Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 39
Filtrar
Más filtros










Intervalo de año de publicación
1.
Foods ; 12(18)2023 Sep 15.
Artículo en Inglés | MEDLINE | ID: mdl-37761148

RESUMEN

Biscuits are bakery products made with wheat flour. Wheat is a good source of minerals and dietary fibre, although the presence of phytate or other components could modify mineral availability. In addition, cereal-based products are usually characterised by high fibre content that can influence satiety. The objectives of this study were to evaluate both the iron and calcium availability and the satiety effect of different types of biscuits (traditional recipe vs. "Digestive") sold in the Spanish market, identifying whether the biscuit type could have effects on these parameters. Nutritional composition and the use of the generic descriptor "Digestive" of biscuits were collected from labels. Phytate and mineral contents were also measured. All samples were previously digested by a simulated process of the gastrointestinal conditions. The satiating effect of biscuits was evaluated according to VAS questionnaires. Results indicated that the mineral content and availability were different between types of biscuits (the traditional recipe showed the highest calcium concentration, while iron was higher in the "Digestive" type). However, mineral availability showed the highest percentages for both minerals, calcium and iron, in the Maria-type samples. Regardless of the different fibre content of both types of biscuits, and despite being higher in the Digestive type than in the Maria type, the satiety measures indicated that the Maria type had more effect on the food intake control. Thus, the descriptor "Digestive¨ in biscuits does not seem to be a marker of better nutritional quality, including parameters of effects on health such as mineral availability or satiety.

2.
Chemistry ; 29(60): e202302110, 2023 Oct 26.
Artículo en Inglés | MEDLINE | ID: mdl-37530441

RESUMEN

The sigma amine-borane complexes [Rh(L1)(η2 :η2 -H3 B⋅NRH2 )][OTf] (L1=2,6-bis-[1-(2,6-diisopropylphenylimino)ethyl]pyridine, R=Me, Et, n Pr) are described, alongside [Rh(L1)(NMeH2 )][OTf]. Using R=Me as a pre-catalyst (1 mol %) the dehydropolymerization of H3 B ⋅ NMeH2 gives [H2 BNMeH]n selectively. Added NMeH2 , or the direct use of [Rh(L1)(NMeH2 )][OTf], is required for initiation of catalysis, which is suggested to operate through the formation of a neutral hydride complex, Rh(L1)H. The formation of small (1-5 nm) nanoparticles is observed at the end of catalysis, but studies are ambiguous as to whether the catalysis is solely nanoparticle promoted or if there is a molecular homogeneous component. [Rh(L1)(NMeH2 )][OTf] is shown to operate at 0.025 mol % loadings on a 2 g scale of H3 B ⋅ NMeH2 to give polyaminoborane [H2 BNMeH]n [Mn =30,900 g/mol, Ð=1.8] that can be purified to a low residual [Rh] (6 µg/g). Addition of Na[N(SiMe3 )2 ] to [H2 BNMeH]n results in selective depolymerization to form the eee-isomer of N,N,N-trimethylcyclotriborazane [H2 BNMeH]3 : the chemical repurposing of a main-group polymer.

3.
Dalton Trans ; 52(37): 13058-13062, 2023 Sep 26.
Artículo en Inglés | MEDLINE | ID: mdl-37335258

RESUMEN

This study reports the first structural elucidation of ß-diketiminate anions (BDI-), known for strong coordination, in their unbound form within caesium complexes. ß-Diketiminate caesium salts (BDICs) were synthesised, and upon the addition of Lewis donor ligands, free BDI- anions and donor-solvated Cs+ cations were observed. Notably, the liberated BDI- anions exhibited an unprecedented dynamic cisoid-transoid exchange in solution.

4.
Adv Mater ; 35(28): e2300536, 2023 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-37042806

RESUMEN

A series of dithienylethene (DTE) photoswitches with aza-heteroaromatic cationic moieties is synthesized. The switches are characterized regarding their photochemical and photophysical properties in acetonitrile and in water. The efficiency of the switching and the photostationary state composition depend on the degree of π-conjugation of the heteroaromatic systems. Thus, DTEs with acridinium-derived moieties have very low quantum yields for the ring-closing process, which is in contrast to switches with pyridinium and quinolinium moieties. All switches emit fluorescence in their open forms. The involved electronic transitions are traced back to an integrative picture including the DTE core and the cationic arms. The emission can be fine-tuned by the π-conjugation of the heteroaromatic cations, reaching the red spectral region for DTEs with acridinium moieties. On ring-closing of the DTEs the fluorescence is not observable anymore. Theoretical calculations point to rather low-lying energy levels of the highly conjugated ring-closed DTEs, which would originate near-infrared emission (> 1200 nm). The latter is predicted to be very weak due to the concurrent non-radiative deactivation, according to the energy-gap law. In essence, an ON-OFF fluorescence switching as the result of the electrocyclic ring-closing reaction is observed.


Asunto(s)
Colorantes , Estructura Molecular , Fluorescencia , Cationes
5.
Organometallics ; 41(3): 284-292, 2022 Feb 14.
Artículo en Inglés | MEDLINE | ID: mdl-35273423

RESUMEN

The sequential solid/gas single-crystal to single-crystal reaction of [Rh(Cy2P(CH2)3PCy2)(COD)][BArF 4] (COD = cyclooctadiene) with H2 or D2 was followed in situ by solid-state 31P{1H} NMR spectroscopy (SSNMR) and ex situ by solution quenching and GC-MS. This was quantified using a two-step Johnson-Mehl-Avrami-Kologoromov (JMAK) model that revealed an inverse isotope effect for the second addition of H2, that forms a σ-alkane complex [Rh(Cy2P(CH2)3PCy2)(COA)][BArF 4]. Using D2, a temporal window is determined in which a structural solution for this σ-alkane complex is possible, which reveals an η2,η2-binding mode to the Rh(I) center, as supported by periodic density functional theory (DFT) calculations. Extensive H/D exchange occurs during the addition of D2, as promoted by the solid-state microenvironment.

6.
Chem Commun (Camb) ; 58(20): 3318-3321, 2022 Mar 08.
Artículo en Inglés | MEDLINE | ID: mdl-35179155

RESUMEN

The synthesis and characterisation of two novel molecular organotelluroxane clusters, comprising of an inorganic Te8O6X4 (X = Cl, Br) core structure are described. The integration of highly electron withdrawing 3,5-bis-trifluoromethylphenyl groups to the constituent Te(IV) centres is determined to be crucial in the chalcogen bonding (ChB) halide template directed assembly. Characterised by multi-nuclear 1H, 125Te, 19F NMR, UV-Vis, IR spectroscopies and X-ray crystal structure analysis, the discrete molecular clusters exhibit excellent organic solvent solubility and remarkable chemical stability. Furthermore, preliminary fluorescence investigations reveal the telluroxanes exhibit aggregation induced emission (AIE) behaviour in organic aqueous solvent mixtures.

7.
Chem Sci ; 12(25): 8832-8843, 2021 Jul 01.
Artículo en Inglés | MEDLINE | ID: mdl-34257884

RESUMEN

The synthesis of new Schrock-Osborn Rh(i) pre-catalysts with ortho-substituted DPEphos ligands, [Rh(DPEphos-R)(NBD)][BArF 4] [R = Me, OMe, iPr; ArF = 3,5-(CF3)2C6H3], is described. Along with the previously reported R = H variant, variable temperature 1H NMR spectroscopic and single-crystal X-ray diffraction studies show that these all have axial (C-H)⋯Rh anagostic interactions relative to the d8 pseudo square planar metal centres, that also result in corresponding downfield chemical shifts. Analysis by NBO, QTAIM and NCI methods shows these to be only very weak C-H⋯Rh bonding interactions, the magnitudes of which do not correlate with the observed chemical shifts. Instead, as informed by Scherer's approach, it is the topological positioning of the C-H bond with regard to the metal centre that is important. For [Rh(DPEphos-iPr)(NBD)][BArF 4] addition of H2 results in a Rh(iii) iPr-C-H activated product, [Rh(κ3,σ-P,O,P-DPEphos-iPr')(H)][BArF 4]. This undergoes H/D exchange with D2 at the iPr groups, reacts with CO or NBD to return Rh(i) products, and reaction with H3B·NMe3/tert-butylethene results in a dehydrogenative borylation to form a complex that shows both a non-classical B-H⋯Rh 3c-2e agostic bond and a C-H⋯Rh anagostic interaction at the same metal centre.

8.
J Am Chem Soc ; 143(13): 5106-5120, 2021 04 07.
Artículo en Inglés | MEDLINE | ID: mdl-33769815

RESUMEN

Using solid-state molecular organometallic (SMOM) techniques, in particular solid/gas single-crystal to single-crystal reactivity, a series of σ-alkane complexes of the general formula [Rh(Cy2PCH2CH2PCy2)(ηn:ηm-alkane)][BArF4] have been prepared (alkane = propane, 2-methylbutane, hexane, 3-methylpentane; ArF = 3,5-(CF3)2C6H3). These new complexes have been characterized using single crystal X-ray diffraction, solid-state NMR spectroscopy and DFT computational techniques and present a variety of Rh(I)···H-C binding motifs at the metal coordination site: 1,2-η2:η2 (2-methylbutane), 1,3-η2:η2 (propane), 2,4-η2:η2 (hexane), and 1,4-η1:η2 (3-methylpentane). For the linear alkanes propane and hexane, some additional Rh(I)···H-C interactions with the geminal C-H bonds are also evident. The stability of these complexes with respect to alkane loss in the solid state varies with the identity of the alkane: from propane that decomposes rapidly at 295 K to 2-methylbutane that is stable and instead undergoes an acceptorless dehydrogenation to form a bound alkene complex. In each case the alkane sits in a binding pocket defined by the {Rh(Cy2PCH2CH2PCy2)}+ fragment and the surrounding array of [BArF4]- anions. For the propane complex, a small alkane binding energy, driven in part by a lack of stabilizing short contacts with the surrounding anions, correlates with the fleeting stability of this species. 2-Methylbutane forms more short contacts within the binding pocket, and as a result the complex is considerably more stable. However, the complex of the larger 3-methylpentane ligand shows lower stability. Empirically, there therefore appears to be an optimal fit between the size and shape of the alkane and overall stability. Such observations are related to guest/host interactions in solution supramolecular chemistry and the holistic role of 1°, 2°, and 3° environments in metalloenzymes.

9.
Chemistry ; 27(29): 7837-7841, 2021 May 20.
Artículo en Inglés | MEDLINE | ID: mdl-33770417

RESUMEN

A series of chalcogen, halogen and hydrogen bonding heteroditopic macrobicyclic cryptands are reported and their potassium halide ion-pair recognition properties investigated. Saliently, the co-bound potassium cation was determined to be crucial in switching on the bromide and iodide recognition properties of the respective cryptand receptor. Importantly, the nature of the sigma-hole mediated interaction employed in the anion recognition component is demonstrated to significantly augment the ion-pair binding behaviour, markedly so for the halogen bonding analogue. Most notably the incorporation of a chelating chalcogen bonding donor motif significantly improves the selectivity towards KBr over KI, relative to halogen and hydrogen bonding analogues.

10.
Inorg Chem ; 60(18): 13903-13912, 2021 Sep 20.
Artículo en Inglés | MEDLINE | ID: mdl-33570930

RESUMEN

Rhodium-alkene complexes of the pincer ligand κ3-C5H3N-2,6-(OPiPr2)2 (PONOP-iPr) have been prepared and structurally characterized: [Rh(PONOP-iPr)(η2-alkene)][BArF4] [alkene = cyclooctadiene (COD), norbornadiene (NBD), ethene; ArF = 3,5-(CF3)2C6H3]. Only one of these, alkene = COD, undergoes a reaction with H2 (1 bar), to form [Rh(PONOP-iPr)(η2-COE)][BArF4] (COE = cyclooctene), while the others show no significant reactivity. This COE complex does not undergo further hydrogenation. This difference in reactivity between COD and the other alkenes is proposed to be due to intramolecular alkene-assisted reductive elimination in the COD complex, in which the η2-bound diene can engage in bonding with its additional alkene unit. H/D exchange experiments on the ethene complex show that reductive elimination from a reversibly formed alkyl hydride intermediate is likely rate-limiting and with a high barrier. The proposed final product of alkene hydrogenation would be the dihydrogen complex [Rh(PONOP-iPr)(η2-H2)][BArF4], which has been independently synthesized and undergoes exchange with free H2 on the NMR time scale, as well as with D2 to form free HD. When the H2 addition to [Rh(PONOP-iPr)(η2-ethene)][BArF4] is interrogated using pH2 at higher pressure (3 bar), this produces the dihydrogen complex as a transient product, for which enhancements in the 1H NMR signal for the bound H2 ligand, as well as that for free H2, are observed. This is a unique example of the partially negative line-shape effect, with the enhanced signals that are observed for the dihydrogen complex being explained by the exchange processes already noted.

11.
Cult. cuid ; 24(58): 253-270, sept.-dic. 2020. tab
Artículo en Español | IBECS | ID: ibc-200403

RESUMEN

Durante el transcurso de los cuidados y especialmente en los denominados de larga duración, es muy proclive el generarse determinadas situaciones conflictivas a consecuencia de diversos factores tales como, un excesivo volumen de trabajo, elevada responsabilidad, problemas relacionales entre cuidador y persona objeto de cuidados etc. Conllevando a la experimentación de cansancio, estrés y agotamiento principalmente. Todas esas situaciones negativas es lo que muchos autores definen con el concepto de carga o sobrecarga de los cuidados, constituyendo un habitual ámbito de estudio en las investigaciones que versan sobre esta temática. El propósito de este artículo, consiste en llevar a cabo una aproximación conceptual del término de carga, experimentada durante el transcurso de las actividades de cuidados, analizando las dimensiones más relevantes de la misma en primer término, haciendo una distinción entre los conceptos de carga objetiva y subjetiva en segundo término, analizar las principales consecuencias que generan a los cuidadores tales como, percibimiento de sentimientos negativos, problemas de salud física, psíquica, trastornos cardiovasculares e inmunológicos en tercer término, las principales variables asociadas al concepto de carga, y finalmente los principales instrumentos de evaluación de la carga del cuidador


During the provision of cares and, particularly in long-term care, conflictive situations are generated frequently as a consequence of factors such as, excessive workload, high responsibility, relational problems between caregiver and the person subject of care etc., mainly leading to the experimentation of fatigue, stress and exhaustion. All these negative situations are what many authors call burden or overload of care, constituting a common field of study in the research dealing with this subject. The purpose of this article is to frame a conceptual approach to the concept of load experienced during the care, analyzing the most relevant factors contributing to such load, first making a distinction between the concepts of objective and subjective burden, secondly by analyzing the principal consequences for caregivers, such as perceived negative feelings, physical and mental health problems, cardiovascular disorders and immunological problems. Principal variables associated with the concept of burden, and finally the main instruments of evaluation of the caregiver burden are shown


Durante o curso dos cuidados e, especialmente, nos chamados longo prazo, é muito provável que os gerados certas situações de conflito, como resultado de vários fatores, como carga de trabalho excessiva, alta responsabilidade, problemas de relacionamento entre cuidador e pessoa a ser cuidada etc. . Levando à experimentação de fadiga, estresse e exaustão principalmente. Todas estas situações negativas é o que muitos autores definem o conceito de carga ou sobrecarga de atendimento, proporcionando um campo comum de estudo em investigações que lidam com este assunto. O objetivo deste artigo é realizar uma abordagem conceitual da carga prazo experimentaram durante o curso das atividades de atendimento, analisando as dimensões mais relevantes da primeira, fazendo uma distinção entre os conceitos de sobrecarga objetiva e subjetivos em segundo lugar, analisar as principais conseqüências geradas cuidadores, como percibimiento sentimentos negativos, problemas físicos de saúde, transtornos mentais, cardiovasculares e imunológicas terceiro, as principais variáveis associadas com o conceito de carga e, finalmente, principais instrumentos de avaliação do ônus do cuidado


Asunto(s)
Humanos , Masculino , Femenino , Cuidadores/psicología , Carga de Trabajo/psicología , Salud Mental , Factores de Tiempo , Encuestas y Cuestionarios , Cuidados a Largo Plazo , Estrés Psicológico , Escalas de Valoración Psiquiátrica
12.
Int J Surg Case Rep ; 76: 409-414, 2020.
Artículo en Inglés | MEDLINE | ID: mdl-33083204

RESUMEN

INTRODUCTION: The coronavirus disease 2019 (COVID-19) affects mainly the respiratory system, other organs may be involved, usually due to coagulation disturbances that lead to a high rate of thrombotic complications. CASE PRESENTATION: The first patient is 45 years-old who has been exposed to SARS CoV-2. Upon admission due to acute abdomen evidence surgery is performed in which an intestinal resection with an adequate post-surgical evolution takes place so the patient is discharged after 4 days with a prescription for oral anticoagulants. The second one is 42 years-old and has comorbidities. The patient is admitted upon evidence of COVID-19, after showing signs of vein mesenteric ischemia in a CT scan surgery is performed, however the patient dies 24 h after the intervention. DISCUSSION: Within severe cases of patients with COVID-19 the incidence of a symptomatology or gastrointestinal complications is high (39-73.8%). Thromboprophylaxis is recommended to all patients admitted for COVID-19, starting with heparin of low molecular weight as prophylaxis, as well as continuing with oral anticoagulants after being discharged. CONCLUSION: Despite the fact that knowledge of the disease is rapidly advancing, all available treatments are still nonspecific to SARS-CoV-2 and the optimal management of COVID-19 remains unclear. An unexplained clinical picture should raise the suspicion for rare conditions such as mesenteric thrombosis. Adequate prophylactic measures should be implemented both during hospitalization and after discharge.

13.
Cureus ; 12(7): e9113, 2020 Jul 10.
Artículo en Inglés | MEDLINE | ID: mdl-32670732

RESUMEN

Background Laparoscopic cholecystectomy is currently one of the most commonly performed procedures globally. Morbidity of laparoscopic cholecystectomy is low; however, bile duct injury is still a feared complication. Despite worldwide efforts, the global incidence of bile duct injury remains higher for laparoscopic cholecystectomy compared with open cholecystectomy. Despite the general belief that the learning curve and lack of laparoscopic skills represent the most common causes of bile duct injuries, the principal cause is the misidentification of biliary anatomy. The aim of our study is to determine if laparoscopic transillumination is a feasible approach to bile and vascular structures visualization during laparoscopic cholecystectomy because the only other method for real-time visualization is fluorescent cholangiography, which can be cost-prohibitive and requires specialized equipment and training. Materials and methods We performed a retrospective comparison of outcomes between the transillumination approach in 10 patients receiving laparoscopic cholecystectomy (group A) and a control group of 50 conventional laparoscopic cholecystectomy patients (group B). We compared demographic data, type of surgery, operative time, bleeding, intraoperative and postoperative complications, and hospital stay. We used a conventional four-port positioning for laparoscopic cholecystectomy, and a 5-mm/30° scope was used as a light source and placed behind the area identified as Calot's triangle. Results Group A consisted of 10 patients (9 women, 1 man), with a mean age of 50.7 (± 17.4) years. The mean body mass index (BMI) in group A was 26.8 (± 0.65) kg/m2. In group A, three of the cholecystectomies were conducted as emergency procedures. Group B consisted of 50 patients (40 women, 10 men), with a mean age of 49.7 (±15.2) years. The mean BMI in group B was 27.5 (±4.5) kg/m2, and two cholecystectomies were emergency procedures. In comparing the transillumination approach with conventional cholecystectomy, we found no statistical differences in operative time, bleeding, complications, or mean hospital stay. Conclusions Laparoscopic transillumination is a feasible method for real-time visualization of Calot's triangle structures. Our initial experience with transillumination did not provide better outcomes than conventional cholecystectomy.

14.
Dalton Trans ; 49(16): 5257-5263, 2020 Apr 28.
Artículo en Inglés | MEDLINE | ID: mdl-32242567

RESUMEN

Bimetallic sodium magnesiates have been employed in metal-halogen exchange for the first time. Utilising the racemic phenoxide ligand 5,5',6,6'-tetramethyl-3,3'-di-tert-butyl-1,1'-biphenyl-2,2'-diol [(rac)-BIPHEN-H2], the dialkyl sodium magnesiates [(rac)-BIPHEN]Na2MgBu2(TMEDA)23 and [(rac)-BIPHEN]Na2MgBu2(PMDETA)24 have been synthesised. Both 3 and 4 can be easily prepared through co-complexation of di-n-butylmagnesium with the sodiated (rac)-BIPHEN precursor which can be prepared in situ in hydrocarbon solvent. Prior to the main investigation, synthesis of the sodiated precursor [BIPHEN]2Na4(THF)41 was explored in order to better understand the formation of sodium magnesiates utilising the dianionic (rac)-BIPHEN ligand as the parent ligand. In addition, a BIPHEN-rich sodium magnesiate [BIPHEN]2Na2Mg(THF)42 was prepared and characterised, and its formation was rationalised. Complex 1 and 4 have also been fully characterised in both solid and solution state. In terms of onward reactivity, 3 and 4 have been tested as potential exchange reagents with aryl and heteroaryl iodides to produce aryl and heteroaryl magnesium phenoxides utilising toluene as a non-polar hydrocarbon solvent. Complex 3 reacted smoothly to give a range of aryl and heteroaryl magnesium phenoxides, whilst 4's reactivity is more sluggish.

15.
ACS Catal ; 10(3): 1984-1992, 2020 Feb 07.
Artículo en Inglés | MEDLINE | ID: mdl-32296595

RESUMEN

The use of solid-state molecular organometallic chemistry (SMOM-chem) to promote the efficient double bond isomerization of 1-butene to 2-butenes under flow-reactor conditions is reported. Single crystalline catalysts based upon the σ-alkane complexes [Rh(R2PCH2CH2PR2)(η2η2-NBA)][BArF 4] (R = Cy, tBu; NBA = norbornane; ArF = 3,5-(CF3)2C6H3) are prepared by hydrogenation of a norbornadiene precursor. For the tBu-substituted system this results in the loss of long-range order, which can be re-established by addition of 1-butene to the material to form a mixture of [Rh(tBu2PCH2CH2PtBu2)(cis-2-butene)][BArF 4] and [Rh(tBu2PCH2CH2PtBu2)(1-butene)][BArF 4], in an order/disorder/order phase change. Deployment under flow-reactor conditions results in very different on-stream stabilities. With R = Cy rapid deactivation (3 h) to the butadiene complex occurs, [Rh(Cy2PCH2CH2PCy2)(butadiene)][BArF 4], which can be reactivated by simple addition of H2. While the equivalent butadiene complex does not form with R = tBu at 298 K and on-stream conversion is retained up to 90 h, deactivation is suggested to occur via loss of crystallinity of the SMOM catalyst. Both systems operate under the industrially relevant conditions of an isobutene co-feed. cis:trans selectivites for 2-butene are biased in favor of cis for the tBu system and are more leveled for Cy.

16.
Chem Commun (Camb) ; 56(31): 4328-4331, 2020 Apr 21.
Artículo en Inglés | MEDLINE | ID: mdl-32191244

RESUMEN

Vapour-phase surface-initiated cationic polymerisation of ethylvinylether occurs at single-crystals of the σ-alkane complex [Rh(Cy2PCH2CH2PCy2)(NBA)][BArF4]. This new surface interface makes these normally very air sensitive materials tolerant to air, while also allowing for onward single-crystal to single-crystal reactivity at metal sites within the lattice.

17.
Angew Chem Int Ed Engl ; 59(15): 6177-6181, 2020 Apr 06.
Artículo en Inglés | MEDLINE | ID: mdl-31943626

RESUMEN

A cobalt σ-alkane complex, [Co(Cy2 P(CH2 )4 PCy2 )(norbornane)][BArF 4 ], was synthesized by a single-crystal to single-crystal solid/gas hydrogenation from a norbornadiene precursor, and its structure was determined by X-ray crystallography. Magnetic data show this complex to be a triplet. Periodic DFT and electronic structure analyses revealed weak C-H→Co σ-interactions, augmented by dispersive stabilization between the alkane ligand and the anion microenvironment. The calculations are most consistent with a η1 :η1 -alkane binding mode.

18.
Dalton Trans ; 48(39): 14724-14736, 2019 Oct 07.
Artículo en Inglés | MEDLINE | ID: mdl-31538996

RESUMEN

The σ-amine-borane pincer complex [Rh(PONOP)(η1-H3B·NMe3)][BArF4] [2, PONOP = κ3-NC5H3-2,6-(OPtBu2)2] is prepared by addition of H3B·NMe3 to the dihydrogen precursor [Rh(PONOP)(η2-H2)][BArF4], 1. In a similar way the related H3B·NMe2H complex [Rh(PONOP)(η1-H3B·NMe2H)][BArF4], 3, can be made in situ, but this undergoes dehydrocoupling to reform 1 and give the aminoborane dimer [H2BNMe2]2. NMR studies on this system reveal an intermediate neutral hydride forms, Rh(PONOP)H, 4, that has been prepared independently. 1 is a competent catalyst (2 mol%, ∼30 min) for the dehydrocoupling of H3B·Me2H. Kinetic, mechanistic and computational studies point to the role of NMe2H in both forming the neutral hydride, via deprotonation of a σ-amine-borane complex and formation of aminoborane, and closing the catalytic cycle by reprotonation of the hydride by the thus-formed dimethyl ammonium [NMe2H2]+. Competitive processes involving the generation of boronium [H2B(NMe2H)2]+ are also discussed, but shown to be higher in energy. Off-cycle adducts between [NMe2H2]+ or [H2B(NMe2H)2]+ and amine-boranes are also discussed that act to modify the kinetics of dehydrocoupling.

19.
Angew Chem Int Ed Engl ; 58(47): 16873-16877, 2019 11 18.
Artículo en Inglés | MEDLINE | ID: mdl-31539184

RESUMEN

Reversible encapsulation of CH2 Cl2 or Xe in a non-porous solid-state molecular organometallic framework of [Rh(Cy2 PCH2 PCy2 )(NBD)][BArF4 ] occurs in single-crystal to single-crystal transformations. These processes are probed by solid-state NMR spectroscopy, including 129 Xe SSNMR. Non-covalent interactions with the -CF3 groups, and hydrophobic channels formed, of [BArF4 ]- anions are shown to be important, and thus have similarity to the transport of substrates and products to and from the active site in metalloenzymes.

20.
Angew Chem Int Ed Engl ; 58(39): 13823-13827, 2019 Sep 23.
Artículo en Inglés | MEDLINE | ID: mdl-31291498

RESUMEN

The covalent attachment of electron deficient perfluoroaryl substituents to a bis-iodotriazole pyridinium group produces a remarkably potent halogen bonding donor motif for anion recognition in aqueous media. Such a motif also establishes halogen bonding anion templation as a highly efficient method for constructing a mechanically interlocked molecule in unprecedented near quantitative yield. The resulting bis-perfluoroaryl substituted iodotriazole pyridinium axle containing halogen bonding [2]rotaxane host exhibits exceptionally strong halide binding affinities in competitive 50 % water containing aqueous media, by a factor of at least three orders of magnitude greater in comparison to a hydrogen bonding rotaxane host analogue. These observations further champion and advance halogen bonding as a powerful tool for recognizing anions in aqueous media.

SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA
...