Relativistic quantum defect calculations on the copper isoelectronic sequence

The quantum defect orbital (QDO ) method and its relativistic (RQDO ) counterpart have been employed in this work to compute oscillator strengths for several fine-structure transitions in members of the copper isoelectronic sequence up to Z = 92. The RQDO results are found to be in quite good agreement with the best estimates derived from other sources, whenever the comparison is possible. © 1994 John Wiley & Sons, Inc.     

Computational study of the reaction of N(2D) atoms with CH2F radicals: an example of a barrier-free reaction involving very high internal energies

The singlet potential-energy surface for the N(2D)+CH2F(2A') reaction has been studied employing both second-order M?ller-Plesset and density-functional theories. The energies of the involved species have been refined using the Gaussian-2, complete basis set, and coupled-cluster singles and doubles (triples) methods. The reaction proceeds through the formation of an initial intermediate, which does not involve any activation barrier. Based on the energy profile for the singlet potential-energy surface, the preferred product should be the most exothermic one, namely, HCN+HF, followed by HNC+HF and FCN+H2. This result seems in contradiction with a computational study of the kinetics of the title reaction in terms of the statistical theories, which leads to the prediction that the production of HNC+HF should be the dominant channel. Consequently, a limited molecular-dynamics study has been carried out, concluding that in fact the system behaves in a nonstatistical way. According to the molecular-dynamics study, the most exothermic channel, HCN+HF, should be the dominant one. An analysis of the possible role of the singlet surface in the reaction of N(4S) with CH2F(2A') has also been carried out. The computational study shows that the microcanonical coefficients for the nonadiabatic channels are much smaller than the competing adiabatic ones. Therefore, the reaction of N(4S) with CH2F(2A') should proceed on the triplet surface without spin change.     

Thermodynamic evidence for Ca2+-mediated self-aggregation of Lewis X gold glyconanoparticles. A model for cell adhesion via carbohydrate-carbohydrate interaction

Thermodynamic evidence for the selective Ca(2+)-mediated self-aggregation via carbohydrate-carbohydrate interactions of gold glyconanoparticles functionalized with the disaccharides lactose (lacto-Au) and maltose (malto-Au), or the biologically relevant trisaccharide Lewis X (Le(X)-Au), was obtained by isothermal titration calorimetry. The aggregation process was also directly visualized by atomic force microscopy. It was shown in the case of the trisaccharide Lewis X that the Ca(2+)-mediated aggregation is a slow process that takes place with a decrease in enthalpy of 160 +/- 30 kcal mol(-)(1), while the heat evolved in the case of lactose and maltose glyconanoparticles was very low and thermal equilibrium was quickly achieved. Measurements in the presence of Mg(2+) and Na(+) cations confirm the selectivity for Ca(2+) of Le(X)-Au glyconanoparticles. The relevance of this result to cell-cell adhesion process mediated by carbohydrate-carbohydrate interactions is discussed.     

Small carbon clusters doped with early transition metals: a theoretical study of ScCn, ScCn+, and ScCn- (n = 1-8) open-chain clusters

A theoretical study of the ScCn, ScCn+, and ScCn- (n = 1-8) open-chain clusters has been carried out. Predictions for their electronic energies, rotational constants, dipole moments and vibrational frequencies have been made using the B3LYP method with different basis set including effective core potentials, ECPs. For the ScCn open-chain clusters the lowest-lying states correspond to quartet states for n-odd members, whereas for n-even species the ground state is found to be a doublet. In the cationic and anionic species, the electronic ground state is found to be a singlet for even n and a triplet for odd n. An even-odd parity effect (n-even clusters being more stable than n-odd ones) is observed in neutral and charged clusters. Ionization energies and electron affinities also exhibit a clear parity alternation trend, with n-even clusters having higher values than n-odd ones.     

Adhesion Forces between LewisX Determinant Antigens as Measured by Atomic Force Microscopy

No Abstract     

Characterization of the cholesteric phase of filamentous bacteriophage fd for molecular alignment

Residual dipolar couplings arise from small degrees of alignment of molecules in a magnetic field and have proven to provide valuable structural information. Colloidal suspensions of rod-shaped viruses and bacteriophages constitute a frequently employed medium for imparting such alignment onto biomolecules. The stability and behavior of the liquid crystalline phases with respect to solution conditions such as pH, ionic strength, and temperature vary, and characterization should benefit practical applications as well as theoretical understanding. In this Communication we describe the pH dependence of the cholesteric liquid crystalline phase of the filamentous bacteriophage fd and demonstrate that the alignment tensor of the solute protein is modulated by pH. We also report the interesting observation that the relative sign of the residual dipolar coupling changes at low pH values. In addition, we demonstrate that the degree of alignment inversely scales with the lengths of the phage particles for phages with identical mass and charge per unit length.     

Heronapyrroles A-C: farnesylated 2-nitropyrroles from an Australian marine-derived Streptomyces sp

Chemical analysis of a marine-derived Streptomyces sp. (CMB-M0423) isolated from beach sand off Heron Island, Australia, yielded three new members of the rare pyrroloterpene biosynthetic structure class. Identified by detailed spectroscopic analysis as the first reported examples of naturally occurring 2-nitropyrroles, heronapyrroles A-C (1-3) displayed promising biological activity-with low to submicromolar IC(50) activity against Gram-positive bacteria but no cytotoxicity toward mammalian cell lines.     

Structural Analysis of Unsaturated Glycosphingolipids Using Shotgun Ozone-Induced Dissociation Mass Spectrometry

Glycosphingolipids are essential biomolecules widely distributed across biological kingdoms yet remain relatively underexplored owing to both compositional and structural complexity. While the glycan head group has been the subject of most studies, there is paucity of reports on the lipid moiety, particularly the location of unsaturation. In this paper, ozone-induced dissociation mass spectrometry (OzID-MS) implemented in a traveling wave-based quadrupole time-of-flight (Q-ToF) mass spectrometer was applied to study unsaturated glycosphingolipids using shotgun approach. Resulting high resolution mass spectra facilitated the unambiguous identification of diagnostic OzID product ions. Using [M+Na]⁺ adducts of authentic standards, we observed that the long chain base and fatty acyl unsaturation had distinct reactivity with ozone. The reactivity of unsaturation in the fatty acyl chain was about 8-fold higher than that in the long chain base, which enables their straightforward differentiation. Influence of the head group, fatty acyl hydroxylation, and length of fatty acyl chain on the oxidative cleavage of double bonds was also observed. Application of this technique to bovine brain galactocerebrosides revealed co-isolated isobaric and regioisomeric species, which otherwise would be incompletely identified using contemporary collision-induced dissociation (CID) alone. These results highlight the potential of OzID-MS in glycosphingolipids research, which not only provides complementary structural information to existing CID technique but also facilitates de novo structural determination of these complex biomolecules.

Open image in new window

Graphical Abstract ?