1H chemical shifts in NMR: Part 23, the effect of dimethyl sulphoxide versus chloroform solvent on 1H chemical shifts

The 1H chemical shifts of 124 compounds containing a variety of functional groups have been recorded in CDCl3 and DMSO-d6 (henceforth DMSO) solvents. The 1H solvent shift Delta delta = delta(DMSO) - delta(CDCl3) varies from -0.3 to +4.6 ppm. This solvent shift can be accurately predicted (rms error 0.05 ppm) using the charge model of alpha, beta, gamma and long-range contributions. The labile protons of alcohols, acids, amines and amides give both, the largest solvent shifts and the largest errors. The contributions for the various groups are tabulated and it is shown that for H.C.C.X gamma-effects (X = OH, NH, =O, NH.CO) there is a dihedral angle dependence of the gamma-effect. The group contributions are discussed in terms of the possible solvent-solute interactions. For protic hydrogens, hydrogen bonding is the dominant interaction, but for the remaining protons solvent anisotropy and electric field effects appear to be the major factors.     

Discovery of lucensimycins A and B from Streptomyces lucensis MA7349 using an antisense strategy

Inhibition of protein synthesis is one of the validated and highly successful targets for inhibition of bacterial growth; this mechanism is a target of a large number of clinical drugs. Ribosomal protein S4, a primary protein, is a potential target for the discovery of antibacterial agents. We describe, using an antisense-sensitized rpsD Streptomyces aureus strain, the discovery and activity of lucensimycins A and B. [structure: see text].     

Were Chinchorros exposed to arsenic? Arsenic determination in Chinchorro mummies' hair by laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS)

Chinchorros, a fishermen culture, who lived about 7000 years ago in the coastal region of the Atacama Desert in the northern outpost of present-day Chile, practiced an intricate system of mummification of their dead. The drinking water in this region is rich with arsenic, and the mummies were found in these arsenic endemic areas. Well preserved mummy hair samples provided a unique opportunity to explore the ancient arsenic exposure of the Chinchorros by laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) using a single hair strand without any elaborate sample preparation. Forty-six hair samples from mummies found in five burial sites around the Atacama Desert, Chile, were used for this study. After cleaning, hair strands were placed on mounting tape and ablated using a Nd-YAG UV laser coupled to ICP-MS. A suite of contemporary human hair from the same region with known arsenic concentrations was used for calibration of LA-ICP-MS. Satisfactory linear calibration functions were obtained for arsenic in hair. The method detection limit was 0.8 µg/g and the sample throughput for this method is ∼ 10 samples per hour. It appears that mummies from the Morro (Arica), Iquique and Camarones had the elevated concentration of arsenic in hair (AsH > 10 µg/g) in this sub-set of samples, where Morro had the broad distribution of As concentrations.     

Structure and NMR assignment in AlPO4-15: A combined study by diffraction,MAS NMR and first-principles calculations

A multi-technique investigation involving X-ray diffraction, solid-state NMR and first-principle calculations was carried out on the aluminophosphate material AlPO₄-15. A synchrotron X-ray single-crystal diffraction study was carried out on the same sample as that used in solid-state NMR studies. The model from the single crystal study, together with a model from a literature high resolution study of the same material, was used as starting points for the first-principles calculations of the NMR parameters. This enabled the ³¹P and ²⁷Al NMR spectra to be unambiguously assigned and all the NMR parameters calculated agreed well with the experimental spectra even without relaxing the X-ray derived structural models.     

Activation analysis for mercury in biological samples at nanogram level

A new method has been devised for determining mercury in samples of biological origin. It is based on complete ignition of the sample in a silica tube, trapping volatile interfering activities such as bromine or chlorine, and selectively adsorbing mercury on a strip of filter paper which has been previously impregnated with elemental selenium. This strip is later counted for quantitative evaluation. The versatility of the method has been demonstrated by the analysis of a wide range of samples such as water, cellulose, flour, fish solubles or animal blood samples with mercury contents between 1 and 200 ng g of sample.     

Nickel determination in biological materials at ultratrace level by fast neutron radiochemical activation analysis

Using radiochemical separation of cobalt following the fast neutron reaction⁵⁸Ni(n, p.)⁵⁸Co and long high fluence irradiation, we attempted to improve the determination limit for Ni to the nanogram and sub-nanogram level. A Compton suppression spectrometer was shown to be the best choice compared to co-axial or well-type HPGe detectors. Results for low level biological reference materials such as serum and milk powder are discussed. Use of both dried and pre-ashed samples showed that losses of Ni and Co on ashing are non-significant. The influence of the silica ampoule blank was also investigated.     

Determination of lead,cadmium and thallium by neutron activation analysis in environmental samples

A radiochemical procedure for simultaneous determination of lead (²⁰³Pb), thallium (²⁰²TI) and cadmium (¹¹⁵Cd^115mIn) after fast neutron activation, based on ion-exchange separation from bromide medium and additional purification steps for Pb and Tl is described. Radioactive tracers²¹⁰Pb and¹⁰⁹Cd were used for determination of the chemical yields of Pb and Cd; for Tl it was determined gravimetrically. Two standard reference materials, BCR CRM No. 146 Sewage Sludge and NIST SRM 1633a Coal Fly Ash were analyzed and satisfactory agreement with certified values was obtained.     

Simultaneous determination of iodine and selenium in biological samples by radiochemical neutron activation analysis

Summary Regarding the favourably sensitive nuclear characteristics of iodine and of selenium but the very different half lives of their induced nuclides ¹²⁸I and ⁷⁵Se, a radiochemical neutron activation analysis method for simultaneous determination of these elements in a single sample was developed. It is based on the double irradiation LICSIR technique — Long Irradiation for Se (40h), Cooling (a week or more), Short Irradiation for iodine (1–15 min) with following Radiochemistry. After the second short irradiation, the sample is ignited in an oxygen flask and iodine and selenium are sequentially and selectively extracted as elemental iodine and 5-nitro-2,1,3 benzoselena diazole chelate. With the described method biological samples were analysed and the reliability of the results was checked by the analyses of different standard reference materials. Good agreement with certified values and high radiochemical purity of the spectra show the applicability of the radiochemical separation developed.