A crystalline germination stimulant (trivial name strigol) for the rootparasite, witchweed (Striga lutea Lour.), has been isolated from cotton rootexudates and characterized as a C(19)H(22)O(6) compound. Although apparently different from known plant hormones, the stimulant is active at hormonal levels, causing germination at concentrations less than 1O(-5) part per million.

https://science.sciencemag.org/content/sci/154/3753/1189.full.pdf

Germination of Witchweed (Striga lutea Lour.): Isolation and Properties of a Potent Stimulant.

A vibrational and attendant conformational analysis of the liquid n‐paraffins and molten polyethylene is presented. For the purposes of the analysis a valence force field was derived which is applicable to both planar and nonplanar chains. The force field was evaluated from observed frequencies of trans (T) and gauche (G) n‐C4H10; TT and GT n‐C5H12; TTT, GTT, and TGT n‐C6H14; and (T)∞ polyethylene, all of whose infrared spectra were assigned in detail. Infrared spectra of the liquid‐n‐paraffins n‐C4H10 through n‐C17H36 were measured at room temperature and n‐C4H10 through n‐C12H26 also at a temperature just above their melting point. Frequencies and normal coordinates were calculated for the extended forms and for forms having one gauche bond of n‐C4H10 through n‐C8H18. These quantities were also calculated for the conformations of n‐C5H12 through n‐C7H16 having two gauche bonds and for the nonplanar but regular conformations (TG)∞ and (G)∞ of polyethylene. Some bands attributable to forms of n‐C5H12 and ...

Vibrational Study of the Chain Conformation of the Liquid n‐Paraffins and Molten Polyethylene

Fourier transform infrared absorption spectroscopy has been utilized to characterize the structure of porous silica gel films, both deposited on c‐Si substrates and free standing. The films were either dried at room temperature or subjected to partial densification at 400–450 °C. The spectra of the gel films are compared to those of thermal SiO2 grown on c‐Si and to Kramers–Kronig analysis of the reflection spectra of bulk SiO2 gels and v‐SiO2. The gel films show small frequency shifts compared to the latter spectra and they also exhibit new bands due to the presence of OH groups, although very little molecular water or residual organic species were found. The results are interpreted in terms of the gel structure. Compared to the thermal oxide, the sharp peak near 1070 cm−1 is narrower for the gels and the spread in intertetrahedral angles is estimated at 24° and 27° for room temperature dried and partially densified gels, respectively, compared to 33° for the thermal oxide. This is in agreement with a st...

Structural investigation of silica gel films by infrared spectroscopy

There is an increasing awareness that the separation of over-lapping bands by the mathematical technique of curve fitting offers many pitfalls and should not be undertaken lightly. This review discusses critically the various factors involved, with particular reference to vibrational band systems; other types of overlapping band systems encountered in analytical work are considered in less detail. Five parameters are involved: the number of component bands, their positions, shapes and widths, and the form of the baseline. Curve fitting, by a least squares optimization method to a suitable goodness of fit criterion, is considerably facilitated if approximate values for some of the parameters are known at the outset. The methods available for peak finding are discussed and, although not free from problems, are reasonably effective. Similarly, band shapes can usually be defined semiquantitatively. However, it is seldom possible to obtain prior information on band widths; these should be determined during the curve fitting calculations. Although statistical goodness of fit criteria are available they should be used in conjunction with a visual plot, to locate any regions of poor fit. Furthermore, the overriding consideration must always be that the computer fit is plausible in terms of acceptable chemical species for the system being examined.

The Scope and Limitations of Curve Fitting

Temperature dependence of the optical constants for liquid H2O and D2O in the far IR region

Certain types of unsaturated lactones exhibit two bands in the region of the spectrum associated with the C=O stretching vibrational mode. This is observed both in the infrared and Raman spectra.Th...

R.N. Jones

Papers

The carbonyl stretching bands in the infrared spectra of unsaturated lactones

The control of errors in i.r. spectrophotometry—IV. Corrections for dispersion distortion and the evaluation of both optical constants

The control of errors in i.r. spectrophotometry—III. Transmission measurements using thin cells

The control ot errors in infrared spectrophotometry—I the reduction of finite slit distortion by the method of ``pseudo-deconvolution''

The intensities of the infra-red absorption bands of n-paraffin hydrocarbons