Daniell L. Mattern

Interstaple Dithiol Cross-Linking in Au25(SR)18 Nanomolecules: A Combined Mass Spectrometric and Computational Study

A systematic study of cross-linking chemistry of the Au(25)(SR)(18) nanomolecule by dithiols of varying chain length, HS-(CH(2))(n)-SH where n = 2, 3, 4, 5, and 6, is presented here. Monothiolated Au(25) has six [RSAuSRAuSR] staple motifs on its surface, and MALDI mass spectrometry data of the ligand exchanged clusters show that propane (C3) and butane (C4) dithiols have ideal chain lengths for interstaple cross-linking and that up to six C3 or C4 dithiols can be facilely exchanged onto the cluster surface. Propanedithiol predominately exchanges with two monothiols at a time, making cross-linking bridges, while butanedithiol can exchange with either one or two monothiols at a time. The extent of cross-linking can be controlled by the Au(25)(SR)(18) to dithiol ratio, the reaction time of ligand exchange, or the addition of a hydrophobic tail to the dithiol. MALDI MS suggests that during ethane (C2) dithiol exchange, two ethanedithiols become connected by a disulfide bond; this result is supported by density functional theory (DFT) prediction of the optimal chain length for the intrastaple coupling. Both optical absorption spectroscopy and DFT computations show that the electronic structure of the Au(25) nanomolecule retains its main features after exchange of up to eight monothiol ligands.

Molecular rectification with M|(D-σ-A LB film)|M junctions

Molecular materials of the form electron donor-sigma-bridge-electron acceptor (D-σ-A) have been synthesized and incorporated into non-centrosymmetric Langmuir-Blodgett (LB) multilayer structures. Electrical characterization has been performed using a metal|(Z-type LB film)|metal (M|LB|M) junction construction. Current density-voltage data demonstrate striking rectification behaviour. Computational modelling of the electronic structure of the material has been carried out using a first principles, density functional approach. Possible conduction mechanisms are discussed with reference to the results of this modelling.

An improved synthesis of 6α-ethylchenodeoxycholic acid (6ECDCA), a potent and selective agonist for the Farnesoid X Receptor (FXR).

The active, potent, and selective Farnesoid X Receptor (FXR) agonist 6α-ethylchenodeoxycholic acid (6ECDCA) has been synthesized in improved yield compared to the published methodologies. The synthesis employed selective oxidation of one of the two hydroxyls of the readily-available starting material chenodeoxycholic acid (CDCA) as a key step. After protection of the remaining hydroxyl, LDA/HMPA/EtI/PPTS provided an efficient deprotonation/ethylation/deprotection sequence. The two synthetic improvements that allow a productive yield are the use of PCC in the oxidation step, and the use of HMPA/ethyl iodide in the stereoselective alkylation step. This synthesis offers an economical and efficient strategy which provides a simple and cost-effective procedure for potential large-scale production of this promising FXR agonist, which is a research tool and potential drug substance of current interest.

Unimolecular electronic devices.

The first active electronic components used vacuum tubes with appropriately-shaped electrodes, then junctions of appropriately-doped Ge, Si, or GaAs semiconductors. Electronic components can now be made with appropriately-designed organic molecules. As the commercial drive to make ever-smaller and faster circuits approaches the 3-nm limit, these unimolecular organic devices may become more useful than doped semiconductors. Here we discuss the electrical contacts between metallic electrodes and organic molecular components, and survey representative organic wires composed of conducting groups and organic rectifiers composed of electron-donor and -acceptor groups, and the Aviram-Ratner proposal for unimolecular rectification. Molecular capacitors and amplifiers are discussed briefly. Molecular electronic devices are not only ultimately small (<3 nm in all directions) and fast, but their excited states may be able to decay by photons, avoiding the enormous heat dissipation endured by Si-based components that decay by phonons. An all-organic computer is an ultimate, but more distant, goal.

Synthesis of donor-σ-perylenebisimide-acceptor molecules having PEG swallowtails and sulfur anchors.

Donor-σ-Acceptor (D-σ-A) molecules, arrayed in a monolayer between electrodes, can serve as molecular rectifiers. Using perylene-3,4,9,10-tetracarboxylic bisimide (PBI) as the acceptor allows the attachment of the donor group to one imide nitrogen and a solubilizing swallowtail, normally a long (e.g., C(19)) alkane connected at midchain, on the other. Such an alkyl tail facilitates the formation of Langmuir-Blodgett (LB) monolayers. We have employed several modified swallowtails to make new D-σ-A molecules: poly(ethylene glycol) (PEG) swallowtails with 6 ether oxygens or with 4 ether oxygens to promote hydrophilicity in orienting LB monolayers, and alkyl swallowtails ending with sulfur anchors (thioacetate, thiol, or methyl disulfide) to stabilize attachment of the D-σ-A molecules to gold electrodes. The preparation and characterization of D-σ-A molecules containing combinations of these swallowtails with pyrene, ferrocene, and tetramethylphenylenediamine donor groups is described.

Stereoselective synthesis, biological evaluation, and modeling of novel bile acid-derived G-protein coupled Bile acid receptor 1 (GP-BAR1, TGR5) agonists

GP-BAR1 (also known as TGR5), a novel G-protein coupled receptor regulating various non-genomic functions via bile acid signaling, has emerged as a promising target for metabolic disorders, including obesity and type II diabetes. However, given that many bile acids (BAs) are poorly tolerated for systemic therapeutic use, there is significant need to develop GP-BAR1 agonists with improved potency and specificity and there also is significant impetus to develop a stereoselective synthetic methodology for GP-BAR1 agonists. Here, we report the development of highly stereo-controlled strategies to investigate a series of naturally occurring bile acid derivatives with markedly enhanced GP-BAR1 activity. These novel GP-BAR1 agonists are evaluated in vitro using luciferase-based reporter and cAMP assays to elucidate their biological properties. In vivo studies revealed that the GP-BAR1 agonist 23(S)-m-LCA increased intestinal GLP-1 transcripts by 26-fold. Additionally, computational modeling studies of selected ligands that exhibit enhanced potency and specificity for GP-BAR1 provide information on potential binding sites for these ligands in GP-BAR1.

A Two-Faced “Janus-like” Unimolecular Rectifier Exhibits Rectification Reversal

A molecule containing an electron donor (pyrene, Py), an insulating tetramethylene bridge, an electron acceptor (perylenebisimide, PBI) and a bis-decyl swallowtail with two terminal thioesters was studied for its electrical rectification as a Langmuir–Blodgett (LB) monolayer between two Au electrodes at room temperature (over a 8 month period, the thioester terminations chemisorbed partially (about 15%) onto the bottom Au electrode). At lower bias (<±1.5 Volts), the direct current was greater at positive than negative bias; at higher bias (±2.0 and ±2.5 Volts), the conduction was larger at negative bias: this “Janus” switching was repeatable when the bias ranges were changed. At constant bias range, repeated scans showed a gradual decrease in conductivity. Ancillary characterization data are reported.

Convenient Preparations of the Three 2,3-dihalo-1,4-benzoquinones

Abstract Efficient preparations of 2,3-dichloro-1,4-benzoquinone (1) and 2,3-dibromo-1,4-benzoquinone (2) from 1,4-benzoquinone are reported, as is the synthesis of the previously unknown 2,3-diiodo-1,4-benzoquinone (3) from 2.

Urea functionalization of ultrasound-treated biochar: A feasible strategy for enhancing heavy metal adsorption capacity

The main objective of a series of our researches is to develop a novel acoustic-based method for activation of biochar. This study investigates the capability of biochar in adsorbing Ni(II) as a hazardous contaminant and aims at enhancing its adsorption capacity by the addition of extra nitrogen and most probably phosphorous and oxygen containing sites using an ultrasono-chemical modification mechanism. To reach this objective, biochar physically modified by low-frequency ultrasound waves (USB) was chemically treated by phosphoric acid (H3PO4) and then functionalized by urea (CO(NH2)2). Cavitation induced by ultrasound waves exfoliates and breaks apart the regular shape of graphitic oxide layers of biochar, cleans smooth surfaces, and increases the porosity and permeability of biochars carbonaceous structure. These phenomena synergistically combined with urea functionalization to attach the amine groups onto the biochar surface and remarkably increased the adsorption of Ni(II). It was found that the modified biochar could remove > 99% of 100 mg Ni(II)/L in only six hours, while the raw biochar removed only 73.5% of Ni(II) in twelve hours. It should be noted that physical treatment of biochar with ultrasound energy, which can be applied at room temperature for a very short duration, followed by chemical functionalization is an economical and efficient method of biochar modification compared with traditional methods, which are usually applied in a very severe temperature (>873 K) for a long duration. Such modified biochars can help protect human health from metal-ion corrosion of degrading piping in cities with aging infrastructure.

Concomitant Ordering and Symmetry Lowering.

Examples of concomitant ordering include magnetic ordering, Jahn�Teller cooperative ordering, electronic ordering, ionic ordering, and ordering of partially-filled sites. Concomitant ordering sets in when a crystal is cooled and always lowers the degree of symmetry of the crystal. Concomitant ordering concepts can also be productively applied to many molecules, ions, and clusters. As an educational aid, the 17 plane groups may be generated by imposing concomitant patterns on designs belonging to p4mm and p6mm, and ornamental designs may be created by applying concomitant patterns on the regular tilings.