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1.
Chem Commun (Camb) ; 2021 Nov 29.
Artigo em Inglês | MEDLINE | ID: mdl-34842250

RESUMO

Imaging finer structural details of atomically precise noble metal cluster crystals has been difficult with electron microscopy, owing to their extreme beam sensitivity. Here we present a simple method whereby lattice planes in single crystals of nanoclusters can be observed using a conventional transmission electron microscope, enabling further expansion of cluster research.

2.
Chem Sci ; 12(18): 6370-6377, 2021 Mar 24.
Artigo em Inglês | MEDLINE | ID: mdl-34084436

RESUMO

Conversion of polydisperse nanoparticles to their monodisperse analogues and formation of organized superstructures using them involve post synthetic modifications, and the process is generally slow. We show that ambient electrospray of preformed polydisperse nanoparticles makes them monodisperse and the product nanoparticles self-assemble spontaneously to form organized films, all within seconds. This phenomenon has been demonstrated with thiol-protected polydisperse silver nanoparticles of 15 ± 10 nm diameter. Uniform silver nanoparticles of 4.0 ± 0.5 nm diameter were formed after microdroplet spray, and this occurred without added chemicals, templates, and temperature, and within the time needed for electrospray, which was of the order of seconds. Well organized nanoparticle assemblies were obtained from such uniform particles. A home-made and simple nanoelectrospray set-up produced charged microdroplets for the generation of such nanostructures, forming cm2 areas of uniform nanoparticles. A free-standing thin film of monodisperse silver nanoparticles was also made on a liquid surface by controlling the electrospray conditions. This unique method may be extended for the creation of advanced materials of many kinds.

3.
Org Biomol Chem ; 19(7): 1604-1609, 2021 02 25.
Artigo em Inglês | MEDLINE | ID: mdl-33527967

RESUMO

We demonstrate herein the first example of a palladium(ii) catalyzed regioselective ortho-C(sp2)-H arylation in aqueous medium (a sustainable solvent) utilizing 8-AIP (8-aminoimidazo[1,2-a]pyridine) as a promising and removable bidentate directing group/auxilliary. This newly developed protocol features a broad substrate scope with excellent functional group tolerance and enables an expeditious route to a library of unsymmetrical amides in good to excellent yields with exclusive site-selectivity.

4.
ACS Nano ; 15(3): 5023-5031, 2021 03 23.
Artigo em Inglês | MEDLINE | ID: mdl-33587609

RESUMO

Generation of current or potential at nanostructures using appropriate stimuli is one of the futuristic methods of energy generation. We developed an ambient soft ionization method for mass spectrometry using 2D-MoS2, termed streaming ionization, which eliminates the use of traditional energy sources needed for ion formation. The ionic dissociation-induced electrokinetic effect at the liquid-solid interface is the reason for energy generation. We report the highest figure of merit of current generation of 1.3 A/m2 by flowing protic solvents at 22 µL/min over a 1 × 1 mm2 surface coated with 2D-MoS2, which is adequate to produce continuous ionization of an array of analytes, making mass spectrometry possible. Weakly bound ion clusters and uric acid in urine have been detected. Further, the methodology was used as a self-energized breath alcohol sensor capable of detecting 3% alcohol in the breath.


Assuntos
Molibdênio , Nanoestruturas , Dissulfetos , Espectrometria de Massas
5.
Plant Genome ; 14(1): e20076, 2021 03.
Artigo em Inglês | MEDLINE | ID: mdl-33480153

RESUMO

With an aim of enhancing drought tolerance using a marker-assisted backcrossing (MABC) approach, we introgressed the "QTL-hotspot" region from ICC 4958 accession that harbors quantitative trait loci (QTLs) for several drought-tolerance related traits into three elite Indian chickpea (Cicer arietinum L.) cultivars: Pusa 372, Pusa 362, and DCP 92-3. Of eight simple sequence repeat (SSR) markers in the QTL-hotspot region, two to three polymorphic markers were used for foreground selection with respective cross-combinations. A total of 47, 53, and 46 SSRs were used for background selection in case of introgression lines (ILs) developed in genetic backgrounds of Pusa 372, Pusa 362, and DCP 92-3, respectively. In total, 61 ILs (20 BC3 F3 in Pusa 372; 20 BC2 F3 in Pusa 362, and 21 BC3 F3 in DCP 92-3), with >90% recurrent parent genome recovery were developed. Six improved lines in different genetic backgrounds (e.g. BGM 10216 in Pusa 372; BG 3097 and BG 4005 in Pusa 362; IPC(L4-14), IPC(L4-16), and IPC(L19-1) in DCP 92-3) showed better performance than their respective recurrent parents. BGM 10216, with 16% yield gain over Pusa 372, has been released as Pusa Chickpea 10216 by the Central Sub-Committees on Crop Standards, Notification and Release of Varieties of Agricultural Crops, Ministry of Agriculture and Farmers Welfare, Government of India, for commercial cultivation in India. In summary, this study reports introgression of the QTL-hotspot for enhancing yield under rainfed conditions, development of several introgression lines, and release of Pusa Chickpea 10216 developed through molecular breeding in India.


Assuntos
Cicer , Locos de Características Quantitativas , Cicer/genética , Secas , Grão Comestível , Índia
6.
ACS Appl Mater Interfaces ; 13(5): 6496-6504, 2021 Feb 10.
Artigo em Inglês | MEDLINE | ID: mdl-33512132

RESUMO

We demonstrate the formation of a versatile luminescent organo-inorganic layered hybrid material, composed of bovine serum albumin (BSA)-protected Au30 clusters and aminoclay sheets. X-ray diffraction revealed the intercalation of Au30@BSA in the layered superstructure of aminoclay sheets. Coulombic attraction of the clusters and the clay initiates the interaction, and the appropriate size of the clusters allowed them to intercalate within the lamellar aminoclay galleries. Electron microscopy measurements confirmed the hierarchical structure of the material and also showed the cluster-attached clay sheets. Zeta potential measurement and dynamic light scattering probed the gradual formation of the ordered aggregates in solution. The hybrid material could be stretched up to 300% without fracture. The emergence of a new peak in the luminescence spectrum was observed during the course of mechanical stretching. This peak increased in intensity gradually with the degree of elongation or strain of the material. A mechanochromic luminescence response was further demonstrated with a writing experiment on a luminescent mat of the material, made by electrospinning.

7.
Org Biomol Chem ; 19(2): 360-364, 2021 01 21.
Artigo em Inglês | MEDLINE | ID: mdl-33320158

RESUMO

Palladium catalyzed arylation of the inert ß-C(sp2)-H bond of carboxylic acid derivatives is reported herein for the first time utilizing 8-aminoimidazo[1,2-a]pyridine (AIP) as an efficacious and new inbuilt 6,5-fused bicyclic removable directing group. This protocol is scalable, exhibits high levels of ß-site selectivity and tolerates a broad spectrum of functional groups.

8.
J Am Chem Soc ; 142(50): 21040-21049, 2020 12 16.
Artigo em Inglês | MEDLINE | ID: mdl-33259190

RESUMO

Considering the importance of water splitting as the best solution for clean and renewable energy, the worldwide efforts for development of increasingly active molecular water oxidation catalysts must be accompanied by studies that focus on elucidating the mode of actions and catalytic pathways. One crucial challenge remains the elucidation of the factors that determine the selectivity of water oxidation by the desired 4e-/4H+ pathway that leads to O2 rather than by 2e-/2H+ to H2O2. We now show that water oxidation with the cobalt-corrole CoBr8 as electrocatalyst affords H2O2 as the main product in homogeneous solutions, while heterogeneous water oxidation by the same catalyst leads exclusively to oxygen. Experimental and computation-based investigations of the species formed during the process uncover the formation of a Co(III)-superoxide intermediate and its preceding high-valent Co-oxyl complex. The competition between the base-catalyzed hydrolysis of Co(III)-hydroperoxide [Co(III)-OOH]- to release H2O2 and the electrochemical oxidation of the same to release O2 via [Co(III)-O2•]- is identified as the key step determining the selectivity of water oxidation.

9.
Dalton Trans ; 49(19): 6328-6340, 2020 May 19.
Artigo em Inglês | MEDLINE | ID: mdl-32342075

RESUMO

Construction of efficient multifunctional materials is one of the greatest challenges of our time. We herein report the magnetic and catalytic characterization of dinuclear [CoIIICoII(HL1)2(EtOH)(H2O)]Cl·2H2O (1) and trinuclear [CoIIICoII2(HL2)2(L2)Cl2]·3H2O (2) mixed valence complexes. Relevant structural features of the complexes have been mentioned to correlate with their magnetic and catalytic properties. Unique structural features, especially in terms of significant distortions around the CoII centre(s), prompted us to test both spin-orbit coupling (SOC) and zero field splitting (ZFS) methodologies for the systems. The positive sign of D values has been established from X-band EPR spectra recorded in the 5-40 K temperature range and reaffirmed by CAS/NEVPT2 calculations. ZFS tensors are also extracted for the compounds along with CoIIGaIII and CoIIZnIICoIII model species. Interestingly, 1 shows slow relaxation of magnetization below 6.5 K in the presence of a 1000 Oe external dc field with two relaxation processes (Ueff = 37.0 K with τ0 = 1.57 × 10-8 s for the SR process and Ueff = 7 K with τ0 = 1.66 × 10-6 s for the FR process). As mixed valence cobalt complexes with various nuclearities are central to the quest for water oxidation catalysts, we were prompted to explore their features and to our surprise, water oxidation ability has been realized for both 1 and 2 with significant nuclearity control.

10.
ACS Cent Sci ; 5(6): 1024-1034, 2019 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-31263762

RESUMO

The selective reduction of O2, typically with the goal of forming H2O, represents a long-standing challenge in the field of catalysis. Macrocyclic transition-metal complexes, and cobalt porphyrins in particular, have been the focus of extensive study as catalysts for this reaction. Here, we show that the mononuclear Co-tetraarylporphyrin complex, Co(porOMe) (porOMe = meso-tetra(4-methoxyphenyl)porphyrin), catalyzes either 2e-/2H+ or 4e-/4H+ reduction of O2 with high selectivity simply by changing the identity of the Brønsted acid in dimethylformamide (DMF). The thermodynamic potentials for O2 reduction to H2O2 or H2O in DMF are determined and exhibit a Nernstian dependence on the acid pK a, while the CoIII/II redox potential is independent of the acid pK a. The reaction product, H2O or H2O2, is defined by the relationship between the thermodynamic potential for O2 reduction to H2O2 and the CoIII/II redox potential: selective H2O2 formation is observed when the CoIII/II potential is below the O2/H2O2 potential, while H2O formation is observed when the CoIII/II potential is above the O2/H2O2 potential. Mechanistic studies reveal that the reactions generating H2O2 and H2O exhibit different rate laws and catalyst resting states, and these differences are manifested as different slopes in linear free energy correlations between the log(rate) versus pK a and log(rate) versus effective overpotential for the reactions. This work shows how scaling relationships may be used to control product selectivity, and it provides a mechanistic basis for the pursuit of molecular catalysts that achieve low overpotential reduction of O2 to H2O.

11.
Dalton Trans ; 48(18): 5965-5977, 2019 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-30608094

RESUMO

Iron porphyrins are potential catalysts for the electrocatalytic and photocatalytic reduction of CO2. It has been recently established that the reduction of CO2 by an iron porphyrin complex with a hydrogen bonding distal pocket involves at least two intermediates: a Fe(ii)-CO22- and a Fe(ii)-COOH species. A distal hydrogen bonding interaction was found to be key in determining the stability of these intermediates and affecting both the selectivity and rate of CO2 reduction. In this report, a series of iron porphyrins that vary only in the distal H-bonding network are further investigated and these exhibit turnover frequencies (TOFs) ranging from 1.0 s-1 to 103 s-1. The experimental TOFs correlate with the H-bonding ability of the distal superstructure of these iron porphyrin complexes and analysis suggests that H-bonding alone can tune the rate of CO2 reduction by as much as 1000 fold. DFT calculations provide a detailed insight into how the, apparently weak, 2nd sphere interactions lead to efficient CO2 activation for reduction. The ability to tune CO2 reduction rates by changing the H-bonding residue instead of the acid source is a convenient way to tune CO2 reduction electrocatalysis without compromising selectivity by introducing competitive hydrogen evolution reaction or formate generation.

12.
Indian Pediatr ; 55(9): 768-772, 2018 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-30345982

RESUMO

OBJECTIVE: To determine efficacy of Point-of-care Quality improvement (POCQI) in early initiation (within 30 minutes) of emergency treatment among sick neonates. DESIGN: Quality improvement project over a period of twenty weeks. SETTING: Special Newborn Care Unit (SNCU) of a tertiary care center of Eastern India. PARTICIPANTS: All consecutive sick neonates (≥ 28 wk gestation) who presented at triage during morning shift (8 am to 2 pm). INTERVENTION: We used a stepwise Plan-do-study-act (PDSA) approach to initiate treatment within 30 min of receiving sick newborns. After baseline phase of one month, a quality improvement (QI) team was formed and conducted three PDSA cycles (PDSA I , PDSA II and PDSA III) of 10 d each, followed by a post-intervention phase over 3 months. MAIN OUTCOME MEASURE(s): Percentage of sick babies getting early emergency management at SNCU triage. RESULTS: 309 neonates were enrolled in the study (56 in baseline phase, 88 in implementation phase and 212 in post- intervention phase). Demographic characteristics including birthweight and gestational age were comparable among baseline and post intervention cohorts. During implementation phase, successful early initiation of management was noted among 47%, 69% and 80% neonates following PDSA I, PDSA II and PDSA III, respectively. In comparison to baseline phase, the percentage of neonates receiving treatment within 30 minutes of arrival at triage increased from 20% to 76% (P<0.001) and the mean (SD) time of initiation of treatment decreased from 80.8 (21.0) to 19.8 (5.6) min (P<0.001) during post-implementation phase. Hospital mortality (33% vs 15%, P=0.004) and need for ventilator support (44% vs 18%, P<0.001) were also significantly lower among post intervention cohort in comparison to baseline cohort. CONCLUSION: Stepwise implementation of PDSA cycles significantly increased the percentage of sick newborns receiving early emergency management at the SNCU triage, thereby resulting in better survival.


Assuntos
Tratamento de Emergência/normas , Doenças do Recém-Nascido/terapia , Sistemas Automatizados de Assistência Junto ao Leito/normas , Melhoria de Qualidade , Triagem/normas , Tratamento de Emergência/estatística & dados numéricos , Feminino , Mortalidade Hospitalar , Humanos , Índia , Recém-Nascido , Unidades de Terapia Intensiva Neonatal/normas , Masculino , Sistemas Automatizados de Assistência Junto ao Leito/estatística & dados numéricos , Centros de Atenção Terciária/normas , Fatores de Tempo , Triagem/estatística & dados numéricos
13.
Angew Chem Int Ed Engl ; 57(22): 6522-6526, 2018 05 28.
Artigo em Inglês | MEDLINE | ID: mdl-29607588

RESUMO

The self-assembled structures of atomically precise, ligand-protected noble metal nanoclusters leading to encapsulation of plasmonic gold nanorods (GNRs) is presented. Unlike highly sophisticated DNA nanotechnology, this strategically simple hydrogen bonding-directed self-assembly of nanoclusters leads to octahedral nanocrystals encapsulating GNRs. Specifically, the p-mercaptobenzoic acid (pMBA)-protected atomically precise silver nanocluster, Na4 [Ag44 (pMBA)30 ], and pMBA-functionalized GNRs were used. High-resolution transmission and scanning transmission electron tomographic reconstructions suggest that the geometry of the GNR surface is responsible for directing the assembly of silver nanoclusters via H-bonding, leading to octahedral symmetry. The use of water-dispersible gold nanoclusters, Au≈250 (pMBA)n and Au102 (pMBA)44 , also formed layered shells encapsulating GNRs. Such cluster assemblies on colloidal particles are a new category of precision hybrids with diverse possibilities.

14.
Nanoscale ; 10(4): 1807-1814, 2018 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-29308798

RESUMO

Understanding the chemical changes happening to nanostructures during a process is vital in selecting them for applications. Here, we investigated the difference in the reactivity of the bulk and nanoscale forms of molybdenum disulfide (MoS2) in solution with lead ions (Pb2+ and Pb4+) as probes, at room temperature. While the bulk form did not show any reactivity in the experimental timescale, the two-dimensional (2D) nanoscale form showed not only reactivity but also quite rapid kinetics that resulted in the formation of distinct products, principally PbMoO4 with anion substitution, in a few seconds. Depending on the charge state of the cation, and the pH of the reaction mixture, two different kinds of morphologies of the same reaction product were formed. Furthermore, we demonstrate that this unusual reactivity of the MoS2 nanosheets (NSs) was retained in its supported form and hence, such supported materials can be effective for the abstraction of toxic lead from water, with fast kinetics.

15.
Water Environ Res ; 90(2): 101-109, 2018 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-28600862

RESUMO

This paper presents the biophysical impact of various interventions made under watershed development programs, in terms of the creation of additional water resources, and resultant changes in land use and cropping patterns in the Bundelkhand region of Madhya Pradesh State, India. Both primary and secondary data gathered from randomly selected watersheds and their corresponding control villages were used in this study. Analysis revealed that emphasis was given primarily to the creation of water resources potential during implementation of the programs, which led to augmentation of surface and groundwater availability for both irrigation and non-agricultural purposes. In addition, other land based interventions for soil and moisture conservation, plantation activities, and so forth, were taken up on both arable and nonarable land, which helped to improve land slope and land use, cropping pattern, agricultural productivity, and vegetation cover.


Assuntos
Agricultura/métodos , Conservação dos Recursos Naturais/métodos , Recursos Hídricos/provisão & distribuição , Abastecimento de Água/métodos , Índia , Solo , Abastecimento de Água/estatística & dados numéricos
16.
Glob Chall ; 2(12): 1800052, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31565316

RESUMO

A new method for creating nanopores in single-layer molybdenum disulfide (MoS2) nanosheets (NSs) by the electrospray deposition of silver ions on a water suspension of the former is introduced. Electrospray-deposited silver ions react with the MoS2 NSs at the liquid-air interface, resulting in Ag2S nanoparticles which enter the solution, leaving the NSs with holes of 3-5 nm diameter. Specific reaction with the S of MoS2 NSs leads to Mo-rich edges. Such Mo-rich defects are highly efficient for the generation of active oxygen species such as H2O2 under visible light which causes efficient disinfection of water. 105 times higher efficiency in disinfection for the holey MoS2 NSs in comparison to normal MoS2 NSs is shown. Experiments are performed with multiple bacterial strains and a virus strain, demonstrating the utility of the method for practical applications. A conceptual prototype is also presented.

17.
Dalton Trans ; 46(40): 13739-13744, 2017 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-28956575

RESUMO

The synthesis, characterization and reactivity studies of iron(ii) complexes [FeII(PySH)4](OTf)2, 1-(OTf)2, [FeII(PySH)4](ClO)4, 1-(ClO4)2, and [FeII(PyS)2]n, (2), of a 2-mercaptopyridine (PySH) ligand are discussed. The X-ray crystal structures of both 1-(OTf)2 and 1-(ClO4)2 reveal a distorted tetrahedral geometry at the iron(ii) center with identical constituents. All the pyridine nitrogen atoms are protonated and thiolate ions are coordinated to the iron(ii) center. The structure and function of complex 1-(OTf)2 or 1-(ClO4)2 resembles the active site of rubredoxin. Complex 2 has octahedral geometry at the iron(ii) center forming a 1-D coordination polymer. Complex 1-(OTf)2 exhibits a high positive redox potential (E1/2 = 0.23 V vs. Ag/AgCl) which reduces to -0.12 V in the presence of triethylamine under an inert atmosphere. This change of the redox potential is highly reversible in the presence of a weak acid such as p-toluenesulfonic acid, pTsOH. DFT studies show that the complex cation [FeII(PySH)4]2+ upon treatment with a base converts to its anionic congener, [FeII(PyS)4]2-, via the deprotonation of the pyridinium moiety. The iron(ii) complexes readily react with molecular oxygen to yield the corresponding iron(iii) complex, which rapidly decays to form pyridine disulphide (Py2S2) and an iron(ii) complex.

18.
Acc Chem Res ; 50(7): 1744-1753, 2017 07 18.
Artigo em Inglês | MEDLINE | ID: mdl-28686419

RESUMO

Reactivity as well as selectivity are crucial in the activation and electrocatalytic reduction of molecular oxygen. Recent developments in the understanding of the mechanism of electrocatalytic O2 reduction by iron porphyrin complexes in situ using surface enhanced resonance Raman spectroscopy coupled to rotating disc electrochemistry (SERRS-RDE) in conjunction with H/D isotope effects on electrocatalytic current reveals that the rate of O2 reduction, ∼104 to 105 M-1 s-1 for simple iron porphyrins, is limited by the rate of O-O bond cleavage of an intermediate ferric peroxide species (FeIII-OOH). SERRS-RDE probes the system in operando when it is under steady state such that any intermediate species that has a greater rate of formation relative to its rate of decay, including the rate determining species, would accumulate and can be identified. This technique is particularly well suited to investigate iron porphyrin electrocatalysts as the intense symmetric ligand vibrations allow determination of the oxidation and spin states of the bound iron with high fidelity. The rate of O2 reduction could be tuned up by 3 orders of magnitude by incorporating residues in the catalyst design that can exert "push" or "pull" effects, that is, axial phenolate and thiolate ligands and distal arginine residues. Similarly the rate of O-O bond cleavage can be enhanced by several orders of magnitude upon incorporating a distal Cu site and installing the active site in a hydrophobic protein environment in synthetic models and biosynthetic protein scaffolds. The selectivity, however, is solely determined by the site of protonation of a ferric peroxide (FeIII-OOH) intermediate and can be governed by installing preorganized second sphere residues in the distal pocket. The 4e-/4H+ reduction of O2 entails protonation of the distal oxygen of the FeIII-OOH species, while 2e-/2H+ reduction requires the proximal oxygen to be protonated. Mechanistic investigations of CO2 reduction by iron porphyrins reveal that the rate-determining step is the C-O bond cleavage of a FeII-COOH species analogous to the O-O bond cleavage step of a FeIII-OOH species in O2 reduction. The selectivity, resulting in either CO or HCOOH, is determined by the site of protonation of this species. These similarities suggests that the chemical principles governing the rate and selectivity of reduction of small molecules like O2, CO2, NOx, and SOx may be quite similar in nature.

19.
Chem Commun (Camb) ; 53(58): 8188-8191, 2017 Jul 18.
Artigo em Inglês | MEDLINE | ID: mdl-28681053

RESUMO

A synthetic mimic of Fe-Fe hydrogenase (H2ase) is reported which bears a terminal alkyne group in the ligand. Using a terminal azide bearing organic linkers, this complex could be covalently attached to various electrode surfaces (e.g. edge plane graphite, reduced graphene oxide, etc.). The electrocatalytic hydrogen evolution (HER) efficiency of these constructs is investigated and the results show that the EPG-H2ase mimic construct is able to produce H2 from acidic water efficiently with over 90% selectivity.

20.
Nanoscale ; 9(24): 8240-8248, 2017 Jun 22.
Artigo em Inglês | MEDLINE | ID: mdl-28581554

RESUMO

We report the synthesis of a new silver cluster, [Ag59(2,5-DCBT)32]3- (I) (2,5-DCBT: 2,5-dichlorobenzenethiol), which acts as a precursor for the synthesis of three well-known silver clusters, [Ag44(2,4-DCBT/4-FTP)30]4- (II) (4-FTP: 4-fluorothiophenol and 2,4-DCBT: 2,4-dichlorobenzenethiol), [Ag25(2,4-DMBT)18]- (III) (2,4-DMBT: 2,4-dimethylbenzenethiol) and [Ag29(1,3-BDT)12(PPh3)4]3- (IV) (1,3-BDT: 1,3-benzenedithiol and PPh3: triphenylphosphine). This newly synthesized silver cluster, I, is characterized using UV-vis absorption studies, high resolution electrospray ionization mass spectrometry (ESI MS) and other analytical tools. The optical absorption spectrum shows distinct features which are completely different from the previously reported silver clusters. We perform the rapid transformations of I to other well-known clusters II, III and IV by reaction with different thiols. The time-dependent UV-vis and ESI MS measurements reveal that I dissociates into distinct thiolate entities in the presence of thiols and the thiolates recombine to produce different clusters. The conversion mechanism is found to be quite different from the previous reports where it occurs through the initial formation of ligand exchanged products. Here, we also show the synthesis of a different cluster core, [Ag44(2,4-DCBT)30]4- (IIa) using 2,4-DCBT, a structural isomer of 2,5-DCBT under the same synthetic conditions used for I. This observation demonstrates the effect of isomeric thiols on controlling the size of silver clusters. The conversion of one cluster to several other clusters under ambient conditions and the effect of ligand structure in silver cluster synthesis give new insights into the cluster chemistry.

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