Page 38 - ITU Journal Future and evolving technologies Volume 2 (2021), Issue 3 – Internet of Bio-Nano Things for health applications

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 3

the two enantiomers, whose mirror images are not equiv‑
alent and non‑superposable on each other. Another ex‑
ample of enantiomers are the molecules of natural sugars,
almost all classi ied as being right handed, including the
sugar that occurs in DNA. Also DNA is a chiral structure,
since its two helixes are not superposable to each other,
as well depicted in Fig. 1 (b).

In this paper we address how to exploit chiral molecules
as messenger molecules for molecular communications.
Fig. 1 – Examples of chiral molecules in case of (a) alanine amino‑acid,
The use of similar molecules i.e., isomers, as enablers of and (b) DNA chains. Enantiomers are non‑superposable mirror images
molecular communications has already been investigated to each other.
in [5], where Kim and Chae proposed three novel mod‑ 2. CHIRAL MOLECULES
ulation techniques, i.e., concentration‑based, molecular‑
type‑based, and molecular‑ratio‑based. However, in [5] A chiral molecule shows the chirality effect that makes the
it did not emerge the main features of such special molecule not equivalent to its mirror image. The chiral
molecules and how it is possible to exploit them for molecule and its mirror image are enantiomers, and the
molecular communications by means of their inner fea‑ relationship between the chiral molecule and its mirror
tures. For example, one of the main features of chiral image is de ined as enantiomeric. The word chiral comes
molecules is their behavior towards plane‑polarized light. from the Greek, and means “hand”. Indeed, a classic exam‑
When a beam of plane‑polarized light passes through an ple of chiral objects are the hands, since the mirror image
enantiomer, the plane of polarization rotates. Also, sepa‑ of the left hand is exactly the right hand. However, the left
rate enantiomers rotate the plane of plane‑polarized light hand is not superposable on the right hand.
at equal amounts but in opposite directions. Then, sepa‑
rate enantiomers are optically active compounds. From the etymology of chiral, chiral objects are said to
possess “handedness”. Although both mirror image forms
are theoretically possible, such as those for the amino acid
In this paper, we focus on the features of chiral molecules alanine, they have evolved in a way that amino acids are
such as (i) the rotation of the polarization plane of the mainly of the mirror image said to be “left‑handed” (see
impinging EM wave and (ii) the chirality transfer effect, Fig. 1 (a)). The reason that most amino acids are of the
in order to model a chiral channel comprised of enan‑ left‑handed form is not known, however.
tiomers that forward data information via a multi‑hop
protocol. Speci ically, in our vision, data information is Chirality is an important phenomenon in the universe.
represented by exploiting the chirality phenomenon with Several plants show chirality, by winding around support‑
a chiral molecule emitting a rotated EM wave when a ing structures. The human body is structurally chiral and
light input impinges on an initial transmitter node after it is not clear why, but most people are right‑handed. Usu‑
a steady state is achieved. Dissemination of data infor‑ ally, only one form of chiral occurs in a given species. Just
mation inside a chiral medium occurs through the chiral‑ as an example, the molecules of white sugars are right
ity transfer mechanism that considers the non‑covalent handed. Enantiomers of a chiral molecule have identi‑
bonds between a chiral and an achiral molecule. Chiral‑ cal physico‑chemical properties, and also the same elec‑
ity is exploited to encode the information in the chiral trochemical behavior. The enantioselective electrochem‑
molecules, and it is decoded at the receiver as a 1 bit when istry represents the ability of discriminating enantiomers
an EM wave (i.e., an optical signal) is applied. When no EM of chiral molecules (i.e., electroanalysis), or to selectively
wave is applied, the information is decoded as a bit 0. activateor achievea givenenantiomer ofachiralmolecule
(i.e., electrosynthesis) and is an issue particularly impor‑
tant in the biological and pharmaceutical ields [6].
This paper is organized as follows. Section 2 intro‑
duces the concept of chirality effect and describes the 2.1 Features of chiral molecules
main enantiomers that can be found in nature, specif‑
ically in the biological context. The features of chiral The speci ic rotation is a property of a chiral molecule. It
molecules are then presented in Subsection 2.1. In Sec‑ is de ined as the change in orientation of monochromatic
tion 3 we characterize the chiral transfer effect from a plane‑polarized light, per unit distance‑concentration
chiral molecule to an achiral molecule. In Section 4, we product, as the light passes through a sample of a com‑
de ine a chiral medium as a channel for molecular com‑ pound in solution. Fig. 2 describes the property of ro‑
munications. Data information is encoded in the chiral tation of the polarization plane of an EM ield that im‑
molecules that transport the chirality effect, which can be pinges on a chiral channel. At the output of the channel,
forwarded hop‑by‑hop in the overall system. Finally, con‑ the polarization plane has been rotated. Speci ically, chi‑
clusions are drawn at the end of this paper. ral molecules can rotate the plane of polarization of an

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