Computational study of the molecular and crystal structure and selected physical properties of octahydridosilasequioxane–(Si2O3H2)4. I. Electronic and structural aspects

The free molecule octahydridosilasequioxane, Si8O12H8, was computationally studied, as well as embedded in the unit cell. The point group of the free molecule is indeed Oh, and its crystal symmetry is reduced to C3i, thus confirming the occurrence of two different types of Si−O−Si bond lengths found experimentally. The molecular orbitals of the free molecule show that some electron density occurs in the cubic cavity, thus contributing to the opening of the Si−O−Si angle. A study of the packing in the unit cell identifies a new type of packing scheme in which eight (partial) molecules participate: each apex H atom of one protruding Si−H bond of every molecule points to the corner of an equilateral triangle having 2.631Å sides. All hydrogen atoms in both the free molecule and in the solid state carry negative partial charges. The reason for this is also explored, as well as its consequences for the unique packing scheme.http://rspa.royalsocietypublishing.org.nf201

A computational study of the molecular and crystal structure and selected physical properties of octahydridosilasequioxane, (Si2O3H2)4. II. Vibrational analysis

A computational study of octahydridosilasequioxane, Si8O12H8, as a free molecule and when embedded in the unit cell R-3, Z =3, showed that the point group of the free molecule is indeed Oh, but that its crystal symmetry is reduced to C3i. Since the molecular and site-group symmetries influence the vibrational structure of a molecule, a full computational vibrational analysis of the isolated molecule and when embedded in the crystal lattice, is reported here. The analysis of the free molecular spectra given here agrees with that of its experimental infra-red (IR)-spectra and allows the assignment of all the vibrational modes, while the computed phonon dispersion of the crystal confirms the assignment of the internal vibrational modes of the molecule in the crystal. The computed and experimental IR spectra as well as Raman spectra show no indication of serious vibrational intermolecular coupling owing to the presence of multiple molecules in the unit cell. This may be the result of a weak intermolecular vibrational coupling in the solid state, which may feature in the low-frequency modes.http://rspa.royalsocietypublishing.org/subscriptionsnf201

Scanning electron microscopy of the teguments of males from five populations of Schistosoma mattheei

The teguments of males from 5 populations of S. mattheei, of which 3 were sympatric and 2 allopatric with S. haematobium, were studied by means of scanning electron microscopy (SEM). A certain percentage of the males of each sympatric population bore tubercle spines while the allopatric populations were spineless. It is postulated that the presence of tubercle spines is a characteristic inherited from S. haematobium.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

Phenotypic differences in Schistosoma mattheei ova from populations sympatric and allopatric to S. haematobium

Schistosoma mattheei ova were collected from cattle in different localities in South Africa and after hatching, miracidia were used to infest Bulinus (Physopsis) globosus. Cercariae harvested from these snails were used to infest the definitive host Praomys (Mastomys) coucha and eggs from the resulting female S. mattheei were collected. These ova were compared with a Schistosoma haematobium X S. mattheei hybrid similarly collected from an infested P. (M.) coucha. The results indicate that S. mattheei populations which are sympatric to S. haematobium possess S. haematobium characteristics. It is suggested that the gene pools of populations of the parasite in these areas are infiltrated with S. haematobium genes via the S. mattheei X S. haematobium hybrid originating from human hosts.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format