High-Efficiency Liquid Chromatography Using Sub-2?��m Columns at Elevated Temperature for the Analysis of Sulfonamides in Wastewater

Efficiency in HPLC can be enhanced by increasing the column length and/or decreasing the particle size. The use of high temperature in HPLC has emerged as a valuable tool to overcome the increase in column backpressure when using small packing particles, as it allows for reduction in mobile phase viscosity. In this study, high plate count was obtained by coupling sub-2 ??m columns at elevated temperature to reduce the viscosity of the mobile phase, thus reducing the column backpressure. At 80 °C, up to three columns of 15 cm × 4.6 mm I.D. packed with 1.8 ??m particles could be coupled generating ~84,000 theoretical plates for the last eluting compound. The number of theoretical plates was increased on average by a factor of ~3.6 when three columns were coupled at 80 °C compared with one column at 30 °C. The relationships between separation efficiency and column length were examined using Van Deemter plots constructed at 30 °C and 80 °C for different column lengths. The advantages of using coupled columns in combination with elevated temperature for the environmental analysis were illustrated using test mixtures comprised of eight sulfonamides separated on one column at 30 °C and three coupled columns at 80 °C by isocratic elution. Sample clean up was carried out by employing solid-phase extraction (SPE) using Oasis HLB cartridges. The method developed was validated based on parameters such as linearity, precision, accuracy, detection and quantification limits. Recoveries generally ranged from 71.7 to 99% (with the exception of sulfanilamide), with standard deviations not higher than 4.7%. The detection limits of the method ranged from 0.6?C2 ??g L^?1, while limits of quantification were in the range 2?C6.7 ??g L^?1 with UV detection.     

Crystallization of the Lewis-Wahnström ortho-terphenyl model

Crystallization is observed during microsecond long molecular dynamics simulations of bent trimers, a molecular model proposed by Lewis and Wahnstro?m for ortho-terphenyl. In the crystal, the three spheres that make up the rigid molecule sit near sites of a body centered cubic lattice. The trimer bond angle is almost optimal for this structure. The crystal exhibits orientational disorder with the molecules aligned randomly along the three Cartesian axis, i.e., cubatic orientational order. The rotational and translational mobilities exhibit only modest decreases on crystallization, by factors of 10 and 3, respectively. The rotational relaxation does change from Debye-like in the liquid to large angle jumps in the crystal. We consider the origin of the superior glass forming ability of the trimer over the monatomic liquid.     

Progress of 1.5～1.6 μm Laser Crystals

Eye-safe 1.5～1.6 μm lasers have important applications in optical fiber communication, medicine, laser-range-finding, lidar, etc. Er^3＋ and Yb^3＋ co-doped crystal pumped by diode laser around 976 nm is an attractive method for obtaining 1.5～1.6 μm laser in compact device with high output beam quality. In this paper, the recent research and progress of several important Er^3＋ and Yb^3＋ co-doped laser crystals at 1.5～1.6 μm in authors’ lab are reported.     

Theoretical Studies of the Electronic Structures and Spectrum Properties of Pt n Ni m (n + m = 7, n, m ≠ 0) Clusters

We studied Pt _n Ni _m (n + m = 7, n, m ≠ 0) clusters within the framework of the density functional theory (B3LYP) at the LANL2DZ level. The calculated results show that the Fermi levels are determined by the number of Pt atoms, which gain electrons from Ni atoms. Meanwhile, multifarious orbital hybridization is found in the frontier molecular orbital, and the more platinum or nickel atoms, the smaller energy gap it has. Moreover, the calculated IR and Raman spectrum indicates the aromatic character, which is vital for transitional metal clusters.     

Determination of debye temperatures of supported ion particles by m?ssbauer spectroscopy

The Debye temperatures of alumina- and titania-supported iron particles were determined using Mössbauer spectroscopy between 5 and 280 K. The Debye temperatures were obtained from a nonlinear optimization algorithm using the temperature dependence of the second order Doppler shift (SOD) and the resonant absorption area (RAA). To test its reliability, the same method was used to determine of an -iron-foil and pyrophoric iron.     

A möbius inversion of the ulam subgraphs conjecture

The generalized Eichinger matrices are defined asE = _j ⁿ ₁( _j S ^T S)^–1, where _j M denotes the matrixM withj th row and column deleted.S is the incidence matrix andM ^T is the transposed matrix. The conjectureS ^T SE = S _K ^TS _K , where SK is the incidence matrix of the complete graph, is proven for trees, simple cycles and complete graphs. The consequence of the conjecture isS _G ^T S _G (E _G -I) = S _G ^TS _G , whereG is the complementary graph ofG. It leads to graphs with imaginary arcs as the complements of graphs with multiple arcs.     

PMI: A ΔΨm Independent Pharmacological Regulator of Mitophagy

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Absolute line intensities of the ν9 band of propyne at 15.5 μm

A tunable diode laser spectrometer was used to perform measurements of absolute line intensities for 20 transitions in the ν₉-fundamental of propyne centered at 15.5 μm. From these data, the vibrational band-strength S^v_o was significantly determined to be S^v_o = 196.8 ± 6.0 cm⁻² atm⁻¹ at 297 K. These results will be used for further applications of astrophysical interest such as a refined contribution for modelling Titan's atmosphere.     

Electronic structure analysis of small gold clusters Au m (m?��?16) by density functional theory

Small gold clusters Au _m (m????16) were analyzed step by step using the density functional theory at B3LYP level with a Lanl2DZ pseudopotential to understand the rules governing the structures obtained for the most stable clusters. After a characterization by means of the NBO population analysis and spin densities, the particular electronic structure of such species was confronted to their structural parameters and stability. It appears that the most stable structures can be described in an original way through resonance structures resulting from an analysis of Au _m clusters into dimeric Au₂ subunits. These are arranged so as to promote: 1. A good overlap between bonding ?? and anti-bonding ??* areas belonging to different Au₂ units. 2. A cyclic flow of electrons over the whole cluster. This model uses relatively simple chemical concepts in order to justify most of the structures already found in the literature as well as to establish a new approach explaining the structural transition from two- to three-dimensional configurations.     

Studies on Effect of Conformation on Spin Multiplicity of m－Phenylene Type of Biradicals by Different Approaches

The effect of the conformation on the spin multiplicity of the ground state and the stability of the ground state were investigated for m-phenylene type of biradicals by means of comparative study with DFT, CASSCF and AM1-CI approaches. It was found that AM1-CI approach is reliable in dealing with the stability of the high-spin ground state with the change of conformation; DFT method can give the reasonable results of the spin density of the high-spin state. Furthermore, when one or two radical centers are twisted sufficiently out of the coniugation with the benzene ring, m-phenylene turns into weak ferromagnetic and weak antiferro-magnetic coupling units, respectively.     

Photoelectron spectroscopy of silicon and germanium-fluorine binary cluster anions (SinF m − , GenF m − )

Electronic properties of silicon-fluorine and germanium-fluorine cluster anions (Si_nF _m ^? n = 1–9, m = 1–3, Ge_nF _m ^? ; n =1–9, m = 1–3) were investigated by photoelectron spectroscopy using a magnetic-bottle type electron spectrometer. The binary cluster anions were generated by a laser vaporization of a silicon/germanium rod in an He carrier gas mixed with a small amount of SiF₄ or F₂ gas. Comparison between photoelectron spectra of Si_nF^?/Ge_nF^? and Sin /Gen (n = 4–9) gives the insight that the doped F atom can remove one electron from the corresponding Sin _n ^? /Ge _n ^? cluster without any serious rearrangement of Sin/Gen framework, because only the first peak of Si _n ^? /Ge _n ^? , corresponding singly occupied molecular orbital (SOMO), disappears and other successive spectral features are unchanged with the F atom doping     

Effect of substitution on the intramolecular 1,3-dipolar cycloaddition of alkene tethered münchnones

A sequence of chemoselective activation of N-acylaminoacids, münchnone generation, intramolecular 1,3-dipolar cycloaddition, and ring opening efficiently generated functionalized polycyclic structures such as cyclopenta[b]pyrroles or zwitterionic bicyclo[4.3.0]nonane or bicyclo[3.3.0]octanes in one operation is given. These zwitterionic species were isolated for the first time and were subsequently reduced to bicyclic aminoalcohols. The effect of the substitution of both the dipolarophile and the münchnone on the intramolecular cycloaddition outcome was examined. It was found that either nonactivated or electron-poor alkenes can react with the münchnone if these alkenes are tethered at position 4 on the münchnone (2, R2 = alkene tether), whereas only an electron-poor alkene at position 2 (2, R3 = alkene tether) could undergo successful cycloaddition. Also, münchnones substituted at position 2 with a phenyl (2, R3 = Ph) showed a dramatic increase in reactivity, whereas a phenyl at position 4 (2, R2 = Ph) had a very limited effect.     

Zur Kenntnis des m,m′-Divinylazobenzols und des m,m′-Divinylazoxybenzols

Ohne Zusammenfassung     

Crystal Structure of Tris（m—nitrobenzoato）Samarium Dihydrate

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Theoretical study of stepwise hydrogenated closo-alane clusters Al13H m − (m = 1–12)

The structure, energy, and vibrational characteristics of different stepwise-hydrogenated closo-alane clusters Al₁₃H _m ^? (m = 1–12) were calculated within the B3LYP approximation of the density functional theory using 6-31G* and 6-311+G* basis sets. For each of the m values, there is a set of several low-lying, closely spaced (within ～0.1–0.3 eV) isomers. In the first half of the series, inner isomers (with the centered cage Al@Al₁₂) are preferable; and in the second half, outer isomers (with the thirteenth Al atom located on the outside of the empty Al₁₂ icosahedron and coordinated to its face) are more favorable. In some of the outer isomers, the aluminum cage is severely distorted and loses its closo form. When a hydrogen atom is attached to paramagnetic radical anions (with odd m values), the most favorable site for attack is the Al* atom located opposite the Al^t-H bond and carrying most of the unpaired electron density. The resulting diamagnetic anions contain a maximum number of linear (or quasi-linear) HAl_H-Al_c-Al_HH or HAl_H…Al_HH fragments in the inner and outer isomers, respectively (the trans addition rule). The energy D _m (H) of successive addition of an H atom to the centered icosahedron Al ₁₃ ^? depends on m in a zigzag manner: the even bonds are always ～1 eV stronger than the odd bonds. This trend is interpreted in the framework of the molecular model of the valence states of the [Al₁₃] “superatom” with a variable valence increasing from 1 to 12 due to the unpairing of one to six electron pairs of the cage when the first, third, etc. odd H atoms are attached to it.     

Syntheses of Two Potential Ligands for Tc-99m Labeling as Diagnosis Agents of Alzheimer''''s Disease

Two types of ligands-biphenyl and stilbene derivatives, whichcan be labeled with Tc-99m for the diagnosis of Alzheimer'sdisease (AD) have been synthesized successfully. The key stepsin these two syntheses involved Suzuki reaction and Wittig reac-tion respectively. The new discovered debromination reactionmay be expanded to the compounds with double or triple bondadjacent to the carbon atom bearing the bromine atoms. Thesetypes of syntheses provide a route to a series of biphenyl andstilbene derivatives that will benefit the search of new imagingagents for AD.     

Some practical comparisons of the efficiency and overloading behaviour of sub-2 μm porous and sub-3 μm shell particles in reversed-phase liquid chromatography

At their optimum flow, sub-3 μm superficially porous or "shell" particles demonstrate similar efficiency to sub-2 μm totally porous particles. The performance of 0.21 cm i.d shell columns is however inferior to those of 0.46 cm i.d., presumably due to packing difficulties. At high flow, shell columns can give flatter Knox curves due to lower operating pressure (half or less of that of the totally porous particles) producing less frictional heating, which combined with the increased thermal conductivity of their non-porous core, gives more efficient heat dissipation. However, the effects of frictional heating for sub-2 μm columns are considerably exaggerated when using pure ACN as mobile phase, as it has a thermal conductivity 3 times less than that of pure water, leading to poorer heat dissipation. Overloading is already problematic for ionised solutes, a group which contains many pharmaceuticals and compounds of clinical relevance, on conventional columns (5 μm porous particles). However, it becomes a more serious issue for both new column types, partially as a result of their very high efficiency, which concentrates the sample as a very narrow band. The sample capacity of one type of shell particle was estimated to be 60% of that of the small totally porous particles, in line with the fraction of the particle volume that is porous. Due to overloading, it is barely possible to achieve perfect peak symmetry for ionised acids or bases with either of these new column types, even by injecting the lowest amounts of sample detectable by UV. While ammonium formate and potassium phosphate buffers gave similar results in overloading studies, use of formic acid as sole mobile phase additive is not recommended for these solutes, as its ionic strength is too low, leading to a catastrophic deterioration in efficiency when sample concentrations of even a few mg/L are injected.     

Analysis of peptides and proteins using sub-2 μm fully porous and sub 3-μm shell particles

The objective of this study was to evaluate the potential of sub-2 μm totally porous particles and sub-3 μm shell particles for peptide and protein analysis. Specific analytical strategies must be developed for these biomolecules as their importance in the pharmaceutical industry increases and as their structural complexity involves some issues when classical LC conditions are employed. Attention was paid on comparing these different columns in various LC conditions (different temperatures, gradient times, and mobile phase flow rates). The comparison of the different supports was assessed considering columns characteristics (quality of packing, silanol activity, pore size, totally porous or shell particles). In this article, peptides were first analyzed with both column technologies. Similar results to those achieved with low molecular weight compounds were obtained (peak capacity >100 for t_grad around 3 min and columns dimensions of 2.1 mm id × 50 mm), but specific conditions were required (elevated temperature and the use of a volatile ion-pairing reagent, namely TFA). For peptide analysis following tryptic digestion, the goal was to improve peak capacity and resolution because of the large number of generated peptides. For this purpose, longer columns packed with porous sub-2 μm or shell sub-3 μm particles (i.e., 150 mm) and gradient times (i.e., up to 30 min) were tested. On the other hand, proteins in their intact forms have higher molecular weights (MW > 5000 Da) and a tertiary structure, thus requiring different conditions in terms of stationary phase hydrophobicity (C₄vs. C₁₈) and pore size (300 vs. 120 Å). In addition, there were issues with adsorption onto the LC system and/or the column itself. This study showed that proteins with MWs lower than 40,000 Da required chromatographic conditions close to those employed for peptide analysis. For larger proteins, a C₄ 300 Å stationary phase gave the best results, confirming theoretical predictions.