An investigation of the structure of butadiene by high resolution infra-red and raman spectroscopy

The rotational Raman spectra of butadiene and butadiene-d₆ are found to consist of discrete lines having small ≈0·4 cm⁻¹) yet almost constant spacings, as would be expected for symmetric or nearly symmetric top molecules. An infra-red absorption band (Type C) of butadiene at 908 cm⁻¹ is observed to have a spacing of about 2·5 cm⁻¹. Both the Raman and infra-red spectra provide evidence for the trans structure of the butadiene molecule. From the rotational constants A″ and ″ the following structural parameters were obtained: C=C---C) = 122·9 ± 0·5° rC---C) = 1·47₆ ± 0·010 Å dy]somewhat shorter than recently determined from electron-diffraction experiments).     

CHEMICALLY MODIFIED PHOTOSYNTHETIC BACTERIAL REACTION CENTERS: CIRCULAR DICHROISM, RAMAN RESONANCE, LOW TEMPERATURE ABSORPTION, FLUORESCENCE AND ODMR SPECTRA AND POLYPEPTIDE COMPOSITION OF BOROHYDRIDE TREATED REACTION CENTERS FROM Rhodobacter sphaeroides R26

Abstract— Reaction centers from Rhodobacter sphaeroides have been modified by treatment with sodium borohydride similar to the original procedure [Ditson et al., Biochim. Biophys. Acta 766 , 623 (1984)], and investigated spectroscopically and by gel electrophoresis.
(1) Low temperature (1.2 K) absorption, fluorescence, absorption- and fluorescence-detected ODMR, and microwave-induced singlet-triplet absorption difference spectra (MIA) suggest that the treatment produces a spectroscopically homogeneous preparation with one of the 'additional' bacteriochlorophylls being removed. The modification does not alter the zero field splitting parameters of the primary donor triplet (^TP870).
(2) From the circular dichroism and Raman resonance spectra in the1500–1800 cm^-1 region, the removed pigment is assigned to Bchl_M, e.g. the "extra" Bchl on the "inactive" M-branch.
(3) A strong coupling among all pigment molecules is deduced from the circular dichroism spectra, because pronounced band-shifts and/or intensity changes occur in the spectral components assigned to all pigments. This is supported by distinct differences among the MIA spectra of untreated and modified reaction centers, as well as by Raman resonance.
(4) The modification is accompanied by partial proteolytic cleavage of the M-subunit. The preparation is thus spectroscopically homogeneous, but biochemically heterogenous.     

The preparation and characterisation of dichloro(1,2,4-trithia-3-azabut-2-ene)gold(III), AuCl2(S3N)

Deprotonation of heptasulphurmonoimide at −78°C using BuLi followed by reaction with HAuCl₄ yields AuCl₂(S₃N), in moderate yield (21%), characterised by IR/Raman and UV/Vis spectroscopies.     

Selective suppression of some radical reactions by iron pentacarbonyl

Conclusions On the example of the homolytic reaction of methallyl chloride with CCl₄ it was found that iron pentacarbonyl in catalytic amounts can selectively suppress the radical process involving chlorine atoms, and at the same time it catalyzes the chain reaction with trichloromethyl radicals, which act as carriers of the kinetic chain.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2320–2322, October, 1972.     

Electronic structures and MCD spectra of trigonal Cr(III)S6 systems

MCD, electronic absorption, external heavy atom, and crystal field data are presented for the low energy region (² E _g, ² T _1g, ⁴ T _2g) and high energy region (² T _2g, ⁴ T _1g) of Cr(dtp)₃, Cr(dtc)₃, and Cr(exan)₃. At low energy, MCD intensities of ² E(² E _g) and ² E(² T _g) are as large or larger than ⁴ T _2g, and the MCD technique is advantageous over electronic absorption in this respect. The MCD positions of ² E _g and ² T _1g are nearly the same for these molecules ( 13 kK and 13.6 kK) · ⁴ T _2g of this region appears trigonally split ( 500 cm^–1) in the MCD of dtp but to a smaller extent than in the electronic crystal spectrum of Lebedda and Palmer ( 600 cm^–1). MCD did not resolve such components for exan and dtc. The higher energy region includes ² T _2g and ⁴ T _1g, and the combined MCD and electronic absorption data of the three compounds taken together lead us to conclude the ordering ² A ₁(² T _2g)<² E(² T _2g)<⁴ E(⁴ T _1g). The potentially useful external heavy atom affect on the solution-observed electronic ² E and ⁴ E bands of Cr(dtp)₃ did not shed additional light on this order of E states. Finally, it is concluded that the order of ⁴ T _1g and ² T _2g cannot be decided from O _h crystal field calculations because of experimental uncertainties about choosing centers of gravity. In addition, ⁴ T _1g and ² T _2g are close together so that ordering ² E<⁴ E does not guarantee ² T _2g<⁴ T _1g. However, it can be concluded that the ratio C/B4 is not correct, whereas the larger 7<(C/B)<8 is consistent with the data of all three molecules because of small B parameters ( 0.4). Locating OO transitions may somewhat decrease C/B and Dq.

---

Zusammenfassung In der vorliegenden Arbeit werden folgende Meßergebnisse mitgeteilt; MCD, elektronische Absorption, Einfluß eines äußeren schweren Atoms sowie Kristallfelddaten für den Bereich niedriger Energie (² E _g, ² T _1g, ⁴ T _2g) und den Bereich hoher Energie (² T _2g, ⁴ T _1g) von Cr(dtp)₃, Cr(dtc)₃ und Cr(exan). Bei niedriger Energie sind die MCD-Intensitäten von ² E(² E _g) und ² E(² T _1g) genau so groß, oder größer als ⁴ T _2g, und die MCD-Technik bietet Vorteile gegenüber der elektronischen Absorptionsmethode. Die MCD-Werte von ² E _g und ² T _1g sind für die genannten Moleküle etwa gleich ( 13 kK und 13,6 kK). ⁴ T _2g dieses Gebietes erscheint trigonal aufgespalten ( 500 cm^–1) bei MCD von dtp, aber in einem geringeren Maß als im elektronischen Kristallspektrum von Lebedda und Palmer ( 600 cm^–1) MCD löste solche Komponenten bei exan und dtc nicht auf. Der Bereich höherer Energie enthält ² T _2g und ⁴ T _1g, und aus der Kombination von Daten der MCD-Methode sowie der elektronischen Absorption schlossen wir auf die Anordnung ² A _1g(² T _2g)<² E(² T _2g)<⁴ E(⁴ T _1g). Der möglicherweise nützliche Effekt eines äußeren schweren Atoms auf die in Lösung beobachteten elektronischen ² E- und ⁴E-Banden von Cr(dtp)₃ brachte bezüglich dieser Anordnung der E-Zustände nichts Neues. Weiterhin wird gefolgert, daß die Ordnung von ⁴ T _1g und ² T _2g nicht aus O _h-Kristallfeldberechnungen entschieden werden kann, da experimentelle Unsicherheiten bezüglich der Wahl von Schwerpunkten bestehen. Außerdem liegen ⁴ T _1g und ² T _2g nahe zusammen, sodaß aus der Anordnung ² E<⁴ E nicht notwendig ² T _2g<⁴ T _1g folgt. Es kann jedoch gefolgert werden, daß das Verhältnis C/B4 nicht korrekt ist, während 7<(C/B)<8 konsistent mit den Daten aller drei Moleküle ist, da die B-parameter klein sind (0,4). Die Vokalisierung der OO-Übergänge könnten C/B und Dq etwas erniedrigen.

---

---

Presented in part at the 161st American Chemical Society National Meeting, Los Angeles, California, March–April, 1971.

---

NDEA Pre-Doctoral Fellow.     

Synthesis of peptides based onβ-(N1-uracilyl)-α-alanine

The synthesis of peptides which include a DL--(N₁-uracilyl)--alanine (DL-willardiine) residue as an N-terminal or C-terminal group was investigated, dipeptides of DL-willardiine with glycine and L-tyrosine were obtained, and DL-willardiyl-DL-willardiine was synthesized; the latter is the simplest representative of the family of monotonic homopeptides which contain, as a repeating side substituent, a natural nucleic base capable of participation in intermolecular interactions of the complementary type.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 404–408, March, 1971.