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Hydrophobic Forces (hydrophobic + force)
Selected AbstractsMeasuring the Interaction Forces between Protein Inclusion Bodies and an Air Bubble Using an Atomic Force MicroscopeBIOTECHNOLOGY PROGRESS, Issue 5 2001N. D. Wangsa-Wirawan Interaction forces between protein inclusion bodies and an air bubble have been quantified using an atomic force microscope (AFM). The inclusion bodies were attached to the AFM tip by covalent bonds. Interaction forces measured in various buffer concentrations varied from 9.7 nN to 25.3 nN (± 4,11%) depending on pH. Hydrophobic forces provide a stronger contribution to overall interaction force than electrostatic double layer forces. It also appears that the ionic strength affects the interaction force in a complex way that cannot be directly predicted by DLVO theory. The effects of pH are significantly stronger for the inclusion body compared to the air bubble. This study provides fundamental information that will subsequently facilitate the rational design of flotation recovery system for inclusion bodies. It has also demonstrated the potential of AFM to facilitate the design of such processes from a practical viewpoint. [source] Interaction between the fluorinated amphiphilic copolymer poly(2,2,3,4,4,4-hexafluorobutyl methacrylate)- graft -poly(SPEG) and DNAJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010Ling Li Abstract A synthesized copolymer, synthesized from HFMA (hexaflurobutyl methacrylate) and SPEG (PHFMA- g -PSPEG), was synthesized. PHFMA- g -PSPEG intercalated to the DNA base pair via a strong hydrophobic force, and this was conformed by ultraviolet spectroscopy, transmittance measurements, micropolarity measurements, resonance light scattering (RLS) spectroscopy, and particle size measurements. The copolymer was used as a new probe to detect DNA according to the RLS technique. The hydrophobic interaction between PHFMA- g -PSPEG and DNA significantly enhanced the RLS signal, and the enhanced RLS intensity at 422 nm was proportional to the nucleic acid concentration within the range of 0.09,0.90 mg/L with a detection limit (3,) of 4.0 ,g/L. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Effects of the Interaction of Rifamycin SV with Serum Albumins on the Resonance Rayleigh Scattering Spectra and Their Analytical ApplicationCHINESE JOURNAL OF CHEMISTRY, Issue 5 2008Ji-Dong YANG Abstract In pH 4.5,4.8 Britton-Robinson buffer solution, rifamycin SV (i.e. rifamycin sodium) can react with serum albumin such as human serum albumin (HSA) and bovine serum albumin (BSA) to form macromolecular complexes by electrostatic attraction and hydrophobic force. As a result, the resonance Rayleigh scattering (RRS) of the drug was enhanced remarkably and the RRS peaks were at 374 and 552 nm. The enhancement of RRS (,I) is directly proportional to the concentration of HSA or BSA. The linear ranges and the detection limits are 0.03,6.0 µg/mL and 9.0 ng/mL for HSA, and 0.01,8.0 µg/mL and 2.0 ng/mL for BSA, respectively. In this work, a sensitive, selective, simple and fast method for the determination of trace amounts of serum albumin by RRS technique has been developed, which was applied to the determination of serum albumin in the synthesized samples and human urine samples with satisfactory results. [source] Thermodynamic analysis of binding of p -substituted benzamidines to trypsinFEBS JOURNAL, Issue 6 2001Reinskje Talhout Understanding the structural basis of inhibitor,enzyme interactions, important for the design of new drugs, requires a complete thermodynamic characterization of the binding process as well as a description of the structure of the complex. In this paper, the binding of p -substituted benzamidinium derivatives to the structurally well-characterized serine proteinase bovine pancreatic trypsin has been studied using isothermal titration calorimetry. These experiments have permitted a complete characterization of the temperature dependence of the inhibitor-binding thermodynamics. At 25 °C, both the enthalpy and entropy of binding are favourable for all studied derivatives, but this is only true for a relatively narrow temperature range. As binding is characterized by a negative change in heat capacity, the process is characterized by enthalpy,entropy compensation, resulting in a change of the net thermodynamic driving force for association from entropic to enthalpic with increasing temperature. These phenomena are not unusual when hydrophobic forces play an important role. The trend in the relative binding potencies can, to a significant extent, be attributed to the electron-donating/withdrawing character of the substituent at the para position, as shown by the Hammett plot for the different inhibitors; the more polar the p -substituted benzamidine, the less potent it will be as a trypsin inhibitor. This behaviour might result from a bulk solvation effect, meaning that the more polar, lower potency inhibitors will be more stabilized in water than the less polar, higher potency inhibitors. [source] Synthetic Hydrophilic Materials with Tunable Strength and a Range of Hydrophobic Interactions,ADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Olha Hoy Abstract The ability to vary, adjust, and control hydrophobic interactions is crucial in manipulating interactions between biological objects and the surface of synthetic materials in aqueous environment. To this end a grafted polymer layer (multi-component mixed polymer brush) is synthesized that is capable of reversibly exposing nanometer-sized hydrophobic fragments at its hydrophilic surface and of tuning, turning on, and turning off the hydrophobic interactions. The reversible switching occurs in response to changes in the environment and alters the strength and range of attractive interactions between the layer and hydrophobic or amphiphilic probes in water. The grafted layer retains its overall hydrophilicity, while local hydrophobic forces enable the grafted layer to sense and attract the hydrophobic domains of protein molecules dissolved in the aqueous environment. The hydrophobic interactions between the material and a hydrophobic probe are investigated using atomic force microscopy measurements and a long-range attractive and contact-adhesive interaction between the material and the probe is observed, which is controlled by environmental conditions. Switching of the layer exterior is also confirmed via protein adsorption measurements. [source] Use of associating polymers as multifunctional thickeners: studies of Their structure in aqueous solutions via nmr, qels, fluorescence, And rheology measurementsINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 5 2007Katsunori Yoshida The solution properties of an associating polymer were studied by NMR, quasi-elastic light scattering (QELS), fluorescence, and rheology measurements. An associative thickening (AT) polymer was designed having a nonionic poly(ethylene oxide) backbone with long alkyl chains at both ends to achieve high viscosity even at relatively high salt concentrations and over a wide pH range. This study focuses on the associative state of the polymer in aqueous solutions at various polymer concentrations. In a fluorescence probe study using pyrene a spectral change in the I3/I1 ratio was observed for pyrene at a polymer concentration (Cp) of 3 x 10 -4%, indicating an apparent critical concentration (cmc) of the amphiphilic polymer. The viscosity, self-diffusion coefficient (Dsel), and hydrodynamic size (Rh) distribution measurements at various Cp all suggest that there is a second transition at Cp, 0.4%. Although we observed the discontinuity in viscosity, Dsel, and Rh at Cp, 0.4%, no changes in the relaxation times (T1 and T2) were recognized for either the alkyl chain or the ethylene oxide moiety of the polymer at C p= 0.1,1%. These data suggest that there are no structural changes or phase transitions at Cp, 0.4%, but that intermicellar networks are presumably formed by bridging of the end alkyl groups of the polymer, which is driven by hydrophobic forces. Because the polymer forms networks by hydrophobic interaction and the polymer itself is nonionic, the viscosity of the polymer solution was influenced very little by either the addition of salt or a pH change, as would be expected. The dynamic viscoelastic study revealed that the polymer solution exhibits a single mode Maxwell type relaxation behavior with a terminal relaxation time of about 0.61 s, which imparts a unique flow appearance to the polymer solutions. The time course measurements of the dynamic elastic modulus of the stratum corneum revealed that the polymer has excellent potential for skin softening. It was concluded that the associative thickening polymer not only is a useful thickener with a salt and pH tolerance but also has beneficial skincare effects. [source] Spectroscopic Investigations on the Binding of the Photosensitizer Chlorin p6 with Amine-modified Silica Nanoparticles in Aqueous MediaPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009Beena Jain Absorption and emission properties of the amphiphilic photosensitizer Chlorin p6 were investigated in aqueous medium in the presence of silica nanoparticles (SiNPs) having positively charged amino groups. The results of these studies reveal that the acid,base ionization equilibrium of Chlorin p6 in aqueous medium is significantly affected as a result of strong electrostatic binding between the negatively charged drug and SiNP. The spectroscopic signature of the drug bound to SiNPs suggests that the tri-anionic form of the drug remains bound to the positively charged SiNPs at pH 8.0. As the pH is progressively decreased the formation of hydrophobic aggregates is disrupted significantly due to the presence of electrostatic binding force, which competes with intermolecular hydrophobic forces. The interplay of hydrophobic and electrostatic forces in the drug,nanoparticle binding process might affect the relative uptake and photodynamic efficacy of the free drug and the drug,nanoparticle complex in cancer cells. [source] Molecular interactions of isoxazolcurcumin with human serum albumin: Spectroscopic and molecular modeling studiesBIOPOLYMERS, Issue 2 2009Bijaya Ketan Sahoo Abstract Curcumin is a nontoxic natural product with diverse pharmacological potencies. We report the interaction of a potent synthetic derivative of curcumin, isoxazolcurcumin (IOC) with human serum albumin (HSA) using various biophysical methods. The observed fluorescence quenching of HSA by IOC is due to a complex formation by a static quenching process with a quenching constant of the order of 105M,1. The binding affinity and the number of binding sites were obtained from a Scatchard analysis. Thermodynamics reveals that the interaction is entropy driven with predominantly hydrophobic forces. From the observed Förster-type fluorescence resonance energy transfer (FRET), the donor (Trp 214 in HSA) to acceptor (IOC) distance is calculated to be 3.2 nm. The conformational changes of HSA due to the interaction were investigated qualitatively from synchronous fluorescence spectra along with a quantitative estimation of the secondary structure from Fourier Transform Infrared (FTIR) and circular dichroism (CD) spectroscopies. Molecular docking studies were performed to obtain information on the possible residues involved in the interaction process, and changes in accessible surface area of the interacting residues were calculated. The preferred binding site of IOC was analyzed by ligand displacement experiments with 1-anilino-8-naphthalenesulfonate (ANS) and warfarin-bound HSA. © 2008 Wiley Periodicals, Inc. Biopolymers 91: 108,119, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] A Close Look at Fluorescence Quenching of Organic Dyes by TryptophanCHEMPHYSCHEM, Issue 11 2005Sören Doose Dr. Abstract Understanding fluorescence quenching processes of organic dyes by biomolecular compounds is of fundamental importance for in-vitro and in-vivo fluorescence studies. It has been reported that the excited singlet state of some oxazine and rhodamine derivatives is efficiently and almost exclusively quenched by the amino acid tryptophan (Trp) and the DNA base guanine via photoinduced electron transfer (PET). We present a detailed analysis of the quenching interactions between the oxazine dye MR121 and Trp in aqueous buffer. Steady-state and time-resolved fluorescence spectroscopy, together with fluorescence correlation spectroscopy (FCS), reveal three contributing quenching mechanisms: 1) diffusion-limited dynamic quenching with a bimolecular quenching rate constant kdof 4.0×109s,1,M,1, 2) static quenching with a bimolecular association constant Ksof 61,M,1, and 3) a sphere-of-action contribution to static quenching described by an exponential factor with a quenching constant , of 22,M,1. The latter two are characterized as nonfluorescent complexes, formed with ,30,% efficiency upon encounter, that are stable for tens of nanoseconds. The measured binding energy of 20,30 kJmol,1is consistent with previous estimates from molecular dynamics simulations that proposed stacked complexes due to hydrophobic forces. We further evaluate the influence of glycerol and denaturant (guanidine hydrochloride) on the formation and stability of quenched complexes. Comparative measurements performed with two other dyes, ATTO 655 and Rhodamine 6G show similar results and thus demonstrate the general applicability of utilizing PET between organic dyes and Trp for the study of conformational dynamics of biopolymers on sub-nanometer length and nanosecond time-scales. [source] | ||||||||||||||||