Simultaneous determination of copper, zinc, cadmium and mercury with high sensitivity is possible by neutron activation analysis. After irradiation, the samples are digested and an initial separation of the four elements made by means of an ion-exchange resin. The elements in the separated fractions are then treated to give radio-chemical purity, precipitated, and their activities measured. A purely instrumental technique for the analysis of zinc in samples of biological material is also described. The samples are irradiated for a week and after the activity has decayed for about three months it is measured on a gamma-spectrometer. 相似文献
Organic solvent nanofiltration (OSN) was used to investigate the mechanism of chiral selectivity in diastereomeric salt formation of alpha-phenylethylamine with D-tartaric acid and di-p-toluoyl-D-tartaric acid as resolving agents; results indicate that for these systems chiral selectivity occurs only upon crystallisation and chiral interactions in solution were negligible. 相似文献
Factor F430 from Methanogenic Bacteria: Structure of the Protein-free Factor Factor F430, the porphinoid nickel-containing coenzyme of the methylcoenzyme-M reductase of metanogenic bacteria is shown to be the 33,83,122,133,182-pentaacid derivative of the pentamethylester F430M, the structure of which had been determined previously (see structural formulae 1 and 2 ). The structure assignment rests on chromatographic, UV/VIS-, CD-, IR-, and 13C-NMR-spectroscopic as well as FAB-mass spectral comparision of F430 with F430M and the pentaacid prepared by acid-catalyzed hydrolysis of F430M. In the cells of Methanobacterium thermoautotrophicum, factor F430 is present in a ‘bound’ and also, depending on the growth conditions, in ‘free’ form, the latter being defined as the part of total F430 that can be extracted from the cells under extremely mild conditions (80% EtOH at 0–4°). From the (protein)-‘bound’ form, F430 is extracted by subsequently treating the cells at 0–4° with 80% EtOH containing (e.g.), 2m LiCi. From both sources, the extracted factor is the same pentaacid, and there is no indication for the existence of a protein-free F430 species that would contain additional (covalently bound) structural elements. 相似文献
Iodobenzene dichloride or diacetate initiates the polymerization of 2,6-dimethylphenolate anion to poly [oxy(2,5-dimethyl)-l, 4-phenylene]. Electron spin resonance spectroscopy was used to identify the polymeric radical that is the growing chain. Infrared and NMR spectroscopy identified the final polymer. The mechanism proposed is probably applicable also to other phenol oxidation processes yielding substituted poly(oxyphenylenes). The anomalous chemistry of those compounds of xenon, iodine, and tellurium in which the number of bonding electrons exceeds that given by Lewis valence theory has been considered in general terms by Musher [1] who coined the term “hypervalent” to describe these substances. The oxidizing properties of these compounds is in a general way similar to that of peroxides and other strong oxidizing agents, but has not been characterized in any exact fashion. We have observed [2] that the iodobenzene esters have polymeric analogs of the formula, [-I(R)OOCXCOO-], and these compounds are stable oxidizing agents (R = aryl; X = alkylene or arylene). We have been interested in determining if -I(R)OXO- compounds can be formed. The first question to consider is the stability of bonds in -OI(R)O- compounds. Only acyl derivatives are known [3]. However, the possibility 相似文献
The photon energy differential shape of the second order matrix element for the two-photon (2E1) decay of the 1s2s1S0 level in He-like gold has been measured. The results are in agreement with a recent fully relativistic calculation. The corresponding 2E1 matrix element deviates from those in lighter He-like systems due to the strong central field in a heavy two-electron ion. 相似文献
The electric form factor of the neutron, GE,n, has been measured at the Mainz Microtron by recoil polarimetry in the quasielastic D(¯e, e¯n)p reaction. Three data points have been extracted at squared four-momentum transfers Q2 = 0.3, 0.6 and 0.8 (GeV/c)2. Corrections for nuclear binding effects have been applied.This revised version was published online in March 2005. In the previous version, the email address of one author was inadvertently assigned to multiple authors. 相似文献
A Seifert matrix is a square integral matrix satisfying
To such a matrix and unit complex number there corresponds a signature,
Let denote the set of unit complex numbers with positive imaginary part. We show that is linearly independent, viewed as a set of functions on the set of all Seifert matrices.
If is metabolic, then unless is a root of the Alexander polynomial, . Let denote the set of all unit roots of all Alexander polynomials with positive imaginary part. We show that is linearly independent when viewed as a set of functions on the set of all metabolic Seifert matrices.
To each knot one can associate a Seifert matrix , and induces a knot invariant. Topological applications of our results include a proof that the set of functions is linearly independent on the set of all knots and that the set of two-sided averaged signature functions, , forms a linearly independent set of homomorphisms on the knot concordance group. Also, if is the root of some Alexander polynomial, then there is a slice knot whose signature function is nontrivial only at and . We demonstrate that the results extend to the higher-dimensional setting.
Fully functional HIV-1-specific CD8 and CD4 effector T-cell responses are vital to the containment of viral activity and disease
progression. These responses are lacking in HIV-1-infected patients with progressive disease. We attempted to augment fully
functional HIV-1-specific CD8 and CD4 effector T-cell responses in patients with advanced chronic HIV-1 infection. 相似文献
An international laboratory intercomparison of actinides in human tissues was organized by the United States Transuranium Registry and the National Institute of Standards and Technology. Five laboratories from the United States, United Kingdom, and Japan participated in the intercomparison. The laboratories were requested to analyze Standard Reference Materials 4351 (Human Lung) and 4352 (Human Liver) for239Pu and240Pu concentration. Approximately equivalent measurement capabilities were generally found among the participants. The results of this intercomparison were statistically comparable to those used for the original certification of the SRM's and were combined for a re-evaluation of the certified values. The combined data sets provide a better characterization of the inhomogeneity of these reference materials and result in a better basis for certification.Deceased. 相似文献