Experiments early

The earliest description of the action of veratrine on the neuromuscular system appeared about 130 years ago (Provost 1866 von Bezold and Hirt 1867). For the next 90 years or so many experiments were carried out on the veratrine response of muscle, a twitch followed, after a relaxation, by a second slow rise and fall of tension. Its electrophysiological basis, a sizeable afterdepolarization following a spike potential, and giving rise to a series of spikes, was studied for decades (see summaries by Krayer and 

Acheson 1946 Shanes 1958 Ulbricht 1969a). Experiments with the pure alkaloid veratridine on the membrane level made it clear that the afterpotential was caused by characteristic changes in the sodium permeability, in particular keeping channels open by preventing fast inactivation (Ulbricht and Flacke 1965 Ulbricht 1969a). 

Other secondary veratridine effects include increased Na+-K+ pump activity in rat myotubes due to increased Na+ influx (Brodie and Sampson 

1990) and the related increased cellular (or synaptosomal) respiration (see, e.g., Mata et al. 1980 Urenjak et al. 1991) or intracellular acidification of repetitively stimulated frog nerve fibers as protons increasingly flow 

It may be mentioned here that veratridine is also reported to partially block Na channels in jellyfish neurones which, however, are tetrodotoxin-insensitive and show other unusual pharmacological features (Spafford et al. 1996). In neuroblastoma ceUs veratridine-induced block of Ca + channels was observed at concentrations which stimulate Na channels (Romey and Lazdunski 1982). Such suppression of Ca + current, however, at relatively large concentrations of veratridine, is also seen in frog muscle fibers (Ndndsi et al. 1994). Even the block of voltage-gated K channels in T lymphocytes and neuroblastoma cells has been reported (Verheugen et al. 

A torricellian barometer. The tube, completely filled with mercury, is inverted in a dish of mercury. Mercury flows out of the tube until the pressure of the column of mercury (shown by black arrow) standing on the surface of the mercury in the dish is equal to the pressure of the air (shown by green arrows) on the rest of the surface of the mercury in the dish. 

Even though the Greeks considered air to be one of the four fundamental elements and various alchemists obtained airs, or vapors, in their experiments, careful study of these elusive substances proved difficult. The first person to attempt a scientific study of the vapors produced in chemical reactions was a Flemish physician named Jan Baptista Van Helmont (1577-1644). Thinking that air and similar substances must be akin to the chaos from which, according to Greek myth, the universe was created, Van Helmont described these substances using the Flemish word for chaos, which was gas. 

Because instruments used for measuring pressure, such as the manometer (see Fig. 5.2), often use columns of mercury because of its high density, the most commonly used units for pressure are based on the height of the mercury column (in millimeters) the gas pressure can support. The unit mm Hg (millimeters of mercury) is called the torr in honor of Torricelli. A related unit for pressure is the standard atmosphere  

Recently, the International Union of Pure and Applied Chemists (IUPAC) has adopted 1 bar (100,000. Pa) as the standard pressure instead of 1 atm (101,325 Pa). Both standards are now widely used. 

1 standard atmosphere = 1 atm = 760 mm Hg = 760 torr However, since pressure is defined as force per unit area, 

---

Potassium chloride actually has the same stnicture as sodium chloride, but, because the atomic scattering factors of potassium and chlorine are almost equal, the reflections with the indices all odd are extremely weak, and could easily have been missed in the early experiments. The zincblende fonn of zinc sulphide, by contrast, has the same pattern of all odd and all even indices, but the pattern of intensities is different. This pattern is consistent with a model that again has zinc atoms at the comers and tlie face centres, but the sulphur positions are displaced by a quarter of tlie body diagonal from the zinc positions. 

Almost every modem spectroscopic approach can be used to study matter at high pressures. Early experiments include NMR [ ], ESR [ ] vibrational infrared [33] and Raman [ ] electronic absorption, reflection and emission [23, 24 and 25, 70] x-ray absorption [Tf] and scattering [72], Mossbauer [73] and gems analysis of products recovered from high-pressure photochemical reactions [74]. The literature contains too many studies to do justice to these fields by describing particular examples in detail, and only some general mles, appropriate to many situations, are given. 

Early experiments witli MOT-trapped atoms were carried out by initially slowing an atomic beam to load tire trap [20, 21]. Later, a continuous uncooled source was used for tliat purjDose, suggesting tliat tire trap could be loaded witli tire slow atoms of a room-temperature vapour [22]. The next advance in tire development of magneto-optical trapping was tire introduction of tire vapour-cell magneto-optical trap (VCMOT). This variation captures cold atoms directly from the low-velocity edge of tire Maxwell-Boltzmann distribution always present in a cell... 

S. C. Trindade and A. V. de Carvalho, "Utilization of Alcohol Euels in Brazil Early Experience, Current Situation, and Euture Prospects," Int. 

Early experiments with pyridine-2,3-dicarboxylic mono- and bis-phenylhydrazides were unsuccessful (32JIC145), but later these were cyclized in acetic acid (66CPBIOIO) to give only the 7-phenylpyrido[2,3-[Pg.242]

By 1900 the only plastics materials available were shellac, gutta percha, ebonite and celluloid (and the bitumens and amber if they are considered as plastics). Early experiments leading to other materials had, however, been carried out. The... 

Since these early experiments, a great deal of additional information about the existence and properties of free-radical intermediates has been developed. In this chapter, we will discuss the structure of free radicals and some of the special properties associated with free radicals. We will also discuss some of the key chemical reactions in which free-radical intermediates are involved. 

In Pedersen s early experiments, the relative binding of cations by crown ethers was assessed by extraction of alkali metal picrates into an organic phase. In these experiments, the crown ether served to draw into the organic phase a colored molecule which was ordinarily insoluble in this medium. An extension and elaboration of this notion has been developed by Dix and Vdgtle and Nakamura, Takagi, and Ueno In efforts by both of these groups, crown ether molecules were appended to chromophoric or colored residues. Ion-selective extraction and interaction with the crown and/or chromophore could produce changes in the absorption spectrum. Examples of molecules so constructed are illustrated below as 7 7 and 18 from refs. 32 and 131, respectively. 

The same author has shown by repetition of the early experiments already referred to (p. 507) that when yohimbine hydrochloride is distilled with zinc dust there is formed in addition to harman (XVII), p-cresol, which must originate from ring E of the yohimbine formula (XIV) by inclusion of C as the methyl group. Witkop s formula for yobyrine (IV6) received prompt confirmation by Clemo and Swan s synthesis of this base by... 

From the time when Thorny and Duval presented the results of their early experiments (late 1960s) the field has grown enormously. Hundreds of papers and several monographs have been published and many eonferenees have been held to present new results of experimental and theoretieal studies and to exehange ideas as well as to stimulate further developments. A vast majority of all that aetivity has been direeted towards the understanding of the fundamental problems of phase transitions on uniform surfaees, whereas problems of the surfaee heterogeneity efleets have been mueh less intensively studied [11,57,122-126],... 

In one of the early experiments designed to elucidate the genetic code, Marshall Nirenberg of the U.S. National Institutes of Health (Nobel Prize in physiology or medicine, 1968) prepared a synthetic mRNA in which all the bases were uracil. He added this poly(U) to a cell-free system containing all the necessary materials for protein biosynthesis. A polymer of a single amino acid was obtained. What amino acid was polymerized ... 

The combination of electrochemical and EPR studies can provide valuable information about unstable S-N radical species. A classic early experiment involved the electrochemical reduction of S4N4 to the anion radical [S4N4] , which was characterized by a nine-line EPR spectrum. The decay of the radical anion was shown by a combination of EPR and... 

The presence of silica to form slag which is vital to large-scale production was perceptively introduced by Robert Boyle in his very early experiments. Two apparendy acceptable mechanisms have been proposed and it is possible that both may be occurring. In the first, the rock is thought to react with molten silica to form slag and P4O10 which is then reduced by the carbon ... 

This induced an increasing number of papers devoted to the study of the hydrogen effect on the mechanical properties of titanium alloys -lo SQjjjg interesting effects of hydrogen in titanium and its alloys are discussed below on the basis of the experimental data obtained at ISSP RAS (the early experiments were carried out in co-operation with the Institute of Metal Physics UD RAS). 

In early experiments, the pentamethyl ether (18) was treated with phosphorus pentachloride in the hope of obtaining a chloropentol reducible to ( — )-proto-quercitol. (Allowing for the benzoyl migration, the expected product would have been (— )-uibo-quercitol (11).) Surprisingly, the quercitol actually obtained after demethylation and dehalogena-tion was neither of these but still another previously known isomer, meso-scyllo-quercitol (24) (27). 

When an enolate is forced to take the E configuration, e.g, the enolate derived from cyclohexanone, predominant formation of the anti-aldol might be expected. Surprisingly, early experiments gave more or less stereorandom results in that the reaction with benzaldehyde gave a ratio of. vvtt/ant/ -aldols of 48 521B 23, Contrarily, recent investigations24 reveal a substantial anti selectivity (16 84), which is lowered in a dramatic manner (50 50) by the presence of lithium salts. Thus, the low stereoselectivity in the early experiments may be attributed to impurities of lithium salts or lithium hydroxide. 

Chirooptical properties give more subtle information on the conformational behavior of biopolymers and peptides in solution. In early experiments, optical rotation and optical rotatory dispersion (ORD) have been recognized as valuable techniques, followed more recently by significant progress and refinements in the equipment which have resulted in the routine measurements of applied circular dichroism (CD). 

Metallo-organic CVD (MOCVD) is a specialized area of CVD, which is a relatively newcomer, as its first reported use was in the 1960s for the deposition of indium phosphide and indium anti-monide. These early experiments demonstrated that deposition of critical semiconductor materials could be obtained at lower temperature than conventional thermal CVD and that epitaxial growth could be successfully achieved. The quality and complexity of the equipment and the diversity and purity of the precursor chemicals have steadily improved since then and MOCVD is now used on a large scale, particularly in semiconductor and opto-electronic applications.91P1... 

Although germanium was the original semiconductor material in early experiments and production, it is now rarely used as such but mostly as an alloy with silicon.li l l l Some applications of silicon/ germanium are ... 

This expression was checked in many early experiments on premixed flames with a fixed equivalence ratio. Light... 

Much has been done to improve laboratory safety over the years. Two examples from the author s early experience can illustrate the lack of precautionary measures as late as the 1940 s. 

---