Diffusion-ordered Spectroscopy Research Articles

Lignin Molar Mass Estimation by Dispersion Analysis.

Lignin's complex and heterogeneous molecular structure poses significant challenges for accurate molar mass determination, which is important for its utilization in industrial applications, such as biochemicals, nanoparticles, biobased binders, and biofuels. This study evaluates the potential of Taylor Dispersion Analysis (TDA) for measuring lignin size and compares it with size-exclusion chromatography (SEC) and diffusion-ordered spectroscopy (DOSY) NMR. Using dual Gaussian fitting, flow-induced dispersion analysis (FIDA), a TDA-based method, successfully determined the average hydrodynamic radii of multiple species in solvent-fractionated soda grass lignin samples, producing results consistent with DOSY. Molar mass calibration enabled comparisons between FIDA and SEC, revealing similar relative differences across lignin fractions. FIDA offers advantages such as rapid analysis and absence of stationary phase interactions, however its accuracy is limited by the variability of lignin fluorescence. Addressing these limitations will be critical for advancing FIDA as a method for lignin size estimation.

Enhanced Efficiency of Anionic Guerbet-Type Amino Acid Surfactants.

This study investigates the surfactant properties and efficiency of linear and Guerbet-type amino acid surfactants. Utilizing a Wilhelmy plate method, we assessed the colloidal efficiency of these surfactants, with the lowest observed critical micelle concentration at 0.046 mmol L-1, significantly reducing surface tension to as low as 25.1 mN·m-1. Furthermore, the self-diffusion coefficients of the various surfactants have been determined through 1H pulsed-field gradient nuclear magnetic resonance diffusion-ordered spectroscopy. The self-diffusion coefficients are linked to the surface tension reduction as a function of concentration to determine the characteristic time scale of diffusion. In this work, the characteristic time scale of diffusion of a series of surfactants was calculated to investigate the interfacial coverage efficiency. Our findings indicate an inverse relationship between the characteristic time scale of diffusion and critical micelle concentrations across surfactants with hydrocarbon tail lengths of 8-22 carbons. Shorter tails correspond to lower colloidal efficiencies, but rapid surface tension reduction, resulting in the characteristic time scale of diffusion values ranging from 120 ns to 2.15 s. This property is crucial for applications requiring rapid action, such as enhancing aerosol efficiency, improving dispersion, and wetting materials in products.

Synthesis and anion binding properties of (thio)urea functionalized Ni(II)-salen complexes.

Salen ligands (salen = N,N'-ethylenebis(salicylimine)) are well-known for their versatility and widespread utility in chelating metal complexes. However, installation of hydrogen-bonding units on the salen framework, particularly functional groups that require amine-based precursors such as (thio)ureas, is difficult to achieve without the use of protecting group strategies. In this report, we show that the phenylketone analog of salicyladehyde is a stable alternative that enables the facile installation of hydrogen bonding (thio)urea groups on the salen scaffold, thus imparting anion binding abilities to a metal salen complex. Synthesis of symmetric N-phenyl(thio)urea salen ligands functionalized at the 3,3'-position and an unsymmetric salen ligand with N-phenylurea at the 5-position was achieved. Subsequent metalation with nickel(II) acetate afforded the nickel(II) complexes that were investigated for their anion binding properties towards F-, Cl-, Br-, CH3COO-, and H2PO4-. Solid-state structures of the nickel(II) complexes as well as the Cl- bound dimer of the symmetric urea complex were obtained. The unusual acidity of the (thio)urea groups is reflected in the pKa-dependent anion binding behavior of the nickel(II) complexes, as elucidated by 1H and 19F Nuclear Magnetic Resonance (NMR) spectroscopy and Diffusion Ordered Spectroscopy (DOSY) experiments.

Transcending Resolution Limits in HPLC and Diffusion NMR.

Mixture analysis is crucial in many areas of chemistry, and a wide variety of separation methods are in use. A common method for physical separation is high-performance liquid chromatography (HPLC), but resolution is a problem: chemically similar species coelute. An alternative approach is diffusion-ordered NMR spectroscopy (DOSY), in which the signals of mixture components are separated according to the diffusion coefficient. Again, separation is limited if species diffuse similarly or have overlap in their NMR spectra. Using the two techniques in combination can resolve both NMR spectra and the elution profiles of individual components, even where both techniques fail when used in isolation. Recording diffusion NMR data as a function of HPLC retention time gives a three-dimensional (3D) data set that can be analyzed using multiway statistical methods. PARAFAC analysis of diffusion NMR data measured from HPLC eluate for commercial "monoacetin" (a mixture of glycerol and its mono-, di-, and triacetates) yielded fully resolved and quantitative NMR spectra and elution profiles for all four components, whereas neither HPLC nor diffusion NMR applied independently was able to resolve the components.

Helical Supramolecular Polymers Formed via Head-to-Tail Host-Guest Complexation of Chiral Bisporphyrin Monomers with Trinitrofluorenone.

The intermolecular host-guest complexation of head-to-tail monomers consisting of cleft-shaped bisporphyrin and trinitrofluorenone units connected by a chiral binaphthyl linker was employed to construct helically twisted supramolecular polymers. Results from 1H NMR, diffusion-ordered NMR spectroscopy, and viscometry experiments revealed that the supramolecular polymerization of these monomers follows a ring-chain competition mechanism. The introduction of bulky substituents at the linker significantly suppressed the formation of macrocyclic oligomers, whereas smaller alkyl chains facilitated the formation of the cyclic form. The chirally twisted structures of the supramolecular polymers were confirmed using circular dichroism spectroscopy. Atomic force microscopy revealed that the (R)- and (S)-configurations of the binaphthyl linkers induced right- and left-handed helical structures, respectively, in the supramolecular polymer chains. The absence of cooperativity in the supramolecular copolymerization of (R)- and (S)-1 a resulted in the formation of stereo-random supramolecular copolymers.

Nuclear Magnetic Resonance Spectroscopic Characterization and Determination of the New Psychoactive Substance Benzylone: Application in a Biological Fluid.

New psychoactive substances (NPS)-designed to mimic various legal or illegal substances-are an emerging worldwide health problem. Their identification and quantification in either complex seized samples or powders are critical; moreover, their determination in biological fluids is an intriguing goal in the forensic toxicology field. Synthetic cathinones are one of the most important groups among NPS. The current paper was designed as a pilot study to investigate the application of NMR techniques to identify and quantify unknown NPS compounds in deuterated dimethyl sulfoxide (DMSO-d6) and in urine using the synthetic cathinone benzylone (3,4-methylenedioxy-N-benzylcathinone, BMDP) as a pilot compound. In the first part of our study, nuclear magnetic resonance (NMR) spectroscopic characterization was performed using 1D and 2D homonuclear and heteronuclear NMR spectroscopic methods as long as diffusion ordered spectroscopy (DOSY). Following the above, the assignment of benzylone in DMSO-d6 was performed, and a distinct spectroscopic pattern was proposed. In the second part of our study, a NMR spectroscopic approach was applied for benzylone identification and quantification in a spiked with benzylone urine. Following the above, the assignment of benzylone in spiked urine was performed. A distinct pattern of the H11, H14, H15, and H8 signals on the 1H NMR spectra was observed and suggested as a "NMR spectroscopic pattern/signature" enabling the identification of benzylone moieties in urine. On the other hand, the applied NMR techniques showed low sensitivity in quantitating benzylone in spiked urine. Overall, our results are promising in using NMR for structure determination of unknown compounds in urine.

Modelling of Cetylpyridinium Chloride Availability in Complex Mixtures for the Prediction of Anti-Microbial Activity Using Diffusion Ordered Spectroscopy, Saturation Transfer Difference and 1D NMR.

Background/Objectives: A range of NMR techniques, including diffusion ordered spectroscopy (DOSY) were used to characterise complex micelles formed by the anti-microbial cationic surfactant cetylpyridium chloride and to quantify the degree of interaction between cetylpyridium chloride and hydroxyethyl cellulose in a variety of commercially relevant formulations as a model for the disk retention assay. Methods: This NMR-derived binding information was then compared with the results of formulation analysis by traditional disk retention assay (DRA) and anti-microbial activity assays to assess the suitability of these NMR techniques for the rapid identification of formulation components that could augment or retard antimicrobial activity DRA. Results: NMR showed a strong ability to predict anti-microbial activity for a diverse range of formulations containing cetylpyridinium chloride (CPC). Conclusions: This demonstrates the value of this NMR-based approach as a rapid, relatively non-destructive method for screening commercial experimental anti-microbial formulations for efficacy and further helps to understand the interplay of excipients and active ingredients.

Comparative Analysis of Bare and Quercetin-Loaded Nonionic Block Copolymer Micelles in an Artificial Gastrointestinal Medium.

Block copolymer micelles have been increasingly used for the solubilization and delivery of hydrophobic drugs. There exists a possibility of dissociation of micelles and formation of other association structures in contact with the gastrointestinal fluid. In this study, we demonstrated the effect of the fed-state intestinal fluid (FeSSIF) upon characteristics of bare and quercetin (QCT)-loaded pluronic 123 (P123) micelles. Characterizations were performed using dynamic light scattering (DLS), 1H NMR, heteronuclear single-quantum coherence (HSQC), two-dimensional 1H-1H nuclear Overhauser effect spectroscopy (2D-NOESY), and diffusion-ordered spectroscopy (DOSY). In the case of bare micelles, we found copolymer-bile salt mixed aggregates without any noticeable change in size. DOSY data revealed that lecithin formed a separate aggregate in the FeSSIF. Complete micellar solubilization of QCT could be verified by the disappearance of its proton signals. At higher dose levels, the diffusion coefficient of micelles increased in the FeSSIF. We speculate that QCT-induced hydrophobicity and availability of FeSSIF components would have driven the formation of small-sized mixed assemblies. On the contrary, the diffusion coefficient of micelles decreased with an increase in the QCT load in the medium devoid of FeSSIF components. We deduce that lack of lecithin and bile salts precluded the formation of mixed assemblies in this case, and therefore, micelles turned heavier at higher QCT loads. Such insights on self-assembled formulations can be valuable in improving their biological performance.

Near-Infinite-Chain Polymers with Ge=Ge Double Bonds.

Despite considerable interest in heteroatom-containing conjugated polymers, there are only few examples with heavier p-block elements in the conjugation path. The recently reported heavier acyclic diene metathesis (HADMET) allowed for the synthesis of a polymer containing Ge=Ge double bonds-albeit insoluble and with limited degree of polymerization. By incorporation of long alkyl chains, we now obtained soluble representatives, which exhibit degrees of polymerization near infinity according to diffusion-ordered NMR spectroscopy (DOSY) and dynamic light scattering (DLS). UV/Vis and NMR data confirm the presence of σ,π-conjugation across the silylene-phenylene linkers between the Ge=Ge double bonds. Favorable intermolecular dispersion interactions lead to ladder-like cylindrical assemblies as confirmed by X-ray diffraction (XRD), small angle X-ray scattering (SAXS) and DLS. AFM and TEM images of deposited thin films reveal lamellar ordering of extended polymer bundles.

Interrogating the photoluminescent properties of carbon dots using quantitative 13C NMR combined with systematic photobleaching

Interrogating the photoluminescent properties of carbon dots using quantitative 13C NMR combined with systematic photobleaching

Speedy Component Resolution Using Spatially Encoded Diffusion NMR Data.

Diffusion-ordered NMR spectroscopy (DOSY) is a powerful tool to analyse mixtures. Spatially encoded (SPEN) DOSY enables recording a full DOSY dataset in just one scan by performing spatial parallelisation of the gradient dimension. The simplest and most widely used approach to processing DOSY data is to fit each peak in the spectrum with a single or multiple exponential decay. However, when there is peak overlap, and/or when the diffusion decays of the contributing components are too similar, this method has limitations. Multivariate analysis of DOSY data, which is an attractive alternative, consists of decomposing the experimental data, into compound-specific diffusion decays and 1D NMR spectra. Multivariate analysis has been very successfully used for conventional DOSY data, but its use for SPEN DOSY data has only recently been reported. Here, we present a comparison, for SPEN DOSY data, of two widely used algorithms, SCORE and OUTSCORE, that aim at unmixing the spectra of overlapped species through a least square fit or a cross-talk minimisation, respectively. Data processing was performed with the General NMR Analysis Toolbox (GNAT), with custom-written code elements that now expands the capabilities, and makes it possible to import and process SPEN DOSY data. This comparison is demonstrated on three different two-component mixtures, each with different characteristics in terms of signal overlap, diffusion coefficient similarity, and component concentration.

An analytical framework to assess the chemical changes in polymer-modified bitumen upon natural and simulated ageing

An analytical framework to assess the chemical changes in polymer-modified bitumen upon natural and simulated ageing

Impacts of Small SBA-15 Mesopores on Translation and Rotational Diffusion of Benzyl Alcohol.

Small SBA-15 pores can enhance the catalytic activity of gold catalysts in the selective oxidation of benzyl alcohol reaction. The goal of this work is to probe the impact of SBA-15 pores on the translational and rotational diffusion of the reactive species (e.g., benzyl alcohol). Herein, we demonstrate the use of nuclear magnetic resonance-based diffusion-ordered spectroscopy (DOSY) and T1 relaxation techniques to measure the translational and rotational diffusion coefficients of liquid benzyl alcohol molecules in three distinct environments: bulk, pore, and near-surface. The DOSY and T1 relaxation techniques render the routine diffusion measurements for liquid molecules confined in small pores possible. Furthermore, we measure the translational and rotational diffusion coefficients of benzyl alcohol molecules in the bulk, pore, and near-surface environments at varying temperatures. These measurements are then correlated via the Arrhenius equation to determine the activation energy associated with their translational (Et) and rotational (Er) diffusion. A higher activation energy suggests a more difficult diffusion process, while a lower activation energy implies a facile diffusion process. Our findings demonstrate that the ranking of Et follows the order of bulk (difficult) > near-surface > pore (easy), whereas the ranking of Er follows the order of pore (difficult) > bulk > near-surface (easy). This result suggests that the small SBA-15 pores can facilitate the translational diffusion but hinder the rotational diffusion of benzyl alcohol molecules.

Amino acid based natural deep eutectic solvents: An efficient catalyst and solvent for N-acetyl-d-glucosamine conversion into organonitrogen chemicals

Amino acid based natural deep eutectic solvents: An efficient catalyst and solvent for N-acetyl-d-glucosamine conversion into organonitrogen chemicals

UV/Visible Diffusion-Ordered Spectroscopy: A Simultaneous Probe of Molecular Size and Electronic Absorption.

Based on concepts from nuclear magnetic resonance, we have developed UV/vis diffusion-ordered spectroscopy, which simultaneously probes the size and electronic absorption spectrum of molecules and particles. We use simple flow technology to create a step-function concentration profile inside an optical sample cell, and by measuring the time-dependent absorption spectrum in an initially solvent-filled part of the sample volume, we obtain the diffusion coefficients and UV/vis spectra of the species present in the sample solution. From these data, we construct a two-dimensional spectrum with absorption wavelength on one axis and diffusion coefficient (or equivalently, size) on the other, in which the UV/vis spectrum of a mixture with different molecular sizes is separated into the spectra of the different species, sorted by size. We demonstrate this method on mixed solutions of fluorescent dyes, biomolecules, and the UV-absorbing components of coffee, caffeine, and chlorogenic acid, all with concentrations in the μM range.

Construction of CO2‐based thermoplastic elastomer via combining aliphatic polycarbonate and polyamide: A multiblock copolymer PPC‐mb‐PA6

AbstractA CO2‐based thermoplastic elastomer, poly(propylene carbonate)‐multiblock‐polyamide6 (PPC‐mb‐PA6) copolymer, was constructed through coupling amorphous/soft PPC blocks with crystalline/hard PA6 blocks. The PPC‐mb‐PA6 copolymers with different block length pairs were designed and synthesized, and then fully characterized by structural, thermal, and mechanical analysis. The proton nuclear magnetic resonance (1H‐NMR), diffusion ordered spectroscopy (DOSY), heteronuclear multiple‐bond correlation (HMBC) and gel permeation chromatography (GPC) results confirm that the multiblock sequence structure of PPC‐mb‐PA6. The differential scanning calorimetry (DSC) tests show that all PPC‐mb‐PA6s possess melting points around 179–206°C. The thermal and mechanical analysis indicates improved service temperatures (T5% up to 270°C) and tensile strength ranging from 15.8 to 39.6 MPa with higher PA6 content. The dynamic mechanical analysis demonstrates excellent shape memory effect of PPC‐mb‐PA6 with thermal stimuli responsiveness derived from the micro phase separation between soft PPC and hard PA6 domains. And the characteristic strain fixity parameter (Rf) and deformation recovery rate (Rr) are 98% and 100%, respectively, which are comparable with other excellent shape memory polymers.

Potential of Benchtop NMR for the Determination of Polymer Molar Masses, Molar Mass Distributions, and Chemical Composition Profiles by Means of Diffusion-Ordered Spectroscopy, DOSY.

The determination of molar masses and their distributions is crucial in polymer synthesis and design. This work presents the current performance and limitations of diffusion-ordered spectroscopy (DOSY) on a low-field (benchtop) NMR spectrometer (at 90MHz) as an alternative to size exclusion chromatography (SEC) for determining diffusion coefficient distributions (DCDs) and molar mass distributions (MMDs). After optimization for narrowly distributed homopolymers, MMDs obtained with inverse Laplace transformation (ILT) and log-normal distribution are compared with average molar masses obtained with mono- and bi-exponential fits, as well as MMDs obtained from SEC. This approach enables ILT to determine DCDs and MMDs even for bimodal homopolymers with fully spectrally overlapping signals and block copolymers with various chemical compositions, for which chemical composition profiles are determined. The feasibility of low-field diffusion NMR with samples dissolved in non-deuterated solvents is further demonstrated and methods for solvent suppression are discussed.

What Is the Molecular Weight of "High" Molecular Weight Dissolved Organic Matter?

The use of ultrafiltration to isolate high molecular weight dissolved organic matter (HMWDOM) from seawater is a fundamental tool in the environmental organic chemist's toolbox. Yet, important characteristics of HMWDOM relevant to its origin and cycling, such as its molecular weight distribution, remain poorly defined. We used diffusion-ordered NMR spectroscopy coupled with mixed-mode chromatography to separate and characterize two major components of marine HMWDOM: acylpolysaccharides (APS) and high molecular weight humic substances (HS). The molecular weights (MWs) of APS and HS both fell within distinct, narrow envelopes; 2.0-16 kDa for APS and 0.9-6.5 kDa for HS. In water samples from the North Pacific Ocean the average MW of both components decreased with depth through the mesopelagic. However, the minimum MW of APS was >2 kDa, well above the molecular weight cutoff of the ultrafilter, suggesting APS removal processes below 2 kDa are highly efficient. The MW distribution of APS shows only small variations with depth, while the MW distribution of HS narrowed due to removal of HMW components. Despite the narrowing of the MW distribution, the concentration of HS did not decrease with depth between 15 and 915 m. This suggests that HMW HS produced in surface waters was either degraded into lower MW compounds without significant remineralization, or that HMW HS was remineralized but replaced by an additional source of HS in the mesopelagic ocean. Based on these results, we propose potential pathways for the production and removal of these major components of HMWDOM.

Reduced nephrotoxicity of epichlorohydrin-crosslinked β-cyclodextrin nanoparticles (βCDNPs) and its enhanced binding with hydrophobic compounds

This paper explores the development and characterization of epichlorohydrin-crosslinked β-cyclodextrin nanoparticles (βCDNPs) for drug delivery, focusing on their interaction with hydrophobic drugs and biocompatibility. We synthesized βCDNPs using β-cyclodextrin (βCD) and epichlorohydrin (ECH). Our study assessed the biocompatibility and safety of βCDNPs, particularly in avoiding nephrotoxicity commonly associated with βCD, by examining their interaction with cholesterol and conducting survival analyses in mice at various dosing concentrations. Additionally, we highlight the advantages of using diffusion-ordered NMR spectroscopy (DOSY) to determine the enhanced binding constants of βCDNPs with hydrophobic compounds, in comparison with the solubility method, Job plot analysis, and isothermal titration calorimetry (ITC). We demonstrated the enhanced binding capacity of βCDNPs compared to βCD alone and established the polymerization of βCD as a significant factor in this enhancement. Our findings suggest that βCDNPs show promise as drug delivery systems due to their improved solubility, stability, and safety profiles.

The use of carbodicarbene for bio-based polyester synthesis via ring-opening copolymerization of cyclic anhydrides and epoxides

The use of carbodicarbene for bio-based polyester synthesis via ring-opening copolymerization of cyclic anhydrides and epoxides