Ligand Chain Length Research Articles

Equimolar CO2 adsorption by two Ni-based MOFs and their kinetic and thermodynamic studies

Metal-organic frameworks (MOFs) show great potential in CO2 capture due to their unique structure. This study investigated two Ni-based MOFs, Ni-MOF-74 and IR-MOF-74, with different organic ligand chain lengths. The optimal activation temperatures for each material were determined, resulting in high CO2 adsorption capacities (1.9401 and 1.9475 mmol/g at 30 °C and 0.16 bar, respectively). The adsorption capacities of the two materials were found to reach the equimolar adsorption by the fitting calculation. The adsorption process of Ni-MOF-74 and IR-MOF-74 were found to follow a pseudo-first-order kinetic model. Thermodynamic analysis revealed an entropy-enthalpy complementarity between Ni-MOF-74 and IR-MOF-74 during CO2 capture. Notably, optimal adsorption and desorption temperatures were determined for these materials, a first in the field of porous solid adsorbents. Finally, the materials demonstrated stable adsorption capacity over 10 cycles.

A series of DNA targeted Cu (II) complexes containing 1,8-naphthalimide ligands: Synthesis, characterization and in vitro anticancer activity

Copper(II) complexes are very promising candidates for platinum-based anticancer agents. Herein, three Cu (II) complexes (1–3) containing 1,8-naphthalimide ligands were synthesized and characterized by FT-IR, elemental analysis, ESI-MS and single crystal X-ray diffraction (complex 3). In addition, a control compound (complex 4) without 1,8-naphthalimide ligand was synthesized and characterized. The in vitro anticancer activity of the synthesized complexes against five cancer cell lines and one normal cell line was evaluated by MTS assay. The results displayed the antitumor activity of complexes 1–3 was controlled by the aliphatic chain length of ligands, their cytotoxicity was in the order 3 > 2 > 1, giving the IC50 values ranging from 2.874 ± 0.155 μM to 31.47 ± 0.29 μM against five cancer cell lines. Complex 4 showed less activity in comparison with complex 1–3. Notably, complexes 1–3 displayed much higher selectivity (SI = 2.65 to 10.16) compared to complex 4 (SI = 1.0), indicated that the introduction of 1,8-naphthalimide group not only increased the activity of this series of compounds but also enhanced their specific selectivity to cancer cells. Compound 3 induced apoptosis in cancer cells and blocked the S-phase and G2/M of cancer cells. The interaction with DNA of complexes 3 and 4 was studied by UV/Vis spectroscopic titrations, competitive DNA-binding experiment, viscometry and CD spectra. The results showed that complex 3 interacted with DNA in an intercalating mode, but the interaction mode of compound 4 with DNA was electrostatic interaction.

Regulating ligand length to improve the PL QY and stability of CsPbCl0.9Br2.1 nanocrystals for LEDs and photoelectric applications

Perovskite luminescent materials have been extensively investigated due to their comprehensive applications for full-color display, lighting, and communication. However, the development of blue-emissive perovskites has seriously lagged behind that of green and red counterparts, primarily because of their low photoluminescence quantum yield (PL QY) and poor stability. Here, we prepared blue-emissive CsPbCl0.9Br2.1 perovskite nanocrystals (PeNCs) and enhanced their QY from 61.3 % to 90.4 % by regulating the chain lengths of ligands. Post-treated PeNCs also exhibit good stability, their PL intensity is maintained at about 90 % after storage at ambient conditions for 10 days. The exciton dynamics results obtained from time-resolved fluorescence spectra and transient absorption spectra show that dodecyldimethylammonium bromide (DDAB), featuring double 12-hydrocarbon chains, is more capable of passivating surface defects and inhibiting non-radiative composites than the other double 8- or double 16-carbon chain ligands, which greatly improved the probability and rate of radiative recombination. Subsequently, the mechanism of ligand chain length regulation on the PL properties and stability of PeNCs was analyzed in terms of ligand-NC surface interaction, ligand polarity, hydrophobicity, and spatial effects. Furthermore, the device based on DDAB-CsPbCl0.9Br2.1 demonstrated stable EL and long operation lifetime, indicating its significant potential as an efficient blue emitter for backlighting in display technologies.

Advanced properties of gold nanoparticles obtained by using long-chain secondary amine for phase transfer from water to chloroform

We have conducted a new comparison of gold nanoparticles functionalized by primary- and secondary amine with the same chain length. Our hypothesis suggests that the adaptive steric conformation of the secondary amine molecular branches makes a marked additional contribution to the well-established role of the ligand chain length. We characterize the importance of this factor based on diOctadecylamine (diODA) and Octadecylamine (ODA) passivated gold nanoparticles by using high-resolution transmission electron microscopy (HR-TEM) and selective area electron diffraction (SAED). The results evidenced that the diODA coordination to the inorganic core forms a more efficient and impenetrable protective coating. The SAED patterns show a more homogeneous distribution of the small crystalline domains in the gold core. TEM images show a smooth spherical shape of the diODA nanoparticles and a lack of interparticle coalescence cases. The diODA-passivation provides nanoparticles with nearly twice the effective ligand length than its ODA equivalent. This results in their spontaneous arrangement in domains with expressed crystal-like order despite the relatively large size-dispersity before passivation. The surface free energy of coatings, formed by diODA passivated gold nanoparticles, is twice as small as measured on the ODA-nanoparticle-coated surfaces.

A switchable zinc-based metal organic framework for the light triggered absorption and release of organic dyes

Due to its adjustable pore structure, the metal–organic frameworks (MOFs) have attracted much attention in the treatment of organic dye molecules in wastewater. However, the general tuning of the pore channels of MOFs is mainly by changing the chain length of the organic ligands and metal nodes. This approach not only limits the types of MOFs, but also limits the treatment of a large number of dye methylene blue (MB) and methyl orange (MO) dye molecules in the wastewater. Hence, we synthesized photoresponsive Zn-AzDC/TPA MOF as adsorbents to adsorb and release organic dye molecules in a photo-controlled manner. The photoresponsive Zn-AzDC/TPA was prepared using a mixed ligand strategy, in which the azobenzene carboxylic acid derivative (AzDC) served as a photoresponsive ligand and terephthalic acid (TPA) served as a non-active ligand in coordination with zinc ion. The optical and structural properties of the synthesized Zn-AzDC/TPA was characterized by UV–vis, FT-IR, PXRD, SEM, TEM, TGA, and pore analysis. Interestingly, it was found that the photoresponsive AzDC unit of Zn-AzDC/TPA demonstrated reversible trans–cis isomerization under the alternating UV and visible light, resulting in reversible changes in the pore size of the Zn-AzDC/TPA. Its photoresponse properties can trapp and release dye molecules under light-driven conditions. This result provides a new direction for the application of photoresponsive MOF and also lays a foundation for the study of diversified optically responsive materials.

In situ cell-scale probing nucleation, growth and evolution of CsPbBr3 nanowires by optical absorption spectroscopy

The growth kinetics of colloidal lead halide perovskite nanomaterials are an integral part of their applications, remains poorly understood due to complex nucleation processes and lack of in situ size monitoring method. Here we demonstrated that absorption spectra can be used to observe in situ growth processes of ultrathin CsPbBr3 nanowires in solution with reference to the effective mass infinite deep square potential well model. By means of this method, we have found that the ultrathin nanowires, fabricated by hot injection method, were firstly formed within one minute. Subsequently, they merge with each other into a thicker structure with increasing reaction time. We revealed that the nucleation, growth, and merging of the CsPbBr3 nanowires are determined by the acid concentration and ligand chain length. At lower acidity, the critical nucleation size of the nanowire is smaller, while the shorter the ligand chain length, the faster the merging among the nanowires. Moreover, the merging mode between nanowires changed with their nucleation size. This growth kinetics of CsPbBr3 nanowires provides a reference for optimizing the synthesis conditions to obtain the one-dimensional CsPbBr3 with desired size, thus enabling accurate control of the nanowire shape.

Tailoring Charge Donor–Acceptor Interaction in CsPbBr3 Perovskite Nanocrystals through Ligand Exchange

The surface ligands in colloidal metal halide perovskites influence not only their intrinsic optoelectronic properties but also their interaction with other materials and molecules. Donor–acceptor interactions of CsPbBr3 perovskite nanocrystals with TiO2 nanoparticles and nanotubes are explored by replacing long‐chain oleylamine ligands with short‐chain butylamines. Through postsynthesis ligand exchange, the nanocrystals are functionalized with butylamine ligands while their intrinsic properties are maintained. In solution, butylamine‐capped nanocrystals exhibit reduced photoluminescence intensity with increasing TiO2 concentration but without any change in photoluminescence lifetime. Intriguingly, the Stern–Volmer plot depicts different slopes at low and high TiO2 concentrations, suggesting donor‐acceptor interaction through mixed static photoluminescence quenching and quenching sphere of action mechanism . Oleylamine‐capped nanocrystals in solution, on the other hand, show no interaction with TiO2, as indicated by consistent photoluminescence intensities and lifetimes before and after TiO2 addition. In films, both types exhibit decreased photoluminescence lifetime with TiO2, indicating enhanced donor–acceptor interaction, which is discussed in terms of electron transfer. TiO2 nanotubes enhance nonradiative recombination more in butylamine‐capped CsPbBr3 perovskite nanocrystals, emphasizing the role of ligand chain length.

Structural characterization, electronic and photophysical properties of phosphane-based copper(I) complexes and their application to cyan LEDs

Two dinuclear Cu(I) complexes, [Cu2(dppe)(dppbz)2I2](1) and [Cu2(dppb)(dppbz)2I2] (2) (dppe = 1, 2-bis(diphenylphosphino)ethane, dppb = 1,4-bis(diphenylphosphino)butane, dppbz = 1,2-bis (diphe nylphosphino)benzene), have been prepared and characterized by IR, TG, XRD, elemental analysis and X-ray crystal structure analysis. Structural analysis indicates that diphosphane ligands connect two Cu atoms to form the S-shape configurations in complexes 1 and 2. DFT calculations demonstrate that the HOMO → LUMO energy gap and Mülliken atomic charges for 1 and 2 are affected by increasing the alkyl chain length of diphosphane ligands, but the composition of HOMOs and LUMOs are hardly changed at the different alkyl chain length of diphosphane ligands. The solid-state luminescent properties of complexes 1 and 2 are observed at 77 K and 298 K, showing that the maximum emission lifetime and quantum yields respectively approach to 6 μs and 26 % at 298 K. Moreover, dinuclear Cu(I) complexes are used to fabricate the cyan light-emitting diodes with the maximum EQE of ca. 20 %.

Characterizing the Ligand Shell Morphology of PEG-Coated ZnO Nanocrystals Using FRET Spectroscopy.

Poly(ethylene glycol) (PEG) ligands can inhibit proteins and other biomolecules from adhering to underlying surfaces, making them excellent surface ligands for nanocrystal (NC)-based drug carriers. Quantifying the PEG ligand shell morphology is important because its structure determines the permeability of biomolecules through the shell to the NC surface. However, few in situ analytical tools can reveal whether the PEG ligands form either an impenetrable barrier or a porous coating surrounding the NC. Here, we present a Förster resonance energy transfer (FRET) spectroscopy-based approach that can assess the permeability of molecules through PEG-coated ZnO NCs. In this approach, ZnO NCs serve as FRET donors, and freely diffusing molecules in the bulk solution are FRET acceptors. We synthesized a series of variable chain length PEG-silane-coated ZnO NCs such that the longest chain length ligands far exceed the Förster radius (R0), where the energy transfer (EnT) efficiency is 50%. We quantified the EnT efficiency as a function of the ligand chain length using time-resolved photoluminescence lifetime (TRPL) spectroscopy within the framework of FRET theory. Unexpectedly, the longest PEG-silane ligand showed equivalent EnT efficiency as that of bare, hydroxyl-passivated ZnO NCs. These results indicate that the "rigid shell" model fails and the PEG ligand shell morphology is more likely porous or in a patchy "mushroom state", consistent with transmission electron microscopy data. While the spectroscopic measurements and data analysis procedures discussed herein cannot directly visualize the ligand shell morphology in real space, the in situ spectroscopy approach can provide researchers with valuable information regarding the permeability of species through the ligand shell under practical biological conditions.

Superhydrophobic Surface Modification of Polymer Microneedles Enables Fabrication of Multimodal Surface-Enhanced Raman Spectroscopy and Mass Spectrometry Substrates for Synthetic Drug Detection in Blood Plasma.

Microneedles are widely used substrates for various chemical and biological sensing applications utilizing surface-enhanced Raman spectroscopy (SERS), which is indeed a highly sensitive and specific analytical approach. This article reports the fabrication of a nanoparticle (NP)-decorated microneedle substrate that is both a SERS substrate and a substrate-supported electrospray ionization (ssESI) mass spectrometry (MS) sample ionization platform. Polymeric ligand-functionalized gold nanorods (Au NRs) are adsorbed onto superhydrophobic surface-modified polydimethylsiloxane (PDMS) microneedles through the control of various interfacial interactions. We show that the chain length of the polymer ligands dictates the NR adsorption process. Importantly, assembling Au NRs onto the micrometer-diameter needle tips allows the formation of highly concentrated electromagnetic hot spots, which provide the SERS enhancement factor as high as 1.0 × 106. The micrometer-sized area of the microneedle top and high electromagnetic field enhancement of our system can be loosely compared with tip-enhanced Raman spectroscopy, where the apex of a plasmonic NP-functionalized sharp probe produces high-intensity plasmonic hot spots. Utilizing our NR-decorated microneedle substrates, the synthetic drugs fentanyl and alprazolam are analyzed with a subpicomolar limit of detection. Further analysis of drug-molecule interactions on the NR surface utilizing the Langmuir adsorption model suggests that the higher polarizability of fentanyl allows for a stronger interaction with hydrophilic polymer layers on the NR surface. We further demonstrate the translational aspect of the microneedle substrate for both SERS- and ssESI-MS-based detection of these two potent drugs in 10 drug-of-abuse (DOA) patient plasma samples with minimal preanalysis sample preparation steps. Chemometric analysis for the SERS-based detection shows a very good classification between fentanyl, alprazolam, or a mixture thereof in our selected 10 samples. Most importantly, ssESI-MS analysis also successfully identifies fentanyl or alprazolam in these same 10 DOA plasma samples. We believe that our multimodal detection approach presented herein is a highly versatile detection technology that can be applicable to the detection of any analyte type without performing any complicated sample preparation.

Ultrafast dynamics and relaxation pathways in Eu(III) complexes with fluorinated β–diketonate ligands

A series of novel β-diketonate Eu3+ complexes with minor variations in the chemical structure of the diketone ligand were systematically studied. Six Eu3+ coordination compounds based on β-diketones, bearing linear perfluorinated substituents of various length (C1, C2, C3 and C6) and fixed pyrazole moiety were obtained. In addition, two water molecules, 1,10-phenanthroline or 4,7-diphenyl-1,10-phenanthroline as an ancillary ligand in compounds with fixed β-diketone ligand were used. Their photophysical properties were investigated by UV–Vis absorption and time-resolved femtosecond transient (fs-TA) absorption spectroscopy techniques. In this study, we investigate the impact of ancillary ligands and the fluorinated chain length of β-diketone ligands on the ultrafast relaxation processes that occur in the ligand environment. Relying on the ultrafast transient absorption measurements, it was demonstrated that the extension of fluorinated chains of β-diketone ligand leads to decrease of first excited singlet and triplet states relaxation rates. The compound with excessively long chain C6F13 exhibits the slowest relaxation of the triplet state T1.Besides, variation in the ancillary ligand alters the electronic energy transfer pathways in the whole complex. It was established, that introducing 4,7-diphenyl-1,10-phenanthroline (bath) instead of 1,10-phenanthroline (phen) dramatically changing the electronic energy transfer dynamics in the whole coordination compound. On the basis of the fs-TA measurements we conclude the bath ligand act as acceptor of electronic energy of diketone ligand in the excited state.

Investigating the role of membrane composition on the stability of decorated nanoparticle aggregates

Gold nanoparticles are a ubiquitous photosensitizer with a broad range of applications in microscopy and targeted drug delivery. Vesicles photosensitized with gold nanoparticles are promising as targeted drug delivery vehicles due to their non-invasive rupture mechanism. Controlling the vesicle properties increases control of the spatial-temporal release of cargo and drug dosage. The aggregation of gold nanoparticles affects the photoporation of these vesicles by interfering with peak SPR wavelengths. These nanoparticles cause leaflet bending deformations on the order of the nanoparticle size, while ligand chains may also disrupt local packing of lipid chains. Aggregation may be driven by the need to minimize one or both effects, but their relative contributions are unknown. In order to test the contributions of these two perturbations to membrane structure, we simulated multi-nanoparticle systems in lipid membranes of varying compositions. We used coarse-grained molecular dynamics simulation via the MARTINI forcefield to simulate simple spherical nanoparticles with a decorated ligand exterior. We found that large-scale nanoparticle aggregation depends more on ligand chain length than nanoparticle size, suggesting that aggregation of gold nanoparticles is dominated by microscopic perturbations to lipid packing.

Electrospun Hydrophobic Interaction Chromatography (HIC) Membranes for Protein Purification.

Responsive membranes for hydrophobic interaction chromatography have been fabricated by functionalizing poly(N-vinylcaprolactam) (PVCL) ligands on the substrate of electrospun regenerated cellulose nanofibers. Both static and dynamic binding capacities and product recovery were investigated using bovine serum albumin (BSA) and Immunoglobulin G (IgG) as model proteins. The effects of ligand chain length and chain density on static binding capacity were also studied. A static binding capacity of ~25 mg/mL of membrane volume (MV) can be achieved in optimal ligand grafting conditions. For dynamic binding studies, protein binding capacity increased with protein concentration from 0.1 to 1.0 g/L. Dynamic binding capacity increased from ~8 mg/mL MV at 0.1 g/L BSA to over 30 mg/mL at 1.0 g/L BSA. However, BSA recovery decreased as protein concentration increased from ~98% at 0.1 g/L BSA to 51% at 1 g/L BSA loading concentration. There is a clear trade-off between binding capacity and recovery rate. The electrospun substrate with thicker fibers and more open pore structures is superior to thinner fibrous membrane substrates.

Effect of Ligand Chain Length for Tuning of Molecular Dimensionality and Magnetic Relaxation in Redox Active Cobalt(II) EDOT Complexes (EDOT=3,4-Ethylenedioxythiophene).

Four cobalt(II) complexes, [Co(L1)2 (NCX)2 (MeOH)2 ] (X=S (1), Se (2)) and {[Co(L2)2 (NCX)2 ]}n (X=S (3), Se (4)) (L1=2,5-dipyridyl-3,4,-ethylenedioxylthiophene and L2=2,5-diethynylpyridinyl-3,4-ethylenedioxythiophene), were synthesized by incorporating ethylenedioxythiophene based redox-active luminescence ligands. All these complexes have been well characterized using single-crystal X-ray diffraction analyses, spectroscopic and magnetic investigations. Magneto-structural studies showed that 1 and 2 adopt a mononuclear structure with CoN4 O2 octahedral coordination geometry while 3 and 4 have a 2D [4×4] rhombic grid coordination networks (CNs) where each cobalt(II) center is in a CoN6 octahedral coordination environment. Static magnetic measurements reveal that all four complexes displayed a high spin (HS) (S=3/2) state between 2 and 280 K which was further confirmed by X-band and Q-band EPR studies. Remarkably, along with the molecular dimensionality (0D and 2D) the modification in the axial coligands lead to a significant difference in the dynamic magnetic properties of the monomers and CNs at low temperatures. All complexes display slow magnetic relaxation behavior under an external dc magnetic field. For the complexes with NCS- as coligand observed higher energy barrier for spin reversal in comparison to the complexes with NCSe- as coligand, while mononuclear complex 1 exhibited a higher energy barrier than that of CN 3. Theoretical calculations at the DFT and CASSCF level of theory have been performed to get more insight into the electronic structure and magnetic properties of all four complexes.

AgAuSe quantum dots with absolute photoluminescence quantum yield of 87.2%: The effect of capping ligand chain length

AgAuSe quantum dots with absolute photoluminescence quantum yield of 87.2%: The effect of capping ligand chain length

Ultrafast Electron Transfer Dynamics Affected by Ligand Chain Length in InP/ZnS Core/Shell Quantum Dots

Ultrafast Electron Transfer Dynamics Affected by Ligand Chain Length in InP/ZnS Core/Shell Quantum Dots

Unraveling the Effect of Surface Ligands on the Auger Process in an Inorganic Perovskite Quantum-Dot System.

This work systematically scrutinizes the role of surface-ligand modification in affecting the Auger process in a porotype perovskite system of CsPbBr3-octanoic acid (OcA) and CsPbBr3-oleic acid (OA) quantum dots (QDs), by means of steady-state/time-resolved/temperature-dependent photoluminescence spectroscopy and ultrafast transient absorption spectroscopy. The difference in the ligand chain length (i.e., C8 and C18 alkyl chains for OcA and OA, respectively) is found to significantly affect Auger recombination and hot-carrier cooling processes. More importantly, we provide fresh insight into the involved carrier dynamics; i.e., the modification of CsPbBr3 QDs with short-chain (long-chain) ligand leads to the formation of trapped (free) carriers, which causes a pronounced difference in the ability to suppress the detrimental Auger process. In addition, a careful analysis of spectral evolution reveals that the Auger suppression is related to the carrier population of a certain transition state. The valuable mechanistic information gleaned from the exciton/carrier dynamics perspective would assist in surface engineering through a facile ligand-modification strategy toward rational design and optimization of QD-based photoelectrochemical applications.

Fabrication of Oriented Colloidal Crystals from Capillary Assembly of Polymer-Tethered Gold Nanoparticles.

Self-assembled colloidal crystals (CCs) or nanoparticle (NPs) superlattices have attracted significant attention due to their potential applications in many fields. However, due to the complex interactions that govern the self-assembly, it is difficult to predict and control the superstructure organization of CCs. Herein, a facile yet effective way is demonstrated to fabricate oriented CCs from capillary assembly of polymer-tethered gold NPs (AuNPs). Assembly mechanism of polymer-tethered AuNPs and their superlattice structures are systematically studied by in situ small-angle X-ray scattering (SAXS) technology. The results show that the oriented CCs of polymer-tethered AuNPs can be obtained upon solvent evaporation in a capillary tube and the oriented structure is mainly determined by the chain length of polymer ligands and size of AuNPs. Assembly of AuNPs tethered by short-chain ligand can result in oriented face-centered cubic (fcc) superlattice, whereas AuNPs tethered by long-chain ligand can assemble into an oriented body-centered tetragonal (bct) superlattice structure. Interestingly, in situ SAXS study shows that for the sample of bct superlattice structure, a transformation from fcc to bct superlattice upon solvent evaporation is observed, which strongly depends on chain length of ligands. This work provides a useful guide for polymer-tethered AuNPs to prepare orientation colloidal crystals.

Size control of cobalt nanoparticles by adjusting the linear carboxylic acid ligand chain length

Size control in the synthesis of Co nanoparticles (NPs) through thermolysis of Co2(CO)8 is achieved by adjusting the chain length of linear carboxylic acids used as ligands. As the chain length increases, steric effects reduce the reactivity of the carboxylic acids, thereby slowing the nucleation rate. In the subsequent growth phase, completing deposition of Co precursor onto fewer nuclei yields an increased NP size. Oxidation of Co NPs under ambient atmosphere causes formation of an antiferromagnetic CoO shell that can exchange couple to the Co core, resulting in exchange bias. The superparamagnetic blocking temperature (TB), coercivity (HC), and exchange shift (HEB) strongly depend on the size of the NP, and the most pronounced effects of exchange bias are observed for the smallest Co core size.

The underlying mechanism for the enhanced radical trapping effects of nanoparticles surface-functionalized with antioxidants: A kinetic study

The enhancement in reactivity of the antioxidant functionalized gold nanoparticles is closely related to the rate constant and activation energy, which were significantly affected by the chain length of the PEG ligands that capped the gold nanoparticles. Meanwile, the enhancement could be attributed to the π-π stacking interaction between the adjacent phenol groups coated on gold nanoparticles' surface.