Thermal conductivities of phosphorene allotropes from first-principles calculations: a comparative study.

Phosphorene has attracted tremendous interest recently due to its intriguing electronic properties. However, the thermal transport properties of phosphorene, especially for its allotropes, are still not well-understood. In this work, we calculate the thermal conductivities of five phosphorene allotropes (α-, ß-, γ-, δ- and ζ-phase) by using phonon Boltzmann transport theory combined with first-principles calculations. It is found that the α-phosphorene exhibits considerable anisotropic thermal transport, while it is less obvious in the other four phosphorene allotropes. The highest thermal conductivity is found in the ß-phosphorene, followed by the δ-, γ- and ζ-phase. The much lower thermal conductivity of the ζ-phase can be attributed to its relatively complex atomic configuration. It is expected that the rich thermal transport properties of phosphorene allotropes can have potential applications in the thermoelectrics and thermal management.

Understanding the electronic and phonon transport properties of a thermoelectric material BiCuSeO: a first-principles study.

Using the first-principles pseudopotential method and Boltzmann transport theory, we give a comprehensive understanding of the electronic and phonon transport properties of the thermoelectric material BiCuSeO. By choosing an appropriate hybrid functional for the exchange-correlation energy, we find that the system is a semiconductor with a direct band gap of ∼0.8 eV, which is quite different from those obtained previously using standard functionals. Detailed analysis of a three-dimensional energy band structure indicates that there is a valley degeneracy of eight around the valence band maximum, which leads to a sharp density of states and is responsible for a large p-type Seebeck coefficient. Moreover, we find that the density of states effective mass is much larger and results in a very low hole mobility for BiCuSeO. On the other hand, we discover two flat phonon branches contributed by the Cu and Se atoms, which can effectively block heat transfer. Combined with large atomic displacement parameters of the Cu atom, we believe that the intrinsically low lattice thermal conductivity in BiCuSeO is mainly caused by the Cu atoms, instead of the prevailingly believed Bi atoms. The thermoelectric figure-of-merit is also predicted and compared with available experimental results.

High thermoelectric performance of the distorted bismuth(110) layer.

The thermoelectric properties of the distorted bismuth(110) layer are investigated using first-principles calculations combined with the Boltzmann transport equation for both electrons and phonons. To accurately predict the electronic and transport properties, the quasiparticle corrections with the GW approximation of many-body effects have been explicitly included. It is found that a maximum ZT value of 6.4 can be achieved for n-type systems, which essentially stemmed from the weak scattering of electrons. Moreover, we demonstrate that the distorted Bi layer retains high ZT values in relatively broad regions of both temperature and carrier concentration. Our theoretical work emphasizes that the deformation potential constant characterizing the electron-phonon scattering strength is an important paradigm for searching high thermoelectric performance materials.

Enhanced thermoelectric performance of carbon nanotubes at elevated temperature.

The electronic and transport properties of the (10, 0) single-walled carbon nanotube are studied by performing first-principles calculations and semi-classical Boltzmann theory. It is found that the (10, 0) tube exhibits a considerably large Seebeck coefficient and electrical conductivity which are highly desirable for good thermoelectric materials. Together with the lattice thermal conductivity predicted by non-equilibrium molecular dynamics simulations, the room temperature ZT value of the (10, 0) tube is estimated to be 0.15 for p-type carriers. Moreover, the ZT value exhibits strong temperature dependence and can reach to 0.77 at 1000 K. Such a ZT value can be further enhanced to as high as 1.9 by isotopic substitution and chemisorptions of hydrogen on the tube surface.

Sarcolectin: complete purification for molecular cloning.

A great variety of vertebrate cells contain detectable amounts of lectins, able to stimulate the initiation of cellular DNA synthesis. One of them, sarcolectin (SCL) can block interferon (IFN) action, by inhibiting the synthesis and the expression of the IFN dependent secondary proteins. As a result, the IFN-induced antiviral state is abolished in the cells, which likely facilitates their replication. We identified a major 65 kDa and a minor 55 kDa protein, which could carry these cellular functions. Their purification, especially that of the 65 kDa, was difficult, because of the proximity of albumin. We devised therefore a two-step primary separation, followed by a four-step final purification, which are reported here. The purification was controlled by high pressure liquid chromatography (HPLC), SDS-PAGE electrophoresis and identified by Western blots. We found that only the minor 55 kDa protein can be considered as being sarcolectin, while the major 65 kDa band results from the binding of some SCL molecules to albumin. The major biological functions, namely, stimulation of DNA synthesis and cell agglutination were preserved to the end of the last purification step. This work is requisite for establishing the molecular structure of SCL by recombinant DNA technology.

Sarcolectin (SCL): structure and expression of the recombinant molecule.

Interferons (IFNs) are major cytokines, responsible for down-regulating cell growth and for promoting cell differentiation. The sarcolectin (SCL) protein presented here blocks in the cells the established IFN-dependent interphase and stimulates DNA synthesis, probably in co-ordination with more specific growth factors or hormones. The SCL-DNA structure is closely related to that of cytokeratine K2C7 intermediate filaments, but the SCL is a monomer, or sometimes a dimer, which is excreted into the serum, where it is frequently bound to albumin. Its specific biological functions are carried by the beta sheets, and can be found on the two terminal domains of the molecule, the lectinic properties being located mainly on the N-terminus. The recombinant SCL molecule possesses the same biological functions as the native one, since it inhibits the IFN-dependent antiviral state both in human and in mouse cell cultures. On the contrary, antibodies raised against amino acids 41-55 located on the N-terminal domain of SCL inhibit this antagonistic effect. We postulate that the IFN and SCL proteins, because of their opposite biological functions, are in balance and are part of a feedback system operating the regulation of normal growth. In pathological cases, SCL could play a role in the development of tumors, as we have found in juvenile osteosarcomas or in AIDS cases.

Localization and structure of v-mos in transformed mouse fibroblasts reverted by long-term interferon treatment to nonmalignancy.

We have reported previously that Moloney virus-transformed cells, when treated for over 200 passages in the presence of low concentrations of mouse interferon-alpha/beta, can be reverted to a stable nonmalignant status. The cells recover full contact inhibition and are unable to raise tumors when grafted in nude mice. In the present report, we show that whether reverted or malignant, these cells contain deleted v-mos oncogenes, which have lost 392 nucleotides. The truncated oncogenes contain a reduced and modified open reading frame but are able, however, to induce tumors when transfected in mouse 3T3 cells. As there is no difference either in the location or in the structure of this modified v-mos, whether yielded by reverted or malignant cells, we postulate that both cell lines derive from the same population and this modification does not play any role in the reversion process obtained through prolonged IFN-dependent selection. We suggest that reversion could be an epigenetic phenomenon, involving the constitutive synthesis of IFN-beta only in the reverted and not in the malignant cells. The continued persistence of such noncancerous cells could result at least partly from a balance involving the expression of v-mos, IFN-beta, and an IFN antagonist, sarcolectin. These reverted cells can undergo an unlimited number of passages, but they must be trypsinized before day 5 in confluent cultures. Thereafter, the cells stop dividing, cannot proliferate anymore, progressively show signs of apoptosis, and die.

[Mechanism of proliferation of cells transformed by the Moloney mouse sarcoma virus after stable reversion to a non-malignant state]. / Mécanisme de la multiplication des cellules transformées par le virus du sarcome de Moloney après réversion stable à l'état non malin.

Prolonged interferon (IFN) treatment can convert Moloney sarcoma-transformed mouse Balb C fibroblasts to a stable non-malignant status. The cells recover a number of differentiated features, which are maintained even when IFN is permanently omitted from the tissue culture medium. We show here that reversion could be at least in part attributed to constitutive IFN beta synthesized only in the reverted cells. The continued replication of these cells, although unable to induce tumours in athymic mice, could be the result of the maintained expression of an IFN antagonist termed sarcolectin (SCL), a balance being struck between the effects of v-mos oncogene, interferon beta and SCLs. In agreement with Lampl et al. [11], we suggest that normal cell growth is discontinuous, consisting of sudden bursts followed by prolonged arrests which could be necessary to promote differentiation during the ensuing interphase.

Sarcolectin and interferon in the regulation of cell growth.

Sarcolectin is an endolectin present in a great variety of conjunctival tissues (muscles, cartilage, sarcomas), but also in brain or placental extracts of vertebrates, including primates. When purified to electrophoretical homogeneity as a 65-kd protein, it agglutinates cells and has an affinity for simple sugars. In addition, it is able to inhibit the synthesis of interferon (IFN)-dependent secondary proteins and to restore cells to their status ad primum. The biological effect of Poly(I).Poly(C)-induced feedback interferon is inhibited by the addition of sarcolectins, which also abolishes cellular refractoriness to repeated IFN induction. Similarly, sequential association of, first, Poly(I).Poly(C); 4-5 h later, sarcolectin restores the full capacity of both to promote cell growth, unrestrained by IFN. Indeed, the secondary proteins which are in the process of being synthesized are inhibited. In a great variety of animal cells, sarcolectin can also initiate growth after it has been blocked by IFN. This is not an all-or-none effect, but a balance may be struck by IFN and sarcolectin, depending on their respective concentrations and specific activity. We propose that the coordination of these cellular functions of Poly(I).Poly(C), IFN, and sarcolectin takes place in the form of a triangular growth-regulatory cycle and postulate that they thus maintain a balance during differentiated normal tissue development.

Interferon- and sarcolectin-dependent cellular regulatory interactions.

Interferons, via specific membrane-bound receptors, induce various cellular functions of which antiviral protection is the most extensively studied. We have previously reported the existence of interferon antagonists (referred to as sarcolectins) in various tissue extracts from placental blood, cartilage, brain, muscle, or from sarcomas. These sarcolectins have been fully characterized and purified to homogeneity. In interferon-treated cells, they restore virus sensitivity 4-6 h after the establishment of antiviral protection. In the present study we investigate the effect of sarcolectins on the steady state levels of two double-stranded RNA dependent enzymes, 2-5A (p chi (A2'p)nA) synthetase and protein kinase. Several authors have previously emphasized the role of these enzymes in the mechanism of interferon's antiviral action. Interferon promotes a 4-8 fold increase in protein kinase and 2-5A synthetase in cells. Addition of sarcolectin 5 h after interferon results in a dramatic reduction in the steady state levels of both these enzymes, as shown by their decreased activity and yield observed in Western blot assays. The degradation of the antiviral response in sarcolectin-treated cells might therefore be at least partially attributed to a reduced synthesis of protein kinase and 2-5A synthetase. Since there are no direct interactions between sarcolectins and interferon or its receptors, it can be postulated that sarcolectins exert their effect through these interferon-dependent proteins. We postulate that the opposing biological effects of interferon and sarcolectins strike a balance which may, however, be modified in one direction or the other, depending on their respective concentrations.

Cell distribution and antigenic properties of mammalian sarcolectins.

Sarcolectins are present in a great variety of tissues from mammalian origin. Such substances were observed to be secreted from cultures of human embryonic fibroblasts, human osteosarcoma and rat Rous sarcoma transformed cells and could be extracted from TG 180 Crocker Sarcoma or normal human placenta. All sarcolectins tested here, were comparable by their physicochemical properties to those previously reported in hamster or human sarcomas. Indeed, they are proteins or glycoproteins, resistant to pepsin and migrate in SDS-PAGE in the 65 kDa area. They agglutinate cells with an affinity for simple sugars and degrade previously established interferon-induced antiviral resistance. Considering the hamster sarcolectin as reference in this comparative study, both differences and similarities in the antigenic properties of mouse, rat and human sarcolectin variants were demonstrated. An indirect immunofluorescence assay showed that sarcolectins were specifically labelled on the cell surface but not detected in the cytoplasm after methanol or acetone permeabilization of the membrane. By electron microscopy, using immunoperoxidase labelling, sarcolectins can be localized on the surface of normal, transformed, human or rat cells. Only limited segments of normal cell membranes were labelled, while transformed cells were frequently stained on their whole surface. Other known extracellular proteins, such as fibronectin and collagen, did not share common antigenic determinants with sarcolectins.

Detection of an interferon antagonist, sarcolectin, in human sarcomas and muscles.

In a variety of human sarcomas we detected the presence of a sarcolectin which reversed an established antiviral protection induced by interferon (IFN). For the same protein concentration, this biological activity was significantly increased when compared to that of normal muscles. All the biological characteristics were comparable to those of a sarcolectin found in hamster tissues; namely the capacity to agglutinate cells and its inhibition by specific sugars, migration in sodium dodecyl sulfate gel, and pepsin, heat and sodium dodecyl sulfate stability. Except for its anti-IFN function and cell agglutinating activity, the biological significances of this sarcolectin is presently poorly understood.

Sarcolectin: an interferon antagonist extracted from hamster sarcomas and normal muscles. Isolation, characterization, and purification.

In the present work we show that sarcoma and normal hamster tissues contain a protein which agglutinates normal and transformed cells. The inhibition of agglutination by galacturonic acid and occasionally by fucose suggests a resemblance of this protein with vegetal lectins. When added 5 h after interferon, the crude semipurified and electrophoretically homogeneous preparations reduce within 20 h the antiviral state pre-established by interferon. These two biological tests have enabled us to monitor the subsequent purification steps. The isolation of the biologically active protein is greatly facilitated by its resistance to pepsin and nucleases, whereas its sensitivity to trypsin and Pronase suggests its proteinaceous character. Furthermore, the molecule is stable when heated 1-2 min at 100 degrees C in the presence or absence of sodium dodecyl sulfate. After pepsin treatment, Sephacryl G-200 gel filtration, and ion exchange chromatography on DEAE-cellulose, 25-40-fold purification can be obtained. When controlled by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, a double band (DEAE-cellulose sample) or single band (octyl-agarose sample) is detected in the 65,000-dalton region and no other contaminator is present. The eluted protein retains full biological activity when assayed by the degradation of the interferon-induced antiviral protection in the cell or titrated by cell agglutination.