A feature of the fragmentation mechanism of exo-2-norbornyl chloride. Stereoselective hydrogen atom abstraction revealed by metastable ion studies

The position of deuterium in the products of the addition of HCL and DCI to exo 5, 6-d₂ norbornene has been determined mass spectrometrically by measuring metastable ion abundances. The results show a stereo-selective hydrogen atom abstraction when the molecular ion of exo-2-norbornyl chloride fragements by loss of a chloroethyl radical.     

Resistance in Higher-Dimensional Sierpiński Carpets

We study the effective resistance between disjoint compact sets relative to the n-th level approximation F _n to the generalized Sierpiski carpet in d dimensions. This yields a simple criterion for determining recurrence of simple random walk on the associated pre-fractal graph in terms of the resistance scaling factor.     

An isoperimetric inequality in the plane with a log-convex density

Ricerche di Matematica - Given a positive lower semi-continuous density f on $$mathbb {R}^2$$ the weighted volume $$V_f:=fmathscr {L}^2$$ is defined on the $$mathscr {L}^2$$ -measurable sets in...     

Specific and random processes in the fragmentation of cyclohexanol

The mass spectra of cyclohexanol and eleven deuterated analogues have been studied. Detailed mechanisms, consistent with peak intensity and defocused metastable abundance data, have been proposed for the loss of water from the molecular ion and for the subsequent loss of a methyl radical. The importance of specific eliminations and the absence of any processes involving complete hydrogen atom scrambling in these fragmentations has been demonstrated. Scrambling has also been shown to be absent in the formation of the base peak m/e 57, the [C₃H₅O]⁺ ion.     

Charge inversion at minute electrolyte concentrations

Anionic dimyristoylphosphatidic acid monolayers spread on LaCl3 solutions reveal strong cation adsorption and a sharp transition to surface overcharging at unexpectedly low bulk salt concentrations. We determine the surface accumulation of La3+ with anomalous x-ray reflectivity and find that La3+ compensates the lipid surface charge by forming a Stern layer with approximately 1 La3+ ion per 3 lipids below a critical bulk concentration, ct approximately 500 nM. Above ct, the surface concentration of La3+ increases to a saturation level with approximately 1 La3+ per lipid, thus implying that the total electric charge of the La3+ exceeds the surface charge. This overcharge is observed at approximately 4 orders of magnitude lower concentration than predicted in ion-ion correlation theories. We suggest that transverse electrostatic correlations between mobile ions and surface charges (interfacial Bjerrum pairing) may contribute to the charge inversion.     

The mass spectra of isomeric hydrocarbons—I: Norbornene and nortricyclene; The mechanisms and energetics of their fragmentations

The mass spectra of norbornene, nortricyclene and deuterium labeled derivatives thereof have been studied. The appearance potentials of the ions [C₇H₁₀]^+·, [C₇H₉]⁺, [C₆H₇]⁺ and [C₅H₆]^+· have been determined for both compounds and heats of formation of the hydrocarbons have been estimated. Detailed fragmentation schemes are proposed for the molecular ions and it is concluded that they dissociate by essentially different mechanisms which do not involve common intermediates. The structures and energy contents of the primary fragment ions are discussed in detail by comparing energetics, labeling experiments and metastable ion abundances.     

Pyrones: V—The mass spectra and fragmentation mechanisms of some 3(5)-methoxy-4-pyrones

The mass spectra of methyl kojate (2-hydroxymethyl-5-methoxy-4H-pyran-4-one), two deuterated analogues and 14 related 3(5)-methoxy-4-pyrones have been studied. These compounds fragment according to a common mechanism, initiated by primary rearrangement of the molecular ion(s). Guidelines which indicate the presence of 3(5)-methoxy-4-pyrones and allow structural determinations to be made from their mass spectra are presented. For the majority of substituents studied, the nature of the substituent has no major effect upon the fragmentation pattern; the cyano group does. The hydroxy counterparts of the above compounds are readily converted for analysis by simple methylation.     

Active antibacterial coating of cotton fabrics with antimicrobial proteins

The prevention of bacteria colonization by immobilizing proteins with antimicrobial activity onto cotton fabrics was investigated. Such coatings have potential applications in medical dressing materials used in wound care and healing. Two antimicrobial proteins lysozyme and hydramacin-1 (HM-1) were surface immobilized through two linkers (3-aminopropyl) triethoxysilane (APTES) and citric acid in the presence of the water soluble carbodiimide coupling reagent 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimide metho-p-toluenesulfonate. Surface composition analysis by attenuated total reflection-Fourier transform infrared and X-ray photoelectron spectroscopies confirmed formation of the protein-cellulose conjugates. Antimicrobial activities of the different functionalized surfaces were found to vary between APTES and citric acid directed coatings. Citric acid immobilized lysozyme treated samples demonstrated superior activity against Gram-positive Bacillus subtilis, whereas APTES immobilized HM-1 treated samples demonstrated an advantage in inhibiting the growth of Gram-negative Escherichia coli. The antibacterial activity and stability of citric acid immobilized protein fabrics following sonication, boiling and chemical treatment were noticeably higher than that of the corresponding APTES immobilized protein fabrics. The dual coating of fibers with both antimicrobial proteins afforded efficient antimicrobial activities against both bacterial species. The results suggest that coating cotton fibers with antimicrobial proteins and peptides represents a feasible approach for developing active surfaces that prohibit growth and colonization of bacterial strains and can be potentially used in medical cotton-based fabrics.

     

Enzyme activity to augment the characterization of tethered bilayer membranes

The rate of Ca2+ -triggered phospholipase A2 (PLA2) degradation of tethered bilayer membranes (tBLMs), composed of a synthetic lipid, beta-mercaptoethanol, and palmitoyloleoylphosphatidylcholine (POPC), is approximately 80 times greater than for those prepared with diphytanoylphosphatidylcholine (DPhyPC). Electrochemical impedance spectroscopy (EIS) and neutron reflectivity (NR) data indicate complete, water-free tBLMs that exhibit near ideal capacitive behavior and the presence of a water reservoir in the bilayer subspace proximal to the substrate (Au) surface for both tBLMs. Together these data indicate that the POPC and the DPhyPC tBLMs are structurally similar along the surface normal but markedly different at the outer leaflet/solution interface and that PLA2 is a sensitive probe of short length scale structural differences not revealed by EIS and NR.     

The mass spectrum and fragmentation mechanism of exo- and endo- norborneol

The mass spectra of exo -and endo-norborneol and a number of deuterium labelled and-logues have been studied in detail. The two alcohols have common fragentation pathways, the major routes of which can be related to specific rearrangements of the molecular ion. The loss of water from the molecular ion consists of two processes, one involving and one4 not involving the hydroxyl hydrogen atom. The limitions of the labelloing experiements are discussed.