while the indirect pathway via isomers in the νCO ≈ 1980 cm-1 group is more favorable, which is a result consistent with recent experimental work. This work provides the first complete mechanistic picture of the ultrafast isomerization of penta-coordinated, distorted SP, d6-transition-metal complexes.

Electronic Structural Studies of the Ru3(III,II,II) Mixed-Valent State of Oxo-Centered Triruthenium Clusters.

The anionic state of basic ruthenium acetate complexes of the type [Ru3O(OAc)6](CO)(L1)(L2) (L = 4-cyanopyridine, pyridine, and N,N-dimethylaminopyridine) feature pronounced optical transitions in the near-infrared region indicative of strongly coupled mixed-valence states. A series of these clusters was prepared and studied spectroscopically in tandem with density functional theory (DFT) computational results to construct an orbital structure-function description of how the electron density is shared between the ruthenium centers in this mixed-valent state. The mixed-valency manifests itself as a combination of the nonbonding atomic orbitals of the equivalent ruthenium centers, with increased energetic splitting between the orbitals with symmetries appropriate for more efficient electronic communication. This DFT-based model agrees with the Marcus-Hush description of mixed-valency, with the added knowledge that specific orbitals contribute to different degrees in the electronic coupling between two redox centers.

Carbonate-promoted C-H carboxylation of electron-rich heteroarenes.

C-H carboxylation is an attractive transformation for both streamlining synthesis and valorizing CO2. The high bond strength and very low acidity of most C-H bonds, as well as the low reactivity of CO2, present fundamental challenges for this chemistry. Conventional methods for carboxylation of electron-rich heteroarenes require very strong organic bases to effect C-H deprotonation. Here we show that alkali carbonates (M2CO3) dispersed in mesoporous TiO2 supports (M2CO3/TiO2) effect CO3 2--promoted C-H carboxylation of thiophene- and indole-based heteroarenes in gas-solid reactions at 200-320 °C. M2CO3/TiO2 materials are strong bases in this temperature regime, which enables deprotonation of very weakly acidic bonds in these substrates to generate reactive carbanions. In addition, we show that M2CO3/TiO2 enables C3 carboxylation of indole substrates via an apparent electrophilic aromatic substitution mechanism. No carboxylations take place when M2CO3/TiO2 is replaced with un-supported M2CO3, demonstrating the critical role of carbonate dispersion and disruption of the M2CO3 lattice. After carboxylation, treatment of the support-bound carboxylate products with dimethyl carbonate affords isolable esters and the M2CO3/TiO2 material can be regenerated upon heating under vacuum. Our results provide the basis for a closed cycle for the esterification of heteroarenes with CO2 and dimethyl carbonate.

Steric and electronic control of an ultrafast isomerization.

Synthetic control of the influence of steric and electronic factors on the ultrafast (picosecond) isomerization of penta-coordinate ruthenium dithietene complexes (Ru((CF3)2C2S2)(CO)(L)2, where L = a monodentate phosphine ligand) is reported. Seven new ruthenium dithietene complexes were prepared and characterized by single crystal X-ray diffraction. The complexes are all square pyramidal and differ only in the axial vs. equatorial coordination of the carbonyl ligand. Fourier Transform Infrared (FTIR) spectroscopy was used to study the ν(CO) bandshapes of the complexes in solution, and these reveal rapid exchange between two or three isomers of each complex. Isomerization is proposed to follow a Berry psuedorotation-like mechanism where a metastable, trigonal bipyramidal (TBP) intermediate is observed spectroscopically. Electronic tuning of the phosphine ligands L = PPh3, P((p-Me)Ph)3, ((p-Cl)Ph)3, at constant cone angle is found to have little effect on the kinetics or thermodynamic stabilities of the axial, equatorial and TBP isomers of the differently substituted complexes. Steric tuning of the phosphine ligands over a range of phosphine cone angles (135 < θ < 165°) has a profound impact on the isomerization process, and in the limit of greatest steric bulk, the axial isomer is not observable. Temperature dependence of the FTIR spectra was used to obtain the relative thermodynamic stabilities of the different isomers of each of the seven ruthenium dithietene complexes. This study details how ligand steric effects can be used to direct the solution state dynamics on the picosecond time scale of discrete isomers energetically separated by <2.2 kcal mol-1. This work provides the most detailed description to date of ultrafast isomerization in the ground states of transition metal complexes.

Thermodynamic targeting of electrocatalytic CO2 reduction: advantages, limitations, and insights for catalyst design.

Herein is reported the electrocatalytic reduction of CO2 with the complex [Ni(bis-NHC)(dmpe)]2+ (1) (bis-NHC = 1,l':3,3'-bis(1,3-propanediyl)dibenzimidazolin-2,2'-diylidene; dmpe = 1,2-bis(dimethylphosphino)ethane). The hydricity of 1 was previously benchmarked to be , equating to a driving force of a minimum of ∼3.4 kcal mol-1 for hydride transfer to CO2. While hydride transfer to CO2 is thermodynamically favorable, electrocatalytic and infrared spectroelectrochemical (IR-SEC) experiments reveal that hydride transfer is blocked by direct reactivity with CO2 in the reduced, Ni(0) state of the catalyst, yielding CO via reductive disproportionation (2CO2 + 2e- = CO + CO32-) and concomitant catalyst degradation. Although thermodynamic scaling relationships provide guidance in catalyst targeting, the findings herein illustrate the fundamental kinetic challenges in balancing substrate reactivity and selectivity in the design of CO2 reduction electrocatalysts. Advantages and limitations of this scaling relationship as well as approaches by which divergence from it may be achieved are discussed, which provides insight on important parameters for future catalyst design.

Photooxidative Generation of Dodecaborate-Based Weakly Coordinating Anions.

Redox-active proanions of the type B12(OCH2Ar)12 [Ar = C6F5 (1), 4-CF3C6H4 (2), 3,5-(CF3)2C6H3 (3)] are introduced in the context of an experimental and computational study of the visible-light-initiated polymerization of a family of styrenes. Neutral, air-stable proanions 1-3 were found to initiate styrene polymerization through single-electron oxidation under blue-light irradiation, resulting in polymers with number-average molecular weights (Mn) ranging from ∼6 to 100 kDa. Shorter polymer products were observed in the majority of experiments, except in the case of monomers containing 4-X (X = F, Cl, Br) substituents on the styrene monomer when polymerized in the presence of 1 in CH2Cl2. Only under these specific conditions are longer polymers (>100 kDa) observed, strongly supporting the formulation that reaction conditions significantly modulate the degree of ion pairing between the dodecaborate anion and cationic chain end. This also suggests that 1-3 behave as weakly coordinating anions (WCA) upon one-electron reduction because no incorporation of the cluster-based photoinitiators is observed in the polymeric products analyzed. Overall, this work is a conceptual realization of a single reagent that can serve as a strong photooxidant, subsequently forming a WCA.

Direct observation of the intermediate in an ultrafast isomerization.

Using a combination of two-dimensional infrared (2D IR) and variable temperature Fourier transform infrared (FTIR) spectroscopies the rapid structural isomerization of a five-coordinate ruthenium complex is investigated. In methylene chloride, three exchanging isomers were observed: (1) square pyramidal equatorial, (1); (2) trigonal bipyramidal, (0); and (3) square pyramidal apical, (2). Exchange between 1 and 0 was found to be an endergonic process (ΔH = 0.84 (0.08) kcal mol-1, ΔS = 0.6 (0.4) eu) with an isomerization time constant of 4.3 (1.5) picoseconds (ps, 10-12 s). Exchange between 0 and 2 however was found to be exergonic (ΔH = -2.18 (0.06) kcal mol-1, ΔS = -5.3 (0.3) eu) and rate limiting with an isomerization time constant of 6.3 (1.6) ps. The trigonal bipyramidal complex was found to be an intermediate, with an activation barrier of 2.2 (0.2) kcal mol-1 and 2.4 (0.2) kcal mol-1 relative to the equatorial and apical square pyramidal isomers respectively. This study provides direct validation of the mechanism of Berry pseudorotation - the pairwise exchange of ligands in a five-coordinate complex - a process that was first described over fifty years ago. This study also clearly demonstrates that the rate of pseudorotation approaches the frequency of molecular vibrations.

Dodecaborane-Based Dopants Designed to Shield Anion Electrostatics Lead to Increased Carrier Mobility in a Doped Conjugated Polymer.

One of the most effective ways to tune the electronic properties of conjugated polymers is to dope them with small-molecule oxidizing agents, creating holes on the polymer and molecular anions. Undesirably, strong electrostatic attraction from the anions of most dopants localizes the holes created on the polymer, reducing their mobility. Here, a new strategy utilizing a substituted boron cluster as a molecular dopant for conjugated polymers is employed. By designing the cluster to have a high redox potential and steric protection of the core-localized electron density, highly delocalized polarons with mobilities equivalent to films doped with no anions present are obtained. AC Hall effect measurements show that P3HT films doped with these boron clusters have conductivities and polaron mobilities roughly an order of magnitude higher than films doped with F4 TCNQ, even though the boron-cluster-doped films have poor crystallinity. Moreover, the number of free carriers approximately matches the number of boron clusters, yielding a doping efficiency of ≈100%. These results suggest that shielding the polaron from the anion is a critically important aspect for producing high carrier mobility, and that the high polymer crystallinity required with dopants such as F4 TCNQ is primarily to keep the counterions far from the polymer backbone.

Stable Mixed-Valent Complexes Formed by Electron Delocalization Across Hydrogen Bonds of Pyrimidinone-Linked Metal Clusters.

Electron transfer across a mixed-valent hydrogen-bonded self-dimer of oxo-centered triruthenium clusters bridged by a pair of 4(3 H)-pyrimidinones is reported. Spectroelectrochemical studies in methylene chloride reveal that 1 rapidly self-dimerizes upon one-electron reduction, forming the strongly coupled mixed-valent hydrogen-bonded dimer (12)-. In the mixed-valent state, significantly broadened, partially coalesced ν(CO) bands are observed, allowing estimation of the electron transfer rate ( kET) by an optical Bloch line shape analysis. Simulation of the FTIR line shapes provides an estimate of kET on the order of 1011 s-1, indicating a highly delocalized electronic structure across the hydrogen bonds. These findings are supported by the determination of the formation constant ( KMV) for (12)-, which is found to be on the order of 106 M-1, or nearly 4 orders of magnitude higher than that for the neutral isovalent dimer (12). This represents a stabilization of approximately 5.7 kcal/mol (1980 cm-1) arising from electron exchange across the hydrogen bonds in the mixed-valent state. Significantly, an enormous intensity enhancement of the amide ν(NH) band (3300 cm-1) of (12)- is observed, supporting strong mixing of the bridging ligand vibrational modes with the electronic wave function of the mixed-valent state. These findings demonstrate strong donor-bridge-acceptor coupling and that highly delocalized electronic structures can be attained in hydrogen-bonded systems, which are often considered to be too weakly bound to support strong electronic communication.

Erratum: Selection of a cut-off for high- and low-methane producers using a spot-methane breath test: results from a large north American dataset of hydrogen, methane and carbon dioxide measurements in breath.

[This corrects the article DOI: 10.1093/gastro/gow048.][This corrects the article DOI: 10.1093/gastro/gow048.].

Effects of electron transfer on the stability of hydrogen bonds.

The measurement of the dimerization constants of hydrogen-bonded ruthenium complexes (12, 22, 32) linked by a self-complementary pair of 4-pyridylcarboxylic acid ligands in different redox states is reported. Using a combination of FTIR and UV/vis/NIR spectroscopies, the dimerization constants (KD) of the isovalent, neutral states, 12, 22, 32, were found to range from 75 to 130 M-1 (ΔG0 = -2.56 to -2.88 kcal mol-1), while the dimerization constants (K2-) of the isovalent, doubly-reduced states, (12)2-, (22)2-, (32)2-, were found to range from 2000 to 2500 M-1 (ΔG0 = -4.5 to -4.63 kcal mol-1). From the aforementioned values and the comproportionation constant for the mixed-valent dimers, the dimerization constants (KMV) of the mixed-valent, hydrogen-bonded dimers, (12)-, (22)-, (32)-, were found to range from 0.5 × 106 to 1.2 × 106 M-1 (ΔG0 = -7.78 to -8.31 kcal mol-1). On average, the hydrogen-bonded, mixed-valent states are stabilized by -5.27 (0.04) kcal mol-1 relative to the isovalent, neutral, hydrogen-bonded dimers and -3.47 (0.06) kcal mol-1 relative to the isovalent, dianionic hydrogen bonded dimers. Electron exchange in the mixed valence states imparts significant stability to hydrogen bonding. This is the first quantitative measurement of the strength of hydrogen bonds in the presence and absence of electronic exchange.

Selection of a cut-off for high- and low-methane producers using a spot-methane breath test: results from a large north American dataset of hydrogen, methane and carbon dioxide measurements in breath.

BACKGROUND: Levels of breath methane, together with breath hydrogen, are determined by means of repeated collections of both, following ingestion of a carbohydrate substrate, at 15-20 minutes intervals, until 10 samples have been obtained. The frequent sampling is required to capture a rise of hydrogen emissions, which typically occur later in the test: in contrast, methane levels are typically elevated at baseline. If methane emissions represent the principal objective of the test, a spot methane test (i.e. a single-time-point sample taken after an overnight fast without administration of substrate) may be sufficient. METHODS: We analysed 10-sample lactulose breath test data from 11 674 consecutive unique subjects who submitted samples to Commonwealth Laboratories (Salem, MA, USA) from sites in all of the states of the USA over a one-year period. The North American Consensus (NAC) guidelines criteria for breath testing served as a reference standard. RESULTS: The overall prevalence of methane-positive subjects (by NAC criteria) was 20.4%, based on corrected methane results, and 18.9% based on raw data. In our USA dataset, the optimal cut-off level to maximize sensitivity and specificity was ≥4 ppm CH4, 94.5% [confidential interval (CI): 93.5-95.4%] and 95.0% (CI: 94.6-95.5%), respectively. The use of a correction factor (CF) (5% CO2 as numerator) led to reclassifications CH4-high to CH4-low in 0.7 % and CH4-low to CH4-high in 2.1%. CONCLUSIONS: A cut-off value for methane at baseline of either ≥4 ppm, as in our USA dataset, or ≥ 5 ppm, as described in a single institution study, are both highly accurate in identifying subjects at baseline that would be diagnosed as 'methane-positive' in a 10-sample lactulose breath test for small intestinal bacterial overgrowth.

Tuning Electron Delocalization and Transfer Rates in Mixed-Valent Ru3O Complexes through "Push-Pull" Effects.

Electron transfer rates in a series of oxo-centered triruthenium clusters featuring an extended aromatic ancillary ligand of the type [Ru3(OAc)6(µ3-O)(CO)(L)(pep)], where L = 4-cyanopyridine (cpy), pyridine (py), or 4-(dimethylamino)pyridine (dmap) and pep = 4-(phenylethynyl)pyridine were investigated. The electron self-exchange rate constants for the 0/- couple were determined by (1)H NMR line broadening experiments and found to range from 4.3 to 9.2 (× 10(7) M(-1) s(-1)) in deuterated acetonitrile (ACN-d3). Relative rates of self-exchange can be rationalized on the basis of increased contact area between self-exchanging pairs, and a push-pull modulation of electron density between the pep vs ancillary pyridine ligands. Faster self-exchange was observed with increasing electron-donating character of the ancillary pyridine ligand substituent (dmap > py > cpy), and this was attributed to increased orbital overlap between self-exchanging pairs. These results are supported by trends observed in (1)H NMR contact shifts of the pep ligand that were found to depend on the electron-donating or -withdrawing nature of the ancillary pyridine ligand.

Importance of co-donor field strength in the preparation of tetradentate α-diimine nickel hydrosilylation catalysts.

Although bis(α-diimine)Ni complexes were prepared when amine-substituted chelates were added to Ni(COD)2, the incorporation of strong-field phosphine donors allowed the isolation of (κ(4)-N,N,P,P-DI)Ni hydrosilylation catalysts. The crystallographic investigation of two different (κ(4)-N,N,P,P-DI)Ni compounds revealed that the geometry about nickel influences the observed degree of α-diimine reduction.