An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
is an assistant professor of instruction with the Undergraduate Engineering Office and the Mechan... more is an assistant professor of instruction with the Undergraduate Engineering Office and the Mechanical Engineering department at Northwestern University. His research was conducted at the intersection of robotics and biomechanics in the field of human-machine interactions, and explored novel ways to control robotic prosthetic hands. He is very passionate about student education and currently teaches five separate courses at the undergraduate level that include manufacturing, design, experimental methods, and thermodynamics. He greatly enjoys advising all levels of undergraduate and early graduate students. He is the producer for the Lightboard studio, and is currently exploring models for effective online and hybrid teaching models.
where she currently teaches first-year engineering design courses. Her research interests in engi... more where she currently teaches first-year engineering design courses. Her research interests in engineering education include the identification of variables that impact the firstyear experience and the development of strategies to enhance it, retention of underrepresented populations in STEM fields and service-learning in engineering.
2018 ASEE Annual Conference & Exposition Proceedings
is an assistant professor of instruction with the Undergraduate Engineering Office and the Mechan... more is an assistant professor of instruction with the Undergraduate Engineering Office and the Mechanical Engineering department at Northwestern University. His research explored novel ways to control robotic prosthetic hands. He is very passionate about student education and has taught multiple courses at the undergraduate level that include manufacturing, freshman and capstone design, experimental methods, and thermodynamics. He greatly enjoys advising all levels of undergraduate and early graduate students. He has been highly involved with the Lightboard studio and exploring models for effective online and hybrid teaching methods.
Her research interests include STEM education at all levels, first-year experience and issues rel... more Her research interests include STEM education at all levels, first-year experience and issues related to the transition from high school to college, and the retention and recruitment of women and minorities to STEM fields.
Recent research indicates that first-year, team-based design courses represent a unique opportuni... more Recent research indicates that first-year, team-based design courses represent a unique opportunity to address such disparities and providing early collaborative learning experiences supports the success of students from underrepresented groups in engineering [10-13]. While lectures and readings may provide teams with basic tools for team and project management, these correlate team success with the creation of a high-quality final design [14]. Such tools may inadvertently cue students to distribute work according to stereotypical social roles in the belief that by having team members "play to their strengths," they are doing what is best for the team [15]. Such task distribution may limit new learning across team members, exclude historically underrepresented students from high profile team tasks (such as design and fabrication) [16], and thus promote the entrenchment of implicit biases. This study leverages a cooperative learning approach [23] to teamwork and learning in a first-year engineering design course at Northwestern University's McCormick School of Engineering in order to provide more equitable access to learning for all students. Implementation of such approaches in first-year contexts is of particular importance, as these classes are formative for how students view teamwork. The study analyzes results from the use of a novel curricular intervention piloted in Design Thinking and Communication 1 (DTC 1) at Northwestern University. Specifically, the intervention required that students on a team rotate through leadership roles in four key areas: primary research, secondary research, training-building-testing, and project management. The team lead for each role completed associated documentation and coached their successor on how to succeed in that role. Research Context This research took place in a required first-year design course during Fall 2019 and Winter 2020 quarters at Northwestern University. The course (entitled Design Thinking and Communication I) focuses on user-centered design for individuals with disabilities, and requires students to collaborate with real-world clients and users. Approximately 140 student participants were enrolled among nine control sections (5 in fall, 4 in winter) that retained the standard course design format or nine experimental sections (5 in fall, 4 in winter), which piloted intentional team role rotation as the curricular innovation. The team roles were (i) primary research, (ii) secondary research, (iii) training-building-testing, and (iv) project management and are described
where she currently teaches first-year engineering design courses. Her research interests in engi... more where she currently teaches first-year engineering design courses. Her research interests in engineering education include the identification of variables that impact the firstyear experience and the development of strategies to enhance it, retention of underrepresented populations in STEM and global engineering experiences.
2015 ASEE Annual Conference and Exposition Proceedings
West Virginia University, where she currently teaches first-year courses in the Freshman Engineer... more West Virginia University, where she currently teaches first-year courses in the Freshman Engineering Program. Her research interests in engineering education include the identification of variables that impact the first-year experience and the development of strategies to enhance it, retention of underrepresented populations in STEM fields and service-learning in engineering.
Crystals of di-2-pyridyl ketone benzoylhydrazone (dpkbh) obtained from a dimethylsulfoxide (DMSO)... more Crystals of di-2-pyridyl ketone benzoylhydrazone (dpkbh) obtained from a dimethylsulfoxide (DMSO) solution of dpkbh are in the monoclinic space group, P2 1/c. Structural analysis reveals anti-parallel, non-planar, one-dimensional tapes of dpkbh with a network of intra-and intermolecular hydrogen bonds. Optical measurements on dpkbh in polar non-aqueous solvents revealed the presence of interlocked low-(a-) and high-(b-) energy intraligand charge-transfer electronic states may be due to dpk p±p p followed by dpk to benzoyl charge-transfer. The equilibrium distribution of the low-(a-) and high-(b-) energy electronic states is solvent dependent, controlled by the hydrogen bonding capacity of surrounding solvent molecules. The interplay between the a-and b-conformations of dpkbh allowed calculations of their extinction coef®cients by forcing the equilibrium to shift to one conformation using chemical stimuli. In N,N-dimethylformamide (DMF), extinction coef®cients of 45,000^2000 and 15,000^2000 M 21 cm 21 were calculated for the a-and b-conformations of dpkbh at l max , respectively, when excess acid was added to a DMF solution of dpkbh. The weak bond energies of the hydrogen bonds, the reversibility and the sensitivity of the high-and low-energy electronic states to their surroundings in polar non-aqueous solvents allow for the use of this system as molecular sensor for a variety of stimuli that include metal ions, acids and bases. Metal ions in concentrations ,10 27 M can be detected and determined using this system (dpkbh and surrounding solvent molecules).
The molecular sensor fac-[Re(CO) 3 (dpkbh)Cl]•DMF (1) where DMF ¼ N,N-dimethyl formamide and dpkb... more The molecular sensor fac-[Re(CO) 3 (dpkbh)Cl]•DMF (1) where DMF ¼ N,N-dimethyl formamide and dpkbh ¼ di-2-pyridylketonebenzoylhydrazone crystallized in the acentric triclinic space group P1. Structural analysis shows two units of (1) with rhenium in distorted octahedral geometry, the carbonyl groups are in facial positions with an average C-Re-C angle of 908 and the N,Nbidentate dpkbh forms six-membered metallocyclic ring with rhenium in a boat conformation. The molecular packing shows the binding of DMF to fac-[Re(CO) 3 (dpkbh)Cl] and helical strands of (1) interlocked via a network of hydrogen bonds. Optical measurements on fac-[Re(CO) 3 (dpkbh)Cl] in DMF show the presence of two interlocked charge transfer bands at 440 and 318 nm that are highly sensitive to slight variations in their surroundings. As the concentration decreases, the intensity of the low energy absorption band at 440 nm increases and the reverse is observed when the concentration increases. Thermo-optical measurements on fac-[Re(CO) 3 (dpkbh)Cl] in DMF established the reversible interconversion between the high and low energy electronic states of fac-Re(CO) 3 (dpkbh)Cl and changes in enthalpy ðDH B Þ of þ 17.44^0.40 kJmol 21 , entropy ðDS B Þ of þ37.45^0.50 J mol 21 and free energy ðDG B Þ of þ6.27^0.30 kJ mol 21 in DMF were calculated. Acids or bases in concentration as low as 1.0 £ 10 29 M can be detected and determined using fac-[Re(CO) 3 (dpkbh)Cl] in DMF. 1 H-NMR measurements on fac-[Re(CO) 3 (dpkbh)Cl] in DMF in non-aqueous media reveal high sensitivity to solvent and temperature variations and points to strong solvent-complex interactions. The amide protons and solvate protons show high sensitivity to temperature variations than the aromatic protons pointing to the participation of the amide proton in solvate-complex hydrogen bonds in non-aqueous solutions of fac-[Re(CO) 3 (dpkbh)Cl].
... Mohammed Bakir Corresponding Author Contact Information , E-mail The Corresponding Author , I... more ... Mohammed Bakir Corresponding Author Contact Information , E-mail The Corresponding Author , Ishmael Hassan , Toni Johnson , Ordel Brown , Orville Green , Colin Gyles and ... [1]. CM Armstrong, PV Bernhardt, P. Chin and DR Richardson. Eur. ... [5]. LM Hayden, W.-K. Kim, AP ...
Crystals of di-2-pyridyl ketone p-nitrophenylhydrazone (dpknph), obtained from a dmso (dimethylsu... more Crystals of di-2-pyridyl ketone p-nitrophenylhydrazone (dpknph), obtained from a dmso (dimethylsulfoxide) solution of dpknph, are in the monoclinic space group, P2 1 =n: Structural analysis reveals non-coplanar pyridine rings and infinite one-dimensional chains of dpknph with a network of classic and non-classic hydrogen bonds. Optical measurements on dpknph in dmso in the presence and absence of CdCl 2 and NaBH 4 gave extinction coefficients of 91,000^2000 and 35,000^2000 M 21 cm 21 for the high and low energy electronic states of dpknph at 295 K. Thermo-optical measurements on dpknph in dmso established the reversible interconversion between the high and low energy electronic states of dpknph and allowed calculations of their thermodynamic activation parameters and gave changes in enthalpy (DH B) of 2 49.05^1.25 kJ mol 21 , entropy (DS B) of þ 0.16^0.04 kJ mol 21 and free energy (DG B) of 2 96.30^2.45 kJ mol 21 at 295 K. Manipulation of the equilibrium distribution of the high and low energy electronic states of dpknph allowed for the use of the system as cation-anion and acid-base sensor. Basic anions such as BH 4 2 and OH 2 favor the low energy electronic state and electron deficient anions such as BF 4 2 , metal ions and protons favor the high-energy electronic state. The reversible BH 4 2 /BF 4 2 and OH 2 /H þ interconversion points to physical interactions between these species and dpknph and the use of dpknph as a spectrophotometric sensor for a variety of physical and chemical stimuli. Metal ions in concentrations as low as 1.00 £ 10 27 M can be detected and determined using dpknph in dmso.
When di-2-pyridyl ketone thiosemicarbazone (dpktsc) was allowed to react with [Re(CO) 5 Cl] in to... more When di-2-pyridyl ketone thiosemicarbazone (dpktsc) was allowed to react with [Re(CO) 5 Cl] in toluene under reflux, fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl] was isolated in good yield. The identity of fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl] was established from the results of its elemental analysis, spectroscopic, and electrochemical properties. The infrared spectra of fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl] show the facial coordination of the carbonyl groups, and the pyridyl N,N-coordination of dpktsc. 1 H NMR measurements on fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl] in d 6-dmso and d 6-acetone confirmed the pyridyl N,N-coordination of dpktsc, and showed strong solvent dependence as manifested by the sensitivity of thioamide and ammine protons to their surroundings. The electronic absorption spectra of fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl] in protophilic solvents (dmso and dmf) display two intra-ligand charge transfer (ILCT) transitions at 476 and 360 nm and in nonprotophilic solvents a single ILCT transition at 346 nm in CH 3 CN and 342 nm in CH 2 Cl 2. Reversible interconversion between fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl] and its conjugate base was established in protophilic solvents using a base to shift the equilibrium to the conjugate base and an acid to shift the equilibrium or conjugate base to the neutral form. Substrates in concentrations as low as 1 Â 10 À10 M can be detected and determined using protophilic solutions of fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl]. When MCl 2 (M = Zn, Cd or Hg) was allowed to interact with fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl] in protophilic solvents, the intensity of the low energy ILCT band disappeared and a shift in the high energy ILCT electronic transition was observed that hints to the coordination of MCl 2 to fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl]. Electrochemical measurements on fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl] in dmf showed sequential irreversible redox processes in accord with the electrochemical reduction or oxidation of the thiosemicarbazone moiety.
ABSTRACT When [Re(CO)5Cl] was allowed to react with di-2-pyridyl ketone semicarbazone hydrochlori... more ABSTRACT When [Re(CO)5Cl] was allowed to react with di-2-pyridyl ketone semicarbazone hydrochloride (dpksc.HCl) in refluxing toluene, fac-[Re(CO)3(κ2-N,N-dpksc)Cl] was isolated. The identity of fac-[Re(CO)3(κ2-N,N-dpksc)Cl] was elucidated from the results of its elemental analysis and confirmed using a number of spectroscopic measurements. Spectroscopic measurements done on non-aqueous solvents divulged sensitivity of fac-[Re(CO)3(κ2-N,N-dpksc)Cl] to changes in its surroundings. 1H NMR studies revealed significant solvent dependence as manifested by the chemical shift variations; the exchange of the amine protons with solvent deuterium in CDCl3 and d6-acetone; the temperature dependence of the chemical shifts of the amine and amide protons and insignificant temperature dependence of the aromatic proton. The electronic absorption spectra of fac-[Re(CO)3(κ2-N,N-dpksc)Cl] measured on non-aqueous solvents disclosed two high energy intra-ligand charge transfer (ILCT) transitions. Optical measurements performed on protophilic solutions of fac-[Re(CO)3(κ2-N,N-dpksc)Cl] in the presence of bases and acids showed the appearance and disappearance of a low energy ILCT electronic transitions and established reversible inter-conversion between fac-[Re(CO)3(κ2-N,N-dpksc)Cl] and its conjugate base, fac-[Re(CO)3(κ2-N,N-dpksc-H)Cl]−. Thermo-optical measurements done on protophilic solutions of fac-[Re(CO)3(κ2-N,N-dpksc)Cl] disclosed the absence of thermal acid–base inter-conversion between fac-[Re(CO)3(κ2-N,N-dpksc)Cl] and fac-[Re(CO)3(κ2-N,N-dpksc-H)Cl]− and established reversible electronic transfer between the high energy electronic transitions of fac-[Re(CO)3(κ2-N,N-dpksc)Cl]. Optosensing measurements done on protophilic solutions of fac-[Re(CO)3(κ2-N,N-dpksc)Cl] showed acids and bases in concentrations as low as 1.00 × 10−10 M can be detected and determined using protophilic solutions of of fac-[Re(CO)3(κ2-N,N-dpksc)Cl]. Electrochemical measurements on dmf solutions of fac-[Re(CO)3(κ2-N,N-dpksc)Cl] showed irreversible electrochemical redox process and electrochemically generated product waves pointing to the instability of fac-[Re(CO)3(κ2-N,N-dpksc)Cl] to redox transformations.
An understanding of the molecular mechanisms of the newly characterized herpes simplex virus (HSV... more An understanding of the molecular mechanisms of the newly characterized herpes simplex virus (HSV) B5 protein is important to further elucidate the HSV cell entry and infection. The synthetic peptide of B5 (wtB5) was functionalized with the nonlinear optical chromophore cascade yellow and its molecular dynamics was probed at physiological and endosomal pH (pH 7.4 and 5.5, respectively). Steady-state CD spectroscopy was utilized to characterize the peptides at different pH. These spectra showed structural changes in the peptide with time measured over several days. Nonlinear optical measurements were carried out to probe the interactions and local environment of the labeled peptide, and the increase in the two-photon cross section of this system suggests an increase in chromophore-peptide interactions. Time-resolved fluorescence upconversion measurements reflected changes in the hydrophilic and hydrophobic local environments of the labeled peptide-chromophore system. Ultrafast depolarization measurements gave rotational correlation times indicative of a reversible change in the size of the peptide. The time-resolved results provide compelling evidence of a reversible dissociation of the coiled coils of the wtB5 peptide. This process was found to be pH-insensitive. The data from this unique combination of techniques provide an initial step to understanding the molecular dynamics of B5 and a framework for the development of novel imaging methods based on two-photon emission, as well as new therapeutics for HSV.
The reaction between Re(CO) 5 Cl and di-2-pyridylketone benzoylhydrazone (dpkbh) in refluxing tol... more The reaction between Re(CO) 5 Cl and di-2-pyridylketone benzoylhydrazone (dpkbh) in refluxing toluene gave fac-Re(CO) 3 (dpkbh)Cl in good yield. Spectroscopic and electrochemical measurements on fac-Re(CO) 3 (dpkbh)Cl revealed strong solvent Á/solute interaction, as manifested by the sensitivity of its reduction potentials and electronic absorption spectra to solvent variations. Spectroscopic and thermo-optical measurements in polar solvents in the presence of NaBH 4 and NaBF 4, or NaOH and citric acid reveal reversible interconversion between the low-and high-energy electronic states of fac-Re(CO) 3 (dpkbh)Cl at 440 and 318 nm. Electrochemical measurements on fac-Re(CO) 3 (dpkbh)Cl show irreversible redox processes pointing to electrochemical transformations following the first electronic transfer(s). Crystals of fac-Re(CO) 3 (dpkbh)Cl obtained from an acetonitrile solution of fac-Re(CO) 3 (dpkbh)Cl are centric and crystals of fac-Re(CO) 3 (dpkbh)Cl ×/dmso obtained from a dmso solutions of fac-Re(CO) 3 (dpkbh)Cl are acentric. Structural studies show non-identical twins of fac-Re(CO) 3 (dpkbh)Cl and fac-Re(CO) 3 (dpkbh)Cl ×/ dmso with distorted octahedral coordination about rhenium and the conformation about the amide group is syn-in fac-Re(CO) 3 (dpkbh)Cl and anti-in fac-Re(CO) 3 (dpkbh)Cl ×/dmso. The packing of molecules shows a web of hydrogen bonds that may account for the stability of different conformations observed in the solid state.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
is an assistant professor of instruction with the Undergraduate Engineering Office and the Mechan... more is an assistant professor of instruction with the Undergraduate Engineering Office and the Mechanical Engineering department at Northwestern University. His research was conducted at the intersection of robotics and biomechanics in the field of human-machine interactions, and explored novel ways to control robotic prosthetic hands. He is very passionate about student education and currently teaches five separate courses at the undergraduate level that include manufacturing, design, experimental methods, and thermodynamics. He greatly enjoys advising all levels of undergraduate and early graduate students. He is the producer for the Lightboard studio, and is currently exploring models for effective online and hybrid teaching models.
where she currently teaches first-year engineering design courses. Her research interests in engi... more where she currently teaches first-year engineering design courses. Her research interests in engineering education include the identification of variables that impact the firstyear experience and the development of strategies to enhance it, retention of underrepresented populations in STEM fields and service-learning in engineering.
2018 ASEE Annual Conference & Exposition Proceedings
is an assistant professor of instruction with the Undergraduate Engineering Office and the Mechan... more is an assistant professor of instruction with the Undergraduate Engineering Office and the Mechanical Engineering department at Northwestern University. His research explored novel ways to control robotic prosthetic hands. He is very passionate about student education and has taught multiple courses at the undergraduate level that include manufacturing, freshman and capstone design, experimental methods, and thermodynamics. He greatly enjoys advising all levels of undergraduate and early graduate students. He has been highly involved with the Lightboard studio and exploring models for effective online and hybrid teaching methods.
Her research interests include STEM education at all levels, first-year experience and issues rel... more Her research interests include STEM education at all levels, first-year experience and issues related to the transition from high school to college, and the retention and recruitment of women and minorities to STEM fields.
Recent research indicates that first-year, team-based design courses represent a unique opportuni... more Recent research indicates that first-year, team-based design courses represent a unique opportunity to address such disparities and providing early collaborative learning experiences supports the success of students from underrepresented groups in engineering [10-13]. While lectures and readings may provide teams with basic tools for team and project management, these correlate team success with the creation of a high-quality final design [14]. Such tools may inadvertently cue students to distribute work according to stereotypical social roles in the belief that by having team members "play to their strengths," they are doing what is best for the team [15]. Such task distribution may limit new learning across team members, exclude historically underrepresented students from high profile team tasks (such as design and fabrication) [16], and thus promote the entrenchment of implicit biases. This study leverages a cooperative learning approach [23] to teamwork and learning in a first-year engineering design course at Northwestern University's McCormick School of Engineering in order to provide more equitable access to learning for all students. Implementation of such approaches in first-year contexts is of particular importance, as these classes are formative for how students view teamwork. The study analyzes results from the use of a novel curricular intervention piloted in Design Thinking and Communication 1 (DTC 1) at Northwestern University. Specifically, the intervention required that students on a team rotate through leadership roles in four key areas: primary research, secondary research, training-building-testing, and project management. The team lead for each role completed associated documentation and coached their successor on how to succeed in that role. Research Context This research took place in a required first-year design course during Fall 2019 and Winter 2020 quarters at Northwestern University. The course (entitled Design Thinking and Communication I) focuses on user-centered design for individuals with disabilities, and requires students to collaborate with real-world clients and users. Approximately 140 student participants were enrolled among nine control sections (5 in fall, 4 in winter) that retained the standard course design format or nine experimental sections (5 in fall, 4 in winter), which piloted intentional team role rotation as the curricular innovation. The team roles were (i) primary research, (ii) secondary research, (iii) training-building-testing, and (iv) project management and are described
where she currently teaches first-year engineering design courses. Her research interests in engi... more where she currently teaches first-year engineering design courses. Her research interests in engineering education include the identification of variables that impact the firstyear experience and the development of strategies to enhance it, retention of underrepresented populations in STEM and global engineering experiences.
2015 ASEE Annual Conference and Exposition Proceedings
West Virginia University, where she currently teaches first-year courses in the Freshman Engineer... more West Virginia University, where she currently teaches first-year courses in the Freshman Engineering Program. Her research interests in engineering education include the identification of variables that impact the first-year experience and the development of strategies to enhance it, retention of underrepresented populations in STEM fields and service-learning in engineering.
Crystals of di-2-pyridyl ketone benzoylhydrazone (dpkbh) obtained from a dimethylsulfoxide (DMSO)... more Crystals of di-2-pyridyl ketone benzoylhydrazone (dpkbh) obtained from a dimethylsulfoxide (DMSO) solution of dpkbh are in the monoclinic space group, P2 1/c. Structural analysis reveals anti-parallel, non-planar, one-dimensional tapes of dpkbh with a network of intra-and intermolecular hydrogen bonds. Optical measurements on dpkbh in polar non-aqueous solvents revealed the presence of interlocked low-(a-) and high-(b-) energy intraligand charge-transfer electronic states may be due to dpk p±p p followed by dpk to benzoyl charge-transfer. The equilibrium distribution of the low-(a-) and high-(b-) energy electronic states is solvent dependent, controlled by the hydrogen bonding capacity of surrounding solvent molecules. The interplay between the a-and b-conformations of dpkbh allowed calculations of their extinction coef®cients by forcing the equilibrium to shift to one conformation using chemical stimuli. In N,N-dimethylformamide (DMF), extinction coef®cients of 45,000^2000 and 15,000^2000 M 21 cm 21 were calculated for the a-and b-conformations of dpkbh at l max , respectively, when excess acid was added to a DMF solution of dpkbh. The weak bond energies of the hydrogen bonds, the reversibility and the sensitivity of the high-and low-energy electronic states to their surroundings in polar non-aqueous solvents allow for the use of this system as molecular sensor for a variety of stimuli that include metal ions, acids and bases. Metal ions in concentrations ,10 27 M can be detected and determined using this system (dpkbh and surrounding solvent molecules).
The molecular sensor fac-[Re(CO) 3 (dpkbh)Cl]•DMF (1) where DMF ¼ N,N-dimethyl formamide and dpkb... more The molecular sensor fac-[Re(CO) 3 (dpkbh)Cl]•DMF (1) where DMF ¼ N,N-dimethyl formamide and dpkbh ¼ di-2-pyridylketonebenzoylhydrazone crystallized in the acentric triclinic space group P1. Structural analysis shows two units of (1) with rhenium in distorted octahedral geometry, the carbonyl groups are in facial positions with an average C-Re-C angle of 908 and the N,Nbidentate dpkbh forms six-membered metallocyclic ring with rhenium in a boat conformation. The molecular packing shows the binding of DMF to fac-[Re(CO) 3 (dpkbh)Cl] and helical strands of (1) interlocked via a network of hydrogen bonds. Optical measurements on fac-[Re(CO) 3 (dpkbh)Cl] in DMF show the presence of two interlocked charge transfer bands at 440 and 318 nm that are highly sensitive to slight variations in their surroundings. As the concentration decreases, the intensity of the low energy absorption band at 440 nm increases and the reverse is observed when the concentration increases. Thermo-optical measurements on fac-[Re(CO) 3 (dpkbh)Cl] in DMF established the reversible interconversion between the high and low energy electronic states of fac-Re(CO) 3 (dpkbh)Cl and changes in enthalpy ðDH B Þ of þ 17.44^0.40 kJmol 21 , entropy ðDS B Þ of þ37.45^0.50 J mol 21 and free energy ðDG B Þ of þ6.27^0.30 kJ mol 21 in DMF were calculated. Acids or bases in concentration as low as 1.0 £ 10 29 M can be detected and determined using fac-[Re(CO) 3 (dpkbh)Cl] in DMF. 1 H-NMR measurements on fac-[Re(CO) 3 (dpkbh)Cl] in DMF in non-aqueous media reveal high sensitivity to solvent and temperature variations and points to strong solvent-complex interactions. The amide protons and solvate protons show high sensitivity to temperature variations than the aromatic protons pointing to the participation of the amide proton in solvate-complex hydrogen bonds in non-aqueous solutions of fac-[Re(CO) 3 (dpkbh)Cl].
... Mohammed Bakir Corresponding Author Contact Information , E-mail The Corresponding Author , I... more ... Mohammed Bakir Corresponding Author Contact Information , E-mail The Corresponding Author , Ishmael Hassan , Toni Johnson , Ordel Brown , Orville Green , Colin Gyles and ... [1]. CM Armstrong, PV Bernhardt, P. Chin and DR Richardson. Eur. ... [5]. LM Hayden, W.-K. Kim, AP ...
Crystals of di-2-pyridyl ketone p-nitrophenylhydrazone (dpknph), obtained from a dmso (dimethylsu... more Crystals of di-2-pyridyl ketone p-nitrophenylhydrazone (dpknph), obtained from a dmso (dimethylsulfoxide) solution of dpknph, are in the monoclinic space group, P2 1 =n: Structural analysis reveals non-coplanar pyridine rings and infinite one-dimensional chains of dpknph with a network of classic and non-classic hydrogen bonds. Optical measurements on dpknph in dmso in the presence and absence of CdCl 2 and NaBH 4 gave extinction coefficients of 91,000^2000 and 35,000^2000 M 21 cm 21 for the high and low energy electronic states of dpknph at 295 K. Thermo-optical measurements on dpknph in dmso established the reversible interconversion between the high and low energy electronic states of dpknph and allowed calculations of their thermodynamic activation parameters and gave changes in enthalpy (DH B) of 2 49.05^1.25 kJ mol 21 , entropy (DS B) of þ 0.16^0.04 kJ mol 21 and free energy (DG B) of 2 96.30^2.45 kJ mol 21 at 295 K. Manipulation of the equilibrium distribution of the high and low energy electronic states of dpknph allowed for the use of the system as cation-anion and acid-base sensor. Basic anions such as BH 4 2 and OH 2 favor the low energy electronic state and electron deficient anions such as BF 4 2 , metal ions and protons favor the high-energy electronic state. The reversible BH 4 2 /BF 4 2 and OH 2 /H þ interconversion points to physical interactions between these species and dpknph and the use of dpknph as a spectrophotometric sensor for a variety of physical and chemical stimuli. Metal ions in concentrations as low as 1.00 £ 10 27 M can be detected and determined using dpknph in dmso.
When di-2-pyridyl ketone thiosemicarbazone (dpktsc) was allowed to react with [Re(CO) 5 Cl] in to... more When di-2-pyridyl ketone thiosemicarbazone (dpktsc) was allowed to react with [Re(CO) 5 Cl] in toluene under reflux, fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl] was isolated in good yield. The identity of fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl] was established from the results of its elemental analysis, spectroscopic, and electrochemical properties. The infrared spectra of fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl] show the facial coordination of the carbonyl groups, and the pyridyl N,N-coordination of dpktsc. 1 H NMR measurements on fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl] in d 6-dmso and d 6-acetone confirmed the pyridyl N,N-coordination of dpktsc, and showed strong solvent dependence as manifested by the sensitivity of thioamide and ammine protons to their surroundings. The electronic absorption spectra of fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl] in protophilic solvents (dmso and dmf) display two intra-ligand charge transfer (ILCT) transitions at 476 and 360 nm and in nonprotophilic solvents a single ILCT transition at 346 nm in CH 3 CN and 342 nm in CH 2 Cl 2. Reversible interconversion between fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl] and its conjugate base was established in protophilic solvents using a base to shift the equilibrium to the conjugate base and an acid to shift the equilibrium or conjugate base to the neutral form. Substrates in concentrations as low as 1 Â 10 À10 M can be detected and determined using protophilic solutions of fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl]. When MCl 2 (M = Zn, Cd or Hg) was allowed to interact with fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl] in protophilic solvents, the intensity of the low energy ILCT band disappeared and a shift in the high energy ILCT electronic transition was observed that hints to the coordination of MCl 2 to fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl]. Electrochemical measurements on fac-[Re(CO) 3 (j 2-N,N-dpktsc)Cl] in dmf showed sequential irreversible redox processes in accord with the electrochemical reduction or oxidation of the thiosemicarbazone moiety.
ABSTRACT When [Re(CO)5Cl] was allowed to react with di-2-pyridyl ketone semicarbazone hydrochlori... more ABSTRACT When [Re(CO)5Cl] was allowed to react with di-2-pyridyl ketone semicarbazone hydrochloride (dpksc.HCl) in refluxing toluene, fac-[Re(CO)3(κ2-N,N-dpksc)Cl] was isolated. The identity of fac-[Re(CO)3(κ2-N,N-dpksc)Cl] was elucidated from the results of its elemental analysis and confirmed using a number of spectroscopic measurements. Spectroscopic measurements done on non-aqueous solvents divulged sensitivity of fac-[Re(CO)3(κ2-N,N-dpksc)Cl] to changes in its surroundings. 1H NMR studies revealed significant solvent dependence as manifested by the chemical shift variations; the exchange of the amine protons with solvent deuterium in CDCl3 and d6-acetone; the temperature dependence of the chemical shifts of the amine and amide protons and insignificant temperature dependence of the aromatic proton. The electronic absorption spectra of fac-[Re(CO)3(κ2-N,N-dpksc)Cl] measured on non-aqueous solvents disclosed two high energy intra-ligand charge transfer (ILCT) transitions. Optical measurements performed on protophilic solutions of fac-[Re(CO)3(κ2-N,N-dpksc)Cl] in the presence of bases and acids showed the appearance and disappearance of a low energy ILCT electronic transitions and established reversible inter-conversion between fac-[Re(CO)3(κ2-N,N-dpksc)Cl] and its conjugate base, fac-[Re(CO)3(κ2-N,N-dpksc-H)Cl]−. Thermo-optical measurements done on protophilic solutions of fac-[Re(CO)3(κ2-N,N-dpksc)Cl] disclosed the absence of thermal acid–base inter-conversion between fac-[Re(CO)3(κ2-N,N-dpksc)Cl] and fac-[Re(CO)3(κ2-N,N-dpksc-H)Cl]− and established reversible electronic transfer between the high energy electronic transitions of fac-[Re(CO)3(κ2-N,N-dpksc)Cl]. Optosensing measurements done on protophilic solutions of fac-[Re(CO)3(κ2-N,N-dpksc)Cl] showed acids and bases in concentrations as low as 1.00 × 10−10 M can be detected and determined using protophilic solutions of of fac-[Re(CO)3(κ2-N,N-dpksc)Cl]. Electrochemical measurements on dmf solutions of fac-[Re(CO)3(κ2-N,N-dpksc)Cl] showed irreversible electrochemical redox process and electrochemically generated product waves pointing to the instability of fac-[Re(CO)3(κ2-N,N-dpksc)Cl] to redox transformations.
An understanding of the molecular mechanisms of the newly characterized herpes simplex virus (HSV... more An understanding of the molecular mechanisms of the newly characterized herpes simplex virus (HSV) B5 protein is important to further elucidate the HSV cell entry and infection. The synthetic peptide of B5 (wtB5) was functionalized with the nonlinear optical chromophore cascade yellow and its molecular dynamics was probed at physiological and endosomal pH (pH 7.4 and 5.5, respectively). Steady-state CD spectroscopy was utilized to characterize the peptides at different pH. These spectra showed structural changes in the peptide with time measured over several days. Nonlinear optical measurements were carried out to probe the interactions and local environment of the labeled peptide, and the increase in the two-photon cross section of this system suggests an increase in chromophore-peptide interactions. Time-resolved fluorescence upconversion measurements reflected changes in the hydrophilic and hydrophobic local environments of the labeled peptide-chromophore system. Ultrafast depolarization measurements gave rotational correlation times indicative of a reversible change in the size of the peptide. The time-resolved results provide compelling evidence of a reversible dissociation of the coiled coils of the wtB5 peptide. This process was found to be pH-insensitive. The data from this unique combination of techniques provide an initial step to understanding the molecular dynamics of B5 and a framework for the development of novel imaging methods based on two-photon emission, as well as new therapeutics for HSV.
The reaction between Re(CO) 5 Cl and di-2-pyridylketone benzoylhydrazone (dpkbh) in refluxing tol... more The reaction between Re(CO) 5 Cl and di-2-pyridylketone benzoylhydrazone (dpkbh) in refluxing toluene gave fac-Re(CO) 3 (dpkbh)Cl in good yield. Spectroscopic and electrochemical measurements on fac-Re(CO) 3 (dpkbh)Cl revealed strong solvent Á/solute interaction, as manifested by the sensitivity of its reduction potentials and electronic absorption spectra to solvent variations. Spectroscopic and thermo-optical measurements in polar solvents in the presence of NaBH 4 and NaBF 4, or NaOH and citric acid reveal reversible interconversion between the low-and high-energy electronic states of fac-Re(CO) 3 (dpkbh)Cl at 440 and 318 nm. Electrochemical measurements on fac-Re(CO) 3 (dpkbh)Cl show irreversible redox processes pointing to electrochemical transformations following the first electronic transfer(s). Crystals of fac-Re(CO) 3 (dpkbh)Cl obtained from an acetonitrile solution of fac-Re(CO) 3 (dpkbh)Cl are centric and crystals of fac-Re(CO) 3 (dpkbh)Cl ×/dmso obtained from a dmso solutions of fac-Re(CO) 3 (dpkbh)Cl are acentric. Structural studies show non-identical twins of fac-Re(CO) 3 (dpkbh)Cl and fac-Re(CO) 3 (dpkbh)Cl ×/ dmso with distorted octahedral coordination about rhenium and the conformation about the amide group is syn-in fac-Re(CO) 3 (dpkbh)Cl and anti-in fac-Re(CO) 3 (dpkbh)Cl ×/dmso. The packing of molecules shows a web of hydrogen bonds that may account for the stability of different conformations observed in the solid state.
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