Preservativity logic: An analogue of interpretability logic for constructive theories

In this paper we study the modal behavior of Σ‐preservativity, an extension of provability which is equivalent to interpretability for classical superarithmetical theories. We explain the connection between the principles of this logic and some well‐known properties of HA, like the disjunction property and its admissible rules. We show that the intuitionistic modal logic given by the preservativity principles of HA known so far, is complete with respect to a certain class of frames.     

Structural measures of element-oxygen bond covalency from the changes to the delocalisation of the carboxylate ligand

The data set of more than 40,000 crystal structures containing the carboxylate group that have been deposited in the CSD has been used to examine the structural changes that occur in the carboxylate C-O bond lengths upon binding to different elemental centres. We report here quantifiable structural changes that are dependent on the elemental centre with which the group is interacting. For the main-group elements the trends are entirely periodic and follow those traditionally associated with covalency; elements exhibiting electronegativity closest to that of oxygen exhibit the largest structural change. In addition, we find the measure is extendable to both the transition metals and the lanthanoids and actinoids. Amongst the transition metals the trends of Pauling neutrality are not only maintained, but are quantifiable. The difference between the two C-O bond lengths increases with oxidation state and decreases with an increase in coordination number. All of the lanthanoids exhibit covalency within error of each other and the bonds to the actinoids are found to be more covalent than those to the lanthanoids. From the data analysis we are able to derive a correlation between the lengths of the two carboxylate arms that allows us to quantify percentage covalent character defined in terms of the resonance contributions to the carboxylate group.     

Mass spectrometric analysis of porcine rhodopsin

Rhodopsin is the dim light photosensitive pigment of animals. In this work, we undertook to study the structure of rhodopsin from swine and compare it with bovine and rat rhodopsin. Porcine rhodopsin was analyzed using methodology developed previously for mass spectrometric analysis of integral membrane proteins. Combining efficient protein cleavage and high performance liquid chromatography separation with the sensitivity of mass spectrometry (MS), this technique allows the observation of the full protein map and the posttranslational modifications of the protein in a single experiment. The rhodopsin protein from a single porcine eye was sequenced completely, with the exception of two single-amino acid fragments and one two-amino acid fragment, and the gene sequence reported previously was confirmed. The posttranslational modifications, similar to the ones reported previously for bovine and rat rhodopsin, were also identified. Although porcine rhodopsin has a high degree of homology to bovine and rat rhodopsins and most of their posttranslational modifications are identical, the glycosylation and phosphorylation patterns observed were different. These results show that rhodopsin from a single porcine eye can be characterized completely by MS. This technology opens the possibility of rhodopsin structural and functional studies aided by powerful mass spectrometric analysis, using the fellow eye as an internal control.     

RPE65 and the Accumulation of Retinyl Esters in Mouse Retinal Pigment Epithelium

The RPE65 protein of the retinal pigment epithelium (RPE) enables the conversion of retinyl esters to the visual pigment chromophore 11‐cis retinal. Fresh 11‐cis retinal is generated from retinyl esters following photoisomerization of the visual pigment chromophore to all‐trans during light detection. Large amounts of esters accumulate in Rpe65^?/? mice, indicating their continuous formation when 11‐cis retinal generation is blocked. We hypothesized that absence of light, by limiting the conversion of esters to 11‐cis retinal, would also result in the build‐up of retinyl esters in the RPE of wild‐type mice. We used HPLC to quantify ester levels in organic extracts of the RPE from wild‐type and Rpe65^?/? mice. Retinyl ester levels in Sv/129 wild‐type mice that were dark adapted for various intervals over a 4‐week period were similar to those in mice raised in cyclic light. In C57BL/6 mice however, which contain less Rpe65 protein, dark adaptation was accompanied by an increase in ester levels compared to cyclic light controls. Retinyl ester levels were much higher in Rpe65^?/? mice compared to wild type and kept increasing with age. The results suggest that the RPE65 role in retinyl ester homeostasis extends beyond enabling the formation of 11‐cis retinal.     

A new ent-clerodane diterpenoid from Crassocephalum bauchiense Huch. (Asteraceae)

A phytochemical investigation of the whole plant of Crassocephalum bauchiense Huch. resulted in the isolation of a new clerodane diterpenoid, ent-2β,18,19-trihydroxycleroda-3,13-dien-16,15-olide (1), together with two known flavonoids 3′,5-dihydroxy-4′,5′,6,7,8-pentamethoxyflavone (2) and 4′,5-dihydroxy-3′,5′,6,7,8-pentamethoxyflavone (3). The compounds were tested against the chloroquine-sensitive 3D7 strain of Plasmodium falciparum. Compound 2 showed weak activity (IC₅₀ = 10.1 g/mL) whilst compounds 1 and 3 were inactive. The structures of the compounds were elucidated by using detailed spectral analyses, especially ¹H and ¹³C NMR, ¹H–¹H COSY, NOESY, HMBC and HR-ESI-MS.     

Precipitate assemblies formed on dislocation loops in aluminium-silver-copper alloys

The precipitation microstructure of the γ′ (AlAg₂) intermetallic phase has been examined in aluminium-silver-copper alloys. The microstructure developed in an Al-0.90at.%Ag-90at.Cu alloy was significantly different from that reported for binary Al-Ag alloys. The orientation relationship between the matrix and precipitate was unchanged; however, the γ′ phase formed assemblies with a two-dimensional, open arrangement of precipitates. Each such assembly contained two variants of the γ′ phase alternately arranged to form a faceted elliptical unit. The θ′ (Al₂Cu) phase formed on these assemblies after further ageing. Each assembly was formed via repeated precipitation of the γ′ phase on dissociated segments of a single dislocation loop. This faceted elliptical assembly has not been previously reported for the γ′ precipitate. The difference between the precipitation behaviour of the γ′ phase in Al-Ag and Al-Ag-Cu alloys was attributed to copper modifying the as-quenched defect structure of the matrix. The formation of faceted elliptical γ′ phase assemblies clarifies earlier observations on the precipitate number density and mechanical properties of aluminium-silver-copper alloys.     

Evolution of Oxygen–Metal Electron Transfer and Metal Electronic States During Manganese Oxide Catalyzed Water Oxidation Revealed with In Situ Soft X‐Ray Spectroscopy

Manganese oxide (MnO_x) electrocatalysts are examined herein by in situ soft X‐ray absorption spectroscopy (XAS) and resonant inelastic X‐ray scattering (RIXS) during the oxidation of water buffered by borate (pH 9.2) at potentials from 0.75 to 2.25 V vs. the reversible hydrogen electrode. Correlation of L‐edge XAS data with previous mechanistic studies indicates Mn^IV is the highest oxidation state involved in the catalytic mechanism. MnO_x is transformed into birnessite at 1.45 V and does not undergo further structural phase changes. At potentials beyond this transformation, RIXS spectra show progressive enhancement of charge transfer transitions from oxygen to manganese. Theoretical analysis of these data indicates increased hybridization of the Mn?O orbitals and withdrawal of electron density from the O ligand shell. In situ XAS experiments at the O K‐edge provide complementary evidence for such a transition. This step is crucial for the formation of O₂ from water.