Water: How Does It Influence the CaCO3 Formation?

Nature produces biomineral‐based materials with a fascinating set of properties using only a limited number of elements. This set of properties is obtained by closely controlling the structure and local composition of the biominerals. We are far from achieving the same degree of control over the properties of synthetic biomineral‐based composites. One reason for this inferior control is our incomplete understanding of the influence of the synthesis conditions and additives on the structure and composition of the forming biominerals. In this Review, we provide an overview of the current understanding of the influence of synthesis conditions and additives during different formation stages of CaCO₃, one of the most abundant biominerals, on the structure, composition, and properties of the resulting CaCO₃ crystals. In addition, we summarize currently known means to tune these parameters. Throughout the Review, we put special emphasis on the role of water in mediating the formation of CaCO₃ and thereby influencing its structure and properties, an often overlooked aspect that is of high relevance.     

CDK versus GSK-3 inhibition: a purple haze no longer?

The ubiquitous ATP binding site offers a global target for protein kinase inhibitors. The corollary is that molecular selectivity with such agents may be difficult to achieve and ascertain. A relevant example is discussed in terms of design and biomedical rationale.     

NMR: A good tool to ascertain σ-silane or σ-borane formulations?

NMR has played a major role in the characterization of dihydrogen complexes and a number of polyhydrides have been reformulated as dihydrogen complexes on the basis of NMR data. If dihydrogen complexes remain the most widely studied class of σ-complexes, silane compounds are also well recognized as an important family of σ-complexes and more recently a few σ-borane compounds have been isolated. One important problem is the discrimination between a σ-formulation and the corresponding hydrido(silyl) or hydrido(boryl) oxidative addition product. In this review we will discuss key literature data on silane and borane complexes to illustrate the benefit gained by using multinuclear NMR spectroscopy to better define the structures and bonding modes. Our goal is also to help the reader to appreciate the limits of the method and to provide valuable insights into the problem of secondary interactions.     

Ti3C2: An Ideal Co‐catalyst?

How 2D Ti₃C₂ enhances photocatalytic efficiency remains unclear. Now, it is shown that it is graphene quantum dots (GQDs) derived from Ti₃C₂, rather than 2D Ti₃C₂ itself, that play the role of co‐catalyst for La₂Ti₂O₇/Ti₃C₂ (LTC) composites during the photocatalytic reaction. After modification of Ti₃C₂ derivatives, the photocatalytic efficiency of La₂Ti₂O₇ is enhanced 16 times over pure La₂Ti₂O₇. Solid‐state NMR, Raman, and HRTEM results confirm the existence of GQDs in Ti₃C₂ and LTC composites. The GQDs are formed during the chemical change from Ti₃AlC₂ to Ti₃C₂ via HF etching, as Ti atoms are removed and unsaturated carbon bonds are left, which react with each other to form sp² π‐conjugation GQDs. 2D Ti₃C₂ is completely oxidized to CO_x modified TiO_x species, causing Ti₃C₂ to lose its electrical conductivity and the role as co‐catalyst. GQDs largely suppress the photogenerated charge recombination of La₂Ti₂O₇, as revealed by the photoluminescence (PL) and transient photocurrent.     

CF3CH3 --> HF + CF2CH2: a non-RRKM reaction?

The experimental shock tube data recently reported by Kiefer et al. [J. Phys. Chem. A 2004, 108, 2443-2450] for the title reaction at temperatures between 1600 and 2400 K have been compared to master equation simulations using three models: (a) standard RRKM theory, (b) RRKM theory modified by local random matrix theory, which introduces dynamical corrections arising from slow intramolecular vibrational energy randomization, and (c) an ad hoc empirical non-RRKM model. Only the third model provides a good fit of the Kiefer et al. unimolecular reaction rate data. In separate simulations, all three models accurately reproduce the experimental 300 K chemical activation data of Marcoux and Setser [J. Phys. Chem. 1978, 82, 97-108] when the energy transfer parameters are freely varied to fit the data. When experimental energy transfer parameters for a geometrical isomer (1,1,2-trifluoroethane) are used, the standard RRKM model fits the chemical activation data better than the other models, but if energy transfer in the 1,1,1-trifluoroethane is significantly reduced in comparison to the 1,1,2 isomer, then the empirical ad hoc non-RRKM model also gives a good fit. While the ad hoc empirical non-RRKM model can be made to fit the data, it is not based on theory, and we argue that it is physically unrealistic. We also show that the master equation simulations can mimic the Kiefer et al. vibrational relaxation data, which was the first shock tube observation of double-exponential relaxation. We conclude that, until more data on the trifluoroethanes become available, the current evidence is insufficient to decide with confidence whether non-RRKM effects are important in this reaction, or whether the Kiefer et al. data can be explained in some other way.     

First stretching overtone of BiH3: an extreme local-mode case for XH3-type molecule?

The first stretching overtone region of short-lived, formerly inaccessible BiH3 near 3405 cm(-1) has been measured by Fourier-transform infrared spectroscopy with a resolution of 0.0066 cm(-1). Only the 2nu1(A1)/nu1+nu3(E) band system has been observed. Rotational analysis, with transitions reaching J'max=14, has revealed almost perfect local-mode behavior for the upper states denoted as (200A1/E) in the local-mode notation. Ratios of vibration-rotation interaction parameters q(eff)/alpha(eff)(BB) and r(eff)/alpha(eff)(BC), and the appropriate rotational constant differences, are in good agreement with theoretical local-mode limit values. A simple stretching vibrational model reproduces the observed vibrational term values well, and the potential parameters obtained are close to true values.     

3-Azidotetrahydrofuran-2-carboxylates: monomers for five-ring templated β-amino acid foldamers?

Four diastereomeric methyl 3-azidotetrahydrofuran-2-carboxylates were prepared from diacetone glucose as precursors for the synthesis of β-amino acid oligomers with secondary structure.     

UV Spectra and Structure of 2-Diethylamino-3-phenylpropenal: Enamine or Enal?

According to the data of UV, IR, ¹H and ¹³NMR spectra and also quantum-chemical calculations (B3LYP/631G*), Z- and E-isomers of 2-diethylamino-3-phenylpropenal in inert environment exist as antiperiplanar conformers. The energy of electron transitions therein depends on the orientation both f the benzene ring and the unshared electron pair of the nitrogen with respect to the C = C bond. 2-Diethylamino-3-phenylpropenal is an enamine, but the extent of the p^* interaction in its prevailing Z-isomer is small.     

ChemInform Abstract: Are the Compounds InH3 and TlH3 Stable Gas Phase or Solid State Species?

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

3-Nitropropions?ure in Pflanzenextrakten

Ohne Zusammenfassung     

Addition of ammonia to AlH3 and BH3. Why does only aluminum form 2:1 adducts?

The electronic structures of the mono- and bisammonia adducts EH3NH3 and EH3(NH3)2, E = B and Al, have been investigated using ab initio electronic structure methods. Geometries were optimized at the MP2/cc-pVTZ level. Higher-level correlated methods (MP4(SDTQ), QCISD(T), CCSD(T)), as well as the G2 and CBS-Q methods, were used to obtain accurate bond dissociation energies. The E-N bond dissociation energy (De) is computed near 33 kcal/mol (E = B) and 31 kca/mol (E = Al), respectively. Whereas the Al-N bond energy pertaining to the second ammonia molecule in AlH3(NH3)2 is 11-12 kcal/mol, only a transition-state structure may be located for the species BH3(NH3)2. We analyze factors which may distinguish Al from B with respect to the formation of stable bisamine adducts. The most significant difference relates to electronegativity and hence the propensity of boron to engage in predominantly covalent bonding, as compared with the bonding of aluminum with ammonia, which shows substantial electrostatic character. Neither steric factors nor the participation of d-orbitals is found to play an important role in differentiating aluminum from boron. The lesser electronegativity of third-row elements appears to be the critical common feature allowing the formation of hypercoordinate complexes of these elements in contrast to their second-row analogues. Consideration of some group 14 analogues and hard/soft acid/base effects supports this view.     

The Role of Dimethylammonium Iodide in CsPbI3 Perovskite Fabrication: Additive or Dopant?

The controllable growth of CsPbI₃ perovskite thin films with desired crystal phase and morphology is crucial for the development of high efficiency inorganic perovskite solar cells (PSCs). The role of dimethylammonium iodide (DMAI) used in CsPbI₃ perovskite fabrication was carefully investigated. We demonstrated that the DMAI is an effective volatile additive to manipulate the crystallization process of CsPbI₃ inorganic perovskite films with different crystal phases and morphologies. The thermogravimetric analysis results indicated that the sublimation of DMAI is sensitive to moisture, and a proper atmosphere is helpful for the DMAI removal. The time‐of‐flight secondary ion mass spectrometry and nuclear magnetic resonance results confirmed that the DMAI additive would not alloy into the crystal lattice of CsPbI₃ perovskite. Moreover, the DMAI residues in CsPbI₃ perovskite can deteriorate the photovoltaic performance and stability. Finally, the PSCs based on phenyltrimethylammonium chloride passivated CsPbI₃ inorganic perovskite achieved a record champion efficiency up to 19.03 %.     

Double-chain cationic surfactant and n-pentanol: an L3 phase in the rich-water domain?

A ternary system containing water, pentanol and a quaternary cationic surfactant, dioctadecyldimethylammonium bromide (DODAB) was investigated. We present the phase diagram and ESR studies that demonstrate the existence of the well-known L3 or sponge phase in the water-rich domain of the diagram. The remarkable fact is the existence of some kind of order in such diluted conditions.     

The critical re-evaluation of the aromatic/antiaromatic nature of Ti3(CO)3: a missed opportunity?

The nature of bonding and aromaticity of Ti(3)(CO)(3), a mill-shaped metal-carbonyl complex, is studied carefully. A unique bonding mechanism between metal and carbonyl groups is found in this species. Ti(3)(CO)(3) is an example of a metal-carbonyl complex with prominent metal to carbonyl donation. Moreover, it is proven that not only is Ti(3)(CO)(3) not an antiaromatic complex but also it is the first synthesized example of d-block, σ+π aromatic species. A quick survey among the first row of transition metals in the periodic table shows that other local minima with similar structures and aromaticity are present and Ti(3)(CO)(3) is the first synthesized species of an unknown family.