The fixation of the catalyst interface
is an important consideration
for the design of practical applications. However, the electronic
structure of MoS2 is sensitive to its embedding environment,
and the catalytic performance of MoS2 catalysts may be
altered significantly by the type of binding agents and interfacial
structure. Interfacial engineering is an effective method for designing
efficient catalysts, arising from the close contact between different
components, which facilitates charge transfer and strong electronic
interactions. Here, we have developed a layer-by-layer (LbL) strategy
for the preparation of interfacial MoS2-based catalyst
structures with two types of conducting polymers on various substrates.
We demonstrate how the assembled partners in the LbL structure can
significantly impact the electronic structures in MoS2.
As the number of bilayers grows, using polypyrrole as a binder remarkably
increases the catalytic efficacy as compared to using polyaniline.
On the one hand, the ratio of S2
2– (or
S2–), which is related to the remaining active hydrogen
evolution reaction (HER) species, is further increased. On the other
hand, density functional theory calculations indicate that the interfacial
charge transport from the conducting polymers to MoS2 may
boost the HER activity of the interfacial structure of the conducting
polymer/MoS2 by decreasing the adsorption free energy of
the intermediate H* at the S sites in the basal plane of MoS2. The optimized catalytic efficacy of the (conducting polymer/MoS2)
n
assembly peaks is obtained
with 16 assembly cycles. In preparing interfacial catalytic structures,
the LbL-based strategy exhibits several key advantages, including
the flexibility of choosing assembly partners, the ability to fine-tune
the structures with precision at the nanometer scale, and planar homogeneity
at the centimeter scale. We expect that this LbL-based catalyst immobilization
strategy will contribute to the fundamental understanding of the scalability
and control of highly efficient electrocatalysts at the interface
for practical applications.
Sphingosine phosphate lyase 1 (SGPL1) is a highly conserved enzyme that irreversibly degrades sphingosine-1-phosphate (S1P). Sgpl1-knockout mice fail to develop germ cells, resulting in infertility. However, the molecular mechanism remains unclear. The results of the present study showed that SGPL1 was expressed mainly in granulosa cells, Leydig cells, spermatocytes, and round spermatids. Sgpl1 deletion led to S1P accumulation in the gonads. In the ovary, S1P decreased natriuretic peptide receptor 2 (NPR2) activity in granulosa cells and inhibited early follicle growth. In the testis, S1P increased the levels of cyclin-dependent kinase inhibitor 1A (p21) and apoptosis in Leydig cells, thus resulting in spermatogenesis arrest. These results indicate that Sgpl1 deletion increases intracellular S1P levels, resulting in the arrest of female and male germ cell development via different signaling pathways.
Germ cell division and differentiation require intimate contact and interaction with the surrounding somatic cells. Luteinizing hormone (LH) triggers epidermal growth factor (EGF)-like growth factors to promote oocyte maturation and developmental competence by activating EGF receptor (EGFR) in somatic cells. Here, we showed that LH-EGFR signaling-activated sphingosine kinases (SphK) in somatic cells. The activation of EGFR by EGF increased S1P and calcium levels in cumulus-oocyte complexes (COCs), and decreased the binding affinity of natriuretic peptide receptor 2 (NPR2) for natriuretic peptide type C (NPPC) to release the cGMP-mediated meiotic arrest. These functions of EGF were blocked by the SphK inhibitor SKI-II, which could be reversed by the addition of S1P. S1P also activated the Akt/mTOR cascade reaction in oocytes and promoted targeting protein for Xklp2 (TPX2) accumulation and oocyte developmental competence. Specifically depleting Sphk1/2 in somatic cells reduced S1P levels and impaired oocyte meiotic maturation and developmental competence, resulting in complete female infertility. Collectively, SphK-produced S1P in somatic cells serves as a functional transmitter of LH-EGFR signaling from somatic cells to oocytes: acting on somatic cells to induce oocyte meiotic maturation, and acting on oocytes to improve oocyte developmental competence.
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