materials Review Dendrimeric Structures in the Synthesis of Fine Chemicals Bruno Mattia Bizzarri * , Angelica Fanelli, Lorenzo Botta , Claudio Zippilli, Silvia Cesarini and Raffaele Saladino *   Citation: Bizzarri, B.M.; Fanelli, A.; Botta, L.; Zippilli, C.; Cesarini, S.; Saladino, R. Dendrimeric Structures in the Synthesis of Fine Chemicals. Materials 2021, 14, 5318. https://doi. org/10.3390/ma14185318 Academic Editor: Ivo Grabchev Received: 21 July 2021 Accepted: 9 September 2021 Published: 15 September 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Biological and Ecological Sciences Department (DEB), University of Tuscia, 01100 Viterbo, Italy; fanelli.angelica@gmail.com (A.F.); lorenzo.botta@unitus.it (L.B.); zippillic@unitus.it (C.Z.); c.cesarinisilvia@gmail.com (S.C.) * Correspondence: bm.bizzarri@unitus.it (B.M.B.); saladino@unitus.it (R.S.) Abstract: Dendrimers are highly branched structures with a defined shape, dimension, and molecular weight. They consist of three major components: the central core, branches, and terminal groups. In recent years, dendrimers have received great attention in medicinal chemistry, diagnostic field, science of materials, electrochemistry, and catalysis. In addition, they are largely applied for the functionalization of biocompatible semiconductors, in gene transfection processes, as well as in the preparation of nano-devices, including heterogeneous catalysts. Here, we describe recent advances in the design and application of dendrimers in catalytic organic and inorganic processes, sustainable and low environmental impact, photosensitive materials, nano-delivery systems, and antiviral agents’ dendrimers. Keywords: dendrimers; heterogenous catalysis; materials; PAMAM; nano-devices; anti-virals 1. Introduction Dendrimers are symmetric and monodisperse macromolecules with a well-defined three- dimensional branched shape inspired by that of a tree [1]. They show three topologically different regions including: (i) the core part; (ii) the branches formed by repetitive monomeric units (dendrons); and (iii) the “periphery” as final appendages of the dendrons [2]. Two different synthetic methodologies are commonly used for the preparation of dendrimers: (a) the divergent approach, in which dendrimers grow from the core proceeding radially outward toward the periphery; (b) the convergent one, in which the growth starts from the periphery of the dendrimer toward the inner part. The choice of the specific synthetic approach is usually related to the desired application field, depending on both the target chemical structure (sequence of dendrons and order of generation) and the building blocks selected for the construction of the dendritic framework. Dendrimers are classified according to the ‘generation’ level, which represents the minimum number of branching nodes from the core to the periphery. These systems are highly ordered three-dimensional structures often characterized by internal cavities in which metal ions and small molecules can be hosted [3,4]. 2. Application of Dendrimers in the Science of Materials Field Dendrimers represent a potent tool in the design of novel sustainable and low envi- ronmental impact materials, as optimal reagents, or, alternatively, as structural components in the preparation and functionalization of advanced fibers and composites. For example, they can solve pollution problems associated with the dyeing of cellulose fibers, usually performed with high amounts of electrolyte and alkali solutions [5]. The application of poly-amidoamine (PAMAM) dendrimers modifies the surface of cotton fibers, increasing the dye uptake and fixation without the use of toxic substances [6]. The PAMAM treat- ment introduces nucleophile amino groups in the polysaccharide able to capture dyes without the use of electrolytes and alkali, minimizing the dye hydrolysis, and reducing Materials 2021, 14, 5318. https://doi.org/10.3390/ma14185318 https://www.mdpi.com/journal/materials