Ashutosh Mittal - Academia.edu (original) (raw)

Papers by Ashutosh Mittal

ACS Sustainable Chemistry and Engineering, Feb 23, 2017

Green Chemistry

The native recalcitrance of lignocellulosic biomass hinders its effective deconstruction for biol... more The native recalcitrance of lignocellulosic biomass hinders its effective deconstruction for biological conversion to fuel ethanol. However, once cellulose is physically available to enzymes/microbes, i.e., macro-accessible, cellulose micro-accessibility, i.e., the...

The Journal of Physical Chemistry C, 2017

Vibrational sum frequency generation (SFG) spectroscopy can selectively detect not only molecules... more Vibrational sum frequency generation (SFG) spectroscopy can selectively detect not only molecules at two-dimensional (2D) interfaces but also noncentrosymmetric domains interspersed in amorphous three-dimensional (3D) matrixes. However, the SFG analysis of 3D systems is more complicated than 2D systems because more variables are involved. One such variable is the distance between SFG-active domains in SFG-inactive matrixes. In this study, we fabricated control samples in which SFG-active cellulose crystals were uniaxially aligned in an amorphous matrix. Assuming uniform separation distances between cellulose crystals, the relative intensities of alkyl (CH) and hydroxyl (OH) SFG peaks of cellulose could be related to the intercrystallite distance. The experimentally measured CH/OH intensity ratio as a function of the intercrystallite distance could be explained reasonably well with a model constructed using the theoretically calculated hyperpolarizabilities of cellulose and the symmetry cancellation princi...

Current Biotechnology, 2016

Commercial fungal cellulases used in biomass-to-biofuels processes can be grouped into three gene... more Commercial fungal cellulases used in biomass-to-biofuels processes can be grouped into three general classes: native, augmented, and engineered. Colorimetric assays for general glycoside hydrolase activities showed distinct differences in enzyme binding to lignin for each enzyme activity. Native cellulase preparations demonstrated low binding of endo- and exocellulases, high binding of xylanase, and moderate binding for β-D-glucosidases. Engineered cellulase formulations exhibited low binding of exocellulases, very strong binding of endocellulases and β-D-glucosidase, and mixed binding of xylanase activity. The augmented cellulase had low binding of exocellulase, high binding of endocellulase and xylanase, and moderate binding of β-D-glucosidase activities. Bound and unbound activities were correlated to general molecular weight ranges of proteins as measured by loss of proteins bands in bound fractions on SDS-PAGE gels. Lignin-bound high molecular weight bands correlated to binding of β-D-glucosidase activity. Whereas β-D-glucosidases demonstrated high binding in many cases, they have been shown to remain active. Bound low molecular weight bands correlated to xylanase activity binding. Contrary to other literature, exocellulase activity did not show strong lignin binding. The variation in enzyme activity binding between these three classes of cellulases preparations indicates that it is possible to alter the binding of specific glycoside hydrolase activities during the enzyme formulation process. It remains unclear whether or not loss of endocellulase activity to lignin binding is problematic for biomass conversion.

Cost-effective production of fuels and chemicals from lignocellulosic biomass often involves enzy... more Cost-effective production of fuels and chemicals from lignocellulosic biomass often involves enzymatic saccharification, which has been the subject of intense research and development. Recently, a mechanistic model for the enzymatic saccharification of cellulose has been developed that accounts for distribution of cellulose-chain lengths, the accessibility of insoluble cellulose to enzymes, and the distinct modes of action of the component cellulases [Griggs et al. (2012) Biotechnol. Bioeng., 109(3):665–675; Griggs et al. (2012) Biotechnol. Bioeng., 109(3):676–685]. However, determining the appropriate values for enzyme adsorption, inhibition, and rate parameters required further experimental investigation. In this work, we performed several sets of experiments to aid in parameter estimation and to quantitatively validate the model. Several cellulosic materials having varied degrees of polymerization, crystallinity, and crystalline allomorph (cellulose-Iβ and cellulose-IIII) were di...

Trichoderma reesei derived cellulase cocktail is comprised of several cellobiohydrolases (Cel 7A ... more Trichoderma reesei derived cellulase cocktail is comprised of several cellobiohydrolases (Cel 7A or CBH I; Cel6A or CBH II) and endoglucanases (EG I through V). Earlier studies showed that the two cellobiohydrolases CBH I and CBH II act preferably from the reducing and non-reducing ends of cellulose, respectively. Thus, it has long been believed that cellulose reducing ends (REs) play a vital role in cellulose enzymatic hydrolysis mediated by fungal enzymes 1,2. However, the fundamental hydrolysis studies investigating the effect of REs were mostly conducted with soluble cellodextrins, and studies applying insoluble substrate are limited. In one such report, Xu et al. recently reported that oxidation of REs and primary hydroxyl groups (PHGs) significantly affected cellulose conversion 3. However, the quantification of cellulose REs following oxidation were not reported in this study. On the contrary, a few other studies reported a limited effect of REs on cellulose conversion 4. The...

Several chemical and physical factors have been proposed to be related to biomass recalcitrance. ... more Several chemical and physical factors have been proposed to be related to biomass recalcitrance. The degree of polymerization (DP) of cellulose has been considered to be one of the most important properties affecting the enzymatic hydrolysis of cellulose. However, there are few studies investigating the effect of pretreatment on cellulose DP in biomass and the relationship between cellulose DP and enzymatic hydrolysis. This study of the effect of dilute acid treatment on cellulose DP was first started with various pure cellulose materials. A substantial reduction in DP was found for all cellulosic materials studied even at conditions that would be considered relatively mild for the pretreatment. Different cellulosic materials decreased to a similar DP upon treatment with acid regardless of the significant differences in the starting DP of the celluloses. The effect of dilute acid pretreatment on cellulose DP in biomass samples was also investigated. The cellulose DP in corn stover w...

This study investigates the buildup of dissolved solids in the mill water system with increased e... more This study investigates the buildup of dissolved solids in the mill water system with increased effluent recycling at Solvay Paperboard (SPB), a paperboard mill located in Solvay, New York. SPB underwent a water reduction program through effluent recycling in three separate phases with the intention of reducing its fresh water consumption. A paper machine, with its associated components, is considered as a process block with various critical species entering the block with the input streams and leaving it with the output streams. For Phase 1 (two paper machines operating in a parallel mode) and Phase 2 (two paper machines operating in parallel connected to a third paper machine in series) operations of SPB, mass balances for critical inorganic substances are formulated in order to deduce their buildup in the mill water system and in the paperboard as the degree of water recycle is progressively increased. The modeling takes into account the partitioning or retention of a critical species to different extents in the output streams of a process block. In order to calibrate and partially validate the models, the theoretical development is complemented with flowrate and composition data of the input (furnish, chemicals, freshwater, and recycled effluent) and output (rejects, paperboard and effluent) streams of a block. As the extent of effluent recycle rises, the theoretical buildup curves suggest sharp increases of sulfate, chloride and sodium in the mill water system whereas low buildups are predicted for calcium, magnesium and silica.

ACS Sustainable Chemistry & Engineering, 2014

ABSTRACT Biomass pretreatment generally aims to increase accessibility to plant cell wall polysac... more ABSTRACT Biomass pretreatment generally aims to increase accessibility to plant cell wall polysaccharides for carbohydrate-active enzymes to produce sugars for biological or catalytic upgrading to ethanol or advanced biofuels. Significant research has been conducted on a suite of pretreatment processes for bioethanol processes. An alternative option, which has received less attention in the biofuels community, is the use of alkaline pretreatment for the partial depolymerization of lignin from intact biomass. A known issue with alkaline pretreatment is the loss of polysaccharides from peeling reactions, but this loss can be mitigated with anthraquinone, as commonly practiced in pulping. Here, we conduct a comprehensive bench-scale evaluation of alkaline pretreatment using corn stover at temperatures of 100, 130, and 160 °C and sodium hydroxide loadings from 35 to 660 mg NaOH/g dry biomass with anthraquinone. Compositional analysis is conducted on the starting material and residual solids after pretreatment, and mass balance is inferred in the liquor by difference. The residual solids after alkaline pretreatment are characterized for crystallinity and imaged by scanning and transmission electron microscopy to reveal the physical changes in the carbohydrate portions of the biomass remaining after pretreatment, which demonstrate dramatic modifications to biomass cell wall architecture with lignin removal but rather insignificant changes in cellulose crystallinity. Our results show that alkaline pretreatment at relatively mild conditions is able to remove substantial amounts of lignin from biomass. Going forward, to be an economically feasibile process, technologies will be required to upgrade the resulting lignin-rich liquor stream.

ACS Sustainable Chemistry & Engineering, 2014

ABSTRACT Organosolv fractionation processes aim to separate the primary biopolymers in lignocellu... more ABSTRACT Organosolv fractionation processes aim to separate the primary biopolymers in lignocellulosic biomass to enable more selective deconstruction and upgrading approaches for the isolated components. Clean fractionation (CF) is a particularly effective organsolv process that was originally applied to woody feedstocks. The original CF pretreatment employed methyl isobutyl ketone (MIBK), ethanol, and water with sulfuric acid as a catalyst at temperatures ranging from 120 to 160 °C. Understanding the feasibility and applicability of organosolv processes for industrial use requires mass balances on the primary polymers in biomass, detailed understanding of the physical and chemical characteristics of the fractionated components, and viable upgrading processes for each fraction. Here, we apply two CF approaches to corn stover, one with MIBK/ethanol/water and acid and the other with MIBK/acetone/water and acid, with the aim of understanding if these fractionation methods are feasible for industrial application. We quantify the full mass balances on the resulting solid, organic, and aqueous fractions and apply multiple analytical methods to characterize the three fractions. Total mass yields of the cellulose-enriched, hemicellulose-enriched, and lignin-enriched fractions are near mass closure in most cases. For corn stover, the MIBK/acetone/water CF solvent system is more effective relative to the original CF method based on the enhanced fractionation susceptibility of the aqueous and organic phases and the lower molecular weight distribution of the lignin-enriched fractions. Overall, this work reports component mass balances for the fractionation of corn stover, providing key inputs for detailed evaluation of CF processes based on bench-scale data.

International Journal of Green Energy, 2006

Evaporative cooling of water in a small porous clay vessel was studied under controlled humidity ... more Evaporative cooling of water in a small porous clay vessel was studied under controlled humidity conditions. In steady-state experiments performed at an ambient temperature of 23 °C, the cooling effect increased from 4.7 to 8.3 °C as the ambient relative humidity decreased from 60 to 15%. External heat and mass transfer coefficients, estimated from the steady-state measurements, were used in mathematical models to predict the experimentally observed transient temperature variation of the water under ramp changes of the ambient relative humidity. With a prototypical cool chamber containing water tested in Kolkata, India under an ambient temperature of 34.5-35 °C, the cooling effect reached a maximum of 7 °C between 3 and 3:30 PM and then declined to 4.5 °C around 6 PM.

Energy & Fuels, 2013

ABSTRACT Xylose reversion reactions to form xylooligomers represent a potentially important mecha... more ABSTRACT Xylose reversion reactions to form xylooligomers represent a potentially important mechanism of sugar loss during dilute acid pretreatment of biomass. We have conducted a study to identify the products that result from these reactions and to determine the kinetics of their formation. A major obstacle is that there are few commercial standards available for xylose disaccharides, which are essential for the identification and quantification of the xylose reversion products formed during these reactions. To overcome this obstacle, we have used GC/MS and NMR analysis of xylose disaccharides isolated by preparative HPLC to identify the reaction products. At the xylose concentration we used (300 g L–1), only xylose disaccharides were observed. As with glucose reversion reactions [Pilath, H. M.; et al. J. Agric. Food Chem. 2010, 58, 6131], the disaccharides contained linkages that involved the anomeric carbon atom of one of the sugar monomers. Eight out of the nine possible disaccharides, including alpha and beta anomers, were observed. Whereas the GC/MS allowed for the identification of the linkages, NMR was needed to distinguish between the α and β isomers of the disaccharides. The kinetics of combined xylose disaccharide formation was measured using HPLC. Arrhenius parameters for the rates of disaccharide formation were calculated by fitting the data to a simple model.

Cellulose, 2013

Sum-frequency-generation (SFG) vibration spectroscopy is a technique only sensitive to functional... more Sum-frequency-generation (SFG) vibration spectroscopy is a technique only sensitive to functional groups arranged without centrosymmetry. For crystalline cellulose, SFG can detect the C6H 2 and intra-chain hydrogen-bonded OH groups in the crystal. The geometries of these groups are sensitive to the hydrogen bonding network that stabilizes each cellulose polymorph. Therefore, SFG can distinguish cellulose polymorphs (I b , II, III I and III II) which have different conformations of the exocyclic hydroxymethylene group or directionalities of glucan chains. The C6H 2 asymmetric stretching peaks at 2,944 cm-1 for cellulose I b and 2,960 cm-1 for cellulose II, III I and III II corresponds to the trans-gauche (tg) and gauche-trans (gt) conformation, respectively. The SFG intensity of the stretch peak of intra-chain hydrogen-bonded O-H group implies that the chain arrangement in cellulose crystal is parallel in I b and III I , and antiparallel in II and III II .

ACS Sustainable Chemistry and Engineering, Feb 23, 2017

Green Chemistry

The native recalcitrance of lignocellulosic biomass hinders its effective deconstruction for biol... more The native recalcitrance of lignocellulosic biomass hinders its effective deconstruction for biological conversion to fuel ethanol. However, once cellulose is physically available to enzymes/microbes, i.e., macro-accessible, cellulose micro-accessibility, i.e., the...

The Journal of Physical Chemistry C, 2017

Vibrational sum frequency generation (SFG) spectroscopy can selectively detect not only molecules... more Vibrational sum frequency generation (SFG) spectroscopy can selectively detect not only molecules at two-dimensional (2D) interfaces but also noncentrosymmetric domains interspersed in amorphous three-dimensional (3D) matrixes. However, the SFG analysis of 3D systems is more complicated than 2D systems because more variables are involved. One such variable is the distance between SFG-active domains in SFG-inactive matrixes. In this study, we fabricated control samples in which SFG-active cellulose crystals were uniaxially aligned in an amorphous matrix. Assuming uniform separation distances between cellulose crystals, the relative intensities of alkyl (CH) and hydroxyl (OH) SFG peaks of cellulose could be related to the intercrystallite distance. The experimentally measured CH/OH intensity ratio as a function of the intercrystallite distance could be explained reasonably well with a model constructed using the theoretically calculated hyperpolarizabilities of cellulose and the symmetry cancellation princi...

Current Biotechnology, 2016

Commercial fungal cellulases used in biomass-to-biofuels processes can be grouped into three gene... more Commercial fungal cellulases used in biomass-to-biofuels processes can be grouped into three general classes: native, augmented, and engineered. Colorimetric assays for general glycoside hydrolase activities showed distinct differences in enzyme binding to lignin for each enzyme activity. Native cellulase preparations demonstrated low binding of endo- and exocellulases, high binding of xylanase, and moderate binding for β-D-glucosidases. Engineered cellulase formulations exhibited low binding of exocellulases, very strong binding of endocellulases and β-D-glucosidase, and mixed binding of xylanase activity. The augmented cellulase had low binding of exocellulase, high binding of endocellulase and xylanase, and moderate binding of β-D-glucosidase activities. Bound and unbound activities were correlated to general molecular weight ranges of proteins as measured by loss of proteins bands in bound fractions on SDS-PAGE gels. Lignin-bound high molecular weight bands correlated to binding of β-D-glucosidase activity. Whereas β-D-glucosidases demonstrated high binding in many cases, they have been shown to remain active. Bound low molecular weight bands correlated to xylanase activity binding. Contrary to other literature, exocellulase activity did not show strong lignin binding. The variation in enzyme activity binding between these three classes of cellulases preparations indicates that it is possible to alter the binding of specific glycoside hydrolase activities during the enzyme formulation process. It remains unclear whether or not loss of endocellulase activity to lignin binding is problematic for biomass conversion.

Cost-effective production of fuels and chemicals from lignocellulosic biomass often involves enzy... more Cost-effective production of fuels and chemicals from lignocellulosic biomass often involves enzymatic saccharification, which has been the subject of intense research and development. Recently, a mechanistic model for the enzymatic saccharification of cellulose has been developed that accounts for distribution of cellulose-chain lengths, the accessibility of insoluble cellulose to enzymes, and the distinct modes of action of the component cellulases [Griggs et al. (2012) Biotechnol. Bioeng., 109(3):665–675; Griggs et al. (2012) Biotechnol. Bioeng., 109(3):676–685]. However, determining the appropriate values for enzyme adsorption, inhibition, and rate parameters required further experimental investigation. In this work, we performed several sets of experiments to aid in parameter estimation and to quantitatively validate the model. Several cellulosic materials having varied degrees of polymerization, crystallinity, and crystalline allomorph (cellulose-Iβ and cellulose-IIII) were di...

Trichoderma reesei derived cellulase cocktail is comprised of several cellobiohydrolases (Cel 7A ... more Trichoderma reesei derived cellulase cocktail is comprised of several cellobiohydrolases (Cel 7A or CBH I; Cel6A or CBH II) and endoglucanases (EG I through V). Earlier studies showed that the two cellobiohydrolases CBH I and CBH II act preferably from the reducing and non-reducing ends of cellulose, respectively. Thus, it has long been believed that cellulose reducing ends (REs) play a vital role in cellulose enzymatic hydrolysis mediated by fungal enzymes 1,2. However, the fundamental hydrolysis studies investigating the effect of REs were mostly conducted with soluble cellodextrins, and studies applying insoluble substrate are limited. In one such report, Xu et al. recently reported that oxidation of REs and primary hydroxyl groups (PHGs) significantly affected cellulose conversion 3. However, the quantification of cellulose REs following oxidation were not reported in this study. On the contrary, a few other studies reported a limited effect of REs on cellulose conversion 4. The...

Several chemical and physical factors have been proposed to be related to biomass recalcitrance. ... more Several chemical and physical factors have been proposed to be related to biomass recalcitrance. The degree of polymerization (DP) of cellulose has been considered to be one of the most important properties affecting the enzymatic hydrolysis of cellulose. However, there are few studies investigating the effect of pretreatment on cellulose DP in biomass and the relationship between cellulose DP and enzymatic hydrolysis. This study of the effect of dilute acid treatment on cellulose DP was first started with various pure cellulose materials. A substantial reduction in DP was found for all cellulosic materials studied even at conditions that would be considered relatively mild for the pretreatment. Different cellulosic materials decreased to a similar DP upon treatment with acid regardless of the significant differences in the starting DP of the celluloses. The effect of dilute acid pretreatment on cellulose DP in biomass samples was also investigated. The cellulose DP in corn stover w...

This study investigates the buildup of dissolved solids in the mill water system with increased e... more This study investigates the buildup of dissolved solids in the mill water system with increased effluent recycling at Solvay Paperboard (SPB), a paperboard mill located in Solvay, New York. SPB underwent a water reduction program through effluent recycling in three separate phases with the intention of reducing its fresh water consumption. A paper machine, with its associated components, is considered as a process block with various critical species entering the block with the input streams and leaving it with the output streams. For Phase 1 (two paper machines operating in a parallel mode) and Phase 2 (two paper machines operating in parallel connected to a third paper machine in series) operations of SPB, mass balances for critical inorganic substances are formulated in order to deduce their buildup in the mill water system and in the paperboard as the degree of water recycle is progressively increased. The modeling takes into account the partitioning or retention of a critical species to different extents in the output streams of a process block. In order to calibrate and partially validate the models, the theoretical development is complemented with flowrate and composition data of the input (furnish, chemicals, freshwater, and recycled effluent) and output (rejects, paperboard and effluent) streams of a block. As the extent of effluent recycle rises, the theoretical buildup curves suggest sharp increases of sulfate, chloride and sodium in the mill water system whereas low buildups are predicted for calcium, magnesium and silica.

ACS Sustainable Chemistry & Engineering, 2014

ABSTRACT Biomass pretreatment generally aims to increase accessibility to plant cell wall polysac... more ABSTRACT Biomass pretreatment generally aims to increase accessibility to plant cell wall polysaccharides for carbohydrate-active enzymes to produce sugars for biological or catalytic upgrading to ethanol or advanced biofuels. Significant research has been conducted on a suite of pretreatment processes for bioethanol processes. An alternative option, which has received less attention in the biofuels community, is the use of alkaline pretreatment for the partial depolymerization of lignin from intact biomass. A known issue with alkaline pretreatment is the loss of polysaccharides from peeling reactions, but this loss can be mitigated with anthraquinone, as commonly practiced in pulping. Here, we conduct a comprehensive bench-scale evaluation of alkaline pretreatment using corn stover at temperatures of 100, 130, and 160 °C and sodium hydroxide loadings from 35 to 660 mg NaOH/g dry biomass with anthraquinone. Compositional analysis is conducted on the starting material and residual solids after pretreatment, and mass balance is inferred in the liquor by difference. The residual solids after alkaline pretreatment are characterized for crystallinity and imaged by scanning and transmission electron microscopy to reveal the physical changes in the carbohydrate portions of the biomass remaining after pretreatment, which demonstrate dramatic modifications to biomass cell wall architecture with lignin removal but rather insignificant changes in cellulose crystallinity. Our results show that alkaline pretreatment at relatively mild conditions is able to remove substantial amounts of lignin from biomass. Going forward, to be an economically feasibile process, technologies will be required to upgrade the resulting lignin-rich liquor stream.

ACS Sustainable Chemistry & Engineering, 2014

ABSTRACT Organosolv fractionation processes aim to separate the primary biopolymers in lignocellu... more ABSTRACT Organosolv fractionation processes aim to separate the primary biopolymers in lignocellulosic biomass to enable more selective deconstruction and upgrading approaches for the isolated components. Clean fractionation (CF) is a particularly effective organsolv process that was originally applied to woody feedstocks. The original CF pretreatment employed methyl isobutyl ketone (MIBK), ethanol, and water with sulfuric acid as a catalyst at temperatures ranging from 120 to 160 °C. Understanding the feasibility and applicability of organosolv processes for industrial use requires mass balances on the primary polymers in biomass, detailed understanding of the physical and chemical characteristics of the fractionated components, and viable upgrading processes for each fraction. Here, we apply two CF approaches to corn stover, one with MIBK/ethanol/water and acid and the other with MIBK/acetone/water and acid, with the aim of understanding if these fractionation methods are feasible for industrial application. We quantify the full mass balances on the resulting solid, organic, and aqueous fractions and apply multiple analytical methods to characterize the three fractions. Total mass yields of the cellulose-enriched, hemicellulose-enriched, and lignin-enriched fractions are near mass closure in most cases. For corn stover, the MIBK/acetone/water CF solvent system is more effective relative to the original CF method based on the enhanced fractionation susceptibility of the aqueous and organic phases and the lower molecular weight distribution of the lignin-enriched fractions. Overall, this work reports component mass balances for the fractionation of corn stover, providing key inputs for detailed evaluation of CF processes based on bench-scale data.

International Journal of Green Energy, 2006

Evaporative cooling of water in a small porous clay vessel was studied under controlled humidity ... more Evaporative cooling of water in a small porous clay vessel was studied under controlled humidity conditions. In steady-state experiments performed at an ambient temperature of 23 °C, the cooling effect increased from 4.7 to 8.3 °C as the ambient relative humidity decreased from 60 to 15%. External heat and mass transfer coefficients, estimated from the steady-state measurements, were used in mathematical models to predict the experimentally observed transient temperature variation of the water under ramp changes of the ambient relative humidity. With a prototypical cool chamber containing water tested in Kolkata, India under an ambient temperature of 34.5-35 °C, the cooling effect reached a maximum of 7 °C between 3 and 3:30 PM and then declined to 4.5 °C around 6 PM.

Energy & Fuels, 2013

ABSTRACT Xylose reversion reactions to form xylooligomers represent a potentially important mecha... more ABSTRACT Xylose reversion reactions to form xylooligomers represent a potentially important mechanism of sugar loss during dilute acid pretreatment of biomass. We have conducted a study to identify the products that result from these reactions and to determine the kinetics of their formation. A major obstacle is that there are few commercial standards available for xylose disaccharides, which are essential for the identification and quantification of the xylose reversion products formed during these reactions. To overcome this obstacle, we have used GC/MS and NMR analysis of xylose disaccharides isolated by preparative HPLC to identify the reaction products. At the xylose concentration we used (300 g L–1), only xylose disaccharides were observed. As with glucose reversion reactions [Pilath, H. M.; et al. J. Agric. Food Chem. 2010, 58, 6131], the disaccharides contained linkages that involved the anomeric carbon atom of one of the sugar monomers. Eight out of the nine possible disaccharides, including alpha and beta anomers, were observed. Whereas the GC/MS allowed for the identification of the linkages, NMR was needed to distinguish between the α and β isomers of the disaccharides. The kinetics of combined xylose disaccharide formation was measured using HPLC. Arrhenius parameters for the rates of disaccharide formation were calculated by fitting the data to a simple model.

Cellulose, 2013

Sum-frequency-generation (SFG) vibration spectroscopy is a technique only sensitive to functional... more Sum-frequency-generation (SFG) vibration spectroscopy is a technique only sensitive to functional groups arranged without centrosymmetry. For crystalline cellulose, SFG can detect the C6H 2 and intra-chain hydrogen-bonded OH groups in the crystal. The geometries of these groups are sensitive to the hydrogen bonding network that stabilizes each cellulose polymorph. Therefore, SFG can distinguish cellulose polymorphs (I b , II, III I and III II) which have different conformations of the exocyclic hydroxymethylene group or directionalities of glucan chains. The C6H 2 asymmetric stretching peaks at 2,944 cm-1 for cellulose I b and 2,960 cm-1 for cellulose II, III I and III II corresponds to the trans-gauche (tg) and gauche-trans (gt) conformation, respectively. The SFG intensity of the stretch peak of intra-chain hydrogen-bonded O-H group implies that the chain arrangement in cellulose crystal is parallel in I b and III I , and antiparallel in II and III II .