Volume 4, Issue 9 -

The basics of the quantum mechanical theory of the light absorption process, the simplifications of the theory in form of models and their application to dyes are reviewed. The factors governing the electronic transition energy, the intensity of the electronic transition and the vibrational fine structure of the absorption bands are examined.

One major challenge in natural product (NP) discovery is the determination of the chemical structure of unknown metabolites using automated software tools from either GC–mass spectrometry (MS) or liquid chromatography–MS/MS data only. This chapter reviews the existing spectral libraries and predictive computational tools used in MS-based untargeted metabolomics, which is currently a hot topic in NP structure elucidation. We begin by focusing on spectral databases and the general workflow of MS annotation. We then describe software and tools used in MS, particularly those used to predict fragmentation patterns, mass spectral classifiers, and tools for fragmentation trees analysis. We then round up the chapter by looking at more advanced approaches implemented in tools for competitive fragmentation modeling and quantum chemical approaches.

Natural product (NP)-derived drugs can be extracts, biological macromolecules, or purified small molecule substances. Small molecule drugs can be originally purified from NPs, can represent semisynthetic molecules, natural fragments containing small molecules, or are fully synthetic molecules that mimic natural compounds. New semisynthetic NP-like drugs are entering the pharmaceutical market almost every year and reveal growing interests in the application of fragment-based approaches for NPs. Thus, several NP databases were constructed to be implemented in the fragment-based drug design (FBDD) workflows. FBDD has been established previously as an approach for hit identification and lead generation. Several biophysical and computational methods are used for fragment screening to identify potential hits. Once the fragments within the binding pocket of the protein are identified, they can be grown, linked, or merged to design more active compounds. This work discusses applications of NPs and NP scaffolds to FBDD. Moreover, it briefly reviews NP databases containing fragments and reports on case studies where the approach has been successfully applied for the design of antimalarial and anticancer drug candidates.

The structural assignment of natural products, even with the very sophisticated one-dimensional and two-dimensional (1D and 2D) spectroscopic methods available today, is still a tedious and time-consuming task. Mass spectrometry (MS) is generally used for molecular mass determination, molecular formula generation and MS/MS n fragmentation patterns of molecules. In the meantime, nuclear magnetic resonance (NMR) spectroscopy provides spectra (e. g. 1  H, 13 C and correlation spectra) whose interpretation allows the structure determination of known or unknown compounds. With the advance of high throughput studies, like metabolomics, the fast and automated identification or annotation of natural products became highly demanded. Some growing tools to meet this demand apply computational methods for structure elucidation. These methods act on characteristic parameters in the structural determination of small molecules. We have numbered and herein present existing and reputed computational methods for peak picking analysis, resonance assignment, nuclear Overhauser effect (NOE) assignment, combinatorial fragmentation and structure calculation and prediction. Fully automated programs in structure determination are also mentioned, together with their integrated algorithms used to elucidate the structure of a metabolite. The use of these automated tools has helped to significantly reduce errors introduced by manual processing and, hence, accelerated the structure identification or annotation of compounds.

Multiferroic materials, showing ordering of both electrical and magnetic degrees of freedom, are promising candidates enabling the design of novel electronic devices. Various mechanisms ranging from geometrically or spin-driven improper ferroelectricity via lone-pairs, charge-order or -transfer support multiferroicity in single-phase or composite compounds. The search for materials showing these effects constitutes one of the most important research fields in solid-state physics during the last years, but scientific interest even traces back to the middle of the past century. Especially, a potentially strong coupling between spin and electric dipoles captured the interest to control via an electric field the magnetization or via a magnetic field the electric polarization. This would imply a promising route for novel electronics. Here, we provide a review about the dielectric and ferroelectric properties of various multiferroic systems ranging from type I multiferroics, in which magnetic and ferroelectric order develop almost independently of each other, to type II multiferroics, which exhibit strong coupling of magnetic and ferroelectric ordering. We thoroughly discuss the dielectric signatures of the ferroelectric polarization for BiFeO 3 , Fe 3 O 4 , DyMnO 3 and an organic charge-transfer salt as well as show electric-field poling studies for the hexagonal manganites and a spin-spiral system LiCuVO 4 .