Monoarsine-protected icosahedral cluster [Au13(AsPh3)8Cl4]+: comparative studies on ligand effect and surface reactivity with its stibine analogue.

Ligand shells of gold nanoclusters play important roles in regulating their molecular and electronic structures. However, the similar but distinct impacts of the homologous analogues of the protecting ligands remain elusive. The C2v symmetric monoarsine-protected cluster [Au13(AsPh3)8Cl4]+ (Au13As8) was facilely prepared by direct reduction of (Ph3As)AuCl with NaBH4. This cluster is isostructural with its previously reported stibine analogue [Au13(SbPh3)8Cl4]+ (Au13Sb8), enabling a comparative study between them. Au13As8 exhibits a blue-shifted electronic absorption band, and this is probably related to the stronger π-back donation interactions between the Au13 core and AsPh3 ligands, which destabilize its superatomic 1P and 1D orbitals. In comparison to the thermodynamically less stable Au13Sb8, Au13As8 achieves a better trade-off between catalytic stability and activity, as demonstrated by its excellent catalytic performance towards the aldehyde-alkyne-amine (A3) coupling reaction. Moreover, the ligand exchange reactions between Au13As8 with phosphines, as exemplified by PPh3 and Ph2P(CH2)2PPh2, suggest that Au13As8 may be a good precursor cluster for further cluster preparation through the "cluster-to-cluster" route.

Ag22 Nanoclusters with Thermally Activated Delayed Fluorescence Protected by Ag/Cyanurate/Phosphine Metallamacrocyclic Monolayers through In-Situ Ligand Transesterification.

The composition of protection monolayer exerts great influence on the molecular and electronic structures of atomically precise monolayer protected metal nanoclusters. Four isostructural Ag/cyanurate/phosphine metallamacrocyclic monolayer protected Ag22 nanoclusters are synthesized by kinetically controlled in-situ ligand formation-driven strategy. These eight-electron superatomic silver nanoclusters feature an unprecedented interfacial bonding structure with diverse E-Ag (E=O/N/P/Ag) interactions between the Ag13 core and metallamacrocyclic monolayer, and displays thermally activated delayed fluorescence (TADF), benefiting from their distinct donor-acceptor type electronic structures. This work not only unmasks a new core-shell interface involving cyanurate ligand but also underlines the significance of high-electron-affinity N-heterocyclic ligand in synthesizing TADF metal nanoclusters. This is the first mixed valence Ag0/I nanocluster with TADF characteristic.

Electrocatalytic activity of salicylic acid on the platinum nanoparticles modified electrode by electrochemical deposition.

Platinum nanoparticles (PNP) were deposited on the Pt disk electrode by electrochemical deposition, it was found that salicylic acid (SA) had good electrocatalytic oxidation response at the prepared Pt nanoparticles modified Pt disk electrode (PNP/Pt). Then the modified electrode was used to detect SA in weak alkali condition, it was found that the response current was 9.2 times that of bare Pt disk electrode, and the linear range of detection was 2.0x10(-5) to 5.0x10(-4)M. After that, the electrode was adopted to detect the SA in Zuguangsan, one kind of Chinese medicine, the results showed that the PNP/Pt electrode has low detection limit, high repeatability and stability as SA sensor, could be applied in the detection of SA reliably.

Electrocatalytic oxidation of phytohormone salicylic acid at copper nanoparticles-modified gold electrode and its detection in oilseed rape infected with fungal pathogen Sclerotinia sclerotiorum.

Salicylic acid (SA) is a biological substance that acts as a phytohormone and plays an important role in signal transduction in plants. It is important to accurately and sensitively detect SA levels. A gold electrode modified with copper nanoparticles was used to assay the electrocatalytic oxidation of salicylic acid. It was found that the electrochemical behavior of salicylic acid was greatly improved at copper nanoparticles, indicating that anodic oxidation could be catalyzed at copper nanoparticles. And the pH had remarkable effect on the electrochemical process, a very well-defined oxidation peak appeared at pH 13.3 (0.2M NaOH). The kinetics parameters of this process were calculated and the heterogeneous electron transfer rate constant (k) was determined to be 1.34x10(-3)cms(-1), and (1-alpha)n(alpha) was 1.22. The gold electrode modified with copper nanoparticles could detect SA at a higher sensitivity than common electrodes. The electrode was used to detect the SA levels in oilseed rape infected with the fungal pathogen Sclerotinia sclerotiorum. The results showed that the SA concentration reached a maximum during the 10th-25th hours after infection. This result was very similar to that determined by HPLC, indicating that the gold electrodes modified with copper nanoparticles could be used as salicylic acid sensors.

Direct electrochemistry and electrocatalytic activity of hemoglobin at CdTe nanoparticle/nafion film-modified electrode.

Water-soluble CdTe nanoparticles and hemoglobin (Hb) were immobilized on a glassy carbon (GC) electrode with Nafion. The direct electrochemistry of Hb on this surface was studied. The results indicated that CdTe nanoparticles could effectively promote the direct electron transfer of Hb at the interface of a electrode. The average surface coverage of Hb on the surface could be calculated as 2.63 x 10(-9) mol/cm2, the heterogeneous electron transfer rate constant, k, was calculated as 0.068 s(-1) and the transfer coefficient, alpha, was 0.59, further study indicated that immobilized Hb still kept its catalytic activity to H2O2 reduction. The apparent Michaelis-Menten constant was calculated to be 17.7 microM. It was also found that the modified electrode could be used as a sensor for H2O2; the linear range of detection was 5.0 x 10(-6)-4.5 x 10(-5) M, with a detection limit of 8.4 x 10(-7) M. The sensor exhibited high sensitivity, reproducibility and stability.

Electrocatalysis of emodin at multi-wall nanotubes.

In this article, the electrochemical behavior of emodin at multi-wall carbon nanotube modified glassy carbon electrodes (MWNTs/GCE) was studied. The result showed that MWNTs/GCE had high electrocatalytic activity for emodin. And the electrocatalytic redox process was a two-charge-two-proton process. Diffusion coefficient (D(R)) of 8.403 x 10(-5) cm(2) s(-1) of emodin was obtained. Further experiments demonstrated that the oxidative peaks increased linearly with emodin concentrations in the range of 1.0 x 10(-6) to 1.0 x 10(-4) M with a limit of detection of 3.0 x 10(-7) M. This electrochemical method was accurate and reliable, therefore, it might provide a novel way for emodin detection.

Alix/AIP1 antagonizes epidermal growth factor receptor downregulation by the Cbl-SETA/CIN85 complex.

The assembly of the Cbl-SETA/CIN85-endophilin complex at the C terminus of the epidermal growth factor receptor (EGFR) following ligand activation mediates its internalization and ubiquitination. We found that the SETA/CIN85-interacting protein Alix/AIP1, which also binds endophilins, modulates this complex. Alix was found to associate indirectly with EGFR, regardless of its activation state, and with DeltaEGFR, which signals at low intensity and does not bind Cbls or SETA/CIN85. In agreement with this, Alix interaction did not occur via SETA/CIN85. However, SETA/CIN85 and Alix were capable of mutually promoting their interaction with the EGFR. Increasing the level of Alix weakened the interaction between SETA/CIN85 and Cbl and reduced the tyrosine phosphorylation of c-Cbl and the level of ubiquitination of EGFR, SETA/CIN85, and Cbls. This antagonism of the Cbl-SETA/CIN85 complex by Alix was reflected in its diminution of EGFR internalization. In agreement with this, small interfering RNA-mediated knockdown of Alix promoted EGFR internalization and downregulation. It has been suggested that SETA/CIN85 promotes receptor internalization by recruiting endophilins. However, Alix was also capable of increasing the level of endophilin associated with EGFR, implying that this is not sufficient to promote receptor internalization. We propose that Alix inhibits EGFR internalization by attenuating the interaction between Cbl and SETA/CIN85 and by inhibiting Cbl-mediated ubiquitination of the EGFR.

Mediator-free phenol sensor based on titania sol-gel encapsulation matrix for immobilization of tyrosinase by a vapor deposition method.

A novel amperometric phenol sensor was constructed by immobilizing tyrosinase in a titania sol-gel matrix. The tyrosinase entrapped sol-gel film was obtained with a vapor deposition method, which simplified the traditional sol-gel process and avoided the shrinkage and cracking of conventional sol-gel-derived glasses. This matrix provided a microenvironment for retaining the native structure and activity of the entrapped enzyme and a very low mass transport barrier to the enzyme substrates. Phenol could be oxidized by dissolving oxygen in presence of immobilized tyrosinase to form a detectable product, which was determined at -150 mV without any mediator. The phenol sensor exhibited a fast response (less than 5 s) and sensitivity as high as 103 microA/mM, which resulted from the porous structure and high enzyme loading of the sol-gel matrix. The linear range for phenol determination was from 1.2x10(-7) to 2.6x10(-4) M with a detection limit of 1.0x10(-7) M. The apparent Michaelis-Menten constant of the encapsulated tyrosinase was calculated to be (0.29+/-0.02) mM. The stability of the biosensor was also evaluated.

Glucose sensor for flow injection analysis of serum glucose based on immobilization of glucose oxidase in titania sol-gel membrane.

A novel amperometric glucose sensor was constructed by immobilizing glucose oxidase (GOD) in a titania sol-gel film, which was prepared with a vapor deposition method. The sol-gel film was uniform, porous and showed a very low mass transport barrier and a regular dense distribution of GOD. Titania sol-gel matrix retained the native structure and activity of entrapped enzyme and prevented the cracking of conventional sol-gel glasses and the leaking of enzyme out of the film. With ferrocenium as a mediator the glucose sensor exhibited a fast response, a wide linear range from 0.07 to 15 mM. It showed a good accuracy and high sensitivity as 7.2 microA cm(-2) mM(-1). The general interferences coexisted in blood except ascorbic acid did not affect glucose determination, and coating Nafion film on the sol-gel film could eliminate the interference from ascorbic acid. The serum glucose determination results obtained with a flow injection analysis (FIA) system showed an acceptable accuracy, a good reproducibility and stability and indicated the sensor could be used in FIA determination of glucose. The vapor deposition method could fabricate glucose sensor in batches with a very small amount of enzyme.

Platelet-derived growth factor (PDGF) receptor-alpha-activated c-Jun NH2-terminal kinase-1 is critical for PDGF-induced p21WAF1/CIP1 promoter activity independent of p53.

Platelet-derived growth factor (PDGF) is a potent mitogen for mesenchymal cells. PDGF AA functions as a "competent factor" that stimulates cell cycle entry but requires additional (progression) factors in serum to transit the cell cycle beyond the G1/S checkpoint. Unlike PDGF AA, PDGF B-chain (c-sis) homodimer (PDGF BB) and its viral counterpart v-sis can serve as both competent and progression factors. PDGF BB activates alpha- and beta-receptor subunits (alpha-PDGFR and beta-PDGFR) and induces phenotypic transformation in NIH 3T3 cells, whereas PDGF AA activates alpha-PDGFR only and fails to induce transformation. We showed previously that alpha-PDGFR antagonizes beta-PDGFR-mediated transformation through activation of stress-activated protein kinase-1/c-Jun NH2-terminal kinase-1, whereas both alpha-PDGFR and beta-PDGFR induce mitogenic signals. These studies revealed a striking feature of PDGF signaling; the specificity and the strength of the PDGF growth signal is modulated by alpha-PDGFR-mediated simultaneous activation of growth stimulatory and inhibitory signals, whereas beta-PDGFR mainly induces a growth-promoting signal. Here we demonstrate that PDGF BB activation of beta-PDGFR alone results in more efficient cell cycle transition from G1 to S phase than PDGF BB activation of both alpha-PDGFR and beta-PDGFR. PDGF AA activation of alpha-PDGFR or PDGF BB activation of both alpha- and beta-PDGFRs up-regulates expression of p21WAF1/CIP1, an inhibitor of cell cycle-dependent kinases and a downstream mediator of the tumor suppressor gene product p53. However, beta-PDGFR activation alone fails to induce p21WAF1/CIP1 expression. We also demonstrate that alpha-PDGFR-activated JNK-1 is a critical signaling component for PDGF induction of p21WAF1/CIP1 promoter activity. The ability of PDGF/JNK-1 to induce p21WAF1/CIP1 promoter activity is independent of p53, although the overall p21WAF1/CIP1 promoter activities are greatly reduced in the absence of p53. These results provide a molecular basis for differential regulation of the cell cycle and transformation by alpha- and beta-PDGFRs.

Syntheses, structures, and properties of imidazolate-bridged Cu(II)-Cu(II) and Cu(II)-Zn(II) dinuclear complexes of a single macrocyclic ligand with two hydroxyethyl pendants.

The imidazolate-bridged homodinuclear Cu(II)-Cu(II) complex, [(CuimCu)L]ClO(4).0.5H(2)O (1), and heterodinuclear Cu(II)-Zn(II) complex, [(CuimZnL(-)(2H))(CuimZnL(-)(H))](ClO(4))(3) (2), of a single macrocyclic ligand with two hydroxyethyl pendants, L (L = 3,6,9,16,19,22-hexaaza-6,19-bis(2-hydroxyethyl)tricyclo[22,2,2,2(11,14)]triaconta-1,11,13,24,27,29-hexaene), have been synthesized as possible models for copper-zinc superoxide dismutase (Cu(2),Zn(2)-SOD). Their crystal structures analyzed by X-ray diffraction methods have shown that the structures of the two complexes are markedly different. Complex 1 crystallizes in the orthorhombic system, containing an imidazolate-bridged dicopper(II) [Cu-im-Cu](3+) core, in which the two copper(II) ions are pentacoordinated by virtue of an N4O environment with a Cu.Cu distance of 5.999(2) A, adopting the geometry of distorted trigonal bipyramid and tetragonal pyramid, respectively. Complex 2 crystallizes in the triclinic system, containing two similar Cu-im-Zn cores in the asymmetric unit, in which both the Cu(II) and Zn(II) ions are pentacoordinated in a distorted trigonal bipyramid geometry, with the Cu.Zn distance of 5.950(1)/5.939(1) A, respectively. Interestingly, the macrocyclic ligand with two arms possesses a chairlike (anti) conformation in complex 1, but a boatlike (syn) conformation in complex 2. Magnetic measurements and ESR spectroscopy of complex 1 have revealed the presence of an antiferromagnetic exchange interaction between the two Cu(II) ions. The ESR spectrum of the Cu(II)-Zn(II) heterodinuclear complex 2 displayed a typical signal for mononuclear trigonal bipyramidal Cu(II) complexes. From pH-dependent ESR and electronic spectroscopic studies, the imidazolate bridges in the two complexes have been found to be stable over broad pH ranges. The cyclic voltammograms of the two complexes have been investigated. Both of the two complexes can catalyze the dismutation of superoxide and show rather high activity.

Platelet-derived growth factor signaling and human cancer.

Platelet-derived growth factor (PDGF) is a critical regulator of mesenchymal cell migration and proliferation. The vital functions of PDGFs for angiogenesis, as well as development of kidney, brain, cardiovascular system and pulmonary alveoli during embryogenesis, have been well demonstrated by gene knock-out approaches. Clinical studies reveal that aberrant expression of PDGF and its receptor is often associated with a variety of disorders including atherosclerosis, fibroproliferative diseases of lungs, kidneys and joints, and neoplasia. PDGF contributes to cancer development and progression by both autocrine and paracrine signaling mechanisms. In this review article, important features of the PDGF isoforms and their cell surface receptor subunits are discussed, with regards to signal transduction, PDGF-isoform specific cellular responses, and involvement in angiogensis, and tumorstromal interactions.

Preparation of porous titania sol-gel matrix for immobilization of horseradish peroxidase by a vapor deposition method.

A new and facile vapor deposition method has been developed for the preparation of sol-gel matrix. This method was used to form a titania sol-gel thin film and to immobilize horseradish peroxidase (HRP) on a glassy carbon electrode surface for the production of an amperometric hydrogen peroxide biosensor. This process prevented the cracking of conventional sol-gel-derived glasses. The morphologies of both titania sol-gel and the enzyme membranes were characterized using scanning electron microscopy and proved to be chemically clean, porous, and homogeneous and to have a very narrow particle size distribution. The sol-gel-derived titania-modified electrode retained the enzyme bioactivity and provided for long-term stability of the enzyme in storage. In the presence of catechol as a mediator, the sensor exhibited a rapid electrocatalytic response (less than 5 s), a linear calibration range from 0.08 to 0.56 mM with a detection limit of 1.5 microM and a high sensitivity (61.5 microA mM(-1)) for monitoring of H2O2. Effects of pH and operating potential were also explored for optimum analytical performance by using the amperometric method. The apparent Michaelis-Menten constant of the encapsulated HRP was 1.89 +/- 0.21 mM.