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Intense geomagnetic storms can have a strong impact on the signals (termed ionospheric scintillations) emitted by any global navigation satellite system (GNSS). The paper reports the first studies of scintillations at the Indore region on the NavIC signals due to the impact of the intense geomagnetic storm event reported on September 8, 2017, at 0151 and 1304 UT. The variation of the planetary indices as well as the DST index which dropped to a value of -124 nT on September 8, 2017, indicates the occurrence of an intense geomagnetic storm on September 8, 2017. The observations presented are carried out at Indore, which is located at the equatorial anomaly crest. The S4 index measurements of colocated GNSS receiver showed values of 0.5 or above on the disturbed day between 15 and 18 UT. The analysis presented clearly signifies the degradation of the carrier to noise measurements of the NavIC L5 signal during the same time, which in turn affected the positional accuracy of NavIC, an important consideration for performance., Comment: 6 pages, 5 figures, accepted as a part of the Lecture Notes in Networks and Systems (LNNS) book series, 2021

This article implements a Convolutional Neural Network (CNN)-based deep learning model for solar-wind prediction. Images from the Atmospheric Imaging Assembly (AIA) at 193\.A wavelength are used for training. Solar-wind speed is taken from the Advanced Composition Explorer (ACE) located at the Lagrangian L1 point. The proposed CNN architecture is designed from scratch for training with four years' data. The solar-wind has been ballistically traced back to the Sun assuming a constant speed during propagation, to obtain the corresponding coronal intensity data from AIA images. This forecasting scheme can predict the solar-wind speed well with a RMSE of 76.3 km\s and an overall correlation coefficient of 0.57 for the year 2018, while significantly outperforming benchmark models. The threat score for the model is around 0.46 in identifying the HSEs with zero false alarms., Comment: 21 pages,13 figures. Accepted for publication in Solar Physics. After published, it will be available at https://www.springer.com/journal/11207

India though being the birthplace of the ancient science of sex, it is really a matter of shame that the post British India, considers it a taboo, to talk and discuss it in the public. Like many other ancient scriptures and technologies that were all initiated by India, but are now used and further developed by the western world, India, in this case too only boasts itself of having just invented this, but, with little implications in their modern life. Like the Vedas, Upansihadas, Ayurveda, Yoga, Mathematics, Kamasutra or the science of sex, had also developed in this part of the world first, but, is considered obscene in present day India. What is even more insane is that there are numerous, monuments, buildings of the ancient and medieval history still present in this country, which openly depicts sex in the form of sculptures and paintings, and are popular tourist destinations, but watching the same over electronic media has been labelled illicit.

This article implements a Convolutional Neural Network (CNN)-based deep learning model for solar-wind prediction. Images from the Atmospheric Imaging Assembly (AIA) at 193\.A wavelength are used for training. Solar-wind speed is taken from the Advanced Composition Explorer (ACE) located at the Lagrangian L1 point. The proposed CNN architecture is designed from scratch for training with four years' data. The solar-wind has been ballistically traced back to the Sun assuming a constant speed during propagation, to obtain the corresponding coronal intensity data from AIA images. This forecasting scheme can predict the solar-wind speed well with a RMSE of 76.3 km\s and an overall correlation coefficient of 0.57 for the year 2018, while significantly outperforming benchmark models. The threat score for the model is around 0.46 in identifying the HSEs with zero false alarms., Comment: 21 pages,13 figures. Accepted for publication in Solar Physics. After published, it will be available at https://www.springer.com/journal/11207

This paper emphasizes on NavIC's performance in ionospheric studies over the Indian subcontinent region. The study is performed using data of one year (2017-18) at IIT Indore, a location near the northern crest of Equatorial Ionization Anomaly (EIA). It has been observed that even without the individual error corrections, the results are within $\pm20\%$ of NavIC VTEC estimates observed over the 1\ensuremath{^{\circ}} x 1\ensuremath{^{\circ}} grid of IPP surrounding the GPS VTEC estimates for most of the time. Additionally, ionospheric response during two distinct geomagnetic storms (September 08 and 28, 2017) at the same location and other IGS stations covering the Indian subcontinent using both GPS and NavIC has also been presented. This analysis revealed similar variations in TEC during the geomagnetic storms of September 2017, indicating the suitability of NavIC to study space weather events along with the ionospheric studies over the Indian subcontinent., Comment: 38 Pages, 16 Figures, Accepted for publication in Advances in Space Research

This paper emphasizes on NavIC's performance in ionospheric studies over the Indian subcontinent region. The study is performed using data of one year (2017-18) at IIT Indore, a location near the northern crest of Equatorial Ionization Anomaly (EIA). It has been observed that even without the individual error corrections, the results are within $\pm20\%$ of NavIC VTEC estimates observed over the 1\ensuremath{^{\circ}} x 1\ensuremath{^{\circ}} grid of IPP surrounding the GPS VTEC estimates for most of the time. Additionally, ionospheric response during two distinct geomagnetic storms (September 08 and 28, 2017) at the same location and other IGS stations covering the Indian subcontinent using both GPS and NavIC has also been presented. This analysis revealed similar variations in TEC during the geomagnetic storms of September 2017, indicating the suitability of NavIC to study space weather events along with the ionospheric studies over the Indian subcontinent., Comment: 38 Pages, 16 Figures, Accepted for publication in Advances in Space Research

The discovery and understanding of gecko 'frictional-adhesion' adhering and climbing mechanism has allowed researchers to mimic and create gecko-inspired adhesives. A few experimental and theoretical approaches have been taken to understand the effect of surface roughness on synthetic adhesive performance, and the implications of stick-slip friction during shearing. This work extends previous studies by using a modified surface forces apparatus to quantitatively measure and model frictional forces between arrays of polydimethylsiloxane gecko footpad-mimetic tilted microflaps against smooth and rough glass surfaces. Constant attachments and detachments occur between the surfaces during shearing, as described by an avalanche model. These detachments ultimately result in failure of the adhesion interface and have been characterized in this study. Stick-slip friction disappears with increasing velocity when the flaps are sheared against a smooth silica surface; however, stick-slip was always present at all velocities and loads tested when shearing the flaps against rough glass surfaces. These results demonstrate the significance of pre-load, shearing velocity, shearing distances, commensurability and shearing direction of gecko-mimetic adhesives and provide us a simple model for analysing and/or designing such systems.

Mussel foot protein-1 (mfp-1) is an essential constituent of the protective cuticle covering all exposed portions of the byssus (plaque and the thread) that marine mussels use to attach to intertidal rocks. The reversible complexation of Fe(3+) by the 3,4-dihydroxyphenylalanine (Dopa) side chains in mfp-1 in Mytilus californianus cuticle is responsible for its high extensibility (120%) as well as its stiffness (2 GPa) due to the formation of sacrificial bonds that help to dissipate energy and avoid accumulation of stresses in the material. We have investigated the interactions between Fe(3+) and mfp-1 from two mussel species, M. californianus (Mc) and M. edulis (Me), using both surface sensitive and solution phase techniques. Our results show that although mfp-1 homologues from both species bind Fe(3+), mfp-1 (Mc) contains Dopa with two distinct Fe(3+)-binding tendencies and prefers to form intramolecular complexes with Fe(3+). In contrast, mfp-1 (Me) is better adapted to intermolecular Fe(3+) binding by Dopa. Addition of Fe(3+) did not significantly increase the cohesion energy between the mfp-1 (Mc) films at pH 5.5. However, iron appears to stabilize the cohesive bridging of mfp-1 (Mc) films at the physiologically relevant pH of 7.5, where most other mfps lose their ability to adhere reversibly. Understanding the molecular mechanisms underpinning the capacity of M. californianus cuticle to withstand twice the strain of M. edulis cuticle is important for engineering of tunable strain tolerant composite coatings for biomedical applications.

The discovery and understanding of gecko 'frictional-adhesion' adhering and climbing mechanism has allowed researchers to mimic and create gecko-inspired adhesives. A few experimental and theoretical approaches have been taken to understand the effect of surface roughness on synthetic adhesive performance, and the implications of stick-slip friction during shearing. This work extends previous studies by using a modified surface forces apparatus to quantitatively measure and model frictional forces between arrays of polydimethylsiloxane gecko footpad-mimetic tilted microflaps against smooth and rough glass surfaces. Constant attachments and detachments occur between the surfaces during shearing, as described by an avalanche model. These detachments ultimately result in failure of the adhesion interface and have been characterized in this study. Stick-slip friction disappears with increasing velocity when the flaps are sheared against a smooth silica surface; however, stick-slip was always present at all velocities and loads tested when shearing the flaps against rough glass surfaces. These results demonstrate the significance of pre-load, shearing velocity, shearing distances, commensurability and shearing direction of gecko-mimetic adhesives and provide us a simple model for analysing and/or designing such systems.

Mussel foot protein-1 (mfp-1) is an essential constituent of the protective cuticle covering all exposed portions of the byssus (plaque and the thread) that marine mussels use to attach to intertidal rocks. The reversible complexation of Fe(3+) by the 3,4-dihydroxyphenylalanine (Dopa) side chains in mfp-1 in Mytilus californianus cuticle is responsible for its high extensibility (120%) as well as its stiffness (2 GPa) due to the formation of sacrificial bonds that help to dissipate energy and avoid accumulation of stresses in the material. We have investigated the interactions between Fe(3+) and mfp-1 from two mussel species, M. californianus (Mc) and M. edulis (Me), using both surface sensitive and solution phase techniques. Our results show that although mfp-1 homologues from both species bind Fe(3+), mfp-1 (Mc) contains Dopa with two distinct Fe(3+)-binding tendencies and prefers to form intramolecular complexes with Fe(3+). In contrast, mfp-1 (Me) is better adapted to intermolecular Fe(3+) binding by Dopa. Addition of Fe(3+) did not significantly increase the cohesion energy between the mfp-1 (Mc) films at pH 5.5. However, iron appears to stabilize the cohesive bridging of mfp-1 (Mc) films at the physiologically relevant pH of 7.5, where most other mfps lose their ability to adhere reversibly. Understanding the molecular mechanisms underpinning the capacity of M. californianus cuticle to withstand twice the strain of M. edulis cuticle is important for engineering of tunable strain tolerant composite coatings for biomedical applications.

The discovery and understanding of gecko 'frictional-adhesion' adhering and climbing mechanism has allowed researchers to mimic and create gecko-inspired adhesives. A few experimental and theoretical approaches have been taken to understand the effect of surface roughness on synthetic adhesive performance, and the implications of stick-slip friction during shearing. This work extends previous studies by using a modified surface forces apparatus to quantitatively measure and model frictional forces between arrays of polydimethylsiloxane gecko footpad-mimetic tilted microflaps against smooth and rough glass surfaces. Constant attachments and detachments occur between the surfaces during shearing, as described by an avalanche model. These detachments ultimately result in failure of the adhesion interface and have been characterized in this study. Stick-slip friction disappears with increasing velocity when the flaps are sheared against a smooth silica surface; however, stick-slip was always present at all velocities and loads tested when shearing the flaps against rough glass surfaces. These results demonstrate the significance of pre-load, shearing velocity, shearing distances, commensurability and shearing direction of gecko-mimetic adhesives and provide us a simple model for analysing and/or designing such systems.

Biological systems have developed elegant adaptations during its evolution to survive and perform its functions efficiently under specific environmental constrains with enormous physical demands. In this dissertation, I make an effort to understand tribological phenomena in biology and translate them into a synthetic system for engineering applications. I emphasize on adhesion, friction and lubrication in three different biologically inspired soft condensed matter as described below.Dopa (3,4-dihydroxyphenylalanine), a post-translational modification from tyrosine (Tyr), features prominently in the mussel foot proteins (mfps), ranging from less than 5 mol % in mfp-4 to 30 mol % in mfp-5. The binding ability of the mfps to different substrates has been mostly attributed to the Dopa functionality in the protein and the role of the other peptide residues in the adhesive properties of the protein remains elusive. Here we have discovered that the adhesion between mfp-1 decapeptide films ([AKPSYPPTYK]2) and mica remained unchanged with or without the Dopa residue. This is a paradigm shift in our understanding of the molecular mechanisms underlying adhesive properties of the mfps and calls for further inquiry into the effects of peptide residues beyond Dopa chemistry. We also developed a systematic body of work linking the adhesive performance to lengths and architectures of peptides. Dopa in a peptide sequence does not necessarily lead to the formation of cross-links between peptide films through metal chelation, and the length of the peptide is a crucial parameter for enabling metal ion mediated bridging between surfaces. More recently, we have been working on designing and characterizing small molecules that mimic the properties of the adhesive mussel foot proteins. The wet adhesion and coacervation of an adhesive protein (mfp-5) was recapitulated in an order of magnitude smaller length scale which shows cohesive properties superior to the mfps. We believe that the resu

Biological systems have developed elegant adaptations during its evolution to survive and perform its functions efficiently under specific environmental constrains with enormous physical demands. In this dissertation, I make an effort to understand tribological phenomena in biology and translate them into a synthetic system for engineering applications. I emphasize on adhesion, friction and lubrication in three different biologically inspired soft condensed matter as described below.Dopa (3,4-dihydroxyphenylalanine), a post-translational modification from tyrosine (Tyr), features prominently in the mussel foot proteins (mfps), ranging from less than 5 mol % in mfp-4 to 30 mol % in mfp-5. The binding ability of the mfps to different substrates has been mostly attributed to the Dopa functionality in the protein and the role of the other peptide residues in the adhesive properties of the protein remains elusive. Here we have discovered that the adhesion between mfp-1 decapeptide films ([AKPSYPPTYK]2) and mica remained unchanged with or without the Dopa residue. This is a paradigm shift in our understanding of the molecular mechanisms underlying adhesive properties of the mfps and calls for further inquiry into the effects of peptide residues beyond Dopa chemistry. We also developed a systematic body of work linking the adhesive performance to lengths and architectures of peptides. Dopa in a peptide sequence does not necessarily lead to the formation of cross-links between peptide films through metal chelation, and the length of the peptide is a crucial parameter for enabling metal ion mediated bridging between surfaces. More recently, we have been working on designing and characterizing small molecules that mimic the properties of the adhesive mussel foot proteins. The wet adhesion and coacervation of an adhesive protein (mfp-5) was recapitulated in an order of magnitude smaller length scale which shows cohesive properties superior to the mfps. We believe that the resu

Geckos are highly efficient climbers and can run over any kind of surface with impeccable dexterity due to the typical design of their hierarchical foot structure. We have fabricated tilted, i.e., asymmetric, poly(dimethylsiloxane) (PDMS) microflaps of two different densities that mimic the function of the micrometer sized setae on the gecko foot pad. The adhesive properties of these microflaps were investigated in a modified surface forces apparatus; both for normal pure loading and unloading (detachment), as well as unloading after the surfaces were sheared, both along and against the tilt direction. The tilted microflaps showed directional, i.e., anisotropic adhesive behavior when sheared against an optically smooth (RMS roughness ≈ 10 ± 8 nm) SiO2 surface. Enhanced adhesion was measured after shearing the flaps along the tilted (gripping) direction and low adhesion when sheared against the tilted (releasing) direction. A Johnson-Kendall-Roberts (JKR) theory using an effective surface energy and modulus of rigidity (stiffness) quantitatively described the contact mechanics of the tilted microflaps against the SiO2 surface. We also find an increasing adhesion and stick-slip of the surfaces during detachment which we explain qualitatively in terms of the density of flaps, considering it to increase from 0% (no flaps, smooth surface) to 100% (close-packed flaps, effectively smooth surface). Large energy dissipation at the PDMS-silica interface caused by the viscoelastic behavior of the polymer results in stick-slip peeling and hence an enhanced adhesion energy is observed during the separation of the microflaps surface from the smooth SiO2 surface after shearing of the surfaces. For structured multiple contact surfaces, hysteresis as manifested by different loading and unloading paths can be due entirely to the elastic JKR micro-contacts. These results have important implications in the design of biomimetic adhesives.

Geckos are highly efficient climbers and can run over any kind of surface with impeccable dexterity due to the typical design of their hierarchical foot structure. We have fabricated tilted, i.e., asymmetric, poly(dimethylsiloxane) (PDMS) microflaps of two different densities that mimic the function of the micrometer sized setae on the gecko foot pad. The adhesive properties of these microflaps were investigated in a modified surface forces apparatus; both for normal pure loading and unloading (detachment), as well as unloading after the surfaces were sheared, both along and against the tilt direction. The tilted microflaps showed directional, i.e., anisotropic adhesive behavior when sheared against an optically smooth (RMS roughness ≈ 10 ± 8 nm) SiO2 surface. Enhanced adhesion was measured after shearing the flaps along the tilted (gripping) direction and low adhesion when sheared against the tilted (releasing) direction. A Johnson-Kendall-Roberts (JKR) theory using an effective surface energy and modulus of rigidity (stiffness) quantitatively described the contact mechanics of the tilted microflaps against the SiO2 surface. We also find an increasing adhesion and stick-slip of the surfaces during detachment which we explain qualitatively in terms of the density of flaps, considering it to increase from 0% (no flaps, smooth surface) to 100% (close-packed flaps, effectively smooth surface). Large energy dissipation at the PDMS-silica interface caused by the viscoelastic behavior of the polymer results in stick-slip peeling and hence an enhanced adhesion energy is observed during the separation of the microflaps surface from the smooth SiO2 surface after shearing of the surfaces. For structured multiple contact surfaces, hysteresis as manifested by different loading and unloading paths can be due entirely to the elastic JKR micro-contacts. These results have important implications in the design of biomimetic adhesives.

Mussel (Mytilus californianus) adhesion to marine surfaces involves an intricate and adaptive synergy of molecules and spatio-temporal processes. Although the molecules, such as mussel foot proteins (mfps), are well characterized, deposition details remain vague and speculative. Developing methods for the precise surveillance of conditions that apply during mfp deposition would aid both in understanding mussel adhesion and translating this adhesion into useful technologies. To probe the interfacial pH at which mussels buffer the local environment during mfp deposition, a lipid bilayer with tethered pH-sensitive fluorochromes was assembled on mica. The interfacial pH during foot contact with modified mica ranged from 2.2 to 3.3, which is well below the seawater pH of ~ 8. The acidic pH serves multiple functions: it limits mfp-Dopa oxidation, thereby enabling the catecholic functionalities to adsorb to surface oxides by H-bonding and metal ion coordination, and provides a solubility switch for mfps, most of which aggregate at pH ≥ 7-8.

Mussel (Mytilus californianus) adhesion to marine surfaces involves an intricate and adaptive synergy of molecules and spatio-temporal processes. Although the molecules, such as mussel foot proteins (mfps), are well characterized, deposition details remain vague and speculative. Developing methods for the precise surveillance of conditions that apply during mfp deposition would aid both in understanding mussel adhesion and translating this adhesion into useful technologies. To probe the interfacial pH at which mussels buffer the local environment during mfp deposition, a lipid bilayer with tethered pH-sensitive fluorochromes was assembled on mica. The interfacial pH during foot contact with modified mica ranged from 2.2 to 3.3, which is well below the seawater pH of ~ 8. The acidic pH serves multiple functions: it limits mfp-Dopa oxidation, thereby enabling the catecholic functionalities to adsorb to surface oxides by H-bonding and metal ion coordination, and provides a solubility switch for mfps, most of which aggregate at pH ≥ 7-8.

Background: Hydroxy-9,10-anthraquinones form the core unit of anthracycline anticancer drugs and are close structural analogues to these drugs. Although they show close resemblance to anthracyclines in physicochemical characteristics and electrochemical behavior their biophysical interactions are somewhat weaker than anthracyclines which is a disadvantage. One reason is the formation of anionic species by hydroxy-9,10-anthraquinones. Hence if formation of anionic species is prevented there could be a possibility hydroxy-9,10-anthraquinones would bind DNA better.Procedure: For this 1, 2, 5, 8-tetrahydroxy-9,10-anthraquinone (THAQ) was acetylated to obtain a tetra-acetylated derivative (THAQ-ace) whose interaction with calf thymus DNA was studied using UV-Vis spectroscopy at different pH.Results: Binding constant values for THAQ-ace (~105) were higher than THAQ at different pH. Increase in binding constant was attributed to anionic species not formed for THAQ-ace at physiological pH. Hence, unlike THAQ, binding constant values for THAQ-ace interacting with calf thymus DNA did not show variation with pH. In fact, it remained more or less constant. Increase in size of the acetylated form (THAQ-ace) compared to THAQ had a negative influence on binding. THAQ-ace showed enhanced superoxide formation. Both DNA binding and superoxide formation were responsible for a significant improvement in anticancer activity for THAQ-ace compared to THAQ on Jurkat T lymphocyte cells.Conclusion: Binding constant values for THAQ-ace binding to DNA were close to that reported for some standard anthracyclines. Hence, suitable modification of the less costly hydroxy-9,10-anthraquinones could provide alternatives to anthracyclines in cancer chemotherapy.

We review recent developments in experimental techniques that simultaneously combine measurements of the interaction forces or energies between two extended surfaces immersed in electrolyte solutions-primarily aqueous-with simultaneous monitoring of their (electro)chemical reactions and controlling the electrochemical surface potential of at least one of the surfaces. Combination of these complementary techniques allows for simultaneous real time monitoring of angstrom level changes in surface thickness and roughness, surface-surface interaction energies, and charge and mass transferred via electrochemical reactions, dissolution, and adsorption, and/or charging of electric double layers. These techniques employ the surface forces apparatus (SFA) combined with various "electrochemical attachments" for in situ measurements of various physical and (electro)chemical properties (e.g., cyclic voltammetry), optical imaging, and electric potentials and currents generated naturally during an interaction, as well as when electric fields (potential differences) are applied between the surfaces and/or solution-in some cases allowing for the chemical reaction equation to be unambiguously determined. We discuss how the physical interactions between two different surfaces when brought close to each other (<10 nm) can affect their chemistry, and suggest further extensions of these techniques to biological systems and simultaneous in situ spectroscopic measurements for chemical analysis.

We have synthesized model hydrophobic silicone thin films on gold surfaces by a two-step covalent grafting procedure. An amino-functionalized gold surface reacts with monoepoxy-terminated polydimethylsiloxane (PDMS) via a click reaction, resulting in a covalently attached nanoscale thin film of PDMS, and the click chemistry synthesis route provides great selectivity, reproducibility, and stability in the resulting model hydrophobic silicone thin films. The asymmetric interaction forces between the PDMS thin films and mica surfaces were measured with the surface forces apparatus in aqueous sodium chloride solutions. At an acidic pH of 3, attractive interactions are measured, resulting in instabilities during both approach (jump-in) and separation (jump-out from adhesive contact). Quantitative analysis of the results indicates that the Derjaguin-Landau-Verwey-Overbeek theory alone, i.e., the combination of electrostatic repulsion and van der Waals attraction, cannot fully describe the measured forces and that the additional measured adhesion is likely due to hydrophobic interactions. The surface interactions are highly pH-dependent, and a basic pH of 10 results in fully repulsive interactions at all distances, due to repulsive electrostatic and steric-hydration interactions, indicating that the PDMS is negatively charged at high pH. We describe an interaction potential with a parameter, known as the Hydra parameter, that can account for the extra attraction (low pH) due to hydrophobicity as well as the extra repulsion (high pH) due to hydrophilic (steric-hydration) interactions. The interaction potential is general and provides a quantitative measure of interfacial hydrophobicity/hydrophilicity for any set of interacting surfaces in aqueous solution.

Mytilus foot protein type 6 (mfp-6) is crucial for maintaining the reducing conditions needed for optimal wet adhesion in marine mussels. In this report, we describe the expression and production of a recombinant Mytilus californianus foot protein type 6 variant 1 (rmfp-6.1) fused with a hexahistidine affinity tag in Escherichia coli and its purification by affinity chromatography. Recombinant mfp-6 showed high purification yields of 5-6 mg L(-1) cell culture and excellent solubility in low pH buffers that retard oxidation of its many thiol groups. Purified rmfp-6.1 protein showed high 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity when compared with vitamin C. Using the highly sensitive surface forces apparatus (SFA) technique to measure interfacial surface forces in the nano-Newton range, we show that rmfp-6.1 is also able to rescue the oxidation-dependent adhesion loss of mussel foot protein 3 (mfp-3) at pH 3. The adhesion rescue is related to a reduction of dopaquinone back to 3,4-dihydroxyphenyl-l-alanine in mfp-3, which is the reverse reaction observed during the detrimental enzymatic browning process in fruits and vegetables. Broadly viewed, rmfp-6.1 has potential as a versatile antioxidant for applications ranging from personal products to antispoilants for perishable foods during processing and storage. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1587-1593, 2013.

The adhesion of mussel foot proteins (Mfps) to a variety of specially engineered mineral and metal oxide surfaces has previously been investigated extensively, but the relevance of these studies to adhesion in biological environments remains unknown. Most solid surfaces exposed to seawater or physiological fluids become fouled by organic conditioning films and biofilms within minutes. Understanding the binding mechanisms of Mfps to organic films with known chemical and physical properties therefore is of considerable theoretical and practical interest. Using self-assembled monolayers (SAMs) on atomically smooth gold substrates and the surface forces apparatus, we explored the force-distance profiles and adhesion energies of three different Mfps, Mfp-1, Mfp-3, and Mfp-5, on (i) hydrophobic methyl (CH3)- and (ii) hydrophilic alcohol (OH)-terminated SAM surfaces between pH 3 and pH 7.5. At acidic pH, all three Mfps adhered strongly to the CH3-terminated SAM surfaces via hydrophobic interactions (range of adhesive interaction energy = -4 to -9 mJ/m(2)) but only weakly to the OH-terminated SAM surfaces through H- bonding (adhesive interaction energy ≤ -0.5 mJ/m(2)). 3, 4-Dihydroxyphenylalanine (Dopa) residues in Mfps mediate binding to both SAM surface types but do so through different interactions: typical bidentate H-bonding by Dopa is frustrated by the longer spacing of OH-SAMs; in contrast, on CH3-SAMs, Dopa in synergy with other nonpolar residues partitions to the hydrophobic surface. Asymmetry in the distribution of hydrophobic residues in intrinsically unstructured proteins, the distortion of bond geometry between H-bonding surfaces, and the manipulation of physisorbed binding lifetimes represent important concepts for the design of adhesive and nonfouling surfaces.

Mytilus foot protein type 6 (mfp-6) is crucial for maintaining the reducing conditions needed for optimal wet adhesion in marine mussels. In this report, we describe the expression and production of a recombinant Mytilus californianus foot protein type 6 variant 1 (rmfp-6.1) fused with a hexahistidine affinity tag in Escherichia coli and its purification by affinity chromatography. Recombinant mfp-6 showed high purification yields of 5-6 mg L(-1) cell culture and excellent solubility in low pH buffers that retard oxidation of its many thiol groups. Purified rmfp-6.1 protein showed high 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity when compared with vitamin C. Using the highly sensitive surface forces apparatus (SFA) technique to measure interfacial surface forces in the nano-Newton range, we show that rmfp-6.1 is also able to rescue the oxidation-dependent adhesion loss of mussel foot protein 3 (mfp-3) at pH 3. The adhesion rescue is related to a reduction of dopaquinone back to 3,4-dihydroxyphenyl-l-alanine in mfp-3, which is the reverse reaction observed during the detrimental enzymatic browning process in fruits and vegetables. Broadly viewed, rmfp-6.1 has potential as a versatile antioxidant for applications ranging from personal products to antispoilants for perishable foods during processing and storage. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1587-1593, 2013.

The adhesion of mussel foot proteins (Mfps) to a variety of specially engineered mineral and metal oxide surfaces has previously been investigated extensively, but the relevance of these studies to adhesion in biological environments remains unknown. Most solid surfaces exposed to seawater or physiological fluids become fouled by organic conditioning films and biofilms within minutes. Understanding the binding mechanisms of Mfps to organic films with known chemical and physical properties therefore is of considerable theoretical and practical interest. Using self-assembled monolayers (SAMs) on atomically smooth gold substrates and the surface forces apparatus, we explored the force-distance profiles and adhesion energies of three different Mfps, Mfp-1, Mfp-3, and Mfp-5, on (i) hydrophobic methyl (CH3)- and (ii) hydrophilic alcohol (OH)-terminated SAM surfaces between pH 3 and pH 7.5. At acidic pH, all three Mfps adhered strongly to the CH3-terminated SAM surfaces via hydrophobic interactions (range of adhesive interaction energy = -4 to -9 mJ/m(2)) but only weakly to the OH-terminated SAM surfaces through H- bonding (adhesive interaction energy ≤ -0.5 mJ/m(2)). 3, 4-Dihydroxyphenylalanine (Dopa) residues in Mfps mediate binding to both SAM surface types but do so through different interactions: typical bidentate H-bonding by Dopa is frustrated by the longer spacing of OH-SAMs; in contrast, on CH3-SAMs, Dopa in synergy with other nonpolar residues partitions to the hydrophobic surface. Asymmetry in the distribution of hydrophobic residues in intrinsically unstructured proteins, the distortion of bond geometry between H-bonding surfaces, and the manipulation of physisorbed binding lifetimes represent important concepts for the design of adhesive and nonfouling surfaces.

We review recent developments in experimental techniques that simultaneously combine measurements of the interaction forces or energies between two extended surfaces immersed in electrolyte solutions-primarily aqueous-with simultaneous monitoring of their (electro)chemical reactions and controlling the electrochemical surface potential of at least one of the surfaces. Combination of these complementary techniques allows for simultaneous real time monitoring of angstrom level changes in surface thickness and roughness, surface-surface interaction energies, and charge and mass transferred via electrochemical reactions, dissolution, and adsorption, and/or charging of electric double layers. These techniques employ the surface forces apparatus (SFA) combined with various "electrochemical attachments" for in situ measurements of various physical and (electro)chemical properties (e.g., cyclic voltammetry), optical imaging, and electric potentials and currents generated naturally during an interaction, as well as when electric fields (potential differences) are applied between the surfaces and/or solution-in some cases allowing for the chemical reaction equation to be unambiguously determined. We discuss how the physical interactions between two different surfaces when brought close to each other (<10 nm) can affect their chemistry, and suggest further extensions of these techniques to biological systems and simultaneous in situ spectroscopic measurements for chemical analysis.

We have synthesized model hydrophobic silicone thin films on gold surfaces by a two-step covalent grafting procedure. An amino-functionalized gold surface reacts with monoepoxy-terminated polydimethylsiloxane (PDMS) via a click reaction, resulting in a covalently attached nanoscale thin film of PDMS, and the click chemistry synthesis route provides great selectivity, reproducibility, and stability in the resulting model hydrophobic silicone thin films. The asymmetric interaction forces between the PDMS thin films and mica surfaces were measured with the surface forces apparatus in aqueous sodium chloride solutions. At an acidic pH of 3, attractive interactions are measured, resulting in instabilities during both approach (jump-in) and separation (jump-out from adhesive contact). Quantitative analysis of the results indicates that the Derjaguin-Landau-Verwey-Overbeek theory alone, i.e., the combination of electrostatic repulsion and van der Waals attraction, cannot fully describe the measured forces and that the additional measured adhesion is likely due to hydrophobic interactions. The surface interactions are highly pH-dependent, and a basic pH of 10 results in fully repulsive interactions at all distances, due to repulsive electrostatic and steric-hydration interactions, indicating that the PDMS is negatively charged at high pH. We describe an interaction potential with a parameter, known as the Hydra parameter, that can account for the extra attraction (low pH) due to hydrophobicity as well as the extra repulsion (high pH) due to hydrophilic (steric-hydration) interactions. The interaction potential is general and provides a quantitative measure of interfacial hydrophobicity/hydrophilicity for any set of interacting surfaces in aqueous solution.