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Xu X, Gupta B, Nguyen JP, Jin R, Garcia M, Kaur S, Hasan SK, Watterson AC, Ruths M. Stability and collapse of amphiphilic copolymer aggregates in contact with hydrophilic mica surfaces. J DISPER SCI TECHNOL 2021. [DOI: 10.1080/01932691.2020.1869563] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Affiliation(s)
- Xin Xu
- Department of Chemistry, University of Massachusetts Lowell, Lowell, Massachusetts, USA
| | - Bhavna Gupta
- Department of Chemistry, University of Massachusetts Lowell, Lowell, Massachusetts, USA
| | - Jennifer P. Nguyen
- Department of Chemistry, University of Massachusetts Lowell, Lowell, Massachusetts, USA
| | - Ruting Jin
- Department of Chemistry, University of Massachusetts Lowell, Lowell, Massachusetts, USA
| | - Manuel Garcia
- Department of Chemistry, University of Massachusetts Lowell, Lowell, Massachusetts, USA
| | - Satvinder Kaur
- Department of Chemistry, University of Massachusetts Lowell, Lowell, Massachusetts, USA
| | - Syed K. Hasan
- Immunotrex Biologics, Inc, North Andover, Massachusetts, USA
| | - Arthur C. Watterson
- Department of Chemistry, University of Massachusetts Lowell, Lowell, Massachusetts, USA
| | - Marina Ruths
- Department of Chemistry, University of Massachusetts Lowell, Lowell, Massachusetts, USA
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Han T, Yi S, Zhang C, Li J, Chen X, Luo J, Banquy X. Superlubrication obtained with mixtures of hydrated ions and polyethylene glycol solutions in the mixed and hydrodynamic lubrication regimes. J Colloid Interface Sci 2020; 579:479-488. [PMID: 32622097 DOI: 10.1016/j.jcis.2020.06.095] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2020] [Revised: 06/21/2020] [Accepted: 06/22/2020] [Indexed: 12/31/2022]
Abstract
HYPOTHESIS Superlubricity is known to dramatically reduce frictional energy consumption and to improve service life of mechanical devices and biological systems. However, reduction of wear during the running-in period of friction pairs, especially under high contact pressures, still remains an unresolved issue affecting all machines. EXPERIMENTS Here the lubrication, adsorption, and conformational properties of hydrated ions and polyethylene glycol (PEG) mixtures were evaluated at different mass fractions and concentrations of PEG and salts by ball-on-disc tribometer, ζ-potential, quartz crystal microbalance with dissipation (QCM-D), and dynamic light scatting (DLS) analyses. FINDINGS These mixtures exhibited superlubricity between Si3N4 and sapphire surfaces in a wide range of concentrations and ions valency. Interestingly, a running-in phase shorter than 1 min and low wear rate of 1.85 μm3/(N·m) were observed at contact pressures up to 555 MPa, significantly higher to earlier findings. PEG chains retain random coils filling the bulk of the interfacial film without strongly adsorbing on the interfaces but significantly increasing the viscosity of lubricating film, thereby favoring hydrodynamic lubrication. Hydrated ions are strongly adsorbed on the negatively charged ceramic surfaces, ensuring a sustained hydration effect maintaining superlubricity. The outstanding lubrication characteristics of the PEG/ions mixtures were attributed to the synergistic action of hydration and hydrodynamic lubrication, which appears as a promising avenue for developing new green lubricants and has implications for industrial and biological applications.
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Affiliation(s)
- Tianyi Han
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China; Faculty of Pharmacy, Université de Montréal, Montreal, Quebec H3C 3J7, Canada
| | - Shuang Yi
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
| | - Chenhui Zhang
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China.
| | - Jinjin Li
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
| | - Xinchun Chen
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
| | - Jianbin Luo
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
| | - Xavier Banquy
- Faculty of Pharmacy, Université de Montréal, Montreal, Quebec H3C 3J7, Canada
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The properties of the polyethylene glycol complex PEG(Na+)(Cu+) on the copper electrodeposited layer by Time-of-Flight Secondary-Ion Mass Spectrometry. The new insights. Electrochim Acta 2020. [DOI: 10.1016/j.electacta.2020.135931] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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4
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Miyamoto T, Yamazaki N, Watanabe S, Yamada S. Aqueous Lubrication with the Molecularly Confined Films of Silicone-Based Amphiphilic Block Copolymer Aggregates. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:15784-15794. [PMID: 31656076 DOI: 10.1021/acs.langmuir.9b03212] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The confined film structures and tribological properties of the dilute aqueous solution of a silicone-based amphiphilic block copolymer, bis-isobutyl poly(ethylene glycol) (PEG)-14/amodimethicone (BIPA) copolymer, between mica surfaces were investigated. The BIPA copolymer existed as positively charged water-soluble aggregates in the solution. The adsorption behavior of the BIPA copolymer aggregates on a mica surface from solution was studied using an atomic force microscope (AFM); the result showed the immediate formation of a uniform adsorbed BIPA copolymer layer, followed by the gradual deposition of BIPA aggregates on the top of the adsorbed layer. Friction measurements were carried out using the surface forces apparatus (SFA) for the confined films of BIPA copolymer solution between mica surfaces, which revealed two different sliding film structures depending on the elapsed time after surface preparation. The sliding film consisting of two adsorbed BIPA copolymer layers was obtained for a relatively short elapsed time (not longer than 3 h), which had an extremely low friction coefficient μ (of the order of 10-5). The sliding film on the following day (elapsed time of approximately 24 h) had the structure of a deposited/kinetically trapped BIPA aggregate layer confined between the opposing adsorbed layers, and the μ values were within the range from 10-4 to 10-3. Our results suggest that the different elapsed time ranges and resulting absence or presence of the intervening layer of trapped aggregates between the absorbed layers determine the tribological properties of the confined films. Molecular friction mechanisms are discussed for the two sliding structures, which give insight into using amphiphilic block copolymer aggregates for a new class of aqueous lubrication system to design extremely low friction interfaces.
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Affiliation(s)
- Takumi Miyamoto
- R&D - Analytical Science Research , Kao Corporation , 1334 Minato , Wakayama , Wakayama 640-8580 , Japan
| | - Naoyuki Yamazaki
- R&D - Hair Care Products Research , Kao Corporation , 2-1-3 Bunka , Sumida-ku , Tokyo 131-8501 , Japan
| | - Shunichi Watanabe
- R&D - Hair Care Products Research , Kao Corporation , 2-1-3 Bunka , Sumida-ku , Tokyo 131-8501 , Japan
| | - Shinji Yamada
- R&D - Analytical Science Research , Kao Corporation , 1334 Minato , Wakayama , Wakayama 640-8580 , Japan
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5
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Angayarkanni SA, Kampf N, Klein J. Surface Interactions between Boundary Layers of Poly(ethylene oxide)-Liposome Complexes: Lubrication, Bridging, and Selective Ligation †. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:15469-15480. [PMID: 31348857 DOI: 10.1021/acs.langmuir.9b01708] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Poly(ethylene oxide), PEO, is widely exploited in biomedical applications, while phosphatidylcholine (PC) lipids (in the form of bilayers or liposomes) have been identified as very efficient boundary lubricants in aqueous media. Here we examine, using a surface force balance (SFB), the interactions between surface-adsorbed layers of PEO complexed with small unilamellar vesicles (SUVs, i.e. liposomes) or with bilayers of PC lipids, both well below and a little above their main gel-to-liquid phase-transition temperatures TM. The morphology of PEO layers (adsorbed onto mica), to which liposomes were added, was examined using atomic force microscopy (AFM) and cryo-scanning electron microscopy (cryo-SEM). Our results reveal that the PC lipids could attach to the PEO either as vesicles or as bilayers, depending on whether they were above or below TM. Under water (no added salt), excellent lubrication, with friction coefficients down to 10-3-10-4, up to contact stresses of 6.5 MPa (comparable to those in the major joints) was observed between two surfaces bearing such PEO-PC complexes. At 0.1 M KNO3 salt concentration (comparable to physiological salt levels), the friction between such surfaces was considerably higher, attributed to bridging by the polymer chains. Remarkably, such bridging could be suppressed and the friction could be restored to its previous low value if the KNO3 was replaced with NaNO3, as a result of the different PEO-mica ligation properties of Na+ compared to those of K+. Our results provide insight into the properties of PEO-PC complexes in potential applications, and large interfacial effects that can result from the seemingly innocuous replacement of K+ by Na+ ions.
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Affiliation(s)
- S A Angayarkanni
- Department of Materials and Interfaces , Weizmann Institute of Science , Rehovot 76100 , Israel
| | - Nir Kampf
- Department of Materials and Interfaces , Weizmann Institute of Science , Rehovot 76100 , Israel
| | - Jacob Klein
- Department of Materials and Interfaces , Weizmann Institute of Science , Rehovot 76100 , Israel
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6
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Lu JE, Chen S. Organized assembling of poly(ethylene glycol)-functionalized Janus nanoparticles induced by select alkali metal ions. INORG CHEM COMMUN 2019. [DOI: 10.1016/j.inoche.2019.107586] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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7
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Wu B, Chun BW, Gu L, Kuhl TL. Effect of Ca2+ ion concentration on adsorption of poly(carboxylate ether)-based (PCE) superplasticizer on mica. J Colloid Interface Sci 2018; 527:195-201. [PMID: 29793174 DOI: 10.1016/j.jcis.2018.05.016] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Revised: 05/08/2018] [Accepted: 05/08/2018] [Indexed: 11/27/2022]
Affiliation(s)
- Bo Wu
- School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China; Department of Chemical Engineering and Materials Science, University of California at Davis, Davis, CA 95616, United States
| | - Byong-Wa Chun
- GCP Applied Technologies, Cambridge, MA 02140, United States
| | - Le Gu
- School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China
| | - Tonya L Kuhl
- Department of Chemical Engineering and Materials Science, University of California at Davis, Davis, CA 95616, United States.
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Abstract
The major synovial joints such as hips and knees are uniquely efficient tribological systems, able to articulate over a wide range of shear rates with a friction coefficient between the sliding cartilage surfaces as low as 0.001 up to pressures of more than 100 atm. No human-made material can match this. The means by which such surfaces maintain their very low friction has been intensively studied for decades and has been attributed to fluid-film and boundary lubrication. Here, we focus especially on the latter: the reduction of friction by molecular layers at the sliding cartilage surfaces. In particular, we discuss such lubrication in the light of very recent advances in our understanding of boundary effects in aqueous media based on the paradigms of hydration lubrication and of the synergism between different molecular components of the synovial joints (namely hyaluronan, lubricin, and phospholipids) in enabling this lubrication.
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Affiliation(s)
- Sabrina Jahn
- Weizmann Institute of Science, Rehovot 76100, Israel;
| | - Jasmine Seror
- Weizmann Institute of Science, Rehovot 76100, Israel;
| | - Jacob Klein
- Weizmann Institute of Science, Rehovot 76100, Israel;
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9
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Gaisinskaya-Kipnis A, Ma L, Kampf N, Klein J. Frictional Dissipation Pathways Mediated by Hydrated Alkali Metal Ions. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:4755-4764. [PMID: 27089022 DOI: 10.1021/acs.langmuir.6b00707] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Frictional energy dissipation between sliding solid surfaces in aqueous media may proceed by different pathways. Using a surface force balance (SFB), we have examined systematically how such dissipation is mediated by the series of hydrated cations M(+) = Li(+), Na(+), and K(+) that are trapped between two atomically smooth, negatively charged, mica surfaces sliding across the ionic solutions over many orders of magnitude loading. By working at local contact pressures up to ca. 30 MPa (∼300 atm), up to 2 orders of magnitude higher than earlier studies, we could show that the frictional dissipation at constant sliding velocity, represented by the coefficient of sliding friction μM+, decreased as μLi+ > μNa+ ≳ μK+. This result contrasts with the expectation (in conceptual analogy with the Hofmeister series) that the lubrication would improve with the extent of ionic hydration, since that would have led to the opposite μM+ sequence. It suggests, rather, that frictional forces, even in such simple systems, can be dominated by rate-activated pathways where the size of the hydration shell becomes a dissipative liability, rather than by the hydration-shell dissipation expected via the hydration lubrication mechanism.
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Affiliation(s)
| | - Liran Ma
- Department of Materials and Interfaces, Weizmann Institute of Science , Rehovot, 76100, Israel
- State Key Laboratory of Tribology, Tsinghua University , Beijing 100084, China
| | - Nir Kampf
- Department of Materials and Interfaces, Weizmann Institute of Science , Rehovot, 76100, Israel
| | - Jacob Klein
- Department of Materials and Interfaces, Weizmann Institute of Science , Rehovot, 76100, Israel
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Penfold J, Thomas RK, Li PX, Tucker I, Petkov J, Petkova RE. Nature of the Intermicellar Interactions in Ethoxylated Polysorbate Surfactants with High Degrees of Ethoxylation. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:1319-1326. [PMID: 26785290 DOI: 10.1021/acs.langmuir.5b04642] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Ethoxylated polysorbate Tween nonionic surfactants are extensively used as foam and emulsion stabilizers and in aqueous solution form globular micelles. The ethoxylated polysorbate surfactants with higher degrees of ethoxylation than the Tween surfactants exhibit some interesting self-assembly properties. Small-angle neutron scattering, SANS, measurements have revealed intermicellar interactions which are more pronounced than the hard-sphere excluded volume interactions normally associated with nonionic surfactant micelles. The interactions are interpreted as arising from the partial charge on the ether oxygen of the ethylene oxide groups. This gives rise to an effective net negative charge on the micelles, which has been determined from the SANS data and zeta potential measurements. For degrees of ethoxylation of ⩽20, the effect is relatively small. The interaction increases with increasing ethoxylation such that for a degree of ethoxylation of 50 the interaction is comparable to that of ionic surfactant micelles. Unlike the intermicellar interaction in ionic surfactant micellar solutions, which results from the charge on the micelle arising from the partial binding of counterions, the interaction between ethoxthylated polysorbate surfactant micelles is unaffected by the addition of electrolyte.
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Affiliation(s)
- J Penfold
- Physical and Theoretical Chemistry Laboratory, Oxford University , South Parks Road, Oxford OX1 3QZ, U.K
- ISIS, STFC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, U.K
| | - R K Thomas
- Physical and Theoretical Chemistry Laboratory, Oxford University , South Parks Road, Oxford OX1 3QZ, U.K
| | - P X Li
- ISIS, STFC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, U.K
| | - I Tucker
- Unilever Research and Development Laboratory, Port Sunlight, Quarry Road East, Bebington, Wirral CH63 2JW, U.K
| | - J Petkov
- Unilever Research and Development Laboratory, Port Sunlight, Quarry Road East, Bebington, Wirral CH63 2JW, U.K
| | - R E Petkova
- Unilever Research and Development Laboratory, Port Sunlight, Quarry Road East, Bebington, Wirral CH63 2JW, U.K
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Affiliation(s)
- Sabrina Jahn
- Department
of Materials and
Interfaces, Weizmann Institute of Science, 76100 Rehovot, Israel
| | - Jacob Klein
- Department
of Materials and
Interfaces, Weizmann Institute of Science, 76100 Rehovot, Israel
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Wei X, Gong X, Ngai T. Interactions between solid surfaces mediated by polyethylene oxide polymers: effect of polymer concentration. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:11038-11045. [PMID: 23915116 DOI: 10.1021/la401671m] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Using total internal reflection microscopy (TIRM), we have systematically measured the interactions between a microsphere and a flat hydrophilic surface in the presence of polyethylene oxide (PEO) polymer solution. Our results reveal that PEO significantly mediates the interaction forces between the two surfaces. At low polymer concentration, the interactions between two surfaces in the presence of PEO are mainly dominated by repulsive forces, originating from diffuse layer overlap. At intermediate polymer concentration, a long-range and weak attraction sets in. This force is likely attributed to the depletion attraction due to the presence of free PEO chains in bulk solution; however, a simple hard-sphere AO model fails to precisely describe the attraction. At high polymer concentration where PEO chains overlap, the attraction disappears, and levitation of the microsphere probe is detected. We argue that at this overlapping region, the correlation length of PEO chains is much smaller than the size of single PEO molecule, leading to weakening and disappearing of the depletion attraction. Finally, at very high concentration, oscillatory structural force is obviously found, indicating the significant structural ordering of the PEO chains under confinement.
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Affiliation(s)
- Xiaoling Wei
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong
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13
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Tanaka M, Abiko S, Koshikawa N, Kinoshita T. A peptide-PEG conjugate-directed nanoperiodic hierarchical architecture by spatial selective self-assembly at the solid/water interface. RSC Adv 2013. [DOI: 10.1039/c3ra40390d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
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14
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Al-Hashmi A, Luckham P, Al-Maamari R, Zaitoun A, Al-Sharji H. The role of hydration degree of cations and anions on the adsorption of high-molecular-weight nonionic polyacrylamide on glass surfaces. Colloids Surf A Physicochem Eng Asp 2012. [DOI: 10.1016/j.colsurfa.2012.09.015] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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15
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Leng Y. Hydration force between mica surfaces in aqueous KCl electrolyte solution. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:5339-5349. [PMID: 22369483 DOI: 10.1021/la204603y] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Liquid-vapor molecular dynamics simulations are performed to study the interaction forces between two mica surfaces in an aqueous KCl electrolyte solution. Strong repulsive hydration force is obtained within a distance of ~2 nm between the two mica surfaces, which cannot be explained by the continuum theory of double-layer repulsion. We find that this short-range repulsive hydration force is much stronger than the double-layer force between mica surfaces. Whereas the simulation system is much smaller than the surface force measurement system, fundamental mechanisms of repulsive hydration force are revealed. In particular, important features of the step-like force oscillatory behavior during normal compression and force hysteresis during retraction are observed. Detailed analysis of the ionic density distributions shows that the "forced adsorption" of diffusive K(+) ions onto mica surfaces during compression and the subsequent "slow desorption" of the absorbed K(+) ions from mica surfaces upon retraction are responsible for the hysteresis phenomenon. From a mechanics point of view, we attribute the load bearing capacity of the dense electrolyte to the very hard hydration shells of K(+) metal ions under confinement. We find that the hydrated K(+) ions and Cl(-) co-ions remain very diffusive in the aqueous film. Water molecules in the hydration layer are also very fluidic, in the sense that the diffusion constant of water molecules is less than its bulk value by at most 3 orders of magnitude under the extreme confinement.
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Affiliation(s)
- Yongsheng Leng
- Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC 20052, USA.
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16
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Gaisinskaya A, Ma L, Silbert G, Sorkin R, Tairy O, Goldberg R, Kampf N, Klein J. Hydration lubrication: exploring a new paradigm. Faraday Discuss 2012; 156:217-33; discussion 293-309. [DOI: 10.1039/c2fd00127f] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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17
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Using atomic force microscopy to probe the adsorption kinetics of poly(ethylene oxide) on glass surfaces from aqueous solutions. Colloids Surf A Physicochem Eng Asp 2012. [DOI: 10.1016/j.colsurfa.2011.10.025] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Dvir H, Silman I, Harel M, Rosenberry TL, Sussman JL. Acetylcholinesterase: from 3D structure to function. Chem Biol Interact 2010; 187:10-22. [PMID: 20138030 DOI: 10.1016/j.cbi.2010.01.042] [Citation(s) in RCA: 456] [Impact Index Per Article: 32.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2009] [Revised: 01/26/2010] [Accepted: 01/28/2010] [Indexed: 11/28/2022]
Abstract
By rapid hydrolysis of the neurotransmitter, acetylcholine, acetylcholinesterase terminates neurotransmission at cholinergic synapses. Acetylcholinesterase is a very fast enzyme, functioning at a rate approaching that of a diffusion-controlled reaction. The powerful toxicity of organophosphate poisons is attributed primarily to their potent inhibition of acetylcholinesterase. Acetylcholinesterase inhibitors are utilized in the treatment of various neurological disorders, and are the principal drugs approved thus far by the FDA for management of Alzheimer's disease. Many organophosphates and carbamates serve as potent insecticides, by selectively inhibiting insect acetylcholinesterase. The determination of the crystal structure of Torpedo californica acetylcholinesterase permitted visualization, for the first time, at atomic resolution, of a binding pocket for acetylcholine. It also allowed identification of the active site of acetylcholinesterase, which, unexpectedly, is located at the bottom of a deep gorge lined largely by aromatic residues. The crystal structure of recombinant human acetylcholinesterase in its apo-state is similar in its overall features to that of the Torpedo enzyme; however, the unique crystal packing reveals a novel peptide sequence which blocks access to the active-site gorge.
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Affiliation(s)
- Hay Dvir
- Department of Structural Biology, Weizmann Institute of Science, Rehovot 76100, Israel
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Perkin S, Goldberg R, Chai L, Kampf N, Klein J. Dynamic properties of confined hydration layers. Faraday Discuss 2009; 141:399-413; discussion 443-65. [DOI: 10.1039/b805244a] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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21
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Goldberg R, Chai L, Perkin S, Kampf N, Klein J. Breakdown of hydration repulsion between charged surfaces in aqueous Cs+ solutions. Phys Chem Chem Phys 2008; 10:4939-45. [PMID: 18688538 DOI: 10.1039/b807459n] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Using a surface force balance, we have measured the normal and shear forces between mica surfaces across aqueous caesium salt solutions (CsNO(3) and CsCl) up to 100 mM concentrations. In contrast to all other alkali metal ions at these concentrations, we find no evidence of hydration repulsion between the mica surfaces on close approach: the surfaces appear to be largely neutralized by condensation of the Cs ions onto the charged lattice sites, and are attracted on approach into adhesive contact. The contact separation at adhesion indicates that the condensed Cs ions protrude by 0.3 +/- 0.2 nm from each surface, an observation supported both by the relatively weak adhesion energies between the surfaces, and the relatively weak frictional yield stress when they are made to slide past each other. These observations show directly that the hydration shells about the Cs(+) ions are removed as the ions condense into the charged surface lattice. This effect is attributed to the low energies-resulting from their large ionic radius-required for dehydration of these ions.
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Affiliation(s)
- Ronit Goldberg
- Dept. of Materials and Interfaces, Weizmann Institute, Rehovot, Israel
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Silman I, Sussman JL. Acetylcholinesterase: how is structure related to function? Chem Biol Interact 2008; 175:3-10. [PMID: 18586019 DOI: 10.1016/j.cbi.2008.05.035] [Citation(s) in RCA: 150] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2007] [Revised: 05/23/2008] [Accepted: 05/29/2008] [Indexed: 10/22/2022]
Abstract
In accordance with its biological role, termination of neurotransmission at cholinergic synapses by rapid hydrolysis of the neurotransmitter, acetylcholine, acetylcholinesterase is one of nature's most efficient enzymes. Solution of its three-dimensional structure revealed that its active site is located at the bottom of a deep and narrow gorge. Such an architecture was unanticipated in view of its high turnover number. The present review examines how the highly specialized structure of acetylcholinesterase, with its sequestered active site, contributes to its catalytic efficacy, and discusses how the traffic of substrate and products to and from the active site is controlled.
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Affiliation(s)
- Israel Silman
- Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel
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