1,720,956 research outputs found
Iron-galls inks: preparation, structure and characterisation
Full text linkThe formation of dark complexes due to the interaction between polyphenols and iron has been empirically exploited since the XII century for the production of the so-called iron-gall inks (IGI), which have been widely used for the production of manuscripts both in Europe and Middle East. Being part of the cultural heritage, these manuscripts are currently objects of interests which have to be carefully preserved. In this paper the current knowledge on IGI is reviewed focusing on the variety of ingredients used for their preparation, the available models describing the formation of the polyphenols-iron complexes, and their degradation patterns. Additionally, the range of instrumental techniques nowadays available for their characterisation is critically discussed highlighting for every technique the most important features for the study of IG
Spiers Memorial Lecture: organic, physical & polymer aspects pivotal in lignin valorization
Full text linkThis article addresses current challenges in lignin chemistry by exploring four thematic areas. We begin by examining the major chemical transformations that occur in lignin and discuss the emerging structural understanding of technical lignins. The discussion then shifts to lignin fractionation strategies, which are essential for reducing its inherent heterogeneity and complexity, thereby enabling its use in practical applications. Next, we delve into the chemical and physical behavior of lignin in solution, with particular emphasis on its self-assembly processes relevant to nanoparticle formation. The supramolecular interactions driving these assemblies - such as π-π stacking, hydrogen bonding, and solvent polarity - are analyzed to identify key parameters for designing lignin-based nanomaterials. These materials show promising applications across sectors including agriculture, packaging, cosmetics, and pharmaceuticals. We then consider the broader valorization of lignin, focusing on the rheological and antioxidant properties of lignin fractions. Particular attention is given to their role in forming polymer blends with polyethylene, highlighting their influence on thermal stability and mechanical performance. Finally, we explore lignin's potential as a non-petroleum precursor for carbon fiber production. We critically assess the main barriers in this field, such as lignin's relatively low molecular weight and thermal behavior, which hinder effective fiber formation and graphitization. Strategies to address these challenges, including the integration of fractionation techniques with chemical modifications, are discussed. The article concludes with a review of recent efforts to overcome the limitations of lignin graphitization and enhance its viability as a sustainable carbon fiber source
The Laccase Catalysed Tandem Lignin Depolymerisation/Polymerisation
No full textThe development of strategies allowing either the production of high value phenolics, or the isolation of properties-enhanced materials from technical lignins represents a fundamental step in the industrial upcycling of technical lignins. Both aims are met by the strategy presented in the present work, relying on the coupling of solvent-based fractionation with the oxidative action of a new type of alkaline-stable genetically modified bacterial laccase. The described approach succeeded in the tandem, high-yield and selective isolation of valuable lignin-monomeric compounds (MCs) and high molecular weight and hydrophobicity-tailored polymerised materials (PMs) from two technical lignins, namely softwood kraft lignin (SKL), and wheat straw organosolv lignin (WSL). With respect to MCs, higher yields as compared to similar studies (up to 17.2 mg/g) were achieved. PMs from SKL samples where characterised by an almost quadrupled Mw, while in the case of WSL the Mw was approximately doubled. Noteworthy, the reaction conditions were optimized in terms of reaction temperature, time, enzymatic loading, and alkalinity for the selective production of single MCs. Most interestingly, technical lignins as well as their fractions and the PMs deriving from their laccase-catalysed oxidation showed increased hydrophobicity
Quantitative P-31 NMR Analysis of Lignins and Tannins
Full text linkThe development of sustainable biorefinery products is confronted, among others, with the challenge of lignin and tannin valorization. These abundant, renewable aromatic biopolymers have not been widely exploited due to their inherent structural complexity and high degrees of variability and species diversity. The lack of a defined primary structure for these polyphenols is further compounded with complex chemical alterations induced during processing, eventually imparting a large variety of structural features of extreme significance for any further utilization efforts.Consequently, a protocol for the rapid, simple, and unequivocal identification and quantification of the various functional groups present in natural polyphenols, is a fundamental prerequisite for understanding and accordingly tailor their reactivity and eventual utility.Quantitative P-31 NMR offers the opportunity to rapidly and reliably identify unsubstituted, o-mono substituted, and o-disubstituted phenols, aliphatic OHs, and carboxylic acid moieties in lignins and tannins with broad application potential.The methodology consists of an in situ quantitative lignin or tannin labeling procedure using a suitable P-31 containing probe, followed by the acquisition of a quantitative P-31 NMR spectrum in the presence of an internal standard. The high natural abundance of the P-31 nucleus allows for small amounts of the sample (similar to 30 mg) and short NMR acquisition times (similar to 30-120 min) with well-resolved P-31 signals that are highly dependent on the surrounding chemical environment of the labeled OH groups
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
- …
