1,720,959 research outputs found
Biocatalysis: A Multifaceted Examination of Free and Immobilized Enzymes
Full text linkIn the current landscape of chemical processes, a predominant focus gravitates toward the integration of green chemistry principles, emphasizing the imperative of maximizing reaction yields while minimizing by-products in adherence to the concept of atom economy. This paradigm shift has underscored the significance of employing biocatalysts, particularly enzymes renowned for their remarkable selectivity and specificity, as pivotal components of sustainable solutions. In essence, enzymes stand as indispensable allies in the pursuit of sustainable chemical processes, offering a multifaceted solution that aligns with the ethos of green chemistry. Their unique catalytic properties and biocompatibility render them not just catalysts but catalysts with an environmentally conscious edge, promising advancements that resonate across various industrial landscapes while fostering a more sustainable and eco-friendly approach from the production of pharmaceutically active compounds to energy production, from fine chemistry to polymer science, and so forth.
In this thesis work, we focused specifically on two classes of enzymes: lipases and dehydrogenases. Lipases exhibit remarkable chemoselectivity, regioselectivity, and stereoselectivity during catalysis. These enzymes, abundant and accessible, can be efficiently produced in significant quantities by microbial organisms, notably fungi and bacteria. Moreover, lipases typically function independently of cofactors and minimize catalyzing side reactions. These combined attributes establish lipases as the primary and widely adopted group of biocatalysts within the realm of organic chemistry. The second group of enzymes under study comprises alcohol dehydrogenases, specifically focusing on horse liver alcohol dehydrogenase (HLADH). Alcohol dehydrogenases (ADHs) have garnered considerable interest owing to their crucial involvement in alcohol metabolism, detoxification of xenobiotics, and broader implications within enzymology and biochemistry research. HLADH, an extensively researched enzyme extracted from equine liver tissue, plays a pivotal role in various enzymatic processes, thus warranting detailed investigation
Characterization of lipase from Candida rugosa entrapped in alginate beads to enhance its thermal stability and recyclability
No full textLipase from Candida rugosa has been immobilized in different formulations of calcium alginate beads, prepared by ionotropic gelation, which differ from each other in CaCl2 concentration and hardening time, to investigate the effects of immobilization conditions on enzyme properties. Morphological studies on all hydrated beads, performed by SEM equipped with a Peltier plate, revealed a different internal compactness. Despite this, all types of beads had an immobilization yield of 100% measured with the Bradford method and about 94% evaluated from the residual activity of the preparation solutions; moreover, all entrapped biocatalysts catalyzed the complete hydrolysis of p-nitrophenyl acetate, even after one month of storage in distilled water at 4 °C. When the internal microstructure of the beads was more compact, the rate of hydrolysis of the most hydrophobic p-nitrophenyl dodecanoate was halved, probably due to mass transfer limiting effects. The immobilized lipase had better resistance to temperature inactivation than the free form: enzyme residual activity at 50 °C after a week were approximately 70% and 20% for the immobilized and free forms respectively. An excellent recyclability in water at 25 °C of entrapped enzyme was also found, having residual activity greater than 80% at the tenth reaction cycle. The best bead formulation was then used for the resolution of (R)-1-phenylethanol in aqueous solution starting from racemic (R,S)-1-phenylethyl acetate. The enantioselectivity found (E=10) was slightly higher but did not differ significantly from that of free lipase towards the same substrate (E=4)
Evaluation of acrylic and silane coatings on limestone through macroscopic and microscopic analyses
Full text linkThe aim of this study was to obtain useful information about the behavior of a coating when it interacts with a
stone substrate, to allow the choice of the most suitable protective agent to preserve stone artworks from
deterioration phenomena in their environmental conditions. The effect of some commercially available silanebased
polymers on Lecce stone was compared with that of two new acrylic ones not yet available for sale.
The performance of each protective treatment was evaluated by colorimetry, contact angle measurements and
NMR relaxometry, which allows to estimate the hygroscopic properties of the stone in terms of open porosity and
water-uptake. The microscopic observations combined with micro-FTIR and SEM-EDS analyses were performed
to investigate the distribution of the protectives on the stone surface and their depth of penetration. The results
showed that the water repellency of the two acrylic products and of one of the silane-based protectives was
mainly due to a surface effect, just slowing down water adsorption. On the contrary, the other two silane-based
products turned out distributed throughout most of the sample volume, completely hindering water absorption
Protein Secondary Structure Patterns in Short‐Range Cross‐Link Atlas
Full text linkCross-linking mass spectrometry (XL-MS) has become a powerful tool in structural biology for investigating protein structure, dynamics, and interactomics. However, short-range cross-links, defined as those connecting residues fewer than 20 positions apart, have traditionally been considered less informative and largely overlooked, leaving significant data unexplored in a systematic manner. Here, we present a system-wide analysis of short-range cross-links, demonstrating their intrinsic correlation with protein secondary structure. We introduce the X-SPAN (Cross-link Structural Pattern Analyzer) software, which integrates publicly available XL-MS datasets from system-wide experiments with AlphaFold-predicted protein structures. Our analysis reveals distinct cross-linking patterns that reflect the spatial constraints imposed by secondary structural elements. Specifically, α-helices exhibit periodic cross-linking patterns consistent with their characteristic helical pitch, whereas coils and β-strands display nearly monotonic distributions. A context-dependent protein grammar reinforces short-range cross-link specificity. Short-range cross-links can enhance the statistical inference of secondary structures within integrative modeling workflows. Additionally, our work establishes a framework for benchmarking AlphaFold's local prediction accuracy and provides novel quality control criteria for XL-MS experiments. We anticipate that X-SPAN and our short-range cross-link database will serve as a valuable resource for exploring local secondary structure rearrangements and their potential roles in protein function and allosteric regulation
Unveiling cofactor inhibition mechanisms in horse liver alcohol dehydrogenase: An allosteric driven regulation
Full text linkHorse Liver Alcohol Dehydrogenase (HLADH) is an extensively studied enzyme isolated from equine liver tissue, and holds a central role in numerous enzymatic processes, underscoring the need for thorough investigation. This study delves into the kinetic behavior and structural dynamics of HLADH, shedding light on complex mechanisms governing its catalytic activity and interactions with the cofactor. Notably, deviations from traditional Michaelis–Menten kinetics are observed, manifesting as a slowdown in catalytic rate under high NADH concentrations. Utilizing molecular dynamics simulations, an allosteric site is identified, clarifying how excessive cofactor levels impact protein dynamics and catalytic properties. Structural alterations induced by inhibitory NADH concentrations are revealed, indicating reduced protein flexibility and modifications in catalytic cavity size, thereby elucidating the inhibitory mechanism at high cofactor concentrations. This comprehensive investigation unveils intricate facets of HLADH’s catalytic mechanisms, providing a platform for further exploration in enzymology and biocatalysis
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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