Computer Simulation of Collision Induced Dissociation and Isolobal Analogy: The Case of Biotin and Its Analogues

We have studied how collision induced dissociation (CID) products and associated mechanism are modified when a chemical group is modified by isolobal groups, and in particular S, O, NH and CH2. At this end, we have considered protonated biotin (vitamin B7) and corresponding oxybiotin, N-biotin and C-biotin, which have the same structures except for one chemical group (the S in biotin which is substituted with the aforementioned isolobal ones). Collisional simulations with Ar were performed to model CID fragmentations and to have directly access to related mechanisms. Simulations have shown that the CID fragmentation of the four compounds were similar and the resulting fragments involve in a similar way the isolobal groups. Details on the mechanisms as obtained from simulations are reported and discussed. This result shows that it is possible in principle to predict, with a reasonable confidence, mass spectra of unknown molecules based on mass spectrum of the known one when isolobal modifications are done.<br>

Computer Simulation of Collision Induced Dissociation and Isolobal Analogy: The Case of Biotin and Its Analogues

We have studied how collision induced dissociation (CID) products and associated mechanism are modified when a chemical group is modified by isolobal groups, and in particular S, O, NH and CH2. At this end, we have considered protonated biotin (vitamin B7) and corresponding oxybiotin, N-biotin and C-biotin, which have the same structures except for one chemical group (the S in biotin which is substituted with the aforementioned isolobal ones). Collisional simulations with Ar were performed to model CID fragmentations and to have directly access to related mechanisms. Simulations have shown that the CID fragmentation of the four compounds were similar and the resulting fragments involve in a similar way the isolobal groups. Details on the mechanisms as obtained from simulations are reported and discussed. This result shows that it is possible in principle to predict, with a reasonable confidence, mass spectra of unknown molecules based on mass spectrum of the known one when isolobal modifications are done.<br>

Computer Simulation of Collision Induced Dissociation and Isolobal Analogy: The Case of Biotin and Its Analogues

We have studied how collision induced dissociation (CID) products and associated mechanism are modified when a chemical group is modified by isolobal groups, and in particular S, O, NH and CH2. At this end, we have considered protonated biotin (vitamin B7) and corresponding oxybiotin, N-biotin and C-biotin, which have the same structures except for one chemical group (the S in biotin which is substituted with the aforementioned isolobal ones). Collisional simulations with Ar were performed to model CID fragmentations and to have directly access to related mechanisms. Simulations have shown that the CID fragmentation of the four compounds were similar and the resulting fragments involve in a similar way the isolobal groups. Details on the mechanisms as obtained from simulations are reported and discussed. This result shows that it is possible in principle to predict, with a reasonable confidence, mass spectra of unknown molecules based on mass spectrum of the known one when isolobal modifications are done.<br>

Half- and mixed-sandwich metallacarboranes for potential applications in medicine

Today, medicinal chemistry is still clearly dominated by organic chemistry, and commercially available boron-based drugs are rare. In contrast to hydrocarbons, boranes prefer the formation of polyhedral clusters via delocalized 3c2e bonds, such as polyhedral dicarba-closo-dodecaborane(12) (closo-C2B10H12). These clusters have remarkable biological stability, and the three isomers, 1,2- (ortho), 1,7- (meta), and 1,12-dicarba-closo-dodecaborane(12) (para), have attracted much interest due to their unique structural features. Furthermore, anionic nido clusters ([7,8-C2B9H11]2−), derived from the neutral icosahedral closo cluster 1,2-dicarba-closo-dodecaborane(12) by deboronation followed by deprotonation are suitable ligands for transition metals and offer the possibility to form metallacarboranes, for example via coordination through the upper pentagonal face of the cluster. The isolobal analogy between the cyclopentadienyl(–1) ligand (Cp−) and [C2B9H11]2− clusters (dicarbollide anion, Cb2−) is the motivation in using Cb2− as ligand for coordination to a metal center to design compounds for various applications. This review focuses on potential applications of half- and mixed-sandwich-type transition metal complexes in medicine.

Ab InitioTheoretical Investigation on the Geometrical and Electronic Structures of Gallium Aurides:GaAun0/-andGa2Aun0/- (n=1–4)

This study presents a systematic investigation of the geometric and electronic properties of GaAun0/-and Ga2Aun0/-(n= 1–4) clusters based on density functional theory and wave function theory. Detailed orbital analyses, adaptive natural density partitioning, and electron localization function analyses are performed and relevant results are discussed. GaAun0/-(n= 1–4) clusters withn-Au terminals and Ga2Aun0/-(n= 1–4) clusters with bridged Au atoms possess geometric structures and bonding patterns similar to those of the corresponding gallium hydrides GaHn0/-and Ga2Hn0/-. Ga–Au interaction is predicted to occur through highly polar covalent bonds in monogallium aurides. In contrast to the highly symmetric ground states ofC2vGa2Au,C2vGa2Au2, andD3hGa2Au3,C3vGa2Au4is composed of strong interactions between a Ga+cation and the face of a tetrahedral GaAu4−anion. The adiabatic and vertical detachment energies of the anions under study are calculated to facilitate their experimental characterization. Geometric and electronic structural comparisons with the corresponding gallium hydrides are conducted to establish an isolobal analogy between gold and hydrogen atoms.

Pd/X group interchange in the [Pd(Br)(PH3)(C6H5)(C6H5X)] system — Theoretical insights from the isolobal analogy perspective

DFT-B3LYP calculations have been carried out to assess the fate of the Pd/X group intermolecular exchange in the [PdBr(PH3)(C6H5)(C6H5X)] system, where X is either H, an electropositive atom, or a group such as Li, Na, BH2, AlH2, BeH or BeCH3, and an electronegative atom, or a group such as F, Cl, Br, CH3, OH, and SH. The transfer of H is best viewed as involving the migration of a proton between the two phenyls. At variance with this result, the transfer of the more electropositive entities such as X = Li, Na, BH2, AlH2, BeH, or BeCH3 is not complete. It stops halfway to yield a stable structure in which X can experience interactions with the two phenyl groups that are quite ionic. These stable structures are rationalized through isolobal analogy arguments. In the case of beryllium, the correspondence has been made also with the experimentally known cyclopentadienylberyllium borohydride system, CpBeH4. The results of the DFT geometry optimization call for a re-examination of the gas-phase electron-diffraction structure determination, especially for the bond distances and angles that pertain to the two bridging hydrogens. For the halogen series X = F, Cl, or Br and for the electronegative groups CH3, OH, or SH, the transfer between the two phenyls takes place via a two-step Pd(II)/Pd(IV) oxidative addition/reductive elimination mechanism. The associated energy barriers are nevertheless quite high, except for Br and SH for which the process might be feasible. The dimerization of the PdBr(PH3)(C6H5) system is also analyzed within the isolobal analogy framework.