Construction of an autocatalytic reaction cycle in neutral medium for synthesis of life-sustaining sugars

Autocatalytic mechanisms in carbon metabolism, such as the Calvin cycle, are responsible for the biological assimilation of CO2 to form organic compounds with complex structures, including sugars. Compounds that form C-C bonds with CO2 are regenerated in these autocatalytic reaction cycles, and the products are concurrently released. The formose reaction in basic aqueous solution has attracted attention as a nonbiological reaction involving an autocatalytic reaction cycle that non-enzymatically synthesizes sugars from the C1 compound formaldehyde. However, formaldehyde and sugars, which are the substrate and products of the formose reaction, respectively, are consumed in Cannizzaro reactions, particularly under basic aqueous conditions, which makes the formose reaction a fragile sugar-production system. Here, we constructed an autocatalytic reaction cycle for sugar synthesis under neutral conditions. We focused on the weak Brønsted basicity of oxometalate anions such as tungstates and molybdates as catalysts, thereby enabling the aldol reaction, retro-aldol reaction, and aldose-ketose transformation, which collectively constitute the autocatalytic reaction cycle. These bases acted on sugar molecules of substrates together with sodium ions of a Lewis acid to promote deprotonation under neutral conditions, which is the initiation step of the reactions forming an autocatalytic cycle, whereas the Cannizzaro reaction was inhibited. The autocatalytic reaction cycle established using this abiotic approach is a robust sugar production system. Furthermore, we found that the synthesized sugars work as energy storage substances that sustain microbial growth despite their absence in nature.

Self-organization in an Open Reaction Network for Developing High-function Organized Molecular Systems

Self-organized molecular systems such as liposomes and supramolecules have attracted considerable attention due to their characteristic properties. An open reaction network (ORN) is another interesting candidate for such systems; however, no stabilization mechanism has been clarified. This work reveals, by computer simulation and experiments, that a network of irreversible processes such as an ORN can be stabilized by self-organization through a full balance between all the involved irreversible processes, thus forming a steady state. The formation of a steady state indicates that a large spontaneous order is formed; specifically, self-organization occurs. Computer simulations also reveal that such a steady state characteristically evolves toward a high-efficiency state through the development of highly ordered structures. These findings indicate that ORN provides a new method for developing high-function organized molecular systems, such as an efficient catalytic system in a composite of ORN and equilibrium molecular structures such as supramolecules and polymers.

Positive Feedback Mechanism to Increase the Charging Voltage of Li-O2 Batteries

The large overpotential of nonaqueous Li-O₂ batteries when charging causes low round-trip efficiency and decomposition of the electrode materials and electrolyte. The origins of this overpotential have been enthusiastically explored to date; however, a full understanding has not yet been reached because of the complexity of multistep reaction mechanisms. Here, we applied structural and electrochemical analysis techniques to investigate the reaction step that results in the increase of the overpotential when charging. Rietveld refinement of ex situ powder X-ray diffraction showed that a Li-deficient phase of Li₂O₂, Li_2-xO₂, formed when discharging and was present over the course of charging. The galvanostatic intermittent titration technique revealed that the rate-determining process in the first step of charging was a solid-solution type of delithiation. The chemical diffusion coefficient of Li⁺ ions in Li_2-xO₂, D_Li, decreases as the cell voltage increases, which in turn leads to a decrease in the oxidation rate of Li_2-xO₂. Under galvanostatic conditions, the deceleration of oxidation induces further increase of the cell voltage; therefore, an intrinsic mechanism of positive feedback to increase the cell voltage occurs in the first step. The results demonstrate that the continuity of the first step can be extended by the suppression of changes in any of the elements of the positive feedback loop, i.e., the oxidation rate, cell voltage, or D_Li.

Isotopic Depth Profiling of Discharge Products Identifies Reactive Interfaces in an Aprotic Li-O2 Battery with a Redox Mediator

Prior to the practical application of rechargeable aprotic Li-O₂ batteries, the high charging overpotentials of these devices (which inevitably cause irreversible parasitic reactions) must be addressed. The use of redox mediators (RMs) that oxidatively decompose the discharge product, Li₂O₂, is one promising solution to this problem. However, the mitigating effect of RMs is currently insufficient, and so it would be beneficial to clarify the Li₂O₂ reductive growth and oxidative decomposition mechanisms. In the present work, Nanoscale secondary ion mass spectrometry (Nano-SIMS) isotopic three-dimensional imaging and differential electrochemical mass spectrometry (DEMS) analyses of individual Li₂O₂ particles established that both growth and decomposition proceeded at the Li₂O₂/electrolyte interface in a system containing the Br^-/Br₃^- redox couple as the RM. The results of this study also indicated that the degree of oxidative decomposition of Li₂O₂ was highly dependent on the cell voltage. These data show that increasing the RM reaction rate at the Li₂O₂/electrolyte interface is critical to improve the cycle life of Li-O₂ batteries.

Dynamic Changes in Charge Transfer Resistances during Cycling of Aprotic Li-O2 Batteries

Various electrolyte components have been investigated with the aim of improving the cycle life of lithium-oxygen (Li-O₂) batteries. A tetraglyme-based electrolyte containing dual anions of Br^- and NO₃^- is a promising electrolyte system in which the cell voltage during charging is reduced because of the redox-mediator function of the Br^-/Br₃^- and NO₂^-/NO₂ couples, while the Li-metal anode is protected by Li₂O formed via the reaction between Li metal and NO₃^-. To maximize the potential of this system, the fundamental factors that limit the cycle life should be clarified. In the present work, we used nondestructive electrochemical impedance spectroscopy to analyze the temporal change of the charge transfer resistances during cycles of Li-O₂ batteries with dual anions. The charge transfer resistance at the cathode was revealed to exhibit good correlation with the reduction of the discharge voltage. These results, combined with the results of electrode surface inspections, revealed that irreversible accumulation of insulating deposits such as Li₂O₂ and Li₂CO₃ on the cathode surface was a major cause of the short cycle life. Furthermore, the analyses of the time course of the solution resistance suggested that diminished reactivity between the redox mediators and Li₂O₂ was a critical factor that led to the irreversible accumulation of the less-reactive Li₂O₂ on the cathode and eventually to a shortened cycle life. These findings indicated that increasing the reactivity between Br₃^- and Li₂O₂ is essentially important for improving the cycle stability of Li-O₂ batteries and the reactivity can be nondestructively assessed by tracking the dynamic changes in the solution resistance.

Five current peaks in voltammograms for oxidations of formic acid, formaldehyde, and methanol on platinum

We have found that five current peaks are present in the voltammograms in the positive and negative sweep directions for the oxidations of formic acid, formaldehyde, and methanol on Pt in the potential range of 0.05-1.8 V, although the experimental conditions for the peaks to appear are different. In particular, a current peak at ca. 0.6 V, the negative slope of which on the positive side is closely related to autocatalysis, inducing oscillation, has been observed even for methanol. We have clarified that the three substances produce very similar voltammograms at a very slow sweep rate, such as 0.1 mV/s, and show some of the same behaviors of the peaks in their voltammograms. All these facts support the idea that the electrochemical oxidation mechanisms for the three substances have the same dominating elementary reaction steps, which induce oscillation phenomena, although with different reaction and adsorption rate constants.

Periodic and chaotic oscillations of the electrochemical potential of p-Si in contact with an aqueous (CuSO4+HF) solution, caused by electroless Cu deposition

Periodic and chaotic oscillations were observed for the potential of p-type Si(111) immersed in an aqueous (HF+CuSO(4)) solution, accompanied by electroless Cu deposition on p-Si. They were, to our knowledge, the first examples of open-circuit potential oscillations observed for semiconductor electrodes. The oscillations appeared only when the Cu deposit formed a continuous porous film composed of mutually connected submicrometer-sized particles. Besides, the Si surface was kept flat within the size less than 50 nm even after the prolonged oscillation for a few hours, though the Si surface should be etched considerably with HF for this time. A plausible model is proposed for the periodic oscillation, in which interestingly coupling of autocatalytic shift in the flat-band potential of Si (U(fb)) caused by the change in the coverage of the Si oxide and the connection and disconnection of the Cu film with the Si surface plays the key role. The appearance of the chaotic oscillation is also explained by taking into account an oscillation-coupled change in the HF or Cu(2+) concentration near the Si surface.

Potential Oscillations in Galvanostatic Electrooxidation of Formic Acid on Platinum: A Mathematical Modeling and Simulation

We have modeled temporal potential oscillations during the electrooxidation of formic acid on platinum on the basis of the experimental results obtained by time-resolved surface-enhanced infrared absorption spectroscopy (J. Phys. Chem. B 2005, 109, 23509). The model was constructed within the framework of the so-called dual-path mechanism; a direct path via a reactive intermediate and an indirect path via strongly bonded CO formed by dehydration of formic acid. The model differs from earlier ones in the intermediate in the direct path. The reactive intermediate in this model is formate, and the oxidation of formate to CO2 is rate-determining. The reaction rate of the latter process is represented by a second-order rate equation. Simulations using this model well reproduce the experimentally observed oscillation patterns and the temporal changes in the coverages of the adsorbed formate and CO. Most properties of the voltammetric behavior of formic acid, including the potential dependence of adsorbate coverages and a negative differential resistance, are also reproduced.

Potential Oscillations in Galvanostatic Electrooxidation of Formic Acid on Platinum: A Time-Resolved Surface-Enhanced Infrared Study

The mechanism of temporal potential oscillations that occur during galvanostatic formic acid oxidation on a Pt electrode has been investigated by time-resolved surface-enhanced infrared absorption spectroscopy (SEIRAS). Carbon monoxide (CO) and formate were found to adsorb on the surface and change their coverages synchronously with the temporal potential oscillations. Isotopic solution exchange (from H13COOH to H12COOH) and potential step experiments revealed that the oxidation of formic acid proceeds dominantly through adsorbed formate and the decomposition of formate to CO2 is the rate-determining step of the reaction. Adsorbed CO blocks the adsorption of formate and also suppresses the decomposition of formate to CO2, which raises the potential to maintain the applied current. The oxidative removal of CO at a high limiting potential increases the coverage of formate and accelerates the decomposition of formate, resulting in a potential drop and leading to the formation of CO. This cycle repeats itself to give the sustained temporal potential oscillations. The oscillatory dynamics can be explained by using a nonlinear rate equation originally proposed to explain the decomposition of formate and acetate on transition metal surfaces in UHV.

Role of Oncostatin M in hematopoiesis and liver development

Definitive hematopoietic stem cells (HSCs) first appear in the aorta/gonad/mesonephros (AGM) region and migrate to the fetal liver where they massively produce hematopoietic cells before establishing hematopoiesis in the bone marrow at a perinatal stage. In the AGM region, Oncostatin M (OSM) enhances the development of both hematopoietic and endothelial cells by possibly stimulating their common precursors, so-called hemangioblasts. During development of HSCs in the AGM region, the liver primodium is formed at the foregut and accepts HSCs. While fetal hepatic cells function as hematopoietic microenvironment for expansion of hematopoietic cells during mid to late gestation, they do not possess most of the metabolic functions of adult liver. Along with the expansion of hematopoietic cells in fetal liver, OSM is produced by hematopoietic cells and induces differentiation of fetal hepatic cells, conferring various metabolic activities of adult liver. Matured hepatic cells then lose the ability to support hematopoiesis. Thus, OSM appears to coordinate the development of liver and hematopoiesis in the fetus.

The AML1 transcription factor functions to develop and maintain hematogenic precursor cells in the embryonic aorta-gonad-mesonephros region

We examined the role of the AML1 transcription factor in the development of hematopoiesis in the paraaortic splanchnopleural (P-Sp) and the aorta-gonad-mesonephros (AGM) regions of mouse embryos. The activity of colony-forming units of colonies from the P-Sp/AGM region was reduced severalfold by heterozygous disruption of the AML1 gene, indicating that AML1 functioned in a dosage-dependent manner to generate hematopoietic progenitors. In addition, no hematopoietic progenitor activity was detected in the P-Sp/AGM region of embryos with an AML1 null mutation. Similar results were obtained when a dispersed culture was first prepared from the P-Sp/AGM region before assay of the activity of the colony-forming units. In a culture of cells with the AML1(+/+) genotype, both hematopoietic and endothelial-like cell types emerged, but in a culture of cells with the AML1(-/-) genotype, only endothelial-like cells emerged. Interestingly, introduction of AML1 cDNA into the P-Sp/AGM culture with the AML1(-/-) genotype partially restored the production of hematopoietic cells. This restoration was observed for cultures prepared from 9.5-day postcoitum (dpc) embryos but not for cultures prepared from 11.5-dpc embryos. Therefore, the population of endothelial-like cells capable of growing in the AML1(-/-) culture would appear to contain inert but nonetheless competent hematogenic precursor cells up until at least the 9.5-dpc period. All these results support the notion that the AML1 transcription factor functions to develop and maintain hematogenic precursor cells in the embryonic P-Sp/AGM region.

Identification of podocalyxin-like protein 1 as a novel cell surface marker for hemangioblasts in the murine aorta-gonad-mesonephros region

Recent studies with avian embryos and murine embryonic stem cells have suggested that hematopoietic cells are derived from hemangioblasts, the common precursors of hematopoietic and endothelial cells. We molecularly cloned podocalyxin-like protein 1 (PCLP1) as a novel surface marker for endothelial-like cells in the aorta-gonad-mesonephros (AGM) region of mouse embryos, where long-term repopulating hematopoietic stem cells (LTR-HSCs) are known to arise. PCLP1+ CD45 cells in the AGM region incorporated acetylated low-density lipoprotein and produced both hematopoietic and endothelial cells when cocultured with OP9 stromal cells. Moreover, multiple lineages of hematopoietic cells were generated in vivo when PCLP1 +CD45-cells were injected into neonatal liver of busulfan-treated mice. Thus, PCLP1 can be used to separate hemangioblasts that give rise to LTR-HSCs.

Distinct roles of oncostatin M and leukemia inhibitory factor in the development of primordial germ cells and sertoli cells in mice

Leukemia inhibitory factor (LIF) stimulates the growth of primordial germ cells (PGCs) in mouse embryo. However, as neither mice lacking LIF nor mice lacking the LIF receptor show defects in PGC growth, an alternate cytokine for PGC growth has been postulated. We investigated the role of mouse oncostatin M (mOSM), which is structurally and functionally related to LIF, in germ cell development. While LIF enhanced the survival of migratory as well as postmigratory PGCs, mOSM acted only on the postmigratory PGCs. Consistent with its biological activity, mOSM was found to be expressed in developing gonads. In the male, Sertoli cells in neonatal testis express mOSM; however, its expression is downregulated in adult testes. Moreover, mOSM enhanced the proliferation of Sertoli cells derived from neonatal testes in vitro more than human OSM or LIF. In contrast, postnatal ovaries do not express mOSM. These results indicate that mOSM is a stage- and sex-specific autocrine growth factor for Sertoli cells.

In vitro expansion of murine multipotential hematopoietic progenitors from the embryonic aorta-gonad-mesonephros region

The origin of hematopoietic stem cells (HSCs) and their growth factor requirement are poorly understood. Here we describe a new in vitro culture system of the aorta-gonad-mesonephros (AGM) region, where long-term repopulating HSCs first arise. We demonstrate that oncostatin M (OSM) is expressed in the AGM and is absolutely required for the expansion of multipotential hematopoietic progenitors in vitro. In addition, OSM enhances the formation of endothelial cell clusters. Thus, OSM appears to be a key cytokine for the development of multipotential hematopoietic progenitors in the AGM, possibly acting on common precursor cells between HSCs and endothelial cells. By using the AGM culture derived from macrophage colony-stimulating factor (M-CSF)-deficient op/op mutant embryos, we also show a pivotal role for M-CSF in fetal myelopoiesis.

Induction of protein tyrosine phosphatase epsilon transcripts during NGF-induced neuronal differentiation of PC12D cells and during the development of the cerebellum

We have investigated a possible role played by protein tyrosine phosphatase epsilon (PTPepsilon), which was recently cloned and predominantly expressed in brain, in neural differentiation and function. During neuronal cell differentiation of PC12D cells triggered by NGF or FGF, PTPepsilon transcripts were transiently induced at a time between the appearance of transcripts for immediate-early genes and for neuronal cell-specific markers. PTPepsilon was the only PTPase whose transcripts were induced during PC12D cell differentiation among over two dozen PTPase transcripts so far examined. Moreover, in situ hybridization revealed that PTPepsilon transcripts were detected in the neural tube of day 12 postcoitum embryo, and in the nervous system including brain, spinal cord, and ganglions in a ubiquitous manner in late gestational stages. In 4-day-old neonatal mice, the transcripts were widely distributed in the central nervous system where the strongest expression was detected in the hippocampus, cerebral cortex, and olfactory bulb. Interestingly, in day 7 and 16 neonatal brains, the strongest PTPepsilon gene expression was localized in the granular cells of cerebellum, which might indicate that PTPepsilon is involved in the differentiation of the granular cells. The biological significance of PTPepsilon in neuronal differentiation and brain functions is discussed.

A receptor tyrosine kinase, Sky, and its ligand Gas 6 are expressed in gonads and support primordial germ cell growth or survival in culture

Although a number of growth factors and their receptors are involved in the proliferation and differentiation of primordial germ cells (PGCs), the only factor that has been shown to be active in vivo is Steel factor, a ligand for c-Kit. To identify new growth factor receptors that may be required for PGCs function in vivo, we used an reverse transcription-polymerase chain reaction-based strategy to screen for protein kinase genes expressed in PGC-derived embryonic germ cells. We report here that one such gene encoding the receptor tyrosine kinase, Sky, is expressed in both PGCs and their supporting cells in male genital ridges after 11.5 dpc. Interestingly, Sky expression was not detected in female genital ridges, although transcripts were detected in supporting cells in the developing ovary at later stages. Gas 6, a ligand for Sky, was also expressed in interstitial cells which surround Sky positive cells in genital ridges, and, in addition, it supported PGC growth or survival in culture. After birth, Sky expression in testis was restricted to Sertoli cells, and Gas 6 was detected around peritubular cells and Leydig cells. These results suggest that Gas 6-Sky signaling plays a role in PGC growth, sexual differentiation, and Sertoli cell functions in vivo. Sky expression in Sertoli cells diminished by 3 weeks of age, when haploid germ cells first appear. On the other hand, the expression in Sertoli cells was markedly upregulated in the testis of germ cell-deficient W/Wv and jsd/jsd mice. The results suggest that signals from differentiated germ cells suppress Sky gene expression in Sertoli cells. High-resolution chromosomal mapping of Sky is also reported.

A novel serine/threonine kinase gene, Gek1, is expressed in meiotic testicular germ cells and primordial germ cells

We have isolated a novel serine/ threonine kinase gene designated Gek1 from mouse primordial germ cell-derived embryonic germ cell. Gek1 is preferentially expressed in meiotic testicular germ cells and primordial germ cells. Gek1 mRNA is also detected in several other tissues, including hematopoietic organs in adult mice and central nervous system in embryos. The Gek1 cDNA encodes a protein with the consensus sequence of the catalytic domain of protein kinases in its N-terminal region. The deduced amino acid sequence of Gek1 in the kinase domain is related to those encoded by the Saccharomyces cerevisiae STE20, CDC15, and Drosophila melanogaster ninaC. The patterns of expression and the structural features of Gek1 suggest that the gene product is involved in signal transduction or nuclear division of germ cells and other proliferating cells. We also show that Gek1 locates on chromosome 11, near the wr locus, showing neuronal and reproductive defects.

Chromosomal location of murine protein tyrosine phosphatase (Ptprj and Ptpre) genes

It is now widely accepted that protein tyrosine phosphatases (PTPases) play important or even critical roles in cell growth, differentiation, and development. Our recent experiments suggested that specific PTPases, PTP beta 2 and PTP epsilon, are involved in the early molecular events for in vitro differentiation of mouse erythroleukemia (MEL) as well as embryonic carcinoma (F9) cells. Using mouse cDNA for PTP beta 2 and PTP epsilon, which we have cloned recently, we attempted to locate the genes to mouse chromosomes. Interspecific backcross analysis indicated that the gene for PTP beta 2, Ptprj, is located in the middle region of chromosome 2, and the gene for PTP epsilon, Ptpre, was mapped in the vicinity of the imprinted regions in the distal part of chromosome 7. Possible biological roles of these PTPases are discussed.

Characterization of a protein tyrosine phosphatase (RIP) expressed at a very early stage of differentiation in both mouse erythroleukemia and embryonal carcinoma cells

From our previous studies, several protein tyrosine phosphatases (PTPase) are implicated in the early events leading to in vitro differentiation of both mouse erythroleukemia (MEL) and embryonal carcinoma (F9) cells. Among the PTPases, recent experiments suggest that a new PTPase (RIP) plays a critical role in differentiation processes, particularly at their early stages. We isolated cDNA clones for RIP from a RNA preparation isolated from differentiating MEL cells, and determined the total 7932 bp base sequence for RIP cDNA. The cDNA codes for a putative 269.8 kDa (2450 amino acids) protein with a PTPase catalytic domain. We have demonstrated that the transcripts exist in multiple forms, and among mouse tissues they were found predominantly in kidney and, to a lesser extent, in lung, heart, brain and testis. The RIP gene was mapped between D5Mit90 and D5Mit25 on mouse chromosome 5.

Dentinal fluid movement associated with loading of restorations

Post-operative biting sensitivity is a significant clinical problem after placement of posterior resin composites and may be due to dentinal fluid movement. The occlusal surfaces of extracted teeth were filled with amalgam (control) or various posterior resin composites, and the movement of the dentinal fluid induced by the loading of the restorations was studied. In addition, the firing of pulpal nerves induced by the loading of class 5 resin composite restorations in canine teeth of dogs was also investigated. When the entire cavity was etched with an acid gel and then filled with resin composite, dentinal fluid movement in response to loading was significantly (p less than 0.01) greater than in the amalgam-filled or unoperated controls. The dog canine tooth filled with resin composite showed firing of pulpal nerves when loaded. These results suggest that the movement of dentinal fluid induced by masticatory pressure on resin composite restorations may elicit biting sensitivity.

[Comparisons of meter reading values in 5 electronic measuring devices]

The root apex values given in the manufacturers' introductions of 5 electronic measuring devices were compared with the mean values measured by each device in the following cases: a) The tip of file was at the apical constriction in the experimental tooth model. b) The tip of file was between 0 mm and -2.0 mm from the root apex in the vital teeth and the pulpless teeth. In the experimental tooth model, when the tip of file was at the apical constriction, the mean values measured by each device except EM were lower than the root apex values given in the manufacturers' introductions of each device. In the case of the vital tooth, when the tip of file was between 0 mm and -2.0 mm from the root apex, the mean values measured by EM-S II and EM were similar to the values given in the manufacturers' introductions of these devices, but not to those obtained by the other devices. Measurements of the pulpless tooth by each device revealed mean values lower than the values given in manufacturers' introductions for the root apex.