1,720,974 research outputs found
Introduction to photoswitches and photopharmacology
No full textMartina Cacciarini, G. Andrew Woolley, Wiktor Szymanski and Nadja A. Simeth introduce the Organic & Biomolecular Chemistry and RSC Medicinal Chemistry cross-journal themed collection on ‘Photoswitches and Photopharmacology’
Application of Ultra-short Peptides as Building Blocks for the Rational Design of Stimuli-responsive Ferrocene-peptide Gels
No full textThe considerable attention given to understanding and utilizing gel based materials in recent years, coupled to the great potential of peptide chemistry for the design and development of stimuli-responsive materials using a bottom-up approach, has led to an ever increasing interest in the fabrication of peptide based functional materials. Considering the fact that serendipity is the usual path to the discovery of molecules capable of gelling water and organic solvents, the rational design of stimuli-responsive gels using a bottom-up approach can be a formidable task. The body of work presented herein strives to tackle the rational design of stimuli-responsive ferrocene-peptide conjugates using a bottom-up approach and relies on the stepwise modification and fine-tuning of the designs to allow the incorporation of molecular features that allow the gel materials to respond to different stimuli, including: temperature, sound, mechanical stress, redox and light.
Based on this stepwise approach the ultra-short peptide Boc-L-Phe-L-Lys(Z)-OMe was selected as the peptide unit responsible for driving the gel formation. This ultra-short peptide was found through serendipitous discovery to undergo gelation in a variety of solvents in response to sonication and change in temperature. Moreover, the gels of Boc-L-Phe-L-Lys(Z)-OMe formed in aromatic solvents demonstrated mechano-responsive properties and thermal chiroptical switching. These key stimuli-responsive features rendered Boc-L-Phe-L-Lys(Z)-OMe as an attractive structural unit for installing smart and responsive behaviour in other molecules.
Consequently, the dipeptide sequences Phe‐Lys(Z) and Lys(Z)‐Phe were incorporated into the structure of a variety of stimuli-responsive molecules, including: ferrocene, azobenzene and pyrene. While the designed derivatives of azobenzene and pyrene retained their inherent light and fluorescence switching behavior, the redox modulated gel to sol transition of the ferrocene containing organogels was limited by the insolubility of the oxidized gelator and oxidizing agent in toluene.
The limitation of the designed stimuli-responsive systems that only allowed gelation in aromatic solvents inspired us to expand the gelation property of the ferrocene derivatives to other organic solvents. By modifying the design, the responsive property of the ferrocene based organogels of Phe‐Lys(Z) and Lys(Z)‐Phe was later expanded to other solvents to allow the reversible redox induced gel to sol phase transition in acetone. Aiming to diversify the stimuli-responsive property of the designed ferrocene gels, a photoresponsive discrete metallogelator was later developed by carefully designing a molecule that retained the photoresponsive and redox active properties of the azobenzene and ferrocene units. The multi-stimuli responsive property of this molecule allowed us to examine this gel system for studying basic logic-gate operations by using different oxidizing agents as input.Ph.D.2017-03-30 00:00:0
Application of Ultra-short Peptides as Building Blocks for the Rational Design of Stimuli-responsive Ferrocene-peptide Gels
Full text linkThe considerable attention given to understanding and utilizing gel based materials in recent years, coupled to the great potential of peptide chemistry for the design and development of stimuli-responsive materials using a bottom-up approach, has led to an ever increasing interest in the fabrication of peptide based functional materials. Considering the fact that serendipity is the usual path to the discovery of molecules capable of gelling water and organic solvents, the rational design of stimuli-responsive gels using a bottom-up approach can be a formidable task. The body of work presented herein strives to tackle the rational design of stimuli-responsive ferrocene-peptide conjugates using a bottom-up approach and relies on the stepwise modification and fine-tuning of the designs to allow the incorporation of molecular features that allow the gel materials to respond to different stimuli, including: temperature, sound, mechanical stress, redox and light.
Based on this stepwise approach the ultra-short peptide Boc-L-Phe-L-Lys(Z)-OMe was selected as the peptide unit responsible for driving the gel formation. This ultra-short peptide was found through serendipitous discovery to undergo gelation in a variety of solvents in response to sonication and change in temperature. Moreover, the gels of Boc-L-Phe-L-Lys(Z)-OMe formed in aromatic solvents demonstrated mechano-responsive properties and thermal chiroptical switching. These key stimuli-responsive features rendered Boc-L-Phe-L-Lys(Z)-OMe as an attractive structural unit for installing smart and responsive behaviour in other molecules.
Consequently, the dipeptide sequences Phe‐Lys(Z) and Lys(Z)‐Phe were incorporated into the structure of a variety of stimuli-responsive molecules, including: ferrocene, azobenzene and pyrene. While the designed derivatives of azobenzene and pyrene retained their inherent light and fluorescence switching behavior, the redox modulated gel to sol transition of the ferrocene containing organogels was limited by the insolubility of the oxidized gelator and oxidizing agent in toluene.
The limitation of the designed stimuli-responsive systems that only allowed gelation in aromatic solvents inspired us to expand the gelation property of the ferrocene derivatives to other organic solvents. By modifying the design, the responsive property of the ferrocene based organogels of Phe‐Lys(Z) and Lys(Z)‐Phe was later expanded to other solvents to allow the reversible redox induced gel to sol phase transition in acetone. Aiming to diversify the stimuli-responsive property of the designed ferrocene gels, a photoresponsive discrete metallogelator was later developed by carefully designing a molecule that retained the photoresponsive and redox active properties of the azobenzene and ferrocene units. The multi-stimuli responsive property of this molecule allowed us to examine this gel system for studying basic logic-gate operations by using different oxidizing agents as input.Ph.D.2017-03-30 00:00:0
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Steps Toward Multichromatic Optogenetic Control with Cyanobacteriochromes
Full text linkOptogenetic tools offer spatial and temporal control of biological processes. Photoswitchable proteins that change conformation upon exposure to light are the core components of optogenetic tools. Current tools rely mostly on photoswitchable proteins that respond to blue light, and some use red light. To enable orthogonal, multicolor control of multiple biological processes, tools must be developed that respond to other colors of light. Cyanobacteriochromes, photoswitchable proteins from cyanobacteria, respond to a wide range of wavelengths from the UV to the near infra-red. This thesis explores the applicability and utility of cyanobacteriochromes as new core components of optogenetic tools. New light inducible dimer pairs from these photoswitchable proteins are developed via directed evolution approaches, permitting orthogonal control of biological processes with red-, green-, and blue-light.Ph.D
Towards Red Light Control of Ion Channel Blockers
Full text linkPhotoswitchable ion channel blockers reported previously have proven effective for modulating the activity of voltage-gated potassium (KV) channels. One limitation of previously reported azobenzene-based blockers was that the wavelength needed to promote trans-to-cis isomerization ranged from ultraviolet (UV) to blue. Light in this wavelength range poorly penetrates tissues and is cytotoxic, which limits the utility of these photoswitchable compounds for in vivo studies of KV channel activity. We designed, synthesized and ran preliminary patch-clamp experiments on analogous ion channel blockers bearing the tetra-ortho-methoxy (TOM) substitution pattern to bathochromically shift the absorption spectrum to permit long-wavelength photo-control. In combination with a bis-para-amino functionality, these blockers can form azonium ions under physiological conditions, which absorb red light strongly and undergo trans-to-cis isomerization. Red-light effectively penetrates tissues, allowing for in vivo studies of biological systems. We also report synthesis and initial characterization of a novel, further red-shifted dioxane ortho-methoxy (DOM) azobenzene substitution pattern.M.Sc.2017-11-17 00:00:0
Towards Red Light Control of Ion Channel Blockers
No full textPhotoswitchable ion channel blockers reported previously have proven effective for modulating the activity of voltage-gated potassium (KV) channels. One limitation of previously reported azobenzene-based blockers was that the wavelength needed to promote trans-to-cis isomerization ranged from ultraviolet (UV) to blue. Light in this wavelength range poorly penetrates tissues and is cytotoxic, which limits the utility of these photoswitchable compounds for in vivo studies of KV channel activity. We designed, synthesized and ran preliminary patch-clamp experiments on analogous ion channel blockers bearing the tetra-ortho-methoxy (TOM) substitution pattern to bathochromically shift the absorption spectrum to permit long-wavelength photo-control. In combination with a bis-para-amino functionality, these blockers can form azonium ions under physiological conditions, which absorb red light strongly and undergo trans-to-cis isomerization. Red-light effectively penetrates tissues, allowing for in vivo studies of biological systems. We also report synthesis and initial characterization of a novel, further red-shifted dioxane ortho-methoxy (DOM) azobenzene substitution pattern.M.Sc.2017-11-17 00:00:0
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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