Crystallization with

C8H10N4O2. An alkaloid occurring in tea, coffee and guarana, from which it may be prepared by extraction, It is also manufactured by the methylation of theobromine and by the condensation of cyanoacetic acid with urea. Crystallizes with H2O or anhydrous from organic solvents. M.p. (anhydrous) 235"C, sublimes at 176 C. Odourless, and with a very bitter taste. Caffeine acts as a stimulant and diuretic, and is a constituent of cola drinks, tea and coffee. 

C7H6O5. Colourless crystals with one molecule of water, m.p. 253" C, sparingly soluble in water and alcohol. It occurs free in woody tissue, in gall-nuts and in tea, and is a constituent of the tannins, from which it can be obtained by fermentation or by acid hydrolysis. It gives a blue-black colour with Fe and is used in the manufacture 6f inks. On heating it gives pyrogallol. 

Naphthalene-1-sulphonic acid crystallizes with 2HiO, m.p. 90 C. Used for the preparation of 1,8- and 1,5-nitronaphlhalene sulphonic acids. 

Naphihalene-2-sulphonic acid crystallizes with 3H2O, m.p. 83 C. It is also used for the preparation of nitro-derivatives. 

C7H6O4. Crystallizes with IH2O m.p. 199" C. It occurs in the free state in the onion and other plants is a constituent of one group of tannins, and is a product of the alkaline decomposition of resins. 

CJH4O5, H02CCH(0H)C02H. Colourless crystals with IH O lost at 60 C. M.p. IhO C (decomp.). Prepared by heating dinitrotartaric acid in aqueous alcohol, taurine, aminoethylsulpbonic acid, C2H7NO3S, NHj CHj CH SOjH. Crystallizes in columns, decomposing at 317 C. In combination with cholic acid it forms one of the bile acids. It is formed in the liver from cysteine. 

Austenitic Steel weld has a well defined transcrystalline (oriented) macrostructure with continuously changing orientation of the crystal axis - from the periphery towards the centre the angle between the axis of the crystal and the axis of the weld is changed from 90 to 0 degrees. Weld metal eould be possible to approximate in the form of a discrete combination of crystals with parallel axes of the crystallites. 

CS. The true two-dimensional crystal with chains oriented vertically exists at low T and high ir in the CS phase. This structure exhibits long-range translational order. 

Most solid surfaces are marred by small cracks, and it appears clear that it is often because of the presence of such surface imperfections that observed tensile strengths fall below the theoretical ones. For sodium chloride, the theoretical tensile strength is about 200 kg/mm [136], while that calculated from the work of cohesion would be 40 kg/mm [137], and actual breaking stresses are a hundreth or a thousandth of this, depending on the surface condition and crystal size. Coating the salt crystals with a saturated solution, causing surface deposition of small crystals to occur, resulted in a much lower tensile strength but not if the solution contained some urea. 

An experimental teclmique that is usefiil for structure studies of biological macromolecules and other crystals with large unit cells uses neither the broad, white , spectrum characteristic of Lane methods nor a sharp, monocliromatic spectrum, but rather a spectral band with AX/X 20%. Because of its relation to the Lane method, this teclmique is called quasi-Laue. It was believed for many years diat the Lane method was not usefiil for structure studies because reflections of different orders would be superposed on the same point of a film or an image plate. It was realized recently, however, that, if there is a definite minimum wavelengdi in the spectral band, more than 80% of all reflections would contain only a single order. Quasi-Laue methods are now used with both neutrons and x-rays, particularly x-rays from synclirotron sources, which give an intense, white spectrum. 

This is demonstrated by the XPS spectra in figure B 1.25.5(a) which show the Si 2p spectra of a silicon crystal with a thin (native) oxide layer, measured under take-off angles of 0° and 60° [12]. When the take-off angle is... 

Figure Bl.25.5. (a) XPS spectra at take-off angles of 0° and 60° as measured from the surface nonnal from a silicon crystal with a thin layer of Si02 on top. The relative intensity of the oxide signal increases significantly at higher take-off angles, illustrating that the surface sensitivity of XPS increases, (b) Plot of...

Addition of halide ions to aqueous copper(II) solutions can give a variety of halo-complexes for example [CuCl4] (yellow square-planar, but in crystals with large cations becomes a flattened tetrahedron) [CuClj] (red, units linked together in crystals to give tetrahedral or distorted octahedral coordination around each copper). 

It can be seen from Table 2 that the intrinsic values of the pK s are close to the model compound value that we use for Cys(8.3), and that interactions with surrounding titratable residues are responsible for the final apparent values of the ionization constants. It can also be seen that the best agreement with the experimental value is obtained for the YPT structure suplemented with the 27 N-terminal amino acids, although both the original YPT structure and the one with the crystal water molecule give values close to the experimentally determined one. Minimization, however, makes the agreement worse, probably because it w s done without the presence of any solvent molecules, which are important for the residues on the surface of the protein. For the YTS structure, which refers to the protein crystallized with an SO4 ion, the results with and without the ion included in the calculations, arc far from the experimental value. This may indicate that con-... 

In order to demonstrate the NDCPA a model of a system of excitons strongly coupled to phonons in a crystal with one molecule per unit cell is chosen. This model is called here the molecular crystal model. The Hamiltonian of... 

To verify effectiveness of NDCPA we carried out the calculations of absorption spectra for a system of excitons locally and linearly coupled to Einstein phonons at zero temperature in cubic crystal with one molecule per unit cell (probably the simplest model of exciton-phonon system of organic crystals). Absorption spectrum is defined as an imaginary part of one-exciton Green s function taken at zero value of exciton momentum vector... 

Into a 1500 ml. round-bottomed flask place 97-5 g. of finely-powdered sodium cyanide (1), 125 ml. of water, and a few chips of porous porcelain. Attach a reflux condenser and warm on a water bath until all the sodium cyanide dissolves. Introduce a solution of 250 g. (196 ml.) of n-butyl bromide (Sections 111,35 and 111,37) in 290 ml. of pure methyl alcohol, and reflux gently on a water bath for 28-30 hours. Cool to room temperature and remove the sodium bromide which has separated by filtration through a sintered glass funnel at the pump wash the crystals with about 100 ml. of methyl alcohol. Transfer the filtrate and washings to From n caproamide by SOClj method. 

Introduce 197 g. of anhydrous brucine or 215 g. of the air-dried dihydrate (4) into a warm solution of 139 g. of dZ-acc.-octyl hj drogen phthalate in 300 ml. of acetone and warm the mixture vmder reflux on a water bath until the solution is clear. Upon cooling, the brucine salt (dA, IB) separates as a crystalline solid. Filter this off on a sintered glass funnel, press it well to remove mother liquor, and wash it in the funnel with 125 ml. of acetone. Set the combined filtrate and washings (W) aside. Cover the crystals with acetone and add, slowly and with stirriug, a slight excess (to Congo red) of dilute hydrochloric acid (1 1 by volume about 60 ml.) if the solution becomes turbid before the introduction of... 

To isolate pure p-dibromobenzene, filter the second portion of the steam distillate through a small Buchner funnel with suction press the crystals as dry as possible. Combine these crystals with the residue (R) and recrystaliise from hot ethyl alcohol (for experimental details, see Section IV,12) with the addition of 1-2 g. of decolourising charcoal use about 4 ml. of alcohol (methylated spirit) for each gram of material. Filter the hot solution through a fluted filter paper, cool in ice, and filter the crystals at the pump. The yield of p-dibromobenzene, m.p. 89°, is about 12 g. 

The partially hydrolysed product may be purified by recrystallisation from one-tliird its weight of pure benzene containing 10-20 per cent, of acetyl chloride, and washing the crystals with light petroleum (b.p. 60-80°) to which a little acetyl chloride has been added. 

Mix 42 5 g. of acetone cyanohydrin (Section 111,75) and 75 g. of freshly powdered ammonium carbonate in a small beaker, warm the mixture on a water bath FUME CUPBOARD) and stir with a thermometer. Gentle action commences at 50° and continues during about 3 hours at 70-80°. To complete the reaction, raise the temperature to 90° and maintain it at this point until the mixture is quiescent (ca. 30 minutes). The colourless (or pale yellow) residue solidifies on coohng. Dissolve it in 60 ml. of hot water, digest with a little decolourising carbon, and filter rapidly through a pre-heated Buchner funnel. Evaporate the filtrate on a hot plate until crystals appear on the surface of the liquid, and then cool in ice. Filter off the white crystals with suction, drain well, and then wash twice with 4 ml. portions of ether this crop of crystals of dimethylhydantoin is almost pure and melts at 176°. Concentrate the mother liquor to the crj staUisation point, cool in ice, and collect the... 

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