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1.
J Am Chem Soc ; 143(45): 19167-19177, 2021 Nov 17.
Artigo em Inglês | MEDLINE | ID: mdl-34738793

RESUMO

Organosilicon compounds and polymers have found wide applications as synthetic building blocks and functional materials. Hydrosilylation is a common strategy toward the synthesis of organosilicon compounds and polymers. Although transition-metal-catalyzed hydrosilylation has achieved great advances, the metal-free hydrosilylation polymerization of dienes and bis(silane)s, especially the one suitable for both electron-rich and electron-deficient dienes, is largely lacking. Herein, we report a visible-light-driven metal-free hydrosilylation polymerization of both electron-rich and electron-deficient dienes with bis(silane)s by using the organic photocatalyst and hydrogen atom transfer (HAT) catalyst. We achieved the well-controlled step-growth hydrosilylation polymerizations of the electron-rich diene and bis(silane) monomer due to the selective activation of Si-H bonds by the organic photocatalyst (4CzIPN) and the thiol polarity reversal reagent (HAT 1). For the electron-deficient dienes, hydrosilylation polymerization and self-polymerization occurred simultaneously in the presence of 4CzIPN and aceclidine (HAT 2), providing the opportunity to produce linear, hyperbranched, and network polymers by rationally tuning the concentration of electron-deficient dienes and the ratio of bis(silane)s and dienes to alter the proportion of the two polymerizations. A wide scope of bis(silane)s and dienes furnished polycarbosilanes with high molecular weight, excellent thermal stability, and tunable architectures.

2.
ACS Omega ; 6(41): 27325-27334, 2021 Oct 19.
Artigo em Inglês | MEDLINE | ID: mdl-34693153

RESUMO

A block copolymer with discotic liquid crystalline behavior was synthesized using Grignard metathesis polymerization (GRIM) and initiators for continuous activator regeneration atom transfer radical polymerization (ICAR-ATRP). A novel discotic liquid crystalline mesogen, 6-(pyren-1-yloxy)hexyl methacrylate (PyMA), comprises a block that is attached to regioregular poly(3-hexylthiophene) (rr-P3HT) generated by GRIM and subjected to end-group modification. Due to the continuous regeneration of Cu+ in the reaction mixture in ICAR-ATRP compared to conventional methods, the synthesis was successfully performed with less catalyst. The purity and yield of the final product are increased by eliminating rigorous post-synthesis purification. Stacked pyrene units have contributed to the enhanced long-range π-π interactions and aligning of the P3HT block as observed in thin-film X-ray diffraction (XRD). Furthermore, field-effect mobilities in the order of 10-2 cm2 V-1 s-1 in bottom-gate, top-contact organic field-effect transistors (OFETs) suggest an enhancement in charge transport due to the discotic electron-rich pyrene units that help mitigate the insulating effect of the methacrylate backbone. The formation of uniform microdomains of P3HT-b-poly(PyMA) observed with tapping mode atomic force microscopy (TMAFM) on the channel regions of OFETs indicates the unique packing of the block copolymer in comparison to pristine P3HT. Thermotropic properties of the novel discotic mesogen in the presence and absence of P3HT were observed with both the poly(3-hexylthiophene)-b-poly(6-(pyren-1-yloxy)hexyl methacrylate) (P3HT-b-poly(PyMA)) block copolymer and poly(6-(pyren-1-yloxy)hexyl methacrylate) (poly(PyMA)) homopolymer using polarized optical microscopy (POM) and differential scanning calorimetry (DSC).

3.
Nat Commun ; 12(1): 5853, 2021 10 06.
Artigo em Inglês | MEDLINE | ID: mdl-34615871

RESUMO

The regulation of polymer topology and the precise control over the monomer sequence is crucial and challenging in polymer science. Herein, we report an efficient solution-phase synthetic strategy to prepare regio- and sequence-controlled conjugated polymers with topological variations via the usage of methyliminodiacetic acid (MIDA) boronates. Based on the solubility of MIDA boronates and their unusual binary affinity for silica gel, the synthesized regio- and sequence-defined conjugated oligomers can be rapidly purified via precipitation or automatic liquid chromatography. These synthesized discrete oligomers can be used for iterative exponential and sequential growth to obtain linear and dendrimer-like star polymers. Moreover, different topological sequence-controlled conjugated polymers are conveniently prepared from these discrete oligomers via condensation polymerization. By investigating the structure-property relationship of these polymers, we find that the optical properties are strongly influenced by the regiochemistry, which may give inspiration to the design of optoelectronic polymeric materials.

4.
Environ Sci Technol ; 55(4): 2628-2638, 2021 02 16.
Artigo em Inglês | MEDLINE | ID: mdl-33529528

RESUMO

Groundwater contamination by halogenated organic compounds, especially fluorinated ones, threatens freshwater sources globally. Sulfidized nanoscale zero-valent iron (SNZVI), which is demonstrably effective for dechlorination of groundwater contaminants, has not been well explored for defluorination. Here, we show that SNZVI nanoparticles synthesized via a modified post-sulfidation method provide rapid dechlorination (∼1100 µmol m-2 day-1) and relatively fast defluorination (∼6 µmol m-2 day-1) of a halogenated emerging contaminant (florfenicol) under ambient conditions, the fastest rates that have ever been reported for Fe0-based technologies. Batch reactivity experiments, material characterizations, and theoretical calculations indicate that coating S onto the metallic Fe surface provides a highly chemically reactive surface and changes the primary dechlorination pathway from atomic H for nanoscale zero-valent iron (NZVI) to electron transfer for SNZVI. S and Fe sites are responsible for the direct electron transfer and atomic H-mediated reaction, respectively, and ß-elimination is the primary defluorination pathway. Notably, the Cl atoms in florfenicol make the surface more chemically reactive for defluorination, either by increasing florfenicol adsorption or by electronic effects. The defluorination rate by SNZVI is ∼132-222 times higher with chlorine attached compared to the absence of chlorine in the molecule. These mechanistic insights could lead to new SNZVI materials for in situ groundwater remediation of fluorinated contaminants.


Assuntos
Água Subterrânea , Tricloroetileno , Poluentes Químicos da Água , Ferro , Enxofre , Tianfenicol/análogos & derivados , Água
5.
PLoS One ; 16(1): e0245317, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-33428672

RESUMO

BACKGROUND: Intolerance to gastric feeding tubes is common among critically ill adults and may increase morbidity. Administration of prokinetics in the ICU is common. However, the efficacy and safety of prokinetics are unclear in critically ill adults with gastric feeding tubes. We conducted a systematic review to determine the efficacy and safety of prokinetics for improving gastric feeding tube tolerance in critically ill adults. METHODS: Randomized controlled trials (RCTs) were identified by systematically searching the Medline, Cochrane and Embase databases. Two independent reviewers extracted the relevant data and assessed the quality of the studies. We calculated pooled relative risks (RRs) for dichotomous outcomes and the mean differences (MDs) for continuous outcomes with the corresponding 95% confidence intervals (CIs). We assessed the risk of bias using the Cochrane risk-of-bias tool and used the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) methodology to rate the quality of the evidence. RESULTS: Fifteen RCTs met the inclusion criteria. A total of 10 RCTs involving 846 participants were eligible for the quantitative analysis. Most studies (10 of 13, 76.92%) showed that prokinetics had beneficial effects on feeding intolerance in critically ill adults. In critically ill adults receiving gastric feeding, prokinetic agents may reduce the ICU length of stay (MD -2.03, 95% CI -3.96, -0.10; P = 0.04; low certainty) and the hospital length of stay (MD -3.21, 95% CI -5.35, -1.06; P = 0.003; low certainty). However, prokinetics failed to improve the outcomes of reported adverse events and all-cause mortality. CONCLUSION: As a class of drugs, prokinetics may improve tolerance to gastric feeding to some extent in critically ill adults. However, the certainty of the evidence suggesting that prokinetics reduce the ICU or hospital length of stay is low. Prokinetics did not significantly decrease the risks of reported adverse events or all-cause mortality among critically ill adults.


Assuntos
Estado Terminal , Preparações Farmacêuticas , Adulto , Nutrição Enteral , Gastroenteropatias/etiologia , Humanos , Unidades de Terapia Intensiva , Tempo de Internação , Viés de Publicação , Ensaios Clínicos Controlados Aleatórios como Assunto , Risco , Resultado do Tratamento
6.
Chem Asian J ; 15(7): 1014-1017, 2020 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-32012458

RESUMO

Aggregation-induced emission (AIE) technology has been demonstrated to be a facile approach for in-situ monitoring atom transfer radical polymerization (ATRP). A series of tertraphenyl ethylene (TPE)-containing α-bromo compounds were synthesized and applied as ATRP initiators. The photoluminescent (PL) emission of the polymerization system is proved to be sensitive to the local viscosity owing to the AIE characteristics of TPE. Linear relationships between the resulting molecular weight Mn and PL intensity were observed in several polymerization systems with different monomers, indicating the variability of this technique. Compared to physical blending, the chemical bonding of the TPE group in the chain end has higher sensitivity and accuracy to the polymer segments and the surrounding environment. This work promoted the combination of the AIE technique and controlled living radical polymerization, and introduced such an optical research platform to the ATRP polymerization process.

7.
Phys Rev Lett ; 125(26): 263002, 2020 Dec 31.
Artigo em Inglês | MEDLINE | ID: mdl-33449790

RESUMO

Chiral induced spin selectivity (CISS) describes efficient spin filtering by chiral molecules. This phenomenon has led to nanoscale manipulation of quantum spins with promising applications to spintronics and quantum computing, since its discovery nearly two decades ago. However, its underlying mechanism still remains mysterious for the required spin-orbit interaction (SOI) strength is unexpectedly large. Here we report a multi-orbital theory for CISS, where an effective SOI emerges from spontaneous formation of electron-hole pairing caused by many-body correlation. This mechanism produces a strong SOI reaching the energy scale of room temperature, which could support the large spin polarization observed in CISS. One central ingredient of our theory is the Wannier functions of the valence and conduction bands correspond, respectively, to one- and two-dimensional representation of the spatial rotation symmetry around the molecule elongation direction. The induced SOI strength is found to decrease when the band gap increases. Our theory may provide important guidance for searching other molecules with CISS effects.

8.
J Polym Sci A Polym Chem ; 57(3): 268-273, 2019 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-31011240

RESUMO

A signature of photo-mediated controlled polymerizations is the ability to modulate the rate of polymerization by turning the light source 'on' and 'off.' However, in many reported systems, growth can be reproducibly observed during dark periods. In this study, emerging photo-mediated controlled radical polymerizations are evaluated with in situ 1H NMR monitoring to assess their behavior in the dark. Interestingly, it is observed that Cu-mediated systems undergo long-lived, linear growth during dark periods in organic media.

9.
J Am Chem Soc ; 141(18): 7486-7497, 2019 05 08.
Artigo em Inglês | MEDLINE | ID: mdl-30977644

RESUMO

Copper-catalyzed atom transfer radical polymerization (Cu-ATRP) is one of the most widely used controlled radical polymerization techniques. Notwithstanding the extensive mechanistic studies in the literature, the transition states of the activation/deactivation of the growing polymer chain, a key equilibrium in Cu-ATRP, have not been investigated computationally. Therefore, the understanding of the origin of ligand and initiator effects on the rates of activation/deactivation is still limited. Here, we present the first computational analysis of Cu-ATRP activation transition states to reveal factors that affect the rates of activation and deactivation. The Br atom transfer between the polymer chain and the Cu catalyst occurs through an unusual bent geometry that involves pronounced interactions between the polymer chain end and the ancillary ligand on the Cu catalyst. Therefore, the rates of activation/deactivation are determined by both the electronic properties of the Cu catalyst and the ligand-initiator steric repulsions. In addition, our calculations revealed the important role of ligand backbone flexibility on the activation. These theoretical analyses led to the identification of three chemically meaningful descriptors, namely HOMO energy of the catalyst ( EHOMO), percent buried volume ( Vbur%), and distortion energy of the catalyst (Δ Edist), to describe the electronic, steric, and flexibility effects on reactivity, respectively. A robust and simple predictive model for ligand effect on reactivity is thereby established by correlating these three descriptors with experimental activation rate constants using multivariate linear regression. Validation using a structurally diverse set of ligands revealed the average error is less than ±2 kcal/mol compared to the experimentally derived activation energies. The same approach was also applied to develop a predictive model for reactivity of different alkyl halide initiators using R-X bond dissociation energy (BDE) and Cu-X halogenophilicity as descriptors.


Assuntos
Cobre/química , Catálise , Radicais Livres/síntese química , Radicais Livres/química , Ligantes , Modelos Moleculares , Polimerização , Estresse Mecânico , Termodinâmica
10.
Chem Soc Rev ; 47(14): 5457-5490, 2018 Jul 17.
Artigo em Inglês | MEDLINE | ID: mdl-29868657

RESUMO

Spatial and temporal regulations of ATRP by external stimuli are presented. Various ATRP techniques, eATRP, photoATRP, and mechanoATRP, are controlled by electrical current, light, and mechanical forces, respectively. Conversely, ARGET and SARA ATRP are controlled by chemical reducing agents. ICAR ATRP is a thermally regulated process through decomposition of a radical initiator. The aim of this review is to highlight the use of external regulations in ATRP and to summarize the state-of-the-art and future perspectives, focusing on mechanistic aspects, synthetic procedures, preparation of polymers with complex architectures and functional materials, and their applications.

11.
Angew Chem Int Ed Engl ; 57(30): 9430-9433, 2018 Jul 20.
Artigo em Inglês | MEDLINE | ID: mdl-29928785

RESUMO

A rapid oxygen-initiated and -regulated controlled radical polymerization was conducted under ambient temperature and atmosphere. The reaction between triethylborane and oxygen provides ethyl radicals, which initiate and mediate the radical polymerization. The controlled radical polymerization was achieved using RAFT chain transfer agents (CTA) without any process of removing oxygen, providing well-defined polymers with almost full conversion (>95 %) in a short period (15 min). High-throughput screening was used to discover the suitable conditions for various CTA and monomers. To show the versatility of this method, a polymer library containing 25 well-defined polymers with different compositions (block and statistical copolymers) and molecular weights were synthesized in 1 h via high-throughput synthesis technique. A polymer-painting technique was developed using this method, forming films with spatial control and excellent control in molecular weight and dispersity.

12.
Angew Chem Int Ed Engl ; 56(10): 2740-2743, 2017 03 01.
Artigo em Inglês | MEDLINE | ID: mdl-28164438

RESUMO

A DNA synthesizer was successfully employed for preparation of well-defined polymers by atom transfer radical polymerization (ATRP), in a technique termed AutoATRP. This method provides well-defined homopolymers, diblock copolymers, and biohybrids under automated photomediated ATRP conditions. PhotoATRP was selected over other ATRP methods because of mild reaction conditions, ambient temperature, tolerance to oxygen, and no need to introduce reducing agents or radical initiators. Both acrylate and methacrylate monomers were successfully polymerized with excellent control in the DNA synthesizer. Diblock copolymers were synthesized with different targeted degrees of polymerization and with high retention of chain-end functionality. Both hydrophobic and hydrophilic monomers were grafted from DNA. The DNA-polymer hybrids were characterized by SEC and DLS. The AutoATRP method provides an efficient route to prepare a range of different polymeric materials, especially polymer-biohybrids.


Assuntos
Automação/instrumentação , DNA/síntese química , Polímeros/síntese química , DNA/química , Radicais Livres/síntese química , Radicais Livres/química , Interações Hidrofóbicas e Hidrofílicas , Estrutura Molecular , Polimerização , Polímeros/química
13.
Chemistry ; 23(25): 5972-5977, 2017 May 02.
Artigo em Inglês | MEDLINE | ID: mdl-28009492

RESUMO

This paper reports use of phenyl benzo[b]phenothiazine (Ph-benzoPTZ) as a visible light-induced metal-free atom transfer radical polymerization (ATRP) photoredox catalyst. Well-controlled polymerizations of various methacrylate monomers were conducted under a 392 nm visible light LED using Ph-benzoPTZ to activate different alkyl halides. The use of the photocatalyst enabled temporal control over the growth of polymer chains during intermittent on/off periods. The polymerization was initiated and progressed only under stimulation by light and completely stopped in the absence of light. Block copolymers were synthesized to demonstrate high retention of chain end fidelity in the polymers and livingness of the process.

14.
Macromol Rapid Commun ; 38(13)2017 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-27995746

RESUMO

A photoinduced atom transfer radical polymerization (photoATRP) of methacrylates is investigated using air-stable FeBr3 as catalyst in the absence of conventional ATRP initiators, additional ligands, reducing agents, and/or radical initiators. The ATRP alkyl halide initiator is formed in situ via photoreduction of FeBr3 by methacrylate monomers. The kinetics of the polymerization display a linear semilogarithmic plot after several hours of induction period. The molecular weight can be modulated by additions of different amounts of FeBr3 , and polymers have narrow molecular weight distributions. Thus, FeBr3 acts as deactivator, as well as a source of activator FeBr2 and initiator. This method features a temporal control, and can provide various polymethacrylates with high chain end functionality.


Assuntos
Ferro/química , Metacrilatos/síntese química , Polimerização , Polímeros/síntese química , Solventes/química , Catálise , Polimerização/efeitos da radiação
15.
J Am Chem Soc ; 138(7): 2411-25, 2016 Feb 24.
Artigo em Inglês | MEDLINE | ID: mdl-26820243

RESUMO

Photoinduced metal-free atom transfer radical polymerization (ATRP) of methyl methacrylate was investigated using several phenothiazine derivatives and other related compounds as photoredox catalysts. The experiments show that all selected catalysts can be involved in the activation step, but not all of them participated efficiently in the deactivation step. The redox properties and the stability of radical cations derived from the catalysts were evaluated by cyclic voltammetry. Laser flash photolysis (LFP) was used to determine the lifetime and activity of photoexcited catalysts. Kinetic analysis of the activation reaction according to dissociative electron-transfer (DET) theory suggests that the activation occurs only with an excited state of catalyst. Density functional theory (DFT) calculations revealed the structures and stabilities of the radical cation intermediates as well as the reaction energy profiles of deactivation pathways with different photoredox catalysts. Both experiments and calculations suggest that the activation process undergoes a DET mechanism, while an associative electron transfer involving a termolecular encounter (the exact reverse of DET pathway) is favored in the deactivation process. This detailed study provides a deeper understanding of the chemical processes of metal-free ATRP that can aid the design of better catalytic systems. Additionally, this work elucidates several important common pathways involved in synthetically useful organic reactions catalyzed by photoredox catalysts.

16.
J Am Chem Soc ; 137(49): 15430-3, 2015 Dec 16.
Artigo em Inglês | MEDLINE | ID: mdl-26634963

RESUMO

Photoinduced ATRP was successfully performed in aqueous media. Polymerization of oligo(ethylene oxide) methyl ether methacrylate (OEOMA) in the presence of CuBr2 catalyst and tris(2-pyridylmethyl)amine ligand when irradiated with visible light of 392 nm wavelength at 0.9 mW/cm(2) intensity was well controlled. Linear semi-logarithmic kinetic plots and molecular weights increasing with conversion were observed. Polymers of OEOMA were synthesized with low dispersity (Mw/Mn = 1.12) using only 22 ppm of copper catalyst in the presence of excess bromide anions in highly diluted (90% v/v) aqueous media. The effects of copper concentration, salt, and targeted degrees of polymerization were investigated. The polymerization could be directly regulated by external stimulation, i.e., switching the irradiation on/off, with a good retention of chain-end functionality, as proved by clean chain extension of the OEOMA polymers. This new system could enable applications for controlled aqueous radical polymerization due to its low catalyst loading in the absence of any other chemicals.

17.
J Org Chem ; 80(9): 4465-9, 2015 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-25843519

RESUMO

Dynamic NMR spectroscopy has been used to measure rotation barriers in five B,B-disubstituted 1,3-dimethylimidazol-2-ylidene boranes. The barriers are attributed to the sp(2)-sp(3) bond between C(1) of the N-heterocyclic carbene ring and the boron atom. Bonds to boron atoms bearing a thexyl (1,1,2-trimethylpropyl) group show especially high barriers, ranging from 75-86 kJ mol(-1). 2-Isopropyl-1,3,5-trimethylbenzene is used as a comparable to help understand the nature and magnitude of the barriers.

18.
Org Lett ; 16(10): 2728-31, 2014 May 16.
Artigo em Inglês | MEDLINE | ID: mdl-24802672

RESUMO

Newly discovered boryl sulfides and N-borylthioamides are shown to serve as neutral sources of sulfur nucleophiles in substitutions reactions. For example, heating of diMe-Imd-BH(SPh)2 with benzyl bromides, primary bromides, or acid chlorides provides the corresponding thioethers or thioesters in high yields. Likewise, N-phenyltetrazole thioethers/esters are made from a readily available N-borylthionotetrazole. The formation of the boryl sulfide and its onward nucleophilic substitution can be telescoped down to a one-pot reaction whose components are an NHC-borane (NHC-BH3), a disulfide, and an electrophile.


Assuntos
Sulfetos/síntese química , Tetrazóis/química , Tetrazóis/síntese química , Catálise , Espectroscopia de Ressonância Magnética , Estrutura Molecular , Estereoisomerismo , Sulfetos/química
19.
J Am Chem Soc ; 135(38): 14433-7, 2013 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-23981246

RESUMO

The hydroboration of alkenes of diverse structural types by assorted N-heterocyclic carbene boranes can be accomplished by addition of 5-10% diiodine. For example, reaction of 1,3-dimethylimidazol-2-ylidene borane (diMe-Imd-BH3) with 10% I2 followed by addition of 2,3-dimethyl-2-butene provided the corresponding thexyl NHC-borane (diMe-Imd-BH2thexyl) in 75% yield. This and related monohydroboration products are stable to chromatography and storage. The scope of the new reaction is described, and the mechanism is probed by (11)B NMR experiments.

20.
J Am Chem Soc ; 135(28): 10484-91, 2013 Jul 17.
Artigo em Inglês | MEDLINE | ID: mdl-23718209

RESUMO

Reactions of 1,3-dimethylimidazol-2-ylidene-borane (diMe-Imd-BH3) and related NHC-boranes with diaryl and diheteroaryl disulfides provide diverse NHC-boryl monosulfides (diMe-Imd-BH2SAr) and NHC-boryl disulfides (diMe-Imd-BH(SAr)2). Heating in the dark with 1 equiv of disulfide favors monosulfide formation, while irradiation with 2 equiv disulfide favors disulfide formation. With heteroaryl disulfides, the NHC-borane in the primary NHC-boryl sulfide product migrates from sulfur to nitrogen to give new products with a thioamide substructure. Most substitution reactions are thought to proceed through radical chains in which homolytic substitution of a disulfide by an NHC-boryl radical is a key step. However, with electrophilic disulfides under dark conditions, a competing ionic path may also be possible.


Assuntos
Boranos/química , Dissulfetos/química , Compostos Heterocíclicos/química , Metano/análogos & derivados , Radicais Livres/síntese química , Radicais Livres/química , Compostos Heterocíclicos/síntese química , Metano/síntese química , Metano/química , Estrutura Molecular
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