Design and synthesis of new carbon allotropes have always been important topics in condensed matter physics and materials science. Here we report a new carbon allotrope, formed from cold-compressed C_{70} peapods, which most likely can be identified with a fully sp^{3}-bonded monoclinic structure, here named V carbon, predicted from our simulation. The simulated x-ray diffraction pattern, near K-edge spectroscopy, and phonon spectrum agree well with our experimental data. Theoretical calculations reveal that V carbon has a Vickers hardness of 90 GPa and a bulk modulus ∼400  GPa, which well explains the "ring crack" left on the diamond anvils by the transformed phase in our experiments. The V carbon is thermodynamically stable over a wide pressure range up to 100 GPa, suggesting that once V carbon forms, it is stable and can be recovered to ambient conditions. A transition pathway from peapod to V carbon has also been suggested. These findings suggest a new strategy for creating new sp^{3}-hybridized carbon structures by using fullerene@nanotubes carbon precursor containing odd-numbered rings in the structures.

The behavior of molecules and molecular chains confined in 1D nanochannels imposed by external interactions is a problem of fundamental interest. Here, we report structural manipulation of iodine confined inside zeolite (AFI) nanochannels by the application of high pressure. Structural transformations of the confined iodine under pressure have been unambiguously identified by polarized Raman spectroscopy combined with theoretical simulation. The length of the iodine chains and the orientation and intermolecular interaction of the confined iodine have been tuned at the molecular level by applied pressure. Almost all the confined iodine can be tuned into an axially oriented state upon compression, favoring the formation of long chains. The long iodine chains can be preserved to ambient pressure when released from intermediate pressures. ■ INTRODUCTIONStudies of the control and manipulation of atoms/molecules and their assemblies generate remarkable new insights into how physical and chemical systems function. They permit direct observation of molecular behavior that can be obscured by ensemble averaging and enables the study of important problems ranging from fundamental physics to the design of nanoscale electro-optical devices. In particular, much effort has been focused on the control of atomic/molecular chains due to their potential application as quantum wires. 1−9 By using simultaneous STM and TEM (transmission electron microscopy), gold nanowires composed of several atomic chains have been fabricated and show quantum conductance behavior. 2 Later, thinner nanowires have been fabricated in high vacuum with an electron beam thinning technique but the stability becomes lower with decreasing size and the length is still limited to a few nanometers (<6 nm). 3 On the other hand, filling materials into one-dimensional channels has been shown to be an efficient way to prepare atomic/molecular chains stable at ambient condition. 9−13 However, the atomic/molecular chains obtained usually show a mixture of different arrangements or have random orientations and are mixed with individual atoms/molecules in the channels due to size mismatch between the host channel and the filled species or because of inhomogeneous filling. 8−14 A typical example is that filling iodine into single wall carbon nanotubes (SWNTs) yields either helicoidal chains, polyiodides, discrete individual molecules, or new crystalline structures of iodine in the nanotube channels, depending on the tube diameter. 14−16 To obtain chains in a particular desired structural arrangement requires further manipulation. 17 For this purpose, understanding the transformation dynamics of the confined iodine imposed by external interactions becomes very important.High pressure serves as a powerful tuning parameter that has been used to tune the intermolecular interaction and structure of bulk materials. 18−23 In the confined environment, the configuration of the material is expected to be modified not only by the applied pressure but also by the evolution of the co...

Pressure-induced transformation and superhard phase in fullerenes: the effect of solvent intercalation.Applied Physics Letters, 103 (7) Abstract:We studied the behavior of solvated and desolvated C 60 crystals under pressure by in situ Raman spectroscopy. The pressure-induced bonding change and structural transformation of C 60 s are similar in the two samples, both undergoing deformation and amorphization.Nevertheless, the high pressure phases of solvated C 60 can indent diamond anvils while that of desolvated C 60 s cannot. Further experiments suggest that the solvents in the solvated C 60 act as both spacers and bridges by forming covalent bonds with neighbors in 3D network at high pressure, and thus, a fraction of fullerenes may preserve the periodic arrangement in spite of their amorphization.

To verify whether amyloid precursor protein (APP) affects the migration and invasion of breast cancer cell lines, and to understand its underlying mechanisms, epithelial-mesenchymal transition (EMT), the mitogen-activated protein kinase (MAPK) signaling pathway and the matrix metalloproteinase (MMP) family were investigated in MDA-MB-231, MCF-7 and BT474 human breast cancer cells. Breast cancer cell lines were transfected with plasmids containing APP coding sequences (pEGFP-n1-APP) and APP short hairpin RNA (pENTR APP shRNA). APP overexpres-sion efficiency, knockout efficiency and the expression levels of related genes were tested using reverse transcription-quantitative PCR (RT-qPCR) and western blot analyses. The effects of APP and mitogen-activated protein kinase kinase (MEK) inhibitor on cell migration and invasion were examined using Transwell assays. The results demonstrated that APP was significantly upregulated in the pEGFP-n1-APP group (P<0.05), and significantly downregulated in the pENTR APP shRNA group (P<0.05), compared with the control group. APP overexpression increased the migratory and invasive ability of human breast cancer cells (P<0.05), whereas APP silencing significantly inhibited cell migration and invasion (P<0.05). RT-qPCR and western blot analysis results suggested that APP overexpression significantly increased the expression of MMP-9, MMP-2, MMP-3, N-cadherin and vimentin (P<0.05). In addition, the enhanced expression of APP markedly affected the phosphorylation of mitogen-activated protein kinase kinase kinase 11 (MLK3), mitogen-activated protein kinase kinase 4 (MEK4) and mitogen-activated protein kinase 10 (JNK3; P<0.05). Additionally, APP overexpression had no effect on the total expression levels of MLK3, MEK4, and JNK3; however, APP overexpression significantly decreased the expression levels of E-cadherin and cytokeratin (P<0.05). Conversely, APP silencing had the opposite effects. When cells were treated with the MEK inhibitor PD0325901, the expression of APP was not altered, nor was the expression levels of MEK and its upstream signaling molecules. Taken together, the present findings suggested that APP could affect the migration and invasion of human breast cancer cells by mediating the activation of the MAPK signaling pathway, thereby promoting the EMT process.

ZIF-8 is a prototypical porous material in the family of zeolitic imidazolate frameworks, and its structural stability is of great significance for a wide range of practical applications. Here, the intrinsic and extrinsic structural and mechanical responses of nanosized ZIF-8 perturbed by high external pressure have been comparatively investigated based on our in situ Raman measurements in different pressure environments, accompanied by synchrotron X-ray diffraction measurements and results from previous reports. An improvement of both the chemical and crystallographic stability of ZIF-8, rather than an intrinsic quick deterioration, can be observed when penetrating guest molecules get into the pores. Spectral evidence demonstrates that the CC section of the imidazolate ring is an optimal interaction site for the penetrating methanol, water, and nitrogen molecules. We further find that water molecules can cleave Zn−N bonds to bring linker-associated defects to ZIF-8. When compressed in the nonpenetrating silicone oil as a pressure transmitting medium (PTM) or when no PTM is used, irreversibility is observed, while samples show a highly reversible transformation both in the short-range and long-range regions upon decompression from a partially or entirely amorphous state in penetrating PTM. Furthermore, the released samples transform to a dense bulk state in the absence of penetrating PTM instead of preserving the original nanosized particles when penetrating pressure transmitting fluids is present. Moreover, the compressible behavior of ZIF-8 varies and is found to be strongly influenced by the size and polarity of molecules in the pores. The present results indicate that the stability, compressibility, and reversibility of ZIF-8 under pressure are closely related to the pressure environments and the characteristics of the guest molecules in the PTM. Thus, this study sheds light on the available mechanical modifications and selectable applications of ZIF-8 as gas absorbents for the future.