Atomically precise pieces of matter of nanometer dimensions composed of noble metals are new categories of materials with many unusual properties. Over 100 molecules of this kind with formulas such as Au25(SR)18, Au38(SR)24, and Au102(SR)44 as well as Ag25(SR)18, Ag29(S2R)12, and Ag44(SR)30 (often with a few counterions to compensate charges) are known now. They can be made reproducibly with robust synthetic protocols, resulting in colored solutions, yielding powders or diffractable crystals. They are distinctly different from nanoparticles in their spectroscopic properties such as optical absorption and emission, showing well-defined features, just like molecules. They show isotopically resolved molecular ion peaks in mass spectra and provide diverse information when examined through multiple instrumental methods. Most important of these properties is luminescence, often in the visible–near-infrared window, useful in biological applications. Luminescence in the visible region, especially by clusters prot...

Atomically Precise Clusters of Noble Metals: Emerging Link between Atoms and Nanoparticles

Fourier transform Infrared (FTIR) spectroscopy is a versatile technique for the characterization of materials belonging to the carbon family. Based on the interaction of the IR radiation with matter this technique may be used for the identification and characterization of chemical structures. Most important features of this method are: non-destructive, real-time measurement and relatively easy to use. Carbon basis for all living systems has found numerous industrial applications from carbon coatings (i.e. amorphous and nanocrystalline carbon films: diamond-like carbon (DLC) films) to nanostructured materials (fullerenes, nanotubes, graphene) and carbon materials at nanoscale or carbon dots (CDots). In this paper, we present the FTIR vibrational spectroscopy for the characterization of diamond, amorphous carbon, graphite, graphene, carbon nanotubes (CNTs), fullerene and carbon quantum dots (CQDs), without claiming to cover entire field.

FTIR Spectroscopy for Carbon Family Study

We model the photoelectric emission from and charging of interstellar dust and obtain photoelectric gas heating efficiencies as a function of grain size and the relevant ambient conditions. We employ improved estimates for photoelectric thresholds, yields, and electron capture rates. Using realistic grain size distributions, we evaluate the net gas heating rate for various interstellar environments and find less heating for dense regions characterized by RV = 5.5 than for diffuse regions with RV = 3.1. We provide fitting functions that reproduce our numerical results for photoelectric heating and recombination cooling for a wide range of interstellar conditions. Finally, we investigate the potential importance of photoelectric heating in H II regions, including the warm ionized medium. We find that photoelectric heating could be comparable to or exceed heating due to photoionization of H for high ratios of the radiation intensity to the gas density. We also find that photoelectric heating by dust can account for the observed variation of temperature with distance from the Galactic midplane in the warm ionized medium.

Photoelectric Emission from Interstellar Dust: Grain Charging and Gas Heating

This review paper deals with proven and potential applications of mesoporous molecular sieves in catalysis. In addition to introduction and conclusion, the text is divided into two parts, respectively, dedicated to the design of solid catalysts and catalyst supports and to some relevant examples of catalytic processes.

/pdf/perspectives-in-catalytic-applications-of-mesostructured-4jgvbmynn3.pdf

Perspectives in catalytic applications of mesostructured materials

Ligand exchange offers an effective way to modify the properties of the recently prepared quantum clusters of gold. To tune optical and photoluminescence properties of one of the most stable quantum clusters of gold, Au25SG18 (SG-glutathione thiolate), we functionalized it by the exchange of −SG with functionalized -SG and with an altogether different ligand, namely, 3-mercapto-2-butanol (MB). The products were characterized by various techniques such as optical absorption (UV−vis), Fourier-transform infrared (FT-IR), nuclear magnetic resonance (NMR), X-ray photoelectron (XPS), and luminescence spectroscopies, mass spectrometry, and thermogravimetry (TG). Analyses of the TG data helped to establish the molecular composition of the products. Ligand exchange reaction was monitored by NMR spectroscopy, and it was found that the exchange reaction follows a first order kinetics. The XPS study showed that after the exchange reaction there was no change in the chemical nature of the metal core and binding energy...

http://www.dstuns.iitm.ac.in/listpdf/172_SI.pdf

Ligand Exchange of Au25SG18 Leading to Functionalized Gold Clusters: Spectroscopy, Kinetics, and Luminescence

Alkanethiol-protected silver clusters of average diameter 4.0 ± 0.5 nm form single-phase superlattice solids, and their X-ray powder diffractograms have been fully indexed to single cubic unit cells. Whereas alkanethiols with five or more carbon atoms form superlattices, the corresponding cluster with four carbons yield only separated clusters. The superlattice solids can be recrystallized from nonpolar solvents. No such superlattices are seen for the corresponding gold clusters. The superlattice collapses upon heating, but the solid retains the structure even at 398 K, much above the melting point of crystalline alkanes and the corresponding self-assembled monolayer. In situ variable-temperature X-ray diffraction investigations did not show any solid-state phase transitions in the superlattice. Temperature-dependent infrared spectroscopy reveals the melting of the alkyl chain, and it is seen that the chain as a whole achieves rotational freedom prior to the collapse of the superlattice. Calorimetric inve...

https://www.dstuns.iitm.ac.in/listpdf/79.pdf

Monolayer-Protected Cluster Superlattices: Structural, Spectroscopic, Calorimetric, and Conductivity Studies

Ion-molecule reactions in a pentaquadrupole mass spectrometer are used to generate cluster ions in which neutral pyridine molecules are bound to a linear polyatomic cation, [OCNCO]+. The dimeric adduct, viz. Py1[OCNCO]+Py2 where Py1 and Py2 represent substituted pyridines, formed upon reaction of mass-selected [OCNCO]+ with a mixture of pyridines, has a loosely bound structure, as suggested by triple stage mass spectrometric (MS3) experiments. Dimeric adducts comprised of meta- and/or para-substituted pyridines (unhindered pyridines) display an excellent linear correlation between the fragment ion abundance ratio ln [Py1[OCNCO]+/Py2[OCNCO]+] and the proton affinity difference of the pyridines. On the assumption that the effective temperature of the [OCNCO]+ -bound dimers is similar to that of the corresponding Cl+-bound dimers, [OCNCO]+ affinities of the substituted pyridines relative to pyridine are estimated to be 3-MePy 2.3, 4-MePy 3.2, 3-EtPy 3.5, 4-EtPy 4.1, 3,5-diMePy 4.9 and 3,4-diMePy 5.6 kcal mol−1 (1 kcal = 4.184 kJ). A linear relationship between the relative [OCNCO]+ cation affinity and the relative proton affinity (PA) is derived as relative [OCNCO]+ affinity (kcal mol−1) = 0.96 ΔPA, using the assumed effective temperature of 555 K. Dimers consisting of ortho-substituted pyridines display substantial steric effects between the ortho-substituted alkyl group and the central [OCNCO]+ cation. A set of gas-phase steric parameters (Sk) is determined and steric effects are ordered 2-MePy (-1.39) <2,5-diMePy (-3.02) < 2,4-diMePy (-3.15) < 2,3-diMePy ( −3.29) < 2,6-diMePy (-5.09) < 2,4,6-triMe (-6.13). A greater steric effect is experienced in the [OCNCO]+ system than in the corresponding Cl+ system, owing to the larger central ion in Py[OCNCO]+ Py. Structural and electronic information regarding the bond angles, bond lengths and charge density distributions in [OCNCO]+, Py[OCNCO]+ and Py[OCNCO]Py+ was obtained from ab initio calculations. The calculations show that [OCNCO]+ is linear with high positive charge densities on the carbon atoms. The calculations also reveal that the Py[OCNCO]+ monomer is a planar ion with the nitrogen atom of pyridine bound to a carbon atom of the [OCNCO]+ cation, and that the Py[OCNCO]Py+ dimer is a symmetrical ion in which the nitrogen atoms on the pyridine molecules bind to the carbon atoms of the central cluster ion, [OCNCO]+.

Relative carbonyl isocyanate cation [OCNCO]+ affinities of pyridines determined by the kinetic method using multiple‐stage (MS3) mass spectrometry

Urea undergoes O-protonation in the gas phase to yield a product that is thermodynamically more stable than the N-protonated isomer, as also is the case in aqueous solution. The proton affinity and...

Proton Affinity and Gas-Phase Basicity of Urea

Efficiency and structural specificity earmark the reaction of phosphonium ions 1 with cyclic acetals and ketals to yield 1,3,2-dioxaphospholanium ions 2 [Eq. (1)]. Potential applications of this reaction are in monitoring trace levels of organophosphorus esters and in developing novel carbonyl deprotection agents. R=OCH3 , CH3 ; R1 =H, CH3 ; R2 =CH3 , C6 H5 ; R3 =H, CH3 .

Replacement of C-O by P-O in Cyclic Acetals and Ketals.

https://link.springer.com/content/pdf/10.1016/1044-0305(95)00630-3.pdf

SiCl3+ and SiCl+ affinities for pyridines determined by using the kinetic method with multiple stage mass spectrometry: Agostic effects in the gas phase

Shuguang Ma

Papers

Monolayer-Protected Cluster Superlattices: Structural, Spectroscopic, Calorimetric, and Conductivity Studies

Relative carbonyl isocyanate cation [OCNCO]+ affinities of pyridines determined by the kinetic method using multiple‐stage (MS3) mass spectrometry

Proton Affinity and Gas-Phase Basicity of Urea

Replacement of C-O by P-O in Cyclic Acetals and Ketals.

SiCl3+ and SiCl+ affinities for pyridines determined by using the kinetic method with multiple stage mass spectrometry: Agostic effects in the gas phase