Tube nucleus

Pig. 26.—White pine (Pinus Strobus). Vertical section through the upper part of an ovule, shortly before fertilization, s.n., sperm-nuclei st. c., stalk-cell t.n. tube-nucleus arch, archegonium e.n., egg-nucleus. (Gager, after Margaret C. Ferguson.)... 

Fig. 11 Fluorescence of pollen grain from Hippeastrum hybridum stained with azulene 10-5 (left, bright lightening of cell wall and less intensive emitted nucleus in centre) or pollen tube stained with colchicine 1CT7 M (right, lightening parts of pollen tube may be tubulinbinding sites).

The staining of germinated pollen of Hippeastrum hybridum with colchicine demonstrates green-yellow emission of microtubules (better vision in black-white image) around nuclei of pollen grain (threads at the division of the nucleus) and spermium on the tip of the pollen tube, where spermium moves, as well as in some bridge sites of the tube (Fig. 10). The similar fluorescent allelochemicals may be also used as fluorescent dyes at the cellular diagnostics (Roshchina, 2005 b). 

Fig. 10 The LSCM images of Hippeastrum hybridum pollen tube stained with colchicine 10" 7 M. The laser excitation wavelength 458 nm. 1. The bright emission is observed in nucleus of vegetative cell of pollen and in the spermium located in the tip of the tube 2. Spermium in the tip of pollen tube. The microtubules contained of tubulin are seen. 

Smaller diameter probes reduce sample volumes from 500 to 600 pi typical with a 5 mm probe down to 120-160 pi with a 3 mm tube. By reducing the sample volume, the relative concentration of the sample can be correspondingly increased for non-solubility limited samples. This dramatically reduces data acquisition times when more abundant samples are available or sample quantity requirements when dealing with scarce samples. At present, the smallest commercially available NMR tubes have a diameter of 1.0 mm and allow the acquisition of heteronuclear shift correlation experiments on samples as small as 1 pg of material, for example in the case of the small drug molecule, ibu-profen [5]. In addition to conventional tube-based NMR probes, there are also a number of other types of small volume NMR probes and flow probes commercially available [6]. Here again, the primary application of these probes is the reduction of sample requirements to facilitate the structural characterization of mass limited samples. Overall, many probe options are available to optimize the NMR hardware configuration for the type and amount of sample, its solubility, the nucleus to be detected as well as the type and number of experiments to be run. 

Phosphorus nuclei have been used for many years in in vivo NMR, especially for intracellular pH measurements. However, because most organic phosphates have similar chemical shifts, compound identification can be difficult without special attention being paid to culture conditions in the NMR tube.15 Carbon NMR also yields significant results because of the large chemical shift dispersion and narrow lines of this nucleus. 13C spectra reflect most of the chemical rearrangements that may take place between substrate and final product. 

Both nitric acid and nitrogen dioxide, in the liquid and vapour phase, have been used for the nitration of the alkyl side chains of various alkyl-substituted aromatics without affecting the aromatic nucleus.Thus, treatment of ethylbenzene with nitric acid of 12.5 % concentration in a sealed tube at 105-108 °C is reported to generate a 44 % yield of phenylnitroethane. The nitration of toluene with nitrogen dioxide at a temperature between 20-95 °C yields a mixture of phenylnitromethane and phenyldinitromethane with the proportion of the latter increasing with reaction temperature. ... 

Figure 9.2—Effect of the magnetic field on a nucleus with spin number of 1/2for an atom of a molecule present in solution. In the upper part of the sample tube, not influenced by the magnetic field, p has no preferred orientation with time. However, in the portion of the tube exposed to the external field, p traces the surface of a cone of revolution whose axis is aligned with B. Both possibilities are represented the projection of p is opposite or in the same direction as B.

---