Growth and interaction of the Tetronic 904 micelles in aqueous alkaline solutions.

The influence of sodium hydroxide (NaOH) on the aggregation characteristics of the Tetronic 904 (T904) has been studied in the aqueous medium by dynamic light scattering (DLS), small angle neutron scattering (SANS), and viscometry methods. This polyethylene oxide (PEO)-polypropylene oxide (PPO) based X-shaped triblock copolymer shows pH sensitive aggregation characteristics due to the presence of a central amine group attached with the PPO block. The aqueous micellar solutions of this copolymer have been found to show a large increase in the room temperature (30 °C) relative viscosity with an increase in NaOH concentration, before they undergo phase separation at 1.25 M NaOH concentration. SANS and DLS studies ascribe this behavior to a sphere to rod growth of the copolymer micelles on approaching the cloud points of the copolymer solutions. DLS studies show that the observed micellar growth is accompanied by critical scattering due to the onset of an attractive intermicellar interaction. To understand the role of NaOH in inducing the observed micellar shape transition, we have also studied the effect of NaOH on the micellar solutions of Pluronic P84, which does not show pH sensitivity due to the absence of the central amine group but has the same weight fraction of the PEO block (40%) as that of T904. Quite interestingly, the P84 micelles too have been found to undergo a similar room temperature sphere to rod shape transition in the presence of NaOH. The observed growth and interaction of the Tetronic micelles have thus been attributed to the dual effects of NaOH in influencing the aggregation characteristics of the Tetronic molecules. On one hand, it stabilizes these micelles by the deprotonation of the copolymer molecules, and on the other hand, its dehydrating effect on the copolymer molecules promotes the onset of micellar growth and intermicellar attractive interaction at the room temperature. The observed results are the first of their kind in the aqueous Tetronic system.

A study of some clinical variables in predicting outcome after acute myocardial infarction.

The univariate analysis of age, previous myocardial infarction, systolic blood pressure, diabetes, smoking, etc, accounted their association with increased mortality in acute myocardial infarction (AMI). Thus, the study was undertaken to determine the significance of some such variables among hospitalised AMI cases by applying univariate statistical techniques. Two years retrospective data of 208 hospitalised AMI cases was collected from patients' records. Impact of each study variable on outcome, survival and non-survival, was assessed by Student's 't' test while association between risk factor and outcome was estimated by Chi-square test. Twenty-five per cent of non-survival was observed in AMI cases. Non-survival was high among those, whose age was more than 60 years (t = 4.37, p < 0.001) and who were village dwellers (t = 3.69, p < 0.001). The non-survival in previous myocardial Infarction (MI) and diabetes cases was 28% and 30% respectively. Thirty per cent of cases with previous MI and hypertension together as common risk factors did not survive. On admission significantly low systolic blood pressure (t = 3.23, p < 0.01), high pulse rate (t = 4.88, p < 0.001) and high blood sugar (t = 2.55, p < 0.05) was observed among non-survivals. There was large variation in explaining survival/non-survival on the basis of each variable, separately. Involvement of single variable in determination of prognosis assuming non-influence of other variable(s), may result in improper determination of prognosis.

Induced micellization and micellar transitions in aqueous solutions of non-linear block copolymer Tetronic® T904.

Tetronics® (Poloxamines) are the least studied block copolymers with an X-shaped molecular geometry formed by four poly (propylene oxide, PPO) and poly (ethylene oxide, PEO) block chains, bonded to a central ethylenediamine group. Compared to their linear counterparts, the Pluronics, Tetronics® are novel, in that they possess superior physicochemical properties, and are relatively less studied. A complete understanding of their solution behavior under different solution conditions can make them competitive candidates for novel drug delivery systems. The micellization behavior and aqueous solution properties of Tetronic® T904 [(EO(15)PO(17)) (2)NCH(2)CH(2)N (PO(17)EO(15))(2)] have been determined by cloud point, viscosity, dynamic light scattering (DLS), small-angle neutron scattering (SANS), and nuclear magnetic resonance (NMR) measurements. The copolymer formed spherical micelles at 30°C with a core radius (R(c)) of about 2.5 nm, a hard sphere radius (R(hs)) of 5.2 nm and an aggregation number (N(agg)) of 10. The effect of copolymer concentration, temperature, pH and salt on the micellar and phase behavior is examined. The copolymer has been found to exist in aggregated form only at higher pH values of >8. An increase in micelle size and aggregation has been observed for an increase in temperature and salt concentration, mainly due to the dehydration of the hydrated PEO shell. The added salts (NaCl, Na(2)SO(4) and Na(3)PO(4)) induce micellization and favor the micellar transition at lower temperatures due to the "salting out effect"; the effect of anions follows the Hofmeister series (PO(4)(3-)>SO(4)(2-)>Cl(-)).

Time dependent sphere-to-rod growth of the pluronic micelles: investigating the role of core and corona solvation in determining the micellar growth rate.

The salt induced sphere-to-rod growth in the micelles of the PEO-PPO triblock copolymers, Pluronic P123 (EO(20)PO(70)PEO(20)) and Pluronic P103 (EO(16)PO(61)PEO(16)), has been studied by dynamic light scattering (DLS), viscometry, and small angle neutron scattering (SANS) techniques. The observed micellar growths are found to be time dependent and have a strong variation in their growth rate with changing anion type and copolymer composition. The rate of growth increases rather significantly with an increase in the water structure making abilities of the anions along the Hofmeister series in the order Cl(-) < F(-)< (PO(4))(3-). This has been attributed to an increasing ability of these ions to dehydrate the micellar corona, a factor that plays an important role in inducing sphere-to-rod shape transition of the micelles. The copolymer composition also has a significant influence on the micellar growth rate, as the P103 with a smaller molecular weight than P123 shows a significantly faster growth of its micelles under similar conditions. The observed time dependence in micellar growth in these systems has been attributed to a slow micellar restructuring process necessary to attain the equilibrium structure of the micelles. A remarkable improvement in the growth rate of the micelles, however, could be achieved in the presence of ethanol, a solvent that has affinity toward both the PPO and PEO blocks. Our spectroscopic studies suggest that the observed improvement in the micellar growth rate by ethanol is due to an accelerated restructuring process of the micelles in the presence of the solvated micellar core. These studies thus highlight the role of changing core and corona solvation characteristics of the pluronic micelles in determining their rearrangement and the growth rate, which is first of its kind in the aqueous pluronic system.