Lakshmi Nilakantan's profile, University of Missouri, Columbia

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Commented on A transformative mission for prioritising nature in Australian cities

Urban greening is of paramount importance in a warming world. With increased urban dwellers, around the world public are getting disconnected from nature. To improve nature human relationship we need to incorporate nature in every stage of urban development. This paper describes the three step greening process for Australian cities, which can be extended to other global cities. The three-step processes for urban nature planning are 1. Evidence based planning and new planning tools to safeguard urban nature. 2. Collaborative planning, Aboriginal knowledge and involvement of local government to save nature. 3. Community involvement and innovation is necessary for nature-positive cities. 1. Evidence based planning and new planning tools to safeguard urban nature. Loss of nature for urban development is compensated elsewhere; defined as offsetting metrics. However, results in loss of local biodiversity therefore the offsetting metrics legislation needs reformation to prevent ecological imbalance. Planning schemes and instruments to save and retain remnant natural areas and trees in private lands is crucial. A new Green factor tool used to quantify the ratio of greening in new built up developments could pave the way forward. 2. Collaborative planning, Aboriginal knowledge and involvement of local government to save nature. Federal and state level planning with local governments to maintain nature in cities. The Aboriginal knowledge to care for nature and sustainable practices must be taken into account in caring for urban nature. Reintroducing cultural burning into nature based urban landscape to protect ecosystems from decline. 3. Community involvement and innovation is necessary for nature-positive cities The success of nature-based cities is possible only by citizen’s involvement. Citizens need to work with other professionals like arborist, horticulturalist, and landscape architects to build and maintain nature positive cities. The COVID-19 pandemic made many of us realize the importance of parks; green spaces and need for nature in our daily life to keep us healthy. Hence, human-nature relationship in urban spaces is important and it is time to plan strategically worldwide to benefit us and nature.

Article

Commented on Including public-health benefits of trees in urban-forestry decision making

Trees are often beneficial to humans in many ways. With increased urbanization and loss of trees, it is important to understand the economic and social benefits offered by trees. This paper clearly explains two terms biophysical and non-physical benefits trees provide. Besides, proper understanding and implementation of these two factors can be beneficial to humans personally and economically. The biophysical benefits of trees are energy savings, carbon sequestration, storm water management and improved air quality. The non-biophysical benefits are reduced crime and improved public health. Hereafter, the non-biophysical benefits will be quoted as social benefits. Extensive research is based on the biophysical benefits of trees, which is used to support investment in urban –forestry. The urban forestry investments hardly focus on social benefits offered by trees. The social benefits offered by trees outweigh their biophysical benefits ( $3 trillion spent on public health expenditure vs $134 billion spent on residential heating and cooling ). This clearly in terms of cost, shows social benefit delivered by tree is higher compared to biophysical benefit and investment in agro-forestry could be more beneficial if social benefits are placed upfront. The paper published by (Hystad et al., 2014; Kardan et al., 2015) highlighting neighborhood trees are beneficial to public health. This promoted a new era encouraging urban greening and urban-forestry. However, significant work needs to be done to convince public health departments and hospitals to support tree-planting programs. The paper supports its claim by performing a simple experiment considering an urban area with three residential blocks, a business/store with paved parking lot, two vacant lots and to its east bordered by a freeway. Here the author considers two scenarios for planting 36 trees. Scenario 1 planting trees considering biophysical benefit: to prevent storm water runoff six trees were planted in the store parking lot, another six trees were planted along the store streets. The remaining trees were planted on south and west side of the houses considering energy savings. No trees were planted on vacant lots or in the grass embankment of the freeway. Scenario 2 planting trees considering social benefit: To absorb air pollution eight trees were planted on the grass embankment of the freeway. To encourage exercise and reduce stress, eight trees were planted on the vacant lots and rest were planted along the streets to encourage walking. In scenario 1 trees are planted considering energy savings and storm water runoff whereas scenario 2 emphasis on public health by planting trees in parks and gardens. Though scenarios 1 and 2 have one thing in common, trees were planted in public of way.

Article

Commented on Preparation and self-aggregation properties of a series of pyrene-imidazolylidene complexes of gold (I)

Reported gold(I) complexes based on pyrene imidazolylidene are interesting, given the fact that they exhibited self aggregation properties in solid state as well as in solution, confirmed by solid state structures as well as NMR spectroscopy. Straight forward synthesis and through characterization of final compounds are noteworthy. Investigation of solution state aggregation phenomena by concentration dependent UV and fluorescent spectroscopy would be good tools to further support the NMR behavior. CV of compound 3 exhibiting one single oxidation wave for two gold(I) center is consistent with analogous compounds with phenyl-di-acetylene ligand (Organometallics 1997, 16, 184–189). Mentioning of these supporting literature would help the novice readers in this field. The authors concluded that the electronic communication between the two metal centres in compound 3 through the phenyl-di-acetylene ligand is negligible. A DFT investigation on these complexes to support/establish this fact would be an interesting future study.

Article

Commented on Continuous synthesis of triacetonamine over sulfonic acid-functionalized mesoporous silicas

The authors efforts to make triacetonamine (TAA), a key starting material for Hindered Amine Light Stabilizers, using sulfonic acid functionalized mesoporous silicas via continuous process is an important step replacing the decades old batch process of using Lewis acid catalysts such as ammonium nitrate and boron trifluoride. The authors put a good effort for characterization of prepared catalysts. The results from the variation of acetone: ammonia ratio, temperature and Gas Hourly Space Velocity are interesting and added value to the findings. However, recyclability studies on the reported catalyst would be beneficial for possible industrial scaling up. In a similar note, information on the removal of water and purification of the prepared TAA would have added more value to the published research. It is interesting to note that the same authors followed this paper with cation exchange resins for the same reaction (Asian Journal of Chemistry; Vol. 27, No. 2 (2015), 541-543).

Article

Commented on Transformation of Thiolatogold(I) to an Au Complex with an (Arylthio)silyl Ligand. Use of an (Aminosilyl)boronic Ester as a Silylene Precursor

Unusual migration of sulfur from Au to Si with the concurrent formation of Au-Si bond in the reaction between gold(I) thiolate complex and aminosilyl)boronic ester is an interesting study. The resultant product was well characterized by NMR and X-ray. The authors reported NMR yield and isolated yield for complex 3 as 90% and 57%. The significant difference between the two emanates from the fact that the NMR yield is based on the formation of amino(pinacol)borane formation and the isolated yield is based on formation of 3. It would have been beneficial for the readers, if this would have been mentioned in the main text. It is interesting to note that the authors ruled out the formation of silylene as the reaction pathway, though a well known silylene precursor (aminosilyl)boronic ester is used. The authors used DFT calculations to support the proposed mechanism. As the reaction is clean and can be monitored by NMR, a more detailed study on the kinetics by NMR would be interesting as this can provide information such as rate limiting step, supporting the DFT calculations.

Article

Commented on Synthesis and properties of multifunctional nitroxyl radical hindered-amine light stabilizers

Reported synthesis of hindered-amine light stabilizers having nitroxyl radical as a component is interesting. Characterization of reported HALS are good. Since the reported HALS are radicals, it would be beneficial for readers to mention the broadening effect shown in NMR. Comparison of UV-Vis data of prepared HALS with the HS508 is unusual, as HS508 does not have any benzene chromophore in contrast with the reported ones in this paper. Observation of better photo stability of reported HALS with HS508 is a welcome result. However, it would be better if they do the comparison of reported ones with a mixture/combination of HS508 and benzotriazole based photostablizers. Also it would be worthy to give literature support for using a radical as stabilizers as it is not a common practice, and are generally used for quenching the polymerization reactions.

Article

Commented on Rhodium(iii)-catalyzed dehydrogenative dialkenylation of the monocarba-closo-decaborate cluster by regioselective B–H activation

Development of regio selective B-H activation in CB9H10 cluster by iridium metal center is indeed a good approach which will facilitate the use of CB9H10 clusters for applications such as material science envisaged by the authors. All reported compounds were thoroughly characterized by NMR, Xray and mass spectroscopic techniques. The authors suggested a nuanced mechanism for the reaction in the supporting information. A more detailed mechanistic investigation including the role of Cu salt giving exclusivity in the dimeric substitution will be an ideal platform for further research. Other minor observations are (i) Color coding in numbering of boron atoms of the cage (Figure 1a) would be helpful (ii) Addition of columns including the yield and the the ratio of mono and di in Table 1 would be beneficial for easy follow up. (iii) I believe the authors determined the degree of substitution (ratio of mono to di) by 11B(1H) NMR. Mention of this in the text would be useful for novice readers.

Article

Commented on Bimetallic Nickel Complexes for Aniline C–H Alkylations

The authors investigation of bimetallic Ni complexes for aniline C-H alkylations as an alternative to noble metals analogs is intriguing. Structure of complexes 2a and 2b were unambiguously characterized by X-ray. However, in depth analysis of CV experiments would be beneficial for the readers. While text represent the E1/2 value of complexes 2a and 2b are 0.4 V and 0.39 V with respect to decamethyl ferrocene, the figure represents the value of ~0.85 V (Figure 1b). In addition, a comparison of current density values with decamethyl ferrocene would also be useful as it involves two Ni atoms. Use of one annotation for representing aromatic groups (either Ar as simple benzene structure in Scheme 4 ) would be useful for better clarity. Mechanistic investigation on the described reaction was in detail. The authors mentioned no product formation in the absence of base (Scheme 5a). However, it would be better to investigate whether there was formation of I or II as per scheme 5 where no base is required to kick start the reaction sequence. Also for the reactions to happen in scheme 4, the corresponding reagents need to replace the simple phenyl ring of catalyst with the formation of their metal complexes. Investigation of such cross over reactions would help for better understanding of the mechanism. The suggested mechanism and conclusion of radical pathway is logical and was well supported by experimental. X-ray structure of 2a was presented twice in the text!

Article

Commented on Synthesis, Characterization, and Theoretical Investigation of a Transition State Analogue for Proton Transfer during C–H Activation by a Rhodium-Pincer Complex

Understanding the reaction pathway of aromatization and dearomatization in pincer metal complexes is a long-standing research in the C-H activation chemistry. In this report, the authors made a valiant attempt to isolate the structure of a transition state with the replace of H atom with Zn metal (compound 6). The confirmation of structure of compound 6 is well done with NMR and X-ray structure analysis without ambiguity. However, choice of Zn for H as a replacement is debatable, as the atomic size of Zn is much larger than the H. Further this is amplified by the C1−Zn distance (2.20 Å) which is greater than the sum of the covalent radii (1.98 Å) implicating the absence of bonding between the C1 and Zn. The observation of single signal for 31P NMR instead of two, also implies the nonexistence of bonding between C1 and Zn. It would be interesting to investigate the ring flipping phenomena in this compound by VT-NMR to see whether ring flipping has any role in the investigated chemistry. Similar investigation was done by Abu-Omar’s group to investigate the structural isomerism of Ir-Re complex (J. Organomet. Chem. 2017, 843, 62-65).

Article

Commented on Ti-amide Catalyzed Synthesis of Cyclic Guanidines from Di-/Triamines and Carbodiimides

This paper describes a good generic synthetic methodology to prepare a variety cyclic guanidines from di/triamines and carbodiimides using titanocarborane as a catalyst. Authors took tremendous synthetic efforts to include a variety of substances. Characterization of products are thorough and in detail. Use of fancy titanocarborane is debatable for this type of reactions, considering the cost and feasible catalyst free reaction of aliphatic amines with carbodiimides. Trial of simple commercially tetraalkyltitanate (for example Ti(OEt)4) for this reaction would be a good idea to see the viability of this reaction. The reactions were carried out in an NMR tube and majority of reactions took a very long time upto 480 h depending on the substrates. In these reactions the co product is the amine (for example isopropylamine from diisopropyl carbodiimide) belonging to the carbodiimides used. It would be a better idea to distill the corresponding amine during the reaction to drive the reaction forward. The authors proposed a mechanism (scheme 3) in which the catalyst 1 first react with the amine 3 to form C and subsequently react with diimide 4 to form D. The following alternative pathway is also feasible. Diimide 4 which is more reactive than 3, could form cyclic complex with catalyst 1 and then subsequently react with 3. In both cases, interestingly catalyst plays a role only to kick start the reaction and subsequent steps did not require the catalyst. Following experiments could be useful to further establish the mechanism of reported reaction. 1. Establishing the stability of catalyst 1 at 140 C under the conditions used, to check whether the catalyst retains the original structure till the end of reaction or changes its form during the course of reaction. Monitoring the reaction by 11B NMR is a good tool to identify this. 2. To find out whether the catalyst first react with amine or diimide, 11B NMR analysis of separate reactions of catalyst with amine in the absence of diimide and vice versa would be ideal. 3. NMR analysis of intermediates, kinetics studies, as well as Density Functional Theory calculations on the possible reaction pathways are also good tools to further explore the proposed mechanism Carbodimides are known eye irritants (Chemical and Engineering News, 68(45)2, 1990). Giving a caution on the hazardous nature of these compounds in the experimental would be useful for researchers advancing this chemistry.

Article

Commented on Fine-tuning polyoxometalate non-linear optical chromophores: a molecular electronic “Goldilocks” effect

This is an interesting paper where the authors have studied three different aryl-imido polyoxometalate (POM) complexes and compared their non-linear optical (NLO) properties. The POM attached to aryl groups owing to its strong acceptor properties, plays an important role in the NLO properties. It is noteworthy that compound 2 with diphenyl-amino (NPh2) groups has highest beta(0) values, outperforming all the organic POM chromophores reported in the literature. The optimal electronic communication between the acceptor-donor groups due to conjugation coined as “Goldilocks” effect, which was established by X-ray crystallography, UV-Vis, electrochemical studies, stark spectroscopy, hyper- Rayleigh scattering (HRS) and DFT studies was the highlight of this study. In the synthesis of compounds 1-3 from the aniline derivative and (n-Bu4N)2[Mo6O19] with DCC as a dehydrating agent, dicylcohexyl urea (DCU) is a byproduct. DCU is either insoluble (ether) or sparingly soluble in majority of the solvents (DMSO, ethanol, acetonitrile) used in this report. It would be beneficial to mention in what stage and how the authors removed DCU during the synthesis/purification. In addition, it would be better to mention the safe handling of DCC as it is a well known eye irritant (Chemical and Engineering News, 68(45)2, 1990). The authors described qualitatively that compound 2 was more susceptible to hydrolysis ie more reactive, when compared with 1, 3 and other reported analogs, and attributed this property to its electronic structure. It would be interesting to confirm this by intentionally introducing moisture in the studied complexes and study their hydrolysis rates. Figure 2 compared beta(0) values for compounds 1-3 (orange) with the analogous phenyl bridged a POMS (red) and organic chromopores (blue) reported in literature. As the authors referred a large number of molecules for comparison, it would be better to give the name and structures of these complexes in the supporting information for better understanding. It also would be better to mention a few lines about the fundamental limit, apparent limit (Figure 2) and its importance for the better understanding of rookie readers. X-ray analysis established that existence of quinoidal resonance form and observation of planarity in the structure leads to better NLO property. In addition, the authors used DFT smartly and established that dominance of NPh2 in highest occupied molecular orbital is the primary reason for the NLO property of compound 2. It would be interesting to investigate further by DFT investigation followed by experimental, whether presence of electron donor or acceptor substituents such as OCH3 or CF3 in the phenyl ring of NPh2 can fine tune the NLO properties of 2. 10-vertex (C2B8H10) and 12-vertex (C2B10H12) carborane cage linkers are analogous to benzene and are well known for their use in NLO properties due to their chemical and thermal robustness and stability (J. Am. Chem. Soc.2008, 130, 3566–3578). N(Carborane)2 analogs of 2 in place of NPh2 would be interesting future studies in this regard.

Article

Commented on C–H Activation of Methyltrioxorhenium by Pincer Iridium Hydride To Give Agile Ir–Re Bimetallic Compounds

Abu-Omar’s group tried an innovative approach of converting alkanes into alcohol by combining the iridium pincer complex (alkane activation) and methyl rhenium trioxide (for selective oxidation of metal-alkyl bond). This approach is an alternative to the Goldberg/Britovsek groups effort of combining iridium pincer complex (alkane activation) with photo active bipyridine (BPY) and terpyridine (TPY) metal complexes via radical pathway using molecular oxygen. The interesting observation of reversible structural isomerism for the reported Ir-Re complexes (one with supported Ir-Re bond and another with unsupported Ir-Re bond) is unprecedented and noteworthy. NMR characterization and X-ray structure analysis of structural isomers unambiguously confirmed their respective structures. Adequate NMR analysis of reaction mixture and kinetic isotope effect (KIE) analysis supported the proposed mechanism of MTO reaction with PNPIrH2 with the elimination of H2. In their follow up papers, the authors nicely explained the mechanism of structural isomerism and the existence of ring flipping by DFT in those Ir-Re complexes (Organometallics 2016, 35, 4, 605-611, J. Organomet. Chem. 2017, 843, 62-65). The author’s use of PNP ligand is debatable as PCP ligand is the preferred one for alkane activation. Trials on the PCPIrH2 reaction with MTO and the effect of resulting chemistry in the alkane to alcohol conversion would be interesting future studies.

Article

Commented on Rodlike Polymers Containing Nickel and Cobalt Metal Bis(dicarbollide) Anions: Synthesis and Characterization

In this piece of work, Dr. Hawthorne’s group attempted a synthetically challenging rod like organometallic polymers having metal bis(dicarbollide) anions linked by spacers such as acetylene and alkyl substituted aromatic functionalities. This fundamental research was very well done and can be branched into several other chemistries. The formidable polymer synthesis involves 12 synthetic steps starting from decaborane, 5 column purifications, 7 recrystallizations, 2 sublimations and multiple dialysis to achieve the desired high molecular weight polymers. Characterization of intermediates was well done confirming their structures. Rightly warning on the decaborane use and safety is very useful for researchers who follow up this chemistry due to its hazardous and explosive nature. Polymer synthesis were attempted via two routes. First route with nido-bis(carborane) linked by acetylene linkers and Co metal via pi coordination resulted oligomers. In this method, introduction of methyl groups on the carborane units increased the solubility of oligomers, however with limited success of having only 7 repeating units at the maximum. This justified their approach to go with the second route of Negishi coupling with long alkyl substituted benzene linkers which were known identities for increased solubilities. Negishi coupling of diiodo-substituted cobaltocarboranes and a zinc-derivatized aromatic linker indeed gave the long chain polymers. The challenges authors faced in determining the molecular weight of polymers were understandable as traditional characterization of polymers such as MALDI-TOF or GPC were not feasible due to the ionic nature of polymers. Therefore, authors used end group analysis and DLS techniques to estimate the molecular weight and number of repeating units. It was surprising that AFM did not provide the single polymer chain images as it could help to locate the cobalt atoms, which in turn helps to determine the number of bis(dicarbollide) repeating units. The alternative approach to counter the ionic nature of polymers for accurate determination of molecular weight by GPC/ MALDI-TOF is to make them charge neutral. This can be achieved by either introducing the amine such as n-butyl amine in the aromatic linker replacing the alkyl chain to have a positive charge as an intramolecular counter ion to the bis(dicarbollide) anion. Introducing the thiol based SMe2 groups on the CH of bis(dicarbollide) starting with 8-iodocarborane to make charge compensated metalla carboranes (Inorg. Chem. 1991, 30, 9, 2024-2031) also will help to achieve this. This fundamental research can also be extrapolated in the following ways. 1. Water soluble polymers of this variety can be made by introducing sulfonic acids/carboxylic acid groups on the aromatic linkers which can be coupled with bis(dicarbollide) anion by the same Negishi coupling methodologies. 2. Different poly fluorene based fluorescent polymers with bis(dicarbollide) anion linkers (water soluble as well as organic soluble based on the substituents on the fluorene moiety) can be tried, following the synthetic strategy reported here ( Angew. Chem. Int. Ed. 2009, 48, 4300 – 4316) 3. The aromatic linkers can be replaced by Pt-acetylide spacers based on the report from Harvey’s group (Inorganic Chemistry 49(6):2614-23) and the resulting polymers are expected to be fluorescent. While the synthetic chemistry will remain the same, the solubility challenge will be taken care of by the tert-butyl groups on the Pt. 4. Based on the Tour’s group on carborane based nano cars (J. Org. Chem. 2007, 72, 9481-9490) nickel bis(dicarbollide) anion can replace p-carborane with this reported synthetic methodology and the movement of corresponding nano cars can be achieved by either light or electrochemically again based on Hawthorne’s report (Science 2004, 303, 1849-1851). 5. MOF analogous similar to Peter Stang’s reported molecules replacing the traditional linkers with bis(dicarbollide) (Chem. Rev. 2013, 734-777).

Article

Commented on Photolysis of Pincer-Ligated PdII–Me Complexes in the Presence of Molecular Oxygen

In this research paper, Goldberg group made significant efforts on the holy grail of converting alkane to alcohol. Converting alkane to alcohol mainly involves two challenges: first is the alkane activation to form metal-alkyl bond and second is the controlled oxidation of metal-alkyl bond. While the former is accomplished with PCP pincer complexes, the latter is majorly restricted to photo active bipyridine (BPY) and terpyridine (TPY) metal complexes via radical pathway using molecular oxygen. Therefore, either use of BPY or TPY complexes in alkane activation or use of PNP or PCP pincer complexes in controlled oxidation will pave the way for addressing both challenges with one chemical identity. Here the authors attempted the use of PCP pincer complexes for controlled oxidation which otherwise are well known for alkane activation. The major challenge here was the reactivity of oxygen towards the oxophillic phosphine ligand resulting the disassociation of metal phosphine bond in the pincer moiety. By using bulky tert-butyl groups around the phosphine arm of pincer complex, the authors had partial success (75% conversion) in achieving the selective oxidation of Pt-Me bond without disintegrating the PCP pincer moiety. Characterization of observed products and control reactions to establish the mechanistic chemistry were noteworthy. Initiating the radical reaction the AIBN and confirming the radical pathway via TEMPO chemistry were innovative. Identifying the Milstein chemistry of deprotonation of the methylene side arm in used PNP metal complexes in the oxidation chemistry via radical pathway was interesting which otherwise known only to happen by the base. Though synthetically challenging, use of more bulkier silyl group on the phosphine arm would possibly improve further the selective oxidation character. Use of oxygen is greener, however commercially batch reactions may not be economically viable considering the inexpensive and abundant methanol availability. Trials of use of H2O2 under atmospheric conditions using these catalysts will be a good future study, which can be extrapolated in column mode using heterogeneous supported solid catalysts with these metal complexes. Though the authors used C6D6 for the oxidation reactions, investigations of using water or fluorinated alcohol such as trifluoroethanol as a solvent would be ideal choices as they can also be used alkane activation.

Article

Commented on Highly efficient aggregation-induced emission and stimuli-responsive fluorochromism triggered by carborane-induced charge transfer state

Establishing the aggregation induced emission (AIE) and stimuli-responsive fluorochromism in bis(naphthyl)phenyl-substituted o-carborane (1) is an interesting study. Starting with commercially available o-carborane and one-step synthesis of desired compound 1 via Suzuki coupling are the advantages in scaling up for real world applications. Spectroscopic characterization and X-ray structure unambiguously established the structure of 1. Interestingly, crystal structure packing showed no pi-pi stacking between the aromatic moieties, which in turn eliminate the aggregation induced quenching. It would be noteworthy to include the details of crystal packing data in the text. Increasing the polarity of solvent from methylene dichloride to acetonitrile resulted weakening of fluorescence and low energy emission shifts. Mentioning the exception of hexane to this conclusion (from figure 2), as well as a reasoning on this phenomena will be helpful for the readers. Explaining the UV data first and then proceed with the PL spectra would be a better option as the excitation wavelength depends on the UV absorption maxima. A detailed investigation on the carborane origin of TICT by DFT as well as an investigation on the p-carborane analog are interesting future studies.