Biological material

The study of biological systems by neutron scattering is restricted by the difficulty, if not impossibility, of deuteriating the molecules. However, solutions or suspensions can still be studied using a contrast-variation technique, which involves altering the scattering density of the solvent by selective deuteriation. 

Work has been carried out on a number of totally different systems. 

Suau et al. studied the conformation of chromatin as a function of ionic strength and Braddock et al. fitted model calculations for the nucleosome core particle in solution to these experimental scattering curves. The best fit to the data was found for a model in which there were 1.7 0.1 turns of DNA wrapped around a hydrophobic core. Models in which this core was cylindrical or wedge-shaped were compatible with the measured scattering curves. However, spherical or ellipsoidal core models were incompatible and had to be rejected. 

Torbef has determined the maximum radii of gyration of the bacteriophages Pf, and fd to be 32 A and 33 A, respectively, and using the known hydrodynamic diameter of fd (90 10 A), he postulated a large counter-ion cloud around this virus. Studies on intact human blood cells have allowed the determination of the distribution of lipid, protein, and water across the membrane.  

Neutron diffraction peaks from oriented sheets of the purple membrane of Halobacterium halobium were measured with different levels of HjO/DjO exchange.  

Another study on this same theme examined the effects of trehalose, glucose and hydroxyethyl starch on the motional properties of the phosphate headgroup of freeze-dried dipalmitoylphosphatidylcholine (DPPC) liposomes, this time employing 31P NMR.110 The work aimed to examine whether there 

Small amounts of non-ionic surfactant (tetraethyleneglycol mono- -dodecyl ether) are found to have a pronounced effect on DPPC bilayers.113 In particular, the order parameter of the lipid chains measured via 2H NMR is found to be significantly reduced, suggesting that the slower chain motions are affected by the surfactant. T studies, though, show that the high-frequency motions, which are dominated by kink motions of the lipid chains, are unaffected. 

Another important area of dynamic studies in biological samples is the effect of hydration upon molecular mobility in proteins and carbohydrates. The reason for these studies is primarily that protein dynamics, in particular, are crucial to their function, and so examining factors, such as the degree of hydration, that affect their dynamics is very important. However, it is obviously near-impossible to study dynamics in aqueous solution as a function of degree of hydration, and, since most proteins are not soluble in nonaqueous solvents, solid-state studies must be used. The motions at three methionine (Met) residues in Streptomyces subtilisin inhibitor (SSI) were studied with 2H NMR using a sample in which the Met residues at two crucial enzyme recognition sites (PI and P4) were specifically deuterated, along with one in the hydrophobic core.114 The motions of the Met side-chains were then examined 

Another study used H T, T2 and 13C T, T p measurements to assess the molecular dynamics in dry and wet solid proteins bacterial RNAase, lysozyme and bovine serum albumin.115 All relaxation time data were analysed assuming three components for the molecular motion methyl group rotation and slow and fast oscillations of all atoms. An inhomogeneous distribution of correlation times was found for all samples, not surprisingly given the inhomogeneous nature of the samples. Interestingly, it was found that dehydration affected only the slow internal motions of the proteins and that the fast ones remained unaltered. 

The one-dimensional exchange experiment ODESSA (see Section 2.4) was used in a study of the effects of hydration in the protein barstar and the polypeptide polyglycine.116 For the experiments on barstar, a uniformly labelled 15N sample was used, and natural-abundance 13C was used for polyglycine. Only the wet barstar sample showed any signs of molecular reorientation in this case, with correlation times between 50 and 100 ms. 

In a procedure for the analysis of radioiodine In vegetation (ref. 376, pp. 94ff), the following reagents were added to the sample carrier copper foil cerlum(IV) sulfate sulfuric acid and potassium permanganate. The mixture was heated until the sample was completely oxidized. Then oxalic acid was added to convert the Iodine to the elemental form and the iodine was distilled Into aqueous sodium hydroxide. The alkaline solution was treated with hydroxylamlne hydrochloride, sodium nitrite, and nitric acid and the free Iodine was extracted Into carbon tetrachloride. The Iodine was back-extracted as Iodide with sul-furous acid and precipitated as the silver salt. 

For thyroid glands (ref. 376, pp. 94 ff), most of the organic matter was first destroyed by fusion with sodium hydroxide in the presence of Iodide carrier. The destruction process was completed by the addition of solid potassium nitrate and ignition. Then the Iodine was converted to the molecular condition by the addition of hydroxylamlne hydrochloride, sodium nitrite, and nitric acid, and the usual extraction and reduction process was carried out. 

Urine samples were also prepared for analysis for radioiodine by oxidative destruction (105). Iodide carrier, sulfuric acid, and solid potassium permanganate were added to a sample and the mixture was boiled under reflux to oxidize the carrier to lodate. Then the following steps were performed reduction of lodate to free Iodine by oxalic acid distillation of the iodine into water reduction to iodide by sulfurous acid and precipitation of silver Iodide. The chemical yield was 84% the standard deviation 4%. 

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Some fairly typical results, obtained by LaMer and co-workers [275] are shown in Fig. IV-24. At the higher film pressures, the reduction in evaporation rate may be 60-90%—a very substantial effect. Similar results have been reported for the various fatty acids and their esters [276,277]. Films of biological materials may offer little resistance, as is the case for cholesterol [278] and dimyristoylphosphatidylcholine (except if present as a bilayer) [279]. 

Modification of an AFM to operate in a dynamic mode aids the study of soft biological materials [58]. Here a stiff cantilever is oscillated near its resonant frequency with an amplitude of about 0.5 nm forces are detected as a shift to a new frequency... 

The infonuation that can be extracted from inorganic samples depends mainly on tlie electron beam/specimen interaction and instrumental parameters [1], in contrast to organic and biological materials, where it depends strongly on specimen preparation. 

Although the technology of an MRI scanner is rather sophisticated it does what we have seen other NMR spectrometers do it detects protons Thus MRI IS especially sensitive to biological materials such as... 

It is evident that the area of water-soluble polymer covets a multitude of appHcations and encompasses a broad spectmm of compositions. Proteins (qv) and other biological materials ate coveted elsewhere in the Eniyclopedia. One of the products of this type, poly(aspartic acid), may be developed into interesting biodegradable commercial appHcations (70,71). 

National Institute of Standards and Technology (NIST). The NIST is the source of many of the standards used in chemical and physical analyses in the United States and throughout the world. The standards prepared and distributed by the NIST are used to caUbrate measurement systems and to provide a central basis for uniformity and accuracy of measurement. At present, over 1200 Standard Reference Materials (SRMs) are available and are described by the NIST (15). Included are many steels, nonferrous alloys, high purity metals, primary standards for use in volumetric analysis, microchemical standards, clinical laboratory standards, biological material certified for trace elements, environmental standards, trace element standards, ion-activity standards (for pH and ion-selective electrodes), freezing and melting point standards, colorimetry standards, optical standards, radioactivity standards, particle-size standards, and density standards. Certificates are issued with the standard reference materials showing values for the parameters that have been determined. 

One of the main uses of osmium tetroxide is as a biological staining agent for microscopic ceU and tissue studies. Osmium tetroxide is unique in that it both fixes and stains biological material. 

Grafts are also frequently employed in the upper part of the body to reconstmct damaged portions of the aorta and carotid arteries. In addition, grafts are used to access the vascular system, such as in hemodialysis to avoid damage of vessels from repeated needle punctures. Most grafts are synthetic and made from materials such as Dacron or Teflon. Less than 5% of grafts utilized are made from biological materials. 

Comprehensive accounts of the various gravimetric, polarographic, spectrophotometric, and neutron activation analytical methods have been pubHshed (1,2,5,17,19,65—67). Sampling and analysis of biological materials and organic compounds is treated in References 60 and 68. Many analytical methods depend on the conversion of selenium in the sample to selenous acid, H2Se02, and reduction to elemental selenium when a gravimetric deterrnination is desired. 

Miscellaneous. Trace analyses have been performed for a variety of other materials. Table 9 Hsts some uses of electrothermal atomic absorption spectrometry (etaas) for determination of trace amounts of elements in a variety of matrices. The appHcations of icp /ms to geological and biological materials include the following (165) ... 

Bioassays are based on the growth response of vitamin-depleted rats or chicks to graded amounts of vitamin B 2 added in the diet. These assays are not specific for vitamin B 2 because factors, other than vitamin B 2 present in biological materials, produce a growth response. Because coen2yme primary form of natural vitamin 2 is light sensitive, assays should be carried out in subdued light. 

In biological materials, various nonspecific precipitants have been used in the gravimetric deterrnination of choline, including potassium triiodide, platinum chloride, gold chloride, and phosphotungstic acid (28). Choline may also be determined spectrophotometricaHy and by microbiological, enzymatic, and physiological assay methods. 

The use of mutant 34486 of Neurospora crassa for the microbiological assay of ch oline has been described (8). A physiological method has also been used in which the ch oline is extracted after hydrolysis from a sample of biological material and acetylated. The acetylcholine is then assayed by a kymographic procedure, in which its effect in causing contraction of a piece of isolated rabbit intestine is measured (33). 

Chromatography is a technique for separating and quantifying the constituents of a mixture. Separation techniques are essential for the characterization of the mixtures that result from most chemical processes. Chromatographic analysis is used in many areas of science and engineering in environmental studies, in the analysis of art objects, in industrial quahty control (qv), in analysis of biological materials, and in forensics (see Biopolymers, analytical TECHNIQUES FiNE ART EXAMINATION AND CONSERVATION FoRENSic CHEMISTRY). Most chemical laboratories employ one or more chromatographs for routine analysis (1). 

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