MHz Unidirectional Rotation of Molecular Rotary Motors

A combination of cryogenic UV-vis and CD spectroscopy and transient absorption spectroscopy at ambient temperature is used to study a new class of unidirectional rotary molecular motors. Stabilization of unstable intermediates is achieved below 95 K in propane solution for the structure with the fastest rotation rate, and below this temperature measurements on the rate limiting step in the rotation cycle can be performed to obtain activation parameters. The results are compared to measurements at ambient temperature using transient absorption spectroscopy, which show that behavior of these motors is similar over the full temperature range investigated, thereby allowing a maximum rotation rate of 3 MHz at room temperature under suitable irradiation conditions

Electron spin dynamics in quantum dots and related nanostructures due to hyperfine interaction with nuclei

We review and summarize recent theoretical and experimental work on electron spin dynamics in quantum dots and related nanostructures due to hyperfine interaction with surrounding nuclear spins. This topic is of particular interest with respect to several proposals for quantum information processing in solid state systems. Specifically, we investigate the hyperfine interaction of an electron spin confined in a quantum dot in an s-type conduction band with the nuclear spins in the dot. This interaction is proportional to the square modulus of the electron wave function at the location of each nucleus leading to an inhomogeneous coupling, i.e. nuclei in different locations are coupled with different strength. In the case of an initially fully polarized nuclear spin system an exact analytical solution for the spin dynamics can be found. For not completely polarized nuclei, approximation-free results can only be obtained numerically in sufficiently small systems. We compare these exact results with findings from several approximation strategies.Comment: 26 pages, 9 figures. Topical Review to appear in J. Phys.: Condens. Matte

Spintronics: Fundamentals and applications

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes from the published versio

Synergistic Interactions between HDAC and Sirtuin Inhibitors in Human Leukemia Cells

Aberrant histone deacetylase (HDAC) activity is frequent in human leukemias. However, while classical, NAD+-independent HDACs are an established therapeutic target, the relevance of NAD+-dependent HDACs (sirtuins) in leukemia treatment remains unclear. Here, we assessed the antileukemic activity of sirtuin inhibitors and of the NAD+-lowering drug FK866, alone and in combination with traditional HDAC inhibitors. Primary leukemia cells, leukemia cell lines, healthy leukocytes and hematopoietic progenitors were treated with sirtuin inhibitors (sirtinol, cambinol, EX527) and with FK866, with or without addition of the HDAC inhibitors valproic acid, sodium butyrate, and vorinostat. Cell death was quantified by propidium iodide cell staining and subsequent flow-cytometry. Apoptosis induction was monitored by cell staining with FITC-Annexin-V/propidium iodide or with TMRE followed by flow-cytometric analysis, and by measuring caspase3/7 activity. Intracellular Bax was detected by flow-cytometry and western blotting. Cellular NAD+ levels were measured by enzymatic cycling assays. Bax was overexpressed by retroviral transduction. Bax and SIRT1 were silenced by RNA-interference. Sirtuin inhibitors and FK866 synergistically enhanced HDAC inhibitor activity in leukemia cells, but not in healthy leukocytes and hematopoietic progenitors. In leukemia cells, HDAC inhibitors were found to induce upregulation of Bax, a pro-apoptotic Bcl2 family-member whose translocation to mitochondria is normally prevented by SIRT1. As a result, leukemia cells become sensitized to sirtuin inhibitor-induced apoptosis. In conclusion, NAD+-independent HDACs and sirtuins cooperate in leukemia cells to avoid apoptosis. Combining sirtuin with HDAC inhibitors results in synergistic antileukemic activity that could be therapeutically exploited

Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers

Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers

Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers

Diagnostik und Therapie der extraabdominalen Desmoidfibromatose

Introduction: The desmoid fibromatosis is a very rare connective tissue disease which is recognized as semimalignant. The aim of this work is to review the relevant literature and to analyze the management of our patient collective. Material and Method: Surgery was performed on 7 patients with extraabdominal desmoid fibromatosis between August 1998 and May 2007. MRI examination as well as biopsy was carried out in all cases. All patients were operated on; the mean follow up was 4 years (1-7). Upon follow up, every patient has undergone clinical and MRI examination. Results: The results show that we have achieved R0 resection in 4 cases and R1 in two cases and Rx in one case. In 4 patients, no recurrence was observed after the single surgery performed in our hospital. In 2 patients a single revision surgery was performed in each case and yielded no further recurrence. In only one case, multiple surgeries (one primary and two revision surgeries) were necessary, after which no recurrence was reported.Conclusion: The early diagnosis of the disease is of utmost importance to the success of the outcome. MRI examination and biopsy are mandatory. Surgery is the therapy of choice. The recurrence rate is high and is linked to the difficulty of recognition of the exact infiltrative extent of the tumour. This necessitates a close follow-up.Einleitung: Die extraabdominelle Desmoidfibromatose ist eine außerordentlich seltene, als semimaligne eingestufte Bindegewebserkrankung. Auf Grund der Seltenheit, der nicht spezifischen Lokalisation, des unspezifischen Erscheinungsbildes und der hohen Rezidivrate bleiben sowohl die Diagnostik als auch Therapie der extraabdominellen Desmoidfibromatose eine Herausforderung. Anhand einer Aufarbeitung des eigenen Patientengutes sowie einer umfassenden Literaturrecherche soll der aktuelle Wissensstand zu diesem Krankheitsbild dargestellt werden. Material und Methoden: Zwischen August 1998 und Mai 2007 wurden 7 Patienten mit einer extraabdominalen Desmoidfibromatose operativ behandelt. Alle Patienten wurden mittels eines definierten Diagnosealgorithmus einschließlich MRT und Biopsie diagnostiziert. Die Therapie war in allen Fällen operativ. Der Nachuntersuchungszeitraum betrug im Durchschnitt 4 (1-7) Jahre. Zum Nachuntersuchungszeitpunkt erfolgten eine Befragung, eine klinische Untersuchung sowie eine MRT-Kontrolle. Ergebnisse: Die Ergebnisse zeigen, dass wir R0-Resektion in 4 Fällen, R1 in zwei Fällen und Rx in einem Fall erreicht haben. Bei 4 Patienten wurde kein Rezidiv nach der einmaligen Operation in unserer Klinik beobachtet. Bei 2 Patienten wurde jeweils eine einzige Revisionsoperation durchgeführt, wonach beide Patienten rezidivfrei waren. In nur einem Fall waren mehrere Operationen (eine primäre und zwei Revisionsoperationen) notwendig, nach denen kein Rezidiv berichtet wurde. Schlussfolgerungen: Die frühzeitige Diagnosestellung ist für den Erfolg der operativen Behandlung von Bedeutung, hierbei ist ein definierter Diagnosealgorithmus einschließlich einer MRT-Untersuchung und einer Biopsie obligat. Die Operation stellt die Behandlung der Wahl dar. Engmaschige Nachkontrollen sind notwendig, um Rezidive frühzeitig erkennen und dann gegebenenfalls operativ behandeln zu können