Alkyl Chain Ligands Research Articles

In-situ growth of PbI2 on ligand-free FAPbBr3 nanocrystals to significantly ameliorate the stability of CO2 photoreduction

Excellent optical properties involving strong visible light response and superior carrier transport endow metal halide perovskites (MHP) with a fascinating prospect in the field of photocatalysis. Nevertheless, the poor stability of MHP nanocrystals (NCs) in water-contained system, especially without the protection of long alkyl chain ligands, severely restricts their photocatalytic performance. In this context, we report an effortless strategy for the generation of ligand-free MHP NCs based photocatalyst with high water tolerance, by coating PbI2 on the surface of ligand-free formamidinium lead bromide (FAPbBr3) NCs via the facile procedure of in-situ conversion with the aid of ZnI2. Under the protection of PbI2 layer, the resultant FAPbBr3/PbI2 composite exhibits significantly ameliorated stability in an artificial photosynthesis system with CO2 and H2O vapor as feedstocks. Moreover, the formation of compact PbI2 layer can accelerate the separation of photogenerated carriers in FAPbBr3 NCs, bringing forth a remarkable improvement of CO2 photoreduction efficiency with an impressive electron consumption yield of 2053 µmol/g in the absence of organic sacrificial agents, which is 7-fold over that of pristine FAPbBr3 NCs.

N,N′‐bridged binuclear NHC palladium complexes: A combined experimental catalytic and computational study for the Suzuki reaction

This work examines how N‐donor bridged spacer ligands affect N‐heterocyclic carbene (NHC) palladium complexes catalytic activities for Suzuki coupling reaction. Different degrees of structural flexibility binuclear NHC palladium complexes were synthesized. The more flexible nitrogen‐based alkyl chain ligand shows similar performance with cycloamine counterparts in the Suzuki coupling reaction. Suzuki coupling examples were used in air and ambient temperature to reach moderate to completion yields in short time. Density functional theory calculations showed that the chelate effect, associated with a single Pd complex mechanism, plays a fundamental role in the pre‐catalysis stage, supporting a reasonable of the kinetic activity observed experimentally.

The Phase Behavior of Nanoparticle Superlattices in the Presence of a Solvent.

Superlattices of nanoparticles coated by alkyl-chain ligands are usually prepared from a stable solution by evaporation, therefore the pathway of superlattice self-assembly critically depends on the amount of solvent present within it. This work addresses the role of the solvent on the structure and the relative stability of the different supercrystalline phases of single-component superlattices (simple cubic, body-centered cubic (BCC), face-centered cubic (FCC), and hexagonal close-packed). The study is performed with a molecular theory for nanoparticle superlattices introduced in this work, which predicts the structure and thermodynamics of the supercrystals explicitly treating the presence and molecular details of the solvent and the ligands. The theory predicts a FCC-BCC transition with decreasing solvent content due to the competition between the translational entropy of the solvent and the entropy and internal energy of the ligands. This result provides an explanation for recent experimental observations by in situ X-ray scattering, which reported a FCC-BCC transition during solvent evaporation. The theory also predicts the effects of the length and surface coverage of the ligands and the radius of the core on the phase behavior in agreement with experimental evidence and previous molecular dynamics simulations. These results validate the use of the dimensionless softness parameter λ (ratio of ligand length to core radius) to predict the phase behavior of wet superlattices. Our results stress the importance of explicitly considering the presence of the solvent in order to reach a complete picture of the mechanisms that mediate the self-assembly of nanoparticle superlattices.

P‐13.6: Efficiency Improvement of CsPbI3 Quantum dot Light Emitting Diodes via Alkyl Chain Ligand Regulation

P‐13.6: Efficiency Improvement of CsPbI₃ Quantum dot Light Emitting Diodes via Alkyl Chain Ligand Regulation

In-situ photopolymerized C4-functionalized organosilicon monoliths for reversed-phase protein separation in nano-liquid chromatography

In this study, polyhedral oligomeric silsesquioxane (POSS)-based capillary monoliths with short alkyl chain ligand in the form of butyl (C4) were synthesized via two different polymerization routes, namely UV-initiated free radical copolymerization of methacrylate-derivatized POSS (POSS-MA) with butylmethacrylate (BMA) and UV-initiated thiol-methacrylate copolymerization of POSS-MA with butanethiol (BT). An organosilicon monolith with a pore size distribution lying on both mesoporous and macroporous scales, a lower mean pore size and a higher specific surface area was obtained with UV-initiated thiol-methacrylate polymerization. Both monoliths were then comparatively evaluated for gradient separation of proteins under reversed phase conditions in nano-liquid chromatography. The chromatographic performance was defined in terms of peak-resolution and peak capacity. Four carbon (C4) functionalized-poly(POSS-MA) monolith produced by UV-initiated thiol-methacrylate polymerization exhibited better separation performance with higher peak resolutions and peak capacities. Both, the morphological characterization of monoliths and the results of gradient separation of proteins showed that thiol-methacrylate polymerization was more suitable for the synthesis of C4 functionalized organosilicon based stationary phases for reversed-phase protein separation. The monolith prepared by thiol-methacrylate polymerization was also successfully applied for impurity analysis of two important hormones, namely insulin and genotropin. A comparison with a commercial poly(styrene-co-divinylbenzene) monolith documented the good chromatographic performance of the new BT-attached poly(POSS-MA) monolith.

Alkanethiol-functionalized organosilicon monoliths for nano-reversed-phase liquid chromatography.

Organosilicon monoliths carrying chromatographic ligands with different alkyl chain lengths were obtained by thiol-methacrylate photopolymerization. The use of thiol-ene chemistry in the presence of a main monomer with a series of methacrylate functionality (i.e., methacrylate substituted polyhedral oligomeric silsesquioxane) allowed the synthesis of organosilicon monoliths with high cross-linking density and carrying hydrophobic alkyl-chain ligands by a one-pot process. In the synthesis runs, 1-butanethiol, 1-octanethiol, and 1-octadecanethiol were used as the hydrophobic thiol ligands with the number of methylene units between 4 and 18. The selectivity analysis performed using cytosine/uracil retention ratio showed that alkanethiol-attached organosilicon monoliths exhibited hydrophobicity close to octadecyl-attached silica-based RP columns. In the RP, chromatographic runs performed in nano-liquid chromatography, phenols, alkylbenzenes, and PAHs were used as the analytes. Among the synthesized monoliths, retention-independent plate height behavior and the smallest plate heights were obtained with 1-octadecanethiol-attached organosilicon monolith for the analytes in a wide polarity range. With this monolith, the mobile phases prepared with ACN contents ranging between 35 and 85% v/v could be used for satisfactory separation of analytes in a wide polarity range.

Copper Sulfide–Zinc Sulfide Janus Nanoparticles and Their Seebeck Characteristics for Sustainable Thermoelectric Materials

A heterostructured copper sulfide–zinc sulfide nanocomposite is explored as a new class of low temperature and sustainable thermoelectric materials. The nanoparticles are created through a wet chemical synthetic technique and display a remarkable Janus structure. These nanoparticles are processed as building blocks by molecular linking with short alkyl chain ligands to enhance their electrical conductivity. The nanomaterials are pressed into a pellet and subjected to subsequent thermal annealing to remove volatiles and enhance particle contacts through sintering. The resulting nanocomposite materials were characterized to assess the thermoelectric characteristics, revealing P-type conductivity.

Influence of ligand exchange on the electrical transport properties of PbS nanocrystals

In this work, FETs are used as a research tool to study charge carrier mobilities in PbS nanocrystals (NCs) thin‐films employed as semiconducting layer in bottom‐gate bottom‐contact (BGBC) field‐effect transistors (FETs). The as‐synthesised NCs are surrounded by long alkyl chain ligands which act as electrical insulators. Therefore, a ligand exchange process with shorter molecules is necessary to enhance the free charges generation and transport. We used two different ligands: 1,2 ethandithiol (EDT) and 1,2,3,4‐tetrabutylammonium iodide (TBAI) and studied the charge mobility of PbS NCs comparing the electrical characteristics of FETs made by exchanged NCs. We analysed also the contemporary presence of both exchanged nanocrystals on the device. All the transistors showed p‐type transport behaviour, enhanced by an annealing process at 100 °C for 10 min. After this, only the TBAI‐treated NCs devices showed a n‐type transport, resulting in an ambipolar behaviour. Inkjet printing deposition techniques was also successfully used to deposit PbS‐(TBAI) NCs and ambipolar devices were obtained. In addition, for printed devices it was found that it is possible to modulate the charge transport properties by applying surface treatment to the substrate with a pentafluorothiophenol (PFTP). Indeed in this case, the p‐type transport was suppressed while n‐type behaviour was induced.

Rapid Preparation of C18 Monoliths for Micro‐column Separation Using Ultraviolet and Microwave Irradiation

AbstractAn organic‐based monolith with long alkyl chain ligands was prepared by UV photo‐initiation using (a) 1‐octadecene as a functional monomer, (b) ethylene glycol dimethacrylate (EDMA) as the cross‐linking agent, (c) 1‐propanol, 1,4‐butanediol and dimethylformamide as triporogenic solvents, and (d) Irgacure 1800 as the initiator. The monoliths containing a high fraction of 1‐octadecene possessed a better total porosity, improved permeability, and result in faster separation. Similar monolithic capillary was quickly fabricated in 3 min by microwave irradiation using azobisisobutyronitrile as the thermal initiator. Conventional polyimide‐coated capillaries were used instead of expensive UV‐transparent capillaries in both methods.

Preparation of palladium(II) complexes with long alkyl chain ligand incorporated in micelle

Three palladium(II) complexes with a bidentate nitrogen ligand having a long alkyl chain (1, [PdCl2(C8-tmen)], C8-tmen=N,N,N′-trimethyl-N′-octylethylenediamine; 2, [PdCl2(C16-tmen)], C16-tmen=N,N,N′-trimethyl-N′-cetylethylenediamine; 3, [PdCl2(C8-bpy)], C8-bpy=4-octyl-2,2′-bipyridine) were prepared. Addition of 1 to an aqueous solution of cetyltrimethylammonium bromide gave a metallomicelle containing the Pd(II) complex (1A). The other palladium complexes (2 and 3) were not incorporated into the CTABr micelle due to the unsuitable matching between the ligand and the micelle. 1A showed good catalytic performance for Suzuki and Heck coupling reactions in water. The catalyst system for the Heck reaction in water was reusable.

Explicit all-atom modeling of realistically sized ligand-capped nanocrystals

We present a study of an explicit all-atom representation of nanocrystals of experimentally relevant sizes (up to 6 nm), "capped" with alkyl chain ligands, in vacuum. We employ all-atom molecular dynamics simulation methods in concert with a well-tested intermolecular potential model, MM3 (molecular mechanics 3), for the studies presented here. These studies include determining the preferred conformation of an isolated single nanocrystal (NC), pairs of isolated NCs, and (presaging studies of superlattice arrays) unit cells of NC superlattices. We observe that very small NCs (3 nm) behave differently in a superlattice as compared to larger NCs (6 nm and above) due to the conformations adopted by the capping ligands on the NC surface. Short ligands adopt a uniform distribution of orientational preferences, including some that lie against the face of the nanocrystal. In contrast, longer ligands prefer to interdigitate. We also study the effect of changing ligand length and ligand coverage on the NCs on the preferred ligand configurations. Since explicit all-atom modeling constrains the maximum system size that can be studied, we discuss issues related to coarse-graining the representation of the ligands, including a comparison of two commonly used coarse-grained models. We find that care has to be exercised in the choice of coarse-grained model. The data provided by these realistically sized ligand-capped NCs, determined using explicit all-atom models, should serve as a reference standard for future models of coarse-graining ligands using united atom models, especially for self-assembly processes.

Hydrophobic interaction membrane chromatography for plasmid DNA purification: Design and optimization

Chromatography is one of the key operations in the downstream processing of plasmid DNA (pDNA). However, the increased demand for highly purified pDNA experienced in recent years has made clear the need for alternative processes capable of retaining the advantages of conventional chromatography, such as selectivity, while providing increased throughput at a lower cost. The work presented in this article outlines the development and optimization of an alternative hydrophobic interaction membrane chromatography process for the purification of pDNA. The studies included the modification of functionalized membrane supports with a linear alkyl chain ligand and the testing of chromatographic performance of these membranes. Three modification procedures were tested and the membranes were screened for their capacity and selectivity. The modified membranes could separate the model plasmid pVAX1-LacZ (6050 bp) from impurities in clarified Escherichia coli cell lysates (specifically RNA), with good resolution. Subsequent optimization of elution profiles with the best-performing modified membrane, resulted in a high purification factor of 4.7, competitive with its bead process counterpart, and a plasmid yield of 73%.

Preparation and evaluation of the highly cross‐linked poly(1‐hexadecane‐co‐trimethylolpropane trimethacrylate) monolithic column for capillary electrochromatography

In this paper, a novel highly cross-linked porous monolithic stationary phase having a long alkyl chain ligand (C16) was introduced and evaluated in CEC. The monolithic stationary phase was prepared by in situ copolymerization of 1-hexadecene, trimethylolpropane trimethacrylate, and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) in the presence of ternary porogenic solvent (cyclohexanol/1,4-butanediol/water). In preparing monoliths, the ternary cross-linker trimethylolpropane trimethacrylate was usually applied to preparing molecularly imprinted polymers or molecularly imprinted solid-phase extraction, instead of binary cross-linker ethylene dimethacrylate. 1-Hexadecene was introduced to provide the non-polar sites (C16) for chromatographic retention, while AMPS was used to generate the EOF for transporting the mobile phase through the monolithic capillary. Monolithic columns were prepared by optimizing proportion of porogenic solvent and AMPS content in the polymerization solution as well as the cross-linkers. The monolithic stationary phases could generate a strong and stable EOF in various pH values and exhibit an RP-chromatographic behavior for neutral compounds. For charged compounds, the separation was mainly based on the association of hydrophobic, electrostatic and electrophoretic interaction.

Luminescence quenching of *[Ru(bpy) 3] 2+ by ruthenium(II) tetraphosphite complexes with different phosphite ligands

The luminescence quenching of excited Tris(2,2-bipyridine)ruthenium(II) ions by trans-[RuCl 2{P(OR) 3} 4] complexes with different alkyl chain ligands (R=C 2H 5, C 2H 5Cl, n C 4H 9, iC 3H 7 o-tolyl and tC 4H 9) was investigated. None of the acceptor Ru(II) phosphite complexes were luminescent, and the rate constants of the bimolecular system were determined within the range of 1.15 and 0.28×10 8 M −1 s −1 for R=C 2H 5 and tC 4H 9, respectively. The results indicate a direct effect of the alkyl chains in the rate constants, showing a decrease of k q as a function of increased of the alkyl chains (R) in the ruthenium(II) tetraphosphite complexes. The greater the R group content in the phosphite ligand, the more difficult the electron transfer is.

Complexes with the fac-{M(CO) 3} + (M = 99mTc, Re) moiety and long alkyl chain ligands as Lipiodol surrogates

Accumulation of radiopharmaceuticals in the liver is frequently observed and represents in general a limiting factor when developing novel labeled compounds for any purpose in nuclear medicine. Aiming at the treatment of liver cancer with radiopharmaceuticals, such accumulation is desired but the compounds have to remain in the liver over an extended time period rather than being washed out or redistributed over time in the whole body. Lipiodol is known to remain in the liver and we present here a study for the preparation of 186Re and 99mTc labeled Lipiodol surrogates expected to behave similarly. We have synthesized two bidentate and two tridentate ligands conjugated to a pendant C18 chain as well as their corresponding fac-[Re(CO) 3] + and fac-[Tc(CO) 3] + complexes. Three of the rhenium complexes have been structurally characterized. Labelling with [ 186Re(OH 2) 3(CO) 3] + and [ 99mTc(OH 2) 3(CO) 3] +, respectively, gave yields in the range of 90%. The complexes could be extracted into Lipiodol due to their high lipophilicity and close structural relationship with the major components of Lipiodol. The complexes are stable in water and in Lipiodol for more than 24 h. These Lipiodol surrogates present new low-valent technetium and rhenium complexes for applications in liver cancer imaging and therapy.

Magnetic nanoparticles through organometallic synthesis: evolution of the magnetic properties from isolated nanoparticles to organised nanostructures.

Co and NiFe nanoparticles (2.7 to 3.3 nm mean diameter) of narrow size distribution have been obtained through the decomposition of organometallic precursors in organic solutions of long alkyl chain ligands, namely oleic acid and hexadecylamine. Materials of various volume fractions were produced. The particles have been structurally characterised by WAXS. Both adopt the bulk structure: HCP in the case of cobalt; a mixture of FCC and BCC for NiFe. Their aptitude to self-assemble either on flat supports or in bulk solid state has been investigated by means of TEM and SAXS. This study suggests the crystallisation of the nanoparticles upon solvent evaporation, especially a local FCC arrangement was observed for the NiFe material. Magnetic measurements (SQUID) confirm this tendency. The blocking temperature depends on the metal volume fraction, i.e. on the anisotropy generated by the dipolar couplings (Ki). We show that, for dense samples, the particles of high intrinsic anisotropy, Ku, (Co) still display an individual behaviour while the soft ones (NiFe) display a collective behaviour.

Capillary electrochromatography with monolithic stationary phases: 1. Preparation of sulfonated stearyl acrylate monoliths and their electrochromatographic characterization with neutral and charged solutes.

A novel monolithic stationary phase having long alkyl chain ligands (C17) was introduced and evaluated in capillary electrochromatography (CEC) of small neutral and charged species. The monolithic stationary phase was prepared by the in situ copolymerization of pentaerythritol diacrylate monostearate (PEDAS) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) in a ternary porogenic solvent consisting of cyclohexanol/ethylene-glycol/water. While AMPS was meant to support the electroosmotic flow (EOF) necessary for transporting the mobile phase through the monolithic capillary, the PEDAS was introduced to provide the nonpolar sites for chromatographic retention. Monolithic columns at various EOF velocities were readily prepared by conveniently adjusting the amount of AMPS in the polymerization solution as well as the composition of the porogenic solvent. The monolithic stationary phases thus obtained exhibited reversed-phase chromatography behavior toward neutral solutes and yielded a relatively strong EOF. For charged solutes (e.g., dansyl amino acids), nonpolar as well as electrostatic interaction/repulsion with the monoliths were observed in addition to electrophoretic migration. Therefore, for charged solutes, selectivity and migration can be readily manipulated by changing various parameters including the nature of the monolith and the composition of the mobile phase (e.g., pH, ionic strength and organic modifier). Ultrafast separation on the time scale of seconds of 17 different charged and neutral pesticides and metabolites were performed using short capillary columns of 8.5 cm x 100 microm ID.