Terahertz spectroscopy and computational investigation of the flufenamic acid/nicotinamide cocrystal.

Terahertz spectroscopy probes the low-frequency vibrations that are sensitive to both the intermolecular and intramolecular interactions of molecules in the solid state. Thus, terahertz spectroscopy can be a useful tool in the investigation of crystalline pharmaceutical compounds, where slight changes in the packing arrangement can modify the overall effectiveness of a drug formulation. This is especially true for cases of polymorphic systems, hydrates/solvates, and cocrystals.

The role of terahertz polariton absorption in the characterization of crystalline iron sulfate hydrates.

Iron sulfate compounds have been used extensively to produce iron gall ink, a widely used writing ink in the western world from the 12th-20th centuries. Iron gall ink is well known to corrode writing supports, so detection of iron species is important for the preservation of historical artwork and documents. Iron(ii) sulfate readily changes hydration states and oxidizes in ambient conditions, forming compounds that contribute to this deterioration.

Origins of hydration differences in homochiral and racemic crystals of aspartic acid.

The propensity for crystalline hydrates of organic molecules to form is related to the strength of the interactions between molecules, including the chiral composition of the molecular solids. Specifically, homochiral versus racemic crystalline samples can exhibit distinct differences in their ability to form energetically stable hydrates. The focus of the current study is a comparison of the crystal structures and intermolecular forces found in solid-state L-aspartic acid, DL-aspartic acid, and L-aspartic acid monohydrate.

Brønsted acid catalyzed monoalkylation of anilines with trichloroacetimidates.

Trichloroacetimidates are useful alkylating agents for aromatic amines, requiring only a catalytic amount of a Brønsted acid to facilitate the reaction. Monoalkylation predominates under these conditions. Electron-poor anilines provide superior yields, with electron-rich anilines sometimes showing competitive Friedel-Crafts alkylation.

London force correction disparity in the modeling of crystalline asparagine and glutamine.

Solid-state density functional theory is a powerful computational method used to provide insight into the low-frequency vibrations of crystalline solids. A known limitation of this method is its general underestimation of weak intermolecular forces. Semiempirical London force corrections have been developed to augment density functional theory calculations with the ultimate goal being corrections that are applicable to a range of compounds.

Ruthenium catalyzed cycloisomerization of silicon-tethered 1,7-enynes to give exocyclic 1,3-dienes.

The cycloisomerization of vinyl silicon-tethered 1,7-enynes has been accomplished using catalytic Cp*Ru(COD)Cl. The products possess a new silane moiety and trisubstituted alkenes as part of the diene system. The reaction scope includes aryl, alkyl, vinyl, and cyclopropyl alkyne functionalities.

Assignment of the terahertz spectra of crystalline copper sulfate and its hydrates via solid-state density functional theory.

Terahertz (THz) vibrational spectroscopy is a promising tool for the nondestructive and potentially noninvasive characterization of historical objects, which can provide information on the materials used for their production as well as identify and monitor their chemical degradation. Copper sulfate (CuSO4) has drawn interest due to its inclusion in the preparation of iron gall inks found in historical artwork and documents. Copper sulfate rapidly forms hydrates which contribute to the formulation of these ink species and may influence their corrosive nature.

Quantitative determination of cellular farnesyltransferase activity: towards defining the minimum substrate reactivity for biologically relevant protein farnesylation.

Prenylation is a post-translational modification wherein an isoprenoid group is attached to a protein substrate by a protein prenyltransferase. Hundreds of peptide sequences are in vitro substrates for protein farnesyltransferase (FTase), but it remains unknown which of these sequences can successfully compete for in vivo prenylation. Translating in vitro studies to predict in vivo protein farnesylation requires determining the minimum reactivity needed for modification by FTase within the cell.

Ethylene transposition: ruthenium hydride catalyzed intramolecular trans-silylvinylation of internal alkynes.

A highly selective intramolecular trans-silylvinylation of internal alkynes catalyzed by RuHCl(CO)(SIMes)(PPh3) has been accomplished. The use of methyl vinyl ketone as an additive increased the efficiency of this transformation. This process was used to successfully form five-, six-, and seven-membered oxasilacycles by a formal anti-exo-dig cyclization.

Rapid synthesis of 3,3' bis-arylated BINOL derivatives using a C-H borylation in situ Suzuki-Miyaura coupling sequence.

The increased interest in BINOL derived catalysts for asymmetric transformations has encouraged us to disclose a rapid and scalable method of preparing 3,3' bis-arylated BINOL derivatives 1 using a one-pot CH borylation/Suzuki-Miyaura coupling sequence. The use of an aldehyde additive was found to be crucial to the success of this in situ tandem approach. This method was applied to the preparation of 10 BINOL derivatives, each completed within 24 h.

Nonchromophoric organic matter suppresses polycyclic aromatic hydrocarbon photolysis in ice and at ice surfaces.

We have investigated the effects of organic matter (OM) that does not absorb sunlight ("nonchromophoric") on the reactive environment presented by bulk ice and ice surfaces. Fluorescence spectroscopy showed that the presence of as little as 2.5 × 10(-4) M octanol or decanol reduces the extent to which naphthalene self-associates at ice surfaces, which indicates that naphthalene partitions between ice and organic phases present there.

Copper- and palladium-catalyzed amidation reactions for the synthesis of substituted imidazo[4,5-c]pyridines.

Imidazo[4,5-c]pyridines were synthesized in three steps utilizing a palladium-catalyzed amidation/cyclization strategy. N-Aryl substrates were synthesized using copper-catalyzed amidation of 3-amino-N-Boc-4-chloropyridine. Complementary protocols for the selective chlorination of imidazo[4,5-c]pyridines at the C2 and C7 positions were also developed.

Terahertz vibrations of crystalline acyclic and cyclic diglycine: benchmarks for London force correction models.

Terahertz spectroscopy provides direct information concerning weak intermolecular forces in crystalline molecular solids and therefore acts as an excellent method for calibrating and evaluating computational models for noncovalent interactions. In this study, the low-frequency vibrations of two dipeptides were compared, acyclic diglycine and cyclic diglycine, as benchmark systems for gauging the performance of semiempirical London force correction approaches. The diglycine samples were investigated using pulsed terahertz spectroscopy from 10 to 100 cm(-1) and then analyzed using solid-state density functional theory (DFT) augmented with existing London force corrections, as well as a new parametrization (DFT-DX) based on known experimental values.

M-F interactions and heterobimetallics: furthering the understanding of heterobimetallic stabilization.

Heterobimetallic complexes containing alkali, alkaline-earth, and divalent europium metals utilizing the perfluoro-tert-butoxide (PFTB) ligand following the general formula, [AM(PFTB)3(co-ligand)x] (A=Na, K; M=Mg, Sr, Ba, Eu; co-ligand=THF, toluene), have been isolated. These compounds sublime at low temperatures with low residual weight indicating their potential as metal-organic chemical-vapor deposition (MOCVD) precursors. The complexes have unique molecular architectures that are strongly influenced by M-F interactions, as was verified in the solid state by using X-ray crystallography.

Synthesis of 2-amino-imidazo[4,5-b]pyridines.

The C2 amination of imidazo[4,5-b]pyridines was accomplished through C2 halogenation followed by substitution (SNAr) with functionalized primary and secondary amines. This regioselective sequence is operationally simple and provides an easy access to derivatives of protected imidazo[4,5-b]pyridines.

Total synthesis of pentosidine.

Pentosidine, a biologically important advanced glycation endproduct, has been accessed in a rapid, high-yielding manner. The synthesis was accomplished via a six-step sequence starting with 3-amino-2-chloropyridine and features a palladium-catalyzed tandem cross-coupling/cyclization to construct the imidazo[4,5-b]pyridine core.

Investigating tautomeric polymorphism in crystalline anthranilic acid using terahertz spectroscopy and solid-state density functional theory.

Terahertz spectroscopy is sensitive to the interactions between molecules in the solid-state and recently has emerged as a new analytical tool for investigating polymorphism. Here, this technique is applied for the first time to the phenomenon of tautomeric polymorphism where the crystal structures of anthranilic acid (2-aminobenzoic acid) have been investigated. Three polymorphs of anthranilic acid (denoted Forms I, II and III) were studied using terahertz spectroscopy and the vibrational modes and relative polymorph stabilities analyzed using solid-state density functional theory calculations augmented with London dispersion force corrections.

Terahertz spectroscopy of the explosive taggant 2,3-dimethyl-2,3-dinitrobutane.

The terahertz spectrum of the crystalline explosive taggant 2,3-dimethyl-2,3-dinitrobutane (C(6)H(12)N(2)O(4)) has been investigated as an alternative means of detecting solid-state explosives. The room-temperature spectrum exhibits two broad absorption features centered at 38.3 and 49.

Regiodivergent synthesis of functionalized indene derivatives via Pt-catalyzed Rautenstrauch reaction of propargyl carbonates.

A regiodivergent synthesis of functionalized indene derivatives from a Pt-catalyzed Rautenstrauch reaction of propargyl carbonate is described. A one-pot Rautenstrauch/Tsuji-Trost reaction delivering 2-indanones was realized efficiently using this methodology.

Synthesis of imidazo[4,5-b]pyridines and imidazo[4,5-b]pyrazines by palladium catalyzed amidation of 2-chloro-3-amino-heterocycles.

A facile synthesis of imidazo[4,5-b]pyridines and -pyrazines is described using a Pd-catalyzed amide coupling reaction. This reaction provides quick access to products with substitution at N1 and C2. A model system relevant to the natural product pentosidine has been demonstrated, as well as the total synthesis of the mutagen 1-Me-5-PhIP.

Analyzing near-infrared scattering from human skin to monitor changes in hematocrit.

Probing tissue with near-infrared radiation (NIR) simultaneously produces remitted fluorescence and Raman scattering (IE) plus Rayleigh∕Mie light scattering (EE) that noninvasively give chemical and physical information about the materials and objects within. We model tissue as a three-phase system: plasma and red blood cell (RBC) phases that are mobile and a static tissue phase. In vivo, any volume of tissue naturally experiences spatial and temporal fluctuations of blood plasma and RBC content.

Investigation of the low-frequency vibrations of crystalline tartaric acid using terahertz spectroscopy and solid-state density functional theory.

The room temperature and cryogenic terahertz (THz) spectra (10-95 cm(-1)) of l-tartaric acid and dl-tartaric acid were investigated. At 293 K, the l-tartaric acid spectrum showed four absorption features at 36.4, 61.

A confidence level algorithm for the determination of absolute configuration using vibrational circular dichroism or Raman optical activity.

Spectral comparison is an important part of the assignment of the absolute configuration (AC) by vibrational circular dichroism (VCD), or equally by Raman optical activity (ROA). In order to avoid bias caused by personal interpretation, numerical methods have been developed to compare measured and calculated spectra. Using a neighbourhood similarity measure, the agreement between a computed and measured VCD or ROA spectrum is expressed numerically to introduce a novel confidence level measure.

Identification and quantification of polymorphism in the pharmaceutical compound diclofenac acid by terahertz spectroscopy and solid-state density functional theory.

Polymorph detection and quantification in crystalline materials is a principle interest of the pharmaceutical industry. Terahertz (THz) spectroscopy can be used for such analytical applications since this technique is sensitive to the intermolecular interactions of molecules in the solid state. Understanding the fundamental nature of the lattice vibrational motions leading to absorptions in THz spectra is challenging, but may be achieved through computational approaches.

Noncovalent interactions in paired DNA nucleobases investigated by terahertz spectroscopy and solid-state density functional theory.

Cocrystallized adenine and thymine derivatives, along with the pure monomeric crystals, were investigated by terahertz spectroscopy and solid-state density functional theory (DFT). The methylated nucleobase derivatives crystallize in planar hydrogen-bonded adenine-thymine pairs similar to the manner found in DNA. The spectra obtained for 1-methylthymine, 9-methyladenine, and the 1:1 cocrystal in the range of 10-100 cm(-1) clearly demonstrate that absorptions in this spectral range originate from the uniquely ordered assembly and the intermolecular interactions found in each individual crystal system.