Tailored Polymeric Materials for Controlled Delivery Systems

Chapter 24

Structural Characterization and Effects of Gibberellic AcidContaining Organotin Polymers on Sawgrass and Cattail Germination and Seedling Growth for Everglades Restoration 1,2

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Charles E. Carraher, Jr. , Anupam Gaonkar , Herbert H. Stewart , Shi Li Miao , and Shawn M. Carraher

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 16, 2015 | http://pubs.acs.org Publication Date: September 24, 1998 | doi: 10.1021/bk-1998-0709.ch024

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Departments of Chemistry and Biological Sciences, Florida Atlantic University, Boca Raton, FL 33431 Florida Center for Environmental Studies, NorthCorp Center, Palm Beach Gardens, FL 33410 Everglades System Research Division, South Florida Water Management District, West Palm Beach, FL 33406 Department of Management and Finance, Indiana State University, Terre Haute, IN 47809 2

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The Florida Everglades is undergoing rapid change with much of the change associated with displacement of sawgrass by cattail. A major part of the Everglades restoration involves the growth of sawgrass plants from seeds. Polymers containing gibberellic acid, GA3, were synthesized from reaction with diorganotin dichlorides. Structural analysis emphasizing mass spectroscopy and infrared spectroscopy are consistent with the products containing tin-oxygen bonds. Through the use of GA3 and polymers containing the GA3 moiety, the percentage germination was increased from about 2-4% to 4-19% and the time required for germination decreased from about 4 weeks to 10-21 days.

The Florida Everglades is called the "River of Grass". The "grass" is actually a sedge called sawgrass (Cladium jamaicense Crantz). The Everglades is a subtropical,freshwaterwetland ecosystem that is about 180 miles long and 90 miles wide. It is dominated by monospecific sawgrass marshes that historically covered about 70% of the land (1,2). It is undergoing rapid change with sawgrass being displaced by cattail (mainly Typha domingensis Pers.). For instance, in Water Conservation Area 2A, located in the heart of the northern Everglades with about 45,000ha cattail dominated about 2,000ha, in the early 1980's. In 1992 this was increased to over 7,000 ha and the cattail dominance is continuing to spread (3-6). Various legislative mandates have recognized the need to halt the recent changes and to re-establish the Everglades as an ongoing, self sustaining and healthy ecosystem (for instance Douglas Act-Chapter 373.4592 and Everglades

©1998 American Chemical Society

In Tailored Polymeric Materials for Controlled Delivery Systems; McCulloch, I., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

295


296 Forever Act-Chapter 94-115). A major part of this restoration involves the "River of Grass". The natural re-establishment of sawgrass after soil disturbances (such as fire) is known to be difficult (7). One of the difficulties of re-establishing sawgrass is their low seed germination (for instance 7,8). Seed germination has only rarely been observed in the field (7). Both sawgrass and cattail replicate through rhizome development and seeds. Reproduction through seeds allows the retention of genetic diversity that is important in the Everglades since the Everglades is a system of extremes where adaptability is a necessary feature for long term survival. The successful transplanting of sawgrass plants into the Everglades has been reported (9). Sawgrass seed germination is a critical part of the restoration of the Everglades either through growth of plants under controlled conditions and their subsequent introduction into the Everglades or through aerial (or other) dispersion of seeds. The latter is lower cost and offers the ability to cover large areas of space at a relatively low cost. In both cases, creation of conditions that favor sawgrass germination is advantageous. The current study is part of a major undertaking aimed at stabilizing and re establishing the Everglades. One of the areas of study involves the treatment of sawgrass seeds in an attempt to increase their germination percentage. Seed treatments are a common practice in the seed industry. One of the major reasons for seed treatments is to increase seed germination mainly through seed protection and/or germination enhancement. The present report involves germination enhancement through treatment of seeds with plant growth regulators. Plant growth regulators, PGRs, have been divided into groups-auxins (such as indole-3-acetic acid), cytokinins (including kinetin, zeatin, zeatin riboside and benzyladenine), gibberellins, ethylene and abscisic acid; and ancillary compounds such as polyamines (such as putrescine, spermidine and spermine) and phenolics. Here, we will focus our attention on gibberellins. Gibberellins are cyclic diterpenes with the ability to induce a number of plant responses including cell elongation and cell division. While they are widespread in nature only a few have been shown to be active and only one, called gibberellic acid or GA3, is commercially available. In general, controlled release formulations can offer •longer "shelf life" and •sustained release For the present study, the controlled release polymer can offer •greater retention of the active agent due to the lowered solubility of the polymer and •the "co-reactant" can offer additional properties such as antifungal activity. Each of these advantages can result in a greater activity with less active agent and by-products in the environment. A "by-product" from the current work is the evaluation of the ability of the polymer to "deliver" through hydrolysis (or other mechanism) the active agent, here GA3. While there are a large number of gibberellins, only one of these,



297 gibberellic acid, has found commercial application and almost all of the other gibberellins are inactive. GA3 is known to play a key role in the germination of most seeds. The most direct effect is in inducing the expression of the gene for a-amylase in germinating seeds (for instance 12). As seen, the polymer is active in regulating the germination and growth of both cattail and sawgrass seeds similar to but not the same as GA3 itself. This is consistent with an active moiety, presumably GA3 itself, being released through either enzymatic or physical hydrolysis of the polymer. The present paper describes the structural characterization of the products emphasizing the product derivedfromthe reaction of GA3 and diorganostannane dichlorides. Further, preliminary seed germination and seedling development results will be presented for GA3 itself and the polymer derivedfromreaction of dimethyltin dichloride and GA3, designated as DMT-GA3. Experimental The polymers were synthesized utilizing the (aqueous) interfacial polycondensation process. Reactions were conducted employing a one quart Kimex emulsifying jar placed upon a Waring Blender (Model 7011G) with a "no-load" stirring rate of 18,000 rpm. The diorganostannane dichloride (1.00 mmole; Aldrich Chemical Company, Milwaukee, WI) was dissolved in 50 cc chloroform. This was added to a stirred solution of water (50 cc) containing gibberellic acid (1.00 mmole; Aldrich Chemical Company) containing sodium hydroxide (2.00 mmole). The product was collected as a precipitate employing suction filtration. The solid was repeatedly washed using water and chloroform to remove unreacted materials. The solid was allowed to dry in the open. Percentage yields were in the range of 20 to 50%. Infrared spectral analysis was achieved using a Mattson Model 4020 Fourier Transform Infrared Spectrometer utilizing KBr pellets. Mass spectra were provided by the Midwest Center for Mass Spectroscopy, Lincoln, NE (Grant Number DIR9017262) using high resolution electron impact mass spectrometry with the samples placed on a heating stage with heating occurring rapidly to the 400 C range. Germination and seedling development experiments were carried out in a greenhouse. "Tap" water was used. The pH of the water-soil combination was about 7 consistent with what is found in the Everglades. Seeds were collected within a 45,000 hectare area in the northern Everglades referred to as Water Conservation Area 2A (WCA 2A). Sawgrass and cattail seeds were collected at a collection and measuring site referred to as Fl within a high phosphorus area. The plants were selected randomly and were separated by at least one meter to ensure that plants were of different clones. Once seeded cattailfruitswere separated from spikes, seeds were further isolated by gently grinding in a blender. The seeds underwent further preparatory procedures previously described by us (10). For cattails, viable seeds were identified as those that sank to the bottom of the blender that was used to separate the seed from the fruit parts (11). Cattail viability was 100% using growth percentages found for the seeds germinated in a petri dish. For sawgrass,



298 seeds were separated from the seed parts using a mortar and pestle. Mature seeds were identified by visual observation. Viability was determined using a standard tetrazolium staining technique (12). Viability was found to be 46%. Rectangular plastic trays (24X40X15(deep) cm) offering a soil surface area of about 860 square cms were used. Holes were drilled in the bottom of the trays to allow exchange of water. Ten cms of potting soil (Jungle Growth Potting Soil) was added to allow for seedling development to occur without need for immediate replanting. A combined seed arrangement was used where 100 seeds of each cattail and sawgrass were used. Seeds were treated with talc-mixtures containing varying amounts of test material. The levels chosen have previously been reported to produce results for other seeds (13). Three replicates were run. The trays were placed in "table top" trenches. The water level was maintained at about 10 cms, presenting what is referred to as "saturated" conditions. The water-filled trenches act to moderate temperatures and temperature changes more closely approximating field conditions. As noted above, the experiment was conducted within a covered greenhouse and watering was done by simply adding waster as needed to the trenches. This allowed water to reach the location of the seedsfrombelow minimizing the "washing-away" of the seed treatments. Talc mixtures containing GA3 or GA3-containing polymer, DMT-GA3, were made up prior to administration of the mixtures to the seeds. The seeds were treated with these known amounts of talc mixtures. The seeds were wetted to allow the talc mixtures to adhere to the seeds. The seeds were spread over the surface of the trays. Germination was defined as the appearance of a small green shoot emanating from the seed. Observations of germination were made three times a week while leaf height measurements were made as indicated in the tables. Results and Discussion Structural Characterization. Gibberellic acid has three groups that can react with diorganotin dichlorides-two alcohol groups and one acid group. We have already reported the synthesis of a number of organotin-containing polyethers and polyestersfromthe analogous reaction of diols and salts of diacids with organotin dichlorides (for instance 14-18). R' R£nCl + HO-R-OH —> -(-O-R-O-Sn-)R' 2

0 0 O O R' R£nCl + HOC-R-COH — >-(-O-C-R-C-O-Sn-)R' 2


299 Thus, the products are probably cross-linked containing Sn-O-R and Sn-O C(0)-R bonding between the organostannane moiety and the GA3 moiety with a repeat unit approximating that shown below.


O

The products are insoluble in all attempted liquids consistent with the presence of some crosslinking. The liquids tested included those that are commonly used to solubilize analogous tin-containing non-crosslinked polymers (for instance 19-21). Infrared spectral results are consistent with the formation of the proposed product. A new band about 600 (all band locations are given in 1/cm) is assigned to the symmetric Sn-O-R (Sn-O) stretch. A new band about 625 is attributed to the combination skeletal Sn-0 and O-CO-R stretching in tin esters (22,23). New bands about 970 and 1000 are assigned to the Sn-O stretch in tin esters. A strong band centering about 3400 is probably due to the presence of unreacted alcohol groups. Bands are present on both sides of 3000 derived from the C-H stretching (aromatic-above; aliphatic-below). The carbonyl-tin bond can be either bridging or non-bridging (22,23). Bridging carbonyl stretching-associated bands appear about 1570 (asymmetric) and 1420 (symmetric) while non-bridging bands appear at about 1610-1650 (asymmetric) and 1360 (symmetric). Large bands about 1610 are consistent with the majority of the bonding being of the non-bridging type. Regions where the symmetrical stretching should appear have other bands present making assignments in these regions difficult. While most organotin polyesters form bridged structures, those derived from reactants with two types of functional groups (such as amino acids) are found to favor non-bridged structures as found here (24,25).


300 O

/\

-Sn n


\/

o -Sn-OC-R-

,l

o Bridging

Non-bridging

Mass spectral analysis is consistent with the proposed structure. Table I contains the most abundant ion fragments from the product from dimethyltin dichloride and GA3. Unlike other products produced in this study that gave ion fragments to m/e = 500 Daltons, the product from dimethyltin dichloride only gave ion fragments to 208. There are no bands in the 35-38 range consistent with the absence of unreacted Sn-Cl groups. Bands are present consistent with the formation of Sn-O- and Sn-OCO linkages with the GA3. Thus ion fragments are present at 138 (Sn-O), 152 (O-SnO), 165 (MejSn-O), 185 (O-Me^n-O), 197 (MejSn-OCO), and 208 (O-Me^nOCO). Ion fragments containing tin are also present at 120 (Sn), 142 (SnMe) and 159 (SnMe 2). Ion fragments are also present derived from the breakage of the GA3 into two ring systems-one of the ring systems will be referred to as the "Gibb" unit and the other the "Lactone" unit as pictured below. For the "Gibb" portion ion fragments are found at 135 (Gibb itself) and 122 (Gibb minus methylene). For the lactone portion, ion fragments are found at 151 (Lactone portion itself), 136 (Lactone minus methyl), 135 (Lactone portion minus OH), 120 (Lactone minus methyl and OH), 107 (Lactone minus OCO), 90 (Lactone minus OCO and OH and 75 Lactone minus OCO, OH and methyl).

O

# 1 § 1 # $

HO

Me Lactone

Gibb



301 Tin has ten natural isotopes. Of these seven can be considered significant with respect to abundance. These seven isotopes comprise over 98% of the natural occurring isotopic fraction and these seven isotopes were used in making isotopic abundance ratio compairsons. Table n contains isotopic matches for Me£n-0 (161-169), 0-Me£n-0 (181-189) and O-Me^Sn-OCO (201-209). Thus, mass spectral results are consistent with the proposed structure with the organotin moiety connected to the GA3 moiety through the hydroxyls and carboxyl groups. Control reactions were carried out where one of the reactants was omitted. No precipitation was found for these control reactions consistent with the precipitate containing portions derived from both reactants. In summary, mass spectral, control reactions, the results from analogous reactions and infrared spectral analyses are consistent with the product containing both Sn-O and Sn-OCO linkages to the GA3 moiety. Biological activity results, given in the following section, are also consistent with the product containing both a tin-containing moiety (reduction in the formation of microorganisms) and GA3containing moiety (effect of polymer on germination rate and seedling growth). Biological Characterization. We previously described the synthesis and some biological characterization of GA3-containing polymers derivedfromthe reaction of titanocene dichloride and GA3 (26). Rooting experiments were conducted using Anderson's Crepe Pink hibiscus. Briefly, those stocks treated with both talc mixtures of GA3 and the polymers formed substantially fewer roots than the stock simply treated with talc alone and without any treatment. Of interest is the number of stocks that formed roots along the stem, but above the treated portion at sites where small branches had been removedfromthe stocks. Seedling development was studied for Kentucky Wonder and Red Kidney pole beans. Results for both bean types were similar. Those plants treated with GA3 and polymer grew at a much faster rate with the rate increasing with increased concentration of GA3 or polymer. For the Kentucky Wonder beans treated with 1000 ppm of the GA3 or polymer, the plants grew so fast that after about two weeks, the stem could not support the growth and the plant "fell over" and subsequently died. By comparison, plants treated with 100 ppm polymer show more rapid growth and height through out the test period of four weeks being able to support the growth. Red Kidney bean stocks treated with GA3 and polymer both showed enhanced growing rates. For instance, plants treated with 1000 ppm polymer or 1000 ppm GA3 showed an increased height of about 50% greater than non-treated beans. Here we will briefly describe results related to the germination and seedling development of the polymer derived from reaction of GA3 and dimethyltin dichloride, designated as DMT-GA3. For sawgrass re-establishment to be successful, a number of factors need to be considered. These factors include: •favorable conditions for sawgrass germination and seedling development (relative to cattail)


302

Table I. Most abundant ions from the product of dimethyltin dichloride and 6 A 3 , DMT-GA3.


m/e

Relative Intensity (%)

55 57 69 71 83 85 97 134 150 161 163 165 181 183 185 187

(Possible) Assignment C«H Above Cfly Above CJly Above

9 16 9 11 7 7 7 6 5 8 13 18 9 16 22 9

y

Gibb unit Gibb unit + CH Me£nO Above Above O-NfejSn-O Above Above Above

Table II. Tin isotopic ratios for selected high molecular weight ion fragments of the product from G A 3 and dimethyltin dichloride. Tin Isotope %-Nat. Abundance

116 117 118 119 120 122 124 14 8

24

9

33

5

6

Ion Fragment %-Abundance

161 162 163 164 165 167 169 11 10 20 11 39 2 2


181 182 183 184 185 187 189 12 6 22 9 33 12 6


201 202 203 204 205 207 209 8 5 23 8 35 12 8



303 "time of germination •fraction of germination •mortality •plant reproduction and •vitality. Cattails and most weeds typically found in the Everglades begin to germinate within 3 to 10 days and to a high percentage (generally >30%). A single cattail produces in the range of 3,000,000 seeds (10). By comparison, sawgrass requires between 4 to 8 weeks, with germination percentages typically in the 0 to 5% range. A single sawgrass produces on the order of 3,000 seeds. Thus, increased germination fraction and decreased germination time are important factors with respect to re-establishment of sawgrass in the Everglades. While a number of organotin-GA3 containing products were made, the dimethyltin-GA3 polymer, DMT-GA3, was chosen for initial study since it is the least hydrophobic of the diorganotin moieties used and should hydrolyze most rapidly. The evidence for degradation is circumstantial and is based on the ability of the polymer to influence the germination and seedling development of sawgrass and cattail and on the fact that while there are many gibberellins, only a few are active so that in order for the polymer to exhibit activity, it (most likely) must degrade giving the GA3 moiety in an "active" form. It is believed that release of the GA3 "active" moiety occurs through simple physical (rather than enzymaticcatalyzed) hydrolysis of the polymer. Qrganotin compounds are known to inhibit microorganisms. While "free" or monomeric organotin compounds are illegal for commercial use, "bound" tin compounds are legal and are used for many applications including marine applications where adverse effects to marine life are unwanted (for instance 27) "Bound" tin compounds are defined as those that are chemically bound within polymers. The polymer tested here, DMT-GA3, is a "bound" organotin compound since the tin moiety is chemically bound as part of a polymer. The amount of organotin involved in the treatment (100 ppm) of a single seed is 5 micrograms or 30 nanomoles. Upon hydrolysis, small amounts of "free" organotin are released. Algae began growing several days after the experiment began in all of the containers except those containing seeds treated with DMT-GA3 polymer. For trays containing seeds treated with DMT-GA3 polymer noticeable algae growth was delayed for four weeks. This is consistent with the effect of the DMT-GA3 polymer lasting at least about three to four weeks longer than GA3 itself. As noted above, gibberellins influence seed germination and they are also endogenous regulators of growth (26). GA3 acts to increase cell wall extensibility for some plants thus functioning as a growth accelerator. Tables m-VI contain mean values as a function of GA3 and DMT-GA3 polymer concentration. Table VII contains summation statistical resluts for the informaiton given in Tables m-VI. The results are treated in two ways with respect to the influence of concentration. First, each of the five concentrations were considered independently. This scenario will be referred to as "nongrouped". Second, the results were "grouped" into two groupings based on concentration-a "low" concentration (0.1,1.0, and 10 ppm) and a "high" (100 and


304 Table HL Onset of germination*.


PGH

SAWGRASS

CATTAIL

CONTROL 29 GA3 11 DMT-GA3 Polymer 20 * in days.

8 7 7

Table IV. Germination percentages of sawgrass as a function of PGH concentration. CONCENTRAHON (PPM) 0.01

1.0

PGH CONTROL-2 GA3 9 DMT-GA3 Polymer 8

11 4

10.0

12 9

100.0

11 7

1000.0

19 6

Table V. Germination percentages of cattail fT. dnminyenstO as a function of PGH concentration. CONCENTRA TION (PPM) 0.1 PGH CONTROL-48 GA3 57 DMT-GA3 Polymer 40

1.0

10.0

100.0

1000.0

66

63

57

65

51

38

38

23

Table VI. Seedling development after 102 days. Height of seedlings (in cm) as a function of PGH concentration (ppm). CONCENTRA TION (PPM) 0.1

1.0

SAWGRASS -CONTROL-8.4 GA3 9.3 12.7 DMT-GA3 Polymer 15.3 14.8 CATTAIL -CONTROL-23.4 GA3 16.3 12.9 DMT-GA3 Polymer 32.0 37.6

10.0

100.0

1000.0

11.7

9.4

10.5

23.7

18.1

9.3

6.4

38.6

35.3

16.0 10.3 32.3


305


Table VII. Analysis of variance for germination and seedling development. Group

F Ratio

F Probability

2.6321 3.7407

0.0794 0.0481

1.2328 1.3497

0.3527 0.2891

0.6858 0.9121

0.6433 0.4228

0.6166 1.3851

0.6899 0.2805

0.2877 0.4618

0.9108 0.6388

4.3583 5.5178

0.0171 0.0160

3.3044 6.8194

0.0417 0.0078

0.5095 1.2233

0.7641 0.3220

Analysis of variance for germination Sawgrass/GA3 Non-grouped Grouped Sawgrass/DMT-GA3 Polymer Non-grouped Grouped Cattail/GA3 Non-grouped Grouped Cattail/DMT-GA3 Non-grouped Grouped Analysis of variance for growth Sawgrass/GA3 Non-grouped Grouped Sawgrass/DMT-GA3 Non-grouped Grouped Cattail/GA3 Non-grouped Grouped Cattail/DMT-GA3 Non-grouped Grouped



306 1000 ppm) concentration grouping. The second "grouping" scenario was done to increase the number of replicants within a "concentration" unit. For sawgrass germination, statistical difference is found for both the "grouped" concentrations and for the highest (1000 ppm) and middle (1 ppm) concentrations for the GA3 treatment. Thus, germination percentages increased from a control mean of 3% to above 10% for sawgrass treated with GA3. Cattail germination was independent of GA3 and DMT-GA3 polymer treatment for the "grouped" scenario. But, an increased germination percentage is found for seeds treated with GA3 when the results are considered for each independent concentration (non-grouped). These increases rangefrom(control mean of 48%) about 20% (57% germination) to 50% (66% germination). Growth of sawgrass seedlings derivedfromseeds treated with DMT-GA3 polymer was (statistically) increased in comparison to the control for the "grouped" concentration scenario and for all but the 1 ppm treatment. A difference was also found between seeds treated with 10 ppm DMT-GA3 polymer and those treated with other concentrations of DMT-GA3 polymer. This relationship is consistent with the presence of an optimum concentration of DMT-GA3 polymer around 10 ppm. The increased growth, based on stem length, varied from about 75% to 150%. Cattail seedling growthfromseeds treated with GA3 was significantly less for both the "grouped" concentration ranges and for all but the lowest (0.1 ppm) concentration level. The growth decreases rangefromabout 30% to 70%. Most plant growth hormones, PGHs, either have no affect on growth or act to increase growth. This is true for GA3. A negative effect on growth has only been recently been reported for GA3. Thus Mauder reported diminished growth of rye grass and Kentucky bluegrass (28,29). The time interval for initial sawgrass germination was shortened (to 11 days; Table III) to within the general time interval required for the initial germination of cattail seeds (control = 8 days). In summary, the use of GA3 and DMT-GA3 polymer affects the seed germination and seedling development of both cattail and sawgrass. GA3 alone shows the most pronounced affect in germination studies. The time interval for initial sawgrass germination was effectively reduced for seeds treated with either DMT-GA3 polymer or GA3. Thefractionof sawgrass germination was also increased for seeds treated with either DMT-GA3 polymer or GA3. For seedling development, both GA3 and DMT-GA3 polymer influence growth. For DMTGA3 polymer treated seeds, seedling growth is enhanced for both cattail and sawgrass, while for GA3 treated seeds, there is increased sawgrass growth, but decreased cattail growth. The results are also consistent with the effects of the DMT-GA3 polymer being long-lasting. This is probably the result of the retension and release of GA3 over a sustained period which may be the result of a. a controlled release mechanism, b. retention of GA3 and/or GA3-containing moieties within the soil, c. and/or retention of the GA3 and/or GA3-containing moiety within the seedling itself-either physically or chemically bound. The results are consistent with the use of GA3 and DMT-GA3 polymer as


307 viable seed treatments to produce shorter sawgrass germination times for a greater fraction of seeds and in the production of more rapidly growing seedlings.


We are pleased to acknowledge partial support of this project by the South florida Water Management District.

References 1. Davis, J. H . , Geological Bulletin 25, Florida Geological Survey (1943) 2. Loveless, C. M . , Ecology 1959, 40, 1-9. 3. Davis, S.M.,In Everglades: The Ecosystem and Its Restoration , (S. M . Davis and J. C. Ogden, Eds.) St. Lucie Press, Delray Beach, FL, 1994, 357-378. 4. Davis, S. M . ; Ogden, J. C . , (Eds) Everglades : The Ecosystem and Its Restoration , St. Lucie Press, Delray Beach, FL, 1994. 5. Jensen, J. R.; Rutchey, K.; Koch, M . S.; Narumalani, S.,Photogrammetric Eng. Remote Sensing, 1995, 61, 199-209. 6. Rutchey, K.;Vilchek, Photogrammetric Eng. Remote Sensing, 1994, 60, 767775. 7. Alexander, T. R., Soil and Crop Sci Soc. Florida Proceedings, 1971,31,72-74. 8. Forsberg, C., Physiologia Plantarum 1966, 19, 1105-1109. 9. Miao, S. L . ; Borer, R. E.; Sklar, F. H . , in review. 10. Stewart, H.; Miao, S.L.,Colbert, M . E.; Carraher, C. E . , Wetlands, 1997, 17, 116-122. 11. McNaughton, S. J., Ecology 1968, 49, 367-369. 12. Hartman, H . ; Kester, D.; Davies, F. T.; Geneve, R., Plant Propagation: Principles and Practices, 6th Ed., Prentice Hall, Upper Saddle River, NJ, 1997. 13. Thompson, W. T., Agricultural Chemicals Book III-Fumigants. Growth Regulators, Repellents and Rodenticides , Thopmson Pubs.,Frensno, CA, 1988-89. 14. Carraher, C. E.; Dammeier, R.L.,J. Polymer Sci. A-1, 1970, 8, 3367-3369. 15. Carraher C. E . ; Butler, C. US Patient 5,043,463,1991. 16. Carraher, C. E . ; Dammeier, R. L.,Die Makromolekulare Chemie, 1979, 135, 107-112. 17. Carraher, C. E . , J. Chem. Ed., 1981, 58(11), 921-934. 18. Carraher, C. E . ; Tisinger, L . ; Solimine, G.; Williams, M . ; Carraher, S.; Strother, R., Polymeric Materials: Sci. Eng., 1986, 55, 469-472. 19. Carraher, C.E.,Structure-Solubility Relationships in Polymers (R. Seymour and F. Harris, Eds.), Academic Press, NY, 1977, 215-224. 20. Carraher, C. E . ; Winter, D. O., Die Makromolekulare Chemie, 1971, 141, 237244. 21. Carraher, C. E . , Polymer Chemistry: An Introduction , 1997, Dekker, NY. 22. Carraher, C. E . ; He, F.;Sterling, D.,Polymeric Materials: Sci. Eng., 1995, 72, 114-115. 23. Carraher, C. E . , Die Angew. Makromolekulare Chemie, 1973, 31, 115-122. 24. Carraher, C. E . ; Li, A., Unpublished results.



308 25. Carraher, C. E.; He, F.; Sterling, D.; Nounou, F.; Pennisi, R.; Louda, J. W.; Sperling, L. H., Polymer P., 1990, 31(2), 430-431. 26. Stewart, H.; Carraher, C. E.; Soldani, W.;Reckleben, L.;de la Torre, J.;Miao, S. L.,Metal-Containing Polymeric Systems (C. Pitmann, C. Carraher, M. Zeldin, B. Culbertson, and J. Sheats, Eds.), Plenum Press, NY, 1996, 93-107. 27. Gebelein, C.; Carraher, C. (Eds.), Polymeric Drugs, Amer. Chem. Soc., Washington, D. C., 1982. 28. Mander, L., Science, 1995, 268, 1571-1573. 29. Mander, L., New Scientist, 1995, June, 19.


Tailored Polymeric Materials for Controlled Delivery Systems

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