Serpentirhabdias mexicanus n. sp. (Nematoda: Rhabdiasidae), a parasitic lungworm of the nauyaca viper Bothrops asper (Serpentes: Viperidae) in the Mexican Neotropics.

Serpentirhabdias mexicanus n. sp. (Nematoda: Rhabdiasidae) is described from the lung of the nauyaca viper Bothrops asper in Puebla State, central Mexico. This new species is the fifth of the genus described having onchia. Among the species included in this group, the new species is morphologically closest to S. viperidicus and S. atroxi. However, it differs from both species mainly by having only one excretory gland (compared to two present in S. viperidicus and S. atroxi). In addition, S. mexicanus n. sp. can be separated of S. viperidicus by tail length, shape of vulval lips, geographic distribution and host species and from S. atroxi by body length, number of papillae in the cephalic region, as well as the host species and geographic distribution. In the present study, we propose the new species based on morphological, host spectrum and genetic evidence. Phylogenetic analysis indicated Serpentirhabdias as a monophyletic group, with two subgroups that are congruent with the presence/absence of onchia in the esophagostome, host association and other relevant morphological characters.

Survey on helminths of bats in the Yucatan Peninsula: infection levels, molecular information and host-parasite networks.

Helminth species of Neotropical bats are poorly known. In Mexico, few studies have been conducted on helminths of bats, especially in regions such as the Yucatan Peninsula where Chiroptera is the mammalian order with the greatest number of species. In this study, we characterized morphologically and molecularly the helminth species of bats and explored their infection levels and parasite­host interactions in the Yucatan Peninsula, Mexico. One hundred and sixty-three bats (representing 21 species) were captured between 2017 and 2022 in 15 sites throughout the Yucatan Peninsula. Conventional morphological techniques and molecular tools were used with the 28S gene to identify the collected helminths. Host­parasite network analyses were carried out to explore interactions by focusing on the level of host species. Helminths were found in 44 (26.9%) bats of 12 species. Twenty helminth taxa were recorded (7 trematodes, 3 cestodes and 10 nematodes), including 4 new host records for the Americas. Prevalence and mean intensity of infection values ranged from 7.1 to 100% and from 1 to 56, respectively. Molecular analyses confirmed the identity of some helminths at species and genus levels; however, some sequences did not correspond to any of the species available on GenBank. The parasite­host network suggests that most of the helminths recorded in bats were host-specific. The highest helminth richness was found in insectivorous bats. This study increases our knowledge of helminths parasitizing Neotropical bats, adding new records and nucleotide sequences.

Clinical outcomes and antibody transfer in a cohort of infants with in utero or perinatal exposure to SARS-CoV-2 (Coronascope Study).

We aimed to describe the outcomes, focusing on the hearing and neurological development, of infants born to mothers with COVID-19 during pregnancy and to evaluate the persistence of maternal antibodies in the first months of life. An observational, prospective study at a tertiary hospital in Madrid (Spain) on infants born to mothers with COVID-19 during pregnancy between March and September 2020 was conducted. A follow-up visit at 1-3 months of age with a physical and neurological examination, cranial ultrasound (cUS), SARS-CoV-2 RT-PCR on nasopharyngeal swab, and SARS-CoV-2 serology were performed. Hearing was evaluated at birth through the automated auditory brainstem response and at six months of age through the auditory steady-state response. A neurodevelopmental examination using the Bayley-III scale was performed at 12 months of age. Of 95 infants studied, neurological examination was normal in all of them at the follow-up visit, as was the cUS in 81/85 (95%) infants, with only mild abnormalities in four of them. Serology was positive in 47/95 (50%) infants, which was not associated with symptoms or severity of maternal infection. No hearing loss was detected, and neurodevelopment was normal in 96% of the infants (median Z score: 0). CONCLUSION: In this cohort, the majority of infants born to mothers with COVID-19 during pregnancy were healthy infants with a normal cUS, no hearing loss, and normal neurodevelopment in the first year of life. Only half of the infants had a positive serological result during the follow-up. WHAT IS KNOWN: • Hearing loss and neurodevelopmental delay in infants born to mothers with COVID-19 during pregnancy has been suggested, although data is inconsistent. Maternal antibody transfer seems to be high, with a rapid decrease during the first weeks of life. WHAT IS NEW: • Most infants born to mothers with COVID-19 during pregnancy had normal hearing screening, cranial ultrasound, and neurodevelopmental status at 12 months of life. Antibodies against SARS-CoV-2 were only detected in 50% of the infants at two months of life.

A High Pressure Operando Spectroscopy Examination of Bimetal Interactions in 'Metal Efficient' Palladium/In2 O3 /Al2 O3 Catalysts for CO2 Hydrogenation.

CO2 hydrogenation to methanol has the potential to serve as a sustainable route to a wide variety of hydrocarbons, fuels and plastics in the quest for net zero. Synergistic Pd/In2 O3 (Palldium on Indium Oxide) catalysts show high CO2 conversion and methanol selectivity, enhancing methanol yield. The identity of the optimal active site for this reaction is unclear, either as a Pd-In alloy, proximate metals, or distinct sites. In this work, we demonstrate that metal-efficient Pd/In2 O3 species dispersed on Al2 O3 can match the performance of pure Pd/In2 O3 systems. Further, we follow the evolution of both Pd and In sites, and surface species, under operando reaction conditions using X-ray Absorption Spectroscpy (XAS) and infrared (IR) spectroscopy. In doing so, we can determine both the nature of the active sites and the influence on the catalytic mechanism.

Integrase inhibitors in children and adolescents: clinical use and resistance.

BACKGROUND: Although integrase inhibitor (INI)-based regimens are now the first-line choice for all people living with HIV, experience among children and adolescents is still scarce. We describe the characteristics and outcomes of a paediatric/adolescent cohort on INI-based ART. METHODS: Retrospective analysis of HIV-infected patients below 18 years of age who started an INI-based regimen from 2007 to 2019, enrolled in the Spanish National Adult (CoRIS) and Paediatric (CoRISpe) cohorts. Resistance mutations were identified by the Stanford HIV Drug Resistance Database. RESULTS: Overall, 318 INI-based regimens were implemented in 288 patients [53.8% female; median age at start of 14.3 years (IQR 12.0-16.3)]. Most were born in Spain (69.1%), vertically infected (87.7%) and treatment-experienced (92.7%). The most frequently prescribed INI was dolutegravir (134; 42.1%), followed by raltegravir (110; 34.6%) and elvitegravir (73; 23.0%). The median exposure was 2.0 years (IQR 1.1-3.0). The main reasons to start an INI-based therapy were treatment simplification (54.4%) and virological failure (34.3%). In total, 103 (32.4%) patients interrupted their regimen: 14.5% for simplification and 8.5% due to virological failure. Most subjects who received dolutegravir (85.8%) and elvitegravir (83.6%) did not interrupt their regimen and maintained undetectable viral load. There were only five virological failures with dolutegravir and three with elvitegravir. There were no interruptions related to adverse events. Seven patients with virological failure presented major resistance mutations to INIs; none of them were on dolutegravir. CONCLUSIONS: INI-based regimens were effective and safe for HIV treatment in children and adolescents. Dolutegravir and elvitegravir presented an excellent profile, and most patients achieved and maintained viral suppression.

Demonstrating Benefit-Risk Profiles of Novel Therapeutic Strategies in Kidney Transplantation: Opportunities and Challenges of Real-World Evidence.

While great progress has been made in transplantation medicine, long-term graft failure and serious side effects still pose a challenge in kidney transplantation. Effective and safe long-term treatments are needed. Therefore, evidence of the lasting benefit-risk of novel therapies is required. Demonstrating superiority of novel therapies is unlikely via conventional randomized controlled trials, as long-term follow-up in large sample sizes pose statistical and operational challenges. Furthermore, endpoints generally accepted in short-term clinical trials need to be translated to real-world (RW) care settings, enabling robust assessments of novel treatments. Hence, there is an evidence gap that calls for innovative clinical trial designs, with RW evidence (RWE) providing an opportunity to facilitate longitudinal transplant research with timely translation to clinical practice. Nonetheless, the current RWE landscape shows considerable heterogeneity, with few registries capturing detailed data to support the establishment of new endpoints. The main recommendations by leading scientists in the field are increased collaboration between registries for data harmonization and leveraging the development of technology innovations for data sharing under high privacy standards. This will aid the development of clinically meaningful endpoints and data models, enabling future long-term research and ultimately establish optimal long-term outcomes for transplant patients.

Multi-inflammatory Syndrome in Children Related to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Spain.

Some clusters of children with a multisystem inflammatory syndrome (MIS-C) associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection have been reported. We describe the epidemiological and clinical features of children with MIS-C in Spain. MIS-C is a potentially severe condition that presents in children with recent SARS-CoV-2 infection.

Prevalence of M184V and K65R in proviral DNA from PBMCs in HIV-infected youths with lamivudine/emtricitabine exposure.

OBJECTIVES: We analysed the prevalence of M184V/I and/or K65R/E/N mutations archived in proviral DNA (pDNA) in youths with perinatal HIV, virological control and who previously carried these resistance mutations in historic plasma samples. METHODS: We included vertically HIV-infected youths/young adults aged ≥10 years in the Madrid Cohort of HIV-1 Infected Children and Adolescents, exposed to lamivudine and/or emtricitabine, with M184V/I and/or K65R/E/N in historic plasma samples, on antiretroviral therapy (ART), virologically suppressed (HIV-1 RNA <50 copies/mL), and with available PBMCs in the Spanish HIV BioBank. Genomic DNA was extracted from PBMCs and HIV-1 RT gene was amplified and sequenced for resistance testing by Stanford HIV Resistance tool. RESULTS: Among the 225 patients under follow-up in the study cohort, 13 (5.8%) met selection criteria, and RT sequences were recovered in 12 (92.3%) of them. All but one were Spaniards, carrying subtype B, with a median age at PBMCs sampling of 21.3 years (IQR: 15.6-23.1) with 4 years (IQR 2.1-6.5) of suppressed viral load (VL). Nine (75%) youths did not present M184V/I in pDNA after at least 1 year of viral suppression. In December 2019, the remaining three subjects carrying M184V/I in pDNA maintained suppressed viraemia, and two still used emtricitabine in ART. CONCLUSIONS: The prevalence of resistance mutations to lamivudine and emtricitabine in pDNA in a cohort of youths perinatally infected with HIV who remain with undetectable VL, previously lamivudine and/or emtricitabine experienced, was infrequent. Our results indicate that ART including lamivudine or emtricitabine may also be safe and successful in youths with perinatal HIV with previous experience of and resistances to these drugs detected in plasma.

Progressive disseminated histoplasmosis in children living with HIV: a case series study.

Progressive disseminated histoplasmosis (PDH) is thought to be on the top of the list of AIDS-defining illnesses in South America. Reported experience in children is very scarce. The aim of this study was to describe the clinical characteristics, management, and outcomes of children living with HIV presenting with PDH in Ecuador. We did a retrospective study using collected data on medical records of children living with HIV attended in Francisco Icaza Bustamante Children's Hospital (Guayaquil) between 1997 and 2019. The inclusion criteria consisted of patients under 18 years of age at admission with documented HIV infection and laboratory-confirmed diagnosis of PDH. Twenty-four children living with HIV were attended due to laboratory-confirmed PDH. Median CD4 cell count was 39 cells/mm³ (p25-p75 21-155) between 1 and 5 years and 22 cells/mm³ (p25-p75 10-57) for those aged 6 years and over. Fever (96%) was the most common clinical manifestation, followed by hepatomegaly (75%), cough (67%), weight loss (63%), diarrhea (63%), and abdominal distension (58%). Most significant laboratory findings were hypoalbuminemia (90%), hypertransaminasemia (78%), and pancytopenia (46%). Intravenous treatment with amphotericin B deoxycholate was started in all but one case in which diagnosis was postmortem. All these 23 patients were discharged after being hospitalized for a median of 68 days (p25-p75 48-90). Two children showed relapse during follow-up, one of whom died during the hospitalization of this second episode of PDH.Conclusion: Clinical manifestations and laboratory findings of PDH in children living with HIV seem similar to those seen in adults, and low CD4 cell count appears to be the most important risk factor. What is Known: • Since 1987, progressive disseminated histoplasmosis has been considered an AIDS-defining illness and, although underdiagnosis is frequent, is thought to be on the top of the list of AIDS-defining illnesses in South America. • Reported experience in children is very scarce. What is New: • Clinical manifestations and laboratory findings of progressive disseminated histoplasmosis in children living with HIV seem similar to those seen in adults. • Low CD4 cell count to be the most important risk factor.

EFAR-MMLA: An Evaluation Framework to Assess and Report Generalizability of Machine Learning Models in MMLA.

Multimodal Learning Analytics (MMLA) researchers are progressively employing machine learning (ML) techniques to develop predictive models to improve learning and teaching practices. These predictive models are often evaluated for their generalizability using methods from the ML domain, which do not take into account MMLA's educational nature. Furthermore, there is a lack of systematization in model evaluation in MMLA, which is also reflected in the heterogeneous reporting of the evaluation results. To overcome these issues, this paper proposes an evaluation framework to assess and report the generalizability of ML models in MMLA (EFAR-MMLA). To illustrate the usefulness of EFAR-MMLA, we present a case study with two datasets, each with audio and log data collected from a classroom during a collaborative learning session. In this case study, regression models are developed for collaboration quality and its sub-dimensions, and their generalizability is evaluated and reported. The framework helped us to systematically detect and report that the models achieved better performance when evaluated using hold-out or cross-validation but quickly degraded when evaluated across different student groups and learning contexts. The framework helps to open up a "wicked problem" in MMLA research that remains fuzzy (i.e., the generalizability of ML models), which is critical to both accumulating knowledge in the research community and demonstrating the practical relevance of these techniques.

Worldwide overview of human infections with Hymenolepis diminuta.

Hymenolepis diminuta is a zoonotic cestode parasitizing the small intestine of rodents (definitive hosts). Humans can accidentally enter into the life cycle of this tapeworm via the ingestion of infected insects (intermediate hosts) containing cestode cysticercoids in their body cavity. More than two centuries after the first record in humans, there are no accurate estimates of the number of human cases around the world. In order to have a more precise idea about the number of human cases with H. diminuta and the current status of the disease (hymenolepiasis) worldwide, we conducted a literature review of published records on human infection with H. diminuta. One thousand five hundred and sixty-one published records of infection with H. diminuta from 80 countries were identified. This review presents an estimate of the number of human cases with H. diminuta and a current overview of the prevalence, geographic distribution, symptoms, diagnosis, exposure to infective stages, and therapeutic approaches for this underestimated zoonotic tapeworm.

Double-blind, randomized, placebo-controlled trial of allergen-specific immunotherapy with the major allergen Alt a 1.

BACKGROUND: There have been few studies conducted on the efficacy and safety of specific immunotherapy with allergen extracts of fungi compared with other allergen extracts, and there are no data on the major allergen Alt a 1 of the fungus Alternaria alternata. OBJECTIVES: We sought to evaluate the efficacy and safety of subcutaneous immunotherapy with 2 different doses of Alt a 1 in patients with rhinoconjunctivitis caused by sensitization to A alternata. METHOD: We performed a multicenter, randomized, double-blind, placebo-controlled trial with Alt a 1 administered subcutaneously in patients with allergic rhinoconjunctivitis with or without controlled asthma aged 12 to 65 years. Three groups were included: the placebo group and active groups receiving 0.2 or 0.37 µg of Alt a 1 per dose. The main end point was the combined symptom and medication score. Secondary end points were cutaneous reactivity and serum IgE and IgG4 levels to Alt a 1. Recorded adverse reactions were graded according to World Allergy Organization criteria. RESULTS: There were significant reductions in the combined symptom and medication score for the 0.37-µg dose of Alt a 1 compared with placebo at 12 months of treatment. Reduced cutaneous reactivity and IgE levels, together with increased IgG4 levels, were demonstrated for the 2 active groups versus the placebo group. A similar safety profile was found for both active groups compared with the placebo group. No serious adverse drug reactions were reported. CONCLUSION: Immunotherapy with Alt a 1 was efficacious and safe, reducing the symptoms and medication consumption associated with rhinoconjunctivitis after only 1 year of treatment. The clinical benefits were associated with reduced skin reactivity and specific IgE levels and increased IgG4 levels.

Organometallic Ruthenium Nanoparticles: Synthesis, Surface Chemistry, and Insights into Ligand Coordination.

Although there has been for the past 20 years great interest in the synthesis and use of metal nanoparticles, little attention has been paid to the complexity of the surface of these species. In particular, the different aspects concerning the ligands present, their location, their mode of binding, and their dynamics have been little studied. Our group has started in the early 1990s an investigation of the surface coordination chemistry of ruthenium and platinum nanoparticles but at that time with a lack of adequate techniques to fulfill our ambition. Over 10 years later, we went back to this problem and could obtain a more precise vision of the surface species. This Account is centered on ruthenium chemistry. This metal has been the most studied in our group, first thanks to the availability of a precursor, Ru(cyclooctadiene)(cyclooctatriene) (Ru(COD)(COT)), which possesses the ability to decompose in very mild conditions without leaving residues on the resulting nanoparticles and second because of the absence of magnetic perturbations (Knight shift, paramagnetism, ferromagnetism, etc.), which has allowed the use of solution and solid state NMR. In this respect, it has been possible to evidence the presence of a high concentration of hydrides on the surface of these particles, to study their dynamics, and to show that since the polarity of the Ru-H bond is similar to that of the C-H bond, a Ru/H NP would behave as a big lipophilic entity. The second point was to characterize the coordination of ancillary ligands. This has been achieved for different ligands, in particular phosphines and carbenes, which made possible the study of the modification of NP reactivity induced by surface ligands. This led to the conclusion that the presence of surface ligands can benefit both the activity of NP catalysts and their selectivity. If it was expected that the selectivity could be modulated, the promoting effect from the presence of ligands on, for example, arene or CO hydrogenation was totally unexpected. Playing with poison atoms (Sn, Fe, etc.) or ligands (CO) may allow us to play with the reactivity of the NPs to make them more selective for selected reactions. Finally, the search for specific ligands for nanoparticles is still in its infancy, but some examples have been found as have specific reactions of nanoparticles. Obviously arene hydrogenation and CO hydrogenation were well-known in heterogeneous catalysis, but we could demonstrate that they can be carried out in very mild conditions on ligand stabilized RuNPs. On the other hand, the enantiospecific C-H activation leading to enantioselective labeling of large organic or biomolecules or the C-C bond cleavage in mild conditions were both unexpected. There is still much work to perform for reaching the degree of control on nanoparticles that is presently achieved in organometallic molecular chemistry, but this work shows that it is possible.

Cellular Senescence and the Immune System in Cancer.

In response to a variety of cancer-inducing stresses, cells may engage a stable cell cycle arrest mechanism, termed cellular senescence, to suppress the proliferation of preneoplastic cells. Despite this cell intrinsic tumor suppression, senescent cells have also been implicated as active contributors to tumorigenesis by extrinsically promoting many hallmarks of cancer, including evasion of the immune system. Here, we discuss these dual, and seemingly contradictory, roles of senescence during tumorigenesis. Furthermore, we highlight findings of how senescent cells can influence the immune system and discuss the possibility that immune cells themselves may be acquiring senescence-associated alterations. Lastly, we discuss how senescent cell avoidance or clearance may impact pathology.

Thirty-day outcomes in patients with acute pulmonary embolism who discontinued anticoagulant therapy before 90 days.

BACKGROUND: The contemporary natural history of patients with acute pulmonary embolism (PE) not receiving (or early discontinuing) anticoagulant therapy has not been consistently evaluated. OBJECTIVE: To assess the rate of the composite outcome of PE-related death, sudden death, or recurrent thromboembolism (VTE) within 30 days in all PE patients in whom anticoagulation was not administered or discontinued prematurely (<90 days of anticoagulation). METHODS: We used the RIETE database to assess the incidence rates (per 100 person-days) of the composite outcome within the subsequent 30 days. The risk of these events was compared to PE patients who were anticoagulated for ≥90 days. RESULTS: Of 34,447 PE recruited from 2001 to 2017, 47 (0.14%) did not receive anticoagulants and 1348 (3.91%) discontinued it before 90 days. Fatal PE developed in 25 (53%) of those without any anticoagulation and in 45 (3.33%) with premature discontinuations. Sudden death or non-fatal recurrent VTE occurred in 6 (0.45%) and 24 (1.48%) patients, respectively. The incidence of the primary outcome declined logarithmically from 6.36 per 100 patient-days in untreated patients to 0.32-0.13 in those treated for 8-90 days. During the first week of follow-up, the incidence rate was 13.9 and 0.60-0.31 per 100 patient-days, respectively. The adjusted odds of the primary outcome was 27 fold higher in untreated than in treated patients, and progressively decreased to 2.5-7 fold higher in patients treated for at least 7 days. CONCLUSION: The incidence of the composite outcome was highest during the first week, and inversely and logarithmically correlated with the duration of anticoagulant therapy.

Iridium versus Iridium: Nanocluster and Monometallic Catalysts Carrying the Same Ligand Behave Differently.

A specific secondary phosphine oxide (SPO) ligand (tert-butyl(phenyl)phosphine oxide) was employed to generate two iridium catalysts, an Ir-SPO complex and IrNPs (iridium nanoparticles) ligated with SPO ligands, which were compared mutually and with several supported iridium catalysts with the aim to establish the differences in their catalytic properties. The Ir-SPO-based catalysts showed totally different activities and selectivities in the hydrogenation of various substituted aldehydes, in which H2 is likely cleaved by a metal-ligand cooperation, that is, the SPO ligand and a neighboring metal centre operate in tandem to activate the hydrogen molecule. In addition, the supported IrNPs behave very differently from both Ir-SPO catalysts. This study exemplifies perfectly the advantages and disadvantages related to the use of the main types of catalysts, and thus the dissimilarities between them.

Soluble Platinum Nanoparticles Ligated by Long-Chain N-Heterocyclic Carbenes as Catalysts.

Soluble platinum nanoparticles (Pt NPs) ligated by two different long-chain N-heterocyclic carbenes (LC-IPr and LC-IMe) were synthesized and fully characterized by TEM, high-resolution TEM, wide-angle X-ray scattering (WAXS), X-ray photoelectron spectroscopy (XPS), and solution NMR. The surface chemistry of these NPs (Pt@LC-IPr and Pt@LC-IMe) was investigated by FT-IR and solid state NMR using CO as a probe molecule. A clear influence of the bulkiness of the N-substituents on the size, surface state, and catalytic activity of these Pt NPs was observed. While Pt@LC-IMe showed no activity in the hydroboration of phenylacetylene, Pt@LC-IPr revealed good selectivity for the trans-isomer, which may be supported by a homogeneous species. This is the first example of hydroboration of acetylenes catalyzed by non-supported Pt NPs.

Evaluation of four commercial virological assays for early infant HIV-1 diagnosis using dried blood specimens.

BACKGROUND: Early infant diagnosis (EID) of HIV-1 is necessary to reduce HIV-related mortality. As maternal antibodies transferred across the placenta may persist up to 18 mo, commercial virological assays (CVAs) are needed. This study compares four CVAs for EID using dried blood specimens (DBS) from HIV-1-exposed infants. METHODS: DBS from 68 infants born to HIV-1-infected women were collected from November 2012 to December 2013 in Equatorial Guinea. Four CVAs were performed: Siemens VERSANT HIV-1 RNA 1.0 kPCR assay, Roche CAP/CTM Quantitative Test v2.0, CAP/CTM Qualitative Tests v1.0 and v2.0. Definitive diagnosis was established following World Health Organization (WHO) recommendations. RESULTS: Two HIV-1-infected infants (2.9%) were detected by the four CVAs while 49 (72%) resulted negative. Discordant results were observed in 17 (25%) infants and HIV-1 infection was excluded in 14 patients when virological and serological testing was performed in additional DBS. Different false-positive rates HIV-1 were observed with Roche assays. CONCLUSION: CVAs using DBS were useful for EID, although discrepant results were common. Further research is required to reduce false-positive results that could result in wrong diagnosis and unneeded treatment. We propose caution with low viral load (VL) values when using VL assays. Clear guidelines are required for EID of HIV-exposed infants with discrepant virological results.

Nickel Pincer Complexes with Frequent Aliphatic Alkoxo Ligands [(iPrPCP)Ni-OR] (R = Et, nBu, iPr, 2-hydroxyethyl). An Assessment of the Hydrolytic Stability of Nickel and Palladium Alkoxides.

A series of nickel pincer complexes with terminal alkoxo ligands [(iPrPCP)Ni-OR] (R = Et, nBu, iPr, CH2CH2OH; iPrPCP is the 2,6-bis(diisopropylphosphinomethyl)phenyl pincer ligand) was synthesized and fully characterized. Together with the previously reported methoxo analogues of Ni and Pd, these complexes constitute a unique series of isostructural late transition-metal alkoxides. Spectroscopic and X-ray diffraction data provide direct indications of the strong polarization of their covalent Ni-OR bonds. One of the most salient features of this class of compounds is their facile hydrolysis with traces of moisture, leading to equilibrium mixtures with the corresponding hydroxides [(iPrPCP)M-OH] (M = Ni or Pd) and alcohols, ROH. To compare the hydrolytic stability of nickel and palladium alkoxides, we performed NMR titrations of both hydroxides with several alcohols and determined the corresponding equilibrium constants. In general, these constants are ca. 1 order of magnitude smaller for M = Ni than Pd, indicating that Ni alkoxide complexes are more readily hydrolyzed than their Pd counterparts. For alkoxide complexes containing heteroatom-free R groups, the tendency to hydrolyze decreases as the parent alcohol ROH becomes more acidic, that is, R = Me > Et > iPr. This intuitive trend is broken for 2-methoxyethanol, the most acidic alcohol investigated. The hydroxo/2-methoxyethanol exchange equilibrium constants are comparable to those of ethanol (M = Ni) or methanol (M = Pd), showing that the corresponding 2-methoxyethoxide complexes are more prone to hydrolysis than anticipated. These experimental observations were rationalized in the light of density functional theory calculations.

Characterization of secondary phosphine oxide ligands on the surface of iridium nanoparticles.

The synthesis of iridium nanoparticles (IrNPs) ligated by various secondary phosphine oxides (SPOs) is described. This highly reproducible and simple method via H2 reduction produces well dispersed, small nanoparticles (NPs), which were characterized by the state-of-the-art techniques, such as TEM, HRTEM, WAXS and ATR FT-IR spectroscopy. In particular, multinuclear solid state MAS-NMR spectroscopy with and without cross polarization (CP) enabled us to investigate the different binding modes adopted by the ligand at the nanoparticle surface, suggesting the presence of three possible types of coordination: as a purely anionic ligand Ir-P(O)R2, as a neutral acid R2P-O-H and as a monoanionic bidentate H-bonded dimer R2P-O-HO[double bond, length as m-dash]PR2. Specifically, the higher basicity of the dicyclohexyl system leads to the formation of IrNPs in which the bidentate binding mode is most abundant. Such cyclohexyl groups are bent towards the edges, as is suggested by the study of 13CO coordination on the NP surface. This study also showed that the number of surface sites on faces available for bridging CO molecules is higher than the number of sites for terminal CO species on edges and apices, which is unexpected taking into account the small size of the nanoparticles. In addition, the IrNPs present a high chemoselectivity in the hydrogenation of cinnamaldehyde to the unsaturated alcohol.