Preface

In chemistry, biology, and physics, "chirality" is an important concept in nature. Especially in chemistry, not only classical stereochemistry but also asymmetric organic synthesis, supramolecular chemistry, construction of bio-related molecules and molecular recognition became indispensable structural chemical keywords. However, in view of synthetic chemistry and its structural chemistry, chemistry dealing with chirality in relation to the more fundamental electronic state is still a minority. This book is particularly aimed at chiroptical spectroscopy, structural or physical features and theoretical computation about chirality.

Indeed, as in many prefaces of numerous textbooks (mainly for chemistry) on this subject, one can easily understand that chirality (not only structural but also electronic aspects) may be one of the important terms in science.

"*Chirality is a phenomenon that is manifested throughout the natural world, ranging from fundamental particles through the realm of molecules and biological organisms to spiral galaxies. Thus, chirality is of interest to physicists, chemists, biologists, and astronomers. Chiroptical spectroscopy utilizes the differential response of chiral objects to circularly polarized electromagnetic radiation. Applications of chiroptical spectroscopy are widespread in chemistry, biochemistry, biology, and physics. It is indispensable for stereochemical elucidation of organic and inorganic molecules. Nearly all biomolecules and natural products are chiral, as are the majority of drugs. This has led to crucial applications of chiroptical spectroscopy ranging from the study of protein folding to characterization of small molecules, pharmaceuticals, and nucleic acids.*"

*N. Berova, P. L. Polavarapu, K. Nakanishi, R. W. Woody* [1]

"*Chiroptical data were acquired as early as the mid nineteenth century, and are thus among the earliest types of physical constants measured. Despite this, and the inherent importance of chiroptical phenomena and chirality, measurement of optical activity is one of the most underutilized of all spectroscopic techniques. Among the factors that lead to this unfortunate trend were the large gaps in our understanding of the relationship between theory and applications, and the empirical nature of many rules used in data interpretation. Fortunately, recent years have brought rapid changes in this situation.*"

*N. Berova, K. Nakanishi, R. W. Woody* [2]

I express my heartfelt gratitude to Ms. Maja Bozicevic et al. for their concern, efforts, and support in the task of publishing this volume.

## **References**

[1] Berova N, Polavarapu PL, Nakanishi K, Woody RW. Comprehensive Chiroptical Spectroscopy. Hoboken: Wiley; 2012. ISBN: 978-0-470-64135-4

[2] Berova N, Nakanishi K, Woody RW. Circular Dichroism Principles and Applications. 2nd ed. NY: Wiley-VCH; 2000. ISBN: 978-0-471-33003-5

**1**

**Chapter 1**

*Takashiro Akitsu*

Introductory Chapter: Chirality

**1. Chiral assembly of proteins and metal complexes**

which is a motivation to emphasis the concept of this book.

from Molecular Electronic States

Needless to say, chirality is an important concept along the fields of biology, chemistry, and physics. Not only steric fitness (stereochemical aspects) but also electronic properties (or electronic states as origin) may be important in such cases,

## **Chapter 1**
