A study on solubilization of poorly soluble drugs by cyclodextrins and micelles: complexation and binding characteristics of sulfamethoxazole and trimethoprim.

The present study is focused on the characterization of solubilization of poorly soluble drugs, that is, sulfamethoxazole (SMX) and trimethoprim (TMP) by cyclodextrins (α-, ß-, and γ-CDs) and anionic surfactant sodium dodecyl sulfate (SDS). The phase solubility diagrams drawn from UV spectral measurements are of the A(L) type and indicate an enhancement of SMX and TMP solubility in the presence of CDs. Complex formation tendency of TMP with CDs followed the order: γ-CD > ß-CD > α-C. However, the complex formation constant values, for SMX-CD system yielded the different affinity and follow the order: ß-CD > γ-CD > α-CD. With taking into consideration of solubilization capacity of SDS micelles, it has been found that the solubility enhancement of TMP is much higher than that of SMX in the presence of SDS micelles. The binding constants of SMX and TMP obtained from the Benesi-Hildebrand equation are also confirmed by the estimated surface properties of SDS, employing the surface tension measurements. In order to elucidate the solubilization characteristics the surface tension measurements were also performed for nonionic surfactant Triton X-100. Polarity of the microenvironment and probable location of SMX and TMP were also discussed in the presence of various organic solvents.

Energy-recovery linac project at Cornell University.

There is considerable interest in using superconducting electron linacs with energy recovery as synchrotron radiation sources. Such energy recovery linacs (ERLs) would open new regimes of X-ray science because they are capable of producing ultra-brilliant X-ray beams [>5 x 10(22) photons s(-1) (0.1% bandwidth)(-1) mm(-2) mrad(-2) at 10 keV], maintaining a very small source size ( approximately 3 micro m r.m.s.) suitable for micro X-ray beams, and making very intense fast ( approximately 100 fs) X-ray pulses. Each of these characteristics would permit the execution of experiments that are not feasible with existing synchrotron sources. Many technical issues must be satisfactorily resolved before the potential of a full-scale ERL can be realised, including the generation of high average current (10 to 100 mA), high-brightness electron beams (0.015 to 0.15 nm rad emittances, respectively); acceleration of these beams to energies of 5-7 GeV without unacceptable emittance degradation; stable and efficient operation of superconducting linear accelerators at very high gradients etc. Cornell University, in collaboration with Jefferson Laboratory, has proposed to resolve these issues by the construction of a 100 MeV, 100 mA prototype ERL. The intention is to then utilize the information that is learned from the prototype to propose the construction of a full-scale ERL light source.

Deflections in magnet fringe fields.

A transverse multipole expansion is derived, including the longitudinal components necessarily present in regions of varying magnetic field profile. It can be used for exact numerical orbit following through the fringe-field regions of magnets whose end designs introduce no extraneous components, i.e., fields not required to be present by Maxwell's equations. Analytic evaluations of the deflections are obtained in various approximations. Mainly emphasized is a "straight-line approximation," in which particle orbits are treated as straight lines through the fringe-field regions. This approximation leads to a readily-evaluated figure of merit, the ratio of rms end deflection to nominal body deflection, that can be used to determine whether or not a fringe field can be neglected. Deflections in "critical" cases (e.g., near intersection regions) are analyzed in the same approximation.

Permeability of normal versus carious dentin.

Although a number of reports have been published demonstrating that carious dentin is less permeable than normal dentin, these reports have been qualitative rather than quantitative. The purpose of this in vitro study was to apply a quantitative technique to the study of the permeability of carious human teeth before and after excavation, before and after removal of the smear layer and before and after preparation of a control cavity of similar size and depth in normal dentin subjected to the same measurements, for comparative purposes. Dentin permeability was measured as a hydraulic conductance. The permeability values measured at each step in the protocol were expressed as a percent of the maximum permeability of both cavities, permitting each tooth the serve as its own control. Carious lesions exhibited a slight degree of permeability (2.3 +/- 0.6% of controls) which remained unchanged after excavation of the lesions. Removal of the smear layer in the excavated carious lesions increased the permeability significantly to 6.9 +/- 3.2%. Preparation of a control cavity of the same area and depth increased the permeability slightly. Removal of its smear layer increased the permeability of the dentin 91%. These results confirm previous qualitative studies that carious dentin, even after excavation and removal of the smear layer has a very low permeability.

Self-threading pin penetration into dentin.

A laboratory study has shown that the first-half of self-shearing 2-in-1 self-threading pins, sizes 0.031 inch and 0.024 inch, fail to reach full channel depth when placed with either a hand wrench or an Auto Klutch handpiece. The average discrepancy of penetration is about 0.75 mm. This discrepancy in seating results in a significant excess pin length extending into the tooth preparation, which compromises the strength characteristics of the amalgam restoration.