Filip Meersman - Academia.edu (original) (raw)

Papers by Filip Meersman

Scientific reports, 2016

Quasielastic neutron scattering (QENS) is an ideal technique for studying water transport and rel... more Quasielastic neutron scattering (QENS) is an ideal technique for studying water transport and relaxation dynamics at pico- to nanosecond timescales and at length scales relevant to cellular dimensions. Studies of high pressure dynamic effects in live organisms are needed to understand Earth's deep biosphere and biotechnology applications. Here we applied QENS to study water transport in Shewanella oneidensis at ambient (0.1 MPa) and high (200 MPa) pressure using H/D isotopic contrast experiments for normal and perdeuterated bacteria and buffer solutions to distinguish intracellular and transmembrane processes. The results indicate that intracellular water dynamics are comparable with bulk diffusion rates in aqueous fluids at ambient conditions but a significant reduction occurs in high pressure mobility. We interpret this as due to enhanced interactions with macromolecules in the nanoconfined environment. Overall diffusion rates across the cell envelope also occur at similar rat...

Food Chemistry, 2008

The thermal stability of purified recombinant Aspergillus aculeatus pectinmethylesterase (PME) in... more The thermal stability of purified recombinant Aspergillus aculeatus pectinmethylesterase (PME) in different media was studied. The influence of pH, ionic strength and additives (salts and polyols) was evaluated. At pH 5.0 and a high ionic strength (0.50 M), the enzyme showed a high thermostability (inactivation at temperatures P60°C). Interestingly, an enhancement of its heat stability was observed at pH 7.0 and temperatures above 55°C, this behaviour was reflected in an atypical evolution of structural changes in the overall conformation of the enzyme, according to FTIR spectroscopy results. Recombinant A. aculeatus PME thermal inactivation at pH 7.0 could be described by a fractional-conversion model. Addition of NaCl increased the thermal stability at pHs 5.0 and 7.0, while addition of CaCl 2 had no influence. With regard to sugars (sucrose, trehalose, glucose and maltose) and polyols (sorbitol, lactitol and glycerol) addition, at the same concentration and pH, the polyols showed a higher protective effect than sugars. Also, the thermostability of recombinant A. aculeatus PME increased with the additive concentration, although the source of OH groups was the main parameter involved.

Biophysical Chemistry, May 1, 2003

The pressure stability of ribonuclease A and bovine pancreatic trypsin inhibitor has been investi... more The pressure stability of ribonuclease A and bovine pancreatic trypsin inhibitor has been investigated with Fourier transform infrared spectroscopy in the presence of the disulfide bond reducing agent 2-mercaptoethanol. The secondary structure of the reduced proteins at high pressure (1 GPa) is not significantly different from the pressure-induced conformation of the native form. Upon decompression under reducing conditions, amorphous aggregates are formed. Such aggregates are not formed upon decompression of the native proteins. Our data demonstrate that high pressure populates, and thus allows the potential characterization of highly aggregation-prone conformations. The relevance of these findings with regard to fibril formation is discussed and the possible role of conformational fluctuations of intermediates on the aggregation pathway is emphasized. ᮊ

Biochemical Journal, 2003

The effect of hydrostatic pressure on the secondary structure of recombinant human interferon-γ (... more The effect of hydrostatic pressure on the secondary structure of recombinant human interferon-γ (rhIFN-γ) and its biologically inactive truncated form rhIFN-∆C15 has been studied using Fourier-transform IR (FTIR) spectroscopy. In situ observation of the pressure-induced changes using the diamond anvil cell shows that the α-helical structure is mainly transformed into disordered structure at high pressure. Increasing pressure also induces the formation of a gel. Addition of 0.5 M MgCl # significantly reduces the pressure stability. Releasing the pressure below 300 MPa results in the formation of intermolecular

The structure of the wheat g46 gliadin was investigated, in aqueous solutions, under high pressur... more The structure of the wheat g46 gliadin was investigated, in aqueous solutions, under high pressure or temperature by the use of ultraviolet and fluorescence spectroscopic techniques. We found that high pressure (above 400 MPa) induces a change in the protein conformation that results in a decrease of the polarity of the environment of aromatic amino acids. This new conformation was able to bind the hydrophobic probe, 8-anilino-1-naphtalene-sulfonic acid (ANS), indicating an increase in the gliadin surface hydrophobicity.

Progress in Biotechnology, 2002

NATO Science for Peace and Security Series B: Physics and Biophysics, 2010

Amorphous x-ray diffraction is used to obtain structural information on amorphous solids and liqu... more Amorphous x-ray diffraction is used to obtain structural information on amorphous solids and liquids at high pressure as well as other materials without long range crystalline order including biologically important macromolecules and nanomaterials. The intense x-ray ...

Separation and Purification Technology, 2015

Sodium hypochlorite (NaOCl) is widely used to remove biofouling in membrane bioreactors (MBRs) to... more Sodium hypochlorite (NaOCl) is widely used to remove biofouling in membrane bioreactors (MBRs) to recover the membrane performance. In this study, the effect of membrane cleaning with different NaOCl concentrations (0.01%, 0.1%, 1% and 10% of a stock solution containing 39.92 g/L of free chlorine) on biofouling was investigated in a molasses based lab-scale MBR. Study of the bacterial biofilm community re-growth after six consecutive cleanings revealed that a minimal concentration of 0.1% NaOCl diminishes the bacterial richness and cell density on the membranes. ATR-FTIR analysis of the layer on the membrane surface revealed the presence of peaks associated with proteins and carbohydrates present in the biofouling layer and their intensity decreased after treatment with NaOCl. Analysis of the membrane performance by chemical oxygen demand (COD) measurement of the permeate and retentate showed that the rejection of the membranes after NaOCl chemical treatment was still high. The data showed that since NaOCl removes the bacterial biofilm and at the same time does not affect the membrane treatment performance, NaOCl can be recommended as a cleaning agent to remove biofouling in a lab-scale molasses based MBR.

Frontiers in Microbiology, 2014

Vibrational Spectroscopy, 2006

Thermal denaturation of ribonuclease A (RNase A) in D 2 O solution is studied by Fourier transfor... more Thermal denaturation of ribonuclease A (RNase A) in D 2 O solution is studied by Fourier transform infrared (FT-IR) spectroscopy. Samplesample two-dimensional correlation (SS 2D) spectroscopy and principal component analysis (PCA) are applied to these spectral data to reveal the thermal kinetics of RNase A. The second scores plot of PCA constructed from temperature-dependent original IR spectra illustrates a pretransition at 46 8C as well as a clear main transition at 66 8C. The latter is revealed by the SS 2D correlation spectra and the first score of PCA because of their illustration of the main denaturation event of RNase A, while the former cannot. Therefore, the present study demonstrates the great potential of PCA in revealing subtle phase transition of proteins in aqueous solutions. #

Progress in Materials Science, 2014

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / p m a t s c i equ... more j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / p m a t s c i equilibration processes are severely constrained. The results will lead to useful new high-density amorphous materials or nanocrystalline composites containing metastable crystalline varieties and the experiments have driven new theoretical approaches to modeling the phenomena. Here we review the incidence and current understanding of PIA along with related phenomena of densityand entropy-driven liquid-liquid phase transitions (LLPT) and polyamorphism. We extend the discussion to include polymeric macromolecules and biologically-related materials, where the phenomena can be correlated with reversible vs irreversible unfolding and other metastable structural transformations.

Physical Chemistry Chemical Physics, 2011

The interaction of the osmolytes trimethylamine N-oxide (TMAO) and urea in aqueous solutions at 4... more The interaction of the osmolytes trimethylamine N-oxide (TMAO) and urea in aqueous solutions at 40 °C was investigated by isotopic substitution neutron scattering at a TMAO mole fraction of 0.05 and TMAO/urea concentration ratios of 1 : 2 and 1 : 4. The partial pair distribution functions obtained by the empirical potential structure refinement method are consistent with those obtained previously for similar pure TMAO and 1 : 1 TMAO-urea solutions and indicate that urea progressively replaces the water molecules in the first coordination shell of the TMAO oxygen atom. The apparent association constant for the TMAO : urea complex (K(1)) was calculated to be 0.14 M(-1), which is of the same order as the experimental urea-protein binding constants per site reported in the literature. This confirms that the two osmolytes act independently at least in the physiological range.

Operative Dentistry, 2014

The purpose of this study was to evaluate how evaporation affects the shelf life of a one-bottle ... more The purpose of this study was to evaluate how evaporation affects the shelf life of a one-bottle universal adhesive. Three different versions of Scotchbond Universal (SBU, 3M ESPE, Seefeld, Germany) were prepared using a weight-loss technique. SBU0 was left open to the air until maximal weight loss was obtained, whereas SBU50 was left open until 50% of evaporation occurred. In contrast, SBU100 was kept closed and was assumed to contain the maximum concentration of all ingredients. The degree of conversion (DC) was determined by using Fourier transform infrared spectroscopy on different substrates (on dentin or glass plate and mixed with dentin powder); ultimate microtensile strength and microtensile bond strength to dentin were measured as well. DC of the 100% solvent-containing adhesive (SBU100) was higher than that of the 50% (SBU50) and 0% (SBU0) solvent-containing adhesives for all substrates. DC of the adhesive applied onto glass and dehydrated dentin was higher than that applied onto dentin. Even though the ultimate microtensile strength of SBU0 was much higher than that of SBU50 and SBU100, its bond strength to dentin was significantly lower. Evaporation of adhesive ingredients may jeopardize the shelf life of a one-bottle universal system by reducing the degree of conversion and impairing bond strength. However, negative effects only became evident after more than 50% evaporation.

Macromolecules, 2006

ABSTRACT We have demonstrated a novel application of hybrid two-dimensional (2D) correlation spec... more ABSTRACT We have demonstrated a novel application of hybrid two-dimensional (2D) correlation spectroscopy in exploring the reversibility of phase separation (or transitions). Pressure-induced phase separation and temperature-induced phase transitions have been studied for poly(N-isopropylacrylamide) (PNiPA) and poly(N-isopropylmethacrylamide) (PNiPMA) in aqueous solutions using Fourier transform infrared (IR) and hybrid 2D correlation spectroscopy. Here we show that pressure-dependent sample−sample (SS) hybrid 2D correlation IR spectroscopy reveals for PNiPA a reversible phase separation with a differential rate of concentration change and separation pressure and a reversible phase separation with similar dynamics for PNiPMA, but involving irreversible hydrogen/deuterium exchange. Subtle differences in concentration dynamics have been revealed clearly by the hybrid SS 2D IR correlation analysis; these include the minor irreversibility of amide I in PNiPA, resulting from the loss of a very few coil populations, and in PNiPMA, resulting from the irreversible H/D exchange. Such events are not apparent from the transition plots constructed on the basis of one-dimensional data analysis.

Macromolecules, 2005

ABSTRACT The hydration properties of poly(N-isopropylacrylamide) in aqueous solution were investi... more ABSTRACT The hydration properties of poly(N-isopropylacrylamide) in aqueous solution were investigated by Fourier transform infrared spectroscopy as a function of high hydrostatic pressure and compared to the thermally induced changes. We show that although both pressure and temperature induce a phase separation the underlying mechanisms are fundamentally different. It is well documented that increasing the temperature above the lower critical solution temperature causes a dehydration of the hydrophilic and hydrophobic moieties. By contrast, high pressure enhances the hydration of the hydrophilic amide group. Moreover, pressure strengthens the weak C−H···O hydrogen bonds between the hydrophobic alkyl groups and water, although a reorganization of the water network around the hydrophobic groups occurs during the phase separation. From this it is concluded that PNiPA remains in a coillike state at high pressure. In addition, we suggest that PNiPA is a good model for the study of the hydration properties of proteins.

Journal of Molecular Structure, 2008

ABSTRACT The analysis of protein unfolding pathways and the identification of specific conformati... more ABSTRACT The analysis of protein unfolding pathways and the identification of specific conformational changes under perturbation are of fundamental importance for protein folding. In this study, thermally induced early unfolding events of bovine pancreatic ribonuclease A (RNase A) in the presence of 2-mercaptoethanol are evidenced successfully by principal component analysis and two-dimensional correlation infrared spectroscopy. The analyses of secondary structural changes in different stages have clearly distinguished the early events from the main unfolding in the temperature course of RNase A. It is revealed that in the early stage of the thermal unfolding subtle structural changes of the more temperature-sensitive β-sheet in RNase A dominates this process; while the main unfolding of RNase A is initiated with the structural changes of the more temperature-sensitive β-sheet, random coils and β-turns, followed by the less temperature-sensitive β-sheet component and the formation of a β-sheet-rich aggregate. The quantitative analysis of the power spectra reveals that the intensity variations from early stages are almost same in the scale, and each accounts for less than 1% that of the main unfolding. These findings demonstrate that the utilization of 2D IR spectrum and its power spectrum is powerful in exploring the minor early events and closely related structural changes of protein.

Journal of Molecular Structure, 2006

The changes in hydration of poly(N-isopropylacrylamide) in aqueous solution have been monitored b... more The changes in hydration of poly(N-isopropylacrylamide) in aqueous solution have been monitored by FTIR spectroscopy as a function of temperature and pressure. Heating the sample above the LCST induces a phase separation that reflects a dehydration of the polymer chain on ...

Journal of Molecular Structure, 2006

Orthogonal signal correction (OSC) is a chemometrical data processing technique used for removing... more Orthogonal signal correction (OSC) is a chemometrical data processing technique used for removing the information unrelated to the target variables based on the constrained principal component analysis (PCA). The combined use of OSC filtering and two-dimensional (2D) correlation analysis, which is called orthogonal signal corrected 2D (OSC 2D) correlation spectroscopy, is proposed in the present study to enable one to develop high quality of 2D correlation spectra by eliminating any information unrelated to the external variables. A set of temperature-dependent infrared spectra of poly(N-isopropylacrylamide) (PNiPa) in aqueous solutions, as well as the simulated spectra developed by adding different random noise spectra or a systematic noise spectrum of contaminating water after multiplied with a random weight factor to the experimental spectra, were used as examples. The results provided by OSC 2D were compared to those obtained by 2D without OSC filtering, and OSC 2D spectrum has demonstrated its substantial power in eliminating signals that are unrelated to the external variable and the great improvement in the synchronous spectrum.

Scientific reports, 2016

Quasielastic neutron scattering (QENS) is an ideal technique for studying water transport and rel... more Quasielastic neutron scattering (QENS) is an ideal technique for studying water transport and relaxation dynamics at pico- to nanosecond timescales and at length scales relevant to cellular dimensions. Studies of high pressure dynamic effects in live organisms are needed to understand Earth's deep biosphere and biotechnology applications. Here we applied QENS to study water transport in Shewanella oneidensis at ambient (0.1 MPa) and high (200 MPa) pressure using H/D isotopic contrast experiments for normal and perdeuterated bacteria and buffer solutions to distinguish intracellular and transmembrane processes. The results indicate that intracellular water dynamics are comparable with bulk diffusion rates in aqueous fluids at ambient conditions but a significant reduction occurs in high pressure mobility. We interpret this as due to enhanced interactions with macromolecules in the nanoconfined environment. Overall diffusion rates across the cell envelope also occur at similar rat...

Food Chemistry, 2008

The thermal stability of purified recombinant Aspergillus aculeatus pectinmethylesterase (PME) in... more The thermal stability of purified recombinant Aspergillus aculeatus pectinmethylesterase (PME) in different media was studied. The influence of pH, ionic strength and additives (salts and polyols) was evaluated. At pH 5.0 and a high ionic strength (0.50 M), the enzyme showed a high thermostability (inactivation at temperatures P60°C). Interestingly, an enhancement of its heat stability was observed at pH 7.0 and temperatures above 55°C, this behaviour was reflected in an atypical evolution of structural changes in the overall conformation of the enzyme, according to FTIR spectroscopy results. Recombinant A. aculeatus PME thermal inactivation at pH 7.0 could be described by a fractional-conversion model. Addition of NaCl increased the thermal stability at pHs 5.0 and 7.0, while addition of CaCl 2 had no influence. With regard to sugars (sucrose, trehalose, glucose and maltose) and polyols (sorbitol, lactitol and glycerol) addition, at the same concentration and pH, the polyols showed a higher protective effect than sugars. Also, the thermostability of recombinant A. aculeatus PME increased with the additive concentration, although the source of OH groups was the main parameter involved.

Biophysical Chemistry, May 1, 2003

The pressure stability of ribonuclease A and bovine pancreatic trypsin inhibitor has been investi... more The pressure stability of ribonuclease A and bovine pancreatic trypsin inhibitor has been investigated with Fourier transform infrared spectroscopy in the presence of the disulfide bond reducing agent 2-mercaptoethanol. The secondary structure of the reduced proteins at high pressure (1 GPa) is not significantly different from the pressure-induced conformation of the native form. Upon decompression under reducing conditions, amorphous aggregates are formed. Such aggregates are not formed upon decompression of the native proteins. Our data demonstrate that high pressure populates, and thus allows the potential characterization of highly aggregation-prone conformations. The relevance of these findings with regard to fibril formation is discussed and the possible role of conformational fluctuations of intermediates on the aggregation pathway is emphasized. ᮊ

Biochemical Journal, 2003

The effect of hydrostatic pressure on the secondary structure of recombinant human interferon-γ (... more The effect of hydrostatic pressure on the secondary structure of recombinant human interferon-γ (rhIFN-γ) and its biologically inactive truncated form rhIFN-∆C15 has been studied using Fourier-transform IR (FTIR) spectroscopy. In situ observation of the pressure-induced changes using the diamond anvil cell shows that the α-helical structure is mainly transformed into disordered structure at high pressure. Increasing pressure also induces the formation of a gel. Addition of 0.5 M MgCl # significantly reduces the pressure stability. Releasing the pressure below 300 MPa results in the formation of intermolecular

The structure of the wheat g46 gliadin was investigated, in aqueous solutions, under high pressur... more The structure of the wheat g46 gliadin was investigated, in aqueous solutions, under high pressure or temperature by the use of ultraviolet and fluorescence spectroscopic techniques. We found that high pressure (above 400 MPa) induces a change in the protein conformation that results in a decrease of the polarity of the environment of aromatic amino acids. This new conformation was able to bind the hydrophobic probe, 8-anilino-1-naphtalene-sulfonic acid (ANS), indicating an increase in the gliadin surface hydrophobicity.

Progress in Biotechnology, 2002

NATO Science for Peace and Security Series B: Physics and Biophysics, 2010

Amorphous x-ray diffraction is used to obtain structural information on amorphous solids and liqu... more Amorphous x-ray diffraction is used to obtain structural information on amorphous solids and liquids at high pressure as well as other materials without long range crystalline order including biologically important macromolecules and nanomaterials. The intense x-ray ...

Separation and Purification Technology, 2015

Sodium hypochlorite (NaOCl) is widely used to remove biofouling in membrane bioreactors (MBRs) to... more Sodium hypochlorite (NaOCl) is widely used to remove biofouling in membrane bioreactors (MBRs) to recover the membrane performance. In this study, the effect of membrane cleaning with different NaOCl concentrations (0.01%, 0.1%, 1% and 10% of a stock solution containing 39.92 g/L of free chlorine) on biofouling was investigated in a molasses based lab-scale MBR. Study of the bacterial biofilm community re-growth after six consecutive cleanings revealed that a minimal concentration of 0.1% NaOCl diminishes the bacterial richness and cell density on the membranes. ATR-FTIR analysis of the layer on the membrane surface revealed the presence of peaks associated with proteins and carbohydrates present in the biofouling layer and their intensity decreased after treatment with NaOCl. Analysis of the membrane performance by chemical oxygen demand (COD) measurement of the permeate and retentate showed that the rejection of the membranes after NaOCl chemical treatment was still high. The data showed that since NaOCl removes the bacterial biofilm and at the same time does not affect the membrane treatment performance, NaOCl can be recommended as a cleaning agent to remove biofouling in a lab-scale molasses based MBR.

Frontiers in Microbiology, 2014

Vibrational Spectroscopy, 2006

Thermal denaturation of ribonuclease A (RNase A) in D 2 O solution is studied by Fourier transfor... more Thermal denaturation of ribonuclease A (RNase A) in D 2 O solution is studied by Fourier transform infrared (FT-IR) spectroscopy. Samplesample two-dimensional correlation (SS 2D) spectroscopy and principal component analysis (PCA) are applied to these spectral data to reveal the thermal kinetics of RNase A. The second scores plot of PCA constructed from temperature-dependent original IR spectra illustrates a pretransition at 46 8C as well as a clear main transition at 66 8C. The latter is revealed by the SS 2D correlation spectra and the first score of PCA because of their illustration of the main denaturation event of RNase A, while the former cannot. Therefore, the present study demonstrates the great potential of PCA in revealing subtle phase transition of proteins in aqueous solutions. #

Progress in Materials Science, 2014

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / p m a t s c i equ... more j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / p m a t s c i equilibration processes are severely constrained. The results will lead to useful new high-density amorphous materials or nanocrystalline composites containing metastable crystalline varieties and the experiments have driven new theoretical approaches to modeling the phenomena. Here we review the incidence and current understanding of PIA along with related phenomena of densityand entropy-driven liquid-liquid phase transitions (LLPT) and polyamorphism. We extend the discussion to include polymeric macromolecules and biologically-related materials, where the phenomena can be correlated with reversible vs irreversible unfolding and other metastable structural transformations.

Physical Chemistry Chemical Physics, 2011

The interaction of the osmolytes trimethylamine N-oxide (TMAO) and urea in aqueous solutions at 4... more The interaction of the osmolytes trimethylamine N-oxide (TMAO) and urea in aqueous solutions at 40 °C was investigated by isotopic substitution neutron scattering at a TMAO mole fraction of 0.05 and TMAO/urea concentration ratios of 1 : 2 and 1 : 4. The partial pair distribution functions obtained by the empirical potential structure refinement method are consistent with those obtained previously for similar pure TMAO and 1 : 1 TMAO-urea solutions and indicate that urea progressively replaces the water molecules in the first coordination shell of the TMAO oxygen atom. The apparent association constant for the TMAO : urea complex (K(1)) was calculated to be 0.14 M(-1), which is of the same order as the experimental urea-protein binding constants per site reported in the literature. This confirms that the two osmolytes act independently at least in the physiological range.

Operative Dentistry, 2014

The purpose of this study was to evaluate how evaporation affects the shelf life of a one-bottle ... more The purpose of this study was to evaluate how evaporation affects the shelf life of a one-bottle universal adhesive. Three different versions of Scotchbond Universal (SBU, 3M ESPE, Seefeld, Germany) were prepared using a weight-loss technique. SBU0 was left open to the air until maximal weight loss was obtained, whereas SBU50 was left open until 50% of evaporation occurred. In contrast, SBU100 was kept closed and was assumed to contain the maximum concentration of all ingredients. The degree of conversion (DC) was determined by using Fourier transform infrared spectroscopy on different substrates (on dentin or glass plate and mixed with dentin powder); ultimate microtensile strength and microtensile bond strength to dentin were measured as well. DC of the 100% solvent-containing adhesive (SBU100) was higher than that of the 50% (SBU50) and 0% (SBU0) solvent-containing adhesives for all substrates. DC of the adhesive applied onto glass and dehydrated dentin was higher than that applied onto dentin. Even though the ultimate microtensile strength of SBU0 was much higher than that of SBU50 and SBU100, its bond strength to dentin was significantly lower. Evaporation of adhesive ingredients may jeopardize the shelf life of a one-bottle universal system by reducing the degree of conversion and impairing bond strength. However, negative effects only became evident after more than 50% evaporation.

Macromolecules, 2006

ABSTRACT We have demonstrated a novel application of hybrid two-dimensional (2D) correlation spec... more ABSTRACT We have demonstrated a novel application of hybrid two-dimensional (2D) correlation spectroscopy in exploring the reversibility of phase separation (or transitions). Pressure-induced phase separation and temperature-induced phase transitions have been studied for poly(N-isopropylacrylamide) (PNiPA) and poly(N-isopropylmethacrylamide) (PNiPMA) in aqueous solutions using Fourier transform infrared (IR) and hybrid 2D correlation spectroscopy. Here we show that pressure-dependent sample−sample (SS) hybrid 2D correlation IR spectroscopy reveals for PNiPA a reversible phase separation with a differential rate of concentration change and separation pressure and a reversible phase separation with similar dynamics for PNiPMA, but involving irreversible hydrogen/deuterium exchange. Subtle differences in concentration dynamics have been revealed clearly by the hybrid SS 2D IR correlation analysis; these include the minor irreversibility of amide I in PNiPA, resulting from the loss of a very few coil populations, and in PNiPMA, resulting from the irreversible H/D exchange. Such events are not apparent from the transition plots constructed on the basis of one-dimensional data analysis.

Macromolecules, 2005

ABSTRACT The hydration properties of poly(N-isopropylacrylamide) in aqueous solution were investi... more ABSTRACT The hydration properties of poly(N-isopropylacrylamide) in aqueous solution were investigated by Fourier transform infrared spectroscopy as a function of high hydrostatic pressure and compared to the thermally induced changes. We show that although both pressure and temperature induce a phase separation the underlying mechanisms are fundamentally different. It is well documented that increasing the temperature above the lower critical solution temperature causes a dehydration of the hydrophilic and hydrophobic moieties. By contrast, high pressure enhances the hydration of the hydrophilic amide group. Moreover, pressure strengthens the weak C−H···O hydrogen bonds between the hydrophobic alkyl groups and water, although a reorganization of the water network around the hydrophobic groups occurs during the phase separation. From this it is concluded that PNiPA remains in a coillike state at high pressure. In addition, we suggest that PNiPA is a good model for the study of the hydration properties of proteins.

Journal of Molecular Structure, 2008

ABSTRACT The analysis of protein unfolding pathways and the identification of specific conformati... more ABSTRACT The analysis of protein unfolding pathways and the identification of specific conformational changes under perturbation are of fundamental importance for protein folding. In this study, thermally induced early unfolding events of bovine pancreatic ribonuclease A (RNase A) in the presence of 2-mercaptoethanol are evidenced successfully by principal component analysis and two-dimensional correlation infrared spectroscopy. The analyses of secondary structural changes in different stages have clearly distinguished the early events from the main unfolding in the temperature course of RNase A. It is revealed that in the early stage of the thermal unfolding subtle structural changes of the more temperature-sensitive β-sheet in RNase A dominates this process; while the main unfolding of RNase A is initiated with the structural changes of the more temperature-sensitive β-sheet, random coils and β-turns, followed by the less temperature-sensitive β-sheet component and the formation of a β-sheet-rich aggregate. The quantitative analysis of the power spectra reveals that the intensity variations from early stages are almost same in the scale, and each accounts for less than 1% that of the main unfolding. These findings demonstrate that the utilization of 2D IR spectrum and its power spectrum is powerful in exploring the minor early events and closely related structural changes of protein.

Journal of Molecular Structure, 2006

The changes in hydration of poly(N-isopropylacrylamide) in aqueous solution have been monitored b... more The changes in hydration of poly(N-isopropylacrylamide) in aqueous solution have been monitored by FTIR spectroscopy as a function of temperature and pressure. Heating the sample above the LCST induces a phase separation that reflects a dehydration of the polymer chain on ...

Journal of Molecular Structure, 2006

Orthogonal signal correction (OSC) is a chemometrical data processing technique used for removing... more Orthogonal signal correction (OSC) is a chemometrical data processing technique used for removing the information unrelated to the target variables based on the constrained principal component analysis (PCA). The combined use of OSC filtering and two-dimensional (2D) correlation analysis, which is called orthogonal signal corrected 2D (OSC 2D) correlation spectroscopy, is proposed in the present study to enable one to develop high quality of 2D correlation spectra by eliminating any information unrelated to the external variables. A set of temperature-dependent infrared spectra of poly(N-isopropylacrylamide) (PNiPa) in aqueous solutions, as well as the simulated spectra developed by adding different random noise spectra or a systematic noise spectrum of contaminating water after multiplied with a random weight factor to the experimental spectra, were used as examples. The results provided by OSC 2D were compared to those obtained by 2D without OSC filtering, and OSC 2D spectrum has demonstrated its substantial power in eliminating signals that are unrelated to the external variable and the great improvement in the synchronous spectrum.