On affine scaling algorithms for nonconvex quadratic programming

We investigate the use of interior algorithms, especially the affine-scaling algorithm, to solve nonconvex — indefinite or negative definite — quadratic programming (QP) problems. Although the nonconvex QP with a polytope constraint is a hard problem, we show that the problem with an ellipsoidal constraint is easy. When the hard QP is solved by successively solving the easy QP, the sequence of points monotonically converge to a feasible point satisfying both the first and the second order optimality conditions.Research supported in part by NSF Grant DDM-8922636 and the College Summer Grant, College of Business Administration, The University of Iowa.     

新型Ni—Pd/碳化树脂催化剂的制备及在微量测定有机氧元素中的应用

本文报道一种新型Ni—Pd／碳化树脂催化剂的制备方法，用该法制备的催化剂具有高金属分散度和高机械强度，用于库仑法微量测定有机氧元素取得满意结果。文中对Ni和Pd颗粒在催化剂上表面形貌和分布、催化活性等作了初步探讨。     

Measurement of nitric oxide by 4,5-diaminofluorescein without interferences

The fluorescent reagent 4,5-diaminofluorescein (DAF-2) has been widely used for specific and quantitative measurements of nitric oxide (NO) in biological tissues. Recently it was reported that dehydroascorbic acid (DHA) and ascorbic acid (AA) interfere with the measurement of NO using DAF-2. A new method of assaying NO using DAF-2 eliminates these interferences; when frozen on dry ice, the NO in the original solution still diffuses and can react with an adjacent frozen block of DAF-2, but the confounding compounds such as DHA do not. Thus, placing the microliter-volume frozen blocks of solutions containing NO and the solutions of DAF-2 adjacent to each other for 30 min results in the concentration dependent formation of fluorescent product (DAF-2T) from the reaction of NO with DAF-2. The product has been characterized and the method validated using both fluorescence spectroscopy and capillary electrophoresis with laser induced fluorescence detection. With this approach, the presence of DHA and AA does not interfere with NO measurements, and product formation is inhibited in the presence of NO scavengers added to either of the solutions before freezing. The contactless DAF-2 method successfully assays NO in nitric oxide synthase-positive vertebrate and invertebrate tissues. This method allows nondestructive NO detection in biological samples that can subsequently be used for morphological and/or biochemical studies.     

Molecular structure and spectral properties of thionaphthalimides

The molecular structure and absorption spectra of monothio- and dithio-naphthalimides were compared to their naphthalimide analogues using AM1, PM3 and ZINDO/S semiempirical quantum chemical methods. The substitution of the 4R-naphthalimide oxygen atoms by sulphur atoms resulted in a red-shift of the absorption spectra by Δλ_max60-65 and 100-140 nm, respectively. The thionated naphthalimide derivatives do not show observable fluorescence due to intersystem crossing to the triplet -states localised at the CS groups. The -absorption bands of monothioimides are located at 525-580 nm (ε=60-80) and those for dithioimides at 535-560 nm (ε=140-390) and 628-686 nm (ε=34-68). None of these transitions are solvent sensitive. The -transitions of N-phenylthioimides have also a small contribution from -states due to a partial conjugation between CS group and π-electronic system of the N-phenyl ring. As a result, the bands of aromatic substituted N-phenylthioimides are red-shifted as compared to those of the aliphatic N-methyl-thioimides.     

New cytotoxic bufadienolides from the biotransformation of resibufogenin by Mucor polymorphosporus

Resibufogenin is a cytotoxic steroid isolated from the Chinese drug ChanSu. The biotransformation of resibufogenin by Mucor polymorphosporus afforded 22 products, and 15 of them were new. The transformation reactions involved hydroxylations at C-1β, C-5, C-7α, C-7β, C-12α, C-12β and C-16α, as well as epimerization or dehydrogenation of 3-OH. Hydroxylations at C-12α, C-12β and C-16α were the major reactions, each giving products in >5% yields, whereas the other products were obtained in fairly low yields. Some of the products showed decreased but still potent cytotoxicities. This investigation provided a useful approach to prepare new bufadienolides and most of them were difficult to obtain by chemical means.     

Photochemical reaction mechanism of cyclobutanone: CASSCF study

The photochemical reaction channels of cyclobutanone have been studied at the CASSCF level with a 6‐31G* basis set. Starting from the n‐π* excited‐state (S₁) cyclobutanone, the three reactions can take place: decarbonylation (produce CO and cyclopropane or propylene), cycloelimination (produce ketene and ethylene), and ring expansion (produce oxacarbene). Our computation indicates that decarbonylation products CO and triplet trimethylene are formed on the triplet n‐π* excited state (T₁) in a stepwise way via a biradical intermediate after intersystem crossing (ISC) to T₁ from S₁. And, then, the triplet trimethylene undergoes a second ISC to the ground state (S₀) to produce the singlet trimethylene from which cyclopropane can be produced rapidly only overcoming a 1 to 2‐kcal/mol barrier while propylene can be formed as a secondary product. The cycloelimination products ketene and ethylene are formed on the S₀ in a concerted mechanism after internal conversion (IC) to S₀ from S₁ via a biradical conical intersection. The reaction channels corresponding to ring expansion on the S₀, T₁, and S₁ states have also been discussed, and the likeliest reaction path is that oxacarbene is formed on the ground state following S₁/S₀ internal conversion. The surface topology of cyclobutanone on the S₁ surface is characterized by a transition state separating the minimum from the S₁/S₀ conical intersection, which is consistent with the previous computations and can explain the wavelength dependence of the fluorescence emission yield. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Synthesis, characterization, and surface immobilization of platinum and palladium nanoparticles encapsulated within amine-terminated poly(amidoamine) dendrimers

Platinum and palladium dendrimer-encapsulated nanoparticles (DENs) were prepared within commercially available, fourth-generation, amine-terminated, poly(amidoamine) dendrimers (G4-NH2). The synthesis is carried out by selectively encapsulating metal complexes within the dendrimer and then reducing the resulting composite. Intradendrimer complexation requires control over the solution pH to prevent attachment of the metal complexes to primary amine groups on the dendrimer periphery. That is, the surface primary amines of the dendrimer must be selectively protonated in the presence of the interior tertiary amines. The metal-ion encapsulation and reduction processes were characterized by UV-vis spectroscopy. Forty-atom Pt and Pd DENs were examined by high-resolution transmission electron microscopy, which showed that the mean particle sizes were 1.4 and 1.5 nm, respectively, and that both were nearly monodisperse (standard deviation = 0.3 nm). The free amine groups on the dendrimer surface were used to link Pd DENs to monolithic Au surfaces via an intermediate self-assembled monolayer adhesion layer.     

Anomalous NMR behavior of meso compounds with remote stereogenic centers on addition of chiral shift reagent or chiral solvating agent

A problem has arisen in using chiral shift reagents (CSR) and chiral solvating agents (CSA) to determine meso and racemic forms of diastereoisomers in which the stereogenic centers of the molecules are separated by achiral spacers. It is found that NMR signals of both meso and racemic forms of diastereoisomers may exhibit doubling on addition of CSR/CSA, which means that unequivocal assignments cannot be made without characterizing the effects for separate meso and racemic forms; this is particularly important for additions of CSR/CSA at relatively low concentrations, which always result in the splitting of some NMR signals of diastereoisomers. The phenomenon is demonstrated in the (31)P NMR spectra of meso and racemic forms of three spermine-bridged gem-disubstituted cyclotriphosphazatrienes, 1a-c, and compared with analogous achiral molecules, the per-substituted spermine-bridged cyclotriphosphazatrienes 2a-d. As expected, only one set of (31)P NMR signals was observed for the achiral compounds 2a-d, even on addition of CSA. Two sets of (31)P NMR ABX multiplets corresponding to meso and racemic diastereoisomers were observed for compounds 1a-c; on addition of CSA, the signals of at least one of the multiplets for each compound separated into more than the expected groups of three lines with an intensity distribution of 2:1:1. To understand this phenomenon, the meso and racemic forms of 1a and 1b and the meso form of 1c have been separated and characterized by X-ray crystallography. On addition of CSA to the racemic forms of 1a and 1b, the (31)P NMR spectrum shows the expected doubling of signals, but, unexpectedly, the same is observed for each of the meso forms of 1a-c. Analogous results using both CSA and CSR have been obtained for the meso and racemic forms of the diastereoisomeric piperazine-bridged macrocyclic-phosphazene compound, 3, whereas no effect was observed for the two meso forms of the doubly bridged macrocyclic-phosphazene compound 4. The phenomenon of doubling of the (31)P NMR signals of the meso form of singly bridged cyclotriphosphazatrienes, 1a-c and 3, is explained by consideration of the equilibrium in solution of independent complexation of a chiral ligand with molecules that have two chiral cyclophosphazene moieties separated by an achiral spacer group. The results show that the stereogenicity of such diastereoisomeric molecules in solution cannot be characterized unequivocally by NMR measurements on addition of either CSR or CSA.