Variable-Amplitude Cross-Polarization MAS NMR

Peersen, Olve B.; Wu, Xiaoling; Kustanovich, I. M.; Smith, Steven O.

doi:10.1006/jmra.1993.1231

Cited by 379 publications

(310 citation statements)

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“…Highresolution, solid-state 13 C NMR spectra were collected at 4.7T with cross-polarization (CP) and magic angle spinning (MAS) in a Bruker Avance 200 MHz spectrometer. Variable amplitude cross-polarization was used to minimize the intensity variations of the non-protonated aromatic carbons that are sensitive to Hartmann-Hahn mismatch at higher MAS rotation rates (Peersen et al, 1993). 1 H and 13 C fields were matched at 53.6 kHz and a 1 dB ramp was applied to the proton radio frequency field during the matching period.…”

Section: Cellulose Crystallinity Measurement By Solid State Nmrmentioning

confidence: 99%

Cellulase digestibility of pretreated biomass is limited by cellulose accessibility

Jeoh¹,

Ishizawa²,

Davis³

et al. 2007

Biotech & Bioengineering

460

321

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Attempts to correlate the physical and chemical properties of biomass to its susceptibility to enzyme digestion are often inconclusive or contradictory depending on variables such as the type of substrate, the pretreatment conditions and measurement techniques. In this study, we present a direct method for measuring the key factors governing cellulose digestibility in a biomass sample by directly probing cellulase binding and activity using a purified cellobiohydrolase (Cel7A) from Trichoderma reesei. Fluorescence-labeled T. reesei Cel7A was used to assay pretreated corn stover samples and pure cellulosic substrates to identify barriers to accessibility by this important component of cellulase preparations. The results showed cellulose conversion improved when T. reesei Cel7A bound in higher concentrations, indicating that the enzyme had greater access to the substrate. Factors such as the pretreatment severity, drying after pretreatment, and cellulose crystallinity were found to directly impact enzyme accessibility. This study provides direct evidence to support the notion that the best pretreatment schemes for rendering biomass more digestible to cellobiohydrolase enzymes are those that improve access to the cellulose in biomass cell walls, as well as those able to reduce the crystallinity of cell wall cellulose.

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Section: Cellulose Crystallinity Measurement By Solid State Nmrmentioning

confidence: 99%

Cellulase digestibility of pretreated biomass is limited by cellulose accessibility

Jeoh¹,

Ishizawa²,

Davis³

et al. 2007

Biotech & Bioengineering

460

321

View full text Add to dashboard Cite

show abstract

“…The cross polarization magic angle spinning (CPMAS) technique (Schaefer and Stejskal, 1976) was applied with a spinning speed of 6.8 kHz and a pulse delay of 1 s. Spectra were obtained after accumulation of 40,000 to 80,000 scans. A ramped 1 H-pulse was used during the contact time of 1 ms to circumvent spin modulation during the Hartmann-Hahn contact (Cook et al, 1996;Peersen et al, 1993). Line broadenings between 10 and 100 Hz were applied.…”

Section: C Nmr Spectrometrymentioning

confidence: 99%

Chemical and spectroscopic characterization of marine dissolved organic matter isolated using coupled reverse osmosis–electrodialysis

Koprivnjak

Pfromm

Ingall

et al. 2009

Geochimica et Cosmochimica Acta

100

117

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The coupled reverse osmosis-electrodialysis (RO/ED) method was used to isolate dissolved organic matter (DOM) from 16 seawater samples. The average yield of organic carbon was 75 ± 12%, which is consistently greater than the yields of organic carbon that have been commonly achieved using XAD resins, C 18 adsorbents, and cross-flow ultrafiltration. UV-visible absorbance spectra and molar C/N ratios of isolated samples were consistent with the corresponding properties of DOM in the original seawater samples, indicating that DOM samples can be isolated using the coupled RO/ED method without any bias for/against these two properties. Five of the samples were desalted sufficiently that reliable measurements of their 13 C and 1 H NMR spectra and their Fourier transform ion cyclotron resonance (FTICR) mass spectra could be obtained. The 13 C and 1 H NMR spectra of RO/ED samples differed distinctly from those of samples that have been isolated in much lower yields by other methods. In particular, RO/ED samples contained a relatively lower proportion of carbohydrate carbon and a relatively greater proportion of alkyl carbon than samples that have been isolated using cross-flow ultrafiltration. From the FTICR mass spectra of RO/ED samples, samples from the open ocean contained a much lower proportion of unsaturated compounds and a much higher proportion of fatty acids than coastal samples.

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“…All 13 C spectra were collected using a Chemagnetics CMX-300 spectrometer using variable amplitude cross-polarization (VACP) [24], magic-angle spinning (MAS) [25], and two pulse phase modulation (TPPM) decoupling [26]. Samples were packed into 7 mm o.d.…”

Section: Solid-state Nmr Spectroscopymentioning

confidence: 99%

NanoCipro encapsulation in monodisperse large porous PLGA microparticles

Arnold

Gorman

Schieber

et al. 2007

Journal of Controlled Release

117

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Pulmonary drug delivery of controlled release formulations may provide an effective adjunct approach to orally delivered antibiotics for clearing persistent lung infections. Dry powder formulations for this indication should possess characteristics including; effective deposition to infected lung compartments, persistence at the infection site, and steady release of antibiotic. Large porous particles (∼10-15 μm) have demonstrated effective lung deposition and enhanced lung residence as a result of their large diameter and reduced clearance by macrophages in comparison to small microparticles (∼1-5 μm). In this report, Precision Particle Fabrication technology was used to create monodisperse large porous particles of poly(D,L-lactic-co-glycolic acid) (PLGA) utilizing oils as extractable porogens. After extraction, the resulting large porous PLGA particles exhibited a low density and a web-like or hollow interior depending on porogen concentration and type, respectively. Ciprofloxacin nanoparticles (nanoCipro) created by homogenization in dichloromethane, possessed a polymorph with a decreased melting temperature. Encapsulating nanoCipro in large porous PLGA particles resulted in a steady release of ciprofloxacin that was extended for larger particle diameters and for the solid particle morphology in comparison to large porous particles. The encapsulation efficiency of nanoCipro was quite low and factors impacting the entrapment of nanoparticles during particle formation were elucidated. A dry powder formulation with the potential to control particle deposition and sustain release to the lung was developed and insight to improve nanoparticle encapsulation is discussed.

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Variable-Amplitude Cross-Polarization MAS NMR

Cited by 379 publications

References 0 publications

Cellulase digestibility of pretreated biomass is limited by cellulose accessibility

Cellulase digestibility of pretreated biomass is limited by cellulose accessibility

Chemical and spectroscopic characterization of marine dissolved organic matter isolated using coupled reverse osmosis–electrodialysis

NanoCipro encapsulation in monodisperse large porous PLGA microparticles

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