In vacuo

The two most eommonly nsed methods in the literatnre for stndying flexible ligands sueh as AA and AEA have been the Monte Carlo and molecnlar dynamics (MD) techniques. In their Monte Carlo study, Rabinovich and Ripatti (Rabinovich and Ripatti, 1991) foimd that polyimsaturated fatty acids whose double bonds are separated by one methylene carbon assume an extended (angle-iron) conformation when all molecnles are efficiently packed below the phase-transition temperature. MD or molecular dynamics/simulated annealing (MD/SA) studies (in vacuo) of AA (9) and of other polyimsaturated fatty acids related to AA have been published by several groups 

Calculations in Nonpolar (CHCI3) vs. Polar (Aqueous) Environments 

These calculations suggested that for fatty add acyl chains that contain homoallylic donble bonds, chains with decreasing amonnts of nnsatnration tend to show a decreasing tendency to form folded stmctnres but still tend to cnrve in the acyl chain regions in which nnsatnration is present. 

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Boron trichloride, BCI3. Colourless mobile liquid, m.p. — 107°C, b.p. 12-5°C. Obtained directly from the elements or by heating B2O3 with pels in a sealed tube. The product may be purified by distillation in vacuo. It is extremely readily hydrolysed by water to boric acid. TetrachJoroborates containing the BCJ4 " ion are prepared by addition of BCI3 to metal chlorides. 

Any measurement of potential must describe a reference point, and we will take as this point the potential of an electron well separated from the metal and at rest in vacuo. By reference to figure A2.4.8 [16], we can define the following quantities. 

The final technique addressed in this chapter is the measurement of the surface work function, the energy required to remove an electron from a solid. This is one of the oldest surface characterization methods, and certainly the oldest carried out in vacuo since it was first measured by Millikan using the photoelectric effect [4]. The observation of this effect led to the proposal of the Einstein equation ... 

If the wavelength of the incident radiation in vacuo is Xq, equation B1. 26.26 becomes ... 

Finally, in 1985, the results of an extensive investigation in which adsorjDtion took place onto an aluminium oxide layer fonned on a film of aluminium deposited in vacuo onto a silicon wafer was published by Allara and Nuzzo 1127, 1281. Various carboxylic acids were dissolved in high-purity hexadecane and allowed to adsorb from this solution onto the prepared aluminium oxide surface. It was found that for chains with more than 12 carbon atoms, chains are nearly in a vertical orientation and are tightly packed. For shorter chains, however, no stable monolayers were found. The kinetic processes involved in layer fonnation can take up to several days. 

When silica (silicon dioxide) and silicon are heated in vacuo to 1700 K,... 

In both reactions above, the oxide dichloride is refluxed with the acid or the hydrated chloride the sulphur dioxide and hydrogen chloride pass off and any unused sulphur oxide dichloride is distilled off in vacuo. 

The iodine distils off and can be collected on a cooled surface. It may be purified by sublimation in vacuo. 

Iodine is a dark-coloured solid which has a glittering crystalline appearance. It is easily sublimed to form a bluish vapour in vacuo. but in air, the vapour is brownish-violet. Since it has a small vapour pressure at ordinary temperatures, iodine slowly sublimes if left in an open vessel for the same reason, iodine is best weighed in a stoppered bottle containing some potassium iodide solution, in which the iodine dissolves to form potassium tri-iodide. The vapour of iodine is composed of I2 molecules up to about 1000 K above this temperature, dissociation into iodine atoms becomes appreciable. 

Manganese is the third most abundant transition metal, and is widely distributed in the earth s crust. The most important ore is pyrolusite, manganese(IV) oxide. Reduction of this ore by heating with aluminium gives an explosive reaction, and the oxide Mn304 must be used to obtain the metal. The latter is purified by distillation in vacuo just above its melting point (1517 K) the pure metal can also he obtained by electrolysis of aqueous manganese(II) sulphate. 

Iron(II) oxide FeO is prepared by heating iron(II) ethanedioate (oxalate) in vacuo ... 

Addition of water gives the hydrated nitrate Cu(N03)2.3H2O, the product obtained when copper (or the +2 oxide or carbonate) is dissolved in nitric acid. Attempts to dehydrate the hydrated nitrate, for example by gently heating in vacuo, yield a basic nitrate, not the anhydrous salt. 

In order to apply the techniques discussed above to the MD simulation o biomolecules, one takes the Liouville operator for a macromolecule in vacuo containing N atoms to be... 

In this model of electrostatic in teraction s, two atoms (i and j) have poin t charges tq and qj. The magnitude of the electrostatic energy (V[. , [ ) varies inversely with the distance between the atoms, Rjj. fh e effective dielectric constant is . For in vacuo simulations or simulation s with explicit water rn olecules, the den om in a tor equals uRjj, In some force fields, a distance-dependent dielectric, where the denominator is uRjj Rjj, represen is solvent implicitly. 

In the generalised Born approach the total electrostatic energy is written as a sum of tin terms, the first of which is the Coulomb interaction between the charges in vacuo ... 

CAUTION. The preparation of o-nitrobenzoyl chloride, o-nitrophenacetyl chloride and all o nitroacid chlorides should not be attempted by the above methods a violent explosion may occur upon distilling the product or when the last traces of thionyl chloride are removed in vacuo at 100°. Perhaps the safest method is to treat the pure acid in benzene solution with 1 1 mols of thionyl chloride and to reflux until evolution of sulphur dioxide and hydrogen chloride has ceased the solution of the acid chloride in benzene may then bo employed for most reactions. 

The addition of N-bromosuccinimide (1.1equiv) to a dichlo-romethane solution containing the alkene (1 equiv) and cyana-mide (4 equiv). The solution was maintained at room temperature (3 days) and then washed with water, dried, and concentrated in vacuo. Treatment of the bromocyanamide [intermediate] with 1% palladium on charcoal in methanol (1h) led to reduction of the for-madine. Addition of base to the reaction mixture (50% aqueous KOH, reflux 6h) followed by extraction with ether gave monoamine. (Yield is 48-64% final amine from alkenes analogous to safrole)... 

Fig. 5. Usual apparatus for the isolation of volatile and/or unstable compounds by evaporation or distillation in vacuo and condensation in a cooled receiver.

With Stirring, hydrazine hydrate (4 ml in 30 ml of THh ) was added over 60 min. The reaction mixture was then cooled to room temperature and filtered through Celite. The filtrate was concentrated in vacuo and the residue purified by chromatography through silica gel using 10% ether in hexane for elution. The fractions containing product were combined and evaporated to give the product as a clear oil (2.94g, 50%). 

The o,p-dinitrostyrene (1 mmol) and ammonium formate (10 mmol) W ere dissolved in methanol and 10% Pd/ C (5% by wt) was added. The mixture was refluxed under nitrogen for 1 h. Formic acid (0.44 ml) w as added and reflux was continued for 0.5-1 h until the completion of the reaction (tic). The solution was filtered through Celite, evaporated in vacuo and eluted through silica gel with CH2CI2. 

Thionyl chloride (11.5g, 96.4 mmol) was added to 2-nitrophenylacetic acid (8.72g, 48.2mmol) and the suspension was warmed to 50°C and stirred until gas evolution was complete. The resulting solution was concentrated in vacuo and the residue dissolved in CHjClj (30 ml). This solution was added dropwise to a stirred solution of Meldrum s acid (6.94 g, 48.2 mmol) in CH2CI2 (200 ml) under nitrogen at 0 C. The solution was stirred at 0" C for 1 h after the addition was complete and then kept at room temperature for an additional hour. The reaction solution was then worked up by successively washing with dil. HC1, water and brine and dried (MgSOJ. The dried solution was concentrated in vacuo and abs. ethanol (200 ml) was added to the residue. The mixture was... 

Diethyl oxalate (29.2 g, 0.20mol) and 4-bromo-2-nitrotoluene (21.6 g, O.lOmol) were added to a cooled solution of sodium cthoxide prepared from sodium (4.6 g, 0.20 mol) and ethanol (90 ml). The mixture was stirred overnight and then refluxed for 10 min. Water (30 ml) was added and the solution refluxed for 2h to effect hydrolysis of the pyruvate ester. The solution was cooled and concentrated in vacuo. The precipitate was washed with ether and dried. The salt was dissolved in water (300 ml) and acidified with cone. HCl. The precipitate was collected, washed with water, dried and recrystallizcd from hexane-EtOAc to give 15.2 g of product. 

Bromo-2-nitrophenylacetic acid (26 g, 0.10 mol) was dissolved in a mixture of 50% HjSO (400 ml) and ethanol (600 ml) and heated to 90°C. Over a period of 1 h, zinc dust (26.2 g, 0.40 mol) was added. slowly and then heating was continued for 2 h. The excess ethanol was removed by distillation. The solution was cooled and filtered. The filtrate was extracted with EtOAc. The filtered product and extract were combined, washed with 5% NaCOj and brine and then dried (MgSO ). The solvent was removed in vacuo and the residue recrystallized from methanol to give 20.5 g (97% yield) of the oxindole. 

Sodium hydride (9.3 g, 0.22 mol) was washed with petroleum ether and DMSO (200 ml) was added and the mixture was heated to 100°C. A solution of diethyl malonate (35.2 g, 0.22mol) in DMSO (50 ml) was then added and stirred for 10 min to give a clear solution. A solution of 4-bromo-3-nitrobenzophenone (30.6 g, 0.10 mol) in DMSO (100 ml) was added and the resulting dark solution kept at 100 C for 1 h. The solution was poured into water (3 1) and extracted (2x) with ether. The extract was washed with water, dried (NajSOj and concentrated in vacuo to give an oil which crystallized. The solid was recrystallized from isopropyl alcohol to give 35.4 g (92% yield) of the product. 

Ethyl o-nitrocinnamate (1 mmol) was dissolved in triethyl phosphite (5 mmol) and heated at 170°C for 3 h. The triethyl phosphite and triethyl phosphate were removed in vacuo. The residue w as eluted through a column of silica gel using CHCI3 and the product recrystallizcd from CHCl3-hexane. The yield was 94%. 

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