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The nematic twist-bend (TB) phase, exhibited by certain achiral thermotropic liquid crystalline (LC) dimers, features a nanometer-scale, heliconical rotation of the average molecular long axis (director) with equally probable left- and right-handed domains. On meso to macroscopic scales, the TB phase may be considered as a stack of equivalent slabs or "pseudo-layers", each one helical pitch in thickness. The long wavelength fluctuation modes should then be analogous to those of a smectic-A phase, and in particular the hydrodynamic mode combining "layer" compression and bending ought to be characterized by an effective layer compression elastic constant $B_{eff}$ and average director splay constant $K_1^{eff}$. The magnitude of $K_1^{eff}$ is expected to be similar to the splay constant of an ordinary nematic LC, but due to the absence of a true mass density wave, $B_{eff}$ could differ substantially from the typical value of $\sim 10^6$ Pa in a conventional smectic-A. Here we report the results of a dynamic light scattering study, which confirms the "pseudo-layer" structure of the TB phase with $B_{eff}$ in the range $\sim 10^3-10^4$ Pa. We show additionally that the temperature dependence of $B_{eff}$ at the TB to nematic transition is accurately described by a coarse-grained free energy density, which is based on a Landau-deGennes expansion in terms of a heli-polar order parameter that characterizes the TB state and is linearly coupled to bend distortion of the director., 9 pages, 7 figures

The phase behaviour of mixtures between two symmetric dimers, CBC9CB and the ether-linked analogue CBOC9OCB was investigated by Polarizing Optical Microscopy (POM), Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) studies. The dimeric constituents are fully miscible and the construction of a temperature-composition phase diagram reveals a surprising amplification of the stability of the Nx phase in compositions of up to 37 wt% of CBOC9OCB in CBC9CB. The origin for this enhancement of stability is discussed and an explanation based on chiral recognition is developed.

Gas Chromatography-Flame Ionization Detection (GC-FID) analysis for quantitation of residual solvents in drugs and synthetic intermediates is one of the most important and frequently used tests in the pharmaceutical industry. However, as currently practiced, the technique requires significant sample preparation time, in addition to having a very poor ‘green factor’ (Analytical Method Volume Intensity, or AMVI). In this study, a simple and fast protocol using multi-solvent standard mixtures combined with a seven minute universal GC-FID method (using either He or H2 as carrier gas) and Empower™ data analysis is presented. We demonstrate that standard mixtures containing solvents commonly used in process chemistry workflows can be stored in crimped HPLC vials at −10 °C for at least 31 months. The 31 months stability data showed over 97% recovery for all 25 solvents, with overall relative standard deviation below 5%. Our approach simplifies tremendously the tedious task of residual solvent quantitation, resulting in significantly less labor, greater reliability, faster time to result and at least a 290 fold reduction in solvent consumption and hazardous waste disposal.

Wavefront shaping, which is often achieved using liquid crystal (LC) spatial light modulators, is particularly important for a wide range of applications including laser microfabrication and micromanipulation, microscopy, and quantum optics. In this work, results are presented for the first integrated LC phase modulator that combines a flexoelectro‐optic LC layer (that behaves as a switchable λ/2 waveplate) with a polymerized reactive mesogen layer (which acts as a λ/4 waveplate) and a mirrored substrate that creates a double‐pass geometry. For a flexoelectro‐optic LC layer that exhibits switching angles of ±45° at a voltage of ±85 V a full 2π phase modulation is observed when driven by a 1 kHz waveform. Experimental results are also compared with modeling using Jones calculus of the amplitude and phase variation when the LC and the polymer layer deviate from their desired waveplate conditions. The development and demonstration of an integrated device is particularly significant for applications where size and cost are critical factors such as in LiDAR for the Space and Automotive industries, respectively.

In this paper, we demonstrate analog phase modulation in a transmissive configuration using the flexoelectro-optic effect in short-pitch chiral nematic liquid crystal (LC) devices. Two different modes are considered, both of which are shown to generate full 2π phase modulation at 1 kHz switching frequency. The first configuration that is considered consists of a half-wave plate that is placed between two flexoelectro-optic LC devices that are subjected to electric fields that are applied in phase. Second, we demonstrate that a similar phase modulation response can be observed by removing the half-wave plate and subjecting the two flexoelectro-optic LC devices to electric fields whereby the polarities are out of phase. Both configurations demonstrated herein are promising for the development of next-generation LC spatial light modulators, particularly when reflective geometries are challenging or impractical.

A cholesteric liquid crystal device having the uniform lying helix (ULH) structure shows stable and reversible characteristics and it has been demonstrated for the analogue modulation in 10 micro-second response time at room temperature. The device comprises a polymer-free chiral nematic liquid crystal mixture and the photoalignment layer is irradiated by the UV light to cause a preferred orientation of the liquid crystal. The ULH structure is obtained by cooling the liquid crystal mixture from the isotropic phase transition temperature in the presence of electric field. On the electrical and thermal cycling, no noticeable hysteresis has been observed. In addition, the tilt angle and response time have been measured in good agreement with Meyer's theory on the flexoelectric effect in liquid crystals.

A modulated and conventional DSC study of the transitions between the twist-bend nematic (Ntb), regular nematic (N) and isotropic liquid (Iso) phases was performed on a series of difluoroterphenyl-based dimers with (CH2)n spacers; n = 5, 7, 9, 11. The enthalpy of Ntb–N transition decreases steeply with increasing n, while that of the N–Iso transition increases with n; hence, the greatest effect of increasing n is a lowering N phase enthalpy. Based on past and present X-ray scattering experiments, we estimate the average molecular conformation in the Ntb phase and perform torsion energy calculations on the spacer. From this, the lowering enthalpy of the N phase is attributed to the decreasing torsional energy cost of bringing the two terphenyls from an inclined twisted conformation in the Ntb phase, to almost parallel in the N phase. With increasing n the C–C bonds of the spacers twist less away from their trans conformation, thereby reducing the overall torsion energy of the N phase. It is speculated that the nearly continuous nature of the Ntb–N transition in n = 11 dimer is associated with the divergence of the helical pitch toward infinity which is intercepted by a final jump at the very weak (0.01 J g−1) first-order transition. Small-angle X-ray scattering results suggest similar local cybotactic layering in both nematic phases, with four sublayers, i.e. tails, mesogens, spacers, mesogens.

2D supramolecular organization of a series of six cyanobiphenyls bimesogens deposited on highly oriented pyrolytic graphite (HOPG) is studied by scanning tunneling microscopy (STM). The adsorbates are 1,ω-bis(4-cyanobiphenyl-4′-yl)alkanes (CBnCB) with different lengths of their flexible alkyl spacer (containing from 7 to 12 methylene groups). Microscopic investigations at the molecular resolution allow for detailed analysis of the effect of the alkyl spacer length on the type and the extent of the resulting 2D organization. It was demonstrated that bimesogens with shorter spacers (7 and 8 methylene units) organize in a similar manner characterized by the formation of two types of differently ordered monolayers: dense packed, wherein the molecules are oriented in one direction and ordered into parallel rows (layer structure), or less densely packed where they are organized into a chiral windmill-like structure. For derivatives with longer spacers (ranging from 9 to 12 methylene units) the additional effect of parity of carbon atoms in the spacer (even versus odd) is observed. In this range of the spacer lengths even membered bimesogens are also organized in a typical layer structure. However, odd-membered dimers exhibit a much more complex 2D supramolecular organization with a larger unit cell and a helical arrangement of the molecules. Careful comparison of this structure with the 3D structural data derived from the X-ray diffraction investigations of single crystals indicates that for these bimesogens a clear correlation exists between the observed complex 2D supramolecular organization in the monolayer and the organization in one of the crystallographic planes of the 3D nematic twist-bent phase.

INTRODUCTION The invention of new chemical reactions provides new bond construction strategies for improved access to diverse regions of structural space. However, a pervasive, long-standing bias toward reporting successful results means that the shortcomings of even mature reaction methods remain poorly defined, making practical syntheses of structurally diverse targets far from certain. Distinct tools and experimental approaches are required to expose and record the problematic structural elements that limit different synthetic methods. The experimental space required to systematically survey reaction failure is vast, and existing ultrahigh-throughput (uHT) reaction screening approaches are inadequate for exploring the diversity of conditions pertaining in modern synthetic methods. Additionally, analytical approaches must continuously improve to meet the throughput demands of this expansive reaction screening. RATIONALE We report a nanomole-scale screening protocol that can be used to execute heterogeneous reactions with heating and agitation, use of volatile solvents, and capacity for photoredox chemistry. These advances in miniaturized chemistry screening were combined with the use of matrix-assisted laser desorption/ionization–time-of-flight mass spectrometry (MALDI-TOF MS), enabling analysis of 1536 reactions in ~10 min. Together, these advances create a platform that can enable systematic reaction evaluation and data capture to survey the dark space of chemical reactions. RESULTS Using the Buchwald-Hartwig C–N coupling reaction to exemplify this process, an uHT Glorius fragment additive poisons diagnostic approach was first applied to demonstrate that MALDI-MS could provide adequate data quality to monitor the formation of a single product under a wide variety of different synthetic conditions. Four catalytic methods—Ir/Ni and Ru/Ni dual-metal photoredox catalysis, as well as heterogeneous and high-temperature Cu and Pd catalysis—with extended nanomole chemistry requirements were evaluated for the synthesis of a single product in the presence of 383 structurally diverse simple and complex potential poisons. Using a normalizing internal standard that was closely related to the product and optimized operating parameters, MALDI-MS provided good correlation with existing ultra performance liquid chromatography (UPLC)–MS approaches (coefficient of determination R2 up to 0.85), allowing correct binning of “hits” and “misses” (defined as >50% product signal knockdown) up to 95% of the time. Next, the more challenging goal of exploring diverse whole-molecule C–N couplings was explored. In this case, it was not practical to have either product standards or closely related internal standards to enable analytical quantitation. A “simplest-partner test” was employed, in which 192 aryl bromides and 192 secondary amines were each coupled with a MS-active “simplest partner,” guaranteeing a somewhat normalized MS response for all products. The formation of 384 different products using the four aforementioned synthetic methods was monitored by MALDI-MS, with pass-fail binning of results correlating well with UPLC-MS in the identification of common structural elements (such as functional group counts, H-bond donors and acceptors, and polar surface area) that lead to reaction failure. CONCLUSION In the near future, each problematic structural element that is identified through systematic dark-space exploration can be promoted for in-depth examination to precisely define the specific parameters that determine reaction outcome at the atomic and quantum molecular level. Predictive machine learning models will use this focused data to enable synthetic practitioners to select the most appropriate reactions for use in a particular synthetic setting. In addition, functionality that persistently fails across synthetic methods can sharply define important challenges for the invention of improved chemical reactions.

Selective reflection of light by oblique helicoidal cholesteric (ChOH) can be tuned in a very broad spectral range by an applied electric field. In this work, we demonstrate that the peak wavelength of the selective reflection can be controlled by surface alignment of the director in sandwich cells. The peak wavelength is blue-shifted when the surface alignment is perpendicular to the bounding plates and red-shifted when it is planar. The effect is explained by the electric field redistribution within the cell caused by spatially varying heliconical ChOH structure. The observed phenomenon can be used in sensing applications., 8 pages, 3 figures

We report the induction of the Ntb phase over a wide temperature and concentration range in a binary system. This was achieved by addition of a flexible dopant without LC properties to a flexible dimer exhibiting only a nematic LC phase. The Ntb phase was identified by Polarising Optical Microscopy (POM), Differential Scanning Calorimetry (DSC) and X-ray Diffraction (XRD) techniques.

The separation of fluorinated active pharmaceutical ingredients (APIs) from their desfluoro analogs is a challenging analytical task due to their structural similarity. In this work, fluorine containing APIs and their corresponding desfluorinated impurities were separated on five new 2.7μm superficially porous particles (SPPs) functionalized with bonded chiral selectors. The unique shape selectivity of bonded macrocyclic glycopeptides and oligosaccharides was utilized to separate seven pairs of fluoro/desfluoro APIs resulting in some unprecedented selectivity values. For example, SPP bonded isopropyl cyclofructan 6 yielded a selectivity of 2.73 for voriconazole and desfluoro voriconazole. Further, the SPP based columns allowed for rapid separations ranging from 9 to 55s with very high efficiencies ranging from 45,000 to 70,000plates/m (at high flow rates) in both reversed phase and polar organic modes. Chromatographic separation and detection by HPLC-ESI-MS was demonstrated using ezetimibe and voriconazole and their desfluorinated impurities. Among the tested phases, SPP hydroxypropyl-β-cyclodextrin separated the most fluorinated and desfluorinated analogs with baseline resolution.

A long-sought-after reactive monophosphine-ligated palladium(0) intermediate, Pd(0)L (L = phosphine ligand), was detected for the first time from the activation of the Buchwald precatalyst with base. The detection was enabled using desorption electrospray ionization mass spectrometry (DESI-MS) in combination with online reaction monitoring. The subsequent oxidative addition of Pd(0)L with aryl halide and C-N coupling with amine via reductive elimination was also probed using DESI-MS.

Chromatographic enantioseparations on the order of a few seconds can be achieved by supercritical fluid chromatography using short columns packed with chiral stationary phases. The evolution of 'world record' speeds for the chromatographic separation of enantiomers has steadily dropped from an industry standard of 20-40 min just two decades ago, to a current ability to perform many enantioseparations in well under a minute. Improvements in instrument and column technologies enabled this revolution, but the ability to predict optimal separation time from an initial method development screening assay using the t(min cc) predictor greatly simplifies the development and optimization of high-speed chiral chromatographic separations. In this study, we illustrate how the use of this simple tool in combination with the workhorse technique of supercritical fluid chromatography on customized short chiral columns (1-2 cm length) allows us to achieve ultrafast enantioseparations of pharmaceutically relevant compounds on the 5-20 s scale, bringing the technique of high-throughput enantiopurity analysis out of the specialist realm and into the laboratories of most researchers.

An improved Cu/nitroxyl catalyst system for aerobic alcohol oxidation has been developed for the oxidation of functionalized primary and secondary alcohols to aldehydes and ketones, suitable for implementation in batch and flow processes. This catalyst, which has been demonstrated in a >50 g scale batch reaction, addresses a number of process limitations associated with a previously reported (MeObpy)CuI/ABNO/NMI catalyst system (MeObpy = 4,4′-dimethoxy-2,2′-bipyridine, ABNO = 9-azabicyclo[3.3.1]nonane N-oxyl, NMI = N-methylimidazole). Important catalyst modifications include the replacement of [Cu(MeCN)4]OTf with a lower-cost Cu source, CuI, reduction of the ABNO loading to 0.05–0.3 mol%, and use of NMI as the only ligand/additive (i.e., without a need for MeObpy). Use of a high flash point solvent, N-methylpyrrolidone, enables safe operation in batch reactions with air as the oxidant. For continuous-flow applications compatible with elevated gas pressures, better performance is observed with acetonitrile...

HPLC and HPLC-MS are powerful and wide ranging analytical tools employed in every aspect of modern chemical and biomedical research. The use of these tools is currently restricted to formal laboratory environments, partly due to cost and complexity but also owing to the special handling requirements for the solvents consumed and waste generated by these instruments. Ongoing innovations targeting the decrease in cost, size, and complexity of HPLC and HPLC-MS instrumentation raise the intriguing possibility that such tools may soon become both mobile and widespread in usage, breaking free of traditional laboratory boundaries. However, the dependence of these techniques on regulated organic solvents currently limits such mobility. In this study, we investigate the use of distilled alcohol spirits (cachaca, rum, vodka, aguardiente, etc.) as well as other household items typically available in a supermarket (vinegar, ammonia) as mobile phases and additives for carrying out HPLC and HPLC-MS experiments, showing...

In recent years, chiral supercritical fluid chromatography (SFC) has emerged as the preferred technique for analytical, semi-preparative and preparative separation of enantiomers in the pharmaceutical industry, due to advantages in speed, high column efficiency and significantly lower mobile-phase consumption than conventional liquid chromatography (LC) techniques. We illustrate the benefits of SFC using chiral stationary phases (CSPs) in method development for separating multicomponent mixtures of closely-related achiral analytes, including hydroxylation isomers, halogen-containing molecules, drug metabolites and analogs, methylation and demethylation species, constitutional isomers, and diastereomers. We present several case studies to illustrate the advantage of using SFC with CSPs for achiral separations, where conventional achiral LC and achiral SFC methods fail or deliver sub-optimal chromatographic performance.

Recent interest in bimesogenic liquid crystals showing two nematic phases has led us to investigate the nematic mean-field interactions in these nematic phases by using rigid solutes as probes. The nematic potential that is modelled by two independent Maier-Saupe terms is successful in fitting the observed dipolar couplings (order parameters) of para-, meta- and ortho-dichlorobenzene solutes in both the nematic phases of 39 wt% of 4-n-pentyl-4′-cyanobiphenyl (5CB) in α,ω-bis(4-4′-cyanobiphenyl)nonane (CB_C9_CB) to better than the 5% level. The derived liquid-crystal potential parameters G1 and G2 for each solute in the N and Ntb phases will be discussed. The most interesting observation is that G1 (associated with size and shape interactions) is almost constant in the Ntb phase, whereas G2 (associated with longer-range electrostatic interactions) has large variation, even changing sign.

Evaluation of a several fluorine-containing stationary phases for the chromatographic separation of fluorine-containing pharmaceuticals from their corresponding desfluoro analogs revealed a number of perfluoroaryl and perfluoroalky stationary phases that afford good separations. These fluorous stationary phases exhibit greater retention for the fluorine-containing compounds relative to the H-containing analogs, consistent with a fluorophilic retention mechanism. While both perfluoroalkyl and perfluoroaryl stationary phases afford adequate resolution, the perfluoroaryl columns generally exhibit superior separation factor (α) and peak efficiency (N), resulting in faster baseline separations, with the Hypersil Gold PFP and Poroshell 120 PFP columns providing the best overall performance for the test group studied.

Dimeric compounds forming twist-bend nematic, Ntb, phase show unusual optical textures related to the formation of arrays of focal conic defects (FCDs). Some of the focal conics exhibit submicron internal structure with 8 nm periodicity, which is very close to that found in the crystalline phase of the material, that might suggest surface freezing.

Breaking through the milligram floor When chemists synthesize compounds, the threshold for success is at least a milligram of product. This has been true for decades—even though biochemical assays have long since descended into microgram territory—and results in part from the constraints of characterization methods. Buitrago Santanilla et al. present an automated dosing and characterization protocol for optimizing chemical reaction conditions on the microgram scale. This allowed them to screen numerous base and ligand combinations for catalytic C-N bond-forming reactions between complex pairs of compounds, in short supply, that resisted standard coupling conditions. Science , this issue p. 49

Directed Evolution is a key technology driving the utility of biocatalysis in pharmaceutical synthesis. Conventional approaches to Directed Evolution are conducted using bacterial cells expressing enzymes in microplates, with catalyzed reactions measured by HPLC, high-performance liquid chromatography-mass spectrometry (HPLC-MS), or optical detectors, which require either long cycle times or tailor-made substrates. To better fit modern, fast-paced process chemistry development where solutions are rapidly needed for new substrates, droplet microfluidics interfaced with electrospray ionization (ESI)-MS provides a label-free high-throughput screening platform. To apply this method to industrial enzyme screening and to explore potential approaches that may further improve the overall throughput, we optimized the existing droplet–MS methods. Carryover between droplets, traditionally a significant issue, was reduced to undetectable level by replacing the stainless steel ESI needle with a Teflon needle within a capillary electrophoresis (CE)–MS source. Throughput was improved to 3 Hz with a wide range of droplet sizes (10–50 nL) by tuning the sheath flow within the CE–MS source. The optimized method was demonstrated by screening reactions using two different transaminase libraries. Good correlations (r2 ∼ 0.95) were found between the droplet–MS and LC–MS methods, with 100% match on hit variants. We further explored the capability of the system by performing in vitro transcription–translation inside the droplets and directly analyzing the intact reaction mixture droplets by MS. The synthesized protein attained comparable activity to the protein standard, and the complex samples appeared well tolerated by the MS. The success of the above applications indicates that the MS analysis of the microfluidic droplets is an available option for considerably accelerating the screening of enzyme evolution libraries.

Photo-polymerization of a reactive mesogen mixed with a mesogenic dimer, shown to exhibit the twist-bend nematic phase ($N_{TB}$), reveals the complex structure of the self-deformation patterns observed in planar cells. The polymerized reactive mesogen retains the structure formed by liquid crystalline molecules in the twist bend phase, thus enabling observation by Scanning Electron Microscope (SEM). Hierarchical ordering scales from tens of nanometers to micrometers are imaged in detail. Submicron features, anticipated from earlier X-ray experiments, are visualized directly. In the self-deformation stripes formed in the $N_{TB}$ phase, the average director field is found tilted in the cell plane by an angle of up to 45$^{\circ}$ from the cell rubbing direction. This tilting explains the sign inversion being observed in the electro-optical studies.

The use of a coulometric array detector in tandem with HPLC-UV was evaluated for the absolute quantitation of pharmaceutical compounds without standards, an important capability gap in contemporary pharmaceutical research and development. The high-efficiency LC flow-through electrochemical detector system allows for the rapid evaluation of up to 16 different potentials, aiding in the identification and quantitation of electrochemically reactive species. By quantifying the number of electrons added or removed from an analyte during its passage through the detector, the number of moles of the analyte can be established. Herein we demonstrate that molecules containing common electroactive functional groups (e.g. anilines, phenols, parabens and tertiary alkyl amines) can in some cases be reliably quantified in HPLC-EC-UV without the need for authentic standards. Furthermore, the multichannel nature of the CoulArray detector makes it well suited for optimizing the conditions for electrochemical reaction, allowing the impact of changes in potential, flow rate, temperature and pH to be conveniently studied. The electrochemical oxidation of albacivir, zomepirac, diclofenac, rosiglitazone and several other marketed drugs resulted in large linear ranges, predictable recoveries and excellent quantitation using the total moles of electrons and back-calculating using Faraday's law. Importantly, we observed several instances where subtle structural changes within a given class of molecules (e.g. aromatic ring isomers) led to unanticipated changes in electrochemical behavior. Consequently, some care should be taken when applying the technique to the routine quantitation of compound libraries where standards are not available.

Small interfering RNA (siRNA) therapeutics have received significant interest in recent years owing to their ability to elicit sequence-specific gene knockdown and subsequent suppression of protein expression. Chemical modifications can improve the hydrolytic stability and susceptibility of siRNAs to enzymatic degradation. One commonly used modification to improve hydrolytic stability, the replacement of the native phosphodiester linkage with a phosphorothioate moiety, introduces an additional phosphorous stereocenter into the molecule, resulting in the formation of diastereomers. The chromatographic separation of stereoisomeric siRNAs containing such phosphothioates is a challenging problem, especially when multiple phosphothioates are present within a modified siRNA duplex giving rise to multiple stereoisomers. In this study, we report an investigation into the use of an ion-pairing reversed phase UHPLC (or IP-RP UHPLC) method for the baseline separation of closely related diastereomers of an Apo-B gene targeting siRNA duplex under denaturing conditions. The related siRNA species consist of two diastereomers from the sense strand and the two pairs of diastereomers from the antisense strand. Key chromatographic parameters critical to stereoisomer separation are highlighted, including the structure of the ion-pairing agent, chemical composition of the stationary phase, and organic modifier. The method was applied to the separation of an siRNA stressed with iodine and demonstrated satisfactory selectivity for the parent siRNA and the desulfurization product.

Synthetic oligonucleotides have become increasingly important molecules as a part of new developments in the use of aptamers, antisense, and small interfering ribonucleic acid (siRNA) for the treatment of different human diseases. The development of chromatographic separation methods for the quantitative and sensitive analysis of oligonucleotides is a critical part for the advancement of this research area. A typical therapeutic oligonucleotide sample is a short ribonucleic acid (RNA) molecule with about 19–21 nucleotide length (~ 7–8 kDa), or a 21-mer base pair length in double-stranded siRNA (~ 16 kDa). Due to their relatively large sizes and multiple negative charges compared with typical, small molecule pharmaceutical compounds, oligonucleotides can be difficult to analyze with conventional reversed-phase liquid chromatography (RPLC) methods. In this chapter, we provide an overview of liquid chromatographic (LC) separation of oligonucleotides, including anion-exchange, ion-pair reversed-phase, and mixed-mode LC.

Fast chiral supercritical fluid chromatography (SFC) separations have become important due to the increasing use of high-throughput experimentation (HTE) in organic synthesis. These HTE experiments can generate hundreds of samples for chiral analysis that need to be assayed in a short time. In general, chiral SFC can provide much faster analysis times compared to liquid chromatography (LC). Additionally, columns packed with smaller particles can provide faster and more efficient separations. In this study, the effect of the particle size on the speed and resolution of chiral separations by SFC was evaluated. The performance of Chiralcel OD columns packed with either 5 or 3 μm particles were compared using van Deemter or other kinetic plots. The benefits of using smaller particle columns for chiral SFC analysis are illustrated.

Several offline and online 2D HPLC methods were investigated for the reversed phase resolution of a complex mixture of closely related warfarin and hydroxywarfarin isomers. By combining reversed phase achiral/chiral HPLC separation with UV-triggered fraction collection and subsequent chiral/achiral reversed phase HPLC analysis of collected fractions, complete resolution of all 12 components of the mixture was possible. In addition, a faster method was developed from online 2D HPLC analysis where multicomponent fractions from the first dimension are simultaneously chromatographed in the second dimension.

The term t(min cc) provides a ready estimate of the shortest time that can be obtained by "column cutting" for baseline resolution of two components showing excess chromatographic resolution. While actual column cutting is impractical, the t(min cc) value is shown to be closely related to the minimum separation time obtainable by adjusting other parameters such as flow rate, mobile phase composition, and temperature, affording scientists interested in the development of fast chromatographic separations a convenient tool for estimating the minimum separation time that can be obtained by modifying a given method development screening result. Furthermore, the relationship between t(min cc) and the minimum separation time obtainable by adjusting other parameters is shown to be dependent on the speed of the screening method, with aggressive screening gradients affording t(min cc) estimates that match the actual minimum separation time, and "lazy" screening gradients affording t(min cc) values that overestimate minimum separation time. Consequently, the analysis of the relationship between t(min cc) and actual minimum separation time may be a useful tool for determining the "fitness" of method development screening methods.

A new core–shell particle column showed excellent performance and durability for separation of short (∼21-mer) ribonucleic acid (RNA) oligonucleotides by ion-pair reversed-phase liquid chromatography (IP-RPLC). Previously investigated core–shell C18 columns showed excellent peak shapes and separations of closely eluting impurities by IP-RPLC. However, these columns showed only modest long-term stability at the neutral pH and elevated column temperatures of ≥60 °C, typically used for IP-RPLC analysis of oligonucleotides. The newly introduced SunShell C18 column provided separations comparable to the previously evaluated core–shell columns, but with significantly improved long-term column stability when operated at neutral pH and elevated column temperature.

Process analytical technologies (PATs) have played an important role in process development and optimization throughout the pharmaceutical industry. Recent new PATs, including in-process video microscopy (PVM), a new generation of focused-beam reflectance measurement (FBRM), miniature process IR spectroscopy, and a flow IR sensor, have been evaluated, demonstrated, and utilized in the process development of many drug substances. First, PVM has filled a technical gap by providing the capability to study morphology for particle engineering by visualizing particles in real time without compromising the integrity of sample. Second, the new FBRM G series has closed gaps associated with the old S series with respect to probe fouling, bearing reliability, data analysis, and software integration. Third, a miniaturized process IR analyzer has brought forth the benefits of increased robustness, enhanced performance, improved usability, and ease of use, especially at scale-up. Finally, a miniaturized flow IR sensor ...

The construction of liquid crystal compositions consisting of the dimeric liquid crystal, CB_C9_CB (cyanobiphenyl dimer = 1'',9''-bis(4-cyanobiphenyl-4'-yl)nonane), and the range of nematic systems is explored. The materials include a laterally functionalized monomer, which was used to construct a phase diagram with CB_C9_CB, as well as one laterally linked dimer liquid crystal material and two liquid crystal gold nanoparticle (LC-Au-NPs) systems. For the Au-NP-LCs, the NP diameters were varied between ~3.3 nm and 10 nm. Stable mixtures that exhibit a nematic-nematic phase transition are reported and were investigated by POM (polarizing optical microscopy), DSC (differential scanning calorimetry) and X-ray diffraction studies.

In this study, we investigate the separation of a variety of mixtures of drugs, metabolites, and related analogs including representatives of the carbamazepine, methylated xanthine, steroid hormone, nicotine, and morphine families using several automated chromatographic method development screening systems including ultra high performance liquid chromatography, core-shell HPLC, achiral supercritical fluid chromatography (SFC), and chiral SFC. Of the 138 column and mobile phase combinations examined for each mixture, a few chromatographic conditions afford the best overall performance, with a single achiral SFC method (4.6 × 250 mm, 3.0 μm GreenSep Ethyl Pyridine, 25 mM isobutylamine in methanol/CO2) affording good separation for all samples. Four of these mixtures were also resolved by achiral SFC on the Luna HILIC and chiral SFC Chiralpak IB columns using methanol or ethanol with 25 mM isobutylamine as polar modifiers. Modifications of standard chromatography screening conditions afforded fast separation methods (from 1 to 5 min) for baseline resolution of all components of each of these challenging sets of closely related compounds.

The presence of dehalogenated impurities is often observed in halogen-containing pharmaceuticals, and can present a difficult analytical challenge, as the chromatographic behavior of the halogenated drug and the hydrogen-containing analog can be quite similar. In this study we describe the chromatographic separation and unambiguous identification of dehalogenation impurities or associated isomers in organohalogenated pharmaceuticals using UHPLC with a pentafluorophenyl column coupled with diode-array and high resolution electrospray ionization mass spectrometry detection (UHPLC-DAD-HRESIMS).

As the pharmaceutical industry continues to explore new ways to stimulate innovation, reduce costs, and streamline operations, the idea of joining forces in cross-pharma collaborations on the development of new and valuable precompetitive technologies becomes increasingly attractive. Before industry-wide precompetitive collaboration can become truly commonplace and more effective, improved approaches for creating and maintaining collaborations between competitors are needed. A recent Council for Chemical Research workshop at the University of Pennsylvania on precompetitive collaborations on enabling chemical and chemical engineering technologies for the pharmaceutical industry revealed widespread interest among participants from industry, academia and government to augment and improve current methods. While it is important not to underestimate the challenges of multiparty collaborations, the value coming from pooling resources and combining intellectual input provides strong incentive to improve and foste...

An evaluation of the use of non-conventional polar modifiers for the supercritical fluid chromatographic separation of enantiomers on immobilized chiral stationary phases is presented. The resolution of a group of nine commercially available racemates is studied on the Chiralpak IA, IB, IC, ID, IE, and IF chiral stationary phases using CO2-based eluents containing non-conventional polar modifiers such as dichloromethane, chloroform, tetrahydrofuran, 2-methyl tetrahydrofuran, methyl tert-butyl ether, cyclopentyl methyl ether, acetone, ethyl acetate, toluene, 2,2,2-trifluoroethanol, and N,N-dimethylformamide. Screening experiments and method development for the commercial racemates on the immobilized columns with the non-conventional solvents demonstrated an ability to adjust the retention and improve resolution. From these results we were able to assign a general eluotropic relationship between the non-conventional solvents and methanol. A general ability to selectively adjust chromatographic retention while improving analyte solubility can lead to improved preparative chromatographic performance.

The advantages of MISER LC-MS (high throughput, simple readout of results) are demonstrated in the analysis of E-capsaicin in chili peppers and hot sauces. The ready availability of samples with a wide range of capsaicin content and the fast and easy detection using the MISER (Multiple Injections in a Single Experimental Run) technique makes this a potentially useful experiment to introduce novices to the important analytical technique of LC-MS. In this study we describe a simple and rapid chromatographic method for evaluation of E-capsaicin in chili peppers using HPLC with 80% organic eluent in a Poroshell SB-C18 column coupled with electrospray ionization mass spectrometry detection and MISER analysis. The misergrams obtained from continuous sample injections every 0.73 min allow the convenient simultaneous visualization of the outcomes of multiple experiments represented as single chromatograms. A considerable variation in E-capsaicin levels is clearly visualized among different types of peppers and sauces, with the ghost pepper (Bhut Jolokia) showing the highest E-capsaicin concentration of the peppers sampled.

Imine-bond formation between a chiral amine analyte and 3-hydroxypyridine-2-carboxaldehyde (HCA) was used to create a fast and robust method for enantiopurity analysis. This approach showed good universality, and was applied to a variety of different classes of chiral amines. The sign of the measured CD signal was enantiospecific across the range of amines tested, allowing some confidence in absolute configuration determination. This technique was transitioned to an HPLC-CD detector to allow for rapid and automated sample introduction, while maintaining the level of accuracy noted for the standalone CD spectrophotometer. Finally, the enantiomeric purity of a series of crude reaction mixtures of synthetic amines produced by biocatalytic transamination was accurately determined using this approach.

Wide band dielectric spectroscopy of bent-shaped achiral liquid-crystal dimers 1″-n″-bis(4-cyanobiphenyl-4′-yl) n-alkanes (CBnCB n = 7, 9, 11) has been investigated in a frequency range 0.1 Hz–100 MHz using planar-aligned cells of sample thicknesses ranging from 2 to 10 (μm) over a temperature range that covers both nematic and twist bend nematic phases. Two peaks in the dielectric spectrum in the higher frequency range are assigned to the molecular relaxation processes. The peak at the highest frequency, ∼40 to 80 MHz, is assigned to an internal precessional rotation of a single unit of the dimer around the director. The mode in the next lower frequency range of 2–10 MHz is assigned to the spinning rotation of the dimer around its long axis. This involves fluctuations of the dipole moment of the bent-shaped conformation that is directed along its arrow direction of the bow shape formed by the dimer. The peak in the frequency range 100 kHz–1 MHz can be assigned to the collective fluctuations of the local director with reference to the helical axis of the NTB structure. The dependence of its frequency on temperature is reminiscent of the soft mode observed at the SmA* to SmC* phase transition. This result clearly corresponds to the electro-clinic effect—the response of the director to the applied electric field in an electro-optic experiment. The lowest frequency mode, observed in the frequency range of 0.1 Hz–100 Hz, is identified with the Goldstone mode. This mode is concerned with the long range azimuthal angle fluctuations of the local director. This leads to an alternating compression and expansion of the periodic structure of the NTB phase.

We present here the first time-resolved tilt-angle and retardance measurements for large-tilt (>45°) flexoelectro-optic liquid crystal modulators. These devices have potential for next generation fast switching (>1 kHz), 0-2π analog phase spatial light modulators (SLMs), with applications in optical beamsteering, microscopy and micromachining. The chiral nematic device used consisted of a mixture of CBC7CB and the chiral dopant R5011 in a nominally 5 µm-thick cell, aligned in the uniform lying helix mode. As the device is dynamically switched over angles of ± 54°, retardance changes of up to 0.17λ are observed. Furthermore, the time-resolved measurements reveal an asymmetry in the tilt in the optic-axis depending on the polarity of the applied electric field. The change in the optic-axis exhibits a pattern dependence, whereby it is determined by both the pulse history and the applied field. This pattern dependence results in tilt-angle errors of up to 8.8°, which could manifest as phase errors as large as 35.2° in potential SLMs. These time domain measurements may allow correction of these deterministic errors, to realize practical devices.

Benzophenone is a popular photophore for photoaffinity-labeling. It is also an important framework for drug development; many drugs contain benzophenone or analogous frameworks. The current work reports that benzophenone and its analogs bind to human glyoxalase 1. The binding, however, has little effect on the catalytic activity of this enzyme. The implications of the finding in terms of both drug development and photoaffinity-labeling are discussed.

The absolute configuration of several hydroxywarfarin isomers was assigned using a comparison of elution order on chiral stationary phases, optical rotation, and circular dichroism (CD) spectra, with confirmation of assignments made by comparison between experimental and calculated CD spectra and selective synthesis of hydroxywarfarin isomers from enantiopure warfarin using human liver microsomes. Chirality 26:95–101, 2014. © 2013 Wiley Periodicals, Inc.

In this study we describe the evaluation of a recently developed miniaturized single-quadrupole mass spectrometer to support pharmaceutical process research investigations. Mass spectrometry is becoming an indispensable tool for analytical support of synthetic chemistry; however, current mass spectrometers are too expensive and too large for widespread deployment. In addition, current instruments often have features and capabilities that, while useful for trace component or bioanalysis applications, are beyond the comparatively simple requirements of synthetic chemists, where samples are often abundant and unit mass resolution is generally sufficient. An evaluation of the Microsaic 3500 MiD shows this small and inexpensive mass spectrometer to be well-suited for providing reliable support for certain pharmaceutical process research investigations.

An investigation into the use of core–shell particle columns for separation of short (∼21 base pairs) RNA oligonucleotides by ion-pair reversed-phase liquid chromatography (IP-RPLC) showed improved resolution for a number of test analytes relative to conventional (fully-porous) reversed-phase columns. The best resolutions were obtained using columns packed with smaller sub-2 μm core–shell particles.

Rapid palladium (Pd) catalyzed deallylation of an uncoloured reagent within a flowing stream affords a dose dependent colour formation that can be used for convenient online analysis of trace levels of Pd contamination using a modified HPLC instrument. An application to the online sensing of Pd breakthrough from a flow through Pd adsorption cartridge is described. An alternative configuration of the instrumentation allows the rapid (

Recent developments in fast chromatographic enantioseparations now make high throughput analysis of enantiopurity on the order of a few seconds achievable. Nevertheless, routine chromatographic determinations of enantiopurity to support stereochemical investigations in pharmaceutical research and development, synthetic chemistry and bioanalysis are still typically performed on the 5–20 min timescale, with many practitioners believing that sub-minute enantioseparations are not representative of the molecules encountered in day to day research. In this study we develop ultrafast chromatographic enantioseparations for a variety of pharmaceutically-related drugs and intermediates, showing that sub-minute resolutions are now possible in the vast majority of cases by both supercritical fluid chromatography (SFC) and reversed phase liquid chromatography (RP-LC). Examples are provided illustrating how such methods can be routinely developed and used for ultrafast high throughput analysis to support enantioselective synthesis investigations.

Pressure is not typically controlled or adjusted independently of flow rate during method development in reversed-phase LC (RPLC). However, it has been shown that pressure has an effect on analyte molecular molar volume, and the magnitude of this effect is greater for proteins and ionizable compounds than neutral small molecules. This phenomenon has received attention recently in the context of porous sub-2-micron particle packed columns. The present study surveys the effect of pressure and frictional heating on RPLC separations using commercially-available monolithic columns at constant flow rate and with controlled external temperature. Because the current monoliths cannot be operated at high pressures, all experiments were conducted with pressures at or below 200 bar. Nonetheless, substantial changes in retention were still observed; for example, an increase in pressure of 75 bar shifted the retention factor for bovine insulin from 1.27 to 1.78, a 40% increase, while a similar experiment with the neutral small molecule, toluene, showed no change in retention. Results are presented from investigations of model peptides and proteins ranging in size from 1 kDa to 30 kDa, as well as experiments performed with a silica-based C18 monolith and a polystyrene divinylbenzene monolith functionalized with a phenyl stationary phase. This work indicates that protein separations in monoliths are highly pressure sensitive, and pressure should therefore be considered as an additional parameter in method development for optimizing retention and selectivity. Given these findings, and the ever-increasing importance of chromatographic separations of proteins in both industrial and academic laboratories, improved instrumentation and mechanisms for directly controlling system backpressure could be of great practical value.