The very peculiar characteristics of zwitterions, as well as a clearand unambiguous definition, have been overlooked in past literature. However, these compounds are particularly important in view of ...the impact they have had in the recent past and will likely continue to have in the future as components of performing functional organic and hybrid materials. In this Account, we primarily aim to define critically important organic concepts of zwitterions regarding both their design and nomenclature. We will particularly focus on a specific kind of zwitterions we define as π-conjugated zwitterions. These types of zwitterions are systems pertaining to the class ofdonor–acceptor (push–pull) molecules. In the ground state, they are preferentially represented in terms of an electron donor moiety bearing a negative net charge, and electron acceptor one bearing a positive net charge connected by a conjugated bridge. As such, they are possibly the most effective example of push–pull structure, possessing relevant features for applications like nonlinear optics, photovoltaics, imaging, and high capacitance dielectrics. In addition, the interaction between these dipolar compounds and the environment is highly specific and can be exploited in the construction of well-organized nanostructures, both in solution and in the solid state. According to the Gold Book of IUPAC for nomenclature, the distinction between zwitterions and the charged molecule called a betaine is subtle. The betaine is a particular class of zwitterion possessing an onium atom not bearing a hydrogen. The two terms are often considered equivalent, thus generating confusion while retrieving literature. In this Account, we define and describe π-conjugated zwitterions systems that are dipolar in the ground state, admitting resonance limiting structures that are neutral and chargeless. For the purpose of this Account and to the benefit of researchers striving to retrieve materials-related zwitterion literature data, we suggest to use the term π-zwitterions instead of the commonly used plain term “zwitterions”. We show that this definition enables the clear identification of a class of compounds having unique properties distinct from “dipolar conjugated compounds.” We describe the most common donor and acceptor groups in π-zwitterions. In particular, we focus our attention on the special case of the nitrile functionality, which tends to be contiguous to a negative charge. We also address special emphasis to benzenoid components that are substituted by heteroaromatic units in π-zwitterions, because the HOMO–LUMO energetic consequences are specifically involved in these cases. We make reference to the paradigmatic case of π-zwitterions second order nonlinear optical properties. Here, the value of the first hyperpolarizability β versus the alternation in bond length turns out to be a measure of the balance of the chargeless and the dipolar contribution to the description of the zwitterion ground state. We also report literature data, collected both from our group and others, concerning π-zwitterions containing heteroaromatic and/or nitrile groups, those based on the most performing acceptors so far described, and merocyanines. With particular reference to merocyanines, we show how π-zwitterions can play a fundamental role in the fast growing field of organic photovoltaics. Finally, we present π-zwitterions made up of heteroaromatic groups that open new scenarios in heteroaromatic chemistry.
Genes specifying long non-coding RNAs (lncRNAs) occupy a large fraction of the genomes of complex organisms. The term 'lncRNAs' encompasses RNA polymerase I (Pol I), Pol II and Pol III transcribed ...RNAs, and RNAs from processed introns. The various functions of lncRNAs and their many isoforms and interleaved relationships with other genes make lncRNA classification and annotation difficult. Most lncRNAs evolve more rapidly than protein-coding sequences, are cell type specific and regulate many aspects of cell differentiation and development and other physiological processes. Many lncRNAs associate with chromatin-modifying complexes, are transcribed from enhancers and nucleate phase separation of nuclear condensates and domains, indicating an intimate link between lncRNA expression and the spatial control of gene expression during development. lncRNAs also have important roles in the cytoplasm and beyond, including in the regulation of translation, metabolism and signalling. lncRNAs often have a modular structure and are rich in repeats, which are increasingly being shown to be relevant to their function. In this Consensus Statement, we address the definition and nomenclature of lncRNAs and their conservation, expression, phenotypic visibility, structure and functions. We also discuss research challenges and provide recommendations to advance the understanding of the roles of lncRNAs in development, cell biology and disease.
Interest in two-dimensional, sheet-like or flake-like carbon forms has expanded beyond monolayer graphene to include related materials with significant variations in layer number, lateral dimension, ...rotational faulting, and chemical modification. Describing this family of “graphene materials” has been causing confusion in the Carbon journal and in the scientific literature as a whole. The international editorial team for Carbon believes that the time has come for a discussion on a rational naming system for two-dimensional carbon forms. We propose here a first nomenclature for two-dimensional carbons that could guide authors toward a more precise description of their subject materials, and could allow the field to move forward with a higher degree of common understanding.
Structure-property relationships of starch components remain a subject of research interest. In recent years, there has been increasing evidence revealing the importance of amylopectin internal ...structure in determining physicochemical properties of starch. The part between the sole reducing end and out branches of amylopectin forms the internal part of the molecule. It contributes to the formation of the amorphous lamellae of the granules.
This mini-review focuses on the impact of amylopectin internal molecular structure on different physicochemical properties of starch. The properties include gelatinization, swelling power, amylose leaching, pasting, retrogradation, and digestibility of starch. The statistical approach to analyze the structure-property relationships of starch is also discussed. Related nomenclatures are described.
Amylopectin with a longer internal chain length tends to give more ordered packing of double helices in the granules with a higher thermal stability. A longer internal chain length of amylopectin also contributes to the formation of recrystallized amylopectin with a more ordered structure and higher thermal stability. The results summarised in this mini-review clearly show that the molecular structure of amylopectin internal part should be considered in order to better understand the complex structure-property relationships of starch components.
•Longer amylopectin internal chain related to more ordered packing of double helices.•Longer amylopectin internal chain related to more efficient recrystallization.•Importance of amylopectin internal chain composition on starch properties discussed.•Related amylopectin nomenclatures described.
•Second- and third-order (multi-way) data and algorithms are reviewed.•Suitable examples of different complexity are provided.•The advantages of multi-way calibration are illustrated.•Multi-way ...analytical figures of merit are discussed.
An introduction to multi-way calibration based on second- and higher-order data generation and processing is provided, with emphasis on practical experimental aspects. After a discussion concerning a proper nomenclature scheme, a suitable classification of the obtainable data, and the general features of the available algorithms and their underlying models, a series of examples is discussed in detail, with the purpose of illustrating the great potentiality of the field for the analytical community. Emphasis is directed toward the most popular multi-way data, i.e., second-order or matrix data, which can be conveniently measured in a variety of instruments. Third-order data are being increasingly studied and are also discussed, along with the less explored field of fourth-order data. The estimation of figures of merit, which analysts need to report during method development, is now sufficiently mature to be provided for the general audience.
Mice are widely used as experimental models for gut microbiome (GM) studies, yet the majority of mouse GM members remain uncharacterized. Here, we report the construction of a mouse gut microbial ...biobank (mGMB) that contains 126 species, represented by 244 strains that have been deposited in the China General Microorganism Culture Collection. We sequence and phenotypically characterize 77 potential new species and propose their nomenclatures. The mGMB includes 22 and 17 species that are significantly enriched in ob/ob and wild-type C57BL/6J mouse cecal samples, respectively. The genomes of the 126 species in the mGMB cover 52% of the metagenomic nonredundant gene catalog (sequence identity ≥ 60%) and represent 93-95% of the KEGG-Orthology-annotated functions of the sampled mouse GMs. The microbial and genome data assembled in the mGMB enlarges the taxonomic characterization of mouse GMs and represents a useful resource for studies of host-microbe interactions and of GM functions associated with host health and diseases.
Gettering in silicon photovoltaics: A review Liu, AnYao; Phang, Sieu Pheng; Macdonald, Daniel
Solar energy materials and solar cells,
January 2022, 2022-01-00, 20220101, Volume:
234
Journal Article
Peer reviewed
A key efficiency-limiting factor in silicon-based photovoltaic (PV) devices is the quality of the silicon material itself. With evolving cell architectures that better address other efficiency-loss ...channels in the device, the final device efficiency becomes increasingly sensitive to the contaminants in the silicon wafer bulk. However, due to cost constraints, silicon materials for PV are inherently less pure and further contamination during device fabrication is commonly found, especially in mass production environments. Metallic impurities are ubiquitous and abundant, and they are strong efficiency-loss channels in the device if not removed. Gettering is the process of removing metallic impurities to a less harmful region of the device, and is therefore an essential aspect of the cell fabrication process. This article presents an up-to-date review of the gettering techniques and processes in silicon solar cells, providing a complete picture of the possible gettering sinks and routes in various cell architectures. The article starts by explaining the common nomenclatures in gettering and summarising recent updates to the solubility and diffusivity data of the common 3d transition metals in silicon. Then the three-step gettering process (release, diffusion, capture) is explained, and its implications for solar-grade cast-grown silicon (in terms of release) and various cell architectures (in terms of diffusion) are discussed. The main focus of the article is to summarise and review the various capture approaches in the context of silicon PV. These include phosphorus diffusion, boron diffusion, selective doping via ion implantation, state-of-the-art polycrystalline-silicon/oxide passivating contact structures, dielectric films (silicon nitride and aluminium oxide), aluminium alloying, surface damaged regions including black silicon, and internal gettering in cast-grown silicon by existing crystallographic defects. Their gettering effects, current understanding of the gettering mechanisms, modelling, improvement strategies, implementation in processing and potential impacts on cell performance are reviewed.
The article deals with some aspects of sustainable development connected with improving its management. The author'sinterpretation of this concept is given, the necessity of managing such development ...is substantiated, and the main tasks of management are formulated. Particular attention is paid to the consideration of various nomenclatures of indicators of sustainable development, including those established by international standard and tothe identification of their advantages and weaknesses.
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