Contribution Of Intermolecular Forces Research Articles

Interconvertible Hydrochlorothiazide–Caffeine Multicomponent Pharmaceutical Materials: A Solvent Issue

The design of new multicomponent pharmaceutical materials that involve different active pharmaceutical ingredients (APIs), e.g., drug-drug cocrystals, is a novel and interesting approach to address new therapeutic challenges. In this work, the hydrochlorothiazide-caffeine (HCT–CAF) codrug and its methanol solvate have been synthesized by mechanochemical methods and thoroughly characterized in the solid state by powder and single crystal X-ray diffraction, respectively, as well as differential scanning calorimetry, thermogravimetric analyses and infrared spectroscopy. In addition, solubility and stability studies have also been performed looking for improved physicochemical properties of the codrug. Interestingly, the two reported structures show great similarity, which allows conversion between them. The desolvated HCT–CAF cocrystal shows great stability at 24 h and an enhancement of solubility with respect to the reference HCT API. Furthermore, the contribution of intermolecular forces on the improved physicochemical properties was evaluated by computational methods showing strong and diverse H-bond and π–π stacking interactions.

Designing Imidazolium Poly(amide-amide) and Poly(amide-imide) Ionenes and Their Interactions with Mono- and Tris(imidazolium) Ionic Liquids.

Here we introduce the synthesis and thermal properties of a series of sophisticated imidazolium ionenes with alternating amide-amide or amide-imide backbone functionality, and investigate the structural effects of mono(imidazolium) and unprecedented tris(imidazolium) ionic liquids (ILs) in these ionenes. The new set of poly(amide-amide) (PAA) and poly(amide-imide) (PAI) ionenes represent the intersection of conventional high-performance polymers with the ionene archetype–presenting polymers with alternating functional and ionic elements precisely sequenced along the backbone. The effects of polymer composition on the thermal properties and morphology were analyzed. Five distinct polymer backbones were synthesized and combined with a stoichiometric equivalent of the IL 1-benzyl-3-methylimidazolium bistriflimide ([Bnmim][Tf2N]), which were studied to probe the self-assembly, structuring, and contributions of intermolecular forces when IL is added. Furthermore, three polyamide (PA) or polyimide (PI) ionenes with simpler xylyl linkages were interfaced with [Bnmim][Tf2N] as well as a novel amide-linked tris(imidazolium) IL, to demonstrate the structural changes imparted by the inclusion of functional, ionic additives dispersed within the ionene matrix. This work highlights the possibilities for utilizing concepts from small molecules which exhibit supramolecular self-assembly to guide creative design and manipulate the structuring of ionenes.

RESEARCH NOTE WCA repulsive and attractive contributions to the thermodynamic properties at the vapour-liquid equilibrium

The Lennard-Jones attractive and repulsive contributions of intermolecular forces (as separated in the Weeks-Chandler-Andersen (WCA) theory) to the pressure and chemical potential of coexisting vapour and liquid phases are obtained by using an equation of state recently proposed by us. Some comments are given about the computer simulation results obtained by Plackov and Sadus (1997, Fluid Phase Equilib., 134, 77) using the McQuarrie-Katz separation of the intermolecular potential.

Vapour pressure of non-polar fluids and their repulsive and attractive contributions

Using a simple equation of state, based on the Weeks-Chandler-Andersen separation of the intermolecular potential, we have obtained the contributions of repulsive and attractive intermolecular forces to the thermodynamic properties of coexisting vapour and liquid phases of a Lennard-Jones (LJ) fluid. In order to obtain the vapour pressure of real non-polar fluids, we take the LJ fluid as a reference model, and propose a new perturbative contribution, which is dependant on the temperature and on the acentric factor of the substance. Using the complete perturbed equation, we determine the corresponding repulsive and attractive contributions to the vapour pressure of non-polar fluids. The results show that the attractive vapour pressure of non-polar fluids increases with increasing acentric factor, i.e., larger deviation of the molecular shape from spherical symmetry. This procedure could be extended to separate the repulsive and attractive contributions of the intermolecular forces to other thermodynamic properties of non-polar fluids as well as of polar fluids and fluid mixtures.

Role of Surface Forces in the Stability of Evaporating Thin Liquid Films That Contain Surfactant Micelles

We consider an evaporating liquid film which lies on a planar heated solid substrate. The film contains a dissolved surfactant at a high concentration, so that micellar aggregates exist in the bulk. Linear stability analysis of this system is performed by investigating the time evolution of the amplitude of fluctuation waves. The liquid-vapor interface is regarded as a two-dimensional continuum characterized by intrinsic viscosity, specific adsorption, and surface tension. The latter quantities depend on the instantaneous subsurface concentration of surfactant monomers (subject to fluctuation) and upon the temperature. At small Reynolds and large Peclet numbers, and for thin films, the lubrication approximation model can be applied to solve the hydrodynamic problem. In the balance of normal stress at the fluid interface, we account for the contribution of intermolecular forces. There are van der Waals, electrostatic, steric, and oscillatory structural interactions, which are described in terms of separate components of disjoining pressure. The oscillatory structural forces are due to the presence of surfactant micelles or other colloidal particles in the film. These forces turn out to have the highest magnitude, and are of great importance for the stability. We solve numerically the evolution equation for the fluctuation, thus finding the critical thickness of film rupture and the critical lateral wave number. The influence of the surfactant type and concentration and the relative significance of the particular interactions under different conditions are discussed in detail.