A-Crystallin

Trichloroethanoic acid, CCI3COOH. A crystalline solid which rapidly absorbs water vapour m.p. 58°C, b.p. 196-5" C. Manufactured by the action of chlorine on ethanoic acid at 160°C in the presence of red phosphorus, sulphur or iodine. It is decomposed into chloroform and carbon dioxide by boiling water. It is a much stronger acid than either the mono- or the dichloro-acids and has been used to extract alkaloids and ascorbic acid from plant and animal tissues. It is a precipitant for proteins and may be used to test for the presence of albumin in urine. The sodium salt is used as a selective weedkiller. 

Ethylamine, monoethylamine, CH3CH2NH2-B.p. 19 C. Prepared by reduction of acetonitrile or by heating ethyl chloride with alcoholic ammonia under pressure. It is a strong base and will displace ammonia from ammonium salts. Forms a crystalline hydrochloride and also crystalline compounds with various metallic chlorides. 

Diethylamine, CH3CH2)2NH. B.p. 55-5°C. Forms a crystalline i hydrate. Prepared by the action of a boiling solution of sodium hydroxide on nitrosodielhylaniline. Forms crystalline compounds with many metallic chlorides. 

CjHiaNO, [Mc3NCH= CH2] OH. A liquid forming a crystalline trihydrate, It is present free and combined in brain and other animal and vegetable products and is formed as a product of putrefaction of lecithin. It can be prepared synthetically from choline and decomposes easily to trimethylamine. neutralization, heat of The amount of heat evolved when I g equivalent of an acid is neutralized by 1 g equivalent of a base. For strong acids and strong bases in dilute solution the only reaction which occurs is H -h OH ---> H2O and the heat of neutral-... 

The oriented overgrowth of a crystalline phase on the surface of a substrate that is also crystalline is called epitaxial growth [104]. Usually it is required that the lattices of the two crystalline phases match, and it can be a rather complicated process [105]. Some new applications enlist amorphous substrates or grow new phases on a surface with a rather poor lattice match. 

There is a fair amount of work reported with films at the mercury-air interface. Rice and co-workers [107] used grazing incidence x-ray diffraction to determine that a crystalline stearic acid monolayer induces order in the Hg substrate. Quinone derivatives spread at the mercury-n-hexane interface form crystalline structures governed primarily by hydrogen bonding interactions [108]. 

The three-dimensional synnnetry that is present in the bulk of a crystalline solid is abruptly lost at the surface. In order to minimize the surface energy, the themiodynamically stable surface atomic structures of many materials differ considerably from the structure of the bulk. These materials are still crystalline at the surface, in that one can define a two-dimensional surface unit cell parallel to the surface, but the atomic positions in the unit cell differ from those of the bulk structure. Such a change in the local structure at the surface is called a reconstruction. 

Figure B3.3.10. Contour plots of the free energy landscape associated with crystal niicleation for spherical particles with short-range attractions. The axes represent the number of atoms identifiable as belonging to a high-density cluster, and as being in a crystalline environment, respectively, (a) State point significantly below the metastable critical temperature. The niicleation pathway involves simple growth of a crystalline nucleus, (b) State point at the metastable critical temperature. The niicleation pathway is significantly curved, and the initial nucleus is liqiiidlike rather than crystalline. Thanks are due to D Frenkel and P R ten Wolde for this figure. For fiirther details see [189].

Figure C2.3.17. Model of half-cylindrical aggregates (hemimicelles) on a crystalline hydrophobic substrate, such as for tetradecyltrimethylammonium bromide on M0S2 [91], Adapted from figure 2 of [89],...

Other authors have attributed the improved corrosion resistance with increasing Cr content with the increasing tendency of the oxide to become more disordered [69]. This would then suggest that an amoriDhous oxide film is more protective than a crystalline one, due to a bond and stmctural flexibility in amoriDhous films. 

For tire purjDoses of tliis review, a nanocrystal is defined as a crystalline solid, witli feature sizes less tlian 50 nm, recovered as a purified powder from a chemical syntliesis and subsequently dissolved as isolated particles in an appropriate solvent. In many ways, tliis definition shares many features witli tliat of colloids , defined broadly as a particle tliat has some linear dimension between 1 and 1000 nm [1] tire study of nanocrystals may be drought of as a new kind of colloid science [2]. Much of die early work on colloidal metal and semiconductor particles stemmed from die photophysics and applications to electrochemistry. (See, for example, die excellent review by Henglein [3].) However, the definition of a colloid does not include any specification of die internal stmcture of die particle. Therein lies die cmcial distinction in nanocrystals, die interior crystalline stmcture is of overwhelming importance. Nanocrystals must tmly be little solids (figure C2.17.1), widi internal stmctures equivalent (or nearly equivalent) to drat of bulk materials. This is a necessary condition if size-dependent studies of nanometre-sized objects are to offer any insight into die behaviour of bulk solids. 

Much of our knowledge of the frequency dependence of VER rates in polyatomic molecules stems from low-temperature studies of molecular crystals [2] such as pentacene (PTC 221 4) guest molecules in a crystalline naphthalene (N C,., H ) host. In naphthalene, the phonon cut-off frequency is -180 cm [97]. At low temperature,... 

Boron trioxide is not particularly soluble in water but it slowly dissolves to form both dioxo(HB02)(meta) and trioxo(H3B03) (ortho) boric acids. It is a dimorphous oxide and exists as either a glassy or a crystalline solid. Boron trioxide is an acidic oxide and combines with metal oxides and hydroxides to form borates, some of which have characteristic colours—a fact utilised in analysis as the "borax bead test , cf alumina p. 150. Boric acid. H3BO3. properly called trioxoboric acid, may be prepared by adding excess hydrochloric or sulphuric acid to a hot saturated solution of borax, sodium heptaoxotetraborate, Na2B407, when the only moderately soluble boric acid separates as white flaky crystals on cooling. Boric acid is a very weak monobasic acid it is, in fact, a Lewis acid since its acidity is due to an initial acceptance of a lone pair of electrons from water rather than direct proton donation as in the case of Lowry-Bronsted acids, i.e. 

Aluminium oxide occurs naturally as emery (an impure form) and as corundum. Corundum is a crystalline form which may be coloured by traces of impurity, for example as ruby (red) and sapphire (blue). Small synthetic rubies and sapphires have been made by heating alumina with the colouring oxide in an oxy-hydrogen flame. 

Pure hydroxylamine is a crystalline solid of low melting point (306 K) but is rarely prepared because it decomposes above 288 K... 

Dinitrogeri pentoxide is the anhydride of nitric acid and is prepared by removing water from pure nitric acid by means of phosphorus (V) oxide. It is a crystalline solid having the ionic structure of (N02) (N03) , nitronium nitrate (the nitronium ion is mentioned later). It decomposes above 273 K, thus ... 

The problems already mentioned at the solvent/vacuum boundary, which always exists regardless of the size of the box of water molecules, led to the definition of so-called periodic boundaries. They can be compared with the unit cell definition of a crystalline system. The unit cell also forms an "endless system without boundaries" when repeated in the three directions of space. Unfortunately, when simulating hquids the situation is not as simple as for a regular crystal, because molecules can diffuse and are in principle able to leave the unit cell. 

Many molecules are obtained and used in a crystalline form, the nature of which can have e significant impact on their properties and behaviour. Moreover, it is sometimes possible foi a given material to exist in more than one crystalline form, depending upon the conditions under which it was prepared. This is the phenomenon of polymorphism. This can be important because the various polymorphs may themselves have different properties. It is Iberefore of interest to be able to predict the three-dimensional atomic structure(s) that a gi en molecule may adopt, for those cases where it is difficult to obtain experimental data and also where one might wish to prioritise molecules not yet synthesised. 

The following oxidation of camphor to camphor-quinone illustrates the oxidising action of selenium dioxide, and readily gives a crystalline product. 

The nitrosamines are insoluble in water, and the lower members are liquid at ordinary temperatures. The separation of an oily liquid when an aqueous solution of an amine salt is treated with sodium nitrite is therefore strong evidence that the amine is secondary. Diphenylnitrosoamine is selected as a preparation because it is a crystalline substance and is thus easier to manipulate on a small scale than one of the lower liquid members. For this preparation, a fairly pure (and therefore almost colourless) sample of diphenyl-amine should be used. Technical diphenylamine, which is almost black in colour, should not be employed. 

Add 5 g. of powdered potassium cyanide to a mixture of 20 ml. of water and 50 ml. of ethanol contained in a 200 ml. conical flask, and then add 25 mi. (26 g.) of freshly distilled benzaldehyde. Fit the flask with a reflux water-condenser, and boil the mixture gently on a water-bath for 30 minutes, a clear solution being rapidly obtained. Then pour the solution into a beaker and cool the benzoin separates as a crystalline mass... 

This preparation illustrates the use of phosphorus pentachloride for the preparation of acyl chlorides in this case no difficulty is experienced in separating the 3,5-dinitrobenzoyl chloride from the phosphorus oxychloride formed simultaneously (c/. p. 240), because the former is readily isolated as a crystalline... 

A crystalline derivative of benzyl alcohol cannot be obtained by using benzoyl chloride, because the benzyl benzoate, C HiCOOCHiCaHj, so obtained has m.p. 18°, and is thus usually liquid the present preparation illustrates therefore the use of a substituted benzoyl chloride (p-nitrobenzoyl chloride, m.p. 75°) in order to obtain a crystalline derivative of suitably high m.p. 

Although benzenesulphonyl chloride has for simplicity been used in the above discussion, tolucne-/>- sulphonyl chloride, CHaCeH SO Cl, is more frequently used in the laboratory, owing to its much lower cost, the latter being due in turn to the fact that toluene-p-sulphonyl chloride is a by-product in the commercial preparation of saccharin. Toluene-p sulphonyl chloride is a crystalline substance, of m.p. 68° the finely powdered chloride will, however, usually react readily with amines in the Schotten-Baumann reaction it does not react so readily with alcohols, but the reaction may be promoted considerably by first dissolving the chloride in some inert water-soluble solvent such as acetone. 

Dissolve I drop of quinoline in 1 ml. of dil. HCl and add a few drops of a saturated solution of potassium dichromate. A copious orange-yellow precipitate of quinoline dichromate, (C,H7N)2 HjCrj07, is formed pyridine does not give a crystalline dichromate under these conditions. 

Continue precisely as for triacetin, but since hexacetyl-mannitol (p. 142) is a crystalline compound, weigh out i o-i 2 g. of the finely powdered substance, either from a weighing-bottle, or by direct weighing in the flask A. The results are excellent. 

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