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Topic Review
Nucleoside Analogs and Coronaviruses
Coronaviruses (CoVs) are positive-sense RNA enveloped viruses, members of the family Coronaviridae, that cause infections in a broad range of mammals including humans. Several CoV species lead to mild upper respiratory infections typically associated with common colds. However, three human CoV (HCoV) species: Severe Acute Respiratory Syndrome (SARS)-CoV-1, Middle East Respiratory Syndrome (MERS)-CoV, and SARS-CoV-2, are responsible for severe respiratory diseases at the origin of two recent epidemics (SARS and MERS), and of the current COronaVIrus Disease 19 (COVID-19), respectively.
  • 593
  • 24 May 2021
Topic Review
Nucleophilic Substitution
A nucleophilic substitution is a class of chemical reactions in which an electron-rich chemical species (known as a nucleophile) replaces a functional group within another electron-deficient molecule (known as the electrophile). The molecule that contains the electrophile and the leaving functional group is called the substrate. The most general form of the reaction may be given as the following: The electron pair (:) from the nucleophile (Nuc) attacks the substrate (R-LG) and bonds with it. Simultaneously, the leaving group (LG) departs with an electron pair. The principal product in this case is R-Nuc. The nucleophile may be electrically neutral or negatively charged, whereas the substrate is typically neutral or positively charged. An example of nucleophilic substitution is the hydrolysis of an alkyl bromide, R-Br under basic conditions, where the attacking nucleophile is OH− and the leaving group is Br−. Nucleophilic substitution reactions are common in organic chemistry (especially introductory organic chemistry). Nucleophiles often attack a saturated aliphatic carbon. Less often, they may attack an aromatic or unsaturated carbon.
  • 802
  • 26 Oct 2022
Topic Review
Nucleobase-Bearing Amino Acid Systems and Self-Assembly
Nucleobase-containing molecules are compounds essential in biology due to the fundamental role of nucleic acids and, in particular, G-quadruplex DNA and RNA in life. Moreover, some molecules different from nucleic acids isolated from different vegetal sources or microorganisms show nucleobase moieties in their structure. Nucleoamino acids and peptidyl nucleosides belong to this molecular class. Closely related to the above, nucleopeptides, also known as nucleobase-bearing peptides, are chimeric derivatives of synthetic origin and more rarely isolated from plants.
  • 337
  • 03 Jan 2024
Topic Review
Nucleic Acid Drugs Delivery Carriers
Nucleic acid drugs are not readily permeable through cell membranes and often exhibit poor blood serum stability, rapid renal clearance and poor endosomal escape/cytoplasmic escape. Therefore, they are commonly used in combination with drug delivery system (DDS) carriers. The drug carrier plays an important role in the process of drug delivery. 
  • 529
  • 04 Aug 2021
Topic Review
Nucleic Acid
Nucleic acids are the biopolymers, or small biomolecules, essential to all known forms of life. The term nucleic acid is the overall name for DNA and RNA. They are composed of nucleotides, which are the monomers made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. If the sugar is a compound ribose, the polymer is RNA (ribonucleic acid); if the sugar is derived from ribose as deoxyribose, the polymer is DNA (deoxyribonucleic acid). Nucleic acids are the most important of all biomolecules. They are found in abundance in all living things, where they function to create and encode and then store information in the nucleus of every living cell of every life-form organism on Earth. In turn, they function to transmit and express that information inside and outside the cell nucleus—to the interior operations of the cell and ultimately to the next generation of each living organism. The encoded information is contained and conveyed via the nucleic acid sequence, which provides the 'ladder-step' ordering of nucleotides within the molecules of RNA and DNA. Strings of nucleotides are bonded to form helical backbones—typically, one for RNA, two for DNA—and assembled into chains of base-pairs selected from the five primary, or canonical, nucleobases, which are: adenine, cytosine, guanine, thymine, and uracil; note, thymine occurs only in DNA and uracil only in RNA. Using amino acids and the process known as protein synthesis, the specific sequencing in DNA of these nucleobase-pairs enables storing and transmitting coded instructions as genes. In RNA, base-pair sequencing provides for manufacturing new proteins that determine the frames and parts and most chemical processes of all life forms.
  • 1.7K
  • 28 Nov 2022
Topic Review
Nucleation of Diamond
Nucleation is a key process for the growth of diamond films. Spontaneously nucleation on heterogeneous substrates is difficult. This is mainly because the high surface energy of diamond. Rapid nucleation (a few minutes commonly) is a necessary condition for the deposition of high-quality diamond films. The characteristics of the substrate, such as surface defects, surface energy, surface diffusion and bulk diffusion of atoms, and chemical reactivity, affect the diamond nucleation process. Especially, a gallium nitride (GaN) substrate, which has a large lattice mismatch and thermal expansion mismatch with diamond, puts forward some difficult requirements for diamond nucleation. The temperature of the substrate also affects the diamond nucleation process. Considering the quality and rate of diamond nucleation and the thermal stability of GaN high electron mobility transistors (HEMTs), researchers regard ~600 °C as a more suitable nucleation temperature. 
  • 660
  • 03 Apr 2023
Topic Review
Nucleation in Polymer Crystallization
Nucleation plays a vital role in polymer crystallization, in which chain connectivity and thus the multiple length and time scales make crystal nucleation of polymer chains an interesting but complex subject. Though the topic has been intensively studied in the past decades, there are still many open questions to answer. The final properties of semicrystalline polymer materials are affected by all of the following: the starting melt, paths of nucleation, organization of lamellar crystals and evolution of the final crystalline structures. In this viewpoint, we attempt to discuss some of the remaining open questions and corresponding concepts: non-equilibrated polymers, self-induced nucleation, microscopic kinetics of different processes, metastability of polymer lamellar crystals, hierarchical order and cooperativity involved in nucleation, etc. Addressing these open questions through a combination of novel concepts, new theories and advanced approaches provides a deeper understanding of the multifaceted process of crystal nucleation of polymers.
  • 1.9K
  • 25 Jun 2021
Topic Review
Nucleation and Growth of Biominerals
Biominerals are extraordinary materials that provide organisms with a variety of functions to support life. The synthesis of biominerals and organization at the macroscopic level is a consequence of the interactions of these materials with proteins. The association of biominerals and proteins is very ancient and has sparked a wealth of research across biological, medical and material sciences. Calcium carbonate, hydroxyapatite, and silica represent widespread natural biominerals. The atomic details of the interface between macromolecules and these biominerals is very intriguing from a chemical perspective, considering the association of chemical entities that are structurally different.
  • 554
  • 02 Sep 2022
Topic Review Peer Reviewed
Nuclear Waste Disposal
Nuclear waste (like radioactive waste) is waste that contains, or is contaminated with, radionuclides, at activity concentrations greater than clearance levels set by the regulators, beyond which no further use is foreseen. Disposal is the emplacement of waste in an appropriate facility without the intention to retrieve it.
  • 900
  • 03 Apr 2023
Topic Review
Nuclear Resonance Vibrational Spectroscopy
Nuclear resonant vibrational spectroscopy (NRVS) is a synchrotron radiation (SR)-based nuclear inelastic scattering spectroscopy that measures the phonons (i.e., vibrational modes) associated with the nuclear transition. It has distinct advantages over traditional vibration spectroscopy and has wide applications in physics, chemistry, bioinorganic chemistry, materials sciences, and geology, as well as many other research areas.
  • 894
  • 17 Aug 2021
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