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Biomedical Sciences Seminar Series

Fall 2004 Poster Presentation

October 29, 2004

Physical Sciences Lobby

Cindy Chau, Eric Fromer, Luis Gomez, Ikenna Madu,
Maira Soto, Kristen Wardlaw, Vivian Galicia,
Jesse Chapman, Heriberto Lima, Norma Sanchez, Wilson Segura,
Jason Lessing, Michael Lispcomb, Teresa Monreal, Mario Vargas,
Marianela Arias, Jake Leon, Mayra Torres, Paul Martinez

Infrared Spectra of Gas Phase Alkyl Peroxy Radicals
Kristen Wardlaw, Jorge A. Martinez, Daisy A. Mah, and Scott L. Nickoliasen
Department of Chemistry & Biochemistry, California State University, Los Angeles

Abstract: Ozone is the most harmful element of photochemical smog. Alkyl peroxy radicals are important intermediates in the formation of ozone. Our goal is to perform kinetic studies of these alkyl peroxy radicals with other troposhperic reactants.
We use FTIR spectrometry to study the formation of these intermediates. The apparatus consists of an FTIR coupled to a long path-length White-type cell. The alkyl radicals were generated via a microwave discharge. The gas samples were introduced into a mixing manifold, where peroxy radicals were then formed.
We observed the mid-infrared spectra of alkyl peroxy radicals of varying concentrations. The absorbance intensity trends are indicative for generating these radicals. Their presence was substantiated through NO titrations.


Identification and mapping of the natural p53 oxidizing ligand.
Jake León, Julian Whitelegge Ph.D., Jamil A. Momand Ph.D.
California State University Los Angeles
University of California Los Angeles

Abstract: The tumor suppressor p53 is a check point protein that controls cell cycle and has relevant importance to cancer prevention. Part of the defense mechanism against cancers requires activation by p53. P53 operates as a transcription factor that up regulates the expression of certain genes that respond to a specific stress. These genes code for proteins that cause apoptosis, cell cycle arrest and DNA repair. Oxidation of p53 is directly related to the prevention of its transactivation activity. Evidence indicates that oxidation of p53 prevents sequence specific DNA binding. What is the target of oxidation? Evidence shows that cysteines within the p53 DNA binding domain need to be in the reduced state in order to bind DNA. There are three kinds of cysteine thiol oxidation to be considered. The first is intra-molecular disulfide bond formation. The second is the formation of a metal-sulfur covalent interaction, and the third is the disulfide bond formed between the cysteine sulfur of the protein and the sulfur of a small molecule. The purpose of this research is to map the oxidation site on the specific cysteines within the protein and identify the oxidant cysteine ligand.


Potential Roles of AMP-Activated Kinase in Ovarian Function
Vivian Galicia

Abstract: The ovary is a critical component of the female reproductive system, playing important roles in oocyte storage and maturation as well as hormone production. The functional unit of the ovary is the follicle, which is composed of the oocyte, surrounded by granulosa and thecal cells. The functional maturation of granulosa cells is dependent upon the actions of follicle-stimulating hormone (FSH). Binding of FSH to receptors on granulosa cells leads to the production of the second messenger cyclic AMP, resulting in cell maturation and increased production of the ovarian steroid hormone, estradiol. Cyclic AMP is hydrolyzed by phosphodiesterases to what has been considered an inactive product, 5'-AMP. However, it is now clear that 5-AMP itself activates a signaling enzyme, adenosine monophosphate-activated protein kinase (AMPK). In other tissues such as liver and skeletal muscle, AMPK helps to protect cells against environmental and metabolic stresses. Preliminary studies in our laboratory have shown that AMPK is expressed in the ovary. The purpose of this study is to evaluate the role of AMPK on FSH-induced estradiol production from granulosa cells. Immature granulosa cells were obtained and cultured for 48 h in the presence of media alone (C), FSH, or FSH plus the AMPK inhibitor adenine 9--D-arabinofuranoside (araA). While treatment with FSH markedly increased estradiol levels, cotreatment with araA inhibited estradiol production. These findings suggest that AMPK activity is required for normal estradiol production. Additional studies examined the effects of AMPK inhibition of granulosa cell viability. Coincubation of FSH-treated cells with araA resulted in a marked increase in granulosa cell death, consistent with a role of AMPK in maintaining cell viability. Together, these findings suggest that AMPK is an important factor influencing granulosa cell viability and maturation.


Up-regulation and post-translational processing of epithelial defensin HD5
in the male urethra during sexually transmitted diseases
Heriberto Lima

Abstract: Innate immunity has been recognized to play an important role in mucosal defense, in part mediated by antimicrobial peptides including defensins. Whereas some progress has been made in understanding mucosal defense in the respiratory and intestinal tract, the genital tract, in particular in the male, is still under-investigated. This is despite the continuing major impact of sexually transmitted diseases on public health. Human defensin 5 (HD5) was first described in the small intestine in Paneth Cell granules as a propeptide (proHD5) that is further processed by Paneth cell derived trypsin upon secretion to the intestinal lumen. We have previously reported HD5 upregulation in the inflamed female genital tract. Employing semi quantitative western blot techniques we describe here the up-regulation of HD5 in urethral washes of men with urethritis caused by Neisseria gonorrhoea (GC) or Chlamydia trachomatis as reflected in the appearance of proHD5. In samples that also contained higher numbers of neutrophils, cellular mediators of innate immunity, HD5 was found as further processed forms. Upon incubation with a neutrophil granule extract recombinant proHD5 was cleaved in vitro. Antimicrobial assays showed that recombinant proHD5 was inactive against N. gonoerrhoea when tested in 70% RPMI medium supplemented with glucose and vitamins, in contrast to processed HD5, which had a bacteriostatic effect. These data suggest that HD5 is likely to contribute to mucosal defense in the male genital tract and they provide first evidence how different components of innate immunity interact to provide a better protection against microbial invasion.


The Role of Deception and Memory on the Pupillary Response
Wilson Segura

Abstract: Past research has shown that increased mental processing load causes the pupil to increase in size.  Past research has also shown that the increased mental processing load associated with deception has this effect.  On the other hand, not much research has been done on the relationship between the pupillary response and memory.  The purpose of this project is to assess the relationship between the pupillary response and deception.  Additionally, this project seeks to assess whether memory also has an effect on the pupillary system.  It is expected for pupil size to be larger on trials where deception is present, and where memory has been activated, than on trials with neutral items.



 "Symptom Presentation of Eating Disorders: a Comparison of Mexican-American
and European American Women"
by Teresa Monreal, Laura Juarez, & Fary Cachelin, Ph.D.

Abstract: Limited research has been conducted on the behavioral symptoms of eating disorders among Mexican American women.  The purpose of this study was to examine the differences in eating disorder symptoms among a sample of Mexican American and European American women with eating disorders and controls without eating disorders.  144 women (80 Mexican American, 64 European American) without eating disorders were administered the Eating Attitudes Scale (EAT) and 191 women (80 Mexican American, 111 European American) with eating disorders (Bulimia Nervosa, Anorexia Nervosa, Binge Eating Disorder, and Eating Disorder Not Otherwise Specified) were administered the Eating Disorder Examination (EDE).  A one way analysis of variance found that Mexican American! women were more likely to experience objective overeating episodes (F=6.341, p=.013); however, European American women are more likely than Mexican American women to eat when not hungry (F=3.708, p=.056), experience distress over bulimic episodes (F=14.801, p=.000), eat alone during binge episodes (F=16.505, p=.000), and place more importance on their weight or shape (F=11.376, p=.001).  Among control women without eating disorders, a one way analysis of variance revealed that Mexican American women scored significantly higher on the EAT subscale of oral control (F=5.893, p=0.016) as well as in overall eating pathology (F=5.306, p=0.023).  These results suggest that European American women may present with more severe behavioral symptoms than their Mexican American counterparts.  In addition, the results suggest that Mexican American women without ea! ting disorders may nevertheless have issues surrounding oral control.  Further research on eating disorder symptoms on Mexican American women can help in the identification and treatment of eating disorders in this understudied minority population.


Racial Identity and Racial Perceptions Among Latinos: A Multifaceted Analysis
Eric L. Kohatsu, Ph.D., Jason Lessing, B.A., & Rodolfo Victoria, Shannen Vong, Katia Barquero, B.A., Anna Arredondo, B.A., Martha Alvarado, B.A., Andrew Lau, & Tony Casasola, B.A.
California State University, Los Angeles

Abstract: To date, few studies have investigated the application of Helms (1990) racial identity theory as it applies to Latinos. Furthermore, research examining the complexities of interracial perceptions and quality of interracial contact between Latinos and Asian Americans is noticeably absent in the field. 70 males and 130 females Latinos from a culturally diverse west coast university participated in this study (N =200). A qualitative content analysis of participants' description of their experiences in the U.S. revealed five racial identity themes: Pride, Struggle, Non-acceptance, Conflicted/Shame, and Integrated. Most participants elaborated on issues pertaining to racism, thus providing further validation for Helms's (1990, 1995) assertion that racial identity develops through socialization due to racial rather than ethnic experiences. Results also suggested that racial identity is predictive of interracial contact between Latinos and Asian Americans.


 Expression and Potential Functions of Cyclic Nucleotide Gated CHannels
in the Rat ovary
Marianela S. Arias and Dr. Philip S. LaPolt

Abstract: In females, the production of the ovarian steroid hormone estradiol (E2) is essential for reproductive function. Previous studies suggest that increased intracellular calcium levels contribute to the stimulatory effects of follicle-stimulating hormone (FSH) on E2 production. Cyclic nucleotide gated channels (CNGs) are cation channels which mediate calcium influx into cells. To determine the role of CNG-mediated calcium flux on E2 production, this study examined the expression of CNG channels in the ovary, and determined the effects of EGTA (a calcium chelator) and LCD (a CNG blocker) on FSH-stimulated E2 levels. The role of CNGs in E2 production was examined using cultured rat granulosa cells. While untreated cells displayed low E2 production, incubation with FSH for 48 hours markedly increased E2 levels. Removal of extracellular calcium by incubation with EGTA markedly inhibited FSH-stimulated E2 levels in a dose-dependent manner, indicating that calcium influx into cells contributes to the stimulation of E2 synthesis. Similarly, blockage of CNG channels with LCD abolished FSH-stimulated E2 production in a dose-dependent manner, indicating a role of CNG channels in calcium-dependent hormone production. Studies of cell viability demonstrated increased cell death with increasing concentrations of either EGTA or LCD, suggesting that CNG channels play important roles in maintaining granulosa cell viability. RT-PCR of ovarian RNA using specific primers for the CNG3 isoform resulted in the amplification of a product of expected size, confirming the presence of CNG3 in the ovary. However, no CNG3 transcript could be detected by Northern analysis of whole ovarian homogenates, suggesting that the CNG3 mRNA was not abundant and/or exhibited limited, cell-specific expression. Immunoflourescence analysis revealed that CNG3 protein was detected only in oocytes and the corpus luteum, but not in granulosa cells as expected. Collectively, these findings suggest that CNG3 may play a role in oocyte maturation and luteal steriodgenesis, while other CNG isoforms may be important for granulosa cell E2 production and cell viability.


H. Paul Martinez, Carlos G. Gutierrez*

Abstract: In response to biochemical need for iron, and its great insolubility in aqueous environment, E. coli produces the siderophore enterobactin (1) to complex, transport and deliver ferric iron to the bacterial cell. One of the proposed mechanism for ferric iron release involves sequential protonation of the m-phenolates , eventually forming salicyl enterobactin complex. We have developed methodology for mono and diacylation of the triserine backbone, allowing us to make enterobactin derivatives where two acyl groups are different from the third, including 2-4 which are close structural models of the sequential protonation intermediates. Furthermore, we have adapted this methodology to synthesize a meta-methoxy enterobactin analog that will mimic the electronic effect of a meta protonated salicylate enterobactin complex.


Inhibitory Effects of RETROCYCLIN on Sendai Virus Infection in vitro
Michael W. Lipscomb, Nancy McQueen, PhD

Abstract: Retrocyclin is a cationic, circular, mini-defensin antimicrobial peptide that has been shown to have lectin-like, antiviral properties against HIV and HSV Types 1 and 2 [1, 3]. Specifically, it has been shown that retrocyclin acts to inhibit viral infection by binding to the O- and N- linked carbohydrate residues on cellular receptors and viral ligands, thus inhibiting viral attachment and/or entry into host cells [1]. The primary goal of this research project is to assess retrocyclin's antiviral properties on Sendai virus infection of LLCMK2 cells. Sendai virus is an enveloped RNA paramyxovirus that attacks the respiratory tract of rodents, causing an infection similar to those caused by human parainfluenza type-1 and influenza viruses. Sendai virus utilizes glycoprotein ligands and receptors for viral attachment, fusion, and penetration in mechanisms very similar to those of HIV and HSV. Thus, we hypothesized that treatment of Sendai virus and/or LLCMK2 cells with retrocyclin will block viral attachment and/or entry. Preliminary data has shown that retrocyclin does demonstrate distinct antiviral inhibitory activities against Sendai virus. Retrocyclin was added as a) pre-adsorption treatment of virus, b) pre-adsorption treatment of cells, b) post-adsorption treatment and c) combination of pre-adsorption treatment of virus, pre-adsorption treatment of cells and post-adsorption treatments, each at a concentration of 25_g/ml. Every 24 hours, during a four-day post-infection incubation, sample aliquots of supernatant were taken and replaced with fresh medium with or without retrocyclin, as indicated. Hemagglutination assays show that retrocyclin treatment of Sendai virus significantly reduces viral titer in each of the four days, with post-adsorption treatment providing the greatest protection. RT-PCR has qualitatively confirmed that Sendai virus is the infectious agent inhibited. Further assays are currently being performed to confirm retrocyclin's antiviral activity against Sendai virus. Although retrocyclin showed no cytolytic activities against the cell lines used in the HIV and HSV studies, our results using LDH-cytotoxicity assays suggest that retrocyclin exhibits cytolytic activity in LLCMK2 cells [1, 3]. Further analysis is underway to determine the potential toxic effects of retrocyclin. Additionally, dose-response experiments with varying concentrations of retrocyclin and titers of Sendai virus suspension are being performed to determine the minimal concentration of retrocyclin required for inhibition of infection.
1. W Wang, Cole A, Hong T, Waring AJ, Lehrer RI. Retrocyclin, an Antiretroviral Theta-Defensin, is a Lectin. J Immunol. 2003 May 1. vol 170(9),4708-16
2. AM Cole, Hong T, Boo L, Ngyuen T, Zhao C, Bristol G, Zack J, Waring AJ, Yang OO, Lehrer RI. Retrocyclin: A primate peptide that protects cells from infection by T- and M-tropic strains of HIV-1. PNAS 2003 vol. 99(4), 1813-1818
3. B Yasin, Wang W, Pang M, Cheshenko N, Hong T, Waring AJ, Herold BC, Wagar EA, Lehrer RI. Theta-defensin protects cells from infection by herpes simplex virus by inhibiting viral adhesion and entry. J Virol. 2004 May. vol. 78(10), 5147-56

Funded in part by NIH MBRS-RISE


 Dietary Jojoba Oil Alters the Kinetics of Enzymes Involved in Plasma Lipoprotein
Cholesterol Metabolism
Maira Soto, Dr Raymond E Garcia

Seven day dietary studies indicate that high density lipoprotein cholesterol (HDL-C) concentration decreases when New Zealand White rabbits are fed a 1% cholesterol diet, but remains at a normal level when fed a 1% cholesterol + 3% jojoba oil diet. Dietary jojoba oil, therefore, alters HDL-C metabolism in cholesterol-fed rabbits. Our objective is to determine the mechanism of action of jojoba oil on HDL metabolism. It is our hypothesis that dietary jojoba oil inhibits cholesteryl ester transfer protein (CETP) and activates lecithin:cholesterol acyltransferase (LCAT) activities. CETP transfers cholesteryl esters from HDL to LDL, whereas LCAT esterifies free cholesterol to cholesteryl esters. The validity of our hypothesis was tested by feeding adult female New Zealand White rabbits the following diets: normal (N), 3% jojoba oil (J), 1% cholesterol (C), 1% cholesterol + 3% jojoba oil (CJ). Blood samples were collected at 0 and 7 days. Total cholesterol (TC) and free cholesterol (FC) concentrations were measured enzymatically, while the rate of CETP and LCAT were obtained with flurometric assays. The CJ-fed rabbits exhibit an increase in HDL-FC concentration as well as a reduction in HDL-CE, keeping total HDL-C concentration at a normal level. CETP activity was slightly lower in rabbits fed the CJ diet than those fed the C diet, but both had greater CETP activity than those fed the N and J diets. LCAT activity decreased in all animals fed dietary cholesterol while dietary jojoba oil had no impact. From this data we can conclude that jojoba oil had no impact on LCAT, but seems to inhibit CETP in the presence of dietary cholesterol. Future studies include increasing the animal pool size and measuring other enzymes that influence cholesterol metabolism. (Supported by NIH MBRS-RISE grant R25 GM61331 and NIH-MARC grant GM 08228.)


 Investigating the Photochemical Dissociation of Nitrate in Water and Water Ice Samples.
Jesse L. Chapman and Dr. Krishna L. Foster

Abstract:The photodissociation of aqueous nitrate (NO3-(aq)) yields nitrite (NO2-(aq)) and hydroxyl radical (OHo) products. We hypothesize that the kinetics of nitrate photolysis is different in water and water ice samples. Utilizing two different quartz cells, ion chromatography, 200-watt Hg-Xe lamp coupled with a 313 ± 10nm UV filter, and a chemical actinometer, the quantum yields (_) of both water and water ice samples were determined. Implications of our findings will be discussed.


Norma Sanchez, Scott Grover

Abstract: Phosphoenolpyruvate carboxylase (PEPc) is a key photosynthetic enzyme in C4 plants such as in maize. The regulatory properties of PEPc include feedback inhibition by malate and activation by glucose-6-phosphate (G6P) and glycine. Our goal has been to understand, at a molecular level, how and where regulatory molecules bind to the enzyme. Based on the three-dimensional structure of the enzyme, and results previously obtained with other mutants, we have evidence that the synergistic activators glycine and G6P bind near each other in a region close to arginine 231 and arginine 232. Furthermore, residues in this region determine the enzyme's sensitivity to inhibitors. In this study we perform mutational analysis on serine 100 and arginine 334, which are near arginine 231 and arginine 232, to test their role in how the enzyme responds to activators and inhibitors. We have also created, but not yet tested, mutations at threonine 227 and lysine 960. These mutations are made to test the importance of functional groups (such as -OH) or charges (such as the positive charge on arginine) in the binding of regulatory molecules to the enzyme.

We hypothesized that the mutation of serine100 to alanine (S100A) and arginine334 to glutamine (R334Q) would desensitize the enzyme to malate inhibition because of their proximity to sites that are important for allosteric inhibition. We also hypothesized that mutating lysine 960 to glutamine (K960Q) and threonine 227 to valine (T227V) would significantly desensitize PEPc to the allosteric activators G6P and glycine, while significantly increasing the enzyme's affinity for the allosteric inhibitor malate. Site-directed mutagenesis was performed using the QuikChange XL system from Stratagene. Recombinant maize PEPc was expressed as a His-Tag fusion protein and purified by metal chelation chromatography. Kinetic studies were performed spectrophotometrically by measuring the disappearance of NADH in a coupled enzyme assay. Kinetic studies showed that S100A and R334Q display wild-type activation kinetics, but are less sensitive to malate inhibition. Residues threonine 227 and lysine 960 have been successfully mutated from threonine at 227 to valine and from lysine at 960 to glutamine. The kinetic analysis for both T227V and K960Q mutants is still in progress. In conclusion, serine 100 and arginine 334 play important roles in controlling the sensitivity of the enzyme to the inhibitor malate. Future kinetic analysis for T227V as well as for K960Q are expected to provide more insight into the role the hydroxyl group of threonine at position 227 and the role of a positive charge at lysine 960 have on the enzyme's ability to bind allosteric activators glycine and G-6-P.



Cindy Chau
 Abstract: Calcium ions, which are second messengers, are released inside certain cells in an oscillatory signal. This signal is associated with a variety of important physiological processes such as hormone secretion. To study their effects on cells and proteins, a molecule that will mimic these oscillations has been designed. An unsubstituted bis-spiropyran is known to be photochromic. Addition of substituted amines (R1=H; R2=CH2CO2-) creates a binding site for Ca2+, which should reversibly be disrupted upon irradiation. Compound (1), R1=CH3; R2=CH2CO2-, was found to bind Ca2+ moderately and selectively over Mg2+, and is not photochromic. To examine the effects of changing R2 on binding strength and selectivity, compound (1), R1= CH3; R2= CH2CH2CO2-, will be synthesized. The results of the multi-step synthesis will be presented.

 The Cultivation of Gratitude: An Online Procedure
 Mayra Torres

Abstract: With the advent of the positive psychology movement, gratitude has emerged as a human quality that has the potential for enhancing an individual's approach to life. In particular, gratitude has been found to contribute to a person's wholeness, spirituality, and subjective well-being (a personal evaluation of one's happiness). Past research suggests that gratitude has a positive emotional valence that involves a two-step cognitive process. Increasing an individual's awareness of positive daily events, can lead to increases in gratitude and an increased sense of subjective well-being. The purpose of the present study was to determine the effectiveness of an on-line procedure for cultivating gratitude (CG), and to determine whether individuals in the CG condition would show enhanced spirituality and subjective well-being.


 Ellipsometric Imaging of p53 and Actin Microarrays.
Ikenna Madu, Xin Li, Margarita Gutova, Jamil Momand,Feimeng Zhou.

Abstract: Imaging Ellipsometry is an optical technique in which changes in polarization of light due to the reflection from film-covered surface are analyzed in terms of thickness and refractive index of the film. Compared to other optical techniques, imaging Ellipsometry has a great advantage of high vertical resolution. Therefore, this technique has been widely used to characterize thin film, especially biological films on a well-defined surface. Ellipsometry is very sensitive to thickness change and this sensitivity is related to the optical and microstructure parameters such as refractive index. In our approach, substrate precipitation is induced which only greatly causes the changes of thickness of the film, but also induces great changes of other structural parameters such as refractive index thus, greatly enhancing the sensitivity of our approach.
The use of imaging Ellipsometry to image the hybridization of p53 and Actin Microarrays has been developed. p53 and Actin arrays are printed on a super aldehyde glass surface are hybridized with a biotinylated target followed by adsorption of streptavdin-HRP. The HRP catalyzed oxidation of an organic compound in the presence of H2O2 and the precipitation of the insoluble product on the region where sequence-specific hybridization will occur. As a consequence of the enzyme-catalyzed staining process, surface thickness of the region where hybridization has taken place increases. Such an increase in thickness can be sensitively detected by an imaging Ellipsometry. The detection level of this method for non-sandwich hybridization was found to be at 4.8 fM for a 10*10 microarray. This value is much more sensitive than that of other detection methods (e.g., fluorescence). Coupled with the alteration of the hybridization temperature, sequence-specific (single-base mismatch) DNA analysis can be accomplished.


Luis F. Gomez, Iris E. Rauda, Alejandro L. Briseno, Jiaxing Huang, Richard B. Kaner, Feimeng Zhou

Abstract: The separation of L- and D- enantiomers has been recently reported. When polyaniline (PAni) is doped with R-camphorsulfonic acid (R-CSA), it adopts a chiral structure. Removing the chiral acid dopant leads to a new form of dedoped chiral polyaniline. We found that the dedoped polyaniline recognizes L-phenylalanine with superiority over D-phenylalanine. This phenomenon suggests that the polymer-based sensor is selective to L-amino acids, which constitute most proteins. Through the use of chiral polyaniline
films, further chiral recognition studies can be extended to other L- and D- isomers. We plan to further study the interactions of chiral polyaniline films with different isomeric amino acids. In this study, the flow injection quartz crystal microbalance (FI-QCM), together with other spectroscopic techniques will be utilized as the technique to examine the molecular recognition events. We also plan to monitor the uptake and ejection of different stereoisomers in real time.


Eric Fromer

Abstract: The chemistry of singlet oxygen (1O2) with a variety of Rh(I) thiolate complexes has been studied.  Both oxidative addition and oxidation of the thiolate ligand are theoretically possible, but for the complex [Rh(CO)(PPh3)(StBu)]2 , sequential oxidative additions to the corresponding Rh(I)-Rh(III) and Rh(III)-Rh(III) peroxo complexes are observed.  The second reaction represents a highly unusual double oxidative addition reaction of a dinuclear species.  These interesting peroxo-thiolato complexes have been characterized by low-temperature 1H and 31P NMR spectroscopy.  The rate of first oxidative addition by sin! glet oxygen to [Rh(CO)(PPh3)(StBu)]2 has been calculated at 6.6 ± 0.9 x 106 M-1 sec-1, while the second reaction is considerably slower.


 A Phosphine Oxide Pretending To Be A Carbonyl: Nucleophilic Addition of Methanol to Tris(ortho-methoxyphenyl) Phosphine Oxide
 Mario Vargas

Abstract:  During the reaction of aryl phosphines, we recently found an unanticipated hemiacetal intermediate stable at temperatures below -60°C. By reacting tris(ortho-methoxyphenyl) phosphine with singlet dioxygen in a protic solvent mixture (CD2Cl2/MeOH), we obtained tris(ortho-methoxyphenyl) hydroxymethoxy phosphorane (the intermediate). The two were found to be in equilibrium at low temperatures. Both are detectable using 31P NMR, with the phosphorane giving a broad peak at 44 ppm and the oxide at 32 ppm. We suggest that the stability of the intermediate is due to H-bonding between the OH group bound to the phosphorus and the ortho methoxy groups on the phenyl rings (intramolecular H-bonding). It was also found that the greater the amount of MeOH in the solvent mixture, the more overall intermediate is formed, but the increase in phosphorane does not show a linear dependence on the methanol concentration. It is possible that the intermolecular H-bonding to the MeOH disrupts the intramolecular H-bond, thereby making it impossible to drive the equilibrium completely to the right. Keq at -80°C, 0.5M MeOH, is about 0.21 M-1.


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