Density Functional Theory Studies on Structure, Ligand Exchange, and Optical Properties of Ligand-Protected Gold Nanoclusters: Thiolate versus Selenolate

Atomically precise thiolate-protected Au nanoclusters (NCs), i.e. Au_<i>m</i>(SR)_<i>n</i>, have attracted intensive research interest during the past few years. Recently, the synthesis and isolation of selenolate-protected gold clusters (Au_<i>m</i>(SeR)_<i>n</i>) via the ligand exchange of thiolate with selenol were achieved, which demonstrated identical compositions to those of thiolate-protected Au NCs. In this study, we perform a comprehensive theoretical study on the structure, electronic structure, and electronic optical absorption properties of 11 selenolate-protected gold clusters on the basis of density functional theory (DFT) calculations. Our results propose that the selenolate-protected Au NCs with framework structure identical to the thiolated ones are stable local minima. The ligand effect is proposed to understand the distinct geometrical structures of Au₂₄(SeR)₂₀ and Au₂₄(SR)₂₀ NCs. In addition, the optical absorption properties of thiolate- and selenolate-protected Au NCs are compared via the time-dependent density functional theory (TD-DFT). The results indicate that two types of Au NCs possess similar shape of electronic optical absorption spectra and electronic structure. The excitation wavelength dependent intermolecular electron transfer between the Au₂₅(ER)⁻ (E = S and Se) and O₂ is revealed as well

Ultrafast Relaxation Dynamics of Luminescent Rod-Shaped, Silver-Doped Ag_<i>x</i>Au_{25–<i>x</i>} Clusters

The luminescent ligand protected metal clusters have attracted considerable attentions while the origin of the emission still remains elusive. As recently reported in our previous work, the rod-shaped Au₂₅ cluster possesses a low photoluminescence quantum yield (QY = 0.1%), whereas substituting silver atoms for central gold atom in the rod-shaped Au₂₅ cluster can drastically enhance the photoluminescence with high quantum yield (QY = 40.1%). To explore the enhancement mechanism of fluorescence, femtosecond transient absorption spectroscopy is performed to determine the electronic structure and ultrafast relaxation dynamics of the highly luminescent silver-doped Ag_<i>x</i>Au_{25–<i>x</i>} cluster by comparing the excited state dynamics of doped and undoped Au₂₅ rod cluster, it is found that the excited state relaxation in Ag_<i>x</i>Au_{25–<i>x</i>} is proceeded with an ultrafast (∼0.58 ps) internal conversion and a subsequent nuclear relaxation (∼20.7 ps), followed by slow (7.4 μs) decay back to the ground state. Meanwhile, the observed nuclear relaxation is much faster in Ag_<i>x</i>Au_{25–<i>x</i>} (∼20.7 ps) compared to that in undoped Au₂₅ rod (∼52 ps). We conclude that it is the central Ag atom that stabilizes the charges on LUMO orbital and enhances the rigidity of Ag_<i>x</i>Au_{25–<i>x</i>} cluster that leads to strong fluorescence. Meanwhile, coherent oscillations around ∼0.8 THz were observed in both clusters, indicating the symmetry preservation from Au cluster to Ag alloying Au clusters. The present results provide new insights for the structure-related excited state behaviors of luminescent ligand protected Ag alloying Au clusters

Electroacupuncture for Tinnitus: A Systematic Review

<div><p>Background</p><p>Treatment effects of electroacupuncture for patients with subjective tinnitus has yet to be clarified.</p><p>Objectives</p><p>To assess the effect of electroacupuncutre for alleviating the symptoms of subjective tinnitus.</p><p>Methods</p><p>Extensive literature searches were carried out in three English and four Chinese databases (PubMed, EMBASE, Cochrane Library, CNKI, Wanfang Chinese Digital Periodical and Conference Database, VIP, and ChiCTR).The date of the most recent search was 1 June 2014. Randomized controlled trials (RCTs) or quasi-RCTs were included. The titles, abstracts, and keywords of all records were reviewed by two authors independently. The data were collected and extracted by three authors. The risk of bias in the trials was assessed in accordance with the Cochrane Handbook, version 5.1.0. (<a href="http://www.handbook.cochrane.org/" target="_blank">http://www.handbook.cochrane.org</a>). Eighty-nine studies were retrieved. After discarding 84 articles, five studies with 322 participants were identified. Assessment of the methodological quality of the studies identified weaknesses in all five studies. All studies were judged as having a high risk of selection and performance bias. The attrition bias was high in four studies. Incompleteness bias was low in all studies. Reporting bias was unclear in all studies. Because of the limited number of trials included and the various types of interventions and outcomes, we were unable to conduct pooled analyses.</p><p>Conclusions</p><p>Due to the poor methodological quality of the primary studies and the small sample sizes, no convincing evidence that electroacupuncture is beneficial for treating tinnitus could be found. There is an urgent need for more high-quality trials with large sample sizes for the investigation of electroacupuncture treatment for tinnitus.</p></div

Crystal Structure and Optical Properties of the [Ag₆₂S₁₂(SBu^t)₃₂]²⁺ Nanocluster with a Complete Face-Centered Cubic Kernel

The crystal structure of the [Ag₆₂S₁₂(SBu^t)₃₂]²⁺ nanocluster (denoted as <b>NC-I</b>) has been successfully determined, and it shows a complete face-centered-cubic (FCC) Ag₁₄ core structure with a Ag₄₈(SBu^t)₃₂ shell configuration interconnected by 12 sulfide ions, which is similar to the [Ag₆₂S₁₃(SBu^t)₃₂]⁴⁺ structure (denoted as <b>NC-II</b> for short) reported by Wang. Interestingly, <b>NC-I</b> exhibits prominent differences in the optical properties in comparison with the case of the <b>NC-II</b> nanocluster. We employed femtosecond transient absorption spectroscopy to further identify the differences between the two nanoclusters. The results show that the quenching of photoluminescence in <b>NC-I</b> in comparison to that of <b>NC-II</b> is caused by the free valence electrons, which dramatically change the ligand to metal charge transfer (LMCT, S 3p → Ag 5s). To get further insight into these, we carried out time-dependent density functional theory (TDDFT) calculations on the electronic structure and optical absorption spectra of <b>NC-I</b> and <b>NC-II</b>. These findings offer a new insight into the structure and property evolution of silver cluster materials

Crystal Structure and Optical Properties of the [Ag₆₂S₁₂(SBu^t)₃₂]²⁺ Nanocluster with a Complete Face-Centered Cubic Kernel

The crystal structure of the [Ag₆₂S₁₂(SBu^t)₃₂]²⁺ nanocluster (denoted as <b>NC-I</b>) has been successfully determined, and it shows a complete face-centered-cubic (FCC) Ag₁₄ core structure with a Ag₄₈(SBu^t)₃₂ shell configuration interconnected by 12 sulfide ions, which is similar to the [Ag₆₂S₁₃(SBu^t)₃₂]⁴⁺ structure (denoted as <b>NC-II</b> for short) reported by Wang. Interestingly, <b>NC-I</b> exhibits prominent differences in the optical properties in comparison with the case of the <b>NC-II</b> nanocluster. We employed femtosecond transient absorption spectroscopy to further identify the differences between the two nanoclusters. The results show that the quenching of photoluminescence in <b>NC-I</b> in comparison to that of <b>NC-II</b> is caused by the free valence electrons, which dramatically change the ligand to metal charge transfer (LMCT, S 3p → Ag 5s). To get further insight into these, we carried out time-dependent density functional theory (TDDFT) calculations on the electronic structure and optical absorption spectra of <b>NC-I</b> and <b>NC-II</b>. These findings offer a new insight into the structure and property evolution of silver cluster materials

Effects of TPP1 overexpression on localization of TRF2 with telomeres, telomere length and telomerase activity.

<div><p>(A) Mean TRF lengths at different PDs were detected by southern blot. PD, population doubling. The position of MWs (kb) is indicated to the left.</p> <p>(B) TRAP PCR ELISA assay was used in the analysis of telomerase activity at different PDs.</p> <p>(C) Western blot analysis revealed that TPP1 overexpression had no significant influence on the expression of hTERT.</p> <p>(D) Telomere-ChIP assays were performed using a TRF2 antibody to examine the telomeric DNA bound to by TRF2. Input, supernatant before immunoprecipitation; ppt, protein-DNA immunoprecipitate complex. Specific (telomeric) and nonspecific (Alu) probes were used.</p> <p>Telomeric DNA in ChIP (%) =Telomeric DNA signals of ppt / Telomeric DNA signals of input* 100%.</p></div

TPP1 overexpression increased <b>ATM</b>/<b>ATR</b> expression and induced prolonged Chk1 (p³⁴⁵) phosphorylation.

<div><p>(A) Western blot analysis revealed that TPP1 overexpression increased the expression of ATM and ATR.</p> <p>(B) HCT116-Mock and-TPP1 cells were irradiated with 6 Gy X-ray and incubated for indicated times. Western blots were preformed to detect the expression of Chk1 and p-Ser³⁴⁵-Chk1.</p></div

TPP1 production, radiosensitivity (SF2) and telomere length (TRF) in human colorectal cancer cell lines.

<div><p>(A) TPP1 production was detected by western blotting.. </p> <p>(B) Telomere length was examined by Southern blot analysis. </p> <p>(C) Relative TPP1 production, radiosensitivity (SF2) and telomere length (TRF) in human colorectal cancer cell lines.</p> <p>(D) Correlation between TPP1 production and radiosensitivity (SF2) in colorectal cancer cells was examined.</p> <p>(E) Correlation between TPP1 production and the TRF length in colorectal cancer cells was examined.</p></div

Effects of TPP1 overexpression on the radiosensitivity and cell cycle in HCT116 cells.

<div><p>(A)Verification of TPP1 overexpression by western blotting.</p> <p>(B) HCT116-Mock and-TPP1 cells were irradiated with X-rays and then cell survival was determined using clonogenic assay.</p> <p>(C) HCT116-Mock and-TPP1 cells were irradiated with 6 Gy X-ray and recovered for indicated times. Cell cycle was analyzed by FACS.</p> <p>(D) The population of cells in G2/M phases over time in HCT116- Mock and -TPP1 cells.</p></div

TPP1 overexpression inhibits IR induced apoptosis.

<div><p>HCT116-Mock and-TPP1 cells were irradiated with 5 Gy X-ray and incubated for 24h. The percentage of apoptotic cells was measured by flow cytometry.</p> <p>(A) Representative results of diffrerent groups are shown.</p> <p>(B) Data shown are means±SEM from three independent experiments.</p> <p>*, P < 0.05.</p></div