Magnetic and structural characterization of magnetite nanoparticles synthesized by magnetotactic bacteria.

129 p.Las bacterias magnetotácticas son un grupo microorganismos capaces de orientarse en presencia delcampo magnético terrestre, lo que les facilita la búsqueda de un entorno rico en nutrientes y con lascondiciones de oxígeno óptimas para su crecimiento. Esta propiedad, conocida como magnetotáxis, sedebe a la presencia de una o más cadenas de nanopatículas magnetita (magnetosomas) en el interior de labacteria. El alto control genético impuesto en la biomineralización de los magnetosomas producenanopartículas de alta calidad química y cristalina, con forma y tamaño controlados por la especiebacteriana en cuestión. El tamaño de los magnetosomas (40 -120 nm), da lugar a monodominiosmagnéticos, difíciles de conseguir mediante síntesis físicas o químicas de nanopartículas magnéticas.Además de ser sistemas modelo para el estudio de propiedades físicas en la nanoescala, losmagnetosomas y las bacterias magnetotácticas presentan prometedoras propiedades, siendo candidatosideales para aplicaciones biomédicas de tratamiento contra el cáncer como la hipertermia magnética odrug delivery. Para un uso óptimo de los mismos se precisa de una exhaustiva caracterización. Lapresente tesis recoge una caracterización detallada desde el punto de vista magnético y estructural de lascadenas de magnetosomas sintetizadas por la especie M. gryphiswaldense, que sintetiza magnetosomascon forma cubooctaédrica y 45 nm de diámetro. La tesis se divide en tres bloques principales en los quese recoge: (i) el estudio de la estructura de la cadena; (ii) el proceso de biomineralización y los primerospasos de la síntesis de los magnetosomas, y (iii) el dopaje de los magnetosomas con distintos metales detransición (Co y Mn) y la consecuente modificación de sus propiedades magnéticas

Magnetosomes could be protective shields against metal stress in magnetotactic bacteria

Magnetotactic bacteria are aquatic microorganisms with the ability to biomineralise membrane-enclosed magnetic nanoparticles, called magnetosomes. These magnetosomes are arranged into a chain that behaves as a magnetic compass, allowing the bacteria to align in and navigate along the Earth's magnetic field lines. According to the magneto-aerotactic hypothesis, the purpose of producing magnetosomes is to provide the bacteria with a more efficient movement within the stratified water column, in search of the optimal positions that satisfy their nutritional requirements. However, magnetosomes could have other physiological roles, as proposed in this work. Here we analyse the role of magnetosomes in the tolerance of Magnetospirillum gryphiswaldense MSR-1 to transition metals (Co, Mn, Ni, Zn, Cu). By exposing bacterial populations with and without magnetosomes to increasing concentrations of metals in the growth medium, we observe that the tolerance is significantly higher when bacteria have magnetosomes. The resistance mechanisms triggered in magnetosome-bearing bacteria under metal stress have been investigated by means of x-ray absorption near edge spectroscopy (XANES). XANES experiments were performed both on magnetosomes isolated from the bacteria and on the whole bacteria, aimed to assess whether bacteria use magnetosomes as metal storages, or whether they incorporate the excess metal in other cell compartments. Our findings reveal that the tolerance mechanisms are metal-specific: Mn, Zn and Cu are incorporated in both the magnetosomes and other cell compartments; Co is only incorporated in the magnetosomes, and Ni is incorporated in other cell compartments. In the case of Co, Zn and Mn, the metal is integrated in the magnetosome magnetite mineral core.Te Spanish and Basque Governments are acknowledged for funding under projects number MAT2017- 83631-C3-R and IT-1245-19, respectively. Dr. L. Marcano acknowledges the fnancial support provided through a postdoctoral fellowship from the Basque Government

Modifying the magnetic response of magnetotactic bacteria: incorporation of Gd and Tb ions into the magnetosome structure

Magnetotactic bacteria Magnetospirillum gryphiswaldense MSR-1 biosynthesise chains of cube-octahedral magnetosomes, which are 40 nm magnetite high quality (Fe3O4) nanoparticles. The magnetic properties of these crystalline magnetite nanoparticles, which can be modified by the addition of other elements into the magnetosome structure (doping), are of prime interest in a plethora of applications, those related to cancer therapy being some of the most promising ones. Although previous studies have focused on transition metal elements, rare earth (RE) elements are very interesting as doping agents, both from a fundamental point of view (e.g. significant differences in ionic sizes) and for the potential applications, especially in biomedicine (e.g. magnetic resonance imaging and luminescence). In this work, we have investigated the impact of Gd and Tb on the magnetic properties of magnetosomes by using different complementary techniques. X-ray diffraction, transmission electron microscopy, and X-ray absorption near edge spectroscopy analyses have revealed that a small amount of RE ions, similar to 3-4%, incorporate into the Fe3O4 structure as Gd3+ and Tb3+ ions. The experimental magnetic characterisation has shown a clear Verwey transition for the RE-doped bacteria, located at T similar to 100 K, which is slightly below the one corresponding to the undoped ones (106 K). However, we report a decrease in the coercivity and remanence of the RE-doped bacteria. Simulations based on the Stoner-Wohlfarth model have allowed us to associate these changes in the magnetic response with a reduction of the magnetocrystalline (K-C) and, especially, the uniaxial (K-uni) anisotropies below the Verwey transition. In this way, K-uni reaches a value of 23 and 26 kJ m(-3) for the Gd- and Tb-doped bacteria, respectively, whilst a value of 37 kJ m(-3) is obtained for the undoped bacteria.This work was supported in part by the Spanish MCIN/AEI under Projects MAT2017-83631-C3-R and PID2020-115704RB-C33. The work of Elizabeth M. Jefremovas was supported by the "Concepci ' on Arenal Grant" awarded by Gobierno de Cantabria and Universidad de Cantabria. The work of Lourdes Marcano was supported by the Postdoctoral Fellowship from the Basque Government under Grant POS-2019-2-0017. The authors would like to thank "Nanotechnology in translational hyperthermia" (HIPERNANO)-RED2018-102626-T. We thank the ALBA (CLAESS beamline) synchrotron radiation facilities and staff for the allocation of beamtime and assistance during the experiments

Elucidating the role of shape anisotropy infaceted magnetic nanoparticles using biogenicmagnetosomes as a model

Shape anisotropy is of primary importance to understand the magnetic behavior of nanoparticles, but a rigorous analysis in polyhedral morphologies is missing. In this work, a model based on finite element techniques has been developed to calculate the shape anisotropy energy landscape for cubic, octahedral, and truncated-octahedral morphologies. In all cases, a cubic shape anisotropy is found that evolves to quasi-uniaxial anisotropy when the nanoparticle is elongated >= 2%. This model is tested on magnetosomes, similar to 45 nm truncated octahedral magnetite nanoparticles forming a chain inside Magnetospirillum gryphiswaldense MSR-1 bacteria. This chain presents a slightly bent helical configuration due to a 20 degrees tilting of the magnetic moment of each magnetosome out of chain axis. Electron cryotomography images reveal that these magnetosomes are not ideal truncated-octahedrons but present approximate to 7.5% extrusion of one of the {001} square faces and approximate to 10% extrusion of an adjacent {111} hexagonal face. Our model shows that this deformation gives rise to a quasi-uniaxial shape anisotropy, a result of the combination of a uniaxial (Ksh-u = 7 kJm(-3)) and a cubic (Ksh-c = 1.5 kJ m(-3)) contribution, which is responsible for the 20 degrees tilting of the magnetic moment. Finally, our results have allowed us to accurately reproduce, within the framework of the Landau-Lifshitz-Gilbert model, the experimental AC loops measured for these magnetotactic bacteria.Spanish Government is acknowledged for funding under the project number MAT2017-83631-C3. Basque Government is acknowledged for funding under the project number IT124519. HRTEM images were obtained in the Laboratorio de Microscopias Avanzadas at Instituto de Nanociencia de Aragon -Universidad de Zaragoza (LMA-INA). Authors acknowledge the LMA-INA for offering access to their instruments and expertise. Authors thank Prof. J. A. Garcia and I. Rodrigo for providing AC hysteresis loops

Nanoflowers Versus Magnetosomes: Comparison Between Two Promising Candidates for Magnetic Hyperthermia Therapy

Magnetic Fluid Hyperthermia mediated by iron oxide nanoparticles is one of the most promising therapies for cancer treatment. Among the different candidates, magnetite and maghemite nanoparticles have revealed to be some of the most promising candidates due to both their performance and their biocompatibility. Nonetheless, up to date, the literature comparing the heating ef ciency of magnetite and maghemite nanoparticles of similar size is scarce. To ll this gap, here we provide a comparison between commercial Synomag Nano owers (pure maghemite) and bacterial magnetosomes (pure magnetite) synthesized by the magnetotactic bacterium Magnetospirillum gryphiswaldense of hDi 40 45 nm. Both types of nanoparticles exhibit a high degree of crystallinity and an excellent degree of chemical purity and stability. The structural and magnetic properties in both nanoparticle ensembles have been studied by means of X Ray Diffraction, Transmission Electron Microscopy, X Ray Absorption Spectroscopy, and SQUID magnetometry. The heating ef ciency has been analyzed in both systems using AC magnetometry at several eld amplitudes (0 88 mT) and frequencies (130, 300, and 530 kHz).This work was supported in part by the Spanish "Ministerio de Ciencia, Investigación y Universidades'' under Project MAT2017-83631-C3-R, and in part by the Nanotechnology in Translational Hyperthermia (HIPERNANO) under Grant RED2018-102626-T. The work of Elizabeth M. Jefremovas was supported by the Beca Concepción Arenal through the Gobierno de Cantabria-Universidad de Cantabria under Grant BDNS: 406333. The work of Irati Rodrigo was supported by the Programa de Perfeccionamiento de Personal Investigador Doctor (Gobierno Vasco) under Grant POS-2020-1-0028 and Grant IT-1005-16. The work of Lourdes Marcano was supported by the Postdoctoral Fellowship from the Basque Government under Grant POS-2019-2-0017

Controlled Magnetic Anisotropy in Single Domain Mn-doped Biosynthesized Nanoparticles

Magnetotactic bacteria Magnetospirillum gryphiswaldense synthesize cubo-octahedral shaped magnetite nanoparticles, called magnetosomes, with a mean diameter of 40 nm. The high quality of the biosynthesized nanoparticles makes them suitable for numerous applications in fields like cancer therapy, among others. The magnetic properties of magnetite magnetosomes can be tailored by doping them with transition metal elements, increasing their potential applications. In this work, we address the effect of Mn doping on the main properties of magnetosomes by the combination of structural and magnetic characterization techniques. Energy-dispersive X-ray spectroscopy, X-ray absorption nearedge structure, and X-ray magnetic circular dichroism results reveal a Mn dopant percentage of utmost 2.3%, where Mn cations are incorporated as a combination of Mn2+ and Mn3+, preferably occupying tetrahedral and octahedral sites, respectively. Fe substitution by Mn notably alters the magnetic behavior of the doped magnetosomes. Theoretical modeling of the experimental hysteresis loops taken between 5 and 300 K with a modified Stoner-Wohlfarth approach highlights the different anisotropy contributions of the doped magnetosomes as a function of temperature. In comparison with the undoped magnetosomes, Mn incorporation alters the magnetocrystalline anisotropy introducing a negative and larger cubic anisotropy down to the Verwey transition, which appears shifted to lower temperature values as a consequence of Mn doping. On the other hand, Mn-doped magnetosomes show a decrease in the uniaxial anisotropy in the whole temperature range, most likely associated with a morphological modification of the Mn-doped magnetosomes.The Spanish and Basque Governments are acknowledged for funding under project numbers MAT2017- 83631-C3-R and IT-1245-19, respectively

Sentido de pertenencia e inclusión social, desde las expectativas de los estudiantes de nuevo ingreso en la UDO Anaco | Sense of belonging and social inclusion from the expectations of newentry students at the UDO Anaco

Los estudios universitarios representan un desafío no siempre fácil; implican enfrentar algunos conflictosque afectan a las universidades, originados por la pérdida o el desconocimiento de los valores humanos quepermiten una convivencia armónica. Por ello, desarrollar el sentido de pertenencia en los estudiantes hacia suinstitución educativa facilitará ambas, su inclusión social en el ámbito universitario y el camino hacia la excelenciaacadémica. En tal sentido, el propósito de esta investigación fue valorar el sentido de pertenencia e inclusiónsocial, desde las expectativas de los estudiantes de nuevo ingreso en la UDO Anaco. El estudio se sustentó en lasteorías del Intercambio Social (Homans 1959), la Elección Racional (Abitbol y Botero 2005) y el Vínculo Afectivo(Buchanans 2000). El análisis se realizó bajo el enfoque cualitativo y el método fenomenológico para interpretarla realidad desde la perspectiva de quienes la viven. Los informantes clave fueron un grupo de estudiantes denuevo ingreso que cursan las carreras Ingeniería Industrial y de Sistemas, del tercer periodo académico de 2011.Las categorías de análisis fueron: sentido de pertenencia, inclusión social y ser estudiante universitario. En lainvestigación fue posible conocer que existen situaciones que reflejan problemas con las actitudes relacionadascon la pertenencia e identificación de los estudiantes con la Universidad de Oriente, Extensión Región Centro-Sur-Anaco. Se concluye que afianzar el sentido de pertenencia de los estudiantes dependerá de los mecanismosinstitucionales de inclusión y de los comportamientos y la valoración o percepción de los estudiantes.Palabras clave: Estudiantes universitarios.ABSTRACTUniversity studies represent a challenge that is not always easy; they involve facing some conflicts thataffect universities, caused by the loss or lack of human values that allow a harmonious coexistence. Therefore,developing a sense of belonging in students to their school will promote both, their social inclusion in the universityenvironment, and the path towards academic excellence. In this sense, the purpose of this study was to evaluatethe sense of belonging and social inclusion, from the expectations of newly admitted students at UDO Anaco. Itwas based on the theories of social exchange (Homans 1959), Rational Choice (Abitbol and Botero 2005), andAffective Link (Buchanans 2000). The analysis was framed on the qualitative approach and the phenomenologicalmethod to interpret reality from the perspective of those whose live it. Key informants were a group of newstudents of Industrial and Systems Engineering, of the third academic period of 2011. The categories of analysiswere: sense of belonging, social inclusion and be a college student. The research made it possible to know thatthere are situations that reflect problems related to the belonging and identification of students with the university.It is concluded that strengthening the sense of belonging of students will depend on the institutional mechanismsof inclusion and the perception of students.Key words: College students

Tuning the Magnetic Response of Magnetospirillum magneticum by Changing the Culture Medium: A Straightforward Approach to Improve Their Hyperthermia Efficiency

Magnetotactic bacteria Magnetospirillum magneticum AMB-1 have been cultured using three different media: magnetic spirillum growth medium with Wolfe’s mineral solution (MSGM + W), magnetic spirillum growth medium without Wolfe’s mineral solution (MSGM – W), and flask standard medium (FSM). The influence of the culture medium on the structural, morphological, and magnetic characteristics of the magnetosome chains biosynthesized by these bacteria has been investigated by using transmission electron microscopy, X-ray absorption spectroscopy, and X-ray magnetic circular dichroism. All bacteria exhibit similar average size for magnetosomes, 40–45 nm, but FSM bacteria present slightly longer subchains. In MSGM + W bacteria, Co2+ ions present in the medium substitute Fe2+ ions in octahedral positions with a total Co doping around 4–5%. In addition, the magnetic response of these bacteria has been thoroughly studied as functions of both the temperature and the applied magnetic field. While MSGM – W and FSM bacteria exhibit similar magnetic behavior, in the case of MSGM + W, the incorporation of the Co ions affects the magnetic response, in particular suppressing the Verwey (∼105 K) and low temperature (∼40 K) transitions and increasing the coercivity and remanence. Moreover, simulations based on a Stoner–Wolhfarth model have allowed us to reproduce the experimentally obtained magnetization versus magnetic field loops, revealing clear changes in different anisotropy contributions for these bacteria depending on the employed culture medium. Finally, we have related how these magnetic changes affect their heating efficiency by using AC magnetometric measurements. The obtained AC hysteresis loops, measured with an AC magnetic field amplitude of up to 90 mT and a frequency, f, of 149 kHz, reveal the influence of the culture medium on the heating properties of these bacteria: below 35 mT, MSGM – W bacteria are the best heating mediators, but above 60 mT, FSM and MSGM + W bacteria give the best heating results, reaching a maximum heating efficiency or specific absorption rate (SAR) of SAR/f ≈ 12 W g–1 kHz–1.This work was supported by the Spanish MICINN/AEI/10.13039/501100011033 under Projects MAT2017-83631-C3-R and PID2020-115704RB-C3, the Basque Government under projects IT-1479-22 and IT-1500-22, and the BBVA Foundation under the Leonardo Fellowships for Researchers and Cultural Creators 2022. We thank the Helmholtz-Zentrum Berlin für Materialien und Energie for the allocation of synchrotron radiation beamtime and the support of the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. We thank the “Nanotechnology in translational hyperthermia” Network (RED2018-102626-T) funded by MCIN/AEI/10.13039/501100011033. Finally, we also thank A. Tato for her help in TEM and hysteresis loops measurements, R. Andrade and J.C. Raposo for technical and human support provided by SGIker (UPV/EHU/FEDER, EU), and A. García Prieto for her helpful comments and continuous support

Magnetic study of co-doped magnetosome chains

Magnetotactic bacteria synthesize a chain of magnetic nanoparticles, called magnetosome chain, used to align and swim along the geomagnetic field lines. In particular, Magnetospirillum gryphiswaldense biomineralize magnetite, Fe3O4. Growing this species in a Co-supplemented medium, Co-doped magnetite is obtained, tailoring in this way the magnetic properties of the magnetosome chain. Combining structural and magnetic techniques such as transmission electron microscopy, energy-dispersive x-ray spectroscopy, X-ray absorption near edge structure, and X-ray magnetic circular dichroism, we determine that 1% of Co2+ substitutes Fe2+ located in octahedral places in the magnetite, thus increasing the coercive field. In the framework of the Stoner-Wohlfarth model, we have analyzed the evolution of the hysteresis loops as a function of temperature determining the different magnetic anisotropy contributions and their evolution with temperature. In contrast with the control magnetosome chains, whose effective anisotropy is uniaxial in the whole temperature range from 300 to 5 K, the effective anisotropy of Codoped magnetosome chains changes appreciably with temperature, from uniaxial down to 150 K, through biaxial down to 100 K, to triaxial below 100 K.L.M. acknowledges the Basque Government for her fellowship (PRE_2015_1_0130). We acknowledge the technical and human support provided by SGIker (UPV/EHU). Funding from the Spanish Government (project nos. MAT2014-55049-C2-R and MAT2017-83631-C3-R) and Basque Government (project n. IT711-13) is acknowledged. We thank the ESRF (CRG BM25 beamline-SpLine) and HZB for the allocation of synchrotron radiation beamtime and funding under the project CALIPSOplus (Grant Agreement 730872) from the EU Framework Programme for Research and Innovation HORIZON 2020. We thank R. Fernández-Pacheco for his assistance in the EDS measurements

Magnetic and structural characterization of magnetite nanoparticles synthesized by magnetotactic bacteria.

129 p.Las bacterias magnetotácticas son un grupo microorganismos capaces de orientarse en presencia delcampo magnético terrestre, lo que les facilita la búsqueda de un entorno rico en nutrientes y con lascondiciones de oxígeno óptimas para su crecimiento. Esta propiedad, conocida como magnetotáxis, sedebe a la presencia de una o más cadenas de nanopatículas magnetita (magnetosomas) en el interior de labacteria. El alto control genético impuesto en la biomineralización de los magnetosomas producenanopartículas de alta calidad química y cristalina, con forma y tamaño controlados por la especiebacteriana en cuestión. El tamaño de los magnetosomas (40 -120 nm), da lugar a monodominiosmagnéticos, difíciles de conseguir mediante síntesis físicas o químicas de nanopartículas magnéticas.Además de ser sistemas modelo para el estudio de propiedades físicas en la nanoescala, losmagnetosomas y las bacterias magnetotácticas presentan prometedoras propiedades, siendo candidatosideales para aplicaciones biomédicas de tratamiento contra el cáncer como la hipertermia magnética odrug delivery. Para un uso óptimo de los mismos se precisa de una exhaustiva caracterización. Lapresente tesis recoge una caracterización detallada desde el punto de vista magnético y estructural de lascadenas de magnetosomas sintetizadas por la especie M. gryphiswaldense, que sintetiza magnetosomascon forma cubooctaédrica y 45 nm de diámetro. La tesis se divide en tres bloques principales en los quese recoge: (i) el estudio de la estructura de la cadena; (ii) el proceso de biomineralización y los primerospasos de la síntesis de los magnetosomas, y (iii) el dopaje de los magnetosomas con distintos metales detransición (Co y Mn) y la consecuente modificación de sus propiedades magnéticas