Quantum Crystallography and Complementary Bonding Analysis of Agostic Interactions in Titanium Amides

Agostic interactions involving titanium are textbook examples for C−H bond activation. Therefore, it is surprising that there is no study in the literature in which the hydrogen atom in the C−H⋅⋅⋅Ti interaction has been determined reliably, although nearly all the criteria for assessing the strength and character of the agostic interaction depend on the hydrogen atom and its position. Here, we demonstrate with quantum crystallographic techniques how hydrogen atoms in a series of three titanium amides can indeed be localized accurately and precisely based on routine single-crystal X-ray diffraction data. Once the hydrogen positions have been established, theoretical and experimentally fitted bonding analyses reveal that the C−H⋅⋅⋅Ti interaction becomes stronger with increasing inter-ligand London dispersion stabilization of bulky alkyl groups.     

Iridium-catalyzed alternative of the Meinwald rearrangement

A novel and easy to handle procedure for the regioselective rearrangement of epoxides has been developed, based on an iridium catalyst.     

Constraint theory,vector percolation and glass formation

We connect the Phillips constraint theory of glass formation to numerical simulations of vector percolation with nearest neighbor central forces. Feng and Sen have shown that the addition of bond-bending forces shifts the vector percolation threshold to the scalar value in two dimensions. Using constraint theory we show that in the mean-field approximation for d > 2 the correct non-central vector threshold lies between the scalar and central vector thresholds. For a fully equilibrated statically disordered network mean-field theory may be almost exact.     

Carbocyclic analogs of thymine nucleosides and related 1-substituted thymines

The carbocyclic analogs of thymidine (IXf), 1-β-ribofuranosylthymine (IXg), and 1-β-3′-deoxyribofuranosyl-thymine (IXe) were synthesized by incorporating modifications into the Shaw method of synthesizing 2,4-(1H,3H)pyrimidinediones via acryloylureas. Simpler analogs of thymine nucleosides were also prepared by this method. The carbocyclic analog of thymidine displayed modest activity against Leukemia L1210 in vivo. It differs from a compound prepared previously by a Prins reaction.     

Comparison of sulfide-selective electrode and gas-stripping monitors for hydrogen sulfide in effluents

A commercial prototype monitor, in which a sulfide-selective electrode detects hydrogen sulfide with a pH electrode used as the reference electrode in a sample acidified to pH <5, is compared to a monitor in which a solid-state sensor detects hydrogen sulfide stripped from the sample by an air—CO₂ mixture. Each monitor has a detection limit of ?0.005 mg kg^-1 and both monitors performed well over a six-month period in the field, sampling a heavy water plant effluent. Both monitors are simple to operate, calibrate, and maintain, but their accuracies are affected by oil and particulates in the sample. Advantages of using the suifide/glass electrode detection system in acidic solutions are presented.     

Extraction of maleic hydrazide residues from potato crisps and their determination using high-performance liquid chromatography with UV and atmospheric pressure chemical ionisation mass spectrometric detection

A method was required for the determination of maleic hydrazide residues in potato crisps. A published method for the extraction of the analyte from onions and potatoes was evaluated and found to be inappropriate due to the inability of the extracting solvent to penetrate the oily matrix. A method was developed to overcome this problem; the resulting recovery data (mean=92.9%. R.S.D.=8.3%, N=16) confirmed its efficiency, and was used to analyse 48 retail potato crisp samples. To confirm possible residues identified by screening with HPLC-UV, and HPLC-atmospheric pressure chemical ionization MS method was developed. There was good agreement between the data obtained from the detection techniques (R²=0.978, slope=1.11).     

Immobilized Biomaterials—Techniques and Applications

The immobilization of enzymes, cofactors and whole cells offers the potential of economical exploitation of biomaterial activity. Enzymes or cells can be immobilized by binding to carriers through adsorption or covalent linkages or by entrapment in a polymer matrix or microencapsulation. The development of immobilized biomaterial systems requires the involvement of biochemical, kinetics and reactor design principles. Examples of commercial scale applications of immobilized biomaterial systems are the production of a fructose-rich syrup from starch and the synthesis of L -amino acids by selective hydrolysis of N-acyl-D ,L -amino acids.