Kloning Manusia

In the last few years, very rapid progress in the cloning technology and its development towards human cloning has become a hotly-debated issue. Cloning, which is the process of formation of a number of individuals with the same genetic structure, can be done by means of embryo-splitting method and nuclear transfer. Human cloning through the nuclear transfer method is directed towards two purposes, i.e. reproduction and therapy. The relatively new transgenic technology can be combined with the cloning technique to produce clones with new genes. However, pros and cons arise concerning the development of research on human cloning, particularly cloning for reproductive purposes. Therefore, there is need for a moratorium period before human cloning can be performed in order that solutions for all kinds of problems related to safety and ethics can be found

Syntheses, Structures, and Mössbauer Effect Spectroscopy of Triple-Decker Complexes Incorporating Nonamethylferrocene

Three new triple-decker complexes were synthesized by the reaction of nonamethylferrocene, Cp′FeCp* (Cp′ = C₅Me₄H, Cp* = C₅Me₅), with coordinatively unsaturated transition-metal complexes. The reaction of ruthenium cations [(C₅R₅)­Ru]⁺ (R = H, Me) with Cp′FeCp* afforded the purple heterometallic triple-decker complexes [(C₅R₅)­Ru­(μ-Cp′)­FeCp*]⁺ by electrophilic addition of ruthenium to the Cp′ ring of nonamethylferrocene. The analogous reaction with the manganese cation [Mn­(CO)₃]⁺ produced the blue homometallic triple-decker complex [Cp*Fe­(μ-Cp′)­FeCp*]⁺ by abstraction of the Cp′ ring from Cp′FeCp* and subsequent addition of the newly generated cation [Cp*Fe]⁺ to 1 equiv of Cp′FeCp*. These experiments demonstrate that the asymmetry of Cp′FeCp* gives rise to a remarkable degree of regioselectivity such that ruthenium electrophiles add only to the Cp′ ring and never to the Cp* ring. In a similar way, [Mn­(CO)₃]⁺ abstracts only the Cp′ ring from Cp′FeCp* to produce [Cp*Fe]⁺, which in turn adds only to the Cp′ ring of Cp′FeCp* to produce [Cp*Fe­(μ-Cp′)­FeCp*]⁺. Three air-stable triple-decker complexes incorporating nonamethylferrocene, [Cp*Fe­(μ-Cp′)­FeCp*]⁺ (<b>1</b>), [CpRu­(μ-Cp′)­FeCp*]⁺ (<b>2</b>), and [Cp*Ru­(μ-Cp′)­FeCp*]⁺ (<b>3</b>), have been characterized by NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction analysis, and temperature-dependent ⁵⁷Fe Mössbauer spectroscopy

Syntheses, Structures, and Mössbauer Effect Spectroscopy of Triple-Decker Complexes Incorporating Nonamethylferrocene

Three new triple-decker complexes were synthesized by the reaction of nonamethylferrocene, Cp′FeCp* (Cp′ = C₅Me₄H, Cp* = C₅Me₅), with coordinatively unsaturated transition-metal complexes. The reaction of ruthenium cations [(C₅R₅)­Ru]⁺ (R = H, Me) with Cp′FeCp* afforded the purple heterometallic triple-decker complexes [(C₅R₅)­Ru­(μ-Cp′)­FeCp*]⁺ by electrophilic addition of ruthenium to the Cp′ ring of nonamethylferrocene. The analogous reaction with the manganese cation [Mn­(CO)₃]⁺ produced the blue homometallic triple-decker complex [Cp*Fe­(μ-Cp′)­FeCp*]⁺ by abstraction of the Cp′ ring from Cp′FeCp* and subsequent addition of the newly generated cation [Cp*Fe]⁺ to 1 equiv of Cp′FeCp*. These experiments demonstrate that the asymmetry of Cp′FeCp* gives rise to a remarkable degree of regioselectivity such that ruthenium electrophiles add only to the Cp′ ring and never to the Cp* ring. In a similar way, [Mn­(CO)₃]⁺ abstracts only the Cp′ ring from Cp′FeCp* to produce [Cp*Fe]⁺, which in turn adds only to the Cp′ ring of Cp′FeCp* to produce [Cp*Fe­(μ-Cp′)­FeCp*]⁺. Three air-stable triple-decker complexes incorporating nonamethylferrocene, [Cp*Fe­(μ-Cp′)­FeCp*]⁺ (<b>1</b>), [CpRu­(μ-Cp′)­FeCp*]⁺ (<b>2</b>), and [Cp*Ru­(μ-Cp′)­FeCp*]⁺ (<b>3</b>), have been characterized by NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction analysis, and temperature-dependent ⁵⁷Fe Mössbauer spectroscopy

Influence of Ligand Modifications on Structural and Spectroscopic Properties in Terphenyl Based Heavier Group 14 Carbene Homologues

The synthesis and characterization of a series of heavier group 14 element (Ge, Sn, and Pb) carbene homologues based on the electronically modified, 2,6-dimesityl substituted terphenyl ligands Ar^#-3,5-ⁱPr₂, Ar^#-4-SiMe₃, and Ar^#-4-Cl (Ar^#-3,5-ⁱPr₂ = C₆H₂-2,6-Mes₂-3,5-ⁱPr₂; Ar^#-4-Cl = C₆H₂-2,6-Mes₂-4-Cl; Ar^#-4-SiMe₃ = C₆H₂-2,6-Mes₂-4-SiMe₃; Mes = C₆H₂-2,4,6-Me₃) are presented. The consequences of introducing electron withdrawing and -releasing substituents on the solid state structures of the newly synthesized germylenes, stannylenes, and plumbylenes as well as their Mössbauer, NMR and UV–vis spectroscopic properties are presented and discussed in the context of a second order Jahn–Teller type mixing of frontier orbitals with appropriate symmetry. Experimental findings were supported by DFT calculations. More electron withdrawing ligands lead to a bonding situation with higher contribution of p-orbitals from the central heavier group 14 element in σ-bonding toward the ligands and thus increased s-electron character of the lone pair. Furthermore, this results in an increase in the energy separation between the frontier orbitals. Experimentally, these changes are manifested in narrower bending angles at the heavy tetrel atoms and hypsochromic in their UV–vis spectra. In contrast, derivatives of more electron rich <i>m</i>-terphenyl ligands are characterized by a smaller HOMO–LUMO gap and wider interligand angles

Histoire et fiction : Que se serait-il passé si… ?

The synthesis and spectroscopic and structural characterization of an extensive series of acyclic, monomeric tetrylene dichalcogenolates of formula M­(ChAr)₂ (M = Si, Ge, Sn, Pb; Ch = O, S, or Se; Ar = bulky <i>m</i>-terphenyl ligand, including two new acyclic silylenes) are described. They were found to possess several unusual featuresthe most notable of which is their strong tendency to display acute interligand, Ch–M–Ch, bond angles that are often well below 90°. Furthermore, and contrary to normal steric expectations, the interligand angles were found to become narrower as the size of the ligand was increased. Experimental and structural data in conjunction with high-level DFT calculations, including corrections for dispersion effects, led to the conclusion that dispersion forces play an important role in stabilizing their acute interligand angles

Reactivity of a Tin(II) (Iminophosphinoyl)(thiophosphinoyl)methanediide Complex Toward Sulfur: Synthesis and ¹¹⁹Sn Mössbauer Spectroscopic Studies of [{(μ-S)SnC(PPh₂NSiMe₃)(PPh₂S)}₃Sn(μ₃-S)]

Reaction of [(PPh₂NSiMe₃)­(PPh₂S)­CSn:]₂ (<b>1</b>) with elemental sulfur in toluene afforded [{(μ-S)Sn^IVC­(PPh₂NSiMe₃)­(PPh₂S)}₃Sn^II(μ₃-S)] (<b>2</b>) and [CH₂(PPh₂NSiMe₃)­(PPh₂S)] (<b>3</b>). Compound <b>2</b> comprises a Sn^IIS moiety coordinated with the Sn^IV and S atoms of a trimeric 2-stannathiomethendiide {(PPh₂NSiMe₃)­(PPh₂S)­CSn­(μ-S)}₃. Compound <b>2</b> has been characterized by NMR spectroscopy, ¹¹⁹Sn Mössbauer studies, X-ray crystallography, and theoretical studies. ¹¹⁹Sn NMR spectroscopy and Mössbauer studies show the presence of Sn^IV and Sn^II atoms in <b>2</b>. X-ray crystallography suggests that the Sn^IIS moiety does not have multiple bond character. Theoretical studies illustrate that the C_methanediide–Sn bonds comprise a lone pair orbital on each C_methanediide atom and an C–Sn occupied σ orbital

Reactivity of a Tin(II) (Iminophosphinoyl)(thiophosphinoyl)methanediide Complex Toward Sulfur: Synthesis and ¹¹⁹Sn Mössbauer Spectroscopic Studies of [{(μ-S)SnC(PPh₂NSiMe₃)(PPh₂S)}₃Sn(μ₃-S)]

Reaction of [(PPh₂NSiMe₃)­(PPh₂S)­CSn:]₂ (<b>1</b>) with elemental sulfur in toluene afforded [{(μ-S)Sn^IVC­(PPh₂NSiMe₃)­(PPh₂S)}₃Sn^II(μ₃-S)] (<b>2</b>) and [CH₂(PPh₂NSiMe₃)­(PPh₂S)] (<b>3</b>). Compound <b>2</b> comprises a Sn^IIS moiety coordinated with the Sn^IV and S atoms of a trimeric 2-stannathiomethendiide {(PPh₂NSiMe₃)­(PPh₂S)­CSn­(μ-S)}₃. Compound <b>2</b> has been characterized by NMR spectroscopy, ¹¹⁹Sn Mössbauer studies, X-ray crystallography, and theoretical studies. ¹¹⁹Sn NMR spectroscopy and Mössbauer studies show the presence of Sn^IV and Sn^II atoms in <b>2</b>. X-ray crystallography suggests that the Sn^IIS moiety does not have multiple bond character. Theoretical studies illustrate that the C_methanediide–Sn bonds comprise a lone pair orbital on each C_methanediide atom and an C–Sn occupied σ orbital

Dispersion Forces and Counterintuitive Steric Effects in Main Group Molecules: Heavier Group 14 (Si–Pb) Dichalcogenolate Carbene Analogues with Sub-90° Interligand Bond Angles

The synthesis and spectroscopic and structural characterization of an extensive series of acyclic, monomeric tetrylene dichalcogenolates of formula M­(ChAr)₂ (M = Si, Ge, Sn, Pb; Ch = O, S, or Se; Ar = bulky <i>m</i>-terphenyl ligand, including two new acyclic silylenes) are described. They were found to possess several unusual featuresthe most notable of which is their strong tendency to display acute interligand, Ch–M–Ch, bond angles that are often well below 90°. Furthermore, and contrary to normal steric expectations, the interligand angles were found to become narrower as the size of the ligand was increased. Experimental and structural data in conjunction with high-level DFT calculations, including corrections for dispersion effects, led to the conclusion that dispersion forces play an important role in stabilizing their acute interligand angles

Dispersion Forces and Counterintuitive Steric Effects in Main Group Molecules: Heavier Group 14 (Si–Pb) Dichalcogenolate Carbene Analogues with Sub-90° Interligand Bond Angles

The synthesis and spectroscopic and structural characterization of an extensive series of acyclic, monomeric tetrylene dichalcogenolates of formula M­(ChAr)₂ (M = Si, Ge, Sn, Pb; Ch = O, S, or Se; Ar = bulky <i>m</i>-terphenyl ligand, including two new acyclic silylenes) are described. They were found to possess several unusual featuresthe most notable of which is their strong tendency to display acute interligand, Ch–M–Ch, bond angles that are often well below 90°. Furthermore, and contrary to normal steric expectations, the interligand angles were found to become narrower as the size of the ligand was increased. Experimental and structural data in conjunction with high-level DFT calculations, including corrections for dispersion effects, led to the conclusion that dispersion forces play an important role in stabilizing their acute interligand angles

Dispersion Forces and Counterintuitive Steric Effects in Main Group Molecules: Heavier Group 14 (Si–Pb) Dichalcogenolate Carbene Analogues with Sub-90° Interligand Bond Angles

The synthesis and spectroscopic and structural characterization of an extensive series of acyclic, monomeric tetrylene dichalcogenolates of formula M­(ChAr)₂ (M = Si, Ge, Sn, Pb; Ch = O, S, or Se; Ar = bulky <i>m</i>-terphenyl ligand, including two new acyclic silylenes) are described. They were found to possess several unusual featuresthe most notable of which is their strong tendency to display acute interligand, Ch–M–Ch, bond angles that are often well below 90°. Furthermore, and contrary to normal steric expectations, the interligand angles were found to become narrower as the size of the ligand was increased. Experimental and structural data in conjunction with high-level DFT calculations, including corrections for dispersion effects, led to the conclusion that dispersion forces play an important role in stabilizing their acute interligand angles