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Polyethylenimine
Polyethylenimine (PEI) or polyaziridine is a polymer with repeating units composed of the amine group and two carbon aliphatic ''CHCH'' spacers. Linear polyethyleneimines contain all secondary amines, in contrast to branched PEIs which contain primary, secondary and tertiary amino groups. Totally branched, dendrimeric forms were also reported. PEI is produced on an industrial scale and finds many applications usually derived from its polycationic character. Properties The linear PEI is a semi-crystalline solid at room temperature while branched PEI is a fully amorphous polymer existing as a liquid at all molecular weights. Linear polyethyleneimine is soluble in hot water, at low pH, in methanol, ethanol, or chloroform. It is insoluble in cold water, benzene, ethyl ether, and acetone. Linear polyethyleneimine has a melting point of around 67 °C. Both linear and branched polyethyleneimine can be stored at room temperature. Linear polyethyleneimine is able to form cryogels up ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aziridine
Aziridine is an organic compound consisting of the three-membered heterocycle . It is a colorless, toxic, volatile liquid that is of significant practical interest. Aziridine was discovered in 1888 by the chemist Siegmund Gabriel. Its derivatives, also referred to as aziridines, are of broader interest in medicinal chemistry. Structure The bond angles in aziridine are approximately 60°, considerably less than the normal hydrocarbon bond angle of 109.5°, which results in angle strain as in the comparable cyclopropane and ethylene oxide molecules. A banana bond model explains bonding in such compounds. Aziridine is less basic than acyclic aliphatic amines, with a pKa of 7.9 for the conjugate acid, due to increased s character of the nitrogen free electron pair. Angle strain in aziridine also increases the barrier to nitrogen inversion. This barrier height permits the isolation of separate ''invertomers'', for example the ''cis'' and ''trans'' invertomers of ''N''-chloro- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Repeat Unit
In polymer chemistry, a repeat unit or repeating unit (or mer) is a part of a polymer whose repetition would produce the complete polymer chain (except for the end-groups) by linking the repeat units together successively along the chain, like the beads of a necklace. A repeat unit is sometimes called a mer (or mer unit). "Mer" originates from the Greek word ''meros'', which means "a part". The word polymer derives its meaning from this, which means "many mers". A repeat unit (mer) is not to be confused with the term monomer, which refers to the small molecule from which a polymer is synthesized.Callister, William D. (2007). ''Materials science and engineering : an introduction'' (7th ed.) New York : John Wiley & Sons. One of the simplest repeat units is that of the addition polymer polyvinyl chloride, - H2-CHClsub>n-, whose repeat unit is - H2-CHCl. In this case the repeat unit has the same atoms as the monomer vinyl chloride CH2=CHCl. When the polymer is formed, the C=C ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polyelectrolytes
Polyelectrolytes are polymers whose repeating units bear an electrolyte group. Polycations and polyanions are polyelectrolytes. These groups dissociate in aqueous solutions (water), making the polymers charged. Polyelectrolyte properties are thus similar to both electrolytes (salts) and polymers (high molecular weight compounds) and are sometimes called polysalts. Like salts, their solutions are electrically conductive. Like polymers, their solutions are often viscous. Charged molecular chains, commonly present in soft matter systems, play a fundamental role in determining structure, stability and the interactions of various molecular assemblies. Theoretical approaches to describing their statistical properties differ profoundly from those of their electrically neutral counterparts, while technological and industrial fields exploit their unique properties. Many biological molecules are polyelectrolytes. For instance, polypeptides, glycosaminoglycans, and DNA are polyelectrolyte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polyetherimide
Polyetherimide (PEI) is an amorphous, amber-to-transparent thermoplastic with characteristics similar to the related plastic PEEK. When comparing PEI to PEEK, the former is cheaper but has lower impact strength and a tighter temperature range. Due to its adhesive properties and chemical stability it became a popular bed material for FFF 3D printers. Structure The molecular formula of the PEI monomer is and the molecular weight is 592.61 g/mol. It contains phthalimide and bisphenol A sub-units. Properties The glass transition temperature of PEI is 217 °C (422 °F). Its amorphous density at 25 °C is 1.27 g/cm3(.046 lb/in³). It is prone to stress cracking in chlorinated solvent An organochloride, organochlorine compound, chlorocarbon, or chlorinated hydrocarbon is an organic compound containing at least one covalently bonded atom of chlorine. The chloroalkane class ( alkanes with one or more hydrogens substituted by chlo ...s. Polyetherimide i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ethylenediamine
Ethylenediamine (abbreviated as en when a ligand) is the organic compound with the formula C2H4(NH2)2. This colorless liquid with an ammonia-like odor is a basic amine. It is a widely used building block in chemical synthesis, with approximately 500,000 tonnes produced in 1998.Karsten Eller, Erhard Henkes, Roland Rossbacher, Hartmut Höke "Amines, Aliphatic" in Ullmann's Encyclopedia of Industrial Chemistry, 2005 Wiley-VCH Verlag, Weinheim. Ethylenediamine is the first member of the so-called polyethylene amines. Synthesis Ethylenediamine is produced industrially by treating 1,2-dichloroethane with ammonia under pressure at 180 °C in an aqueous medium:Hans-Jürgen Arpe, Industrielle Organische Chemie, 6. Auflage (2007), Seite 245, Wiley VCH : In this reaction hydrogen chloride is generated, which forms a salt with the amine. The amine is liberated by addition of sodium hydroxide and can then be recovered by . Diethylenetriamine (DETA) and triethylenetetramine (TETA) a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tetraethylenepentamine
Tetraethylenepentamine (TEPA) is an organic compound and is in the class of chemicals known as ethyleneamines. It is a slightly viscous liquid and is not colorless but, like many amines, has a yellow color. It is soluble in most polar solvents. Diethylenetriamine (DETA), triethylenetetramine (TETA), piperazine, and aminoethylpiperazine are also usually present in commercial available TEPA. Uses The reactivity and uses of TEPA are similar to those for the related ethylene amines ethylenediamine and diethylenetriamine and triethylenetetramine. It is primarily used as a curing agent or hardener in epoxy chemistry. This can be on its own or reacted with tall oil fatty acid (TOFA) and its dimer to make an amidoamine. This amidoamine is then used as the curing agent for epoxy resin systems. TEPA is a pentadentate ligand in coordination chemistry A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gram-negative Bacteria
Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall sandwiched between an inner cytoplasmic cell membrane and a bacterial outer membrane. Gram-negative bacteria are found in virtually all environments on Earth that support life. The gram-negative bacteria include the model organism ''Escherichia coli'', as well as many pathogenic bacteria, such as ''Pseudomonas aeruginosa'', '' Chlamydia trachomatis'', and ''Yersinia pestis''. They are a significant medical challenge as their outer membrane protects them from many antibiotics (including penicillin), detergents that would normally damage the inner cell membrane, and lysozyme, an antimicrobial enzyme produced by animals that forms part of the innate immune system. Additionally, the outer leaflet of this membrane comprises a complex lipopol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Endocytosis
Endocytosis is a cellular process in which substances are brought into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material. Endocytosis includes pinocytosis (cell drinking) and phagocytosis (cell eating). It is a form of active transport. History The term was proposed by De Duve in 1963. Phagocytosis was discovered by Élie Metchnikoff in 1882. Pathways Endocytosis pathways can be subdivided into four categories: namely, receptor-mediated endocytosis (also known as clathrin-mediated endocytosis), caveolae, pinocytosis, and phagocytosis Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is .... *Clathrin-mediated endocytosis is mediated by the production of smal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tissue Culture
Tissue culture is the growth of tissues or cells in an artificial medium separate from the parent organism. This technique is also called micropropagation. This is typically facilitated via use of a liquid, semi-solid, or solid growth medium, such as broth or agar. Tissue culture commonly refers to the culture of animal cells and tissues, with the more specific term plant tissue culture being used for plants. The term "tissue culture" was coined by American pathologist Montrose Thomas Burrows. Historical use In 1885 Wilhelm Roux removed a section of the medullary plate of an embryonic chicken and maintained it in a warm saline solution for several days, establishing the basic principle of tissue culture. In 1907 the zoologist Ross Granville Harrison demonstrated the growth of frog embryonic cells that would give rise to nerve cells in a medium of clotted lymph. In 1913, E. Steinhardt, C. Israeli, and R. A. Lambert grew vaccinia virus in fragments of guinea pig corneal tiss ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Papermaking
Papermaking is the manufacture of paper and cardboard, which are used widely for printing, writing, and packaging, among many other purposes. Today almost all paper is made using industrial machinery, while handmade paper survives as a specialized craft and a medium for artistic expression. In papermaking, a dilute suspension consisting mostly of separate cellulose fibres in water is drained through a sieve-like screen, so that a mat of randomly interwoven fibres is laid down. Water is further removed from this sheet by pressing, sometimes aided by suction or vacuum, or heating. Once dry, a generally flat, uniform and strong sheet of paper is achieved. Before the invention and current widespread adoption of automated machinery, all paper was made by hand, formed or laid one sheet at a time by specialized laborers. Even today those who make paper by hand use tools and technologies quite similar to those existing hundreds of years ago, as originally developed in China and other ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ring Opening Polymerization
In polymer chemistry, ring-opening polymerization (ROP) is a form of chain-growth polymerization, in which the terminus of a polymer chain attacks cyclic monomers to form a longer polymer (see figure). The reactive center can be radical, anionic or cationic. Some cyclic monomers such as norbornene or cyclooctadiene can be polymerized to high molecular weight polymers by using metal catalysts. ROP is a versatile method for the synthesis of biopolymers. Ring-opening of cyclic monomers is often driven by the relief of bond-angle strain. Thus, as is the case for other types of polymerization, the enthalpy change in ring-opening is negative. Monomers Cyclic monomers that are amenable to ROP include epoxides, cyclic trisiloxanes, some lactones, lactides, cyclic carbonates, and amino acid N-carboxyanhydrides. Many strained cycloalkenes, e.g norbornene, are suitable monomers via ring-opening metathesis polymerization. History Ring-opening polymerization has been used since th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amine
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group (these may respectively be called alkylamines and arylamines; amines in which both types of substituent are attached to one nitrogen atom may be called alkylarylamines). Important amines include amino acids, biogenic amines, trimethylamine, and aniline; Inorganic derivatives of ammonia are also called amines, such as monochloramine (). The substituent is called an amino group. Compounds with a nitrogen atom attached to a carbonyl group, thus having the structure , are called amides and have different chemical properties from amines. Classification of amines Amines can be classified according to the nature and number of substituents on nitrogen. Aliphatic amines contain only H and alkyl substituents. A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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