Synthesis and characterization of new D-π-A and A-π-D-π-A type oligothiophene derivatives

In this work we present a series of newly synthesized conjugated oligothiophene derivatives, with different numbers of central thiophene units, and different donor/acceptor architectures. Electrochemical and spectroscopic data have also been reported. We used thiophene or bithiophene as central Donor core units, 3-octylthiophenes as π-bridge and solubilizing sub-units, and ethyl cyanoacetate or rhodanine moieties as Acceptor end groups, in order to get D-π-A and A-π-D-π-A molecular architectures. The length of synthesized oligothiophenes ranges from three to eight thiophene units, a variety that is sufficient to put in evidence different optical and electrochemical as well as semiconducting characteristics. Oligothiophene compounds can be regarded not only as models for the study of structure-property relationships relatives to polythiophenes, but also they present a large number of applications in the field of Organic Electronics (i.e.: as donors in bulk-heterojunction solar cells as well as hole-transporting layer materials in perovskite solar cells, among others)

NHC in Imidazolium Acetate Ionic Liquids: Actual or Potential Presence?

Ionic liquids (ILs) are considered in the majority of cases green solvents, due to their virtually null vapor pressure and to the easiness in recycling them. In particular, imidazolium ILs are widely used in many fields of Chemistry, as solvents or precursors of N-heterocyclic carbenes (NHCs). The latter are easily obtained by deprotonation of the C2-H, usually using strong bases or cathodic reduction. Nevertheless, it is known that weaker bases (e.g., triethylamine) are able to promote C2-H/D exchange. From this perspective, the possibility of deprotonating C2-H group of an imidazolium cation by means of a basic counter-ion was seriously considered and led to the synthesis of imidazolium ILs spontaneously containing NHCs. The most famous of this class of ILs are N,N'-disubstituted imidazolium acetates. Due to the particular reactivity of this kind of ILs, they were appointed as "organocatalytic ionic liquids" or "proto-carbenes." Many papers report the use of these imidazolium acetates in organocatalytic reactions (i. e., catalyzed by NHC) or in stoichiometric NHC reactions (e.g., with elemental sulfur to yield the corresponding imidazole-2-thiones). Nevertheless, the actual presence of NHC in N,N'-disubstituted imidazolium acetate is still controversial. Moreover, theoretical studies seem to rule out the presence of NHC in such a polar environment as an IL. Aim of this Mini Review is to give the reader an up-to-date overview on the actual or potential presence of NHC in such an "organocatalytic ionic liquid," both from the experimental and theoretical point of view, without the intent to be exhaustive on N,N'-disubstituted imidazolium acetate applications

Xanthine scaffold: available synthesis routes to deliver diversity by derivatization

The functionalization of the skeletal systems of heterocycles represents a significant goal for the development of new compounds. The heterocyclic molecule xanthine (3,7-dihydro-1Hpurine- 2,6-dione) is a purine base with a bicyclic ring skeleton and four different nitrogen atoms, three of them are -NH groups. The principal derivatives are the well known natural methylxanthines (e.g., caffeine, theophylline and theobromine) that have prominent physiological effects at a very low dose. The natural methylated xanthines, theophylline, theobromine and caffeine, are present in different plants such as the tea, cocoa and coffee species. For this reason natural xanthines can be considered as bio-based and renewable starting materials; their use in organic synthesis is strongly recommended in order to carry out sustainable chemistry. Essentially, the xanthine scaffold led to the preparation of numerous compounds very attractive in the pharmaceutical field, and these drugs are commercialized for a wide range of biological activities. The scope of this mini-review is to consider the use of natural xanthines as starting material in chemical transformations carried out in organic solvents, without the intent to be exhaustive of all the synthetically chemical applications. More information on the chemical and electrochemical reactivity of this structural core in an organic solvent can be useful for the scientific community. The effectiveness of natural xanthines can be improved by modifying the structures of these already biologically active compounds

Organic electrochemistry: Synthesis and functionalization of β-lactams in the twenty-first century

Organic electrochemistry is a technique that allows for the heterogeneous redox reactions avoiding both the use of stoichiometric amounts of redox reagents and the resulting formation of stoichiometric by-pro- ducts. In fact, the redox reagent in these reactions is the electron, which is naturally eco-friendly and pro- duces no side compounds. It is therefore quite obvious that electrochemistry can be classified as a “green” tech- nology. The use of this methodology in the synthesis of β-lactams is not a novelty, but the growing interest in this class of biologically active compounds, due to the dis- covery of new fields of application (after a moment of decrease in interest due to antibiotic resistance) has been a stimulus for the search for more efficient electro- chemical ways to synthesize and transform β-lactams. Thus, this review deals with the twenty-first-century applications of electroorganic technique to the chemistry of β-lactams, by analyzing first the syntheses classified by the type of reactions (cyclization, cycloaddition, etc.) and then by manipulating the β-lactam structure, using it as a synthon. Lastly, the importance of this technique is demonstrated by a study of a pilot plant scale reduction of a cephalosporanic acid derivative to a commercially important antibiotic

An insight into the reactivity of the electrogenerated radical cation of caffeine

Controlled potential electrolyses of caffeine (CAF) were carried out at a Pt electrode in undried acetonitrile (ACN) and ACN-H2O and the products of the anodic oxidation were analyzed by HPLC-PDA-ESI-MS/MS. A higher current efficiency occurred in ACN-H2O, but an analogous chromatographic outline was found in both media, evidencing a reactive pathway of the electrogenerated radical cation CAF•+ with water, added or in trace, as nucleophile. No dimeric forms were evidenced, excluding any coupling reactions. Neither was 1,3,7-trimethyluric acid found, reported in the literature as the main oxidative route for CAF in water. Four main chromatographic peaks were evidenced, assigned to four proposed structures on the base of chromatographic and spectral data: a 4,5-diol derivative and an oxazolidin-2-one derivative were assigned as principal oxidation products, supporting a mechanism proposed in a previous work for the primary anodic oxidation of the methylxanthines olefinic C4 = C 5 bond. Two highly polar degradation products were also tentatively assigned, that seemed generating along two different pathways, one opening the imidazolic moiety and another one opening the purinic one

Characterization of Fiber Types in Different Muscles of the Hindlimb in Female Weanling and Adult Wistar Rats

We analyzed lesser diameter and distribution of fiber types in different skeletal muscles from female Wistar rats using a histoenzymology Myofibrillar Adenosine Tri-phosphatase (mATPase) method. Fragments from muscles were frozen and processed by mATPase in different pH. Adult and weanling rat soleus muscles presented a predominance of type I fibers and larger fiber diameters. In the plantar muscle in adult rats, the type IIB fibers demonstrated greater lesser diameter while in the weanling animals, types I and IIB fibers were larger. The plantar muscle of animals of both ages was composed predominantly of the type IID fibers. The type IID fibers were observed in similar amounts in the lateral gastrocnemius and the medial gastrocnemius muscles. Type IIB fibers showed predominance and presented higher size in comparison with other types in the EDL muscle. The present study shows that data on fiber type distribution and fiber lesser diameter obtained in adult animals cannot always be applied to weanling animals of the same species. Using the mATPase, despite the difficult handling, is an important tool to determine the different characteristics of the specific fibers in the skeletal muscle tissue

A new push–pull dye for semi-transparent p-type dye-sensitized solar cells: tuning conjugation by sexithiophene chain engineering

We report on the synthesis of two new dyes to be employed as sensitizers in p-type dye-sensitized solar cells (DSCs). The design of the two new molecules under consideration has been inspired by the state-of-art dye PMI-6 T-TPA. In particular, a specific engineering of the thiophene-based central core is here considered to favour structural planarity between an oligothiophenic π-spacer (a sexithiophene), and the acceptor and donor units made by peryleneimide (PMI) and triphenylamine (TPA) moieties, respectively. This leads to a wide absorption in the NIR with stabilization of the HOMO energy level in the resulting dyes, as supported by TD-DFT simulations and spectroscopic characterization. When tested as sensitizers in NiOx-based p-type DSCs, A6D (with an Acceptor-π-Donor structure) outperforms both its counterpart with a Donor-π-Donor structure (D6D) and P1, a benchmark dye in the field of p-DSCs. With A6D dye-sensitizer the resulting DSC device presents the quite remarkable value of stabilized efficiency as high as 0.15 % when I-/I3- is employed as redox couple and nanostructured NiOx photocathode is thick less than 2 μm and does not contain any blocking layer. Notwithstanding the panchromatic feature of the sensitizer, A6D-based devices show an average visible transmittance (AVT) of 8 %. Such a result paves the way toward the application of these types of multifunctional dyes in semi-transparent solar cells

Electrochemistry of a spirolactone

The 1,2,6,7-tetraphenyl-4-oxa-spiro [2.4]hepta-1, 6-dien-5-one (spirolactone, 1) has been prepared and investigated with reference to its redox properties, using cyclic voltammetry and controlled potential electrolysis in dimethylformamide (DMF) using Et4NClO4 as supporting electrolyte. The most relevant features are the three reduction steps, E-p(1) = -1.68 V, E-p(2) = -2.34 V, E-p(3) = -2.62 V (SCE) which are irreversible on the time scale of the voltammetric experiments used. The first electron/molecule transfer, with no corresponding anodic process, gives rise to an unstable radical anion, which, by rupture of the three-membered ring at the spiro carbon, rearranges to a distonic radical anion. The presence of 5-(1,2-diphenyl-vinyl)-3-(5-hydroxy-1,2,6,7-tetraphenyl-4-oxa-spiro[2.4]hepta-1,6-dien-5-yl)-3,4-diphenyl-3H-furan-2-one (5) (40%) among the isolated products, after controlled potential electrolysis, points to a further attack of the distonic radical anionic species on the starting compound 1. Thus, the dimeric unsymmetric lactone 5 retains the spiro structure in one half of the molecule. (C) 2001 Elsevier Science B.V. All rights reserved