New Structures

Reviews published include a summary of progress in the chemistry and biology of fat-soluble vitamins and carotenoids over the past 10 years, chapters on carotenoids and hormones in filamentous fungi, and a survey of ionones, irones, and their derivatives in Nature.  

New Structures.—The Key to Carotenoids lists all carotenoids found in Nature up to the middle of 1975, and gives extensive references to occurrence and physical, chemical, and spectroscopic properties. An outline of work on the eluci- 

---

We describe here a new structure representation which extends the valence bond concept by new bond types that account for multi-haptic and electron-deficient bonds. This representation is called Representation Architecture for Molecular Structures by Electron Systems (RAMSES) it tries to incorporate ideas from Molecular Orbital (MO) Theory [8T]. 

The trained counterpvopagation network is then able to predict the spectrum for a new structure when operating as a look-up table (see Figure 10.2-9) the encoded query or th.c input structure is input into the trained network and the winning neuron is determined by considering just the upper part of the network. The neuron points to the corresponding neuron in the lower part of the network, which then provides the simulated IR spectrum. 

Ch aracteri/e a poten tial en ergy m in im u m. A geom etry optim i-zalioti results in a new structure at a m in itn urn. You can examine atomic coordinates and energy of this slruetiire. 

Characterize a potential energy maximum along the reaction coordinate, fransition state searching results in a new structure. You can exam in e the atom ic coordin ates and en ergy of th is structure. 

In a systematic search there is a defined endpoint to the procedure, which is reached whe all possible combinations of bond rotations have been considered. In a random search, ther is no natural endpoint one can never be absolutely sure that all of the minimum energ conformations have been found. The usual strategy is to generate conformations until n new structures can be obtained. This usually requires each structure to be generate many times and so the random methods inevitably explore each region of the conformc tional space a large number of times. 

Keeping the same atomic connections and moving only electrons write a more stable Lewis structure for each of the following Be sure to specify formal charges if any in the new structure... 

In the search for new structures with antiinflammatory activities some 1-substituted 3-dimethylaminoalkoxy-lJ/-indazoles (704) have been synthesized and pharmacologically tested (66JMC38). Doses of 20-40 mg g i.p. produced sedation, muscle relaxation and motor incoordination, whereas doses of 80-100 mg kg produced depression. Toxicity was fairly constant in all series, varying from 120 to 150 mg kg i.p., with the exception of compounds possessing a nitro group or an amino group in the indazole nucleus, which provoked cyanosis. 

At room temperature, diffusion is so slow that the alloy just stays like this, frozen as a single phase. But if you heat it up just a little - to 160°C, for example - and hold it there ("ageing"), the copper starts to diffuse together to form an enormous number of very tiny (nm) plate-like particles, of composition roughly CuAlj. On recooling to room temperature, this new structure is again frozen in. 

Early diffraction photographs of such DNA fibers taken by Rosalind Franklin and Maurice Wilkins in London and interpreted by James Watson and Francis Crick in Cambridge revealed two types of DNA structures A-DNA and B-DNA. The B-DNA form is obtained when DNA is fully hydrated as it is in vivo. A-DNA is obtained under dehydrated nonphysiological conditions. Improvements in the methods for the chemical synthesis of DNA have recently made it possible to study crystals of short DNA molecules of any selected sequence. These studies have essentially confirmed the refined fiber diffraction models for A- and B-DNA and in addition have given details of small structural variations for different DNA sequences. Furthermore, a new structural form of DNA, called Z-DNA, has been discovered. 

Wilson, I.A., 5tanfield, R.L. Antibody-antigen interactions new structures and new conformational changes. 

Several programs are now available that use multiple alignment of homologous proteins for prediction of secondary structure. One such program, called PHD, which was developed by Chris Sander and coworkers, EMBL, Heidelberg, has reached a mean accuracy of prediction of 72% for new structures. 

The problems at the end of each chapter represent application of concepts to new structures and circumstances, rather than review of material explicitly presented in the text. The level of difficulty is similar to that of earlier editions, and we expect that many will present a considerable challenge to students. Some new problems have been added in this... 

As in any new field, new structures demand novel names. As the variety of structures has increased, the names have kept pace. Although some may be dismayed by this, the different names connote not only different structural types or functional groups, but conceptual differences among the various classes as well. In order to introduce the novitiate and perljaps remind the journeyman, we provide a few definitions and explanations herewith. 

The maximum displacement is the largest change in any coordinate in the molecular strucmre. The threshold column indicates the cutoff value for each criterion. The new structure generated at this step follows this ou ut. 

Lnpas, A., 1996. Coiled coils New structures and new functions. Trends in Biochemical Sciences 21 375—382. 

Cramer, W. A., et al., 1996. Some new structural aspects and old controversies concerning die cytochrome b /complex of oxygenic photosyndie-... 

Indeed, this is perhaps the earliest example of a new structural species to be established by Raman spectroscopy. (L. A. Woodward, Phil. Mag. 18, 823-7 (1934).)... 

Once we had provided the background data up to 1976, it seemed logical to keep the series current by adding discussion of newer agents. Reports of drugs for new indications as well as the occurrence of brand-new structural types as drugs made it particularly important to update the existing volumes. The five-year cycle for preparation of new volumes represents a compromise between timeliness and comprehensiveness. A shorter period would date earlier entries. This volume thus covers compounds reported up to 1982. 

---