Solvation and lon association in the system AgNO3−CH3CN: A Raman and infrared spectral study

Detailed studies of the Raman and infrared line parameters of AgNO₃?CH₃CN systems ranging from dilute solutions to 9M are reported. A concentration quotient of 1.1M ^?1 was obtained for the formation of the Ag⁺NO ₃ ^? ion pair when C<4M. The complex appears to have point group C_s(σ_V) with Ag⁺ in a “roll-on” position. The Ag⁺ ion is solvated by four molecules of CH₃CN; nitrate ion replaces three of these when bound to Ag⁺. When C>4M, multiple ion aggregates form in the solution. A low-frequency 110 cm^?1 line is ascribed to librational motions of NO ₃ ^? , probably bound to Ag⁺.     

Analysis of the composition of immunoconjugates using size-exclusion chromatography coupled to mass spectrometry

Recombinant monoclonal antibody drug products play an increasingly important role in the treatment of various diseases. Antibodies are large, multi-chain proteins and antibody preparations often contain several molecular variants, which renders them heterogeneous. The heterogeneity is further increased in immunoconjugates prepared by covalently linking several drug molecules per antibody molecule. As part of the product characterization, the molecular weights of the antibodies or their drug conjugates need to be measured. Electrospray ionization mass spectrometry (ESI-MS) is well suited for the analysis of recombinant antibodies and immunoconjugates. Sample preparation is an important element of ESI-MS analysis, in particular samples need to be freed of interfering charged species, such as salts and buffer components. In this paper, Amicon centrifugal filters, reversed-phase high-performance liquid chromatography (HPLC), and size-exclusion HPLC were evaluated for sample desalting. Size-exclusion HPLC, using aqueous acetonitrile as the mobile phase, directly coupled to ESI-MS provided the best performance and was optimized for the study of immunoconjugates. The results showed that antibodies carrying covalently linked maytansinoid molecules generated charge envelope profiles that differ from those of the non-conjugated antibody. For the determination of the distribution of the various conjugate species in an immunoconjugate sample prepared by randomly linking in the average 3.6 drug molecules per antibody molecule, the experimental conditions needed to be carefully selected to allow acquisition of the whole spectrum containing the charge envelopes of all species.     

Integral equation theory for hard spheres confined on a cylindrical surface: anisotropic packing entropically driven

The structure of two-dimensional (2D) hard-sphere fluids on a cylindrical surface is investigated by means of the Ornstein-Zernike integral equation with the Percus-Yevick and the hypernetted-chain approximation. The 2D cylindrical coordinate breaks the spherical symmetry. Hence, the pair-correlation function is reformulated as a two-variable function to account for the packing along and around the cylinder. Detailed pair-correlation function calculations based on the two integral equation theories are compared with Monte Carlo simulations. In general, the Percus-Yevick theory is more accurate than the hypernetted-chain theory, but exceptions are observed for smaller cylinders. Moreover, analysis of the angular-dependent contact values shows that particles are preferentially packed anisotropically. The origin of such an anisotropic packing is driven by the entropic effect because the energy of all the possible system configurations of a dense hard-sphere fluid is the same. In addition, the anisotropic packing observed in our model studies serves as a basis for linking the close packing with the morphology of an ordered structure for particles adsorbed onto a cylindrical nanotube.     

Viscosity of Milk: Influence of Cluster Formation

Recently, a new theory of viscosity of concentrated emulsions dependence on volume fraction of droplets (Starov, V. and Zhdanov, V., J. Colloid Interface Sci., 2003, vol. 258, p. 404) has been proposed that relates the viscosity of concentrated emulsions to the formation of clusters. Through experiments with milk at different fat concentrations, cluster formation has been validated using optical microscopy and their properties determined using the aforementioned theory. Viscometric studies have shown that, within the studied range of shear rates, both the packing density of fat droplets inside clusters and the relative viscosity of milk (viscosity over skim milk viscosity) are independent of shear rate but vary with volume fraction. Comparison of the experimental data with previous theories that assumed that the particles remained discrete shows wide variation. We attribute the discrepancy to cluster formation.     

Microwave-optical double resonance in molecular ions. Co+

Microwave—optical double resonance signals have been detected in a mass-selected ion-beam spectrometer for ¹²C¹⁶O⁺. With the optical excitation of fluorescence from the R₁ ($\text{1}\text{2}$) line of the (0,0) band of the A²Π_{$\text{3}\text{2}$} ← X²∑ transition of 20350.6 cm^?1, the microwave resonances occurred at 118101.8 ± 0.2 MHz and at 117694 ± 2 MHz corresponding to the N= 1, J = $\text{3}\text{2}$ ← N = 0, J = $\text{1}\text{2}$ and the N = 1, J = $\text{1}\text{2}$ ← N = 0, J = $\text{1}\text{2}$ transitions.     

A comparison of the solid state structures of the selenium(IV) compounds PhSeX3(X=Cl, Br)

The crystal structures of PhSeX3(X=Cl, Br,) and their spectroscopic data are reported, with the structure of PhSeBr3 exhibiting interesting molecular, charge transfer, and ionic bonding aspects.     

Evaluation of DFT methods for computing the interaction energies of homomolecular and heteromolecular dimers of monosubstituted benzene

We present density functional theory (DFT) interaction energies for the sandwich and T‐shaped conformers of substituted benzene dimers. The DFT functionals studied include TPSS, HCTH407, B3LYP, and X3LYP. We also include Hartree–Fock (HF) and second‐order Møller–Plesset perturbation theory calculations (MP2), as well as calculations using a new functional, P3LYP, which includes PBE and HF exchange and LYP correlation. Although DFT methods do not explicitly account for the dispersion interactions important in the benzene–dimer interactions, we find that our new method, P3LYP, as well as HCTH407 and TPSS, match MP2 and CCSD(T) calculations much better than the hybrid methods B3LYP and X3LYP methods do. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006