Enhanced degradation of emerging contaminants by Far-UVC photolysis of peracetic acid: Synergistic effect and mechanisms.

Krypton chloride (KrCl*) excimer lamps (222 nm) are used as a promising irradiation source to drive ultraviolet-based advanced oxidation processes (UV-AOPs) in water treatment. In this study, the UV222/peracetic acid (PAA) process is implemented as a novel UV-AOPs for the degradation of emerging contaminants (ECs) in water. The results demonstrate that UV222/PAA process exhibits excellent degradation performance for carbamazepine (CBZ), with a removal rate of 90.8 % within 45 min. Notably, the degradation of CBZ in the UV222/PAA process (90.8 %) was significantly higher than that in the UV254/PAA process (15.1 %) at the same UV dose. The UV222/PAA process exhibits superior electrical energy per order (EE/O) performance while reducing resource consumption associated with the high-energy UV254/PAA process. Quenching experiments and electron paramagnetic resonance (EPR) detection confirm that HO• play a dominant role in the reaction. The contributions of direct photolysis, HO•, and other active species (RO• and 1O2) are estimated to be 5 %, 88 %, and 7 %, respectively. In addition, the effects of Cl-, HCO3-, and humic acid (HA) on the degradation of CBZ are evaluated. The presence of relatively low concentrations of Cl-, HCO3-, and HA can inhibit CBZ degradation. The UV222/PAA oxidation process could also effectively degrade several other ECs (i.e., iohexol, sulfamethoxazole, acetochlor, ibuprofen), indicating the potential application of this process in pollutant removal. These findings will propel the development of the UV222/PAA process and provide valuable insights for its application in water treatment.

Sequential combination of pre-chlorination and powdered activated carbon adsorption on iodine removal and I-THMs control in drinking water.

Combining pre-oxidation with activated carbon adsorption was explored as an ideal approach for removing iodine from water source to eliminate the formation of Iodinated trihalomethanes (I-THMs). Compared with permanganate and monochloramine, chlorine is more suitable as pre-oxidant to obtain higher active iodine species (HOI/I2). Active iodine species adsorption using both powdered activated carbon (PAC) and granular activated carbon (GAC) can be well fitted the pseudo-second-order kinetic model indicating that chemical adsorption was the dominant mechanism for HOI/I2 adsorption. The average pore size of activated carbons was the most strongly correlated with the adsorption capacity (R2 > 0.98), followed by methylene blue (R2 > 0.76), pore volume (R2 > 0.70) and iodine number (R2 > 0.67). Moreover, three models, including intraparticle diffusion, Byod kinetic, and diffusion-chemisorption were used to illustrate the mechanisms of HOI/I2 adsorption. Chemical adsorption was the dominant mechanism for HOI/I2 adsorption. In summary, at the molar ratio of [NaClO] and [I-] as 1.2, pre-chloriantion time of 5 min, subsequently dosage of 15 mg/L of PAC E with 20 min adsorption can remove 79.8% iodine. In addition, the combined process can eliminate 61%-87.2% of I-THMs in the subsequent chlor(am)ination. The results indicate that pre-chlorination combined with PAC can effectively removed HOI/I2 and attenuate I-THMs formation in the subsequent disinfection process.

Enhanced coagulation and oxidation by the Mn(VII)-Fe(III)/peroxymonosulfate process: Performance and mechanisms.

To improve the performance of the conventional coagulation process, a permanganate (Mn(VII)) pre-oxidation combined with Fe(III)/peroxymonosulfate (PMS) coagulation process (Mn(VII)-Fe(III)/PMS) that can significantly improve the removal of dissolved organic carbon (DOC), turbidity, and micropollutants is proposed in this study. Compared with conventional Fe(III) coagulation, the Mn(VII)-Fe(III)/PMS process can also significantly enhance the removal of iohexol and sulfamethoxazole in raw water. During this process, the primary reduction product, Mn(IV), after Mn(VII) pre-oxidation was adsorbed on the floc surfaces and involved in the Fe(III)/PMS process. The natural organic matter (NOM) in raw water mediated the redox cycle of iron. The synergistic effect of NOM, Fe, and Mn facilitated the redox cycle of Mn(III)/Mn(IV) and Fe(III)/Fe(II) to promote the activation of PMS. The sulfate radical (SO4•-) played an important role in the degradation of micropollutants. The formation potential of the detected volatile disinfection by-product (DBP) during the subsequent chlorination was reduced by 21.9% after the Mn(VII)-Fe(III)/PMS process. This study demonstrated the promising application of the Mn(VII)-Fe(III)/PMS process for coagulation and micropollutant control and illustrated the reaction mechanism. This study provides guidance for improving conventional drinking water treatment processes.

Translation and validation of the Chinese ABCD risk questionnaire to evaluate adults' awareness and knowledge of the risks of cardiovascular diseases.

BACKGROUND: Assessment of health beliefs and risk perception is a critical means to prevent coronary heart disease, but there are few such studies on assessment in the Chinese population. Given the demonstrated value and widespread use of the Attitudes and Beliefs about Cardiovascular Disease Risk Questionnaire (ABCD), this study was designed to translate it into Chinese, and to evaluate its reliability and validity in a Chinese population. METHODS: The Chinese version of the ABCD was created using the Beaton translation model, which included forward and backward translation. The reliability and construct validity of the Chinese ABCD were examined in a sample of 353 adults who participated in the public welfare projects of the Chinese National Center for Cardiovascular Diseases in Guilin city, Guangxi. Exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) were performed to examine the factor structure of the Chinse ABCD. The internal consistency of the questionnaire was assessed using Cronbach's α and corrected item-total correlations. RESULTS: We deleted item 7 in the knowledge dimension of the Chinese ABCD and added two items about smoking and sleep knowledge, while retaining 25 of the original items, so that it finally included 27 items. The correlations were .20-.90; the correlations between each item and the total score of the ABCD were .34-.86; and the item-level Content Validity Index (I-CVI) was .86-1.00. The results of the EFA showed that all items were close to .40, and the cumulative variance contribution rate was 63.88%. The model fit was acceptable (χ2 = 698.79, df = 243, χ2/df = 2.87, P < 0.001, SRMR = 0.06, RMSEA = 0.05, CFI = 0.96, and TLI = 0.94) according to the CFA. The Cronbach' s α of the entire questionnaire was .86, and the α of each of dimension was .65, .90, .88, and .78. The split-half reliability of the entire the ABCD was .67, and the test-retest reliability was .97 (P < 0.05). The questionnaire had good reliability and validity and was associated with sociodemographic and health-related characteristics (smoking and Body Mass Index). CONCLUSION: The Chinese version of the ABCD has good reliability and validity, and provides a reliable assessment tool for measuring public health beliefs about the risk of cardiovascular disease, promoting the primary prevention of coronary heart disease.

Micropollutant removal and disinfection byproduct control by sequential peroxymonosulfate-UV treatment in water: A case study with sulfamethoxazole.

UV/peroxymonosulfate (UV/PMS) advanced oxidation process has attracted significant attention for removal of micropollutants in water. However, during practical water treatment applications, the PMS treatment must be performed before the UV treatment to achieve full contact. In this study, sulfamethoxazole (SMX) was selected as the target micropollutant. Four different operational approaches, including UV alone, PMS alone, simultaneous UV/PMS and sequential PMS-UV, were compared for their differences in SMX removal and disinfection by-product (DBP) formation potentials during chlorine-driven disinfection. Among the four approaches, UV/PMS and PMS-UV achieved over 90% removal efficiencies for SMX without substantial differences. For raw water, the trichloronitromethane (TCNM) formation potential after treatment with PMS-UV was lower than that after UV/PMS treatment. The time interval over which the PMS-UV process was conducted had little effect on the final removal efficiency for SMX. However, a brief (5 min) pre-PMS treatment significantly reduced the TCNM formation potential and the genotoxicity from DBPs. The formation risk for TCNM during chlorination increased markedly with increasing PMS dosages, and the appropriate dosage under these experimental conditions was suggested to be 0.5-1.0 mmol/L. Under alkaline conditions, PMS-UV treatment can enhance SMX degradation as well as dramatically reduced the formation potentials for haloketones, haloacetonitriles and halonitromethanes. This study suggests that proper optimization of UV/PMS processes can remove SMX and reduce its DBP formation.

Insight into the formation of iodinated trihalomethanes during chlorination, monochloramination, and dichloramination of iodide-containing water.

In this study, the formation of iodinated trihalomethanes (I-THMs) was systematically evaluated and compared for three treatment processes - (i) chlorination, (ii) monochloramine, and (iii) dichloramination - under different pH conditions. The results demonstrated that I-THM formation decreased in the order of monochloramination > dichloramination > chlorination in acidic and neutral pH. However, the generation of I-THMs increased in the dichloramination < chlorination < monochloramination order in alkaline condition. Specifically, the formation of I-THMs increased as pH increased from 5 to 9 during chlorination and monochloramination processes, while the maximum I-THM formation occurred at pH 7 during dichloramination. The discrepancy could be mainly related to the stability of the three chlor (am) ine disinfectants at different pH conditions. Moreover, in order to gain a thorough insight into the mechanisms of I-THM formation during dichloramination, further investigation was conducted on the influencing factors of DOC concentration and Br-/I- molar ratio. I-THM formation exhibited an increasing and then decreasing trend as the concentration of DOC increased from 1 to 7 mg-C/L, while the yield of I-THMs increased with increasing Br-/I- molar ratio from 5:0 to 5:10. During the three processes mentioned above, similar I-THM formation results were also obtained in real water, which indicates that the excessive generation of I-THMs should be paid special attention during the disinfection of iodide-containing water.

Enhanced degradation of emerging contaminants by permanganate/quinone process: Case study with bisphenol A.

Permanganate (Mn(VII)) is widely used as a mild oxidant in water treatment. However, the reaction rates of some emerging contaminants with Mn(VII) are extremely low. In this study, benzoquinone (BQ), a redox mediator with the important component in dissolved organic matter (DOM), enhanced the oxidation of bisphenol A (BPA) by Mn(VII) in a wide pH range of 4.0-10.0. The redox cycle of BQ would produce semiquinone radicals, which could act as ligands to stabilize the formed Mn(III) in the system to promote the oxidation of BPA. Notably, the presence of BQ might promote the formation of MnO2. A novel mechanism was proposed that singlet oxygen (1O2), Mn(III)-ligands (Mn(III)-L) and in-situ formed MnO2 were the main contributors to accelerate BPA degradation in the Mn(VII)/BQ system. Under acidic conditions, the in-situ formed MnO2 involved in the redox reaction and part of the Mn(IV) was reduced to Mn(III), indicating that the electron transfer of BQ promoted the formation of active Mn species and enhanced the Mn(VII) oxidation performance. Semiquinone radicals generated by BQ transformation would couple with the hydrogen substitution products of BPA to inhibit BPA self-coupling and promote the ring-opening reactions of BPA. Mn(VII)/BQ had better effect in raw water than in pure water, indicating that the Mn(VII)/BQ system has high potential for practical application. This study provided insights into the role of DOM in enhancing the Mn(VII) oxidation in water treatment.

The formation, analysis, and control of chlor(am)ination-derived odor problems: A review.

Odors and tastes have become universal problems related to drinking water quality. In addition to the typical odor problems caused by algae or microorganisms, the occurrence of odors derived from drinking water disinfection have attracted attention. The chlor(am)ination-derived odor substances have certain toxicity and odor-causing characteristics, and would enter the tap water through water distribution systems, directly affecting drinking water safety and customer experience. This study provided a comprehensive overview of the occurrence, detection, and control of odor substances derived from drinking water chlor(am)ination disinfection. The occurrence and formation mechanisms of several typical types of disinfection derived odor substances were summarized, including haloanisoles, N-chloroaldimines, iodotrihalomethanes, and halophenoles. They are mainly derived from specific precursors such as halophenols, anisoles, and amino acids species during the disinfection or distribution networks. In addition, the change of disinfectant during chlor(am)ination was also one of the causes of disinfection odors. Due to the extremely low odor threshold concentrations (OTCs) of these odor substances, the effective sample pre-enrichment for instrument identification and quantification are essential. The control strategies of odor problems mainly include adsorption, chemical oxidation, and combined processes such as ozonation and biological activated carbon processes (O3/BAC) and ultraviolet-based advanced oxidation processes (UV-AOPs). Finally, the challenges and possible future research directions in this research field were discussed and proposed.

The application of UV-C laser in persulfate activation for micropollutant removal: Case study with iodinated X-ray contrast medias.

A novel light source UV-C laser was applied in persulfate (PS) activation to effectively remove iodinated X-ray contrast medias (ICMs) including iohexol (IOX), iopamidol (IPM) and diatrizoate (DTZ) in this study. Significant ICMs degradation was observed in UV-C laser/PS systems with pseudo first-order rate constants of 0.022-0.067 s-1. Sulfate radicals (SO4•-) were the main active species in the three ICMs degradation, and the steady-state concentrations ([SO4•-]ss) were 3.629 × 10-11 M (IOX), 1.702 × 10-11 M (IPM) and 1.148 × 10-11 M (DTZ), respectively. Under the high intensity of UV-C laser, the optimal reaction efficiency was achieved at pH = 7.0 with PS concentration of 1.0 mM, and the degradation efficiency for IOX reached 93.8% within only 40 s. Both bicarbonate and chloride ions could inhibit the three ICMs degradation and the inhibition rate increased with the increase of ions concentration. The kinetic models were established and the steady-state concentrations of radicals were calculated. Density functional theory (DFT) calculations combined with experiments were used to derive the reaction pathways for three ICMs. Cyclic voltammetry measurements detected a lower redox potential peak in IOX degradation, revealing the existence of electron shuttles under the UV-C laser irradiation to promote the redox reaction. This study is the first report of UV-C laser activation of persulfate. It is a new advanced oxidation process mediated by very effective photolysis and active species formation.

Iodinated trihalomethanes formation in iopamidol-contained water during ferrate/chlor(am)ination treatment.

Iopamidol is a commonly used iodinated X-ray contrast media in medical field, and its residue in water can react with disinfectants to form highly toxic iodinated disinfection by-products (I-DBPs). This study investigated the degradation of iopamidol and formation of DBPs, especially iodinated trihalomethanes (I-THMs), during ferrate (Fe(VI)) pre-oxidation and subsequent chlor(am)ination under raw water background. It was found that iopamidol degradation efficiency in raw water by Fe(VI) at pH 9 could reach about 80%, which was much higher than that at pH 5 and pH 7 (both about 25%). With Fe(VI) dose increasing, iopamidol removal efficiency increased obviously. During the iopamidol degradation by Fe(VI), IO3- was the dominant product among all the iodine species. After pre-treated by Fe(VI), yields of THM4 and I-THMs can be reduced in subsequent chlor(am)ination. Besides, pH was a crucial factor for Fe(VI) pre-oxidition controlling DBPs. With the pH increasing from 5 to 9, the yield of THM4 kept increasing in subsequent chlorination but showed the highest amount at pH 6 in subsequent chloramination. The yield of I-THMs increased first and then decreased with the increase of pH in both subsequent chlorination and chloramination. I-THM concentrations in chlorinated samples were lower than chloraminated ones under acidic conditions but became higher under neutral and alkaline conditions. The total CTI of THMs during Fe(VI)-chloramination was higher than that during Fe(VI)-chlorination under neutral condition, but sharply decreased under alkaline conditions. In summary, Fe(VI)-chloramination subsequent treatment under alkaline conditions should be an effective method for iopamidol removal and DBP control.

Formation of disinfection by-products in a UV-activated mixed chlorine/chloramine system.

In recent years, ultraviolet (UV) irradiation coupled with chlor(am)ination process is ubiquitous in secondary water supply systems in many cities of China. However, the disinfection by-products (DBPs) formation in a UV-activated mixed chlorine/chloramine system (MCCS) still remains unclear. In this study, the DBPs formation in a UV-activated MCCS was systematically investigated, considering influencing factors including the mass ratios of free chlorine to NH2Cl, UV irradiation, pH values, NOM types, Br- concentration and toxicity of the DBPs. Results indicated that DBPs formation decreased remarkably as mass ratio of free chlorine to NH2Cl changed from 5:0 to 0:5. The DBPs formation in humic acid (HA)-containing water was the highest, followed by those in fulvic acid (FA) and algal organic matter (AOM). Besides, better control of the DBP-related calculated toxicity can be achieved in acidic conditions regardless of the UV irradiation. Furthermore, in the presence of Br-, a significant reduction of DBPs formation could be achieved in a UV-activated MCCS. The findings also demonstrated that DBPs formation in real water can be effectively reduced at high UV fluence in a MCCS.

[Degradation of RBK5 by High Crystallinity Mn-Fe LDH Catalyst Activating Peroxymonosulfate].

High crystallinity Mn-Fe LDH was synthesized by improved co-precipitation combined with the hydrothermal method and was utilized as a catalyst for peroxymonosulfate (PMS) activation to degrade reactive black 5. The high crystal purity and clear lamellar structure were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The operating parameters such as Mn/Fe molar ratio, catalyst dosage, PMS concentration, and initial pH value on the absorption efficiency, catalytic degradation, and reaction kinetics of RBK5 were also investigated. The results demonstrated that high crystallinity Mn-Fe LDH has good adsorption capacity and high catalytic efficiency. The degradation efficiency of RBK5 (20 mg·L-1) could reach 86% within 90 min when the Mn/Fe molar ratio was 1, the catalyst dosage was 0.2 g·L-1, the PMS concentration was 1 mmol·L-1, and the initial pH value was 7.0. The reaction process follows pseudo-first-order reaction kinetics (R2>0.9). In addition, the quenching experiment indicated that SO4-·and·OH were the main active species that degraded RBK5 from the Mn-Fe LDH/PMS system. The XPS analysis of the catalyst before and after the reaction confirmed the synergistic effect between Mn and Fe. The charge balance between Mn(Ⅱ) and Fe(Ⅲ) on the LDH surface and CO32- in layers stabilized the structure, thus promoting the synergistic effect of Mn and Fe on the lamellar surface and improving the activation efficiency of PMS by Mn-Fe LDH. Three-dimensional fluorescence and the UV-Vis scanning spectral analysis were preliminarily discussed to understand the degradation process of RBK5.

[Degradation of RBk5 with Peroxymonosulfate Efficiently Activated by N-Doped Graphene].

The large loss of catalysts and secondary pollution problems are bottlenecks for the utilization of persulfate advanced oxidation processes. Thus, a modified Hummers method combined with a hydrothermal method was used to prepare N-doped graphene as a catalyst for peroxymonosulfate (PMS) activation. The produced sulfate radical (SO4-·) and hydroxyl radical (·OH) were able to degrade RBk5. N-doped graphene was characterized by Fourier transform infrared, X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy. The influences of vital parameters (i. e., initial pH, catalyst dosage, and PMS dosage) on RBk5 removal were investigated systematically to examine the catalytic performance. The results showed that the N element doping can effectively improve the catalytic activity of graphene, and the activity is greatly affected by the N doping ratio. The initial pH of the wastewater had no significant effect on the degradation efficiency. Under the condition of 1.5 g·L-1 catalyst dosage and 0.3 g·L-1 PMS dosage, the removal rate of RBk5 dye reached 99% after 25 min of reaction. The reaction process accorded with first-order reaction kinetics. Radical quenching experiments were done and indicated that the degradation of RBk5 in N-doped graphene/PMS systems was a surface reaction, and SO4-· and ·OH were identified as the main radical species. The catalyst exhibited excellent stability over five successive degradation cycles.

Degradation of bisphenol A by persulfate activation via oxygen vacancy-rich CoFe2O4-x.

This research describes the function of oxygen vacancy on CoFe2O4-x for persulfate (PS) activation. Novel CoFe2O4-x with different vacancy degrees that were successfully developed via hydrogen calcination were characterized using X-ray diffraction analyzer (XRD), Fourier transform infrared (FTIR) spectra, Raman spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), cyclic voltammetry (CV), electrochemical impedance spectra (EIS), nitrogen adsorption-desorption isotherms and dynamic light scattering. The activation of catalysts was analyzed using Bisphenol A (BPA) as pollutant, and the main active species generated during the reaction were identified by using N2 bubbling and scavenger experiments. Possible oxidation degradation pathways of BPA were speculated using gas chromatography-mass spectrophotometry (GC-MS) and total organic carbon (TOC) analysis. Findings indicated that the oxygen vacancies promoted electronic transfer and participated in the redox cycle from Co3+/Fe3+ to Co2+/Fe2+ to generate 1O2 and O2-. O2-, OH and SO4- generated from oxygen vacancy; moreover, PS activation could further degrade BPA to small molecules, such as benzenes and quinones. Finally, the toxicity of the reaction mixtures was evaluated and found that the acute toxicity to Daphnia magna decreased after 120 min treatment.

Degradation of acetaminophen with ferrous/copperoxide activate persulfate: Synergism of iron and copper.

To enhance the advanced oxidation process based on persulfate, CuO was introduced into the Fe2+/PS system to achieve a synergistic effect between Fe and Cu. Results showed that Fe2+ was able to adsorb onto the CuO surface to form Fe(II) and further reduced Cu(II) into Cu(I), which can further release into the solution to participate in oxidation reactions. In this case, SO4·- can be generated via Fe2+ and Cu+ reactions with PS and ·OH from Cu+ reaction with dissolved oxygen (DO). The degradation efficiency of APAP was studied under the optimal condition (initial pH 6.5, PS = 0.8 g L-1, Fe2+ = 0.7 mM, CuO = 0.3 g L-1), and the results indicated that the Fe2+/CuO/PS system can achieve a higher degradation rate of APAP (92% within 90 min) rather than Fe2+/PS and CuO/PS system (79% and 10%). Quenching experiment was performed to verify the active radicals in the Fe2+/CuO/PS system. Sulfate and hydroxyl radicals were generated in the Fe2+/CuO/PS system. Besides, some critical factors, such as Fe2+ concentration, catalyst dosage, PS concentration, initial pH (buffers and nonbuffers), and dissolved oxygen were evaluated in bath experiments. Results indicated that dissolved oxygen was essential in the Fe2+/CuO/PS system. APAP degradation experiments were conducted in surface water, and the intermediates were detected via GC-MS. The results indicated that the Fe2+/CuO/PS system is effective in the treatment of APAP in natural waters.

Identification of amino acid residues essential for heparin binding by the A1 domain of human von Willebrand factor.

Platelet adhesion is mediated by von Willebrand factor (VWF) that binds platelet glycoprotein Ib (GPIb). Previous observations suggested that heparin competitively inhibits the binding of VWF to GPIb and may down-regulate platelet adhesion. We performed charged-to-alanine scanning mutagenesis of domain A1 and studied dose-dependent binding to heparin-Sepharose beads. Mutations at Lys1362 and Arg1395, at which the GPIb binding was markedly decreased, showed 41% and 42% binding, respectively. Clustered mutations in the segments 1332KDRKR1336 and 1405KKKK1408, which have been proposed as heparin binding sequences, showed 72% and 52% binding, respectively. However, single alanine substitutions within these clusters showed normal binding. Our findings suggest that heparin may inhibit the binding of VWF to GPIb by interacting with GPIb binding and interpret why some hemorrhagic complications of heparin therapy are not predictable based on techniques for monitoring the conventional anticoagulant effects of heparin.

Identification of the regulatory elements of the human von Willebrand factor for binding to platelet GPIb. Importance of structural integrity of the regions flanked by the CYS1272-CYS1458 disulfide bond.

In vitro platelet glycoprotein Ib (GPIb) binding of the human von Willebrand factor (VWF) increases markedly by exogenous modulators such as ristocetin or botrocetin, and the binding does not occur in normal circulation. GPIb binding sites have been assigned in the VWF A1 domain, which consists of a disulfide loop Cys1272(509)-Cys1458(695) where amino acid residues are numbered from the starting methionine as +1. The previous numbering from the N-terminal Ser of the mature processed VWF is indicated in parentheses. In contrast, several gain-of-function mutations have been found in two regions comprised of the disulfide loop and its N- and C-terminal flanking regions. In this study, Cys1222(459)-Tyr1271(508), Gln1238(475)-Tyr1271(508), Glu1260(497)-Tyr1271(508), and Asp1459(696)-Asp1472(709) were sequentially deleted of full-length multimeric recombinant VWF. Deletions at either side resulted in normal GPIb binding, indicating that the flanking regions are not GPIb binding sites. However, the addition of a mutation at Arg1308(545) on each deletion mutant resulted in spontaneous GPIb binding without requiring modulators, suggesting that both regions are important for the inhibition of GPIb binding. Spontaneous binding was completely inhibited by monoclonal antibodies that recognize the GPIb binding sites. Interestingly, mutant proteins with N-terminal but not C-terminal deletions lost binding to monoclonal antibodies B328, B710, and 23C7, which selectively inhibit ristocetin-induced GPI binding. Their epitopes were found at His1268(505) or Asp1269(506). The crystallographic structure of the A1 domain suggests that GPIb binding is influenced by the molecular interface between the two regions and that the antibody binding to the interface inhibits binding.