Jochen Rall

Bio: Jochen Rall is an academic researcher from University of Stuttgart. The author has contributed to research in topics: Tautomer & Ligand. The author has an hindex of 7, co-authored 8 publications receiving 764 citations.

Copper—A “Modern” Bioelement

Abstract: Copper is a bioessential element in biology with truly unique chemical characteristics in its two relevant oxidation states +I and +II. Significant progress has been made in recent years in the elucidation of the frequently surprising biochemistry of this trace element. Those advances were especially furthered through mutual stimulation involving results from biochemistry, molecular biology, and medicine on one hand and the synthesis as well as the structural and spectroscopic characterization of low molecular weight model complexes on the other. The most notable features of protein-bound active copper are its almost exclusive function in the metabolism of O2 or N/O compounds (NO, N2O) and its frequent association with oxidizing organic and inorganic radicals such as tyrosyl, semiquinones, superoxide, or nitrosyl. This unique biological role of copper can be rationalized given its chemical and assumed evolutionary background.

Kupfer – ein “modernes” Bioelement

Abstract: Kupfer ist ein bioessentielles Element, das in den beiden relevanten Oxidationsstufen I und II einzigartige chemische Eigenschaften aufweist. Biochemische, molekularbiologische und medizinische Erkenntnisse einerseits sowie die Synthese und Untersuchung niedermolekularer “Modell”-Komplexverbindungen andererseits haben in den letzten Jahren zu wesentlichen Fortschritten bei der Erforschung der teilweise uberraschenden Biochemie dieses Spurenelements gefuhrt. Auffallend, jedoch aufgrund des chemischen und des vermuteten evolutionsgeschichtlichen Hintergrundes nachvollziehbar, sind die Funktionen von proteingebundenem Kupfer vor allem im Metabolismus von O2 und N/O-Verbindungen (NO2−, N2O) sowie seine haufige Assoziation mit oxidierenden organischen und anorganischen Radikalen wie etwa Tyrosyl, Semichinonen, Superoxid-Ionen oder Nitrosyl-Radikalen.

Metal-induced tautomerization of p- to o-quinone compounds: experimental evidence from CuI and ReI complexes of azophenine and DFT studies.

Abstract: Azophenine (7,8-diphenyl-2,5-bis(phenylamino)-p-quinonediimine, Lp) reacts with [Cu(PPh3)4](BF4) or [Re(CO)5Cl] to yield the (Ph3P)2Cu+ or [(OC)3ClRe] complex of the tautomeric form 7,8-diphenyl-4,5-bis(phenylamino)-o-quinonediimine, Lo, as evident from structure determinations and from very intense metal-to-ligand charge transfer (MLCT) transitions in the visible region. Time-dependent DFT (TD-DFT) calculations on model complexes [(N∩N)Re(CO)3Cl] confirm the spectroscopic results, showing considerably higher oscillator strengths of the MLCT transition for the o-quinonediimine complexes in comparison to compounds with N∩N=1,4-dialkyl-1,4-diazabutadiene. The complexes are additionally stabilized through hydrogen bonding between two now ortho-positioned NHPh substituents and one fluoride of the BF4− anion (Cu complex) or the chloride ligand (Re complex). DFT Calculations on the model ligands p-quinonediimine or 2,5-diamino-p-quinonediimine and their ortho-quinonoid forms with and without Li+ or Cu+ are presented to discuss the relevance for metal-dependent quinoproteins.

Ligand-controlled oxidation state ambivalence in copper–quinone complexes. Replacement of N-donor by S-donor ligands favours the copper(I)–semiquinone over the copper(II)–catecholate form

Abstract: Paramagnetic complexes between chelating o-quinone derivatives Qn–(Q = 3,5-di-tert-butyl-o-benzoquinone) and coordinatively unsaturated copper compounds (L)Cu have been obtained and studied by EPR spectroscopy. With nitrogen donor co-ligands, L, e.g. saturated polyamines or a bis(imidazole) chelate ligand, the CuII(Q2–) form was observed. In contrast, tetrahydrothiophene and bi-, tri- or tetra-dentate chelating thioethers favour the CuI(Q.–) form as ground state as evident from small 63,65Cu coupling (<1.5 mT), from semiquinone hyperfine splitting and from g factors (<2.010) which are relatively close to the free-electron value. However, the thioether co-ligands generally effect higher metal-coupling constants and g factors in (L)CuI(Q.–) systems than triorganophosphine, triorganoarsine, carbonyl, π-coordinated alkyne or alkene ligands.

Control of magnetic properties through external stimuli.

Abstract: The magnetic properties of many magnetic materials can be controlled by external stimuli. The principal focus here is on the thermal, photochemical, electrochemical, and chemical control of phase transitions that involve changes in magnetization. The molecular compounds described herein range from metal complexes, through pure organic compounds to composite materials. Most of the Review is devoted to the properties of valence-tautomeric compounds, molecular magnets, and spin-crossover complexes, which could find future application in memory devices or optical switches.

Catechol-Based Biomimetic Functional Materials

Abstract: Catechols are found in nature taking part in a remarkably broad scope of biochemical processes and functions. Though not exclusively, such versatility may be traced back to several properties uniquely found together in the o-dihydroxyaryl chemical function; namely, its ability to establish reversible equilibria at moderate redox potentials and pHs and to irreversibly cross-link through complex oxidation mechanisms; its excellent chelating properties, greatly exemplified by, but by no means exclusive, to the binding of Fe(3+); and the diverse modes of interaction of the vicinal hydroxyl groups with all kinds of surfaces of remarkably different chemical and physical nature. Thanks to this diversity, catechols can be found either as simple molecular systems, forming part of supramolacular structures, coordinated to different metal ions or as macromolecules mostly arising from polymerization mechanisms through covalent bonds. Such versatility has allowed catechols to participate in several natural processes and functions that range from the adhesive properties of marine organisms to the storage of some transition metal ions. As a result of such an astonishing range of functionalities, catechol-based systems have in recent years been subject to intense research, aimed at mimicking these natural systems in order to develop new functional materials and coatings. A comprehensive review of these studies is discussed in this paper.

Copper in diseases and treatments, and copper-based anticancer strategies.

Abstract: Copper is found in all living organisms and is a crucial trace element in redox chemistry, growth and development. It is important for the function of several enzymes and proteins involved in energy metabolism, respiration, and DNA synthesis, notably cytochrome oxidase, superoxide dismutase, ascorbate oxidase, and tyrosinase. The major functions of copper-biological molecules involve oxidation-reduction reactions in which they react directly with molecular oxygen to produce free radicals. Therefore, copper requires tightly regulated homeostatic mechanisms to ensure adequate supplies without any toxic effects. Overload or deficiency of copper is associated, respectively, with Wilson disease (WD) and Menkes disease (MD), which are of genetic origin. Researches on Menkes and Wilson disorders have provided useful insights in the field of copper homeostasis and in particular into the understanding of intracellular trafficking and distribution of copper at molecular levels. Therapies based on metal supplementation with copper histidine or removal of copper excess by means of specific copper chelators are currently effective in treating MD and WD, respectively. Copper chelation therapy is now attracting much attention for the investigation and treatment of various neurodegenerative disorders such as Alzheimer, Parkinson and CreutzfeldtJakob. An excess of copper appears to be an essential co-factor for angiogenesis. Moreover, elevated levels of copper have been found in many types of human cancers, including prostate, breast, colon, lung, and brain. On these basis, the employment of copper chelators has been reported to be of therapeutic value in the treatment of several types of cancers as anti-angiogenic molecules. More recently, mixtures of copper chelators with copper salts have been found to act as efficient proteasome inhibitors and apoptosis inducers, specifically in cancer cells. Moreover, following the worldwide success of platinum(II) compounds in cancer chemotherapy, several families of individual copper complexes have been studied as potential antitumor agents. These investigations, revealing the occurrence of mechanisms of action quite different from platinum drugs, head toward the development of new anticancer metallodrugs with improved specificity and decreased toxic side effects.