Application of the JKR Method to the Measurement of Adhesion to Langmuir-Blodgett Cellulose Surfaces

The JKR method has been applied for studying adhesion between poly(dimethylsiloxane) (PDMS) caps and Langmuir–Blodgett cellulose surfaces including the substrate, hydrophobized mica, and two flat mineral surfaces, bare mica and glass. The self-adhesion of PDMS caps and oxidized PDMS caps are included as a reference to compare with literature data. The results of the measurements have been compared with previous studies using the surface force apparatus and similar systems. A satisfactory agreement is obtained for simple systems showing no, or very limited, hysteresis between loading and unloading curves. In several cases, however, a large hysteresis is found between loading and unloading curves, with a larger adhesion measured from the pull-off force than from the JKR-curve determined on loading. This is, for instance, the case for PDMS against cellulose. The situation is analogous to that found in wetting studies showing a large hysteresis between advancing and receding contact angles.     

Message to the participants of the conference

The activity of²³²Th and its daughters in Th-based gas sockets is required for health risk assessment. By absolute measurement of the²²⁸Ac- and²¹²Pb/²⁰⁸Tl-activities, the total activity of the sockets can be assessed. It is governed by²²⁸Ra and²²⁸Th and the product age.     

Application of flow chemistry to the reduction of nitriles to aldehydes

Reduction of nitriles to aldehydes with diisobutylaluminium hydride (DIBAL-H) is an important transformation in organic chemistry. But the use of this reaction is limited for the lack of reproducibility due to the instability of the intermediates formed. In the current article we disclose the improvement of the reaction applying continuous flow technology.     

Chemoenzymatic Routes to Polyoxygenated Cyclooctenones Related to the Eastern Hemisphere of the Macrolactam Tripartilactam

Polyoxygenated cyclooctenones closely related to the enantiomeric form of the Eastern hemisphere of the structurally and biogenetically unusual macrolactam tripartilactam have been assembled from an enzymatically‐derived and homochiral cis‐1,2‐dihydrocatechol. Key steps include the oxidative cleavage of the chlorinated double bond within a derivative of the starting cis‐1,2‐dihydrocatechol and a ring‐closing metathesis reaction to establish the required eight‐membered ring.     

A novel approach to the calculation of the free energy due to molecular flexibility

The contribution of the molecular flexibility to the solvation excess free energy is expressed in terms of probabilities of reaching hard limits on intramolecular coordinates in a series of calculations successively relaxing those limits. Numerical tests on the harmonic oscillator are also presented and used to make suggestion about computational issues.     

An approach to the synthesis of the phomoidrides

The phomoidrides are a structurally fascinating family of natural products which possess moderate inhibitory activity against Ras farnesyl transferase and squalene synthase. Since their discovery they have inspired a great deal of attention from synthetic chemists. Our own work, culminating in an efficient synthesis of the fully elaborated tetracyclic core of phomoidrides B and D, is described herein. The synthesis relies on a late stage tandem reaction involving a novel carbonylation reaction that delivers the strained bicyclic pseudoester system, which strain in turn drives a highly efficient silyloxy-Cope rearrangement that delivers the tetracyclic core of phomoidrides B and D. Several examples of this powerful tandem reaction are presented that document its tolerance of significant structural variation. The application of this methodology to the synthesis of a phomoidride D precursor lacking only the maleic anhydride is described, and the prospects for the completion of a total synthesis are discussed.     

Surface tension of aqueous solutions of salts close to the temperature of transition of the solution to the supersaturated state

Conclusions The polytherms of the surface tension of solutions of K₂Cr₂O₇, saturated at 20 and 25°, were studied. Close to the transition point of the solutions in the supercooled state, there is a discontinuity on the polytherm of the derivative of the surface tension with respect to the temperature.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 671–672, March, 1967.     

Contribution to the kinetics of the process of dissolution

Some characteristics of the kinetic equation of dissolution are discussed, bearing in mind that in the course of the process, along with the concentration of the solution, the surface of the soluble substance is also changed. The opportunity for the appication of an exponential kinetic equation is pointed out. Methods are proposed for calculating the solubility and also for using the integral forms of the exponential equation. The meaning of the coefficient of proportionality is explained.

---

, , ◹ . . , . .

     

Approaches to the description and prediction of the binding affinity of small-molecule ligands to macromolecular receptors

The influence of a xenobiotic compound on an organism is usually summarized by the expression biological activity. If a controlled, therapeutically relevant, and regulatory action is observed the compound has potential as a drug, otherwise its toxicity on the biological system is of interest. However, what do we understand by the biological activity? In principle, the overall effect on an organism has to be considered. However, because of the complexity of the interrelated processes involved, as a simplification primarily the "main action" on the organism is taken into consideration. On the molecular level, biological activity corresponds to the binding of a (low-molecular weight) compound to a macromolecular receptor, usually a protein. Enzymatic reactions or signal-transduction cascades are thereby influenced with respect to their function for the organism. We regard this binding as a process under equilibrium conditions; thus, binding can be described as an association or dissociation process. Accordingly, biological activity is expressed as the affinity of both partners for each other, as a thermodynamic equilibrium quantity. How well do we understand these terms and how well are they theoretically predictable today? The holy grail of rational drug design is the prediction of the biological activity of a compound. The processes involving ligand binding are extremely complicated, both ligand and protein are flexible molecules, and the energy inventory between the bound and unbound states must be considered in aqueous solution. How sophisticated and reliable are our experimental approaches to obtaining the necessary insight? The present review summarizes our current understanding of the binding affinity of a small-molecule ligand to a protein. Both theoretical and empirical approaches for predicting binding affinity, starting from the three-dimensional structure of a protein-ligand complex, will be described and compared. Experimental methods, primarily microcalorimetry, will be discussed. As a perspective, our own knowledge-based approach towards affinity prediction and experimental data on factorizing binding contributions to protein-ligand binding will be presented.     

Efficient route to atropisomeric ligands--application to the synthesis of MeOBIPHEP analogues

A highly efficient Pd-catalyzed P-C coupling reaction of easily accessible atropisomeric bisphosphane is described in the presence of various electron-poor aromatic iodides. The reactions are conducted in the presence of a Pd(II)/dppf catalyst in acetonitrile at 80 °C. The reaction conditions are compatible with several electron-withdrawing groups such as esters, cyano, chloro, and trifluoromethyl groups and lead to atropisomeric MeOBIPHEP derivatives in good to excellent yields and high enantiomeric purities.     

Applications of the Internet to PT

The Internet provides laboratory professionals with a unique opportunity to come together as a network and to develop an integrated system for monitoring the quality of testing in their laboratories on a real-time basis. Once established this network could provide a quality and standards promoting infrastructure for catalyzing the standardization process. Through a collaborative sharing of information on performance and through the use of a common database with harmonized test materials, proficiency testing providers can play a pivotal role in developing such a system. The challenge is now up to us.