Chemical studies

Microchemical or ultramicrochemical techniques are used extensively ia chemical studies of actinide elements (16). If extremely small volumes are used, microgram or lesser quantities of material can give relatively high concentrations in solution. Balances of sufficient sensitivity have been developed for quantitative measurements with these minute quantities of material. Since the amounts of material involved are too small to be seen with the unaided eye, the actual chemical work is usually done on the mechanical stage of a microscope, where all of the essential apparatus is in view. Compounds prepared on such a small scale are often identified by x-ray crystallographic methods. 

Study of the chemical properties of element 104 has confirmed that it is indeed homologous to hafnium as demanded by its position in the Periodic Table (20). Chemical studies have been made for element 105, showing some similarity to tantalum (25) no chemical studies have been made for elements 106—109. Such studies are very difficult because the longest-Hved isotope of 104 ( 104) has a half-Hfe of only about 1 min, of 105 ( 105) a half-Hfe of about 40 s, of 106 ( 106) a half-Hfe of about 1 s, and of elements 107—109 half-Hves in the range of milliseconds. 

Chemiluminescent Immunoassay. Chemiluminescence is the emission of visible light resulting from a chemical reaction. The majority of such reactions are oxidations, using oxygen or peroxides, and among the first chemicals studied for chemiluminescence were luminol (5-amino-2,3-dihydro-l,4-phthalazinedione [521-31-3]) and its derivatives (see Luminescent materials, chemiluminescence). Luminol or isoluminol can be directly linked to antibodies and used in a system with peroxidase to detect specific antigens. One of the first appHcations of this approach was for the detection of biotin (31). 

Foi chemical studies the chiomatogiaphic methods oi solution viscosities ate methods of piefeience, but for practical apphcations, melt flow is most... 

The role of the physico-chemical study of materials processing has been consigned to a secondary position of interest by drose engaged directly in... 

There have been extensive physical and chemical studies of cyclopropenone, cyclo-pentadienone, and cycloheptatrienone (tropone). The results of these studies can be briefly summarized as follows ... 

Shock-compressed solids and shock-compression processes have been described in this book from a perspective of solid state physics and solid state chemistry. This viewpoint has been developed independently from the traditional emphasis on mechanical deformation as determined from measurements of shock and particle velocities, or from time-resolved wave profiles. The physical and chemical studies show that the mechanical descriptions provide an overly restrictive basis for identifying and quantifying shock processes in solids. These equations of state or strength investigations are certainly necessary to the description of shock-compressed matter, and are of great value, but they are not sufficient to develop a fundamental understanding of the processes. 

Until recently, the catalytic role of Asp ° in trypsin and the other serine proteases had been surmised on the basis of its proximity to His in structures obtained from X-ray diffraction studies, but it had never been demonstrated with certainty in physical or chemical studies. As can be seen in Figure 16.17, Asp ° is buried at the active site and is normally inaccessible to chemical modifying reagents. In 1987, however, Charles Craik, William Rutter, and their colleagues used site-directed mutagenesis (see Chapter 13) to prepare a mutant trypsin with an asparagine in place of Asp °. This mutant trypsin possessed a hydrolytic activity with ester substrates only 1/10,000 that of native trypsin, demonstrating that Asp ° is indeed essential for catalysis and that its ability to immobilize and orient His is crucial to the function of the catalytic triad. 

J. S. Elsholtz described emission of bluish-white light when fluorspar was heated. Also described by J. G. Wallerius, 1750 the name fluorescence was coined in 1852 by G. G. Stokes 1768 First chemical study of fluorite undertaken by A. S. Marggraf... 

Chemical studies on nyctinastic leaf movement regulated mainly by heterocycles 99H(51)927. 

Eurther quantum chemical studies involving uracil derivatives concern the conformations and properties of uridines [98CEJ621,98JA5488,98JOC1033, OOJCS (P2)677], the nucleophilic attack in pseudouridine synthases [99JA9928], and the aza analogs of uracil [99JST349]. 

Most studies concerning pyrimidines originate from biochemical questions. Since these systems are dominated by hydrogen-bonding and/or dispersion contributions, methods beyond the Hartree-Fock level are mandatory. The success of quantum chemical studies in this field is impressive and many effects could be explained on the basis of these theoretical investigations. 

This class of medicinal agents was uncovered quite adventitiously in a chemical study, although due credit must be given for the acute pharmacologic studies that uncovered this novel type of activity. 

BP Chemicals studied the use of chloroaluminates as acidic catalysts and solvents for aromatic hydrocarbon allcylation [41]. At present, the existing AICI3 technology (based on red oil catalyst) is still used industrially, but continues to suffer from poor catalyst separation and recycling [42]. The aim of the work was to evaluate the AlCl3-based ionic liquids, with the emphasis placed on the development of a clean... 

We still, however, mark off a large area of chemical study by the term biochemistry. This... 

Another dihydro derivative has been described in connection with medicinal chemical studies. Thus, reaction of 2-(chloromethyl)quinazoline-3-oxide (3) with hydrazine gives hydr-oxytriazocinamine 4 (and not a diazepine derivative as originally assigned), vigorous acetylation of which results in a rearrangement to give oxazolotriazocine 5.10... 

Since ancient times, the light emitted by fireflies and glow-worms has attracted the curiosity of people. Descriptions of the phenomena are frequently found in old poems, songs and folklores of many countries. Old scientific studies of these phenomena are also numerous, particularly after the 17th century. However, the chemical study was not begun until the early 20th century. 

The phylum Arthropoda includes the classes Diplopoda (millipedes), Chilopoda (centipedes), Crustacea (see Chapter 3), and Insecta (see Chapter 1). All luminous arthropods other than crustaceans are terrestrial, and not very many luminous millipedes and centipedes are known. The luminescence of millipedes is usually intracellular, whereas luminous centipedes discharge luminous secretion. Substantial chemical studies have been made only with the millipede Luminodesmus sequoiae and the centipede Orphaneus brevilabiatus, of which the latter is discussed in the Section 10.3. 

Chemical studies on fish luminescence have been hampered by difficulties in obtaining specimens and the minute sizes of the luminous organs and photophores. Despite the setbacks, it might be possible to find out the basic nature of a luminescence reaction when coelenterazine (or Cypridina luciferin) is utilized in the luminescence. Once the basic nature of the luminescence reaction is found, then further details might become available by comparison with an organism having the same type of luminescence system. 

The first step of a chemical study should be the quantitative measurements of coelenterazine, dehydrocoelenterazine, and a coelenter-azine-specific luciferase, in the light organs, liver, digestive tract (with empty stomach), and eggs if available (see Section C5 of Appendix for the method). A clear, unequivocal presence of a coelenterazine luciferase indicates the involvement of a luciferin-luciferase system,... 

The amount of raw material required for the chemical study of luminescent substances today is much less than that required 20 or 30 years ago, due to the advance in instrumentation. In the case of a luciferin, try to obtain 1-2 mg of purified luciferin. If that is not feasible, try to obtain at least 0.1 mg of purified material, and with some luck, the structure may be obtained. 

Inoue, S., Okada, K., Tanino, H., and Kakoi, H. (1987). Chemical studies of myctophina fish bioluminescence. Chem. Lett., pp. 417-418. 

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