State Nuclear Magnetic Resonance Spectroscopy Research Articles

Structural Dimerization Analysis of the G44V CrgA Mutant from the M. Tuberculosis Divisome

CrgA is a 93 amino acid residue protein with two transmembrane helices. It is thought that CrgA plays an important role in the formation of the divisome complex for Mycobacterium tuberculosis by recruiting other proteins to the divisome. Previous research has suggested that CrgA strongly interacts with FtsZ, FtsQ, CwsA, and Penicillin-binding proteins, PBPA and FtsI. In particular, CrgA is likely to play a key role in the activation and maintenance of FtsI in the divisome. While the functional role of CrgA with these other proteins is still being investigated, efforts to structurally characterize this protein has led to the discovery that CrgA appears to be functioning as a dimer based on 2-hybrid assays. Mutagenesis was conducted on the CrgA sequence, leading to the development of several new constructs. Among these, two mutants are of special interest with the mutation of Glycine-44 to Valine and Alanine-78 to Valine resulting in increased stability of the dimer. Based on SDS-PAGE gels, the G44V mutant was seen as the most dramatically stabilized dimer. Usually, glycine residues, when exposed to the fatty acyl environment of a lipid bilayer, facilitates binding. Consequently, this mutant is of particular interest, not only for its role in Mtb but also pertaining to membrane protein biophysics. This structure is now being characterized through solid state nuclear magnetic resonance (ssNMR) spectroscopy. In particular, Magic Angle Spinning (MAS) spectroscopy is being employed to measure inter-helical and inter-monomer distance restraints with the protein in liquid crystalline liposomes of POPC and POPG with differentially-13C labeled monomers. The results of these experiments will be described.

Solution state nuclear magnetic resonance spectroscopy for biological metabolism and pathway intermediate analysis

Using nuclear magnetic resonance (NMR) spectroscopy in the study of metabolism has been immensely popular in medical- and health-related research but has yet to be widely applied to more fundamental biological problems. This review provides some NMR background relevant to metabolism, describes why 1H NMR spectra are complex as well as introducing relevant terminology and definitions. The applications and practical considerations of NMR metabolic profiling and 13C NMR-based flux analyses are discussed together with the elegant 'enzyme trap' approach for identifying novel metabolic pathway intermediates. The importance of sample preparation and data analysis are also described and explained with reference to data precision and multivariate analysis to introduce researchers unfamiliar with NMR and metabolism to consider this technique for their research interests. Finally, a brief glance into the future suggests NMR-based metabolism has room to expand in the 21st century through new isotope labels, and NMR technologies and methodologies.

Strong Impact of the Oxygen Content in Na3V2(PO4)2F3–yOy (0 ≤ y ≤ 0.5) on Its Structural and Electrochemical Properties

Polyanionic materials such as Na3V2(PO4)2F3–yOy (0 ≤ y ≤ 2) are of high interest as positive electrode for Na-ion batteries since they offer competitive electrochemical performances compared to sodiated transition metal oxides. The composition Na3V2(PO4)2F3 (y = 0) has the highest theoretical energy density among the series, but surprisingly a lot of discrepancies are reported throughout the literature considering its structure and its electrochemical properties. We will show that most of the compounds reported as being Na3VIII2(PO4)2F3 are in fact slightly oxidized due to synthesis conditions resulting in a partial oxygen substitution for fluorine. To get an in-depth understanding of this system, a series of compositions Na3V2(PO4)2F3–yOy (0 ≤ y ≤ 0.5, i.e., near the fluorine-rich composition) was synthesized and characterized combining synchrotron X-ray diffraction, X-ray absorption spectroscopy, solid state nuclear magnetic resonance spectroscopy, and galvanostatic electrochemical tests. The structural...

Influence of ionic liquid on the polymer–filler coupling and mechanical properties of nano‐silica filled elastomer

ABSTRACTThe natural rubber (NR) nanocomposites were fabricated by filling ionic liquid (1‐allyl‐3‐methyl‐imidazolium chloride, AMI) modified nano‐silica (nSiO2) in NR matrix through mechanical mixing and followed by a cure process. Based on the measurements of differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), solid state nuclear magnetic resonance spectroscopy, and Raman spectroscopy, it was proved that AMI could interact with nSiO2 through hydrogen bonds. With the increase of AMI content, the curing rate of nSiO2/NR increased. The results of bound rubber and dynamic mechanical properties showed that polymer–filler interaction increased with the modification of nSiO2. Morphology studies revealed that modification of nSiO2 resulted in a homogenous dispersion of nSiO2 in NR matrix. AMI modified nSiO2 could greatly enhance the tensile strength and tear strength of nSiO2/NR nanocomposites. Compared to unmodified nSiO2/NR nanocomposite, the tensile strength of AMI modified nSiO2/NR nanocomposite increased by 102%. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44478.

Molecular motifs for additives that retard PEO crystallization

We investigate the influence of several bifunctional phenol additives (resorcinol: RES, hydroquinone: HYD, p-hydroxybenzoic acid: PHBA, and p-nitrophenol: PNP) on the crystallization of matrix polymer, polyethyleneoxide. We employ solid state Nuclear Magnetic Resonance spectroscopy (NMR), Differential Scanning Calorimetry (DSC), optical microscopy, and Small Angle X-ray Scattering (SAXS) to investigate crystallization of the additivated PEO and compare with Density Functional Theory (DFT) calculations of additive-PEO interactions. Additive-polymer interactions are a function of the functional groups on the additive. Temperature-dependent spherulitic growth rate measurements from optical microscopy and SAXS lamellar long spacings indicate a distinct trend in the effect of additives on PEO crystallization. Change in PEO crystallization is most pronounced with PNP, followed by PHBA and finally RES and HYD. This trend correlates qualitatively with the binding energies of additive-PEO interactions from DFT studies. Our results suggest that DFT calculations might be a useful screening tool to evaluate the influence of additives on polymer crystallization. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

Solvent effects in the development of a drug delivery system for 5-fluorouracil using magnetic mesoporous silica nanoparticles

5-Fluorouracil (5-FU), an anticancer drug, was loaded into magnetic iron oxide/mesoporous silica nanocomposites (m-MCM-41) with and without aminopropyl functionalization using three different solvents (water, water/acetone, dimethyl sulfoxide). The parent and the drug-loaded samples were characterized using physicochemical techniques, such as powder X-Ray diffraction (pXRD), nitrogen adsorption-desorption isotherms and thermogravimetric analysis (TGA). Fourier Transform Infrared spectroscopy (FT-IR) and solid state Nuclear Magnetic Resonance (ssNMR) spectroscopy techniques were used to obtain molecular level insights into the loading of 5-FU into m-MCM-41 with different solvents and surface functionalization. The loading and release characteristics of 5-FU from m-MCM-41 depended on the solvent polarity and the surface functionalization of the host. The chemical insights provided by this study can be used in the future design and development of magnetic mesoporous silica nanocomposites for theranostic applications.

Pleurotus ostreatus decreases cornstalk lignin content, potentially improving its suitability for animal feed.

The capacity of Pleurotus ostreatus to degrade lignin was investigated in the fermentation of cornstalk. Cornstalk was incubated with P. ostreatus for 30 days, and acid-soluble and acid-insoluble lignins were assessed. The microscopic structure of cornstalk samples was studied by scanning electron microscopy (SEM), and spectroscopic characteristics were measured by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and solid state nuclear magnetic resonance (13 C NMR) spectroscopy. During fermentation of cornstalk, the proportion of acid-soluble lignin did not vary significantly (P > 0.05), but that of acid-insoluble lignin decreased gradually from 17.8% on day 0 to 7.6% on day 30 (P < 0.01). SEM revealed that the surface of cornstalk was gradually damaged with cavities increasing in number and size, forming a quasi-network structure. Crystallinity decreased from 35.0 on day 0 to 15.2 on day 30. FTIR and cross-polarization magic angle spinning (CPMAS) 13 C NMR spectra showed that the intensity of the peaks corresponding to lignin, cellulose and hemicellulose also decreased gradually over 30 days. Cornstalk can be effectively degraded by P. ostreatus within 30 days. Pleurotus ostreatus decreases cornstalk lignin content, potentially improving its suitability for animal feed. © 2016 Society of Chemical Industry.

Evaluation of network parameters and drug release behavior of gum acacia-crosslinked-carbopol hydrogel wound dressings

Present article discusses the synthesis, characterization, biodegradation, network parameter and drug release of gum acacia-crosslinked-carbopol hydrogel wound dressing. Polymers have been characterized by 13C solid state nuclear magnetic resonance spectroscopy, elemental analysis, cryo-scanning electron microscopy, atomic force microscopy, thermogravimetric analysis, differential thermal analysis, differential thermogravimetry, and differential scanning calorimetry studies. Network parameters of hydrogel wound dressings such as polymer volume fraction in the swollen state φ, Flory–Huggins interaction parameter χ, molecular weight of the polymer chain between two neighboring cross links Mc, crosslink density ρ and the corresponding mesh size ξ have also been determined. Different in vitro release kinetic models (zero order, first order, Higuchi square root law, Korsmeyer-Peppas, and Hixson-Crowell cube root models) have been applied on the drug release profile. The release of antibiotic drug moxifloxacin from the drug loaded hydrogel matrix occurred through non-Fickian diffusion mechanism and release profile best fitted in the Korsmeyer-Peppas model. Semi-contact mode atomic force microscopic imaging showed that rough surface with root mean square roughness 82.868 nm of the polymer films.

Poly(Vinyl Alcohol) (Core)-Polyurethane (Shell) Nanofibers Produced by Coaxial Electrospinning

Nanoweb fabricated by electrospinning has a large specific area and a small pore size which can be controlled through a spinning process to enable a strong adsorption and selective permeability. It is required to produce nanofiber of different polymer mixture with a limited miscibility for improvement of physical, chemical, or biological properties. In this study, poly (vinyl alcohol) (PVA)/polyurethane (PU) nanofibers were produced by coaxial electrospinning. PVA (core)/PU (shell) nanofibers were defect-free and had a uniform thickness. The pseudo core/shell structure of PVA/PU nanofibers was confirmed by transmission electron microscopy. The presence of PVA and PU in the nanofibers was identified by 13C solid state nuclear magnetic resonance spectroscopy, fourier transform infrared spectroscopy, and X-ray diffraction analysis. Water contact angle was reduced by incorporation of PVA in a core of PU nanofiber. For variety of biomedical applications, bioactive substances such as antibiotics and proteins can be incorporated in a core of hydrophobic PU nanofiber by coaxial electrospinning of water-soluble polymer/bioactive substance mixture.

Radiation formation of functionalized polysaccharide-protein based skin mimicking semi- inter penetrating network for biomedical application

Radiation treatment of chitosan, gelatin, polyvinyl alcohol (PVA) and polyacrylamide [poly(AAm)] will form the sterile hydrogel wound dressings which can mimic the artificial skin function in wound therapy. These polymers have been characterized by cryo-scanning electron micrographs (cryo-SEMs), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR) and 13C solid state nuclear magnetic resonance (NMR) spectroscopy and swelling studies. Some important properties of hydrogel wound dressings like drug delivery, blood compatibility, wound fluid absorption, antioxidant activity, oxygen permeability, water vapour permeability, microbial penetration, mucoadhesion and mechanical properties have also been determined. The release profile of moxifloxacin from the polyacrylamide functionalized chitosan-gelatin matrix followed Fickian diffusion mechanism and release profile best fitted in Korsmeyer-Peppas kinetic model. The hydrogel films are permeable to O2 and H2O vapour and impermeable to microbes in open environment and showed high wound absorption, good mucoadhesion and antioxidant activity. Beside release of antibiotic, the inherent wound healing potential of chitosan, adhesion capacity of gelatin, film forming ability of PVA and wound fluid absorption of poly(AAm), may enhance wound healing potential of these hydrogel wound dressings.

Investigation of Ester- and Amide-Linker-Based Porous Organic Polymers for Carbon Dioxide Capture and Separation at Wide Temperatures and Pressures.

Organic compounds, such as covalent organic framework, metal-organic frameworks, and covalent organic polymers have been under investigation to replace the well-known amine-based solvent sorption technology of CO2 and introduce the most efficient and economical material for CO2 capture and storage. Various organic polymers having different function groups have been under investigation both for low and high pressure CO2 capture. However, search for a promising material to overcome the issues of lower selectivity, less capturing capacity, lower mass transfer coefficient and instability in materials performance at high pressure and various temperatures is still ongoing process. Herein, we report synthesis of six covalent organic polymers (COPs) and their CO2, N2, and CH4 adsorption performances at low and high pressures up to 200 bar. All the presented COPs materials were characterized by using elemental analysis method, Fourier transform infrared spectroscopy (FTIR) and solid state nuclear magnetic resonance (NMR) spectroscopy techniques. Physical properties of the materials such as surface areas, pore volume and pore size were determined through BET analysis at 77 K. All the materials were tested for CO2, CH4, and N2 adsorption using state of the art equipment, magnetic suspension balance (MSB). Results indicated that, amide based material i.e. COP-33 has the largest pore volume of 0.2 cm(2)/g which can capture up to the maximum of 1.44 mmol/g CO2 at room temperature and at pressure of 10 bar. However, at higher pressure of 200 bar and 308 K ester-based compound, that is, COP-35 adsorb as large as 144 mmol/g, which is the largest gas capturing capacity of any COPs material obtained so far. Importantly, single gas measurement based selectivity of COP-33 was comparatively better than all other COPs materials at all condition. Nevertheless, overall performance of COP-35 rate of adsorption and heat of adsorption has indicated that this material can be considered for further exploration as efficient and cheaply available solid sorbent material for CO2 capture and separation.

Exploring thiol-yne based monomers as low cytotoxic building blocks for radical photopolymerization

The last decade has seen a remarkable interest in the development of biocompatible monomers for the realization of patient specific medical devices by means of UV-based additive manufacturing technologies. This contribution deals with the synthesis and investigation of novel thiol-yne based monomers with a focus on their biocompatibility and also the mechanical properties in their cured state. It could be successfully shown that propargyl and but-1-yne-4-yl ether derivatives have a significant lower cytotoxicity than the corresponding (meth)acrylates with similar backbones. Together with appropriate thiol monomers, these compounds show reactivities in the range of (meth)acrylates and almost quantitative triple bond conversions. A particular highlight is the investigation of the network properties of photo cured alkynyl ether/thiol resins by means of low field solid state nuclear magnetic resonance spectroscopy. Additionally, dynamic mechanical analysis of those polymers revealed that monomers containing rigid backbones lead to moduli and glass transition temperatures (Tg's), sufficiently high for the fabrication of medical devices by UV based additive manufacturing methods. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3484–3494

Design of Phosphonated Imidazolium-Based Ionic Liquids Grafted on γ-Alumina: Potential Model for Hybrid Membranes.

Imidazolium bromide-based ionic liquids bearing phosphonyl groups on the cationic part were synthesized and grafted on γ-alumina (γ-Al2O3) powders. These powders were prepared as companion samples of conventional mesoporous γ-alumina membranes, in order to favor a possible transfer of the results to supported membrane materials, which could be used for CO2 separation applications. Effective grafting was demonstrated using energy dispersive X-ray spectrometry (EDX), N2 adsorption measurements, fourier transform infrared spectroscopy (FTIR), and special attention was paid to 31P and 13C solid state nuclear magnetic resonance spectroscopy (NMR).

Decomposition Dynamics and Changes in Chemical Composition of Wheat Straw Residue under Anaerobic and Aerobic Conditions.

Soil aeration is a crucial factor that regulates crop residue decomposition, and the chemical composition of decomposing crop residues may change the forms and availability of soil nutrients, such as N and P. However, to date, differences in the chemical composition of crop straw residues after incorporation into soil and during its decomposition under anaerobic vs. aerobic conditions have not been well documented. The objective of the present study was to assess changes in the C-containing functional groups of wheat straw residue during its decomposition in anaerobic and aerobic environments. A 12-month incubation experiment was carried out to investigate the temporal variations of mass, carbon, and nitrogen loss, as well as changes in the chemical composition of wheat (Triticum aestivum L) straw residues under anaerobic and aerobic conditions by measuring C-containing functional groups using solid state nuclear magnetic resonance (NMR) spectroscopy. The residual mass, carbon content, and nitrogen content of the straw residue sharply declined during the initial 3 months, and then slowly decreased during the last incubation period from 3 to 12 months. The decomposition rate constant (k) for mass loss under aerobic conditions (0.022 d-1) was higher than that under anaerobic conditions (0.014 d-1). The residual mass percentage of cellulose and hemicellulose in the wheat straw gradually declined, whereas that of lignin gradually increased during the entire 12-month incubation period. The NMR spectra of C-containing functional groups in the decomposing straw under both aerobic and anaerobic conditions were similar at the beginning of the incubation as well as at 1 month, 6 months, and 12 months. The main alterations in C-containing functional groups during the decomposition of wheat straw were a decrease in the relative abundances of O-alkyl C and an increase in the relative abundances of alkyl C, aromatic C and COO/N-C = O functional groups. The NMR signals of alkyl C and aromatic C in decomposing wheat straw residues under anaerobic condition were higher than those under aerobic conditions. The higher mass percentages of lignin and the higher signals of aromatic C and alkyl C functional groups in decomposing wheat residues under anaerobic conditions than under aerobic conditions were due to the slower decomposition rates of aryl C and alkyl C in wheat straw residues under anaerobic conditions.

Biochar applications and modern techniques for characterization

Biochar simply is the material produced when biomass undergoes any chemical processes under the conditions of pyrolysis. The variety of biomasses, including wood waste, agricultural crop leftover, organic waste, animal manure, and forestry residues, have been considered as raw material to produce biochar. Biochar is widely used for generation of heat and power and an addition to soils, in which it serves as a fertilizer and carbon sequestration agent. Also in the form of being activated, it finds significant role for various adsorption applications. The most beneficial use of a given char depends on its physical and chemical characteristics, even though the relationship of char properties to these applications is not well defined. Various widely used modern analytical techniques, which are applicable and crucial for biochar characterization, have been reviewed in the present work, such as solid state nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-rays photoelectron spectroscopy, X-rays diffraction, thermogravimetric analysis, near edge X-rays absorption fine structure spectroscopy, and gas chromatography-mass spectroscopy. Utilization of these modern techniques provides the quantitative as well as qualitative information, i.e., determining the sizes, shapes, and physicochemical characteristics of biochar, which is reliable to track changes in the carbon arrangement over reaction time and temperature, and will be useful for efficient production of biochar and application. It provides the useful information for the researchers in this area and is beneficial not only for the effective biochar production, but also for potential utilization/application, and not only for environment but also for agriculture.

Fluorinated polyhedral oligomeric silsesquioxane nanoparticles to boost the dirt repellence of high pressure laminates

High pressure laminates (HPLs) are attractive, resistant to environmental effects and good cost-benefit decorative surface composite materials whose properties can be tailored to meet specific market demands. In this study, the substantial improvement of dirt repellence of HPLs with simultaneous enhancement of its abrasion resistance was achieved for the first time by incorporating nonafluorohexyl polyhedral oligomeric silsesquioxane (FH-POSS) nanoparticles (up to 1% w/w) into a melamine–formaldehyde (MF) resin matrix used to impregnate decorative and overlay papers required for HPLs production. FH-POSS particles were synthesized and thoroughly characterized by 13C and 29Si solid state nuclear magnetic resonance (NMR) spectroscopy, and by X-ray diffraction (XRD) analysis. Fluoroalkyl moieties in FH-POSS afforded increased hydrophobicity to HPLs thus providing improved surface cleanability, whereas abrasion resistance was improved due to the robust silica core of the POSS particles. Hydrophobicity of HPLs doped with FH-POSS increased with time, after resin curing, and this was attributed to migration of FH-POSS nanoparticles to the composite surface.

Chemistry of developing bordered-pit rims in balsam-fir trees

Rims of bordered pits form on the primary walls of radially enlarged cambial derivatives prior to the onset of general secondary-wall formation. A recent report (Botany, 2014, 92(7): 495–511) raised the possibility that the chemical composition of the rim might be different from that of the secondary wall. To investigate this, early-stage nonfluorescent and late-stage autofluorescent rims were separated from cambial derivatives of Abies balsamea (L.) Mill. and purified to homogeneity by density-gradient centrifugation. Solid state nuclear magnetic resonance spectroscopy, Raman microspectroscopy, combined gas chromatography – mass spectroscopy, enzyme digestion, and chemical resilience data support the interpretation that cellulose alone is the microfibrillar polysaccharide of nonfluorescent early-stage rims. A lignin is additionally present in late-stage rims, and it evidently bonds with cellulose because rims are extraordinarily resistant to hydrolysis by either enzymes or strong acid.

Editorial: Optogenetic Tools in the Molecular Spotlight.

Editorial: Optogenetic Tools in the Molecular Spotlight.

Mechanistic Insights into the Role of Water in Backbone Dynamics of Native Collagen Protein by Natural Abundance 15N NMR Spectroscopy

Collagen being the most abundant animal protein is an integral component of muscle, connective tissues, cartilage, and bones, having function to provide strength, load bearing, and flexibility to organisms. The structural and functional role of water mediated hydrogen bonding network of collagen has been debated. We present here a solid–state nuclear magnetic resonance (ssNMR) spectroscopy method to observe water dependent backbone dynamics of collagen protein in its absolute native environment inside bone. The load bearing function of collagen is directly dependent on its backbone dynamics. The picoseconds backbone dynamics has been measured by relaxation rate measurement (R1) of natural isotopic abundance 15N (∼0.37%) resonance. The sensitivity of natural abundance 15N ssNMR spectrum is enhanced by paramagnetic doping of copper-ethylenediaminetetraacetic acid (Cu (II) EDTA) inside bone matrix. Exclusive backbone resonances originating from proline/hydroxyproline (Pro/Hyp) and glycine (Gly) resonances ar...

Synthesis of Zeolites from A Low-Quality Colombian Kaolin

AbstractAt present, no production of zeolites is ongoing in Colombia; thus, because of the high demand in the industrial sector, ~2500 tons is imported annually from other countries such as Cuba, Ecuador, Mexico, and the United States. In order minimize the need for these costly imports, the present study sought to evaluate the viability of producing low-silica zeolites through the hydrothermal synthesis of a Colombian kaolin, which contains quartz (40%) and iron-oxide impurities. The kaolin was subjected to a milling process to reduce the particle size to the order of 11 μm, and was heat treated to transform it to metakaolin. Optimization of the synthesis variables (Na2O/SiO2 and H2O/Al2O3 ratios, time, and temperature) was accomplished by applying an experimental design based on the ‘Response Surface Methodology’ technique. The degree of crystallinity and the cation exchange capacity (CEC) were used as response variables. The CEC was determined from the NTC 5167 standard. In addition, the mineralogical composition and the zeolite microstructure were evaluated using techniques such as scanning electron microscopy, X-ray diffraction, and solid state nuclear magnetic resonance spectroscopy. The results indicated that synthetic type A zeolites with a CEC value of 442 cmol(+)/kg can be obtained from the Colombian kaolin, with the following optimal processing conditions: Na2O/SiO2 molar ratio of 2.7, H2O/Al2O3 molar ratio of 150, temperature = 66°C, and processing time = 8 h. Note that this value (442 cmol(+)/kg) is greater than that reported for an imported commercial zeolite (408 cmol(+)/kg) of the same type, which is currently being used in industry in Colombia. The nationwide availability of the raw material and the quality of the final product present opportunities to make this material available to the Colombian market.