Decrease In Relaxation Time Research Articles

Evidence of Solid Water Bridges Found in Hydrating Tricalcium Silicate Paste

The D2O hydration of pure tricalcium silicate (Ca3SiO5) was examined at 23°C with parallel measurements using deuterium NMR spectral analysis, deuterium NMR T1 relaxation measurements at several magnetic fields, isothermal calorimetry, scanning electron microscopy, and Vicat needle tests. The results show that the maximum rate of decrease in the deuterium T1 relaxation time of the D2O resonance, the maximum rate of increase in heat production, and the maximum rate of decrease in Vicat needle penetration occur simultaneously within experimental error. Together with results from other recent deuterium NMR studies in our laboratory, these observations support the new hypothesis that the formation of solid water bridges between closely adjacent developing hydrate surfaces causes initial setting. As a confirmatory experiment, it was found that microwave heating immediately after setting, i.e. immediately after zero Vicat needle penetration, softened the paste sufficiently to once again allow some needle penetration, and furthermore, that upon cooling, the paste reset. This process could be repeated several times.

Development of nanoparticle-based magnetic resonance colonography

This study was to develop a novel method of nanoparticle-based MR colonography. Two types of solid lipid nanoparticles (SLNs) were synthesized with loading of (a) gadolinium (Gd) diethylenetriaminepenta acetic acid to construct Gd-SLNs as an MR T1 contrast agent and (b) otcadecylamine-fluorescein-isothiocyanate to construct Gd-fluorescein isothiocyanate (FITC)-SLNs for histologic confirmation of MR findings. Through an in vitro experiment, we first evaluated the size distribution and gadolinium diethylenetriaminepenta acetic acid entrapment efficiency of these SLNs. The SLNs displayed a size distribution of 50-300 nm and a gadolinium diethylenetriaminepenta acetic acid entrapment efficiency of 56%. For in vivo validation, 30 mice were divided into five groups, each of which was administered a transrectal enema using: (i) Gd-SLNs (n=6); (ii) Gd-FITC-SLNs (n=6); (iii) blank SLNs (n=6); (iv) gadolinium diethylenetriaminepenta acetic acid (n=6); and (v) water (n=6). T1-weighted fluid-attenuated inversion-recovery MRI was then performed on mice after transrectal infusion of Gd-SLNs or Gd-FITC-SLNs, which demonstrated bright enhancement of the colonic walls, with decrease in T1 relaxation time. When Gd-FITC-SLNs were delivered, green fluorescent spots were visualized in both the extracelluar space and the cytoplasm through colonic walls under confocal microscopy and fluorescence microscopy. This study establishes the "proof-of-principle" of a new imaging technique, called "nanoparticle-based MR colonography," which may provide a useful imaging tool for the diagnosis of colorectal diseases.

Monitoring of Magnetic Targeting to Tumor Vasculature Through MRI and Biodistribution

The development of noninvasive imaging techniques for the assessment of cancer treatment is rapidly becoming highly important. The aim of the present study is to show that magnetic cationic liposomes (MCLs), incorporating superparamagnetic iron oxide nanoparticles (SPIONs), are a versatile theranostic nanoplatform for enhanced drug delivery and monitoring of cancer treatment. MCLs (with incorporated high SPION cargo) were administered to a severe combined immunodeficiency mouse with metastatic (B16-F10) melanoma grown in the right flank. Pre- and post-injection magnetic resonance (MR) images were used to assess response to magnetic targeting effects. Biodistribution studies were conducted by ¹¹¹In-labeled MCLs and the amount of radioactivity recovered was used to confirm the effect of targeting for intratumoral administrations. We have shown that tumor signal intensities in T₂-weighted MR images decreased by an average of 20 ± 5% and T₂* relaxation times decreased by 14 ± 7 ms 24 h after intravenous administration of our MCL formulation. This compares to an average decrease in tumor signal intensity of 57 ± 12% and a T₂* relaxation time decrease of 27 ± 8 ms after the same time period with the aid of magnetic guidance. MR and biodistribution analysis clearly show the efficacy of MCLs as MRI contrast agents, prove the use of magnetic guidance, and demonstrate the potential of MCLs as agents for imaging, guidance and therapeutic delivery.

Deformation induced evolution of mobility in PMMA

AbstractThe stress relaxation response in the glassy state just below Tg was measured for poly(methylmethacrylate) following application of constant strain rate uniaxial tensile deformation at various locations on the stress–strain curve, including the yield and post‐yield region. The macroscopic mobility was determined from analysis of the relaxation response. Up to a factor of 3 decrease in relaxation time was observed with the fastest relaxation occurring in the post‐yield softening region. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010

Ferritin Overexpression for Noninvasive Magnetic Resonance Imaging–Based Tracking of Stem Cells Transplanted into the Heart

An unmet need in cardiac cell therapy is a noninvasive imaging technique capable of tracking changes in graft size over time and monitoring cell dynamics such as replication and death, factors to which commonly used superparamagnetic nanoparticles are insensitive. Our goal was to explore if overexpression of ferritin, a nontoxic iron-binding protein, can be used for noninvasive magnetic resonance imaging (MRI) of cells transplanted into the infarcted heart. Mouse skeletal myoblasts (C2C12 cells) were engineered to overexpress ferritin. Ferritin overexpression did not interfere with cell viability, proliferation, or differentiation into multinucleated myotubes. Ferritin overexpression caused a 25% decrease in T2 relaxation time in vitro compared to wild-type cells. Transgenic grafts were detected in vivo 3 weeks after transplantation into infarcted hearts of syngeneic mice as areas of hypointensity caused by iron accumulation in overexpressed ferritin complexes. Graft size evaluation by MRI correlated tighly with histologic measurements (R2 = .8). Our studies demonstrated the feasibility of ferritin overexpression in mouse skeletal myoblasts and the successful detection of transgenic cells by MRI in vitro and in vivo after transplantation into the infarcted mouse heart. These experiments lay the groundwork for using the MRI gene reporter ferritin to track stem cells transplanted to the heart.

Effect of invert sugar on the drying kinetics and water mobility of osmosed-air dried cantaloupe

Effect of partially replacing sucrose with invert sugar on drying kinetics of osmosed cantaloupe was evaluated using four levels of invert sugar (0, 5, 10 and 15% (v/v)) to partially replace sucrose syrup at 50 °Brix. The osmosed samples were then dried at 60 °C. The osmosed cantaloupe without invert sugar exhibited the fastest drying rate. The drying rate decreased with increasing amounts of invert sugar. An increase in the degree of water binding to invert sugar is the most likely explanation for this effect and is supported by the observed decrease in the NMR relaxation time. The use of invert sugar could reduce water activity of final product but not significantly improve overall appearance. Six different mathematical models were tested for their goodness of fit with experimental data. Modified Henderson and Pabis model was found to give the best fit and was able to predict the drying time accurately.

AC conductivity studies and relaxation behaviour in (LiX) y [(Li2O)0.6(P2O5)0.4](1 − y) glasses

The electrical conductivity of (LiX) y [(Li2O)0.6(P2O5)0.4](1 − y) (X = Cl, Br, y = 0, 0.1, 0.15, 0.2) glasses has been determined over a wide range of temperature and frequency by means of impedance spectroscopy. The real part of the frequency-dependent conductivity exhibits a simple power law feature, and the dimensionless frequency exponent n has been determined. The conductivity spectra show scaling behaviour when the conductivity spectra are scaled by ω/(σ dc T) and ω/ω p . The conductivity relaxation time and activation energy have been estimated from the modulus spectra. Increases of ionic conductivity values with addition of LiX content are in line with the decrease of activation energy and relaxation time.

Abstract 4344: Virus-templated magnetic nanowires for tumor-targeted imaging

Abstract In an effort towards early tumor detection, various diagnostic probes, such as tumor marker-specific fluorescent and magnetic nanoparticles, have been developed. Nanoparticles detected using magnetic resonance (MR) imaging is an attractive approach due to its non-invasiveness. Current work has focused on single functionalized spherical nanoparticle systems, one example being cross-linked iron oxide nanoparticles (CLIO). However, these ‘shaped’ particles can be cleared by the reticuloendothelial system upon intravenous injection due to opsonization. Recent work suggests that longer filamentous shaped structures can persist almost 10 times longer in circulation in vivo compared to spherical particles. For clinical diagnostics, it would be desirable to engineer filamentous shaped imaging agents that allow for longer circulation and better homing towards the tumor before immune clearance. M13 filamentous bacteriophage can potentially allow for longer circulation of the imaging agents. Recent work indicates that the virus can circulate in vivo for at least 24 hours compared to the 5-6 hour circulation of various spherical particles (unpublished data). Using the M13 virus as a scaffold, we can uniquely combine multiple nanoparticles with engineered cell-targeting peptide ligands for tumor-targeted imaging. Exploiting the multiple coat proteins on M13 amenable for peptide display, we have genetically engineered peptides that bind iron oxide nanoparticles (γ-Fe2O3 NPs) and that target secreted protein, acidic and rich in cysteine (SPARC), a protein overexpressed in metastatic prostate and breast cancers. We have been able to assemble monocrystalline, monodisperse γ-Fe2O3 NPs along the virus coat and demonstrate enhanced MR contrast properties, compared to commercially available CLIO. We have investigated specific targeting against prostate cancer in vitro and in vivo. There is a decrease in transverse relaxation times (‘dark contrast’) using targeted nanowires compared to negative control and is specific towards SPARC positive C4-2B cell line compared to DU145 control. SPARC-targeted nanowires were injected intravenously in LNCaP and C4-2B and control DU145 xenograft tumors. MR images indicate dark image contrast in SPARC expressing tumors, compared to control. Histology suggests iron accumulation in the stroma and capsule of SPARC-positive tumors compared to control, suggesting tumor targeting in vivo. These virus-templated probes may have potential as long circulating, targeted non-invasive imaging agents for the early detection of tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4344.

Renal Inflammation: Targeted Iron Oxide Nanoparticles for Molecular MR Imaging in Mice

To determine the feasibility of T2-weighted magnetic resonance (MR) imaging in the noninvasive quantification of renal inflammation by using superparamagnetic iron oxide (SPIO) nanoparticles targeted to tissue-bound C3 activation fragments in a mouse model of lupus nephritis. All animal procedures were approved by the University of Colorado-Denver animal care and use committee. SPIO nanoparticles were encapsulated by using amine-functionalized phospholipids. A recombinant protein containing the C3d-binding region of complement receptor type 2 (CR2) was then conjugated to the surface of the SPIO nanoparticle. Five MRL/lpr mice (a model of lupus nephritis) and six C57BL/6 wild-type mice were assessed with T2-weighted MR imaging at baseline and after SPIO injection. The same five MRL/lpr mice and three C57BL/6 mice also underwent MR imaging after injection of CR2-targeted SPIO. A series of T2-weighted pulses with 16 echo times was used to enable precise T2 mapping and calculation of T2 relaxation times in the cortex and outer and inner medulla of the kidneys, as well as in the spleen, muscle, and fat. The effects of treatment and animal genotype on T2 relaxation times were analyzed with repeated-measures analysis of variance. At baseline, the T2-weighted signal intensity in the kidneys of MRL/lpr mice was higher than that in the kidneys of wild-type mice. Injection of untargeted SPIO did not alter the T2-weighted signal in the kidneys in either strain of mice. Injection of CR2-targeted SPIO in MRL/lpr mice, however, caused a significant accumulation of targeted iron oxide with a subsequent decrease in T2 relaxation times in the cortex and outer and inner medulla of the kidneys. No changes in T2 relaxation time were observed in the wild-type mice after injection of targeted SPIO. Injection of CR2-conjugated SPIO caused a significant reduction in T2-weighted MR imaging signal and T2 relaxation time in nephritic kidneys.

Vibrational Förster Transfer in Ice Ih

We have studied Förster energy transfer between O-H vibrations in H(2)O/D(2)O ice Ih using femtosecond, two-color, mid-infrared pump-probe spectroscopy. We found that as a result of couplings to nearby O-H stretch modes, the vibrational relaxation time decreases from 480 fs for dilute HDO in D(2)O down to 300 fs for pure H(2)O ice. The anisotropy shows an initial 140 fs decay down to a concentration-dependent end level. This end level for low concentrations can be explained from the limited rotational freedom ( approximately 20 degrees ) of a water molecule in the ice lattice over time scales > 15 ps. The decreasing end levels for higher concentrations of H(2)O result from Forster energy transfer to the next-nearest six O-H groups. No Förster transfer beyond these neighbors is observed. Variation of the ice temperature between 200 and 270 K was found to have negligible effect on the dynamics.

Specific Absorption Rates and Magnetic Properties of Ferrofluids with Interaction Effects at Low Concentrations

The specific absorption rate (SAR) of a maghemite-based ferrofluid, measured at 315 K, 3 kA/m, and 109 kHz, was found to double as the ferrofluid concentration was decreased by a factor of 4. The ferrofluid contained nonagglomerated, highly crystalline, and monodisperse nanoparticles with an average size of 11.6 nm and an initial concentration of 8.14 mg/mL. The magnetic characterization of three different concentrations of this ferrofluid revealed several effects typical of the presence of magnetic interactions, such as the decrease of initial susceptibility values (liquid ferrofluid) and Neel relaxation times, τN (frozen ferrofluid), with increasing concentration. The accurate SAR determination in adiabatic conditions allowed estimating the τN values of the liquid ferrofluid, which displayed the same trend against concentration as those obtained in the frozen state. Such a trend allowed explaining qualitatively the degradation of the heating performance of the ferrofluid upon increasing concentration. E...

Dynamics in water-AOT-n-decane microemulsions with poly(ethylene glycol) probed by dielectric spectroscopy

Water in oil microemulsions, consisting of water, AOT and n-decane, have been used as a model system to investigate the influence of the water soluble polymer PEO on the dynamical behavior of the system. Therefore dielectric relaxation spectroscopy and conductivity, extracted from dielectric spectroscopy, measurements in a wide frequency and temperature range have been applied. The pure microemulsion displays the known phenomenon of percolation that manifests in a steep increase of conductivity at the percolation temperature \(T_\text{P}\). The percolation temperature has been found to be strongly dependent on droplet volume fraction and droplet size. The latter additionally shows that percolation temperature and surfactant film rigidity are proportional. Far from percolation water-AOT-n-decane microemulsions display two dielectric relaxations. The slower one has a relaxation time of \(\tau \approx 3\cdot 10^{-6}~\text{s}\) and can be related to an interfacial polarization at the interface of the water core and the AOT shell (core relaxation). The faster one has a relaxation time of \(\tau \approx 10^{-9}~\text{s}\) and can be related to the ions in the AOT shell(shell or cluster relaxation). While the first is mainly untouched by the percolation phenomenon, the latter undergoes a slowdown and an increase of relaxation strength, both over about two decades, on approaching the percolation transition. Addition of PEO tremendously shifts the percolation transition to higher temperatures, due to adsorption at the AOT layer which leads to an increase in rigidity. Furthermore a lower phase boundary temperature evolves, below which the microemulsion phase separates. The conductivity of the microemulsion is also slightly increased with polymer. The effect on the dielectric properties is only small, where dielectric relaxation times are reduced by the polymer, while only the relaxation strength of the faster relaxation is influenced and also decreases with polymer. The decreased relaxation time of core relaxation can be either due to changes in the core to shell volume ratio or an increased conductivity of the water core. The decrease in relaxation time and strength of the shell relaxation suggest that the ion mobility in the shell increase, while the dipole moment is reduced. Additionally we applied a cluster relaxation model proposed by Cametti et al. (Phys Rev Lett 75(3):569, 1995) and Bordi et al. (J Phys, Condens Matter 8:A19, 1996) to estimate the cluster size evolution.

Effect of monomeric and polymeric co-solutes on cetyltrimethylammonium bromide wormlike micelles: Rheology, Cryo-TEM and Small-angle neutron scattering

The effect of hydrophobic and hydrophilic co-solutes on the rheological properties of wormlike micelles of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) or sodium bromide (NaBr) was investigated. Monomeric (ethanol, 2-propanol, benzene and benzylic alcohol) and polymeric species (poly(ethylene oxide), poly(vinyl alcohol) and poly(propylene oxide), respectively PEO, PVA and PPO) of varying molecular weight were studied in order to assess the effect of co-solute ‘length’ on the interactions with the wormlike micelles. Rheological properties were characterised by the plateau modulus G 0 and the relaxation time τ R obtained from fits to the Maxwell model, and by the zero-shear viscosity η 0. The rheological properties were unaltered by the addition of all hydrophilic solutes (up to 20 mM). With hydrophobic co-solutes instead, both η 0 and τ R decreased considerably, while G 0 was unaffected. The effects were particularly remarkable with PPO for concentrations as low as 5 mM (ca. 0.3 g L −1), and τ R was seen to follow an exponential decrease with polymer M w . The effect of the aromatic solutes (benzene and benzyl alcohol) on the rheology was highly dependent on the counterions used to induce micellar growth (Sal − or Br −), revealing a different type of interaction. Surprisingly, small-angle neutron scattering and Cryo-TEM measurements showed that the drastic changes observed in the rheology were not correlated to any visible structural change. Therefore the strong decrease in viscosity and relaxation time are to be attributed to other mechanisms than micellar break-up or rod-to-sphere transition.

Crystallization behavior of melt-spun poly(vinyl alcohol) fibers during drawing process

The crystallization behavior of melt-spun poly(vinyl alcohol) (PVA) fibers during hot drawing process was studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and computer controlled electronic universal testing machine. The effects of drawing temperature and drawing speed on the crystallinity and the stress induced crystallization of PVA fibers were discussed. The results showed that the crystallization process of PVA fibers during hot drawing presented three stages: initial stage, stress induced crystallization stage and slowly increasing stage. And PVA fibers with high crystallinity can be obtained by properly increasing the drawing temperature and drawing speed, especially when the drawing temperature and speed were 453 K and 100 mm/min respectively. The stress induced crystallinity of PVA fibers during drawing process was the difference between the crystallinity of PVA fibers after drawing and after only heat treatment. At the low drawing speed, i.e. 50 mm/min, due to the strong molecular movement and orientation relaxation under high temperature, the effect of stress induced crystallization weakens with the increase of drawing temperature, the ratio between stress induced crystallinity and thermal induced crystallinity changed from 8.7%:0%(393 K) to 1.7%:5% (453 K). While at the high drawing speeds, i.e. 100 mm/min and 500 mm/min, with the decrease of available orientation relaxation time, the stress induced crystallization plays an important role during the drawing process, the ratio between stress induced crystallinity and thermal induced crystallinity were 8%:2.9% and 10.2%:0.5% at 453 K respectively.

Echocardiographic evaluation and comparison of the effects of isoflurane, sevoflurane and desflurane on left ventricular relaxation indices in patients with diastolic dysfunction

This prospective randomized study aims to evaluate and compare the effects of isoflurane, sevoflurane and desflurane (study drugs) on left ventricular (LV) diastolic function in patients with impaired LV relaxation due to ischemic heart disease using transesophageal Doppler echocardiography. After approval of the local ethics committee and informed consent, 45 patients scheduled for coronary artery bypass grafting surgery were enrolled in the study. Patients were selected by a preoperative Transthoracic Echocardiographic diagnosis of impaired relaxation or Grade 1 Diastolic Dysfunction. They randomly received fentanyl and midazolam anesthesia with 1 MAC of isoflurane (n=16), sevoflurane (n=14) or desflurane (n=15). Hemodynamic parameters and TEE derived ventricular diastolic relaxation indices before and after the study drug administration were compared. LV filling pressures were kept constant throughout the study period to exclude the effect of the loading conditions on diastolic function. Four patients in the sevoflurane group and three in the desflurane group were excluded from the study, after baseline TEE examination revealed normal diastolic filling pattern. All the three study drugs significantly reduced the systemic vascular resistance index with a significant increase in cardiac index. Mean arterial pressure was reduced by all the drugs, although the decrease was not statistically significant. Hemodynamic changes were comparable between all the three groups. In terms of LV relaxation indices, all three agents led to a significant improvement in diastolic function. Transmitral and Tissue Doppler E/A and Em/Am ratios improved significantly Transmitral and Tissue Doppler E/A and Em/Am ratios improved significantly accompanied by a significant decrease in deceleration time and isovolumetric relaxation time. The effect of all three agents on diastolic relaxation parameters was comparable. In conclusion , Isoflurane, sevoflurane and desflurane, do not appear to have a detrimental effect in patients with early diastolic dysfunction. On the contrary, these inhalational agents actually improve the LV relaxation. A significant reduction in afterload produced by these vapors can be a possible reason for these findings. The positive effect of these inhalational agents on LV relaxation can have a profound effect on the perioperative anesthetic management of patients with diastolic dysfunction.

MR Reporter Gene Imaging of Endostatin Expression and Therapy

The aim of this study is to monitor endostatin gene expression and therapy using transferrin receptor (TfR) as reporter gene and transferrin conjugate of ultrasmall supramagnetic iron oxide nanoparticle (Tf-USPIO) as magnetic resonance (MR) reporter probe. A retroviral plasmid (pLP-LNCX) encoding mouse endostatin and TfR was constructed, and packaged with a titer of 4 × 10(7)colony-forming units per millimeter. MDA-MB-231 breast tumors were established in BALB/c mice by subcutaneous injection of 2 × 10(6) MDA-MB-231 cells. Mice were intratumorally injected with recombinant retrovirus and imaged with MR using Tf-USPIO. Western blot, Prussian blue, and immunohistochemical staining were performed to validate the magnetic resonance imaging results. The antitumor effect of retro-endostatin (ES)-TfR was also evaluated by intratumoral injection of the viral vector. The expression of both endostatin and TfR genes in MDA-MB-231 cells after retroviral transfection was confirmed by Western blot and flow cytometry. Tf-USPIO conjugate binds specifically to cells stably transfected with retro-ES-TfR. After intravenous injection of the Tf-USPIO conjugate, there was a more pronounced decrease in T2 relaxation time in tumors treated with retro-ES-TfR than in tumors treated with empty retrovirus retro-LNCX. The expression of ES gene significantly delayed the growth of MDA-MB-231 tumor and reduction of microvessel density and VEGF level as compared to those without viral transfection or transfected with empty retro-LNCX vector. Endostatin therapeutic gene expression was visualized successfully using TfR reporter gene and Tf-USPIO MR reporter probe, which indicates that MR reporter gene imaging may be valuable in gene therapy to evaluate therapeutic gene expression and treatment efficacy.

Electrical properties of layered FeGaInS4 single crystals with an alternating current

The frequency and temperature dependences of the permittivity and conductivity of FeGaInS4 single crystals in an ac current have been investigated. The permittivities of single crystals and activation energies of permittivity and conductivity are determined. It is established that the conduction of these crystals in the temperature range under study has an activation nature. A frequency dependence of the activation energy is observed, which is related to the decrease in the relaxation time of blocking layers with an increase in frequency.

Study of the kinetics of free volume in Zr 45.0Cu 39.3Al 7.0Ag 8.7 bulk metallic glasses during isothermal relaxation by enthalpy relaxation experiments

Enthalpy relaxation experiments were conducted to study the kinetics of free volume in Zr 45.0Cu 39.3Al 7.0Ag 8.7 bulk metallic glasses (BMGs) during isothermal relaxation using differential scanning calorimetry (DSC) at the temperature within the range from 648 to 684 K. Stretched exponential relaxation functions and the Šesták–Berggren SB ( m, n) model were employed to analyze the kinetics of free volume. It is found that the relaxation time decreases from 2643.5 to 242.8 s while the Kohlrausch exponents increase from 0.717 to 0.892 in the investigated temperature range. The activation energy fluctuates slightly in the course of the relaxation process and its mean value is determined to be 239.7 kJ/mol. By fitting the first derivative of the conversion degree as a function of annealing time using the Šesták–Berggren SB ( m, n) model, it is found that the values of m at all annealing temperatures are very small and can be approximated as zero. The values of the pre-exponential factors Z and the kinetic parameter n are found to be slightly varying with the annealing temperature, indicating the complexity of the kinetics of the isothermal relaxation. Finally, an approximate rate equation describing the kinetics of free volume during isothermal relaxation is proposed.

Photophysics and rotational relaxation dynamics of cationic phenazinium dyes in anionic reverse micelles: Effect of methyl substitution

We present here, a detailed photophysical and rotational relaxation dynamical study of three structurally analogous cationic dyes, namely, phenosafranin (PSF), safranin-T (ST), and safranin-O (SO), carried out in well characterized, monodispersed biomimicking anionic reverse micellar nanocavities composed of sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/heptane with increasing water contents. The dyes belong to the phenazinium family and they differ in terms of methyl substitution on the planar phenazinium skeleton. The objective of the present study is to investigate the modification in the photophysical and dynamical behavior of the dyes with the change in the size of the water pool of the reverse micelle and thereby to explore the role of methyl substitution. Steady state and time resolved emission and anisotropy studies have been exploited for the purpose. The dyes are found to exhibit a marked decrease in the fluorescence anisotropy with increasing water/surfactant mole ratio (w), i.e., the water pool size in the reverse micellar core, implying that overall motional restriction experienced by the molecules are decreased with increasing hydration. Some of the depth dependent fluorescence parameters such as fluorescence maximum, fluorescence anisotropy (r) have been monitored for exploring the microenvironment around the probes in the reverse micelles. Fluorescence studies suggest that at low w values, the probes do not penetrate into the reverse micellar core; rather it binds at the interfacial region. Estimates of the micropolarity at the binding sites of the probe molecule have been determined as a function of w. Finally, dynamic studies reveal that both the lifetime and rotational relaxation time decrease with an increase in w for all the three probes, the extent of the decrease being more for PSF than ST and SO. This indicates a stronger binding of the reverse micelle with ST and SO compared to that with PSF which is rationalized in terms of an increase in the hydrophobicity of the former two dyes because of the methyl substitution on the phenazinium moiety.

A Fast Field Cycling Nuclear Magnetic Resonance Relaxometry Study of Natural Soils

This study used nuclear magnetic resonance (NMR) relaxometry at different Larmor frequencies to investigate water dynamics in the pore space of natural porous media. Spin‐lattice NMR relaxation times (T1) were determined in purified fine sand and two natural soils, Kaldenkirchen sandy loam and Merzenhausen silt loam, by means of fast field cycling relaxometry. This technique investigates relaxation processes as a function of the Larmor frequency ν in the range between 0.005 and 20 MHz, yielding so‐called relaxation dispersion curves (1/T1vs. log ν). The data were further analyzed by means of inverse Laplace transformation to calculate theT1relaxation time distribution functions. Only the fine sand was characterized by monomodal distribution withT1of about 1 s at 20 MHz, whereas the natural soil samples showed multimodal distribution functions in the range between 2 and 70 ms. With decreasing Larmor frequency, all distribution functions kept their shapes but were shifted to faster relaxation times. The corresponding relaxation dispersion curves indicate predominance of two‐dimensional diffusion of water in the soils, whereas in the macroporous sand, diffusion behaved like unrestricted three‐dimensional diffusion. In terms of the Brownstein–Tarr model, the decrease in theT1relaxation times with increasing silt and clay content can be explained by an increase of the surface/volume ratios (S/V) of these porous media, i.e., by a decrease in the pore sizes. Finally, distribution functions of the pore size parameterV/Swere obtained from the spin‐lattice relaxation time distributions by normalizing on the specific surface area. They ranged from submicrometers in the Merzenhausen soil to micrometers and submillimeters in the Kaldenkirchen soil and fine sand, respectively.