Jenkins - Chirality at Solid Surfaces

This edition first published 2018

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Library of Congress Cataloging-in-Publication Data

Names: Jenkins, Stephen J. (Stephen John), author.

Title: Chirality at solid surfaces / by Stephen J. Jenkins.

Description: First edition. | Hoboken, NJ : John Wiley & Sons, 2018. | Includes bibliographical references and index. |

Identifiers: LCCN 2017042876 (print) | LCCN 2017049498 (ebook) | ISBN 9781118880166 (pdf) | ISBN 9781118880142 (epub) | ISBN 9781118880128 (cloth)

Subjects: LCSH: Chirality. | Surface chemistry.

Classification: LCC QD481 (ebook) | LCC QD481 .J45 2018 (print) | DDC 541/.223-dc23

LC record available at https://lccn.loc.gov/2017042876

Cover Design: Wiley

Cover Image: Courtesy of Stephen J. Jenkins

To Victoria

The Tragedy of Julius Caesar, William Shakespeare, 1599

We shall present a formal definition of chirality by and by, but for the moment let us be guided by etymology. The word chiral derives from the Ancient Greek (cheir) meaning hand; it denotes the property of an entity (tangible or otherwise) that can (even if only hypothetically) exist in two forms related to one another in the same manner as one's right hand is related to one's left. That is, both forms are essentially identical in every regard apart from the fact that one is the mirror image of the other. Across a broad range of circumstances, one's left and right hands are functionally equivalent in form, action and apprehension equally capable but try to place one hand into a glove designed for the other and the distinction soon becomes clear. From this, we learn the most important lesson of chirality that chirality only matters when chiral entities interact with other chiral entities. Chirality, therefore, is at one and the same time the most profound of characteristics and the most subtle. Chiral distinctions of crucial importance surround us, but our control over chirality (in all its forms) is limited by our access to chiral tools.

Most of us are right-handed, although a significant minority (around 1 in 10) are left-handed. The origins of this disparity are not entirely understood, although genetic, epigenetic and even environmental influences have been proposed as partial explanations; the truth lies, one imagines, in some combination of all three. Whatever the whys and wherefores, right-handedness has long been considered the cultural norm, with left-handedness generally regarded as aberrant. Returning briefly to etymology, the Latin adjective dexter not only denotes the right-hand direction, but also connotes propriety, good fortune and (foreshadowing modern English usage) dexterity. Similarly, its antonym sinister denotes not only the left-hand direction, but also conveys the sense of perversity, hostility or (in its current English meaning) ill-omen. When Shakespeare has Caesar tell Antony to speak only into his right ear, he reveals not merely the dictator's infirmity, but also his hubris in cutting short talk of conspiracy Caesar has an ear only for good news.

Practical implications of human chirality abound, from the design of tools

At any rate, chiral discrimination in the human realm is commonplace, so it is hardly surprising that examples from elsewhere in nature also abound. The shells of gastropods, for instance, typically spiral clockwise from their apex to their aperture (albeit not in all species, see

Fossil shells of two marine gastropod species. In panel (a) the shell of Neptunea angulata is a rare example that spirals anticlockwise from apex to aperture, while in panel (b) that of Neptunea despecta spirals in the more common clockwise sense.

Reproduced from [10].

All of this suggests that chirality is not merely a particular and superficial property of the natural world, but rather a pervasive and fundamental one. We ought, therefore, to seek for the origins of chiral phenomena in living systems not merely at the macroscopic level but also at the microscopic scale of their biochemistry. The familiar double helix of DNA, for example, presents the obvious question of whether it spirals in the right- or left-handed sense. In fact, three distinct types of DNA exist, with the A and B forms exhibiting right-handed helices and the Z form a left-handed helix. There is no