Conditions experimental

The conditions for enzymatic reactions are usually very mild. The solvents employed when isolated enzymes are used are typically aqueous birffer around pH of 7 or hydrophobic organic solvent such as hexane or isopropyl ether. In whole-cell reactions distilled water or tap water is normally used. 

The reaction temperature is around room temperature, although some enzymes from extremophiles, microorganisms from extreme environmental conditions, can react very effectively at temperatures up to 120°C and down to -50°C. Sometimes, enantioselectivity can be improved by a decrease or increase in the reaction temperature. 

To improve the efficiency of an enzymatic reaction various additives are often used. In reductions, for example, sugar is used as a hydrogen source. When an isolated enzyme is used, the addition of one or several cofactors is sometimes necessary. In whole-cell reductions, however, this is not needed as the cell already contains all the required cofactors. 

The irradiation and measurement conditions for the analyses are given in the Table 4.2. 

This shows the cyclotron energy used in each case, the different foils inserted in front of the samples inorder to monitor the beam intensity and to decrease the 

To determine the thickness of a thin layer, the composition and the density of the sputtered layer should be exactly known. The partial mass thickness cxDx must be divided by cx (the concentration of the analyte in the thin layer) to determine the total mass thickness Dx. Division of Dx by the density of the thin layer gives the thickness of the thin layer expressed in units of length. In their thickness calculations, De Neve et al. (2000) assumed their TiOx layers to be Ti02 with a density of 4.26gem-3.  

Each sample was analysed three times, and their results shown Table 4.3 indicate that such layers with a thickness of a few nanometres can be determined with a precision of 2% or better. The standard deviations are given in parentheses. 

Results obtained by CPAA for composition and partial mass thickness have been shown to be consistent with the results obtained via other analytical methods. The main advantage of the use of CPAA as a surface characterization method are its purely instrumental character, requiring no sample preparation, its high accuracy, and its low detection limits. 

Shifting the equilibrium so as to oxidize a valuable alcohol, rather than to reduce a valuable carbonyl compound, is more demanding from the experimental point of view. In this case, the removal of the alcohol, resulting from the reduction of a cheap aldehyde or ketone used as oxidant, meets the problem of alcohol being less volatile than the corresponding carbonyl compound. Nevertheless, the practical realization of such oxidation was proved by Oppenauer in 1937.4 

In the foundational paper of Oppenauer, the equilibrium is shifted to the oxidation of  

Oppenauer was able to shift the equilibrium towards the oxidation of a number of sterols, by employing an excess of cheap acetone as oxidant and taking advantage of some very favourable thermodynamics in oxidations, in which an alkene enters into conjugation with the resulting ketone. 

In the vast majority of cases, the equilibrium in Oppenauer oxidations is shifted to the right by employing an excess of oxidant. When aldehydes or ketones with a certain volatility are formed during Oppenauer oxidations, it is possible to shift the equilibrium by removing the product by distillation under reduced pressure, while oxidants with a low volatility, such as benzaldehyde, cinnamaldehyde or piperonal, are used.5 This experimental procedure, although very suitable for multigram scale reactions, is seldom employed because of the inconvenience of running a reaction while a distillation under vacuum is performed. 

The so-called Oppenauer oxidation proved to be extremely successful in the oxidation of sterols. On the other hand, its application—in the original formulation—to the obtention of ketones outside the field of steroids and to the preparation of aldehydes met a more limited success because of less favourable thermodynamics and side reactions, induced by the basic character of the aluminium alkoxides. 

Many of the synthetically useful reactions of organosilicon hydrides are conducted in solution using solvents such as CH2CI2, CHCI3, CCI4, MeCN, or THF. In general, it is important that anhydrous reaction conditions be used and that normal purification procedures be followed to ensure that the solvents used are pure and anhydrous. 

Argon (99.999%) was used as the carrier gas at a flow rate of 200 cm min Gas analysis was performed continuously by means of an IR gas analyzer. The experimental conditions are listed below. 

Anode-cathode distance - 40 mm Anode - graphite and prebaked Cathode - copper plate 

Working temperature - 960 °C Electrolysis time - 6 h Data sampling frequency - 20 s. 

Anodes with different sulfur contents were selected, prepared, and supplied by the Carbon Laboratory in Ardal. Four runs were made with graphite anodes as a zero sulfur carbon material. The sulfur content in the carbon anodes are given in Table 1.5.1. 

Both samples, the peracetylated p-D-glucose (30mg) and the peracetylated oligosaccharide of unknown structure (6mg) were dissolved in CDCI, (99.8% D), doped with a trace of tetramethylsilane (TMS) as the internal standard. 

All spectra were measured on a Bruker DRX 500 spectrometer, at 500.13MHz ( H) and at 125.76MHz ( C). Sample spinning (20Hz) was used for all ID experiments with the exception of the ID NOE and ID ROESY experiments. As is now common, all 2D experiments were performed with the sample static. All experiments were performed at ambient magnet temperature without any special temperature control. 

For more experimental details please inspect the parameter files of the corresponding experiments accessible from within ID and 2D WIN-NMR. 

Instead of lead tetraacetate, red lead itself, suspended in organic solvents containing acetic acid or in aqueous acetic acid, has been used as a glycol-cleaving agent.64 This procedure permits the generation of lead tetraacetate in the reaction mixture while the concentration of excess oxidant is simultaneously kept at a minimum, and it retards hydrolysis of lead tetraacetate in an aqueous system. 

Acetic acid is the reaction medium most commonly used, since it is a good solvent for most sugars and their derivatives. With free sugars and oligosaccharides, it is often advantageous to dissolve the compound first in a small proportion of water27 and then to dilute this solution with the 

In preparative experiments, excess lead tetraacetate may be smoothly reduced by addition of a stoichiometric quantity of hydrazine in acetic acid.43 Oxalic acid is also useful,28 additional acid being added to precipitate the divalent lead formed. When no excess of tetravalent lead is present, sulfuric acid, oxalic acid, or a cation-exchange resin may be used for removing divalent lead. 

Lead tetraacetate consumption is measured conveniently by iodometry.4 The reaction mixture is added to excess potassium iodide solution, usually in the presence of sodium acetate,6 and the iodine liberated is then titrated with standard thiosulfate. Oxidation may also be measured potentiometri-cally,78 210 211 a procedure especially useful for fast glycol groups,78 or with redox indicators.211 

Structural examination of a sugar by lead tetraacetate oxidation should include a preliminary measurement of the oxidation rate and of products 

Recently, the use of mercuric bromide (in acetonitrile or benzene) in the Hilbert-Johnson reaction has been investigated.20,35,49 Thus, with 3,5-di-0-p-toluyl-2-deoxy-D-ribofuranosyl chloride, the reaction rate was higher in the presence of one or more molar equivalents of mercuric bromide, but the total yield of the anomeric mixture was considerably decreased because of the rapid decomposition of the deoxyhalogenose the amount of the j3 anomer in the anomeric mixture increased in this case. With stable halogenoses,49,60 the use of mercuric bromide leads to shorter reaction times (the total yield is not lowered to such an extent as with deoxyhalogenoses). 

The Isolation Technique Chromatography. Two alternatives are possible either to isolate the primary Hilbert-Johnson intermediates, i.e., l-peracylglycosyl-4-alkoxy-2(lH)-pyrimidinones, or to treat them with alcoholic hydrogen chloride or alcoholic ammonia and separate the corresponding A-l-glycosyl derivatives of uracil or cytosine. The latter alternative has been used by the earlier authors more frequently because of the higher crystallization ability of 

Although a typical wood contains about 50-70% voids, the voids are interconnected in a very tortuous manner so that permeation of a monomer, even a highly fluid one, is difficult (Stamm, 1964, p. 363), and only part of the water initially contained in the pores can be replaced. To improve the permeation, the wood is evacuated (at a pressure of say, 5 mm Hg), excess monomer is added, pressure is applied using an inert gas, and the wood is soaked in the monomer for several hours. The monomer-impregnated specimen is then subjected to irradiation until polymerization of the monomer is essentially complete (90-100% conversion) the specimen is then dried in air, or in a kiln. 

Many types of hardwoods and softwoods have been used, including oak, pine, poplar, birch, elm, and sycamore (Boyle et al, 1971 Hills et al, 1969). Not surprisingly, the response to impregnation is quite dependent on the nature of the wood selected. Thus, for a series of woods, polymer loadings of from 5 to 110% were obtained (Hills et al, 1969), depending on the wood and on the monomer. Methyl methacrylate, styrene, and styrene-acrylonitrile combinations are among some of the monomers used successfully. If a monomer mixture is used, the composition of the copolymer will. 

Low Molecular Weight Compounds. GPC may be used for low molecular weight compounds since efficient gels with small pore sizes are available. Since these gels are less cross-linked than the regular ones, they are more sensitive to swelling. This property r tricts the choice of solvents. In this case, elution volumes are less controlled by steric exclusion mechanism and the relationship between molecular si and molecular weight is not well-defined and depends on 

Separation of diphenyl-2,4-pentane stereoisomers by recyde-GPC in di-isopropyl ether (DIPEy [78]. 19 cycles were necessary to separate the two isomers 1 and Ip 

Classical Calculations. As the chromatogram provides continuous information on concentration, data reduction amounts to summing up the properties of slices of the chromatogram, each slice being characterized by its elution volume Vj and its intensity hj proportional to the concentration Q. Molecular weights M are determined from Vj through the calibration curve 

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A motor fuel has an octane number X if it behaves under tightly defined experimental conditions the same as a mixture of X volume % of isooctane and (100 - X)% of n-heptane. The isooctane-heptane binary mixtures are called primary reference fuels. Octane numbers higher than 100 can also be defined the reference material is isooctane with small quantities of tetraethyl lead added the way in which this additive acts will be discussed later. 

A gasoline s MON is always lower than its RON their difference, an average of 10 to 12 points, is called the sensitivity, S. This is an indication of a fuei s sensitivity to a modification of the experimental conditions and more... 

The experimental conditions used to determine the CFPP do not exactly reflect those observed in vehicles the differences are due to the spaces in the filter mesh which are much larger in the laboratory filter, the back-pressure and the cooling rate. Also, research is continuing on procedures that are more representative of the actual behavior of diesel fuel in a vehicle and which correlate better with the temperature said to be operability , the threshold value for the Incident. In 1993, the CEN looked at two new methods, one called SFPP proposed by Exxon Chemicals (David et al., 1993), the other called AGELFI and recommended by Agip, Elf and Fina (Hamon et al., 1993). 

For each type of component, its relative reactivity in ozone formation was taken into account which makes it possible to characterize by weighting the behavior of the overall motor fuel under the given experimental conditions. The overall reactivity is in fact governed by a limited number of substances ethylene, isobutene, butadiene, toluene, xylenes, formaldehyde, and acetaldehyde. The fuels of most interest for reducing ozone formation are those which contribute towards minimizing emissions of the above substances. 

In the wide field of applications, a visibility level VL = 3 - 60 is recommended. For our recognition task, we are obliged to take into account that our random conditions are far from the experimental conditions of the basic researches (Young test person with a high visus under ideal environmental conditions) [4]. Furthermore in our case we have a more difficult visual searching task. Parameter variations as the increase of presentation time from 0,2 to 1.0 s. and the detection propability from 50% to 100% are taken into account [5] In spite of the gliding variations of the parameters as well as the visibility level, for simplification let us assume VL = 10 as minimum requirement. 

The central quantity of interest in homogeneous nucleation is the nucleation rate J, which gives the number of droplets nucleated per unit volume per unit time for a given supersaturation. The free energy barrier is the dommant factor in detenuining J J depends on it exponentially. Thus, a small difference in the different model predictions for the barrier can lead to orders of magnitude differences in J. Similarly, experimental measurements of J are sensitive to the purity of the sample and to experimental conditions such as temperature. In modem field theories, J has a general fonu... 

As these examples have demonstrated, in particular for fast reactions, chemical kinetics can only be appropriately described if one takes into account dynamic effects, though in practice it may prove extremely difficult to separate and identify different phenomena. It seems that more experiments under systematically controlled variation of solvent enviromnent parameters are needed, in conjunction with numerical simulations that as closely as possible mimic the experimental conditions to improve our understanding of condensed-phase reaction kmetics. The theoretical tools that are available to do so are covered in more depth in other chapters of this encyclopedia and also in comprehensive reviews [6, 118. 119],... 

In step (1) and step (2) there is an increase from one to two chain carriers . (For brevity, step (x) is used to refer to equation (A3.14.V) tliroughout.) Under typical experimental conditions close to the first and second explosion limits (see section A3.14.2.3). step (2) and step (3) are fast relative to the rate detemiining step (1). 

Figure A3.14.12. The first experimental observation of a Turing pattern in a gel strip reactor. Solutions containing separate components of the CIMA/CDIMA reaction are flowed along each edge of the strip and a spatial pattern along the horizontal axis develops for a range of experimental conditions. (Reprinted with pennission from [38], The American Physical Society.)...

The cleaning or depassivation eflect is of great importance in sonoelectrochemistry, as it can be employed to wash off surface-adsorbed species and reduce blocking of the electrode by adsorption of reaction products. This eflect has been reported, for example, for the depassivation of iron electrodes and for the removal of deposits and in the presence of polymer films on the electrode surface. However, damage of the electrode surface, especially for materials of low hardness such as lead or copper, can also occur under harsh experimental conditions and applied intensities [70, Tf, 80]. 

We have found that display of nuclear trajectories and the simultaneous evolution of charge distributions to yield insightful details of complicated processes. Such descriptions also map more readily to the actual experimental conditions than do the more conventional time-independent scattering matrix descriptions. 

Specinfo, from Chemical Concepts, is a factual database information system for spectroscopic data with more than 660000 digital spectra of 150000 associated structures [24], The database covers nuclear magnetic resonance spectra ( H-, C-, N-, O-, F-, P-NMR), infrared spectra (IR), and mass spectra (MS). In addition, experimental conditions (instrument, solvent, temperature), coupling constants, relaxation time, and bibliographic data are included. The data is cross-linked to CAS Registry, Beilstein, and NUMERIGUIDE. 

It ls not surprising chat such a relation should hold at the Limit of Knudsen diffusion, since Che Knudsen diffusion coefficients are themselves inversely proportional to the square roots of molecular weights, but the pore diameters in Graham s stucco plugs were certainly many times larger chan the gaseous mean free path lengths at the experimental conditions. 

They then compared measured and predicted fluxes for diffusion experiments in the mixture He-N. The tests covered a range of pressures and a variety of compositions at the pellet faces but, like the model itself, they were confined to binary mixtures and isobaric conditions. Feng and Stewart [49] compared their models with isobaric flux measurements in binary mixtures and with some non-isobaric measurements in mixtures of helium and nitrogen, using data from a variety of sources. Unfortunately the information on experimental conditions provided in their paper is very sparse, so it is difficult to assess how broadly based are the conclusions they reached about the relative merits oi their different models. 

As a consequence of these simple deductions, Graham s experiments c effusion through an orifice came to be regarded as one of the earliest direct experimental checks on the kinetic theory of gases. However, a closer examination of his experimental conditions reveals that this view is mistaken. As mentioned earlier, his orifice diameters ranged upwards from 1/500 in., while the upstream pressure was never very much less thai atmospheric. Under these circumstances the molecular mean free path len ... 

Many different approaches have been suggested as possible approaches to this problem, from the 1960s onwards [Verwer and Leusen 1998]. What is obvious from all of these ellorts is that this is an extremely difficult problem. Both thermodynamics and kinetics can be important in determining which crystalline form is obtained under a certain se1 of experimental conditions. Kinetic effects are particularly difficult to take into accouni and so are usually ignored. A proper treatment of the thermodynamic factors would lequire one to deal with the relative free energies of the different possible polymorphs... 

Three compounds may be formed by the interaction of ethanol and sulphuric acid, according to the experimental conditions ... 

The method depends for its success on the quantitative liberation of the nitrogen content of substances as molecular nitrogen this can be rather difficult in certain cases [e.g., polynitro compounds) but satisfactory determinations can be carried out by slight modification of the experimental conditions. 

Some liquids are practically immiscible e.g., water and mercury), whilst others e.g., water and ethyl alcohol or acetone) mix with one another in all proportions. Many examples are known, however, in which the liquids are partially miscible with one another. If, for example, water be added to ether or if ether be added to water and the mixture shaken, solution will take place up to a certain point beyond this point further addition of water on the one hand, or of ether on the other, will result in the formation of two liquid layers, one consisting of a saturated solution of water in ether and the other a saturated solution of ether in water. Two such mutually saturated solutions in equilibrium at a particular temperature are called conjugate solutions. It must be mentioned that there is no essential theoretical difference between liquids of partial and complete miscibility for, as wdll be shown below, the one may pass into the other with change of experimental conditions, such as temperature and, less frequently, of pressure. 

A careful study of the nature of the Grignard reagent RMgX (X = halogen) has revealed the feet that under suitable experimental conditions the following equilibria may be present in solution ... 

Nitro derivatives. No general experimental details for the preparation of nitro derivatives can be given, as the ease of nitration and the product formed frequently depend upon the exact experimental conditions. Moreover, some organic compounds react violently so that nitrations should always be conducted on a small scale. The derivatives already described are usually more satisfactory for this reason the nitro derivatives have been omitted from Table IV,9. 

The experimental conditions for conducting the above reaction in the presence of dimethylformamide as a solvent are as follows. In a 250 ml. three-necked flask, equipped with a reflux condenser and a tantalum wire Hershberg-type stirrer, place 20 g. of o-chloronitrobenzene and 100 ml. of diinethylform-amide (dried over anhydrous calcium sulphate). Heat the solution to reflux and add 20 g. of activated copper bronze in one portion. Heat under reflux for 4 hours, add another 20 g. portion of copper powder, and continue refluxing for a second 4-hour period. Allow to cool, pour the reaction mixture into 2 litres of water, and filter with suction. Extract the solids with three 200 ml. portions of boiling ethanol alternatively, use 300 ml. of ethanol in a Soxhlet apparatus. Isolate the 2 2- dinitrodiphenyl from the alcoholic extracts as described above the 3ueld of product, m.p. 124-125°, is 11 - 5 g. 

The experimental conditions necessary for the preparation of a solution of a diazonium salt, diazotisation of a primary amine, are as follows. The amine is dissolved in a suitable volume of water containing 2 5-3 equivalents of hydrochloric acid (or of sulphuric acid) by the application of heat if necessary, and the solution is cooled in ice when the amine hydrochloride (or sulphate) usually crystallises. The temperature is maintained at 0-5°, an aqueous solution of sodium nitrite is added portion-wise until, after allowing 3-4 minutes for reaction, the solution gives an immediate positive test for excess of nitrous acid with an external indicator—moist potassium iodide - starch paper f ... 

Prepare a solution of p-tolyldiazonium chloride from 53 -5 g. of p-tolui-dine using the proportions and experimental conditions given under p-Chlorotoluene (Section IV,61). Add the diazonium chloride solution to the boiling cuprous bromide solution, and proceed as in Method 1. The yield of pure, colourless p-bromotoluene, b.p, 182-184° (mainly 183°), is 40 g. m.p. 26°,... 

Diphenic acid. Phenanthrene upon oxidation in acetic acid solution at 85° with 30 per cent, hydrogen peroxide gives diphenic acid (diphenyl-2 2 -di-carboxyHc acid) no phenanthraquinone is formed under these experimental conditions. The reaction is essentially an oxidation of phenanthrene with peracetic acid. (For another method of preparation, see Section I V,74.)... 

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