Novel phase-transition behavior near liquid/liquid critical points of aqueous solutions: Formation of a third phase at the interface

We report a novel phase behavior in aqueous solutions of simple organic solutes near their liquid/liquid critical points, where a solid-like third phase appears at the liquid/liquid interface. The phenomenon has been found in three different laboratories. It appears in many aqueous systems of organic solutes and becomes enhanced upon the addition of salt to these solutions.

Determination of critical micelle concentration by hyper-Rayleigh scattering

The critical micelle concentration (CMC) of several surfactants that contain an NLO chromophore, either at the hydrocarbon tail, or at the hydrophilic headgroup, or even as a counterion, was determined by hyper-Rayleigh scattering (HRS). In all cases, the HRS signal exhibited a similar variation with surfactant concentration, wherein the CMC is inferred from a rather unprecedented drop in the signal intensity. This drop is attributed to the formation of small pre-micellar aggregates, whose concentrations become negligible above CMC. In addition, a probe molecule, which upon protonation yielded a species with significantly enhanced HRS intensity, was developed and its utility for the determination of the CIVIC of simple fatty acids was demonstrated.

The carboxy terminal WD domain of the pre-mRNA splicing factor Prp17p is critical for function

In Saccharomyces cerevisiae, Prp17p is required for the efficient completion of the second step of pre-mRNA splicing. The function and interacting factors for this protein have not been elucidated. We have performed a mutational analysis of yPrp17p to identify protein domains critical for function. A series of deletions were made throughout the region spanning the N-terminal 158 amino acids of the protein, which do not contain any identified structural motifs. The C-terminal portion (amino acids 160–455) contains a WD domain containing seven WD repeats. We determined that a minimal functional Prp17p consists of the WD domain and 40 amino acids N-terminal to it. We generated a three-dimensional model of the WD repeats in Prp17p based on the crystal structure of the [beta]-transducin WD domain. This model was used to identify potentially important amino acids for in vivo functional characterization. Through analysis of mutations in four different loops of Prp17p that lie between [beta] strands in the WD repeats, we have identified four amino acids, 235TETG238, that are critical for function. These amino acids are predicted to be surface exposed and may be involved in interactions that are important for splicing. Temperature-sensitive prp17 alleles with mutations of these four amino acids are defective for the second step of splicing and are synthetically lethal with a U5 snRNA loop I mutation, which is also required for the second step of splicing. These data reinforce the functional significance of this region within the WD domain of Prp17p in the second step of splicing.

Vortex dynamics and upper critical fields in ultrathin Bi films

Current-voltage (I-V) characteristics of quench condensed, superconducting, ultrathin Bi films in a magnetic field are reported. These I-V's show hysteresis for all films, grown both with and without thin Ge underlayers. Films on Ge underlayers, close to superconductor-insulator transition, show a peak in the critical current, indicating a structural transformation of the vortex solid. These underlayers, used to make the films more homogeneous, are found to be more effective in pinning the vortices. The upper critical fields (B-c2) of these films are determined from the resistive transitions in perpendicular magnetic field. The temperature dependence of the upper critical field is found to differ significantly from Ginzburg-Landau theory, after modifications for disorder.

Immunotherapeutic efficacy of Mycobacterium indicus pranii in eliciting anti-tumor T cell responses: Critical roles of IFN gamma

Mycobacterium indicus pranii (MIP) is approved for use as an adjuvant (Immuvac/Cadi-05) in the treatment of leprosy. In addition, its efficacy is being investigated in clinical trials on patients with tuberculosis and different tumors. To evaluate and delineate the mechanisms by which autoclaved MIP enhances anti-tumor responses, the growth of solid tumors consisting of Sp2/0 (myeloma) and EL4 (thymoma) cells was studied in BALB/c and C57BL/6 mice, respectively. Treatment of mice with a single intra-dermal (i.d.) injection of MIP 3 days after Sp2/0 implantation greatly suppresses tumor growth. MIP treatment of tumor bearing mice lowers Interleukin (IL)6 but increases IL12p70 and IFN? amounts in sera. Also, increase in CD8+ T cell mediated lysis of specific tumor targets and production of high amounts of IL2 and IFN? by CD4+ T cells upon stimulation with specific tumor antigens in MIP treated mice is observed. Furthermore, MIP is also effective in reducing the growth of EL4 tumors; however, this efficacy is reduced in Ifn?-/- mice. In fact, several MIP mediated anti-tumor responses are greatly abrogated in Ifn?-/- mice: increase in serum Interleukin (IL)12p70 amounts, induction of IL2 and lysis of EL4 targets by splenocytes upon stimulation with specific tumor antigens. Interestingly, tumor-induced increase in serum IL12p70 and IFN? and reduction in growth of Sp2/0 and EL4 tumors by MIP are not observed in nonobese diabetic severe combined immunodeficiency mice. Overall, our study clearly demonstrates the importance of a functional immune network, in particular endogenous CD4+ and CD8+ T cells and IFN?, in mediating the anti-tumor responses by MIP.

Continuous phase transition in mixed-valent manganite Nd0.6Pb0.4MnO3

The critical behaviour has been investigated in single crystalline Nd0.6Pb0.4MnO3 near the paramagnetic to ferromagnetic transition temperature (TC) by static magnetic measurements. The values of TC and the critical exponents β, γ and δ are estimated by analysing the data in the critical region. The exponent values are very close to those expected for 3D Heisenberg ferromagnets with short-range interactions. Specific heat measurements show a broad cusp at TC (i.e., exponent α<0) being consistent with Heisenberg-like behaviour.

Deviation from 3-D Ising critical behaviour in aqueous electrolyte solutions

The near-critical behaviour in complex fluids, comprising electrolyte solutions, polymer solutions and amphiphilic systems, reveals a marked departure from the 3-D Ising behaviour. This departure manifests itself either in terms of a crossover from Ising to mean-field (or classical) critical behaviour, when moving away from a given critical point (Tc), or by the persistence of only mean-field region in the surprisingly close vicinity of Tc. The ilo,non-Ising features of the osmotic compressibility (chi(T,p)) in solutions of electrolytes, that exhibit orle or many liquid-liquid transitions, will be presented. The underlying cause of the breakdown of the anticipated 3-D Ising behaviour in aqueous electrolyte solutions is traced to the structuring induced by the electrolytes. New evidence constituting, measurements of small-angle X-ray scattering (SAXS) and the excess molar volume, is advanced to support the thesis of the close relationship, between the structuring and the deviation from the 3-D Ising critical behaviour in aqueous electrolyte solutions.