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Chemistry & Chemical Biology / New Brunswick |
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Laurence S. Romsted Professor A.B. 1964, DePauw Ph.D. 1975, Indiana Postdoctoral Fellow 1976-80, Santa Barbara |
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Research
Summary
Research in our group ranges across bioorganic, biophysical and association colloid chemistries. The ultimate goal is to develop a deeper understanding of the balance of forces that control the structure and compositions of aggregated systems such as micelles, microemulsions, vesicles, biological membranes and macroemulsions and the organization of aqueous polyelectrolyte solutions. A variety of experimental methods are used including, NMR, UV/Visible and Fluroescence spectroscopies, kinetics, high performance liquid chromagtography. Amphiphiles used in the preparation in aggregated systems, organic substrates used in kinetics and probe molecules for quantitative HPLC studies are synthesized as needed.Compositions of Aggregates by Chemical Trapping
Component concentrations at aggregate interfaces, e.g., water, halide ions, alcohols, are generally difficult to determine, especially in multicomponent systems. We have developed a novel chemical trapping reaction that is applicable to many of the components commonly used in studies of aggregate systems. Product yields from reaction of weakly basic ions and molecules with the aggregate bound arenediazonium ion, Figure 1 and Scheme 1, are proportional to the concentrations of ions and molecules ar the aggregate interface. The power of the method has been demonstrated in a variety of systems (see representative publications). Currently we are using the method to determine the affect of urea on aggregate structure, the distribution of alcohols and benzene in aqueous and reverse micelles and microemulsions and the hydration state of ionic and nonionic aggregates. The results should provide new insight in to the balance of forces that control the size, shape and phase states of these aggregated systems.Chemical trapping reagent and a cartoon of a spherical cationic micelle in aqueous solution. The empty section faces illustrate the organization of amphiphiles in the aggregate; the micellar core filled by flexible tails of amphiphiles, their head groups (open circles) and hydrated counterions (filled circles). Space filling representations of the surfactant head and arenediazonium groups illustrate their similar size.
Dediazoniation mechanism. Spontaneous loss of nitrogen to form a reactive aryl cation that is trapped by available nucleophiles. Product yields from dediazoniations at aggregate interfaces, Figure 1, are used to estimate simultaneously, ion, molecule and, for the first time, water concentrations at aggregate surfaces.
Polypeptide Conformations and Orientations at Aggregate Interfaces
We have discovered that the chemical trapping reaction tags the nitrogen and oxygen atoms of the amide bond, an extremely difficult group to derivatize in aqueous solution. Tagging patterns from reaction of aggregate bound arenediazonium ions with polypeptides, e.g., hormones, at the aggregate interface should distinguish polypeptides with different conformations and orientations at the interface. Surprisingly, reactions between amide bonds and arenediazonium ions have never been studied and we recently completed a series of physical organic studies as the mechanism.Domain Formation in Polyelectrolytes
Like charged polyelectrolytes in semidilute aqueous solutions appear to form domains, regions enriched in polyelectrolyte, instead of being randomly distributed. Based on his counterion condensation theory, Professor Manning, of this department and a collaborator on this project, predicts that the driving force for the attractive interaction is entropic, produced by a sharing and dilution of counterions on neighboring chains. We have designed a experimental test of this theory that exploits the power of the chemical trapping reaction to estimate counterion concentrations in the immediate vicinity of the polyelectrolyte chains.Representative Publications
Determining Antioxidant Distributions in Model Food Systems: Development of a New Kinetic Method Based on the Pseudophase Model in Micelles and Opaque Emulsions. Romsted, L. S.; Zhang, J. Progress in Colloid and Polymer Science, in press.
Effect of Alkyl Group Size on the Mechanism of Acid Hydrolysis of Benzaldehyde Acetals. Belarmino, A. T. N.; Froehner, S.; Zanette, D.; Bunton, C. A.; Farah, J. P. S.; Romsted, L. S., Journal of Organic Chemistry, 2003, 68, 706-717.
Snared by Trapping: Chemical Explorations of Interfacial Compositions of Cationic Micelles. Romsted, L. S., in Adsorption and Aggregation of Surfactants in Solution, Mittal, K. L.; Shah, D. O., Eds, Marcel Decker, New York, 2002, pp. 149-170.
Estimating Concentrations of Condensed Counterions Around a Polyelectrolyte by Chemical Trapping. McKernan, B. A.; Romsted, L. S. Symposium Series No. 832: Conducting Polymers and Polyelectrolytes: From Biology to Photovoltaics, Rubinson, J. F.; Mark, H. B. Jr, editors, Washington, 2003, Chapter 14, pp. 184-199.
A Kinetic Method for Determining Antioxidants Distributions in Model Food Emulsions: Distribution Constants of t-Butylhydroquinone in Mixtures of Octane, Water and a Nonionic Emulsifier. Romsted, L. S.; Zhang, J. Journal of Agricultural and Food Chemistry, 2002, 50, 3328-3336.
Effect of Urea on Biomimetic Systems: Neither Water 3-D Structure Rupture or direct Mechanism, Simply a More "Polar Water". Dias, L. G.; Florenzano, F. H.; Reed, W. F.; Baptista, M. S.; Silvia, M. B. S.; Alvarez, E. B.; Chaimovich, H.; Cuccovia, I. M.; Carmen, L. C. A.; Brasil, C. R.; Romsted, L. S.; Politi, J. J., Langmuir 2002, 18, 319-324
Interfacial Compositions of Surfactant Assemblies by Chemical Trapping with Arenediazonium Ions: Method and Its Applications. Romsted, L. S., In Reactions and Synthesis in Surfactant Systems, Texter, J., Ed., Marcel Dekker, New York, 2001, pp. 265-294.
Urea Effect on Biomimetic Aggregates. Amaral, C. L. C; Chaimovich, H.; Cuccovia, I. M.; Florenzano, F. H.; Politi, M. J.; Reed, W.; Romsted, L. S.; Souza, S. M. B. Abstract, First Mercosur Workshop on Biomembranes, Nov 30-Dec. 1, 2000, Buenos Aires, Argentina.
Interfacial Composition of Gemini Surfactant Micelles Determined by Chemical Trapping. Menger, F. M.; Keiper, J. S.; Mbadugha, B. N. A.; Caran, K. L.; Romsted, L. S. Langmuir, 2000, 16, 9095-9098.
J. Yao, L. S. Romsted. Arenediazonium Salts: New Probes of the Compositions of Association Colloids. 7. Average Hydration Numbers and Cl– Concentrations in the Surfactant Film of Nonionic C12E5/Octane/Water Macroemulsions: Temperature and NaCl Concentration Effects. Yao, J.; Romsted, L. S. Langmuir, 2000 16, 8771-8779.
F. M. Menger, J. S. Keiper, B. N. A. Mbadugha, K. L. Caran, L. S. Romsted, Interfacial Composition of Gemini Surfactant Micelles Determined by Chemical Trapping Langmuir, 2000 , 16, 9095-9098.
J. Keiper, L. S. Romsted, V. Soldi, and J. Yao. Chemical Trapping: A New Method for Characterizing the Properties of Amphiphilic Aggregates. At the 12th International Symposium on Surfactants in Solution, June 7-11, 1998, 1998, Stockholm, Sweden, appears in Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2000, 176, 53-67.
V. Soldi, J. Keiper, L. S. Romsted, I. M. Cuccovia and H. Chaimovich. Arenediazonium Salts: New Probes of the Interfacial Compositions of Association Colloids. 6. Relationships between Interfacial Counterion and Water Concentrations and Surfactant Head Group Size, Sphere-to-Rod Transitions, and Chemical Reactivity in Cationic Micelles, Langmuir, 2000, 16, 59-71.
C. A. Bunton and L. S. Romsted Organic Reactivity in Microemulsions. in "Handbook of Microemulsion Science and Technology", Dumar, P., Mittal, K. L., eds., Marcel Dekker, New York, 1999 , 457-482.
C. Bravo-Diaz, L. S. Romsted, M. Harbowy, E. Romero-Nieto and E. Gonzalez-Romero. Rates and pH Dependent Product Distributions of the Chlorocuprate(II) Catalyzed Dediazoniation of p-Nitrobenzenediazonium Tetrafluoroborate in Aqueous, Acidic, NaCl Solutions: A New Method for Monitoring the Sandmeyer Reaction. Journal of Physical Organic Chemistry, 1999, 12, 130-140.
L. S. Romsted and J. Yao. Arenediazonium Salts: New Probes of the Interfacial Compositions of Association Colloids. 5. Determination of Hydration Numbers and Radial Distributions of Terminal Hydroxyl Groups in Mixed Nonionic CmEnMicelles by Chemical Trapping.Langmuir, 1999, 15, 326-336.
L. S. Romsted, J. Zhang and L. Zhuang. Mechanism of Reaction of an Arenediazonium Ion in Aqueous Amide Solutions. Development of a Novel Reagent for Chemically Tagging Peptide Bonds at Aggregate Interfaces, in "Atualidades de Fisico-Quimica Organica," , 1998, 214-230. Presented at the 14th International Conference on Physical Organic Chemistry, August 16-21, 1998, Florianópolis, Santa Catarina, Brasil.
L. S. Romsted, J. Zhang and L. Zhuang. Mechanism of Reaction of an Arenediazonium Ion in Aqueous Solutions of Acetamide, N-Methylacetamide and N,N-Dimethylacetamide. Development of a Novel Reagent for Chemically Tagging Peptide Bonds at Aggregate Interfaces. Journal of the American Chemical Society, 1998, 120, 10046-10054.
M. C. Garcia-Meijide, C. Bravo-Diaz and L. S. Romsted. A New Method for Monitoring Dediazoniation Reactions: Simultaneous Monitoring of Concentration and Rates of Product Formation and Loss of Starting Material for the Dediazoniation of p-Methylbenzenediazonium Tetrafluoroborate. International Journal of Chemical Kinetics, 1998, 30, 31-39.
C. A. Bunton, L. S. Romsted and J. Yao. Micellar Catalysis, A Useful Misnomer. Current Opinion in Colloid and Interface Science, 1997, 2, 622-628.
M. K. Jain, J. Rogers, B.-Z. Yu, J. Yao, L. S. Romsted, O. G. Berg. Thermodynamic and Kinetic Basis of Interfacial Activation: Resolution of Binding and Allosteric Effects on Pancreatic Phospholipase A2 at Zwitterionic Interfaces. Biochemistry, 1997,36, 14512-14530.
I. M. Cuccovia, A. Agostinho-Neto, C. M. A. Wendel, H. Chaimovich and L. S. Romsted. Determination of Interfacial Co-Ion Concentration in Ionic Micelles by Chemical Trapping: Halide Concentration at the Interface of Sodium Dodecyl Sulfate Micelles. Langmuir, 1997, 13, 5032 -5035.
J. Yao and L. S. Romsted. Effects of Hydrocarbon and Triglyceride Oils on Butanol Distribution in Water-in-Oil Cationic Microemulsions. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1997, 123-124, 89-105.
I. M. Cuccovia, I. N. da Silva, H. Chaimovich and L. S. Romsted. A New Method for Estimating the Degree of Ionization and Counterion Selectivity of Cetyltrimethylammonium Halide Micelles: Chemical Trapping of Free Counterions by a Water Soluble Arenediazonium Ion. Langmuir, 1997, 13, 647-652.
L. S. Romsted and J. Yao. Arenediazonium Salts: New Probes of the Interfacial Compositions of Association Colloids. 4. Estimating Hydration Numbers of Aqueous Hexaethylene Glycol Mono Dodecyl Ether Micelles by Chemical Trapping. Langmuir, 1996, 12, 2425-2432.
A. A. Ruzza, F. Nome, D. Zanette and L. S. Romsted. Kinetic Evidence for Temperature Induced Demixing of a Long Chain Dioxolane in Aqueous Micellar Solutions of Sodium Dodecyl Sulfate: A New Application of the Pseudophase Ion Exchange Model. L. S. Langmuir, 1995, 11, 2393-2398.
M. A. B. Marin, F. Nome, D. Zanette, C. Zucco and L. S. Romsted. Effect of Cetyltrimethylammonium Micelles with Bromide, Chloride and Hydroxide Counterions on the Rates of Decomposition of Para Substituted Aryl-2,2,2-trichloroethanols in Aqueous NaOH. The Journal of Physical Chemistry 1995, 99, 10879-10882.
L. S. Romsted and J. Yao. Arenediazonium Salts: New Probes of the Interfacial Compositions of Association Colloids. 3. Distributions of Butanol, Hexanol and Water in Four-Component Cationic Microemulsions. Journal of the American Chemical Society 1994, 116, 11779-11786.
A. Chaudhuri, L. S. Romsted and J. Yao. Arenediazonium Salts: New Probes of the Interfacial Compositions of Association Colloids. 2. Binding Constants of Butanol and Hexanol in Aqueous, Three Component, Cetyltrimethylammonium Bromide Microemulsions. Journal of the Americal Chemical Society 1993, 115, 8362-8367.
A. Chaudhuri, J. A. Loughlin, L. S. Romsted and J. Yao. Arenediazonium Salts: New Probes of the Interfacial Compositions of Association Colloids. 1. Basic Approach, Methods and Illustrative Applications. Journal of the American Chemical Society 1993, 115, 8351-8361.
L. Romsted, C.-O. Yoon. Counterion Affinity Orders in Aqueous Micellar Solutions of Sodium Decyl Phosphate and Sodium Dodecyl Sulfate Determined by Changes in 23 Na NMR Relaxation Rates. A Surprising Dependence on Head Group Charge. Journal of the American Chemical Society 1993, 115, 989-994.
A. Chaudhuri, J. A. Loughlin and L. S. Romsted. Arenediazonium Salts: New Probes of the Interfacial Composition of Association Colloids. Atualidades de Fisico-Quimica Organica-1991, Humeres, E. J. J., Ed., pp. 176-196.
C. A. Bunton, F. Nome, F. H. Quina and L. S. Romsted. Ion Binding and Reactivity at Charged Aqueous Interfaces. Accounts of Chemical Research 1991, 24, 357-364.
A. Blasko, C. A. Bunton, C. Armstrong, W. Gotham, Z.-M. He, J. Nikles and L. S. Romsted. Acid Hydrolyses of Hydrophobic Dioxolanes in Cationic Micelles: A Quantitative Treatment Based on the Poisson-Boltzmann Equation. The Journal of Physical Chemistry 1991, 95, 6747-6750.
A. Chaudhuri and L. S. Romsted. Simultaneous Determination of Counterion, Alcohol, and Water Concentrations at a Three Component Microemulsion Interface Using Product Distributions from a Dediazoniation Reaction. Journal of the American Chemical Society 1991, 113, 5052-5053.
J. A. Loughlin and L. S. Romsted. A New Method for Estimating Counter-Ion Selectivity of a Cationic Association Colloid: Trapping of Interfacial Chloride and Bromide Counter-Ions by Reaction with Micellar Bound Aryldiazonium Salts. Colloids and Surfaces 1990, 48, 123-137.