Chemical binding

About: Chemical binding is a research topic. Over the lifetime, 1822 publications have been published within this topic receiving 52516 citations.

First passage and cooperativity of queuing kinetics

Abstract: We model the kinetics of ligand-receptor systems, where multiple ligands may bind and unbind to the receptor, either randomly or in a specific order. Equilibrium occupation and first occurrence of complete filling of the receptor are determined and compared. At equilibrium, receptors that bind ligands sequentially are more likely to be saturated than those that bind in random order. Surprisingly however, for low cooperativity, the random process first reaches full occupancy faster than the sequential one. This is true except near a critical binding energy where a "kinetic trap" arises and the random process dramatically slows down when the number of binding sites N > or = 8. These results demonstrate the subtle interplay between cooperativity and sequentiality for a wide class of kinetic phenomena, including chemical binding, nucleation, and assembly line strategies.

Thermodynamics of Methane Adsorption on Copper HKUST-1 at Low Pressure.

Abstract: Metal-organic frameworks (MOFs) can be engineered as natural gas storage materials by tuning the pore structures and surface properties. Here we report the direct measurement of CH4 adsorption enthalpy on a paddlewheel MOF (Cu HKUST-1) using gas adsorption calorimetry at 25 °C at low pressures (below 1 bar). In this pressure region, the CH4-CH4 intermolecular interactions are minimized and the energetics solely reflects the CH4-MOF interactions. Our results suggest moderately exothermic physisorption with an enthalpy of -21.1 ± 1.1 kJ/mol CH4 independent of coverage. This calorimetric investigation complements previous computational and crystallographic studies by providing zero coverage enthalpies of CH4 adsorption. The analysis of the new and literature data suggests that in initial stages of adsorption the CH4-HKUST-1 interaction tends to be more sensitive to the pore dimension than to the guest polarizability, suggesting a less specific chemical binding role for the open Cu site.

Effects of Chemical Combination with Oxygen and Fluorine on the K 1,2 -Doublet of some of the Lighter Elements

Abstract: IT is well known that the K1,2-doublet from the elements 12 (Mg) to 17 (Cl) is influenced by chemical binding, apparent, for example, through its displacement towards shorter wave-lengths. Earlier measurements I have made1 with the elements 12 (Mg), 13 (Al) and 14 (Si), which were carried out with special regard to the effects from oxygen and fluorine on the K1,2-doublet, have recently been extended by measurements with sodium. No conclusive evidence of any displacement in either direction could be found. These and previous results are summarized in the accompanying table; the measurements on the oxygen compounds of phosphorus, sulphur and chlorine were made by Lundquist2.

Complexation of As(III) by phosphonate ligands in aqueous fluids: Thermodynamic behavior, chemical binding forms and sequestering abilities.

Abstract: In recent years, the contamination of water by arsenic reached alarming levels in many countries of the world, attracting the interest of many researchers engaged in testing methodologies able to remove this harmful pollutant. An important aspect that must be taken into consideration is the possibility to find arsenic in different chemical forms which could require different approaches for its removal. At this aim, a speciation analysis appears to be crucial for better understanding the behavior of arsenic species in aqueous solutions, especially in presence of compounds with marked chelating properties. Phosphonates can be identified as good sequestering agents and, at this purpose, this manuscript intends to investigate the interaction of As(III) with three phosphonic acids derived from nitrilotriacetic acid (NTA) by replacements of one (N-(Phosphonomethyl) iminodiacetic acid, NTAP), two (N,N-Bis-(phosphonomethyl) glycine, NTA2P) and three (Nitrilotri(methylphosphonic acid), NTA3P) carboxylic groups with the same number of phosphonate groups. An in-depth potentiometric and calorimetric investigation allowed to determine speciation models featured by simple ML, MLHi and ML(OH) species. A complete thermodynamic characterization of the systems is reported together with the definition of coordination mode by mass spectrometry measurements. On the light of the speciation models, the possibility of using these ligands in arsenic removal techniques was assessed by determining the pL0.5 (the concentration of ligand able to remove the 50% of metal ion present in trace). All ligands show a good sequestering ability, in particular under the conditions of fresh water, following the trend NTA3P > NTA2P > NTAP.

Method for the cooling of solid residues of gasification

Abstract: The present specification describes and claims a method and apparatus for use in cooling the solid residue of gasification of a reactor operated at a pressure above atmospheric for the gasification of carbonaceous materials. The residue of gasification is conducted out of the reactor into a cooling apparatus located therebelow and flows through the cooling apparatus from the top to the bottom thereof. A cooling liquid is introduced into the solid residue in the upper region of the cooling apparatus and is metered such that the greater portion of the heat contained in the residue is eliminated in the form of heat of vaporization, sensible heat and chemical binding energy with the resultant steam and reaction products produced. The remaining residual heat which corresponds to the difference between the desired final temperature and the temperature after cooling by the liquid, is eliminated by a gas blown into the bottom region of the cooling apparatus and/or by indirect heat exchange.