|
Cucurbituril
In host–guest chemistry, cucurbiturils are macrocyclic molecules made of glycoluril () monomers linked by methylene bridges (). The oxygen atoms are located along the edges of the band and are tilted inwards, forming a partly enclosed cavity ( cavitand). The name is derived from the resemblance of this molecule with a pumpkin of the family of Cucurbitaceae. Cucurbiturils are commonly written as cucurbit 'n''ril, where ''n'' is the number of glycoluril units. Two common abbreviations are CB 'n'''', or simply CB''n''. These compounds are particularly interesting to chemists because they are suitable hosts for an array of neutral and cationic species. The binding mode is thought to occur through hydrophobic interactions, and, in the case of cationic guests, through cation-dipole interactions as well. The dimensions of cucurbiturils are generally on the ~10 Å size scale. For instance, the cavity of cucurbit ril has a height ~9.1 Å, an outer diameter ~5.8 Å, and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Models Of Cucurbiturils
A model is an informative representation of an object, person, or system. The term originally denoted the plans of a building in late 16th-century English, and derived via French and Italian ultimately from Latin , . Models can be divided into physical models (e.g. a ship model or a fashion model) and abstract models (e.g. a set of mathematical equations describing the workings of the atmosphere for the purpose of weather forecasting). Abstract or conceptual models are central to philosophy of science. In scholarly research and applied science, a model should not be confused with a theory: while a model seeks only to represent reality with the purpose of better understanding or predicting the world, a theory is more ambitious in that it claims to be an explanation of reality. Types of model ''Model'' in specific contexts As a noun, ''model'' has specific meanings in certain fields, derived from its original meaning of "structural design or layout": * Model (art), a person ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Calixarene
A calixarene is a macrocycle or cyclic oligomer based on a methylene-linked phenols. With hydrophobic cavities that can hold smaller molecules or ions, calixarenes belong to the class of cavitands known in host–guest chemistry. Nomenclature Calixarene nomenclature is straightforward and involves counting the number of repeating units in the ring and including it in the name. A calix rene has 4 units in the ring and a calix rene has 6. A substituent in the meso position Rb is added to the name with a prefix C- as in C-methylcalix rene The word calixarene is derived from the Greek calix or chalice because this type of molecule resembles a vase (or cup) and from the word arene that refers to the aromatic building block. Synthesis Calixarenes are generally produced by condensation of two components: an electron-rich aromatic compound, classically a 4-substituted phenol, and an aldehyde, classically formaldehyde. *The scope for the aromatic component is broad diverse. The ke ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cucurbituril Gyroscope AngewChemIntEd 2002 V41 P275 Hires
In host–guest chemistry, cucurbiturils are macrocyclic molecules made of glycoluril () monomers linked by methylene bridges (). The oxygen atoms are located along the edges of the band and are tilted inwards, forming a partly enclosed cavity ( cavitand). The name is derived from the resemblance of this molecule with a pumpkin of the family of Cucurbitaceae. Cucurbiturils are commonly written as cucurbit 'n''ril, where ''n'' is the number of glycoluril units. Two common abbreviations are CB 'n'''', or simply CB''n''. These compounds are particularly interesting to chemists because they are suitable hosts for an array of neutral and cationic species. The binding mode is thought to occur through hydrophobic interactions, and, in the case of cationic guests, through cation-dipole interactions as well. The dimensions of cucurbiturils are generally on the ~10 Å size scale. For instance, the cavity of cucurbit ril has a height ~9.1 Å, an outer diameter ~5.8 Å, and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrogen Bond
In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently bonded to a more Electronegativity, electronegative donor atom or group (Dn), interacts with another electronegative atom bearing a lone pair of electrons—the hydrogen bond acceptor (Ac). Unlike simple Dipole–dipole attraction, dipole–dipole interactions, hydrogen bonding arises from charge transfer (nB → σ*AH), Atomic orbital, orbital interactions, and quantum mechanical Delocalized electron, delocalization, making it a resonance-assisted interaction rather than a mere electrostatic attraction. The general notation for hydrogen bonding is Dn−H···Ac, where the solid line represents a polar covalent bond, and the dotted or dashed line indicates the hydrogen bond. The most frequent donor and acceptor atoms are nitrogen (N), oxyg ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strain (chemistry)
In chemistry, a molecule experiences strain when its chemical structure undergoes some Stress (mechanics), stress which raises its internal energy in comparison to a strain-free reference Chemical compound, compound. The internal energy of a molecule consists of all the energy stored within it. A strained molecule has an additional amount of internal energy which an unstrained molecule does not. This extra internal energy, or strain energy, can be likened to a compression (physics), compressed spring (device), spring.Anslyn and Dougherty, ''Modern Physical Organic Chemistry'', University Science Books, 2006, Much like a compressed spring must be held in place to prevent release of its potential energy, a molecule can be held in an energetically unfavorable conformation by the Chemical bond, bonds within that molecule. Without the bonds holding the conformation in place, the strain energy would be released. Summary Thermodynamics The Chemical equilibrium, equilibrium of two c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Step-growth Polymerization
In polymer chemistry, step-growth polymerization refers to a type of polymerization mechanism in which bi-functional or multifunctional monomers react to form first dimers, then trimers, longer oligomers and eventually long chain polymers. Many naturally-occurring and some synthetic polymers are produced by step-growth polymerization, e.g. polyesters, polyamides, polyurethanes, etc. Due to the nature of the polymerization mechanism, a high extent of reaction is required to achieve high molecular weight. The easiest way to visualize the mechanism of a step-growth polymerization is a group of people reaching out to hold their hands to form a human chain—each person has two hands (= reactive sites). There also is the possibility to have more than two reactive sites on a monomer: In this case branched polymers production take place. IUPAC has deprecated the term ''step-growth polymerization'', and recommends use of the terms polyaddition (when the propagation steps are addition ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hexamer
In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomer, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relative molecular mass, the structure of which essentially comprises a small plurality of units derived, actually or conceptually, from molecules of lower relative molecular mass.'' The name is composed of Greek language, Greek elements ''wikt:oligo-, oligo-'', "a few" and ''wikt:-mer, -mer'', "parts". An adjective form is ''oligomeric''. The oligomer concept is contrasted to that of a polymer, which is usually understood to have a large number of units, possibly thousands or millions. However, there is no sharp distinction between these two concepts. One proposed criterion is whether the molecule's properties vary significantly with the removal of one or a few of the units. An oligomer with a specific number of units is referred t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Condensation Reaction
In organic chemistry, a condensation reaction is a type of chemical reaction in which two molecules are combined to form a single molecule, usually with the loss of a small molecule such as water. If water is lost, the reaction is also known as a dehydration synthesis. However other molecules can also be lost, such as ammonia, ethanol, acetic acid and hydrogen sulfide. The addition of the two molecules typically proceeds in a step-wise fashion to the addition product, usually in equilibrium, and with loss of a water molecule (hence the name condensation). The reaction may otherwise involve the functional groups of the molecule, and is a versatile class of reactions that can occur in acidic or basic conditions or in the presence of a catalyst. This class of reactions is a vital part of life as it is essential to the formation of peptide bonds between amino acids and to the biosynthesis of fatty acids. Many variations of condensation reactions exist. Common examples include ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleophilic Addition
In organic chemistry, a nucleophilic addition (AN) reaction is an addition reaction where a chemical compound with an electrophilic double or triple bond reacts with a nucleophile, such that the double or triple bond is broken. Nucleophilic additions differ from electrophilic additions in that the former reactions involve the group to which atoms are added accepting electron pairs, whereas the latter reactions involve the group donating electron pairs. Addition to carbon–heteroatom double bonds Nucleophilic addition reactions of nucleophiles with electrophilic double or triple bond (π bonds) create a new carbon center with two additional single, or σ, bonds.March Jerry; (1985). Advanced Organic Chemistry reactions, mechanisms and structure (3rd ed.). New York: John Wiley & Sons, inc. Addition of a nucleophile to carbon–heteroatom double or triple bonds such as >C=O or -C≡N show great variety. These types of bonds are polar (have a large difference in electronegativit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glyoxal
Glyoxal is an organic compound with the chemical formula OCHCHO. It is the smallest dialdehyde (a compound with two aldehyde groups). It is a crystalline solid, white at low temperatures and yellow near the melting point (15 °C). The liquid is yellow, and the vapor is green.O'Neil, M.J. (2001): ''The Merck Index'', 13th Edition, page 803. Pure glyoxal is not commonly encountered because glyoxal is usually handled as a 40% aqueous solution (density near 1.24 g/mL). It forms a series of hydrates, including oligomers. For many purposes, these hydrated oligomers behave equivalently to glyoxal. Glyoxal is produced industrially as a precursor to many products. Production Glyoxal was first prepared and named by the German-British chemist Heinrich Debus (chemist), Heinrich Debus (1824–1915) by reacting ethanol with nitric acid. Commercial glyoxal is prepared either by the gas-phase oxidation of ethylene glycol in the presence of a silver or copper catalyst (the Laporte process) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dialdehyde
In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl group. Aldehydes are a common motif in many chemicals important in technology and biology. Structure and bonding Aldehyde molecules have a central carbon atom that is connected by a double bond to oxygen, a single bond to hydrogen and another single bond to a third substituent, which is carbon or, in the case of formaldehyde, hydrogen. The central carbon is often described as being sp2- hybridized. The aldehyde group is somewhat polar. The bond length is about 120–122 picometers. Physical properties and characterization Aldehydes have properties that are diverse and that depend on the remainder of the molecule. Smaller aldehydes such as formaldehyde and acetaldehyde are soluble ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Urea
Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important role in the cellular metabolism of nitrogen-containing compounds by animals and is the main nitrogen-containing substance in the urine of mammals. ''Urea'' is Neo-Latin, , , itself from Proto-Indo-European ''*h₂worsom''. It is a colorless, odorless solid, highly soluble in water, and practically non-toxic ( is 15 g/kg for rats). Dissolved in water, it is neither acidic nor base (chemistry), alkaline. The body uses it in many processes, most notably metabolic waste#Nitrogen wastes, nitrogen excretion. The liver forms it by combining two ammonia molecules () with a carbon dioxide () molecule in the urea cycle. Urea is widely used in fertilizers as a source of nitrogen (N) and is an important ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
