Rotational and translational diffusion of peptide-coated CdSe/CdS/ZnS nanorods studied by fluorescence correlation spectroscopy

CdSe/CdS/ZnS nanorods (NRs) of three aspect ratios were coated with phytochelatin-related peptides and studied using fluorescence correlation spectroscopy (FCS). Theoretical predictions of the NRs' rotational diffusion contribution to the correlation curves were experimentally confirmed. We monitored rotational and translational diffusion of NRs and extracted hydrodynamic radii from the extracted diffusion constants. Translational and rotational diffusion constants (D(trans) and D(rot)) for NRs were in good agreement with Tirado and Garcia de la Torre's as well as with Broersma's theories when accounting for the ligand dimensions. NRs fall in the size range where rotational diffusion can be monitored with higher sensitivity than translational diffusion due to a steeper length dependence, D(rot) approximately L(-)(3) versus D(trans) approximately L(-)(1). By titrating peptide-coated NRs with bovine serum albumin, we monitored (nonspecific) binding through rotational diffusion and showed that D(rot) is an advantageous observable for monitoring binding. Monitoring rotational diffusion of bioconjugated NRs using FCS might prove to be useful for observing binding and conformational dynamics in biological systems.     

Rotational diffusion of fluorescein family markers in solutions of human serum albumin

Rotational diffusion of fluorescein family nanomarkers (initial fluorescein and its halogenated derivatives, eosin and erythrosine) in solutions of human serum albumin (HSA) was studied at various pH values. In solutions of HSA, the degree of fluorescence polarization, rotational relaxation time, and Einstein radius of nanomarkers are larger and the rotational diffusion coefficient of nanomarkers smaller than in solutions without the protein. An increase in the electronegativity of atoms in the structural formulas of nanomarkers increases the degree of polarization of their fluorescence, decreases the coefficient of their rotational diffusion, and increases rotational relaxation time and the effective Einstein radius.     

Denaturation of human serum albumin under the action of cetyltrimethylammonium bromide according to fluorescence polarization data of protein

Denaturation of human serum albumin (HSA) under the action of cationic detergent cetyltrimethylammonium bromide (CTAB) is studied at different pH values by estimating the rotational diffusion of protein via fluorescence polarization. The degree of polarization of HSA tryptophan fluorescence, the rotational relaxation time, the rotational diffusion coefficient and the effective Einstein radius of the HSA molecules in solutions with different CTAB concentrations at different pH values are determined. The obtained rotational diffusion parameters of the HSA molecules show that under the action of CTAB, HSA denaturation has a one-stage character and proceeds more intensely and effectively at pH values higher than the pI value of protein (4.7).     

Dependence of the optical saturation of fluorescence on rotational diffusion

Optical saturation of fluorescence is studied taking into account the effect of rotational diffusion of molecules. It is shown that if the rotational diffusion time adopts values on the order of the fluorescence lifetime, optical saturation of the fluorescence increasingly deviates from the classical saturation curve towards lower fluorescence intensity values.     

Rotational brownian motion and fluorescence intensify fluctuations

A theory, which connects rotational brownian motion with intensity fluctuations of the light emitted from fluorescent molecules excited by linearly polarized light, is given. Analysis of rotational diffusion in this way does not depend on the close relationship between fluorescence lifetime and rotational relaxation times, which is necessary in present methods and thus makes an enlarged time range available for fluorescence spectroscopy.When short fluorescence lifetimes are used the rotational diffusion of the molecule in its ground state will be observed.     

Carbon-13 spin–lattice relaxation of tropane alkaloids. Anisotropic rotational motion of tropine and pseudotropine

The ¹³C spin–lattice relaxation times of tropine and pseudotropine have been measured in CDCl₃ as a function of concentration. The same relative increase in concentration serves to increase the relaxation rates much less in the region 0.9–5.0 wt.% than in the region 5.0–14.3 wt.%. The rotational diffusion coefficients have been calculated from the relaxation data using Woessner's anisotropic rotational diffusion model. Reorientation of both molecules is shown to be moderately anisotropic. The principal axes of the rotational diffusion tensor in the symmetry plane of both molecules are rotationally shifted from the principal axes of the moment of inertia tensor of the free molecules, and the main rotational axis is parallel with a line passing through the centre of mass of the molecule and the nitrogen atom.     

Brownian Motion of Lipid Molecules

Lateral and transmembrane diffusions in lipid molecules are discussed in terms of translational and rotational motions of a long cylinder. A procedure is suggested to deduce the dimensions (length and radius) of lipid molecules using experimental diffusion or viscosity data. It is shown that the hydrodynamic equation for transmembrane diffusion predicts a slower motion than for lateral diffusion, in qualitative agreement with experimental results. Further, the consequences of coupling transmembrane motion with rotational motion are discussed.     

Effects of water model and simulation box size on protein diffusional motions

We performed molecular dynamics simulations of ubiquitin with the distinct water models, TIP3P, SPC, SPC/E, and SPC/Fw, in different system sizes with different box shapes. The translational diffusion constants of pure water linearly depend on the effective box length, which is known as finite size effect, whereas the first and second rotational times of pure water are nearly constant. We then observed that both the overall translation and rotational motions of the protein are linearly correlated to the viscosity of pure water. As expected from the finite size effect in pure water, the translational diffusion of the protein is significantly affected by the system size, and rotational diffusion is nearly size-independent. After correction for the finite size effect, the SPC/E and SPC/Fw models reproduce both the translational and rotational motion of the protein relatively well. Thus, water models that reproduce the experimentally derived diffusional properties of pure water accurately are expected to also be suitable for simulating protein diffusion quantitatively.     

Picosecond time dependent rotational diffusion of rhodamine 6G in micellar solution

The rotational diffusion time constants of rhodamine 6G in water, cetyldimethylbenzylammonium chloride, and sodium dodecylsulfate micellar solution has been determined with a picosecond phase fluorimeter in the temperature range 10°C to 80°C. Data analysis shows a strong micellar influence leading to anisotropic rotational diffusion in sodium dodecylsulfate micellar solution.     

Characteristic behavior of short-term dynamics in reorientation for Gay-Berne particles near the nematic-isotropic phase transition temperature

A specific transition behavior was found in the tumbling motion near the nematic-isotropic phase boundary using molecular dynamics simulations of the Gay-Berne mesogenic model under isobaric conditions at a reduced pressure P* of 2.0. The relaxation time for the motion obtained from the second-rank orientational time correlation function and the rotational diffusion coefficient showed a clear jump at the nematic-isotropic phase transition temperature. Regardless of the temperature dependence of the relaxation time, the change in the rotational diffusion coefficient evaluated from the orientational order parameters and the relaxation time agreed qualitatively with that of real mesogens. The rotational viscosity coefficients gamma(1) and gamma(2) were obtained from the simulation data for the relaxation time for the short-term dynamics and for the rotational diffusion coefficients. gamma(1) was proportional to (2), where is the second-rank orientational parameter. Furthermore, the rotational behavior of the model was compared with that of the Debye approximation in the isotropic phase.     

Photophysics and Rotational Dynamics of a Hydrophilic Molecule in a Room Temperature Ionic Liquid

We have studied the photophysics and rotational diffusion of hydrophilic solute 7‐(N, N′‐diethylamino)coumarin‐3‐carboxylic acid (7‐DCCA) in a room temperature ionic liquid methyltrioctylammonium bis(trifluoromethylsulfonyl) imide ([N₁₈₈₈][NTf₂]). Comparison of activation energies of viscous flow and nonradiative decay shows that the photophysical properties of 7‐DCCA are not guided by the bulk viscosity of the medium but are dependent on the specific solute solvent interaction and structural heterogeneity of the medium. The rotational relaxation behaviour of 7‐DCCA in [N₁₈₈₈][NTf₂] shows significant deviation from the Stokes Einstein Debye hydrodynamic model of rotational diffusion. This is indicative of the influence of specific solute solvent interaction on the rotational relaxation behaviour of 7‐DCCA. Comparison of activation energy of rotational relaxation with activation energy of viscous flow clearly reinforces our assumption that the structural heterogeneity of the medium and specific solute solvent interaction plays a dominant role on the rotational diffusion instead of bulk viscosity.     

Dynamics of 4-benzylamino-7-nitrobenzofurazan in the 1-propanol/water binary solvent system. Evidence for composition-dependent solvent organization

We report on the fluorescence lifetime and rotational diffusion dynamics of 4-benzylamino-7-nitrobenzofurazan (BBD) in a series of 1-propanol/water binary solvent systems. The fluorescence lifetime of BBD increases monotonically with increasing 1-propanol concentration. The rotational diffusion dynamics of BBD also vary with solution 1-propanol content, but this variation is not monotonic. Comparison of the BBD rotational diffusion time constant to solution viscosity and 1-propanol composition reveals the presence of a solution composition dependence of solvent-solute interactions, with a relative decrease in solvent-solute interaction strength for solvent system compositions where the 1-propanol/water azeotrope is known to exist. These data point collectively to the existence of microscopic heterogeneity in these binary solvent systems.     

Ishtar: An interactive system for quantitative investigation on dipolar and quadrupolar spin-lattice relaxation

Within the model of anisotropic rotational diffusion, the quantitative treatment of dipolar and quadrupolar spin-lattice relaxation provides valuable information about molecular structures and molecular associations. When quadrupolar relaxation is involved, the title program calculates: (1) the electric field gradient tensor (EFGT) which is diagonalized; (2) the assymetry parameter, the components of the principal axes of the EFGT in the molecular frame of reference and the quadrupole coupling constant; and (3) the rotational diffusion constants which are iteratively determined from the experimental quadrupolar relaxation times. Analogously, for dipolar relaxation ISHTAR calculates the tensor of inertia, the diagonalization of which leads to diffusion constants and free rotor correlation times and the rotational diffusion constants from the experimental spectral densities.     

Rotational diffusion of colloidal particles near confining walls

We study the rotational diffusion of a spherical colloid confined in a narrow channel between parallel plane hard walls. The walls damp translational diffusion much more than rotational diffusion so that there is expected to be little translation-rotation coupling. Using a recent calculation of the nonisotropic rotational mobilities arising from the hydrodynamic interactions with the walls, we set up the rotational Smoluchowski equation for either a particle with a permanent dipole moment or a polarizable particle with axisymmetric polarizabilities subject to an external electric field. Using the Smoluchowski equation dynamics we calculate the time-correlation functions of orientation that are measured in depolarized light scattering for the cases of no external field, external field normal to the walls, and external field parallel to the walls. The decay of correlations is shown to be given by a weighted sum of decaying exponentials and can be characterized by an initial and a mean characteristic decay time. The weights and decay rates of each component and the characteristic decay times are studied numerically for a range of field strengths. The nonisotropic rotational mobilities make these decay times highly sensitive to the distance of the particle from the confining walls. This position dependence can be used as a method of measuring the rotational mobilities or, conversely, the rate of decay of correlations can be used as a probe of particle position between the confining walls.     

Effect of flexible polymers on the dielectric dispersion of rod-like macromolecules

The rotational diffusion of rod-like polar macromolecules (poly-γ-benzyl-l-glutamate or poly-n-hexylisocyanate) within entangled non polar polymer coils (polystyrene) is studied by dielectric absorption in solution. The dielectric increment as well as the rotatory diffusion constant is studied as a function of molecular weight of both components and increasing concentration of the non-polar polymer as well as the temperature. The classical theory of rotational diffusion is not obeyed if the viscosity of the polystyrene solution is taken as the medium viscosity. An increase in molecular aggregation on polystyrene addition is suspected.     

Spin—rotational relaxation study of molecular reorientation in the presence of internal extended rotational diffusion

Molecular reorientation in the presence of internal rotation is investigated and an analytical expression for the spin—rotational rate of a nucleus attached to the internal rotor is obtained in terms of the internal angular-momentum correlation time. A model of a symmetric-top molecule undergoing anisotropic rotational diffusion is extended to include a modified extended diffusion of internal rotation. The result is applied to liquid toluene and the internal angular-momentum correlation time is evaluated from the ¹³C nuclear spin—rotational relaxation rate of the methyl carbon. A comparison with the previous result on the dipole—dipole relaxation data is made and the consistency of the present theory is discussed.     

Effects of diffusion-controlled association in kinetic model of crystal nucleation in external orienting field

Translational and rotational diffusion equation of orientable single elements in external orienting potential field is used to discuss effective rate of association and dissociation during cluster growth. First and second harmonic terms of orientation-dependent potential energy of single elements are taken into consideration. Tolerance angle accounting for orientational limitations for association is introduced.Effective rate of association of single elements is derived with first-order correction for the effects of orienting potential. Net rate of cluster growth depends on orientation in the field, and it is controlled by longrange diffusion (rotational and translational) of single elements. Influence of diffusion is higher, the narrower the tolerance angle and the faster the association.At slow association, long-range diffusion does not influence the process, the growth of a cluster is controlled by thermodynamic, orientation-dependent potential of the species involved in the process.Effective rate constants of association and dissociation, as well as effective concentration of single elements are derived as functions of orientation angle in the field.The Fokker-Planck equation is proposed for the distribution of cluster size in external orienting potential, with the effects of finite translational and rotational diffusion of single elements, for the case of non-polar clusters.     

Transport of Acids through Polyether-Sulfone Anion-Exchange Membrane

Diffusion dialysis of sulfuric acid and hydrochloric acid into water with a polyether-sulfone anion-exchange membrane was studied. Transport of sulfuric acid and hydrochloric acid through the membrane has been quantified by diffusion coefficients and mass transfer coefficients. The mass transfer coefficients were investigated as a function of the rotational speed of the stirring rate of both sides of the membrane and with different pH ranges. It was observed that the diffusion dialysis seems to be dependent on the rotational speed of the stirrer; in contrast, the membrane mass transfer coefficients are independent of rotational speed, but they are slightly affected by the initial acid concentration in donor phase. Copyright 2001 Academic Press.     

Effects of the bead-bead potential on the restricted rotational diffusion of nonrigid macromolecules

The influence of the bead-bead interaction on the rotational dynamics of macromolecules which are immersed into a solution has been investigated by starting from the microscopic theory of the macromolecular motion, i.e., from a Fokker-Planck equation for the phase-space distribution function. From this equation, we then derived an explicit expression for the configuration-space distribution function of a nonrigid molecule which is immobilized on a surface. This function contains all the information about the interaction among the beads as well as the effects from the surrounding solvent particles and from the surface. For the restricted rotational motion, the dynamics of the macromolecules can now be characterized in terms of a rotational diffusion coefficient as well as a radial distribution functions. Detailed computations for the rotational diffusion coefficient and the distribution functions have been carried out for HOOKEAN, finitely extensible nonlinear elastic, and a DNA type bead-bead interaction.