Observations of phase changes in monoolein during high viscous injection.

Serial crystallography of membrane proteins often employs high-viscosity injectors (HVIs) to deliver micrometre-sized crystals to the X-ray beam. Typically, the carrier medium is a lipidic cubic phase (LCP) media, which can also be used to nucleate and grow the crystals. However, despite the fact that the LCP is widely used with HVIs, the potential impact of the injection process on the LCP structure has not been reported and hence is not yet well understood. The self-assembled structure of the LCP can be affected by pressure, dehydration and temperature changes, all of which occur during continuous flow injection. These changes to the LCP structure may in turn impact the results of X-ray diffraction measurements from membrane protein crystals. To investigate the influence of HVIs on the structure of the LCP we conducted a study of the phase changes in monoolein/water and monoolein/buffer mixtures during continuous flow injection, at both atmospheric pressure and under vacuum. The reservoir pressure in the HVI was tracked to determine if there is any correlation with the phase behaviour of the LCP. The results indicated that, even though the reservoir pressure underwent (at times) significant variation, this did not appear to correlate with observed phase changes in the sample stream or correspond to shifts in the LCP lattice parameter. During vacuum injection, there was a three-way coexistence of the gyroid cubic phase, diamond cubic phase and lamellar phase. During injection at atmospheric pressure, the coexistence of a cubic phase and lamellar phase in the monoolein/water mixtures was also observed. The degree to which the lamellar phase is formed was found to be strongly dependent on the co-flowing gas conditions used to stabilize the LCP stream. A combination of laboratory-based optical polarization microscopy and simulation studies was used to investigate these observations.

Stability, flow alignment and a phase transition of the lipidic cubic phase during continuous flow injection.

Continuous flow injection is a key technology for serial crystallography measurements of protein crystals suspended in the lipidic cubic phase (LCP). To date, there has been little discussion in the literature regarding the impact of the injection process itself on the structure of the lipidic phase. This is despite the fact that the phase of the injection matrix is critical for the flow properties of the stream and potentially for sample stability. Here we report small-angle X-ray scattering measurements of a monoolein:water mixture during continuous delivery using a high viscosity injector. We observe both an alignment and modification of the LCP as a direct result of the injection process. The orientation of the cubic lattice with respect to the beam was estimated based on the anisotropy of the diffraction pattern and does not correspond to a single low order zone axis. The solvent fraction was also observed to impact the stability of the cubic phase during injection. In addition, depending on the distance traveled by the lipid after exiting the needle, the phase is observed to transition from a pure diamond phase (Pn3m) to a mixture containing both gyriod (Ia3d) and lamellar (Lα) phases. Finite element modelling of the observed phase behaviour during injection indicates that the pressure exerted on the lipid stream during extrusion accounts for the variations in the phase composition of the monoolein:water mixture.

Perils of prolonged impaction of oesophageal foreign bodies.

Ill-conceived effort at removal of impacted foreign bodies (FBs) in oesophagus vies with delay in removal as the causes of morbidity and mortality. Most oesophageal FBs are safely removed endoscopically when attempted early. However, large sharp FBs like dentures and meat bones can get deeply embedded in the wall with prolonged impaction or injudicious attempts at removal leading to life-threatening mediastinitis. Open surgery to access the oesophageal-impacted FB in such an event is hazardous. This report emphasizes the need for early site-specific surgical approaches that may be required, albeit rarely, for oesophageal-impacted FBs, where attempts at endoscopic removal have failed or complications have ensued.

Surgical innovation.

Innovation has been an integral part of the progress of surgery. Technological advances have given a different dimension to the intricacies of modern surgery. While some innovations have been ground-breaking, others made only a transitory impression. This article attempts to distinguish between a true innovation and a technical refinement and explores the ethos and socio-economic factors that propel surgical innovation. The role of validation and regulation of these innovative procedures in producing improved outcomes are also discussed.

The attachment of amino fragment to purine: inner-shell structures and spectra.

The impact of the amino fragment (-NH(2)) attachment on the inner-shell structures and spectra of unsubstituted purine and the purine ring of adenine are studied. Density functional theory calculations, using the LB94/TZ2P//B3LYP/TZVP model, reveal significant site-dependent electronic structural changes in the inner shell of the species. A condensed Fukui function indicates that all of the N and C sites, except for N((1)) and C((5)), demonstrate significant electrophilic reactivity (f(-) > 0.5 in |e|) in the unsubstituted purine. Once the amino fragment binds to the C((6)) position of purine to form adenine, the electrophilic reactivity of these N and C sites is greatly reduced. As expected, the C((6)) position experiences substantial changes in energy and charge transfer, owing to the formation of the C-NH(2) bond in adenine. The present study reveals that the N1s spectra of adenine inherit the N1s spectra of the unsubstituted purine, whereas the C1s spectra experience significant changes although purine and adenine have geometrically similar carbon frames. The findings also indicate that the attachment of the NH(2) fragment to purine exhibits deeply rooted influences to the inner-shell structures of DNA/RNA bases. The present study suggests that some fragment-based methods may not be applicable to spectral analyses in the inner shell.

Percutaneous endoscopic gastrostomy (PEG) - An useful 'surgical' measure.

Eight patients were studied to evaluate the efficacy of a surgeonled percutaneous endoscopic gastrostomy (PEG). Three patients underwent PEG at the time of elective surgery (carcinoma larynx-2, carcinoma tonsil-1), two underwent placements during emergency surgery for neck trauma (blunt injury-1, penetrating injury-1) and three for palliation (recurrent tongue carcinoma-1, recurrent epilaryngeal carcinoma-1, metastatic neck nodes-1). For patients undergoing intraoperative PEG, the operative time was prolonged by an average of 12 minutes. There were no major procedural or feedingrelated complications in any of the patients. Individual subjective tolerability was good in all patients. A surgeonled PEG is a simple and safe means of combining all the advantages of enteral nutrition with none of the disadvantages of nasogastric tube feeding in emergency, elective head and neck operations and in palliation. The procedure merits wider use in head and neck surgery units in India.

Coexistence of 1,3-butadiene conformers in ionization energies and Dyson orbitals.

The minimum-energy structures on the torsional potential-energy surface of 1,3-butadiene have been studied quantum mechanically using a range of models including ab initio Hartree-Fock and second-order Møller-Plesset theories, outer valence Green's function, and density-functional theory with a hybrid functional and statistical average orbital potential model in order to understand the binding-energy (ionization energy) spectra and orbital cross sections observed by experiments. The unique full geometry optimization process locates the s-trans-1,3-butadiene as the global minimum structure and the s-gauche-1,3-butadiene as the local minimum structure. The latter possesses the dihedral angle of the central carbon bond of 32.81 degrees in agreement with the range of 30 degrees-41 degrees obtained by other theoretical models. Ionization energies in the outer valence space of the conformer pair have been obtained using Hartree-Fock, outer valence Green's function, and density-functional (statistical average orbital potentials) models, respectively. The Hartree-Fock results indicate that electron correlation (and orbital relaxation) effects become more significant towards the inner shell. The spectroscopic pole strengths calculated in the Green's function model are in the range of 0.85-0.91, suggesting that the independent particle picture is a good approximation in the present study. The binding energies from the density-functional (statisticaly averaged orbital potential) model are in good agreement with photoelectron spectroscopy, and the simulated Dyson orbitals in momentum space approximated by the density-functional orbitals using plane-wave impulse approximation agree well with those from experimental electron momentum spectroscopy. The coexistence of the conformer pair under the experimental conditions is supported by the approximated experimental binding-energy spectra due to the split conformer orbital energies, as well as the orbital momentum distributions of the mixed conformer pair observed in the orbital cross sections of electron momentum spectroscopy.