Racemic dielectric metasurfaces for arbitrary terahertz polarization rotation and wavefront manipulation

Dielectric chiral metasurface is a new type of planar and efficient chiral optical device that shows strong circular dichroism or optical activity,which has important application potential in optical sensing and display.However,the two types of chiral optical responses in conventional chiral metasurfaces are often interdependent,as their modulation of the amplitudes and phases of orthogonal circularly polarized components is correlated,which limits the further progress of chiral meta-devices.Here we propose a new scheme for independently designing the circular dichroism and optical activity of chiral metasurfaces to further control the polarization and wavefront of transmitted waves.Inspired by mixtures of chiral molecular isomers,we use the dielectric isomer resonators to form“super-units”instead of single meta-atoms for chiral responses in terahertz band,which is called racemic metasurface.By introducing two levels of Pancharatnam-Berry phases between meta-atoms and“super-units”,the polarization rotation angle and wavefront of the beam can be designed without the far-field circular dichroism.We demonstrate the strong control ability on terahertz waves of this scheme through simulation and experiments.In addition,this new type of device with near-field chirality but no far-field circular dichroism may also have important value in optical sensing and other technologies.

Is the required therapeutic effect always achieved by racemic switch of proton-pump inhibitors?

Many of the drugs currently used in medical practice are racemates. The enantiomers of a racemic drug differ in pharmacodynamics and/or pharmacokinetics, thus in some cases it is preferable to develop pure enantiomers by racemic switch. In a recent study by Pai et al, dexrabeprazole [R(+)-rabeprazole] (10 mg) was found to be more effective than rabeprazole (20 mg) in the treatment of gastroesophageal reflux disease. We read with great interest in this study and discussed whether such racemic switch would be applicable to other proton-pump inhibitors (PPIs). A literature review indicates that stereoselective pharmacokinetics, rather than stereoselective pharmacological activity, is the main cause of differences in clinical efficacy between pure enantiomer and racemic PPI. Racemic switches of PPI provide the therapeutic advantages such as reducing metabolic load on the body, simplifying pharmacokinetics, providing benefit to the non-responders to standard dose of racemate, more homogenous response to treatment and better efficacy with equal safety. Further studies in quantitative structure-activity relationships (QSARs) are needed to address the fact that the preferred enantiomer of PPI is not always in the same absolute configuration, i.e., S-form is for omeprazole, pantoprazole and tenatoprazole whereas R-form is for lansoprazole and rabeprazole.

Lipase-catalyzed Kinetic Resolution of Racemic 1-Trimethylsilylethanol in Organic Solvent

The enantioselective esterification of racemic 1-trimethylsilylethanol with acids catalyzed by lipase in organic solvent was successfully performed. The influence of some factors on the reaction was investigated. Among the four lipases explored, Candida rugosa lipase (CRL) showed the highest activity and enantioselectivity. Octanoic acid was the best acyl donor among the eleven acids studied and n-hexane was the most suitable medium for the reaction. The optimum shaking rate and temperature were found to be 150r·min-1 and 20℃ to 30℃, respectively. The enantiomeric excess of the remaining (5)-(-)-1-trimethylsilylethanol was 93% when substrate conversion was 53% upon incubation of the reaction mixture at 30℃, 150r·min-1 for 12 h.

ENZYME REACTION IN AQUEGUB-ORGANIC BYSTEM —KINETIC RESOLUTION OP RACEMIC OXIRANECARBOXYLIC ESTERS WITH LIPASE

The chiral oxiranecarboxylic acids or esters 2a-e were obtained with lipase (CCL) in aqueous-organic system.The ee and the absolute configurations of the products were determined.

Enantioseparation of some Racemic Compounds on Cellulose Tris (3,5-dimethylphenylcarbamate) Chiral Stationary Phase

Seven chiral compounds were resolved on cellulose tris (3,5-dimethylphenylcarbamate) chiral stationary phase (CDMPC-CSP) using n-hexane/alcohol as mobile phase. Solvent strength and structural characteristics of the compounds effecting on the retention and resolution were discussed. Satisfactory separation was obtained.

Synthesis of a Chain Aluminophosphate Containing Racemic 1, 2-Diaminopropane

A one-dimensional chain aluminophosphate C1.5H7.5N1.5Al0.5PO4 containing diprotonated racemic 1, 2-diaminopropane cations was synthesized from an alcoholic system. The compound consists of infinite inorganic [AlP2O8] chains of alternately connected AlO4 and PO2(=O)2 tetrahedral units and the racemic template molecules. The macroanionic chains contain corner-shared double four-membered rings.

A New Organo-templated Layered Zincophosphate Synthesized from a Solvothermal System Containing Racemic 1,2-Diaminopropane

A new layered zincophosphate was synthesized under solvothermal conditions by employing racemic 1,2-diaminopropane as the structure-directing agent. The structure of the compound was solved by means of single-crystal X-ray diffraction analysis. It crystallized in the monoclinic space group P2_1/c (No. 14) with a= 1.047 0(3) nm, b=0.787 31(18) nm, c=0.662 68(16) nm, β=103.120(5)°, V=0.532 0(2) nm 3 and Z=4. The structure is made up of anionic zincophosphate sheets stacked in an AAAA sequence. The individual sheet contains three- and four-membered rings and the infinite Zn-O-Zn chains can also be envisaged in the sheet. The charge-balancing diprotonated racemic 1,2-diaminopropane cations are sandwiched between the layers, whereas the inorganic layers are stabilized by strong H-bonds formed between the N atoms of the amine and the O atoms in the inorganic sheets.

Hollow fiber liquid-supported membrane technology for enantioseparation of racemic salbutamol by combinatorial chiral selectors

Enantioseparation of salbutamol solute was carried out in liquid-supported membrane by using a polyvinylidene fluoride hollow-fiber module. The enantioselective transport of solute was facilitated by combinatorial chiral selectors, which were dissolved in toluene organic solvent. The effects of molar concentration ratios of salbutamol to combinatorial chiral selectors, and the pH value of buffer solution on enantioseparation were investigated. The results show that when the molar concentration ratio is 2∶1∶1, the maximum separation factor and enantiomer excess are 1.49 and 19.74%, respectively, and the R-enantiomer flux is more than S-enantiomer; the pH value of buffer solution influences the performances of enantioseparartion obviously, and the appropriate range of pH value is 7.07.2.

Facile Resolution of Racemic 4-Phenyl-2-hydroxy Butyrate via Enzymatic Esterification and Transesterification

The optically active R-4-phenyl-2-hydroxy butyrates were prepared by esterification of the racemic acid or transesterification of the racemic ester catalyzed by lipase from Candida cyclindra (CCL) in organic media.

Enantioselective Conversion of Racemic Felodipine to S(-)-Felodipine by Aspergillus niger and Lipase AP6 Enzyme

The present study involves the enantioselective resolution of racemic Felodipine by using free and immobilized forms of microbial cultures as well as an enzyme (Lipase AP6). Among the microbial cultures employed in the present study, Aspergillus niger, Sphingomonas paucimobilis, Cunninghamella elegans, Escherichia coli, Pseudomonas putida and Cunninghamella blakesleeana were found to possess capability of enantioselective resolution of racemic Felodipine. The enantiomeric excess (ee%) of Felodipine after reaction catalyzed by whole-cell A. niger and S. paucimobilis was found as 81.59 and 71.67%, respectively. Immobilization enhanced the enantioselectivity (enantiomeric ratio (E)) of the biocatalysts and hence this led to enhanced enantiomeric purity of the drug. The ee% values were found to be enhanced in reactions catalyzed by A. niger and S. paucimobilis cultures after immobilization as 98.27 and 93.56%, respectively. Enantiomeric ratio (E) of the reactions catalyzed by all the biocatalysts has been improved after immobilization. E value of the reaction catalyzed by immobilized A. niger was found to be excellent (E > 100) and hence the drug showed high enantiomeric purity. In lipase AP6 catalyzed study, the enantioselectivity was enhanced after immobilization with excellent E value, which led to enhanced enantiomeric purity of the drug (99.21% ee%).

Racemic X-ray structure of L-type calcium channel antagonist Calciseptine prepared by total chemical synthesis

Snake toxin Calciseptine as a natural antagonist of L-type calcium channel has potential drug values, but its structural information remains unknown. Here, we report the total chemical synthesis of Calciseptine by using hydrazide based native chemical ligation. The crystal structure of Calciseptine was determined by racemic protein crystallography technique. Compared to the structure of its homologous family protein, we found that Calciseptine is adopting a typical three-finger structure.

Racemic ofloxacin separation by supported-liquid membrane extraction with two organic phases

Based on chemical thermodynamic theory, racemic ofloxacin is separated in chiral sys-tems by hollow fiber liquid-supported membrane technology combining with countercurrently frac-tional extraction. The two chiral solutions containing L-dibenzoyltartaric acid and D-dibenzoylta- rtaric acid in 1-octanol, flow through the lumen side and the shell side of fibers, respectively. The solution which flows through the lumen side of fibers also contains racemic ofloxacin. The wall of hollow fibers is filled with an aqueous of 0.1 mol/L Na2HPO4/H3PO4 buffer solution of pH = 6.86 containing 2 mmol/L of cetyltrimethyl ammonium bromide for 48 h. The fairly polar ofloxacin can cross the membrane back and forth, but dibenzoyltartaric acids cannot cross it. Fractional chiral extraction theory, mass transfer performance of hollow fiber membrane and enantioselectivity are investigated. Mathematical model of R/S = 0.96e0.03NTU for racemic ofloxacin separation by hollow fiber extraction, is established. The optical purity for ofloxacin enantiomers is up to 90% when 11 hollow fiber membrane modules of 22 cm in length in series are used.

Chemical synthesis and racemic crystallization of rat C5a-desArg

The deletion of the C-terminal arginine of the anaphylatoxin protein C5a reduces it receptor binding affinity.Understanding how C-terminal arginine affects the structure and bioactivity of C5a is important for the development of C5a C-terminal mimics as drug candidates.Herein,we report the total chemical synthesis of rat C5a and its D-enantiomer with its C-terminal arginine deleted,namely L-rC5a-desArg and D-rC5a-desArg.The structure of rC5a-desArg was then determined by racemic crystallography for the first time.The C-terminal residues of rC5a-Arg were found to expand from the fourth helix in a continuous helical confo rmation.This C-terminal conformation is significantly different from that of the previously reported full-length of C5a,indicating that the deletion of C-terminal arginine residue could result in the destruction of a positively charged surface formed by two adjacent Arg residues in C5a.

Inpatient use of racemic epinephrine for children admitted with croup

Background Pediatric patients with croup are frequently admitted if they require two doses of racemic epinephrine(RE)in the emergency department(ED).We aimed to identify factors associated with the need for additional therapy(>2 RE doses)among pediatric patients with croup.Methods We performed a single-center retrospective study of consecutive patients admitted from the ED with a diagnosis of croup between January 1,2011 and December 31,2015.Primary outcome was need for>2 doses of RE.Secondary out-comes included time to third RE and 72-hour return visits.We performed logistic regression to identify factors associated with use of>2 RE doses during hospitalization,and survival analysis to identify time to dosing of 3rd RE from 2nd RE.Results Of 353 included admissions[250(70.8%)males,median age 1.48,interquartile range 0.97-2.51 years],106/353(30.0%)required>2 RE.In univariate logistic regression,only recent use of steroids within 1 day prior to presentation(4.18,1.48-11.83;P=0.007)was associated with need for>2 RE.Survival from third RE was 0.74(95%CI 0.69-0.78),which was similar to the survival at 12 hours(0.70,95%CI 0.65-0.75).Return visits occurred in 19(5.4%)patients,of whom 12/19(63.2%)were given RE.Conclusions Patients hospitalized for croup with recent use of steroids prior to ED presentation have a greater need for>2 RE during hospitalization.The majority who require inpatient RE will do so within 8-12 hours.These data provide informa-tion for risk stratification and duration of monitoring for patients hospitalized with croup.

Preparation of (+)-1-Phenylethylamine by Optical Resolution of Racemic 1-Phenylethylamine with a Chiral Biopolymer,Casein

1 Results It has been reported that crystalline form racemates can be resoluted by various methods[1],but for optical resolution of liquid form racemates,the method is limited in chromatograph.So chiral compounds cannot be obtained on large scale by such method.In our previous paper,(+)-3-chloro-1,2-propanediol has been obtained by optical resolution of its racemata (liquid) with a chiral biopolymer,casein[2].

A New Synthetic Route to Diastereomerically Pure Cyclopropane-Phosphorus Derivatives Utilizing the Chiron 5-L-Men-thyloxy-3-bromo-2(5H)-furanone and Racemic Dialkyl α-Hydroxyalkanephosphonate

A new chemical transformation for the construction of diversely functionalized cyclopropane-phosphorus derivatives utilizing chiron 4 and racemic diethyl α-hydroxylbenzylphosphonate as the key precursors is described. The diastereomeric pure phosphorus-containing derivatives 5a, 5′a, 5b and 5′b were obtained respectively, in good yields with d. e. 98% via asymmetric tandem double Michael addition/internal nucleophilic substitution of the corresponding compounds and further through the separation of the diastereomeric mixture by column chromatography. The diversely functionalized phosphorus derivatives are identified on the basis of their elemental analysis and spectroscopic data, such as K, 1H NMR, 13C NMR and MS. The absolute configuration of the interesting cyclopropane-phosphorus compound 5a was established by X-ray crystallography. Thus, these results provide a valuable strategy for synthesizing some biologically active molecules.

Standardized Management of Acute Pulmonary Hemorrhage after Percutaneous Pulmonary Vein Intervention

Introduction:Pulmonary hemorrhage(PHm)is a life-threatening complication that can occur after catheter-based interventions in patients with pulmonary vein stenosis(PVS).Inhaled racemic epinephrine(iRE)and tra-nexamic acid(iTXA)have been used in other conditions,but a standardized approach in PVS has not been described.We aimed to describe the current management of PHm after PVS catheter-based interventions.Methods:We present a retrospective review of episodes of PHm from July 2022 to February 2024.PHm was defined as frank blood suctioned from the endotracheal tube including blood-tinged secretions and>3%decrease in saturations and/or ventilatory changes with or without acute chest X-ray changes.Each individual episode of PHm was considered a separate event.Incidence was calculated based on the total number of PVS interventions during the study period.Results:Eleven episodes of PHm were identified out of 108 PVS interventions,resulting in an incidence of 10.2%.Five(45.5%)had primary PVS,and seven(63.6%)had bilateral PVS.The median age at PHm was 23 months(3-91 months).Four episodes were treated with iRE,five with both iRE and iTXA,and two with only iTXA due to a history of suprasystemic right ventricular pressures.Median time on mechanical ventila-tion after PHm was 24 h(15-72 h)and a median ICU stay of 2 days(1-8 days).Hemostasis was achieved in all events.There were no adverse events after iTXA,however,transient hypertension was observed after iRE which was dose-related.Conclusions:The implementation of a standardized protocol for the treatment of PHm in PVS has the potential to improve procedural planning,has a wider availability of medications,and greater awareness by the providers involved,possibly leading to earlier detection of PHm and appropriate treatment.

Molecular Chirality and Chiral Superlattice in Crystal of Tetrakis[(pyrrol-1-yl)methyl]methane

The crystal structure of tetrakis[(pyrrol-1-yl)methyl]methane was determined by X-ray diffraction measurement, and the result shows that it belongs to monoclinic crystal system, space group is P2 1/n, with a=0.9284(3) nm, b=1.0950(6) nm, c=1.8749(8) nm; α=γ= 90.00(4)°, β=103.63(3)°, V=1.8523(14) nm 3, Z=4, ρ calcd. =1.192 kg/m 3, μ=0.072 nm -1 , F(000)=712, R 1=0.0854, wR 2=0.1884. It has been found that the molecules exist in two enantiomeric states. Enantioselective self-assemblies such as one-dimensional molecular stacks in a single handedness, homochiral monolayers and a chiral superlattice are specified in this racemic crystal. In addition, a simple technique is advocated to distinguish chiral states from tetrahedral molecules in the solid state. The present R/S nomenclature of the tetracooradinated carbon centers is used solely for its convenience to distinguish the two enantiomeric states, but not used to determine the absolute configurations.

Activity and Enantioselectivity of Lipase Immobilized in CTAB Microemulsion-based Gels

Introduction The formation of gelatin-containing mieroemulsionbased gels（MBGs） was first described in 1986 and the physical/structural characterization was carried out by a number of groups with a variety of techniques including tracer diffusion, electrical conductivity, NMR, X-ray and small angle neutron scattering. The MBGs were proposed to comprise an extensive, rigid, interconnected network of gelatin/water rods stabilized by a monolayer of surfactant, in coexistence with a po- pulation of conventional W/O microemulsion droplets.

Enantiomeric Resolution on L-Carnitine Selective Polymers Prepared by Molecular Imprinting

L-carnitine selective polymers were prepared by molecular imprinting using methacrylic acid as the functional monomer. The acid function of the monomer is expected to form hydrogen bond and ionic interactions with the amine function of the target molecule L-carnitine. The imprinted polymers were used as stationary phases in high-performance liquid chromatography (HPLC). It was shown that L-carnitine imprinted polymer exhibited a higher affinity to its template molecule, while the non-imprinted polymer had no affinity to the compounds tested. Racemic carnitine hydrochloride was efficiently resolved on the L-carnitine imprinted polymer, and the separation factor is 1.9.