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.     

Nucleation theory: Fisher's droplet picture and microscopic surface tension

Fisher's droplet picture is used to define a “microscopic” surface tension for small droplets. The nucleation rate is then calculated. Excellent agreement between experiments and our calculations has been found for H₂O, CH₃OH, C₂H₅OH, NH₃, C₆H₆, CHCl₃ and CCl₃F.     

A Highly stereospecific and efficient synthesis of homopentafluoro- phenylalanine

A short and efficient synthesis of homopentafluorophenylalanine (6) from oxazolidine aldehyde 1 in 57% overall yield and in > 98% ee is described. The enantiomeric excess of the product was determined by 19F NMR analysis of the coupling product derived from 5 and L-Ser(O-t-Bu)-OCH3, by comparison to a dipeptide obtained from racemic 5.     

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.     

A linked risk group model for investigating the spread of HIV

This paper describes a model that simulates the spread of HIV and progression to AIDS. The model is based on classical models of disease transmission. It consists of six linked risk groups and tracks the numbers of infectives, AIDS cases, AIDS related deaths, and other deaths of infected persons in each risk group. Parametric functions are used to represent risk-group-specific and time-dependent average contact rates. Contacts are needle sharing, sexual contacts, or blood product transfers.

An important feature of the model is that the contact rate parameters are estimated by minimizing differences between AIDS incidence and reported AIDS cases adjusted for undercounting biases. This feature results in an HIV epidemic curve that is analogous to one estimated by backcalculation models but whose dynamics are determined by simulating disease transmission. The model exhibits characteristics of both the disease transmission and the backcalculation approaches, i.e., the model:

• reconstructs the historical behavior patterns of the different risk groups,

• includes separate effects of treatment and changes in average contact rates,

• accounts for other mortality risks for persons infected with HIV,

• calculates short-term projections of AIDS incidence, HIV incidence, and HIV prevalence,

• calculates cumulative HIV infections (the quantity calculated by backcalculation approaches) and HIV prevalence (the quantity measured by seroprevalence and sentinel surveys). This latter feature permits the validation of the estimates generated by two distinct approaches.

We demonstrate the use of the model with an application to U.S. AIDS data through 1991.