Boosting the Faradaic Efficiency of Br--Mediated Photoelectrochemical Epoxidation by Local Acidity on α-Fe2O3.

The redox mediated photoelectrochemical (PEC) or electrochemical (EC) alkene oxidation process is a promising method to produce high value-added epoxides. However, due to the competitive reaction of water oxidation and overoxidation of the mediator, the utilization of the electricity is far below the ideal value, where the loss of epoxidation's faradaic efficiency (FE) is ≈50%. In this study, a Br-/HOBr-mediated method is developed to achieve a near-quantitative selectivity and ≈100% FE of styrene oxide on α-Fe2O3, in which low concentration of Br- as mediator and locally generated acidic micro-environment work together to produce the higher active HOBr species. A variety of styrene derivatives are investigated with satisfied epoxidation performance. Based on the analysis of local pH-dependent epoxidation FE and products distribution, the study further verified that HOBr serves as the true active mediator to generate the bromohydrin intermediate. It is believed that this strategy can greatly overcome the limitation of epoxidation FE to enable future industrial applications.

Plasmonic Silver-Nanoparticle-Catalysed Hydrogen Abstraction from the C(sp3 )-H Bond of the Benzylic Cα atom for Cleavage of Alkyl Aryl Ether Bonds.

Selective activation of the C(sp3 )-H bond is an important process in organic synthesis, where efficiently activating a specific C(sp3 )-H bond without causing side reactions remains one of chemistry's great challenges. Here we report that illuminated plasmonic silver metal nanoparticles (NPs) can abstract hydrogen from the C(sp3 )-H bond of the Cα atom of an alkyl aryl ether ß-O-4 linkage. The intense electromagnetic near-field generated at the illuminated plasmonic NPs promotes chemisorption of the ß-O-4 compound and the transfer of photo-generated hot electrons from the NPs to the adsorbed molecules leads to hydrogen abstraction and direct cleavage of the unreactive ether Cß -O bond under moderate reaction conditions (≈90 °C). The plasmon-driven process has certain exceptional features: enabling hydrogen abstraction from a specific C(sp3 )-H bond, along with precise scission of the targeted C-O bond to form aromatic compounds containing unsaturated, substituted groups in excellent yields.

Photon Energy Threshold in Direct Photocatalysis with Metal Nanoparticles: Key Evidence from the Action Spectrum of the Reaction.

By investigating the action spectra (the relationship between the irradiation wavelength and apparent quantum efficiency of reactions under constant irradiance) of a number of reactions catalyzed by nanoparticles including plasmonic metals, nonplasmonic metals, and their alloys at near-ambient temperatures, we found that a photon energy threshold exists in each photocatalytic reaction; only photons with sufficient energy (e.g., higher than the energy level of the lowest unoccupied molecular orbitals) can initiate the reactions. This energy alignment (and the photon energy threshold) is determined by various factors, including the wavelength and intensity of irradiation, molecule structure, reaction temperature, and so forth. Hence, distinct action spectra were observed in the same type of reaction catalyzed by the same catalyst due to a different substituent group, a slightly changed reaction temperature. These results indicate that photon-electron excitations, instead of the photothermal effect, play a dominant role in direct photocatalysis of metal nanoparticles for many reactions.

Enhancing photoactivity of TiO2(B)/anatase core-shell nanofibers by selectively doping cerium ions into the TiO2(B) core.

Cerium ions (Ce(3+)) can be selectively doped into the TiO2(B) core of TiO2(B)/anatase core-shell nanofibers by means of a simple one-pot hydrothermal treatment of a starting material of hydrogen trititanate (H2Ti3O7) nanofibers. These Ce(3+) ions (≈0.202 nm) are located on the (110) lattice planes of the TiO2(B) core in tunnels (width≈0.297 nm). The introduction of Ce(3+) ions reduces the defects of the TiO2(B) core by inhibiting the faster growth of (110) lattice planes. More importantly, the redox potential of the Ce(3+)/Ce(4+) couple (E°(Ce(3+)/Ce(4+))=1.715 V versus the normal hydrogen electrode) is more negative than the valence band of TiO2(B). Therefore, once the Ce(3+)-doped nanofibers are irradiated by UV light, the doped Ce(3+) ions--in close vicinity to the interface between the TiO2(B) core and anatase nanoshell--can efficiently trap the photogenerated holes. This facilitates the migration of holes from the anatase shell and leaves more photogenerated electrons in the anatase nanoshell, which results in a highly efficient separation of photogenerated charges in the anatase nanoshell. Hence, this enhanced charge-separation mechanism accelerates dye degradation and alcohol oxidation processes. The one-pot treatment doping strategy is also used to selectively dope other metal ions with variable oxidation states such as Co(2+/3+) and Cu(+/2+) ions. The doping substantially improves the photocatalytic activity of the mixed-phase nanofibers. In contrast, the doping of ions with an invariable oxidation state, such as Zn(2+), Ca(2+), or Mg(2+), does not enhance the photoactivity of the mixed-phase nanofibers as the ions could not trap the photogenerated holes.

Coherent interfaces between crystals in nanocrystal composites.

Numerous materials are polycrystalline or consist with crystals of different phases. However, materials consisting of crystals on the nanometer scale (nanocrystals) are not simply aggregates of randomly oriented crystals as is generally regarded. We found, that in four different materials that consist of nanocrystals of two different phases and were obtained by different approaches, the nanocrystals of different phases are combined coherently forming interfaces with a close crystallographic registry between adjacent crystals (coherent interfaces). The four materials were fabricated by (i) depositing Ag(2)O nanoparticles on titanate nanofibers, (ii) phase transition from TiO(2)(B) nanofibers to the nanofibers of mixed TiO(2)(B) and anatase phases, (iii) dehydration of the single crystal fibril titanate core coated with anatase nanocrystals, and (iv) attaching zeolite Y nanocrystals on the surface of titanate nanofibers. The finding suggests that preferred orientations and coherent interfaces generally exist in nanocrystal systems, and according to our results, they are largely unaffected by the fabrication process that was used. This is because the preferred orientations require that the engaged crystal planes from two connected crystals have the same basal spacing and that the crystals can interlock tightly at the atomic level to form thermodynamically stable interfaces. Hence it is rational that the preferred orientations and coherent interfaces dominant the nanostructures formed between the different nanocrystals and play a key role in assembling the composite nanostructures. The orientation and interfaces between crystals of different phases in mixed-phase materials are extremely difficult to determine. Nonetheless, the thermodynamic stability of the coherent interfaces allows us to apply phase-transformation invariant line strain theory to predict the preferred orientation (and thus the structure of the coherent interfaces). The theoretical predications agree remarkably with the transmission electron microscopy (TEM) analysis. This implies that we may acquire knowledge of the orientation and the interface structures in the mixed-phase materials without TEM measurement, and the knowledge is essential for comprehensively understanding properties of the many materials and processes that depend on the interfaces.

An efficient photocatalyst structure: TiO(2)(B) nanofibers with a shell of anatase nanocrystals.

A new efficient photocatalyst structure, a shell of anatase nanocrystals on the fibril core of a single TiO(2)(B) crystal, was obtained via two consecutive partial phase transition processes. In the first stage of the process, titanate nanofibers reacted with dilute acid solution under moderate hydrothermal conditions, yielding the anatase nanocrystals on the fiber. In the subsequent heating process, the fibril core of titanate was converted into a TiO(2)(B) single crystal while the anatase crystals in the shell remained unchanged. The anatase nanocrystals do not attach to the TiO(2)(B) core randomly but coherently with a close crystallographic registry to the core to form a stable phase interface. For instance, (001) planes in anatase and (100) planes of TiO(2)(B) join together to form a stable interface. Such a unique structure has several features that enhance the photocatalytic activity of these fibers. First, the differences in the band edges of the two phases promote migration of the photogenerated holes from anatase shell to the TiO(2)(B) core. Second, the well-matched phase interfaces allow photogenerated electrons and holes to readily migrate across the interfaces because the holes migrate much faster than excited electrons, more holes than electrons migrate to TiO(2)(B) and this reduces the recombination of the photogenerated charges in anatase shell. Third, the surface of the anatase shell has both a strong ability to regenerate surface hydroxyl groups and adsorb O(2), the oxidant of the reaction, to yield reactive hydroxyl radicals (OH(.)) through reaction between photogenerated holes and surface hydroxyl groups. The adsorbed O(2) molecules can capture the excited electrons on the surface, forming reactive O(2)(-) species. The more reactive species generated on the external surface, the higher the photocatalytic activity will be, and generation of the reactive species also contributes to reducing recombination of the photogenerated charges. Indeed, the mixed-phase nanofibers exhibited superior photocatalytic activity for degradation of sulforhodamine B under UV light to the nanofibers of either pure phase alone or mechanical mixtures of the pure phase nanofibers with a similar phase composition. Finally, the nanofibril morphology has an additional advantage that they can be separated readily after reaction for reuse by sedimentation. This is very important because the high cost for separating the catalyst nanocrystals has seriously impeded the applications of TiO(2) photocatalysts on an industrial scale.

[Tandem application of flow cytometry and polymerase chain reaction for choice targets of minimal residual disease in childhood acute lymphoblastic leukemia].

OBJECTIVE: Minimal residual disease (MRD) is one of the most important prognostic factors in childhood acute lymphoblastic leukemia (ALL). Flow cytometry and PCR are two common techniques for examining MRD in ALL. This study aimed to identify MRD targets by tandem application of both techniques in children with ALL. METHODS: From September 2001 to October 2003, 126 children with newly diagnosed ALL were enrolled on the treatment protocol ALL-XH-99. Tandem application of flow cytometry and PCR was performed to identify MRD targets in these patients. RESULTS: 1. Using sets of combined antibodies, immunophenotypic expression of leukemia cells was observed in 95 of 106 B-lineage ALL cases (89.6%). Only one aberrant immunophenotype was observed in 11 cases (11.6%) and most patients with B-lineage ALL (88.4%) expressed at least two suitable targets. 2. Using PCR technique, T-cell receptor (TCR) or immunoglobulin gene rearrangements were identified in 26 of 27 patients (96.3%). Two or more monoclonal/ bi-allelic gene rearrangements were identified in 17 cases (65.4%). The majority (70%) of T-lineage ALL cases contained TCRVgammaI-Jgamma1.3/2.3. Cross-lineage TCR rearrangements were found in 57.1% of cases with B-lineage ALL. 3. Suitable MRD targets of immunophenotypic abnormalities or antigen receptor gene rearrangements were detected in 121 patients (96.0%). CONCLUSIONS: MRD targets were identified using tandem application of flow cytometry and PCR in almost of children with ALL. Cross-lineage TCR rearrangements and bi-allelic gene rearrangements were observed in many patients.

Detection of intermediates in the TiO2-assisted photodegradation of Rhodamine B under visible light irradiation.

The photocatalytic degradation of dye Rhodamine B (RhB) in the presence of TiO2 nanostripe or P25 under visible light irradiation was investigated. The degradation intermediates were identified using Infrared spectra (IR spectra), 1H nuclear magnetic resonance (1HNMR) spectra, and gas chromatography-mass spectroscopy (GC-MS). The IR and the 1HNMR results showed that the large conjugated chromophore structure of RhB was efficiently destroyed under visible light irradiation in both the photocatalytic systems (TiO2 nanostripe or P25 and Rhodamine B systems). GC-MS results showed that the main identified intermediates were ethanediotic acid, 1,2-benzenedicarboxylic acid, 4-hydroxy benzoic acid and benzoic acid, which were almost the same in the TiO2 nanostripes and P25 systems. This work provides a good insight into the reaction pathway(s) for the TiO2-assisted photocatalytic degradation of dye pollutants under visible light irradiation.

[Preliminary study of VEGF and its receptor expression on childhood acute lymphoblastic leukemia and its relativity to clinical manifestations].

OBJECTIVE: To investigate the relationship between differential expression of VEGF and its receptors and clinical characteristics of childhood acute lymphoblastic leukemia (ALL). METHODS: Expressions of VEGF and its receptors (Flt-1, KDR) were assayed by ELISA and RT-PCR in healthy donors(20 cases), ALL patients in remission (20 cases), with low risk (29 cases) and with high risk (10 cases). The clinical data of all the patients and volunteers enrolled in this study were collected and analyzed according to the expression of VEGF and its receptors. RESULTS: The expressions of VEGF were (574.37 +/- 208.45) ng/L, (387.93 +/- 175.86) ng/L, (135.80 +/- 111.28) ng/L and (91.16 +/- 41.34) ng/L in patients with high risk, standard risk, in remission and healthy donors, respectively. Expression levels of VEGF receptors were downwards with risk grades. The clinical manifestations were also in accord with the expression levels of VEGF and its receptors. CONCLUSION: ALL patients with highly expressed VEGF and its receptors are usually with higher tumor burden, and refractory treatment. Detection of VEGF and its receptors might be one of prognostic marker for ALL treatment.

[Apoptosis mechanism in human chronic myelogenous leukemia K562 cells induced by tetra-arsenic tetra-sulfide].

To explore the effects of tetra-arsenic tetra-sulfide (As(4)S(4)) in treatment of human chronic myelogenous leukemia K562 cells and its mechanism, trypan blue staining and microculture MTS assay were used to measure the effects of As(4)S(4) on growth inhibition of K562 cells; the morphologic change was determined by Wright's staining assay. The apoptosis rate and cell cycle were detected by flow cytometry; the changes of transcript and protein level were determined by real-time quantitative RT-PCR and Western blot analysis, respectively. The results indicated that As(4)S(4) had significant cytotoxicity on K562 cells. At the concentration of 0.5 micromol/L, the cell viability decreased significantly after being cultured with As(4)S(4) for 24 hours. When the concentration was lower than 0.1 micromol/L, As(4)S(4) had a little effect on K562 cells. The effect of As(4)S(4) on K562 was time- and concentration- dependent. After being cultured with As(4)S(4) at the concentration of 1.0 micromol/L for 24 to 48 hours, K562 cells displayed typical morphological changes of apoptosis. At a concentration greater than or equal to 1.0 micromol/L, As(4)S(4) could induce apoptosis significantly. After 12 hours of incubation with 1.0 micromol/L As(4)S(4), the apoptosis rate increased from (3.47 +/- 0.42)% to (6.16 +/- 0.98%). At the same time, the percentage of cells in G(1) phase decreased from (69.65 +/- 3.24)% to (50.53 +/- 2.86)%, whereas the percentage of cells in G(2)/M phase increased from (9.56 +/- 2.51)% to (12.91 +/- 2.13)%. The mRNA level of Bcl-X(L) and the protein level of pAkt were down-regulated after the inhibition of As(4)S(4), while the mRNA expression of Bcl-2, Bad and Bax had no change. Both of the transcript and protein level of bcr-abl had no change after incubation with As(4)S(4). It is concluded that As(4)S(4) can inhibit the growth of K562 cells efficiently through inducing apoptosis and cell cycle arrest. It seems that As(4)S(4) interferes with pAkt pathway and down-regulates Bcl-X(L), which may be involved in the response of K562 to this agent.

[Analysis on GST-Pi genetic polymorphism in children with acute leukemia].

OBJECTIVES: To study the frequency distribution patterns of the genetic polymorphisms for glutathione S-transferase Pi (GST-Pi) in children with acute leukemia, and explore the possible relationship of GST-Pi gene mutation to the vulnerability of children with leukemia and the chemotherapeutic response. METHOD: Direct DNA sequencing was applied to detect the genotype polymorphism in 85 healthy children as the control group and 120 children with acute leukemia. The distribution difference of the genotypes between them was analyzed. RESULTS: Gene mutation rate of GST-Pi exon5 was 47.5% in children with acute leukemia, significantly higher than that of 31.8% in the control group (OR = 1.944, 95% CI 1.088-3.473), and this polymorphism distribution pattern was similar to that reported abroad. The mutation rate was much higher in ALL group than in others groups and was not significantly between the AML children and the control group. The overall mutation rate of B-lineage ALL (60.3%) was markedly higher than that of T-ALL (47.1%), but the homozygous mutation rate of the latter group (17.6%) was much higher than that of the former group (3.4%) (P < 0.05). The average survival time of the children with wild type exon5 was 24 months, longer than that of the mutation group (17.6 months), however with no statistical difference (P > 0.05). The genotype of exon5 had no effect on the survival time of AML children. No Ala(114)Val variant genotype of GST-Pi exon6 reported in literatures was found in this study, but two new mutant genotypes were discovered. A/G hybridity at 99 loci of exon6 was found in one healthy child and such hybrid genotype did not result in amino acid alteration. G-->T/G bases hybridity at 103 loci of exon6 occurred in two children with leukemia, leading to GAC of Asp (aspartic acid) replaced by TAC of Try (tyrosine) at 147 loci of the protein peptide chain, producing Asp(147) Try hybrid mutation with a genotypic frequency of 1.7%. CONCLUSION: The gene mutation of GST-Pi exon5 is one of the potential vulnerable factors in leukemogenesis of the Chinese children and the genetic polymorphism of exon6 in Chinese is greatly different from that in other races. The role of the newly discovered variant genotype Asp(147) Try in leukemogenesis remains to be further studied.

[Significance of TPMT activity and TGNs level detection for individualizing 6-mercaptopurine chemotherapy].

OBJECTIVE: To evaluate the activity and genotype of thiopurine methyltransferase (TPMT) and the concentration of thioguanine nucleotides (TGNs) as parameters for individualizing mercaptopurine (6-MP) therapy. METHODS: Erythrocyte TPMT activity was measured by means of radiochemical assay. Sequence specific primer (SSP) PCR and restriction fragment length polymorphism (RFLP) were used to determine the mutations in TPMT genomic DNAs. Erythrocyte TGNs concentration in acute lymphoblastic leukemia (ALL) patients after 6-MP treatment was detected by high-performance liquid chromatography (HPLC). RESULTS: The erythrocyte TPMT activity in Han population was 16.6 +/- 4.5U/ml pRBCs (man 16.8 +/- 5.0 U/ml pRBCs, woman 16.5 +/- 4.4 U/ml pRBCs), the activity in 8.1% of the samples was lower than 10 U/ml pRBCs. There was no difference for TPMT activity by gender, age, and between healthy donors and ALL patients. For TPMT genotypes, there were 5 cases of TPMT * 2, 4 TPMT * 3A, 6 TPMT * 3B, 10 TPMT * 3C and 5 unknown in 30 subjects who had low TPMT activity. In children with ALL, the TGNs level did show a negative correlation with TPMT activity at diagnosis and 7 approximately 14 days after 6-MP therapy and with WBC count 14 days after the determination of TGNs. CONCLUSION: Detection of TPMT activity before 6-MP therapy and TGNs level during 6-MP therapy may be helpful for preventing side effects from antipurine metabolic drug overdose, and individualizing 6-MP chemotherapy in children with ALL.

Telomerase activity and its correlation with the proliferative potential of bone marrow in aplastic anemia in children.

OBJECTIVE: To explore telomerase activity and its association with the proliferative potential of hematopoietic stem cells in bone marrow (BM) in patients with aplastic anemia (AA). METHODS: Telomerase activity of mononuclear cells separated from BM was determined with the TRAPeze kit. BM specimens from 22 cases with AA and 7 normal controls were included. SPSS10.0 was applied to analyze data derived from telomerase activity and colony-forming unit-granulocyte and monocyte. RESULTS: The median telomerase activity level of BM in AA was 2-fold higher than that in normal controls. There was an inverse correlation in AA between telomerase activity and colony-forming unit (r = 0.78, p < 0.05). BM of chronic AA expressed higher telomerase than that of acute AA. CONCLUSIONS: Telomerase activity in AA was increased and may be the result of the negative feedback of hematopoietic potential. Telomerase activity varied between the subtypes of AA. Telomerase activity was conversely correlated with the proliferative potential of BM in AA.