Infrared multiple photon dissociation spectra of proton- and sodium ion-bound glycine dimers in the N-H and O-H stretching region

The proton- and the sodium ion-bound glycine homodimers are studied by a combination of infrared multiple photon dissociation (IRMPD) spectroscopy in the N-H and O-H stretching region and electronic structure calculations. For the proton-bound glycine dimer, in the region above 3100 cm (-1), the present spectrum agrees well with one recorded previously. The present work also reveals a weak, broad absorption spanning the region from 2650 to 3300 cm (-1). This feature is assigned to the strongly hydrogen-bonded and anharmonic N-H and O-H stretching modes. As well, the shared proton stretch is observed at 2440 cm (-1). The IRMPD spectra for the proton-bound glycine dimer confirms that the lowest energy structure is an ion-dipole complex between N-protonated glycine and the carboxyl group of the second glycine. This spectrum also helps to eliminate the existence of any of the higher-energy structures considered. The IRMPD spectrum for the sodium ion-bound dimer is a much simpler spectrum consisting of three bands assigned to the O-H stretch and the asymmetric and symmetric NH 2 stretching modes. The positions of these bands are very similar to those observed for the proton-bound glycine dimer. Numerous structures were considered and the experimental spectrum agrees with the B3LYP/6-31+G(d,p) predicted spectrum for the lowest energy structure, two bidentate glycine molecules bound to Na (+). Though some of the structures cannot be completely ruled out by comparing the experimental and theoretical spectra, they are energetically disfavored by at least 20 kJ mol (-1).     

Efficient and Mild Synthesis of Novel Schiff Bases Via One-Pot,Three-Component Reaction Under Solvent-Free Conditions

A simple, efficient, and cost-effective method has been developed for the synthesis of N,N′-bis(2-hydroxybenzylidene)-1,1-diaminoalkanes through one-pot, three-component reaction of salicylaldehyde, aliphatic aldehydes, and ammonium nitrate in the presence of a base under solvent-free conditions at room temperature.     

Existence of turbulent behavior for non-chaotic two dimensional jets

The classic models of mass transfer for free turbulent jets very often contain neglected terms. This is because these terms are considered so small that their effect can be neglected; however, because the models are usually structurally unstable, these neglected terms, even if they are small, may change the behavior of the system. Furthermore, the existing classic models cannot simulate the far behavior of the fluid, for example, the eddies existing in the jet region of the fluid stream. In this paper, we consider a general implicit small perturbation of the classic model and study the effect of it on the system. We will show that the local bifurcations may imply the existence of eddies for the fluid stream; for example, we will see that, under some conditions, the Hopf bifurcation generates permanent eddies for the system.     

在色氨酸存在下利用多壁碳纳米管糊电极和萘酚介质构成的伏安传感器测定N-乙酰半胱氨酸(英文)

A multiwall carbon nanotube modified electrode prepared by incorporating multiwall carbon nanotubes in the electrode of a sensor and naphthol green as a homogeneous mediator was used as a voltammetric sensor for the determination of N‐actylcysteine(N‐AC) in the presence of trypto-phan(Trp). The voltammograms of differential pulse voltammetry of N‐AC in a mixture with Trp were separated from each other by a potential difference of 200 mV, which allowed the determina-tion of both N‐AC and Trp simultaneously. Under the optimum conditions, the electrocatalytic cur-rents increased linearly with N‐AC concentration in the range of 0.25–400 μmol/L(two linear seg-ments with different slopes). The detection limit for N‐AC was 0.08 μmol/L. The kinetic parameters of the system were determined using electrochemical methods. The method was applied for the determination of N‐AC in drug and urine samples.     

K7[PW11CoO40]: Efficient and Ecofriendly Catalyst for the Enamination of β-Dicarbonyl Compounds

Condensation of a variety of β-dicarbonyl compounds with primary and secondary amines carried out in the presence of catalytic amounts of K₇[PW₁₁CoO₄₀]. From this reaction N-substituted β-enamino esters and ketones were obtained in high yields.     

The Effect of a Covalent and a Noncovalent Small-Molecule Inhibitor on the Structure of Abg β-Glucosidase in the Gas-Phase

The effects of binding two small-molecule inhibitors to Agrobacterium sp. strain ATCC 21400 (Abg) β-glucosidase on the conformations and stability of gas-phase ions of Abg have been investigated. Biotin-iminosugar conjugate (BIC) binds noncovalently to Abg while 2,4-dinitro-2-deoxy-2-fluoro-β-d-glucopyranoside (2FG-DNP) binds covalently with loss of DNP. In solution, Abg is a dimer. Mass spectra show predominantly dimer ions, provided care is taken to avoid dissociation of dimers in solution and dimer ions in the ion sampling interface. When excess inhibitor, either covalent or noncovalent, is added to solutions of Abg, mass spectra show peaks almost entirely from 2:2 inhibitor-enzyme dimer complexes. Tandem mass spectrometry experiments show similar dissociation channels for the apo-enzyme and 2FG-enzyme dimers. The +21 dimer produces +10 and +11 monomers. The internal energy required to dissociate the +21 2FG-enzyme to its monomers (767?±?30 eV) is about 36 eV higher than that for the apo-enzyme dimer (731?±?6 eV), reflecting the stabilization of the free enzyme dimer by the 2FG inhibitor. The primary dissociation channels for the noncovalent BIC-enzyme dimer are loss of neutral and charged BIC. The internal energy required to induce loss of BIC is 482?±?8 eV, considerably less than that required to dissociate the dimers. For a given charge state, ions of the covalent and noncovalent complexes have about 15 % and 25 % lower cross sections, respectively, compared with the apo-enzyme. Thus, binding the inhibitors causes the gas-phase protein to adopt more compact conformations. Noncovalent binding surprisingly produces the greatest change in protein ion conformation, despite the weaker inhibitor binding.

Cupric Sulfate Pentahydrate: A Mild and Efficient Catalyst for the Chemoselective Synthesis of 1,1-Diacetates from Aldehydes in a Solvent-Free System

Cupric sulfate pentahydrate was found to be an efficient catalyst for the protection of aldehydes as 1,1-diacetates in high yields in a solvent-free system at room temperature. Ketones are not affected under these reaction conditions.