Questo blog contiene una breve introduzione alla programmazione della Unix shell csh/tcsh. Per altri tipi di shells, il lettore può consultare manuali dedicati a questo argomento riportati nella bibliografia alla fine di questa questo blog. Continue reading
Author: Danilo Roccatano
Il calcolo della entalpia reticolare: il ciclo di Born-Haber
La stabilità di un reticolo cristallino, in condizioni di T e P costanti, è legata all’ energia libera di Gibbs di formazione del reticolo:
Se 
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The lattice energy
The lattice energy is the energy necessary in order to decompose, at the temperature T=0 K, an ionic crystal in its fundamental atomic component by carrying them at a distance infinite.
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The calculation of the Madelung constant
A previous article showed that the electrostatic term of the lattice energy of a crystal contains a factor (A) that depends on the type of crystalline reticulum. This article will look more in detail how to calculate this term and its value for a simple ionic system.
The total Coulomb interaction energy of a crystal is given by the sum of the single pair interaction terms:
for ions with charges qA and qB and distance rAB. The sum extends to all pairs of ions present in the solid for any crystalline structure.
The sum converges very slowly because the first neighbours give a first substantial contribution with a negative summation term. Second neighbour atoms produce a slightly weaker positive term. It then continues to infinity with terms of alternating signs by smaller and smaller values. In this way, the resulting effect will be that the attraction between cations and anions predominates and provides a favourable negative contribution to the solid’s energy.
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Introduzione alla Dinamica Molecolare
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Lex. I. Corpus omne perseverare in statu suo quiescendi vel movendi uniformiter in directum, nili quatenus a viribus impressis cogitur statum illum mutare.
- Lex. II. Muationem motus proportionalem esse vi motrici impressae, et fieri fecundum lineam rectam qua vis illa imprimitur.
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Lex. III. Actioni contrariam semper et equalem esse reactionem: sive corporum duorum actiones in se mutuo semper esse aequales et in partes contrarias dirigi.
Isaac Newton.
Philosophiae Naturalis Principia Mathematica.
London, 1686.
Nel 1648 Isaac Newton diede alle stampe la sua prima edizione dei Principia Mathematica, uno dei più grandi capolavori scientifici di tutti i tempi. Nelle prime pagine di questa summa scientifica si trovano enunciate le famose tre leggi che portano il suo nome, dalle quali ha avuto inizio la fisica-matematica classica. Continue reading
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The Lignin Peroxidase
Lignin Peroxidase (LiP), a hemoprotein isolated from the ligninolytic cultures of the white-rot fungus Phenerochaete Chrysosporium is one of the most important lignin-degrading enzymes. We have investigated the dynamical and structural properties of lignin peroxidase and its Trp171Ala mutant in aqueous solution using MD simulations [1].
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Molecular Machines within us: The human neutrophil collagenase MMP8
Human neutrophil collagenase (HNC, MMP8) is one of the target enzymes for drug treatment of pathologic extracellular matrix degradation. Peptidomimetic inhibitors bind in the S-side of the enzyme active site occupying the S1 primary specificity pocket by their large hydrophobic side-chains. Continue reading
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Molecular Machines within us: The Carbon Monoxide Migration in Sperm Whale Myoglobin
Myoglobin is a small ancient protein of ~150 amino acids specialized in the transport of respiratory gases to muscular tissues and back to the lungs of the superior organisms. Even though, it was one of the first protein having the three-dimensional structure solved using X-ray crystallography, the detail of the transport mechanism of gases in and out the active site is yet not completely understood. More recently, time-resolved x-ray studies have provided clues on the possible pockets in the protein interior where gases can transit but the detail of the migrations dynamics is unclear.
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Molecular Machines within us: The Nucleosome core particle
The nucleosome core particle (NCP) constitutes the basic structural unit of the eukaryotic chromatin. It consists of 147 base-pairs (bp) of DNA wrapped in a left-handed superhelix 1.65 times around a histone octamer. The octamer is formed by two copies of the histone proteins H2A, H2B, H3, and H4. Continue reading
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The β-lactamases TEM-1
β-lactamases are enzymes produced by bacteria (also known as penicillinase) that provide multi-resistance to β-lactam antibiotics such as penicillins, cephamycins, and carbapenems. Continue reading
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