Direct chlorination of 1-CH(3)-CB(11)H(11)(-) in glacial acetic acid gave the highly chlorinated carborane anion 1-CH(3)-CB(11)Cl(11)(-), and treatment of 1-CH(3)-CB(11)H(11)(-) with ICl in triflic acid afforded the highly iodinated carborane anion 1-CH(3)-CB(11)I(11)(-). Under similar or more vigorous reaction conditions, however, the reaction of 1-CH(3)-CB(11)H(11)(-) with Br(2) in triflic acid did not proceed to completion. The highly brominated carborane anion 1-CH(3)-CB(11)Br(11)(-) was achieved via a sealed-tube reaction. This new method has led to the isolation of 1-H-CB(11)X(11)(-) (X = Cl, Br, I) and 1-Br-CB(11)Br(11)(-) in high yield. The lithiation of 1-H-CB(11)X(11)(-) resembles that of its parent anion CB(11)H(12)(-). Treatment of these lithio species with methyl iodide gave the methylated carborane anions 1-CH(3)-CB(11)X(11)(-). These new weakly coordinating anions were fully characterized by (1)H, (13)C, and (11)B NMR, IR, and negative-ion MALDI MS spectroscopy. Some were further confirmed by single-crystal X-ray analysis.

We report a simple method for converting solid matrices into useful matrix solutions for matrix-assisted laser desorption/ionization (MALDI). This method is based on the dissolution of the solid matrix in a liquid support of low volatility such as glycerol. An appropriate solubilizing reagent was added to promote the dissolution of the matrix materials into the liquid support. Selection of the solubilizing reagent is empirically related to an acid-base relationship, i.e., an acidic solid matrix requires a basic organic compound to form a stable matrix solution in the liquid support and vice versa. A tenfold increase in the solubility can be obtained for many solid matrices when appropriate solubilizing reagents are added into the glycerol support. This solubility enhancement is tentatively attributed to the ion-pair formation in a polar nonvolatile liquid support. In addition, the hydrophobicity of the solid matrix seems to play an important role in the efficiency of the resulting matrix solution. By using glycerol as liquid support, a hydrophilic matrix, such as 2,5-dihydroxybenzoic acid (DHB), showed a substantial "peripheral effect," in which good analyte ion signals could only be recorded at the peripheral region of the sample droplet. More hydrophobic matrices, such as alpha-cyano-4-hydroxycinnamic acid (alpha-CCA), exhibit better and more homogeneous responses at different regions of the droplets. The performance of these matrix solutions was evaluated in terms of the durability, reproducibility, sensitivity, high mass capability, and generality. A typical sample droplet can afford more than an hour of repeated sampling with excellent shot-to-shot reproducibility. A low picomole sensitivity was demonstrated using a luteinizing hormone releasing hormone (LHRH) in a Fourier transform ion cyclotron resonance mass spectrometer with a homemade external MALDI ion source. By using a commercial MALDI time-of-flight mass spectrometer, proteins with masses as high as 66,000 Da were successfully analyzed by using these matrix solutions.

Mixed halocarborane anions, 1-H-CB11Y5X6- (X, Y = Cl, Br, I), have been prepared by treatment of [Me3NH][1-H-CB11H5X6] (X = Cl, Br, I) with proper halogenating reagents at 180-220 degrees C in a sealed tube in high yield. These new anions are fully characterized by 1H, 13C, and 11B NMR, IR, and negative-ion MALDI MS spectroscopy. Some are further confirmed by single-crystal X-ray analyses. The weakly coordinating nature of these anions is probed by 29Si chemical shifts of the resulting Pri3Si(1-H-CB11Y5X6) compounds. The results suggest that the coordinating ability of these anions is mainly dependent on the substituents at 7-12 positions (namely, X atoms), and the contribution from the upper belt substituents Y is relatively small. These suggestions are consistent with the results obtained from the structural study of silver salts of mixed halo- and perhalocarborane anions.

The highly chlorinated, brominated, and iodinated carborane anions 1-R-CB9X9- (R = H, NH2; X = Cl, Br, I) were prepared in high yields by treatment of [Me3NH][1-R-CB9H9] with excess ICl, Br2/triflic acid, and I2/triflic acid, respectively, in sealed tubes at 180-240 degrees C. With the aid of a Pd catalyst, B-I bonds could be converted into the B-Me bonds by treatment with excess MeMgBr, which led to the preparation of the permethylated species 1-H-CB9Me9- in good yield. These new anions were fully characterized by 1H, 13C, and 11B NMR, IR, and negative-ion MALDI MS spectroscopy. Some were further characterized by single-crystal X-ray analyses. The weakly coordinating nature of these new anions was probed by 29Si chemical shifts.

In contrast to an isolated molecule with identical geometry, the electron density of a molecule in the crystalline solid state is influenced by the field of surrounding molecules and by intermolecular hydrogen bonding. These influences have not yet found wide study on the level of the molecular electron-density distribution, which can be obtained both from high-resolution X-ray single-crystal diffraction as well as from ab initio quantum chemistry. To investigate this 'crystal-field effect' on the non-standard amino acid l-homoserine, three approaches were taken: (i) an ab initio point-charge isolated-molecule model; (ii) structure refinement with Hirshfeld atoms with and without surrounding point charges and dipoles; (iii) benchmark periodic calculations using density functional theory. For (i) and (iii) multipole models were fitted to static structure factors. The difference between the electron density obtained from the respective in-crystal model and from the isolatedmolecular calculations yields detailed information on the crystal-field effect and dipole-moment enhancements. The point-charge model produces features of interaction density which are in good agreement with those from periodic ab initio quantum chemistry. On the other hand the multipole model is unable to reproduce fine details of the interaction density for zwitterionic homoserine.