Biomedical subjects

S P Bates

Publications and source records attributed to S P Bates.

6 recordsLinked to original sources

PubMed2006

Structure and hydrogen bonding in neat N-methylacetamide: classical molecular dynamics and Raman spectroscopy studies of a liquid of peptidic fragments.

The results of classical molecular dynamics (MD) simulations and Raman spectroscopy studies of neat liquid N-methylacetamide (NMA), the simplest model system relevant to the peptides, are reported as a function of temperature and pressure. The MD simulations predict that near ambient conditions, the molecules form a hydrogen bond network consisting primarily of linear chains. Both the links between molecules within the hydrogen-bonded chains and the associations between chains are stabilized by weak methyl-donated "improper" hydrogen bonds. The three-dimensional structural motifs observed in the liquid show some similarity to protein beta-sheets. The temperature and pressure dependence of the hydrogen bond network, as probed by the mode frequency of the experimentally determined amide-I Raman band, blue shifts on heating and red shifts under compression, respectively, suggesting weakened and enhanced hydrogen bonding in response to temperature and pressure increases. Disruption of the hydrogen-bonding network is clearly observed in the simulation data as temperature is increased, whereas the improper hydrogen bonding is enhanced under compression to reduce the energetic cost of increasing the packing fraction. Because of the neglect of polarizability in the molecular model, the computed dielectric constant is underestimated compared to the experimental value, indicating that the simulation may underestimate dipolar coupling in the liquid.

Acetamides↗

PubMed2005

Segregation in aqueous methanol enhanced by cooling and compression.

Molecular segregation in methanol-water mixtures is studied across a wide concentration range as a function of temperature and pressure. Cluster distributions obtained from both neutron diffraction and molecular dynamics simulations point to significantly enhanced segregation as the mixtures are cooled or compressed. This evolution toward greater molecular heterogenity in the mixture accounts for the observed changes in the water-water radial distribution function and there are indications also of a change in the topology of the water clusters. The observed behavior is consistent with an approach to an upper critical solution point. Such a point would appear to be "hidden" below the freezing line, thereby precluding observation of the two-fluid region.

Journal Article↗

PubMed2004

Methanol-water solutions: a bi-percolating liquid mixture.

An extensive series of neutron diffraction experiments and molecular dynamics simulations has shown that mixtures of methanol and water exhibit extended structures in solution despite the components being fully miscible in all proportions. Of particular interest is a concentration region (methanol mole fraction between 0.27 and 0.54) where both methanol and water appear to form separate, percolating networks. This is the concentration range where many transport properties and thermodynamic excess functions reach extremal values. The observed concentration dependence of several of these material properties of the solution may therefore have a structural origin.

Journal Article↗

PubMed1997

3-D histo-radiographic comparison of surgical clearances of microcalcified lesions in breast localization biopsies.

There is controversy as to the value of the radiological or pathological estimation of surgical clearance of microcalcifying breast lesions. An important part of this issue has been addressed by coordinated three-dimensional radiographic and histological examination of a prospective consecutive series of 40 benign and malignant mammographically detected lesions in surgical breast biopsy specimens containing microcalcifications, including 20 cases of ductal carcinoma in situ. They were radiographed from four viewpoints by means of rotation in a radiolucent tetrahedral container. The planes of histological examination were then chosen to correspond to the radiographic view showing the minimum separation of the edge of the specimen and the outermost microcalcification. There was a close correlation (Spearman ranked) between the least tetrahedral radiographic distance and the corresponding histological distance separating the surgical margin of excision. There were, however, incompatible Wilcoxon signed ranking orders when comparing the least tetrahedral distance or the histological distance with all four single radiographic views, including the conventional specimen radiographic view. Two-dimensional specimen mammography and standardized histological examination are suboptimal and may thus have contributed to confusion as to the value of determining adequate surgical excision of ductal carcinoma in situ of the breast. Although labour-intensive, use of four-view radiography and choice of the appropriate plane of histological examination give a better correlation of the radiographic estimates of surgical clearance with histology than single-view specimen radiography and arbitrary histological sectioning.

Biopsy↗

PubMed1977

Propionyl-CoA carboxylase deficiency in a patient with biotin-responsive 3-methylcrotonylglycinuria.

The abnormal metabolites 3-hydroxypropionic acid (1.6-4.0 mg/day) and methylcitric acid (3.7-5.8 mg/day) were identified and quantitated in the urine of a patient in whom biotin-responsive 3-methylcrotonylglycinuria and deficiency of 3-methylcrotonyl-CoA carboxylase had previously been documented. The level of excretion of these metabolites was in the lower range of those found in patients with propionic acidemia in whom there is a deficiency of propionyl-CoA carboxylase. The activity of this enzyme in fibroblasts derived from the patient and grown in media low in biotin was 4% of normal. This is the range of patients with propionyl-CoA carboxylase deficiency. Documented deficiency in this patient of two carboxylase, both of which contain biotin, suggests that the primary defect is in the metabolism of biotin.

Biotin↗

PubMedDate not supplied

New avenues in 3-D computerised (stereopathological) imaging of breast cancer (review).

Multimodal methods of three-dimensional (3-D) imaging of breast cancer are described. These involve scanning confocal microscopy, using 50 MHz acoustic or near-infrared images, four-view (tetrahedral) radiography and x-ray projection microscopy. Computerised volume data from these techniques can be used to produce three-dimensional images of tissue ranging from 500 microns to approximately 4 mm in thickness. Preliminary findings indicate that stereoscopic images or 3-D computerised reconstructions are capable of advancing the understanding of the structure of ductal carcinoma in situ, lesions simulating microinvasive breast carcinoma, surgical clearance of high-grade calcifying ductal carcinoma in situ, and the 3-D growth patterns of invasive forms of breast carcinoma. In the future computerised image fusion techniques seem likely to be able to take advantage of multimodal imaging of breast cancers, thus correcting primary imaging artefacts, improving robustness, and combining complementary information. In addition, the use of computerised tetrahedral radiography may change the intraoperative assessment of breast cancers, which mostly depend at present upon subsequent laboratory procedures that take days to perform.

Breast Neoplasms↗