PhB

Poly-P-hydroxybutyrate (PHB) is a biodegradable thermoplastic that is produced by several microorganism. The PHB synthesis has been characterized eutrophus and the operon iavolved ia PHB productioa has beea cloaed. Recombiaant E. coli straias that can produce high levels of... 

Fig. 22. Photochemical hole burning (PHB) (1,173) where CO is frequency CO, frequency of the laser and CO p, frequency of the photoproduct.

Another possible advantage of the PHB method is its potential multiplexing characteristics by synchronous recording and read-out, exceptional data transfer rates can be achieved. These high transfer rates are of equal importance in practical data technology as high storage densities. 

An interesting development of the PHB technique leads to four-dimensional data storage. By variation of an electric field appHed to the sample the spectral profile of the absorption holes can specifically be altered. This adds two more dimensions to the geometrically two-dimensional matrix frequency of laser light and electrical field strength (174). 

A great disadvantage of PHB is the necessity to operate at very low temperatures (<20 K). Therefore, this recording technique currently has no practical significance but it is subject to intensive research activity (175). One future aspect which may be important, if room temperature materials become available, is the usage of inexpensive semiconductor lasers in the near ir-regime (176). 

Materials. Beside inorganic materials (eg, barium chloride/fluoride crystals, doped with 0.05% samarium), transparent thermoplasts are preferred for the PHB technique, eg, poly (methyl methacrylate) (PMAIA), polycarbonate, and polybutyral doped with small amounts of suitable organic dyes, organic pigments like phthalocyanines, 9-arninoacridine, 1,4-dihydroxyanthraquinone [81-64-1] (quinizarin) (1), and 2,3-dihydroporphyrin (chlorin) (2). 

Current research aims at high efficiency PHB materials with both the high speed recording and high recording density that are required for future memory appHcations. To achieve this aim, donor—acceptor electron transfer (DA-ET) as the hole formation reaction is adopted (177). Novel PHB materials have been developed in which spectral holes can be burnt on sub- or nanosecond time scales in some D-A combinations (178). The type of hole formation can be controlled and changed between the one-photon type and the photon-gated two-photon type (179). 

New PHB materials are composed of Zn-tetraben2oporphyrin—aromatic cyanide—poly (methyl methacrylate) (180) or of tetraphenylporphyrin derivatives dispersed in polymer matrices such as PMMA and polyethylene (181). A survey of such materials has been given (181). 

Shenoy, U. V. (1995). Heat Exchange Network Synthesis Process Optimization by Energy and Resource Analysis. Gulf Phb. Co., Houston, TX. 

PhB(OH)2, PhH or Pyr. A polymeric version of the phenyl boronate has been developed.Phenyl boronates are stable to the conditions of stannyla-tion and have been used for selective sulfation to produce monosulfated monosaccharides. Phenyl boronates were found to be stable to oxidation with pcc ... 

It is well-known that para substituents on the phenyl groups of H2TPP have no influence on the tautomerism rates in the ground state (see Section III,A,1). In the case of PHB, there seems to be only a small substituent effect on <1>phb (the quantum efficiency for hole burning) through modification of the relative energy of Ti (93CM366). 

PBT - polybutylene terephthalate PDMS - polydimethyl siloxane rubber PE - polyethylene PET - polyethylene terephthalate PHB - poly[D(-)]-3-hydroxy butyrate PP - polypropylene... 

Tests by Gatenholm et al. [8,10] on PHB-HV copolymers containing cellulose fibers (for example, the tradenamed Biopol) show that the mechanical properties of these systems are determined by the fiber and the fiber matrix interface on the one hand, and on the other hand by the composition of the matrix, that is, of HV proportion in the matrix. At an increased proportion of HV, the stiffness of the composite is reduced up to 30%, whereas elongation at break increases until about 60%. 

PHB Hagler Bailly, Itic., Washington, DC Coal, Transportation and Storage of (with Jamie N. Heller)... 

The lithium cnolate generated by deprotonation of 2-/m-butyl-6-methyl-l,3-dioxan-4-onc, readily available from polyhydroxybutyric acid (PHB), predominantly affords the diastereo-mers 7 when reacted with aldehydes. The diastereomeric ratios of aldol adducts 7/8, produced by reactions with aliphatic aldehydes, range from 87.5 12.5 to >99 1. Pure diastereoiners7are obtained by recrystallization in 25-74% yield116-118. Only marginal diastereoselectivities with respect to the carbinol center are obtained with aromatic aldehydes111-119. Benzoylation of the dioxanones 7, followed by reduction with lithium aluminum hydride, affords enan-tiomerically and diastereomerically pure triols 9 in >85% yield 11. ... 

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