Kinetic investigation on carbamate formation from the reaction of carbon dioxide with amino acids in homogeneous aqueous solution

The kinetics of carbamate formation from the reaction of carbon dioxide with α‐amino acids in D₂O was first investigated by means of nuclear magnetic resonance spectroscopy. Potassium carbonate was used as the CO₂ source. For each amino acid, the maximum carbamate yield, the apparent rate constant for the carbamate formation k_app, and the rate constants for the formation k₁ and the breakdown k_?1 of the carbamate were estimated. Plots of log k₁ or log k_?1 versus pK_a of amino acids indicated that the formation rate k₁ increased with the basicity (pK_a) of amino acid, while the decomposition rate k_?1 decreased. A Br?nsted β value of 0.39 was obtained from the former plot, being in good agreement with the previously reported ones (0.26–0.43). The observed negative pK_a dependence of log k_?1 (Br?nsted α = 0.34) is reasonable, because the carbamate decomposition is acid‐catalyzed and the steady‐state concentration of H⁺ should be higher for weaker basic amines. The charge (σ) and the lone‐pair energy (E_N) at the nitrogen atom of the amino group were calculated. Although log k₁ correlated with σ and E_N, log k_?1 was unrelated with both of these parameters. Considering that the carbamate formation (k₁) is not only base‐catalyzed but should also be promoted by the nucleophilicity of the amino nitrogen, its correlation with σ and E_N in addition to pK_a is rational. The irrelevance of log k_?1 to σ and E_N is not surprising, because σ and E_N are not a direct measure of [H⁺] of the solution. Copyright © 2011 John Wiley & Sons, Ltd.     

Coherence effect on decryption characteristics in message modulation type chaos secure communication systems using fiber-optic ring resonators

We numerically investigated the dependence of the decryption characteristics in a message modulation type chaos secure communication system using optical fiber ring resonators (OFRRs) on the coherence condition of carrier light. Since the output dynamics of OFRRs were formed on the basis of interference phenomenon among the circulated components in OFRRs, the coherence condition of input light affected inherently the OFRR output dynamics, resulting in the decryption characteristics. It was found that the decryption characteristics degraded as coherence length increased, i.e., as the spectral width of the input light decreased. The decryption characteristics also grew worse as the parameter differences between the transmitter and the receiver became larger.     

Chiral bicyclic imidazolium salts as a new class of N-heterocyclic carbene precursors

A N(1)-C(5) bridged chiral bicyclic imidazole with a morpholine framework was synthesized from an enantiopure 2-amino alcohol. The resultant imidazole reacted with various electrophiles, including primary and secondary alkyl halides, benzyne, and an electron-deficient aryl halide, to give the corresponding imidazolium salts. Some of the imidazolium salts were found to have potential as the precursor of a chiral N-heterocyclic carbene catalyst; by the direct annulation of an enal and a ketone through the intermediacy of a homoenolate and an activated carboxylate, the target lactone was obtained in an enantiomerically enriched form (up to 66% ee).     

Bremsstrahlung emission in α-decay of210Po

Bremsstrahlung photons associated with the α-decay of²¹⁰Po were measured in α-γ coincidence measurements with Si and Ge detectors. Emission probabilities of the bremsstrahlung deduced for²¹⁰Po were 10⁻¹¹∼10⁻¹²/keV/sr/decay for 100≤E _γ≤600 keV. It was found that the bremsstrahlung yields are much smaller than those predicted by a Coulomb acceleration model. This suggests that α-particles also emit photons inside the barrier. The bremsstrahlung spectrum was compared with a quasi-classical calculation in which the bremsstrahlung emission in tunneling motion of α-particles is taken into account. It is shown that the data can be interpreted as a consequence of destructive interference of radiative amplitudes outside the Coulomb barrier with those in tunneling.     

Visualization of acetylcholine distribution in central nervous system tissue sections by tandem imaging mass spectrometry

Metabolite distribution imaging via imaging mass spectrometry (IMS) is an increasingly utilized tool in the field of neurochemistry. As most previous IMS studies analyzed the relative abundances of larger metabolite species, it is important to expand its application to smaller molecules, such as neurotransmitters. This study aimed to develop an IMS application to visualize neurotransmitter distribution in central nervous system tissue sections. Here, we raise two technical problems that must be resolved to achieve neurotransmitter imaging: (1) the lower concentrations of bioactive molecules, compared with those of membrane lipids, require higher sensitivity and/or signal-to-noise (S/N) ratios in signal detection, and (2) the molecular turnover of the neurotransmitters is rapid; thus, tissue preparation procedures should be performed carefully to minimize postmortem changes. We first evaluated intrinsic sensitivity and matrix interference using Matrix Assisted Laser Desorption/Ionization (MALDI) mass spectrometry (MS) to detect six neurotransmitters and chose acetylcholine (ACh) as a model for study. Next, we examined both single MS imaging and MS/MS imaging for ACh and found that via an ion transition from m/z 146 to m/z 87 in MS/MS imaging, ACh could be visualized with a high S/N ratio. Furthermore, we found that in situ freezing method of brain samples improved IMS data quality in terms of the number of effective pixels and the image contrast (i.e., the sensitivity and dynamic range). Therefore, by addressing the aforementioned problems, we demonstrated the tissue distribution of ACh, the most suitable molecular specimen for positive ion detection by IMS, to reveal its localization in central nervous system tissues.     

Interchenar retrotransfer of aureothin intermediates in an iterative polyketide synthase module

The course of the enigmatic iterative use of a polyketide synthase module was deduced from targeted domain inactivation in the aureothin assembly line. Mutational analyses revealed that the N-terminus of AurA is not involved in the iteration process, ruling out an ACP-ACP shuttle. Furthermore, an AurA(KS°, ACP°)-AurA(AT(0)) heterodimer proved to be nonfunctional, whereas aureothin production was restored in a ΔaurA mutant complemented with AurA(KS°)-AurA(ACP°). This finding supports a model according to which the ACP-bound polyketide intermediate is transferred back to the KS domain on the opposite PKS strand.     

Diastereoselective addition of allyltitanocenes to cyclic enones

The reaction of allyltitanocenes with five- to seven-membered cyclic enones proceeded with good to high diastereoselectivity depending on the ring size of enones. The stereochemistry of the major isomers produced by the reaction of cinnamyltitanocene was opposite to that of crotyltitanocene.     

Shape- and size-controlled synthesis in hard templates: sophisticated chemical reduction for mesoporous monocrystalline platinum nanoparticles

Here we report a novel hard-templating strategy for the synthesis of mesoporous monocrystalline Pt nanoparticles (NPs) with uniform shapes and sizes. Mesoporous Pt NPs were successfully prepared through controlled chemical reduction using ascorbic acid by employing 3D bicontinuous mesoporous silica (KIT-6) and 2D mesoporous silica (SBA-15) as a hard template. The particle size could be controlled by changing the reduction time. Interestingly, the Pt replicas prepared from KIT-6 showed polyhedral morphology. The single crystallinity of the Pt fcc structure coherently extended over the whole particle.