Generation of cw 243 nm radiation and application to laser spectroscopy of the strontium isotopes

Intra-cavity second harmonic generation in a ring dye laser using lithium formate monohydrate has been observed to produce tunable cw UV radiation around 243 nm with single frequency powers of up to 1.4 mW. This wavelength region is of particular interest in the context of Doppler-free spectroscopy of atomic hydrogen. The radiation was used to excite an atomic beam of strontium to study the transition 5s^{2 1}S₀-4d5p ¹P₁ of Sr I. The isotope shifts were determined as follows: ⁸⁸Sr-⁸⁷Sr 123.7(8) MHz; ⁸⁸Sr 285.0(8) MHz; ⁸⁸Sr-⁸⁴Sr 600.1(9) MHz. The values are compared with results for other lines and muonic isotope shifts to obtain the specific mass shift and field shift in this transition and to study the configuration mixing effects. The hyperfine structure of ⁸⁷Sr was not resolved, the intervals being very much less than the measured linewidth of 25 MHz.     

A simple route to 1-bromobicyclo[1.1.0]butanes by intramolecular trapping of 1-bromo-1-lithiocyclopropanes

Reaction of the dibromides (5) and (10) with methyl lithium in ether leads to products derived by 1,3-dehalogenation, (6) and (11), whereas (15) and (16) undergo 1,1-dehalogenation and rearrangement to allenes, (17) and (18).     

A new series of potentially hexadentate ligands derived from 2,2′-bipyridine

Reaction of 2,2′-bipyridine-6-carboxaldehyde with the appropriate aliphatic diamine in MeOH and subsequent reduction with NaBH₄ gives the new, potentially hexadentate, ligands N,N′-bis(2,2′-bipyridin-6-ylmethyl)ethane-1,2-diamine (bmet), N,N′-bis(2,2′-bipyridin-6-ylmethyl)propane-1,3-diamine (bmpp) and N,N′-bis(2,2′-bipyridin-6-ylmethyl)hexane-1,6-diamine (bmhx). The syntheses and characterisation of these ligands are reported; the ligands are isolated as the hydrochloride salts, with purification effected by either recrystallisation or cation exchange chromatography. [Co(bmet)](ClO₄)₃ · H₂O is obtained on reaction of bmet · 4.25HCl · 2.5H₂O with Na₃[Co(O₂CO)₃] · 3H₂O, and X-ray structural analysis shows this to have a pair of very short Co–N bonds. The synthesis and characterisation of the first coordination complex containing 6-(aminomethyl)-2,2′-bipyridine (amb) is also described.     

Reactions of π-benzeneruthenium(II) complexes with alkylating reagents

The compounds (π-C₆H₆)Ru(R)Cl(PPh₃) (RCH₃, C₆H₅), (π-C₆H₆)RuCl(π-C₃H₅) and [(π-C₆H₆)Ru(π-C₅H₅)]Cl are described. The ³¹P NMR spectra of a series of tertiary phosphine complexes of the π-benzeneruthenium system are also reported.     

Ionic character

The concept of ionic character in and bond systems is considered in the light of recent definitions of orbital electronegativity [6, 14].

---

Zusammenfassung Das Konzept des ionischen Charakters in und Bindungen wird im Lichte neuerer Definitionen von Orbitalelektronegativitäten diskutiert.

---

Résumé Le caractère ionique des liaisons et est discuté en tenant compte des définitions récentes de l'électronégativité des orbitales.

---

---

We wish to acknowledge financial support from the National Research Council of Canada. One of us (N.C.B.) thanks the council for the award of a studentship.     

Twisted amides inferred from QSAR analysis of hydrophobicity and electronic effects on the affinity of fluoroaromatic inhibitors of carbonic anhydrase.

QSAR has been used to elucidate the origin of the hydrophobicity and binding affinity of a small library of fluoroaromatic inhibitors of F131V carbonic anhydrase II. Our analysis predicted the presence of a twisted amide conformation for several bound inhibitors, which we confirmed crystallographically. We also determined that the hydrophobicity of the inhibitors as a whole results from the fragment hydrophobicities of their fluorobenzyl rings, corrected for field effects and the presence of an intramolecular F.H contact in solution. The loss of this interaction on binding to the enzyme makes the affinity sensitive to the same terms, but with the opposite dependence on the F.H contact. In the case of the four inhibitors bound as twisted amides, this F.H contact must be retained to some extent in the bound state in order for their affinities to be consistent with our QSAR analysis of the entire set of 17 molecules.