X-ray absorption spectroscopy of molecular-based spin-hybrid systems

Im Rahmen dieser Arbeit werden molekulare Spin-Hybrid Systeme auf ihre strukturellen, elektronischen und magnetischen Eigenschaften untersucht. Die Resultate sind entsprechend der verwendeten Molekülklassen in zwei Kapitel unterteilt. Im ersten Teil werden Systeme mit (quasi-)planaren paramagnetischen Molekülen mit einem 3d-Übergangsmetallion im Zentrum des Moleküls untersucht. Mit Hilfe von XMCD-Messungen wird gezeigt, dass sich die magnetischen Momente von FePc- Molekülen auf ferromagnetischen Co-Filmen ausrichten. Bei direktem Kontakt existiert eine ferromagnetische Kopplung bei Raumtemperatur. Durch eine Zwischenlage Sauerstoff, die die Moleküle von der Co-Oberfläche trennt, wird die Kopplung zwischen Molekül und Substrat antiferromagnetisch. Hingegen wird die Kopplung durch eine Graphen-Zwischenlage auf einem Ni(111)-Substrat lediglich geschwächt, aber die parallele Spinausrichtung von Co-Substrat und Fe-Ionen des FePc-Moleküls bleibt erhalten. Anders stellt sich die Situation bei CoOEP-Molekülen dar. Auf dem gleichen Substrat Graphen/Ni(111) koppeln die Co-Ionen antiferromagnetisch durch die Graphenschicht an das Ni-Substrat. Die magnetische Kopplung kann jedoch nur für die erste Moleküllage gezeigt werden, weitere Lagen sind entkoppelt. Durch die zwei verschieden gekoppelten Moleküllagen kann die Netto-Magnetisierung der CoOEP-Moleküle in der Multilage durch Veränderung des äußeren Magnetfeldes umgeschaltet werden. Die zweite Molekülklasse sind sogenannte Einzelmolekülmagneten des Typs LnPc2. Mit feldabhängigen XMCD-Messungen wird eine magnetische Remanenz der Moleküle bei Submonolagenbedeckung auf einem HOPG-Substrat nachgewiesen. Desweiteren kann eine magnetische Remanenz auch durch die antiferromagnetische Kopplung zu ferromagnetischen Filmen erzielt werden. Auf einem Ni-Film mit senkrechter Anisotropie ist die Kopplung stärker als auf dem Co-Film mit paralleler Anisotropie bezüglich der Oberfläche. Eine systematische Studie von XMCD Messungen und DFT-Rechnungen an den drei Molekülen TbPc2, DyPc2 und ErPc2 auf einem Ni(111)-Einkristall zeigt eine antiferromagnetische Kopplung zwischen dem Ni-Substrat und jedem der drei Moleküle. TbPc2 und DyPc2 weisen dabei eine senkrechte Anisotropie auf, wohingegen ErPc2 die leichte magnetische Richtung in der Pc-Ebene besitzt. Die Kopplung ist stark anisotrop und ist im Falle von TbPc2 stabil bis zu einer Tempe-ratur von 120 K. Mit Hilfe von DFT-Rechnungen werden die Kommunikationskanäle im Ln-Ion und dem Liganden bestimmt, die für die magnetische Wechselwirkung wichtig sind. Die antiferromagnetische Kopplung wird durch Graphen zwischen dem Substrat und den TbPc2 Molekülen übertragen, ist jedoch deutlich schwächer als bei direktem Kontakt zwischen Ni und TbPc2.Within the framework of this thesis, molecular spin-hybrid systems are studied for their structural, electronic and magnetic properties. The results are divided into two chapters with respect to the investigated classes of molecules. In the first part, systems including (quasi-)planar paramagnetic molecules having a 3d transition metal ion in the molecules’ center have been investigated. By means of XMCD measurements it is shown that the magnetic moments of the FePc molecules align on a ferromagnetic Co film. In direct contact, a ferromagnetic coupling exists at room temperature. Due to an interlayer of oxygen separating the molecules from the Co surface, the coupling becomes antiferromagnetic. However, a graphene interlayer on a Ni(111) single crystal solely reduces the coupling strength, but the parallel spin alignment of the Co substrate and the Fe ions of the FePc molecules is maintained. The situation is different in the case of CoOEP molecules. On the same substrate graphene/Ni(111), the Co ions couple antiferromagnetically via the graphene layer to the Ni substrate. The magnetic coupling can be shown for the first layer only, additional layers are decoupled. Due to the two different coupled molecular layers, the net magnetization of the CoOEP molecules in a multilayer can be switched by variation of the external magnetic field. The second molecular class are so-called single molecule magnets of the type LnPc2. By field-dependent XMCD measurements, a magnetic remanence of the molecules is proven at submonolayer coverage on HOPG substrate. Furthermore, a magnetic remanence can be achieved by antiferromagnetic coupling to ferromagnetic films. On a Ni film with perpendicular anisotropy the coupling is stronger than on the Co film with parallel anisotropy with respect to the surface. A systematic study of XMCD measurements and DFT calculations on the three molecules TbPc2, DyPc2 and ErPc2 on a Ni(111) single crstal shows antiferromagnetic coupling between the Ni substrate and each of the molecules. TbPc2 and DyPc2 feature a perpendicular anisotropy, while ErPc2 has an easy axis of magnetization in the Pc plane. The coupling is highly anisotropic and in case of TbPc2 stable up to 120 K. By means of DFT calculations the communication channels in the Ln ion and the ligands which are responsible for the magnetic interaction are determined. The antiferromagnetic character of the coupling is also mediated via a graphene layer between the substrate and the TbPc2 molecules, but is significantly weaker than for the direct contact between Ni and TbPc2

Developmental expression profile of the yy2 gene in mice

<p>Abstract</p> <p>Background</p> <p>The transcription factor Yin Yang 2 (YY2) shares a structural and functional highly homologue DNA-binding domain with the ubiquitously expressed YY1 protein, which has been implicated in regulating fundamental biological processes. However, the biological relevance of YY2 has not been identified yet.</p> <p>Results</p> <p>Towards the understanding of YY2 biology, we analyzed in detail the expression pattern of <it>yy</it>2 in various organs during embryonic and postnatal mouse development till adulthood. Thereby, a constant <it>yy2 </it>level was detected in heart and lung tissue, whereas in different brain regions <it>yy2 </it>expression was dynamically regulated. Interestingly, in any analyzed tissue neither the homologue <it>yy1 </it>nor the <it>mbtps2 </it>gene showed changes in mRNA expression levels like <it>yy2</it>, although the intronless <it>yy2 </it>gene is located within the <it>mbtps2 </it>locus.</p> <p>Furthermore, we detected <it>yy1</it>, <it>yy2</it>, and <it>mbtps2 </it>mRNA in primary mouse neurons, microglia cells, and astrocytes. In comparison to <it>yy2 </it>and <it>mbtps2</it>, <it>yy1 </it>revealed the highest expression level in all cell types. Again, only <it>yy2 </it>showed significantly altered gene expression levels among the cell types. Higher <it>yy2 </it>expression levels were detected in microglia cells and astrocytes than in primary neurons.</p> <p>Conclusion</p> <p><it>Yy</it>2 expression in the heart and lung is constitutively expressed during embryogenesis and in adult mice. For the first time, developmental changes of <it>yy2 </it>transcription became obvious in various areas of the brain. This suggests that yy2 is involved in developmental gene regulation.</p

Foxp1 and lhx1 coordinate motor neuron migration with axon trajectory choice by gating Reelin signalling.

Topographic neuronal maps arise as a consequence of axon trajectory choice correlated with the localisation of neuronal soma, but the identity of the pathways coordinating these processes is unknown. We addressed this question in the context of the myotopic map formed by limb muscles innervated by spinal lateral motor column (LMC) motor axons where the Eph receptor signals specifying growth cone trajectory are restricted by Foxp1 and Lhx1 transcription factors. We show that the localisation of LMC neuron cell bodies can be dissociated from axon trajectory choice by either the loss or gain of function of the Reelin signalling pathway. The response of LMC motor neurons to Reelin is gated by Foxp1- and Lhx1-mediated regulation of expression of the critical Reelin signalling intermediate Dab1. Together, these observations point to identical transcription factors that control motor axon guidance and soma migration and reveal the molecular hierarchy of myotopic organisation

An exposure prevention rating method for intervention needs assessment and effectiveness evaluation

This article describes a new method for (1) systematically prioritizing needs for intervention on hazardous substance exposures in manufacturing work sites, and (2) evaluating intervention effectiveness. We developed a checklist containing six unique sets of yes/no variables organized in a 2 &times; 3 matrix of exposure potential versus protection (two columns) at the levels of materials, processes, and human interface (three rows). The three levels correspond to a simplified hierarchy of controls. Each of the six sets of indicator variables was reduced to a high/moderate/low rating. Ratings from the matrix were then combined to generate a single overall exposure prevention rating for each area. Reflecting the hierarchy of controls, material factors were weighted highest, followed by process, and then human interface. The checklist was filled out by an industrial hygienist while conducting a walk-through inspection (N = 131 manufacturing processes/areas in 17 large work sites). One area or process per manufacturing department was assessed and rated. Based on the resulting Exposure Prevention ratings, we concluded that exposures were well controlled in the majority of areas assessed (64% with rating of 1 or 2 on a 6-point scale), that there is some room for improvement in 26 percent of areas (rating of 3 or 4), and that roughly 10 percent of the areas assessed are urgently in need of intervention (rated as 5 or 6). A second hygienist independently assessed a subset of areas to evaluate inter-rater reliability. The reliability of the overall exposure prevention ratings was excellent (weighted kappa = 0.84). The rating scheme has good discriminatory power and reliability and shows promise as a broadly applicable and inexpensive tool for intervention needs assessment and effectiveness evaluation. Validation studies are needed as a next step. This assessment method complements quantitative exposure assessment with an upstream prevention focus

Characterization of Distinct Chondrogenic Cell Populations of Patients Suffering from Microtia Using Single-Cell Micro-Raman Spectroscopy

Microtia is a congenital condition of abnormal development of the outer ear. Tissue engineering of the ear is an alternative treatment option for microtia patients. However, for this approach, the identification of high regenerative cartilage progenitor cells is of vital importance. Raman analysis provides a novel, non-invasive, label-free diagnostic tool to detect distinctive biochemical features of single cells or tissues. Using micro-Raman spectroscopy, we were able to distinguish and characterize the particular molecular fingerprints of differentiated chondrocytes and perichondrocytes and their respective progenitors isolated from healthy individuals and microtia patients. We found that microtia chondrocytes exhibited lower lipid concentrations in comparison to healthy cells, thus indicating the importance of fat storage. Moreover, we suggest that collagen is a useful biomarker for distinguishing between populations obtained from the cartilage and perichondrium because of the higher spectral contributions of collagen in the chondrocytes compared to perichondrocytes from healthy individuals and microtia patients. Our results represent a contribution to the identification of cell markers that may allow the selection of specific cell populations for cartilage tissue engineering. Moreover, the observed differences between microtia and healthy cells are essential for gaining better knowledge of the cause of microtia. It can be useful for designing novel treatment options based on further investigations of the discovered biochemical substrate alterations

Sex-Specific Prediction Models for Sleep Apnea From the Hispanic Community Health Study/Study of Latinos

OBJECTIVE: We developed and validated the first-ever sleep apnea (SA) risk calculator in a large population-based cohort of Hispanic/Latino subjects. METHODS: Cross-sectional data on adults from the Hispanic Community Health Study/Study of Latinos (2008-2011) were analyzed. Subjective and objective sleep measurements were obtained. Clinically significant SA was defined as an apnea-hypopnea index ≥ 15 events per hour. Using logistic regression, four prediction models were created: three sex-specific models (female-only, male-only, and a sex × covariate interaction model to allow differential predictor effects), and one overall model with sex included as a main effect only. Models underwent 10-fold cross-validation and were assessed by using the C statistic. SA and its predictive variables; a total of 17 variables were considered. RESULTS: A total of 12,158 participants had complete sleep data available; 7,363 (61%) were women. The population-weighted prevalence of SA (apnea-hypopnea index ≥ 15 events per hour) was 6.1% in female subjects and 13.5% in male subjects. Male-only (C statistic, 0.808) and female-only (C statistic, 0.836) prediction models had the same predictor variables (ie, age, BMI, self-reported snoring). The sex-interaction model (C statistic, 0.836) contained sex, age, age × sex, BMI, BMI × sex, and self-reported snoring. The final overall model (C statistic, 0.832) contained age, BMI, snoring, and sex. We developed two websites for our SA risk calculator: one in English (https://www.montefiore.org/sleepapneariskcalc.html) and another in Spanish (http://www.montefiore.org/sleepapneariskcalc-es.html). CONCLUSIONS: We created an internally validated, highly discriminating, well-calibrated, and parsimonious prediction model for SA. Contrary to the study hypothesis, the variables did not have different predictive magnitudes in male and female subjects

Magnetic interplay between two different lanthanides in a tris-phthalocyaninato complex: a viable synthetic route and detailed investigation in the bulk and on the surface

Future applications of molecular units in quantum information technologies require a fine control at the single molecule level. This includes the choice of each functional element, the intramolecular interaction and the robustness of molecules when dispersed on a substrate. Keeping these goals in mind, we designed and synthesized a heterometallic phthalocyaninato-complex including two different lanthanides in each moiety, namely [PcDyPcTbPc*] (Pc being phthalocyanines; and Pc* being 2,3,9,10,16,17,23,24- octahexyl-substituted phthalocyanines). Full magnetic characterization was performed down to the mK temperature range on bulk microcrystals by means of AC susceptibility, DC magnetization (including microSQUID) and specific heat measurements. A weak, yet sizeable, interaction between the two lanthanides is clearly detected by different techniques, altering the magnetic behavior of the single lanthanide as observed in the parent [LnPc2] complexes. Isolated [PcDyPcTbPc*] molecules dispersed on HOPG and the Au surface by liquid phase deposition are proven to maintain their main chemical and magnetic features by combined XPS, XAS and XMCD analysis and to lie with one Pc ligand flat to the surface. Opening of a small but sizable hysteresis loop at 1.8 K is directly observed on both Tb and Dy sites proving the retention of magnetization at the single molecule level

Correlation functions quantify super-resolution images and estimate apparent clustering due to over-counting

We present an analytical method to quantify clustering in super-resolution localization images of static surfaces in two dimensions. The method also describes how over-counting of labeled molecules contributes to apparent self-clustering and how the effective lateral resolution of an image can be determined. This treatment applies to clustering of proteins and lipids in membranes, where there is significant interest in using super-resolution localization techniques to probe membrane heterogeneity. When images are quantified using pair correlation functions, the magnitude of apparent clustering due to over-counting will vary inversely with the surface density of labeled molecules and does not depend on the number of times an average molecule is counted. Over-counting does not yield apparent co-clustering in double label experiments when pair cross-correlation functions are measured. We apply our analytical method to quantify the distribution of the IgE receptor (Fc{\epsilon}RI) on the plasma membranes of chemically fixed RBL-2H3 mast cells from images acquired using stochastic optical reconstruction microscopy (STORM) and scanning electron microscopy (SEM). We find that apparent clustering of labeled IgE bound to Fc{\epsilon}RI detected with both methods arises from over-counting of individual complexes. Thus our results indicate that these receptors are randomly distributed within the resolution and sensitivity limits of these experiments.Comment: 22 pages, 5 figure

Antiferromagnetic coupling of TbPc2 molecules to ultrathin Ni and Co films

The magnetic and electronic properties of single-molecule magnets are studied by X-ray absorption spectroscopy and X-ray magnetic circular dichroism. We study the magnetic coupling of ultrathin Co and Ni films that are epitaxially grown onto a Cu(100) substrate, to an in situ deposited submonolayer of TbPc2 molecules. Because of the element specificity of the X-ray absorption spectroscopy we are able to individually determine the field dependence of the magnetization of the Tb ions and the Ni or Co film. On both substrates the TbPc2 moleculescouple antiferromagnetically to the ferromagnetic films, which is possibly due to a superexchange interaction via the phthalocyanine ligand that contacts the magnetic surface