Solid-State Characterization of Acetylpyridine Copper Complexes for the Activation of H2 O2 in Advanced Oxidation Processes.

This work describes the synthesis of 4-(4-AcPy) and 3-acetylpyridine (3-AcPy) copper soluble complexes for the activation of hydrogen peroxide and the concomitant generation of reactive oxygen species (ROS). Given the paramagnetic effects of copper ions in the Nuclear Magnetic Resonance (NMR) lines, we aimed at demonstrating that the combination of high-resolution 2D solid-state NMR experiments, Electron Paramagnetic Resonance (EPR), single-crystal X-ray crystallography and Density Functional Theory (DFT) calculations allows a detailed study of the chemical structure of the ligands and the surrounding metal ions. The copper complexes synthesized with CuCl2 were useful for the activation of H2 O2 during which the only ROS was the hydroxyl one, as demonstrated by EPR experiments. A removal of methyl orange (MO) azo-dye higher than 85 % was achieved in 200 minutes, combining 1.7 mM of copper complexes with 60 mM of H2 O2 and 40 µM of MO.

Membrane interactions of Ocellatins. Where do antimicrobial gaps stem from?

The antimicrobial peptides Ocellatin-LB1, -LB2 and -F1, isolated from frogs, are identical from residue 1 to 22, which correspond to the -LB1 sequence, whereas -LB2 carries an extra N and -F1 additional NKL residues at their C-termini. Despite the similar sequences, previous investigations showed different spectra of activities and biophysical investigations indicated a direct correlation between both membrane-disruptive properties and activities, i.e., ocellatin-F1 > ocellatin-LB1 > ocellatin-LB2. This study presents experimental evidence as well as results from theoretical studies that contribute to a deeper understanding on how these peptides exert their antimicrobial activities and how small differences in the amino acid composition and their secondary structure can be correlated to these activity gaps. Solid-state NMR experiments allied to the simulation of anisotropic NMR parameters allowed the determination of the membrane topologies of these ocellatins. Interestingly, the extra Asn residue at the Ocellatin-LB2 C-terminus results in increased topological flexibility, which is mainly related to wobbling of the helix main axis as noticed by molecular dynamics simulations. Binding kinetics and thermodynamics of the interactions have also been assessed by Surface Plasmon Resonance and Isothermal Titration Calorimetry. Therefore, these investigations allowed to understand in atomic detail the relationships between peptide structure and membrane topology, which are in tune within the series -F1 > > -LB1 ≥ -LB2, as well as how peptide dynamics can affect membrane topology, insertion and binding.

Solid-state NMR spectroscopy for disentangling structural and motional features of lyophilized ripened cheese water-soluble extracts related to antimicrobial activity.

Present work comprises the use of different solid-state Nuclear Magnetic Resonance strategies for characterizing structural and motional aspects of the peptide matrix that compose a set of four lyophilized Mexican cheese aqueous soluble extracts, each with a controlled ripening. Heteronuclear dipolar coupling modulation schemes allowed to characterize local mobility and structural homogeneity of cheeses' peptide segments in the solid-state as a function of ripening. Results suggest that ripened samples with certain local flexibility but important structural homogeneity present efficient microbial inhibition against tested bacterial strains, whilst high local rigidity of peptides within ripened cheese soluble fractions could partially explain the observed lack of antimicrobial activity. The present study attempts to propose novel observables for lyophilized cheese water soluble extracts that could be partially associated to their ripening-dependent antimicrobial activities, whereas said observables shall contribute to the better targeting, design and optimization of solid-state natural food bio-preservatives.

Power-optimized, time-reversal pulse sequence for a robust recovery of signals from rigid segments using time domain NMR.

Time domain NMR (TD-NMR) has been widely used on the analysis of liquids or liquid components in heterogeneous materials such as food, biological tissues, synthetic and bio polymers, oil-bearing rocks, biomasses and cement-based materials. The use of TD-NMR for studying solid and soft mater has been growing in number and variety of applications, mostly for organic systems where the detection of 1H signals is highly advantageous. However, the strong 1H-1H dipolar interactions in solids make the 1H FID to decay in the same order of the dead time of most commercially available NMR probe heads. Thus, solid echoes are often used for recovering signals from solid components. In this article we reinvestigate the time-reversal solid-echo pulse sequence proposed by Rhim and Kessemeier, seeking for optimal pulse power and timing conditions that maximize its efficiency on recovering 1H signals from rigid segments. We show that under these optimized conditions, which we denote as Rhim and Kessemeier - Radiofrequency Optimized Solid-Echo (RK-ROSE), the experiment can be more efficient than its most popular counterparts Solid-Echo (SE) and mixed-Magic Sandwich Echoes (mixed-MSE). Our results also suggest that, despite the finite pulse power, with current probe technology the RK-ROSE experiment is potentially able to provide an accurate estimation of rigid components, without relying on an external calibration using multiple standard samples, as usually done in SFC analysis of the FID signal. At last, we demonstrate that RK-ROSE can be adapted as a simple filter to supress signals from mobile segments in heterogeneous materials.

Synthesis and application of sugarcane bagasse cellulose mixed esters. Part II: Removal of Co2+ and Ni2+ from single spiked aqueous solutions in batch and continuous mode.

Sugarcane bagasse cellulose succinate trimellitate (SBST) was prepared by a one-pot synthesis method. The synthesis of this novel mixed ester was investigated by a 23-factorial design. The parameters investigated were time, temperature, and succinic anhydride mole fraction (χSA). The responses evaluated were the adsorption capacity (qCo2+ and qNi2+), weight gain (wg), and number of carboxylic acid groups (nT,COOH). 13C Multiple Cross-Polarization solid-state NMR spectroscopy, 1H NMR relaxometry, and Fourier-transform infrared spectroscopy were used to elucidate the SBST structure. The best SBST reaction conditions were 100 °C, 660 min, and χSA of 0.2, which yielded SBST with a wg of 57.1%, nT,COOH of 4.48 mmol g-1, and qCo2+ and qNi2+ of 0.900 and 0.963 mmol g-1, respectively. The maximum adsorption capacities (Qmax) (pH 5.75, 25 °C) estimated by the Redlich-Peterson model for Co2+ and Ni2+ were 1.16 and 1.29 mmol g-1. The ΔadsH° values for Co2+ and Ni2+ adsorption obtained by isothermal titration calorimetry were 8.03 and 6.94 kJ mol-1. Regeneration and reuse of SBST were investigated and the best conditions applied for fixed-bed column adsorption in five consecutive cycles. SBST was fully desorbed and Qmax values for Co2+ (0.95 mmol g-1) and Ni2+ (1.02 mmol g-1) were estimated using the Bohart-Adams model.

Synthesis and application of sugarcane bagasse cellulose mixed esters. Part I: Removal of Co2+ and Ni2+ from single spiked aqueous solutions in batch mode using sugarcane bagasse cellulose succinate phthalate.

Sugarcane bagasse cellulose mixed ester succinate phthalate (SBSPh) was synthesized by a novel one-pot reaction method. The effects of temperature, time and mole fraction of succinic anhydride (χSA) on the responses weight gain (wg), number of carboxylic acid groups (nT,COOH), and adsorption capacity (q) of Co2+ and Ni2+ were evaluated by a 23 experimental design. The chemical structure of the material was elucidated by Fourier transform infrared, 13C Multiple Cross-Polarization solid-state NMR spectroscopy and 1H NMR relaxometry. The best SBSPh synthesis condition (100 °C, 11 h, χSA of 0.2) yielded a wg of 59.1%, nT,COOH of 3.41 mmol g-1, and values of qCo2+ and qNi2+ of 0.348 and 0.346 mmol g-1, respectively. The Sips model fitted better the equilibrium data, and the maximum adsorption capacities (pH 5.75 and 25 °C) estimated by this model were 0.62 and 0.53 mmol g-1 for Co2+ and Ni2+, respectively. The ΔadsH° values estimated by isothermal titration calorimetry were 8.43 and 7.79 kJ mol-1 for Co2+ and Ni2+, respectively. Desorption and re-adsorption efficiencies were evaluated by a 22 experimental design, which showed that SBSPh adsorbent can be recovered and reused without significant loss of adsorption capacity.

Succinyl-ß-cyclodextrin: Influence of the substitution degree on albendazole inclusion complexes probed by NMR.

Succinyl-ß-CD derivatives were obtained by green synthesis with degrees of substitution (DS) 1.3 and 2.9. The spray-drying technique was used to obtain albendazole (ABZ):succinyl-ß-CD inclusion complexes. Phase solubility diagrams indicated that both succinyl-ß-CD derivatives formed 1:1 molar ratio ABZ complexes, but the complex with DS 2.9 has a lower formation constant. The presence of stable inclusion complexes in aqueous solution was confirmed by NMR. For both complexes the aromatic moiety is encapsulated into the host cavity. In the solid-state, 13C and 15N NMR spectral differences between ABZ and ABZ included in spray-dried systems showed that strong structural changes occurred in the systems. At least two different ABZ amorphous species were identified based on DS. ABZ species were stable over more than six months based on spectral data. Finally, the influence of DS in the number and type of the inclusion complexes was elucidated.

Structural Elucidation of Poloxamer 237 and Poloxamer 237/Praziquantel Solid Dispersions: Impact of Poly(Vinylpyrrolidone) over Drug Recrystallization and Dissolution.

Praziquantel (PZQ) is the recommended, effective, and safe treatment against all forms of schistosomiasis. Solid dispersions (SDs) in water-soluble polymers have been reported to increase solubility and bioavailability of poorly water-soluble drugs like PZQ, generally due to the amorphous form stabilization. In this work, poloxamer (PLX) 237 and poly(vinylpyrrolidone) (PVP) K30 were evaluated as potential carriers to revert PZQ crystallization. Binary and ternary SDs were prepared by the solvent evaporation method. PZQ solubility increased similarly with PLX either as binary physical mixtures or SDs. Such unpredicted data correlated well with crystalline PZQ and PLX as detected by solid-state NMR (ssNMR) and differential scanning calorimetry in those samples. Ternary PVP/PLX/PZQ SDs showed both ssNMR broad and narrow superimposed signals, thus revealing the presence of amorphous and crystalline PZQ, respectively, and exhibited the highest PZQ dissolution efficiency (up to 82% at 180 min). SDs with PVP provided a promising way to enhance solubility and dissolution rate of PZQ since PLX alone did not prevent recrystallization of amorphous PZQ. Based on ssNMR data, novel evidences on PLX structure and molecular dynamics were also obtained. As shown for the first time using ssNMR, propylene glycol and ethylene glycol constitute the PLX amorphous and crystalline components, respectively.

Comparative studies of cutins from lime (Citrus aurantifolia) and grapefruit (Citrus paradisi) after TFA hydrolysis.

Grapefruit and lime cutins were analyzed and compared in order to obtain information about their cutin architecture. This was performed using a sequential hydrolysis, first with trifluoroacetic acid to remove most of the polysaccharides present in the cutins, followed by an alkaline hydrolysis in order to obtain the main aliphatic compounds. Analysis by CPMAS 13C NMR and ATR FT-IR of the cutins after 2.0 M TFA revealed that grapefruit cutin has independent aliphatic and polysaccharide domains while in the lime cutin these components could be homogeneously distributed. These observations were in agreement with an AFM analysis of the cutins obtained in the hydrolysis reactions. The main aliphatic compounds were detected and characterized as 16-hydroxy-10-oxo-hexadecanoic acid and 10,16-dihydroxyhexadecanoic acid. These were present in grapefruit cutin at 35.80% and 21.86% and in lime cutin at 20.44% and 40.36% respectively.

Preparation of Chloramphenicol/Amino Acid Combinations Exhibiting Enhanced Dissolution Rates and Reduced Drug-Induced Oxidative Stress.

Chloramphenicol is an old antibiotic agent that is re-emerging as a valuable alternative for the treatment of multidrug-resistant pathogens. However, it exhibits suboptimal biopharmaceutical properties and toxicity profiles. In this work, chloramphenicol was combined with essential amino acids (arginine, cysteine, glycine, and leucine) with the aim of improving its dissolution rate and reduce its toxicity towards leukocytes. The chloramphenicol/amino acid solid samples were prepared by freeze-drying method and characterized in the solid state by using Fourier transform infrared spectroscopy, powder X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and solid-state nuclear magnetic resonance. The dissolution properties, antimicrobial activity, reactive oxygen species production, and stability of the different samples were studied. The dissolution rate of all combinations was significantly increased in comparison to that of the pure active pharmaceutical ingredient. Additionally, oxidative stress production in human leukocytes caused by chloramphenicol was decreased in the chloramphenicol/amino acid combinations, while the antimicrobial activity of the antibiotic was maintained. The CAP:Leu binary combination resulted in the most outstanding solid system makes it suitable candidate for the development of pharmaceutical formulations of this antimicrobial agent with an improved safety profile.

Laccase induction by synthetic dyes in Pycnoporus sanguineus and their possible use for sugar cane bagasse delignification.

The use of synthetic dyes for laccase induction in vivo has been scarcely explored. We characterized the effect of adding different synthetic dyes to liquid cultures of Pycnoporus sanguineus on laccase production. We found that carminic acid (CA) can induce 722 % and alizarin yellow 317 % more laccase than control does, and they promoted better fungal biomass development in liquid cultures. Aniline blue and crystal violet did not show such positive effect. CA and alizarin yellow were degraded up to 95 % during P. sanguineus culturing (12 days). With this basis, CA was selected as the best inducer and used to evaluate the induction of laccase on solid-state fermentation (SSF), using sugarcane bagasse (SCB) as substrate, in an attempt to reach selective delignification. We found that laccase induction occurred in SSF, and a slight inhibition of cellulase production was observed when CA was added to the substrate; also, a transformation of SCB under SSF was followed by the 13C cross polarization magic angle spinning (CPMAS) solid-state nuclear magnetic resonance (NMR). Results showed that P. sanguineus can selectively delignify SCB, decreasing aromatic C compounds by 32.67 % in 16 days; O-alkyl C region (polysaccharides) was degraded less than 2 %; delignification values were not correlated with laccase activities. Cellulose-crystallinity index was increased by 27.24 % in absence of CA and 15.94 % when 0.01 mM of CA was added to SCB; this dye also inhibits the production of fungal biomass in SSF (measured as alkyl C gain). We conclude that CA is a good inducer of laccase in liquid media, and that P. sanguineus is a fungus with high potential for biomass delignification.

Quantification of protein secondary structure by (13)C solid-state NMR.

High-resolution (13)C solid-state NMR stands out as one of the most promising techniques to solve the structure of insoluble proteins featuring biological and technological importance. The simplest nuclear magnetic resonance (NMR) spectroscopy method to quantify the secondary structure of proteins uses the areas of carbonyl and alpha carbon peaks. The quantification obtained by fitting procedures depends on the assignment of the peaks to the structure, type of line shape, number of peaks to be used, and other parameters that are set by the operator. In this paper, we demonstrate that the analysis of (13)C NMR spectra by a pattern recognition method-based on the singular value decomposition (SVD) regression, which does not depend on the operator-shows higher correlation coefficients for α-helix and ß-sheet (0.96 and 0.91, respectively) than Fourier transform infrared spectroscopy (FTIR) method. Therefore, the use of (13)C solid-state NMR spectra and SVD is a simple and reliable method for quantifying the secondary structures of insoluble proteins in solid-state.

Combining Nuclear Magnetic Resonance Spectroscopy and Density Functional Theory Calculations to Characterize Carvedilol Polymorphs.

The experiments of carvedilol form II, form III, and hydrate by (13)C and (15)N cross-polarization magic-angle spinning (CP MAS) are reported. The GIPAW (gauge-including projector-augmented wave) method from DFT (density functional theory) calculations was used to simulate (13)C and (15)N chemical shifts. A very good agreement was found for the comparison between the global results of experimental and calculated nuclear magnetic resonance (NMR) chemical shifts for carvedilol polymorphs. This work aims a comprehensive understanding of carvedilol crystalline forms employing solution and solid-state NMR as well as DFT calculations.

Elucidating the guest-host interactions and complex formation of praziquantel and cyclodextrin derivatives by (13)C and (15)N solid-state NMR spectroscopy.

Praziquantel is the drug of choice to treat several parasitic infections including the neglected tropical disease schistosomiasis. Due to its low aqueous solubility, cyclodextrins have been tested as potential host candidates to prepare praziquantel inclusion complexes with improved solubility. For the first time, the interactions of praziquantel with ß-cyclodextrin and ß-cyclodextrin derivatives (methyl-ß-cyclodextrin and hydroxypropyl-ß-cyclodextrin) were investigated using high resolution solid-state NMR spectroscopy. The results of this work confirmed that solid-state NMR experiments provided structural characterization, demonstrating the formation of inclusion complexes most probably with PZQ adopting an anti conformation, also the most likely in amorphous raw PZQ. Further information on the interaction of praziquantel with methyl-ß-cyclodextrin was obtained from proton rotating-frame relaxation time measurements, sensitive to kilohertz-regime motions but modulated by spin-diffusion. Evidences were presented in all cases for praziquantel complexation through the aromatic ring. In addition, 1:2 drug:carrier molar ratio appears to be the most probable and therefore suitable stoichiometry to improve pharmaceutical formulations of this antischistosomal drug.

First solid-state NMR spectroscopy evaluation of complexes of benznidazole with cyclodextrin derivatives.

Complexation of benznidazole (BZL), a drug of choice for the treatment of Chagas'neglected disease, with cyclodextrin (CD) derivatives was analyzed by solid-state NMR. (13)C cross polarization/magic angle spinning spectra were recorded from BZL and from BZL:ß-CD, BZL:methyl ß-CD and BZL:hydroxypropyl ß-CD complexes, which were obtained by the solvent evaporation technique. No significant evidence was obtained on BZL inclusion complexes involving either ß-CD or hydroxypropyl ß-CD. Conversely, BZL:methyl ß-CD displayed BZL resonances characteristic of an amorphous drug and data analysis confirmed the presence of stable BZL:methyl ß-CD inclusion complexes, with benzene encapsulated into the host cavity. Further evidences on complex structure and dynamics were obtained from proton and carbon spin-lattice relaxation times in the rotating frame. These data are consistent with a common guest-host spin reservoir. The BZL interaction with methyl ß-CD provided a route to stabilize amorphous BZL. Physical mixtures with identical BZL and CD compositions were also studied for comparison.

Investigating albendazole desmotropes by solid-state NMR spectroscopy.

Characterization of the molecular structure and physicochemical solid-state properties of the solid forms of pharmaceutical compounds is a key requirement for successful commercialization as potential active ingredients in drug products. These properties can ultimately have a critical effect on the solubility and bioavailability of the final drug product. Here, the desmotropy of Albendazole forms I and II was investigated at the atomic level. Ultrafast magic angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) spectroscopy, together with powder X-ray diffraction, thermal analysis, and Fourier transform infrared spectroscopy, were performed on polycrystalline samples of the two solids in order to fully characterize and distinguish the two forms. High-resolution one-dimensional (1)H, (13)C, and (15)N together with two-dimensional (1)H/(1)H single quantum-single quantum, (1)H/(1)H single quantum-double quantum, and (1)H/(13)C chemical shift correlation solid-state NMR experiments under MAS conditions were extensively used to decipher the intramolecular and intermolecular hydrogen bonding interactions present in both solid forms. These experiments enabled the unequivocal identification of the tautomers of each desmotrope. Our results also revealed that both solid forms may be described as dimeric structures, with different intermolecular hydrogen bonds connecting the tautomers in each dimer.

insights into novel supramolecular complexes of two solid forms of norfloxacin and ß-cyclodextrin.

The solid-state properties of novel complexes of ß-cyclodextrin and two different solid forms of norfloxacin were investigated at the molecular level, in an attempt to obtain promising candidates for the preparation of alternative matrices used in pharmaceutical oral formulations. In order to evaluate the physical properties inherited from the different polymorphs, these supramolecular systems were characterized using a variety of spectroscopic techniques including natural-abundance (13) C cross-polarization magic-angle-spinning (CP-MAS) nuclear magnetic resonance (NMR), powder X-ray diffraction, and Fourier transform infrared spectroscopy. The intrinsic proton spin-lattice relaxation times detected in (13) C CP-MAS NMR spectra are used to confirm and distinguish the complex formation, as well as to provide better insights into the molecular fragments that are involved in the interaction with ß-cyclodextrin.