The multimodality cell segmentation challenge: toward universal solutions.

Cell segmentation is a critical step for quantitative single-cell analysis in microscopy images. Existing cell segmentation methods are often tailored to specific modalities or require manual interventions to specify hyper-parameters in different experimental settings. Here, we present a multimodality cell segmentation benchmark, comprising more than 1,500 labeled images derived from more than 50 diverse biological experiments. The top participants developed a Transformer-based deep-learning algorithm that not only exceeds existing methods but can also be applied to diverse microscopy images across imaging platforms and tissue types without manual parameter adjustments. This benchmark and the improved algorithm offer promising avenues for more accurate and versatile cell analysis in microscopy imaging.

Dietary and exercise interventions for metabolic health in perimenopausal women in Beijing.

BACKGROUND AND OBJECTIVES: This study aims to investigate the effects of individualised dietary guidance and anti-resistance exercise intervention on blood pressure and metabolic indexes of perimenopausal women. METHODS AND STUDY DESIGN: Between June 2018 to August 2018, 78 perimenopausal women were recruited at the Gynaecological Outpatient Department of Beijing Pinggu District Hospital. After coding, they were randomly divided into three groups, A, B and C, by lottery. Group A was required to participate in educational seminars. Group B was required to participate in educational seminars and received individualised dietary guidance from professional nutritionists. Group C had the same intensive education classes and individualised dietary guidance as Group B, along with intensive resistance exercise. The difference in the various observation indexes was reviewed after three months of intervention. RESULTS: The number of patients with abnormal metabolic indexes in the diet and comprehensive groups decreased significantly after intervention, compared with the statistics before intervention. The number of patients with a waist circumference ≥80 cm in the diet and comprehensive groups decreased significantly, and the difference was statistically significant (χ2=5.976, p=0.014; χ2=4.433, p=0.035). Before and after observation, the control and diet groups had a higher incidence of HDL <1.29 mmol/L than the comprehensive group, and the difference was statistically significant (p<0.05). After intervention, TGs in the comprehensive group were significantly lower than the control group (≥1.7 mmol/L), and the difference was statistically significant. CONCLUSIONS: Individualised dietary intervention combined with anti-resistance exercise can significantly improve eating and exercise habits, correct metabolic disorders and reduce the occurrence of metabolic syndrome.

Anorectal melanoma and gene analysis of personalized adjuvant therapy: a case report.

Melanoma is derived from malignancies of melanocytes. Anorectal melanoma differs significantly from cutaneous melanoma in clinical presentation, genetic profile, staging system, and response to treatment. Anorectal melanoma is seldom diagnosed because most melanoma occurrences are found in the skin tissues. Here, we report 1 case of advanced anorectal melanoma, including its clinical presentation, laboratory findings, imaging, surgical treatment, and pathology. The patient complained of hematochezia and tenesmus. Colonoscopy, computed tomography (CT) scan and digital rectal examination (DRE) revealed a mass near the pectinate line. The patient underwent proctectomy along with colostomy, and subsequent pathological examinations suggested anorectal melanoma with serosa involvement (positive markers: S100, HMB-45, etc.). Evidence-based analyses (single-nucleotide polymorphism (SNPs) and programmed death-ligand 1 (PD-L1) expression) were conducted on the tumor tissue to identify the sensitivity to adjuvant therapies. SNP tests suggested no definite efficacies of commonly used chemotherapeutic agents, with PD-L1 expression implying poor sensitivity to PD-L1 inhibitors. The postoperative recovery was uneventful and the patient was discharged on day 7 after admission. However, the patient refused adjuvant therapies and died 11 months after surgery. In conclusion, anorectal melanoma tends to be mistaken for other common diseases in this region owing to its non-specific clinical presentations. Multidisciplinary treatments are recommended to yield the best possible outcome, despite poor prognosis.

Dietary and Exercise Interventions for Perimenopausal Women: A Health Status Impact Study.

PURPOSE: To explore the impact of different intervention methods on physical health indexes of perimenopausal women. METHODS: Seventy-eight perimenopausal women were divided into three groups. Group A received routine gynecological diagnosis and treatment and participated in centralized lifestyle health education. Group B was required to participate in all intensive education content, and professional dietitians gave individualized dietary guidance. Group C received intensive education, individualized diet intervention and intensified resistance exercise. Dietary scores, exercise habits, waist circumference, body mass index, fat and muscle mass were observed after three months. RESULTS: After the intervention, the total diet score of group C was higher than groups A and B, and the red meat score was significantly reduced. The number of patients in groups B and C who exercised >3 times per week and the number of resistance exercises were significantly increased, while the number of aerobic exercises per week in group C was significantly increased. The body fat and waist circumference were significantly reduced, and skeletal muscle weight was significantly increased. Body mass index, trunk fat ratio and waist-to-hip ratio were significantly decreased in groups B and C, while trunk muscle was significantly increased in group C. CONCLUSION: The combined intervention of the three methods can give full play to the synergistic effect of various interventions. The improvement effect of increasing the appropriate amount of resistance exercise is more obvious, which is worthy of further promotion and application.

Effect of technological progress on carbon emissions: New evidence from a decomposition and spatiotemporal perspective in China.

The continuously increasing carbon emissions have become a significant hurdle for global sustainable development. Technological progress is considered essential for controlling carbon emissions. However, previous literature has analyzed technological progress as a whole, largely ignoring its spatial spillovers. Therefore, our understanding of how technological progress influences carbon emissions is still limited. To fill this gap, we conduct an in-depth analysis of the effect of technological progress regarding carbon emissions by introducing a new framework that combines the slacks-based measure of the Malmquist-Luenberger index and the spatial dynamic model. Employing a Chinese provincial panel dataset for 2000-2016 as a case study, the conventional analysis indicates that both technological progress and its components have not played a significant role in decreasing carbon emissions. A further analysis using the spatial dynamic model suggests that the technological progress of neighbouring regions plays a significant role in reducing carbon emissions. Moreover, the effect of efficiency change is stronger than that of technical change, which provides new evidence on how technological progress influences carbon emissions.

The role of domestic R&D activities played in carbon intensity: Evidence from China.

Most of the existing empirical studies exploring the role of domestic research and development (R&D) played in carbon intensity has confirmed that domestic R&D activities can effectively reduce carbon intensity. Unfortunately, the heterogeneity of R&D activities was ignored and the effect of domestic R&D on carbon intensity was discussed homogenously, that is, as a whole. Since R&D activities can be distinguished from stages and actors, we cannot obtain additional details such as the stages of R&D activities influencing carbon intensity. Additionally, regional differences were neglected. With these gaps in mind, the roles of R&D activities played in carbon intensity are deeply investigated by classifying them into different stages and actors. The empirical results based on a unique panel dataset from 2000 to 2016 imply that R&D can reduce carbon intensity and that carbon intensity is affected by R&D activities depending on its different stages and actors. The major positive role of R&D activities played in decreasing carbon intensity is generated through the activities at the experimental and developmental stages and industrial enterprises. Further analysis of China's regional carbon intensity also suggests that policymakers should consider regional characteristics.

Convergence analysis of China's energy intensity at the industrial sector level.

China's industrial energy consumption accounted for approximately 70% of national energy demand in the past four decades. Regarding energy demand and environmental pollution, success in controlling energy demand and reducing energy intensity for industrial sectors in China would play a crucial role for the country's sustainable growth problems. To formulate targeted energy plans, the features and characters of China's industrial energy intensity should be carefully evaluated. In this study, a carefully designed econometric model that considers different technological factors including indigenous R&D and technology spillovers from foreign direct investment and trade under a united framework is applied to investigate the ß-convergence characteristics for China's industrial energy intensity by employing a panel dataset covering China's 34 industrial sectors over 2000-2010. The results verify the existence of ß-convergence in industrial energy intensity during the sample period. For the industrial sectors overall and the light industrial sectors, the empirical results indicate that indigenous R&D and technology spillovers from FDI and imports are beneficial in curbing energy intensity. However, technology spillover through exports makes it harder to reduce energy intensity. In addition, not all technological factors have played a significant role in reducing energy intensity for the heavy industrial sectors.

Ligand-Directed Reactivity in Dioxygen and Water Binding to cis-[Pd(NHC)2(η2-O2)].

Reaction of [Pd(IPr)2] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and O2 leads to the surprising discovery that at low temperature the initial reaction product is a highly labile peroxide complex cis-[Pd(IPr)2(η2-O2)]. At temperatures ≳ -40 °C, cis-[Pd(IPr)2(η2-O2)] adds a second O2 to form trans-[Pd(IPr)2(η1-O2)2]. Squid magnetometry and EPR studies yield data that are consistent with a singlet diradical ground state with a thermally accessible triplet state for this unique bis-superoxide complex. In addition to reaction with O2, cis-[Pd(IPr)2(η2-O2)] reacts at low temperature with H2O in methanol/ether solution to form trans-[Pd(IPr)2(OH)(OOH)]. The crystal structure of trans-[Pd(IPr)2(OOH)(OH)] is reported. Neither reaction with O2 nor reaction with H2O occurs under comparable conditions for cis-[Pd(IMes)2(η2-O2)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene). The increased reactivity of cis-[Pd(IPr)2(η2-O2)] is attributed to the enthalpy of binding of O2 to [Pd(IPr)2] (-14.5 ± 1.0 kcal/mol) that is approximately one-half that of [Pd(IMes)2] (-27.9 ± 1.5 kcal/mol). Computational studies identify the cause as interligand repulsion forcing a wider C-Pd-C angle and tilting of the NHC plane in cis-[Pd(IPr)2(η2-O2)]. Arene-arene interactions are more favorable and serve to further stabilize cis-[Pd(IMes)2(η2-O2)]. Inclusion of dispersion effects in DFT calculations leads to improved agreement between experimental and computational enthalpies of O2 binding. A complete reaction diagram is constructed for formation of trans-[Pd(IPr)2(η1-O2)2] and leads to the conclusion that kinetic factors inhibit formation of trans-[Pd(IMes)2(η1-O2)2] at the low temperatures at which it is thermodynamically favored. Failure to detect the predicted T-shaped intermediate trans-[Pd(NHC)2(η1-O2)] for either NHC = IMes or IPr is attributed to dynamic effects. A partial potential energy diagram for initial binding of O2 is constructed. A range of low-energy pathways at different angles of approach are present and blur the distinction between pure "side-on" or "end-on" trajectories for oxygen binding.

Thermodynamic, Kinetic, Structural, and Computational Studies of the Ph3Sn-H, Ph3Sn-SnPh3, and Ph3Sn-Cr(CO)3C5Me5 Bond Dissociation Enthalpies.

The kinetics of the reaction of Ph3SnH with excess •Cr(CO)3C5Me5 = •Cr, producing HCr and Ph3Sn-Cr, was studied in toluene solution under 2-3 atm CO pressure in the temperature range of 17-43.5 °C. It was found to obey the rate equation d[Ph3Sn-Cr]/dt = k[Ph3SnH][•Cr] and exhibit a normal kinetic isotope effect (kH/kD = 1.12 ± 0.04). Variable-temperature studies yielded ΔH‡ = 15.7 ± 1.5 kcal/mol and ΔS‡ = -11 ± 5 cal/(mol·K) for the reaction. These data are interpreted in terms of a two-step mechanism involving a thermodynamically uphill hydrogen atom transfer (HAT) producing Ph3Sn• and HCr, followed by rapid trapping of Ph3Sn• by excess •Cr to produce Ph3Sn-Cr. Assuming an overbarrier of 2 ± 1 kcal/mol in the HAT step leads to a derived value of 76.0 ± 3.0 kcal/mol for the Ph3Sn-H bond dissociation enthalpy (BDE) in toluene solution. The reaction enthalpy of Ph3SnH with excess •Cr was measured by reaction calorimetry in toluene solution, and a value of the Sn-Cr BDE in Ph3Sn-Cr of 50.4 ± 3.5 kcal/mol was derived. Qualitative studies of the reactions of other R3SnH compounds with •Cr are described for R = nBu, tBu, and Cy. The dehydrogenation reaction of 2Ph3SnH → H2 + Ph3SnSnPh3 was found to be rapid and quantitative in the presence of catalytic amounts of the complex Pd(IPr)(P(p-tolyl)3). The thermochemistry of this process was also studied in toluene solution using varying amounts of the Pd(0) catalyst. The value of ΔH = -15.8 ± 2.2 kcal/mol yields a value of the Sn-Sn BDE in Ph3SnSnPh3 of 63.8 ± 3.7 kcal/mol. Computational studies of the Sn-H, Sn-Sn, and Sn-Cr BDEs are in good agreement with experimental data and provide additional insight into factors controlling reactivity in these systems. The structures of Ph3Sn-Cr and Cy3Sn-Cr were determined by X-ray crystallography and are reported. Mechanistic aspects of oxidative addition reactions in this system are discussed.

iPSCs Derived from Malignant Tumor Cells: Potential Application for Cancer Research.

The development of induced pluripotent stem cell (iPSC) technology has inspired a series of methods to manipulate cell fate and has provided novel insight into the profound molecular events underlying the development of diseases. Reprogramming somatic cells into iPSCs has been intensively investigated. However, few studies have investigated the reprogramming of malignant cells and its potential application. Herein, we review the recent progress of iPSCs derived from malignant cells, and highlight tumor iPSCs applications on cancer research which mainly focus on mesenchymal-epithelial transition, genetic and epigenetic change, diseases model construction, drug screening and tumor pathway study.

Role of axial base coordination in isonitrile binding and chalcogen atom transfer to vanadium(III) complexes.

The enthalpy of oxygen atom transfer (OAT) to V[(Me3SiNCH2CH2)3N], 1, forming OV[(Me3SiNCH2CH2)3N], 1-O, and the enthalpies of sulfur atom transfer (SAT) to 1 and V(N[t-Bu]Ar)3, 2 (Ar = 3,5-C6H3Me2), forming the corresponding sulfides SV[(Me3SiNCH2CH2)3N], 1-S, and SV(N[t-Bu]Ar)3, 2-S, have been measured by solution calorimetry in toluene solution using dbabhNO (dbabhNO = 7-nitroso-2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene) and Ph3SbS as chalcogen atom transfer reagents. The V-O BDE in 1-O is 6.3 ± 3.2 kcal·mol(-1) lower than the previously reported value for 2-O and the V-S BDE in 1-S is 3.3 ± 3.1 kcal·mol(-1) lower than that in 2-S. These differences are attributed primarily to a weakening of the V-Naxial bond present in complexes of 1 upon oxidation. The rate of reaction of 1 with dbabhNO has been studied by low temperature stopped-flow kinetics. Rate constants for OAT are over 20 times greater than those reported for 2. Adamantyl isonitrile (AdNC) binds rapidly and quantitatively to both 1 and 2 forming high spin adducts of V(III). The enthalpies of ligand addition to 1 and 2 in toluene solution are -19.9 ± 0.6 and -17.1 ± 0.7 kcal·mol(-1), respectively. The more exothermic ligand addition to 1 as compared to 2 is opposite to what was observed for OAT and SAT. This is attributed to less weakening of the V-Naxial bond in ligand binding as opposed to chalcogen atom transfer and is in keeping with structural data and computations. The structures of 1, 1-O, 1-S, 1-CNAd, and 2-CNAd have been determined by X-ray crystallography and are reported.

Thermodynamic and kinetic study of cleavage of the N-O bond of N-oxides by a vanadium(III) complex: enhanced oxygen atom transfer reaction rates for adducts of nitrous oxide and mesityl nitrile oxide.

Thermodynamic, kinetic, and computational studies are reported for oxygen atom transfer (OAT) to the complex V(N[t-Bu]Ar)3 (Ar = 3,5-C6H3Me2, 1) from compounds containing N-O bonds with a range of BDEs spanning nearly 100 kcal mol(-1): PhNO (108) > SIPr/MesCNO (75) > PyO (63) > IPr/N2O (62) > MesCNO (53) > N2O (40) > dbabhNO (10) (Mes = mesityl; SIPr = 1,3-bis(diisopropyl)phenylimidazolin-2-ylidene; Py = pyridine; IPr = 1,3-bis(diisopropyl)phenylimidazol-2-ylidene; dbabh = 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene). Stopped flow kinetic studies of the OAT reactions show a range of kinetic behavior influenced by both the mode and strength of coordination of the O donor and its ease of atom transfer. Four categories of kinetic behavior are observed depending upon the magnitudes of the rate constants involved: (I) dinuclear OAT following an overall third order rate law (N2O); (II) formation of stable oxidant-bound complexes followed by OAT in a separate step (PyO and PhNO); (III) transient formation and decay of metastable oxidant-bound intermediates on the same time scale as OAT (SIPr/MesCNO and IPr/N2O); (IV) steady-state kinetics in which no detectable intermediates are observed (dbabhNO and MesCNO). Thermochemical studies of OAT to 1 show that the V-O bond in O≡V(N[t-Bu]Ar)3 is strong (BDE = 154 ± 3 kcal mol(-1)) compared with all the N-O bonds cleaved. In contrast, measurement of the N-O bond in dbabhNO show it to be especially weak (BDE = 10 ± 3 kcal mol(-1)) and that dissociation of dbabhNO to anthracene, N2, and a (3)O atom is thermodynamically favorable at room temperature. Comparison of the OAT of adducts of N2O and MesCNO to the bulky complex 1 show a faster rate than in the case of free N2O or MesCNO despite increased steric hindrance of the adducts.

High quantum yield molecular bromine photoelimination from mononuclear platinum(IV) complexes.

Pt(IV) complexes trans-Pt(PEt3)2(R)(Br)3 (R = Br, aryl and polycyclic aromatic fragments) photoeliminate molecular bromine with quantum yields as high as 82%. Photoelimination occurs both in the solid state and in solution. Calorimetry measurements and DFT calculations (PMe3 analogs) indicate endothermic and endergonic photoeliminations with free energies from 2 to 22 kcal/mol of Br2. Solution trapping experiments with high concentrations of 2,3-dimethyl-2-butene suggest a radical-like excited state precursor to bromine elimination.

Two-step binding of O2 to a vanadium(III) trisanilide complex to form a non-vanadyl vanadium(V) peroxo complex.

Treatment of V(N[(t)Bu]Ar)(3) (1) (Ar = 3,5-Me(2)C(6)H(3)) with O(2) was shown by stopped-flow kinetic studies to result in the rapid formation of (η(1)-O(2))V(N[(t)Bu]Ar)(3) (2) (ΔH(‡) = 3.3 ± 0.2 kcal/mol and ΔS(‡) = -22 ± 1 cal mol(-1) K(-1)), which subsequently isomerizes to (η(2)-O(2))V(N[(t)Bu]Ar)(3) (3) (ΔH(‡) = 10.3 ± 0.9 kcal/mol and ΔS(‡) = -6 ± 4 cal mol(-1) K(-1)). The enthalpy of binding of O(2) to form 3 is -75.0 ± 2.0 kcal/mol, as measured by solution calorimetry. The reaction of 3 and 1 to form 2 equiv of O≡V(N[(t)Bu]Ar)(3) (4) occurs by initial isomerization of 3 to 2. The results of computational studies of this rearrangement (ΔH = 4.2 kcal/mol; ΔH(‡) = 16 kcal/mol) are in accord with experimental data (ΔH = 4 ± 3 kcal/mol; ΔH(‡) = 14 ± 3 kcal/mol). With the aim of suppressing the formation of 4, the reaction of O(2) with 1 in the presence of (t)BuCN was studied. At -45 °C, the principal products of this reaction are 3 and (t)BuC(═O)N≡V(N[(t)Bu]Ar)(3) (5), in which the bound nitrile has been oxidized. Crystal structures of 3 and 5 are reported.

microRNA signature for human pancreatic cancer invasion and metastasis.

Pancreatic cancer has the poorest prognosis among all human malignant solid tumors, mainly due to its high invasive and metastatic biological features. microRNAs (miRNAs) are a group of endogenous and small non-coding RNA molecules 18-25 nucleotides in length, functioning as either tumor-suppressor genes or oncogenes. Evidence has shown that regulation of miRNAs in pancreatic cancer is associated with tumor growth, invasion, metastasis and resistance to therapy. Over the last decade, many studies have also found that there is a close relationship between miRNAs and biological characteristics of pancreatic cancer invasion and metastasis, such as the presence of cancer stem cells, epithelial-mesenchymal transition (EMT) phenotype, DNA methylation or epigenetic alteration, and the activation of some specific signaling pathways. Therefore, better understanding of the complex role of miRNAs in the development and progression of pancreatic cancer metastasis may provide new insights that could be of therapeutic consequence. In this brief review, we discuss the literature concerning the correlation between miRNAs and pancreatic cancer, focusing on miRNAs that contribute to pancreatic cancer invasion and metastasis, particularly on cancer stem cell characteristics, the EMT process, epigenetic modifications and tumor-associated signaling pathways.

Effects of naltrexone on smoking cessation outcomes and weight gain in nicotine-dependent men and women.

This study examined whether the opioid receptor antagonist naltrexone is efficacious in smoking cessation and whether sex moderates the response. We assessed smoking quit rates and weight gain in a double-blind randomized trial comparing oral naltrexone (n = 162) with placebo (n = 154) in nicotine-dependent participants who wanted to quit smoking. The medication was gradually titrated up to 50 mg during the week before the quit date and then maintained at this dose for 12 weeks. For the first 4 weeks after the quit date, all participants received a nicotine patch to mitigate tobacco withdrawal and attended weekly individual cognitive-behavioral smoking cessation counseling sessions. After this time, participants continued with naltrexone or placebo through 12 weeks. Follow-up assessments were conducted at 26 and 52 weeks. During treatment, naltrexone (vs placebo) increased quit rates, attenuated smoking urge, and reduced weight gain. At follow-up, after medication discontinuation, the effect of naltrexone on improving quit rates was no longer evident. Men and women experienced different benefits from naltrexone; men showed greater reductions in smoking, whereas women showed greater reductions in weight gain. In sum, naltrexone showed acute efficacy in treating nicotine dependence, but after the medication was discontinued, the effect on quit rate was not maintained. Further study of naltrexone in smoking cessation treatment and reduction of cessation-related weight gain, as well as preclinical investigation of mechanisms underlying sex differences, is warranted.

XM: association testing on the X-chromosome in case-control samples with related individuals.

Genetic variants on the X-chromosome could potentially play an important role in some complex traits. However, development of methods for detecting association with X-linked markers has lagged behind that for autosomal markers. We propose methods for case-control association testing with X-chromosome markers in samples with related individuals. Our method, XM, appropriately adjusts for both correlation among relatives and male-female allele copy number differences. Features of XM include: (1) it is applicable to and computationally feasible for completely general combinations of family and case-control designs; (2) it allows for both unaffected controls and controls of unknown phenotype to be included in the same analysis; (3) it can incorporate phenotype information on relatives with missing genotype data; and (4) it adjusts for sex-specific trait prevalence values. We propose two other tests, Xχ and XW, which can also be useful in certain contexts. We derive the best linear unbiased estimator of allele frequency, and its variance, for X-linked markers. In simulation studies with related individuals, we demonstrate the power and validity of the proposed methods. We apply the methods to X-chromosome association analysis of (1) asthma in a Hutterite sample and (2) alcohol dependence in the GAW 14 COGA data. In analysis (1), we demonstrate computational feasibility of XM and the applicability of our robust variance estimator. In analysis (2), we detect significant association, after Bonferroni correction, between alcohol dependence and single nucleotide polymorphism rs979606 in the monoamine oxidases A gene, where this gene has previously been found to be associated with substance abuse and antisocial behavior.

Thermodynamic, kinetic, and mechanistic study of oxygen atom transfer from mesityl nitrile oxide to phosphines and to a terminal metal phosphido complex.

The enthalpies of oxygen atom transfer (OAT) from mesityl nitrile oxide (MesCNO) to Me(3)P, Cy(3)P, Ph(3)P, and the complex (Ar[(t)Bu]N)(3)MoP (Ar = 3,5-C(6)H(3)Me(2)) have been measured by solution calorimetry yielding the following P-O bond dissociation enthalpy estimates in toluene solution (±3 kcal mol(-1)): Me(3)PO [138.5], Cy(3)PO [137.6], Ph(3)PO [132.2], (Ar[(t)Bu]N)(3)MoPO [108.9]. The data for (Ar[(t)Bu]N)(3)MoPO yield an estimate of 60.2 kcal mol(-1) for dissociation of PO from (Ar[(t)Bu]N)(3)MoPO. The mechanism of OAT from MesCNO to R(3)P and (Ar[(t)Bu]N)(3)MoP has been investigated by UV-vis and FTIR kinetic studies as well as computationally. Reactivity of R(3)P and (Ar[(t)Bu]N)(3)MoP with MesCNO is proposed to occur by nucleophilic attack by the lone pair of electrons on the phosphine or phosphide to the electrophilic C atom of MesCNO forming an adduct rather than direct attack at the terminal O. This mechanism is supported by computational studies. In addition, reaction of the N-heterocyclic carbene SIPr (SIPr = 1,3-bis(diisopropyl)phenylimidazolin-2-ylidene) with MesCNO results in formation of a stable adduct in which the lone pair of the carbene attacks the C atom of MesCNO. The crystal structure of the blue SIPr·MesCNO adduct is reported, and resembles one of the computed structures for attack of the lone pair of electrons of Me(3)P on the C atom of MesCNO. Furthermore, this adduct in which the electrophilic C atom of MesCNO is blocked by coordination to the NHC does not undergo OAT with R(3)P. However, it does undergo rapid OAT with coordinatively unsaturated metal complexes such as (Ar[(t)Bu]N)(3)V since these proceed by attack of the unblocked terminal O site of the SIPr·MesCNO adduct rather than at the blocked C site. OAT from MesCNO to pyridine, tetrahydrothiophene, and (Ar[(t)Bu]N)(3)MoN was found not to proceed in spite of thermochemical favorability.

Oxygen binding to [Pd(L)(L')] (L= NHC, L' = NHC or PR3, NHC = N-heterocyclic carbene). synthesis and structure of a paramagnetic trans-[Pd(NHC)2(η(1)-O2)2] complex.

The reactivity of a number of two-coordinate [Pd(L)(L')] (L = N-heterocyclic carbene (NHC) and L' = NHC or PR(3)) complexes with O(2) has been examined. Stopped-flow kinetic studies show that O(2) binding to [Pd(IPr)(P(p-tolyl)(3))] to form cis-[Pd(IPr)(P(p-tolyl)(3))(η(2)-O(2))] occurs in a rapid, second-order process. The enthalpy of O(2) binding to the Pd(0) center has been determined by solution calorimetry to be -26.2(1.9) kcal/mol. Extension of this work to the bis-NHC complex [Pd(IPr)(2)], however, did not lead to the formation of the expected diamagnetic complex cis-[Pd(IPr)(2)(η(2)-O(2))] but to paramagnetic trans-[(Pd(IPr)(2)(η(1)-O(2))(2)], which has been fully characterized. Computational studies addressing the energetics of O(2) binding have been performed and provide insight into reactivity changes as steric pressure is increased.

Experimental and computational studies of binding of dinitrogen, nitriles, azides, diazoalkanes, pyridine, and pyrazines to M(PR(3))(2)(CO)(3) (M = Mo, W; R = Me, (i)Pr).

The enthalpies of binding of a number of N-donor ligands to the complex Mo(P(i)Pr(3))(2)(CO)(3) in toluene have been determined by solution calorimetry and equilibrium measurements. The measured binding enthalpies span a range of approximately 10 kcal mol(-1): DeltaH(binding) = -8.8 +/- 1.2 (N(2)-Mo(P(i)Pr(3))(2)(CO)(3)); -10.3 +/- 0.8 (N(2)); -11.2 +/- 0.4 (AdN(3) (Ad = 1-adamantyl)); -13.8 +/- 0.5 (N(2)CHSiMe(3)); -14.9 +/- 0.9 (pyrazine = pz); -14.8 +/- 0.6 (2,6-Me(2)pz); -15.5 +/- 1.8 (Me(2)NCN); -16.6 +/- 0.4 (CH(3)CN); -17.0 +/- 0.4 (pyridine); -17.5 +/- 0.8 ([4-CH(3)pz][PF(6)] (in tetrahydrofuran)); -17.6 +/- 0.4 (C(6)H(5)CN); -18.6 +/- 1.8 (N(2)CHC( horizontal lineO)OEt); and -19.3 +/- 2.5 kcal mol(-1) (pz)Mo(P(i)Pr(3))(2)(CO)(3)). The value for the isonitrile AdNC (-29.0 +/- 0.3) is 12.3 kcal mol(-1) more exothermic than that of the nitrile AdCN (-16.7 +/- 0.6 kcal mol(-1)). The enthalpies of binding of a range of arene nitrile ligands were also studied, and remarkably, most nitrile complexes were clustered within a 1 kcal mol(-1) range despite dramatic color changes and variation of nu(CN). Computed structural and spectroscopic parameters for the complexes Mo(P(i)Pr(3))(2)(CO)(3)L are in good agreement with experimental data. Computed binding enthalpies for Mo(P(i)Pr(3))(2)(CO)(3)L exhibit considerable scatter and are generally smaller compared to the experimental values, but relative agreement is reasonable. Computed enthalpies of binding using a larger basis set for Mo(PMe(3))(2)(CO)(3)L show a better fit to experimental data than that for Mo(P(i)Pr(3))(2)(CO)(3)L using a smaller basis set. Crystal structures of Mo(P(i)Pr(3))(2)(CO)(3)(AdCN), W(P(i)Pr(3))(2)(CO)(3)(Me(2)NCN), W(P(i)Pr(3))(2)(CO)(3)(2,6-F(2)C(6)H(3)CN), W(P(i)Pr(3))(2)(CO)(3)(2,4,6-Me(3)C(6)H(2)CN), W(P(i)Pr(3))(2)(CO)(3)(2,6-Me(2)pz), W(P(i)Pr(3))(2)(CO)(3)(AdCN), Mo(P(i)Pr(3))(2)(CO)(3)(AdNC), and W(P(i)Pr(3))(2)(CO)(3)(AdNC) are reported.