Light-mediated biosynthesis of size-tuned silver nanoparticles using Saccharomyces cerevisiae extract.

Bio-based production of silver nanoparticles represents a sustainable alternative to commercially applied physicochemical manufacturing approaches and provides qualitatively highly valuable nanomaterials due to their narrow size dispersity, high stability and biocompatibility with broad application potentials. The intrinsic features of nanoparticles depend on size and shape, whereby the controlled synthesis is a challenging necessity. In the present study, the biosynthesis of size-tuned silver nanoparticles based on cell-free extracts of Saccharomyces cerevisiae DSM 1333 was investigated.

Observation of SOMO-HOMO Inversion in a Neutral Polycyclic Conjugated Hydrocarbon.

We report the generation of a nonbenzenoid polycyclic conjugated hydrocarbon, which consists of a biphenyl moiety substituted by indenyl units at the 4,4' positions, on ultrathin sodium chloride films by tip-induced chemistry. Single-molecule characterization by scanning tunneling and atomic force microscopy reveals an open-shell biradical ground state with a peculiar electronic configuration wherein the singly occupied molecular orbitals (SOMOs) are lower in energy than the highest occupied molecular orbital (HOMO).

The odd-number cyclo[13]carbon and its dimer, cyclo[26]carbon.

Molecular rings of carbon atoms (cyclo[]carbons, or C) are excellent benchmarking systems for testing quantum chemical theoretical methods and valuable precursors to other carbon-rich materials. Odd- cyclocarbons, which have been elusive to date, are predicted to be even less stable than even- cyclocarbons. We report the on-surface synthesis of cyclo[13]carbon, C, by manipulation of decachlorofluorene with a scanning probe microscope tip.

Bistability between π-diradical open-shell and closed-shell states in indeno[1,2-a]fluorene.

Indenofluorenes are non-benzenoid conjugated hydrocarbons that have received great interest owing to their unusual electronic structure and potential applications in nonlinear optics and photovoltaics. Here we report the generation of unsubstituted indeno[1,2-a]fluorene on various surfaces by the cleavage of two C-H bonds in 7,12-dihydroindeno[1,2-a]fluorene through voltage pulses applied by the tip of a combined scanning tunnelling microscope and atomic force microscope. On bilayer NaCl on Au(111), indeno[1,2-a]fluorene is in the neutral charge state, but it exhibits charge bistability between neutral and anionic states on the lower-workfunction surfaces of bilayer NaCl on Ag(111) and Cu(111).

On-surface synthesis of a doubly anti-aromatic carbon allotrope.

Synthetic carbon allotropes such as graphene, carbon nanotubes and fullerenes have revolutionized materials science and led to new technologies. Many hypothetical carbon allotropes have been discussed, but few have been studied experimentally. Recently, unconventional synthetic strategies such as dynamic covalent chemistry and on-surface synthesis have been used to create new forms of carbon, including γ-graphyne, fullerene polymers, biphenylene networks and cyclocarbons.

Selectivity in single-molecule reactions by tip-induced redox chemistry.

Controlling selectivity of reactions is an ongoing quest in chemistry. In this work, we demonstrate reversible and selective bond formation and dissociation promoted by tip-induced reduction-oxidation reactions on a surface. Molecular rearrangements leading to different constitutional isomers are selected by the polarity and magnitude of applied voltage pulses from the tip of a combined scanning tunneling and atomic force microscope.

An on-surface Diels-Alder reaction.

The Diels-Alder reaction is one of the most popular reactions in organic chemistry. However, its use in the field of on-surface synthesis is hampered by the spatial restrictions of this cycloaddition reaction. Herein we selected a cyclic strained triyne to demonstrate an on-surface hexadehydro-Diels-Alder reaction in a single molecule.

Probing Molecular Excited States by Atomic Force Microscopy.

By employing single charge injections with an atomic force microscope, we investigated redox reactions of a molecule on a multilayer insulating film. First, we charged the molecule positively by attaching a single hole. Then we neutralized it by attaching an electron and observed three channels for the neutralization.

Sub-cycle atomic-scale forces coherently control a single-molecule switch.

Scanning probe techniques can leverage atomically precise forces to sculpt matter at surfaces, atom by atom. These forces have been applied quasi-statically to create surface structures and influence chemical processes, but exploiting local dynamics to realize coherent control on the atomic scale remains an intriguing prospect. Chemical reactions, conformational changes and desorption have been followed on ultrafast timescales, but directly exerting femtosecond forces on individual atoms to selectively induce molecular motion has yet to be realized.

Intramolecular Coupling of Terminal Alkynes by Atom Manipulation.

Glaser-like coupling of terminal alkynes by thermal activation is extensively used in on-surface chemistry. Here we demonstrate an intramolecular version of this reaction performed by atom manipulation. We used voltage pulses from the tip to trigger a Glaser-like coupling between terminal alkyne carbons within a custom-synthesized precursor molecule adsorbed on bilayer NaCl on Cu(111).

Biotechnological Production of Odor-Active Methyl-Branched Aldehydes by a Novel α-Dioxygenase from .

As a result of their pleasant odor qualities and low odor thresholds, iso- and anteiso-fatty aldehydes represent promising candidates for applications in flavoring preparations. A novel cyanobacterial α-dioxygenase from was heterologously expressed in and applied for the biotechnological production of C-C branched-chain fatty aldehydes. The enzyme has a sequence identity of less than 40% to well-investigated α-dioxygenase from rice.

Molecular structure elucidation with charge-state control.

The charge state of a molecule governs its physicochemical properties, such as conformation, reactivity, and aromaticity, with implications for on-surface synthesis, catalysis, photoconversion, and applications in molecular electronics. On insulating, multilayer sodium chloride (NaCl) films, we controlled the charge state of organic molecules and resolved their structures in neutral, cationic, anionic, and dianionic states by atomic force microscopy, obtaining atomic resolution and bond-order discrimination using carbon monoxide (CO)-functionalized tips. We detected changes in conformation, adsorption geometry, and bond-order relations for azobenzene, tetracyanoquinodimethane, and pentacene in multiple charge states.

Interface dipoles of Ir(ppy) on Cu(111).

The interplay of adsorption geometry and interface dipoles of the transition-metal complex Ir(ppy) on Cu(111) was studied using low-temperature scanning probe microscopy and density-functional-theory calculations. We find that the orientation of the molecule's intrinsic dipole moment with respect to the surface has a strong influence on the total energy of the different configurations, where the most stable one has the molecular dipole moment pointing out of the surface plane along the surface normal. Adsorption-induced redistribution of charges results in an additional dipole moment that also points out of the surface plane for all configurations.

Direct Identification and Determination of Conformational Response in Adsorbed Individual Nonplanar Molecular Species Using Noncontact Atomic Force Microscopy.

In recent years atomic force microscopy (AFM) at highest resolution was widely applied to mostly planar molecules, while its application toward exploring species with structural flexibility and a distinct 3D character remains a challenge. Herein, the scope of noncontact AFM is widened by investigating subtle conformational differences occurring in the well-studied reference systems 2H-TPP and Cu-TPP on Cu(111). Different saddle-shape conformations of both species can be recognized in conventional constant-height AFM images.

Characterization of a surface reaction by means of atomic force microscopy.

We study a thermally activated on-surface planarization reaction by a detailed analysis of the reactant and reaction products from atomically resolved atomic force microscopy (AFM) images and spectroscopy. The three-dimensional (3D) structure of the reactant, a helical diphenanthrene derivative, requires going beyond constant-height imaging. The characterization in three dimensions is enabled by acquisition and analysis of the AFM signal in a 3D data set.

Design and characterization of a modular membrane protein anchor to functionalize the moss Physcomitrella patens with extracellular catalytic and/or binding activities.

Heterologous enzymes and binding proteins were secreted by the moss Physcomitrella patens or anchored extracellularly on its cell membrane in order to functionalize the apoplast as a biochemical reaction compartment. This modular membrane anchoring system utilizes the signal peptide and the transmembrane segment of the somatic embryogenesis receptor-like kinase (SERK), which were identified in a comprehensive bioinformatic analysis of the P. patens genome.

Formation and characterization of a molecule-metal-molecule bridge in real space.

Metal-organic complexes were formed by means of inelastic excitations in a scanning tunneling microscope (STM). The electronic structure of the complex was characterized using STM imaging and spectroscopy. By exploiting the symmetry of the complex, its electronic structure can be rationalized from linear combinations of molecular orbitals.