Formation and Transformation of CdS Clusters during the Prenucleation Stage and in a Dilute Dispersion at Room Temperature.

The formation and transformation of colloidal semiconductor clusters remain poorly understood. With CdS as a model system, we show that, in the reaction of cadmium myristate (Cd(MA)2) and S powder in 1-octadecene (ODE), clusters form in the prenucleation stage of quantum dots (QDs). Called precursor compounds (PCs), the clusters can transform to magic-size clusters (MSCs) in reaction at a relatively high temperature (MSC-322 displaying optical absorption peaking at 322 nm) or in a dispersion at room temperature (MSC-360). When the reaction temperature is increased, PC-360 forms at 140 °C, while PC-322 and MSC-322 form at 180 °C. In a dispersion of cyclohexane and octylamine, MSC-322 transforms to MSC-360 via MSC-345. The MSC-345 to MSC-360 transformation displays continuous and discontinuous shifts in the optical absorption. The PCs and MSCs are a group of isomers. The present findings bring insight into the cluster formation and isomerization in the prenucleation stage of QDs and in a dispersion.

Association of Insomnia, Sleep Quality, and Sleep Duration With Risk of Physical Frailty in Middle-aged and Older People With HIV.

Background: Frailty is one of the major concerns among aging people with HIV (PWH). Evidence regarding the association between sleep disorders and physical frailty in PWH is limited. Methods: PWH and HIV-negative individuals aged ≥40 years were included and frequency-matched in a 1:2 ratio by sex and age. Logistic regression models were used to estimate the odds ratios (ORs) and 95% CIs of the association between sleep disorders and physical frailty, and restricted cubic splines were used to describe the dose-response association. The contribution of depression to the association was estimated by mediation analysis. Results: A total of 1526 PWH and 3052 HIV-negative individuals were included. Logistic regression indicated that insomnia (OR, 3.05; 95% CI, 1.63-5.72) and poor sleep quality (OR, 2.32; 95% CI, 1.21-4.45) were significantly associated with physical frailty in middle-aged and older PWH, especially in those with current CD4+ T-cell counts <350 cells/µL, but not in HIV-negative participants. A U-shaped and J-shaped dose-response relation between sleep duration and physical frailty was observed in PWH and HIV-negative participants, respectively. Shorter and longer sleep duration was associated with an increased risk of physical frailty in PWH. However, in HIV-negative participants, only longer sleep duration was associated with physical frailty. Mediation analysis revealed that depression mediated the relation between sleep disorders and frailty among PWH. Conclusions: Sleep disorders including insomnia, poor sleep quality, and short and long sleep duration were significantly associated with physical frailty among middle-aged and older PWH. Depression may play a mediating role in the sleep-frailty association.

Thermally-Induced Isomerization of Prenucleation Clusters During the Prenucleation Stage of CdTe Quantum Dots.

The evolution of prenucleation clusters in the prenucleation stage of colloidal semiconductor quantum dots (QDs) has remained unexplored. With CdTe as a model system, we show that substances form and isomerize prior to the nucleation and growth of QDs. Called precursor compounds (PCs), the prenucleation clusters are relatively optically transparent and can transform to absorbing magic-size clusters (MSCs). When a prenucleation-stage sample at 25, 45, or 80 °C is dispersed in a mixture of cyclohexane (CH) and octylamine (OTA) at room temperature, either MSC-371, MSC-417, or MSC-448 evolves with absorption peaking at 371, 417, or 448 nm, respectively. We propose that PC-371 forms at 25 °C, and isomerizes to PC-417 at 45 °C and to PC-448 at 80 °C. The PCs and MSCs are quasi isomers. Relatively large and small amounts of OTA favor PC-371 and PC-448 in dispersion, respectively. The present findings suggest the existence of PC-to-PC isomerization in the QD prenucleation stage.

Evolution of Aqueous-Phase CdTe Magic-Size Clusters from Their Precursor Compounds.

Aqueous-phase semiconductor CdTe magic-size clusters (MSCs) have not been reported. Here, we report the first synthesis of aqueous-phase CdTe MSCs and propose that they evolve from their nonabsorbing precursor compounds (PCs). CdCl2 and Na2TeO3 are used as the respective Cd and Te sources, with l-cysteine as a ligand and NaBH4 as a reductant. When a 5 °C reaction mixture is dispersed in butylamine (BTA), CdTe MSCs evolve. We argue that the self-assembly of the Cd and Te precursors followed by the formation of the Cd-Te covalent bond inside each assembly results in one CdTe PC, which quasi-isomerizes to one CdTe MSC in the presence of BTA. At higher temperatures such as 25 °C, the PCs fragmentize, assisting the nucleation and growth of CdTe quantum dots. We introduce a novel synthetic approach to aqueous-phase CdTe PCs, which transform to CdTe MSCs in the presence of primary amines.

Direct and Indirect Evolution of Photoluminescent Semiconductor CdS Magic-Size Clusters through Their Precursor Compounds.

Colloidal semiconductor II-VI metal chalcogenide (ME) magic-size clusters (MSCs) exhibit either an optical absorption singlet or doublet. In the latter case, a sharp photoluminescence (PL) signal is observed. Whether the PL-inactive MSCs transform to the PL-active ones is unknown. We show that PL-inactive CdS MSC-322 transforms to PL-active CdS MSC-328 and MSC-373 in the presence of acetic acid (HOAc). MSC-322 displays a sharp absorption at ≈322 nm, whereas MSC-328 and MSC-373 both have broad absorptions respectively around 328 and 373 nm. In a reaction of cadmium myristate and S powder in 1-octadecene, MSC-322 develops; with HOAc, MSC-328 and MSC-373 are present. We propose that the MSCs evolve from their relatively transparent precursor compounds (PCs). The PC-322 to PC-328 quasi-isomerization involves monomer substitution, while monomer addition occurs for the PC-328 to PC-373 transformation. Our findings suggest that S dominates the precursor self-assembly quantitatively, and ligand-bonded Cd mainly controls MSC optical properties.

Loneliness and depressive symptoms among men who have sex with men in China: A cross-sectional study.

Background: While psychosocial problems and their related factors in men who have sex with men (MSM) have been well documented in developed countries, there are still not many studies addressing this issue in China and the results are inconsistent. This study aimed to assess the prevalence of loneliness and depressive symptoms among MSM, examine their associated factors, and investigate potential factors moderating the link between depressive symptoms and loneliness. Methods: A cross-sectional study was conducted in Taizhou of Zhejiang Province in China between April and November 2021. Loneliness was assessed using the 3-item UCLA Loneliness Scale (UCLA-3), and depressive symptoms were measured using the Patient Health Questionaire-9 (PHQ-9). Data from 655 MSM were eligible for analysis. Logistic regression models were used to examine the associations between independent variables and the outcomes of loneliness and depression. The interaction terms were added in the models to assess the moderating effects. Results: Of the MSM sample, 13.28 and 7.48% perceived loneliness and reported moderate-to-severe depressive symptoms, respectively. We found that participants who experienced loneliness were more likely to have younger age (OR 0.44, 95% CI 0.21, 0.93, 15-32 years as reference group), low social support (OR 3.60, 95% CI 2.14, 6.04), low self-esteem (OR 3.03, 95% CI 1.45, 6.32) and moderate-to-severe depressive symptoms (OR 5.45, 95% CI 2.66, 11.15). The participants with moderate-to-severe depressive symptoms were more likely to have low self-esteem (OR 6.78, 95% CI 3.08, 14.95) and feelings of loneliness (OR 5.51, 95% CI 2.66, 11.40). Stratified analyzes showed that the magnitude of the associations between depressive symptoms and loneliness varied in MSM with different age, marital status, and self-esteem. Conclusion: Our study suggests that we need to pay attention to feelings of loneliness and depressive symptoms and their closely associated factors such as social support and self-esteem among MSM in China. The MSM who were young, not married, and had low self-esteem were especially vulnerable to the impact of depressive symptoms on loneliness.

Development and validation of a risk score for predicting inconsistent condom use with women among men who have sex with men and women.

BACKGROUND: Men who have sex with men and women (MSMW) are the most important bridge population for HIV transmission. Condom use plays an important role for HIV infection. However the predictors for condom ues with females are not well characterized. METHODS: This was a cross-sectional study. Participants were enrolled by four community-based organizations (CBOs) by offline (bathrooms, bars), and online (gay applications, chat room) from April to December 2019. Electronic questionnare was fulfilled after a face-to-face training led by CBOs. We identified predictors of inconsistent condom use with females by creating a risk score based on regression coefficients. We externally validated this score via an independent cross-sectional survey conducted in Zhejiang Province in 2021. A total of 917, 615 MSMW were included in analysis in 2019 and 2021, seperately. RESULTS: Among 917 MSMW, 73.2% reported heterosexual behavior in the prior 6 months and 38.3% reported inconsistent condom use with females (ICUF) over that time. Compared with heterosexual/unsure MSMW, bisexual MSMW reported more male and female sex partners, higher proportion of inconsistent condom use with males, less commercial sex with males (p < 0.05). Four risky predictors of ICUF were identified: Duration of local residence ≦6 months; more than one male partner in the prior 6 months; inconsistent condom use with males in the prior 6 months; and never heard post-exposure prophylaxis (PEP). The proportions of respondents indicating ICUF in the low- (0), medium- (2-4) and high-risk (6-20) groups (according to our risk scoring system) were 11.7% (14/120), 26.9% (96/357), and 78.1% (125/160), respectively (Ptrend < 0.001). In the validation survey, the respective proportions of those reporting ICUF were 13.4% (15/112), 17.8% (24/185) and 87.3% (96/110) (Ptrend < 0.001). CONCLUSIONS: We developed and validated a predictive risk score for ICUF among MSMW; four factors were identified, of which inconsistent condom use with men was the most important. Risk reduction intervention programs should focus on MSM who report inconsistent condom use with males, never heard PEP, having multiple partners and living in local less than 6 months.

Analysis of the first measurement of CD4+T lymphocyte cell counts of newly reported HIV/AIDS cases in Taizhou City from 2012 to 2021 / 预防医学

Objective@#To investigate the level and timeliness of CD4+T lymphocyte cell (CD4 cell) counts at first measurement among newly reported HIV/AIDS cases in Taizhou City, Zhejiang Province from 2012 to 2021, so as to provide insights into improving the management of HIV/AIDS cases. @*Methods@#Demographic data and first measurement of CD4 cell counts of newly reported HIV/AIDS cases in Taizhou City from 2012 to 2021 were collected from the HIV/AIDS Comprehensive Control System of Chinese Disease Prevention and Control Information System. The level and time of CD4 cell counts at first measurement were descriptively analyzed, and factors affecting CD4 cell counts at first measurement were identified using a multivariable logistic regression model. @*Results@#A total of 4 834 newly reported HIV/AIDS cases were recorded in Taizhou City from 2012 to 2021, including 3 889 men (80.45%), 2 005 cases at ages of 20 to 39 years (41.48%), and 2 130 farmers (44.06%). There were 1 664 cases (34.42%) with CD4 cell counts of <200/mm3 at first detection, 2 576 (53.29%) with CD4 cell counts of 200/mm3 to 499/mm3, and 594 (12.29%) with CD4 cell counts of ≥500/mm3. The proportion of CD4 cell counts of <200/mm3 showed a tendency towards a rise from 2012 to 2021 (χ2trend =4.250, P<0.001). There were 3 465 cases (71.68%) that had an interval of ≤14 days between the first detection of CD4 cell counts and confirmatory HIV test, 740 (15.31%) that had an interval of >14 to 30 days, 315 (6.52%) that had an interval of >30 to 90 days, 135 (2.79%) that had an interval of >90 to 180 days, and 179 (3.70%) that had an interval of >180 days. The proportion of an interval of ≤14 days appeared a tendency towards a rise from 2012 to 2021 (χ2trend=6.874, P<0.001). Multivariable logistic regression analysis identified women (OR=0.630, 95%CI: 0.529-0.751), age of ≥20 years (OR: 1.958 to 3.218, 95%CI: 1.216-5.412), other or unknown routes of HIV infection (OR=1.785, 95%CI: 1.100-2.896), and identification by medical institutions (OR=1.779, 95%CI: 1.497-2.114) as factors affecting CD4 cell counts of <200/mm3 at first measurement. @*Conclusions@#The timely detection of CD4 cell counts at first measurement gradually increased with year among newly reported HIV/AIDS cases in Taizhou City from 2012 to 2021; however, there were still 34.42% of cases with CD4 cell counts of <200/mm3. Gender, age, route of HIV infection, and sample source were factors affecting CD4 cell counts of <200/mm3 at first measurement.

Controlling the quantity of γ-Fe inside multiwall carbon nano-onions: the key role of sulfur.

One of the most interesting structural features of multiwall carbon onions (MWCNOs) and nanotubes (MWCNTs) is the excellent chemical stability, which allows in situ encapsulation of chosen magnetic materials of interest and multifunctional applications. In this letter, we present an innovative chemical vapour synthesis (CVS) approach, in which the inclusion of small quantities of sulfur during the pyrolysis of ferrocene/dichlorobenzene mixtures allows for an important control in the relative abundance of FCC γ-Fe, up to a maximum value of ∼86.5% (structural- and phase-control). The variation in the relative percentage of the encapsulated Fe-based phases was estimated by employing X-ray diffraction (XRD) and Rietveld refinement analyses. The magnetic characterization was achieved by employing superconducting quantum interference device (SQUID) magnetometry, with zero field cooled (ZFC) and field cooled (FC) curves acquired at applied fields of 300 Oe and ∼50 000 Oe.

Manipulating Reaction Intermediates to Aqueous-Phase ZnSe Magic-Size Clusters and Quantum Dots at Room Temperature.

It is not resolved which model describes better the aqueous-phase nucleation and growth of semiconductor quantum dots (QDs), the classical one-step one or the nonclassical multi-step one. Here, we design a room-temperature reaction to trap reaction intermediates in the prenucleation stage of ZnSe QDs (as a model system). We show that the trapped intermediate can transform to magic-size clusters (MSCs) via intra-molecular reorganization and can fragment to enable the growth of QDs. The MSCs exhibit a sharp optical absorption peaking at 299 nm, labelled MSC-299. The intermediate, the precursor compound (PC-299) of MSC-299, is optically transparent at 299 nm and to longer wavelengths. This intermediate forms in various Zn and Se reaction systems. The present study provides unambiguous evidence that the nonclassical and classical pathways are both necessary to explain the nucleation and growth of aqueous-phase QDs, with the former pathway favored more by high reaction concentrations.

Association between complete right bundle branch block and atrial fibrillation development.

BACKGROUND: Complete right bundle branch block (CRBBB) is an important predictor of atrial fibrillation (AF) recurrence after pulmonary vein isolation. However, the association between CRBBB and AF development remains unclear. METHODS: We performed a retrospective study of 2639 patients (male, n = 1549; female, n = 1090; mean age, 58 ± 13 years). CRBBB was defined as a late R (R') wave in lead V1 or V2 with a slurred S wave in lead I and/or lead V6 with a prolonged QRS duration (≥120 ms). RESULTS: Among the 2639 patients, CRBBB was detected in 40 patients (1.5%), and the prevalence of AF was 7.4% (196/2639). The proportion of patients with AF and CRBBB was higher than the proportion of patients with AF without CRBBB (22.5% vs. 7.2%; p = 0.001). In the forward multivariate logistic analysis, CRBBB (odds ratio [OR], 3.329; 95% confidence interval [CI], 1.350-8.211; p = 0.009), complete left bundle branch block (OR, 2.209; 95% CI, 1.238-3.940; p = 0.007), age (OR, 1.020; 95% CI, 1.005-1.035; p = 0.009), valvular heart disease (OR, 2.332; 95% CI, 1.531-3.552; p < 0.001), left atrial diameter (OR, 1.133; 95% CI, 1.104-1.163; p < 0.001), left ventricular ejection fraction (OR, 1.023; 95% CI, 1.006-1.041; p = 0.007), and class I or III anti-arrhythmic drug use (OR, 10.534; 95% CI, 7.090-15.651; p < 0.001) were associated with AF. CONCLUSION: Complete right bundle branch block was significantly associated with AF development in hospitalized patients with cardiovascular diseases.

Transformation Pathways in Colloidal CdTeSe Magic-Size Clusters.

A rarely studied transformation in colloidal ternary magic-size clusters (MSCs) is addressed. We report the first observation of the transformation from ternary CdTeSe MSC-399 to MSC-422, which occurs at room temperature. These two MSC types display sharp optical absorption resonances at 399 and 422 nm, respectively, and are related in that they are quasi isomers, together with their counterpart precursor compounds (PCs). Binary CdTe and CdSe samples were prepared in the prenucleation stage also called the induction period (IP). After they were mixed and placed in a mixture of toluene and octylamine, the transformation was found to take place and to be assisted by the addition of the CdSe IP sample. A binary IP sample contains corresponding binary PCs and monomers (Mo) and fragments (Fr). We argue that the transformation pathway is enabled by the corresponding ternary PCs, involving the substitution reaction, namely CdTeSe PC-399 + CdSe (Mo/Fr)-1 ⇒ CdTeSe PC-422 + CdSe (Mo/Fr)-2. The present study provides an in-depth understanding of the formation characteristics of the MSCs.

Effect of catheter ablation on clinical outcomes in patients with atrial fibrillation and significant functional mitral regurgitation.

BACKGROUND: In patients with atrial fibrillation (AF) and functional mitral regurgitation (MR), catheter ablation reduces the severity of MR and improves cardiac remodeling. However, its effects on prognosis are uncertain. METHODS: This retrospective study included 151 consecutive patients with AF and functional MR, 82 (54.3%) of whom were treated by catheter ablation (Ablation group) and 69 (45.7%) with drug therapy without ablation (Non-ablation group). Forty-three pairs of these patients were propensity matched on the basis of age, CHA2DS2-VASc scores, and left ventricular ejection fraction. The primary outcome evaluated was severity of MR, cardiac remodeling and the combined incidence of subsequent heart failure-related hospitalization and strokes/transient ischemic attacks. RESULTS: Patients in the Ablation group showed a significant decrease in the severity of MR (p < 0.001), a significant decrease in the left atrial diameter (p = 0.010), and significant improvement in the left ventricular ejection fraction (p = 0.015). However, patients in the Non-ablation group showed only a significant decrease in the severity of MR (p = 0.004). The annual incidence of the studied events was 4.9% in the Ablation group and 16.7% in the Non-ablation group, the incidence being significantly lower in the ablation than Non-ablation group (p = 0.026) according to Kaplan-Meier curve analyses. According to multivariate Cox regression analysis, catheter ablation therapy (hazard ratio [HR] 0.27, 95% confidence interval [CI] 0.09-0.84; p = 0.024) and heart failure at baseline (HR 3.84, 95% CI 1.07-13.74; p = 0.038) were independent predictors of the incidence of the studied events. CONCLUSIONS: Among patients with AF and functional MR, catheter ablation was associated with a significantly lower combined risk of heart failure-related hospitalization and stroke than in a matched cohort of patients receiving drug therapy alone.

Evolution of Photoluminescent CdS Magic-Size Clusters Assisted by Adding Small Molecules with Carboxylic Group.

We report our investigation on the formation of photoluminescent CdS magic-size clusters (MSCs), which exhibit absorption peaking at 373 nm, along with sharp band edge emission at ∼385 nm. Denoted as MSC-373, the MSCs were synthesized from the reaction of cadmium oleate (Cd(OA)2) and S powder in 1-octadecene at room temperature, together with the addition of acetic acid (HOAc) or acetate salts (M(OAc)2, M = Zn and Mn) during the prenucleation stage (120 °C). The morphology of as-synthesized MSC-373 was dot-like, which could be altered to flake-like morphology after purification. We found the formation of MSC-373 was related to the ligand exchange, resulting from the addition of small molecules with carboxylic group. The addition of HOAc not only promotes the formation of CdS MSC-373 but suppresses the formation of MSC-311 and nucleation and growth of quantum dots (QDs). When the amount of HOAc addition was increased, another photoluminescent CdS MSCs, namely, MSC-406, evolved. This study provides an overall understanding of the CdS MSC-373 and introduces a new approach to synthesize photoluminescent CdS MSCs.

PU.1 inhibition attenuates atrial fibrosis and atrial fibrillation vulnerability induced by angiotensin-II by reducing TGF-ß1/Smads pathway activation.

Fibrosis serves a critical role in driving atrial remodelling-mediated atrial fibrillation (AF). Abnormal levels of the transcription factor PU.1, a key regulator of fibrosis, are associated with cardiac injury and dysfunction following acute viral myocarditis. However, the role of PU.1 in atrial fibrosis and vulnerability to AF remain unclear. Here, an in vivo atrial fibrosis model was developed by the continuous infusion of C57 mice with subcutaneous Ang-II, while the in vitro model comprised atrial fibroblasts that were isolated and cultured. The expression of PU.1 was significantly up-regulated in the Ang-II-induced group compared with the sham/control group in vivo and in vitro. Moreover, protein expression along the TGF-ß1/Smads pathway and the proliferation and differentiation of atrial fibroblasts induced by Ang-II were significantly higher in the Ang-II-induced group than in the sham/control group. These effects were attenuated by exposure to DB1976, a PU.1 inhibitor, both in vivo and in vitro. Importantly, in vitro treatment with small interfering RNA against Smad3 (key protein of TGF-ß1/Smads signalling pathway) diminished these Ang-II-mediated effects, and the si-Smad3-mediated effects were, in turn, antagonized by the addition of a PU.1-overexpression adenoviral vector. Finally, PU.1 inhibition reduced the atrial fibrosis induced by Ang-II and attenuated vulnerability to AF, at least in part through the TGF-ß1/Smads pathway. Overall, the study implicates PU.1 as a potential therapeutic target to inhibit Ang-II-induced atrial fibrosis and vulnerability to AF.

Transformation Pathway from CdSe Magic-Size Clusters with Absorption Doublets at 373/393†nm to Clusters at 434/460†nm.

Divergent interpretations have appeared in the literature regarding the structural nature and evolutionary behavior for photoluminescent CdSe nanospecies with sharp doublets in optical absorption. We report a comprehensive description of the transformation pathway from one CdSe nanospecies displaying an absorption doublet at 373/393 nm to another species with a doublet at 433/460 nm. These two nanospecies are zero-dimensional (0D) magic-size clusters (MSCs) with 3D quantum confinement, and are labeled dMSC-393 and dMSC-460, respectively. Synchrotron-based small-angle X-ray scattering (SAXS) returns a radius of gyration of 0.92 nm for dMSC-393 and 1.14 nm for dMSC-460, and indicates that both types are disc shaped with the exponent of the SAXS form factor equal to 2.1. The MSCs develop from their unique counterpart precursor compounds (PCs), which are labeled PC-393 and PC-460, respectively. For the dMSC-393 to dMSC-460 transformation, the proposed PC-enabled pathway is comprised of three key steps, dMSC-393 to PC-393 (Step 1), PC-393 to PC-460 (Step 2 involving monomer addition), and PC-460 to dMSC-460 (Step 3). The present study provides a framework for understanding the PC-based evolution of MSCs and how PCs enable transformations between MSCs.

Effect of pulmonary vein isolation on atrial fibrillation recurrence after accessory pathway ablation in patients with Wolff-Parkinson-White syndrome.

BACKGROUND: Although successful ablation of the accessory pathway (AP) eliminates atrial fibrillation (AF) in some of patients with Wolff-Parkinson-White (WPW) syndrome and paroxysmal AF, in other patients it can recur. HYPOTHESIS: Whether adding pulmonary vein isolation (PVI) after successful AP ablation effectively prevents AF recurrence in patients with WPW syndrome is unknown. METHODS: We retrospectively studied 160 patients (102 men, 58 women; mean age, 46 ± 14 years) with WPW syndrome and paroxysmal AF who underwent AP ablation, namely 103 (64.4%) undergoing only AP ablation (AP group) and 57 (35.6%) undergoing AP ablation plus PVI (AP + PVI group). Advanced interatrial block (IAB) was defined as a P-wave duration of >120 ms and biphasic (±) morphology in the inferior leads, using 12-lead electrocardiography (ECG). RESULTS: During the mean follow-up period of 30.9 ± 9.2 months (range, 3-36 months), 22 patients (13.8%) developed AF recurrence. The recurrence rate did not differ in patients in the AP + PVI group and AP group (15.5% vs 10.5%, respectively; P = .373). Univariable and multivariable Cox regression analyses showed that PVI was not associated with the risk of AF recurrence (hazard ratio, 0.66; 95% confidence interval, 0.26-1.68; P = .380). In WPW patients with advanced IAB, the recurrence rate was lower in patients in the AP + PVI group vs the AP group (90% vs 33.3%, respectively; P = .032). CONCLUSIONS: PVI after successful AP ablation significantly reduced the AF recurrence rate in WPW patients with advanced IAB. Screening of a resting 12-lead ECG immediately after AP ablation helps identify patients in whom PVI is beneficial.

Room-temperature formation of CdS magic-size clusters in aqueous solutions assisted by primary amines.

Aqueous-phase approaches to semiconductor CdS magic-size clusters (MSCs) and the formation pathway have remained relatively unexplored. Here, we report the demonstration of an aqueous-phase, room-temperature approach to CdS MSCs, together with an exploration of their evolution pathway. The resulting CdS MSCs display a sharp optical absorption peak at about 360 nm and are labeled MSC-360. With CdCl2 and thiourea as the respective Cd and S sources, and 3-mercarpotopropionic acid as the ligand, CdS MSC-360 develops in a mixture of a primary amine and water. We argue that the primary amine facilitates room-temperature decomposition of thiourea when CdCl2 is present, and the formation pathway of MSCs is similar to that in organic-phase approaches. Our findings show there is a viable avenue to room-temperature aqueous-phase formation of CdS MSCs. Providing explanations of the procedure developed including the formation of large aggregates, the present study represents an important advance towards a mechanistic understanding of nanocrystal synthesis.

Fragmentation of Magic-Size Cluster Precursor Compounds into Ultrasmall CdS Quantum Dots with Enhanced Particle Yield at Low Temperatures.

Colloidal small-size CdS quantum dots (QDs) are produced usually with low particle yield, together with side products such as the particular precursor compounds (PCs) of magic-size clusters (MSC). Here, we report our synthesis of small-size CdS QDs without the coexistence of the PC and thus with enhanced particle yield. For a conventional reaction of cadmium oleate (Cd(OA)2 ) and sulfur (S) in 1-octadecene (ODE), we show that after the formation of the PC in the pre-nucleation stage, the addition of tri-n-octylphosphine oxide (TOPO) facilitates the production of small-size QDs. We demonstrate that TOPO fragmentizes the PC that have formed, which enables the nucleation and growth of small-size QDs even at room temperature. Our findings introduce a new approach to making small-size QDs without the coexistence of the PC and with improved particle yield. Providing experimental evidence for the two-pathway model proposed for the pre-nucleation stage of colloidal binary QDs, the present study aids in the advance of non-classical nucleation theory.

Evolution of CdTe Magic-Size Clusters with Single Absorption Doublet Assisted by Adding Small Molecules during Prenucleation.

An approach is reported for the exclusive production of CdTe magic-size clusters (MSCs) that exhibit an optical absorption doublet peaking at 385/427 nm, with an explanation of the synthesis procedure. The MSCs, defined as dMSC-427, were produced from the reaction of cadmium oleate (Cd(OA)2) and tri-n-octylphosphine telluride in octadecene at 100 °C, with the addition of acetic acid (HOAc) or acetate (M(OAc)2) during the prenucleation stage (40 °C). Without such an addition or when it was performed in the postnucleation stage (100 °C), quantum dots (QDs) developed. The production of dMSC-427 or QDs is hypothesized to be related to the solubility of the Cd precursor, such as Cd(OA)1(OAc)1 or Cd(OA)2, respectively. Also, the reactions that lead to Cd(OA)1(OAc)1 are proposed. The present study provides an in-depth understanding of the two-pathway model proposed for the prenucleation stage of binary colloidal QDs, as well as of the formation of MSCs and/or QDs.