Intramolecular Charge Transfer and Spin-Orbit Coupled Intersystem Crossing in Hypervalent Phosphorus(V) and Antimony(V) Porphyrin Black Dyes.

Porphyrin dyes with strong push-pull type intramolecular charge transfer (ICT) character and broad absorption across the visible spectrum are reported. This combination of properties has been achieved by functionalizing the periphery of hypervalent and highly electron-deficient phosphorus(V) and antimony(V) centered porphyrins with electron-rich triphenylamine (TPA) groups. As a result of the large difference in electronegativity between the porphyrin ring and the peripheral groups, their absorption profiles show several strong charge transfer transitions, which in addition to the porphyrin-centered π → π* transitions, make them panchromatic black dyes with high absorption coefficients between 200 and 800 nm. Time-resolved optical and electron paramagnetic resonance (EPR) studies show that the lowest triplet state also has ICT character and is populated by spin-orbit coupled intersystem crossing.

Anti-Ceramide ScFv Prophylaxis for First Responders to a Limited Nuclear Attack.

BACKGROUND/AIMS: After 9/11, multiple government agencies instituted programs aimed at developing medical radiation countermeasures (MRCs) for two syndromes lethal within weeks of a limited nuclear attack; the hematopoietic-acute radiation syndrome (H-ARS) and the higher-dose gastrointestinal-acute radiation syndrome (GI-ARS). While re-purposing drugs that enhance marrow repopulation treats H-ARS, no mitigator protects GI tract. METHODS: We recently reported anti-ceramide 6B5 single-chain variable fragment (scFv) pre-treatment abrogates ongoing small intestinal endothelial apoptosis to rescue Lgr5+ stem cells, preventing GI-ARS lethality in C57B/L6J mice. Here, with US Department of Defense support, we provide evidence that humanized anti-ceramide scFv (CX-01) is a promising prophylactic MRC for first responders, who risk exposure upon entering a radiation-contaminated site. RESULTS: CX-01, when delivered up to 90 min before irradiation, is highly-effective in preventing small intestinal endothelial apoptosis in mice and lethality in both sexes. Unexpectedly, females require an ~2-fold higher CX-01 dose than males for full protection. CX-01 is effective subcutaneously and intramuscularly, a property critical for battlefield use. Increasing the maximally-effective dose 5-fold does not extend duration of bioeffectiveness. CONCLUSION: While CX-01 prevents GI-ARS lethality, structural modification to extend half-life may be necessary to optimize first responder prophylaxis.

Fluorinated Antimony(V) Tetraarylporphyrins as High-Valent Electron Acceptors with Unparalleled Reduction Potentials.

A series of fluorinated antimony(V) porphyrins, SbTPP(OMe)2·PF6, SbTPP(OTFE)2·PF6, SbT(4F)PP(OMe)2·PF6, SbT(35F)PP(OMe)2·PF6, SbT(345F)PP(OMe)2·PF6, SbT(4CF3)PP(OMe)2·PF6, SbT(35CF3)PP(OMe)2·PF6, and SbT(35CF3)PP(OTFE)2·PF6, have been synthesized with phenyl [P], 4-fluorophenyl [(4F)P], 3,5-difluorophenyl [(35F)P], 3,4,5-difluorophenyl [(345F)P], 4-trifluoromethylphenyl [(4CF3)P], and 3,5-bis(trifluoromethyl)phenyl [(35CF3)P], in the meso-positions. Additionally, the SbTPP(OTFE)2·PF6 and SbT(35CF3)PP(OTFE)2·PF6 carry trifluoroethoxy units in their axial-positions. The fluorination on the porphyrin peripherals ranges from zero fluorine atoms in SbTPP(OMe)2·PF6 to 30 fluorine atoms in SbT(35CF3)PP(OTFE)2·PF6. X-ray crystallography confirmed the structures of the investigated antimony(V) porphyrins. The absorption spectra depend on the number of fluorine atoms as it is blue-shifted with increasing fluorination. The series also exhibited rich redox chemistry with two reduction processes and one oxidation process. Remarkably, these porphyrins manifested the lowest reduction potentials reported among the main-group porphyrins, which are as low as -0.08 V vs SCE for SbT(35CF3)PP(OTFE)2·PF6. On the contrary, the oxidation potentials were found to be very large, that is equal to 2.20 V vs SCE or even higher for SbT(4CF3)PP(OMe)2·PF6 or SbT(35CF3)PP(OMe)2·PF6 and SbT(35CF3)PP(OTFE)2·PF6, respectively. These unprecedented potentials are due to a combination of two factors: (i) the +5-oxidation state of antimony in the porphyrin cavity and (ii) the presence of the strong electron-withdrawing fluorine atoms on the porphyrin peripherals. Density functional theory (DFT) calculations were used to support the experimental results. The systematic study of antimony(V) porphyrins, especially their high potentials, make them ideal for the construction of photoelectrodes and excellent electron acceptors for photoelectrochemical cells and artificial photosynthetic systems, respectively, for solar energy conversion and storage applications.

Correction: Solvent dependent triplet state delocalization in a co-facial porphyrin heterodimer.

Correction for 'Solvent dependent triplet state delocalization in a co-facial porphyrin heterodimer' by Susanna Ciuti et al., Phys. Chem. Chem. Phys., 2022, https://doi.org/10.1039/D2CP04291F.

Structural characteristics and functional properties of a fucose containing prebiotic exopolysaccharide from Bifidobacterium breve NCIM 5671.

AIM: To evaluate the structure and functions of capsular exopolysaccharide (CPS) from Bifidobacterium breve NCIM 5671. METHODS AND RESULTS: A CPS produced by the probiotic bacteria B. breve NCIM 5671 was isolated and subjected to characterization through GC analysis, which indicated the presence of rhamnose, fucose, galactose, and glucose in a molar ratio of 3:1:5:3. The average molecular weight of the CPS was determined to be ∼8.5 × 105 Da. Further, NMR analysis revealed the probable CPS structure to be composed of major branched tetra- and penta-saccharide units alternately repeating and having both α- and ß-configuration sugar residues. CPS displayed an encouraging prebiotic score for some of the studied probiotic bacteria. Compared to standard inulin, CPS showed better resistance to digestibility against human GI tract in vitro. DPPH, total antioxidant, and ferric reducing assays carried out for CPS displayed decent antioxidant activity too. CONCLUSION: This study indicates that the CPS from B. breve NCIM 5671 has the potential to be utilized as a prebiotic food supplement. It is a high-molecular-weight (∼8.5 × 105 Da) capsular heteropolysaccharide containing rhamnose, fucose, galactose, and glucose.

Hypervalent Phosphorus(V) Porphyrins with meso-Methoxyphenyl Substituents: Significance of the Number and Position of Methoxy Groups in Promoting Intramolecular Charge Transfer.

To study the photophysical and redox properties as a function of meso-aryl units, a series of hypervalent phosphorus(V) porphyrins, PP(OMe)2·PF6, PMP(OMe)2·PF6, PDMP(OMe)2·PF6, P345TMP(OMe)2·PF6, and P246TMP(OMe)2·PF6, with phenyl (P), 4-methoxyphenyl (MP), 3,5-dimethoxyphenyl (DMP), 3,4,5-trimethoxyphenyl (345TMP), and 2,4,6-trimethoxyphenyl (246TMP) units, respectively, have been synthesized. The P(+5) in the cavity makes the porphyrin ring electron-poor, whereas the methoxy groups make the meso-phenyl rings electron-rich. The presence of electron-rich and electron-poor portions within the porphyrin molecule promoted an intramolecular charge transfer (ICT). Also, the study suggests that the ICT depends on the number and position of the methoxy groups. The ICT is more prominent in m-methoxy-substituted phosphorus(V) porphyrins (PDMP(OMe)2.PF6, P345TMP(OMe)2·PF6) and almost no ICT was found in no-methoxy, o-methoxy, and/or p-methoxy phosphorus(V) porphyrins (PP(OMe)2·PF6, PMP(OMe)2·PF6, P246TMP(OMe)2·PF6). Transient absorption studies indicate that the ICT takes place on the picosecond time scale. The most striking results come from P246TMP(OMe)2·PF6, where each phenyl ring carries three methoxy units, like the P345TMP(OMe)2·PF6, but it failed to induce the ICT process. Electrochemical studies and time-dependent density functional theory (TD-DFT) calculations were used to support the experimental results. This study extensively explores why and how slight variations in meso-aryl substitutions lead to intricate changes in the photophysical and redox properties of phosphorus(V) porphyrins.

Solvent dependent triplet state delocalization in a co-facial porphyrin heterodimer.

The excited triplet state of a cofacial aluminum(III) porphyrin-phosphorus(V) porphyrin heterodimer is investigated using transient EPR spectroscopy and quantum chemical calculations. In the dimer, the two porphyrins are bound covalently to each other via a µ-oxo bond between the Al and P centres, which results in strong electronic interaction between the porphyrin rings. The spin polarized transient EPR spectrum of the dimer is narrower than the spectra of the constituent monomers and the magnitude of the zero-field splitting parameter D is solvent dependent, decreasing as the polarity of the solvent increases. The quantum chemical calculations show that the spin density of the triplet state is delocalized over both porphyrins, while magnetophotoselection measurements reveal that, in contrast to the value of D, the relative orientation of the ZFS axes and the excitation transition dipole moments are not solvent dependent. Together the results indicate that triplet state wavefunction is delocalized over both porphyrins and has a modest degree of charge-transfer character that increases with increasing solvent polarity. The sign of the spin polarization pattern of the dimer triplet state is opposite to that of the monomers. The positive sign of D predicted for the monomers and dimer by the quantum chemical calculations implies that the different signs of the spin polarization patterns is a result of a difference in the spin selectivity of the intersystem crossing.

Rational Design and Synthesis of OEP and TPP Centered Phosphorus(V) Porphyrin-Naphthalene Conjugates: Triplet Formation via Rapid Charge Recombination.

Six new "axial-bonding" type "phosphorus(V) porphyrin-naphthalene" conjugates have been prepared consisting of octaethylporphyrinatophosphorus(V) (POEP+)/tetraphenylporphyrinatophosphorus(V) (PTPP+) and naphthalene (NP). The distance between the porphyrin and NP was systematically varied using polyether bridges. The unique structural topology of the octaethylporphyrinatophosphorus(V) (POEP+) and tetraphenylporphyrinatophosphorus(V) (PTPP+) enabled construction of mono- and disubstituted phosphorus(V) porphyrin-naphthalene conjugates, respectively. The steady-state and transient spectral properties were investigated as a function of redox properties, distance, and molecular topology. Strong electronic interactions between the phosphorus(V) porphyrin and NP in directly bound conjugates were observed. The established energy diagrams predicted reductive electron transfer involving singlet excited phosphorus(V) porphyrin and NP to generate high-energy (∼1.83-2.11 eV) charge-separated states (POEP/PTPP)•-(NP)•+. Femtosecond transient absorption spectral studies revealed rapid deactivation of singlet excited phosphorus(V) porphyrin due to charge separation wherein the estimated forward rate constants were in the range of 109-1010 s-1 and were dependent on the distance between the NP and porphyrins units, as well as the redox potentials of the type of the phosphorus(V) porphyrin. Additionally, due to high exothermicity and low-lying triplet states, the charge recombination process was found to be rapid, leading to populating the triplet states of phosphorus(V) porphyrins.

A charge transfer state induced by strong exciton coupling in a cofacial µ-oxo-bridged porphyrin heterodimer.

Photosensitizers with high energy, long lasting charge-transfer states are important components in systems designed for solar energy conversion by multistep electron transfer. Here, we show that in a push-pull type, µ-oxo-bridged porphyrin heterodimer composed of octaethylporphyrinatoaluminum(iii) and octaethylporphyrinatophosphorus(v), the strong excitonic coupling between the porphyrins and the different electron withdrawing abilities of Al(iii) and P(v) promote the formation of a high energy CT state. Using, an array of optical and magnetic resonance spectroscopic methods along with theoretical calculations, we demonstrate photodynamics of the heterodimer that involves the initial formation of a singlet CT which relaxes to a triplet CT state with a lifetime of ∼130 ps. The high-energy triplet CT state (3CT = 1.68 eV) lasts for nearly 105 µs prior to relaxing to the ground state.

Widespread and interrelated gray matter reductions in child sexual offenders with and without pedophilia: Evidence from a multivariate structural MRI study.

AIM: To further investigate the neuroanatomical correlates of child sexual offending and disentangle them from the neural correlates of pedophilia, using a multivariate analytical approach in order to minimize loss of statistical power. METHODS: This study presents structural MRI data on gray matter in an incarcerated, male population of 22 pedophilic and 21 non-pedophilic child sexual offenders, and 20 violent non-sexual offender controls, based on a multivariate whole-brain approach using source-based morphometry. RESULTS: We identify a network of several neuroanatomical regions exhibiting interrelated reduced gray matter in both child sexual offender groups relative to controls, comprising extensive clusters in the bilateral cerebellum and frontal lobe, as well as smaller clusters in the bilateral parietal, temporal, and occipital lobes, the bilateral basal ganglia, the medial cingulate and the hippocampus. CONCLUSION: Our results speak to the interpretation that there are inter- and possibly connectivity-related brain structural abnormalities in child sexual offenders that are not (only) pertaining to pedophilia per se. Interpretations and limitations of the present data are discussed and recommendations for future works are given.

Physicochemical Composition and Characterization of Bioactive Compounds of Mulberry (Morus indica L.) Fruit During Ontogeny.

Mulberry fruit is well recognized as one of the richest sources of bioactive compounds. We investigated the physicochemical composition and characterized the bioactive compounds during different ripening stages of mulberry (Morus indica) fruit and evaluated their anti-quorum sensing activity on Chromobacterium violaceum. The proximate components such as carbohydrates, proteins and lipids were found to be high in the ripe fruit compared to unripe and mid-ripe fruit. The ripe fruit contained higher content of total phenolics and flavonoids (336.05 and 282.55 mg/100 g fresh weight (FW), respectively). Epicatechin and resveratrol were the major polyphenols detected in the fruit with the range 5.13-19.46 and 4.07-14.45 mg/100 g FW, respectively. Chlorogenic acid and myricetin were predominant in the unripe and mid-ripe fruit (7.14 and 1.84 mg/100 g FW, respectively). The fruit was found to be an excellent source of anti-diabetic compound 1-deoxynojirimycin. The highest content of 1-deoxynojirimycin was present in the mid-ripe fruit, with a content of 2.91 mg/100 g FW. Furthermore, fruit extracts exhibited anti-quorum sensing activity against Chromobacterium violaceum by effectively inhibiting violacein production. Ripe fruit extracts showed the highest activity of 76.30% at 1 mg/mL and thus, could be used as a potent anti-quorum sensing agent. The results could be promising in the selection of appropriate developmental stages for M. indica fruit commercial exploitation in the food formulations rich in potential health components.

Decelerating Charge Recombination Using Fluorinated Porphyrins in N,N-Bis(3,4,5-trimethoxyphenyl)aniline-Aluminum(III) Porphyrin-Fullerene Reaction Center Models.

In supramolecular reaction center models, the lifetime of the charge-separated state depends on many factors. However, little attention has been paid to the redox potential of the species that lie between the donor and acceptor in the final charge separated state. Here, we report on a series of self-assembled aluminum porphyrin-based triads that provide a unique opportunity to study the influence of the porphyrin redox potential independently of other factors. The triads, BTMPA-Im→AlPorFn-Ph-C60 (n = 0, 3, 5), were constructed by linking the fullerene (C60) and bis(3,4,5-trimethoxyphenyl)aniline (BTMPA) to the aluminum(III) porphyrin. The porphyrin (AlPor, AlPorF3, or AlPorF5) redox potentials are tuned by the substitution of phenyl (Ph), 3,4,5-trifluorophenyl (PhF3), or 2,3,4,5,6-pentafluorophenyl (PhF5) groups in its meso positions. The C60 and BTMPA units are bound axially to opposite faces of the porphyrin plane via covalent and coordination bonds, respectively. Excitation of all of the triads results in sequential electron transfer that generates the identical final charge separated state, BTMPA•+-Im→AlPorFn-Ph-C60•-, which lies energetically 1.50 eV above the ground state. Despite the fact that the radical pair is identical in all of the triads, remarkably, the lifetime of the BTMPA•+-Im→AlPorFn-Ph-C60•- radical pair was found to be very different in each of them, that is, 1240, 740, and 56 ns for BTMPA-Im→AlPorF5-Ph-C60, BTMPA-Im→AlPorF3-Ph-C60, and BTMPA-Im→AlPor-Ph-C60, respectively. These results clearly suggest that the charge recombination is an activated process that depends on the midpoint potential of the central aluminum(III) porphyrin (AlPorFn).

Reversible and adaptive resistance to BRAF(V600E) inhibition in melanoma.

Treatment of BRAF(V600E) mutant melanoma by small molecule drugs that target the BRAF or MEK kinases can be effective, but resistance develops invariably. In contrast, colon cancers that harbour the same BRAF(V600E) mutation are intrinsically resistant to BRAF inhibitors, due to feedback activation of the epidermal growth factor receptor (EGFR). Here we show that 6 out of 16 melanoma tumours analysed acquired EGFR expression after the development of resistance to BRAF or MEK inhibitors. Using a chromatin-regulator-focused short hairpin RNA (shRNA) library, we find that suppression of sex determining region Y-box 10 (SOX10) in melanoma causes activation of TGF-ß signalling, thus leading to upregulation of EGFR and platelet-derived growth factor receptor-ß (PDGFRB), which confer resistance to BRAF and MEK inhibitors. Expression of EGFR in melanoma or treatment with TGF-ß results in a slow-growth phenotype with cells displaying hallmarks of oncogene-induced senescence. However, EGFR expression or exposure to TGF-ß becomes beneficial for proliferation in the presence of BRAF or MEK inhibitors. In a heterogeneous population of melanoma cells having varying levels of SOX10 suppression, cells with low SOX10 and consequently high EGFR expression are rapidly enriched in the presence of drug, but this is reversed when the drug treatment is discontinued. We find evidence for SOX10 loss and/or activation of TGF-ß signalling in 4 of the 6 EGFR-positive drug-resistant melanoma patient samples. Our findings provide a rationale for why some BRAF or MEK inhibitor-resistant melanoma patients may regain sensitivity to these drugs after a 'drug holiday' and identify patients with EGFR-positive melanoma as a group that may benefit from re-treatment after a drug holiday.

Structural and functional analysis of an OB-fold in human Ctc1 implicated in telomere maintenance and bone marrow syndromes.

The human CST (Ctc1, Stn1 and Ten1) complex binds the telomeric overhang and regulates telomere length by promoting C-strand replication and inhibiting telomerase-dependent G-strand synthesis. Structural and biochemical studies on the human Stn1 and Ten1 complex revealed its mechanism of assembly and nucleic acid binding. However, little is known about the structural organization of the multi-domain Ctc1 protein and how each of these domains contribute to telomere length regulation. Here, we report the structure of a central domain of human Ctc1. The structure reveals a canonical OB-fold with the two identified disease mutations (R840W and V871M) contributing to the fold of the protein. In vitro assays suggest that although this domain is not contributing directly to Ctc1's substrate binding properties, it affects full-length Ctc1 localization to telomeres and Stn1-Ten1 binding. Moreover, functional assays show that deletion of the entire OB-fold domain leads to significant increase in telomere length, frequency of internal single G-strands and fragile telomeres. Our findings demonstrate that a previously unknown OB-fold domain contributes to efficient Ctc1 telomere localization and chromosome end maintenance.

Evaluation of feeding value of combination of alternate protein sources in White Leghorn layers.

1. A study was conducted to evaluate the effects of including graded levels of an alternate protein mixture (APM) containing cottonseed meal, distillery dried grain with solubles and mustard seed meal in a fixed ratio as a substitute for soybean meal in layer diets (hens aged 27 to 46 weeks). The trial studied the possibility of higher inclusion levels of APM with increased dietary concentrations of crude protein (CP) or critical amino acids (CAA). 2. Maize-soybean meal diet was used as the control diet. In experiment 1, APM was included at 0, 120, 160 and 200 g/kg diet (145 g/kg CP). In experiment 2, the control and three test diets (200 g/kg APM) with three levels of CP (145, 155 and 165 g/kg) were used. In experiment 3, a control and four test diets (200 g/kg APM) with four concentrations of CAA (100%, 105%, 110% and 115% relative to the control) were used. In all experiments, each diet was fed ad libitum to nine replicates of 88 birds each, housed in colony cages. 3. In experiment 1, egg production (EP) and feed intake (FI) were not affected by feeding up to 160 g/kg APM, but, at 200 g/kg, EP was significantly reduced. Feed conversion ratio (FCR) for the hens fed the highest level of APM was similar to the control. Egg weight (EW) and egg mass (EM) in the 160 and 200 g/kg AMS groups were lower than the control group. 4. Increase in dietary CP from 145 to 155 g/kg improved EP and reduced FCR to levels similar to the control group. EM in hens fed 165 g/kg APM was similar to the control in experiment 2. 5. Increasing concentrations of CAA progressively improved EP and reduced FCR in experiment 3. The EP at CAA 110% and FCR at CAA 105% were similar to the control group. 6. Based on the results, it was concluded that the APM can be included up to 160 g/kg diet without affecting layer performance, as long as the diet supplied the recommended levels of protein and amino acids. By increasing either protein from 145 to 155 g/kg or CAA concentrations by 10%, the dietary levels of the APM could be increased to 200 g/kg without affecting the layer performance.

Surface anchored self-assembled reaction centre mimics as photoanodes consisting of a secondary electron donor, aluminium(iii) porphyrin and TiO2 semiconductor.

A series of vertically assembled photoanodes, consisting of 5,10,15,20-tetrakis(3,4,5-trifluorophenyl)aluminum(iii) porphyrin (AlPorF3), a pyridine appended electron donor (PTZ-Py, PTZ = phenothiazine; TTF-Py, TTF = tetrathiafulvalene), and semiconductor TiO2, have been fabricated by exploiting the unique axial properties of AlPorF3. The new photoanodes were characterized by steady-state and transient spectroscopic techniques. Transient-absorption studies show that in the absence of a donor, both the photoanodes (AlPorF3-TiO2 and AlPorF3-Ph-TiO2) exhibit electron injection from AlPorF3 into the conduction band of TiO2 and the injection efficiencies are strongly dependent on the linker. Faster electron injection and recombination is revealed when AlPorF3 is directly bound to TiO2. Although a secondary electron donor is coordinated to AlPorF3 (viz., Donor-Py-AlPorF3-TiO2 and Donor-Py-AlPorF3-Ph-TiO2), the primary charge separation occurs in the form of electron injection from AlPorF3 to TiO2 followed by a secondary process involving photooxidation of the donor (PTZ and TTF) with AlPorF3˙+. The estimated electron injection lifetimes and the AlPorF3˙+ decay lifetimes strongly depend on the electron richness of the donor; the higher the electron density of the donor, the faster the electron injection and photooxidation witnessed. The photoanodes with TTF (TTF-Py-AlPorF3-TiO2 and TTF-Py-AlPorF3-Ph-TiO2) show faster injection and shorter decay lifetimes of AlPorF3˙+ over their PTZ counterparts (PTZ-Py-AlPorF3-TiO2 and PTZ-Py-AlPorF3-Ph-TiO2). The observed trends suggest that the strong secondary electron donor enhances the injection and the subsequent photooxidation processes in the investigated photoanodes. The successful mimicking of a sequential charge-separation process makes aluminum(iii) porphyrins potential sensitizers for the construction of photoanodes, especially for photocatalytic and dye-sensitized solar cells for conversion and storage of solar energy.

M-CSF instructs myeloid lineage fate in single haematopoietic stem cells.

Under stress conditions such as infection or inflammation the body rapidly needs to generate new blood cells that are adapted to the challenge. Haematopoietic cytokines are known to increase output of specific mature cells by affecting survival, expansion and differentiation of lineage-committed progenitors, but it has been debated whether long-term haematopoietic stem cells (HSCs) are susceptible to direct lineage-specifying effects of cytokines. Although genetic changes in transcription factor balance can sensitize HSCs to cytokine instruction, the initiation of HSC commitment is generally thought to be triggered by stochastic fluctuation in cell-intrinsic regulators such as lineage-specific transcription factors, leaving cytokines to ensure survival and proliferation of the progeny cells. Here we show that macrophage colony-stimulating factor (M-CSF, also called CSF1), a myeloid cytokine released during infection and inflammation, can directly induce the myeloid master regulator PU.1 and instruct myeloid cell-fate change in mouse HSCs, independently of selective survival or proliferation. Video imaging and single-cell gene expression analysis revealed that stimulation of highly purified HSCs with M-CSF in culture resulted in activation of the PU.1 promoter and an increased number of PU.1(+) cells with myeloid gene signature and differentiation potential. In vivo, high systemic levels of M-CSF directly stimulated M-CSF-receptor-dependent activation of endogenous PU.1 protein in single HSCs and induced a PU.1-dependent myeloid differentiation preference. Our data demonstrate that lineage-specific cytokines can act directly on HSCs in vitro and in vivo to instruct a change of cell identity. This fundamentally changes the current view of how HSCs respond to environmental challenge and implicates stress-induced cytokines as direct instructors of HSC fate.

Electron spin polarization in an Al(III) porphyrin complex with an axially bound nitroxide radical.

The generation and transfer of electron spin polarization and coherence plays an important role in quantum information technologies and spintronics. In this context, the excited state spin dynamics of molecular systems in which a stable free radical is attached to a chromophore are of particular interest. In such complexes, the coupling between the electron spin on the free radical with those on the chromophore generates excited states referred to as sing-doublet, trip-doublet, and trip-quartet. Here, we study the light-induced electron spin polarization in an aluminum(iii) porphyrin (AlPor) complex in which the nitroxide (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) is covalently bound to the Al center via an ester linkage. In addition to the covalent bond to the TEMPO moiety, the Al center in AlPor also acts as a Lewis acid and can coordinate Lewis bases such as pyridine. Without pyridine bound, the spin polarized transient electron paramagnetic resonance spectrum of the complex at 80 K is unusual and displays a strong absorptive pattern with a Lorentzian lineshape. Coordination of pyridine to AlPor-TEMPO results in a dramatic change in the spin polarization pattern and a spectrum typical of the quartet state with broad wings from the ms = ±1/2 ↔ ±3/2 transitions with emissive/absorptive polarization and a narrow absorptive peak from the ms = ±1/2 ↔ ±1/2 transitions. At later times, the pattern evolves to a purely absorptive spectrum similar to that observed without pyridine. These changes are discussed in terms of a model in which back and forth transitions between the nearly degenerate lowest trip-doublet and trip-quartet states occur. It is argued that these transitions lead to the observed net polarization in AlPor-TEMPO and are fast enough that the outer lines are broadened. Density functional theory computations and the UV/Vis spectra suggest that the exchange interaction between TEMPO and the triplet state of AlPor increases when pyridine is bound, and the near degeneracy of the lowest excited states is lifted. It is argued that this slows the back and forth transitions which results in the strong change in the polarization pattern.

C. Elegans Fatty Acid Two-Hydroxylase Regulates Intestinal Homeostasis by Affecting Heptadecenoic Acid Production.

BACKGROUND/AIMS: The hydroxylation of fatty acids at the C-2 position is the first step of fatty acid α-oxidation and generates sphingolipids containing 2-hydroxy fatty acyl moieties. Fatty acid 2-hydroxylation is catalyzed by Fatty acid 2-hydroxylase (FA2H) enzyme. However, the precise roles of FA2H and fatty acid 2-hydroxylation in whole cell homeostasis still remain unclear. METHODS: Here we utilize Caenorhabditis elegans as the model and systemically investigate the physiological functions of FATH-1/C25A1.5, the highly conserved worm homolog for mammalian FA2H enzyme. Immunostaining, dye-staining and translational fusion reporters were used to visualize FATH-1 protein and a variety of subcellular structures. The "click chemistry" method was employed to label 2-OH fatty acid in vivo. Global and tissue-specific RNAi knockdown experiments were performed to inactivate FATH-1 function. Lipid analysis of the fath-1 deficient mutants was achieved by mass spectrometry. RESULTS: C. elegans FATH-1 is expressed at most developmental stages and in most tissues. Loss of fath-1 expression results in severe growth retardation and shortened lifespan. FATH-1 function is crucially required in the intestine but not the epidermis with stereospecificity. The "click chemistry" labeling technique showed that the FATH-1 metabolites are mainly enriched in membrane structures preferable to the apical side of the intestinal cells. At the subcellular level, we found that loss of fath-1 expression inhibits lipid droplets formation, as well as selectively disrupts peroxisomes and apical endosomes. Lipid analysis of the fath-1 deficient animals revealed a significant reduction in the content of heptadecenoic acid, while other major FAs remain unaffected. Feeding of exogenous heptadecenoic acid (C17: 1), but not oleic acid (C18: 1), rescues the global and subcellular defects of fath-1 knockdown worms. CONCLUSION: Our study revealed that FATH-1 and its catalytic products are highly specific in the context of chirality, C-chain length, spatial distribution, as well as the types of cellular organelles they affect. Such an unexpected degree of specificity for the synthesis and functions of hydroxylated FAs helps to regulate protein transport and fat metabolism, therefore maintaining the cellular homeostasis of the intestinal cells. These findings may help our understanding of FA2H functions across species, and offer potential therapeutical targets for treating FA2H-related diseases.

Reversible Solution π-Dimerization and Long Multicenter Bonding in a Stable Phenoxyl Radical.

Reversible solution π-dimerization is observed in the stable neutral phenoxyl radical 2,6-bis-(8-quinolylamino)-4-(tert-butyl)phenoxyl baqp and is spectroscopically characterized. This behavior, not previously observed for π-extended phenoxyl radicals, is relevant to the formation of long multicenter bonding in the π-dimer at low temperature akin to previously reported phenalenyl radicals. Our experimental data are supported in a quantitative manner by results from density functional theory (DFT) and ab initio molecular orbital theory calculations. Our theoretical results indicate that the solution dimer features strong bonding interactions between the two phenoxyl rings but that the stability of the dimer is also related to dispersion interactions between the flanking nearly parallel quinolyl rings.