The present work describes the synthesis of new nanomaterials based on gold nanoclusters (AuNCs) supported on poly(
N
-isopropylacrylamide) (PNIPAM) and polyacrylamide (PAAM) hydrogels, as well as ...their characterization in terms of structure and physicochemical properties. AuNCs were synthesized by incorporating the metallic precursor (Au
3+
) into the polymeric matrices and subsequently reducing it with UV-vis light (
λ
= 365 nm). The materials were characterized by UV-vis, FT-IR, fluorescence spectroscopy, TEM and SEM. Likewise, the thermal properties and the swelling capacity of the different polymer matrices were determined. In addition, we present a comparative study with two nanomaterials regarding their behavior for the selective detection of Hg
2+
in water. Furthermore, it is demonstrated that the polymer matrices influence the nanomaterials' selectivity to mercury. As the AuNCs fluorescence incorporated in both matrices is quenched by Hg
2+
, the materials can be used to sense sensitively and selectively Hg
2+
in water with a detection limit of 4.1 nM and 1.3 nM for Au-PNIPAM and Au-PAAM NCs, respectively. Summarizing, our study presents a novel, easy and straightforward route to synthesized nanomaterials with unique optical and chemical properties, which could be used for the construction of a portable Hg
2+
detection device.
AuNCs supported on PNIPAM and PAAM polymer matrices were synthesized and characterized. Nanomaterials are selective and sensitive to detect mercury in water by fluorescence.
•Two-dimensional relaxation maps at low field NMR.•Kerogen and bitumen detection at low field NMR.•Simultaneous determination of liquid and solid components in unconventional reservoirs.•Acquisition ...of fast decaying signals enables the detection of solid components of rocks.
Quantification of organic matter and fluids contained in oil source rocks from shale plays is a fundamental goal for the petrophysical and geochemical assessment of the production potential of a well. Laboratory 1H nuclear magnetic resonance (NMR) is a fast, reliable, and non-destructive method widely used in the oil industry. Measurement of T1-T2 correlation maps have been found to be critical for identifying the presence of solid organic matter, liquid hydrocarbons, and brine in these formations. However, the inherent long echo times associated with standard laboratory equipment for large sample volume challenge the detection of contribution from kerogen and viscous bitumen. In this work, we use a commercial low field NMR rock-core analyzer where a novel T1- T2*&T2 pulse sequence is implemented to enable the detection of solid organic matter by acquiring the free induction decay after the first excitation pulse. This acquisition is followed by a train of refocusing pulses that generate multiple echoes from which liquid components are detected. A set of outcrop and well samples from the Vaca Muerta Formation in Argentina, with a varying amount of total organic content, were measured. The signal intensity assigned to solid matter was correlated with RockEval 6 pyrolisis. The novel pulse sequence presented here can be implemented in any commercial apparatus without the need for hardware modifications.
Complex materials composed of two and three elements with high Li-ion storage capacity are investigated and tested as lithium-ion battery (LiB) negative electrodes. Namely, anodes containing tin, ...silicon, and graphite show very good performance because of the large gravimetric and volumetric capacity of silicon and structural support provided by tin and graphite. The performance of the composites during the first cycles was studied using
ex situ
magic angle spinning (MAS)
7
Li Nuclear Magnetic Resonance (NMR), density functional theory (DFT) calculations, and electrochemical techniques. The best performance was obtained for Sn/Si/graphite in a 1 : 1 : 1 proportion, due to an emergent effect of the interaction between Sn and Si. The results suggest a stabilization effect of Sn over Si, providing a physical constraint that prevents Si pulverization. This mechanism ensures good cyclability over more than one hundred cycles, low capacity fading and high specific capacity.
Complex materials composed of two and three elements with high Li-ion storage capacity are investigated and tested as lithium-ion battery (LiB) negative electrodes.
Display omitted
•Diffusion-relaxation correlation maps in single-sided NMR.•Reduced experimental time with increased sensitivity.•Saturation recovery-diffusion is faster than diffusion-transverse ...relaxation.
Diffusion-relaxation correlation experiments in nuclear magnetic resonance are a powerful technique for the characterization of fluid dynamics in confined geometries or soft matter, in which relaxation may be either spin-spin (T2) or spin-lattice (T1). The general approach is to acquire a set of bidimensional data in which diffusion is codified by the evolution of the magnetization with either Hahn or stimulated echoes (STE) in the presence of a constant magnetic field gradient. While T2 is codified by a Carr-Purcell-Meiboom-Gil (CPMG) sequence, T1 is either encoded by saturation or inversion-recovery methods. In this work, we analyse the measurement time of diffusion-relaxation times in single-sided NMR and show that T1-D acquisition is always shorter than D-T2. Depending on the hardware characteristics, this time reduction can be up to an order of magnitude. We present analytical calculations and examples in model porous media saturated with water and in a dairy product.
To obtain detailed information about the position of hydrogen atoms in hydrogen bonds, HBs, of crystalline organic molecular compounds is not an easy task. In this work we propose a combination of ...ssNMR experimental data with theoretical procedures to get such information. Furthermore, the combination of experimental and theoretical models provides us with well-defined grounds to analyse the strength of π-stacking interactions between layers of hydrogen bonded molecules. Two different theoretical models were considered, both approaches being quite different. The first one is a solid-state model, so that the periodicity of a crystalline system underlies calculations of the electronic energy, the electronic density and NMR parameters. The other one is a molecular model in which molecules are taken as isolated monomers, dimers and tetramers. These two models were applied to the tizoxanide, TIZ, molecular crystal though it can widely be applied to any other molecular crystal. By the application of the quantum molecular model it was possible to learn about the way the intermolecular HBs affect the position of hydrogen atoms that belong to HBs in TIZ. This molecule has two intermolecular HBs that stabilize the structure of a basic dimer, but it also has an intramolecular HB in each monomer whose position should be optimized together with the other ones. We found that by doing this it is possible to obtain reliable results of calculations of NMR spectroscopic parameters. Working with the solid-state model we found that any local variation of the TIZ crystalline structure is correlated with the variation of the values of the NMR parameters of each nucleus. The excellent agreement between experimental and calculated chemical shifts leads to the conclusion that the N
10
-H
10
bond distance should be (1.00 ± 0.02) Å.
In this work, we present a combination of ssNMR spectroscopy and two different theoretical methods to get a full description of an intramolecular hydrogen bond in tizoxanide.
In this work, we present an investigation of the influence of water encapsulated in 1,4-bis-2-ethylhexylsulfosuccinate/methyl laurate and 1,4-bis-2-ethylhexylsulfosuccinate/isopropyl myristate ...reverse micelles on the enzymatic hydrolysis of 1-naphthyl phosphate by alkaline phosphatase. Our results show that the enzyme is active in the biocompatible reverse micelles studied and that the Michaelis-Menten kinetic model is valid in all systems. We found that both micellar systems studied have a particular behavior toward pH and that the penetration of external solvents into the interfaces is crucial to understanding the effect. Methyl laurate does not disrupt the interface and is not necessary to control the pH value since alkaline phosphatase in the center of the micelles is always solvated similarly. In contrast, isopropyl myristate disrupts the interfaces so that the water and 1-naphthol molecules cannot form hydrogen bond interactions with the polar head of the surfactant. Then, when the water is at pH = 7, the 1-naphthol moves away to the interfaces inhibiting alkaline phosphatase which is not observable when the water is at pH = 10. Our study shows that the concept of pH cannot be used directly in a confined environment. In addition, our research is of great importance in the field of reactions that occur in reverse micelles, catalyzed by enzymes.
Schematic representation of the effect on ML/AOT/water and IPM/AOT/water at different pH values.
A structure/catalytic activity study of water-soluble gold nanoparticles, stabilized by zwitterionic ligands derived from imidazolium salts, in the reduction of aromatic nitro compounds in pure water ...at different temperature, as well as their recyclability, was performed. Our studies indicate that the nanoparticles synthesized by an easy, fast and reproducible process, need a short characteristic induction time to restructure the surfaces and make them active. The differences observed in the catalytic activity of the nanoparticles, determined by using the typical Langmuir-Hinshelwood model, are strongly based on the degree of coverage and spatial arrangement of the imidazolium salts on them. Finally, we demonstrate that gold nanoparticles stabilized by non-traditional ligands can be an excellent choice for nitro compound degradation.
A structure/catalytic activity study of water-soluble gold nanoparticles, stabilized by zwitterionic ligands derived from imidazolium salts, in the reduction of aromatic nitro compounds in pure water, as well as their recyclability, was performed.
Background: Nitazoxanide (NTZ) is a broad spectrum antimicrobial agent with poor aqueous solubility and low bioavailability. Thus, the generation of new solid forms of NTZ is relevant to improve its ...unfavorable properties. The present study deals with the application of mechanochemistry for the preparation of alternate solid forms of NTZ, using saccharine (SAC) as coformer. Methods: NTZ-SAC mixtures were prepared by neat and liquid-assisted grinding (LAG) and characterized using differential scanning calorimetry (DSC), hot stage microscopy (HSM), X-ray Powder Diffraction (XRPD), 13C Solid-state Nuclear Magnetic Resonance (SSNMR) and Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy. Powder dissolution (PD) profiles were obtained with USP apparatus 2 in buffer phosphate pH 6.5 with 0.25% Tween 80 - 0.25% triethanolamine and in 0.25% sodium lauryl sulfate, at 37 ºC ± 0.5 ºC and 75 rpm. Drug release was characterized in terms of dissolution efficiency (DE). Results: XRPD, SSNMR and DRIFT indicated that NTZ and SAC did not cocrystallize but DSC and HSM revealed that they formed a binary eutectic mixture which melted near 176 °C, a melting temperature lower than those of NTZ and SAC. PD data indicated that the 1:1 NTZ-SAC sample obtained by LAG exhibited a slightly higher DE than pure NTZ in the two assayed media. Conclusion: NTZ and SAC formed a eutectic, the first reported for this drug, which improved its dissolution rate and opened the pathway for studies searching for new eutectics with better biopharmaceutical attributes than NTZ and the NTZ-SAC eutectic reported herein.
Relaxation in nuclear magnetic resonance (NMR), both transverse and longitudinal, provides information on microscopic features of a wide variety of systems and may be used to monitor dynamic ...processes such as cementation, chemical reactions, gelatinization, and evaporation. Dynamic relaxometry, in combination with spatial resolution, is a useful technique that provides deep insight into complex systems evolution. In this work, we explore the range of applicability of single-sided NMR to determine the evaporation kinetics of fluid from porous media. We show that, due to technical experimental restrictions, the determination of the time-dependent amount of fluid in different voids as a function of the position is in general not feasible with transverse relaxation experiments. However, as opposed to common intuition, longitudinal relaxation experiments provide reliable and fast acquisition, compatible with the requirements needed to monitor a water evaporation process from a model oil-reservoir rock sample.
Antiprotozoal tinidazole (TNZ) exhibits low aqueous solubility (Sw) and poor photochemical stability. In this work, TNZ was used to form cocrystals and eutectics with the aim of enhancing its ...solubility and physical stability. The choice of coformers was based on a crystal engineering strategy focused on the success rate of supramolecular heterosynthon formation between azoles and carboxylic acids. By liquid-assisted grinding, three cocrystals with p-aminobenzoic acid (PABA), citric acid (CA), and salicylic acid (SA) and two eutectics with nicotinamide and succinic acid were obtained and characterized using powder X-ray diffraction, 13C solid-state nuclear magnetic resonance, infrared spectroscopy, differential scanning calorimetry, thermogravimetry, and hot-stage microscopy. The crystal structures of TNZ-PABA and TNZ-SA were resolved by means of single-crystal X-ray diffraction, which revealed that they are a solvated and an unsolvated cocrystal, respectively. The Sw values of the obtained samples were determined at 37 °C, with the outcome that only the TNZ-CA cocrystal had a slightly higher Sw than pure TNZ. A physical stability study was also performed under UV–visible irradiation, and it was found that the three cocrystals showed better photostability when compared to TNZ, the two eutectics, and each respective physical mixture, a finding that could be relevant from the pharmacotechnical point of view.
PDF
