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Biodegradable amphiphilic PLGA–PEG–PLGA triblock copolymers end-terminated with itaconic acid (ITA) having reactive double bond were end-linked by light and swelled in water. Hydrolytical stability of prepared hydrogels was evaluated.

15N NMR chemical shifts of 40 tertiary and quaternary isoquinoline alkaloids of six constitutional types are reported. The selected compounds belong to the classes of benzo[c]phenanthridine, protoberberine, benzylisoquinoline, aporphine, pavinane, and β‐carboline‐proaporphine alkaloids. The 15N chemical shifts were measured by gradient‐enhanced inverse‐detected single‐quantum (GSQMBC) and multiple‐quantum (GHMBC) multiple‐bond correlation experiments. The 1H–15N long‐range coupling constants determined from the phase‐sensitive GSQMBC spectra are also reported in order to facilitate optimization of multiple‐bond correlation experiments. Copyright © 1999 John Wiley & Sons, Ltd.

Samples of 1,3- (1) and 1,5-dicaffeoylquinic acid (2) and their hexaacetate derivatives were examined using positive and negative electrospray ionization mass spectrometry and tandem mass spectrometry. Differences in the various spectra allow the discrimination of each of the isomers. Specific losses in the spectra of 2 also permit the identification of the site of substitution of one of the caffeic acid moieties as being at the 5-position. The spectra of 3,5- (3) and 4,5-dicaffeoylquinic (4) acids and their hexaacetate derivatives were compared with those of 1 and 2 and their derivatives, and differences in ion abundances or the presence/absence of specific ions can be used to identify uniquely each of the compounds.

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The (1)H and (13)C NMR resonances of 16 purine glucosides were assigned by a combination of one- and two-dimensional NMR experiments, including gs-COSY, gs-HSQC, and gs-HMBC, in order to characterize the effect of substituent and the position of glucose unit on the NMR chemical shifts. In addition, (15)N NMR chemical shifts for selected derivatives were investigated by using (1)H-(15)N chemical shift correlation techniques. To map the influence of sugar moiety on the directly bonded nitrogen atom, selected N(9)-glucosides and their ribose analogs were compared. Characteristic long-range (1)H-(15)N coupling constants, measured by using (1)H-(15)N gradient-selected single-quantum multiple bond correlation (GSQMBC), are also reported and discussed. All compounds investigated here belong to cytokinins, an important group of plant hormones.

The specific retention volumes are reported of several alkane solutes on five poly(methy1phe-nylsiloxane) (PMPS) stationary phases with different methyllphenyl proportions at temperatures within 30-95 OC. The amounts of polymers in the columns employed have been determined by elemental analysis of the column packings. The methyl/phenyl proportions in the siloxane polymers have been obtained by NMR spectrometry. The activity coefficients and interaction parameters of the solutes at infinite dilution in the PMPS samples have been calculated from the specific retention volumes. From the activity coefficients and interaction parameters, the partial molar excess enthalpies of the solutes (hHIEm) and the polymer solubility parameters (62) have been obtained. The effects of temperature and polymer composition on the values of alEm and 62 are discussed.