Separation of globins using free zone capillary electrophoresis.

This paper describes the use of high-performance capillary electrophoresis for the separation of globin chains. Adult and newborn haemolysates from normal individuals and children suspected of having thalassaemia were analysed using free zone electrophoresis. Separation of globins was accomplished using a 25 mM phosphate buffer at pH 11.8. Distinct peaks of alpha-, beta- and gamma-chains were resolved within 8 min. The coefficient of variation for within-day and between-day runs was 4.1% and 5.7%, respectively. This method is simple and rapid, and it can be used to screen for thalassaemia and for the clinical study of various haemoglobinopathies.     

Process optimization of preparing spherical titania colloids with uniform distribution using artificial neural networks

Optimal operating variables for preparing submicron uniform titania colloids were estimated using the artificial neural networks (ANN) modeling and the process optimization algorithms. Titania colloids were synthesized by a sol–gel method using mixture recipes of titanium tetraisopropoxide (TTIP), NH₃, and H₂O with ethanol/acetonitrile under temperature-controlled conditions. Different sets of the operating variables, such as [NH₃], [H₂O], and reaction temperature, were selected within an operating range to carry out Design of Experiment to evaluate the prepared particle size (PS) and the particle size distribution (PSD) data. The relationship between the operating variables and PS and PSD of the prepared samples can be constructed by an ANN modeling approach. The built ANN model was then used to predict PS and PSD values corresponding to the operating variables. The optimal operating conditions to fabricate different PS values with narrow PSD were determined by the ANN model with the optimization method. Meanwhile, the monodispersed colloids between 150 and 400 nm were fabricated using the determined optimal operating conditions.     

Monodentate and bidentate trifluoroacetato ligands in bis(trifluoroacetato)-(N-methyl-meso-tetraphenylporphyrinato)thallium(III)—a new dynamic 4:3 piano stool seven-coordinate geometry

The crystal structure of bis(trifluoroacetato)-(N-methyl-meso-tetraphenylporphyrinato) thallium(III), Tl(N---Me---tpp)(CF₃CO₂)₂ (2), was established and the coordination sphere around the Tl³⁺ ion is described as 4:3 tetragonal base–trigonal base piano stool seven-coordinate geometry in which the two cis CF₃CO₂ ⁻ groups occupy two apical sites. The plane of the three pyrrole nitrogen atoms [i.e. N(2), N(3) and N(4)] strongly bonded to Tl³⁺ is adopted as the reference plane 3N. The pyrrole N(1) ring bearing the methyl group [i.e. C(45)H₃] is the most deviated one from the 3N plane making a dihedral angle of 23.3° whereas smaller angles of 9.9, 2.7 and 4.7° occur with pyrroles N(2), N(3), and N(4), respectively. Because of the larger size of the thallium(III) ion, Tl is considerably out of the 3N plane; its displacement of 1.02 Å is in the same direction as that of the two apical CF₃CO₂ ⁻ ligands. The intermolecular trifluoroacetate exchange process for 2 in CD₂Cl₂ solvent is examined through ¹⁹F and ¹³C NMR temperature-dependent measurements. In the slow-exchange region, the CF₃ and carbonyl (CO) carbons of the CF₃CO₂ ⁻ groups in 2 are separately located at δ 114.3 [¹J(C–F)=290 Hz, ³J(Tl–C)=411 Hz] and 155.1 [²J(C–F)=37 Hz, ²J(Tl–C)=204 Hz], respectively, at −106 °C. In the same slow-exchange region, the fluorine atoms of 2, Tl(N---Me---tpp)(CF₃CO₂)⁺ and the free CF₃CO₂ ⁻ are located at δ −73.76 [⁴J(Tl–F)=44 Hz], −73.30 [⁴J(Tl–F)=22 Hz], and −76.15 ppm at −97 °C, respectively.     

Excited-state behavior of N-phenyl-substituted trans-3-aminostilbenes: where the "m-amino effect" meets the "amino-conjugation effect"

The electronic spectroscopy and photochemistry of the trans isomers of 3-(N-phenylamino)stilbene (m1c), 3-(N-methyl-N-phenylamino)stilbene (m1d), 3-(N,N-diphenylamino)stilbene (m1e), and 3-(N-(2,6-dimethylphenyl)amino)stilbene (m1f) and their double-bond constrained analogues m2a-m2c and m2e are reported. When compared with trans-3-aminostilbene (m1a), m1c-m1e display a red shift of the S0 --> S1 absorption and fluorescence spectra, lower oscillator strength and fluorescence rate constants, and more efficient S1 --> T1 intersystem crossing. Consequently, the N-phenyl derivatives m1c-m1e have lower fluorescence quantum yields and higher photoisomerization quantum yields. The corresponding N-phenyl substituent effect in m2a-m2e is similar in cyclohexane but smaller in acetonitrile. This is attributed to the weaker intramolecular charge transfer character for the S1 state of m2 so that the rates for intersystem crossing are less sensitive to solvent polarity. It is also concluded that N-phenyl substitutions do not change the triplet mechanism of photoisomerization for m1 in both nonpolar and polar solvents. Therefore, the "m-amino conjugation effect" reinforces the "m-amino effect" on fluorescence by further reducing its rate constants and highlights the N-phenyl-enhanced intersystem crossing from the "amino-conjugation effect" by making S1 --> T1 the predominant nonradiative decay pathway.     

Fluorescence enhancement of trans-4-aminostilbene by N-phenyl substitutions: the "amino conjugation effect"

The synthesis, structure, and photochemical behavior of the trans isomers of 4-(N-phenylamino)stilbene (1c), 4-(N-methyl-N-phenylamino)stilbene (1d), 4-(N,N-diphenylamino)stilbene (1e), and 4-(N-(2,6-dimethylphenyl)amino)stilbene (1f) are reported and compared to that of 4-aminostilbene (1a) and 4-N,N-dimethylaminostilbene (1b). Results for the corresponding 3-styrylpyridine (2) and 2-styrylnaphthalene analogues (3) are also included. The introduction of N-phenyl substituents to 4-aminostilbenes leads to a more planar ground-state geometry about the nitrogen atom, a red shift of the absorption and fluorescence spectra, and a less distorted structure with a larger charge-transfer character for the fluorescent excited state. Consequently, the N-phenyl derivatives 1c-e have low photoisomerization quantum yields and high fluorescence quantum yields at room temperature, in contrast to the behavior of 1a, 1b, and most unconstrained monosubstituted trans-stilbenes. The isomerization of 1c and 1d is a singlet-state process, whereas it is a triplet-state process for 1e, presumably due to a relatively higher singlet-state torsional barrier. The excited-state behavior of 1f resembles 1a and 1b instead of 1c-e as a consequence of the less planar amine geometry and weaker orbital interactions between the N-phenyl and the aminostilbene groups. Such an N-phenyl substituent effect is also found for 2 and 3 and thus appears to be general for stilbenoid systems. The nature of this effect can be described as an "amino conjugation effect".     

Real-time image linearization in a rotating prism-pair scanning system by using laser-diode encoding techniques

Rotating prism-pair scanning is a conventional method used to achieve large angles with a straight-line configuration. A disadvantage of prism scanners for line scanning is that the sinusoidal scan produces a non-linear image. We use a laser-diode encoding technique to carry out real-time image linearization in a rotating prism-pair scanning system. In this study, we report on the results obtained in a thermal image system.     

Supercritical fluid extraction and quantification of aflatoxins in Zizyphi Fructus by liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry

An integrated method combining supercritical fluid extraction (SFE) with liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry (LC/APCI-MS/MS) was developed and successfully applied to quantify aflatoxins (AFs) in Zizyphi Fructus (fruits of Zizyphus jujube), a traditional Chinese medicine. To minimize the potential interferences caused by the complex matrix in Zizyphi Fructus, a SFE pretreatment was performed. In addition, electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) spectra were also compared. The results showed that the calibration curves of AFB(1), AFB(2), AFG(1), and AFG(2) were all linear over the range of concentration from 1 to 50 ng/g, the squared correlation coefficients (r(2)) were over 0.995, and the detection limits of the method were between 0.17 and 0.32 ng/g. It showed high recovery and good precision in quantitating AFs in Zizyphi Fructus without further clean-up. Further, fragmentation pathways of protonated AFs in APCI-MS/MS were clearly proposed which could predict the existence of AFB or AFG series. To test the empirical validity of the proposed methodology in this paper, eight random samples of Zizyphi Fructus collected from supermarkets and traditional Chinese medicine stores in different geographical areas of Taiwan were analyzed. The results indicated that low levels of AFs were detected in only one of them.     

Meta conjugation effect on the torsional motion of aminostilbenes in the photoinduced intramolecular charge-transfer state

The photochemical behavior of a series of trans-3-(N-arylamino)stilbenes (m1, aryl = 4-substituted phenyl with a substituent of cyano (CN), hydrogen (H), methyl (Me), or methoxy (OM)) in both nonpolar and polar solvents is reported and compared to that of the corresponding para isomers (p1CN, p1H, p1Me, and p1OM). The distinct propensity of torsional motion toward a low-lying twisted intramolecular charge-transfer (TICT) state from the planar ICT (PICT) precursor between the meta and para isomers of 1CN and 1Me reveals the intriguing meta conjugation effect and the importance of the reaction kinetics. Whereas the poor charge-redistribution (delocalization) ability through the meta-phenylene bridge accounts for the unfavorable TICT-forming process for m1CN, it is such a property that slows down the decay processes of fluorescence and photoisomerization for m1Me, facilitating the competition of the single-bond torsional reaction. In contrast, the quinoidal character for p1Me in the PICT state kinetically favors both fluorescence and photoisomerization but disfavors the single-bond torsion. The resulting concept of thermodynamically allowed but kinetically inhibited TICT formation could also apply to understanding the other D-A systems, including trans-4-cyano-4'-(N,N-dimethylamino)stilbene (DCS) and 3-(N,N-dimethylamino)benzonitrile (3DMABN).     

A study of the effect of Z- and E-olefinic geometry on the rates of ring closure of 13-membered dienes

An analysis is presented to explain the faster rate of ring formation 5 --> 7 as compared to 6 --> 8.