Receptorphin: A conserved peptide derived from the sequence of the opioid receptor, with opioid displacement activity and potent antiproliferative actions in tumor cells

BACKGROUND: In addition to endogenous opioids, a number of peptide sequences, derived from endogenous (hemorphins, alphaS1-casomorphin), and exogenous proteins (casomorphins, exorphins) have been reported, possessing opioid activity. In the present work, we report the identification of a new peptide, receptorphin (Tyr-Ile-Phe-Asn-Leu), derived from the sequence of the second transmembrane loop of the opioid receptor. This sequence is unique for the opioid receptor, and conserved in all species and receptor-types. RESULTS AND DISCUSSION: Receptorphin competes for opioid binding, presenting a kappa-receptor interaction, while it binds equally to delta- and mu- opioid and somatostatin-binding sites, and inhibits the cell proliferation of a number of human cancer cell lines, in a dose-dependent and reversible manner, at the picomolar or the nanomolar range. Receptorphin shows a preferential action on prostate cancer cells. CONCLUSION: Our work identifies, for the first time a peptide, in a receptor sequence, possessing ligand-agonistic activities. A hypothesis, based on receptorphin liberation after cell death, is presented, which could tentatively explain the time-lag observed during opioid antiproliferative action

Conduction mechanisms at distinct resistive levels of Pt/TiO_2-x/Pt memristors

Resistive random access memories (RRAMs) are considered as key enabling components for a variety of emerging applications due to their capacity to support multiple resistive states. Deciphering the underlying mechanisms that support resistive switching remains to date a topic of debate, particularly for metal-oxide technologies and is very much needed for optimizing their performance. This work aims to identify the dominant conduction mechanisms during switching operation of Pt/TiO2-x/Pt stacks, which is without a doubt one of the most celebrated ones. A number of identical devices were accordingly electroformed for acquiring distinct resistive levels through a pulsing-based and compliance-free protocol. For each obtained level the switching current-voltage (I-V) characteristics were recorded and analyzed in the temperature range of 300 K to 350 K. This allowed the extraction of the corresponding signature plots revealing the dominant transport mechanism for each of the I-V branches. Gradual (analogue) switching was obtained for all cases and two major regimes were identified. For the higher resistance regime the transport at both the high and low resistive states was found to be interface controlled due to Schottky emission. As the resistance of devices reduces to lower levels, the dominant conduction changes from an interface to core-material controlled mechanism. This study overall supports that engineering the metal-oxide/metal electrode interface can lead to tailored barrier modifications for controlling the switching characteristics of TiO2 RRAM

Interface barriers at Metal – TiO₂ contacts

Metal-oxides combine a unique ensemble of properties presenting great potential to meet the diverse requirements of modern electronics and in particular of brain-inspired applications. Among others, TiO2 is without a doubt one of the most celebrated materials. The ability of TiO2 to obtain different microstructures (i.e. amorphous, rutile etc.) and thus a plethora of electronic properties that can be determined/controlled by the fabrication and/or biasing conditions augmented its use in practical applications, such as memristors, TFTs and sensors. Notwithstanding the importance of the active layer, identifying appropriate metal contacts and deciphering their interfacial role is also of paramount importance to a device’s electrical behaviour. This paper aims to present a detailed quantitative electrical characterization study of Metal-TiO2 interface characteristics.&amp; more...<br/

An electrical characterisation methodology for identifying the switching mechanism in TiO₂ memristive stacks

Resistive random access memories (RRAMs) can be programmed to discrete resistive levels on demand via voltage pulses with appropriate amplitude and widths. This tuneability enables the design of various emerging concepts, to name a few: neuromorphic applications and reconfigurable circuits. Despite the wide interest in RRAM technologies there is still room for improvement and the key lies with understanding better the underpinning mechanism responsible for resistive switching. This work presents a methodology that aids such efforts, by revealing the nature of the resistive switching through assessing the transport properties in the non-switching operation regimes, before and after switching occurs. Variation in the transport properties obtained by analysing the current-voltage characteristics at distinct temperatures provides experimental evidence for understanding the nature of the responsible mechanism. This study is performed on prototyped device stacks that possess common Au bottom electrodes, identical TiO2 active layers while employing three different top electrodes, Au, Ni and Pt. Our results support in all cases an interface controlled transport due to Schottky emission and suggest that the acquired gradual switching originates by the bias induced modification of the interfacial barrier. Throughout this study, the top electrode material was found to play a role in determining the electroforming requirements and thus indirectly the devices’ memristive characteristics whilst both the top and bottom metal/oxide interfaces are found to be modified as result of this process

Electrical characteristics of interfacial barriers at Metal – TiO₂ contacts

The electrical properties of thin TiO2 films have recently been extensively exploited towards enabling a variety of metal-oxide electron devices: unipolar/bipolar semiconductor devices and/or memristors. In such efforts, investigations on the role of TiO2 as active material have been the main focus, however, electrode materials are equally important. In this work, we address this need by presenting a systematic quantitative electrical characterization study on the interface characteristics of Metal-TiO2-Metal structures. Our study employs typical contact materials that are used both as top and bottom electrodes in a Metal-TiO2-Metal setting. This allows investigating the characteristics of the interfaces as well as holistically studying an electrode’s influence to the opposite interface, referred to in this work as top/bottom electrodes interrelationship. Our methodology comprises the recording of current-voltage (I-V) characteristics from a variety of solid-state prototypes in the temperature range of 300-350 K and by analysing them through appropriate modelling. Clear field and temperature dependent signature plots were also obtained towards shinning more light on the role of each material as top/bottom electrodes in Metal-TiO2-Metal configurations. Our results highlight that these are not conventional metal-semiconductor contacts and several parameters such as the electrodes position (atop or below the film), the electronegativity, the interface states and even the opposite interface electrode material are involved on the formation of the interfacial barriers. Overall our study provides a useful database for selecting appropriate electrode materials in TiO2 based devices, offering new insights on the role of electrodes on metal-oxide electronics applications

Conduction mechanisms in Pt/TiO₂/Pt memristors

Resistive random access memories (RRAMs) receive increasing attention as very promising candidates for the next generation of nonvolatile memories, as well as for artificial neuronetworks and reconfigurable systems developments. A key feature for the aforementioned applications is their ability to obtain multiple resistive levels by proper tuning of the biasing schemes. Therefore, clarification of the dominant conduction mechanism, which remains to date a topic of debate, is of a paramount importance. This strongly depends on the device characteristics (oxide and electrodes’ materials) and the programming bias schemes. &amp; more..

Dataset for article &quot;Electrical characteristics of interfacial barriers at Metal &ndash; TiO2 contacts&quot;

Dataset to support the publication: Michalas, L., Khiat, A., Stathopoulos, S., &amp; Prodromakis, T. (2018). Electrical characteristics of interfacial barriers at Metal &ndash; TiO2 contacts. Journal of Physics D: Applied Physics. DOI: 10.1088/1361-6463/aadbd2</span

Dataset for article &quot;Conduction mechanisms at distinct resistive levels of Pt/TiO2-x/Pt memristrors&quot;

Dataset supports: Michalas, L. et al (2018). Conduction mechanisms at distinct resistive levels of Pt/TiO2-x/Pt memristrors. Applied Physics Letters, 13.</span

Data for &#39;An electrical characterisation methodology for identifying the switching mechanism in TiO2 memristive stacks&#39;

Data supports the paper: L. Michalas, S. Stathopoulos, A. Khiat and T. Prodromakis (2019) An electrical characterisation methodology for identifying the switching mechanism in TiO2 memristive stacks Scientific Reports (https://www.nature.com/srep/)</span