An examination of UHF methods for atoms in the first three rows

The reliability and usefulness of UHF methods of calculating hyperfine parameters has been examined. Comparisons with CI and SEHF methods are made.A detailed analysis of OPHF calculations for first and second row atoms has shown that various one-electron properties are accurately described by physically reasonable functions of the atomic number Z. In addition there is a strong correlation between these properties. This has led to a method whereby UHF spin densities across a row of atoms can be obtained from UHF calculations of only two atoms in that row.A strong correlation between experimental and UHF spin densities is shown to exist for atoms of the first three rows. This is used to predict experimental spin densities for atoms in these rows which have not yet been measured experimentally.     

Insights into the hydrogen-abstraction reactions of diol dehydratase: relevance to the catalytic mechanism and suicide inactivation

High-level quantum chemistry calculations have been used to examine the hydrogen-abstraction reactions of diol dehydratase (DDH) in the context of both the catalytic mechanism and the enzyme dysfunction phenomenon termed suicide inactivation. The barriers for the catalytic hydrogen-abstraction reactions of ethane-1,2-diol and propane-1,2-diol are examined in isolation, as well as in the presence of various Br?nsted acids and bases. Modest changes in the magnitudes of the initial and final abstraction barriers are seen, depending on the strength of the acid or base, and on whether these effects are considered individually or together. The most significant changes (ca. 20 kJ mol(-1)) are found for the initial abstraction barrier when the spectator OH group is partially deprotonated. Kinetic isotope effects including Eckart tunneling corrections (KIEs) have also been calculated for these model systems. We find that contributions from tunneling are of a magnitude similar to that of the contributions from semiclassical theory alone, meaning that quantum effects serve to significantly accelerate the rate of hydrogen transfer. The calculated KIEs for the partially deprotonated system are in qualitative agreement with experimentally determined values. In complementary investigations, the ability of DDH to become deactivated by certain substrate analogues is examined. In all cases, the formation of a stable radical intermediate causes the hydrogen re-abstraction step to become an extremely endothermic process. The consequent inability of 5'-deoxyadenosyl radical to be regenerated breaks the catalytic cycle, resulting in the suicide inactivation of DDH.     

Pore-Scale Numerical Investigation on Chemical Stimulation in Coal and Permeability Enhancement for Coal Seam Gas Production

Permeability is a controlling factor for gas migration in coal seam reservoirs and has invariably been the barrier to economically viable gas production in certain deposits. Cleats are the main conduits for gas flow in coal seams though cleat mineralisation is known to significantly reduce permeability. Cleat demineralisation by the use of acids may enhance the effective cleat aperture and therefore permeability. This modelling study examines how acids transport through coal subject to reactive cleat mineralisation, and develops a fundamental understanding of the mechanisms controlling permeability change from pore scale to sample scale. A novel Lattice Boltzmann Method (LBM)-based numerical model for the simulation, prediction, and visualisation of the reaction transport is proposed to numerically investigate relationships between physio-chemical changes and permeability during coal stimulation. In particular, the work studies the interaction of acidic fluids (HCl) with reactive mineral (e.g. calcite) and assumed non-reactive mineral (e.g. coal) surfaces, mineral dissolution and mass transfer, and resultant porosity change. The reaction of a calcite cemented core sub-plug from the Bandanna Formation of Bowen Basin (Australia), is used as a study case. LBM simulations revealed a permeability enhancement (27.15 times of the pre-flooding permeability) along the x-axis after 20 min HCl flooding of a \(5.3~\hbox {cm} \times 5.3~\hbox {cm} \times 1.3~\hbox {cm}\) sub-section. The analysis and evaluation of the 4D permeability evolution is conducted as a contribution work for the fluid flow modelling in the subsurface petrophysical conditions, at the micron to centimetre scales. The simulation results demonstrate the proposed algorithm is capable for studies of multiple mineral reactions with disparate reaction rates.     

Assembly of polyamines via amino acids from three components using cobalt(III) template methodology

A versatile and efficient template synthesis has been developed to synthesise novel polyamines [e.g. rac-N3-(3-aminopropyl)butane-1,3-diamine, isospermidine 1] via amino acids [e.g. (2R,4S/2S,4R)-N4-(3-aminopropyl)-2,4-diaminopentanoic acid] using cobalt(III) to assemble the three precursor components in a biomimetic manner.     

Stereochemistry of hydrogen removal from the 'unactivated' C-3 position of 4-hydroxybutyryl-CoA catalysed by 4-hydroxybutyryl-CoA dehydratase

(R)- and (S)-gamma-[3-(2)H(1)]butyrolactones have been synthesised from (R)- and (S)-glycidol, respectively, and used to demonstrate that it is the pro-(S) hydrogen atom that is stereospecifically abstracted from C-3 of 4-hydroxybutyryl-CoA by 4-hydroxybutyryl-CoA dehydratase, and that this atom is not returned to C-4.     

Spurious nature of certain unitarity corrections to the isobar model for three hadron final states

Various methods of implementing unitarity corrections to the isobar model for three hadron final states are discussed, and it is explained why some lead to spurious effects because insufficient attention is paid to analyticity. Recent calculations of unitarity corrections in the processes A1 → πππ and πN → ππN are shown to contain spuriously large effects. This may explain why fits to the first process were worsened when these corrections were included.     

Recent Advances in the Biological Investigation of Organometallic Platinum-Group Metal (Ir,Ru, Rh,Os, Pd,Pt) Complexes as Antimalarial Agents

In the face of the recent pandemic and emergence of infectious diseases of viral origin, research on parasitic diseases such as malaria continues to remain critical and innovative methods are required to target the rising widespread resistance that renders conventional therapies unusable. The prolific use of auxiliary metallo-fragments has augmented the search for novel drug regimens in an attempt to combat rising resistance. The development of organometallic compounds (those containing metal-carbon bonds) as antimalarial drugs has been exemplified by the clinical development of ferroquine in the nascent field of Bioorganometallic Chemistry. With their inherent physicochemical properties, organometallic complexes can modulate the discipline of chemical biology by proffering different modes of action and targeting various enzymes. With the beneficiation of platinum group metals (PGMs) in mind, this review aims to describe recent studies on the antimalarial activity of PGM-based organometallic complexes. This review does not provide an exhaustive coverage of the literature but focusses on recent advances of bioorganometallic antimalarial drug leads, including a brief mention of recent trends comprising interactions with biomolecules such as heme and intracellular catalysis. This resource can be used in parallel with complementary reviews on metal-based complexes tested against malaria.     

Versatile synthesis of functionalised dibenzothiophenes via Suzuki coupling and microwave-assisted ring closure

Amino-substituted biphenyls were obtained by Suzuki cross-coupling of 2,6-dibromoaniline with a phenylboronic acid (substituted with Me, NO(2), OH, OMe or Cl) preferably assisted by microwave irradiation. Conversion of the amino group into a thiol preceded a base-induced intramolecular substitution, also facilitated by microwave heating, to generate the second C-S bond of the target dibenzothiophene. The 1-, 2-, 3- or 4-substituted 6-halodibenzothiophenes obtained were subjected to a palladium-mediated coupling with 2-morpholin-4-yl-8-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-4H-chromen-4-one to give the respective 6-, 7-, 8- or 9-substituted dibenzothiophen-4-ylchromenones. These compounds were evaluated as inhibitors of DNA-dependent protein kinase (DNA-PK) and compared to the parent 8-(dibenzo[b,d]thiophen-4-yl)-2-morpholin-4-yl-4H-chromen-4-one. Notably, derivatives bearing hydroxy or methoxy substituents at C-8 or C-9 retained activity, whereas substitution at C-7 lowered activity. Substitution with chloro at C-6 was not detrimental to activity, but a chloro group at C-7 or C-8 reduced potency. The data indicate permissive elaboration of hydroxyl at C-8 or C-9, enabling the possibility of improved pharmaceutical properties, whilst retaining potency against DNA-PK.