Novel Dithiolene Complexes and Tetrathiafulvalenes

Abstract

Novel dithiolene metal complexes, some of which absorb in the near infrared, and tetrathiafulvalenes, in particular tetraiodotetrathia- fulvalene, have been prepared, and their magnetic properties studied.     

Mass transfer limitation in thermogravimetry of biomass gasification

In order to determine the intrinsic reactivity behavior from thermogravimetry studies, the experimental conditions should be such that the reactions are not mass transfer limited. Biomass char usually has a higher reactivity than coal chars. Therefore, mass transfer limitations may be more problematic when studying biomass char reactivity. Chemical reaction kinetics and mass transfer processes present in thermogravimetry are used for modeling the overall reaction rate for spruce bark CO₂ gasification. Thermogravimetric experiments are carried out between 700 and 900 °C, and the CO₂ concentration is varied between 10 and 90 vol%. The intrinsic activation energy is found to be 120 kJ mol^?1. The transition temperature between regimes I and II is here defined when the fraction apparent to true activation energy equals 0.75. Higher external mass transfer (e.g., by decreasing the diffusion path through the crucible’s freeboard), decreasing the sample amounts, and higher CO₂ partial pressures for the Langmuir–Hinshelwood reaction type increase the transition temperature. The results show that the transition temperature between regimes I and II conditions is approx. 1,030 °C for 90 vol% CO₂.     

Nanoscale Control of Polyoxometalate Assembly: A {Mn8W4} Cluster within a {W36Si4Mn10} Cluster Showing a New Type of Isomerism

Two near isomeric clusters containing a novel {Mn₈W₄} Keggin cluster within a [W₃₆Mn₁₀Si₄O₁₃₆(OH)₄(H₂O)8]^24? cluster are reported: K₁₀Li₁₄ [W₃₆Si₄O₁₃₆Mn^II₁₀(OH)₄(H₂O)₈] ( 1 ) and K₁₀Li1_3.5Mn_0.25[W₃₆Si₄O₁₃₆Mn^II₁₀(OH)₄(H₂O)₈] ( 1′ ). Bulk characterization of the clusters has been carried out by single crystal X‐ray structure analysis, ICP‐MS, TGA, ESI‐MS, CV and SQUID‐magnetometer analysis. X‐ray analysis revealed that 1′ has eight positions within the central Keggin core that were disordered W/Mn whereas 1 contained no such disorder. This subtle difference is due to a differences is how the two clusters assemble and recrystallize from the same mother liquor and represents a new type of isomerism. The rapid recrystallization process was captured via digital microscopy and this uncovered two “intermediate” types of crystal which formed temporarily and provided nucleation sites for the final clusters to assemble. The intermediates were investigated by single crystal X‐ray analysis and revealed to be novel clusters K₄Li₂₂[W₃₆Si₄Mn₇O₁₃₆(H₂O)₈]?56 H₂O ( 2 ) and Mn₂K₈Li₁₄[W₃₆Si₄Mn₇O₁₃₆(H₂O)₈]?45 H₂O ( 3 ). The intermediate clusters contained different yet related building blocks to the final clusters which allowed for the postulation of a mechanism of assembly. This demonstrates a rare example where the use X‐ray crystallography directly facilitated understanding the means by which a POM assembled.     

Preparation, characterization and thiol-thione tautomeric studies of 2-thiono-4-methyl-5-(2,2,2-trifluoro-1-trifluoromethylethyl)-1,3-thiazoline

The synthesis of a new trifluoromethyl 2-mercapto-1,3-thiadiazole derivative from 5,5,5-trifluoro-4-(trifluoromethyl)-3-penten-2-one, its structural study in the solid state and in the liquid phase and the thiol-thione tautomeric equilibrium study of the title compound are reported. The crystalline structure shows short intermolecular FF contacts. Theoretical calculations using HF and DFT methods were performed. Vibrational spectra were calculated for both tautomers and compared with experimental data. The experimental and theoretical results can be interpreted in terms of the existence of a thione tautomer in the solid and in solution.     

Chemical Sensors and Biosensors—Principles and Applications

Chemical and environmental engineering and biotechnology are among the fields now being transformed by continually increasing levels of automation. Whereas the objective in other sectors of industry is simply to increase efficiency, here considerations of system theory or safety demand a high level of automation. Either the processes are too complex and require multifunctional control with feedback, or an analysis of the safety requirements shows the necessity for a certain degree of redundancy in the safety measures, and for elimination of human error as a risk factor. With regard to quality control, cost-benefit analyses lead to striking conclusions which again indicate the need for highly automated, and above all reliable, systems to eliminate rejects. The crux of any automated system is the measurement and control technology; of central importance is the rapid, reliable, and in some cases continuous, measurement and interpretation of key processes or control variables. For this purpose a wide variety of recording instruments and sensors are used to give as accurate a picture as possible of the state of the system. It is obvious from this that the performance of the control system is critically dependent on the sensors. Errors in the measured quantities can become amplified in the control variables or, in dynamic systems, can lead to undesirable operating conditions. Moreover, as a consequence of great advances in microelectronics, “intelligent sensors” which can calibrate and control themselves will be one of the key technologies of the nineties. Unless fast and immediate information on the true current status of a system is available, microprocessors as control devices react blindly and unpredictably to errors in input information. New discoveries in the fields of electronic, electrochemical, and optical transducers are now being applied in heterogeneous catalysis and surface physics, and in biochemistry (enzymology and immunology); in these fields new chemical sensor principles are being tested, which could revolutionize instrumental methods of molecular analysis in particular, owing to their very favorable cost-performance relationship. This article aims to give an up-to-date overview of the current state of the art in these developments, with emphasis on their importance for analysis and their significance in relation to the chemist's interest in mechanisms for identifying substances.     

An Organoruthenium Anticancer Agent Shows Unexpected Target Selectivity For Plectin

Organometallic metal(arene) anticancer agents require ligand exchange for their anticancer activity and this is generally believed to confer low selectivity for potential cellular targets. However, using an integrated proteomics-based target-response profiling approach as a potent hypothesis-generating procedure, we found an unexpected target selectivity of a ruthenium(arene) pyridinecarbothioamide (plecstatin) for plectin, a scaffold protein and cytolinker, which was validated in a plectin knock-out model in vitro. Plectin targeting shows potential as a strategy to inhibit tumor invasiveness as shown in cultured tumor spheroids while oral administration of plecstatin-1 to mice reduces tumor growth more efficiently in the invasive B16 melanoma than in the CT26 colon tumor model.     

Synthesis of 2′-Deoxy-5-(isothiazol-5-yl)uridine and Its Interaction with the HSV-1 Thymidine Kinase

2′-Deoxy-5-(isothiazol-5-yl)uridine ( 12 ) was synthesized starting from 2′-deoxy-5-iodouridine using a Pd-catalysed cross-coupling reaction with propiolaldehyde diethyl acetal followed by deprotection and ring closure using thiosulfate. 2′-Deoxyuridine 12 has a particular place among the 5-heteroaryl-substituted 2′-deoxyuridines in that it has a high affinity for herpes simplex virus type 1 (HSV-1)-encoded thymidine kinase (TK) without antiviral activity. Biochemical studies revealed that 12 is a substrate for viral TK. We further investigated the interaction of 12 with the HSV-1 thymidine kinase. The conformation of 12 in solution was established by NMR spectroscopy. The most stable conformer 12A has the S-atom of the isothiazole ring placed in the neighbourhood of the C(4)?O group of the pyrimidine moiety. The compound was docked in its most stable conformation in the active site of HSV-1 TK and subjected to energy minimization. This demonstrated that the isothiazole moiety binds in a cavity lined by the side chains of Tyr-132, Arg-163, Ala-167, and Ala-168 and that the C(3) atom of the isothiazole moiety is located in close proximity of the phenolic O-atom of Tyr-132 and the aliphatic part of the Arg-163 side chain.     

The closo-Cluster Triad: B9X9, [B9X9]· –, and [B9X9]2– with Tricapped Trigonal Prisms (X = Cl,Br, I). Syntheses,Crystal and Electronic Structures

Halogenation of nido-B₁₀H₁₄ with C₂H₂Cl₄, C₂Cl₆, Br₂, or I₂, produces by cluster degradation the (2 n)-closo-clusters B₉X₉ (X = Cl, Br, I). The synthesis of salts of the perhalogenated radical anions of the type (2 n + 1)-closo-[B₉X₉]^{· –} and of the corresponding dianions (2 n + 2)-closo-[B₉X₉]^2– from neutral B₉X₉ is described [n is the number of cluster atoms; (2 n), (2 n + 1), and (2 n + 2) is the number of cluster electrons]. Molecular and crystal structures of B₉Cl₉, B₉Br₉, [(C₆H₅)₄P][B₉Br₉] · CH₂Cl₂, and [(C₄H₉)₄N]₂[B₉Br₉] · CH₂Cl₂ have been determined via X-ray diffraction. All three oxidation states of the cluster retain the tricapped trigonal prism. The reduction of the clusters B₉X₉ was shown by cyclic voltammetry in CH₂Cl₂ to proceed via two successive one-electron reversible steps, separated by at least 0.4 V. The paramagnetic radical anions [B₉X₉]^{· –} (X = Cl, Br) were further characterized by magnetic susceptibility measurements of [Cp₂Fe][B₉X₉] and [Cp₂Co][B₉X₉], respectively. The EPR spectra of [B₉X₉]^{· –} (X = Cl, Br, I) in glassy frozen CH₂Cl₂ solutions showed increasing g anisotropy for the heavier halogen derivatives, illustrating significant halogen participation at the singly occupied MO. The ¹¹B NMR spectra of CD₂Cl₂ solutions of the neutral clusters B₉X₉ exhibit only one sharp resonance, indicating that the boron atoms are highly fluxional in solution. In contrast, two different boron resonances as expected for a rigid tricapped trigonal prism are clearly observed for the [B₉X₉]^2– dianions in solutions and for solid B₉Br₉ in the ¹¹B MAS NMR spectra. Temperature dependent ¹¹B MAS NMR experiments on B₉Br₉ and [B₉Br₉]^2– in the solid state show a reversible coalescence of the two resonances at higher temperature. ¹¹B MAS NMR spectra and DTA measurements of [B₉Br₉]^2– showed a phase transition.     

Studies on the Anode/Electrolyte Interfacein Lithium Ion Batteries

Summary.  Rechargeable lithium ion cells operate at voltages of 3.5–4.5 V, which is far beyond the thermodynamic stability window of the battery electrolyte. Strong electrolyte reduction and anode corrosion has to be anticipated, leading to irreversible loss of electroactive material and electrolyte and thus strongly deteriorating cell performance. To minimize these reactions, anode and electrolyte components have to be combined that induce the electrolyte reduction products to form an effectively protecting film at the anode/electrolyte interface, which hinders further electrolyte decomposition reactions, but acts as membrane for the lithium cations, i.e. behaving as a solid electrolyte interphase (SEI). This paper focuses on important aspects of the SEI. By using key examples, the effects of film forming electrolyte additives and the change of the active anode material from carbons to lithium storage alloys are highlighted. Received May 30, 2000. Accepted June 14, 2000