Saturday May 5th – Presentations

In by admin

Molecular dynamics of metal-organic framework [(CH3)2NH2]Mn(HCOO)3 near magnetic and ferroelectric transitions using 1H, 55Mn NMR.

Sanath Ramakrishna1

2. Rhea Reyes2

3. John Haddock1

4. Arneil Reyes3

5. Naresh Dalal1

 

1. Florida State University
2. New York University
3. National High Magnetic Field Laboratory

02:05 PM
Materials Chemisry

Dimethylammonium Manganese Formate (DMMnF) is of interest as a multiferroic metal-organic framework. For the first time, 1H and 55Mn NMR are used to study the known ferroelectric transition at TFE~184K and antiferromagnetic (AF) transition at TN ~8.5K. A broad and strong zero-field 55Mn NMR signal was found below TN, with a calculated 8T internal field due to ordered Mn moments. This signal is suppressed above 0.3T, consistent with the known spin-flop transition. Dramatic changes in 1H spectra correlate to the magnetic ordering with a critical exponent of β =1/4, in contrast to the mean field prediction’s value of 0.5. The spin-lattice relaxation T1 recovery exhibits a double exponential behavior, with the long and short components differing by 3 orders of magnitude. The long T1 component dips near 150K and 8.5K, while the short component exhibits a huge enhancement approaching the critical regime followed by an exponential decay at low temperatures. This behavior is suggestive of an opening of a spin gap, Δ ~ 4.45K, about half of TN. Implications of these results will be discussed.

 

Ligand-induced ground state spin changes in Ce3Mn8 perovskite model clusters

Thai Son Cao, Khalil A. Abboud, and George Christou

Department of Chemistry, University of Florida, PO Box 117200, Gainesville, FL 32611

09:05 AM
Inorganic Chemistry

The AMnO3 manganites (A = main group or lanthanide metal) with a perovskite structure are under intense study because of their fascinating properties, such as multiferroicity, colossal magnetoresistance, piezoelectricity, and magnetoelasticity. We recently reported the molecular cluster [Ce3Mn8O8(O2CPh)18(HO2CPh)2], henceforth Ce3Mn8, with a structure related to the perovskite repeating unit and which provided insight into the origin of perovskite properties by possessing the same spin vector configurations as the C-type AF perovskites (AF = antiferromagnetic). It also has A-type AF low-lying excited states, suggesting that small structural changes could alter the ground state of the molecule to A-type AF; such changes are common in perovskites under different pressures and temperatures. To investigate this, we have synthesized derivatives of the Ce3Mn8 cluster in which Cl or Me substituents have been introduced into the ortho position of the benzoate ligands to introduce some structural perturbations. This presentation will describe the syntheses and structures of these 2-Cl-Ph and 2-Me-Ph derivatives, and the analysis of their magnetic properties to assess whether their ground states have changed.

Interactions of Ruthenocenyl-Conjugated Antibiotics with CTX-M β-Lactamase

Eric M. Lewandowski

University of South Florida

02:25 PM
Biochemistry / Chem Bio.

A series of novel ruthenocenyl-conjugated β-lactams were synthesized in order to investigate the antibacterial properties of the ruthenocenyl moiety against Penicillin Binding Proteins (PBPs). The β-lactams inhibit PBPs by forming a covalent acyl-enzyme complex with the catalytic residue. The active site of PBPs share a high level of homology with that of Class A β-lactamases, with a key difference being the presence of Glu166 in the β-lactamase active site. Glu166 allows β-lactamase to cleave the acyl-enzyme bond, thus allowing for the constant “turn over” of β-lactam antibiotics. We have solved a series of high-resolution X-ray crystal structures of ruthenocenyl-conjugated β-lactams in complex with CTX-M-14 Class A β-lactamase. Using a variety of CTX-M-14 mutants, we were able to capture several versions of hydrolyzed products, as well as intact compounds, in the CTX-M active site. These structures allowed us to make great insight into the CTX-M catalytic mechanism, and therefore, make inferences about the PBP catalytic mechanism. We also discovered that these compounds bind readily away from the active site and at the crystal-packing interface, with the ruthenocenyl moiety making many interactions with the surrounding residues. Some of the ruthenocenyl-conjugated β-lactams found to bind at the crystal-packing interface were compounds that had previously eluded small molecule crystallography efforts, suggesting that the CTX-M crystal system could potentially be used to solve the structure of other hard to crystallize small molecules.

Conformational free energy calculations with the confinement method

 

Arjan van der Vaart

University of South Florida, Department of Chemistry

02:20 PM
Computational Chemistry

The confinement method is a robust and conceptually simple free energy simulation method that allows for the calculation of conformational free energy differences between highly dissimilar states. We have developed protocols to make the calculations more accurate and efficient. Moreover, we have developed a simple method to allow accurate treatment in explicit water. Together, these improvements allow for the treatment of conformational changes in complex systems.

 

Ring Distortion of Complex Indole Alkaloids: Reengineering Biological Activity to Address New Disease Areas

Prof. Robert W. Huigens III

University of Florida

08:50 AM
Organic Chemistry

Various natural products, such as taxol, morphine and vancomycin, play a prominent role in medicine due to their ability to modulate biological targets critical to human disease. Current drug discovery efforts have shifted away from natural products and to the screening of large collections of compound libraries composed of structurally simple organic molecules. Despite their success against certain biological targets (e.g., kinases), these compound libraries have failed to produce viable leads in certain disease areas (e.g., antibiotics) which have been attributed to a lack of chemical diversity. Our lab aims to address deficiencies in chemical diversity through the development of a unified ring distortion approach targeting available, indole alkaloids as starting points for the rapid generation of an array of diverse complex scaffolds for biological screening in drug discovery. We recently reported a new tryptoline ring distortion approach from yohimbine, an indole alkaloid with a complex fused ring system.  In addition, we have utilized vinamine to produce novel complex small molecule scaffolds for drug discovery. Combined, our group has synthesized a library of >200 complex and diverse small molecules using short synthetic sequences and screening campaigns are underway. From these efforts, multiple hit compounds have been identified from various biological screens in diverse disease areas which will be presented during this talk.

Tunable Solid State Fluorescence in Isoreticular Metal Organic Frameworks

Wesley Newsome

Fernando Uribe-Romo

University of Central Florida

02:25 PM
Materials Chemisry

In this work highly stable zirconium based metal organic frameworks isoreticular to UiO-66 were prepared utilizing highly fluorescent links. These links allow for the systematic control over the emissive profile of the prepared material. This study shows how the tailoring of organic linkers with specific properties can be incorporated into a MOF in order to produce tunable properties. Three organic linkers were synthesized with Blue, Green, and Orange fluorescence to prepare solid solutions with properties similar to those observed in solution. This tunability allows for complete control of the emission profile as well as the temperature of the emitted white light. This careful design of organic linkers provides a strategy that can give insight into the photophysical manipulation of MOF monomers and their projected properties inside the MOF.

Study of tri-t-butyl tin hydride complexes of transition metals towards activation of small molecules

Sedigheh Etezadi, Burjor Captain

University of Miami

09:25 AM
Inorganic Chemistry

We have been actively pursuing the chemistry of transition metal complexes containing sterically demanding tin ligands. The ability of tin compounds to modify both heterogeneous and homogeneous catalysts is known and our recent efforts center on utilizing the reagent But3SnH to investigate the influence of this ligand, which combines a steric profile similar to that of PBut3, with functional reactivity at the Sn-H bond. These properties of the SnBut3 ligand allow preparation of new complexes and comparison of their structures and reactivities with less encumbered tri-alkyl stannanes. This has allowed fine-tuning of the strained molecular geometry at the coordinatively unsaturated site and study of how that influences small molecule activation. Reversible H2 binding and activation, H2-D2 scrambling to form HD, C-H activation of bound ligands and solvents, catalytic hydrogenation, and catalytic hydrostannylation have all been observed for select complexes. In addition, a range of metal cluster complexes incorporating stannane moieties have been prepared and structurally characterized. The bulky SnBut3 group can serve as a reagent in the hydrostannylation reactions of alkynes to furnish vinylstannanes of high regio- and stereochemical specificity. The potential role of designed and selectively modified stannane ligands has been demonstrated by power and others but full utilization of the added dimension that stannanes bring to catalyst design remains a goal for future exploration. In this manner, we synthesized the new
14-electron unsaturated complex Pt(IPr)(SnBut3)(H), which was shown to undergo facile reactions with small molecules as well as function as a catalyst,
is an active and highly selective catalyst in more than one arena, where the bulky SnBut3 group first serves as a ligand and imparts electronic unsaturation about the platinum metal center, and also serves at facilitating catalytic reactions due to its versatility to eliminate and hence generate reactive sites on the transition metal center.

Evolution of hybridization probes to DNA nanorobots for biosensing and gene therapy

Dmitry M. Kolpashchikova,b,c Amanda Cox,a,b Christopher Roldan,a,b Ola Kamar,a Anna F. Fakhardo,c Tatiana A. Lyalina,c Daria D. Nedorezova,c Alexander A. Spelkov,c Nadejda Y. Prokofeva, c Ekaterina A. Bryushkova, c Daria V. Nemirichc

ITMO University, Laboratory of Solution Chemistry of Advanced Materials and Technologies, Lomonosova St. 9, 191002, St. Petersburg, Russian Federation
Chemistry Department, University of Central Florida, Orlando, 32816, Florida, USA.
Burnett School of Biomedical Sciences, University of Central Florida, Orlando, 32816, Florida, USA

03:00 PM
Biochemistry / Chem Bio.

Hybridization probes remains one of the most common strategies for biosensing of specific DNA or RNA and have been extensively used in such formats as qualitative PCR, microarrays, florescent in situ hybridization (FISH), to name a few. Moreover, sequence specific recognition of RNA and DNA is on demand by gene silencing approaches including antisense, RNAi and CRISPR/cas9 technologies. However, all commonly used hybridization biosensors suffer from low selectivity at temperatures <40oC, inability to bind to long folded biological RNAs, high cost, low sensitivity. To address these problems, we construct multifunctional DNA nanomachines, in which each particular function is accomplished by a highly specialized component attached to a common DNA-based scaffold. Specialized functional units that are responsible for (i) highly selective sequence recognition; (ii) tight binding to target nucleic acids; (iii) unwinding RNA secondary structure; (iv) signal amplification; (v) fluorescent signaling and others, operate in cooperative manner upon target recognition. We designed DNA nanomachines for highly selective recognition of viral RNA and DNA, cleavage of viral RNA and cancer cell suppression. DNA nanomachines demonstrate improvements in the detection limits, recognition selectivity and efficiency of RNA cleavage in comparison with the traditional hybridization probes and cleaving agents. Possible future evolution of DNA nanomachines to DNA nanorobots for biomedical applications will be discussed.

Funding from NIAID (R15AI10388001A1) and NSF CCF 1423219 is greatly appreciated. D.M.K. was partially supported by the ITMO University Fellowship and Professorship Program.

Accuracy of density functional theory for predicting kinetics of methanol synthesis from CO and CO2 hydrogenation on copper

Maliheh Shaban Tameh, Albert Dearden, and Chen Huang

Department of Scientific Computing, Florida State University

03:00 PM
Computational Chemistry

Methanol synthesis is an important industrial process to produce methanol which is the building block for synthesizing many other chemicals and is also used in fuel cells. Despite extensive research on methanol synthesis, the active sites for this catalytic process are still under debates. Density functional theory (DFT) is widely used to gain insight into the kinetics of heterogeneous catalysis with atomistic resolution, however its accuracy heavily depends on the approximated exchange-correlation (XC) functionals. In this work, we examine the effect of XC functionals on the prediction of the kinetics of methanol synthesis on copper surface by using XC functionals of three different levels of accuracy: Perdew-Burke-Ernzerhof (PBE) XC functional, Heyd-Scuseria-Ernzerhof (HSE) hybrid XC functional, and the exact exchange and random phase approximation (RPA) correlation functional. Microkinetic modeling based on PBE and HSE predicts that the turnover frequencies of methanol are two orders of magnitude faster than the RPA predictions. PBE predicts that CO is the carbon source which is contradictory to the previous isotope-labeling experiments which suggested that CO2 is the carbon source. This contradiction indicates that metallic copper is not the active site. A different picture is obtained with RPA calculations which show that both CO and CO2 contribute to the methanol production, therefore suggesting that we cannot rule out the possibility that metallic copper is the active site in industrial methanol synthesis. Our results suggest that sufficiently accurate XC functionals are needed to achieve predictive computational modeling of methanol synthesis in which competing processes, such as CO and CO2 hydrogenation, exist.

 

A submonomer-based approach towards piperazic acid (Piz) natural products. The total synthesis of L-156,373

Yassin M. Elbatrawi, Chang Won Kang and J. R. Del Valle*

Department of Chemistry, University of South Florida, Tampa, FL 33620, USA

09:20 AM
Organic Chemistry

The piperazic acid (Piz) residue is found in a number of biologically active natural products and there exist numerous methods for its synthesis and incorporation into host peptides. Most approaches introduce pre-formed orthogonally protected Piz residues, synthesized in many steps, onto a growing peptide chain. L-156,373, a cyclic hexapeptide and oxytocin antagonist isolated from Streptomyces silvensis, features two consecutive enantiomeric forms of the Piz residue. Here, we present the first total synthesis of L-156,373 and its analogues via a sub-monomer-based electrophilic amination approach. Our strategy relies on a tandem SN2 cyclization to afford both Piz residues in one step and employs l- and d- glutamic acid residues as chiral synthons. This approach provides a means to introduce Piz and δ-oxo piperazic acid (oxoPiz) residues into host peptides using readily available amino acid building blocks.

High Refractive Index Polymer Composites

Edmundo Bello

Albert Stiegman

Florida State University

03:00 PM
Materials Chemisry

Hybrid organic/inorganic thermoset polymers synthesized through the thiol-ene coupling reaction have proved to produce materials with a high refractive index (n) making them potentially suitable for optical applications. A series of hard transparent polymer composites were made from tetravinylsilane (TVS) and 1.3-Benzenedithiol (BDTH) with varying concentrations of zirconium oxo-cluster Zr6(OH)4O4(OMc)12 (ZOC) incorporated. The resulting polymers exhibited a significant improvement in the refractive index relative to the parent polymer, TVS and BDTH (n = 1.693). This improvement reaches a maximum value of 1.719 at a loading of 2.5 wt.% ZOC and then decreased as the concentration of ZOC in the polymer matrix increased. The refractive index of ZOC itself was determined to be 1.539 by the Becke Line method which is well below the observed refractive index of the polymer composites. The trend in the refractive index of the composites as a function of ZOC loading and the high refractive index achieved (1.719), despite the low inherent refractive index of the ZOC itself, was found to be due to changes in the bulk density of the composites. Finally, the glass transition temperatures (Tg) of the polymers seemed to decrease as the mole fraction of ZOC increases, resulting in a compromise of its hardness. Solid state Si29 NMR and RAMAN spectra show evidence that a significant amount of unreacted vinyl groups are left over when high concentration of ZOC is present in the polymer matrix.

Design and synthesis of concentration gradient Prussian blue analogues

Su Kyung Jeon, Daniel R. Talham

Department of Chemistry, University of Florida

10:15 AM
Inorganic Chemistry

Analogues within the Prussian blue family of coordination polymer networks are studied for wide ranging applications including electrochromics, ion storage for battery electrodes, magnetism and light-switchable magnetism, as well as for biomedical agents and in catalysis.  A new architecture of coordination polymer particles, concentration gradient Prussian blue analogues, is introduced in this presentation. In these particles, a gradient between two single phases of PBA is achieved by varying the occupancy of divalent metals from core to the surface within the particle. The synthetic conditions under which uniform gradient particles can be reproducibly synthesized will be described. In addition, discussion of systems that behave well and those that show new behavior is presented. The concentration gradient particles are compared to analogous single phase and core-shell heterostructure particles.

Structure Studies of Spider Silk Dope

Geoffrey M. Gray and Arjan van der Vaart

Department of Chemistry, University of South Florida

03:20 PM
Biochemistry / Chem Bio.

Spider dragline silk possesses a unique combination of strength and elasticity. Its main constituents are two proteins (MaSp1 and MaSp2), that are stored in a high concentration (30-50%) dope before the silk is spun into a fiber. The dope is thought to form micelles that aggregate into liquid crystals, but the microstructure of the proteins in the dope remains unclear. To help elucidate secondary structure characteristics, enhanced sampling simulations were performed on several common dragline silk sequence motifs at various concentrations under dope-like conditions. Enhanced sampling was also performed in octanol to mimic a fiber environment. Additional pulling experiments were used to assess structural changes that occur under spinning-like conditions. Results show that the motifs resemble random coils under aqueous conditions, while showing some turns and helices in octanol. Pulling showed an increase in the 31-helical content, consistent with the idea that these structures form as part of the spinning process.

TD-DFT Calculations to Assign Ground and Excited State Electronic Structures of DioxoCr(VI) sites

David Jeffcoat, Albert Stiegman

Florida State University

03:20 PM
Computational Chemistry

Assignment of the excited states was facilitated using time-dependent density functional theory (TD-DFT) calculations performed on cluster models. All of the observed electronic transitions and their energies are accounted for by dioxoCr(VI) sites. The lowest energy observed excitation at 22 800 cm–1 populates a singlet excited state, while the emitting state is the corresponding triplet state, accessed by intersystem crossing from the singlet state. Spectroscopic bands observed at 29 100, 36 900, and 41 500 cm–1 were assigned, based on the TD-DFT calculation, to spin-allowed transitions that are consistent with emission polarization anisotropy measurements.

Anti-infective and Neurodegenerative Drug Discovery – Something Old, Something New…

James W. Leahy

University of South Florida

10:15 AM
Organic Chemistry

Recent results from our efforts aimed at the discovery of anti-infective and neurodegenerative results will be discussed. Included in these will be both novel compounds and the discovery of a well-known agent that might be exploited for its activity in both areas.

Synthesis of High Refractive Index Lens Materials

Yue Su, Albert Stiegman

Florida State University

03:20 PM
Materials Chemisry

High refractive index polymer materials are synthesized from with the self-initiating thiol-ene coupling reaction between the trivinylphosphine derivatives and selected dithiols.  The presence of highly polarizable elements of P, S and Se in P=S/P=Se bonds in the vinyl monomers and the presence of aromatic structures and S in thiols generates polymers exhibiting high refractive indices ranging from 1.64 to 1.75. The polymers also have Abbe Numbers from 22.73 to 37.18 depending on the composition. After undergoing a slow graduated curing process that reached a final temperature of 120, hard, transparent optical materials were obtained. Solid-state 31P NMR was performed to characterize the the degree of cross-linking in the thiol-ene polymer. DSC and DMA are used to measure Tg and Young’s modulus respectively. The transmittance over visible range of the spectrum was carried out by UV-vis spectroscopy and other physical properties such as the density were measured.

Catalytic Synthesis of Cyclic Polymer via Ring Expansion Metathesis Polymerization.

Vineet K. Jakhar, Muhammad T. Jan, Poppy W. J. P. Disney, Khalil A. Abboud, Adam S. Veige

University of Florida

10:35 AM
Inorganic Chemistry

This report describes an approach to building Mo complexes featuring metal-carbon multiple bonds using a trianionic pincer ligand. Treating [tBuOCO]MoNMe2(NHMe2)2, a d2 Mo(IV) ion, with terminal alkynes (H–C≡CR, R = tBu, Ph, and SiMe3) produces in quantitative yield the corresponding metallocyclopropylidene complexes. X-Ray diffraction studies on a single crystal of these complexes reveal three notable features: (1) a highly distorted hexacoordinate Mo(VI) center, (2) a metallocyclopropene fragment, and (3) a highly distorted CH group in the metallocyclopropene unit. These complexes are capable of polymerizing norbornene via ring expansion metathesis polymerization (REMP) to yield highly cis-syndiotactic cyclic polynorbornene (poly(NBE)). The tacticity of the polymer was determined by examination of 1H and 13C{1H} NMR spectra of the polymer in solution. Polymerization conducted at ambient temperature generated >98% cis, >98% syndiotactic poly(NBE) over 21 h. The timeframe was reduced to 6-10 h by gradually increasing the temperature to 60 °C, which led to a decrease in cis to trans ratio (>93, cis).

Mechanistic studies of hydrogen evolution reactions over low-dimensional, Pt-free transition metal catalysts

Abdulrahiman Nijamudheen,a,b Srimanta Pakhira,a,b Carlos I. Aguirre-Velez,a,b and Jose L. Mendoza-Cortesa,b,c

a. Department of Chemical & Biomedical Engineering, Florida A&M University, and Florida State University, Joint College of Engineering, Tallahassee FL, 32310, USA
b. Scientific Computing Department, Materials Science and Engineering Program, High-Performance Material Institute, Florida State University, Tallahassee FL, 32310, USA.
c. Condensed Matter Theory, National High Magnetic Field Laboratory, Florida State University, Tallahassee FL, 32310, USA.

03:40 PM
Computational Chemistry

Low-dimensional Pt-free catalysts are attractive candidate materials for performing hydrogen evolution reactions (HER). In this regard, transition metal dichalcogenides and phosphides have been proposed as efficient catalysts. Experiments indicate that S doping can be used to enhance the HER efficiency of MoP. In fact, S-doped MoP shows superior catalytic activities than other conventional transition metal dichalcogenide catalysts. We use hybrid density functional theory methods to understand the electronic structure and catalytic properties of MoS2, MoP, and S-doped MoP (MoPS). By studying the detailed mechanisms and kinetics for the reactions over various systems, we explain how S doping increases the activity of MoP. The current theoretical study establishes the HER mechanisms over doped and undoped catalysts under different electrochemical conditions. Based on our calculations, we propose a number of design principles for improving the catalytic activities of low-dimensional Pt-free HER catalysts.

 

Investigations in Organobarium Chemistry: Synthesis of 3,4-dihydroxyphenylacetaldehyde (DOPAL): a Potential Target for Neuroprotective Therapy in Parkinson's Disease.

Ralph N. Salvatore*, Nicholas Schofield, Jacob R. Hobby, Josue F. Deslauriers, and Tori Scheffler

Southeastern University
Department of Natural Scienes
1000 Longfellow Blvd
Lakeland, FL 33801

10:45 AM
Organic Chemistry

3,4-dihydroxyphenylacetaldehyde (DOPAL), an important biogenic aldehyde, serves as a critical endogenous toxin which triggers dopamine (DA) neuron loss in Parkinson’s disease (PD). Despite the immense biochemical significance of DOPAL, attempts to synthesize this compound in pure form have been met with grave difficulty. In fact, most methods lack detailed experimental procedures, full characterization, and suffer from extremely low product yield (~4%). Therefore, considerable effort to produce DOPAL in a higher yield would be clearly warranted. In an effort to mitigate these problems, we have directed our attention toward a more efficient synthesis of DOPAL using organobarium reagents. These novel reagents, standardized against various carbon-carbon bond forming reactions fundamental to organic synthesis, were then applied toward the total synthesis of DOPAL. These studies may provide important insight on future drug action to combat PD and, when the scope of this research is expanded, may aid in the treatment of other neurodegenerative disorders.

The pH Effect in Seed-Mediated Growth of Gold Nanorods

Gang Chen, Reese Gallagher, Xing Zhang

Department of Chemistry, University of Central Florida

03:40 PM
Materials Chemisry

Although various gold nanorods (AuNRs) have been produced with different aspect ratio, current synthesis methods through seed-mediated growth are far from ideal, sharing the same drawbacks, such as low yield of gold conversion (~20%), poor shape uniformity and reproducibility, due to a lack of understanding of the reaction mechanism. While the mechanism of the anisotropic growth of AuNRs is not clear yet, the experimental detail in the literature show that the final products depend on the rate of chemical reduction of metal ion. Basically, the reduction rate depends on both the reactivity and concentration of the reactants (gold salts and ascorbic acid (AA)). The concentration of AA is commonly utilized to control the reduction rate. For example, to decrease the reduction rate, the ratio of AA to gold ion has been optimized to be 1.1 which is far below the stoichiometric ratio (1.5), giving extremely poor yield of gold conversion (~20%). In this research, to achieve a high gold conversion yield, we keep the stoichiometric ratio of AA to gold ion (1.5) but tuning the reduction rate by reactivity. As a polyol compound, the reactivity of AA depends on the pH of the system. At stoichiometric ratio (1.5), the optimal pH range for AA has been discovered to get prefect AuNRs with improved uniformity, reproducibility and gold conversion yield (> 80%). The gold conversion yield can be improved further at higher ratio of AA to gold ion than the stoichiometry. With the same idea, the PI has extended the reducing agent to other polyol compounds, such as phenol, hydroquinone, catechol, resorcinol, and phloroglucinol.

Growth mechanisms of Prussian blue analogue nanoparticles in surfactant-free synthesis

Jiamin Liang, Carissa H. Li, Daniel R. Talham

Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, United States

10:55 AM
Inorganic Chemistry

The growth mechanism of Prussian blue analogue (PBA) nanoparticles synthesized via surfactant-free coprecipitation has been investigated. This study suggests that PBA nanoparticles form via different mechanisms, depending on composition.  Particles of the rubidium cobalt hexacyanometallate(III) series, RbCoM’ PBA with M’ = Cr, Fe, Co, form through a complex nonclassical growth mechanism, whereas rubidium nickel hexacyanometallate(III), RbNiM’ PBA with M’ = Cr, Fe, Co, nanoparticles form via a classical dissolution-recrystallization growth process. Factors affecting the growth behavior including reaction time and precursor concentration have been probed using transmission electron microscopy (TEM), real-time conductance measurement and dynamic light scattering (DLS). Although nanoscale and mesoscale Prussian blue analogue particles are used in many areas of study, including magnetism, battery cathodes, electrochromics and catalysis, this is the first detailed analysis of their particle growth mechanisms.

Investigating plasticization and swelling in polymers of intrinsic microporosity (PIM-1) from atomistic molecular simulations

Grit Kupgan1, Alexander Demidov2, Coray M. Colina1,2

1Department of Materials Science and Engineering, University of Florida, Gainesville, FL, 32611, USA
2Department of Chemistry, University of Florida, Gainesville, FL, 32611, USA

04:00 PM
Computational Chemistry

Polymers of intrinsic microporosity (PIMs) are a promising class of polymeric membranes for gas separation. Their design is based on their semi-rigid and contorted backbones, yielding polymers with high free volume architectures. Although PIMs have gained significant attention recently, they can be subjected to undesirable plasticization. Plasticization is defined as the rearrangement of polymers chains due to local swelling of microstructure by condensable penetrants. Understanding the effect of plasticization on polymers is crucial since the process can significantly deteriorate the performance of these materials. In this work, we investigated the plasticization behavior in PIM-1 using atomistic molecular simulations. PIM-1 was constructed with Polymatic which is based on a simulated polymerization approach. To account for plasticization and swelling, a hybrid approach is implemented using Monte Carlo (GCMC) and molecular dynamics (NPT). An open-source python package, Pysimm, was used to communicate simulation data between Cassandra and LAMMPS software. When the systems are equilibrated based on proposed convergence criteria, structural and adsorption properties of the simulated samples can be probed at various loading while considering the flexibility of the polymer. This approach allows the study of the effects of plasticization on the performance of PIM-1 for their industrial employment in membrane and pressure swing adsorption applications. Our results showed that the gas loading has a major impact on most structural and adsorption properties. From MC/MD simulation, we found that gas loading can initiate swelling within PIM-1 around ~3 mmol/g at 300 K. Moreover, we found that plasticization does not always result in the decline of material’s performance.

Sigma Receptor Ligands: From Discovery to Clinical Translation

Christopher R. McCurdy

Department of Medicinal Chemistry, College of Pharmacy, University of Florida, Gainesville, Florida, USA 32610

11:05 AM
Organic Chemistry

Peripheral nerve injury, as a consequence of trauma, surgery, inflammation, or other causes, is a major medical problem.  This type of injury is often associated with chronic pain.  About 100 million people suffer from chronic pain in the United States alone.  Diagnosis and treatment are still considered as unmet medical needs.  Current clinical imaging methods used to evaluate chronic pain are centered on anatomic alterations, which do not necessarily reflect the origin of chronic pain.  A potential biomarker associated with nerve injury and neuroinflammation is the sigma-1 receptor (S1R).  In addition, S1Rs appear to play an active role in pain modulation, both peripherally and centrally.  We recently identified a highly selective S1R antagonist that was transformed into a PET probe candidate and demonstrated high specificity and selectivity for imaging S1Rs in mice, rats, and monkeys.  We have utilized this probe in a rat model of nerve injury via PET/MRI.  The results have helped promote the clinical use of the agent in identifying peripheral pain generators in patients suffering from neuropathic pain.  Furthermore, we have investigated the cold compound and similar derivatives as potential pharmacotherapies for neuropathic pain in mouse models of nerve injury.  These compounds have equipotent or superior analgesic efficacy to the clinically utilized gabapentin.  The compounds have also been examined for liabilities in locomotor, rotorod, conditioned place preference and in some cases, self-administration assays.  The results indicate the analgesic effects produced by S1Rs antagonists are not associated with these potential liabilities.  These results confirm the ability of S1Rs to serve as potential diagnostic and analgesic agents for neuropathic pain without CNS liabilities.

Funding provided by NIDA (DA023205), NIGMS (GM104932), US Department of Defense, the Center for Biomedical Imaging at Stanford University, and the State of Florida, Executive Office of the Governor’s Office of Tourism, Trade, and Economic Development.

New Strategies for the C–H Functionalization of Amines

Daniel Seidel

University of Florida

01:30 PM
Organic Chemistry

This lecture will cover our recent efforts in the development of reaction cascades for the rapid buildup of molecular complexity via the mild α- and β-C–H bond functionalization of amines. Mechanistically distinct approaches will be discussed.

Hierarchical Self-assembly of Supramolecular Norias

Bo Song, Xiaopeng Li

Department of Chemistry, University of South Florida

02:00 PM
Organic Chemistry

In biological systems, the shapes, complexity and functions of DNA- and protein-based assemblies are encoded by the defined sequence of nucleotides and amino acids. Inspired by nature, we herein introduced the concept of “programming of sequence-specific ligands” and designed a series of linear building blocks with specific sequence through bridging terpyridine ligands with Ru(II) coordination. Being different from traditional methods such as controlling the size, angle, dimensionality of the ligand, this strategy allows us to predict and design structures based on the linkage of the building blocks in ligand. Different generations of “Supramolecular Norias” (N1 to N5) with increasing complexity were thus obtained after the self-assembly with different transition metals. The resulting structures were characterized via multi-dimensional mass spectrometry analysis (ESI-MS, TWIM-MS) as well as a series of NMR (1H, COSY, NOESY) analysis. Moreover, the larger size supramolecules N4 and N5 were hierarchically self-assemble into uniform 2D nanostructures on HOPG surface as recorded by STM, or uniform nanotubes, which were observed under TEM.