Basic pH Conditions Research Articles

Self-Cleaning Bending Sensors Based on Semitransparent ZnO Nanostructured Films.

The design of multifunctional nanostructured materials is the key to the development of smart wearable devices. For instance, nanostructures endowed with both piezoelectric and photocatalytic activities could well be the workhorse for solar-light-driven self-cleaning wearable sensors. In this work, a simple strategy for the assembly of a flexible, semitransparent piezophotocatalytic system is demonstrated by leveraging rational wet chemistry synthesis of ZnO-based nanosheets/nanoflowers (NSs/NFs) under basic pH conditions onto flexible ITO/PET supports. A KMnO4 pretreatment before the ZnO synthesis (seeded ZnO) allows for the control of the density, size, and orientation of the NSs/NFs systems compared to the systems produced in the absence of seeding (seedless ZnO). The electrical response of the sensors is extracted at a 1 V bias as a function of bending in the interval between 0 and 90°, being the responsivity toward bending significantly enhanced by the KMnO4 treatment effect. The photocatalytic activity of the sensors is analyzed in aqueous solution (methylene blue, 25 μM) by a solar simulator, resulting in similar values between seedless and seeded ZnO. Upon bending the sensor, the photocatalytic activity of seedless ZnO is almost unaffected, whereas that of seeded ZnO is improved by about 25%. The sensor's reusability and repeatability are tested in up to three different cycles. These results open up the way toward the seamless integration of bending sensitivity and photocatalysis into a single device.

Selective lithium separation from desalination concentrates via the synergy of extractant mixtures

Seawater reverse osmosis (SWRO) desalination plants generate high volumes of concentrates, which contain, in addition to major salts, some elements of growing interest in minor concentrations. This is the case of lithium, highly demanded in the battery industry. In this work, the separation of Li+ from model SWRO brines has been evaluated by obtaining Li+ extraction curves with the combination of extractants DBM•TOPO and FDOD•TOPO, proving that both mixtures are capable of extracting Li+ under basic pH conditions, due to the keto-enolic tautomerism of the β-diketones. Li+ extraction values of 95.4 % for DBM•TOPO (pH = 12.2) and 100 % for FDOD•TOPO (pH = 9.0) were achieved. This behaviour was verified by the FT-IR analysis of the sample before and after the Li+ extraction. Finally, the selective separation of Li+ against other cations, such as Na+, K+, Mg2+, Ca2+ and Sr2+, present in the model brines at higher concentrations, was determined. Under mentioned experimental conditions, these cations are not extracted, reaching to Li+ selective separation close to 100 %. This study shows the first results on the selective extraction of lithium in complex SWRO brines, fostered through promising extractants mixtures showing a synergic effect towards Li+ in such multicomponent matrices.

The sponge effect of phosphogypsum-based cemented paste backfill in the atmospheric carbon capture: Roles of fluorides, phosphates, and alkalinity

The use of cement for solid waste solidification/stabilization is one of the most practised methods but is under scrutiny due to its substantial emission of greenhouse gases. However, the dual role of cement-immobilized solid waste may serve as a CO2sink and promisingly reabsorb a great content of atmospheric CO2, which is hitherto unexplored. In this study, we detail the inherent potential sponge effect of phosphogypsum (PG) based cemented paste backfill (PCPB), finding that, at a high PG utilization rate, the PCPB application may produce 16.7 Mt/year of CO2 in China, whereas a reduction of 5.76 Mt/year could promisingly reach up when considering the future reabsorption. However, industrial applications are limited by the remained impurities and the maintenance of alkalinity. The results suggest that the phosphate impurities within PG have an adverse effect on CO2 uptake, which inhibits the precipitation of hydration products and inversely favors the formation of calcium-phosphate species that retard the dissolution of cement particles. By contrast, the fluorides imply an acceleration of the hydration reactions and accordingly hasten the carbonation process. Furthermore, geochemical modeling suggests that maintaining a basic pH condition of the system is another significant factor in promoting the CO2 capture capacity, of which a 35% increase in CO2 uptake can be acquired with a continuous low concentration NaOH supply, but this enhancement will require the widespread deployment of future validation. From the perspectives of CO2 balance, environmental requirements, and technological feasibility, PCPB is an effective way for in situ immobilizing PG with scalable potential. These new observations are expected to provide a deeper understanding and reliable guidance for the sustainable management of dumped PG and the zero emissions of the phosphorus fertilizer industry.

Evaluation of Crosslinking Degree on the Characteristics and Performance of Membranes Formulated from Quaternized Chitosan

Chitosan is a polymer produced from chitin that is insoluble in neutral or basic pH conditions. Although chitosan has good biodegradability, non-toxicity, and biocompatibility properties, it has limited applications due to its low solubility in neutral or slightly alkaline conditions. Quaternization came out as a way of altering this natural polymer to enhance its solubility over a wide pH range and boost permanent positive charges. In this study, the quaternized chitosan (QCs) was prepared by using 3-chloro-2-hydroxypropyltrimethyl ammonium chloride (CHTAC) as the quaternizing agent, which was then formulated into the integral membrane with a blend of polyvinyl alcohol (PVA), polysulfone (PSF), and tetraethylorthosilicate (TEOS). The membrane characterizations and performance analysis were done in terms of functional groups, surface charge, surface morphology, pure water flux analysis, and antifouling analysis. The results revealed that the incorporation of TEOS produced a dense membrane structure but did not help much in enhancing the hydrophilicity and the positive charge of membranes. Membrane from the polymer blend without TEOS was found to have better hydrophilicity, and antifouling characteristics in terms of relative flux recovery (RFR) and relative flux decay (RFD) and possessed a slightly negative charge. The dense structure of the membrane due to crosslinking process might result in a high degree of integral stability, with the additional benefit of providing more adsorption area for a potential application in the heavy metal ion removal process

PAMAM-G4 protect the N-(2-hydroxyphenyl)-2-propylpentanamide (HO-AAVPA) and maintain its antiproliferative effects on MCF-7

Our work group designed and synthesized a promissory compound N-(2-hydroxyphenyl)-2-propylpentanamide (HO-AAVPA). The HO-AAVPA is a HDAC1 inhibitor and antiproliferative in cancer cell lines. However, HO-AAVPA is poor water solubility and enzymatically metabolized. In this work, the fourth-generation poly(amidoamine) dendrimer (PAMAM-G4) was used as a drug deliver carrier of HO-AAVPA. Moreover, HO-AAVPA and HO-AAVPA-PAMAM complex were submitted to forced degradation studies (heat, acid, base, oxidation and sunlight). Also, the HO-AAVPA-PAMAM-G4 complex was assayed as antiproliferative in a breast cancer cell line (MCF-7). The HO-AAVPA-PAMAM-G4 complex was obtained by docking and experimentally using three pH conditions: acid (pH = 3.0), neutral (pH = 7.0) and basic (pH = 9.0) showing that PAMAM-G4 captureand protect the HO-AAVPA from forced degradation, it is due to sunlight yielded a by-product from HO-AAVPA. In addition, the PAMAM-G4 favored the HO-AAVPA water solubility under basic and neutral pH conditions with significant difference (F(2,18) = 259.9, p < 0.001) between the slopes of the three conditions being the basic condition which solubilizes the greatest amount of HO-AAVPA. Finally, the HO-AAVPA-PAMAM-G4 complex showed better antiproliferative effects on MCF-7 (IC50 = 75.3 μM) than HO-AAVPA (IC50 = 192 μM). These results evidence that PAMAM-G4 complex improve the biological effects of HO-AAVPA.

Rapid LC-MS/MS quantification of Organophosphate non-specific metabolites in hair using alkaline extraction approach

Assessing human exposure to commonly used, highly toxic, but non-persistent organophosphates (OPs) is challenging because these toxicants are readily biotransformed into dialkyl phosphates (DAPs) and other metabolites. Growing hair accumulates toxicants and their metabolites, which makes hair a valuable non-invasively sampled matrix that can be used to retrospectively examine chemical exposure. However, the efficient quantification of hydrophilic DAP compounds in hair is challenging due to complex hair matrix effects. To improve upon existing methods, we first examined the acid dissociation constants (pKa) of DAPs and amino acids (major components in hair) and identified the best pH conditions for minimizing matrix effects. We hypothesized that under basic pH conditions DAPs and amino acids would be negatively charged and have weak interactions favorable to DAP dissociation from the matrix. To test this, we compared the efficiency of various pH conditions of suitable solvents to extract six DAPs from hair samples, and we quantified these DAPs using liquid chromatography-tandem mass spectroscopy (LC-MS/MS). As expected, a basic extraction (methanol with 2% NH4OH) approach had the highest extraction efficiency and yielded satisfactory recoveries for all six DAPs (72%-152%) without matrix effects. Additionally, the alkaline extract can be directly injected into the LC-MS/MS. This relatively rapid and simple procedure allowed us to process up to 90 samples per week with reproducible results. To our knowledge, this is the first method to quantify all six DAPs simultaneously in hair using LC-MS/MS with electrospray ionization (ESI) in negative ion mode. Finally, we demonstrated the feasibility of measuring DAP levels in hair samples from patients affected with amyotrophic lateral sclerosis (ALS), a neurodegenerative disease potentially linked to OP exposure. Due to our optimized solvent extraction process, the method we have developed is compatible with the rapidity and sensitivity needed for hair analysis applied to population biomonitoring.

The effect of kosmotropic salts on aggregate removal from monoclonal antibodies in mixed-mode anion exchange chromatography

Efficacious and safe application of recombinant proteins in humans as drugs depends on their high purity accomplished by downstream processing. The present study evaluates the effects of kosmotropic salts used in the flow-through mode of mixed-mode anion exchange (MMAEX) chromatography to remove high molecular weight (HMW) impurities efficiently from monoclonal antibody (mAb) products. For this purpose, the impact of different kosmotropic salts at varying concentrations along with changes of the pH were systematically assessed by high throughput screens on a set of mAbs differing in their relative hydrophobicity. In contrast to the more hydrophobic mAbs, for the more hydrophilic mAbs, a clear and consistent removal of HMW species to values > 80% (achieving up to 2.5-fold improvement) occurred with the addition of increasing amounts of a kosmotropic salt (sodium chloride, sodium sulfate, ammonium sulfate, potassium chloride and potassium sulfate) to the loads applied to MMAEX chromatography. Overall, the herein described effect on the removal of HMW species by MMAEX resins was specific for kosmotropic salts, independent of conductivity, and facilitated by slightly basic pH conditions. These findings were confirmed at lab-scale operation achieving > 99% purity, indicating the potential to implement MMAEX in combination with kosmotropic salts as a polishing step for hydrophilic mAbs.

Comprehensive Characterization of an "Off/On" Rhodol-Based Lysosomal Tracker for Orthogonal Cellular Analysis by Confocal Imaging.

Two florescent xanthene-cyanamide lysosomal trackers emitting strongly at ∼525 nm were prepared from fluorescein and rhodol methyl esters in microwave-assisted reactions. Both forms named "off" (nonfluorescent lactam) and "on" (strongly fluorescent ring-opened amide) have been comprehensively characterized out by using a combination of NMR spectroscopy, X-ray analysis, fluorimetry and confocal microscopy. Known rhodamines bearing electron-withdrawing groups (EWGs) exhibit an equilibrium between non-fluorescent (off) and fluorescent (on) depending on the dielectric constant of the medium. Here, cyanamide was introduced as EWG amine into the fluorescein and rhodol framework. Unlike rhodamine-type dyes, the ring-opened forms of fluorescein- and rhodol-cyanamides are stable in protic solvents under circumneutral and basic pH conditions. The osteoblastic cell line MC3T3-E1 from C57BL/6 mouse calvaria was used for confocal imaging where the different organelles and nuclei were distinguished by using an orthogonal combination of fluorescent dyes.

Novel Crosslinked HA Hydrogel Films for the Immediate Release of Active Ingredients

Novel crosslinked hyaluronic acid (HA) hydrogel films were previously invented by reacting the HA polymer with the PT (Pentaerythritol Tetra-acrylate) crosslinker over basic pH conditions in the oven. HA is considered a natural polymer present in cosmetic as well as pharmaceutical formulations. This current study aimed to highlight the effect of loading method (post-loading and in situ) of selected actives (salicylic acid and niacinamide B3) in the hydrogel films and then study their release kinetics. Differential scanning colometry (DSC) and Fourier transform infrared spectroscopy (FTIR) analysis evidenced the loading of the actives and full release from the HA hydrogel films, while the scanning electron microscopy (SEM) demonstrated the morphological changes to the films during the study by comparing the average molecular weight between crosslinks (M¯c), gel fraction, crosslinking density (Ve) and mesh size (ξ) of the films. The loading percentage of the SA and B3 showed high percentage loading of actives via both loading methods. In conclusion, the (95–100%) release of the actives achieved from the HA hydrogel films within 10 min revealed that the films are an efficient immediate release system of actives.

Development of Silymarin Entrapped Chitosan Phthalate Nanoparticles for Targeting Colon Cancer

The present paper deals with the development of silymarin entrapped Chitosan Phthalate (CP) nanoparticles for targeting colon cancer. The QbD approach is applied to optimize the silymarin loaded chitosan phthalate nanoparticles. DOE was employed to evaluate the dependent variables from the responses of CP nanoparticles. The CP NPs were found to be 140% of mucoadhesivity at pH 7.4, superior to pH 1.2 (10%). The result revealed the chemical or ionic bond formation between the positively charged amino groups of chitosan phthalate and the negatively charged sialic acid residue of mucin present in the mucous membrane. In vitro drug release profiles were carried out under acidic and basic pH conditions. The release of encapsulated silymarin was found to be poor in acidic conditions and maximum in basic conditions. The results suggested that chitosan phthalate nanoparticles could have the potential to enhance the bioavailability of silymarin.

Effective arsenite adsorption from aqueous solution using N- and S-functionalized tetragonal nano-zirconia on chitosan-derived carbon

Arsenic pollution in water is a recurring problem for countries where groundwater is the only source of survival. Adsorption is considered as a promising treatment method to abate arsenic pollution in water due to its numerous admirable advantages. In this paper, a facile functionalization of N- and S-rich nano-zirconia (ZrO2) is presented in-conjunction with in situ precipitation using l-cysteine (Cys), a non-essential amino acid, and prepared with a semi-carbonized (500 °C) chitosan biopolymer, ChiC, (ZrO2-Cys@ChiC) by a hydrothermally assisted method. The interaction of Cys on ZrO2 and ChiC moieties in ZrO2-Cys@ChiC was investigated for the adsorption of toxic arsenite (AsO33-) from water by batch and column adsorption methods. The structure of the prepared materials before and after adsorption of arsenite was characterized by a series of techniques such as powder XRD, XPS, BET, SEM, EDAX, mapping, CHN analysis. The adsorption of arsenite on the prepared ZrO2-Cys@ChiC hybrid adsorbent was best described by the Langmuir adsorption isotherm and the pseudo-second-order kinetic models. Apart from the isostructural and isoelectronic nature of the phosphate ions in the selectivity assay, arsenite adsorption is not hindered at basic pH conditions. After adsorption, the stability of the material was maintained without any change in the surfaces and crystalline nature, as shown by XPS, SEM, and powdered XRD. The reusability and column test results confirmed the potential use of the ZrO2-Cys@ChiC adsorbent for the effective removal of arsenite from water. Combining the high removal density and selectivity with fast kinetics, the prepared ZrO2-Cys@ChiC hybrid adsorbent has great potential for the removal of arsenite from aqueous solutions.

Degradation of diclofenac under irradiation of UV lamp and solar light using ZnO photo catalyst

Diclofenac sodium (DCF) is a non-steroidal anti-inflammatory drug mainly used as an analgesic, arthritic and anti-rheumatic. This study deals with the degradation of diclofenac by photo catalytic-based advanced oxidation processes. The solar reactor system is comprised of quartz and borosilicate tubes for the absorption of the solar rays and transmission to the pollutant sample. Artificial UV lamp and solar rays have been applied to activate the ZnO catalyst, thereby generating highly oxidizing species. These species initiate the degradation process of the drug, which results in intermediates that finally dissociate into carbon dioxide and water. The degradation rate has been analyzed by composition analysis using high performance liquid chromatography. TOC and COD tests have also been conducted for degraded samples. ZnO catalyst loading was tested from 0.1 gm/L to 1 gm/L and the degradation rate showed a rising trend up to 0.250 gm/L, but further increase in loading resulted in a drop in degradation. Similarly, degradation is higher in acidic condition as compared to neutral or basic pH condition. The results showed a higher degradation rate for UV lamp irradiation as compared to the solar system. Moreover, TOC and COD reduction results were also found to be higher for UV lamp photo catalysis.

Green synthesis, characterization and sorption efficiency of MnO2 nanoparticles and MnO2@waste eggshell nanocomposite

ABSTRACT This study reported the biological synthesis of MnO2 nanoparticles and MnO2@eggshell nanocomposite. Optimum conditions for the biosynthesis of MnO2 NPs were observed for 0.025 M MnCl2 solution with 1.0% (m/v) of plant powder (Ocimum basilicum) content-based extract under basic pH conditions. Afterwards, nanocomposite (NC) was prepared by fabricating manganese-based nanoparticles on waste eggshell powder. Different techniques were applied for characterization of prepared materials. Synthesized NPs and NCs were further utilized for the adsorption studies of crystal violet dye. Studies were conducted to delineate the effect of dye concentration, prepared material dosage, pH, temperature and contact time. In the end, adsorption isotherms and thermodynamic studies were applied to the data. The Langmuir model better fits the data in both the cases and predicted adsorption capacity of 149.254 and 52.6 mg/g for NC and NPs, respectively. The possible mechanism of the dye removal process, nanoparticle and nanocomposite formation has also been discussed.

Preparation of sputter-deposited Cu-doped BiVO4 nanoporous thin films comprised of amorphous/crystalline heterostructure as enhanced visible-light photocatalyst

The synthesis of Cu-doped BiVO4 nanoporous thin films with various Cu contents was performed using reactive magnetron sputtering to prepare a stable and inexpensive photocatalyst with high photoactivity under visible light for wastewater treatment applications. The X-ray diffraction (XRD) analysis showed exclusively the formation of the photoactive monoclinic BiVO4 phase up to 17 at.% Cu. Beyond, a Cu-based compound crystallizes in addition to the BiVO4 monoclinic phase. The field-emission scanning electron microscopy (FESEM) and elemental mappings results revealed the formation of shard-like nodules composed of V, O and Cu in the films having less than 6 at. % Cu. From 6 at. % Cu, the morphology appears more homogeneous. X-ray photoelectron spectroscopy (XPS) showed the presence of Cu2+ and Cu+, as well as the rise of V4+/V5+ ions. Transmission electron microscopy (TEM) verified the amorphous structure of the Cu-O-V phase, as well as demonstrated the crystallographic interplanar spacings of BiVO4. The thin film with a 2 at. % Cu exhibited superior photoactivity (100, 99 and 63 %) over pristine BiVO4 in photocatalytic dye degradation (Rhodamine-B, Methylene Blue and Methyl Orange). The thin films’ stability, recyclability and reusability were demonstrated in the recycling experiment, and the crucial role of photogenerated charge carriers and hydroxyl radicals was identified in the experiment involving scavengers. The photocatalytic performance towards various dye pollutions at acidic, basic and neutral pH conditions is also discussed in detail.

Reversible Discrete-to-Extended Metal-Organic Polyhedra Transformation by Sulfonic Acid Surface Functionalization.

Metal-organic polyhedra (MOPs) are molecular porous units in which desired functionalities can be installed with precise geometrical and compositional control. By combing two complementary chemical moieties, such as sulfonic acid groups and Rh(II)-carboxylate paddlewheel, we synthesized a robust water-soluble cuboctahedral MOP with excellent features in both solution and solid states. Herein, we demonstrate that the superior chemical stability of the Rh2 unit and the elevated number of functional groups on the surface (24 per cage) result in a porous cage with high solubility and stability in water, including acidic, neutral, and basic pH conditions. We also prove that the sulfonic acid-rich form of the cage can be isolated through postsynthetic acid treatment. This transformation involves an improved gas uptake capacity and the capability to reversibly assemble the cages into a three-dimensional (3D) metal-organic framework (MOF) structure. Likewise, this sulfonic acid functionalization provides both MOP and MOF solids with high proton conductivities (>10-3 S cm-1), comparable to previously reported high conducting metal-organic materials. The influence of the MOP-to-MOF processing in the gas adsorption capacity indicates that this structural transformation can provide materials with higher and more controllable porous properties. These results illustrate the high potential of acidic MOPs as more flexible porous building units in terms of processability, structural complexity, and tunability of the properties.

Visible light-driven complete photocatalytic oxidation of organic dye by plasmonic Au-TiO2 nanocatalyst under batch and continuous flow condition

The present work demonstrates a facile hydrothermal synthesis of Plasmonic Au–TiO2 nanocatalyst followed by its successful application for complete photocatalytic dye degradation (oxidation) in batch and continuous flow process under natural sunlight as well as visible and UV light. The Au-TiO2 nanocatalyst was synthesized by a hydrothermal method at basic pH conditions. It was meticulously analyzed by a variety of spectroscopic (UV-Vis, Raman, FTIR, PL, Powder XRD, ED-XRF, XPS), microscopic (FE-SEM with elemental mapping, TEM), and thermal (DSC) techniques. The characterization results showed that monodisperse Plasmonic Au(0) nanoparticles with a mean diameter of 12 ± 1 nm are homogeneously deposited on Anatase TiO2 crystals. The nanocatalyst showed complete photocatalytic degradation of various dye compounds (Eosin Yellowish, Indigo Carmine, Methyl Orange, Methylene Blue, and Rhodamine B) under visible light or sunlight as confirmed through UV-Vis spectra, mass spectral study, and TOC analysis of dye solutions. A continuous flow process using a specially designed photoreactor was accomplished with a long catalyst lifespan, easy processibility, and low cost. Easy synthesis of the catalyst, its very detailed characterization, and its efficient catalytic studies to completely degrade various dye molecules under visible light source in the absence of any added oxidizer (O2, H2O2, KMnO4, Organic peroxides) and the demonstration of continuous flow process are significant highlights of the present work. A plausible mechanistic pathway is also presented in line with the previous literature reports and presently observed phenomenon.

Novel S-scheme 2D/2D Bi4O5Br2 nanoplatelets/g-C3N5 heterojunctions with enhanced photocatalytic activity towards organic pollutants removal

Removal of organic pollutants and pharma products in waste water using semiconductor photocatalysts has gained huge interest among recent days. However, low visible light absorption, recombination rate of charge carriers and less availability of reaction sites are still major obstacles for the photocatalysis process. Herein, an in situ-forming Bi4O5Br2 nanosheets decorated on the surface g-C3N5 were prepared via simple hydrothermal method under ambient temperature. The basic pH condition plays a vital role in growing for Bi4O5Br2 nanosheets. Various characterization studies such as TEM, SEM, PL and UV-DRS studies confirmed the formation of close contact between the Bi4O5Br2 and g-C3N5 nanosheets. The construction of Bi4O5Br2 nanoplatelets/g-C3N5 nanocomposite increases the surface-active sites and improving the separation efficiencies of excitons, which is greatly influenced in the degradation of ciprofloxacin and bisphenol-A pollutants. Meanwhile, the flow of electrons from the layered structured graphite carbon of g-C3N5 which enables excellent electrical contact in the heterojunction. Besides, the main free radicals were determined as e− and •O2−, and production level of free radicals were confirmed by radical trapping experiments. The possible degradation mechanism was proposed and discussed. Finally, this work provides a unique approach to in-situ preparation of heterojunction photocatalysts and demonstrates the prepared Bi4O5Br2 nanoplatelets/g-C3N5 photocatalysts have great potential in the waste water management.

Assessment of dopamine-conjugated decellularized bovine tendon extracellular matrix as a bioadhesive

In this study, a bioadhesive based on catechol and extracellular matrix was developed and characterized in detail. At first, cells were removed from bovine tendon tissue to obtain tendon extracellular matrix (t-ECM), then its acellularity was confirmed. The decellularized tissue was digested enzymatically to yield an injectable form of t-ECM with a high content of protein, collagen and sulfated glycosaminoglycans. Next, conjugation of dopamine to t-ECM was performed under acidic, neutral, and basic pH conditions, either in the presence of O2 or under N2 flow. Conjugation of dopamine to t-ECM was determined by FT-IR, 1H NMR and UV–vis analysis, while catechol groups in the structures were quantified by Arnow method. The findings revealed that neutral and basic conditions are more suitable for dopamine conjugation. The physical properties of the bioadhesive were also determined by swelling and mass loss analysis. The conjugates exhibited good cytocompatibility and hemocompatibility and showed good cell adhesion. The lap-shear test using skin tissue showed that the t-ECM-dopamine conjugate has high adhesive strength and can be considered as a potential bioadhesive for the future.

Selective Homocysteine Assay with Cucurbit[7]uril by pH Regulation.

We report the effect of pH on the supramolecular complexation of two biothiols, viz., homocysteine (Hcy) and cysteine (Cys), with cucurbit[7]uril (CB[7]). Under basic pH conditions, Cys did not complex with CB[7], whereas Hcy efficiently complexed with CB[7], as confirmed by 1H NMR spectroscopy and Ellman's reagent (5,5'-dithio-bis(2-nitrobenzoic acid), DTNB) assay. 1H NMR and Raman spectroscopic studies revealed that, in the absence of CB[7], Hcy auto-oxidized slowly (~36 h) to homocystine (HSSH) under basic pH conditions. However, the rate of Hcy oxidation increased by up to 150 fold in the presence of CB[7], as suggested by the DTNB assay. Thus, supramolecular complexation under basic pH conditions led to the formation of a HSSH-CB[7] complex, and not Hcy-CB[7]. The results indicate that Hcy is rapidly oxidized to HSSH under the catalysis of CB[7], which acts as a reaction chamber, in basic pH conditions. Our studies suggest that Hcy concentration, a risk factor for cardiovascular disease, can be selectively and more easily quantified by supramolecular complexation with CB [7].

Part-Per-Billion Level Chemical Sensing with a Gold-Based SERS-Active Substrate.

We used surface-enhanced Raman spectroscopy (SERS) for the rapid and sensitive detection and quantification of caffeine in solution. Such a technique incorporated into a portable device is finding wide applications in trace chemical analysis in various fields, including law enforcement, medicine, environmental monitoring, and food quality control. To realize such applications, we are currently developing portable and handheld trace chemical analyzers based on SERS, which are integrated with a sensor embedded with activated gold nanoparticles in a porous glass matrix. In this study, we used this gold SERS-active substrate to measure aqueous solutions of the drug caffeine as a test chemical to benchmark sensor performance by defining sensitivity (lowest measured concentration (LMC) and estimated limit of detection (LOD)), determining concentration dependence and quantification capabilities by constructing calibration curves; by evaluating the effects of pH values of 3, 7, and 11; and by examining the reproducibility of the SERS measurements. The results demonstrate that the SERS sensor is sensitive, with caffeine detected at an LMC of 50 parts per billion (ppb) with an LOD of 0.63 ppb. The results further show that the sensor is very stable and can be used to make reproducible measurements, even under extremely acidic to basic pH conditions. Vibrational assignments of all observed SERS peaks are made and reported for the first time for caffeine on a gold substrate.