Clipping reaction

The clipping reaction used in [52, 53, 55] to synthesize tetralactam-based squaraine rotaxanes such as 14 and 15 afforded only moderate yields (ca. 28-35%) of the rotaxanes, possibly because of the unavoidable presence of nucleophiles that react with the chemically unstable squaraines during the reaction. The slippage approach [62] minimizes the squaraine dye s contact with nucleophiles during the rotaxane formation process and therefore can be used to efficiently encapsulate a squaraine dye such as 23 in a macrocycle such as 25 [63],... 

Higher adducts of Cjq can also be synthesized regiospecifically using this tether approach. For example, a clipping reaction sequence leads to the tetrakisadduct 87 with an all-ds-2 addition pahern along an equatorial belt (Scheme 10.18) [29]. 

Even tris- and tetrakis-adducts of C6o were accessible in a regioselective way by sequential tether-directed macrocyclization steps. A clipping reaction starting from mono-adduct 40 with two tether-linked malonate residues thus yielded tris-adduct ( )-41 (Scheme 1.5).125 Under the assumption that both m-xylylene tethers enforce the expected cis-2 addition, the C2-symmetry of... 

A template-directed synthesis of [2]-rotaxanes, with a yield in one case of 72%, has been reported. The experiments employed dumb-bell-shaped components incorporating terminal triisopropylsilyl stoppers connected to a central 1,5-dioxynaph-thalene recognition site by [-CH2CH20-] spacers (n = 1-3). - These components were used as templates for the synthesis ( clipping reaction ) of the corresponding rotaxanes incorporating cyclobis(paraquat-p-phenylene) as the ring component. The... 

This method has been applied in other studies to obtain a bistable fullerene-rotaxane, where the CBPQT + macrocycle was able to switch from two different electron-rich stations, a 1,5-dihy-droxynaphthalene (DNP), and a TTF. The macrocycle closes at the TTF station after the clipping reaction with p-xylylene dibromide, because the TTF template unit is more electron-rich than DNP. The further oxidation of TTF to the cation caused an electrostatic repulsion between the station and the positively charged macrocycle that switches to the other electron-rich DNP station (Figure 2.19). 

The alternative approach is to use the computational equivalent of a chemical reaction, or reaction transform. Here, one does not need to define a common template or to generate sets of clipped reagents. Rather, the library can be enumerated using as input the initial reagent structures and the chemical transforms required to operate upon them. In this... 

Alkyl radicals, R, react very rapidly with O2 to form alkylperoxy radicals. H reacts to form the hydroperoxy radical HO2. Alkoxy radicals, RO, react with O2 to form HO2 and R CHO, where R contains one less carbon. This formation of an aldehyde from an alkoxy radical ultimately leads to the process of hydrocarbon chain shortening or clipping upon subsequent reaction of the aldehyde. This aldehyde can undergo photodecomposition forming R, H, and CO or, after OH attack, forming CH(0)00, the peroxyacyi radical. 

Video clips include many of the reactions described in the book. 

One attraction of MD simulation is the possibility of computer animation. The mobility of ions inside a charged cylindrical pore can be visualized. Some movie clips of EMD and NEMD are downloadable at http //chem.hku.hk/ kyc/movies/. mpg. Some features that escape statistical averages can be learned in watching the animation. While the coions are present mainly in the center of the pore, occasional collisions with the wall do occur, as observed in the movie. The time scale of a coion staying near the wall is of the order of 1 ps, compared to 10 ps for the counterion. While the averaged equilibrium distributions indicate an infinitesimal concentration of coion at the wall, reaction of coion with the wall can occur within a time scale of 1 ps. From the video, it can also be observed that the radial mobility of the counterion is more significant compared to the coion s and compared to the axial mobility. It is consistent with the statistical results. 

Excretion of hydrogen sulfide was documented after dermal exposure in rabbits. Trunk fiir of rabbits was clipped and left intact or abraded for exposure to hydrogen sulfide gas (unknown concentrations) for 1.5-2 hours the animals then breathed clean air (Laug and Draize 1942). Evidence for the excretion of hydrogen sulfide by the rabbits was a sulfide reaction of the expired air with lead acetate paper (Laug and Draize 1942). Sulfides in the expired air were noted in one rabbit with intact skin after 7 minutes of exposure. This study was limited by the lack of measurement of exposure concentrations and the small number of animals used. 

FIGURE 18-7 Processing of the proopiomelanocortin (POMC) precursor proceeds in an ordered, stepwise fashion. Cleavage of the POMC precursor occurs at seven sites, with some of the reactions being tissue-specific. The circled numbers indicate the temporal order of cleavage in tissues where these proteolytic events occur. ACTH, adrenocorticotropic hormone CLIP, corticotropin-like intermediate lobe peptide JP, joining peptide LPH, lipotropin MSH, melanocyte-stimulating hormone PC, prohormone convertase. 

L. Jones II, J. S. Schumm, J. M. Tour, Rapid Solution and Solid Phase Syntheses of Oiigo(l,4-phenylene-ethynylene)s With Thioester Termini Molecular Scale Wires With Alligator Clips. Derivation of Iterative Reaction Efficiencies on a Polymer Support, J. Org. Chem. 1997, 62,1388-1410. 

An apparatus for producing pure nitric oxide is set up as follows. As in the apparatus for preparing hydrogen chloride, a filter flask (capacity 750 c.c.) is fitted with a dropping funnel, from which 42V-sulphuric acid is dropped into concentrated sodium nitrite solution, containing 70 g. of NaN02 in 150 c.c. of water. For this amount of nitrite 250 c.c. of the 42V-acid are required. The side tube of the flask leads first to a wash-bottle with concentrated sodium (or potassium) hydroxide, and then to one with concentrated sulphuric acid. By means of a short rubber tube a T-tube is attached to the second wash-bottle. One branch of the tube is connected to a carbon dioxide Kipp, the other to the reaction vessel. The rubber tube carries a screw clip so that, at the end of the experiment, the nitric oxide generator can be removed. 

Clipping. The clipping method relies on the synthesis of the rotaxane by formation of the macrocycle (host) in the presence of a dumbbell shaped molecule. The partial macrocycle undergoes a ring closing reaction around the dumbbell shaped molecule, thereby forming the rotaxane. 

Watch the video clip giving an overview of reaction kinetics at www. brightredbooks.net... 

The A -demethylation pathway is common to the metabolism of Ml 25 (Vllf) and morphine, both drugs being converted to secondary amines by liver micro-somes under the same condition [55]. Reaction rates were depressed when microsomes from rats repeatedly treated with Ml25 or morphine were used. In the same work, rats were-shown to become tolerant to the pharmacological effects of M125 (shock avoidance and tail clip tests) and cross tolerance to morphine was also found. 

Repeated exposure of rats to an aerosol at a concentration of 470mg/m for 10 weeks caused only mild nasal irritation repeated exposure of rats to 77mg/m for 23 weeks resulted in elevated creatinine and boron content of the urine in addition to increased urinary volume. Conjunctivitis resulted when the dust was applied to the eyes of rabbits, probably the result of the exothermic reaction of boron oxide with water to form boric acid topical application of boron oxide dust to the clipped backs of rabbits produced erythema that persisted for 2-3 days. ... 

The most important applications of nickel metal involve its use in numerous alloys. Such alloys are used to construct various equipment, reaction vessels, plumbing parts, missile, and aerospace components. Such nickel-based alloys include Monel, Inconel, HasteUoy, Nichrome, Duranickel, Udinet, Incoloy and many other alloys under various other trade names. The metal itself has some major uses. Nickel anodes are used for nickel plating of many base metals to enhance their resistance to corrosion. Nickel-plated metals are used in various equipment, machine parts, printing plates, and many household items such as scissors, keys, clips, pins, and decorative pieces. Nickel powder is used as porous electrodes in storage batteries and fuel cells. 

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