Molecular dimension plays a role in transvascular filtration, v ease the transport right into the interstitium gift inversely proportional to size.

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S. Winiwarter, ... I. Zamora, in comprehensive Medicinal Chemistry II, 2007

5.22.2.1 molecular Size and also Shape

Molecular dimension is generally crucial for the permeability the compounds. There are reports in the literature showing a correlation between transcellular and/or paracellular permeability and also molecular size,25,27 whereas rather emphasize that molecular dimension determines i m sorry absorption course a drug can take: that is suggested that polar compounds v low molecular weight (below 200) may have the ability to use the paracellular route.28,29 However, the size limit different in different regions of the intestine and types differences in paracellular deliver have additionally been shown.30,31


Molecular size deserve to be assessed in various ways. The molecular load is conveniently calculated indigenous the molecular formula. Likewise a simple atom count can be seen as a crude measure up of molecule size. Various other descriptors regularly used room molecular volume and molecular surface. The molecular surface can be defined as the van der Waals surface ar of the molecule, assuming all atoms to be spheres defined by your Van der Waals radii. An additional possibility is to define a solvent-accessible surface area v the aid of a spherical probe that is ‘rolled’ end the van der Waals surface. This probe usually has actually a radius of around 1.4 or 1.5 Å, hence being the size of a water molecule. However, the solvent-accessible surface ar area have the right to be identified in 2 ways, one of two people by the center of the spherical probe32 or by the contact and re-entrant surface ar of together a probe.33,34 The latter type of solvent-accessible surface ar is regularly referred to as the Connolly surface, due to the fact that Connolly et al. propose a feasible and also fast algorithm to acquire such a surface.34 The computational method used will affect the results; in particular, the difference between the solvent-accessible surface ar area as identified by Lee and Richards and the Connolly surface need to be detailed (see figure 2). Other molecular surfaces are contour surface that can be defined by molecular properties like electron isodensity, molecule electrostatic potential, or molecular orbitals.


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The molecule volume have the right to be characterized according come the molecular surface, e.g., the van der Waals volume. That can also be established experimentally from the molecular weight, the fluid density, and also the Avogadro number. McGowan's properties volume is identified by the amount of atom volume parameters corrected by a factor for the number of atoms.35 another size descriptor is the molar refractivity, i beg your pardon is directly related to the molar volume (molecular weight split by the fluid density) and a role of the refractive table of contents of the liquid, therefore containing information about polarizability. Refractivity is one additive property similar to the volume descriptors and can thus quickly be calculate by a group contribution method. Molecular dimension descriptors are usually extremely correlated,10,17 which provides it unnecessary to usage all available descriptors.

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Shape descriptors are likewise often highly associated to molecule size. Ovality is identified as the ratio in between the surface ar of the molecule and also the surface ar of a round with the very same volume. Topological indices favor connectivity36,37 or shape indices38 also give information about the molecular shape. Furthermore, flexibility measures, e.g., the variety of rotatable bonds, can be interpreted as information around both size and also variable form of the molecule. It was said that less versatility as measure by the number of rotatable bonds enhances oral bioavailability.39

Molecular size and also shape descriptors space usually part of every descriptor set used in ADME modeling, although they space not necessarily essential in the last model. This does not imply that molecular dimension does not affect the ADME home in question, but rather that molecular size might be considered implicitly in various other descriptors like lipophilicity or polar surface area.