Organic thin-film transistors are attracting a great deal of attention due to the relatively high field-effect mobility in several organic materials. In these organic semiconductors, however, researchers have not established a reliable method of doping at a very low density level, although this has been crucial for the technological development of inorganic semiconductors. In the field-effect device structures, the conduction channel exists at the interface between organic thin films and SiO(2) gate insulators. Here, we discuss a new technique that enables us to control the charge density in the channel by using organosilane self-assembled monolayers (SAMs) on SiO(2) gate insulators. SAMs with fluorine and amino groups have been shown to accumulate holes and electrons, respectively, in the transistor channel: these properties are understood in terms of the effects of electric dipoles of the SAMs molecules, and weak charge transfer between organic films and SAMs.

Protein L-isoaspartyl methyltransferase (PIMT) is suggested to play a role in the repair of aged protein spontaneously incorporated with isoaspartyl residues. We generated PIMT-deficient mice by targeted disruption of the PIMT gene to elucidate the biological role of the gene in vivo. PIMT-deficient mice died from progressive epileptic seizures with grand mal and myoclonus between 4 and 12 weeks of age. An anticonvulsive drug, dipropylacetic acid (DPA), improved their survival but failed to cure the fatal outcome. L-Isoaspartatate, the putative substrate for PIMT, was increased ninefold in the brains of PIMT-deficient mice. The brains of PIMT-deficient mice started to enlarge after 4 weeks of age when the apical dendrites of pyramidal neurons in cerebral cortices showed aberrant arborizations with disorganized microtubules. We conclude that methylation of modified proteins with isoaspartyl residues is essential for the maintenance of a mature CNS and that a deficiency in PIMT results in fatal progressive epilepsy in mice.

We report an improvement in performance of C60 thin-film field-effect transistors (TFTs) fabricated by molecular-beam deposition. Devices, fabricated and characterized under a high vacuum without exposure to air, routinely showed current on/off ratios >108 and field-effect mobilities in the range of 0.5–0.3 cm2/V s. The mobility obtained is close to that derived from the photocurrent measurements on C60 thin films and comparable to a very high value among n-type organic TFTs.

The surface conductivity is measured by a four-probe technique for pentacene and rubrene singlecrystals laminated on polarized and nearly unpolarized molecular monolayers with application of perpendicular electric fields. The polarization of the self-assembled monolayers (SAMs) shifts the threshold gate voltage, while maintaining a very low subthreshold swing of the single-crystal devices (0.11 V/decade). The results, excluding influences of parasitic contacts and grain boundaries, demonstrate SAM-induced nanoscale charge injection up to ∼ 10 12 cm −2 at the surface of the organic single crystals. PACS numbers:Significant efforts are being made to bring organic field-effect transistors (OFETs) into practical use, taking advantages of their potential of low-cost production, mechanical flexibility and optical as well as chemical sensitivities [1]. To promote the development, some basic questions are to be further elucidated, such as the intrinsic nature of the transport of charge induced at the surface of the organic semiconductors. Following this direction, a growing number of experiments has recently been reported on the single-crystal devices that avoid complication due to grain boundaries [2,3,4,5,6,7]. In an early study of the single-crystal OFETs, Takeya et al. proposed a method of laminating organic crystals on SiO 2 /doped Si substrates by natural electrostatic force [3]. Four-probe measurements on the single-crystal devices revealed genuine transfer characteristics of the OFETs, free from parasitic contact effects. In addition, the laminated single-crystal devices are also useful to examine whether a new finding in polycrystalline thinfilm OFETs is intrinsic to the semiconductor-SiO 2 interface or is an artifact due to grain-boundaries, because the process of single-crystal device fabrication is identical to the commonly studied bottom-electrode thin-film OFETs. Note that inter-grain charge dynamics dominates the field-effect properties in some thin-film devices [8] Self-assembled monolayers (SAMs) of neutral organosilane molecules are often incorporated in thin-film OFETs to passivate the SiO 2 surface before evaporating the organic semiconductor [9]. Very recently, Kobayashi et al. reported that the threshold gate voltage V th is shifted in their polycrystalline thin-film devices when the neutral * Electronic address: takeya@criepi.denken.or.jp SAMs are replaced with highly electron-affine ones [10]. The mechanism of the threshold shift ∆V th , however, was not clear; rather large standard deviation among the samples causes difficulty in quantitative comparison of ∆V th among different thin-film materials and to the calculated dipole moment of the SAMs. Since the inclusion of grain boundaries and contact resistances may introduce complications [11], single-crystal samples are more appropriate to further study the microscopic mechanism of the observed shift. In the present work, we laminated pentacene and rubrene crystals on both polarized and on nearly unpolarized SAMs, to measure the field-effect conduc...

Prostaglandin F2 alpha (PGF2 alpha) is a primary luteolysin in the cow. Although the mechanisms involved in luteolysis are thought to be a complex of its direct action on luteal cells and indirect effect on luteal blood flow, the detailed mechanisms remain to be elucidated. This study focuses on the possible interaction of endothelial cells-derived endothelin-1 (ET-1) with PGF2 alpha in the rapid suppression of progesterone release from the bovine corpus luteum (CL). In in vitro microdialysis system (MDS) of CL, PGF2 alpha acutely stimulated the release of progesterone and oxytocin during infusion and ET-1 release after infusion. Moreover, PGF2 alpha induced slight decrease of progesterone release during the last period of the experiment (8-11 h after PGF2 alpha exposure). Two 1 h-perfusions of ET-1 at 3 h intervals induced only a slight decrease of progesterone release after the second perfusion. This treatment also affected the oxytocin release; the first ET-1 perfusion produced an acute stimulation, whereas the second ET-1 perfusion inhibited the release to below 50%. When the CL pieces were pre-perfused with PGF2 alpha for 2 h, the two consecutive perfusion of ET-1 at 3 h intervals induced drastic decrease in progesterone and oxytocin release only after the second ET-1 perfusion. Thus, a pre-exposure with PGF2 alpha clearly potentiated the inhibiting activity of ET-1 in the progesterone release. These results suggest a physiological impact of PGF2 alpha and ET-1 in the rapid cascade of functional luteolysis in vivo, and a possible interaction between endothelial cells and luteal cells.

We first demonstrate a field-effect-transistor operation of dimetallofullerene La2@C80 with the icosahedral cage symmetry. The thin-film device showed an n-type behavior with a mobility of 1.1 x 10-4 cm2/V s at room temperature under high vacuum. Taking the nature of LUMO into account, the n-type behavior indicates an occurrence of carrier conduction through encapsulated La ions. The low mobility, suggesting an intermolecular hopping mechanism, is ascribed to the intrinsic and extrinsic reasons, which are discussed in the text.

The newly formed corpus luteum (CL) rapidly develops after ovulation and has the features of active vascularisation and mitosis of steroidogenic cells. These stage-specific mechanisms also may contribute to gain the function of prostaglandin F2 (PGF2 )-resistant CL at this stage. Recent studies suggest that the vasoactive peptide angiotensin II (Ang II) regulates luteal function. Thus, this study aimed to investigate (i) the expression of angiotensinconverting enzyme (ACE) mRNA by RT-PCR and the ACE protein expression by immunohistochemistry, (ii) the effects of angiogenic growth factors, basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF), on the secretion of Ang II, PGF2 , progesterone and oxytocin (OT), and (iii) the effects of luteal vasoactive peptides (Ang II and endothelin-1 (ET-1)) or OT on the secretion of PGF2 , progesterone and OT from bovine early CL (days 3-4 of the oestrous cycle), and evaluate a possible interaction of these substances with PGF2 . The expression of mRNA for ACE was found in theca interna of mature follicle, early CL and endothelial cells from developing CL as well as pituitary and kidney, but granulosa cells of mature follicle were negative. The immunohistochemical analysis revealed that blood capillaries (endothelial cells) were stained for ACE, but luteal cells were negative in early CL. To examine the effects of substances on the secretory function of the CL, an in vitro microdialysis system was used as a model. The infusion of bFGF and VEGF stimulated Ang II and PGF2 secretion as well as progesterone, but not OT secretion in early CL. The infusion of Ang II after PGF2 infusion continued the stimulatory effect on progesterone and OT release within early CL until 3 h thereafter. However, the infusion of ET-1 alone had no effect on progesterone or OT release. The infusion of luteal peptides such as Ang II and OT stimulated PGF2 secretion, whereas the infusion of ET-1 did not. In conclusion, the overall results of this study indicate that a functional angiotensin system exists on the endothelial cells of early CL, and that angiogenic factors bFGF and VEGF upregulate luteal Ang II and PGF2 secretion, which fundamentally supports the mechanism of progesterone secretion in bovine early CL. This idea supports the concept that the local regulatory mechanism involved in active angiogenesis ensures the progesterone secretion in the developing CL in vivo.

We report an ambipolar operation in field-effect transistors of C60 and metallofullerene Dy@C82 by modification of semiconductor/metal electrode interface with perfluoroalkylsilane (FAS) molecules. Kelvin probe experiments revealed that the work function of the gold surface modified with FAS molecules increased by 0.55eV as compared to the untreated gold. Hole injection into fullerenes is qualitatively understood in terms of this work-function change induced by the FAS molecules. The present results indicate that the charge injection from electrodes to organic semiconductors can be controlled simply by modification of semiconductor/metal interface without changing materials themselves.