Preliminary study of finger temperature recovery in patients with diabetes mellitus following cold stimulation.

OBJECTIVE: To explore the difference in temperature recovery following cold stimulation between participants with and without diabetes mellitus (DM). MATERIALS AND METHODS: The participants without (control group; n = 25) and with (DM group; n = 26) DM were subjected to local cold stimulation (10º C for 90 s). The thermal images of their hands were continuously captured using a thermal camera within 7 min following cold stimulation, and the highest temperature of each fingertip was calculated. According to the temperature values at different timepoints, the temperature recovery curves were drawn, and the baseline temperature (T-base), initial temperature after cooling (T0), temperature decline amplitude (T-range), and area under the temperature recovery curve > T0 (S) were calculated. Finally, symmetry differences between the two groups were analysed. RESULTS: No statistical differences in the T-base, T0, and T-range were observed between the DM and control groups. After drawing the rewarming curve according to the temperature of the fingertips of the patients following cold stimulation, the S in the DM group was significantly lower than that in the control group (p < 0.05). Furthermore, the asymmetry of the base temperature of the hand was observed in the DM group. CONCLUSIONS: Following cold stimulation, the patients with DM exhibited a different rewarming pattern than those without DM. Thus, cold stimulation tests under infrared thermography may contribute to the early screening of diabetic peripheral neuropathy in future.

Anti-Aging Effects of Anthocyanin Extracts of Sambucus canadensis Caused by Targeting Mitochondrial-Induced Oxidative Stress.

Anthocyanin is a natural antioxidant agent extracted from the fruits of Sambucus canadensis, which has been considered to have potential anti-aging effects. Cell senescence is the primary cause of aging and related diseases. Recently, research on the development of compounds for eliminating senescent cells or damaged organs have shown prospects. The compounds which promote the clearing of senescent cells are called "senolytics". Though anthocyanin is considered to have potential anti-aging effects owing to its anti-inflammatory and antioxidant activities, the mechanism of the elimination of senescent cells remains unclear. In this study, we prepared anthocyanins extracted from the fruits of Sambucus canadensis and evaluated their anti-aging effects in vivo and in vitro. We found that anthocyanin could significantly reduce cell senescence and aging of the lens by inhibiting the activity of the PI3K/AKT/mTOR signaling pathway, consequently promoting the apoptosis of senescent cells, increasing the autophagic and mitophagic flux, and enhancing the renewal of mitochondria and the cell to maintain cellular homeostasis, leading to attenuating aging. Therefore, our study provided a basis for anthocyanin to be used as new "senolytics" in anti-aging.

First Indirect Drive Experiment Using a Six-Cylinder-Port Hohlraum.

The new hohlraum experimental platform and the quasi-3D simulation model are developed to enable the study of the indirect drive experiment using the six-cylinder-port hohlraum for the first time. It is also the first implosion experiment for the six laser-entrance-hole hohlraum to effectively use all the laser beams of the laser facility that is primarily designed for the cylindrical hohlraum. The experiments performed at the 100 kJ Laser Facility produce a peak hohlraum radiation temperature of ∼222 eV for ∼80 kJ and 2 ns square laser pulse. The inferred x-ray conversion efficiency η∼87% is similar to the cylindrical hohlraum and higher than the octahedral spherical hohlraum at the same laser facility, while the low laser backscatter is similar to the outer cone of the cylindrical hohlraum. The hohlraum radiation temperature and M-band (>1.6 keV) flux can be well reproduced by the quasi-3D simulation. The variations of the yield-over-clean and the hot spot shape can also be semiquantitatively explained by the calculated major radiation asymmetry of the quasi-3D simulation. Our work demonstrates the capability for the study of the indirect drive with the six-cylinder-port hohlraum at the cylindrically configured laser facility, which is essential for numerically assessing the laser energy required by the ignition-scale six-cylinder-port hohlraum.

Measurement of Time-Dependent Drive Flux on the Capsule for Indirectly Driven Inertial Confinement Fusion Experiments.

A new method for measuring the time-dependent drive flux at the hohlraum center is proposed as a better alternative to conventional wall-based techniques. The drive flux here is obtained by simultaneous measurement of the reemitted flux and shock velocity from a three-layered "cakelike" sample. With these two independent observables, the influence induced by the uncertainty of the material parameters of the sample can be effectively decreased. The influence from the closure of the laser entrance hole, which was the main challenge in conventional wall-based techniques, was avoided through localized reemitted flux measurement, facilitating drive flux measurement throughout the entire time history. These studies pave a new way for probing the time-dependent drive flux, for both cylindrical hohlraums and novel hohlraums with six laser entrance holes.

Hyaluronic Acid-Enwrapped Polyoxometalate Complex for Synergistic Near Infrared-II Photothermal/Chemo-Therapy and Chemodynamic Therapy.

To enhance the efficacy of tumor therapy, the collection of functional components into a targeting system shows advantages over most homogeneous materials in inducing apoptosis of cancer cells. The security and targeting of therapeutic agents also require the effect combination of additional components. However, the construction of multifunctional composites in a simple system with intelligent cooperative responsiveness remains a challenge. Herein, a reduced polyanionic cluster (rP2W18) bearing the absorption at the near infrared (NIR) II region is used as a core carrier to bind the positively charged doxorubicin hydrochloride (DOX) through ionic interaction. To reduce the physiological toxicity, hyaluronic acid grafting ß-cyclodextrin side chains is used to cover the ionic complex through host-guest inclusion to DOX. When the nanocomposite is activated by local laser exposure, the final three-component therapeutic agent is demonstrated to present targeted photothermal conversion capability and chemodynamic activity together with chemotherapy. With the controlled release of DOX under the stimulation of mild acidity in the tumor region and photothermal effect, the exposed rP2W18 is aroused by hydrogen peroxide overexpressed in a tumor microenvironment to produce toxic reactive oxygen species, 1O2. This work presents an opportunity for the development of a nanocomposite in NIR-II photothermal/chemo-therapy and chemodynamic synergistic therapy.

Highly thermal stable RNase A@PbS/ZnS quantum dots as NIR-IIb image contrast for visualizing temporal changes of microvasculature remodeling in flap.

Surgeons face great challenges in acquiring high-performance imaging because fluorescence probes with desired thermal stability remains rare. Here, hybrid lead sulfide/zinc sulfide quantum dots (PbS/ZnS QDs) nanostructures emitting in the long-wavelength end of the second near-infrared (NIR-IIb) window were synthesized and conjugated with Ribonuclease-A (RNase A). Such formed RNase A@PbS/ZnS QDs exhibited strong NIR IIb fluorescence and thermal stability, as supported by the photoluminescent emission assessment at different temperatures. This will allow the RNase A@PbS/ZnS QDs to provide stable fluorescence signals for long-time intraoperative imaging navigation, despite often happened, undesirable thermal accumulation in vivo. Compared to NIR-IIa fluorescence imaging, NIR-IIb vascular fluorescence imaging achieved larger penetration depth, higher signal/background ratios and nearly zero endogenous tissue autofluorescence. Moreover, these QDs illustrate the reliability during the real-time and long-time precise assessment of flap perfusion by clearly visualizing microvasculature map. These findings contribute to intraoperative imaging navigation with higher precision and lower risk.

Metformin Attenuates UVA-Induced Skin Photoaging by Suppressing Mitophagy and the PI3K/AKT/mTOR Pathway.

Ultraviolet (UV) radiation is a major cause of photoaging that can induce DNA damage, oxidative stress, and cellular aging. Metformin (MF) can repair DNA damage, scavenge reactive oxygen species (ROS), and protect cells. However, the mechanism by which MF inhibits cell senescence in chronic skin damage induced by UVA is unclear. In this study, human foreskin fibroblasts (HFFs) treated with UVA were used as an in vitro model and UVA-induced skin photoaging in Kunming mice was used as an in vivo model to investigate the potential skin protective mechanism of MF. The results revealed that MF treatment attenuated UVA-induced cell viability, skin aging, and activation of the PI3K/AKT/mTOR signaling pathway. Furthermore, MF treatment alleviated the mitochondrial oxidative stress and decreased mitophagy. Knockdown of Parkin by siRNA increased the clearance of MF in senescent cells. The treatment of Kunming mice with MF at a dose of 10 mg/kg/day significantly reduced UVA-induced skin roughness, epidermal thinning, collagen degradation, and skin aging. In conclusion, our experimental results suggest that MF exerts anti-photoaging effects by inhibiting mitophagy and the PI3K/AKT/mTOR signaling pathway. Therefore, our study improves the current understanding of the protective mechanism of MF against photoaging.

In Vivo Dynamic Monitoring of Bacterial Infection by NIR-II Fluorescence Imaging.

Time window of antibiotic administration is a critical but long-neglected point in the treatment of bacterial infection, as unnecessary prolonged antibiotics are increasingly causing catastrophic drug-resistance. Here, a second near-infrared (NIR-II) fluorescence imaging strategy based on lead sulfide quantum dots (PbS QDs) is presented to dynamically monitor bacterial infection in vivo in a real-time manner. The prepared PbS QDs not only provide a low detection limit (104 CFU mL-1 ) of four typical bacteria strains in vitro but also show a particularly high labeling efficiency with Escherichia coli (E. coli). The NIR-II in vivo imaging results reveal that the number of invading bacteria first decreases after post-injection, then increases from 1 d to 1 week and drop again over time in infected mouse models. Meanwhile, there is a simultaneous variation of dendritic cells, neutrophils, macrophages, and CD8+ T lymphocytes against bacterial infection at the same time points. Notably, the infected mouse self-heals eventually without antibiotic treatment, as a robust immune system can successfully prevent further health deterioration. The NIR-II imaging approach enables real-time monitoring of bacterial infection in vivo, thus facilitating spatiotemporal deciphering of time window for antibiotic treatment.

Reconstruction of the medial patellofemoral ligament and reinforcement of the medial patellotibial ligament is an effective treatment for patellofemoral instability with patella alta.

PURPOSE: To evaluate the clinical outcome of the combined reconstruction of the medial patellofemoral ligament (MPFL) and medial patellotibial ligament (MPTL) for patellar instability with patella alta. METHODS: A total of 108 patients underwent a combined reconstruction of the MPFL and MPTL, and 58 patients were included in this study. The clinical results were evaluated and compared using the International Knee Documentation Committee (IKDC) scores, Kujala scores, and visual analogue scale (VAS) scores. The tibial tuberosity-trochlear groove (TT-TG) distance, three indices of patellar height (Insall-Salvati ratio, modified Insall-Salvati ratio, and Caton-Deschamps index), and patellar shift and tilt were defined preoperatively and at the 12- and 24-month follow-up visits. RESULTS: At the 12- and 24-month follow-up visits, 86.2% (50/58) and 87.9% (51/58) of the subjective outcomes were excellent, 5/58 (8.6%) and 4/58 (6.9%) were good, 1/58 (1.7%) and 2/58 (3.4%) were fair, and 2/58 (3.4%) and 1/58 (1.7%) were poor. There were significant improvements in the IKDC scores, from 51.9 ± 13.8 preoperatively to 80 ± 19.2 (P < 0.05) at 12 months and 85 ± 13.9 (P < 0.05) at 24 months; Kujala scores, from 55.1 ± 15.2 preoperatively to 82.6 ± 14.9 (P < 0.05) at 12 months and 89.5 ± 10.2 (P < 0.05) at 24 months; and VAS scores, from 58 ± 11 preoperatively to 12 ± 5 (P < 0.05) at 12 months and 11 ± 4 (P < 0.05) at 24 months. The patellar tilt, patellar shift, Insall-Salvati ratio, modified Insall-Salvati ratio, Caton-Deschamps index, and TT-TG distance all decreased significantly compared with the preoperative values, and there were no significant differences between the values at the 12- and 24-month follow-ups. CONCLUSION: The results of this study show that a combined reconstruction of the MPFL and MPTL is an effective treatment for patellar instability with patella alta. This article emphasizes the combined effect of MPFL and MPTL instead of MPFL alone and provides an effective option for the treatment of recurrent patellar dislocation with patella alta. LEVEL OF EVIDENCE: Case series, Level IV.

Functional double-bundle anterior cruciate ligament reconstruction using hamstring tendon autografts with preserved insertions is an effective treatment for tibiofemoral instability.

PURPOSE: The aim of this study was to introduce a modified anatomical anterior cruciate ligament reconstruction using functional double bundles (F-DBACLR), which achieved sequential tensioning at all flexion angles postoperatively, and compare its clinical outcomes with the anatomical single-bundle technique (A-SBACLR). METHODS: A total of 156 patients with an ACL injury underwent ACLR (A-SB group, n = 78; F-DB group, n = 78). All operations were performed by anatomically identifying the ACL footprints and fixing the graft at a pre-determined degree of knee flexion. Two observers blinded to the patient identities examined the patients preoperatively and during follow-up (median 28.2 months; range 26-31 months). Multiple subjective and objective clinical evaluation tests and assessment of clinical outcomes concerning the translational and rotational stability of the knee including the International Knee Documentation Committee (IKDC) questionnaire, Lysholm Knee Scoring Scale, Knee Injury and Osteoarthritis Outcome Score (KOOS), Tegner Activity Scale, KT-1000 laxity measurements, Lachman test and pivot-shift test were performed preoperatively and postoperatively. RESULTS: Preoperatively, no differences were found between the two groups. During the 2-year observation period, patients in the F-DB group revealed better clinical outcomes in terms of the Tegner Activity Scale Score, IKDC, KOOS and Lysholm Knee Scoring Scale. Similar results were shown in regard to the translational stability in both groups, while the F-DB group had more rotational stability at 2 years of follow-up. CONCLUSIONS: The clinical outcomes indicated that F-DBACLR is clinically practicable and advantageous in the treatment of the ACL-deficient knee. LEVEL OF EVIDENCE: II.

Arthroscopic Fixation for Tibial Eminence Fractures: Comparison of Double-Row and Transosseous Anchor Knot Fixation Techniques with Suture Anchors.

BACKGROUND Tibial eminence fractures often occur during sports participation, but the optimum choice of technique for treatment is still controversial. The aim of the current work was to compare the clinical outcomes of 2 new arthroscopic anchor fixation techniques for tibial eminence fracture. MATERIAL AND METHODS We included 72 isolated tibial eminence fracture patients treated at our hospital from October 2010 to August 2015; 37 patients received the classic double-row (DR) suture anchor fixation technique and 35 received the transosseous anchor knot (TAK) fixation under arthroscopy. The clinical efficacies of the 2 techniques were assessed by radiographs, Lysholm score, and International Knee Documentation Committee (IKDC) score in follow-ups. RESULTS Patients were followed for 37.6 months (range, 18-54 months). There was no significant difference of the operative time between groups (P=0.169). Postoperative radiographs of all patients showed accurate reduction and fracture healing within 3 months. Lysholm and IKDC scores improved significantly compared with preoperative scores (P<0.001). However, no significant difference in the knee range of motion or improvement of Lysholm and IKDC scores was found between groups (P>0.05). CONCLUSIONS The DR and TAK techniques provide precise reduction and stable fixation methods for treating tibial eminence fractures, and the clinical outcomes of the 2 arthroscopic techniques with suture anchors are satisfactory.

Bone Marrow Stem Cells-Seeded Polyethylene Terephthalate Scaffold in Repair and Regeneration of Rabbit Achilles Tendon.

The objective of this study was to evaluate the effect of bone marrow stem cells (BMSCs)-seeded polyethylene terephthalate (PET) scaffold for Achilles tendon repair in a rabbit model. The allogeneic BMSCs were seeded onto the PET scaffold and cultured in vitro for 14 days. Sixteen mature New Zealand rabbits underwent surgery to establish a 2-cm Achilles tendon defect model. The BMSCs-seeded PET scaffold was implanted into the defect of one limb (BMSCs-PET group), while the PET scaffold without BMSCs was implanted into the defect of contralateral limb as the control (PET group). All rabbits were sacrificed at 6 and 12 weeks after surgery. At 12 weeks after surgery, macroscopic and histological results showed formation of tendon-like tissues, and the structure was more mature in the BMSCs-PET group. Immunohistochemical analysis and real-time polymerase chain reaction (RT-PCR) demonstrated that the collagen I and collagen III were significantly higher in the BMSCs-PET group compared with those in the PET group. Mechanically, both the failure load and the average stiffness were significantly higher in the BMSCs-PET group than those in the PET group. In conclusion, BMSCs-seeded PET scaffold could effectively facilitate the healing process after being implanted in a rabbit Achilles tendon defect model.

Aspergillus fumigatus during COPD exacerbation: a pair-matched retrospective study.

BACKGROUND: Recently awareness of the importance of Aspergillus colonization in the airway of patients with chronic obstructive pulmonary disease (COPD) was rising. The aim of this study was to investigate the clinical features and short-term outcomes of COPD patients with Aspergillus colonization during acute exacerbation. METHODS: A pair-matched retrospective study on patients presenting with COPD exacerbation was conducted from January 2014 to March 2016 in Beijing Hospital, China. RESULTS: Twenty-three patients with Aspergillus colonization and 69 patients as controls, diagnosed of COPD exacerbation, were included in this study at a pair-matched ratio of 1:3. In stable stage, the percentage of patients with high-dose corticosteroids inhalation in the Aspergillus colonization group is higher than that of in control group (65.5% vs 33.3%, p = 0.048). Multivariate analysis showed that corticosteroids use was the risk factor for isolation of Aspergillus. In acute exacerbation stage, patients in Aspergillus colonization group received higher dose of inhaled corticosteroids and more types of antibiotics than control group. The short-time outcome hinted that the remission time and the duration of hospitalization were longer in the Aspergillus colonization group than in the control group (remission time: 11 ± 4 days vs 7 ± 4 days, p = 0.001; duration: 15 ± 5 days vs 12 ± 4 days, p = 0.011). CONCLUSIONS: Aspergillus colonization in the lower respiratory tract of COPD patients showed typical clinical manifestations, affected their short time outcome and provided a dilemma of clinical treatment strategy.

Mechanistic Investigation of Visible-Light-Induced Intermolecular [2 + 2] Photocycloaddition Catalyzed with Chiral Thioxanthone.

The recent thioxanthone-sensitizer-catalyzed intermolecular [2 + 2] cycloaddition induced by visible-light irradiation set the stage for the future development of feasible photocycloadditions. Nonetheless, the mechanism of this reaction still remains under debate, especially on the activation mode of the thioxanthone photosensitizer (energy transfer, bielectron exchange, and hydrogen transfer are all possible mechanisms). To settle this issue, systematic density functional theory calculations have been carried out. The results indicate that the energy-transfer pathway is more favorable than the bielectron-exchange and the hydrogen-transfer pathways. Meanwhile, the overall transformations involve the complexation and excitation of photosensitizer, the first C-C bond formation, the dissociation of the sensitizer, the triplet-to-singlet electronic state crossing, and the second C-C bond formation. The first C-C bond formation is the rate- and selectivity-determining step, and synergistic energy and electron transfer from photosensitizer to substrate moieties takes place along this process. On this basis, the effect of olefin substrates (ethyl vinyl ketone vs vinyl acetate) on the stereoselectivity was finally analyzed.

Density functional theory investigation on Pd-catalyzed cross-coupling of azoles with aryl thioethers.

In the present study, a density functional theory (DFT) study has been carried out on the Pd-catalyzed coupling of azoles with aryl thioethers. Our effort is mainly put into identifying the most feasible catalytic cycle, and especially the origin of chemoselectivity for the exclusive aromatic Csp(2)-S bond activation (in the presence of an alkyl Csp(3)-S bond). The coupling mainly consists of three steps: C-S activation, NaO(t)Bu mediated C-H palladation, and reductive elimination. The Csp(2)-S activation is favored over Csp(3)-S activation, and thus di(hetero)aryls are the predicted products. This conclusion well reproduces Wang's recent experimental observations. The rate- and chemoselectivity determining steps of the C-H/Csp(2)-S activation mechanism are C-H palladation and C-S activation steps, respectively. Analyzing the origin of chemoselectivity, we found that the easiness of Pd catalyzed C-S activation is independent of the C-S bond strengths in thioether substrates. By contrast, d-π* backdonation in Csp(2)-S-Pd intermediates is the main driving force for the favorable Csp(2)-S activation (over the Csp(3)-S activation).

Arthroscopic Fixation of Tibial Eminence Fractures: A Clinical Comparative Study of Nonabsorbable Sutures Versus Absorbable Suture Anchors.

PURPOSE: To compare clinical outcomes of arthroscopic therapy for tibial eminence fracture with nonabsorbable suture and absorbable suture anchor. METHODS: Between February 2010 and September 2012, a total of 60 tibial eminence fracture patients were treated with nonabsorbable suture fixation or absorbable suture anchor fixation under arthroscopy. Patients with tibial plateau fractures and other significant injuries, including osteochondral lesions, meniscal tear, and anterior cruciate ligament (ACL) or mutiligament injuries, were excluded from the study. Radiographs, anterior drawer test (ADT), Lachman test, Lysholm score, and International Knee Documentation Committee (IKDC) 2000 subjective score were employed to evaluate clinical outcomes in follow-up. RESULTS: A total of 41 patients were analyzed. Among these patients, 22 were treated with nonabsorbable suture fixation and 19 with absorbable suture anchor fixation. According to the modified Meyers-McKeever classification, 15 cases were categorized as type II, 21 as type III, and 5 as type IV fractures. The mean time from injury to surgery was 7.1 days (range, 3 to 12 days). All patients were followed up for a median period of 33.7 months (range, 24 to 45 months). Radiographic evaluation showed optimal reduction immediately after operation and bone union within 3 months in all patients. At the final follow-up, there was no limitation of knee motion range in any patient. Grade II laxity was found in 2 cases from suture group and 1 from suture anchor group, showing no significant difference based on ADT (χ(2) = 0.538, P = .764) and Lachman test (χ(2) = 0.550, P = .760). Lysholm and IKDC 2000 subjective scores were significantly improved (P < .001). However, there were no significant differences in the improvement of Lysholm (t = 0.522, P = .604) and IKDC 2000 subjective scores (t = 0.644, P = .523) between the 2 groups. CONCLUSIONS: Nonabsorbable suture fixation and absorbable suture anchor fixation are equivalent techniques in terms of the clinical efficacy of arthroscopic tibial eminence fracture treatment. LEVEL OF EVIDENCE: Level III, retrospective comparative study.

Registration of the rotation axis in X-ray tomography.

There is high demand for efficient, robust and automated routines for tomographic data reduction, particularly for synchrotron data. Registration of the rotation axis in data processing is a critical step affecting the quality of the reconstruction and is not easily implemented with automation. Existing methods for calculating the center of rotation have been reviewed and an improved algorithm to register the rotation axis in tomographic data is presented. The performance of the proposed method is evaluated using synchrotron-based microtomography data on geological samples with and without artificial reduction of the signal-to-noise ratio. The proposed method improves the reconstruction quality by correcting both the tilting error and the translational offset of the rotation axis. The limitation of this promising method is also discussed.

[Desmosine plasma levels and exacerbation risk assessment of chronic obstructive pulmonary disease].

OBJECTIVE: To explore the relationship between desmosine plasma levels and exacerbation risk in patients with chronic obstructive pulmonary disease (COPD). METHODS: COPD patients and normal subjects were recruited from Beijing Hospital during March 2013 to March 2014. COPD patients were divided into COPD low risk and COPD high risk groups according to the criteria of Global Initiative for Chronic Obstructive Lung Disease (GOLD) strategy. The plasma concentrations of desmosine were measured by enzyme-linked immunosorbent assay (ELISA) for exploring the inter-group difference in desmosine levels. RESULTS: Sixty-three COPD patients (COPD low risk group, n = 30; COPD high risk group, n = 33) and 50 normal subjects (24 healthy non-smokers, 26 healthy smokers) were recruited. The plasma desmosine concentrations in healthy non-smokers, healthy smokers, low risk and high risk COPD patients were (200 ± 159), (191 ± 105), (197 ± 118) and (131 ± 47) ng/L respectively. The plasma concentration of desmosine was significantly lower in COPD high risk group than healthy non-smokers (mean difference -70, 95%CI: -128--11, P = 0.021), healthy smokers (mean difference -60, 95%CI: -118--3, P = 0.039) and COPD low risk group (mean difference -67, 95%CI: -122--12, P = 0.018). The plasma concentration of desmosine was negatively correlated with exacerbation frequency (r = -0.409, P = 0.002), mMRC scores (r = -0.447, P = 0.010) and emphysema severity (r = -0.386, P = 0.047) in COPD patients. No significant correlation existed between desmosine plasma levels and forced expiratory volume in one second (FEV1%pred) in COPD patients (r = 0.225, P = 0.084). CONCLUSIONS: The plasma levels of desmosine are lower in high risk COPD patients than those in normal subjects or low risk COPD patients. And it is negatively correlated with exacerbation frequency in COPD patients.

Mechanistic study on Rh-catalyzed stereoselective C-C/C-H activation of tert-cyclobutanols.

A mechanistic study was performed on the Rh-catalyzed stereoselective C-C/C-H activation of tert-cyclobutanols. The present study corroborated the previous proposal that the reaction occurs by metalation, ß-C elimination, 1,4-Rh transfer, C=O insertion, and a final catalyst-regeneration step. The rate-determining step was found to be the 1,4-Rh transfer step, whereas the stereoselectivity-determining step did not correspond to any of the aforementioned steps. It was found that both the thermodynamic stability of the product of the ß-C elimination and the kinetic feasibility of the 1,4-Rh transfer and C=O insertion steps made important contributions. In other words, three steps (i.e., ß-C elimination, 1,4-Rh transfer, and C=O insertion) were found to be important in determining the configurations of the two quaternary stereocenters.

Quantum-chemical predictions of pKa's of thiols in DMSO.

The deprotonation of thiols (on the S-H bond) is widely involved in organic and bio-organic reactions. With the aid of density functional theory (DFT) calculations, the present study focuses on predicting the pKa's of thiols. Efforts were first put in searching for an appropriate computational method. To achieve this goal, the accuracy of 13 different DFT functionals (i.e., B3LYP, BB1K, PBE, M06, M05, M06-2X, M06-L, M05-2X, TPSS, MPW1K, MPWB1K, MPW3LYP, TPSSLYP1W) and 6 different total electron basis sets (6-31G(d), 6-31+G(d), 6-31+G(d,p), 6-311+G(d,p), 6-311++G(d,p), 6-311++G(2df,2p)) (with DMSO solvent and SMD solvation model) were examined. The M06-2X/6-311++G(2df,2p) (M1) method was found to give the best performance in reproducing the reported 16 pKa's of thiols, with a standard deviation (SD) of about 0.5 pKa unit. Meanwhile, the M1 method was found to be excellent in reproducing the gas phase Gibbs free energies of 17 thiols, providing extra evidence for the reliability of the M1 method in treating thiol systems. On this basis, M1 was then used to predict the pKa's of 291 thiols whose experimental pKa values remain unknown. Accordingly, the scope of pKa's of different thiols was constructed.