Two-dimensional subband Steiglitz–McBride algorithm for automatic analysis of two-dimensional nuclear magnetic resonance data

Rapid, accurate, and automatic quantitation of two-dimensional nuclear magnetic resonance(2D-NMR) data is a challenging problem. Recently, a Bayesian information criterion based subband Steiglitz–McBride algorithm has been shown to exhibit superior performance on all three fronts when applied to the quantitation of one-dimensional NMR free induction decay data. In this paper, we demonstrate that the 2D Steiglitz–McBride algorithm, in conjunction with 2D subband decomposition and the 2D Bayesian information criterion, also achieves excellent results for 2D-NMR data in terms of speed, accuracy, and automation—especially when compared in these respects to the previously published analysis techniques for 2D-NMR data.     

Note: Counterintuitive gauge-dependence of nuclear magnetic resonance shieldings for rare-gas dimers: does a natural gauge-origin for spherical atoms exist?

A counterintuitive gauge-dependence of NMR shieldings for rare-gas dimers is presented and analyzed. It is shown that common belief about the existence of a natural gauge-origin for spherical atoms with respect to NMR shielding calculations is wrong.     

Correlations between nuclear magnetic resonance spectra and crystal structure: II. The observation of 199Hg13C scalaar coupling in the solid state for some methylmercury derivatives.

Scalar coupling in the solid state between the ¹⁹⁹Hg and ¹³C nuclei is reported for the methylmercury moiety in some MeHgX compounds. Values of J(¹⁹⁹Hg¹³C) are 1445, 1807, and 1847 Hz for X  S₂COMe, O₂CMe, and Cl respectively.     

X-ray crystal structure and magnetic properties of a heteronuclear copper–neodymium unsaturated carboxylate complex

A novel heteronuclear complex, [NdCuL₅(EtOH)(phen)]₂(HL = -methylacrylic acid, phen = 1,10-phenanthroline), was prepared and its molecular structure determined by X-ray analysis. The complex is a tetranuclear molecule. Magnetic properties of the complex were also measured and are discussed.     

On-line high-performance liquid chromatography–ultraviolet–nuclear magnetic resonance method of the markers of nerve agents for verification of the Chemical Weapons Convention

This paper details an on-flow liquid chromatography–ultraviolet–nuclear magnetic resonance (LC–UV–NMR) method for the retrospective detection and identification of alkyl alkylphosphonic acids (AAPAs) and alkylphosphonic acids (APAs), the markers of the toxic nerve agents for verification of the Chemical Weapons Convention (CWC). Initially, the LC–UV–NMR parameters were optimized for benzyl derivatives of the APAs and AAPAs. The optimized parameters include stationary phase C₁₈, mobile phase methanol:water 78:22 (v/v), UV detection at 268 nm and ¹H NMR acquisition conditions. The protocol described herein allowed the detection of analytes through acquisition of high quality NMR spectra from the aqueous solution of the APAs and AAPAs with high concentrations of interfering background chemicals which have been removed by preceding sample preparation. The reported standard deviation for the quantification is related to the UV detector which showed relative standard deviations (RSDs) for quantification within ±1.1%, while lower limit of detection upto 16 μg (in μg absolute) for the NMR detector. Finally the developed LC–UV–NMR method was applied to identify the APAs and AAPAs in real water samples, consequent to solid phase extraction and derivatization. The method is fast (total experiment time ∼2 h), sensitive, rugged and efficient.     

Relaxivity studies and X-ray structure of Gd(III)-diethylenetriamine-N,N′,N″-triacetic acid-N,N″-bis(2-methoxyphenethylamide) as a potential contrast agent for magnetic resonance imaging

A new bis(amide) derivative of diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (H₅dtpa), diethylenetriamine-N,N′,N″-triacetic-N,N″-bis(2-methoxyphenethylamide) (H₃L), has been synthesized. The crystal structure of gadolinium(III) complex of H₃L ([GdL]) has been determined by X-ray crystallography. The coordination sphere of Gd(III) comprises three amine nitrogens, two amide oxygens, three carboxylic acid oxygens, and one water molecule. ¹⁷O NMR shifts showed that the [DyL] complex had one inner-sphere water molecule. Relaxivity studies with the gadolinium(III) complex showed that they associate strongly with proteins leading to a significant relaxivity enhancement.     

Host–guest interactions between dapsone and β-cyclodextrin (part I): study of the inclusion compound by nuclear magnetic resonance techniques

Dapsone (4,4′diaminodiphenylsulfone) is a very effective drug to treat leprosy and a broad range of infectious conditions such as Pneumocystis carinii pneumonia, toxoplasmosis and tuberculosis. However, the oral administration of this drug generally is related to serious side effects and treatment failures. It is believed that the inclusion compound of this drug and cyclodextrins would increase the wettability and the solubility of the encapsulated drug for a supported and gradual release, maximizing its biodisponibility over time. The encapsulation of dapsone in β-cyclodextrin was investigated by five nuclear magnetic resonance spectroscopy techniques. The data obtained for the complex in aqueous solution and in solid-state revealed a strong interaction between host and guest, showing that the drug molecule is deeply inserted in the CD cavity. The diffusion experiments (diffusion ordered spectroscopy) showed a high percentage of complexation (86 %) and that the drug molecule is preferentially interacting with the large side of the β-cyclodextrin cavity.     

Synthesis and characterization of chitosan–polyvinylpyrrolidone–bovine serum albumin-coated magnetic iron oxide nanoparticles as potential carrier for delivery of tamoxifen

The proposed study examined the preparation of chitosan (CS)–polyvinylpyrrolidone (PVP)–bovine serum albumin (BSA)-coated magnetic iron oxide (Fe₃O₄) nanoparticles (Fe₃O₄–CS–PVP–BSA) to use as potential drug delivery carriers for delivery of tamoxifen drug (TAM) . The anticancer drug selected in this study was tamoxifen which can be used for the human breast cancer treatment. These prepared nanoparticles were characterized by FTIR, XRD, SEM, AFM, TEM, CD and VSM techniques. The swelling studies have been measured at different (10, 20, 30, 40, 50%) drug loading. The mean particle size of the tamoxifen-loaded nanoparticles system (Fe₃O₄–CS–TAM, Fe₃O₄–CS–TAM–PVP and Fe₃O₄–CS–TAM–PVP–BSA) as measured by Malvern Zetasizer ranged between 350 ± 2.3 and 601 ± 1.7 nm. As well as these drug-loaded nanoparticles were positively charged. The zeta potential was in the range of 28.9 ± 3.5 and 50.8 ± 3.9 mV. The encapsulation efficiency was between 63.60 ± 2.11 and 96.45 ± 2.12%. Furthermore, in vitro release and drug loading efficiency from the nanoparticles were investigated. The cytotoxicity of prepared nanoparticles was verified by MTT assay. In vitro release studies were executed in 4.0 and 7.4 pH media to simulate the intestinal and gastric conditions and different temperature (37 and 42 °C). Hence, the prepared tamoxifen-loaded nanoparticles system (Fe₃O₄–CS–TAM, Fe₃O₄–CS–TAM–PVP and Fe₃O₄–CS–TAM–PVP–BSA) could be a promising candidate in cancer therapy.     

The nuclear magnetic resonance relaxation data analysis in solids: general R1/R1(ρ) equations and the model-free approach

The advantage of the solid state NMR for studying molecular dynamics is the capability to study slow motions without limitations: in the liquid state, if orienting media are not used, all anisotropic magnetic interactions are averaged out by fast overall Brownian tumbling of a molecule and thus investigation of slow internal conformational motions (e.g., of proteins) in solution can be conducted using only isotropic interactions. One of the main tools for obtaining amplitudes and correlation times of molecular motions in the μs time scale is measuring relaxation rate R(1)(ρ). Yet, there have been a couple of unresolved problems in the quantitative analysis of the relaxation rates. First, when the resonance offset of the spin-lock pulse is used, the spin-lock field can be oriented under an arbitrary angle in respect to B(0). Second, the spin-lock frequency can be comparable or even less than the magic angle spinning rate. Up to now, there have been no equations for R(1)(ρ) that would be applicable for any values of the spin-lock frequency, magic angle spinning rate and resonance offset of the spin-lock pulse. In this work such equations were derived for two most important relaxation mechanisms: heteronuclear dipolar coupling and chemical shift anisotropy. The validity of the equations was checked by numerical simulation of the R(1)(ρ) experiment using SPINEVOLUTION program. In addition to that, the applicability of the well-known model-free approach to the solid state NMR relaxation data analysis was considered. For the wobbling in a cone at 30° and 90° cone angles and two-site jump models, it has been demonstrated that the auto-correlation functions G(0)(t), G(1)(t), G(2)(t), corresponding to different spherical harmonics, for isotropic samples (powders, polycrystals, etc.) are practically the same regardless of the correlation time of motion. This means that the model-free approach which is widely used in liquids can be equally applied, at least assuming these two motional models, to the analysis of the solid state NMR relaxation data.     

The general concept of signal–noise separation (SNS): mathematical aspects and implementation in magnetic resonance spectroscopy

Magnetic resonance spectroscopy (MRS) and spectroscopic imaging (MRSI) are increasingly recognized as potentially key modalities in cancer diagnostics. It is, therefore, urgent to overcome the shortcomings of current applications of MRS and MRSI. We explain and substantiate why more advanced signal processing methods are needed, and demonstrate that the fast Padé transform (FPT), as the quotient of two polynomials, is the signal processing method of choice to achieve this goal. In this paper, the focus is upon distinguishing genuine from spurious (noisy and noise-like) resonances; this has been one of the thorniest challenges to MRS. The number of spurious resonances is always several times larger than the true ones. Within the FPT convergence is achieved through stabilization or constancy of the reconstructed frequencies and amplitudes. This stabilization is a veritable signature of the exact number of resonances. With any further increase of the partial signal length N, towards the full signal length N, i.e., passing the stage at which full convergence has been reached, it is found that all the fundamental frequencies and amplitudes “stay put”, i.e., they still remain constant. Moreover, machine accuracy is achieved here, proving that when the FPT is nearing convergence, it approaches straight towards the exact result with an exponential convergence rate (the spectral convergence). This proves that the FPT is an exponentially accurate representation of functions customarily encountered in spectral analysis in MRS and beyond. The mechanism by which this is achieved, i.e., the mechanism which secures the maintenance of stability of all the spectral parameters and, by implication, constancy of the estimate for the true number of resonances is provided by the so-called pole-zero cancellation, or equivalently, the Froissart doublets. This signifies that all the additional poles and zeros of the Padé spectrum will cancel each other, a remarkable feature unique to the FPT. The FPT is safe-guarded against contamination of the final results by extraneous resonances, since each pole due to spurious resonances stemming from the denominator polynomial will automatically coincide with the corresponding zero of the numerator polynomial, thus leading to the pole-zero cancellation in the polynomial quotient of the FPT. Such pole-zero cancellations can be advantageously exploited to differentiate between spurious and genuine content of the signal. Since these unphysical poles and zeros always appear as pairs in the FPT, they are viewed as doublets. Therefore, the pole-zero cancellation can be used to disentangle noise as an unphysical burden from the physical content in the considered signal, and this is the most important usage of the Froissart doublets in MRS. The general concept of signal–noise separation (SNS) is thereby introduced as a reliable procedure for separating physical from non-physical information in MRS, MRSI and beyond.     

Application of high-field proton nuclear magnetic resonance (1H-NMR) spectroscopy for the analysis of explosives and related compounds in groundwater samples – a comparison with the high-performance liquid chromatography (HPLC) method

High-field proton nuclear magnetic resonance (¹H-NMR) spectroscopy was applied to the analysis of nitroaromatics and nitramines in ammunition waste water. The ¹H-chemical shifts data of a variety of reference compounds are presented. Three groundwater samples, taken near the former ammunition plant Elsnig (Saxony), were analysed by high-performance liquid chromatography (HPLC) and by proton nuclear magnetic resonance spectroscopy. The results of HPLC and NMR analyses are compared and discussed.     

Copper(I)–creatine complex on magnetic nanoparticles as a green catalyst for N- and O-arylation in deep eutectic solvent

Immobilization of copper(I) ions on magnetic nanoparticles was performed using surface modification of Fe₃O₄ with creatine. Fe₃O₄@creatine-Cu(I) magnetic catalyst was synthesized and applied in C&bond;X cross-coupling reactions with aryl halides in a deep eutectic as a green solvent. The results indicate the Fe₃O₄@creatine-Cu(I) magnetic nanoparticles showed excellent activity and high stability. In addition, it was revealed that this catalyst can be recycled five times without significant loss in catalytic activity.     

Application of an LC–ESI–QTOF–MS method for evaluating clindamycin concentrations in plasma and prostate microdialysate of rats

Clindamycin is used for infections caused by Gram-positive and Gram-negative anaerobic pathogens and Gram-positive aerobes. Propionibacterium acnes is an important opportunistic microorganism of the human skin and is related to prostatitis. An LC–electrospray ionization–quadrupole time-of-flight–MS method was validated for determining clindamycin concentrations in plasma and prostate microdialysate. Clindamycin separation was carried out on a C₁₈ column at 0.5 mL/min. The mobile phase employed gradient elution of formic acid and methanol. A mass spectrometer was operated in positive electrospray ionization mode to monitor ion 425.1784 and 253.1152 for clindamycin and cimetidine (internal standard), respectively. Linearity was obtained at 0.5–10.0 μg/mL (plasma) and 0.05–1.0 μg/mL (microdialysate) with coefficients of determination ≥0.999. The intra- and inter-day precision (coefficient of variation - CV%) values were ≤13.83% and 12.51% for plasma, respectively, and ≤10.90% and 9.35% for microdialysate, respectively. The accuracy was between 90.82% and 108.25% for plasma, and 96.97% and 106.98% for microdialysate. The present method was fully validated and applied to investigate clindamycin concentrations in both plasma and prostate by microdialysis in Wistar rats (80 mg/kg, intravenous). Because the penetration of antibiotics into the prostate may be restricted, this method allows us to investigate the prostate concentrations of clindamycin for the first time.     

Poiseuille and extensional flow small-angle scattering for developing structure–rheology relationships in soft matter systems

As the rheoscattering community has grown, so has the breadth of experiments both in terms of materials systems, and also in terms of flow types and analysis approaches. In this review, we seek to highlight important recent developments in rheoscattering that go beyond simple shear measurements. In particular, this review will focus on Poiseuille flow and extensional flow small-angle scattering and results from recent experiments that lead to the development of structure–function relationships in a wide variety of soft materials.     

Synthesis and characterization of chitosan–poly(acrylamide–co-acrylic acid) magnetic nanocomposite hydrogels for use in catalysis

A novel hydrogel based on chitosan–poly(acrylamide-co-acrylic acid) (CAA) with different formulations were synthesized by the effect of gamma radiation. The magnetic CAA hydrogels were also synthesized and characterized by using different techniques, e.g., TEM and XRD. The prepared hydrogels and magnetic hydrogel nanocomposite were utilized for in situ cobalt nanoparticle preparation and employed as a reaction media in catalytic reduction of 2-nitrophenol (2-NP), to 2-aminophenol (2-AP). The experimental parameters that affect the reduction rates such as temperature and amount of catalyst were also, investigated.