On the history of photoemission

Historical aspects of science are usually confined to special conferences, and receive only a brief mention in the introduction to talks at meetings addressing current topics. However, at the previous Seminar, several theoretical and experimental contributions were made, which discussed the historical development of surface science. Because of the considerable interest aroused by these presentations, we decided to keep the historical spirit alive, by telling the story of photoemission.

While field emission is the oldest area of surface science, photoemission is certainly one of the most important branches. Here, emphasis is placed on the early investigations, which are often scarcely mentioned, and on more recent work that has had significant impact on the progress of surface science.     

Cis-trans-isomerization of cationic-anionic polymethine dyes

The effect of solvent polarity and ion pair formation oncis-trans-isomerization of cationic-anionic polymethine dyes and of related simple cationic and anionic dyes is studied by flash photolysis. The change in the rate constant for reversecis-trans- isomerization of photoisomers due to the interaction of a cation with an anion in an ion pair is observed in nonpolar solvents. A drop in the yield of the photoisomers to zero is observed for a number of cationic-anionic dyes in weakly polar and nonpolar solvents which is possibly due to steric hindrances in the photoisomerization process in ion pairs.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 719–724, April, 1993.     

Zur photometrischen Aktivit?tsbestimmung von Actinomycin C

Zusammenfassung Es wurde festgestellt, daß die Farbe einer Actinomycin C-Lösung in sehr engem Zusammenhang mit der Konzentration dieser Substanz in der Lösung steht. Die photometrisch ermittelte Farbabnahme geht mit dem durch mikrobiologischen Test bestimmten Aktivitätsverlust in vieler Hinsicht parallel. Bei der Aktivitätsabnahme spielt die Art des Lösungsmittels eine wichtige Rolle. Die stärkste Aktivitätsminderung nach dem Erhitzen wurde in bidest. Wasser, die geringste Aktivitätsabnahme in Glykokollpuffer beobachtet.

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Summary The concentration of active actinomycin C in a solution can be determined quite simply by a photometric method. Comparison of results showed good agreement between the microbiological tests and the photometric method. Actinomycin C suffers most loss of activity by heating when dissolved in distilled water and least when dissolved in glycine buffer.

     

Rotational band crossings in the actinides

In the actinides bothi _13/2 protons andj _15/2 neutrons are close to the Fermi surface. At rapid rotation these high-j particles will unpair and align their orbital angular momentum along the axis of rotation giving rise tos-bands that cross the ground-state band. Coulomb excitation of the odd nuclei ₂₃₇ ⁹³ Np (established up to the 45/2⁺ state) and ₂₃₅ ⁹² U (established up to the 51/2^? state) provides specific information about these band crossings: From the saturating alignment of the odd high-j particle in both nuclei at intermediate rotational frequencies we find the aligned angular momentum of thei _13/2 protons-band to be 6.6? while the corresponding value for thej _15/2 neutrons-band is 5.5?. At more rapid rotation above ?ω=0.18 MeV we observe additional alignment in²³⁵U. This is ascribed to the interaction of the protons-band. From the gradual onset of the additional alignment we deduce that forZ=92 the protons-band interacts strongly with the ground-state band and from a comparison of the actual amount of alignment with the full value of 6.6? we estimate the crossing to occur around ?gw _c ^p =0.25 MeV.     

Composition of the neutral fraction of the oleoresin ofPinus sibirica

Summary Three sesquiterpene hydrocarbons, muurolene-1, muurolene-2, and muurolene-3, have been isolated from the oleoresin ofPinus sibirica R. Mayr.Muurolene-3 is D--muurolene and has the structure (VIII).Khimiya Prirodnykh Soedinenii, Vol. 2, No. 3, pp. 173–176, 1966     

Benzoid-quinoid tautomerism in azomethines and their structural analogs. 46. Synthesis and reactions of 2-(N-isatinomethylene)-3(2H)-benzo[b]thiophenone

Electronic, IR and UV spectroscopy has shown that 2-(N-isatinomethylene)-3(2H)-benzo[b]thiophenone in solution displays photo- and solvatochromism as a result of reversible E Z isomerization, and it readily undergoes alcoholysis of the lactam bond. The resulting aminovinyl ketones exist as mixtures of the thermodynamically stable E- and Z-isomers.For Communication 45, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1217–1220, September, 1989.     

LiBF4-Catalyzed three-component coupling of an aldehyde, acetic anhydride and allyltrimethylsilane/TMSCN

Lithium tetrafluoroborate is found to be an efficient catalyst for allylation and cyanation of aldehydes with allyltrimethylsilane and trimethylsilyl cyanide in the presence of acetic anhydride at room temperature to produce homoallylic acetates and α-cyano acetates in excellent yields. A solution of 10 mol % of LiBF₄ in acetonitrile provides a convenient reaction medium to carry out allylation and cyanation reactions under very mild and neutral conditions.     

Systems Tl2MoO4-E(MoO4)2, where E = Zr or Hf, and the crystal structure of Tl8Hf(MoO4)6

Systems Tl₂MoO₄-E(MoO₄)₂ (E = Zr, Hf) are studied using X-ray powder diffraction, DTA, and IR spectroscopy. Compounds Tl₈E(MoO₄)₆ and Tl₂E(MoO₄)₂ are found in these systems. T-x diagrams for the Tl₂MoO₄-Zr(MoO₄)₂ system are designed. Single crystals are grown and structure is solved for Tl₈Hf(MoO₄)₆. The compound crystallizes in a monoclinic structure with the unit cell parameters a = 9.9688(6) Å, b = 18.830(1) Å, c = 7.8488(5) Å, β = 108.538(1)°, Z = 2, space group C2/m. The main structural fragment is a [HfMo₆O₂₄]^8? isle group. Three crystallographically independent types of Tl polyhedra uniformly fill spaces between [HfMo₆O₂₄]^8? fragments to form a three-dimensional framework.     

Die Konstitution von Roridin D. Verrucarine und Roridine, 12. Mitteilung

The antibiotic roridin D (C₂₉H₃₈O₉), a companion of roridin A, yields on base catalysed hydrolysis verrucarol ( 3 ) and the hitherto unknown 2, 3-epoxy-2-anhydrororidinic acid ( 4 ) (C₁₄H₁₈O₇). Roridin D is a macrocyclic diester to which structure 1 is assigned. In roridin D an epoxy group replaces the hydroxyl group of roridin A.     

Stereochemistry of Macrocyclization of cis-4-Cyclohexene-1,2-dicarboxylic Acid with Dihalogen Derivatives

Stereochemistry of [2+2]- and [1+1]-macrocylization of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,2-dibromoethane, 1,3-dichloro-2-propanol, and 1,5-dichloro-3-oxapentane was studied. The reaction of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,2-dibromoethane according to the [2+2]-cyclization scheme gave a mixture of stereoisomeric macroheterocycles with cis,syn,cis- and cis,anti,cis-junction of the polyether and cyclohexene rings. In the reaction of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,5-dichloro-3-oxapentane, a mixture of crown compounds with cis,anti,cis- and cis-junction of the polyether and cyclohexene rings was obtained. The structure of the products was established on the basis of their chemical transformations and spectral data.