Concise and enantioselective synthesis of the aminocyclitol core of hygromycin A

[reaction: see text] Stereoselective aminohydroxylation and dihydroxylation using osmium(VIII) oxidants enabled the short and efficient synthesis of the aminocyclitol core of hygromycin A. In addition to allowing the selective introduction of the heteroatoms N and O, the use of osmium (via an osmate ester) as a protecting group for a 1,2-glycol is also reported. This tactic allowed efficient differentiation of otherwise equivalent hydroxyl groups and allowed us to complete the synthesis in short order (14 steps) and excellent overall yield (12%).     

Efficient acyclic stereocontrol using the tethered aminohydroxylation reaction

[reaction: see text] The tethered aminohydroxylation (TA) of acyclic allylic carbamates has been achieved in a stereospecific and stereoselective manner. Unusually high levels of stereocontrol were observed in the oxidation of 1,1-disubstituted substrates.     

The lignol approach to biorefining of woody biomass to produce ethanol and chemicals

Processes that produce only ethanol from lignocellulosics display poor economics. This is generally overcome by constructing large facilities having satisfactory economies of scale, thus making financing onerous and hindering the development of suitable technologies. Lignol Innovations has developed a biorefining technology that employs an ethanol-based organosolv step to separate lignin, hemicellulose components, and extractives from the cellulosic fraction of woody biomass. The resultant cellulosic fraction is highly susceptible to enzymatic hydrolysis, generating very high yields of glucose (>90% in 12–24h) with typical enzyme loadings of 10–20 FPU (filter paper units)/g. This glucose is readily converted to ethanol, or possibly other sugar platform chemicals, either by sequential or simultaneous saccharification and fermentation. The liquor from the organosolv step is processed by well-established unit operations to recover lignin, furfural, xylose, acetic acid, and a lipophylic extractives fraction. The process ethanol is recovered and recycled back to the process. The resulting recycled process water is of a very high quality, low BOD₅, and suitable for overall system process closure. Significant benefits can be attained in greenhouse gas (GHG) emission reductions, as per the Kyoto Protocol. Revenues from the multiple products, particularly the lignin, ethanol and xylose fractions, ensure excellent economics for the process even in plants as small as 100 mtpd (metric tonnes per day) dry woody biomass input—a scale suitable for processing wood residues produced by a single large sawmill.     

Zinc(II) Hydration in Aqueous Solution: A Raman Spectroscopic Investigation and An ab initio Molecular Orbital Study of Zinc(II) Water Clusters

Raman spectra of aqueous Zn(II)–perchlorate solutions were measured over broad concentration (0.50–3.54 mol-L^–1) and temperature (25–120°C) ranges. The weak polarized band at 390 cm^–1 and two depolarized modes at 270 and 214 cm^–1 have been assigned to ₁(a _1g), ₂(e _g), and ₅(f _2g) of the zinc–hexaaqua ion. The infrared-active mode at 365 cm^–1 has been assigned to ₃(f _1u). The vibrational analysis of the species [Zn(OH₂) ₂ ⁺ ] was done on the basis of O _h symmetry (OH₂ as point mass). The polarized mode ₁(a _1g)-ZnO₆ has been followed over the full temperature range and band parameters (band maximum, full width at half height, and intensity) have been examined. The position of the ₁(a _1g)-ZnO₆ mode shifts only about 4 cm^–1 to lower frequencies and broadens by about 32 cm^–1 for a 95°C temperature increase. The Raman spectroscopic data suggest that the hexaaqua–Zn(II) ion is thermodynamically stable in perchlorate solution over the temperature and concentration range measured. These findings are in contrast to ZnSO₄ solutions, recently measured by one of us, where sulfate replaces a water molecule of the first hydration sphere. Ab initio geometry optimizations and frequency calculations of [Zn(OH₂) ₂ ⁺ ] were carried out at the Hartree–Fock and second-order Møller–Plesset levels of theory, using various basis sets up to 6-31 + G*. The global minimum structure of the hexaaqua–Zn(II) species corresponds with symmetry T _h. The unscaled vibrational frequencies of the [Zn(OH₂) ₂ ⁺ ] are reported. The unscaled vibrational frequencies of the ZnO₆, unit are lower than the experimental frequencies (ca. 15%), but scaling the frequencies reproduces the measured frequencies. The theoretical binding enthalpy for [Zn(OH₂) ₂ ⁺ ] was calculated and accounts for ca. 66% of the experimental single-ion hydration enthalpy for Zn(II).Ab initio geometry optimizations and frequency calculations are also reported for a [Zn(OH₂) ₂ ¹⁸ ] (Zn[6 + 12]) cluster with 6 water molecules in the first sphere and 12 in the second sphere. The global minimum corresponds with T symmetry. Calculated frequencies of the zinc [6 + 12] cluster correspond well with the observed frequencies in solution. The ₁-ZnO₆ (unscaled) mode occurs at 388 cm^–1 almost in perfect correspondence to the experimental value. The theoretical binding enthalpy for [Zn(OH₂) ₂ ¹⁸ ] was calculated and is very close to the experimental single ion-hydration enthalpy for Zn(II). The water molecules of the first sphere form strong hydrogen bonds with water molecules in the second hydration shell because of the strong polarizing effect of the Zn(II) ion. The importance of the second hydration sphere is discussed.     

The potential use of continuous-flow isotope-ratio mass spectrometry as a tool in forensic soil analysis: a preliminary report

The use of continuous-flow isotope-ratio mass spectrometry (CF-IRMS) as a tool in soil analysis has been assessed as part of a larger study using a number of geological techniques applied in a forensic context. Carbon and nitrogen isotopic ratios, delta13C and delta15N, have been analysed to investigate situations which have arisen from crime casework. Three questions have been addressed: the role of spatial variation found over the short-scale (less than 20 m), temporal variation over a period of almost 2 years, and the variation found between source soils and soil transferred to footwear soles during a simple one-stage transfer process. Results are presented for the three experiments. The use of carbon and nitrogen isotopes has been shown to be useful in discriminating between soil types and sample locations, even when sampling occurs at a different time (as might be the case with a crime scene). In cases of primary transfer (from a source soil by a one-stage transfer to another surface, in this case, shoes and boots), the combination of carbon and nitrogen isotope ratios is a valuable tool in discriminating between sites and in showing the relationship of the transferred samples to the relevant source soils. Used in combination with other analytical techniques, isotopic analysis may prove to be a useful tool in a forensic context.     

Isomerism in poly(tetrafluoroethylene-alt-trifluoronitrosomethane)

The structures of samples of poly(tetrafluoroethylene-alt-trifluoronitrosomethane) prepared by bulk copolymerization at temperatures in the range ?30 to +90° have been investigated using ¹⁹F-NMR spectroscopy. Whilst the predominant mode of addition of CF₃NO to a growing copolymer chain gives the

radical, occasional reverse additions occur, giving

. The activation energy for the reverse addition is ca 8.5 kJ mol^?1 greater than that of the predominant propagation reaction.