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Topic Review
Electronic Circular Dichroism
This entry provides an introduction to the basic concepts of Electronic Circular Dichroism (ECD) spectroscopy. It describes the fundamental principles, instrumentation, and different approaches for interpreting and predicting ECD spectra. It surveys the most popular modern applications of ECD for the structural analysis of organic compounds.
  • 32.7K
  • 24 May 2022
Topic Review
Structure and Chemistry of 3(5)-Substituted Pyrazoles
Pyrazoles are known as versatile scaffolds in organic synthesis and medicinal chemistry, often used as starting materials for the preparation of more complex heterocyclic systems with relevance in the pharmaceutical field. Pyrazoles are also interesting compounds from a structural viewpoint, mainly because they exhibit tautomerism. This phenomenon may influence their reactivity, with possible impact on the synthetic strategies where pyrazoles take part, as well as on the biological activities of targets bearing a pyrazole moiety, since a change in structure translates into changes in properties. Investigations of the structure of pyrazoles that unravel the tautomeric and conformational preferences are therefore of upmost relevance. 3(5)-Aminopyrazoles are largely explored as precursors in the synthesis of condensed heterocyclic systems, namely pyrazolo[1,5-a]pyrimidines.
  • 18.4K
  • 04 Jul 2022
Topic Review
Methanol Mitigation during Fruit-Spirits Manufacturing
Methanol is a natural ingredient with major occurrence in fruit spirits, such as apple, pear, plum or cherry spirits, but also in spirits made from coffee pulp. The compound is formed during fermentation and the following mash storage by enzymatic hydrolysis of naturally present pectins. Methanol is toxic above certain threshold levels and legal limits have been set in most jurisdictions. Therefore, the methanol content needs to be mitigated and its level must be controlled. This article will review the several factors that influence the methanol content including the pH value of the mash, the addition of various yeast and enzyme preparations, fermentation temperature, mash storage, and most importantly the raw material quality and hygiene
  • 14.6K
  • 10 May 2021
Topic Review
Direct Amidations of Carboxylic Acids with Amines
The prevalence of amides in biological systems and chemical fields such as polymers, materials and natural products drives continuous research on novel procedures to obtain these ubiquitous functional groups. Efforts to this purpose are mainly focused around the discovery of direct and catalytic methods that are more atom economic, safe and practical for diversified applications (e.g., organic, medicinal and peptide chemistries, material and polymer purposes, etc.), in accordance with green chemistry principles. 
  • 11.3K
  • 22 Feb 2023
Topic Review
Synthesis and Properties of Pyrazoles
Pyrazole derivatives are a special class of N-heterocyclic compounds (NHCps) bearing a heteroaromatic five-membered ring with two adjacent nitrogen atoms in the annular structure, one pyrrole-type (proton donor) and one pyridine-type (proton acceptor). Pyrazoles can act as weak bases or acids, with possible strength highly dependent on the nature of their substituent groups. The other three positions in the ring permit structural variants starting from the appropriate precursors or using post-functionalization reactions once the pyrazole ring is formed; these variations give the pyrazoles diverse and valuable synthetical, biological, and photophysical properties; indeed, more complex structures with various relevant examples can be formed from them.
  • 10.8K
  • 09 Sep 2022
Topic Review
Ascorbic Acid-Mediated Reactions
Ascorbic acid is a vitamin found in different types of food. It has tremendous medical applications in several different fields such as in pharmaceuticals, cosmetics, and in organic synthesis. 
  • 8.6K
  • 25 Nov 2020
Topic Review
Classical Nucleation Theory
Crystal nucleation determining the formation and assembly pathway of first organic materials is the central science of various scientific disciplines such as chemical, geochemical, biological, and synthetic materials. Classical nucleation theory (CNT)  applies to systems of small organic molecules with an emphasis on the molecular interpretation of nucleation kinetics. CNT holds that density fluctuations are concomitant with the development of crystalline order. In other words, a crystal nucleus has an identical structure to its bulk crystal. 
  • 8.2K
  • 22 Jul 2022
Topic Review
MOFs and COFs
Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are two innovative classes of porous coordination polymers. MOFs are three-dimensional materials made up of secondary building blocks comprised of metal ions/clusters and organic ligands whereas COFs are 2D or 3D highly porous organic solids made up by light elements (i.e., H, B, C, N, O). Both MOFs and COFs, being highly conjugated scaffolds, are very promising as photoactive materials for applications in photocatalysis and artificial photosynthesis because of their tunable electronic properties, high surface area, remarkable light and thermal stability, easy and relative low-cost synthesis, and structural versatility. 
  • 7.1K
  • 08 Dec 2020
Topic Review
Tropylium Ion
The tropylium ion is a non-benzenoid aromatic species that works as a catalyst. This chemical entity brings about a large number of organic transformations, such as hydroboration reactions, ring contraction, the trapping of enolates, oxidative functionalization, metathesis, insertion, acetalization, and trans-acetalization reactions. The tropylium ion also functions as a coupling reagent in synthetic reactions. This cation’s versatility can be seen in its role in the synthesis of macrocyclic compounds and cage structures.
  • 7.1K
  • 01 Jun 2023
Topic Review
Indane-1,3-Dione: From Synthetic Strategies to Applications
Indane-1,3-dione is a versatile building block used in numerous applications ranging from biosensing, bioactivity, bioimaging to electronics or photopolymerization. Indane-1-3-dione is among one of the most privileged scaffolds in chemistry, as the derivatives of this structure can find applications in various research fields ranging from medicinal chemistry, organic electronics, photopolymerization, to optical sensing and non-linear optical (NLO) applications. 
  • 6.9K
  • 29 Sep 2022
Topic Review
Thiazoles and Bisthiazoles
Thiazole, a five-membered heteroaromatic ring, is an important scaffold of a large number of synthetic compounds. Its diverse pharmacological activity is reflected in many clinically approved thiazole-containing molecules, with an extensive range of biological activities, such as antibacterial, antifungal, antiviral, antiparasitic, antitumor, antiparkinsonian, and anti-inflammatory effects.
  • 6.9K
  • 29 Mar 2021
Topic Review
Synthesis of Fragrances via Cycloaddition or Formal Cycloaddition
Fragrances, short for fragrance ingredients, is a type of compounds with a sweet smell or pleasant odor that has wide applications in the fine chemical industry, especially in perfumes, cosmetics, detergents and food additives. Since the discovery of the Diels–Alder reaction, the cycloaddition of π reactants serves as one of the most powerful methods for the construction of carbocycles, which has a broad application in the fragrance industry.
  • 6.4K
  • 21 Jun 2022
Topic Review
Michael Addition of Carbonyl Compounds to α,β-Unsaturated Nitroalkenes
The proline-catalyzed asymmetric Michael addition reaction of acetaldehyde with α,β-unsaturated nitroalkenes as synthetically useful routes to β-substituted derivatives of γ-Aminobutyric acid (GABA).
  • 5.8K
  • 01 Jul 2022
Topic Review
Metabolic N-Dealkylation and N-Oxidation
Metabolic reactions that occur at alkylamino moieties may provide insight into the roles of these moieties when they are parts of drug molecules that act at different receptors. N-dealkylation of N,N-dialkylamino moieties has been associated with retaining, attenuation or loss of pharmacologic activities of metabolites compared to their parent drugs. Further, N-dealkylation has resulted in clinically used drugs, activation of prodrugs, change of receptor selectivity, and providing potential for developing fully-fledged drugs.
  • 5.7K
  • 13 Apr 2021
Topic Review
Beta-Carotene
β-Carotene is an organic, strongly coloured red-orange pigment abundant in fungi, plants, and fruits. It is a member of the carotenes, which are terpenoids (isoprenoids), synthesized biochemically from eight isoprene units and thus having 40 carbons. Among the carotenes, β-carotene is distinguished by having beta-rings at both ends of the molecule. β-Carotene is biosynthesized from geranylgeranyl pyrophosphate. In some Mucoralean fungi, β-Carotene is a precursor to the synthesis of trisporic acid. β-Carotene is the most common form of carotene in plants. When used as a food coloring, it has the E number E160a.:119 The structure was deduced by Karrer et al. in 1930. In nature, β-carotene is a precursor (inactive form) to vitamin A via the action of beta-carotene 15,15'-monooxygenase. Isolation of β-carotene from fruits abundant in carotenoids is commonly done using column chromatography. It can also be extracted from the beta-carotene rich algae, Dunaliella salina. The separation of β-carotene from the mixture of other carotenoids is based on the polarity of a compound. β-Carotene is a non-polar compound, so it is separated with a non-polar solvent such as hexane. Being highly conjugated, it is deeply colored, and as a hydrocarbon lacking functional groups, it is very lipophilic.
  • 5.6K
  • 16 Nov 2022
Topic Review
Covalent Adaptable Networks
Thermosets are known to be very reliable polymeric materials for high-performance and light-weight applications, due to their retained dimensional stability, chemical inertia and rigidity over a broad range of temperatures. However, once fully cured, they cannot be easily reshaped or reprocessed, thus leaving still unsolved the issues of recycling and the lack of technological flexibility. Vitrimers, introduced by Leibler et al. in 2011, are a valiant step in the direction of bridging the chasm between thermoplastics and thermosets. Owing to their dynamic covalent networks, they can retain mechanical stability and solvent resistance, but can also flow on demand upon heating. More generally, the family of Covalent Adaptable Networks (CANs) is gleaming with astounding potential, thanks to the huge variety of chemistries that may enable bond exchange. Arising from this signature feature, intriguing properties such as self-healing, recyclability and weldability may expand the horizons for thermosets in terms of improved life-span, sustainability and overall enhanced functionality and versatility. In this review, we present a comprehensive overview of the most promising studies featuring CANs and vitrimers specifically, with particular regard for their industrial applications. Investigations into composites and sustainable vitrimers from epoxy-based and elastomeric networks are covered in detail.
  • 5.2K
  • 26 Oct 2020
Topic Review
Paan
Paan (from Sanskrit: पर्ण, romanized: parṇá, lit. leaf, cognate with English fern) is a preparation combining betel leaf with areca nut widely consumed throughout South Asia and East Asia (mainly Taiwan). It is chewed for its stimulant effects. After chewing, it is either spat out or swallowed. Paan has many variations. Slaked lime (chuna) paste is commonly added to bind the leaves. Some preparations in the Indian subcontinent include katha paste or mukhwas to freshen the breath. Magahi paan is an expensive variety of betel which is grown in Aurangabad, Gaya and Nalanda districts of central Bihar. It is non-fibrous, sweeter, tastier and the softest of the lot. The origin and diffusion of betel chewing originates from and is closely tied to the Neolithic expansion of the Austronesian peoples. It was spread to the Indo-Pacific during prehistoric times, reaching Near Oceania at 3,400 to 3,000 BP; South India and Sri Lanka by 3,500 BP; Mainland Southeast Asia by 3,000 to 2,500 BP; Northern India by 1500 BP; and Madagascar by 600 BP. From India, it was also spread westwards to Persia and the Mediterranean. Paan (under a variety of names) is also consumed in many other Asian countries and elsewhere in the world by some Asian emigrants, with or without tobacco. It can be an addictive and stimulating formulation with adverse health effects, both with and without tobacco. The spit from chewing betel nuts, known as "buai pekpek" in Papua New Guinea, is often considered an eyesore. Because of this, many places have banned selling and chewing "buai".
  • 5.2K
  • 30 Sep 2022
Topic Review
Principles of the Suzuki Coupling Reaction
The Suzuki coupling is a transition metal-catalyzed, cross-coupling carbon–carbon (C–C) bond forming reaction between organic boron compounds and organic halides. As an operationally simple and versatilely applicable procedure, the Suzuki coupling reaction has found immense applications in drug discovery and development in the pharmaceutical industry. 
  • 5.1K
  • 06 Jan 2023
Topic Review
Heteroaromatic Diazirines in Material and Medicinal Chemistry
In materials (polymer) science and medicinal chemistry, heteroaromatic derivatives play the role of the central skeleton in development of novel devices and discovery of new drugs. On the other hand, (3-trifluoromethyl)phenyldiazirine (TPD) is a crucial chemical method for understanding biological processes such as ligand–receptor, nucleic acid–protein, lipid–protein, and protein–protein interactions. In particular, use of TPD has increased in materials science to create novel electric and polymer devices with comparative ease and reduced costs. Therefore, a combination of heteroaromatics and (3-trifluoromethyl)diazirine is a promising option for creating better materials and elucidating the unknown mechanisms of action of bioactive heteroaromatic compounds.
  • 5.0K
  • 15 Feb 2023
Topic Review
Dipole Moment
Synthesis, biological activity and structure-activity relationships of diverse compounds are described. The relationships between dipole moment and biological activities are discussed. Despite the progress of interdisciplinary science, the use of dipole moment values of organic compounds to understand their potent medicinal activities in various diseases remains unexplored.
  • 5.0K
  • 25 Nov 2020
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