A series of dicationic N, N’‐disubstituted benzimidazolium salts with Br− and PF6− as the counter... more A series of dicationic N, N’‐disubstituted benzimidazolium salts with Br− and PF6− as the counter anions were synthesized in 75–98 % yields. The single crystal X‐ray diffraction studies of one of the benzimidazolium salts confirmed the structure of these dicationic compounds. These salts exhibited a selective “turn‐off” fluorescence response toward Fe3+ ions in aqueous solution over the other competitive metal ions such as Ag+, Al3+, Ba2+, Ca2+, Co2+, Cr3+, Cu2+, Fe2+, K+, Mg2+, Na+, Ni2+, Pb2+, and Zn2+. Upon addition of 5 equivalents Fe3+ ions, emission intensity was quenched by 94–99 % in pure aqueous media. Detection limits for all probes with Fe3+ ions were found in micromolar range. Further, drug combination analysis was conducted by evaluating the combinatorial treatment effects of two benzimidazolium salts with doxorubicin on breast cancer cells using the Chou‐Talalay method and the Highest Single Agent (HSA) model, and it was found that these compounds showed synergism with doxorubicin. Further, molecular docking studies revealed the best docking score (−6.11) for one of the benzimidazolium salts, and explained its binding affinity with checkpoint kinase 2 (chk2) protein.
The hydroboration reaction of methyl cyanide has been investigated by the MNDO method. It has bee... more The hydroboration reaction of methyl cyanide has been investigated by the MNDO method. It has been shown that the reaction requires an activation energy of 25.3 kcal/mol and involves a four-center-like transition state in the rate-determining step. This reaction has been compared with the corresponding reaction of hydrogen cyanide, and the effect of methyl substitution on the reaction has been discussed. The charge-transfer effects accompanying the reaction have also been studied.
La lumie‵re (…) donne la couleur et l'e′clat a ‵toutes les productions de la nature et de l&#... more La lumie‵re (…) donne la couleur et l'e′clat a ‵toutes les productions de la nature et de l'art; elle multiplie l'univers en le peignant dans les yeux de tout ce qui respire. Light (…) gives colour and brilliance to all works of nature and of art; it multiplies the universe by painting it in the eyes of all that breathe. Abbe′Nollet, 1783 INTRODUCTION “Science is spectral analysis. Art is light synthesis”, so wrote Karl Kraus, Austrian writer. Light has intrigued both poets and scientists. What exactly is light? What effect does it have on matter? These are questions that have baffled scientists for many years, prompting Einstein in 1917 to say “For the rest of my life I will reflect on what light is”. The branch of science that deals with the study of electromagnetic radiation (of which visible light is a part) and its interaction with matter is called spectroscopy . The word is derived from the Latin: spectron – spectre (ghost or spirit), or the Greek: σκοπeιν – to see. This literally means that in spectroscopy, you do not look directly at the molecule – the matter – but what you see is its ‘ghost’ or image. To begin our study, we must, therefore, first discuss the nature of electromagnetic radiation and matter, and then the interaction between the two. We start this chapter by giving basic formulae and definitions relating to waves, including travelling waves. We then go on to the wave description of electromagnetic radiation and its manifestations, and then discuss the properties emerging from a particulate description of radiation. The entire electromagnetic spectrum, its divisions and sub-divisions, the kind of spectroscopy observed in each region, are the topics of the next section. The populations of energy levels play an important role in the observed intensities. Einstein's coefficients and their interrelation are introduced in this chapter, but the quantum mechanical treatment is reserved for the next chapter. We wind up this chapter with a discussion of line shapes and broadening, followed by a brief introduction to Fourier transform spectroscopy, the almost magical transformation of a time decay to a line width, and the experimental recording of spectra.
The computational methods, B3LYP and MP2 with the basis set 6‐311++G(d,p) have been used to decip... more The computational methods, B3LYP and MP2 with the basis set 6‐311++G(d,p) have been used to decipher the energetics and mechanisms of different nitrene reactions, namely organic azide decomposition, singlet and triplet nitrene addition to different kinds of C−H bonds, azide insertion into C−H bonds and substitution reaction of azides to alkanes. The addition of singlet nitrene to the C−H bond is exothermic, with one‐step addition accompanied by a considerable barrier, where the sequence of facility H>Ac>Me indicates the electrophilic nature of the nitrene reactant. In the case of triplet nitrene, the initial step involves smaller barriers and is endothermic due to the formation of radicals as intermediate products, and the final step involves the coupling of radicals and is hence exothermic. The direct azide addition has higher barrier then the stepwise addition reaction. The Hammond postulate can be used to differentiate the transition state geometries for different reaction steps as “early” or “late”.
A series of dicationic N, N’‐disubstituted benzimidazolium salts with Br− and PF6− as the counter... more A series of dicationic N, N’‐disubstituted benzimidazolium salts with Br− and PF6− as the counter anions were synthesized in 75–98 % yields. The single crystal X‐ray diffraction studies of one of the benzimidazolium salts confirmed the structure of these dicationic compounds. These salts exhibited a selective “turn‐off” fluorescence response toward Fe3+ ions in aqueous solution over the other competitive metal ions such as Ag+, Al3+, Ba2+, Ca2+, Co2+, Cr3+, Cu2+, Fe2+, K+, Mg2+, Na+, Ni2+, Pb2+, and Zn2+. Upon addition of 5 equivalents Fe3+ ions, emission intensity was quenched by 94–99 % in pure aqueous media. Detection limits for all probes with Fe3+ ions were found in micromolar range. Further, drug combination analysis was conducted by evaluating the combinatorial treatment effects of two benzimidazolium salts with doxorubicin on breast cancer cells using the Chou‐Talalay method and the Highest Single Agent (HSA) model, and it was found that these compounds showed synergism with doxorubicin. Further, molecular docking studies revealed the best docking score (−6.11) for one of the benzimidazolium salts, and explained its binding affinity with checkpoint kinase 2 (chk2) protein.
The hydroboration reaction of methyl cyanide has been investigated by the MNDO method. It has bee... more The hydroboration reaction of methyl cyanide has been investigated by the MNDO method. It has been shown that the reaction requires an activation energy of 25.3 kcal/mol and involves a four-center-like transition state in the rate-determining step. This reaction has been compared with the corresponding reaction of hydrogen cyanide, and the effect of methyl substitution on the reaction has been discussed. The charge-transfer effects accompanying the reaction have also been studied.
La lumie‵re (…) donne la couleur et l'e′clat a ‵toutes les productions de la nature et de l&#... more La lumie‵re (…) donne la couleur et l'e′clat a ‵toutes les productions de la nature et de l'art; elle multiplie l'univers en le peignant dans les yeux de tout ce qui respire. Light (…) gives colour and brilliance to all works of nature and of art; it multiplies the universe by painting it in the eyes of all that breathe. Abbe′Nollet, 1783 INTRODUCTION “Science is spectral analysis. Art is light synthesis”, so wrote Karl Kraus, Austrian writer. Light has intrigued both poets and scientists. What exactly is light? What effect does it have on matter? These are questions that have baffled scientists for many years, prompting Einstein in 1917 to say “For the rest of my life I will reflect on what light is”. The branch of science that deals with the study of electromagnetic radiation (of which visible light is a part) and its interaction with matter is called spectroscopy . The word is derived from the Latin: spectron – spectre (ghost or spirit), or the Greek: σκοπeιν – to see. This literally means that in spectroscopy, you do not look directly at the molecule – the matter – but what you see is its ‘ghost’ or image. To begin our study, we must, therefore, first discuss the nature of electromagnetic radiation and matter, and then the interaction between the two. We start this chapter by giving basic formulae and definitions relating to waves, including travelling waves. We then go on to the wave description of electromagnetic radiation and its manifestations, and then discuss the properties emerging from a particulate description of radiation. The entire electromagnetic spectrum, its divisions and sub-divisions, the kind of spectroscopy observed in each region, are the topics of the next section. The populations of energy levels play an important role in the observed intensities. Einstein's coefficients and their interrelation are introduced in this chapter, but the quantum mechanical treatment is reserved for the next chapter. We wind up this chapter with a discussion of line shapes and broadening, followed by a brief introduction to Fourier transform spectroscopy, the almost magical transformation of a time decay to a line width, and the experimental recording of spectra.
The computational methods, B3LYP and MP2 with the basis set 6‐311++G(d,p) have been used to decip... more The computational methods, B3LYP and MP2 with the basis set 6‐311++G(d,p) have been used to decipher the energetics and mechanisms of different nitrene reactions, namely organic azide decomposition, singlet and triplet nitrene addition to different kinds of C−H bonds, azide insertion into C−H bonds and substitution reaction of azides to alkanes. The addition of singlet nitrene to the C−H bond is exothermic, with one‐step addition accompanied by a considerable barrier, where the sequence of facility H>Ac>Me indicates the electrophilic nature of the nitrene reactant. In the case of triplet nitrene, the initial step involves smaller barriers and is endothermic due to the formation of radicals as intermediate products, and the final step involves the coupling of radicals and is hence exothermic. The direct azide addition has higher barrier then the stepwise addition reaction. The Hammond postulate can be used to differentiate the transition state geometries for different reaction steps as “early” or “late”.
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Papers by Rita Kakkar