Determination of the Concentration of Single-Walled Carbon Nanotubes in Aqueous Dispersions Using UV−Visible Absorption Spectroscopy

Stable, homogeneous, aqueous dispersions of single-walled carbon nanotubes (SWNTs) are prepared by nonspecific physical adsorption of surfactants enhanced by sonication. Upon centrifugation, supernatant and precipitate phases are obtained. The initial weights of the SWNTs and the surfactant are divided between these two phases, and the respective SWNT concentration in each phase is unknown. The focus of this work is on the determination of the true concentration of raw, exfoliated HiPCO SWNTs in the supernatant phase. A UV-visible absorption-based approach is suggested for a direct measurement of the SWNT and the surfactant concentration in the supernatant. UV-visible absorbance spectra of SWNTs-surfactant dispersions and surfactants alone reveal that the intensity of a certain peak, attributed to the pi-plasmon resonance absorption, is unaffected by the presence of most surfactants. A calibration plot is then made by monitoring the intensity of the peak as a function of the true concentration of the exfoliated SWNTs. Thus, we are able to determine the unknown concentration of surfactant-dispersed HiPCO SWNTs in the supernatant solution, simply by measuring its optical absorbance. Moreover, we can now calculate the surfactant efficiency in dispersing SWNTs. Cryogenic-transmission electron microscopy and thermogravimetric analysis techniques are used for the characterization of these dispersions and to complement the UV-visible measurements.

Aggregation Behavior of Tyloxapol, a Nonionic Surfactant Oligomer, in Aqueous Solution

The aggregation behavior of Tyloxapol, a nonionic surfactant oligomer with a repeating unit close to Triton X-100 (TX100), and a maximum degree of polymerization of about 7, has been investigated in aqueous solution by means of fluorescence probing, time-resolved fluorescence quenching (TRFQ) and transmission electron microscopy at cryogenic temperature (cryo-TEM). The plot of the pyrene fluorescence intensity ratio I1/I3 against the Tyloxapol concentration shows no clear evidence of a critical micelle concentration contrary to TX100. Nevertheless, the fitting of these data, assuming a partition of pyrene between Tyloxapol aggregates and water, yields cmc values in the micromolar range, i.e., about a hundred times lower than for the "monomer" TX100. The values of I1/I3 at high surfactant concentrations indicate that Tyloxapol micelles provide pyrene a less polar environment than TX100 micelles. The use of the viscosity-sensitive probe 1,3-dipyrenylpropane indicates that the microviscosity of Tyloxapol micelles is quite high, three to four times larger than that for TX100 micelles, and decreases rapidly with increasing temperature. Also the microviscosities of both TX100 and Tyloxapol micelles are larger than those for the micelles of the nonionic ethoxylated surfactant C12E9. The aggregation numbers of Tyloxapol and of TX100 micelles measured using TRFQ increase with temperature, with the Tyloxapol micelles being smaller than the TX100 micelles. Cryo-TEM shows that the Tyloxapol micelles remain spheroidal up to a concentration of about 10 wt%. At 15 wt%, some regions of ordered elongated micelles are also observed which may be the precursors of the hexagonal phase known to occur at about 35 wt%. Copyright 1999 Academic Press.

p53 in Bronchial Club Cells Facilitates Chronic Lung Inflammation by Promoting Senescence

The tumor suppressor p53 limits tumorigenesis by inducing apoptosis, cell cycle arrest, and senescence. Although p53 is known to limit inflammation during tumor development, its role in regulating chronic lung inflammation is less well understood. To elucidate the function of airway epithelial p53 in such inflammation, we subjected genetically modified mice, whose bronchial epithelial club cells lack p53, to repetitive inhalations of lipopolysaccharide (LPS), an exposure that leads to severe chronic bronchitis and airway senescence in wild-type mice. Surprisingly, the club cell p53 knockout mice exhibited reduced airway senescence and bronchitis in response to chronic LPS exposure and were significantly protected from global lung destruction. Furthermore, pharmacological elimination of senescent cells also protected wild-type mice from chronic LPS-induced bronchitis. Our results implicate p53 in induction of club-cell senescence and correlate epithelial cell senescence of chronic airway inflammation and lung destruction.

High gas barrier imparted by similarly charged multilayers in nanobrick wall thin films

Super oxygen barrier trilayer thin films have been deposited using two successive anionic layers of clay and polymer following every cationic polymer layer.

Multi stimuli response of a single surfactant presenting a rich self-assembly behavior

A bile salt derived surfactant shows an unusually rich multi responsive self-assembly, involving interesting opening/closure mechanisms of supramolecular tubules and drastic spectroscopic variations, potentially exploitable in sensing.

A Cryo-TEM Study of Protein-Surfactant Gels and Solutions

Oppositely charged globular protein and surfactant systems, such as lysozyme-sodium dodecyl sulfate (SDS) and ovalbumin-dodecyltrimethylammonium chloride (DOTAC) form precipitate, gel, and colorless solution in water over a wide concentration range. Bluish solutions are also recognized in connection with the redissolution of precipitate as well as prior to the gel formation. For the lysozyme-SDS system the bluish solution has been suggested to consist of finely dispersed gel particles in solution. The oppositely charged bovine serum albumin (BSA)-DOTAC-water system forms only a large, clear solution phase and a narrow, bluish solution region within a very limited surfactant concentration range. In the lysozyme-SDS system the formation of protein-surfactant aggregates and their growth and breakdown are studied in detail by cryogenic-transmission electron microscopy (cryo-TEM) method. In particular a series of samples with an increased surfactant concentration at fixed 4 wt% of lysozyme is studied. Imaging of the bluish solution at different protein concentrations exhibits large aggregates in the form of rod-like, sheet-like, and star-like objects which are attributed to the gel. At excess amounts of SDS, in the colorless solution, only small objects are detected. In the ovalbumin-DOTAC-water and BSA-DOTAC-water systems large aggregates are also observed in the bluish solutions. Colorless solutions for these two systems show the presence of small objects in the cryo-TEM micrographs. Ultrathin sections of the lysozyme and ovalbumin gels fixed with OsO(4) also show the presence of aggregated structures as judged from the transmission electron microscopy observations. Copyright 2000 Academic Press.

Enhancing the immunogenicity of liposomal hepatitis B surface antigen (HBsAg) by controlling its delivery from polymeric microspheres

Microencapsulated liposome systems (MELs) were investigated as a potential immunization carrier for a recombinant 22-nm hepatitis B surface antigen (HBsAg) particle. MELs were prepared by first entrapping the HBsAg particles within liposomes composed of phosphatidylcholine:cholesterol (1:1 molar ratio), which were then encapsulated within alginate-poly(L-lysine) (PLL) hydrogel microspheres. The entrapped HBsAg particles retained immunoreactivity, as judged by an enzyme-linked immunosorbent assay (ELISA). Direct imaging of HBsAg particles and HBsAg incorporated into liposomes by cryo-transmission electron microscopy (cryo-TEM) indicated that HBsAg is embedded in the liposomal membrane. The antigenic particles were released from MELs mainly within the context of liposomes. The release rates in vitro and in vivo depended on the molecular weight of PLL used for MEL coating; MELs-214, coated with 214 kDa PLL, released the liposomal HBsAg at much higher rates than MELs-25, which was coated with 25 kDa PLL. Concomitantly, the specific anti-HBsAg titers in mice receiving HBsAg in MELs-214 were higher than those induced by MELs-25. MELs-214 were more efficient than conventional liposomes or alum in eliciting higher and prolonged antibody levels in mice. The ability of MELs to provide an HBsAg depot as well as a sustained release of liposomal HBsAg suggests that these carriers may be an ideal immunoadjuvant.

Lung-surfactant-meconium interaction: in vitro study in bulk and at the air-solution interface

Lung surfactants (LSs) form a monolayer at the lung's alveoli air-solution interface and play a crucial role in making normal breathing possible by reducing the surface tension. LS are affected by various agents that hamper their normal functioning. Tobacco smoke [Bringezu, F.; Pinkerton, K. E.; Zasadzinski, J. A. Langmuir 2003, 19, 2900-2907] and meconium, the first excrement of the newborn, are examples for such LS poison. In neonates, intrauterine aspiration of meconium is a known cause for morbidity and mortality. We studied in vitro the interactions between modified porcine LSs (Curosurf), used as LS replacement, and meconium, as well as between their artificial analogues, phospholipids mixture, and taurocholic acid (TA), respectively. The interactions were examined both in the bulk solution and at the air-water interface, representing the pre- and postnatal situations. It was found that the artificial analogues represent the natural system reliably and exhibit similar effects. TA, a principle component of bile, is an amphiphilic sterol compound in which the hydrophilic and hydrophobic moieties are presented at different faces of the sterol plane. Here we found that TA affects the structure of both monolayers at the interface and surfactant aggregates in solution. A likely poisoning mechanism is by stereoselective penetration of TA into the lamellar or monolayer structures, thus disrupting the contiguous structure of the intact monolayer or the bilayer vesicle structure.

Conception and realization of a non-cationic non-viral DNA vector

Cationic non-viral DNA vectors are very successful in in vitro transfections but less efficient in in vivo tests. This seems mainly due to the cationic nature of the molecules used to complex DNA. In this article, we describe the design and the route towards the realization of a non-viral non-cationic vector. The strategy follows three steps: first, the incorporation of DNA to a lamellar phase; second, the making of multilamellar vesicles containing a high loading of DNA by shearing the lamellar phase and, finally, the grafting of peptides onto the surface of the vesicles to target a specific receptor on the cells. Throughout this process, we had to overcome many obstacles; this review describes the present state of our work and summarizes the remaining steps.

p21 facilitates chronic lung inflammation via epithelial and endothelial cells

Cellular senescence is a stable state of cell cycle arrest that regulates tissue integrity and protects the organism from tumorigenesis. However, the accumulation of senescent cells during aging contributes to age-related pathologies. One such pathology is chronic lung inflammation. p21 (CDKN1A) regulates cellular senescence via inhibition of cyclin-dependent kinases (CDKs). However, its role in chronic lung inflammation and functional impact on chronic lung disease, where senescent cells accumulate, is less understood. To elucidate the role of p21 in chronic lung inflammation, we subjected p21 knockout (p21-/-) mice to repetitive inhalations of lipopolysaccharide (LPS), an exposure that leads to chronic bronchitis and accumulation of senescent cells. p21 knockout led to a reduced presence of senescent cells, alleviated the pathological manifestations of chronic lung inflammation, and improved the fitness of the mice. The expression profiling of the lung cells revealed that resident epithelial and endothelial cells, but not immune cells, play a significant role in mediating the p21-dependent inflammatory response following chronic LPS exposure. Our results implicate p21 as a critical regulator of chronic bronchitis and a driver of chronic airway inflammation and lung destruction.

Dendritic cell ICAM-1 strengthens synapses with CD8 T cells but is not required for their early differentiation

Lymphocyte priming in lymph nodes (LNs) was postulated to depend on the formation of stable T cell receptor (TCR)-specific immune synapses (ISs) with antigen (Ag)-presenting dendritic cells (DCs). The high-affinity LFA-1 ligand ICAM-1 was implicated in different ISs studied in vitro. We dissect the in vivo roles of endogenous DC ICAM-1 in Ag-stimulated T cell proliferation and differentiation and find that under type 1 polarizing conditions in vaccinated or vaccinia virus-infected skin-draining LNs, Ag-presenting DCs engage in ICAM-1-dependent stable conjugates with a subset of Ag-specific CD8 blasts. Nevertheless, in the absence of these conjugates, CD8 lymphocyte proliferation and differentiation into functional cytotoxic T cells (CTLs) and skin homing effector lymphocytes takes place normally. Our results suggest that although CD8 T cell blasts engage in tight ICAM-1-dependent DC-T ISs, firm ISs are dispensable for TCR-triggered proliferation and differentiation into productive effector lymphocytes.

Health promotion programs in prison: attendance and role in promoting physical activity and subjective health status

Introduction

Maintaining an inmate's health can serve as a challenge due to unhealthy background, risky behavior, and long imprisonment. This study aimed to analyze the prevalence of participation in health promotion activities among Israeli inmates and its association with their physical activity levels and subjective health status.

Methods

A cross-sectional study was designed to examine 522 inmates (429 males, 93 females). The data were collected by trained face-to-face interviewers and self-report questionnaires.

Results

Most of the participants (82.37%) did not meet the recommended physical activity level. Half of the participants reported that their physical activity levels decreased since they were in prison compared with 29.50% who reported that their physical activity levels increased. Physical activity and subjective health status were significantly higher among younger male inmates. Furthermore, participation in health-promoting activities was associated with higher levels of physical activity and subjective health status.

Discussion

Health promotion activities may play an important role in addressing the challenges of maintaining inmate health. Implications of the findings are further discussed.

Weakly nonlinear analysis of the magnetorotational instability in a model channel flow

We show by means of a perturbative weakly nonlinear analysis that the axisymmetric magnetorotational instability (MRI) of a viscous, resistive, incompressible rotating shear flow subject to a background vertical magnetic field in a thin channel gives rise to a Ginzburg-Landau equation for the disturbance amplitude. For small magnetic Prandtl number (P(m)), the saturation amplitude is proportional square root P(m) and the resulting momentum transport scales as R(-1), where R is the hydrodynamic Reynolds number. Simplifying assumptions, such as linear shear base flow, mathematically expedient boundary conditions, and continuous spectrum of the vertical linear modes, are used to facilitate this analysis. The asymptotic results are shown to comply with numerical calculations using a spectral code. They suggest that the transport due to the nonlinearly developed MRI may be very small in experimental setups with P(m)<<1.

Microtubule destabilization is a critical checkpoint of chemotaxis and transendothelial migration in melanoma cells but not in T cells

Microtubules (MTs) control cell shape and intracellular cargo transport. The role of MT turnover in the migration of slow-moving cells through endothelial barriers remains unclear. To irreversibly interfere with MT disassembly, we have used the MT-stabilizing agent zampanolide (ZMP) in Β16F10 melanoma as amodel of slow-moving cells. ZMP-treated B16 cells failed to follow chemotactic gradients across rigid confinements and could not generate stable sub-endothelial pseudopodia under endothelial monolayers. In vivo, ZMP-treated Β16 cells failed to extravasate though lung capillaries. In contrast to melanoma cells, the chemotaxis and transendothelial migration of ZMP-treated Tcells were largely conserved. This is afirst demonstration that MT disassembly is akey checkpoint in the directional migration of cancer cells but not of lymphocytes.

Nonlinear saturation of the magnetorotational instability near threshold in a thin-gap Taylor-Couette setup

We study the saturation near threshold of the axisymmetric magnetorotational instability (MRI) of a viscous, resistive, incompressible fluid in a thin-gap Taylor-Couette configuration. A vertical magnetic field, Keplerian shear, and no-slip conducting radial boundary conditions are adopted. The weakly nonlinear theory leads to a real Ginzburg-Landau equation for the disturbance amplitude, as in our previous idealized analysis. For small magnetic Prandtl number (Pm<<1) , the saturation amplitude scales as Pm2/3 while the magnitude of angular momentum transport scales as Pm4/3. The difference from the previous scalings (proportional to Pm1/2 and Pm respectively) is attributed to the emergence of radial boundary layers. Away from those, steady-state nonlinear saturation is achieved through a modest reduction in the destabilizing shear. These results will be useful in understanding MRI laboratory experiments and associated numerical simulations.

High avidity TCR-peptide interactions between CD4 lymphocytes and lymph node dendritic cells promote normal lymphocyte arrest, activation, proliferation, and differentiation independently of dendritic cell ICAM-1 and 2

The two main LFA-1 ligands ICAM-1 and ICAM-2 are constitutively co-expressed on antigen presenting cells (APCs) and on the lymph node stroma. We find abrogated antigen specific CD4 T cell priming in ICAM-1 and ICAM-2 deficient spleens. Nevertheless, the in vivo contribution of these ligands to lymphocyte activation proliferation and differentiation in lymph nodes has been difficult to dissect in total knockout mice due to their multiple roles in lymphocyte entry and priming in these organs. We therefore constructed lethally irradiated chimeric mice reconstituted with ICAM-1 and 2 double knock out (DKO) APCs in which lymphocyte entry into peripheral lymph nodes was reconstituted. Strikingly, these mice elicited normal antigen specific OT-II T cell activation, proliferation and differentiation into Th1 and Tfh effectors. OT-II T cells could also normally arrest on DCs deficient in ICAM-1 and 2. A compensatory role of VCAM-1 in ICAM deficient DCs was ruled out. Nevertheless, polyclonal T cell proliferation in response to endogenous self-antigens required the presence of ICAM-1 and ICAM-2 on endogenous lymph node DCs. Our results are the first indication that high avidity TCR peptide-MHC-II recognition can bypass integrin-mediated lymphocyte adhesions to DCs under specific settings.