Lin Mei-rong

Studies of artificial hydrolytic metalloenzymes: the catalytic carboxyester hydrolysis by new macrocyclic polyamine zinc(II) complexes with a phenolic-pendant as novel nucleophile

Abstract Zinc(II) complexes of new macrocyclic tetraamines (cyclam derivatives) having a strategically appended phenolic group, 6-(2′-hydroxy)-benzyl-1,4,8,11-tetraazacyclotetradecane (LA), 6-(2′-hydroxy-5′-bromo)-benzyl-1,4,8,11- tetraazacyclotetradecane (LB) and 6-(2′-hydroxy-3′,5′-dibromo)-benzyl-1,4,8,11-tetraazacyclotetradecane (LC), have been examined as catalysts for the hydrolyses of 4-nitrophenylacetate (NA). The phenolic functionalized macrocycles from 1:1 ZnL complexes at pH ca 5. The potentiometric pH titration of LA, LB and LCZnII complexes showed dissociation of a phenolic proton with pKa values of 8,8, 8.7 and 8.5 at 298 K and I = 0.10 mol.l−1 KNO3 for LA, LB and LCZnII complexes respectively. In the kinetic studies using the zinc complex in 10% (v/v) CH3CN at 298 K, I = 0.10 mol.l−1 KNO3 and pH 7.0–9.5, we proved that the coordinated phenolate can serve as a good nucleophile that effectively catalyzes NA hydrolysis. The hydrolysis rate follows the law v = (kcat[complex]+KOH[OH−]+k0[NA]. The pH rate profile gave a sigmoidal curve with inflection points at pH 8.8, 8.7 and 8.6 for LA, LB and LC, respectively, which correspond to the pKa value of the complex. The second-order (first-order each in complex and NA) rate constants are 0.056, 0.084 and 0.127 mol.l−1. s−1 for LA, LB and LC are obviously larger than the corresponding value of 0.047 mol.l−1. s−1 for N-methylcyclen-Zn(II)-OH− complex catalyst. This is, to our knowledge, the first phenolate coordinated zinc complex that efficiently catalyses the hydrolysis of 4-nitrophenyl acetate (NA). The present study also proves that solvolysis of NA (i.e. water attack on the ester) does exist, but the reaction rate (k0 = 1.12 × 10−5 s−1) is rather small.

STUDY OF DIAGNOSIS CRITERIA FOR PATHOLOGICAL TISSUES BY LASER-INDUCED FLUORESCENCE

It has been confirmed that the differences in fluorescence spectra of normal and pathological biotissues can be used as a sensitive and nondestructive diagnostic probe. However, experiments show that not only are the fluorescence spectral features of different tissues very different but the features of the same tissue under different detection conditions are different too. Therefore, the diagnosis criteria of pathological tissues must be changed in accordance with different spectral features. In this paper, several diagnosis methods using native fluorescence characteristics of biotissues given in existing reports are analyzed. With the fourth harmonic at 266 nm of a Q-switched YAG laser as an excitation source, laser-induced fluorescence (LIF) spectra of native human normal and pathological breast and blood vessel tissues in vitro were measured and studied. According to their spectral characteristics, two diagnosis criteria are suggested: by the fluorescence intensity ratios at several specific wavelengths, cancerous (with p < 0.001) and benign tumor (p < 0.005) can be distinguished from the normal tissue; by the fluorescence intensity ratios of the two main peaks, atherosclerotic plague and thrombus (both with p < 0.005) can be distinguished from normal blood vessel. In order to make comparisons with the results from human cancerous breast tissues, spectra of a model mouse were also observed.

Detection of higher excited states of p-fluorotoluene with (3 + 1)RMPI spectra

Abstract In this paper the results of detection of higher excited states of p -fluorotoluene in the gas phase are presented. Within a laser scanning range of 547.0–570.0 nm (3+1) RMPI spectra are obtained, and some vibrational structures on the third electronically excited valence state are observed. According to the polarization characteristic of the multiphoton transition the symmetry of the electronic state is determined as A 1 +B 1 +3pB 2 . Correlated to excited states of benzene, the results show that A 1 +B 1 corresponds to 1 E 1u and 3pB 2 to 3p 1 A 2u . It indicates that the double degeneracy of 1 E 1u state does not yet degrade in p -fluorotoluene. Moreover, it occasionally degenerates with 3p 1 A 2u . Furthermore, the electron distribution in the phenyl ring maintains the symmetry of the D 6h point group consistently like in benzene.

STUDY OF THREE-PHOTON RESONANCE MULTIPHOTON IONIZATION SPECTROSCOPY OF 3p RYDBERG STATES OF m-DIMETHYLBENZENE WITHIN DYE Rh560

In this paper, we studied experimentally the three-photon resonance four-photon ionization spectroscopy of m-dimethylbenzene within dye Rh560. We found several new 3p Rydberg vibronic states and measured their polarization characters. With the help of the measured polarization quantities, we gave the assignment results of these vibronic states: 9b01, A1; 1301, A1; 19a01, A1; 8a01, A1.

CW Nd:YAG thermo-stable resonators operating in power-steady states

There are two dynamical stable zones in the operation of solid laser containing a thermal lens. In this paper, we point out that in the two stable zones two kinds of dynamical stable states can exist in a laser resonator: mode-steady thermo-stable state and power-steady thermo-stable state. They are different from each other in general. The operating conditions for power-steady thermo-stable state are presented. A cw Nd:YAG thermo-stable resonator operating in power-steady states has been designed, and 40 W TEM00 output power in 1.06 μm is obtained experimentally.

NEW METHOD FOR DETERMINING THREE-PHOTON TRANSITION TENSOR PATTERNS FOR RANDOMLY ORIENTED MOLECULES

The method and results are given for the tensor patterns and polarization ratios of three-photon absorption excited by single-laser for randomly oriented molecules. The ratio of oriented average of transition rate for circularly polarized light to that for linearly polarized light, Ω, can be obtained by the simple three-photon transition tensor. For transition of which the tensor has one independent element, we give the value of polarization ratio; for transition of which the tensor contains two independent elements, we also give the possible range of polarization ratio. These results may be helpful for the symmetry assignment of the excited states.

SYSTEMATIC STUDY OF POLARIZATION OF TWO-PHOTON ABSORPTION IN SYMMETRY ASSIGNMENTS

In this paper, we have systematically analyzed the degenerate and nondegenerate two-photon polarization ratios of various point groups. We present the maximum of symmetry assignments of two-photon transition with the combination of degenerate and nondegenerate two-photon absorption. These results provide the theoretical basis for the experimental assignments.

STUDY OF THE POLARIZATION SPECTROSCOPY OF 3p RYDBERG STATES OF m-DIMETHYLBENZENE

A polarization-selected three-photon resonant multiphoton ionization investigation of the 3p Rydberg region of the spectra of m-dimethylbenzene has been conducted. Several vibronic states have been discovered and also assigned for the first time.

Effect of the laser transverse spatial distribution on multiphoton ionization processes

In this paper, the dependence of the photoionization cross section σ2, total ion number Ni and the FWHM of photoionization spectral line in resonant multiphoton ionization processes (RMPI) upon the parameter C of the laser transverse spatial distribution has been studied. Considering the effects of spatial coordinate on the resonant multiphoton absorption cross section σ1, the limited dimension of the laser-molecular interaction volume and threshold of laser intensity for RMPI, we deduce the expression of σ2 vs the parameter C. We calculated the value of σ2 for (2+2)PI of benzene by numerical method, and compared the result with that obtained by Bruzzeste et al. In addition, we also present the total ion number of photoionization and the FWHM of photoionization spectral line as a function of the parameter C.