Search

Your search keyword '"Asher, Sanford A"' showing total 148 results
Start Over Author "Asher, Sanford A" Publication Year Range Last 10 years
148 results on '"Asher, Sanford A"'

1. Diverse organic-mineral associations in Jezero crater, Mars

Author

Sharma, Sunanda, Roppel, Ryan D., Murphy, Ashley E., Beegle, Luther W., Bhartia, Rohit, Steele, Andrew, Hollis, Joseph Razzell, Siljeström, Sandra, McCubbin, Francis M., Asher, Sanford A., Abbey, William J., Allwood, Abigail C., Berger, Eve L., Bleefeld, Benjamin L., Burton, Aaron S., Bykov, Sergei V., Cardarelli, Emily L., Conrad, Pamela G., Corpolongo, Andrea, Czaja, Andrew D., DeFlores, Lauren P., Edgett, Kenneth, Farley, Kenneth A., Fornaro, Teresa, Fox, Allison C., Fries, Marc D., Harker, David, Hickman-Lewis, Keyron, Huggett, Joshua, Imbeah, Samara, Jakubek, Ryan S., Kah, Linda C., Lee, Carina, Liu, Yang, Magee, Angela, Minitti, Michelle, Moore, Kelsey R., Pascuzzo, Alyssa, Rodriguez Sanchez-Vahamonde, Carolina, Scheller, Eva L., Shkolyar, Svetlana, Stack, Kathryn M., Steadman, Kim, Tuite, Michael, Uckert, Kyle, Werynski, Alyssa, Wiens, Roger C., Williams, Amy J., Winchell, Katherine, Kennedy, Megan R., and Yanchilina, Anastasia

Published
2023
Full Text
View/download PDF

3. Evidence of Sulfate‐Rich Fluid Alteration in Jezero Crater Floor, Mars

Author

Siljeström, Sandra, primary, Czaja, Andrew D., additional, Corpolongo, Andrea, additional, Berger, Eve L., additional, Li, An Y., additional, Cardarelli, Emily, additional, Abbey, William, additional, Asher, Sanford A., additional, Beegle, Luther W., additional, Benison, Kathleen C., additional, Bhartia, Rohit, additional, Bleefeld, Benjamin L., additional, Burton, Aaron S., additional, Bykov, Sergei V., additional, Clark, Benton, additional, DeFlores, Lauren, additional, Ehlmann, Bethany L., additional, Fornaro, Teresa, additional, Fox, Allie, additional, Gómez, Felipe, additional, Hand, Kevin, additional, Haney, Nikole C., additional, Hickman‐Lewis, Keyron, additional, Hug, William F., additional, Imbeah, Samara, additional, Jakubek, Ryan S., additional, Kah, Linda C., additional, Kivrak, Lydia, additional, Lee, Carina, additional, Liu, Yang, additional, Martínez‐Frías, Jesús, additional, McCubbin, Francis M., additional, Minitti, Michelle, additional, Moore, Kelsey, additional, Morris, Richard V., additional, Núñez, Jorge I., additional, Osterhout, Jeffrey T., additional, Phua, Yu Yu, additional, Randazzo, Nicolas, additional, Hollis, Joseph Razzell, additional, Rodriguez, Carolina, additional, Roppel, Ryan, additional, Scheller, Eva L., additional, Sephton, Mark, additional, Sharma, Shiv K., additional, Sharma, Sunanda, additional, Steadman, Kim, additional, Steele, Andrew, additional, Tice, Michael, additional, Uckert, Kyle, additional, VanBommel, Scott, additional, Williams, Amy J., additional, Williford, Kenneth H., additional, Winchell, Katherine, additional, Wu, Megan Kennedy, additional, Yanchilina, Anastasia, additional, and Zorzano, Maria‐Paz, additional

Published
2024
Full Text
View/download PDF

4. Perseverance’s Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) Investigation

Author

Bhartia, Rohit, Beegle, Luther W., DeFlores, Lauren, Abbey, William, Razzell Hollis, Joseph, Uckert, Kyle, Monacelli, Brian, Edgett, Kenneth S., Kennedy, Megan R., Sylvia, Margarite, Aldrich, David, Anderson, Mark, Asher, Sanford A., Bailey, Zachary, Boyd, Kerry, Burton, Aaron S., Caffrey, Michael, Calaway, Michael J., Calvet, Robert, Cameron, Bruce, Caplinger, Michael A., Carrier, Brandi L., Chen, Nataly, Chen, Amy, Clark, Matthew J., Clegg, Samuel, Conrad, Pamela G., Cooper, Moogega, Davis, Kristine N., Ehlmann, Bethany, Facto, Linda, Fries, Marc D., Garrison, Dan H., Gasway, Denine, Ghaemi, F. Tony, Graff, Trevor G., Hand, Kevin P., Harris, Cathleen, Hein, Jeffrey D., Heinz, Nicholas, Herzog, Harrison, Hochberg, Eric, Houck, Andrew, Hug, William F., Jensen, Elsa H., Kah, Linda C., Kennedy, John, Krylo, Robert, Lam, Johnathan, Lindeman, Mark, McGlown, Justin, Michel, John, Miller, Ed, Mills, Zachary, Minitti, Michelle E., Mok, Fai, Moore, James, Nealson, Kenneth H., Nelson, Anthony, Newell, Raymond, Nixon, Brian E., Nordman, Daniel A., Nuding, Danielle, Orellana, Sonny, Pauken, Michael, Peterson, Glen, Pollock, Randy, Quinn, Heather, Quinto, Claire, Ravine, Michael A., Reid, Ray D., Riendeau, Joe, Ross, Amy J., Sackos, Joshua, Schaffner, Jacob A., Schwochert, Mark, O Shelton, Molly, Simon, Rufus, Smith, Caroline L., Sobron, Pablo, Steadman, Kimberly, Steele, Andrew, Thiessen, Dave, Tran, Vinh D., Tsai, Tony, Tuite, Michael, Tung, Eric, Wehbe, Rami, Weinberg, Rachel, Weiner, Ryan H., Wiens, Roger C., Williford, Kenneth, Wollonciej, Chris, Wu, Yen-Hung, Yingst, R. Aileen, and Zan, Jason

Published
2021
Full Text
View/download PDF

8. Calibration of Raman Bandwidths on the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) Deep Ultraviolet Raman and Fluorescence Instrument Aboard the Perseverance Rover

Author

Jakubek, Ryan S., primary, Bhartia, Rohit, additional, Uckert, Kyle, additional, Asher, Sanford A., additional, Czaja, Andrew D., additional, Fries, Marc D., additional, Hand, Kevin, additional, Haney, Nikole C., additional, Razzell Hollis, Joseph, additional, Minitti, Michelle, additional, Sharma, Shiv K., additional, Sharma, Sunanda, additional, and Siljeström, Sandra, additional

Published
2023
Full Text
View/download PDF

9. Continuously wavelength tunable, continuous wave laser ideal for UV Raman spectroscopy.

Author

Roppel, Ryan D. and Asher, Sanford A.

Subjects
*CONTINUOUS wave lasers, *ULTRAVIOLET lasers, *RAMAN spectroscopy, *RESONANCE Raman effect, *RAMAN scattering, *DIELECTRIC breakdown
Abstract

We utilize a novel, high-power, tunable, continuous wave (CW) deep UV laser to measure resonance Raman spectra of phenolate solutions with high signalto-noise ratios (SNR). In UV resonance Raman (UVRR), increased coupling of the excitation light with a chromophore can transfer molecules into excited states that cause increased heating and photochemistry. Deep UV lasers have traditionally utilized high peak powers to enable efficient single-pass nonlinear conversion from visible into near infrared light. Nonlinear phenomena such as the formation of transient radical species, Raman saturation, thermal heating, and dielectric breakdown can introduce extraneous light sources that can complicate the interpretation of the Raman spectrum. Dielectric breakdown can increase the baseline, increase noise, and sometimes saturate the detector, preventing Raman detection. Spontaneous Raman scattering intensities should scale linearly with the excitation light intensity. However, this linear behavior does not always occur with pulsed laser excitation. This occurs because stimulated Raman scattering can cause a superlinear intensity response, or transient absorption can cause sublinear intensity responses. CW laser excitation excites samples with electric fields that are much lower than typical pulsed laser excitation. This eliminates the nonlinear responses. The geometry of our new CW laser enables high gain in the harmonic generation cavities that achieve high harmonic generation efficiencies. Average power in the deep UV is >30 mW for wavelengths as short as 206 nm. In the work here, we demonstrate that CW excitation is ideal for resonance Raman measurements in general to reduce spectral complexity. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

10. A Brief Introduction to SHERLOC

Author

Zan, Jason, Yingst, R. Aileen, Wu, Yen-Hung, Wollonciej, Chris, Williford, Kenneth, Wiens, Roger C, Weiner, Ryan H, Weinberg, Rachel, Wehbe, Rami, Tung, Eric, Tuite, Michael, Tsai, Tony, Tran, Vinh D, Thiessen, Dave, Steele, Andrew, Steadman, Kimberly, Sobron, Pablo, Smith, Caroline L, Simon, Rufus, Shelton, Molly O, Schwochert, Mark, Schaffner, Jacob A, Sackos, Joshua, Ross, Amy J, Riendeau, Joe, Reid, Ray, Ravine, Michael A, Quinto, Claire, Quinn, Heather, Pollock, Randy, Peterson, Glen, Pauken, Michael, Orellana, Sonny, Nuding, Danielle, Nordman, Daniel A, Nixon, Brian E, Newell, Raymond, Nelson, Anthony, Nealson, Kenneth H, Moore, James, Mok, Fai, Minitti, Michelle E, Mills, Zachary, Miller, Ed, Michel, John, McGlown, Justin, Lindeman, Mark, Lam, Johnathan, Krylo, Robert, Kennedy, John, Kah, Linda C, Jensen, Elsa H, Hug, William, Houck, Andrew, Hochberg, Eric, Herzog, Harrison, Heinz, Nicholas, Hein, Jeffrey D, Harris, Cathleen, Hand, Kevin H, Graff, Trevor G, Ghaemi, F. Tony, Gasway, Denine, Garrison, Dan H, Fries, Marc D, Facto, Linda, Ehlmann, Bethany, Davis, Kristine N, Cooper, Moogega, Conrad, Pamela G, Clegg, Samuel, Clark, Matthew J, Chen, Amy, Chen, Nataly, Caplinger, Michael A, Cameron, Bruce, Calvet, Robert, Calaway, Michael J, Caffrey, Michael, Burton, Aaron S, Boyd, Kerry, Bailey, Zachary, Asher, Sanford A, Anderson, Mark, Aldrich, David, Sylvia, Margarite, Kennedy, Megan R, Edgett, Kenneth S, Monacelli, Brian, Uckert, Kyle, Hollis, Joseph Razzell, Abbey, William, DeFlores, Lauren, Bhartia, Rohit, and Beegle, L.W

Published
2020

11. A Brief Introduction to SHERLOC

Author

Beegle, L.W, Bhartia, Rohit, DeFlores, Lauren, Abbey, William, Hollis, Joseph Razzell, Uckert, Kyle, Monacelli, Brian, Edgett, Kenneth S, Kennedy, Megan R, Sylvia, Margarite, Aldrich, David, Anderson, Mark, Asher, Sanford A, Bailey, Zachary, Boyd, Kerry, Burton, Aaron S, Caffrey, Michael, Calaway, Michael J, Calvet, Robert, Cameron, Bruce, Caplinger, Michael A, Chen, Nataly, Chen, Amy, Clark, Matthew J, Clegg, Samuel, Conrad, Pamela G, Cooper, Moogega, Davis, Kristine N, Ehlmann, Bethany, Facto, Linda, Fries, Marc D, Garrison, Dan H, Gasway, Denine, Ghaemi, F. Tony, Graff, Trevor G, Hand, Kevin H, Harris, Cathleen, Hein, Jeffrey D, Heinz, Nicholas, Herzog, Harrison, Hochberg, Eric, Houck, Andrew, Hug, William, Jensen, Elsa H, Kah, Linda C, Kennedy, John, Krylo, Robert, Lam, Johnathan, Lindeman, Mark, McGlown, Justin, Michel, John, Miller, Ed, Mills, Zachary, Minitti, Michelle E, Mok, Fai, Moore, James, Nealson, Kenneth H, Nelson, Anthony, Newell, Raymond, Nixon, Brian E, Nordman, Daniel A, Nuding, Danielle, Orellana, Sonny, Pauken, Michael, Peterson, Glen, Pollock, Randy, Quinn, Heather, Quinto, Claire, Ravine, Michael A, Reid, Ray, Riendeau, Joe, Ross, Amy J, Sackos, Joshua, Schaffner, Jacob A, Schwochert, Mark, Shelton, Molly O, Simon, Rufus, Smith, Caroline L, Sobron, Pablo, Steadman, Kimberly, Steele, Andrew, Thiessen, Dave, Tran, Vinh D, Tsai, Tony, Tuite, Michael, Tung, Eric, Wehbe, Rami, Weinberg, Rachel, Weiner, Ryan H, Wiens, Roger C, Williford, Kenneth, Wollonciej, Chris, Wu, Yen-Hung, Yingst, R. Aileen, and Zan, Jason

Published
2020

13. Standoff Deep Ultraviolet Raman Spectrometer for Trace Detection.

Author

Bykov, Sergei V. and Asher, Sanford A.

Abstract

We developed a state-of-the-art, high-sensitivity, low-stray-light standoff deep-ultraviolet (DUV) Raman spectrometer for the trace detection of resonance Raman-enhanced chemical species. As an excitation source for Raman measurements, we utilized our recently developed, second-generation, miniaturized, diode-pumped, solid-state neodymium-doped gadolinium orthovanadate (Nd:GdVO4) laser that generates quasi-continuous wave 228 nm light. This 228 nm excitation enhances the Raman intensities of vibrations of NOx groups in explosive molecules, aromatic groups in biological molecules, and various aromatic hydrocarbons. Our DUV Raman spectrograph utilizes a custom DUV f /8 Cassegrain telescope with an ∼200 mm diameter primary mirror, high-efficiency DUV transmission gratings, custom DUV mirrors, and a custom 228 nm Rayleigh rejection filter. We utilized our new standoff DUV Raman spectrometer to measure high signal-to-noise ratio spectra of ∼50 μg/cm2 drop-cast explosives: ammonium nitrate (AN), trinitrotoluene, pentaerythritol tetranitrate as well as aromatic biological molecules: lysozyme, tryptophan, tyrosine, deoxycytidine monophosphate, deoxyadenosine monophosphate at an ∼3 m distance within 10–30 s accumulation times. We roughly estimate the average ultraviolet resonance Raman (UVRR) detection limits for the relatively homogeneous drop-cast films of explosives and biological molecules to be ∼1 μg/cm2 when utilizing a continuous raster scanning that averages Raman signal over ∼1 cm2 sample area to avoid quick analyte depletion due to ultraviolet (UV) photolysis. We determined 3 m standoff UVRR detection limits for drop-cast AN films and identified factors impacting UVRR detection limits such as analyte photochemistry and analyte morphology. We found a detection limit of ∼0.5 μg/cm2 for drop-cast AN films on glass substrates when the Raman signal is averaged over ∼0.5 cm2 of sample surface using a continuous raster scan. For a step raster scan, when the probed sample area is limited to the laser spot size, the detection limit is approximately tenfold higher (∼5 μg/cm2) due to the impact of UV photochemistry. Graphical abstract This is a visual representation of the abstract. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

14. SHERLOC Raman Mineral Class Detections of the Mars 2020 Crater Floor Campaign

Author

Corpolongo, Andrea, primary, Jakubek, Ryan S., additional, Burton, Aaron S., additional, Brown, Adrian J., additional, Yanchilina, Anastasia, additional, Czaja, Andrew D., additional, Steele, Andrew, additional, Wogsland, Brittan V., additional, Lee, Carina, additional, Flannery, David, additional, Baker, Desirée, additional, Cloutis, Edward A., additional, Cardarelli, Emily, additional, Scheller, Eva L., additional, Berger, Eve L., additional, McCubbin, Francis M., additional, Hollis, Joseph Razzell, additional, Hickman‐Lewis, Keyron, additional, Steadman, Kim, additional, Uckert, Kyle, additional, DeFlores, Lauren, additional, Kah, Linda, additional, Beegle, Luther W., additional, Fries, Marc, additional, Minitti, Michelle, additional, Haney, Nikole C., additional, Conrad, Pamela, additional, Morris, Richard V., additional, Bhartia, Rohit, additional, Roppel, Ryan, additional, Siljeström, Sandra, additional, Asher, Sanford A., additional, Bykov, Sergei V., additional, Sharma, Sunanda, additional, Shkolyar, Svetlana, additional, Fornaro, Teresa, additional, and Abbey, William, additional

Published
2023
Full Text
View/download PDF

15. Aqueous alteration processes in Jezero crater, Mars—implications for organic geochemistry

Author

Scheller, Eva L., primary, Razzell Hollis, Joseph, additional, Cardarelli, Emily L., additional, Steele, Andrew, additional, Beegle, Luther W., additional, Bhartia, Rohit, additional, Conrad, Pamela, additional, Uckert, Kyle, additional, Sharma, Sunanda, additional, Ehlmann, Bethany L., additional, Abbey, William J., additional, Asher, Sanford A., additional, Benison, Kathleen C., additional, Berger, Eve L., additional, Beyssac, Olivier, additional, Bleefeld, Benjamin L., additional, Bosak, Tanja, additional, Brown, Adrian J., additional, Burton, Aaron S., additional, Bykov, Sergei V., additional, Cloutis, Ed, additional, Fairén, Alberto G., additional, DeFlores, Lauren, additional, Farley, Kenneth A., additional, Fey, Deidra M., additional, Fornaro, Teresa, additional, Fox, Allison C., additional, Fries, Marc, additional, Hickman-Lewis, Keyron, additional, Hug, William F., additional, Huggett, Joshua E., additional, Imbeah, Samara, additional, Jakubek, Ryan S., additional, Kah, Linda C., additional, Kelemen, Peter, additional, Kennedy, Megan R., additional, Kizovski, Tanya, additional, Lee, Carina, additional, Liu, Yang, additional, Mandon, Lucia, additional, McCubbin, Francis M., additional, Moore, Kelsey R., additional, Nixon, Brian E., additional, Núñez, Jorge I., additional, Rodriguez Sanchez-Vahamonde, Carolina, additional, Roppel, Ryan D., additional, Schulte, Mitchell, additional, Sephton, Mark A., additional, Sharma, Shiv K., additional, Siljeström, Sandra, additional, Shkolyar, Svetlana, additional, Shuster, David L., additional, Simon, Justin I., additional, Smith, Rebecca J., additional, Stack, Kathryn M., additional, Steadman, Kim, additional, Weiss, Benjamin P., additional, Werynski, Alyssa, additional, Williams, Amy J., additional, Wiens, Roger C., additional, Williford, Kenneth H., additional, Winchell, Kathrine, additional, Wogsland, Brittan, additional, Yanchilina, Anastasia, additional, Yingling, Rachel, additional, and Zorzano, Maria-Paz, additional

Published
2022
Full Text
View/download PDF

18. Calibration of the SHERLOC Deep Ultraviolet Fluorescence–Raman Spectrometer on the Perseverance Rover

Author

Uckert, Kyle, primary, Bhartia, Rohit, additional, Beegle, Luther W., additional, Monacelli, Brian, additional, Asher, Sanford A., additional, Burton, Aaron S., additional, Bykov, Sergei V., additional, Davis, Kristine, additional, Fries, Marc D., additional, Jakubek, Ryan S., additional, Hollis, Joseph Razzell, additional, Roppel, Ryan D., additional, and Wu, Yen-Hung, additional

Published
2021
Full Text
View/download PDF

19. Solid State Vanadate Laser and 213 nm Rayleigh Rejection Filter Enable Miniaturized Deep Ultraviolet Raman Spectrometers.

Author

Bykov, Sergei V. and Asher, Sanford A.

Abstract

A combination of a highly efficient 213 nm Rayleigh rejection filter (RRF) and a miniaturized 213 nm neodymium-doped vanadate laser enables portable deep ultraviolet (UV) Raman spectrometers. We demonstrate the high efficiency of 213 nm RRF manufactured by Green Optics Co., Ltd by utilizing our compact 213 nm vanadate laser to measure high signal-to-noise ratio UV Raman spectra of Teflon and UV resonance Raman (UVRR) spectra of solid ammonium nitrate. We also demonstrate UVRR detection of trace amounts of ammonia formed during ammonium nitrate UV photolysis. We roughly estimate the ammonia UVRR detection limit of ∼10 ng under our experimental conditions. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

23. Photonic crystal protein hydrogel sensor materials enabled by conformationally induced volume phase transition† †Electronic supplementary information (ESI) available: Mechanism of the crosslinking reaction, protein sequence of GGBP, UVRR spectra, UV-Vis reflection spectra of 2-D PC-GGBP sensor at different glucose concentrations and additional information of crystal structures of GGBP. See DOI: 10.1039/c6sc00682e

Author

Cai, Zhongyu, Luck, Linda A., Punihaole, David, Madura, Jeffry D., and Asher, Sanford A.

Subjects
Chemistry, technology, industry, and agriculture, sense organs
Abstract

We fabricated photonic crystal glucose/galactose binding protein sensing hydrogels for glucose detection using protein conformational change induced volume phase transition., Hydrogels that change volume in response to specific molecular stimuli can serve as platforms for sensors, actuators and drug delivery devices. There is great interest in designing intelligent hydrogels for tissue engineering, drug delivery, and microfluidics that utilize protein binding specificities and conformational changes. Protein conformational change induced by ligand binding can cause volume phase transitions (VPTs). Here, we develop a highly selective glucose sensing protein photonic crystal (PC) hydrogel that is fabricated from genetically engineered E. coli glucose/galactose binding protein (GGBP). The resulting 2-D PC-GGBP hydrogel undergoes a VPT in response to glucose. The volume change causes the 2-D PC array particle spacing to decrease, leading to a blue-shifted diffraction which enables our sensors to report on glucose concentrations. This 2-D PC-GGBP responsive hydrogel functions as a selective and sensitive sensor that easily monitors glucose concentrations from ∼0.2 μM to ∼10 mM. This work demonstrates a proof-of-concept for developing responsive, “smart” protein hydrogel materials with VPTs that utilize ligand binding induced protein conformational changes. This innovation may enable the development of other novel chemical sensors and high-throughput screening devices that can monitor protein–drug binding interactions.

Published
2016

30. 228‐nm quadrupled quasi‐three‐level Nd:GdVO4 laser for ultraviolet resonance Raman spectroscopy of explosives and biological molecules.

Author

Bykov, Sergei V., Roppel, Ryan D., Mao, Michael, and Asher, Sanford A.

Subjects
RESONANCE Raman spectroscopy, BIOMOLECULES, DIFFERENTIAL cross sections, LIGHT sources, CONTINUOUS wave lasers, EXPLOSIVES, ULTRAVIOLET lasers
Abstract

We describe a new compact diode‐pumped solid‐state frequency quadrupled quasi‐three‐level neodymium‐doped gadolinium vanadate (Nd:GdVO4) laser that generates ~50 mW of 228‐nm quasi‐continuous wave light as ns pulses at a tunable kilohertz repetition rate. We developed two generations of this laser. The first generation has a high duty cycle and a tunable repetition rate. The second generation is optimized for maximum output power. We utilize these new lasers to measure ultraviolet resonance Raman (UVRR) spectra of many important chromophores that absorb in deep ultraviolet (UV). We demonstrate the utility of this excitation by measuring the 228‐nm absolute differential Raman cross sections of explosives, peptides, aromatic amino acids, and DNA/RNA nucleotides. Deep UV excitation at 228 nm occurs within the π → π* electronic transitions of these molecules. The 228‐nm resonance excitation enhances the Raman intensities of vibrations of NOx groups, peptide bonds, aromatic amino acid side chains, and DNA/RNA nucleotides. The measured 228‐nm UVRR cross sections of these molecules are 103–104 fold greater than those excited in the visible spectral region. These new lasers should be of great interest for UVRR spectroscopy and for other applications that benefit from compact, high average power deep UV laser light sources with low peak powers. [ABSTRACT FROM AUTHOR]

Published
2020
Full Text
View/download PDF

38. Stimuli-Responsive Pure Protein Organogel Sensors and Biocatalytic Materials

Author

Smith, Natasha L., Coukouma, Andrew E., Wilson, David C., Ho, Brenda, Gray, Vincent, and Asher, Sanford A.

Abstract

Utilizing protein chemistry in organic solvents has important biotechnology applications. Typically, organic solvents negatively impact protein structure and function. Immobilizing proteins via cross-links to a support matrix or to other proteins is a common strategy to preserve the native protein function. Recently, we developed methods to fabricate macroscopic responsive pure protein hydrogels by lightly cross-linking the proteins with glutaraldehyde for chemical sensing and enzymatic catalysis applications. The water in the resulting protein hydrogel can be exchanged for organic solvents. The resulting organogel contains pure organic solvents as their mobile phases. The organogel proteins retain much of their native protein function, i.e., protein–ligand binding and enzymatic activity. A stepwise ethylene glycol (EG) solvent exchange was performed to transform these hydrogels into organogels with a very low vapor pressure mobile phase. These responsive organogels are not limited by solvent/mobile phase evaporation. The solvent exchange to pure EG is accompanied by a volume phase transition (VPT) that decreases the organogel volume compared to that of the hydrogel. Our organogel sensor systems utilize shifts in the particle spacing of an attached two-dimensional photonic crystal (2DPC) to report on the volume changes induced by protein–ligand binding. Our 2DPC bovine serum albumin (BSA) organogels exhibit VPT that swell the organogels in response to the BSA binding of charged ligands like ibuprofen and fatty acids. To our knowledge, this is the first report of a pure protein organogel VPT induced by protein–ligand binding. Catalytic protein organogels were also fabricated that utilize the enzyme organophosphorus hydrolase (OPH) to hydrolyze toxic organophosphate (OP) nerve agents. Our OPH organogels retain significant enzymatic activity. The OPH organogel rate of OP hydrolysis is ∼160 times higher than that of un-cross-linked OPH monomers in a 1:1 ethylene glycol/water mixture.

Published
2020
Full Text
View/download PDF

44. Mechanisms by Which Organic Solvent Exchange Transforms Responsive Pure Protein Hydrogels into Responsive Organogels

Author

Smith, Natasha Lynn, Coukouma, Andrew Eagle, Jakubek, Ryan S., and Asher, Sanford A.

Abstract

Responsive pure protein organogel sensors and catalysts are fabricated by replacing the aqueous mobile phase of protein hydrogels with pure ethylene glycol (EG). Exchanging water for EG causes irreversible volume phase transitions (VPT) in bovine serum albumin (BSA) polymers; however, BSA hydrogel and organogel sensors show similar volume responses to protein–ligand binding. This work elucidates the mechanisms involved in this enabling irreversible VPT by examining the protein secondary structure, hydration, and protein polymer morphology. Organogel proteins retain their native activity because their secondary structure and hydration shell are relatively unperturbed by the EG exchange. Conversely, the decreasing solvent quality initiates polymer phase separation to minimize the BSA polymer surface area exposed to EG, thus decreasing distances between BSA polymer strands. These protein polymer morphology changes promote interprotein interactions between BSA polymer strands, which increase the effective polymer cross-link density and prevent organogel swelling as the mobile phase is exchanged back to water.

Published
2020
Full Text
View/download PDF

45. Langevin Dynamics Simulation of 3D Colloidal Crystal Vacancies and Phase Transitions

Author

Laghaei, Rozita, Asher, Sanford A., and Coalson, Rob D.

Abstract

We study the mechanism of vacancy migration and phase transitions of 3D crystalline colloidal arrays (CCA) using Langevin dynamics simulations. We calculate the self-diffusion coefficient of the colloid particles and the diffusion constant for vacancies as a function of temperature and DLVO potential parameters. We investigate the phase behavior of several systems with different interaction potential parameters using Voronoi analysis. Voronoi polyhedra tessellation, which is a useful method for characterizing the nearest neighbor environment around each atom, provides an efficient and effective way to identify phase transitions as well as geometrical changes in crystals. Using Voronoi analysis, we show that several neighboring particles are involved in the vacancy migration process that causes the vacancy to diffuse.

Published
2024
Full Text
View/download PDF

46. UV Resonance Raman Finds Peptide Bond−Arg Side Chain Electronic Interactions

Author

Sharma, Bhavya and Asher, Sanford A.

Abstract

We measured the UV resonance Raman excitation profiles and Raman depolarization ratios of the arginine (Arg) vibrations of the amino acid monomer as well as Arg in the 21-residue predominantly alanine peptide AAAAA(AAARA)3A (AP) between 194 and 218 nm. Excitation within the π → π* peptide bond electronic transitions result in UVRR spectra dominated by amide peptide bond vibrations. The Raman cross sections and excitation profiles indicate that the Arg side chain electronic transitions mix with the AP peptide bond electronic transitions. The Arg Raman bands in AP exhibit Raman excitation profiles similar to those of the amide bands in AP which are conformation specific. These Arg excitation profiles distinctly differ from the Arg monomer. The Raman depolarization ratios of Arg in monomeric solution are quite simple with ρ = 0.33 indicating enhancement by a single electronic transition. In contrast, we see very complex depolarization ratios of Arg in AP that indicate that the Arg residues are resonance enhanced by multiple electronic transitions.

Published
2024
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results