5 research outputs found
Honeycomb Films of Cellulose Azide: Molecular Structure and Formation of Porous Films
Development of value-added micropatterned porous materials
from
naturally abundant polymers, such as cellulose, are of growing interest.
In this paper, regioselectively modified amphiphilic cellulose azide,
3-<i>O</i>-azidopropoxypoly(ethylene glycol)-2,6-di-<i>O</i>-thexyldimethylsilyl cellulose, with different degrees
of substitution (DS) and degrees of polymerization (DP) of the poly(ethylene
glycol) (PEG) side chain, was synthesized and employed in the formation
of honeycomb-patterned films. With the variation of the DP and/or
DS, the amphiphilicity of the polymer and the pore size of the formed
films changed accordingly. It was found that amphiphilicity of the
cellulose azide played a significant role in the formation of honeycomb
films. Balanced amphiphilicity was of particular importance in the
formation of uniform honeycomb films. Via the Cu<sup>I</sup>-catalyzed
alkyne–azide [2 + 3] cycloaddition reaction, fluorescent avidin
and quantum dots were attached to the films. By means of confocal
microscopy, it was confirmed that the functional azido group was preferentially
allocated inside the pores. This provides a platform for the development
of advanced honeycomb materials with site-specific functionalities,
such as biosensors
Preparation and Characterization of Kraft Lignin-Based Moisture-Responsive Films with Reversible Shape-Change Capability
Preparation of moisture-responsive
Kraft lignin-based materials
by electrospinning blends of Kraft lignin fractions with different
physical properties is presented. The differences in thermal mobility
between lignin fractions are shown to influence the degree of interfiber
fusion occurring during oxidative thermostabilization of electrospun
nonwoven fabrics, resulting in different material morphologies including
submicrometer fibers, bonded nonwovens, porous films, and smooth films.
The relative amount of different lignin fractions and degree of fiber
flow and fiber fusion is shown to influence the tendency for the electrospun
materials to be transformed into moisture-responsive materials capable
of reversible changes in shape. Material characterization by scanning
electron microscopy and atomic force microscopy as well characterization
of the chemical and physical properties of Kraft lignin fractions
by dynamic rheology, <sup>1</sup>H and <sup>13</sup>C NMR, and gel
permeation chromatography combined with multiangle laser light scattering
are presented. A proposed mechanism underlying moisture-responsiveness,
shape change, and shape recovery is discussed based on the differences
in chemical structure and physical properties of Kraft lignin fractions
Design of Functionalized Cellulosic Honeycomb Films: Site-Specific Biomolecule Modification via “Click Chemistry”
Value-added materials from naturally abundant polymers
such as
cellulose are of significant importance. In particular, cellulosic
open-framework structures with controlled chemical functionality of
the internal surface have great potential in many biosensor applications.
Although various cellulose derivatives can form porous honeycomb structured
materials, solubility issues and problems with film formation exist.
To address this, we have generated robust cellulosic open-framework
structures that can be post-functionalized through site-specific modification.
Regioselectively modified amphiphilic cellulose azides, 3-<i>O</i>-azidopropoxypoly(ethylene glycol)-2,6-di-<i>O</i>-thexyldimethylsilyl cellulosics, were synthesized, and honeycomb-patterned
films were readily produced by the simple breath figures method. Changing
the degree of polymerization (DP) of the pendent ethylene glycol (EG<sub>DP</sub>) groups from 22 to 4 increased the corresponding honeycomb
film pore diameters from ∼1.2 to ∼2.6 μm, enabling
the potential tuning of pore size. Moreover, these novel azido-functionalized
honeycomb films were easily functionalized using Cu(I)-catalyzed alkyne–azide
[2 + 3] cycloaddition reaction; biotin was “clicked”
onto the azide functionalized cellulosic honeycomb films without any
effect to the film structure. These results indicate this system may
serve as a platform for the design and development of biosensors
Characterization of Fractions Obtained from Two Industrial Softwood Kraft Lignins
With increasing interest in using
lignin as an alternative material
to petroleum-based chemicals (e.g., in the manufacture of carbon fibers
or adhesives), it is becoming important to understand what properties
of lignin are required to impart key features in the final product.
Commercial lignins are complex, heterogeneous, macromolecular mixtures.
To obtain maximum value, lignins will require classification and possibly
fractionation or modification to improve properties and enable their
utilization in high-value applications. To this end, the physicochemical
properties of fractions derived from two industrial softwood Kraft
lignins (New Bern Mill, Weyerhaeuser, U.S.A., and Backhammar Mill
in Kristinehamn, Sweden) have been determined and compared to previously
published data on commercially available Indulin AT lignin from MeadWestvaco., The fractions were obtained by successive extraction with organic
solvents and analyzed using a range of techniques (e.g., DSC, <sup>13</sup>C NMR, <sup>31</sup>P NMR). The results showed that these
industrial softwood Kraft lignins varied significantly in both the
amounts of the various fractions and in the properties of the analogous
fractions. These differences emphasize the issues industry faces in
the utilization of industrial lignins for high-value applications
where minor inconsistencies between lignin sources could pose major
technical challenges
Improved Manganese-Oxidizing Activity of DypB, a Peroxidase from a Lignolytic Bacterium
DypB, a dye-decolorizing peroxidase from the lignolytic
soil bacterium <i>Rhodococcus jostii</i> RHA1, catalyzes
the peroxide-dependent
oxidation of divalent manganese (Mn<sup>2+</sup>), albeit less efficiently
than fungal manganese peroxidases. Substitution of Asn246, a distal
heme residue, with alanine increased the enzyme’s apparent <i>k</i><sub>cat</sub> and <i>k</i><sub>cat</sub>/<i>K</i><sub>m</sub> values for Mn<sup>2+</sup> by 80- and 15-fold,
respectively. A 2.2 Å resolution X-ray crystal structure of the
N246A variant revealed the Mn<sup>2+</sup> to be bound within a pocket
of acidic residues at the heme edge, reminiscent of the binding site
in fungal manganese peroxidase and very different from that of another
bacterial Mn<sup>2+</sup>-oxidizing peroxidase. The first coordination
sphere was entirely composed of solvent, consistent with the variant’s
high <i>K</i><sub>m</sub> for Mn<sup>2+</sup> (17 ±
2 mM). N246A catalyzed the manganese-dependent transformation of hard
wood kraft lignin and its solvent-extracted fractions. Two of the
major degradation products were identified as 2,6-dimethoxybenzoquinone
and 4-hydroxy-3,5-dimethoxybenzaldehyde, respectively. These results
highlight the potential of bacterial enzymes as biocatalysts to transform
lignin