Elimination of the diagonalization bottleneck in parallel Direct-SCF methods

Summary It is shown that the matrix diagonalization bottleneck associated with thesequential O(N _BFN ³ ) diagonalization of the fock matrix within each iteration of the Direct-SCF procedure may be eliminated, and replaced instead with a combination ofparallel O(N _BFN ^<4 ) andsequential O(N _Sub ³ ) steps. For large basis sets, the relation N_Sub N_BFN between the dimension of the expansion subspace and the number of basis functions leads to a method of wave-function optimization in which the sequential bottleneck is eliminated. As a side benefit, the second-order iterative procedure on which this method is based displays superior convergence properties, and provides greater insight into the behavior of the energy with respect to orbital variations, than the traditional first-order, fixed-point, iterative approaches. The implementation of this method may be incorporated into essentially any existing Direct-SCF program with only minimal, and localized, changes.     

The origins of the colours of yellow,green and blue sapphires

The absorption spectra of natural yellow sapphires are shown to be due to single Fe³⁺ and Fe³⁺  O²⁻  Fe³⁺ pairs, with the latter dominant. Blue and green sapphires have spectra dominated by Fe³⁺  O²⁻  Ti⁴⁺ and Fe²⁺  O²⁻  Fe³⁺ pairs.     

Synthesis and H-NMR complexation studies of alkalimetal bithioxanthylidene crown ether complexes

Two synthetic routes to a novel class of sterically overcrowded alkenes, bithioxanthylidene crown ethers 1, are described. The ¹H spin-lattice relaxation times (T₁) of the crown ethers as well as those of the corresponding complexes with Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ in CDCl₃ were measured and the results were interpreted in terms of complexation affinities.     

Supercritical fluid chromatography of petroleum products using flameless sulfur chemiluminescence detection

Supercritical fluid chromatography using flameless sulfur chemiluminescence detection has been investigated for the analysis of sulfur compounds in petroleum products. The chromatography and detection system was easy to implement and exhibited good precision, linearity, selectivity, and sensitivity. A minimum detectable limit of 0.3 pg sulfur/s was obtained, and response to sulfur in different sulfur species was nearly equimolar.     

Aromatic Polynitro Ether Derivatives of Cellulose

The nucleophilic reaction of sodium cellulosate in the form of membrane or cotton fabric with 2, 4-dinitrohalo-benzenes, 2, 4, 6-trinitrochlorobenzene, 2, 4, 6-trinitrobenzyl bromide, and 2, 4, 6-trinitrostyrene was investigated. The degree of substitution attained with the dinitroaryl derivatives was much higher than that with the trinitroaryl derivatives. The reaction proceeded through Meisen-heimer complexes, which in the case of the trinitro derivatives could be isolated. The ability of the polynitro phenyl ether derivatives of the cellulose to form n- and π-complexes was investigated using naphthalene and p-toluidine. No -π- complex was formed with the former, and the latter gave complexes only with the 2, 4, 6-trinitrobenzyl or -phenethyl cellulose derivatives but not with the trinitrophenyl. The results were explained as due to steric hindrance from the polymeric cellulosic backbone.     

Maximum feasibility guideline in the design and analysis of protein folding potentials

Protein folding potentials are expected to have the lowest energy for the native shape. The Linear Programming (LP) approach achieves exactly that goal for a training set, or indicates that this goal is impossible to obtain. If a solution cannot be found (i.e., the problem is infeasible) two possible routes are possible: (a) choosing a new functional form for the potential, (b) finding the best potential with a feasible subset of the data, and (or) detecting inconsistent subset of the data in the training set. Here, we explore option (b). A simple heuristic for finding an approximate solution to an infeasible set of linear inequalities is outlined. An approximately feasible solution is obtained iteratively, starting from a certain initial guess, by computing a series of analytic centers of the polyhedra defined by all the inequalities satisfied at the subsequent iterations. Standard interior point algorithms for Linear Programming can be used to compute efficiently the analytic center of a polyhedron. We demonstrate how this procedure can be used for the design of folding potentials that are linear in their parameters. The procedure shows an improvement in the quality of the potentials and sometimes points to flaws in the original data.     

Determination of dissociation temperature for ArO in inductively coupled plasma-mass spectrometry: Effects of excited electronic states and dissociation pathways

The method of comparing experimental and calculated ion ratios to determine a gas kinetic temperature (T_gas) characteristic of the origin of a polyatomic ion in inductively coupled plasma-mass spectrometry (ICP-MS) is applied to ArO⁺. Repeated measurements of ion ratios involving this species yield erratic T_gas values. Complications arise from the predicted presence of a low-lying excited electronic state (²Π) above the ⁴Σ ground state. Omission of this excited state yields unreasonably high temperatures (> 10,000 K) for nine out of nineteen trials. Inclusion of the excited electronic state in the partition function of ArO⁺ causes temperatures to increase further. The problem appears to be related to the prediction that ArO⁺ in the ²Π excited state dissociates into Ar⁺ and O, different products than ArO^{+ 4}Σ which dissociates into Ar and O⁺. Adjustments to the calculations to account for these different products yield reasonable temperatures (2100 to 3500 K) that are consistent from day-to-day and similar to those seen for other weakly-bound polyatomic ions.     

Quantification of midazolam,morphine and metabolites in plasma using 96‐well solid‐phase extraction and ultra‐performance liquid chromatography–tandem mass spectrometry

Currently, pharmacokinetic–pharmacodynamic studies of sedatives and analgesics are performed in neonates and children to find suitable dose regimens. As a result, sensitive assays using only small volumes of blood are necessary to determine drug and metabolite concentrations. We developed an ultra‐performance liquid chromatographic method with tandem mass spectrometry detection for quantification of midazolam, 1‐hydroxymidazolam, hydroxymidazolamglucuronide, morphine, morphine‐3‐glucuronide and morphine‐6‐glucuronide in 100 μL of plasma. Cleanup consisted of 96 wells micro‐solid phase extraction, before reversed‐phase chromatographic separation (ultra‐performance liquid chromatography) and selective detection using electrospray ionization tandem mass spectrometry. Separate solid‐phase extraction methods were necessary to quantify morphine, midazolam and their metabolites because of each group's physicochemical properties. Standard curves were linear over a large dynamic range with adequate limits of quantitation. Intra‐ and interrun accuracy and precision were within 85–115% (of nominal concentration using a fresh calibration curve) and 15% (coefficient of variation, CV) respectively. Recoveries were >80% for all analytes, with interbatch CVs (as a measure of matrix effects) of less than 15% over six batches of plasma. Stability in plasma and extracts was sufficient, allowing large autosampler loads. Runtime was 3.00 min per sample for each method. The combination of 96‐well micro‐SPE and UPLC‐MS/MS allows reliable quantification of morphine, midazolam and their major metabolites in 100 μL of plasma. Copyright © 2010 John Wiley & Sons, Ltd.