Take your Positions and Shine: Effects of Positioning Aggregation-Induced Emission Luminophores within Sequence-Defined Macromolecules

A luminophore with aggregation-induced emission (AIE) is employed for the conjugation onto supramolecular ligands to allow for detection of ligand binding. Supramolecular ligands are based on the combination of sequence-defined oligo(amidoamine) scaffolds and guanidiniocarbonyl-pyrrole (GCP) as binding motif. We hypothesize that AIE properties are strongly affected by positioning of the luminophore within the ligand scaffold. Therefore, we systematically investigate the effects placing the AIE luminophore at different positions within the overall construct, for example, in the main or side chain of the olig(amidoamine). Indeed, we can show that the position within the ligand structure strongly affects AIE, both for the ligand itself as well as when applying the ligand for the detection of different biological and synthetic polyanions.     

Synthesis of Bifunctional Azobenzene Glycoconjugates for Cysteine‐Based Photosensitive Cross‐Linking with Bioactive Peptides

Azobenzene linker molecules can be utilized to control peptide/protein function when they are ligated to appropriately spaced amino acid side chains of the peptide. This is because the photochemical E/Z isomerization of the azobenzene N?N double bond allows to switch peptide conformation between folded and unfolded. In this context, we have introduced carbohydrate‐functionalized azobenzene derivatives in order to advance the biocompatible properties of azobenzene peptide linkers. Chloroacetamide‐functionalized and O‐allylated carbohydrate derivatives were synthesized and conjugated with azobenzene to achieve new bifunctional cross‐linkers, in order to allow ligation to cysteine side chains by nucleophilic substitution or thiol‐ene reaction, respectively. The photochromic properties of the new linker glycoconjugates were determined and first ligation reactions performed.     

Electronic structures of organometallic complexes of f elements LXVI : Parametric analysis of the linear dichroism spectrum of an oriented tris(η-tetramethylcyclopentadienyl)samarium(III) single crystal

The absorption spectra of pseudo (ψ) trigonal planar Sm(η⁵-C₅Me₄H)₃ (1) and La(η⁵-C₅Me₄H)₃ (2) in KBr pellets have been measured at room temperature and 77 K, respectively. Additionally, the linear dichroism spectra of σ and π type of an oriented single crystal of 1 have been recorded at ambient temperature. The observed polarization properties of the f-f transitions allowed the assignment of the transitions. The free parameters of a phenomenological Hamiltonian were fitted to the energies of the assigned terminal levels, leading to a reduced r.m.s. deviation of 19.1 cm⁻¹ for 19 assignments. On the basis of these phenomenological CF parameters, the global CF strength experienced by the Sm³⁺ central ion was estimated, and seems to be the largest one ever encountered in samarium(III) chemistry. The obtained Slater parameter F² and the spin-orbit coupling parameter ζ_4f allow the insertion of compound 1 into empirical nephelauxetic and relativistic nephelauxetic series, respectively. On the basis of these models, complex 1 turns out to be the most covalent Sm^III compound found to date. The experimentally-based non-relativistic molecular orbital scheme (in the f range) of complex 1 was determined and compared with the results of a previous Xα-SW calculation on the ψ trigonal planar model compound Sm(η⁵-C₅H₅)₃.     

A Straightforward Approach to Multifunctional Graphene

Graphene has been covalently functionalized through a one-pot reductive pathway using graphite intercalation compounds (GICs), in particular KC₈, with three different orthogonally protected derivatives of 4-aminobenzylamine. This novel multifunctional platform exhibits excellent bulk functionalization homogeneity (H_bulk) and degree of addition while preserving the chemical functionalities of the organic addends through different protecting groups, namely: tert-butyloxycarbonyl (Boc), benzyloxycarbonyl (Cbz) and phthalimide (Pht). We have employed (temperature-dependent) statistical Raman spectroscopy (SRS), X-ray photoelectron spectroscopy (XPS), magic angle spinning solid state ¹³C NMR (MAS-NMR), and a characterization tool consisting of thermogravimetric analysis coupled with gas chromatography and mass spectrometry (TG-GC-MS) to unambiguously demonstrate the covalent binding and the chemical nature of the different molecular linkers. This work paves the way for the development of smart graphene-based materials of great interest in biomedicine or electronics, to name a few, and will serve as a guide in the design of new 2D multifunctional materials.     

Exohedral Addition Chemistry of the Fullerenide Anions C602− and C60⋅−

A systematic screening study of the exohedral reactivity of the reduced fullerenes (fullerenides) C₆₀²⁻ and C₆₀^⋅− is reported. These doubly and singly negatively charged carbon cages were prepared by two-fold reduction of C₆₀ with potassium, leading to K₂C₆₀, or by in situ monoreduction with the radical anion of benzonitrile PhCN^⋅−, respectively. Several series of electrophiles, including geminal and distant dihalides, benzyl bromides, and diazonium compounds, were employed as addition partners. In general, the investigated bromides proved to be the most suitable reaction partners. A series of fullerene adducts and cycloadducts involving either 1,2- or 1,4-addition patterns, depending on the precise architecture and the steric demand of the addends, were synthesized and fully characterized. Some of the reaction products are unprecedented and inaccessible forms of neutral C₆₀. The fullerenide chemistry presented here closely resembles related reactions of graphenides and carbon nanotubides, which are the most powerful methods for the functionalization of these macromolecular forms of synthetic carbon allotropes (SCAs). Activation of C₆₀ by negative charging represents a little explored concept of fullerene chemistry, providing both new insights of fullerene reactivity itself and new types of exohedral derivatives.     

Controlling the Degree of Functionalization: In-Depth Quantification and Side-Product Analysis of Diazonium Chemistry on SWCNTs

We present an in-depth qualitative and quantitative analysis of a reaction between 4-iodobenzenediazonium tetrafluoroborate and single-walled carbon nanotubes (SWCNTs) via thermogravimetric analysis coupled with mass spectrometry (TG-MS) or a gas chromatography and mass spectrometry (TG-GC-MS) as well as Raman spectroscopy. We propose a method for precise determination of the degree of functionalization and quantification of physisorbed aromates, detaching around their boiling point, alongside covalently bonded ones (cleavage over 200 °C). While the presence of some side products like phenol- or biphenyl species could be excluded, residual surfactant and minor amounts of benzene could be identified. A concentration-dependent experiment shows that the degree of functionalization increases with the logarithm of the concentration of applied diazonium salt, which can be exploited to precisely adjust the amount of aryl addends on the nanotube sidewall, up to 1 moiety per 100 carbon atoms.     

Models of the membrane-bound cytochromes: mössbauer spectra of crystalline low-spin ferriheme complexes having axial ligand plane dihedral angles ranging from 0 degree to 90 degrees

Crystalline samples of four low-spin Fe(III) octaalkyltetraphenylporphyrinate and two low-spin Fe(III) tetramesitylporphyrinate complexes, all of which are models of the bis-histidine-coordinated cytochromes of mitochondrial complexes II, III, and IV and chloroplast complex b(6)f, and whose molecular structures and EPR spectra have been reported previously, have been investigated in detail by M?ssbauer spectroscopy. The six complexes and the dihedral angles between axial ligand planes of each are [(TMP)Fe(1-MeIm)(2)]ClO(4) (0 degree), paral-[(OMTPP)Fe(1-MeIm)(2)]Cl (19.5 degrees), paral-[(TMP)Fe(5-MeHIm)(2)]ClO(4) (26 degrees, 30 degrees for two molecules in the unit cell whose EPR spectra overlap), [(OETPP)Fe(4-Me(2)NPy)(2)]Cl (70 degrees), perp-[(OETPP)Fe(1-MeIm)(2)]Cl (73 degrees), and perp-[(OMTPP)Fe(1-MeIm)(2)]Cl (90 degrees). Of these, the first three have been shown to exhibit normal rhombic EPR spectra, each with three clearly resolved g-values, while the last three have been shown to exhibit "large g(max)" EPR spectra at 4.2 K. It is found that the hyperfine coupling constants of the complexes are consistent with those reported previously for low-spin ferriheme systems, with the largest-magnitude hyperfine coupling constant, A(zz), being considerably smaller for the "parallel" complexes (400-540 kG) than for the strictly perpendicular complex (902 kG), A(xx) being negative for all six complexes, and A(zz) and A(xx) being of similar magnitude for the "parallel" complexes (for example, for [(TMP)Fe(1-MeIm)(2)]Cl, A(zz) = 400 kG, A(xx) = -400 kG). In all cases, A(yy) is small but difficult to estimate with accuracy. With results for six structurally characterized model systems, we find for the first time qualitative correlations of g(zz), A(zz), and DeltaE(Q) with axial ligand plane dihedral angle Deltavarphi.     

Functionalization of graphene by electrophilic alkylation of reduced graphite

The reaction of Na/K-reduced graphite with hexyliodide represents a new, versatile and mild approach to synthesize alkylated graphene derivatives, which were characterized by a combination of Raman spectroscopy, TEM and TGA/MS analysis.     

Vibrational spectrum of the spin crossover complex [Fe(phen)(2)(NCS)(2)] studied by IR and Raman spectroscopy, nuclear inelastic scattering and DFT calculations

The vibrational modes of the low-spin and high-spin isomers of the spin crossover complex [Fe(phen)(2)(NCS)(2)] (phen = 1,10-phenanthroline) have been measured by IR and Raman spectroscopy and by nuclear inelastic scattering. The vibrational frequencies and normal modes and the IR and Raman intensities have been calculated by density functional methods. The vibrational entropy difference between the two isomers, DeltaS(vib), which is--together with the electronic entropy difference DeltaS(el)--the driving force for the spin-transition, has been determined from the measured and from the calculated frequencies. The calculated difference (DeltaS(vib) = 57-70 J mol(-1) K(-1), depending on the method) is in qualitative agreement with experimental values (20-36 J mol(-1) K(-1)). Only the low energy vibrational modes (20% of the 147 modes of the free molecule) contribute to the entropy difference and about three quarters of the vibrational entropy difference are due to the 15 modes of the central FeN(6) octahedron.     

Electronic structures of organometallic complexes of f elements LXXV: Parametric analysis of the crystal field splitting pattern of Nd(η5-C5Me5)3

By comparing the FIR, MIR, NIR and vis spectra (pellets) of NdCp¹₃ (Cp¹ = η⁵-C₅Me₅) (1) with those of Nd(C₅Me₄H)₃ (2) and LaCp¹₃ (3) the energies of a number of crystal field (CF) levels of 1 could be determined. The levels of the ground multiplet ⁴I_9/2 could be assigned on the basis of the polarized luminescence transition ⁴F_3/2 → ⁴I_9/2 of an oriented single crystal of 1, and the CF levels of the excited multiplets by assuming equal sequences of CF levels for 1 and those of 2 assigned previously on the basis of linear dichroism, luminescence anisotropy and electronic Raman measurements of oriented single crystals. In order to prove some uncertain assignments, the expected polarizations were checked against the observed ones in the σ and π absorption spectra of an oriented single crystal of 1 recorded by making use of the “inner filter effect”. The free parameters of a phenomenological Hamiltonian were fitted to the thus derived truncated CF splitting pattern of 1, leading to a reduced r.m.s. deviation of 14.0 cm^?1 for 36 assignments. On the basis of the phenomenological CF parameters, the global CF strength experienced by the Nd³⁺ central ion was estimated, and seems to be the fourth largest one ever encountered in Nd^III chemistry. The obtained Slater parameter F² and the spin-orbit coupling parameter ζ_4f allow the insertion of compound 1 into empirical nephelauxetic and relativistic nephelauxetic series, respectively, of Nd^III compounds. The experimentally based nonrelativistic molecular orbital scheme (in the f range) of complex 1 was determined and compared with the results of a previous nonrelativistic Xα-SW calculation on the pseudo-trigonal-planar model compound Nd(η⁵-C₅H₅)₃. The vibronic sidebands of the hypersensitive absorption transition ⁴I_9/2 → ⁴G_5/2 of 1 were correlated with inner-ligand vibrations. The temperature dependence of μ²_eff of 1 was calculated and compared to the experimental data of the likewise pseudo-trigonal-planar complex Nd(C₅H₄^tBu)₃.