Plume Expansion Dynamics of Matrix‐Assisted Laser Desorption Ionization

High‐resolution angular and velocity distributions for neutral analytes (tryptophan and poly‐tryptophan) and matrix (2,4,6‐trihydroxyacetophenon, THAP) are measured by using 355 nm laser desorption. The information suggests that two separate mechanisms dominate the angular and velocity distributions at the beginning and before the end of desorption. A molecular jet‐like isentropic expansion dominates the plume expansion at the beginning of desorption. This only occurs at high surface temperature, thus resulting in a large velocity normal to the surface and a very narrow angular distribution. Most of the analytes are produced under these conditions. Before the end of desorption, the surface temperature decreases and the mechanism of thermal desorption at low vapor pressure takes over. The velocities become small and the angular distribution is close to cosθ. Only a very small amount of analytes are generated under these conditions. Compared to tryptophan, poly‐tryptophan has a much narrower angular distribution, thereby suggesting that it is only produced at the higher surface temperatures.     

Synthesis of 1,4-naphthoquinone methides via acid-catalyzed cascade cyclizations of benzannulated enediynyl alcohols

Treatment of benzannulated enediynyl alcohols with trifluoroacetic acid at room temperature promoted a cascade sequence of cyclization reactions, leading to 1,4-naphthoquinone methides. The transformation involved an unusual two-carbon ring expansion from the cyclic alcohols and the construction of the p-quinone methide ring from an acyclic system along the reaction pathway.     

Optimal Portfolio Decision Rule Under Nonparametric Characterization of the Interest Rate Dynamics

This study develops an optimal portfolio decision rule under nonparametric characterization of the interest rate dynamics. To proceed, we first derive an optimal decision rule based on the long rate and the spread (where $\mathrm{spread} = \mathrm{long\ rate} - \mathrm{short\ rate}$ ); then we employ nonparametric kernel regression to estimate, based on the Nadaraya–Watson (N–W) estimators, the parameters related to the two variables; and finally, using the N–W estimates as inputs, we implement our decision rule by the explicit finite difference scheme to find specifically the optimal allocation of wealth between short and long bonds for an investor with power utility at each time over a ten-year horizon. The following four stylized facts can be observed from our results: (i) the optimal fractions in short bond do not appear to vary with the short rate; (ii) the optimal fractions decrease as the long rate rises and increase as it falls; (iii) the optimal fractions increase as the horizon becomes shorter; and (iv) the optimal fractions generally decrease in the early part of the horizon for more risk-averse investor.     

A periodic array of nano‐scale parallel slats for high‐efficiency electroosmotic pumping

It is known that the eletroosmotic (EO) flow rate through a nano‐scale channel is extremely small. A channel made of a periodic array of slats is proposed to effectively promote the EO pumping, and thus greatly improve the EO flow rate. The geometrically simple array is complicated enough that four length scales are involved: the vertical period 2L, lateral period 2aL, width of the slat 2cL as well as the Debye length . The EO pumping rate is determined by the normalized lengths: a, c, or the perforation fraction of slats and the dimensionless electrokinetic width . In a nano‐scale channel, K is of order unity or less. EO pumping in both longitudinal and transverse directions (denoted as longitudinal EO pumping (LEOP) and transverse EO pumping (TEOP), respectively) is investigated by solving the Debye–Hückel approximation and viscous electro‐kinetic equation. The main findings include that (i) the EO pumping rates of LEOP for small K are remarkably improved (by one order of magnitude) when we have longer slats () and a large perforation fraction of slats (η > 0.7); (ii) the EO pumping rates of TEOP for small K can also be much improved but less significantly with longer slats and a large perforation fraction of slats. Nevertheless, it must be noted that in practice K cannot be made arbitrarily small as the criterion of for the reference potential at the channel center put lower bounds on K; in other words, there are geometrical limits for the use of the Poisson–Boltzmann equation.     

New gelators of urea-containing triazine derivatives: effects of aggregation and optical features in different organic solvents

New gelators for urea-containing triazine derivatives were synthesised, and their gelation potential was examined using different organic solvents. These compounds were found to form the organogels with a variety of organic solvents, such as hexane and other solvents. The elongated alkyl tails of the gelators displayed an obvious decrease in the critical gelation concentrations of apolar solvents and an increase in the compatibility of gelation in polar solvents. The resulting thermo-reversible gels were characterised by using the dropping ball method and a number of other instruments. The melting temperature (Tm) of the gels in decalin and CCl₄ increased with the gelator concentrations. The intermolecular hydrogen bonding of gelation in different organic solvents was observed using an FT-IR spectrometer. Temperature-dependent UV–vis and fluorescence analysis showed that the organogels displayed diverse aggregations and various fluorescence effects in different organic solvents. Blue fluorescence and J-aggregation in decalin and the quenched effect and π–π stacking in CCl₄ were observed. Further, the morphological self-assembled feature in different organic solvents was studied with a scanning electron microscope, and the morphological features demonstrated that there were different aggregations in different solvents. In conductivity electrolyte experiments, the organogel electrolytes exhibited high conductivity (σ) compared with the corresponding tetrabutylammonium perchlorate (TBAP)/THF solution. The conductivity of the gel electrolytes increased with the concentration of the electrolyte salts and temperature. When the sol–gel temperature was achieved, a high ion conductivity was observed compared with the corresponding TBAP/THF solution. When the ratio of the added electrolyte salts exceeded 5%, gelation was inhibited. Furthermore, the effect of the electrolyte salts on the Tm of the gel was confirmed. The added electrolyte salts affected the gelation ability, but did not affect the sol–gel temperature.     

Microwave-assisted extractions of active ingredients from plants

Microwave-assisted extraction (MAE) is widely employed in the analysis and the extraction of active compounds from plants. This review summarizes the research done during the last decade on the MAE of active ingredients from plants. Advances and modifications to improve the performance of MAE are presented and discussed in detail. Modified MAE such as vacuum microwave-assisted extraction (VMAE), nitrogen-protected microwave-assisted extraction (NPMAE), ultrasonic microwave-assisted extraction (UMAE), dynamic microwave-assisted extraction (DMAE) and other advancements in MAE are also detailed in this article. In addition, the microwave extraction procedures and the important parameters influencing its performance are also included, together with the advantages and the drawbacks of each MAE techniques.     

Separation of oxidized variants of a monoclonal antibody by anion-exchange

Monoclonal antibodies are subject to a variety of degradation mechanisms, therefore orthogonal techniques are required to demonstrate product quality. In this study, the three individual antibodies comprising a multi-antibody drug product, XOMA 3AB were evaluated by both cation-exchange (CEX) and anion-exchange chromatography (AEX). In contrast to CEX analysis which showed only a single, broad peak for the force-oxidized antibodies, AEX analysis of Ab-A (pI=7.6) revealed two more basic peaks. Ab-B (pI=6.7) bound but exhibited only a single major peak while Ab-C (pI=8.6) flowed through. Peptide mapping LC/MS analysis of the isolated Ab-A fractions demonstrated that the basic peaks resulted from oxidation in a complementary determining region (CDR). Differential scanning calorimetry (DSC) analysis of the oxidized Ab-A species showed a decrease in the Fab melting point for the oxidized species consistent with unfolding of the molecule. Greater/lesser surface exposure of ionic residues resulting from a conformational change provides a likely explanation for the dramatic shift in retention behavior for the Ab-A oxidized variants. Peptide mapping analysis of the Ab-B antibody showed, in contrast to Ab-A, no detectable CDR oxidation. Hence, the lack of separation of oxidized variants in Ab-B can be explained by the absence of CDR oxidation and the associated changes in secondary/tertiary structure which were observed for oxidized Ab-A. In summary, anion-exchange HPLC shows potential as an orthogonal analytical technique for assessing product quality of monoclonal antibody therapeutics. In the case of the XOMA 3AB drug product, two of the antibodies bound and one, Ab-A, exhibited separation of CDR oxidized variants.     

Application of Li2SiO3 as a heterogeneous catalyst in the production of biodiesel from soybean oil

Biodiesel was synthesized from soybean oil by transesterification over Li₂SiO₃ catalyst.The Li₂SiO₃ can be used for biodiesel production directly without further drying or thermal pretreatment,no obvious difference in the FAME conversion（92.4-96.7%） between the air-exposed catalyst（24-72 h） and the fresh one（94.2%）.This leads to important benefits when considering industrial applications of Li₂SiO₃ as a solid catalyst for storing and handling catalyst without taking special actions.     

The development of anisotropic behaviours of 3T3 fibroblasts on microgrooved patterns

3T3 fibroblasts cultured on microgrooved polydimethylsiloxane (PDMS) surfaces of two different widths (25μm and 55μm) were individually tracked using confocal microscopy with a novel live-cell staining technique over several hours without noticeable cytotoxic effects. By quantifying the cell morphology, orientation, and migration over time, we identified the timescale (about 2-4h after seeding) over which cell behaviours transitioned from isotropy to anisotropy, where the preference is in the direction parallel to the pattern. The development of anisotropy occurred more rapidly and distinctly when a narrower ridge width was used, suggesting that it is the ridge width that imposed a physical barrier on the cells' morphology and motility. Furthermore, while we found a weak but statistically significant correlation between cell orientation and morphology on the single-cell level, there is a lack of correlation on the same level between cell orientation and migratory direction. This suggests that while morphology and migration are affected anisotropically by topographical patterns in a similar way, the underlying processes giving rise to the anisotropy is slightly different in the two cases.     

Sub-single-cycle optical pulse train with constant carrier envelope phase

We describe the synthesis of periodic waveforms consisting of a train of pulses that are 0.83 cycles long and have an electric field pulse width of 0.44 fs using 7 Raman sidebands generated by molecular modulation in H2. We verify by optical correlation that the carrier-envelope phase is constant in these waveforms when they are synthesized from commensurate sidebands. The estimated overall shift of the carrier-envelope phase is less than 0.18 cycles from the first to the last pulse of nearly 10(6) pulses in the pulse train.