Publications by authors named "Rafael Gutierrez"

107 Publications

A nanographene disk rotating a single molecule gear on a Cu(111) surface.

Nanotechnology 2022 Jan 13. Epub 2022 Jan 13.

Institute for Materials Science, Technische Universität Dresden, Hallwachsstr. 3, Dresden, Sachsen, 01062, GERMANY.

We perform molecular dynamics simulations to study the collective rotation of a graphene nanodisk functionalized on its circumference by tert-butylphenyl chemical groups in interaction with a molecule-gear hexa-tert-butylphenylbenzene supported by a Cu(111) surface. The rotational motion can be categorized underdriving, driving and overdriving regimes calculating the locking coefficient of this machinery as a function of external torque applied. Moreover, the rotational friction with the surface of both the phononic and electronic contributions is investigated. It shows that for small size graphene nanodisks the phononic friction is the main contribution, whereas the electronic one dominates for the larger disks putting constrains on the experimental way of achieving the transfer of rotation from a graphene nanodisk to single molecule-gear.
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http://dx.doi.org/10.1088/1361-6528/ac4b4bDOI Listing
January 2022

Entropy and Entropic Forces to Model Biological Fluids.

Entropy (Basel) 2021 Sep 4;23(9). Epub 2021 Sep 4.

Science Division, Physics, New York University Abu Dhabi, Saadiyat Island, Abu Dhabi, United Arab Emirates.

Living cells are complex systems characterized by fluids crowded by hundreds of different elements, including, in particular, a high density of polymers. They are an excellent and challenging laboratory to study exotic emerging physical phenomena, where entropic forces emerge from the organization processes of many-body interactions. The competition between microscopic and entropic forces may generate complex behaviors, such as phase transitions, which living cells may use to accomplish their functions. In the era of big data, where biological information abounds, but general principles and precise understanding of the microscopic interactions is scarce, entropy methods may offer significant information. In this work, we developed a model where a complex thermodynamic equilibrium resulted from the competition between an effective electrostatic short-range interaction and the entropic forces emerging in a fluid crowded by different sized polymers. The target audience for this article are interdisciplinary researchers in complex systems, particularly in thermodynamics and biophysics modeling.
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http://dx.doi.org/10.3390/e23091166DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8465225PMC
September 2021

Apoptosis-related gene expression induced by Colombian propolis samples in canine osteosarcoma cell line.

Vet World 2021 Apr 22;14(4):964-971. Epub 2021 Apr 22.

Department of Chemical and Biological Sciences, São Paulo State University (UNESP), Institute of Biosciences, Campus Botucatu, Brazil.

Background And Aim: Osteosarcoma (OSA) is the most common bone tumor in canines and humans. This study aimed to assess the cytotoxic and apoptotic effects of Colombian propolis samples on a canine OSA cell line (OSCA-8) by evaluating the expression of , , , , and genes involved in the apoptosis pathway.

Materials And Methods: After treating the cells with five Colombian propolis samples (Usm, Met, Fus, Sil, and Caj), we evaluated cell viability and lactate dehydrogenase (LDH) release. Early and late apoptosis was determined by flow cytometry using annexin V/propidium iodide. Furthermore, the effects of three selected samples on gene expression were analyzed by real-time polymerase chain reaction.

Results: The Colombian propolis samples reduced OSCA-8 cell viability and increased LDH release. All samples induced apoptosis significantly and upregulated and expression. Usm and Sil increased expression, Met and Sil induced expression, and Usm increased .

Conclusion: Colombian propolis samples exhibited cytotoxic and apoptotic effects on canine OSA cells, and upregulation indicated apoptosis induction by the extrinsic pathway.
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http://dx.doi.org/10.14202/vetworld.2021.964-971DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8167511PMC
April 2021

Functional expression of TrkB receptors on interneurones and pyramidal cells of area CA3 of the rat hippocampus.

Neuropharmacology 2021 01 30;182:108379. Epub 2020 Oct 30.

Departamento de Farmacobiología, Cinvestav Sur, México City, México. Electronic address:

The dentate gyrus and hippocampal area CA3 region of the mammalian brain contains the highest levels of brain-derived neurotrophic factor (BDNF) and its canonical membrane receptor, tropomyosin-related kinase B (TrkB). Therefore, the present study examines the expression and physiological responses triggered by activation of TrkB on hippocampal area CA3 interneurones and pyramidal cells of the rat hippocampus. Triple immunolabelling for TrkB, glutamate decarboxylase 67, and the calcium-binding proteins parvalbumin, calbindin or calretinin confirms the somatic expression of TrkB in all CA3 sublayers. TrkB-positive interneurones with fast-spiking discharge are restricted to strata oriens and lucidum, whereas regular-spiking interneurones are found in the strata lucidum, radiatum and lacunosum-moleculare. Activation of TrkB receptors with 7,8-dihydroxyflavone (DHF) modulates amplitude and frequency of spontaneous synaptic currents recorded from CA3 interneurones. Furthermore, the isolated excitatory postsynaptic currents (EPSC) of CA3 interneurones evoked by the mossy fibres (MF) or commissural/associational (C/A) axons, show input-specific synaptic potentiation in response to TrkB stimulation. On CA3 pyramidal cells, stimulation with DHF potentiates the MF synaptic transmission and increases the MF-EPSP - spike coupling. The latter exhibits a dramatic increase when picrotoxin is bath perfused after DHF, indicating that local interneurones restrain the excitability mediated by activation of TrkB. Therefore, we propose that release of BDNF on area CA3 reshapes the output of this hippocampal region by simultaneous activation of TrkB on GABAergic interneurones and pyramidal cells.
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http://dx.doi.org/10.1016/j.neuropharm.2020.108379DOI Listing
January 2021

Predicting Neuropsychological Impairment in Relapsing Remitting Multiple Sclerosis: The Role of Clinical Measures, Treatment, and Neuropsychiatry Symptoms.

Arch Clin Neuropsychol 2021 May;36(4):475-484

Psychophysiology and Neuroimaging Group, Institute of Biomedical Research and Innovation of Cádiz (INiBICA), Cádiz, Spain.

Objective: This retrospective observational study aimed to define neuropsychological impairment (NI) profiles and determine the influence of clinical, demographic, and neuropsychiatric measures in specific cognitive domains in a cohort of relapsing-remitting multiple sclerosis (RRMS) patients.

Methods: Ninety-one RRMS patients underwent a neurological examination and a brief neuropsychological assessment. Patients were classified according to the disease-modifying therapies (DMTs) received (platform or high-efficacy). Differences between groups and multiple regression analyses were performed to determine the predictive value of the assessed measures in cognitive performance.

Results: More than two-thirds of the patients showed NI. Specifically, mild to moderate NI was presented in approximately half of the participants. Paced Auditory Serial Addition Test (PASAT-3) and Symbol Digit Modalities Test (SDMT) were the most frequently impaired cognitive tests (45.3% and 41.3%, respectively) followed by phonemic verbal fluency (PVF) (27.8%). Expanded Disability Status Scale (EDSS), age, depressive symptoms, and disease duration were the best predictors of SDMT (R2 = .34; p < .01), whereas disease duration, EDSS, and anxiety-state levels predicted PASAT-3 (R2 = .33, p < .01). Educational level, age, EDSS, and depressive symptoms demonstrated the strongest association with PVF (R2 = .31, p < .01).

Conclusions: Our results indicated a significant prevalence of NI in RRMS patients that was not dependent on the DMT type. In addition to the meaningful working memory (PASAT-3) and information processing speed (SDMT) impairments found, PVF deficits may also be an important marker of cognitive impairment in RRMS patients. This study supports the relevance of standard clinical measures and reinforces the importance of quantifying clinical and neuropsychiatric symptoms to predict subsequent cognitive performance on a similar multiple sclerosis phenotype and disease stage.
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http://dx.doi.org/10.1093/arclin/acaa088DOI Listing
May 2021

Activation of STAT3 Regulates Reactive Astrogliosis and Neuronal Death Induced by AβO Neurotoxicity.

Int J Mol Sci 2020 Oct 10;21(20). Epub 2020 Oct 10.

Laboratorio Experimental de Enfermedades Neurodegenerativas, Instituto Nacional de Neurología y Neurocirugía Manuel Velasco Suárez, Ciudad de Mexico 14269, Mexico.

Amyloid-beta oligomers (AβO) have been proposed as the most potent neurotoxic and inflammation inducers in Alzheimer's disease (AD). AβO contribute to AD pathogenesis by impairing the production of several cytokines and inflammation-related signaling pathways, such as the Janus kinases/signal transducer of transcription factor-3 (JAK/STAT3) pathway. STAT3 modulates glial activation, indirectly regulates Aβ deposition, and induces cognitive decline in AD transgenic models. However, in vivo studies using an AβO microinjection rat model have not yet explored STAT3 role. The main purpose of this study was to elucidate if a single microinjection of AβO could promote an increased expression of STAT3 in glial cells favoring neuroinflammation and neurodegeneration. We designed a model of intrahippocampal microinjection and assessed glial activation, cytokines production, STAT3 expression, and neurodegeneration in time. Our results showed robust expression of STAT3 in glial cells (mainly in astrocytes) and neurons, correlating with neuronal death in response to AβO administration. A STAT3 inhibition assay conducted in rat primary hippocampal cultures, suggested that the induction of the transcription factor by AβO in astrocytes leads them to an activation state that may favor neuronal death. Notwithstanding, pharmacological inhibition of the JAK2/STAT3 pathway should be focused on astrocytes because it is also essential in neurons survival. Overall, these findings strongly suggest the participation of STAT3 in the development of neurodegeneration.
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http://dx.doi.org/10.3390/ijms21207458DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7590075PMC
October 2020

Interactions of Long-Chain Polyamines with Silica Studied by Molecular Dynamics Simulations and Solid-State NMR Spectroscopy.

Langmuir 2020 10 24;36(39):11600-11609. Epub 2020 Sep 24.

Institute for Materials Science and Max Bergmann Center of Biomaterials, TU Dresden, 01062 Dresden, Germany.

The investigation of molecular interactions between silica phases and organic components is crucial for elucidating the main steps involved in the biosilica mineralization process. In this respect, the structural characterization of the organic/inorganic interface is particularly useful for a deeper understanding of the dominant mechanisms of biomineralization. In this work, we have investigated the interaction of selectively C- and N-labeled atoms of organic long-chain polyamines (LCPAs) with Si-labeled atoms of a silica layer at the molecular level. In particular, silica/LCPA nanocomposites were analyzed by solid-state NMR spectroscopy in combination with all-atom molecular dynamics simulations. Solid-state NMR experiments allow the determination of Si-N and Si-C internuclear distances, providing the parameters for direct verification of atomistic simulations. Our results elucidate the relevant molecular conformations as well as the nature of the interaction between the LCPA and a silica substrate. Specifically, distances and second moments suggest a picture compatible with (i) LCPA completely embedded in the silica phase and (ii) the charged amino groups located in close vicinity of silanol groups.
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http://dx.doi.org/10.1021/acs.langmuir.0c02157DOI Listing
October 2020

Role of Exchange Interactions in the Magnetic Response and Intermolecular Recognition of Chiral Molecules.

Nano Lett 2020 10 2;20(10):7077-7086. Epub 2020 Sep 2.

Institute for Materials Science and Max Bergmann Center of Biomaterials, TU Dresden, 01062 Dresden, Germany.

The physical origin of the so-called chirality-induced spin selectivity (CISS) effect has puzzled experimental and theoretical researchers over the past few years. Early experiments were interpreted in terms of unconventional spin-orbit interactions mediated by the helical geometry. However, more recent experimental studies have clearly revealed that electronic exchange interactions also play a key role in the magnetic response of chiral molecules in singlet states. In this investigation, we use spin-polarized closed-shell density functional theory calculations to address the influence of exchange contributions to the interaction between helical molecules as well as of helical molecules with magnetized substrates. We show that exchange effects result in differences in the interaction properties with magnetized surfaces, shedding light into the possible origin of two recent important experimental results: enantiomer separation and magnetic exchange force microscopy with AFM tips functionalized with helical peptides.
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http://dx.doi.org/10.1021/acs.nanolett.0c02216DOI Listing
October 2020

Emotional support for parents with premature children admitted to a neonatal intensive care unit: a qualitative phenomenological study.

Turk J Pediatr 2020 ;62(3):436-449

Department of Nursing, Autonomous University of Barcelona, Barcelona.

Background And Objectives: Parents who have a premature child in neonatal intensive care units (NICUs) are in a stressful situation. The aim of this paper is to analyze the emotional support received by parents with premature children admitted to NICUs.

Methods: A phenomenological qualitative study with an explanatory and interpretative approach was employed.

Results: The findings are: 1) The experience and emotions of a premature delivery; showing sadness, guilt and despair, stress, anxiety, and uncertainty over the future of their child. 2) The emotional support received by the father/mother of the partner; discussion of how their partner is cared for, as well as the care given to the premature child and other children in the family; the stress that this causes them on not being able visit all at once. 3) The emotional support offered by the health professionals (doctors, nurses, etc.); parents indicate that they have received very strong support from the nurses, but also that they were not always asked about their feelings when in the NICU. 4) The informal emotional support of relatives and parents in the NICU. After talking with other support mothers, the mothers then felt less guilty.

Conclusion: As regards premature birth, the mothers showed feelings of sadness and guilt, asked themselves where they had failed and what they had done wrong.
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http://dx.doi.org/10.24953/turkjped.2020.03.011DOI Listing
August 2021

Effective Hamiltonian model for helically constrained quantum systems within adiabatic perturbation theory: Application to the chirality-induced spin selectivity (CISS) effect.

J Chem Phys 2020 Jun;152(21):214105

Institute for Materials Science and Max Bergmann Center of Biomaterials, TU Dresden, 01062 Dresden, Germany.

The chirality-induced spin selectivity effect has been confirmed experimentally for a large class of organic molecules. Adequately modeling the effect remains a challenging task, with both phenomenological models and first-principles simulations yielding inconclusive results. Building upon a previously presented model by K. Michaeli and R. Naaman [J. Phys. Chem. C 123, 17043 (2019)], we systematically investigate an effective 1-dimensional model derived as the limit of a 3-dimensional quantum system with strong confinement and including spin-orbit coupling. Having a simple analytic structure, such models can be considered a minimal setup for the description of spin-dependent effects. We use adiabatic perturbation theory to provide a mathematically sound approximation procedure applicable to a large class of spin-dependent continuum models. We take advantage of the simplicity of the models by analyzing its structure to gain a better understanding how the occurrence and magnitude of spin polarization effects relate to the model's parameters and geometry. The obtained spin polarization is not strongly dependent on the strength of the spin-orbit interaction, but it rather results from breaking time-reversal invariance upon selection of a given angular momentum of the incoming electrons.
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http://dx.doi.org/10.1063/5.0005181DOI Listing
June 2020

Neuronal Glutamatergic Network Electrically Wired with Silent But Activatable Gap Junctions.

J Neurosci 2020 06 11;40(24):4661-4672. Epub 2020 May 11.

Departamento de Farmacobiología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, 14330 Mexico City, Mexico

It is widely assumed that electrical synapses in the mammalian brain, especially between interneurons, underlie neuronal synchrony. In the hippocampus, principal cells also establish electrical synapses with each other and have also been implicated in network oscillations, whereby the origin of fast electrical activity has been attributed to ectopic spikelets and dendro-dendritic or axo-axonal gap junctions. However, if electrical synapses were in axo-dendritic connections, where chemical synapses occur, the synaptic events would be mixed, having an electrical component preceding the chemical one. This type of communication is less well studied, mainly because it is not easily detected. Moreover, a possible scenario could be that an electrical synapse coexisted with a chemical one, but in a nonconductive state; hence, it would be considered inexistent. Could chemical synapses have a quiescent electrical component? If so, can silent electrical synapses be activated to be detected? We addressed this possibility, and we here report that, indeed, the connexin-36-containing glutamatergic mossy fiber synapses of the rat hippocampus express previously unrecognized electrical synapses, which are normally silent. We reveal that these synapses are pH sensitive, actuate and , and that the electrical signaling is bidirectional. With the simultaneous recording of hundreds of cells, we could reveal the existence of an electrical circuit in the hippocampus of adult rats of either sex consisting of principal cells where the nodes are interregional glutamatergic synapses containing silent but ready-to-use gap junctions. In this work, we present a series of experiments, both and , that reveal previously unrecognized silent pH-sensitive electrical synapses coexisting in one of the best studied glutamatergic synapses of the brain, the mossy fiber synapse of the hippocampus. This type of connectivity underlies an "electrical circuit" between two substructures of the adult rat hippocampus consisting of principal cells where the nodes are glutamatergic synapses containing silent but ready-to-use gap junctions. Its identification will allow us to explore the participation of such a circuit in physiological and pathophysiological functions and will provide valuable conceptual tools to understanding computational and regulatory mechanisms that may underlie network activity.
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http://dx.doi.org/10.1523/JNEUROSCI.2590-19.2020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7294797PMC
June 2020

Spin-Polarized Electron Transmission in DNA-Like Systems.

Biomolecules 2019 12 28;10(1). Epub 2019 Dec 28.

GISC, Departamento de Física de Materiales, Universidad Complutense, E-28040 Madrid, Spain.

The helical distribution of the electronic density in chiral molecules, such as DNA and bacteriorhodopsin, has been suggested to induce a spin-orbit coupling interaction that may lead to the so-called chirality-induced spin selectivity (CISS) effect. Key ingredients for the theoretical modelling are, in this context, the helically shaped potential of the molecule and, concomitantly, a Rashba-like spin-orbit coupling due to the appearance of a magnetic field in the electron reference frame. Symmetries of these models clearly play a crucial role in explaining the observed effect, but a thorough analysis has been largely ignored in the literature. In this work, we present a study of these symmetries and how they can be exploited to enhance chiral-induced spin selectivity in helical molecular systems.
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http://dx.doi.org/10.3390/biom10010049DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7022823PMC
December 2019

A zinc selective oxytocin based biosensor.

J Mater Chem B 2020 01 29;8(1):155-160. Epub 2019 Nov 29.

Institute of Chemistry and The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.

Oxytocin is a peptide hormone with high affinity to both Zn and Cu ions compared to other metal ions. This affinity makes oxytocin an attractive recognition layer for monitoring the levels of these essential ions in biofluids. Native oxytocin cannot differentiate between Cu and Zn ions and hence it is not useful for sensing Zn in the presence of Cu. We elucidated the effect of the terminal amine group of oxytocin on the affinity toward Cu using theoretical calculations. We designed a new Zn selective oxytocin-based biosensor that utilizes the terminal amine for surface anchoring, also preventing the response to Cu. The biosensor shows exceptional selectivity and very high sensitivity to Zn in impedimetric biosensing. This study shows for the first time an oxytocin derived sensor that can be used directly for sensing Zn in the presence of Cu.
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http://dx.doi.org/10.1039/c9tb01932dDOI Listing
January 2020

Direct Assembly and Metal-Ion Binding Properties of Oxytocin Monolayer on Gold Surfaces.

Langmuir 2019 08 8;35(34):11114-11122. Epub 2019 Aug 8.

Institute for Materials Science and Max Bergmann Center of Biomaterials , Hallwachsstraße 3 , 01062 Dresden , Germany.

Peptides are very common recognition entities that are usually attached to surfaces using multistep processes. These processes require modification of the native peptides and of the substrates. Using functional groups in native peptides for their assembly on surfaces without affecting their biological activity can facilitate the preparation of biosensors. Herein, we present a simple single-step formation of native oxytocin monolayer on gold surface. These surfaces were characterized by atomic force spectroscopy, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy. We took advantage of the native disulfide bridge of the oxytocin for anchoring the peptide to the Au surface, while preserving the metal-ion binding properties. Self-assembled oxytocin monolayer was used by electrochemical impedance spectroscopy for metal-ion sensing leading to subnanomolar sensitivities for zinc or copper ions.
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http://dx.doi.org/10.1021/acs.langmuir.9b01830DOI Listing
August 2019

Quantum Phonon Transport in Nanomaterials: Combining Atomistic with Non-Equilibrium Green's Function Techniques.

Entropy (Basel) 2019 Jul 27;21(8). Epub 2019 Jul 27.

Institute for Materials Science and Max Bergmann Center of Biomaterials, TU Dresden, 01062 Dresden, Germany.

A crucial goal for increasing thermal energy harvesting will be to progress towards atomistic design strategies for smart nanodevices and nanomaterials. This requires the combination of computationally efficient atomistic methodologies with quantum transport based approaches. Here, we review our recent work on this problem, by presenting selected applications of the PHONON tool to the description of phonon transport in nanostructured materials. The PHONON tool is a module developed as part of the Density-Functional Tight-Binding (DFTB) software platform. We discuss the anisotropic phonon band structure of selected puckered two-dimensional materials, helical and horizontal doping effects in the phonon thermal conductivity of boron nitride-carbon heteronanotubes, phonon filtering in molecular junctions, and a novel computational methodology to investigate time-dependent phonon transport at the atomistic level. These examples illustrate the versatility of our implementation of phonon transport in combination with density functional-based methods to address specific nanoscale functionalities, thus potentially allowing for designing novel thermal devices.
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http://dx.doi.org/10.3390/e21080735DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7515264PMC
July 2019

Exploring the write-in process in molecular quantum cellular automata: a combined modelingand first-principle approach.

J Phys Condens Matter 2019 Oct 13;31(40):405502. Epub 2019 Jun 13.

Institute for Materials Science and Max Bergmann Center of Biomaterials, Dresden University of Technology, 01062 Dresden, Germany. Max Planck Institute for the Physics of Complex Systems, 01187 Dresden, Germany.

The molecular quantum cellular automata paradigm (m-QCA) offers a promising alternative framework to current CMOS implementations. A crucial aspect for implementing this technology concerns the construction of a device which effectively controls intramolecular charge-transfer processes. Tentative experimental implementations have been developed in which a voltage drop is created generating the forces that drive a molecule into a logic state. However, important factors such as the electric field profile, its possible time-dependency and the influence of temperature in the overall success of charge-transfer are relevant issues to be considered in the design of a reliable device. In this work, we theoretically study the role played by these processes in the overall intramolecular charge-transfer process. We have used a Landau-Zener (LZ) model, where different time-dependent electric field profiles have been simulated. The results have been further corroborated employing density functional tight-binding method. The role played by the nuclear motions in the electron-transfer process has been investigated beyond the Born-Oppenheimer approximation by computing the effect of the external electric field in the behavior of the potential energy surface. Hence, we demonstrate that the intramolecular charge-transfer process is a direct consequence of the coherent LZ nonadiabatic tunneling and the hybridization of the diabatic vibronic states which effectively reduces the trapping of the itinerant electron at the donor group.
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http://dx.doi.org/10.1088/1361-648X/ab29c1DOI Listing
October 2019

ITO Work Function Tunability by Polarizable Chromophore Monolayers.

Langmuir 2019 Feb 13;35(8):2997-3004. Epub 2019 Feb 13.

Azrieli College of Engineering , Jerusalem 9103501 , Israel.

The ability to tune the electronic properties of oxide-bearing semiconductors such as Si/SiO or transparent metal oxides such as indium-tin oxide (ITO) is of great importance in both electronic and optoelectronic device applications. In this work, we describe a process that was conducted on n-type Si/SiO and ITO to induce changes in the substrate work function (WF). The substrates were modified by a two-step synthesis comprising a covalent attachment of coupling agents' monolayer followed by in situ anchoring reactions of polarizable chromophores. The coupling agents and chromophores were chosen with opposite dipole orientations, which enabled the tunability of the substrates' WF. In the first step, two coupling agents with opposite molecular dipole were assembled. The coupling agent with a negative dipole induced a decrease in WF of modified substrates, while the coupling agent with a positive dipole produced an increase in WFs of both ITO and Si substrates. The second modification step consisted of in situ anchoring reaction of polarizable chromophores with opposite dipoles to the coupling layer. This modification led to an additional change in the WFs of both Si/SiO and ITO substrates. The WF was measured by contact potential difference and modeled by density functional theory-based theoretical calculations of the WF for each of the assembly steps. A good fit was obtained between the calculated and experimental trends. This ability to design and tune the WF of ITO substrates was implemented in an organic electronic device with improved I- V characteristics in comparison to a bare ITO-based device.
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http://dx.doi.org/10.1021/acs.langmuir.8b03943DOI Listing
February 2019

Doping engineering of thermoelectric transport in BNC heteronanotubes.

Phys Chem Chem Phys 2019 Jan;21(4):1904-1911

Institute for Materials Science and Max Bergmann Center of Biomaterials, TU Dresden, 01062 Dresden, Germany.

BNC heteronanotubes are promising materials for the design of nanoscale thermoelectric devices. In particular, the structural BN doping pattern can be exploited to control the electrical and thermal transport properties of BNC nanostructures. We here address the thermoelectric transport properties of (6,6)-BNC heteronanotubes with helical and horizontal BN doping patterns. For this, we use a density functional tight-binding method combined with the Green's function technique. Our results show that the electron transmission is reduced and the electronic bandgap increased as a function of the BN concentration for different doping distribution patterns, so that (6,6)-BNC heteronanotubes become semiconducting with a tunable bandgap. The thermal conductance of helical (6,6)-BNC heteronanotubes, which is dominated by phonons, is weakly dependent on BN concentration in the range of 30-80%. Also, the Seebeck coefficient is enhanced by increasing the concentration of helical BN strips. In particular, helical (6,6)-BNC heteronanotubes with a high BN concentration (>20%) display a larger figure of merit compared to other doping distributions and, for a concentration of 50%, reach values up to 2.3 times and 3.4 times the corresponding values of a CNT at 300 K and 800 K, respectively. Our study yields new insights into the parameters tuning the thermoelectric efficiency and thus provides a starting point for designing thermoelectric devices based on BNC nanostructures.
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http://dx.doi.org/10.1039/c8cp05592kDOI Listing
January 2019

The chemical composition and events related to the cytotoxic effects of propolis on osteosarcoma cells: A comparative assessment of Colombian samples.

Phytother Res 2019 Mar 28;33(3):591-601. Epub 2018 Nov 28.

Institute of Biosciences, São Paulo State University (UNESP), Campus Botucatu, Brazil.

Osteosarcoma (OSA) is a type of bone cancer showing an aggressive biological behavior with metastatic progression. Because propolis potential for the development of new antitumoral drugs has been indicated, we evaluated the chemical composition of Colombian propolis samples and the mechanisms involved in their cytotoxic effects on OSA cells. The chemical composition was analyzed by GC-MS and the DPPH free radical scavenging activity was measured. Cluster and principal components analysis were used to establish an association with their inhibitory concentration 50% (IC ). Cell viability was analyzed by MTT assay; apoptosis was determined by flow cytometry; mitochondrial membrane permeability and reactive oxygen species were evaluated by rhodamine 123 and DCFH-DA. Transwell assay was used to evaluate the invasiveness of propolis-treated cells. Samples were grouped: Cluster 1 contained diterpenes and benzophenones and showed the highest antiradical activity; Cluster 2 was characterized by triterpenes, fatty acid, and diterpenes. Usm contained diterpenes and triterpenes different of the other samples and Sil contained triterpenes and flavonoids. Apoptosis, mitochondrial membrane alteration, and suppression of cell invasion were the main mechanisms involved in the inhibition of OSA cells in vitro, suggesting the potential of Colombian propolis to discover new antitumor drugs.
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http://dx.doi.org/10.1002/ptr.6246DOI Listing
March 2019

Polymerization driven monomer passage through monolayer chemical vapour deposition graphene.

Nat Commun 2018 10 3;9(1):4051. Epub 2018 Oct 3.

Chair of Macromolecular Chemistry, Faculty of Chemistry and Food Chemistry, School of Science, Technische Universität Dresden, Mommsenstr. 4, 01062, Dresden, Germany.

Mass transport through graphene is receiving increasing attention due to the potential for molecular sieving. Experimental studies are mostly limited to the translocation of protons, ions, and water molecules, and results for larger molecules through graphene are rare. Here, we perform controlled radical polymerization with surface-anchored self-assembled initiator monolayer in a monomer solution with single-layer graphene separating the initiator from the monomer. We demonstrate that neutral monomers are able to pass through the graphene (via native defects) and increase the graphene defects ratio (Raman I/I) from ca. 0.09 to 0.22. The translocations of anionic and cationic monomers through graphene are significantly slower due to chemical interactions of monomers with the graphene defects. Interestingly, if micropatterned initiator-monolayers are used, the translocations of anionic monomers apparently cut the graphene sheet into congruent microscopic structures. The varied interactions between monomers and graphene defects are further investigated by quantum molecular dynamics simulations.
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http://dx.doi.org/10.1038/s41467-018-06599-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6170411PMC
October 2018

Diversification of Device Platforms by Molecular Layers: Hybrid Sensing Platforms, Monolayer Doping, and Modeling.

Langmuir 2018 11 10;34(47):14103-14123. Epub 2018 Oct 10.

Institute of Chemistry and the Center for Nanoscience and Nanotechnology , The Hebrew University of Jerusalem , Edmond J. Safra Campus , Givat Ram Jerusalem , 91904 Israel.

Inorganic materials such as semiconductors, oxides, and metals are ubiquitous in a wide range of device technologies owing to the outstanding robustness and mature processing technologies available for such materials. However, while the important contribution of inorganic materials to the advancement of device technologies has been well established for decades, organic-inorganic hybrid device systems, which merge molecular functionalities with inorganic platforms, represent a newer domain that is rapidly evolving at an increasing pace. Such devices benefit from the great versatility and flexibility of the organic building blocks merged with the robustness of the inorganic platforms. Given the overwhelming wealth of literature covering various approaches for modifying and using inorganic devices, this feature article selectively highlights some of the advances made in the context of the diversification of devices by surface chemistry. Particular attention is given to oxide-semiconductor systems and metallic surfaces modified with organic monolayers. The inorganic device components, such as semiconductors, metals, and oxides, are modified by organic monolayers, which may serve as either active, static, or sacrificial components. We portray research directions within the broader field of organic-inorganic hybrid device systems that can be viewed as specific examples of the potential of such hybrid device systems given their comprehensive capabilities of design and diversification. Monolayer doping techniques where sacrificial organic monolayers are introduced into semiconducting elements are reviewed as a specific case, together with associated requirements for nanosystems, devices, and sensors for controlling doping levels and doping profiles on the nanometric scale. Another series of examples of the flexibility provided by the marriage of organic functional monolayers and inorganic device components are represented by a new class of biosensors, where the organic layer functionality is exploited in a functioning device for sensing. Considerations for relying on oxide-terminated semiconductors rather than the pristine semiconductor material as a platform both for processing and sensing are discussed. Finally, we cover aspects related to the use of various theoretical and computational approaches to model organic-inorganic systems. The main objectives of the topics covered here are (i) to present the advances made in each respective domain and (ii) to provide a comprehensive view of the potential uses of organic monolayers and self-assembly processes in the rapidly evolving field of molecular-inorganic hybrid device platforms and processing methodologies. The directions highlighted here provide a perspective on a future, not yet fully realized, integrated approach where organic monolayers are combined with inorganic platforms in order to obtain versatile, robust, and flexible systems with enhanced capabilities.
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http://dx.doi.org/10.1021/acs.langmuir.8b02369DOI Listing
November 2018

Thermal Decoherence and Disorder Effects on Chiral-Induced Spin Selectivity.

J Phys Chem Lett 2018 Oct 19;9(19):5753-5758. Epub 2018 Sep 19.

School of Molecular Sciences , Arizona State University , Tempe , Arizona 85287 , United States.

We use a nonlinear master equation formalism to account for thermal and disorder effects on spin-dependent electron transport in helical organic molecules coupled to two ideal leads. The inclusion of these two effects has important consequences in understanding the observed length and temperature dependence of spin polarization in experiments, which cannot be accounted for in a purely coherent tunneling model. Our approach considers a tight-binding helical Hamiltonian with disordered onsite energies to describe the resulting electronic states when low-frequency interacting modes break the electron coherence. The high-frequency fluctuating counterpart of these interactions, typical of intramolecular modes, is included by means of temperature-dependent thermally activated transfer probabilities in the master equation, which lead to hopping between localized states. We focus on the spin-dependent conductance and the spin-polarization in the linear regime (low voltage), which are analyzed as a function of the molecular length and the temperature of the system. Our results at room temperature agree well with experiments because our model predicts that the degree of spin-polarization increases for longer molecules. Also, this effect is temperature-dependent because thermal excitation competes with disorder-induced Anderson localization. We conclude that a transport mechanism based on thermally activated hopping in a disordered system can account for the unexpected behavior of the spin polarization.
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http://dx.doi.org/10.1021/acs.jpclett.8b02196DOI Listing
October 2018

Early Appearance and Spread of Fast Ripples in the Hippocampus in a Model of Cortical Traumatic Brain Injury.

J Neurosci 2018 10 6;38(42):9034-9046. Epub 2018 Sep 6.

Departamento de Farmacobiología del Centro de Investigación y de Estudios Avanzados del IPN México City, 14330,

Fast ripples (FRs; activity of >250 Hz) have been considered as a biomarker of epileptic activity in the hippocampus and entorhinal cortex; it is thought that they signal the focus of seizure generation. Similar high-frequency network activity has been produced by changing extracellular medium composition, by using pro-epileptic substances, or by electrical stimulation. Here we study the propagation of these events between different subregions of the male rat hippocampus in a recently introduced experimental model of FRs in entorhinal cortex-hippocampal slices By using a matrix of 4096 microelectrodes, the sites of initiation, propagation pathways, and spatiotemporal characteristics of activity patterns could be studied with unprecedented high resolution. To this end, we developed an analytic tool based on bidimensional current source density estimation, which delimits sinks and sources with a high precision and evaluates their trajectories using the concept of center of mass. With this methodology, we found that FRs can arise almost simultaneously at noncontiguous sites in the CA3-to-CA1 direction, underlying the spatial heterogeneity of epileptogenic foci, while continuous somatodendritic waves of activity develop. An unexpected, yet important propagation route is the propagation of activity from CA3 into the hilus and dentate gyrus. This pathway may cause reverberating activation of both regions, supporting sustained pathological network events and altered information processing in hippocampal networks. Fast ripples (FRs) have been considered as a biomarker of epileptic activity and may signal the focus of seizure generation. In a model of traumatic brain injury in the rat, FRs appear in the hippocampus within a couple of hours after an extrahippocampal, cortical lesion. We analyzed the origin and dynamics of the FRs in the hippocampus using massive electrophysiological recordings, allowing an unprecedented high spatiotemporal resolution. We show that FRs originate in distinct and noncontiguous locations within the CA3 region and uncover, with high precision, the extent and dynamics of their current density. This activity propagates toward CA1 but also backpropagates to the hilus and the dentate gyrus, suggesting activation of defined microcircuits that can sustain recurrent excitation.
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http://dx.doi.org/10.1523/JNEUROSCI.3507-17.2018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6705981PMC
October 2018

Enhanced Magnetoresistance in Chiral Molecular Junctions.

J Phys Chem Lett 2018 Sep 10;9(18):5453-5459. Epub 2018 Sep 10.

Institute for Materials Science and Max Bergmann Center of Biomaterials , Dresden University of Technology , 01062 Dresden , Germany.

Chirality-induced spin selectivity (CISS) is a recently discovered effect, whose precise microscopic origin has not yet been fully elucidated; it seems, however, clear that spin-orbit interaction plays a pivotal role. Various model Hamiltonian approaches have been proposed, suggesting a close connection between spin selectivity and filtering and helical symmetry. However, first-principles studies revealing the influence of chirality on the spin polarization are missing. To clearly demonstrate the influence of the helical conformation on the spin polarization properties, we have carried out spin-dependent Density-Functional Theory (DFT) based transport calculations for a model molecular system. It consists of α-helix and β-strand conformations of an oligo-glycine peptide, which is bonded to a nickel electrode and to a gold electrode in a two-terminal setup, similar to a molecular junction or a local probe, for example, in STM or AFM configurations. We have found that the α-helix conformation displays a spin polarization, calculated through the intrinsic magneto-resistance of the junction, about 100-1000 times larger than the linear β-strand, clearly demonstrating the crucial role played by the molecular helical geometry on the enhancement of spin polarization associated with the CISS effect.
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http://dx.doi.org/10.1021/acs.jpclett.8b02360DOI Listing
September 2018

Electrical coupling between hippocampal neurons: contrasting roles of principal cell gap junctions and interneuron gap junctions.

Cell Tissue Res 2018 Sep 15;373(3):671-691. Epub 2018 Aug 15.

Institut für Physiologie und Pathophysiologie, Universität Heidelberg, Im Neuenheimer Feld 326, 69120, Heidelberg, Germany.

There is considerable experimental evidence, anatomical and physiological, that gap junctions exist in the hippocampus. Electrical coupling through these gap junctions may be divided into three types: between principal neurons, between interneurons and at mixed chemical (glutamatergic)/electrical synapses. An approach, combining in vitro experimental with modeling techniques, sheds some light on the functional consequences of electrical coupling, for network oscillations and for seizures. Additionally, in vivo experiments, using mouse connexin knockouts, suggest that the presence of electrical coupling is important for optimal performance on selected behavioral tasks; however, the interpretation of such data, in cellular terms, has so far proven difficult. Given that invertebrate central pattern generators so often depend on both chemical and electrical synapses, our hypothesis is that hippocampus-mediated and -influenced behaviors will act likewise. Experiments, likely hard ones, will be required to test this intuition.
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http://dx.doi.org/10.1007/s00441-018-2881-3DOI Listing
September 2018

Self-Assembled Two-Dimensional Supramolecular Networks Characterized by Scanning Tunneling Microscopy and Spectroscopy in Air and under Vacuum.

Langmuir 2018 07 20;34(26):7698-7707. Epub 2018 Jun 20.

Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN) & School of Chemistry , Trinity College Dublin , Dublin 2 , Ireland.

We combine ambient (air) and ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) and spectroscopy (STS) investigations together with density functional theory (DFT) calculations to gain a subnanometer insight into the structure and dynamic of two-dimensional (2D) surface-supported molecular networks. The planar tetraferrocene-porphyrin molecules employed in this study undergo spontaneous self-assembly via the formation of hydrogen bonded networks at the gold substrate-solution interface. To mimic liquid phase ambient deposition conditions, film formation was accomplished in UHV by electro-spraying a solution of the molecule in chloroform onto an Au(111) substrate, thereby providing access to the full spectroscopic capabilities of STM that can be hardly attained under ambient conditions. We show that molecular assembly on Au (111) is identical in films prepared under the two different conditions, and in good agreement with the theoretical predictions. However, we observe the contrast found for a given STM bias condition to be different in ambient and UHV conditions despite the similarity of the structures, and we propose possible origins of the different imaging contrast. This approach could be valuable for the thorough characterization of surface systems that involve large molecules and are prepared mainly in ambient conditions.
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http://dx.doi.org/10.1021/acs.langmuir.8b01374DOI Listing
July 2018

First-Principle-Based Phonon Transport Properties of Nanoscale Graphene Grain Boundaries.

Adv Sci (Weinh) 2018 02 11;5(2):1700365. Epub 2018 Jan 11.

Institute for Materials Science and Max Bergmann Center of Biomaterials TU Dresden 01062 Dresden Germany.

The integrity of phonon transport properties of large graphene (linear and curved) grain boundaries (GBs) is investigated under the influence of structural and dynamical disorder. To do this, density functional tight-binding (DFTB) method is combined with atomistic Green's function technique. The results show that curved GBs have lower thermal conductance than linear GBs. Its magnitude depends on the length of the curvature and out-of-plane structural distortions at the boundary, having stronger influence the latter one. Moreover, it is found that by increasing the defects at the boundary, the transport properties can strongly be reduced in comparison to the effect produced by heating up the boundary region. This is due to the large reduction of the phonon transmission for in-plane and out-of-plane vibrational modes after increasing the structural disorder in the GBs.
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http://dx.doi.org/10.1002/advs.201700365DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5827104PMC
February 2018

Chirality-Dependent Electron Spin Filtering by Molecular Monolayers of Helicenes.

J Phys Chem Lett 2018 Apr 9;9(8):2025-2030. Epub 2018 Apr 9.

Center for Soft Nanoscience and Physikalisches Institut , University of Münster , 48149 Münster , Germany.

The interaction of low-energy photoelectrons with well-ordered monolayers of enantiopure helical heptahelicene molecules adsorbed on metal surfaces leads to a preferential transmission of one longitudinally polarized spin component, which is strongly coupled to the helical sense of the molecules. Heptahelicene, composed of only carbon and hydrogen atoms, exhibits only a single helical turn but shows excess in longitudinal spin polarization of about P = 6 to 8% after transmission of initially balanced left- and right-handed spin polarized electrons. Insight into the electronic structure, that is, the projected density of states, and the spin-dependent electron scattering in the helicene molecule is gained by using spin-resolved density functional theory calculations and a model Hamiltonian approach, respectively. Our results support the semiclassical picture of electronic transport along a helical pathway under the influence of spin-orbit coupling induced by the electrostatic molecular potential.
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http://dx.doi.org/10.1021/acs.jpclett.8b00208DOI Listing
April 2018

Bi-national cross-validation of an evidence-based conduct problem prevention model.

Cultur Divers Ethnic Minor Psychol 2018 04 1;24(2):231-241. Epub 2018 Mar 1.

Department of Family Social Science, University of Minnesota.

Objectives: To (a) explore the preferences of Mexican parents and Spanish-speaking professionals working with migrant Latino families in Minnesota regarding the Mexican-adapted brief model versus the original conduct problems intervention and (b) identifying the potential challenges, and preferred solutions, to implementation of a conduct problems preventive intervention.

Method: The core practice elements of a conduct problems prevention program originating in the United States were adapted for prevention efforts in Mexico. Three focus groups were conducted in the United States, with Latino parents (n = 24; 2 focus groups) and professionals serving Latino families (n = 9; 1 focus group), to compare and discuss the Mexican-adapted model and the original conduct problems prevention program. Thematic analysis was conducted on the verbatim focus group transcripts in the original language spoken.

Results: Participants preferred the Mexican-adapted model. The following key areas were identified for cultural adaptation when delivering a conduct problems prevention program with Latino families: recruitment/enrollment strategies, program delivery format, and program content (i.e., child skills training, parent skills training, child-parent activities, and child-parent support). For both models, strengths, concerns, barriers, and strategies for overcoming concerns and barriers were identified.

Conclusions: We summarize recommendations offered by participants to strengthen the effective implementation of a conduct problems prevention model with Latino families in the United States. This project demonstrates the strength in binational collaboration to critically examine cultural adaptations of evidence-based prevention programs that could be useful to diverse communities, families, and youth in other settings. (PsycINFO Database Record
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http://dx.doi.org/10.1037/cdp0000178DOI Listing
April 2018
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