Topic Review
σ-hole is a region of depleted electronic density located on the outer side of a covalently-bonded atom, situated roughly along an extension of the bond axis  
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  • 24 May 2021
Topic Review
Β-lactam Antibiotic
β-lactam antibiotics (beta-lactam antibiotics) are antibiotics that contain a beta-lactam ring in their molecular structure. This includes penicillin derivatives (penams), cephalosporins and cephamycins (cephems), monobactams, carbapenems and carbacephems. Most β-lactam antibiotics work by inhibiting cell wall biosynthesis in the bacterial organism and are the most widely used group of antibiotics. Until 2003, when measured by sales, more than half of all commercially available antibiotics in use were β-lactam compounds. The first β-lactam antibiotic discovered, penicillin, was isolated from a rare variant of Penicillium notatum (since renamed Penicillium chrysogenum). Bacteria often develop resistance to β-lactam antibiotics by synthesizing a β-lactamase, an enzyme that attacks the β-lactam ring. To overcome this resistance, β-lactam antibiotics can be given with β-lactamase inhibitors such as clavulanic acid.
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  • 24 Nov 2022
Topic Review
β-Ionone is a natural plant volatile compound, and it is the 9,10 and 9′,10′ cleavage product of β-carotene by the carotenoid cleavage dioxygenase. β-Ionone is widely distributed in flowers, fruits, and vegetables. β-Ionone and other apocarotenoids comprise flavors, aromas, pigments, growth regulators, and defense compounds; serve as ecological cues; have roles as insect attractants or repellants, and have antibacterial and fungicidal properties. In recent years, β-ionone has also received increased attention from the biomedical community for its potential as an anticancer treatment and for other human health benefits. However, β-ionone is typically produced at relatively low levels in plants. Thus, expressing plant biosynthetic pathway genes in microbial hosts and engineering the metabolic pathway/host to increase metabolite production is an appealing alternative.
  • 1.8K
  • 26 Apr 2021
Topic Review
Over 35 years ago, researchers originally reported on the anionic ring-opening polymerization (ROP) of β-butyrolactone (BBL) into poly(β-butyrolactone) (poly(BBL)), which is an amorphous, atactic analogue of isotactic poly([R]-β-hydroxybutyrate) (PHB), a promising and widely used natural biodegradable polyester. 
  • 919
  • 30 Dec 2021
Topic Review
Zwitterionics Surfactants
Zwitterions are molecules that contain both a positive and negative charge within the same molecule. They are electrically neutral as a whole, but have distinct positive and negative regions within the molecule. The most common example of a zwitterion is the amino acid molecule, which contains both a carboxyl group (-COOH) and an amino group (-NH2) within the same molecule. The carboxyl group is negatively charged at physiological pH, while the amino group is positively charged, resulting in a net charge of zero for the molecule as a whole. Zwitterions have unique properties that make them useful in various applications. They are often used as buffer solutions in biochemistry and molecular biology, as they can maintain a stable pH even when small amounts of acid or base are added. Zwitterions are also used as surfactants, due to their amphipathic nature (i.e. they have both hydrophilic and hydrophobic regions). They are used in applications such as detergents and fabric softeners, where they can help to reduce surface tension and improve the wetting and dispersibility of the product. Zwitterionic surfactants have a unique structure that allows them to interact with a wide range of substances, making them useful in various applications. The unique combination of positive and negative charges in the same molecule provides a balance that enables them to interact with both hydrophilic and hydrophobic substances, allowing them to solubilize oils and greases, emulsify water-insoluble substances, and reduce surface tension.
  • 1.9K
  • 24 Mar 2023
Topic Review
Zwitterionic Dental Biomaterials
Biofilms are formed on surfaces inside the oral cavity covered by the acquired pellicle and develop into a complex, dynamic, microbial environment. Oral biofilm is a causative factor of dental and periodontal diseases. Accordingly, novel materials that can resist biofilm formation have attracted significant attention. Zwitterionic polymers (ZPs) have unique features that resist protein adhesion and prevent biofilm formation while maintaining biocompatibility. Recent literature has reflected a rapid increase in the application of ZPs as coatings and additives with promising outcomes. 
  • 5.9K
  • 29 Dec 2020
Topic Review
ZrB2 Nanopowders Solid-State Synthesis
ZrB2 is of particular interest among ultra-high temperature ceramics because it exhibits excellent thermal resistance at high temperature, as well as chemical stability, high hardness, low cost, and good electrical and thermal conductivity, which meet the requirements of high-temperature components of hyper-sonic aircraft in extreme environments. In recent years, the development of ZrB2 powders’ synthesis method has broken through the classification of traditional solid-phase method, liquid-phase method, and gas-phase method, and there is a trend of integration of them. Solid-state synthesis, including the borothermic reduction method, carbothermic reduction method, and metallothermic reduction method, is mostly used because the process is simple and the raw materials are cheap and easily available. 
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  • 26 Oct 2021
Topic Review
Zooceuticals and Cosmetic Ingredients Derived from Animals
Many substances derived from animals are used as ingredients in the cosmetic industry and constitute a particular type of product: zooceuticals. The main ingredients used can come from insects, such as snail slime; land animals, such as lanolin; and marine animals, such as marine collagen. Today, they are used less than in the past for hygienic–sanitary, ethical, and ecological reasons. Moreover, some can give rise to irritative or allergic dermatitis. However, they still represent a fraction of the common ingredients in certain types of cosmetic products today.
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  • 07 Mar 2022
Topic Review
Zone Refining
Zone refining is a technology of deeply purifying metals. Its essence is to use the difference in solubility of impurity elements in the solid and molten state of the main metal to precipitate the impurities or change the distribution of the impurity elements. It provides an effective and easy method for preparing high-purity metals. 
  • 2.5K
  • 18 May 2021
Topic Review
ZnO Photocatalysts for the Treatment of Wastewater
The presence of contaminants in wastewater, surface water, groundwater, and drinking water is a serious threat to human and environmental health. Their toxic effects and resistance towards conventional water treatment methods have compelled the scientific community to search for an environmentally friendly method that could efficiently degrade toxic contaminants. In this regard, visible light active photocatalysts have proved to be efficient in eliminating a wide variety of water toxins. A plethora of research activities have been carried out and significant amounts of funds are spent on the monitoring and removal of water contaminants, but relatively little attention has been paid to the degradation of persistent water pollutants. In this regard, nanoparticles of doped ZnO are preferred options owing to their low recombination rate and excellent photocatalytic and antimicrobial activity under irradiation of solar light. 
  • 2.4K
  • 18 Feb 2022
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