Molecular force fields obtained using the nonempirical stabilizer of the regularizing functional

A new approach to the analysis of the force fields of polyatomic molecules is discussed. The results of quantum chemical calculations in combination with experimental data are used in a regularizing procedure, where the nonempirical matrix of the force constants determines the stabilizer of Tikhonov's functional. The use of stable numerical methods allows the specific modeling of the force fields of polyatomic molecules with due account of rotational isomerism. M. V. Lomonosov Moscow State University, Chemical Faculty. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 204–216, March–April, 1995. Translated by I. Izvekova     

Totally geodesic boundaries of knot complements

Given a compact orientable -manifold whose boundary is a hyperbolic surface and a simple closed curve in its boundary, every knot in is homotopic to one whose complement admits a complete hyperbolic structure with totally geodesic boundary in which the geodesic representative of is as small as you like.

     

Absolute quantitation of host cell proteins in recombinant human monoclonal antibodies with an automated CZE‐ESI‐MS/MS system

We report the first use of CZE for absolute characterization of host cell proteins (HCPs) in recombinant human monoclonal antibodies. An electrokinetically pumped nanoelectrospray interface was used to couple CZE with a tandem mass spectrometer. Three isotopic‐labeled peptides (LSFDKDAMVAR, VDIVENQAMDTR, and LVSDEMVVELIEK) were synthesized by direct incorporation of an isotope‐labeled lysine or arginine. The heavy‐labeled peptides were spiked in the HCP digests at known concentrations. After CZE‐ESI‐MS/MS analysis, the peaks of native and isotopic‐labeled peptides were extracted with mass tolerance ≤ 5 ppm from the electropherograms, and the ratios of peak area between native and isotopic‐labeled peptides pairs were calculated. Calibration curves (the ratios of peak area versus spiked peptide amount) with R² values of 0.999, 0.997, and 0.999 were obtained for the three HCP peptides, and the absolute amounts of the three proteins present were determined to be at the picomole level in a 20 μg sample of digested HCPs. The target proteins were present at the 7–30 ppt level in the purified HCP samples.     

A charge iteration-corrected extended-Hückel study of the electronic and spectroscopic properties of conjugated heterocycles

A computationally inexpensive modified extended-Hückel method using coordinates from STO-6G(d,p) geometry optimizations is described and shown to accurately simulate the spectra of conjugated heterocycles. The origins of the natural optical activities of blue indophenines and diheptylindophenines, and several related brown, red, and colorless compounds, were investigated with this method to show how it can be used to examine the changes in spectra and electronic structure that occur with substituent additions and changes. Diheptylindophenines were found to be blue because of absorptions from electronic transitions between spatially congruent π and π* molecular orbitals delocalized across carbon, nitrogen, oxygen, and sulfur atomic orbitals. The effects of conjugated thiophene moieties replacing the isatin moiety β-carbonyls move these absorptions to the blue relative to their locations in n-heptylisatin, and the diheptyl groups move these absorptions slightly to the red relative to indophenines.