Tandem time-of-flight mass spectrometer for photodissociation of biopolymer ions generated by matrix-assisted laser desorption ionization (MALDI-TOF-PD-TOF) using a linear-plus-quadratic potential reflectron

A tandem time-of-flight mass spectrometer for the study of photodissociation of biopolymer ions generated by matrix-assisted laser desorption ionization was designed and constructed. A reflectron with linear and quadratic (LPQ) potential components was used. Characteristics of the LPQ reflectron and its utility as the second stage analyzer of the tandem mass spectrometer were investigated. Performance of the instrument was tested by observing photodissociation of [M + H](+) from angiotensin II, a prototype polypeptide. Quality of the photodissociation tandem mass spectrum was almost comparable to that of the post-source decay spectrum. Monoisotopic selection of the parent ion was possible, which was achieved through the ion beam-laser beam synchronization. General theoretical considerations needed for a successful photodissociation of large biopolymer ions are also presented.     

Using quaternions to calculate RMSD

A widely used way to compare the structures of biomolecules or solid bodies is to translate and rotate one structure with respect to the other to minimize the root-mean-square deviation (RMSD). We present a simple derivation, based on quaternions, for the optimal solid body transformation (rotation-translation) that minimizes the RMSD between two sets of vectors. We prove that the quaternion method is equivalent to the well-known formula due to Kabsch. We analyze the various cases that may arise, and give a complete enumeration of the special cases in terms of the arrangement of the eigenvalues of a traceless, 4 x 4 symmetric matrix. A key result here is an expression for the gradient of the RMSD as a function of model parameters. This can be useful, for example, in finding the minimum energy path of a reaction using the elastic band methods or in optimizing model parameters to best fit a target structure.     

Aqua dissociation nature of cesium hydroxide

To understand the mechanism of aqueous base dissociation chemistry, the ionic dissociation of cesium-hydroxide in water clusters is examined using density functional theory and ab initio calculations. In this study, we report hydrated structures, stabilities, thermodynamic quantities, dissociation energies, infrared spectra, and electronic properties of CsOH(H(2)O)(n=0-4). With the addition of water molecules, the Cs-OH bond lengthened significantly from 2.46 A for n=1 to 3.08 A for n=4, which causes redshift in Cs-O stretching frequency. It is found that three water molecules are needed for the dissociation of Cs-OH, in contrast to the case of strong acid dissociation which requires at least four water molecules. However, the dissociation for n=3 could be considered as incomplete because a very weak CS em leader OH stretch mode is still present, while that for n=4 is complete since the Cs em leader OH mode no longer exists. This study can be related with hydration chemistry of cations and anions, and extended into the intra- and intercharge-transfer phenomena.     

Kinetics and mechanism of benzylamine additions to ethyl alpha-acetyl-beta-phenylacrylates in acetonitrile

Kinetic studies of the addition of benzylamines to a noncyclic dicarbonyl group activated olefin, ethyl alpha-acetyl-beta-phenylacrylate (EAP), in acetonitrile at 25.0 degrees C are reported. The rates are lower than those for the cyclic dicarbonyl group activated olefins. The addition occurs in a single step with concurrent formation of the Calpha-N and Cbeta-H bonds through a four-center hydrogen bonded transition state.The kinetic isotope effects (kH/kD > 1.0) measured with deuterated benzylamines (XC6H4CH2ND2) increase with a stronger electron acceptor substituent (deltasigmaX > 0) which is the same trend as those found for other dicarbonyl group activated series (1-4), but is in contrast to those for other (noncarbonyl) group activated series (5-9). For the dicarbonyl series, the reactivity-selectivity principle (RSP) holds, but for others the anti-RSP applies. These are interpreted to indicate an insignificant imbalance for the former, but substantial lag in the resonance delocalization in the transition state for the latter series.     

Development of New Atom Transfer Radical Polymerization System by Iron (III)‐Metal Salts Without Using any External Initiator and Reducing Agent

Atom transfer radical polymerization (ATRP) catalyzed by high oxidation state metal salts of FeX₃ is developed for the first time in the absence of both external initiator and reducing agent. Methyl methacrylate (MMA) and styrene are polymerized successfully using FeX₃/Phosphorous ligands with well‐controlled molecular weight distributions (=1.5). The molecular weight of the polymers increases with monomer consumption with the progress of time and the polymerization behaviors show a decent ATRP trend. Activators and initiators are suggested to generate in situ by the addition reaction of MMA and one equivalent of FeX₃. The PMMA synthesized from without‐initiator system is characterized by ¹H, ¹³C and DEPT (distortionless enhancement by polarization transfer nuclear magnetic resonance) nuclear magnetic resonance spectroscopy. Chain extension and copolymerization experiments prove the livingness of the obtained polymer.

     

Hollow Polydimethylsiloxane Beads with a Porous Structure for Cell Encapsulation

Based on a water‐in‐oil‐in‐water emulsion system, porous and hollow polydimethylsiloxane (PDMS) beads containing cells using a simple fluidic device with three flow channels are fabricated. Poly(ethylene glycol) (PEG) in the PDMS oil phase is served as a porogen for pore development. The feasibility of the porous PDMS beads prepared with different PEG concentrations (10, 20, and 30 wt%) for cell encapsulation in terms of pore size, protein diffusion, and cell proliferation inside the PDMS beads is evaluated. The PDMS beads prepared with PEG 30 wt% are exhibited a highly porous structure and facilitated fast diffusion of protein from the core domain to the outer phase, eventually leading to enhanced cell proliferation. The results clearly indicate that hollow PDMS beads with a porous structure could provide a favorable microenvironment for cell survival due to the large porous structure.

     

Discrete electrostatic charge transfer by the electrophoresis of a charged droplet in a dielectric liquid

We have experimentally investigated the electrostatic charging of a water droplet on an electrified electrode surface to explain the detailed inductive charging processes and use them for the detection of droplet position in a lab-on-a-chip system. The periodic bouncing motion of a droplet between two planar electrodes has been examined by using a high-resolution electrometer and an image analysis method. We have found that this charging process consists of three steps. The first step is inductive charge accumulation on the opposite electrode by the charge of a droplet. This induction process occurs while the droplet approaches the electrode, and it produces an induction current signal at the electrometer. The second step is the discharging of the droplet by the accumulated induced charge at the moment of contact. For this second step, there is no charge-transfer detection at the electrometer. The third step is the charging of the neutralized droplet to a certain charged state while the droplet is in contact with the electrode. The charge transfer of the third step is detected as the pulse-type signal of an electrometer. The second and third steps occur simultaneously and rapidly. We have found that the induction current by the movement of a charged droplet can be accurately used to measure the charge of the droplet and can also be used to monitor the position of a droplet under actuation. The implications of the current findings for understanding and measuring the charging process are discussed.     

SSA-MOA: a novel CTC isolation platform using selective size amplification (SSA) and a multi-obstacle architecture (MOA) filter

Circulating tumor cells (CTCs) have gained increasing attention as physicians and scientists learn more about the role these extraordinarily rare cells play in metastatic cancer. In developing CTC technology, the critical criteria are high recovery rates and high purity. Current isolation methods suffer from an inherent trade-off between these two goals. Moreover, ensuring minimal cell stress and robust reproducibility is also important for the clinical application of CTCs. In this paper, we introduce a novel CTC isolation technology using selective size amplification (SSA) for target cells and a multi-obstacle architecture (MOA) filter to overcome this trade-off, improving both recovery rate and purity. We also demonstrate SSA-MOA's advantages in minimizing cell deformation during filter transit, resulting in more stable and robust CTC isolation. In this technique, polymer microbeads conjugated with anti-epithelial cell adhesion molecules (anti-EpCAM) were used to selectively size-amplify MCF-7 breast cancer cells, definitively differentiating from the white blood cells (WBCs) by avoiding the size overlap that compromises other size selection methods. 3 μm was determined to be the optimal microbead diameter, not only for size discrimination but also in maximizing CTC surface coverage. A multi-obstacle architecture filter was fabricated using silicon-on-glass (SOG) technology-a first such application of this fabrication technique-to create a precise microfilter structure with a high aspect ratio. The filter was designed to minimize cell deformation as simulation results predicted that cells captured via this MOA filter would experience 22% less moving force than with a single-obstacle architecture. This was verified by experiments, as we observed reliable cell capture and reduced cell deformation, with a 92% average recovery rate and 351 peripheral blood leukocytes (PBL) per millilitre (average). We expect the SSA-MOA platform to optimize CTC recovery rates, purity, and stability, increasing the sensitivity and reliability of such tests, thereby potentially expanding the utilization of CTC technologies in the clinic.