Mécanismes cérébraux de la régulation de la douleur : perception de la douleur et hypoalgésie induite psychologiquement

Objectif : Cette thèse a pour but de préciser les mécanismes neuropsychologiques de la douleur, de la régulation endogène de la douleur et de l'hypoalgésie induite psychologiquement (HIP) par la synthèse de près de trente ans de recherche imagerie cérébrale fonctionnelle. Méthodologie : Étant donné l'abondance des études sur le sujet et le manque d'intégration de leurs résultats, la technique de métaanalyse quantitative basée sur les coordonnées d'activation cérébrale fut privilégiée dans cette thèse, telle qu’implémentée dans l'algorithme ALE (Activation Likelyhood Estimate). Une force supplémentaire de cette thèse repose sur la rigueur du processus de sélection des articles. En effet, les études incluses dans les métaanalyses devaient satisfaire des critères stricts d'inclusion, ceci dans le but de favoriser la précision et la validité des conclusions subséquentes. Étude 1 : Le premier article visait à identifier les aires cérébrales impliquées dans la réduction de la douleur par des méthodes psychologiques d'interventions. Les articles retenus portent sur une variété de méthodes d'intervention, telles que le placebo, l'hypnose, la méditation, la perception de contrôle sur la stimulation douloureuse et l'induction d'émotions. Les résultats indiquent que l'HIP implique un vaste réseau d'activation qui comprend le cortex cingulaire antérieur, l'insula antérieure, les zones orbitofrontale et préfrontale latérale, ainsi que les régions pariétale, temporale et souscorticales. Ces activations reflèteraient l'implication des mécanismes neuropsychologiques cognitifs et émotionnels sous-tendent les interventions psychologiques ciblées par ces études, incluant la conscience de soi et la motivation. De plus, les divergences de patron d'activation entre les approches ont été explorées, notamment pour le placebo et la distraction. Étude 2 : Le deuxième article a identifié des patrons d'activations préférentiellement associés à la perception de la douleur, à l'HIP, ainsi que des activations communément associées à la douleur et l'HIP. Les résultats indiquent que 1) la perception de la douleur est associée à l'activation d'aires somatosensorielles et motrices, ce qui pourrait être le reflet de la préparation d'une action adaptative, 2) l'HIP est liée à l'engagement de régions préfrontales antéromédianes et orbitales, possiblement en lien avec des processus motivationnels et émotionnels, et 3) la douleur et l'HIP sont associés à l'activation d'aires préfrontales dorsolatérales, de l'insula antérieure et du cortex cingulaire moyen, ce qui pourrait refléter l'engagement spontané pendant la douleur de mécanismes endogènes de régulation descendante. Conclusion : Par ces études, cette thèse fait le point sur les mécanismes cérébraux impliqués différentiellement dans la perception de la douleur, dans sa régulation endogène et dans l'hypoalgésie induite psychologiquement.

Entrepreneurship and Motivation in Small Business Sector of Kerala

This thesis Entitled entrepreneurship and motivation in small business sector of kerala -A study of rubber products manufacturing industry.Rubber-based industry in Kerala was established only in the first half of the 20th century.the number of licensed manufacturers in the State has increased substantially over the years, particularly in the post- independence period. 54 rubber manufacturing units in 1965-66, the number of licensed rubber-based industrial units has increased to 1300 units in 2001-02. In 2001-02 Kerala occupied the primary position in the number of rubber goods manufacturers in the country.As per the latest report of the Third All India Census of Small Scale Industries 2001-02, Kerala has the third largest number of registered small scale units in the country next after Tamil Nadu and Utter Pradesh.This study of entrepreneurship in the small-scale rubber goods manufacturing industry in Kerala compares a cross section of successful and unsuccessful entrepreneurs with respect to socio-economic characteristics and motivational dynamics. Based on a sample survey of 120 entrepreneurs of Kottayam and Ernakulam districts successful and unsuccessful entrepreneurs were selected using multiple criteria. The study provides guidelines for the development of entrepreneurship in Kerala.The results on the socio-economic survey support the hypothesis that the successful entrepreneurs will differ from unsuccessful entrepreneurs with respect to education, social contacts, initial investment, sales turnover, profits, capital employed, personal income, and number of employees.Successful entrepreneurs were found to be self~starters. Successful entrepreneurs adopted a lot more technological changes than unsuccessful entrepreneurs. Successful entrepreneurs were more innovative — the percent of successful entrepreneurs and unsuccessful entrepreneurs reporting innovations in business were 31.50 and 8.50 percent respectively.

Design and study of self-assembled functional organic and hybrid systems for biological applications

The focus of self-assembly as a strategy for the synthesis has been confined largely to molecules, because of the importance of manipulating the structure of matter at the molecular scale. We have investigated the influence of temperature and pH, in addition to the concentration of the capping agent used for the formation of the nano-bio conjugates. For example, the formation of the narrower size distribution of the nanoparticles was observed with the increase in the concentration of the protein, which supports the fact that γ-globulin acts both as a controller of nucleation as well as stabiliser. As analyzed through various photophysical, biophysical and microscopic techniques such as TEM, AFM, C-AFM, SEM, DLS, OPM, CD and FTIR, we observed that the initial photoactivation of γ-globulin at pH 12 for 3 h resulted in small protein fibres of ca. Further irradiation for 24 h, led to the formation of selfassembled long fibres of the protein of ca. 5-6 nm and observation of surface plasmon resonance band at around 520 nm with the concomitant quenching of luminescence intensity at 680 nm. The observation of light triggered self-assembly of the protein and its effect on controlling the fate of the anchored nanoparticles can be compared with the naturally occurring process such as photomorphogenesis.Furthermore,our approach offers a way to understand the role played by the self-assembly of the protein in ordering and knock out of the metal nanoparticles and also in the design of nano-biohybrid materials for medicinal and optoelectronic applications. Investigation of the potential applications of NIR absorbing and water soluble squaraine dyes 1-3 for protein labeling and anti-amyloid agents forms the subject matter of the third chapter of the thesis. The study of their interactions with various proteins revealed that 1-3 showed unique interactions towards serum albumins as well as lysozyme. 69%, 71% and 49% in the absorption spectra as well as significant quenching in the fluorescence intensity of the dyes 1-3, respectively. Half-reciprocal analysis of the absorption data and isothermal titration calorimetric (ITC) analysis of the titration experiments gave a 1:1 stoichiometry for the complexes formed between the lysozyme and squaraine dyes with association constants (Kass) in the range 104-105 M-1. We have determined the changes in the free energy (ΔG) for the complex formation and the values are found to be -30.78, -32.31 and -28.58 kJmol-1, respectively for the dyes 1, 2 and 3. Furthermore, we have observed a strong induced CD (ICD) signal corresponding to the squaraine chromophore in the case of the halogenated squaraine dyes 2 and 3 at 636 and 637 nm confirming the complex formation in these cases. To understand the nature of interaction of the squaraine dyes 1-3 with lysozyme, we have investigated the interaction of dyes 1-3 with different amino acids. These results indicated that the dyes 1-3 showed significant interactions with cysteine and glutamic acid which are present in the side chains of lysozyme. In addition the temperature dependent studies have revealed that the interaction of the dye and the lysozyme are irreversible. Furthermore, we have investigated the interactions of these NIR dyes 1-3 with β- amyloid fibres derived from lysozyme to evaluate their potential as inhibitors of this biologically important protein aggregation. These β-amyloid fibrils were insoluble protein aggregates that have been associated with a range of neurodegenerative diseases, including Huntington, Alzheimer’s, Parkinson’s, and Creutzfeldt-Jakob diseases. We have synthesized amyloid fibres from lysozyme through its incubation in acidic solution below pH 4 and by allowing to form amyloid fibres at elevated temperature. To quantify the binding affinities of the squaraine dyes 1-3 with β-amyloids, we have carried out the isothermal titration calorimetric (ITC) measurements. The association constants were determined and are found to be 1.2 × 105, 3.6× 105 and 3.2 × 105 M-1 for the dyes, 1-3, respectively. To gain more insights into the amyloid inhibiting nature of the squaraine dyes under investigations, we have carried out thioflavin assay, CD, isothermal titration calorimetry and microscopic analysis. The addition of the dyes 1-3 (5μM) led to the complete quenching in the apparent thioflavin fluorescence, thereby indicating the destabilization of β-amyloid fibres in the presence of the squaraine dyes. Further, the inhibition of the amyloid fibres by the squaraine dyes 1-3, has been evidenced though the DLS, TEM AFM and SAED, wherein we observed the complete destabilization of the amyloid fibre and transformation of the fibre into spherical particles of ca. These results demonstrate the fact that the squaraine dyes 1-3 can act as protein labeling agents as well as the inhibitors of the protein amyloidogenesis. The last chapter of the thesis describes the synthesis and investigation of selfassembly as well as bio-imaging aspects of a few novel tetraphenylethene conjugates 4-6.Expectedly, these conjugates showed significant solvatochromism and exhibited a hypsochromic shift (negative solvatochromism) as the solvent polarity increased, and these observations were justified though theoretical studies employing the B3LYP/6-31g method. We have investigated the self-assembly properties of these D-A conjugates though variation in the percentage of water in acetonitrile solution due to the formation of nanoaggregates. Further the contour map of the observed fluorescence intensity as a function of the fluorescence excitation and emission wavelength confirmed the formation of J-type aggregates in these cases. To have a better understanding of the type of self-assemblies formed from the TPE conjugates 4-6, we have carried out the morphological analysis through various microscopic techniques such as DLS, SEM and TEM. 70%, we observed rod shape architectures having ~ 780 nm in diameter and ~ 12 μM in length as evidenced through TEM and SEM analysis. We have made similar observations with the dodecyl conjugate 5 at ca. 70% and 50% water/acetonitrile mixtures, the aggregates formed from 4 and 5 were found to be highly crystalline and such structures were transformed to amorphous nature as the water fraction was increased to 99%. To evaluate the potential of the conjugate as bio-imaging agents, we have carried out their in vitro cytotoxicity and cellular uptake studies though MTT assay, flow cytometric and confocal laser scanning microscopic techniques. Thus nanoparticle of these conjugates which exhibited efficient emission, large stoke shift, good stability, biocompatibility and excellent cellular imaging properties can have potential applications for tracking cells as well as in cell-based therapies. In summary we have synthesized novel functional organic chromophores and have studied systematic investigation of self-assembly of these synthetic and biological building blocks under a variety of conditions. The investigation of interaction of water soluble NIR squaraine dyes with lysozyme indicates that these dyes can act as the protein labeling agents and the efficiency of inhibition of β-amyloid indicate, thereby their potential as anti-amyloid agents.

Physik lernen, um Physik zu lehren

Aus mehreren Untersuchungen zum Interesse der Schülerinnen und Schüler am Physikunterricht ist bekannt, dass der Unterricht dann für sie interessant ist, wenn die fachlichen Inhalte in einen für die Schülerinnen und Schüler relevanten Kontext eingebunden sind. Die vorliegende empirische Untersuchung beschäftigt sich mit dem Kontext „Physik lernen durch lehren“. Bei diesem Kontext sollen Schülerinnen und Schüler des Gymnasiums Physik lernen, um anschließend Kindern in der Vor- und Grundschule selbst naturwissenschaftliche Inhalte zu vermitteln. Der Kontext wurde dahingehend untersucht, inwiefern er das situationale Interesse der Schülerinnen und Schüler am Physikunterricht beeinflusst und welchen Einfluss er auf die Vermittlung fachlicher und überfachlicher Kompetenzen hat. Die Arbeit basiert auf der Selbstbestimmungstheorie der Motivation von Deci u. Ryan (1993) sowie der pädagogischen Interessentheorie von Krapp u. Prenzel (1992). Um die Interessantheit des Unterrichts im Kontext und den Erwerb von Kompetenzen festzustellen, wurden im Rahmen der Untersuchung zwei quantitative Studien mittels Fragebogenerhebungen und eine qualitative Studie in Form von Leitfaden-Interviews sowohl mit Schülerinnen und Schülern als auch mit Lehrkräften durchgeführt. Die Ergebnisse der Untersuchung zeigen, dass der Unterricht im Kontext „Physik lernen durch lehren“ hinsichtlich der Interessantheit deutlich den herkömmlichen Zugängen überlegen ist. In der Untersuchung wurde eine Reihe von potenziellen Einflussvariablen auf die festgestellte Interessantheit am Unterricht in dem zu unter-suchenden Kontext ermittelt. Der Unterricht wurde in erster Linie aufgrund der naturwissenschaftlichen Veranstaltungen mit den Vor- und Grundschulkindern für die Schülerinnen und Schüler interessanter. Es wurde festgestellt, dass der Kontext besonders bei Schülerinnen und Schülern, die am Unterrichtsfach Physik allgemein unterdurchschnittlich interessiert sind, auf ein größeres situationales Interesse stößt. Insbesondere Mädchen zeigen ein großes situationales Interesse an dem Kontext. Bei dem kontextorientierten Unterricht werden neben fachlichen Kompetenzen vor allem überfachliche Kompetenzen bei den Schülerinnen und Schülern gefördert. Der Schwerpunkt bei den fachlichen Kompetenzen liegt im Bereich des Prozesswissens, und bei den überfachlichen Kompetenzen werden primär das methodisch-problemlösende Lernen und das sozial-kommunikative Lernen gefördert.

Akzeptanz und Motivation beim selbstregulierten Lernen unter Einsatz von neuen Medien in der berufsbegleitenden Weiterbildung

Das Ziel der Dissertation war die Untersuchung des Computereinsatzes zur Lern- und Betreuungsunterstützung beim selbstgesteuerten Lernen in der Weiterbildung. In einem bisher konventionell durchgeführten Selbstlernkurs eines berufsbegleitenden Studiengangs, der an das Datenmanagement der Bürodatenverarbeitung heranführt, wurden die Kursunterlagen digitalisiert, die Betreuung auf eine online-basierte Lernbegleitung umgestellt und ein auf die neuen Lernmedien abgestimmtes Lernkonzept entwickelt. Dieses neue Lernkonzept wurde hinsichtlich der Motivation und der Akzeptanz von digitalen Lernmedien evaluiert. Die Evaluation bestand aus zwei Teilen: 1. eine formative, den Entwicklungsprozess begleitende Evaluation zur Optimierung der entwickelten Lernsoftware und des eingeführten Lernkonzeptes, 2. eine sowohl qualitative wie quantitative summative Evaluation der Entwicklungen. Ein zentraler Aspekt der Untersuchung war die freie Wahl der Lernmedien (multimediale Lernsoftware oder konventionelles Begleitbuch) und der Kommunikationsmedien (online-basierte Lernplattform oder die bisher genutzten Kommunikationskanäle: E-Mail, Telefon und Präsenztreffen). Diese Zweigleisigkeit erlaubte eine differenzierte Gegenüberstellung von konventionellen und innovativen Lernarrangements. Die Verbindung von qualitativen und quantitativen Vorgehensweisen, auf Grund derer die subjektiven Einstellungen der Probanden in das Zentrum der Betrachtung rückten, ließen einen Blickwinkel auf den Nutzen und die Wirkung der Neuen Medien in Lernprozessen zu, der es erlaubte einige in der Literatur als gängig angesehene Interpretationen in Frage zu stellen und neu zu diskutieren. So konnten durch eine Kategorisierung des Teilnehmerverhaltens nach online-typisch und nicht online-typisch die Ursache-Wirkungs-Beziehungen der in vielen Untersuchungen angeführten Störungen in Online-Seminaren verdeutlicht werden. In den untersuchten Kursen zeigte sich beispielsweise keine Abhängigkeit der Drop-out-Quote von den Lern- und Betreuungsformen und dass diese Quote mit dem neuen Lernkonzept nur geringfügig beeinflusst werden konnte. Die freie Wahl der Lernmedien führte zu einer gezielten Nutzung der multimedialen Lernsoftware, wodurch die Akzeptanz dieses Lernmedium stieg. Dagegen war die Akzeptanz der Lernenden gegenüber der Lernbegleitung mittels einer Online-Lernplattform von hoch bis sehr niedrig breit gestreut. Unabhängig davon reichte in allen Kursdurchgängen die Online-Betreuung nicht aus, so dass Präsenztreffen erbeten wurde. Hinsichtlich der Motivation war die Wirkung der digitalen Medien niedriger als erwartet. Insgesamt bieten die Ergebnisse Empfehlungen für die Planung und Durchführung von computerunterstützten, online-begleiteten Kursen.

Student self-assessment a feedback seeking strategy through competence evaluation

There is a body of literature that suggests that student self-assessment is a main goal in higher education (Boud et al., 1995; Tan, 2008); moreover new forms of work organization require a high level of skills and competences. The efforts to deal with competence gaps could be developed at many levels, such as employers, educational institutions, individuals and public agents. Employers could put into practice competence development programs to moderate these gaps. Educational institutions can restructure the curriculum to support students in attaining the competences that are essential in the labour market. Individuals themselves may deploy their resources (time and money) in general or specific competence training. Further, government agencies could fund competence promotion programs. Such challenges for education drive change in learning curricula and method, to properly include the competences required for developing global workers who can move beyond basic competence, to enhanced flexibility and adaptability. In performance assessment methods, there is a shift from the traditional exam-based assessments to more innovative task assessment, which considers performance in multiple different tasks carry out by students. ICTs make it technologically feasible to carry out a complete and complex selfassessment of competences, which provides immediate results to students or other recipients. In the case of students, the evaluation of competences is relevant as developing competences is part - if not all - of the objectives of education. Therefore, it is an important element of the quality of educational organizations (e.g., universities), and of their organizational success. Further, educational organizations may put special emphasis on some differentiating competences, which can be a means of positioning and differentiation from competitors. Competence assessment is an instrument to make students conscious of their strengths and weaknesses, leading to higher motivation to develop their own learning career

Foundation Year RTS Part 3 Motivation Quiz

A short self evaluation quiz looking at motivation

Self-organized sociopolitical interactions as the best way to achieve organized patterns in human social systems: going beyond the top-down control of classical political regimes

La monografía presenta la auto-organización sociopolítica como la mejor manera de lograr patrones organizados en los sistemas sociales humanos, dada su naturaleza compleja y la imposibilidad de las tareas computacionales de los regímenes políticos clásico, debido a que operan con control jerárquico, el cual ha demostrado no ser óptimo en la producción de orden en los sistemas sociales humanos. En la monografía se extrapola la teoría de la auto-organización en los sistemas biológicos a las dinámicas sociopolíticas humanas, buscando maneras óptimas de organizarlas, y se afirma que redes complejas anárquicas son la estructura emergente de la auto-organización sociopolítica.

Diferencias individuales y desarrollo de habilidades de liderazgo : el rol del locus de control

El presente proyecto se ha elaborado con la finalidad de encontrar la relación existente entre el liderazgo y el locus de control, por medio de una revisión documental que permita dar una visión más amplia de estos dos fenómenos. De acuerdo con investigaciones realizadas, existen características individuales que afectan el desarrollo de liderazgo, lo cual a su vez tiene un impacto sobre el comportamiento de los individuos dentro de una sociedad. Uno de estos factores es el locus de control, el cual sesta determinado por características del individuo, y por el ambiente en el cual se desenvuelven las personas. Existen diferentes evidencias que soportan ésta relación entre locus de control y liderazgo. En éste estudio documental se describirán estos hallazgos, identificando las características del individuo y del contexto que influyen sobre ellos. Asimismo se pondrá en contexto a través del trabajo las características principales de los líderes y como se presentan las interacciones entre los lideres y seguidores, teniendo en cuenta que no todas las veces los seguidores desarrollan este papel al seguir a su líder, sino que por otro lado y estos pueden tomar parte fundamental en la interacción, influyendo de manera directa sobre el líder. Se recuerda que a los lideres los hacen sus seguidores y que sin estos no podrían desarrollar el papel de líder.

Electronic structure of point defects in controlled self-doping of the TiO2 (110) surface: Combined photoemission spectroscopy and density functional theory study

Point defects in metal oxides such as TiO2 are key to their applications in numerous technologies. The investigation of thermally induced nonstoichiometry in TiO2 is complicated by the difficulties in preparing and determining a desired degree of nonstoichiometry. We study controlled self-doping of TiO2 by adsorption of 1/8 and 1/16 monolayer Ti at the (110) surface using a combination of experimental and computational approaches to unravel the details of the adsorption process and the oxidation state of Ti. Upon adsorption of Ti, x-ray and ultraviolet photoemission spectroscopy (XPS and UPS) show formation of reduced Ti. Comparison of pure density functional theory (DFT) with experiment shows that pure DFT provides an inconsistent description of the electronic structure. To surmount this difficulty, we apply DFT corrected for on-site Coulomb interaction (DFT+U) to describe reduced Ti ions. The optimal value of U is 3 eV, determined from comparison of the computed Ti 3d electronic density of states with the UPS data. DFT+U and UPS show the appearance of a Ti 3d adsorbate-induced state at 1.3 eV above the valence band and 1.0 eV below the conduction band. The computations show that the adsorbed Ti atom is oxidized to Ti2+ and a fivefold coordinated surface Ti atom is reduced to Ti3+, while the remaining electron is distributed among other surface Ti atoms. The UPS data are best fitted with reduced Ti2+ and Ti3+ ions. These results demonstrate that the complexity of doped metal oxides is best understood with a combination of experiment and appropriate computations.

Self assembly of a model amphiphilic phenylalanine peptide/polyethylene glycol block copolymer in aqueous solution

There has been great interest recently in peptide amphiphiles and block copolymers containing biomimetic peptide sequences due to applications in bionanotechnology. We investigate the self-assembly of the peptide-PEG amphiphile FFFF-PEG5000 containing the hydrophobic sequence of four phenylalanine residues conjugated to PEG of molar mass 5000. This serves as a simple model peptide amphiphile. At very low concentration, association of hydrophobic aromatic phenylalanine residues occurs, as revealed by circular dichroism and UV/vis fluorescence experiments. A critical aggregation concentration associated with the formation of hydrophobic domains is determined through pyrene fluorescence assays. At higher concentration, defined beta-sheets develop as revealed by FTIR spectroscopy and X-ray diffraction. Transmission electron microscopy reveals self-assembled straight fibril structures. These are much shorter than those observed for amyloid peptides, the finite length may be set by the end cap energy due to the hydrophobicity of phenylalanine. The combination of these techniques points to different aggregation processes depending on concentration. Hydrophobic association into irregular aggregates occurs at low concentration, well-developed beta-sheets only developing at higher concentration. Drying of FFFF-PEG5000 solutions leads to crystallization of PEG, as confirmed by polarized optical microscopy (POM), FTIR and X-ray diffraction (XRD). PEG crystallization does not disrupt local beta-sheet structure (as indicated by FTIR and XRD). However on longer lengthscales the beta-sheet fibrillar structure is perturbed because spheruilites from PEG crystallization are observed by POM. (C) 2009 Elsevier B.V. All rights reserved.

Self-assembly in aqueous solution of a modified amyloid beta peptide fragment

The self-assembly in films dried from aqueous solutions of a modified amyloid beta peptide fragment is studied. We focus on sequence A beta(16-20), KLVFF, extended by two alanines at the N-terminus to give AAKLVFF. Self-assembly into twisted ribbon fibrils is observed, as confirmed by transmission electron microscopy (TEM). Dynamic light scattering reveals the semi-flexible nature of the AAKLVFF fibrils, while polarized optical microscopy shows that the peptide fibrils crystallize after an aqueous solution of AAKLVFF is matured over 5 days. The secondary structure of the fibrils is studied by FT-IR, circular dichroism and X-ray diffraction (XRD), which provide evidence for beta-sheet structure in the fibril. From high resolution TEM it is concluded that the average width of an AAKLVFF fibril is (63 +/- 18) nm, indicating that these fibrils comprise beta-sheets with multiple repeats of the unit cell, determined by XRD to have b and c dimensions 1.9 and 4.4 nm with an a axis 0.96 nm, corresponding to twice the peptide backbone spacing in the antiparallel beta-sheet. (C) 2008 Elsevier B.V. All rights reserved.

Low-molecular-weight gelators: Elucidating the principles of gelation based on gelator solubility and a cooperative self-assembly model

This paper highlights the key role played by solubility in influencing gelation and demonstrates that many facets of the gelation process depend on this vital parameter. In particular, we relate thermal stability (T-gel) and minimum gelation concentration (MGC) values of small-molecule gelation in terms of the solubility and cooperative self-assembly of gelator building blocks. By employing a van't Hoff analysis of solubility data, determined from simple NMR measurements, we are able to generate T-calc values that reflect the calculated temperature for complete solubilization of the networked gelator. The concentration dependence of T-calc allows the previously difficult to rationalize "plateau-region" thermal stability values to be elucidated in terms of gelator molecular design. This is demonstrated for a family of four gelators with lysine units attached to each end of an aliphatic diamine, with different peripheral groups (Z or Bee) in different locations on the periphery of the molecule. By tuning the peripheral protecting groups of the gelators, the solubility of the system is modified, which in turn controls the saturation point of the system and hence controls the concentration at which network formation takes place. We report that the critical concentration (C-crit) of gelator incorporated into the solid-phase sample-spanning network within the gel is invariant of gelator structural design. However, because some systems have higher solubilities, they are less effective gelators and require the application of higher total concentrations to achieve gelation, hence shedding light on the role of the MGC parameter in gelation. Furthermore, gelator structural design also modulates the level of cooperative self-assembly through solubility effects, as determined by applying a cooperative binding model to NMR data. Finally, the effect of gelator chemical design on the spatial organization of the networked gelator was probed by small-angle neutron and X-ray scattering (SANS/SAXS) on the native gel, and a tentative self-assembly model was proposed.

Solvent-Assisted Formation of Vesicles by a Self-Assembling Ni-3-Schiff Base Complex

A linear trinuclear Ni-Schiff base complex [Ni-3(salpen)(2)(PhCH2COO)(2)(EtOH)] has been synthesized by combining Ni(ClO4)(2)center dot 6H(2)O, phenyl acetic acid (C6H5CH2COOH), and the Schiff base ligand, N,N'-bis(salicylidene)-1,3-pentanediamine (H(2)salpen). This complex is self-assembled through hydrogen bonding and C-H-g interaction in the solid state to generate a sheet-like architecture, while in organic solvent (CH2Cl2), it forms vesicles with a mean diameter of 290 nm and fused vesicles, depending upon the concentration of the solution. These vesicles act as an excellent carrier of dye molecules in CH2Cl2. The morphology of the complex has been determined by scanning electron microscopy and transmission electron microscopy experiments, and the encapsulation of dye has been examined by confocal microscopic image and electronic absorption spectra.

Self-nucleation and crystallization kinetics of double crystalline poly(p-dioxanone)-b-poly(epsilon-caprolactone) diblock copolymers

The crystallization kinetics of each constituent of poly(p-dioxanone)-b-poly(epsilon-caprolactone) diblock copolymers (PPDX-b-PCL) has been determined in a wide composition range by differential scanning calorimetry and compared to that of the equivalent homopolymers. Spherulitic growth rates were also measured by polarized optical microscopy while atomic force microscopy was employed to reveal the morphology of one selected diblock copolymer. It was found that crystallization drives structure formation and both components form lamellae within mixed spherulitic superstructures. The overall isothermal crystallization kinetics of the PPDX block at high temperatures, where the PCL is molten, was determined by accelerating the kinetics through a previous self-nucleation procedure. The application of the Lauritzen and Ho. man theory to overall growth rate data yielded successful results for PPDX and the diblock copolymers. The theory was applied to isothermal overall crystallization of previously self-nucleated PPDX ( where growth should be the dominant factor if self-nucleation was effective) and the energetic parameters obtained were perfectly matched with those obtained from spherulitic growth rate data of neat PPDX. A quantitative estimate of the increase in the energy barrier for crystallization of the PPDX block, caused by the covalently bonded molten PCL as compared to homo-PPDX, was thus determined. This energy increase can dramatically reduce the crystallization rate of the PPDX block as compared to homo-PPDX. In the case of the PCL block, both the crystallization kinetics and the self-nucleation results indicate that the PPDX is able to nucleate the PCL within the copolymers and heterogeneous nucleation is always present regardless of composition. Finally, preliminary results on hydrolytic degradation showed that the presence of relatively small amounts of PCL within PPDX-bPCL copolymers substantially retards hydrolytic degradation of the material in comparison to homo-PPDX. This increased resistance to hydrolysis is a complex function of composition and its knowledge may allow future prediction of the lifetime of the material for biomedical applications.